Classifications

• • 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
  • C08L9/02—Copolymers with acrylonitrile
  • C08L9/04—Latex
• • 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
  • B60C11/00—Tyre tread bands; Tread patterns; Anti-skid inserts
  • B60C11/0041—Tyre tread bands; Tread patterns; Anti-skid inserts comprising different tread rubber layers
  • B60C11/005—Tyre tread bands; Tread patterns; Anti-skid inserts comprising different tread rubber layers with cap and base layers
• • 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
• • 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
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L61/00—Compositions of condensation polymers of aldehydes or ketones; Compositions of derivatives of such polymers
  • C08L61/04—Condensation polymers of aldehydes or ketones with phenols only
  • C08L61/06—Condensation polymers of aldehydes or ketones with phenols only of aldehydes with phenols
• • 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
• • 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
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S152/00—Resilient tires and wheels
  • Y10S152/905—Tread composition

Definitions

• the present invention relates to tire treads and to the rubber compositions used for the manufacture of such treads.
• treads of tires with low rolling resistance mainly reinforced with reinforcing inorganic fillers such as siliceous or aluminous, these treads being intended in particular for tires fitted to vehicles such as motorcycles, passenger cars. , vans or HGV.
• Such rubber compositions comprising reinforcing inorganic fillers of the siliceous or aluminous type, have for example been described in the patents or patent applications EP-A-0 501 227 (or US-A-5,227,425), EP-A -0 735 088 (or US-A-5.852.099), EP-A-0 810 258 (or US-A-5.900.449), EP-A-0 881 252, WO99 / 02590, WO99 / 02601, WO99 / 02602, WO99 / 28376, WOOO / 05300, WO00 / 05301.
• a tire tread must obey a large number of technical requirements, often contradictory, among which a high resistance to wear, a low rolling resistance, a high grip as well on dry ground as on wet ground, snowy or icy, while offering the tire a very good level of handling ("handling") on a motor vehicle, in particular a high drift thrust or "cornering".
• handling a very good level of handling
• a higher rigidity of the tread is desirable, this stiffening of the tread can be obtained for example by increasing the rate of reinforcing filler or by incorporating certain reinforcing resins in the compositions of rubber constituting these treads.
• treads ie, hybrids
• cap-base structure formed by two radially superposed layers (“cap-base structure") of different stiffnesses, made up of two rubber compositions of different formulations: the radially outer layer, in contact with the road, is made up of the most flexible composition, to meet the adhesion requirements; the radially inner layer consists of the most rigid composition, to meet the requirements of road handling.
• the manufacture of a composite tread is by definition more complex and therefore more expensive than that of a conventional tread, requiring in particular the use of complex coextrusion machines; -
• manufacture after cutting the tread to the correct dimensions at the outlet of the extruder, it is moreover necessary to manage falls of materials of different natures, which further increases production costs appreciably; finally, and this is not the slightest drawback, once the radially external (flexible) part of the tread has been worn out, it is the initially internal part of the tread which comes into contact with the road: Then, of course, finds the disadvantages of a tread that is too rigid, with unsatisfactory performance from the point of view of the technical compromise initially targeted.
• a first subject of the invention relates to a tire tread formed, at least in part, of a rubber composition based on at least (phr: parts by weight per hundred parts of elastomer): - (i) a diene elastomer;
• the invention also relates to the use of such a tread for the manufacture of new tires or the retreading of used tires.
• the tread according to the invention is particularly suitable for tires intended to equip passenger vehicles, 4x4 vehicles (4-wheel drive), motorcycles, vans, heavy goods vehicles.
• the invention also relates to these tires themselves when they have a tread according to the invention. It relates in particular to "winter" type tires intended for snowy or icy roads.
• the subject of the invention is also a process for preparing a tread for a tire vulcanizable with sulfur, capable of exhibiting, after a mechanical running-in of the tire for which it is intended, a stiffness gradient radially increasing from the surface towards the interior of the tread, this process being characterized in that it comprises the following stages:
• stiffness variation curves (module M10) as a function of the depth ("e" in mm) in these treads.
• treads and rubber compositions constituting these treads 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 (i.e., 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.
• 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 (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 dynamic properties ⁇ G * and tan (sont) max are measured on a viscoanalyzer (Metravib NA4000), according to standard ASTM D5992-96.
• 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 standard ASTM D1349 - 99.
• a deformation amplitude sweep is carried out from 0.1% to 50% (outward cycle), then from 50% to 1% (return cycle).
• the exploited results are the complex dynamic shear modulus (G *) and the loss factor tan ( ⁇ ).
• the maximum value of tan ( ⁇ ) observed (tan ( ⁇ ) max ) is indicated, as well as the difference in complex modulus ( ⁇ G *) between the values at 0.15% and 50% deformation (Payne effect).
• 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 drift thrust indicated in the tables is the slope at the origin of the curve D (Z).
• the tires are mounted on a motor vehicle equipped with an ABS braking system and the distance required to go from 40 km / h to 10 km / h is measured during brutal braking on watered ground (bituminous concrete).
• 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.
• the treads according to the invention are formed at least in part from a rubber composition based on at least: (i) one (at least one) diene elastomer; (ii) a minimum quantity (more than 50 cc) of one (at least one) inorganic filler as reinforcing filler; (iii) a (at least one) coupling agent (between 2 and 15 phr) ensuring the connection between the reinforcing inorganic filler and this diene elastomer; (iv) one (at least one) acceptor (between 1 and 10 phr) and (v) one (at least one) methylene donor (between 0.5 and 5 phr).
• composition based on
• a composition comprising the mixture and / or the reaction product in situ of the various constituents used, some of these basic constituents (for example the coupling agent, the acceptor and the methylene donor) being capable of, or intended to react with each other, at least in part, during the various phases of manufacture of the treads , in particular during their vulcanization (cooking).
• diene elastomer or rubber is generally meant 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).
• 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) .
• diene elastomers such as butyl rubbers or copolymers of dienes and alpha-olefins of the EPDM type do not fall within this definition and can on the contrary be qualified 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-alkyl (C 1 -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% 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 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.
• polybutadienes and in particular those having a content of units -1,2 between 4% and 80% or those having a content of cis-1,4 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) from -40 ° C to -80 ° C, isoprene-styrene copolymers and in particular those having a styrene content of between 5% and 50% by weight and a Tg of 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% are suitable.
• the diem 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 (DR), natural rubber (NR), butadiene copolymers, isoprene copolymers and mixtures of these elastomers.
• BR polybutadienes
• DR synthetic polyisoprenes
• NR natural rubber
• butadiene copolymers butadiene copolymers
• isoprene copolymers and mixtures of these elastomers.
• Such copolymers are more preferably chosen from the group consisting of butadiene-styrene copolymers (SBR), isoprene-butadiene copolymers (BIR), isoprene-styrene copolymers (SIR), isoprene copolymers- butadiene-styrene (SBIR) and mixtures of such copolymers.
• SBR butadiene-styrene copolymers
• BIR isoprene-butadiene copolymers
• SIR isoprene-styrene copolymers
• SBIR isoprene copolymers- butadiene-styrene
• the tread according to the invention is preferably intended for a tire for passenger vehicle.
• the diene elastomer is preferably an SBR copolymer, in particular an SBR prepared in solution, preferably used in admixture with a polybutadiene; more preferably, the SBR has a styrene content of between 20% and 30% by weight, a content of vinyhque bonds of the butadiene part of between 15% and 65%, a content of trans-1,4 bonds of between 15% and 75%) and a Tg of between -20 ° C and -55 ° C, and the polybutadiene has more than 90% of cis-1,4 bonds.
• compositions of the treads of the invention may contain a single diem elastomer or a mixture of several diene elastomers, the diene elastomer or elastomers can be used in combination with any type of synthetic elastomer other than diene, or even with polymers other than elastomers, for example thermoplastic polymers.
• reinforcing inorganic filler should be understood here any inorganic or mineral filler, whatever its color and its origin (natural or synthetic), also called “white” filler or sometimes “clear” filler as opposed to carbon black , capable of reinforcing on its own, without other means than an intermediate coupling agent, a rubber composition intended for the manufacture of a tire tread, in other words capable of replacing, in its reinforcement function , a conventional pneumatic grade carbon black (for tread).
• the reinforcing inorganic filler is a filler of the siliceous or aluminous type, or a mixture of these two types of filler.
• the silica (SiO 2 ) used can be any reinforcing silica known to those skilled in the art, in particular any precipitated or pyrogenic silica having a BET surface as well as a CTAB specific surface, both less than 450 m 2 / g, preferably of 30 to 400 m 2 / g.
• Highly dispersible precipitated silicas (called "HD") are preferred, in particular when the invention is implemented for the manufacture of tires having a low rolling resistance; the term “highly dispersible silica” is understood to mean, in known manner, any silica having a significant ability to disaggregate and to disperse in an elastomeric matrix, observable in known manner by electron or optical microscopy, on fine sections.
• silicas BN3380 and Ultrasil 7000 from the company Degussa
• the silicas Zeosil 1165 MP and 1115 MP from the company Rhodia
• the silica Hi-Sil 2000 from the company PPG
• Zeopol 8715 or 8745 silicas from the company Huber
• precipitated silicas treated such as for example the "doped" silicas with aluminum described in application EP-A-0735 088.
• the reinforcing alumina (AI 2 O 3 ) preferably used is a highly dispersible alumina having a BET surface ranging from 30 to 400 m 2 / g, more preferably between 60 and 250 mVg, an average particle size at most equal to 500 nm , more preferably at most equal to 200 nm, as described in the above-mentioned application EP-A-0 810 258.
• Such reinforcing aluminas there may be mentioned in particular the aluminas A125 or CR125 (company Ba ⁇ l owski), APA-10ORDX (company Condisputeda), Aluminoxid C (company Degussa) or AKP-G015 (Sumitomo Chemicals).
• the invention can also be implemented using as reinforcing inorganic filler the specific aluminum (oxide-) hydroxides as described in the aforementioned application WO99 / 28376.
• reinforcing inorganic filler is also understood to mean mixtures of different reinforcing inorganic fillers, in particular highly dispersible siliceous and / or aluminous fillers as described above.
• the reinforcing inorganic filler used in particular if it is silica, preferably has a BET surface of between 60 and 250 m / g, more preferably between 80 and 230 m 2 / g.
• the inorganic filler used as reinforcing filler must be present at a rate greater than 50 phr, which is one of the essential characteristics of the invention.
• This reinforcing inorganic filler can constitute all or the majority of the total reinforcing filler, in the latter case associated for example with a minority amount of carbon black.
• the rate of reinforcing inorganic filler is between 60 and 120 phr, more preferably still within a range ranging from approximately 70 to 100 phr, in particular when the tread is intended for a passenger car tire.
• the optimum will be different according to the nature of the reinforcing inorganic filler used and according to the type of tire concerned, for example tire for motorbike, for passenger vehicle or also for commercial vehicle such as van or Weight heavy.
• the reinforcing inorganic filler constitutes more than 80% by weight of the total reinforcing filler, more preferably more than 90% by weight (or even all) of this total reinforcing filler.
• Carbon black if used, is preferably present at a level of between 2 and 15 phr, more preferably between 4 and 12 phr. It can be used in particular as a simple black pigmentation agent, or even to protect the tread from different sources of atmospheric aging such as ozone, oxidation, UN radiation. It is also known that certain rubber additives, in particular certain coupling agents, are available in a form supported by carbon black, the use of such additives therefore involving the incorporation, in small proportion, of carbon black. carbon.
• carbon blacks all carbon blacks are suitable, in particular blacks of the HAF, ISAF, SAF type, conventionally used in tires and particularly in the treads of these tires; by way of nonlimiting examples of such blacks, mention may be made of blacks ⁇ l 15, ⁇ 134, N234, N339, N347, N375.
• the specific surface "BET” is determined in a known manner, according to the method of Brunauer-Emmett-Teller described in "The Journal of the American Chemical Society", vol. 60, page 309, February 1938 and corresponding to French standard NF T 45-007 (November 1987); the CTAB specific surface is the external surface determined according to this same standard NF T 45-007.
• a reinforcing filler of the organic type could be used, in particular a carbon black, covered at least in part with an inorganic layer (for example, a layer of silica). , requiring the use of a coupling agent to ensure the bond with the elastomer.
• a coupling agent also called a binding agent, which has the function of ensuring the connection or bonding between the surface of the particles of this inorganic filler and the diene elastomer, while facilitating the dispersion of this inorganic charge within the elastomeric matrix during thermomechanical mixing.
• Coupled agent inorganic filler / elastomer
• an agent capable of establishing a sufficient connection, of chemical and / or physical nature, between the inorganic filler and the elastomer must be understood; such a coupling agent, therefore 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 diene elastomer, for example via a sulfur atom; - T represents a divalent organic group making it possible to link Y and X.
• Coupling agents should in particular not be confused with simple inorganic charge covering agents which, in known materials, may contain the active Y function with respect to the inorganic charge but are devoid of the active X function with respect to - screw of the 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.
• Polysulphurized silanes are used in particular, as described for example in patents or applications for Patent FR 2 149 339, FR 2 206 330, US 3 842 111, US 3 873 489, US 3 978 103, US 3 997 581, US 4 002 594, US 4 072 701, US 4 129 585, US 5 580 919 , US 5 583 245, US 5 650 457, US 5 663 358, US 5 663 395, US 5 663 396, US 5 674 932, US 5 675 014, US 5 684 171, US 5 684 172, US 5 696 197 , US 5,708,053, US 5,892,085, EP 1,043,357.
• - n is an integer from 2 to 8 (preferably from 2 to 5);
• - A is a divalent hydrocarbon radical (preferably alkylene groups or groups CJ g arylene, C 6 -C 12, especially alkylenes C r C, 0, in particular - in particular propylene);
• radicals R 1 substituted or unsubstituted, identical or different, represent alkyl, Cj-C j g, cycloalkyl C 5 -C 18 aryl or C 6 -C 1S (preferably alkyl C ⁇ , cyclohexyl or phenyl, in particular C r C 4 alkyl groups, more particularly methyl and / or ethyl).
• radicals R 2 substituted or unsubstituted, identical or different from each other, represent a - g alkoxyl or C 5 -C 18 cycloalkoxyl group (preferably a group chosen from C 5 alkoxy and C 5 -C cycloalkoxy) 8 , more preferably still a group chosen from C 1 -C 4 alkoxyls, in particular methoxyl and ethoxyl).
• n is a fractional number preferably between 2 and 5, more preferably close to 4.
• polysulphurized silanes By way of examples of polysulphurized silanes, mention will be made more particularly of the polysulphides (in particular disulphides, trisulphides or tefrasulphides) of bis- (alkoxyl (C ⁇ -C 4 ) -a] kyl (C 1 -C 4 ) silyl-alkyl (C 1 -C 4 )), such as for example the polysulphides of bis (3-trimethoxysilylpropyl) or of bis (3-triethoxysilylpropyl).
• polysulphides in particular disulphides, trisulphides or tefrasulphides
• TESPT tetrasulfide bis (3-tri-ethoxysilyl ⁇ ropyl), abbreviated TESPT, of formula [(C 2 H 5 O) 3 Si (CH 2 ) 3 S 2 ] 2 or bis- (triethoxysilylpropyl) disulfide, abbreviated TESPD, of formula [(C 2 H 5 O) 3 Si (CH 2 ) 3 S] 2 .
• 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 polysulphides), or also by the company Witco under the name Silquest A1589.
• 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 the two cases, commercial mixture of polysulphides with an average value for n which is close to 4).
• the content of coupling agent is preferably between 4 and 12 phr, more preferably between 3 and 8 phr. But it is generally desirable to use as little as possible.
• the level of coupling agent preferably represents between 0.5 and 15% by weight relative to the amount of reinforcing inorganic filler. More preferably, in the case of tire treads for passenger vehicles, the coupling agent is present at a rate of less than 12%, or even less than 10% by weight relative to this quantity of reinforcing inorganic filler.
• the polysulphurized alkoxysilane 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 inorganic charge reinforcing.
• the polysulphurized alkoxysilane 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 function "X".
• the coupling agent may optionally be associated 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 effectiveness of this coupling agent.
• Activators for coupling polysulphurized alkoxysilanes have for example been described in the international applications WO00 / 5300 and WO00 / 5301 mentioned above, consisting in the association of a substituted guanidine, in particular N, N'-diphenylguanidine (abbreviated " DPG "), with an enamine or a zinc dithiophospate.
• coupling activators will, for example, make it possible to maintain the level of coupling agent at a preferential level of less than 10%>, or even even less than 8%> by weight relative to the amount of reinforcing inorganic filler, or else reduce the rate of reinforcing inorganic filler due to the improved coupling with the diene elastomer.
• methylene acceptor and "methylene donor” are well known to those skilled in the art and widely used to denote compounds capable of reacting together to generate by condensation a three-dimensional reinforcing resin.
• the rubber compositions of the treads of the invention contain, in combination, at least one methylene acceptor associated with at least one methylene donor, intended to form in situ, after curing (vulcanization) of the tread, a three-dimensional resin network which is superimposed, interpenetrating with the network (inorganic filler / elastomer) on the one hand, with the network (elastomer / sulfur) on the other hand (if the crosslinking agent is sulfur).
• Methylene acceptors in particular novolak resins, associated or not with a methylene donor, had certainly already been described in rubber compositions, in particular intended for tires or tire treads, for applications as varied as adhesion or reinforcement: reference will be made, for example, to documents EP-A-0 967 244, US-A-6 028 137, US-A-6 015 851, US-A-5 990 210, US-A-5 872 167, US-A-5 859 115 or EP-A-0 736 399, US-A-5 840 113 or EP-A-0 875 532, US-A-5 405 897, US-A-5 049 418, US- A-4,837,266.
• methylene acceptor designates the reactant with which the methylene donor compound reacts by formation of methylene bridges (-CH2-), during the curing of the composition, thus leading to the formation in situ of the network three-dimensional resin.
• the methylene acceptor must be able to disperse perfectly in the rubber matrix, together with the reinforcing inorganic filler and its coupling agent.
• phenols a generic name for hydroxylated derivatives of arenas and equivalent compounds; such a definition covers in particular monophenols, for example phenol itself or hydroxybenzene, bisphenols, polyphenols (polyhydroxyarenes), substituted phenols such as alkylphenols or aralkylphenols, for example bisphenols, diphenylolpropane, diphenylolmethane, naphthols, cresol , octylphenol, nonylphenol, xylenol, resorcinol or the like.
• novolaks also called phenol-aldehyde precondensates, resulting from the precondensation of phenolic compounds and aldehydes, in particular formaldehyde.
• these novolak resins also called two-step resins
• methylene donor a hardening agent
• resols which are thermosetting
• they have sufficient plasticity so as not to hinder the processing of the rubber composition.
• thermoset novolak resins
• they are characterized in particular by a three-dimensional network tighter than that of the resols.
• the amount of methylene acceptor must be between 1 and 10 phr; below the minimum indicated, the targeted technical effect is insufficient, while beyond the maximum indicated, there is a risk of stiffening too high and excessive penalization of the hysteresis.
• an amount between 2 and 8 phr is more preferably chosen, rates comprised in a range of 3 to 6 phr being particularly advantageous in the case of treads for passenger car tires.
• the amount of methylene acceptor in the ranges indicated above, is advantageously adjusted so as to represent between 2% and 15%, more preferably between 4% and 10% by weight relative to the amount of reinforcing inorganic filler.
• the methylene donor is chosen from the group consisting of hexamethylenetetramine (abbreviated HMT), hexamethoxymethylmelamine (abbreviated HMMM or H3M), rhexaethoxymethylmelamine, formaldehyde polymers such as p-formaldehyde, N derivatives -methylol of melamine, or mixtures of these compounds. More preferably, a methylene donor chosen from HMT, H3M or a mixture of these compounds is used.
• the amount of methylene donor must be between 0.5 and 5 phr; below the minimum indicated, the targeted technical effect has been found to be insufficient, while beyond the maximum indicated, there is a risk of penalizing the raw use of the compositions (for example , solubility problem of HMT) or vulcanization (slowing down in the presence of H3M).
• an amount of between 0.5 and 3.5 phr is more preferably chosen, rates comprised in a range of 1 to 3 phr being particularly advantageous in the case of treads for passenger car tires.
• the amount of methylene donor, in the ranges indicated above, is advantageously adjusted so as to represent between 10%> and 80%, more preferably in a range of 40 to 60% by weight relative to the amount of acceptor methylene.
• the rubber compositions of the treads according to the invention also comprise all or part of the additives usually used in diem rubber compositions crosslinkable with sulfur and intended for the manufacture of treads, such as for example plasticizers, pigments, protective agents 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.
• the reinforcing inorganic filler can also be associated, if necessary, with a conventional non-reinforcing white filler, such as for example particles of clay, bentonite, talc, chalk, kaolin, titanium oxides .
• the rubber compositions of the treads of the invention may also contain, in addition to the coupling agents, covering agents (comprising for example the only function Y) of the reinforcing inorganic filler or more generally agents for assisting in the use likely of known material, thanks to an improvement in the dispersion of the inorganic filler in the rubber matrix and to a lowering of the viscosity of the compositions, to improve their ability to be used in the raw state, these agents being for example alkylalkoxysilanes (in particular alkyltriethoxysilanes), polyols, polyethers (for example polyethylene glycols), primary, secondary or tertiary amines, hydroxylated or hydrolysable polyorganosiloxanes, for example, ⁇ -dihydroxy-polyorganosiloxanes (in particular ⁇ , ⁇ -dihydroxypolydimethylsiloxanes).
• covering agents comprising for example the only function Y
• the rubber compositions of the treads of the invention are produced in suitable mixers, using two successive preparation phases according to a general procedure well known to those skilled in the art (see for example documents EP-A-0 501 227 or O00 / 05300 mentioned above): a first working phase or thermomechanical kneading (sometimes called a "non-productive" phase) at high temperature, up to a maximum temperature between 130 ° C and 200 ° C, preferably between 145 ° C and 185 ° C, followed by a second mechanical working phase (sometimes called a "productive" phase) at a lower temperature, typically below 120 ° C, for example between 60 ° C and 100 ° C, phase of finish during which the crosslinking or vulcanization system is incorporated.
• a first working phase or thermomechanical kneading sometimes called a "non-productive" phase
• a second mechanical working phase sometimes called a "productive” phase
• the process according to the invention for preparing a tire tread vulcanizable with sulfur, capable of exhibiting, after a mechanical running-in of the tire for which it is intended, a gradient of rigidity radially increasing from the surface towards the interior of the tread, includes the following steps: incorporate into a diene elastomer, in a mixer:
• all the basic constituents of the tread compositions in accordance with the invention with the exception of the methylene donor and the vulcanization system, namely the reinforcing inorganic filler, l coupling agent (and its optional activator) and the methylene acceptor are intimately incorporated, by kneading, into the diene elastomer during the first so-called non-productive phase, that is to say that at least these various basic constituents are introduced into the mixer and kneaded thermomechanically, in one or more stages, until the maximum temperature of between 130 ° C. and 200 ° C. is reached, preferably between 145 ° C. ° C and 185 ° C.
• the methylene acceptor is incorporated into the mixer later than the elastomer, the reinforcing inorganic filler and its coupling agent, when the temperature of the composition in the mixer , during mixing, has reached a value between 80 ° C and 130 ° C, more preferably between 90 ° C and 110 ° C. In fact, the A.D.M. for such temperature conditions.
• the first (non-productive) phase is carried out in a single thermomechanical step during which all the necessary constituents, any covering agents, are introduced into a suitable mixer such as a conventional internal mixer. or complementary processing and other various additives, with the exception of the methylene donor and the vulcanization system.
• a second thermomechanical working step can optionally be added, in this internal mixer, for example after an intermediate cooling step (preferably at a temperature below 100 ° C.), in order to subject the compositions to a complementary heat treatment, in particular to improve the dispersion, in the elastomeric matrix, of the reinforcing inorganic filler, of the coupling agent and of the methylene acceptor.
• the methylene donor and the low-vulcanization system are then incorporated.
• 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 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 secondary accelerators or known vulcanization activators such as zinc oxide, stearic acid, guanidine derivatives (especially diphenylguanidine), etc.
• the sulfur content is preferably between 0.5 and 3.0 phr, that of the primary accelerator is preferably between 0.5 and 5.0 phr.
• the final composition thus obtained is then calendered, for example in the form of a sheet or a plate, in particular for characterization in the laboratory, or else extradited in the form of a rubber profile which can be used directly as a tire tread. .
• the vulcanization (or baking) is carried out in a known manner at a temperature generally between 130 ° C and 200 ° C, for a sufficient time which can vary for example between 5 and 90 min depending in particular on the baking temperature, the system of vulcanization adopted and of the vulcanization kinetics of the composition considered.
• the amount of reinforcing inorganic filler is between 60 and 120 phr; the amount of coupling agent is between 4 and 12 phr; - The quantity of methylene acceptor is between 2 and 8 phr; the amount of methylene donor is between 0.5 and 3.5 phr; the maximum thermomechanical mixing temperature is between 145 ° C and
• the reinforcing inorganic filler is a siliceous or aluminous filler; - The amount of carbon black is between 2 and 15 phr; the at least bifunctional coupling agent is an organosilane or a polyorganosiloxane; the methylene acceptor is chosen from the group consisting of phenolic resins; the methylene donor is chosen from the group consisting of HMT, H3M, rhexaethoxymethylmelamine, para-formaldehyde polymers, N-methylol derivatives of melamine, or a mixture of these compounds; the amount of methylene acceptor represents between 2% 0 and 15% by weight relative to the weight of reinforcing inorganic filler; the amount of methylene donor represents between 10% and 80% by weight relative to the weight of methylene acceptor.
• the diene elastomer is a butadiene-styrene copolymer (SBR), preferably used in admixture with a polybutadiene;
• SBR butadiene-styrene copolymer
• the reinforcing inorganic filler representing more than 80%> of the total reinforcing filler;
• the amount of inorganic filler is within a range of 70 to 100 phr; - The amount of coupling agent is between 3 and 8 phr; the amount of methylene acceptor is within a range of 3 to 6 phr; the amount of methylene donor is within a range of 1 to 3 phr; the reinforcing inorganic filler is silica; the amount of carbon black is between 4 and 12 phr; -
• the coupling agent is a bis-alkoxyl (CC 4 ) silylpropyl polysulphide; the methylene acceptor is a novolak phenolic resin; the methylene donor is chosen from the group consisting of HMT, H3M or a mixture of these compounds; the amount of methylene acceptor represents between 4% and 10% by weight relative to the weight of reinforcing inorganic filler; the amount of methylene donor represents from 40% to 60%> by weight relative to the weight of methylene acceptor; SBR is an SBR prepared
• the rubber compositions described above, based on diene elastomer, of a high level of reinforcing inorganic filler, of a coupling agent and of a methylene acceptor / donor system, in the proportions indicated above, can advantageously constitute the entire tread according to the invention.
• the base part of the ADM system can then constitute 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, in cases where it is desired, for example, to "delay" the technical effect of self-accommodation provided by the invention.
• the invention relates to the treads previously described both in the raw state (ie, before baking) and in the baked state (ie, after crosslinking or vulcanization).
• an internal mixer filled to 70% and whose initial tank temperature is approximately 60 ° C., is introduced successively, the reinforcing filler, the coupling agent and its any associated coupling activator, the diene elastomer or the mixture of diene elastomers, the methylene acceptor as well as the various other ingredients, with the exception of the vulcanization system and the methylene donor.
• Thermomechanical work (non-productive phase) is then carried out in one step, which lasts a total of approximately 3 to 4 minutes, until a maximum "fall" temperature of 165 ° C. is reached.
• the methylene acceptor is introduced into the mixer when the composition being kneaded has reached a temperature in the region of 100 ° C.
• compositions thus obtained are then calendered either in the form of plates (thickness of 2 to 3 mm) or thin sheets of rubber for the measurement of their physical or mechanical properties, or extradited in the form of treads for passenger car tires.
• the reinforcing inorganic filler (silica type "HD") is present at a rate greater than 60 phr; it also constitutes more than 90%> by weight of the entire reinforcing filler, a minority fraction (less than 10%) of the latter being constituted by carbon black.
• compositions noted C1 to C-4, are essentially distinguished by the following characteristics: Cl: reinforced with carbon black (70 pce), without ADM system; C-2: reinforced with carbon black (70 pce), with ADM system; C-3: reinforced with silica (80 phr), without ADM system; C-4: reinforced with silica (80 pce), with ADM system.
• compositions C-1 and C-3 constitute the “black” and “silica” controls for this test. Their respective formulation was adjusted so as to bring them both to initial iso-rigidity (Shore A hardness and module M10 equivalent), before incorporation of the A.D.M.
• Composition C-3 additionally contains the coupling agent TESPT (rate of 8% by weight relative to the amount of silica) and DPG (approximately 2.6%> by weight relative to the amount of silica).
• carbon black is essentially used as a black pigmentation agent, and present at a very low rate (6 phr or about 7% of the total reinforcing filler).
• compositions C-2 and C-4 correspond respectively to compositions C-1 and C-3 to which the A.D.M. system has been added. ; only the tread comprising composition C-4 is therefore in accordance with the invention.
• Tables 1 and 2 give the formulation of the different compositions (Table 1 - rate of the different products expressed in pce), their properties before and after cooking (40 min at 150 ° C).
• compositions C-2 and C-4 difference relating to the evolution of the module (M10 Ac ) under slight deformation, after mechanical accommodation (15%).
• the module M10 Ac remains very high after accommodation (9.1 MPa to be compared to 5.5 MPa initial on the composition C-1, ie approximately 65%>higher); on the contrary, this same M10 Ac module drops very sharply (from 12.0 MPa to 7.2 MPa) for composition C-4 (silica), practically covering the initial value M10 (6.0 MPa) recorded on the control composition C-3 without ADM system.
• compositions C-1 to C-4 previously described are used in this test as treads for passenger car tires with radial carcass, of size 195/65 RI 5 (speed index H), conventionally manufactured and in all identical points except the rubber composition constituting the tread.
• control tires P-1 and P-3 devoid of the A.D.M. system, show an equivalent performance (base 100 used for the tire P-1);
• the control P-2 tire after incorporating the ADM system, the control P-2 tire, whose tread is reinforced with carbon black, shows an unacceptable drop (loss of 20% ”) in this braking performance, which is quite predictable, moreover, taking into account the strong stiffening of the tread provided by the ADM system;
• the unexpected result lies in the behavior of the tire of the invention P-4, the tread of which is reinforced with silica: not only is its braking performance on wet surfaces not degraded - which is already a very surprising result for a person skilled in the art - but it is significantly improved since a gain of 8% is obtained compared to the control tires P1 and P-3; this behavior is quite remarkable and radically opposed to that of the control tire P-2;
• the tire according to the invention P-4 shows, quite unexpectedly, a simultaneous increase in two properties which are nevertheless considered to be contradictory, namely road behavior (drift thrust) and grip on wet ground.
• This third test provides, a posteriori, an explanation for the improved results of the previous tests 1 and 2, by revealing an unexpected property for the tread of the invention: this indeed has, in the radial direction, a gradient of very marked stiffness, with increasing stiffness when moving from the surface to the inside of the tread; such a characteristic does not exist in the control tread loaded with carbon black.
• the single appended figure represents, for the treads of tires P-2 and P-4 of the previous test, the evolution of module M10 (in MPa) as a function of the depth "e” (from 0 to 6 mm ), before (new condition) and after a "standard running-in” of these tires on the aforementioned Renault Website vehicle.
• curve A corresponds to the control tires Pl and P-3, that is to say the treads without ADM system, the module profiles being essentially the same (except for the measurement accuracy) between the two types of reinforcing load used (carbon black or silica);
• - curve B corresponds to tires P-2 and P-4, that is to say the treads with ADM system, these tires being in new condition, that is to say before any running-in or mechanical accommodation; here again, the module profiles are essentially confused between carbon black and silica;
• curve C corresponds to tire P-2 (carbon black) after running in;
• - curve D corresponds to the P-4 tire (silica) after running in.
• the surface stiffness and that in depth are little different for the P-2 tire of the prior art, the reinforcing load of which is carbon black; whereas, in the case of the tire P-4 of the invention, the surface stiffness is very much lower, practically equal to that of the control tires Pl and P-3, with in addition a very marked gradient of radial stiffness, increasing when moving from the surface of the tread towards the interior thereof.
• the control composition (denoted C-5) has no ADM system while the other four (denoted C-6 to C-9) include such a system; the methylene acceptor is made up of different variants of novolak resins (6 phr), the methylene donor being HMT (2 phr).
• Each composition comprises in particular a coupling agent for silica.
• the treads comprising compositions C-6 to C-9 therefore all conform to the invention.
• Tables 4 and 5 give the precise formulation of the different compositions (Table 4 - rate of the different products expressed in pce), their properties before and after cooking (40 min at 150 ° C).
• compositions used as treads according to the invention have the following characteristics:
• substantially equivalent reinforcement properties illustrated by values close to the high deformation modules (M100 and M300), as well as breaking properties; - a significantly higher rigidity, illustrated both by a Shore A hardness increased by about 16% (passage from 67 points to an average value of 78 points) and by an M10 module under low deformation which is substantially doubled (from 6.3 MPa to 12.5 MPa, on average); correlatively, an expected increase in hysteresis (increase in dynamic properties ⁇ G * and tan ( ⁇ ) max ); finally, after mechanical accommodation, modulus values under low deformation (M10 Ac ) which drop very sharply, covering values close to the initial value observed on the control composition C-5 devoid of the resin network.
• M10 Ac modulus values under low deformation
• compositions C-6 to C-9 in accordance with the invention have very similar properties, whatever the novolak resin used as the methylene acceptor.
• compositions loaded with silica (denoted C-10 to C-14) are compared here, similar to those of test 4 above.
• a first control composition does not have an ADM system
• a second control composition comprises the methylene acceptor but not the methylene donor.
• the other three compositions (C-12 to C-14) constitute three new variants, with different ADM systems, of compositions which can be used as treads according to the invention; it is noted in particular that composition C-14 comprises, as an ADM system, two acceptors and two different methylene donors.
• Tables 6 and 7 show the formulation of the different compositions (Table 6 - rate of the different products expressed in phr), their properties before and after cooking (40 min at 150 ° C).
• control composition C-11 comprising a methylene acceptor without curing agent, reveals intermediate properties which are not very advantageous.
• composition C-14 comprising two different methylene acceptors (formophenol + diphenynolpropane) associated with two methylene donors (HMT and H3M), it shows the best overall compromise of properties for this test, before cooking (viscosity and toasting time) as after baking (rigidity, reinforcement and hysteresis).
• Composition C-16 is identical to composition C-15, with the difference that a coupling activating system as described in the above-mentioned application WO00 / 05301, formed by the association of '' a zinc dithiophosphate (DTPZn) and a guanidine derivative (DPG); such an activator has the capacity to improve the efficiency of a polysulphurized alkoxysilane coupling agent.
• a coupling activating system as described in the above-mentioned application WO00 / 05301, formed by the association of '' a zinc dithiophosphate (DTPZn) and a guanidine derivative (DPG); such an activator has the capacity to improve the efficiency of a polysulphurized alkoxysilane coupling agent.
• Tables 8 and 9 give the formulation of the different compositions, their properties before and after cooking (40 min at 150 ° C).
• composition C-16 has a beneficial effect on most of the properties, with in particular:
• the control composition (noted C-17) is devoid of the A.D.M.
• the other 4 compositions (noted C-18 to C-21) include such a system; the methylene acceptor is used therein at rates varying from 2 to 5 phr, the quantity of methylene donor being chosen equal to 60% by weight relative to the quantity of acceptor.
• Tables 10 and 11 give the formulation of the different compositions, some of their properties after curing (40 min at 150 ° C), as well as the properties of the tires (noted respectively P-17 to P-21) comprising the corresponding treads. These tires are manufactured and tested as indicated above for test 2.
• the treads comprising the compositions C-18 to C-21 as well as the tires Pl 8 to P-21 are therefore all in accordance with the invention. Reading the results in Table 11, it is noted first of all that, compared to the control composition C-17, the compositions C-18 to C-21 have, and this all the more so since the quantity of ADM system is significant, higher rigidity illustrated by Shore A hardness and an M10 module both significantly increased, the M10 module being substantially doubled (from 5.6 MPa to 11.3 MPa) for the highest ADM system rate.
• composition according to the invention (C-23) comprises the A.D.M. system, while the control composition (C-22) is devoid of it.
• the formulation of the 2 compositions is close to those of Table 6 (test 5), with the difference, in particular, that the diene elastomer used here is a mixture of two SBRs with different microstructures.
• Tables 12 and 13 give this detailed formulation of the 2 compositions, some of their properties after curing (40 min at 150 ° C), as well as the properties of the corresponding tires (noted P-22 and P-23), manufactured and tested. as indicated for test 2 above, with the following details:
• the tread of the control tires P-22 consists exclusively of the control composition C-22;
• the tread of the P-23 tires according to the invention is a composite tread with a "cap / base” structure as described above, constituted by the two compositions C-22 and C-23 radially superimposed, the composition according to invention C-23 constituting the base, that is to say the radially internal part (on a new tire) of the tread.
• the beneficial effect of the invention obtained thanks to the self-accommodation phenomenon, is once again demonstrated, even in the case where the composition based on the A.D.M. constitutes only a part of the tread, in this case in this test the radially internal part of the tread intended to come into contact with the road only later, after wear of its part (radially) external of this tread.
• compositions C-3 and C-4 are compared, similar to those of test 1 (compositions C-3 and C-4) with the difference, in particular, that a more HD silica is used here. low specific surface.
• the composition according to the invention (C-25) comprises the A.D.M. whereas the control composition (C-24) is devoid of it; these 2 compositions are used as treads for passenger car tires.
• Tables 14 and 15 give the formulation of the compositions, some of their properties before and after curing (40 min at 150 ° C.), as well as the properties of the corresponding tires (denoted P-24 and P-25) (manufactured and tested as indicated for test 2 above).
• treads according to the invention described in the previous examples offer the major advantage, compared to the "composite" treads of the prior art, on the one hand, to maintain their performance compromise throughout life the tire, thanks to the unexpected phenomenon of self-accommodation, on the other hand to present a true gradient of radial rigidity, and not a simple, very localized “accident” of rigidity.
• This true stiffness gradient leads to optimal "work” of the rubber rolls in contact with the ground, during rolling and the many forces transmitted to the tread, in other words is synonymous with a tire which grips even better on the road.
• the invention will find a very advantageous application in tires fitted to vehicles such as motorbike, passenger car, vans or HGV, in particular in high grip tires of the "snow” or “ice” type (also called tires “ winter ”) which, due to a voluntarily relaxed tread, could so far exhibit qualities of road handling, on dry ground, considered sometimes insufficient.
• total aromatic oil (including SBR extension oil);

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