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
• • 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
• • 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
  • B60C1/0008—Compositions of the inner liner
• • 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
• • 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
  • B60C1/0025—Compositions of the sidewalls
• • 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
  • C08K3/01—Use of inorganic substances as compounding ingredients characterized by their specific function
  • C08K3/013—Fillers, pigments or reinforcing additives

Definitions

• the present invention relates to diene rubber compositions which can be used for the manufacture of tires or semi-finished products for tires, in particular treads for these tires, as well as to reinforcing fillers capable of reinforcing such rubber compositions.
• these inorganic fillers of the siliceous or aluminous type also have the known drawback of significantly disturbing the vulcanization kinetics of the elastomeric compositions, compared to the conventional compositions loaded with carbon black.
• these inorganic fillers of the siliceous or aluminous type also have the known drawback of significantly disturbing the vulcanization kinetics of the elastomeric compositions, compared to the conventional compositions loaded with carbon black.
• the longer cooking times which result therefrom can penalize the industrial processing of elastomeric compositions, like that of the rubber articles containing them.
• a first subject of the invention relates to a rubber composition based on at least (i) a diene elastomer, (ii) an inorganic reinforcing filler, (iii) a coupling agent ensuring the connection between the reinforcing filler and the elastomer, characterized in that said inorganic filler comprises a silicon nitride (hereinafter called "reinforcing silicon nitride”) having the following characteristics: - (a) a BET specific surface area of between 20 and 200 m 2 / g;
• silicon nitrides have been used essentially in tire treads to improve grip on snowy or icy conditions (see for example JP-A-1985/258235, JP-A-1987/198503 , JP-A- 1990/135241).
• the particles of silicon nitride chosen for their coarse size and their very high hardness have the function, not of reinforcement, but of improvement of adhesion by a well-known "claw" effect on snow or ice.
• Silicon nitrides have also been used to improve the thermal conductivity of various types of materials, in particular membranes for tire curing molds as described in JP-A-1986/040114. Again the size of the silicon nitride particles is coarse. It is also essential to note that these conventional silicon nitrides are always added to rubber compositions which also contain a real reinforcing filler such as carbon black and / or silica.
• the invention also relates to a process for obtaining a rubber composition which can be used for the manufacture of tires, in which at least one diene elastomer is incorporated, at least one reinforcing inorganic filler and a coupling agent ensuring the connection. between the reinforcing inorganic filler and the elastomer, this process being characterized in that said inorganic filler comprises a silicon nitride having the following characteristics: (a) a BET specific surface area of between 20 and 200 m 2 / g;
• thermomechanically kneaded in one or more stages, until a maximum temperature of between 110 ° C. and 190 ° C. is reached.
• the invention also relates to the use of a composition in accordance with the invention for the manufacture of finished articles or semi-finished products, as well as these finished articles and semi-finished products themselves, comprising a composition of rubber in accordance with the invention, these articles or products being intended for any ground connection system of motor vehicles, such as tires, internal safety supports for tires, wheels, rubber springs, elastomeric joints, other suspension and anti-vibration elements .
• the invention particularly relates to the use of a composition according to the invention for the manufacture of tires or semi-finished rubber products intended for these tires, these semi-finished articles being chosen in particular from the group consisting by the treads, the sub-layers intended for example to be placed under these treads, the crown reinforcement plies, the sides, the carcass reinforcement plies, the heels, the protectors, the chambers air and waterproof inner liners for tubeless tires.
• the invention particularly relates to tires comprising an elastomeric composition according to the invention and intended to equip passenger vehicles, 4x4 vehicles (4-wheel drive), SUV ("Sport Utility Vehicles"), two wheels (in particular bicycles or motorcycles), such as industrial vehicles chosen from vans, "Heavy vehicles” - Le., metro, bus, road transport equipment (trucks, tractors, trailers), off-road vehicles, agricultural or civil engineering machinery , airplanes, other transport or handling vehicles.
• 4x4 vehicles (4-wheel drive
• SUV Sport Utility Vehicles
• two wheels in particular bicycles or motorcycles
• industrial vehicles chosen from vans, "Heavy vehicles” - Le., metro, bus, road transport equipment (trucks, tractors, trailers), off-road vehicles, agricultural or civil engineering machinery , airplanes, other transport or handling vehicles.
• the invention relates in particular to tire treads, these treads being able to be used during the manufacture of new tires or for retreading used tires; thanks to the compositions of the invention, these treads have both a low rolling resistance, a very good grip and a high resistance to wear.
• the invention also relates to the use as reinforcing filler, in a diene rubber composition, of a reinforcing silicon nitride as defined above.
• the invention finally relates to a process for reinforcing a diene rubber composition, characterized in that there is incorporated into this composition in the raw state, by thermo-mechanical kneading, a reinforcing silicon nitride as defined above .
• the charges described below consist, in a known manner, of agglomerates of particles, capable of disaggregating into these particles under the effect of an external force, for example under the action of mechanical work or ultrasound.
• 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 necessary, part of this aggregate; "aggregate” means in a known manner the non-breaking set (ie, which cannot be cut, divided, shared) which is produced during the synthesis of the charge, generally formed of elementary (primary) particles aggregated between they.
• 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 the 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].
• the average size (by mass) of the particles is measured in a conventional manner after ultrasonic dispersion of the charge to be analyzed in demineralized water.
• the measurement is carried out using a centrifugal sedimentometer with X-ray detection type "XDC” ("X Ray Disc Centrifuge Sedimentometer"), sold by the company Brookhaven Instruments, a known device used in particular for the characterization of silica particles.
• XDC X Ray Disc Centrifuge Sedimentometer
• a suspension of 1 to 4 g (for example 1.7 g is suitable) of load sample to be analyzed is produced in 40 ml of water, per action for 8 minutes, at 60% power (60% of the maximum position of the "output control"), a 1500 W ultrasonic probe (3/4 inch Vibracell sonicator sold by the company Bioblock under the reference M75450).
• the suspension is preferably placed in a cold water bath (for example at a temperature of 5 to 10 ° C).
• the deagglomeration speed (denoted ⁇ ) is measured in the so-called “ultrasonic deagglomeration test” test, at 15% power of a 600 W (watt) probe operating here in pulsed mode (ie 1 second "ON”, 3 seconds “OFF") to avoid overheating of the ultrasonic probe during the measurement.
• This known principle test in particular the subject of patent application WO 99/28376, makes it possible to continuously measure the change in the average size (in volume) of the particle agglomerates during sonication (see WO99 / 28376, WO99 / 28380, WO99 / 28391). Given the very small size of the objects observed, the operating mode was adapted using in this case the Mie method.
• the assembly used consists of a laser granulometer (type "Mastersizer S”, marketed 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 was 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 under the reference M72412).
• a quantity of 100 mg of filler to be analyzed is introduced into 30 ml of water.
• the suspension obtained is introduced into the preparer with 130 ml of water, the circulation speed being fixed at its maximum (approximately 3 liters per minute).
• o ie 15% of the maximum position of the "amplitude tip
• the rubber compositions are characterized, before and after curing, as indicated below.
• a processing of the traction records also makes it possible to plot the modulus curve as a function of the elongation (see attached FIG. 2), the module used here being the true secant module measured in first elongation (module "M").
• the level of elastomer which cannot be extracted with toluene is measured, after swelling for 15 days of a sample of rubber composition (typically 300-350 mg) in this solvent (for example in 80-100 cm 3 toluene), followed by a 24-hour drying step at 100 ° C, under vacuum, before weighing the rubber composition sample thus treated.
• the above swelling step is carried out at ambient temperature (approximately 20 ° C.) and protected from light, and the solvent (toluene) is changed once, for example after the first five days of swelling.
• the rate of "bound rubber” (% by weight) is calculated in a known manner by difference between the initial weight and the final weight of the sample of rubber composition, after taking into account and elimination, in the calculation, of the fraction components which are inherently insoluble, other than the elastomer, present initially in the rubber composition.
• the rubber compositions according to the invention are based on the following constituents: (i) (at least) a diene elastomer, (ii) (at least) a reinforcing inorganic filler and (iii) (at least) a coupling agent ensuring the bond between this filler and this diene elastomer, said inorganic filler comprising a reinforcing silicon nitride as described in detail below.
• composition based on is meant a composition comprising the mixture and / or the in situ reaction product of the various base constituents used, some of these constituents being able to react and / or being intended to react with each other, at least partially, during the various stages of manufacturing the composition, or during its subsequent baking.
• iene elastomer or rubber in known manner an elastomer derived at least in part (i.e. a homopolymer or a copolymer) from diene monomers (monomers carrying two carbon-carbon double bonds, conjugated or not).
• diene elastomer a diene elastomer derived at least in part from conjugated diene monomers, having a rate of units or units of diene origin (conjugated dienes) which is greater than 15% (% in moles).
• diene elastomers such as butyl rubbers or copolymers of dienes and alpha-olefins of the EPDM type do not enter into the preceding definition and can be qualified in particular as "essentially saturated diene elastomers". "(rate of motifs of diene origin low or very low, always less than 15%).
• 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 (C 1 -C alkyl) -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 from 1% to 80%) by weight of vinyl aromatic units.
• the 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 be, for example, block, statistics, sequences, microsequences and be prepared in dispersion or in solution; they can be coupled and / or star or functionalized with a coupling and / or star-forming or functionalizing agent.
• polybutadienes are suitable and in particular those having a content of -1,2 units between 4% and 80% or those having a cis-1,4 content greater than 80%, polyisoprenes, butadiene copolymers- styrene and in particular those having a styrene content of between 5%> and 50% by weight and more particularly between 20% and 40%, a content of -1,2 bonds in the butadiene part of between 4% 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 glass transition temperature (" Tg "- measured according to standard ASTM D3418-82) between -40 ° C and -80 ° C, isoprene-styrene copolymers and in particular those having a styrene content between 5% and 50%) by weight and a Tg between -25
• butadiene-styrene-isoprene copolymers especially those having a styrene content of between 5% and 50% by weight and more particularly between 10% and 40%, an isoprene content of between 15%) and 60% by weight and more particularly between 20% and 50% ", a butadiene content of between 5% and 50% by weight and more particularly between 20% and 40%, a content of -1.2 units of the portion butadiene between 4% and 85%, a content of traris units -1.4 of the butadiene part between 6% and 80%, a content of units -1.2 plus -3.4 of the isoprene part between 5 % and 70% and a content of trans units -1.4 of the isoprene part between 10%) and 50%, and more generally any butadiene-styrene-isoprene copolymer having a Tg between -20 ° C and -70 ° vs.
• the diene elastomer of the composition in accordance with the invention is chosen from the group of highly unsaturated diene elastomers constituted by polybutadienes (BR), synthetic polyisoprenes (IR), natural rubber (NR), butadiene-styrene copolymers (SBR), butadiene-isoprene copolymers (BIR), butadiene-acrylonitrile copolymers (NBR), isoprene-styrene copolymers (SIR), copolymers of butadiene-styrene-isoprene (SBIR), and mixtures of these elastomers.
• BR polybutadienes
• IR synthetic polyisoprenes
• NR natural rubber
• SBR butadiene-styrene copolymers
• BIR butadiene-isoprene copolymers
• NBR butadiene-acrylonitrile copolymers
• SIR iso
• composition according to the invention is in particular intended for a tread for a tire, whether it is a new or used tire (in the case of retreading).
• the diene elastomer is preferably an SBR or a blend (mixture) SBR / BR, SBR / NR (or SBR / IR), or even BR / NR (or BR / IR).
• an SBR elastomer use is in particular of an SBR having a styrene content of between 20% and 30% by weight, a content of vinyl bonds in the butadiene part of between 15% and 65%, a content of trans-1,4 bonds between 15% and 75% and a Tg between -20 ° C and -55 ° C, this SBR copolymer, preferably prepared in solution (SSBR), being optionally used in admixture with a polybutadiene ( BR) preferably having more than 90%> of cis-1,4 bonds.
• SSBR polybutadiene
• the diene elastomer is preferably an isoprene elastomer.
• isoprene elastomer means, in a known manner, a homopolymer or a copolymer of isoprene, in other words a diene elastomer chosen from the group consisting of natural rubber (NR), synthetic polyisoprenes (IR), the various isoprene copolymers and mixtures of these elastomers.
• isoprene copolymers mention will be made in particular of isobutene-isoprene (butyl rubber - IIR), isoprene-styrene (SIR), isoprene-butadiene (BIR) or isoprene-butadiene-styrene copolymers (SBIR).
• the isoprene elastomer is preferably natural rubber or a synthetic polyisoprene of the cis-1,4 type.
• polyisoprenes are preferably used having a rate (%> molar) of cis-1,4 bonds greater than 90%), more preferably still greater than 98%.
• the diene elastomer can also consist, in part, of another highly unsaturated elastomer such as, for example, an SBR elastomer.
• the composition according to the invention may contain at least one essentially saturated diene elastomer, in particular at least one EPDM copolymer, which this copolymer is for example used or not in admixture with one or more of the highly unsaturated diene elastomers mentioned above.
• compositions of the invention may contain a single diene elastomer or a mixture of several diene elastomers, the diene elastomer (s) being able to be used in combination with any type of synthetic elastomer other than diene, or even with polymers other than elastomers, for example thermoplastic polymers.
• the silicon nitride used as reinforcing inorganic filler may constitute all or only part of the total reinforcing filler, in the latter case associated for example with another reinforcing inorganic filler such as silica, or with carbon black conventional.
• the reinforcing silicon nitride can constitute the entire reinforcing (inorganic) filler.
• the term "reinforcing" filler is generally understood to mean a filler capable of reinforcing on its own, without other means than an intermediate coupling agent, a rubber composition intended for the manufacture of tires; in other words, an inorganic filler qualified as reinforcing is capable of replacing, in its reinforcement function, a conventional filler of carbon black of pneumatic grade.
• composition in accordance with the invention therefore uses, as reinforcing filler, a silicon nitride having the following characteristics:
• silicon nitride means any compound corresponding, apart from impurities, to the known formula Si 3 N, whatever its form, crystalline or amorphous.
• the compositions certainly exhibit easier processing and reduced hysteresis, but there is a decline in the properties at break and a wear resistance, in tires, which decreases; for BET surfaces greater than 200 m 2 / g, processing in the raw state becomes more difficult (higher Mooney plasticity) and the dispersion of the charge is degraded.
• BET surfaces greater than 200 m 2 / g processing in the raw state becomes more difficult (higher Mooney plasticity) and the dispersion of the charge is degraded.
• d w For excessively large sizes d w , greater than 350 nm, the particles behave like defects which localize the stresses and are detrimental to wear; sizes d w too small, less than 10 nm, on the other hand will penalize the implementation in the raw state and the dispersion of the charge during this implementation.
• the BET surface is preferably between 40 and 180 m 2 / g and the particle size d w is preferably within a range from 20 to 300 nm and more particularly from 20 to 250 nm.
• the intrinsic dispersibility of a charge can be evaluated using the known ultrasonic deagglomeration test described in chapter I above, by measuring the deagglomeration speed ⁇ of this charge.
• the reinforcing silicon nitride described above has a speed ⁇ which is greater than 1.10 " 3 ⁇ nrVmin measured in the deagglomeration test at 15%) of power of a 600 W ultrasonic probe operating in pulsed mode (1 second" ON " / 3 seconds "OFF").
• the reinforcing silicon nitrides used verify at least one of the following characteristics, preferably both:
• a BET surface in a range of 50 to 170 m 2 / g; a particle size d w comprised within a range of 20 to 250 nm.
• the reinforcing silicon nitride particles also have good surface reactivity, that is to say a high level of surface hydroxyl functions (-OH) reactive with respect to the coupling agent, which is particularly favorable to the reinforcement function fulfilled by the filler, and therefore to the mechanical properties of the rubber compositions of the invention.
• -OH surface hydroxyl functions
• the physical state in which the reinforcing silicon nitride may appear is immaterial, whether in the form of powder, microbeads, granules, pellets, beads or any other densified form, provided of course that the mode densification does not alter the essential or preferential characteristics recommended for this load.
• the reinforcing silicon nitride described above can be used alone or combined with another reinforcing inorganic filler, or even several, for example with a silica or an alumina. It is recalled here that, in contrast to conventional carbon black, must be understood by charge “white” (sometimes also called “clear” filler) any inorganic or mineral filler, whatever its color and its origin (natural or synthetic).
• a highly dispersible precipitated silica is preferably used, in particular when the invention is implemented for the manufacture of tires having a low rolling resistance; as nonlimiting examples of such preferred highly dispersible silicas, mention may be made of the Ultrasil 7000 and Ultrasil 7005 silicas from the company Degussa, the Zeosil silicones 1165MP, 1135MP and 1115MP from the company Rhodia, the Hi-Sil silica EZ150G from the company PPG, the silicas Zeopol 8715, 8745 and 8755 from the company Huber, precipitated silicas treated such as for example the silicas "doped" with aluminum described in the aforementioned application EP-A-0735088.
• a reinforcing alumina is used, it is preferably a highly dispersible alumina as described in the abovementioned application EP-A-0810258, for example "Baikalox” "A125” or “CR125” aluminas (Baikowski company), "APA-100RDX” (company Condea), “Aluminoxid C” (company Degussa) or “AKP-G015" (Sumitomo Chemicals).
• the reinforcing silicon nitride can also be used in cutting, i.e., in mixture, with one or more conventional carbon blacks of pneumatic grade.
• carbon blacks all carbon blacks are suitable, in particular blacks of the HAF, ISAF, SAF type, conventionally used in tires and particularly in tire treads.
• the amount of carbon black present in the total reinforcing filler can vary within wide limits, this amount however preferably being less than the amount of silicon nitride present in the rubber composition.
• compositions in accordance with the invention advantageously is used, in combination with the reinforcing silicon nitride, a carbon black in small proportion, at a preferential rate of between 2 and 20 phr, more preferably within a range of 5 to 15 pce (parts by weight per hundred parts of elastomer).
• a carbon black in small proportion, at a preferential rate of between 2 and 20 phr, more preferably within a range of 5 to 15 pce (parts by weight per hundred parts of elastomer).
• the coloring properties (black pigmentation agent) and anti-UV properties of the carbon blacks are benefited, without, moreover, penalizing the typical performances provided by the reinforcing silicon nitride.
• the rate of total reinforcing filler in the compositions of the invention is included in a range from 20 to 400 phr, more preferably from 30 to 200 phr as regards also the rate of inorganic filler.
• the optimum is in fact different depending on the intended applications: in known manner, the level of reinforcement expected on a bicycle tire, for example, is much lower than that required on a tire for a passenger vehicle or for a commercial vehicle such as Weight- heavy.
• the rate of reinforcing inorganic filler is preferably chosen greater than 50 phr, for example between 50 and 150 phr, more preferably still greater than 60 phr.
• reinforcing silicon nitrides which may be suitable for the rubber compositions of the invention, mention will in particular be made of silicon nitrides obtained in known manner by a CO2 laser technique CVD (Chemical Vapor Deposition) (see for example FR -A-2677558); their synthesis has been described in detail, in particular in the following publication: "Synthesis of ultrafine powders by laser", M. Cauchetier, Le Vide, N ° 243, August-September-October (1988).
• reinforcing silicon nitride which can be used in the compositions in accordance with the invention is the silicon nitride sold by the company MarkeTech International Inc. (USA, Port Townsend - WA) under the reference "NP-S1050".
• a coupling agent white filler / elastomer
• bond which has the function of ensuring the bond or "coupling” between the white filler and the elastomer, while facilitating the dispersion of this inorganic filler within the elastomeric matrix.
• the reinforcing silicon nitride described above also requires the use of such a coupling agent to ensure its function of reinforcing filler in the rubber compositions according to the invention.
• Coupled agent is understood to mean more specifically an agent capable of establishing a sufficient connection, of chemical and / or physical nature, between the filler considered and the elastomer; such 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 the 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 binding physically and / or chemically to the elastomer, for example via a sulfur atom; - T represents a group making it possible to connect Y and X.
• Coupling agents should in particular not be confused with simple agents for recovery of the charge considered which, in known manner, may include the function Y active with respect to the charge but are devoid of the function X active vis -to the elastomer.
• Such coupling agents have been described in a very large number of documents and are well known to those skilled in the art. Any coupling agent known for, or capable of ensuring effectively, in diene rubber compositions which can be used for the manufacture of tires, can be used in fact for the bonding or coupling between a reinforcing white filler such as silica and an elastomer.
• diene such as for example organosilanes, in particular polysulphurized alkoxysilanes or mercaptosilanes, or alternatively polyorganosiloxanes carrying the abovementioned X and Y functions.
• Silica / elastomer coupling agents in particular, have been described in a large number of documents, the best known being bifunctional alkoxysilanes such as polysulphurized alkoxysilanes.
• polysulphurized alkoxysilanes called “symmetrical” or “asymmetrical” according to their particular structure, are used, as described for example in US Pat. Nos. 3,842
• - n is an integer from 2 to 8 (preferably from 2 to 5);
• - A is a divalent hydrocarbon radical (preferably C 1 -C 8 alkylene groups or C 6 -C 1 arylene groups, more particularly C 0 -C 10 alkylene, in particular - especially propylene);
• radicals R 1 substituted or unsubstituted, identical or different from each other, represent a C 1 -C alkyl group, C 5 -C 18 cycloalkyl or C 6 -C 18 aryl group (preferably C 1 -C alkyl groups) C 6 , cyclohexyl or phenyl, in particular 0 alkyl groups in -, more particularly methyl and / or ethyl).
• radicals R 2 substituted or unsubstituted, identical or different from each other, represent a C ⁇ -C 18 alkoxyl or C 5 -C 18 cycloalkoxyl group (preferably C ⁇ -C 8 alkoxyl or C 5 -C 8 cycloalkoxyl groups, more preferably Cj alkoxyl groups . -C, in particular methoxyl and / or ethoxyl).
• n is a fractional number preferably between 2 and 5, more preferably close to 4.
• polysulphurized alkoxysilanes mention will be made more particularly of polysulphides (in particular disulphides, trisulphides or tetrasulphides) of bis- (alkoxyl (dC 4 ) -alkyl (C ⁇ -C 4 ) silylalkyl (C ! -C)), such as for example polysulphides bis (3-trimethoxysilylpropyl) or bis (3-triethoxysilylpropyl).
• TESPD bis (3-triethoxysilylpropyl) tetrasulfide, in short TESPT, of formula [(CH 5 O) 3 Si (CH 2 ) 3 S 2 ] 2 or bis (triethoxysilylpropyl) disulfide, is used in particular abbreviated TESPD, of formula [(C 2 H 5 O) 3 Si (CH 2 ) 3 S].
• TESPD is marketed for example by the company Degussa under the names Si266 or Si75 (in the second case, 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 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 optimum rate of coupling agent in moles per square meter of reinforcing inorganic filler for each reinforcing inorganic filler (silicon nitride plus, if applicable, associated additional inorganic filler) used; this optimal rate is calculated from the weight ratio [coupling agent / reinforcing inorganic filler], the BET surface area of the filler and the molar mass of the coupling agent (denoted M below), according to the known relationship next:
• the amount of coupling agent used in the compositions in accordance with the invention is between 10 " 7 and 10" 5 moles per m 2 of reinforcing inorganic filler, or per m 2 of reinforcing silicon nitride when the latter is used without associated reinforcing inorganic filler. Even more preferably, the amount of coupling agent is between 5.10 -7 and 5.10 " 6 moles per square meter of total inorganic charge (silicon nitride plus, where appropriate, associated additional inorganic charge).
• the level of coupling agent, reduced to the weight of diene elastomer will preferably be between 0.1 and 25 phr, more preferably between 0.5 and 20 pc.
• 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 “precoupled” then comprising the free "Y” function for the reinforcing silicon nitride.
• the coupling agent could also be grafted beforehand (via the "Y” function) onto the reinforcing silicon nitride, the charge thus "precoupled” can then be linked to the diene elastomer via the free functions "X” .
• the coupling agent may optionally be associated with an appropriate "coupling activator", ie a body (ie, a single compound or a combination of compounds) which, mixed with this coupling agent, increases the effectiveness of this coupling agent.
• an appropriate "coupling activator” ie a body (ie, a single compound or a combination of compounds) which, mixed with this coupling agent, increases the effectiveness of this coupling agent.
• Activators for coupling polysulphurized alkoxysilanes have for example been described in applications WO00 / 5300 and WO00 / 5301, consisting in the association of a substituted guanidine, in particular N, N'-diphenylguanidine (abbreviated to "DPG" ), with an enamine or a zinc dithiophospate. Thanks to the improved coupling with the elastomer, the presence of these coupling activators will, for example, make it possible to reduce the rate of reinforcing inorganic filler.
• compositions in accordance with the invention contain, in addition to the compounds already described, all or part of the constituents usually used in diene rubber compositions intended for the manufacture of tires, such as for example plasticizers, pigments, protection of the antioxidant, antiozonant type, a crosslinking system based either on sulfur or on sulfur and / or peroxide and / or bismaleimide donors, vulcanization accelerators, vulcanization activators, extension oils, etc. ..
• a conventional non-reinforcing white filler such as for example clays, bentonite, talc, chalk, kaolin.
• the rubber compositions in accordance with the invention may also contain, in addition to the above-mentioned coupling agents, covering agents (comprising, for example, the only function Y) of the reinforcing inorganic filler or, more generally, setting aid agents.
• these agents used for example at a preferential rate of between 0.5 and 3 phr, being for example alkylalkoxysilanes (in particular alkyltriethoxysilanes such as for example 1-octyl-triethoxysilane marketed by the company Degussa-Huls under the name Dynasylan Octeo or 1-hexa-decyl-triethoxysilane sold by the company Degussa- Ha-ls under the name Si216), polyols, polyethers (for example polyethylene glycols), primary, secondary or tertiary amines (for example trialcanol-amines) , hydroxylated or hydrolyzable polyorganosiloxanes, for example ⁇ , ⁇
• compositions are produced in suitable mixers, using two successive preparation phases well known to those skilled in the art: a first working or thermo-mechanical kneading phase (sometimes called a "non-productive" phase) at high temperature, up to a maximum temperature (noted T max ) of between 110 ° C and 190 ° C, preferably between 130 ° C and 180 ° C, followed by a second phase of mechanical work (sometimes referred to as the "productive" phase) at a lower temperature, typically less than 110 ° C, for example between 60 ° C and 100 ° C, finishing phase during which the crosslinking or vulcanization system is incorporated; such phases have been described for example in applications EP-A-0501227, EP-A-0735088, EP-A-0810258, WO00 / 05300 or WO00 / 05301 mentioned above.
• a first working or thermo-mechanical kneading phase (sometimes called a "non-productive" phase) at high temperature, up to a
• the manufacturing method according to the invention is characterized in that at least the reinforcing filler and the coupling agent are incorporated by kneading with the diene elastomer during the first so-called non-productive phase, that is to say -to say that one introduces into the mixer and that one thermomechanically kneads, in one or more steps, at least these different basic constituents until reaching a maximum temperature of between 110 ° C and 190 ° C, preferably between 130 ° C and 180 ° C.
• the first (non-productive) phase is carried out in a single thermomechanical step during which all the necessary basic constituents, any agents, are introduced into a suitable mixer such as a conventional internal mixer. covering or additional processing and other various additives, with the exception of the vulcanization system.
• a second thermomechanical working step 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 heat treatment, in particular to improve still the dispersion, in the elastomeric matrix, of the reinforcing filler and of its coupling agent.
• the total duration of the kneading, in this non-productive phase is preferably between 2 and 20 minutes.
• the vulcanization system is 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 min.
• 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, to form for example a rubber profile used for the manufacture of semi-finished products. finishes such as treads, crown plies, sidewalls, carcass plies, heels, protectors, air chambers or internal rubber compounds for tubeless tires.
• Vulcanization (or baking) is carried out in a known manner at a temperature generally between 130 ° C and 200 ° C, under pressure, for a sufficient time which can vary for example between 5 and 90 min depending in particular on the baking temperature.
• a temperature generally between 130 ° C and 200 ° C, 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 of the vulcanization kinetics of the composition considered or also of the size of the tire.
• the vulcanization system proper is preferably based on sulfur and a primary vulcanization accelerator, in particular an accelerator of the sulfenamide type.
• a primary vulcanization accelerator in particular an accelerator of the sulfenamide type.
• various known secondary accelerators or activators of vulcanization such as zinc oxide, stearic acid, derivatives guanidiques (in particular diphenylguanidine), etc.
• Sulfur is used at a preferential rate of between 0.5 and 10 phr, more preferably of between 0.5 and 5.0 phr, for example between 0.5 and 3.0 phr when the invention is applied to a strip. tire bearing.
• the primary vulcanization accelerator is used at a preferential rate of between 0.5 and 10 phr, more preferably between 0.5 and 5.0 phr in particular when the invention applies to a tire tread.
• the invention relates to the rubber compositions described above, both in the so-called “raw” state (ie, before baking) and in the so-called “cooked” or vulcanized state (ie, after crosslinking or vulcanization). .
• compositions in accordance with the invention can be used alone or as a blend (i.e., as a mixture) with any other rubber composition which can be used for the manufacture of tires.
• Load A is tire grade carbon black (N234), conventionally used in tire treads.
• Load B is a coarser carbon black (N550) conventionally used in a tire carcass.
• Filler C is a conventional silica with a high specific surface (BET of around 160 m 2 / g), a reference inorganic filler for reinforcing the treads of "Green Tires” (“Zeosil 1165MP" silica from the company Rhodia).
• the filler D is a reinforcing silicon nitride, that is to say usable in the compositions in accordance with the invention (characteristics a and b verified).
• the filler D has a particle size d w much smaller than that of the filler C.
• the BET surface area of the silicon nitride D is close to that of the silica C tested. Its 10. agglomeration speed is advantageously very high (greater than 4.10 " ⁇ m " / min). Since the ability of the carbon blacks to disaggregate is known to be excellent, very clearly superior to that of the other charges, the measurement of the speed ⁇ for the charges A and B is not necessary.
• the filler E is a conventional non-reinforcing silicon nitride. It is commercially available (INTERCHIM company under reference 0429429, lot Kl 1 Jl 1)
• compositions tested below are prepared in a known manner, as follows: the diene elastomer (or the mixture of diene elastomers, if necessary) is introduced into an internal mixer filled to 80%, the initial temperature of which is tank is about 90 ° C; then, after an appropriate mixing time, for example of the order of 30 seconds, all the other ingredients, including the filler and the associated coupling agent, are added, with the exception of the vulcanization system. Thermomechanical work is then carried out for a duration of approximately 16 minutes, with an average speed of the pallets of 70 revolutions / min, until a drop temperature of approximately 140 ° C. is obtained.
• the mixture thus obtained is recovered, it is cooled and then the vulcanization system 0 (sulfur and primary accelerator of the sulfenamide type) is added on an external mixer (homo-finisher) at 30 ° C., mixing the whole (productive phase) for one appropriate time, between 5 and 12 min depending on the case.
• vulcanization system 0 sulfur and primary accelerator of the sulfenamide type
• compositions thus obtained are then calendered in the form of plates (thickness of 2 to 3 mm) of rubber for the measurement of their mechanical properties.
• the vulcanization 5 (baking) is carried out at 150 ° C for 40 min, under pressure.
• the reinforcing silicon nitride is present, in the compositions in accordance with the invention, at a preferential rate greater than 70 phr; it also constitutes all or more than 90% by weight of the whole of the reinforcing filler, a minority fraction (less than 10%) of the latter being able to consist of carbon black.
• the purpose of this test is to demonstrate that a reinforcing silicon nitride as described above can, on the contrary, claim the qualification of reinforcing inorganic filler.
• the diene elastomer is an SSBR comprising 27% by mass of styrene, and of which the polybutadiene units are for 24% of the 1,2-polybutadiene units and for 46%> of the trans-1,4-polybutadiene units.
• composition C-1 (control): filler A (carbon black, N234); composition C-2 (control): filler B (carbon black, N550) composition C-3 (control): filler C (silica), with coupling agent (TESPT) - composition C-4: filler in accordance with the invention (Si 3 N), with coupling agent (TESPT) composition C-5 (control): charge E, Si 3 N not in accordance with the invention, with coupling agent (TESPT)
• the carbon black chosen for the control composition C-1 is a tire grade black with very high reinforcing power, usually used to reinforce treads of passenger car tires.
• the carbon black chosen for the control composition C-2 is a tire grade black usually used in a tire carcass.
• silicon nitride is used at iso-volume with respect to carbon black (composition C-1).
• the coupling agent TESPT Si69
• the compositions C-1 and C-2 which serve here as references do not, in known manner, require a coupling agent since they are reinforced with carbon black.
• Tables 2 and 3 successively give the formulation of the different compositions (Table 2 - rate of the different products expressed in phr), their properties before and after cooking at 150 ° C for 40 min (Table 3).
• FIG. 2 reproduces the curves of true secant modulus "M" (in MPa) as a function of the elongation (in%); these curves are noted C1 to C5 and correspond respectively to the rubber compositions C-1 to C-5.
• composition of the invention exhibits, after firing, a level of reinforcement greater than that of the control compositions, with higher modules, in particular with strong deformations (M100 and M250), a ratio M250 / M100 neighbor, significantly higher measurements on the "bound rubber” test, as many reinforcement indices well known to those skilled in the art who are there to attest to the remarkable reinforcing activity of the charge D, in the presence of the coupling agent.
• Figure 2 attached clearly confirms the above observations. Results as remarkable as surprising could not have been foreseen by a person skilled in the art.
• the specific silicon nitride of the composition in accordance with the invention confers on the latter very interesting properties, in particular a remarkable reinforcement capacity and therefore of wear resistance at least equal if not greater than that achieved with carbon black or a conventional HDS silica, hitherto unknown with the silicon nitrides conventionally used in rubber compositions for tires of the prior art.
• the invention thus finds preferential applications in rubber compositions which can be used for the manufacture of tire treads having both a low rolling resistance and a high resistance to wear, in particular when these treads are intended tires for passenger vehicles or for industrial vehicles of the Truck type.

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