Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F279/00—Macromolecular compounds obtained by polymerising monomers on to polymers of monomers having two or more carbon-to-carbon double bonds as defined in group C08F36/00
  • C08F279/02—Macromolecular compounds obtained by polymerising monomers on to polymers of monomers having two or more carbon-to-carbon double bonds as defined in group C08F36/00 on to polymers of conjugated dienes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
  • B60C1/00—Tyres characterised by the chemical composition or the physical arrangement or mixture of the composition
  • B60C1/0016—Compositions of the tread
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08C—TREATMENT OR CHEMICAL MODIFICATION OF RUBBERS
  • C08C19/00—Chemical modification of rubber
  • C08C19/20—Incorporating sulfur atoms into the molecule
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/01—Use of inorganic substances as compounding ingredients characterized by their specific function
  • C08K3/013—Fillers, pigments or reinforcing additives
• • 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
  • C08L51/00—Compositions of graft polymers in which the grafted component is obtained by reactions only involving carbon-to-carbon unsaturated bonds; Compositions of derivatives of such polymers
  • C08L51/04—Compositions of graft polymers in which the grafted component is obtained by reactions only involving carbon-to-carbon unsaturated bonds; Compositions of derivatives of such polymers grafted on to rubbers
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
  • Y02T10/00—Road transport of goods or passengers
  • Y02T10/80—Technologies aiming to reduce greenhouse gasses emissions common to all road transportation technologies
  • Y02T10/86—Optimisation of rolling resistance, e.g. weight reduction 

Definitions

• the present invention relates to a process for obtaining a grafted diene elastomer comprising functional groups along the chain, a rubber composition comprising this grafted elastomer and in particular having improved hysteretic properties in the crosslinked state, and a process for preparation of this composition.
• the invention also relates to a tire tread comprising this composition and to a tire with reduced rolling resistance which incorporates this tread.
• the functionalized polymers obtained can be separated from the reaction medium, leading to their formation by steam extraction of the solvent, without their macrostructure and, consequently, their physical properties changing. Mention may also be made of the European patent document EP-A-877 047, which discloses the incorporation of such polymers with silanol function. to rubber compositions comprising as reinforcing filler carbon black having silica attached to its surface.
• EP-A-692 493 which establishes that diene polymers carrying at the chain end alkoxysilane groups as well as an epoxy group lead to improved reinforcing properties and to reduced hysteretic losses. small and large deformations.
• a disadvantage of these polymers, which have an active functional group for coupling to silica or to carbon black modified on the surface by silica, is that the improvement of the hysteresis and reinforcement properties which they confer on the compositions of Rubber incorporating them is generally accompanied by an ability to process non-crosslinked mixtures which is penalized compared to that of non-functionalized "control" polymers.
• This carboxylic acid functionalization along the chain can also be implemented by means of carbon monoxide, either by hydroformylation followed by oxidation of the aldehyde formed (as described in the US patent document US-A -4,912,145), or by direct hydrocarboxylation of the polymer (as described in the article "A. Nait Ajjou, H. Alper, Macromolecules 29, 1784 (1996)”).
• the catalysts used for these reactions are based on rhodium or palladium.
• a drawback of this functionalization with carbon monoxide lies, on the one hand, in the drastic nature of the operating conditions and, on the other hand, in the frequent formation of a gel in the reaction medium.
• Carboxylic acid functionalization along the chain by means of maleic anhydride is more widespread. It makes it possible to obtain succinic anhydride units along the chain, which are precursors of carboxylic groups. Reference may be made to patent documents US-A-4,082,817 and US-A-4,082,493 for examples of such functionalization.
• the US patent document US-A-5,804,619 presents bitumen / polymer compositions formed from a bituminous matrix in which is distributed a diene elastomer functionalized by functional carboxylic groups, obtained by grafting reaction of the diene elastomer with a precursor compound of the sequences with carboxylic functionality in the presence of a blocked phenol, alone or in combination with a dialkenyl triphosphite, which prevents crosslinking of the elastomer during the grafting operation.
• These compositions can be used as road surfaces or as waterproofing coatings.
• European patent document EP-A-1000 971 presents rubber compositions for tread which are essentially intended to present an improved grip on wet ground and a reduced rolling resistance.
• These compositions include any known reinforcing filler and a graft copolymer comprising carboxylic acid groups along the chain, which is obtained from a starting copolymer prepared in solution derived from a diene and a vinyl aromatic. These groups can, for example, be introduced following copolymerization by means of a radical grafting reaction carried out via a carboxylmercaptan, ' such as 3-mercaptopropionic acid, and a radical initiator, such as dilauroyl peroxide.
• a major drawback of the elastomers grafted by means of this carboxylmercaptan is that they exhibit significant changes in macrostructure compared to the starting elastomers, which result in particular in appreciable increases in Mooney viscosity, in number average molecular mass and in index of polydispersity. This results in an undesirable change in the physical properties of the elastomers following grafting.
• An object of the present invention is to remedy this drawback and it is achieved by implementing a process for obtaining a grafted diene elastomer comprising functional groups along its chain, comprising a radical grafting reaction which is used in solution or in bulk by means of a reagent of the mercaptan type and which is intended to graft said groups on the chain of the starting elastomer and comprises a step of antioxidant treatment, before said radical grafting reaction , by means of an antioxidant agent comprising at least one aromatic amino function.
• the diene elastomer thus treated has, after grafting, a macrostructure practically identical to that of the starting elastomer; preferably, its Mooney viscosity in particular, measured according to standard ASTM D-1646, does not deviate no more than 10 points, more preferably 5 points, of its initial viscosity before grafting.
• diene elastomer in known manner an elastomer (homopolymer or copolymer) which is derived at least in part from diene monomers (monomers carrying two carbon-carbon double bonds, conjugated or not).
• said starting elastomer comprises a molar ratio of units derived from conjugated dienes greater than 30%, which makes it usable for constituting the elastomer matrix of a tire tread composition.
• diene elastomers such as butyl rubbers, nitrile rubbers or copolymers of dienes and of alpha-olefins of the EPDM type, for example, cannot be used in tread compositions because of their level. in motifs of diene origin much less than 30%.
• said starting elastomer is a "highly unsaturated" diene elastomer, that is to say a diene elastomer having a proportion of units of diene origin (conjugated dienes) which is greater than 50%.
• a homopolymer obtained by solution polymerization of a conjugated diene monomer having from 4 to 12 carbon atoms, such as a polybutadiene or a polyisoprene, or a copolymer obtained by copolymerization can be used.
• butadiene-1,3, 2-methyl-1,3-butadiene, 2,3-di (C1-C5 alkyl) -1,3-butadienes such as, for example, are suitable.
• vinyl aromatic compounds for example, styrene, ortho-, meta-, para-methylstyrene, the "vinyl-toluene" commercial mixture, para-tertiobutylstyrene, methoxystyrenes, chlorostyrenes, vinyl mesitylene, divinylbenzene, are suitable. vinylnaphthalene.
• the copolymers can contain between 99% and 20% by weight of diene units and between
• elastomers can for example be block, statistics, sequences, microsequences.
• polybutadienes are suitable and in particular those having a content of -1,2 units between 4% and 80% or those having a cis-1,4 content greater than 80%, synthetic 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 between 20% and 80%, butadiene-isoprene copolymers and in particular those having an isoprene content between 5%> and 90% by weight and a glass transition temperature Tg of -40 at -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 and -50 ° C.
• synthetic polyisoprenes butadiene cop
• butadiene-styrene-isoprene copolymers are particularly suitable those having a styrene content of between 5% and 50% by weight and more particularly between 10% and 40%, an isoprene content of between 15% and 60% by by weight and more particularly between 20% and 50%, a butadiene content of between 5% and 50% by weight and more particularly between 20%> and 40%), a content of -1.2 units of the butadiene part included between 4% and 85%, a content of trans units -1.4 of the butadiene part between 6% and 80%, a content of units -1.2 plus -3.4 of the isoprene part between 5% and 70% "and a content of trans-1,4 units of the isoprene part of between 10% and 50%), and more generally any butadiene-styrene-isoprene copolymer of Tg of between -20 and -70 ° C.
• said starting elastomer is chosen from the group of “highly unsaturated” diene elastomers prepared in solution consisting of polybutadienes (BR), synthetic polyisoprenes (IR), butadiene-styrene copolymers, butadiene-isoprene copolymers (BIR), isoprene-styrene copolymers (SIR), butadiene-styrene-isoprene copolymers (SBIR).
• BR polybutadienes
• IR synthetic polyisoprenes
• BIR butadiene-styrene copolymers
• BIR butadiene-isoprene copolymers
• SIR isoprene-styrene copolymers
• SBIR butadiene-styrene-isoprene copolymers
• said starting elastomer belongs to the family consisting of polybutadienes, butadiene-styrene copolymers and butadiene-styrene-isoprene copolymers prepared in solution.
• said starting elastomer is a butadiene-styrene copolymer prepared in solution.
• said starting elastomer is a butadiene-styrene copolymer prepared in solution having a styrene content of between 20% and 30%> by weight, a vinyl bond content of the part butadiene between 15% and 65%, a content of trans-1,4 bonds between 15% and 75% and a Tg between -20 and -55 ° C.
• the abovementioned starting elastomers which are obtained, for example, in solution from any anionic initiator, whether it is mono-functional or poly-functional, or non-anionic, can be used in the invention.
• an anionic initiator containing an alkali metal such as lithium or an alkaline earth metal such as barium.
• organolithium initiators suitable in particular are those comprising one or more carbon-lithium bonds.
• organolithians such as ethyllithium, n-butyllithium (nBuLi), isobutyllithium, polymethylene dilithium such as 1-4 dilithiobutane.
• Lithium amides can also be used, which are obtained from an acyclic or cyclic secondary amine, such as pyrrolidine or hexamethyleneimine.
• diene elastomers which are initiated by compounds of transition metals, such as compounds of titanium, cobalt or nickel for example, or by rare earths, such as neodymium.
• the polymerization is, as known to those skilled in the art, preferably carried out in the presence of an inert solvent which can for example be an aliphatic or alicyclic hydrocarbon such as pentane, hexane, iso-octane, cyclohexane, methylcyclohexane, cyclopentane, or an aromatic hydrocarbon such as benzene, toluene or xylene.
• This polymerization can be carried out continuously or discontinuously.
• the antioxidant treatment according to the invention to which said starting diene elastomer is subjected is implemented by means of at least one antioxidant agent, comprising at least one aromatic amino function during said grafting reaction, intended to trap the free radicals formed so as to minimize the interactions of said radicals with the chain of said elastomer.
• said antioxidant agent further comprises at least one phenol function which is preferably sterically hindered.
• at least one second antioxidant comprising at least one phenol function which is preferably sterically hindered and which is. lacking an aromatic amino function or an antioxidant of the dialkylphenyl triphosphite type, etc.
• said or at least one of said amino-type antioxidant (s) is chosen from the group consisting of naphthylamines, diphenylamines and p-phenylenediamines.
• the said antioxidant agent (s) of phenolic type is chosen from the group consisting of trialkyl phenols, hydroquinones and polyphenols (it is for example possible to use pyrogallol as polyphenol).
• the antioxidant treatment comprises a second step after the radical grafting reaction.
• This antioxidant treatment is preferably carried out by means of a quantity of said antioxidant agent (s) ranging from 0.2 phr to 1 phr (phr: parts by weight per hundred parts of said starting diene elastomer) .
• the mercaptan type reagent according to the invention which is used for the radical grafting reaction to which said starting elastomer thus treated is subjected, comprises a functional group belonging to the family consisting of hydroxyl, carbonyl, ether, amino groups, nitrile and silane, so that the grafted elastomer obtained optionally comprises, along its chain, hydroxyl, carbonyl, ether, amine, nitrile or silane groups, respectively.
• said mercaptan type reagent comprises a carbonyl functional group belonging to the family consisting of the carboxylic acid, carboxylic acid ester, amide and ketone groups, so that said grafted elastomer has a choice along its chain of carboxylic acid, carboxylic acid ester, amide or ketone groups.
• said reagent of mercaptan type such as a mercaptopropionic acid. or mercaptoundecanoic, contains a carboxylic acid functional group, so that said grafted elastomer comprises along its chain carboxylic acid groups.
• Said grafting reaction is optionally carried out in the presence of a radical initiator, such as a peroxide.
• Another object of the invention is any grafted diene elastomer comprising functional groups along its chain capable of being obtained by the process described below.
• Another object of the invention is to provide a new crosslinkable or crosslinked rubber composition, which exhibits reduced hysteretic losses in the crosslinked state, an improved processability in the non crosslinked state and which can be used for constitute a tire tread.
• This object is achieved in that the applicants have discovered, surprisingly, that a crosslinkable or crosslinked rubber composition obtained by the association with a reinforcing inorganic filler of said grafted diene elastomer having a molar rate of units derived from dienes conjugated greater than 30%>, which contains said functional groups along its chain and which is obtained by said radical grafting reaction, which is carried out in solution or in bulk 'by means of said mercaptan reagent, and is intended to grafting said groups onto the chain of said starting diene elastomer, said grafted elastomer being capable of being obtained by an antioxidant treatment, using at least one antioxidant agent comprising at least one aromatic inactive function, applied to said elastomer of departure prior to said grafting
• composition according to the invention usable for constituting a tire tread having in particular a reduced rolling resistance.
• Said functional groups which comprise said grafted elastomer preferably belong to the family consisting of hydroxyl, carbonyl, ether, amine, nitrile and silane groups and, even more preferably, said functional groups are of carbonyl type and belong to the family constituted by the carboxylic acid, carboxylic acid ester, amide and ketone groups.
• said functional groups are of the carboxylic acid type.
• Said grafted elastomer preferably comes from:
• said grafted elastomer is derived from a butadiene / vinyl aromatic copolymer prepared in solution.
• said rubber composition is such that said grafted elastomer has a number average molecular mass Mn which is greater than 100,000 g / mol.
• said composition is based on an elastomer matrix comprising mainly said grafted elastomer and, even more preferably, this elastomer matrix consists of said grafted elastomer.
• the compositions according to the invention may contain a single grafted diene elastomer such as that mentioned above or a mixture of several of these grafted elastomers.
• the grafted diene elastomer or elastomers according to the invention can be used alone in the composition in accordance with the invention or as a blend with any other diene elastomer functionalized or not which is conventionally used in tires.
• the improvement in the properties of the composition according to the invention will be all the higher as the proportion of the conventional elastomer (s) in this composition will be reduced.
• this or these conventional elastomers may if necessary be present in the composition according to the invention in an amount ranging from 1 to 70 parts by weight per 100 parts by weight of elastomer (s) grafted according to the invention .
• the term "reinforcing inorganic filler” is understood, in a known manner, an inorganic or mineral filler, whatever its color and its origin (natural or synthetic), also called “white” filler or sometimes “clear” filler "In contrast to carbon black (considered as an organic filler in the context of the present description), this inorganic filler being capable of reinforcing on its own, without other means than an intermediate coupling agent, a rubber composition intended for the manufacture of tires, in other words capable of replacing, in its reinforcement function, a conventional charge of tire grade carbon black.
• Such a charge is generally characterized, in a known manner, by the presence of hydroxyl groups (-OH) on its surface.
• the reinforcing inorganic filler is present in the composition of the invention in an amount equal to or greater than 40 phr (phr: parts by weight per hundred parts of elastomer (s)). Also preferably, said reinforcing inorganic filler is present in the reinforcing filler which comprises the composition of the invention according to a mass fraction greater than 50%> and which can range up to 100%.
• said reinforcing inorganic filler is, in whole or at least mainly, silica (SiO 2 ).
• the silica used can be any reinforcing silica known to a person skilled in the art, in particular any precipitated or pyrogenic silica having a BET surface. as well as a CTAB specific surface area both of less than 450 m 2 / g, although highly dispersible precipitated silicas are preferred.
• 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-
• CTAB specific surface is the external surface determined according to the same standard AFNOR-NFT-45007 of November 1987.
• highly dispersible silica means any silica having a very high ability to disaggregate and to disperse in an elastomer matrix, observable in known manner by electron or optical microscopy, on fine sections.
• preferential highly dispersible silicas mention may be made of Perkasil KS 430 silica from Akzo, BV 3380 silica from Degussa, Zeosil 1165 MP and 1115 MP silica from Rhodia, Hi- silica Sil 2000 from the company PPG, the Zeopol 8741 or 8745 silicas from the Huber company, treated precipitated silicas such as for example the silicas "doped" with aluminum described in patent document EP-A-735 088.
• the physical state under which the reinforcing inorganic charge occurs is indifferent, whether in the form of powder, microbeads, granules, or beads.
• the term “reinforcing inorganic filler” is also understood to mean mixtures of different reinforcing inorganic fillers, in particular highly dispersible silicas as described above.
• the reinforcing filler of a rubber composition according to the invention may contain, as a blend (mixture), in addition to the abovementioned reinforcing inorganic filler (s), carbon black in the minority (that is to say according to a mass fraction of less than 50%).
• 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.
• black / silica blends or blacks partially or completely covered with silica are suitable for constituting the reinforcing filler.
• reinforcing fillers comprising carbon blacks covered at least in part with an inorganic layer, for example of silica, which in turn requires the use of a coupling to establish the connection with the elastomer, such as, without limitation, the fillers which are marketed by the company CABOT under the name "CRX 2000", and which are described in the patent document WO-A-96 / 37547.
• aluminas of formula Al 2 O 3
• aluminas with high dispersibility which are described in European patent document EP-A-810 258
• aluminum hydroxides such as those described in patent document WO-A-99/28376.
• the mass fraction of this carbon black in said reinforcing filler is preferably chosen to be less than or equal to 30%>.
• the rubber composition according to the invention also comprises, in conventional manner, a reinforcing inorganic filler / elastomer matrix (also called coupling agent) bonding agent, which has the function of ensuring a sufficient bonding (or coupling), of a nature chemical and / or physical, between said inorganic charge and the matrix, while facilitating the dispersion of this inorganic charge within said matrix.
• a reinforcing inorganic filler / elastomer matrix also called coupling agent
• coupling agent is meant more precisely an agent capable of establishing a sufficient connection of chemical and / or physical nature between the filler considered and the elastomer, while facilitating the dispersion of this filler within the elastomer matrix.
• a coupling agent at least bifunctional, has for example as simplified general formula "Y-T-X", in which:
• Y represents a functional group ("Y" function) which is capable of physically and / or chemically binding to the inorganic charge, such a bond being able to be established, for example, between a silicon atom of the coupling agent and the groups surface hydroxyl (OH) of the inorganic filler (for example surface silanols when it is silica);
• - X represents a functional group (function "X") capable of physically and / or chemically bonding to the elastomer, for example by means of a sulfur atom;
• - T represents a group making it possible to connect Y and X.
• Coupling agents should not be confused with simple agents for recovering the charge considered which, in known manner, may include the Y function active with respect to the charge but are devoid of the X function active with respect to - screw of the elastomer.
• Any coupling agent known for, or capable of ensuring effectively, in rubber compositions which can be used for the manufacture of tires can be used for coupling between a reinforcing inorganic filler such as silica and a diene elastomer, such as, for example, organosilanes, in particular polysulphurized alkoxysilanes or mercaptosilanes, or alternatively polyorganosiloxanes carrying the abovementioned X and Y functions.
• Silica / elastomer coupling agents in particular, have been described in a large number of documents, the best known being bifunctional alkoxysilanes such as polysulphurized alkoxysilanes.
• polysulphurized alkoxysilanes called “symmetrical” or “asymmetrical” according to their particular structure, are used, as described for example in patents US-A-3,842,111, US-A-3,873,489, US-A-3 978 103, US-A-3 997 581, US-A-4 002 594, US-A-4 072 701, US-A-4 129 585, or in more recent patents US-A-5 580 919, US -A-5 583 245, US-A-5 650 457, US-A-5 663 358, US-A-5 663 395, US-A-5 663 396, US-A-5 674 932, US-A -5,675,014, US-A-5,684,171, US-A-5,684,172, US-A-5,696,197, US-A-5,708,053, US-A-5,892,085, EP-A-1 043 357 which detail such known compounds. Particularly suitable, without the following definition being
• - n is an integer from 2 to 8 (preferably from 2 to 5);
• - A is a divalent hydrocarbon radical (preferably alkylene groups in C ⁇ -C ⁇ 8 or arylene groups in C 6 -C ⁇ 2 , more particularly alkylene in Ci- o, in particular in C ⁇ -C 4 in particular propylene);
• radicals R 1 substituted or unsubstituted, identical or different, represent alkyl, C ⁇ -C ⁇ 8 cycloalkyl, C 5 -C ⁇ 8 or C 6 -C ⁇ 8 (preferably alkyl, C ⁇ -C 6 , cyclohexyl or phenyl, in particular C ⁇ -C 4 alkyl groups, more particularly methyl and / or ethyl).
• the radicals R 2 substituted or unsubstituted, identical or different between them, represent a C1-Cis alkoxyl group or C 5 -C ⁇ 8 cycloalkoxyl (preferably C ⁇ -C 8 alkoxyl or Cs-C cycloalkoxyl groups 8 , more preferably C ⁇ -C 4 alkoxyl groups, in particular methoxyl and / or ethoxyl).
• the average value of "h" is a fractional number, preferably ranging from 2 to 5.
• polysulphides in particular disulphides, trisulphides or tetrasulphides
• bis- (alkoxyl (C ⁇ -C 4 ) -alkyl (C ⁇ - C 4 ) silylalkyl (C ! -C) for example bis (3-trimethoxysilylpropyl) or bis (3-triethoxysilylpropyl) polysulphides.
• TESPD bis (3-triethoxysilylpropyl) tetrasulfide, in short TESPT, of formula [(C 2 H 5 O) 3 Si (CH 2 ) 3 S 2 ] or bis (triethoxysilylpropyl) disulfide, is used in particular abbreviated as TESPD, of the formula [(C 2 H 5 O) 3Si (CH 2 ) 3S] 2 .
• the TESPD is marketed for example by the company Degussa under the names Si266 or Si75 (in the second case, in the form of a mixture of disulfide (75% by weight) and polysulfides), or also by the company Witco under the name Silquest Al 589.
• TESPT is marketed for example by the company Degussa under the name Si69 (or X50S when it is supported at 50%> by weight on carbon black), or also by the company Osi Specialties under the denomination.
• Silquest A1289 in both cases, commercial mixture of polysulphides with an average value for n which is close to 4).
• MESPT monoethoxydimethylsilylpropyl tetrasulphide
• compositions in accordance with the invention also comprise, in addition to said grafted elastomer and said reinforcing inorganic filler, plasticizers, pigments, antioxidants, anti-ozone waxes, a crosslinking system based on either sulfur and / or peroxide and / or bismaleimides, crosslinking activators comprising zinc monoxide and stearic acid, extension oils, one or more silica covering agents such as alkoxysilanes, polyols, or amines.
• compositions can be such that said grafted elastomer is extended to a paraffmic, aromatic or naphthenic oil, with an amount of extension oil between 0 and 50 phr.
• the invention also relates to a process for the preparation of a crosslinkable rubber composition in accordance with the invention.
• This process includes:
• a grafted diene elastomer comprising functional groups along its chain and having a molar ratio of units derived from conjugated dienes which is greater than 30%, said grafted elastomer being obtained by a radical grafting reaction implemented in solution or in bulk by means of a reagent of mercaptan type and intended to graft said groups on the chain of a starting diene elastomer, said grafted elastomer being obtained by an antioxidant treatment using at least one antioxidant comprising at least one aromatic amino function applied to said starting elastomer prior to said grafting reaction, (ii) carrying out, at a maximum temperature between 130 ° C.
• thermo working time -mechanics of the constituents of said composition comprising said grafted elastomer and a reinforcing inorganic filler, with the exception of a retic system ulation then (iii) carrying out, at a temperature below said maximum temperature of said first time, a .second mechanical working time during which said crosslinking system is incorporated.
• a subject of the invention is also a tire tread which is such that it comprises a crosslinkable or crosslinked rubber composition such as that mentioned above, or which is such that it consists of this composition.
• a tire according to the invention is such that it includes this tread.
• the macromolecules are physically separated according to their respective sizes in the swollen state, in columns filled with a porous stationary phase. Having implemented this separation, the polymer sample is solubilized at a concentration of approximately 1 g / 1 in tetrahydrofuran.
• a chromatograph sold under the name “WATERS” and under the model “150C” is used for the above-mentioned separation.
• the elution solvent is tetrahydrofuran
• the flow rate is 1 ml / min
• the system temperature is 35 ° C
• the analysis time is 30 min.
• a set of two “WATERS” columns is used, the type of which is “STYRAGEL HT6E”.
• the injected volume of the polymer sample solution is 100 ⁇ l.
• the detector is a "WATERS” differential refractometer whose model is “R401”. Chromatographic data processing software is also used, the trade name of which is "WATERS MILLENIUM”.
• the diazomethane is prepared beforehand as follows. It is obtained by the action of alcoholic potash on N-methyl-N-nitroso-paratoluene sulfonamide, in the presence of diethyl ether and at the temperature of melting ice. The ethereal phase containing the reagent is then recovered by simple distillation.
• the esterification reaction is then carried out in the following manner.
• the elastomer thus treated is then dried in an oven at 50 ° C., under vacuum and under a nitrogen atmosphere.
• the rate of COOH functions is quickly estimated using the Infra-Red (IR) technique. This is made possible by comparing the integration ratio of the signal surface of the carbonyl (1709 cm “1 ) with the signal, of the aromatic protons of styrene (1602 cm “ 1 ).
• the analysis is carried out on a film evaporated on a KBr plate, this being carried out after re-solution of 1 g of dry gum in 50 ml of toluene.
• the infrared spectrometer used is marketed under the name BRUCKER Vector 22.
• An oscillating consistometer is used, as described in standard ASTM D-1646.
• 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 useful torque is measured to maintain this movement after 4 minutes of rotation.
• Copolymer of styrene and butadiene prepared in solution having the following microstructure characteristics, determined by 1 H NMR: mass rate of styrene units: 25.7%> mass rate of 1,2 (vinyl) sequences in units from butadiene: 43.0%.
• a treatment in accordance with the invention applied to this starting SBR consisted of an antioxidant treatment comprising the addition of 0.4 phr of 6-PPD (N- (1,3-dimethylbutyl) -N'-p- phenylenediamine) and to introduce COOH groups by grafting with a part of the thus antioxidized SBR (SBR No. 3), the other part serving as a non-functional control elastomer in the rest of the example (SBR No. 1).
• a treatment not in accordance with the invention consisted in carrying out the grafting without having previously antioxidized the polymer (SBR No. 2). 3) Implementation of radical grafting:
• each of the antioxidant SBRs (SBR n ° 1 and SBR n ° 3) are dissolved in 404 ml of cyclohexane (i.e. 315 g) in a 750 ml Steinie bottle. Heated to 80 ° C after 10 minutes with stirring in a tank at 80 ° C, each polymer solution is bubbled with nitrogen for 10 minutes, then heated again in a tank at 80 ° C for 10 minutes.
• a solution of lauroyl peroxide (Aldrich, 97%) in cyclohexane is prepared from peroxide powder, previously bubbled into a 250 ml Steinie bottle.
• the quantity of peroxide introduced is such that the mercaptan / peroxide molar ratio is equal to 48 (quantity of mercaptan indicated in table 1).
• This peroxide solution is introduced with a double needle into the polymer solution, previously prepared at 80 ° C.
• 3-mercaptopropionic acid (Aldrich, 99%) is injected using a syringe according to the different quantities indicated in table 1.
• the bottle is then placed in a tank at 80 ° C. After 2 hours at 80 ° C, 6.4 mL of a cyclohexane solution of 6-PPD at 40 g / L (i.e. 0.255 g) are added, and the bottle is returned to the tank at 80 ° C for 15 minutes.
• the stripped polymer is drained on rolls and finally dried in an oven at 50 ° C under reduced pressure and under a stream of nitrogen. If one or two coagulations are performed in addition to stripping (see table
• This table 1 shows that the radical grafting of COOH groups on the SBR n ° 2 devoid of antioxidant is accompanied by an evolution of macrostructure, as evidenced by the increase in the Mooney viscosity (+ 20.4 points).
• This table 1 also shows that the presence of the antioxidant comprising an aromatic amino function in the SBR n ° 3 according to the invention prevents the evolution of macrostructure without inhibiting the grafting reaction.
• the yield of the grafting reaction is better in the absence of the antioxidant comprising an aromatic amine function.
• This table 2 shows that the level of grafted COOH groups is practically the same whatever the treatment carried out after the grafting reaction: stripping or stripping followed by coagulation (s). The stripping step is therefore sufficient to remove the mercaptan which is not grafted onto the elastomer.
• the three elastomers SBR No. 1, SBR No. 2 and SBR No. 3a were used for the preparation of rubber compositions No. 1, No. 2 and No. 3a of the tread type, each comprising silica as a reinforcing filler.
• Each of these compositions No. 1, No. 2 and No. 3a has the following formulation (expressed in phr: parts per hundred parts of elastomer):
• Antioxidant (3) 1.9 Anti-ozone wax “C32ST” (6) 1.5
• thermo-mechanical work is carried out for 4 to 5 minutes, up to a maximum drop temperature of approximately 160 ° C.
• the elastomer block is then recovered and cooled.
• thermomechanical working step is carried out in the same mixer for a period of 3 to 4 minutes, with the addition of the antioxidant, up to a maximum drop temperature of approximately 160 ° C.
• thermo-mechanical working time is thus achieved, it being specified that the average speed of the pallets during this first time is 45 rpm.
• compositions thus obtained are then calendered, either in the form of plates (of a thickness ranging from 2 to 3 mm) or thin sheets of rubber, for the measurement of their physical or mechanical properties, or in the form of directly usable profiles, after cutting and / or assembling to the desired dimensions, for example as semi-finished products for tires, in particular for treads.
• Crosslinking is carried out at 150 ° C for 40 min. It will be noted that the introduction of all of the zinc monoxide (ZnO) is carried out at 120 ° C. during the first thermomechanical working step, in order to obtain compositions no 1, no 2 and no 3a crosslinkable.
• ZnO zinc monoxide
• MA300 / MA100 relating to compositions n ° 2 and n ° 3a is superior to that relating to composition n ° 1 and, on the other hand, that the hysteretic properties (at low and strong deformations) are greatly improved compared to those presented by said composition n ° 1.
• composition No. 3a according to the invention has a Mooney “mixture” value which is lower than that of composition No. 2 based on an elastomer which comprises COOH functions along the chain without anti- oxidant.
• composition No. 3a based on SBR No. 3a, which comprises COOH functions along the chain, of silica and characterized by the introduction of all of ZnO at 120 ° C during the first mixing step of the first thermomechanical working time, has rubber properties in the crosslinked state which are improved compared to that of composition No. 1 due to reduced hysteresis and compared to the composition n ° 2 because of an improved aptitude for implementation.
• Example 2 Tests for grafting of COOH groups with 3-mercaptopropionic acid or mercaptoundecanoic acid, in the presence or not of lauroyl peroxide.
• a treatment in accordance with the invention applied to this starting SBR consisted of an antioxidant treatment comprising the addition of 0 , 4 or 0.2 phr of 6-PPD (N- (1,3-dimethylbutyl) - N'-p-phenylenediamine) and to graft as it is the SBR thus protected (SBR n ° 4 or SBR n ° 5 respectively).
• the starting polymers are SBRs of variable microstructure and a BR. All of them underwent, before grafting, a treatment in accordance with the invention consisting of the addition of 0.4 phr of 6-PPD or 0.2 phr of 6-PPD plus 0.2 phr of BPH (2,2 '-methylene bis -4-methyl-6-butylphenol).
• the eight elastomers SBR # 6, SBR # 7b, SBR # 8b, SBR # 9b, SBR # 10, SBR # 1 lb, BR # 12 and BR # 13 were used for the preparation of rubber compositions n ° 6, n ° 7, n ° 8, n ° 9, n ° 10, n ° l 1, n ° 12 and n ° 13 of tread type, each comprising silica as a reinforcing filler.
• compositions No. 6 and No. 7 has the following formulation (expressed in phr: parts per hundred parts of elastomer):
• compositions no. 8 and no. 9b has the following formulation (expressed in pce: parts per hundred parts of elastomer):
• compositions n ° 6, n ° 7, n ° 8, n ° 9, n ° 10, n ° ll, n ° 12 and n ° 13 is carried out, in a first time of thermo-mechanical work, by two stages separated by a cooling phase, then, in a second finishing phase, by mechanical work.
• thermo-mechanical work is carried out for 4 to 5 minutes, up to a maximum drop temperature of approximately 160 ° C.
• the elastomer block is then recovered and cooled.
• thermomechanical working step is carried out in the same mixer for a period of 3 to 4 minutes, with the addition of the antioxidant, up to a maximum drop temperature of approximately 160 ° C.
• thermo-mechanical working time is thus achieved, it being specified that the average speed of the pallets during this first time is 45 rpm.
• the mixture thus obtained is recovered, it is cooled and then, in an external mixer (homo-finisher), the sulfur, the sulfenamide and the ZBEC (where there are) are added at 30 ° C., still mixing the whole for a period of 3 to 4 minutes (aforementioned second time of mechanical work).
• an external mixer homo-finisher
• the sulfur, the sulfenamide and the ZBEC are added at 30 ° C., still mixing the whole for a period of 3 to 4 minutes (aforementioned second time of mechanical work).
• compositions thus obtained are then calendered, either in the form of plates (of a thickness ranging from 2 to 3 mm) or thin sheets of rubber, for the measurement of their physical or mechanical properties, or in the form of directly usable profiles, after cutting and / or assembling to the desired dimensions, for example as semi-finished products for tires, in particular for treads.
• Crosslinking is carried out at 150 ° C for 40 min.
• composition No. 7 based on SBR No. 7b which comprises COOH functions along the chain, of silica and characterized by the introduction of all of the ZnO at 120 ° C. during the first mixing step of the first thermomechanical working time, exhibits rubber properties in the crosslinked state (in particular hysteretic properties with low deformations) which are markedly improved compared to that of composition no.
• MA300 / MA100 relating to composition no. 9 (based on SBR no. 9b) is superior to that relating to composition no. improved compared to those presented by said composition No. 8.
• composition No. 9 based on SBR No. 9b which comprises COOH functions along the chain, of silica and characterized by the introduction of all of the ZnO at 120 ° C. during the first mixing step of the first thermomechanical working time, exhibits rubber properties in the crosslinked state (in particular hysteretic properties with low deformations) which are markedly improved compared to that of composition No. 8.
• MA300 / MA100 relating to composition no.11 (based on SBR no.1 lb) is superior to that relating to composition no.10 and, on the other hand, that the hysteretic properties (at low and high deformations) are greatly improved compared to those presented by said composition No. 10.
• composition No. 1 based on SBR No. l lb which comprises COOH functions along 'of chain, silica and characterized by introducing the entire ZnO at 120 ° C during the first mixing step of the first thermomechanical working time, exhibits rubber properties in the crosslinked state (in particular hysteretic properties with small deformations) which are markedly improved compared to that of composition No. 10.
• MA300 / MA100 relating to composition no. 13 is greater than that relating to composition no. 12 and, on the other hand, that the hysteretic properties (at low and high deformations) are strongly improved compared to those presented by said composition No. 12.
• Example 4 Tests for grafting of COOH groups with mass 3-mercaptoundecanoic acid.
• a treatment in accordance with the invention applied to this starting SBR consisted of an antioxidant treatment comprising the addition of 0.4 or 0.2 phr of 6-PPD (N- (1,3-dimethylbutyl) - N'-p- phenylenediamine) and to graft as is the thus antioxidant SBR (SBR n ° 14).
• the operating mode implemented is as follows:
• reaction is carried out in the open air on a mixing tool of the Brabender type maintained at 40 ° C. or at 100 ° C., throughout the duration of the operations, as indicated in table 12.

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