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
  • C08K5/00—Use of organic ingredients
  • C08K5/54—Silicon-containing compounds
• • 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
  • C08K5/00—Use of organic ingredients
  • C08K5/54—Silicon-containing compounds
  • C08K5/541—Silicon-containing compounds containing oxygen
  • C08K5/5425—Silicon-containing compounds containing oxygen containing at least one C=C bond
• • 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 diene rubber compositions reinforced with a white filler, intended in particular for the manufacture of tires or semi-finished products for tires, in particular the treads of these tires.
• EP-A-0 810 258 discloses a diene rubber composition reinforced with another particular white filler, in this case a specific alumina (AI2O3) with high dispersibility, which also allows the obtaining tires or treads having such an excellent compromise of contradictory properties.
• a specific alumina AI2O3
• a coupling agent also called a bonding agent, which has the function of ensuring the connection between the surface of the particles of white filler and the elastomer, while facilitating the dispersion of this filler white within the elastomeric matrix.
• coupling agent white filler / elastomer
• an agent capable of establishing a sufficient connection, of chemical and / or physical nature, between the white filler and the diene elastomer has for example as simplified general formula "Y-A-X", in which:
• Y represents a functional group ("Y" function) which is capable of physically and / or chemically binding to the white charge, such a bond being able to be established, for example, between a silicon atom of the coupling agent and the hydroxyl (OH) groups on the surface of the white filler (for example surface silanols when it is silica);
• X represents a functional group ("X" function) capable of physically and / or chemically bonding to the diene elastomer, for example via a sulfur atom;
• A represents a hydrocarbon group making it possible to link Y and X.
• Coupling agents should in particular not be confused with simple white charge recovery agents which in known manner may include the active Y function with respect to the white charge but are devoid of the active X function with respect to - screw of the diene elastomer.
• Coupling agents in particular (silica / diene elastomer), have been described in a large number of documents, the best known being bifunctional alkoxysilanes. Thus, it has been proposed in patent application FR-A-2 094 859 to use a mercaptosilane for the manufacture of tire treads.
• TESPT bis 3-triethoxysilylpropyl tetrasulphide
• a first subject of the invention relates to a rubber composition vulcanizable with sulfur and usable for the manufacture of tires, based on at least:
• component A a diene elastomer chosen from the group consisting of polybutadienes, natural rubber, synthetic polyisoprenes, butadiene copolymers, isoprene copolymers and mixtures of these elastomers (hereinafter denoted component A);
• component B a reinforcing white filler
• component C a coupling agent (white filler / diene elastomer) carrying at least one activated ethylenic double bond (hereinafter denoted component C), with which is associated:
• D - between 0.05 and 1 phr ( parts by weight percent of elastomer) of a radical initiator with thermal initiation (hereinafter denoted component D).
• the subject of the invention is also the use of a rubber composition in accordance with the invention for the manufacture of tires or for the manufacture of semi-finished products intended for such tires, these semi-finished products being chosen in particular from the group consisting of treads, underlayments intended for example to be placed under these treads, crown plies, sidewalls, plies carcass, beads, protectors, inner tubes and waterproof inner liners for tubeless tires.
• the subject of the invention is also these tires and these semi-finished products themselves, when they comprise a rubber composition in accordance with the invention.
• 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 and a high resistance to wear.
• the invention also relates to a process for preparing a rubber composition which can be used for the manufacture of tires, this process being characterized in that at least (i) is incorporated in a diene elastomer chosen from the group consisting of polybutadienes, natural rubber, synthetic polyisoprenes, butadiene copolymers, isoprene copolymers and mixtures of these elastomers (component A), at least:
• thermomechanically kneaded in one or more stages, until a maximum temperature of between 110 ° C. and 190 ° C. is reached.
• Another subject of the invention is the use of a radical initiator with thermal initiation as coupling activator (white filler / diene elastomer) of a coupling agent with activated ethylenic double bond, in a rubber composition with diene elastomer base reinforced with a white filler, said diene elastomer being chosen from the group consisting of polybutadians, natural rubber, synthetic polyisoprenes, butadiene copolymers, isoprene copolymers and mixtures of these elastomers .
• the subject of the invention is finally a method for activating, in a sulfur-vulcanizable rubber composition based on diene elastomer and reinforced with a white filler, the coupling function (white filler / diene elastomer) of a coupling with an activated ethylene double bond, this process being characterized in that at least (i) a diene elastomer chosen from the group consisting of polybutadienes, natural rubber, synthetic polyisoprenes, butadiene copolymers is incorporated by kneading isoprene copolymers and mixtures of these elastomers (component A), at least: (ii) - a white filler as a reinforcing filler (component B); (iii) - a coupling agent (white filler / diene elastomer) carrying at least one activated ethylenic double bond (component C), with which is associated: (iv) - between 0.05
• thermomechanically kneaded in one or more stages, until a maximum temperature of between 110 ° C. and 190 ° C. is reached.
• the rubber compositions are characterized before and after curing, as indicated below.
• the Mooney plasticity measurement is made 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 standard AFNOR-NFT-43004 (November 1980).
• 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 the parameter T5, expressed in minutes, and defined as being the time necessary to obtain an increase.
• the consistometric index (expressed in MU) of 5 units above the minimum value measured for this index.
• a processing of the tensile recordings also makes it possible to plot the modulus curve as a function of the elongation (see attached figures 1-3), the module used here being the true secant module measured in first elongation, calculated by returning to the section real of the test piece and not in the initial section as previously for the nominal modules.
• Hysteretic losses (denoted PH) are measured by rebound at 60 ° C on the 6th shock, and expressed in% according to the following relationship:
• the dynamic properties, noted ⁇ G * and tan ( ⁇ ) max , measured as a function of the deformation, are carried out at 10 Hertz with a peak-peak deformation ranging from 0.15% to 50%.
• the non-linearity ⁇ G * is the difference in shear modulus between 0.15% and 50% of deformation, expressed in MPa.
• the hysteresis is expressed by the measurement of tan ( ⁇ ) max which corresponds to the maximum of tan ( ⁇ ).
• the rubber compositions according to the invention are based on at least each of the following constituents: (i) at least one diene elastomer (component A), (ii) at least one white filler as reinforcing filler (component B) , (iii) at least one coupling agent carrying at least one activated ethylenic double bond (component C) as coupling agent (white filler / diene elastomer), with which is associated (iv) at least one radical initiator (component D) with thermal initiation, as a coupling activator.
• composition based on
• a composition comprising the mixture and / or the reaction product in situ of the above-mentioned compounds (constituents A, B, C and D), some of these compounds being capable of, or intended to react with each other, at least partially, during the various stages of manufacture of the composition, in particular during its vulcanization.
• diene elastomer component A
• diene elastomer or rubber is meant in known manner an elastomer derived at least in part (ie a homopolymer or a copolymer) from diene monomers, that is to say from 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).
• the expression “highly unsaturated” diene elastomer is understood in particular to mean a diene elastomer having a rate of units of diene origin (conjugated dienes) which is greater than 50%).
• the diene elastomer of the composition in accordance with the invention (component A) is chosen from the group consisting of polybutadienes (BR), natural rubber (NR), synthetic polyisoprenes (IR), different butadiene copolymers, different isoprene copolymers, and mixtures of these elastomers.
• component A is chosen from the group consisting of polybutadienes (BR), natural rubber (NR), synthetic polyisoprenes (IR), different butadiene copolymers, different isoprene copolymers, and mixtures of these elastomers.
• polybutadienes in particular those having a content of units -1,2 of between 4%> and 80%> or those having a content of cis-1,4 greater than 80% are suitable.
• the synthetic polyisoprenes the cis-1,4-polyisoprenes are particularly suitable.
• butadiene or isoprene copolymers we mean in particular the copolymers obtained by copolymerization of at least one of these two monomers with one or more vinyl-aromatic compounds having from 8 to 20 carbon atoms.
• 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.
• butadiene-styrene copolymers known as "SBR"
• BIR butadiene-isoprene
• SBIR butadiene-styrene-isoprene copolymers
• isoprene copolymers mention will be made in particular of isobutene-isoprene (butyl rubber - IIR), isoprene-styrene (SIR), as well as isoprene-butadiene (BIR) or isoprene copolymers.
• SBIR isoprene copolymers.
• butadiene-styrene copolymers particularly suitable are 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 of the butadiene part included between 4% and 65%, a content of trans-1,4 bonds between 20% and 80%.
• the butadiene-isoprene copolymers especially those having an isoprene content of between 5% and 90%> by weight and a glass transition temperature (Tg) of -40 ° C. to -80 ° C. are suitable.
• isoprene-styrene copolymers those having a styrene content of between 5% and 50% by weight and a Tg of between -25 ° C. and -50 ° C. are particularly suitable.
• butadiene-styrene-isoprene copolymers those which have a styrene content of between 5% and 50% by weight and more particularly between 10%) and 40% are particularly suitable.
• isoprene content between 15% and 60% by weight and more particularly between 20%) and 50%, a butadiene content between 5% and 50% by weight and more particularly between 20%> and 40%, a content in units -1.2 of the butadiene part of between 4%> and 85%), a content of trans units -1.4 of the butadiene part of between 6% and 80% o, 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 copolymer- isoprene having a Tg of between -20 ° C and -70 ° C.
• a diene elastomer particularly chosen from the group of highly unsaturated diene elastomers constituted by polybutadians, natural rubber, synthetic polyisoprenes, butadiene-styrene copolymers, butadiene-isoprene copolymers is particularly suitable.
• the diene elastomer chosen may 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. It can for example be block, statistical, sequence, microsequenced, and be prepared in dispersion or in solution; it can be coupled and / or star or functionalized with a coupling and / or star-forming or functionalizing agent.
• composition according to the invention is particularly intended for a tread for a tire, whether it is a new or used tire (retreading).
• component A is for example an SBR or a blend (mixture) of SBR BR, SBR / NR (or SBR IR), or even BR / NR (or BR / IR).
• SBR elastomer use is in particular of an SBR having a styrene content of between 20% and 30%> by weight, a vinyl bond content of the butadiene part of between 15% and 65%, a content in trans-1,4 bonds between 15% and 75% o and a Tg between -20 ° C and -55 ° C, this SBR copolymer, preferably prepared in solution, being optionally used in admixture with a polybutadiene (BR ) preferably having more than 90%> of cis-1,4 bonds.
• BR polybutadiene
• component A is for example chosen from the group consisting of natural rubber, synthetic polyisoprenes, isoprene copolymers (isoprene-butadiene, isoprene-styrene, butadiene-styrene-isoprene) or a mixture of two or more of these compounds.
• component A can also consist, in whole or in part, of another highly unsaturated elastomer such as, for example, an SBR elastomer.
• the improvement in coupling provided by the invention is particularly notable in compositions based on natural rubber or synthetic polyisoprene.
• rubber compositions in which the diene elastomer (component A) is predominantly (ie, more than 50% by weight) of natural rubber, synthetic polyisoprene or a mixture of these compounds.
• component A can consist exclusively of natural rubber, synthetic polyisoprene or a mixture of these compounds.
• compositions of the invention could contain, in addition to the component A defined above, diene elastomers other than component A, non-diene elastomers, or even polymers other than elastomers, for example thermoplastic polymers.
• the white filler used as reinforcing filler can constitute all or only part of the total reinforcing filler, in the latter case associated for example with carbon black.
• the white reinforcing filler constitutes the majority, i.e. more than 50% by weight of the total reinforcing filler, more preferably more than 80%> by weight of this total reinforcing filler.
• the term "reinforcing white filler” means a “white” filler (ie, inorganic or mineral), whatever its color (as opposed to carbon black), sometimes also called “clear” filler, capable of reinforcing alone, without any other means than an intermediate coupling system, a rubber composition intended for the manufacture of tires, in other words capable of replacing in its reinforcing function a conventional charge of pneumatic grade carbon black .
• the reinforcing white filler is an inorganic filler of the silica (Si ⁇ 2) or alumina (AI2O3) type, or a mixture of these two fillers.
• the silica 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 from 30 to 400 m 2 / g.
• Highly dispersible precipitated silicas (called "HD") are preferred, in particular when the invention is used for the manufacture of tires having 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.
• Nonlimiting examples of such preferential highly dispersible silicas mention may be made of Perkasil KS 430 silica from Akzo, BV3380 silica from Degussa, Zeosil 1165 MP and 1115 MP silica from Rhodia, Hi-Silica 2000 from the company PPG, the silicas Zeopol 8741 or 8745 from the company Huber, precipitated silicas treated such as for example the silicas "doped" with aluminum described in application EP-A-0 735 088.
• the reinforcing alumina preferably used is a highly dispersible alumina having a BET surface area ranging from 30 to 400 m 2 / g, more preferably between 60 and 250 m 2 / g, 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.
• BET surface area ranging from 30 to 400 m 2 / g, more preferably between 60 and 250 m 2 / g, 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 mention may in particular be made of aluminas A125, CR125, D65CR from the company Baikowski.
• reinforcing white filler is also understood to mean mixtures of different reinforcing white fillers, in particular of highly dispersible silicas and / or aluminas as described above.
• the reinforcing white filler used in particular if it is silica, preferably has a BET surface area of between 60 and 250 m 2 / g , more preferably between 80 and 200 m 2 / g.
• the reinforcing white filler can also be used in cutting (mixing) with carbon black.
• 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.
• blacks NI 15, N134, N234, N339, N347, N375 mention may be made of blacks NI 15, N134, N234, N339, N347, N375.
• the quantity of carbon black present in the total reinforcing filler can vary within wide limits, this quantity of carbon black preferably being less than the quantity of white reinforcing filler present in the rubber composition.
• the rate of total reinforcing filler is between 10 and 200 phr, more preferably between 20 and 150 phr, the optimum being different depending on the intended applications; in fact, the level of reinforcement expected on a bicycle tire, for example, is in known manner significantly lower than that required on a tire capable of traveling at high speed in a sustained manner, for example a motorcycle tire, a tire for a passenger vehicle or for a utility vehicle such as Truck.
• the quantity of reinforcing white filler is preferably between 30 and 120 phr, more preferably between 40 and 100 phr .
• the BET specific surface is determined in a known manner, according to the Brunauer-Emmet-Teller method described in "The Journal of the American Chemical Society” Vol. 60, page 309, February 1938 and corresponding to standard AFNOR-NFT-45007 (November 1987); the CTAB specific surface is the external surface determined according to the same standard AFNOR-NFT-45007 of November 1987. II-3.
• the coupling (white filler / diene elastomer) is ensured by a specific coupling agent (component C) with which, to activate this coupling, a specific coupling activator (component D) is associated.
• the coupling agent (component C) used in the rubber compositions in accordance with the invention has the essential characteristic of being the carrier of an activated ethylenic double bond ("X" function) allowing it to be grafted onto the elastomer diene.
• activated bond is meant in a known manner a bond made more capable of reacting (in the present case, with the diene elastomer).
• Y second function
• Alkoxysilanes for example, carrying an activated ethylenic double bond are known to a person skilled in the art, in particular as coupling agents (white filler / diene elastomer) in rubber compositions; documents US-A-4 370 448, US-A-4 603 158, DE-A-4319142, the patent application published under the number JP64-29385 describe in detail such known compounds and / or their processes for obtaining .
• the ethylenic double bond is preferably activated by the presence of an adjacent electron-withdrawing group, that is to say attached to one of the two carbon atoms of the ethylenic double bond.
• an "electron-attracting” group is a radical or functional group capable of attracting electrons to itself more than a hydrogen atom would if it occupied the same place in the molecule considered.
• coupling agents which are preferably suitable for implementing the invention, use is made, without the following definition being limiting, of coupling agents of the alkoxysilane type, in particular those corresponding to the general formula (I ) next:
• - Z is a group carrying the function X (activated ethylenic double bond) capable of reacting with the diene elastomer;
• - T is a divalent hydrocarbon group
• - Y responds to one of the formulas below:
• radicals R 1 substituted or unsubstituted, identical or different from each other, represent a C1-Cis alkyl, C 5 -C 18 cycloalkyl or C 6 -C 18 aryl group;
• radicals R 2 substituted or unsubstituted, identical or different from each other, represent a C t -Cis alkoxyl or C 5 -C 1 cycloalkoxyl group.
• the group T substituted or unsubstituted, is preferably a divalent hydrocarbon radical, saturated or unsaturated, containing from 1 to 18 carbon atoms.
• Particularly suitable are C 1 -C alkylene groups or C 6 -C 12 arylene groups, more particularly C 1 -C 10 , especially C 2 -C 4 alkylene, in particular propylene.
• the radicals R 1 are preferably alkyl, -C O, cyclohexyl or phenyl, especially alkyl groups, C 1 -C, more particularly methyl and / or ethyl.
• the radicals R 2 are preferably C 6 -C 8 alkoxyl or C 5 -C 8 cycloalkoxyl groups, more particularly methoxyl and / or ethoxyl.
• the group Z is the group carrying the activated carbon-carbon double bond (“X” function) intended to be grafted onto the diene elastomer during the vulcanization step, by forming a covalent bond with the latter.
• the group Z of formula (I) above is chosen from the structures of formulas (Z-1), (Z-2) or (Z-3) below:
• - Wi is O, NH, S or CH 2 ;
• - W 2 is N or CH;
• R 3 and R 4 identical or different from each other, represent hydrogen, a C1-C6 alkyl, substituted or unsubstituted, or a halogen, in particular bromine, with the proviso that when R 4 is the group COOH, R 3 is a hydrogen atom.
• the coupling agent of formula (I) used in the composition according to the invention, carrying the group Z above is a (mono-, di- or tri-) alkoxy (C 1 -C) - silylalkyl (C ⁇ -C 4 ) silane, ie, a silane carrying, as the function "Y", at least one C 1 -C 4 alkoxyl radical (radicals R 2 ), the hydrocarbon group T being an alkylene in (-C 4 ).
• Particularly suitable are (mono-, di- or tri-) alkoxy (Ci-C 4 ) -silylpropyl-silanes, the hydrocarbon group T being propylene.
• the coupling agent is selected from the group consisting of alkoxy acrylates (C 1 -C 4) -silylpropyl methacrylates, alkoxy (C 1 -C 4) -silylpropyl acrylamides, alkoxy ( C 1 -C 4 ) -silylpropyl, alkoxy methacrylamides (C ⁇ -C 4 ) -silylpropyl, alkoxy maleimides (C!
• the content of component (C) is preferably between 0.5% > and 20% by weight relative to the weight of reinforcing white filler. Below the minimum rates indicated, the effect may be insufficient, while at beyond the maximum levels indicated above, there is generally no longer any improvement in the coupling, while the costs of the composition increase. For these reasons, the content of component C is preferably between 3 and 15% by weight relative to the weight of reinforcing white filler, more preferably still between 5 and 12%.
• component D the radical initiator (component D) makes it possible, in a large number of cases, to use component C at a preferential rate of less than 10%, more preferably still of less than 8%> relative to the weight of reinforcing white filler; rates between 4%> and 8%> are for example possible.
• the coupling agent (component C) described above could be grafted beforehand (via the "Y” function) onto the reinforcing white filler, the filler thus “precoupled” possibly being subsequently linked to the diene elastomer, via the free function "X".
• the second essential component for coupling (white filler / diene elastomer) is a coupling activator, capable of activating, that is to say increasing the coupling function of the coupling agent described above; this coupling activator, used in very small proportion (less than 1 phr), is a radical initiator (also called radical initiator) of the type with thermal initiation.
• a radical initiator is an organic compound capable, following an energetic activation, of generating free radicals in situ, in its surrounding medium.
• the radical initiator of the compositions of the invention is an initiator of the thermal initiation type, that is to say that the supply of energy, for the creation of free radicals, must be in thermal form. It is believed that the generation of these free radicals promotes, during the manufacture (thermomechanical kneading) of the rubber compositions, a better interaction between the coupling agent and the diene elastomer.
• a radical initiator is chosen whose decomposition temperature is less than 180 ° C., more preferably less than 160 ° C., such temperature ranges making it possible to fully benefit from the activation effect of the coupling, during manufacture. compositions according to the invention.
• Component D is therefore preferably chosen from the group consisting of peroxides, hydroperoxides, azido compounds, bis (azo) compounds, peracids, peresters and mixtures of these compounds.
• component D is chosen from the group consisting of peroxides, bis (azo) compounds, peresters and mixtures of two or more of these compounds.
• peroxides bis (azo) compounds
• component D is chosen from the group consisting of peroxides, bis (azo) compounds, peresters and mixtures of two or more of these compounds.
• benzoyl peroxide acetyl peroxide, lauryl peroxide, cumyl peroxide, t-butyl peroxide, t-butyl peracetate, t- hydroperoxide butyl, cumene hydroperoxide, t-butyl cumyl peroxide, 2,5-dimethyl-2,5-bis (t-butyl) 3-hexyne peroxide, 1,3-bis (t-butyl-isopropyl) benzene peroxide, 2,4-dichlorobenzoyl peroxide, perbenzoate of t-butyl, 1,1 bis (t-but
• Such a compound is known as a crosslinking agent, in particular for diene rubbers (see for example Kempermann, Rubber Chem. Tech. (1987), 61, p. 422); it is marketed for example by the company Flexsys under the name Trigonox 29-40 (40%> by weight of peroxide on a solid support of calcium carbonate).
• the radical initiator used is 1,1 '-azobis (isobutyronitrile) - abbreviated AIBN - corresponding in known manner to the formula (III-2) which follows:
• Such a compound is known as a radical initiator polymerization initiator (see for example J. Org. Chem. (1987), 52, p. 2859); it is marketed for example by the company Du Pont de Nemours under the name Vazo 64.
• the radical initiator is used in very small proportion in the compositions according to the invention, namely at a rate of between 0.05 and 1 phr.
• radical initiators with thermal initiation are not able to lead to crosslinking of the compositions (which would then result by a significant increase in rigidity) even if these initiators have, if necessary, at much higher rates, a crosslinking power with respect to diene elastomers.
• component D the optimal content of component D will also be adjusted, within the ranges indicated above, according to the particular conditions for carrying out the invention, namely the type of diene elastomer (component A), the nature of the reinforcing white filler (component B), in particular the nature and the amount of coupling agent (component C) used.
• the amount of component D represents between 1% and 10%, more preferably between 2%> and 5% by weight relative to the amount of component C.
• the rubber compositions in accordance with the invention also comprise all or part of the additives usually used in diene rubber compositions intended for the manufacture of tires, such as for example plasticizers, protective agents, a crosslinking system with base either of sulfur, or of sulfur donors, vulcanization accelerators, extension oils, etc.
• plasticizers such as for example plasticizers, protective agents, a crosslinking system with base either of sulfur, or of sulfur donors, vulcanization accelerators, extension oils, etc.
• the reinforcing white filler can also be associated, if necessary, with a conventional white filler little or not reinforcing, by example of clay particles, bentonite, talc, chalk, kaolin, titanium oxides.
• the rubber compositions in accordance with the invention may also contain, in addition to coupling agents (activated double bond) and coupling activators
• agents for recovering the reinforcing white filler comprising for example the only function Y, or more generally agents for assisting in the implementation, capable in known manner, thanks to an improvement in the dispersion white filler in the rubber matrix and 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 (for example trialcanol-amines), hydroxylated or hydrolyzable polyorganosiloxanes, for example ⁇ , ⁇ -dihydroxy-polyorganosiloxanes (in particular, ⁇ -dihydroxy-polydimethylsiloxanes ).
• the compositions in accordance with the invention could also contain other coupling agents, in addition to coupling agents carrying at least one activated ethyl, or more generally agents
• 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 the aforementioned application EP-A-0 501 227.
• 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
• the manufacturing process according to the invention is characterized in that at least all of the basic constituents of the compositions according to the invention, namely component B, component C and component D (at a rate of between 0, 05 and 1 pce) are incorporated by mixing into component A during the first so-called non-productive phase, that is to say that is introduced into the mixer and that is thermomechanically kneaded, in one or more stages, at least these various basic constituents until reaching a maximum temperature between 110 ° C and 190 ° C, preferably between 130 ° C and 180 ° C.
• a radical initiator is chosen whose decomposition temperature is lower than the maximum temperature T max reached during thermo-mechanical mixing.
• the first (non-productive) phase is carried out in a single thermomechanical step during which all the necessary components, including the coupling system, are introduced into a suitable mixer such as a conventional internal mixer. formed by the association of components C and D, any additional covering or processing agents 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 white filler and its coupling system.
• the total duration of the kneading, in this non-productive phase is preferably between 2 and 10 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 minutes.
• the final composition thus obtained is then calendered, for example in the form of a sheet, a plate or even a rubber profile usable for the manufacture of semi-finished products such as treads.
• 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 invention relates to the rubber compositions previously described both in the raw state (i.e., before baking) and in the baked state (i.e., 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.
• a diene elastomer or a mixture of diene elastomers is introduced into an internal mixer, filled to 70% and whose initial tank temperature is approximately 60 ° C., the reinforcing filler, the coupling agent (component C) and its activator (component D), then the various other ingredients with the exception of the vulcanization system.
• Thermomechanical work (non-productive phase) is then carried out in one or two stages depending on the case (total mixing time between 2 and 10 minutes), until a maximum "fall" temperature of approximately 165 ° C is reached. .
• compositions thus obtained are then calendered either in the form of plates (thickness of 2 to 3 mm) or of thin sheets of rubber for the measurement of their physical or mechanical properties, or in the form of profiles which can be used directly, after cutting and or assembly to the desired dimensions, for example as semi-finished products for tires, in particular as treads.
• the reinforcing white filler (silica and / or alumina) constitutes the whole of the reinforcing filler; but a fraction of the latter, preferably a minority, could be replaced by carbon black.
• the aim of this first test is to demonstrate the improved coupling performance of an activated double bond alkoxysilane when it is associated with a radical initiator with thermal initiation. These performances are compared on the one hand to those of a coupling agent conventional TESPT, on the other hand to the activated double bond alkoxysilane itself when the latter is used alone, that is to say without free radical initiator.
• compositions No. 1 and No. 3 are the reference compositions of the prior art; only composition No. 4 is in accordance with the invention.
• the two coupling agents tested (TESPT and TMSPM) are used at an isomolar rate in triethoxysilane functions, that is to say that whatever the composition tested, the same number of moles of reactive triethoxysilane functions is used. -with respect to silica and its surface hydroxyl groups.
• the rate of TESPT is equal to 8%>, that of TMSPM is less than 8%> (precisely 7.4%>); the amount of radical initiator used in the composition according to the invention is very low (0.16 phr, or 4.3%> relative to the weight of component C).
• 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 (25 min at 150 ° C).
• Figure 1 reproduces the modulus curves (in MPa) as a function of the elongation (in%>); these curves are denoted C1 to C5 and correspond respectively to compositions No. 1 to No. 5.
• the vulcanization system consists of sulfur and sulfenamide, to which 0.16 phr of peroxide is added in the case of composition No. 5.
• the peroxide used here is a peroxide of 1.1 bis (t-butyl) 3,3,5-trimethylcyclohexane (formula (III- 1) above), commercially available (“Trigonox 29/40") in a form called “supported ", at a rate of 40%> by weight of peroxide on a solid support of calcium carbonate; the rates indicated in the various tables which follow correspond to the actual proportion of peroxide, corrected by (i.e., without) the quantity of calcium carbonate.
• the toasting times (T5) are sufficiently long in all cases (22 to 30 minutes), offering a significant margin of safety with regard to the problem of toasting;
• the Mooney plasticity values remain low (much less than 60 MU) whatever the composition considered, which is an indicator of a very good ability of the compositions to be used in the raw state;
• the Mooney plasticities are substantially identical between compositions No. 1 and No. 2 on the one hand, between compositions No. 3 and No.
• composition No. 4 which has the highest values of modulus under strong deformation (M300) and of ratio M300 / M100, indicators known to the skilled person of the quality the reinforcement provided by the white charge; - it is also composition No. 4 which presents, and this in a clear manner, the most advantageous compromise with regard to the hysteretic properties: very low PH losses, very significant reduction in the non-linearity ⁇ G and of tan ( ⁇ ) max ; these improved results of composition No. 4 are obtained by the combined use of the activated ethylenic double bond alkoxysilane and of the radical initiator, as clearly shown a comparison between composition No. 4 on the one hand and the compositions of the prior art No. 1 to No. 3 (compare in particular compositions No.
• composition No. 4 curve C4 reveals a level of reinforcement (module) greater than large deformation
• composition No. 4 suggest both low rolling resistance and very good wear resistance for tire treads based on compositions in accordance with the invention.
• the peroxide also known as a crosslinking agent at a higher rate, typically of the order of 5 to 7 phr
• the peroxide must be introduced into the internal mixer, that is to say during the non-productive phase at the same time as the coupling agent, and not incorporated in the external mixer (productive phase) as usually practiced for a crosslinking agent.
• compositions tested are identical except for the following differences:
• composition No. 6 coupling agent 1-octene-triethoxysilane used alone (4 phr);
• composition No. 7 1-octene-triethoxysilane (4 phr) with which 0.16 phr of the peroxide of formula III-1 is associated;
• composition No. 8 isomeimide of N- (propyltriethoxysilane) (4 phr) with which 0.16 phr of the peroxide of formula III-1 is associated;
• composition No. 9 N- (propyltriethoxysilane) maleamic acid (4 pce) with which it is associated
• the various coupling agents tested are used as before at an isomolar rate with triethoxysilane functions. Relative to the weight of white filler, the rate of coupling agent is in all cases less than 10%> (precisely 9.6%>); the amount of peroxide (component D) in the composition according to the invention is very low: 0.16 phr, or only 3.3% relative to the weight of component C.
• N- (propyltriethoxysilane) maleic acid (formula II-2): in a three-necked flask of 500 ml topped with a condenser, 17.7 g (0.18 mol) of maleic anhydride are dissolved in 60 ml of THF (tetrahydrofuran ) anhydrous; a solution of 41 g (0.1 mol) of 3-aminopropyl-triethoxysilane diluted in 155 ml of anhydrous THF is added slowly (duration: approximately 1 h 30 min), at room temperature (20 ° C); the initially colorless solution then takes on a yellow tint; stirring is continued at room temperature for two hours after which the starting materials have been completely consumed; the reaction medium is concentrated on a rotary evaporator and 57g of a yellow solid is obtained, the NMR analysis of which reveals that it is indeed N- (propyltriethoxysilane) maleamic acid of formula (II-2) mentioned above
• N- (3-propyltriethoxysilane) isomeimide is obtained by the action of dicyclohexylcarbodiimide (DCC) on the N- (3-propyltriethoxysilane) maleic acid in THF, generated in situ from maleic anhydride and 3- aminopropyltriethoxysilane; 41.8 g (0.2 mol) of DCC dissolved in 115 ml of anhydrous THF containing 0.2 mol of N- (3-propyltriethoxy silane) maleamic acid generated in droplets are added dropwise to a 1 liter three-necked flask located in 235 ml of anhydrous THF; a white precipitate of dicyclohexylurea (DHU) appears; stirring at room temperature is continued overnight; the DHU is filtered, the THF is evaporated and the reaction medium filtered a last time to remove the residual DCC; 55 g of an orange-brown liquid are thus obtained, the NMR analysis
• Tables 3 and 4 give the formulation of the various compositions, their properties before and after cooking (150 ° C., 25 minutes).
• Figure 2 reproduces meanwhile the modulus curves (in MPa) as a function of the elongation (in%>); these curves are denoted C6 to C9 and correspond respectively to compositions No. 6 to No. 9.
• modules with the greatest deformations (Ml 00, M300) and higher M300 / M100 ratio, which is indicative of better reinforcement by the reinforcing white charge; - more advantageous hysteretic properties: PH, non-linearity ⁇ G and tan max ( ⁇ ) max significantly lower; higher breaking stresses.
• the incorporation of the peroxide into composition No. 7 comprising as coupling agent the non-activated double-bonded alkoxysilane has, at the very low rate used of 0.16 phr, no effect on the properties of the composition, both in the raw state and in the cooked state; that in other words, the peroxide has no activation effect on the coupling level (white filler / diene elastomer) if the alkoxysilane used does not carry an ethylenic double bond of the activated type.
• FIG. 2 appended clearly confirms the net improvement effect of the coupling provided by the radical initiator in the case of alkoxysilanes with an activated ethylenic double bond: it is clearly seen that the modulus values, for elongations of 100% and more, are substantially identical on compositions N ° 8 and N ° 9 (curves C8 and C9 very close) but very clearly superior to those observed on control compositions N ° 6 and N ° 7 (curves C6 and C7).
• curves C6 and C7 are almost identical, which shows once again that the addition of 0.16 phr of peroxide has no effect on the level of coupling offered by the coupling agent 1- octene-triethoxysilane.
• composition No. 10 SBIR elastomer with TESPT coupling agent (6.4 pce) alone;
• composition No. 1 l SBIR elastomer with TMSPM coupling agent (6 pce) activated by
• composition No. 13 SBR elastomer with TMSPM coupling agent (6 pce) activated by
• compositions No. 11 and No. 13 are in accordance with the invention, compositions No. 10 and No. 12 using the conventional coupling agent (TESPT) are the control compositions.
• the two coupling agents tested are used at an isomolar rate, that is to say approximately 7-8%> by weight relative to the weight of reinforcing white filler; the amount of radical initiator used in the compositions in accordance with the invention is very low (0.20 pce); it represents only 3.3%) by weight of component C.
• compositions No. 11 and No. 13 in accordance with the invention compared to the control compositions, have, and this regardless of the elastomer considered, characteristics which are generally improved: Mooney plasticity sufficiently low in all cases (less than 55 MU); high safety at roasting (T5 of 30 min); high deformation module (M300) and higher M300 / M100 ratio, synonymous with better reinforcement and therefore with an improved level of coupling between the diene elastomer and the reinforcing white filler; lower hysteretic losses (PH).
• the conventional reference coupling agent here provides coupling performance which is lower than that offered by the activated double bond alkoxysilane with which is associated, in the very low proportions recommended, a radical initiator with priming. thermal peroxide type.
• composition No. 14 TESPT coupling agent (4 pce) used alone;
• TMSPM (3 phr) activated by 0.16 phr of radical initiator; addition of a collection agent (2 pce).
• Composition No. 14 is the test control and contains 8%> by weight of TESPT relative to the weight of silica.
• Composition No. 15 is the composition in accordance with the invention and advantageously contains, relative to the weight of silica, less than 8%> of TMSPM coupling agent (precisely 6%>) and, as coupling activator , a very small amount of peroxide (0.16 phr or 5.3% relative to the weight of TMSPM).
• the covering agent is incorporated into the composition, at the same time as TMSPM and peroxide (non-productive stage) to further improve the processing in the raw state (lowering of the viscosity) and the dispersion of the white filler in the elastomeric matrix.
• composition No. 15 compared to control composition No. 14, has reinforcement properties after baking (M300 and M300 / M100 ratio) which are significantly superior, as well as improved hysteresis (PH, ⁇ G and tan ( ⁇ ) max lower): all this is due to a better coupling efficiency of the activated double bond alkoxysilane, in the presence of peroxide, compared to the conventional TESPT alkoxysilane.
• reinforcement properties after baking M300 and M300 / M100 ratio
• compositions comprising, as reinforcing white filler, a blend (50/50 by volume) of silica and alumina (alumina as described in application EP-A-0 810 258 cited above).
• compositions No. 16 and No. 17 are the compositions according to the prior art, only composition No. 18 is in accordance with the invention.
• the two coupling agents tested are used at an isomolar rate in triethoxysilane functions (same number of moles of reactive functions with respect to the total white charge). Relative to white load weight
• the rate of TESPT is equal to around 6% (precisely 6.2%>), that of TMSPM is less than 6% (precisely 5.7%).
• Tables 9 and 10 give the formulation of the various compositions, their properties before and after cooking (20 min at 150 ° C).
• composition No. 19 (control): TMSPM (3.7pce) used alone;
• composition No. 20 composition No. 20 (invention): TMSPM (3.7pce) which is associated with 0.5 pce of AIBN (i.e.
• Tables 11 and 12 give the formulation of the compositions, their properties before and after cooking (25 min at 150 ° C.).
• Figure 3 shows the module curves (in MPa) as a function of the elongation (in%>); these curves are denoted Cl 9 and C20 and correspond respectively to compositions No. 19 and No. 20.
• composition according to the invention is revealed in particular by the properties after baking: - an increase in the modules with strong deformations (Ml 00, M300) and in the ratio (M300 / M100), clear indicators of an improved, correlated reinforcement with more advantageous hysteretic properties: lower tan ( ⁇ ) max , very lower non-linearity ⁇ G *, significantly reduced PH losses.
• Figure 3 confirms the beneficial action of AIBN on the coupling agent, with a modulus curve (C20) which, for the greatest deformations (elongations of 100% and more), is clearly above the control curve (Cl 9), the difference being all the more pronounced as the elongation increases.
• the combination of a coupling agent carrying an activated ethylenic double bond with, in very small quantity, a radical initiator with thermal initiation offers the compositions of the invention a particularly advantageous compromise of properties compared to the compositions of the prior art reinforced with a white filler such as silica.
• the invention finds particularly advantageous 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 based on natural rubber or synthetic polyisoprene and intended for tires for industrial vehicles of the Truck type.
• Table 1

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