Classifications

• • 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
  • C08K3/34—Silicon-containing compounds
  • C08K3/36—Silica
• • 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
  • C08K9/00—Use of pretreated ingredients
  • C08K9/12—Adsorbed ingredients, e.g. ingredients on carriers
• • 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
• • 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
  • C08L9/06—Copolymers with styrene
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
  • Y02T10/00—Road transport of goods or passengers
  • Y02T10/80—Technologies aiming to reduce greenhouse gasses emissions common to all road transportation technologies
  • Y02T10/86—Optimisation of rolling resistance, e.g. weight reduction 

Definitions

• the present invention relates to tire treads, more particularly to treads reinforced with an inorganic filler, in particular silica, and to tires comprising such treads.
• the tire treads must in a known manner obey numerous technical requirements, often contradictory, in the first place having a high resistance to wear or abrasion and a high grip while offering the tire a very good level of road behavior ( "handling") on a motor vehicle, requiring in particular a high drift thrust or cornering.
• carbon black exhibits such aptitudes, which is generally not the case for inorganic fillers, in particular silicas. Indeed, for reasons of reciprocal affinities, these particles of inorganic charge have an unfortunate tendency, in the elastomeric matrix, to agglomerate between them. These interactions have the harmful consequence of limiting the dispersion of the filler and therefore the reinforcing properties to a level substantially lower than that which would theoretically be possible to achieve if all the bonds (inorganic filler / elastomer) capable of being created. during the mixing operation, were actually obtained; on the other hand, these interactions tend to increase the consistency in the raw state of the rubber compositions and therefore to make their implementation ("processability") more difficult than in the presence of carbon black.
• a coupling agent also called bonding agent, which has the function of ensuring the connection or bonding entered the surface of the particles (silanol groups Si-OH) of silica and the elastomer , while facilitating the dispersion of this charge within the elastomeric matrix, the high specific surface recommended for these silicas being precisely intended to increase the number and quality of the connections between the silica and the coupling agent, in order to reach the top expected level of reinforcement.
• Such coupling agents are well known to those skilled in the art, essentially polyfunctional organosilanes or polysiloxanes.
• the best known are polysulphurized alkoxysilanes, in particular bis- (alkoxylsilylalkyl) polysulphides such as bis- (alkoxylsilylpropyl) polysulphides, more particularly bis 3-triethoxysilylpropyl tetrasulphide and disulphide (in short TESPT and TESPD, respectively) generally considered like products providing, for silica-laden treads, the best compromise in terms of safety in roasting, ease of implementation and reinforcing power. As such, they are the coupling agents most used today in "Green Tires".
• LS silica a diene elastomer
• Such silicas denoted “LS” for "Low Surface" are known and could have been used, as adhesion promoting fillers or additives, in certain parts of tires, essentially in internal mixtures based on natural rubber intended in particular for calendering plies of crown reinforcement or tire carcass.
• LS Low Surface
• the invention also relates to the use as reinforcing filler, in a tire tread, of a silica LS having the characteristics a and b above.
• the invention also relates to the use of a tread according to the invention for the manufacture or retreading of tires, as well as these tires themselves when they comprise a tread according to the invention .
• the tires of the invention are particularly intended for equipping vehicles capable of traveling at high speed in a sustained manner such as passenger vehicles, 4x4 vehicles (4-wheel drive), SUV ("Sport Utility Vehicles"), two wheels (in particular motorcycles), vans, "Heavy goods vehicles” (notably metro, bus, road transport equipment such as trucks, tractors, trailers).
• the treads according to the invention can be prepared by a process constituting another object of the present invention.
• This improved process for preparing a tire vulcanizable with sulfur, with performance compromise (wear resistance / rolling resistance / adhesion / drift thrust), based on diene elastomer, of a reinforcing inorganic filler and of a vulcanization system comprises the following stages: • incorporating into a diene elastomer, during a first stage known as "non-productive", at least: as reinforcing filler, more than 80 phr of a inorganic filler consisting in whole or in part of a silica having the following characteristics (so-called "LS" silica): - (a) a BET specific surface of between 50 and 100 m 2 / g;
• LS silica constitutes the majority, more preferably still all of the reinforcing inorganic filler.
• the invention thus makes it possible to significantly reduce the levels of vulcanizing agents, sulfur and vulcanization accelerators.
• Another particularly preferred embodiment consists in using, as vulcanization activator, a substantially reduced rate, namely between only 0.5 and 1.5 phr of zinc, provided in particular in the form of zinc oxide or zinc stearate. It has in fact been found that the use of LS silicas has the drawback of significantly increasing the induction times during vulcanization (time required at the start of the vulcanization reaction) and that, unexpectedly, this drawback could be overcome by a reduction in the usual level of zinc.
• the silicas described below consist, in known manner, of agglomerates of particles,
• particle used in the present application must be understood in its usual generic sense of aggregate (also called “secondary particle”), and not in that of elementary particle (also called “primary particle”) which may form, the if applicable, part of this aggregate; by “aggregate” means in a known manner the non-breaking set (Le., which cannot be cut, divided, shared) which is produced during the synthesis of the charge, generally formed of aggregated elementary (primary) particles between them. "'
• the BET specific surface area (“mass area”) is determined by gas adsorption using the Brunauer-Emmett-Teller method described in "The Journal of the American Chemical Society” Vol. 60, page 309, February 1938), more precisely according to French standard NF ISO 9277 of December 1996 [multi-point volumetric method (5 points) - gas: nitrogen - degassing: hour at 160 ° C - relative pressure range p / in: 0.05 to 0.17]
• CTAB specific surface is the external surface determined according to French standard NF T 45-007 of November 1987 (method B).
• the average size (by mass) of the particles is measured in a conventional manner after dispersion, by ultrasonic deagglomeration, of the charge to be analyzed in water.
• the measurement is carried out using a centrifugal sedimentometer with X-ray detection type "XDC"("X-rays Disk Centrifuge”), sold by the company Brookhaven Instruments, according to the following operating mode.
• the deagglomeration speed noted ⁇ is measured by means of an ultrasonic deagglomeration test, at 100% power of a 600 W (watt) probe, operating here in pulsed mode (i.e.: 1 second ON, 1 second OFF ) to avoid excessive heating of the ultrasound probe during the measurement.
• This known test which is in particular the subject of patent application WO99 / 28376 (see also O99 / 28380, WO00 / 73372, WOOO / 73373), makes it possible to continuously measure the change in the average size (in volume) of particle agglomerates during sonication, as indicated below.
• the assembly used consists of a laser granulometer (type "Mastersizer S”, sold by Malvern Instruments - He-Ne laser source emitting in the red, wavelength 632.8 nm) and its preparer ("Malvern Small Sample Unit MSX1 "), between which has been inserted a continuous flow treatment cell (Bioblock M72410) fitted with an ultrasonic probe (1/2 inch sonicator type Vibracell of 600 W sold by the company Bioblock).
• a small amount (150 mg) of silica to be analyzed is introduced into the preparer with 160 ml of water, the circulation speed being fixed at its maximum. At least three consecutive measurements are made to determine according to the known Fraunhofer calculation method (Malvern calculation matrix 3 $$ D) the average initial diameter (in volume) of the agglomerates, denoted d v [0].
• the sonication (pulsed mode: 1 s ON, 1 s OFF) is then established at a power of 100% (ie 100% of the maximum position of the "tip amplitude") and the evolution of the mean diameter is followed for approximately 8 minutes. in volume d v [t] as a function of time "t" at the rate of a measurement every 10 seconds approximately.
• the aforementioned application WO99 / 28376 describes in detail a measuring device which can be used for carrying out this ultrasonic deagglomeration test.
• This device consists of a closed circuit in which a flow of agglomerates of particles in suspension in a liquid can flow.
• This device essentially comprises a sample preparer, a laser granulometer and a processing cell. A setting at atmospheric pressure, at level of the sample preparer and of the treatment cell itself, allows the continuous elimination of air bubbles which form during sonication (action of the ultrasonic probe).
• the sample preparer (“Malvern Small Sample Unit MSX1”) is intended to receive the silica sample to be tested (suspended in liquid 3) and to circulate it through the circuit at the preset speed (potentiometer - speed maximum of about 3 1 / min), in the form of a flow of liquid suspension.
• This preparer simply consists of a receiving tank which contains, and through which circulates, the suspension to be analyzed.
• a centrifugal mini-pump is intended to ensure the circulation of the suspension in the circuit;
• the inlet of the preparer is connected to the open air via an opening intended to receive the load sample to be tested and / or the liquid used for the suspension.
• the preparer is connected to a laser granulometer ("Mastersizer S") whose function is to continuously measure, at regular time intervals, the volume average size "d v " of the agglomerates, as the flow passes, thanks to a measurement to which the automatic recording and calculating means of the granulometer are coupled.
• Mastersizer S a laser granulometer
• laser granulometers exploit, in a known manner, the principle of diffraction of light by solid objects suspended in a medium whose refractive index is different from that of the solid. According to Fraunhofer's theory, there is a relationship between the size of the object and the angle of diffraction of light (the smaller the object, the larger the angle of diffraction).
• a processing cell Interposed between the preparer and the laser granulometer is finally a processing cell equipped with an ultrasonic probe, which can operate in continuous or pulsed mode, intended to continuously break up the agglomerates of particles as the flow passes.
• This flow is thermostatically controlled by means of a cooling circuit arranged, at the level of the cell, in a double envelope surrounding the probe, the temperature being controlled for example by a temperature probe immersed in the liquid at the level of the preparer.
• the rubber compositions are characterized, before and after curing, as indicated below.
• the Mooney plasticity measurement is carried out according to the following principle: the composition in the raw state (Le., Before baking) is molded in a cylindrical enclosure heated to 100 ° C. After one minute of preheating, the rotor turns within the test tube at 2 revolutions / minute and the torque useful for maintaining this movement is measured after 4 minutes of rotation.
• the measurements are carried out at 130 ° C, in accordance with French standard NF T 43-005 (1991).
• the evolution of the consistometric index as a function of time makes it possible to determine the toasting time of the rubber compositions, assessed in accordance with the aforementioned standard by parameter T5 (in the case of a large rotor), expressed in minutes, and defined as being the time necessary to obtain an increase in the consistometric index (expressed in MU) of 5 units above the minimum value measured for this index.
• the measurements are carried out at 150 ° C. with an oscillating chamber rheometer, according to standard DIN 53529 - part 3 (June 1983).
• the evolution of the rheometric torque as a function of time describes the evolution of the stiffening of the composition as a result of the vulcanization reaction.
• the measurements are processed according to DIN 53529 - part 2 (March 1983): tj is the induction time, that is to say the time necessary for the start of the vulcanization reaction; t ⁇ (for example t 90 or t 99 ) is the time necessary to reach a conversion of ⁇ %, i.e. ⁇ % (for example 90% or 99%, respectively) of the difference between the couples minimum and maximum.
• the conversion speed constant denoted K (expressed in min '1 ), of order 1, calculated between 30% and 80% of conversion, is also measured, which makes it possible to assess the vulcanization kinetics.
• a processing of the traction records also makes it possible to plot the module curve as a function of the elongation (see attached figure), the module used here being the true secant module measured in first elongation, calculated by reducing to the real section of the 'test tube and not in the initial section as previously for the nominal modules.
• Dynamic properties The dynamic properties ⁇ G * and tan max ( ⁇ ) are measured on a viscoanalyzer (Metravib VA4000), according to standard ASTM D 5992-96. The response of a sample of vulcanized composition (4 mm thick cylindrical test piece and 400 mm 2 section) is recorded, subjected to a sinusoidal stress in alternating single shear, at the frequency of 10 Hz, under normal conditions of temperature (23 ° C) according to ASTM D 1349-99, or as the case may be at a different temperature. A deformation amplitude sweep is carried out from 0.1 to 50%) (outward cycle), then from 50%) to 1% (return cycle).
• the Shore A hardness of the compositions after curing is assessed in accordance with standard ASTM D 2240-86.
• Rolling resistance is measured on a steering wheel, according to ISO 87-67, (1992). A value greater than that of the control, arbitrarily set to 100, indicates an improved result, that is to say a lower rolling resistance.
• the tires are subjected to actual rolling on the road, on a specific motor vehicle, until the wear due to rolling reaches the wear indicators arranged in the grooves of the tread.
• the tires are mounted on a motor vehicle equipped with an ABS braking system and the distance required to go from 100 km / h to 0 km / h is measured during brutal braking on dry ground (bituminous concrete). A value greater than that of the control, arbitrarily fixed at 100, indicates an improved result, that is to say a shorter braking distance.
• the tires are mounted 'on a motor vehicle equipped with a braking system
• ABS and we measure the distance required to go from 50 km h to 10 km / h during brutal braking on watered ground (bituminous concrete). A value higher than that of the witness, arbitrarily set to 100, indicates an improved result i.e. a shorter braking distance.
• the tires are mounted on a motor vehicle equipped with an ABS braking system on all four wheels, and the distance required to go from 20 km / h to 5 km h is measured when braking on ice.
• the professional driver of the vehicle also gives a global, subjective rating of the road behavior of the vehicle - and therefore of the tires - on this watered virgin circuit; a score higher than that of the witness, arbitrarily set at 100, indicates improved overall behavior.
• Each tire tested is mounted on a wheel of suitable size and inflated to 2.2 bars. It is made to run at a constant speed of 80 km / h on an appropriate automatic machine ("ground-plane" type machine sold by the company MTS).
• the load denoted “Z” is varied, under a drift angle of 1 degree, and the stiffness or drift thrust denoted “D” (corrected for zero drift thrust) is measured in a known manner, by recording at using sensors the transverse force on the wheel as a function of this load Z.
• the edge thrust indicated in the tables is the slope at the origin of the curve D (Z); a value greater than that of the control, arbitrarily set at 100, indicates an improved result, that is to say a stronger drift thrust.
• An increase in drift thrust is favorable to road behavior on dry ground.
• the tire treads according to the invention are therefore formed, in whole or in part, of a rubber composition based on at least: (i) a diene elastomer; (ii) by way of reinforcing filler, more than 80 phr of an inorganic filler constituted in whole or in part of a silica having the following characteristics:
• composition based on
• a composition comprising the mixture and / or the in situ reaction product of the various constituents used, some of these base constituents being capable of, or intended to react between them, at least in part, during the different manufacturing phases of the treads and tires, in particular during their vulcanization.
• diene elastomer or rubber
• elastomer derived at least in part (ie, a homopolymer or a copolymer) from diene monomers, that is to say from monomers carrying two carbon double bonds -carbon, conjugated or not.
• essentially unsaturated diene elastomer is meant here 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% (% by moles) .
• the expression “highly unsaturated” diene elastomer is understood in particular to mean a diene elastomer having a content of units of diene origin (conjugated dienes) which is greater than 50%.
• 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-di-alkyl (C ⁇ -C 5 ) -1, 3-butadienes such as for example, are suitable.
• Suitable vinyl-aromatic compounds are, for example, styrene, ortho-, meta-, para-methylstyrene, the commercial "vinyl-toluene" mixture, para-tertiobutylstyrene, methoxystyrenes, chlorostyrenes, vinyl mesitylene, divinylbenzene. , vinylnaphthalene.
• the copolymers can contain between 99% and 20% by weight of diene units and between 1% and 80% or by weight of vinyl-aromatic units.
• Elastomers can have any microstructure which is a function of the polymerization conditions used, in particular the presence or absence of a modifying and / or randomizing agent and the quantities of modifying and / or randomizing agent used.
• the elastomers can for example be block, statistical, sequence, microsequenced, and be prepared in dispersion or in solution; they can be coupled and / or stars or functionalized with a coupling and / or star-forming or functionalizing agent.
• the diene elastomer of the tread according to the invention is preferably made, in whole or in part, in an amount of at least 40 phr, more preferably still at least 50 phr, by a highly unsaturated elastomer of the type butadiene, that is to say chosen from the group of highly unsaturated diene elastomers constituted by polybutadienes (BR), butadiene copolymers and mixtures of these elastomers.
• a highly unsaturated elastomer of the type butadiene that is to say chosen from the group of highly unsaturated diene elastomers constituted by polybutadienes (BR), butadiene copolymers and mixtures of these elastomers.
• butadiene copolymers are in particular butadiene-styrene copolymers (SBR), isoprene-butadiene copolymers (BIR), isoprene-butadiene-styrene copolymers (SBIR).
• SBR butadiene-styrene copolymers
• BIR isoprene-butadiene copolymers
• SBIR isoprene-butadiene-styrene copolymers
• the BRs having a content of -1.2 units between 4% and 80% or those having a cis-1,4 content greater than 80%), the SBRs having a content in styrene between 5%> and 50% by weight and more particularly between 20% and 40%>, a content of -1,2 bonds of the butadiene part between 4% and 65%, a content of trans-1 bonds , 4 between 20%> and 80%>, the BIRs having an isoprene content of between 5%> and 90%> by weight and a glass transition temperature ("Tg" measured according to standard ASTM D3418-82) of - 40 ° C to -80 ° C.
• Tg glass transition temperature
• SBIR copolymers especially those having a styrene content of between 5% and 50% by weight and more particularly of between 10%) and 40%, an isoprene content of between 15%) and 60% by weight are suitable; more particularly between 20% and 50%, a content of butadiene between 5% and 50%) by weight and more particularly between 10% and 40%>, a content of units -1,2 of the butadiene part of between 4 % and 85% o, a content in trans units -1.4 of the butadiene part between 6% and 80%, a content in units -1.2 plus -3.4 of the isoprenic part between 5% and 70 % and a content in trans units -1.4 of the isoprenic part between 10% and 50%), and more generally any SBIR having a Tg ime between -20 ° C and -70 ° C.
• the butadiene elastomer is particularly chosen from BR, SBR and mixtures of these elastomers.
• the butadiene elastomer is mainly an SBR elastomer, whether it is an SBR prepared in emulsion ("ESBR") or a SBR prepared in solution (“SSBR”), or a mixture of SBR and another diene elastomer, in particular butadiene, for example a blend of SBR and BR, of SBR and NR (natural rubber), of SBR and IR (synthetic polyisoprene).
• an SBR having a styrene content of between 10% and 30%> by weight, a content of vinyl bonds of the butadiene part of between 15%) and 65% o, a content of trans-1,4 bonds included between 15%) and 75%) and a Tg of between -20 ° C and -55 ° C.
• SBR copolymer preferably an SSBR, is optionally used in admixture with BR preferably having more than 90% of cis-1,4 bonds.
• compositions of the treads of the invention may contain a single diene elastomer or a mixture of several diene elastomers, the diene elastomer or elastomers being able to be used in combination with any type of synthetic elastomer other than diene, or even with other polymers.
• elastomers for example thermoplastic polymers.
• the essential characteristic of the tread according to the invention is that it is reinforced by more than 80 phr of a reinforcing inorganic filler comprising, preferably in the majority, a specific silica with very low specific surface having the following characteristics:
• Silicas with a small BET surface capable of meeting this definition are known and have been described in particular in applications EP 157 703, EP 396 450 or EP 722 977. As already indicated, their known application in tires has hitherto been limited to parts of the tire other than its tread, in particular in internal mixtures used, for example, for calendering plies of crown or carcass reinforcement. •
• This specific silica "LS" (for "Low Surface) firstly has an unusual BET surface for a tread application, between 50 and 100 m 2 / g.
• BET surface area of less than 50 m 2 / g, the rubber compositions certainly exhibit easier processing as well as reduced hysteresis, but there is a decline in the properties at break and resistance to wear, in tires , which decreases prohibitively.
• the silica LS must on the other hand have a size d w of between 50 and 350 nm. For excessively large sizes d w , greater than 350 nm, the particles behave like defects which locate the constraints and are harmful to wear; sizes d w that are too small, less than 50 nm, on the other hand penalize implementation in the raw state and the dispersion of the charge during this implementation.
• the LS silica used will also preferably have a high intrinsic dispersibility, illustrated by 1 a deagglomeration speed ⁇ (measured in the ultrasonic deagglomeration test described in previous chapter I) greater than 5.10 -3 ⁇ rVmin, more preferably at least equal to 1.10 -2 ⁇ rVmin.
• ⁇ deagglomeration speed
• the silica LS exhibited a very high dispersibility, that is to say that few micron agglomerates are observed by reflection under optical microscopy on a section of rubber composition prepared according to the rules. art.
• the silica LS selected preferably checks at least one, more preferably all, of the following characteristics:
• a BET surface in a range of 60 to 90 m 2 / g; a particle size d w of between 100 and 300 nm; a disagglomeration speed ⁇ greater than 5.10 " 3 ⁇ m'Vmin.
• this LS silica verifies all of the following characteristics:
• a BET surface in a range of 60 to 90 m 2 / g; - A particle size d w in a range of 150 to 250 nm; a disagglomeration speed ⁇ at least equal to 1.10 " 2 ⁇ nrVmin.
• the physical state under which LS silica may appear is indifferent, whether in the form of powder, microbeads, granules, pellets, beads or any other densified form; it can be a precipitated silica such as a pyrolysis silica. Its BET / CTAB surface ratio is preferably within a range from 1.0 to 1.5, more preferably from 1.0 to 1.2.
• the silica LS above can advantageously constitute all of the reinforcing inorganic filler.
• this LS silica may optionally be associated with another reinforcing inorganic filler, for example a conventional reinforcing silica with a higher specific surface.
• the silica LS preferably constitutes at least 50% by weight of the total reinforcing inorganic filler, more preferably still more than 80%) by weight of this total reinforcing inorganic filler.
• the rate of reinforcing inorganic filler is greater than 90 phr, more preferably comprised within a range of 100 to 150 phr. , the optimum of course being different depending on the type of tire concerned.
• Silica LS can also be combined with a conventional carbon black of pneumatic grade, chosen in particular from blacks of the HAF, ISAF, SAF type conventionally used in tire treads (for example, blacks NI 15, N134, N234, N330, N339, N347, N375).
• This carbon black is then preferably used in small proportion, at a rate preferably between 2 and 20 phr, more preferably in a range of 5 to 15 phr.
• the coloring properties (black pigmentation agent) and anti-UV properties of the carbon blacks are benefited, without, moreover, penalizing the typical performances provided by LS silica.
• a reinforcing filler of the organic type could be used, in particular a carbon black for tires, covered at least in part with an inorganic layer.
• a reinforcing filler of the organic type could be used, in particular a carbon black for tires, covered at least in part with an inorganic layer.
• silica in particular of silica, requiring as for it the use of a coupling agent to ensure the connection with the elastomer.
• coupling agent inorganic filler / elastomer
• organic filler / elastomer an agent capable of establishing a sufficient bond, of chemical and / or physical nature, between the inorganic filler and the diene elastomer ;
• a coupling agent at least bifunctional, has for example as simplified general formula "Y-T-X", in which:
• Y represents a functional group (“Y” function) which is capable of physically and / or chemically binding to the inorganic charge, such a bond being able to be established, for example, between a silicon atom of the coupling agent and surface hydroxyl groups (OH) of the inorganic filler (for example surface silanols when it is silica);
• - X represents a functional group (“X" function) capable of physically and / or chemically bonding to the diene elastomer, for example by means of a sulfur atom;
• T represents a divalent organic group making it possible to connect Y and X.
• the coupling agents should not be confused with simple agents for recovering the inorganic charge which, in known manner, may include the "Y" function active with respect to the inorganic charge but are devoid of the "X” function active with respect to the diene elastomer.
• Coupling agents (silica / diene elastomer), of variable effectiveness, have been described in a very large number of documents and are well known to those skilled in the art. Any known coupling agent can be used capable of effectively ensuring, in diene rubber compositions which can be used for the manufacture of tire treads, the connection between a reinforcing inorganic filler such as silica and a diene elastomer, in particular organosilanes or polyfunctional polyorganosiloxanes carrying the functions X and Y above.
• - n is an integer from 2 to 8 (preferably from 2 to 5);
• - A is a di valent hydrocarbon radical (preferably C 1 -C 8 alkylene groups or C 6 -C 1 arylene groups, more particularly C 1 -C 10, especially C 1 -C 4 alkylene groups, in particular propylene);
• radicals R 1 substituted or unsubstituted, identical or different from each other, represent a C ⁇ -C ⁇ 8 alkyl, C 5 -C 18 cycloalkyl or C 6 -C 18 aryl group (preferably C ⁇ alkyl groups -C 6 , cyclohexyl or phenyl, in particular C ⁇ -C 4 alkyl groups, more particularly methyl and / or ethyl).
• radicals R 2 substituted or unsubstituted, identical or different, represent a hydroxyl, alkoxyl or Ci-C 18 cycloalkoxy, C 5 -C 18 (preferably a group selected from hydroxyl, alkoxyl C ⁇ -C 8 and C 5 -C 8 cycloalkoxyls, more preferably still a group chosen from hydroxyl and C ⁇ -C alkoxyls, in particular methoxyl and ethoxyl).
• n is a fractional number, preferably included in a range of 2 to
• polysulphide silanes By way of examples of polysulphide silanes, mention will be made more particularly of the polysulphides (in particular disulphides, trisulphides or tetrasulphides) of bis- (alkoxyl (C ⁇ -C 4 ) -alkyl (C 1 -C 4 ) silyl- alkyl (C ⁇ -C 4 )), such as for example the polysulphides of bis (3-trimethoxysilylpropyl) or bis (3-triethoxysilylpropyl).
• polysulphides in particular disulphides, trisulphides or tetrasulphides
• TESPT bis (3-tri-ethoxysilylpropyl) tetrasulfide
• TESPD bis (3-tri-ethoxysilylpropyl) tetrasulfide
• TESPD bis disulfide - (triethoxysilylpropyle)
• the TESPD is marketed for example by the company Degussa under the name Si75 (in the form of a mixture of disulfide - at 75% by weight - and polysulfides), or also by the company Witco under the name Silquest Al 589.
• TESPT is marketed for example by the company Degussa under the name Si69 (or X50S when it is supported at 50%) by weight on carbon black), or also by the company Osi Specialties under the name Silquest A1289 (in both cases , commercial mixture of polysulphides with an average value for n which is close to 4).
• the use of LS silica, in the treads according to the invention makes it possible to significantly reduce the level of coupling agent, in particular of polysulphurized silane, compared to the usual levels. practiced in the presence of a conventional silica with a higher specific surface.
• the level of coupling agent, in particular of polysulphurized silane is preferably between 2 and 5 phr, more preferably comprised within a range of 3 to 4.5 phr.
• this rate of coupling agent is advantageously less than 8%>, more preferably less than 6% by weight relative the weight of reinforcing inorganic filler.
• the coupling agent used could be grafted beforehand (via the "X" function) on the diene elastomer of the composition of the invention, the elastomer thus functionalized or
• the coupling agent could also be grafted beforehand (via the "Y” function) onto the reinforcing inorganic filler, the filler thus “precoupled” can then be linked to the diene elastomer via the free "X” functions.
• the coupling agent can optionally be combined with an appropriate “coupling activator”, that is to say a body (single compound or combination of compounds) which, mixed with this coupling agent, increases the efficiency of the latter (see for example applications WO00 / 5300 and WO00 / 5301 above).
• an appropriate “coupling activator” that is to say a body (single compound or combination of compounds) which, mixed with this coupling agent, increases the efficiency of the latter (see for example applications WO00 / 5300 and WO00 / 5301 above).
• Vulcanization system The basic vulcanization system consists of sulfur and a primary vulcanization accelerator. To this basic vulcanization system are added, incorporated during the first non-productive phase and / or during the productive phase, various known secondary accelerators or activators of vulcanization.
• the primary vulcanization accelerator is preferably an accelerator of the sulfenamide type.
• the use of LS silica makes it possible to significantly reduce the overall level of sulfur and of sulfenamide accelerator to a preferential value of between 1.25 and 2.75 phr, more preferably within a range of 1.5 to 2.5 phr, sulfur and sulfenamide accelerator being also each used, even more preferably, at a rate of between 0.5 and 1.5 phr.
• a guanidine derivative is preferably used, in particular there diphenylguanidine (DPG), incorporated during the first non-productive phase (preferred mode of the invention) and / or during the productive phase.
• DPG diphenylguanidine
• This guanidine derivative also plays the advantageous role of agent for covering silica LS.
• LS silica again makes it possible to advantageously reduce the overall level of sulfur, sulfenamide and guanidine derivative to a preferential value comprised in a range from 1.75 to 4.25, more preferably in a range from 2 to 4 phr.
• a very small amount of zinc is used as vulcanization activator, between 0.50 and 1.5 phr, more preferably within a range from 0.7 to 1.3 pc.
• This specific quantity of zinc can be added to the rubber composition in any manner known to those skilled in the art, preferably in the form of zinc oxide, in this case therefore used at an equivalent preferential rate of between 0.6 and 1.9 pce, more preferably within a range of 0.9 to 1.6 pce.
• this zinc oxide is preferably associated a fatty acid, more preferably stearic acid, present at a preferential rate of 0.5 to 3 phr, more preferably of 1 to 3 phr.
• All or part of the zinc used can also be incorporated into the treads and their compositions in the form of a zinc salt of fatty acid, in particular in the form of zinc stearate, or of another active zinc donor compound.
• Induction times and therefore reduced cooking times are particularly advantageous for. treads intended for retreading, whether it is "cold” retreading (use of a prebaked tread) or conventional "hot” retreading (using a tread in the state In the latter case, a reduced baking time, in addition to reducing production costs, limits the overcooking (or postcooking) imposed on the rest of the casing ("carcass") of the used tire (already vulcanized).
• the elastomeric compositions of the treads according to the invention also comprise all or part of the usual additives used in rubber compositions intended for the manufacture of tire treads, such as for example extension oils, plasticizers, protective agents such as anti-ozone waxes, chemical ozonants, antioxidants, anti-fatigue agents, coupling activators, reinforcing resins, methylene acceptors and / or donors.
• Silica LS can also be associated, if necessary, with a conventional white filler that is not very reinforcing or not, for example particles of clay, bentonite, talc, chalk, kaolin, which can be used, for example, in colored tire treads.
• the elastomeric compositions can also contain, in addition to the agents.
• these agents, used at a preferential rate of between 0.5 and 3 phr are for example alkylalkoxysilanes, in particular alkyltriethoxysilanes, such as 1-octyl-triethoxysilane sold by the company Degussa-H ⁇ ls under the name Dynasylan Octeo or 1- hexa-decyl-triethoxysilane sold by the company Degussa-H ⁇ ls under the name Si216, polyols, polyethers (for example polyethylene glycol
• thermo-mechanical kneading sometimes called a "non-productive" phase
• T max a maximum temperature of between 110 ° C and 190 ° C, preferably between 130 ° C and 180 ° C
• second phase of mechanical work sometimes qualified as a "productive" phase
• the process for manufacturing the compositions according to the invention is characterized in that at least the LS silica (associated or not with another reinforcing inorganic filler or with a carbon black) and the coupling agent are incorporated by kneading with diene elastomer during the first so-called non-productive phase, that is to say that one introduces into the mixer and that one thermomechanically kneads, in one or more times, at least these different basic constituents until a maximum temperature between 110 ° C and 190 ° C is reached, preferably between 130 ° C and 180 ° C.
• All or part of the vulcanization activator consisting of the very small amount of zinc of between 0.50 and 1.5 phr, can be introduced during the non-productive phase or else during the productive phase.
• the first (non-productive) phase is carried out in a single thermomechanical step during which all the necessary basic components are introduced into a suitable mixer such as a conventional internal mixer. (diene elastomer, reinforcing inorganic filler and coupling agent), then in a second step, for example after one to two minutes of mixing, any additional covering or implementing agents and other various additives, including in particular zinc and DPG, with the exception of the basic vulcanization system consisting of sulfur and primary accelerator, in particular sulfenamide; the apparent density of LS silica being generally low, it may be advantageous to split its introduction into two or more parts.
• a suitable mixer such as a conventional internal mixer.
• any additional covering or implementing agents and other various additives including in particular zinc and DPG, with the exception of the basic vulcanization system consisting of sulfur and primary accelerator, in particular sulfenamide; the apparent density of LS silica being generally low, it may be advantageous to split its introduction into two or more parts.
• thermomechanical work can be added to this internal mixer, after the mixture has fallen and intermediate cooling (cooling temperature preferably less than 100 ° C.), with the aim of subjecting the compositions to a complementary thermomechanical treatment , in particular to further improve the dispersion in the elastomeric matrix of the reinforcing inorganic filler and its coupling agent.
• the total duration of the kneading, in this non-productive phase is preferably between 2 and 10 minutes.
• sulfur and primary accelerator are then incorporated at low temperature, generally in an external mixer such as a cylinder mixer; the whole is then mixed (productive phase) for a few minutes, for example between 5 and 15 minutes.
• the final composition thus obtained is then calendered, for example in the form of plates (thickness of 2 to 3 mm) or of thin sheets of rubber for the measurement of its physical or mechanical properties, in particular for a characterization in the laboratory, or also extruded to form rubber profiles used directly, after cutting or assembling to the desired dimensions, as tire treads.
• the method for preparing a tire tread according to the invention comprises the following steps: • incorporating into a diene elastomer, during a first step called “non-productive": . by way of reinforcing filler, more than 80 phr of an inorganic filler constituted in whole or in part of silica having the following characteristics:
• a coupling agent ensuring the connection between the silica and the diene elastomer; by thermomechanically kneading the whole, in one or more times, until reaching a maximum temperature of between 110 ° C and 190 ° C; • cool the assembly to a temperature below 100 ° C; then incorporate, during a second so-called "productive" step, sulfur and a primary vulcanization accelerator; knead everything up to a maximum temperature below 110 ° C; • calendering or extruding the elastomeric composition thus obtained in the form of a tire tread.
• the vulcanization or curing of the tread or of the tire is carried out in a known manner at a temperature preferably between 130 ° C. and 200 ° C., preferably under pressure, for a sufficient time which can vary for example between 5 and 90 min depending in particular on the baking temperature, the vulcanization system adopted, the vulcanization kinetics of the composition considered and the size of the tire.
• the rubber compositions described above based on LS silica generally constitute the entire tread according to the invention.
• the invention also applies to cases where these rubber compositions form only part of a tread of the composite type, consisting for example of transversely different adjacent bands, or else of two radially superposed layers of different constitutions, the part loaded with silica LS which can constitute, for example, the radially external layer of the tread intended to come into contact with the ground from the start of rolling of the new tire, or on the contrary its radially internal layer intended to come into contact with the ground later.
• the present invention relates to the treads and tires previously described both in the so-called “raw” state (Le., Before baking) and in the so-called “cooked” or vulcanized state (Le., After vulcanization).
• the characteristics of the fillers used in the following examples are summarized in Table 1.
• the filler denoted A is a conventional reinforcing silica, with high specific surface (BET of about 160 m 2 / g), reference inorganic filler for reinforcement "Green Tires” treads ("Zeosil 1165MP" silica from Rhodia).
• Filler B is a silica with very low specific surface (BET close to 90 m 2 / g) intended usually with internal mixtures for calendering of tire crown reinforcement plies (BET / CTAB ratio equal to 1.1).
• the BET surface and size d w characteristics therefore clearly differentiate the two charges, charge B having a surface area twice as low per unit mass and an average particle size d w more than twice as large.
• the two silicas are also characterized both by a high intrinsic dispersibility, illustrated by a speed of
• a BET surface in a range of 60 to 90 m 2 / g; a particle size d w within a range of 150 to 250 nm; - a deagglomeration speed ⁇ at least equal to 1.10 " 2 ⁇ m'Vmin.
• a diene elastomer (or mixture of elastomers) is introduced into an internal mixer, filled to 70%> and whose initial tank temperature is approximately 60 ° C. diene, if applicable), the reinforcing filler, the coupling agent, then, after one to two minutes of mixing, the various other ingredients with the exception of sulfur and the primary accelerator sulfenamide.
• Thermomechanical work (non-productive phase) is then carried out in one or two stages (total mixing time equal to approximately 7 min), until a maximum "fall" temperature of approximately 160-165 ° C. is reached.
• compositions are then either calendered in the form of plates (thickness of 2 to 3 mm) for the measurement of their physical or mechanical properties, or directly extruded in the form of tire treads.
• LS silica advantageously constitutes all of the reinforcing inorganic filler, associated with a low level of carbon black (less than 10 phr).
• This test is to demonstrate the improved performance of an elastomeric composition based on LS silica, compared to a control composition using a conventional silica (high specific surface) for a "Green Tire” tread.
• compositions SBR / BR cutting
• composition noted Cl control: silica A (60 phr) with TESPT coupling agent
• composition C-2 invention: silica B (85 phr) with TESPT coupling agent
• composition C-3 invention: silica B (85 phr) with TESPD coupling agent.
• the butadiene elastomer consists of an SSBR comprising 25%) of styrene, 58%> of polybutadiene units 1-2 and 23% of polybutadiene units 1-4 trans, with which is associated a BR having more than 90% of cis bonds -1.4.
• the rate of total reinforcing filler constituted by silica LS and a small amount of carbon black (less than 10 phr) is greater than 90 phr in the compositions according to the invention.
• Tables 2 and 3 show in succession the formulation of the different compositions (Table. 2 - rate of the different products expressed in phr), and their properties before and after curing at 150 ° C for 40 minutes (Table 3).
• the appended figure reproduces the module curves (in MPa) as a function of the elongation (in%>); these curves are denoted C1 to C3 and correspond respectively to compositions C1 to C-3.
• the silica content is therefore more than 40% higher> (85 phr instead of 60 phr) in the compositions according to the invention (C-2 and C-3) which, compared to the control composition (Cl), have moreover the following advantageous characteristics, in particular from the point of view of costs:
• the level of ZnO was reduced by 40%> (1.5 phr instead of 2.5 phr in the control composition) in compositions C-2 and C-3 in order to reduce their induction time (tj) to a value comparable to that of the control, a rate of 2.5 phr leading, for example, for composition C-2 to an induction time increased by almost 50%, an increase considered prohibitive with regard to industrial cooking conditions .
• compositions Cl and C-2 are used in this test as treads for passenger car tires with a radial carcass, of dimension 175/70 RI 4 (speed index T), conventionally manufactured and in all points identical except for the rubber composition constituting the tread: composition Cl for the "Green Tires” witnesses (denoted Pl), composition C-2 for the tires of the invention (denoted P-2).
• the tires were first tested on a machine to determine their rolling resistance and their drift thrust, then mounted on the vehicle for further testing.
• the tires are then subjected to road rolling, on a passenger vehicle of the Citro ⁇ n Xsara brand, to determine the resistance to wear.
• the wear resistance of the tread is directly correlated to the level of reinforcement provided by the reinforcing filler and its associated coupling agent.
• the measurement of the resistance to wear is an excellent indicator, if not the best since evaluated on the final manufactured product, of the overall performance of the inorganic filler used. It can then be seen that the tire according to the invention shows a performance identical to that of the control tire.
• VW vehicle "Polo GT” model nominal pressures at the front and rear
• VW "Golf” model vehicle nominal pressures at the front and rear
• the tires to be tested being fitted at the front and rear of the vehicle.
• the P-2 tires firstly show a significant gain of 4%> in braking on wet surfaces.
• the running test on a wet and bumpy track confirms that the use of LS silica results in a significant improvement in grip, illustrated both by a reduction in the minimum time required to cover the track in speed conditions limit (journey time reduced by one second per lap) only by the change in the behavior score awarded by the pilot (8% increase>), these two variations being very significant for such a test.
• the tire of the invention shows a compromise (rolling resistance / resistance to wear / behavior / adhesion) which is generally improved compared to the reference constituted by the treads of the "Green Tires" controls Pl, with in particular an improvement both in road behavior and grip on wet, snowy or icy conditions.
• composition C-4 control: silica A (65 phr); composition C-5 (according to the invention): silica B (85 phr).
• Tables 5 and 6 successively give the formulation of the different compositions (Table 5 - rate of the various products expressed in phr), their properties before and after cooking at 150 ° C. for 40 minutes (Table 6).
• the level of silica is therefore significantly higher in the tread according to the invention, the rate of total reinforcing charge (LS silica plus carbon black) is greater than 90 pce.
• the coupling agent is TESPT in both cases, its weight ratio relative to the weight of silica being however significantly reduced in the tread according to the invention (less than 5% compared to 8.7% for the control solution ).
• compositions C-4 and C-5 were then tested as winter tire treads, dimension 175/70 RI 4, conventionally manufactured and in all respects identical except for the composition used: C-4 for the control tires (noted P-4), C-5 for the tires of the invention (denoted P-5).
• the tires were tested on a machine and on a vehicle, in accordance with the indications of the previous test 2 and of paragraph 1-3, to determine on the one hand their rolling resistance on the one hand, and on the other hand their grip. (brake test) both on wet ground and on ice.
• the specific silicas meeting the characteristics described above, with a very low specific surface and preferably with high dispersibility, when they are used in treads at a rate of reinforcing inorganic filler as high as that recommended, are unexpectedly revealed to those skilled in the art, capable of offering these treads an overall compromise in improved rolling performance, while making it possible to reduce their additional cost thanks to a possible reduction in the rates of coupling agent like those of vulcanizers.

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