EP1620471A2

EP1620471A2 - Method for obtaining an elastomer graft with functional groups along the chain and rubber compositions

Info

Publication number: EP1620471A2
Application number: EP04730253A
Authority: EP
Inventors: Sylvie Gandon-Pain
Original assignee: Michelin Recherche et Technique SA Switzerland; Michelin Recherche et Technique SA France; Societe de Technologie Michelin SAS
Current assignee: Compagnie Generale des Etablissements Michelin SCA
Priority date: 2003-04-29
Filing date: 2004-04-29
Publication date: 2006-02-01
Also published as: FR2854404B1; RU2005136980A; CN1780859B; FR2854404A1; JP4874791B2; AU2004234058A1; BRPI0409806A; WO2004096865A2; KR101186129B1; CN1780859A; WO2004096865A3; KR20060008938A; US7312264B2; JP2006524725A; US20060089445A1; RU2337923C2

Abstract

The invention concerns a method for obtaining a grafted diene elastomer comprising functional groups along the chain, a rubber composition comprising said grafted elastomer and having in particular hysteretic properties when crosslinked, and a method for preparing said composition. The invention also concerns a tyre running tread comprising said composition and a tyre with reduced running resistance incorporating said running tread. The method for obtaining said grafted elastomer consists in performing a free radical grafting reaction carried out in solution or in mass using a mercaptan type reagent and designed to graft said groups on the chain of an initial elastomer. The invention is characterized in that it consists in treating said initial elastomer with an antioxidant comprising at least one aromatic amine function prior to the grafting reaction, so that the grafted elastomer has a macrostructure almost identical to that of the initial elastomer. The inventive rubber composition comprises a reinforcing inorganic filler, and said grafted elastomer has a proportion of molar units derived from conjugated dienes higher than 30 %.

Description

PROCESS FOR OBTAINING A GRAFT ELASTOMER WITH FUNCTIONAL GROUPS ALONG THE CHAIN AND RUBBER COMPOSITION

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.

Since fuel economy and the need to preserve the environment have become a priority, it is desirable to produce mixtures with good mechanical properties and as little hysteresis as possible so that they can be used in the form of rubber usable for the manufacture of various semi-finished products used in the composition of tire casings, such as for example underlayments, sidewalls, treads, and in order to obtain tires having a rolling resistance scaled down.

To achieve such an objective, numerous solutions have been proposed consisting in particular of modifying the structure of the diene polymers and copolymers at the end of polymerization by means of functionalization, coupling or staring agents. The vast majority of these solutions have concentrated on the use of functionalized polymers which are active with respect to carbon black, with the aim of obtaining a good interaction between the polymer thus modified and carbon black. .

By way of illustration of this prior art relating to reinforcing fillers consisting of carbon black, mention may for example be made of the American patent document US-A-3 135 716, which describes the reaction of living diene polymers at the end of the chain. with a polyfunctional organic coupling agent to obtain polymers with improved properties. Mention may also be made of American patent document US-A-3 244 664, which discloses the use of tetra alkoxysilanes, as coupling or staring agent for diene polymers. The use of silica as reinforcing filler in crosslinkable rubber compositions, in particular intended to enter into the constitution of tire treads, is old. However, this use has remained very limited, due to the unsatisfactory level of certain physical properties of such compositions, in particular the abrasion resistance.

This is the reason why it has been proposed to use, in order to overcome these drawbacks, functionalized diene polymers in place of the non-functionalized polymers which were previously used, and in particular polymers functionalized by alkoxysilane derivatives, such as tetra ethoxysilanes. One can for example quote the American patent document US-A-5,066,721, which describes a rubber composition comprising a diene polymer functionalized by an alkoxysilane having at least one non-hydrolysable alkoxyl residue, which allows the removal of the solvent from polymerization by stripping with water vapor.

A disadvantage of these functionalization reactions lies in the coupling reactions which accompany them, which generally requires the use of an excess of alkoxysilane and / or intense mixing, to minimize these coupling reactions.

Another drawback of these reactions lies in the subsequent implementation of the steam stripping operation, which is necessary to remove the polymerization solvent.

In general, experience shows that the functionalized polymers obtained undergo changes in macrostructure during this stripping operation, which leads to severe degradation of their properties, unless they limit themselves to using them as of functionalizing agent an alkoxysilane belonging to a restricted family, such as that which is described in the aforementioned document US-A-5,066,721.

Consequently, it follows from the above that the use of diene polymers comprising an alkoxysilane function to obtain rubber compositions comprising silica as reinforcing filler is not satisfactory, despite the improved physical properties of these compositions .

This is the reason why research has been carried out on other functionalization reactions, always with a view to obtaining such rubber compositions. By way of example, mention may be made of French patent document FR-A-2 740 778 in the name of the applicant, which discloses the incorporation into rubber compositions comprising, as reinforcing filler, silica in the majority ( for example comprising a blend of silica and carbon black), diene polymers bearing at the chain end a silanol function or ^• a polysiloxane block having a silanol end. For example, a functionalizing agent consisting of a cyclic polysiloxane, such as hexamethylcyclotrisiloxane, is used. 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.

It has been established that these polymers confer rubber properties, in particular hysteretic and of reinforcement in the crosslinked state, which are improved compared to those of control compositions based on nonfunctionalized diene polymers, and which are at least analogous to those of compositions based on diene polymers comprising an alkoxysilane function.

Mention may also be made of European patent document 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.

Among the other functionalization reactions studied, mention may, for example, be made of functionalization along the chain by carboxylic acid groups. This carboxylic acid functionalization along the chain can be carried out by direct metallation, in the presence of N, N, N ', N'-tetramethylethylenediamine (TMED), by means of butyl lithium or metallic sodium (as described in the documents US -A-3 978 161 and US-A-3 976 628, respectively), followed by carbonation by means of carbon dioxide. Such a method has the disadvantage of generally leading to cuts in the chain of the modified polymer.

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.

However, this functionalization can also lead to the formation of a gel.

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.

Thanks to the process of the invention, 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.

By diene elastomer is meant 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).

Preferably, 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. It will be noted that certain 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%.

Even more preferably, 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%.

As the starting elastomer, 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. solution of one or more dienes conjugated with one another or with one or more vinyl aromatic compounds having 8 to 20 carbon atoms, such as a butadiene / vinyl aromatic or butadiene / vinyl aromatic / isoprene copolymer.

By way of conjugated dienes, butadiene-1,3, 2-methyl-1,3-butadiene, 2,3-di (C1-C5 alkyl) -1,3-butadienes such as, for example, are suitable. , 3-dimethyl-1,3-butadiene, 2,3-diethyl-1,3-butadiene, 2-methyl-3-ethyl-1,3-butadiene, 2-methyl-3-isopropyl-1, 3 -butadiene, an aryl-1,3-butadiene, 1,3-pentadiene, 2,4-hexadiene.

As 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

1% and 80% by weight of vinyl aromatic units, and 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 agent and / or randomizing employed. The elastomers can for example be block, statistics, sequences, microsequences.

Preferably, 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. In the case of 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. In a particularly preferred manner, 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). Even more preferably, said starting elastomer belongs to the family consisting of polybutadienes, butadiene-styrene copolymers and butadiene-styrene-isoprene copolymers prepared in solution.

Advantageously, said starting elastomer is a butadiene-styrene copolymer prepared in solution.

According to an advantageous embodiment of the invention, 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. However, use is preferably made of an anionic initiator containing an alkali metal such as lithium or an alkaline earth metal such as barium.

As organolithium initiators suitable in particular are those comprising one or more carbon-lithium bonds. We can for example cite aliphatic 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.

Also usable in the invention are the 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. It is generally carried out at a temperature between 20 ° C and 120 ° C, preferably between 30 ° C and 100 ° C. 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.

According to an alternative embodiment, said antioxidant agent further comprises at least one phenol function which is preferably sterically hindered. According to another variant, use is also made of 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.

Advantageously, 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). According to an alternative embodiment, advantageously, 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. According to an advantageous embodiment of the invention, 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.

Even more advantageously, 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 reaction, so that said grafted elastomer has a macrostru practically identical to that of said starting elastomer, exhibits losses hysteretics reduced to small and large deformations, analogous to those presented by known compositions based on polymers comprising active functional groups for coupling with silica (such as the abovementioned alkoxysilane or silanol groups), while having setting properties implemented in the non-crosslinked state which are improved compared to those of these known compositions loaded with silica and which are comparable to those of compositions loaded with silica based on non-functionalized polymers.

These characteristics make the 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. Advantageously, said functional groups are of the carboxylic acid type.

Said grafted elastomer preferably comes from:

- a homopolymer obtained by solution polymerization of a conjugated diene monomer having 4 to 12 carbon atoms, such as a polybutadiene or a polyisoprene, or

- A copolymer obtained by solution copolymerization of one or more dienes conjugated with one another and / or with one or more vinylaromatics of 8 to 20 carbon atoms, such as a butadiene / vinylaromatic or butadiene / vinylaromatic / isoprene copolymer.

Even more preferably, said grafted elastomer is derived from a butadiene / vinyl aromatic copolymer prepared in solution.

According to another preferred characteristic of the invention, said rubber composition is such that said grafted elastomer has a number average molecular mass Mn which is greater than 100,000 g / mol.

According to another preferred characteristic of the invention, 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. Of course, 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.

It will be noted that 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. Advantageously, 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 .

In the present application, 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.

Preferably, 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%.

Advantageously, 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.

In the present description, 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.

The term “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. As nonlimiting examples of such 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. Of course, the term “reinforcing inorganic filler” is also understood to mean mixtures of different reinforcing inorganic fillers, in particular highly dispersible silicas as described above. It will be noted that 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%). As 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. By way of nonlimiting examples of such blacks, mention may be made of blacks NI 15, N134, N234, N339, N347, N375.

For example, black / silica blends or blacks partially or completely covered with silica are suitable for constituting the reinforcing filler. Also suitable are 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.

As reinforcing inorganic filler, it is also possible to use, without limitation, aluminas (of formula Al ₂ O ₃ ), such as aluminas with high dispersibility which are described in European patent document EP-A-810 258 , or also aluminum hydroxides, such as those described in patent document WO-A-99/28376.

In the case where the reinforcing filler contains only an inorganic reinforcing filler and carbon black, the mass fraction of this carbon black in said reinforcing filler is preferably chosen to be less than or equal to 30%>.

However, experience shows that the aforementioned properties of the composition according to the invention are all the more improved, that the reinforcing filler which it comprises contains a higher mass fraction of reinforcing inorganic filler, and that said properties are optimal when said composition contains only an inorganic reinforcing filler, for example silica, as reinforcing filler. The latter case therefore constitutes a preferred example of a rubber composition according to the invention.

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.

By 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. Such a coupling agent, at least bifunctional, has for example as simplified general formula "Y-T-X", in which:

Y represents a functional group ("Y" function) which is capable of physically and / or chemically binding to the inorganic charge, such a bond being able to be established, for example, between a silicon atom of the coupling agent and the 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.

In particular, 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 limiting, symmetrical polysulphurized alkoxysilanes corresponding to the following general formula (I): (I) Z - A - S _n - TO - Z, in which:

- n is an integer from 2 to 8 (preferably from 2 to 5); - A is a divalent hydrocarbon radical (preferably alkylene groups in Cι-Cι ₈ or arylene groups in C ₆ -Cι ₂ , more particularly alkylene in Ci- o, in particular in Cι-C ₄ in particular propylene);

- Z responds to one of the formulas below:

R2, in which:

- the radicals R ^1, substituted or unsubstituted, identical or different, represent alkyl, Cι-Cι ₈ cycloalkyl, C ₅ -Cι ₈ or C ₆ -Cι ₈ (preferably alkyl, Cι -C ₆ , cyclohexyl or phenyl, in particular Cι-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 -Cι ₈ cycloalkoxyl (preferably Cι-C ₈ alkoxyl or Cs-C cycloalkoxyl groups ₈ , more preferably Cι-C ₄ alkoxyl groups, in particular methoxyl and / or ethoxyl). In the case of a mixture of polysulphurized alkoxysilanes corresponding to formula (I) above, in particular the usual mixtures commercially available, it will be understood that the average value of "h" is a fractional number, preferably ranging from 2 to 5.

As polysulphurized alkoxysilanes, mention will be made more particularly of polysulphides (in particular disulphides, trisulphides or tetrasulphides) of bis- (alkoxyl (Cι-C ₄ ) -alkyl (Cι- C ₄ ) silylalkyl (C _! -C)), for example bis (3-trimethoxysilylpropyl) or bis (3-triethoxysilylpropyl) polysulphides. Among these compounds, 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). Mention will also be made of monoalkoxysilanes tetrasulphides, such as monoethoxydimethylsilylpropyl tetrasulphide (abbreviated as MESPT), which are the subject of international patent application PCT / EP02 / 03774 in the name of the applicants. The 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.

In particular, these 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:

(i) the preparation of 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. and 200 ° C., a first 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.

Due to the reduced hysteresis which characterizes a rubber composition according to the invention in the crosslinked state, it will be noted that a tire whose tread comprises said composition has an advantageously reduced rolling resistance.

A tire according to the invention is such that it includes this tread.

The aforementioned characteristics of the present invention, as well as others, will be better understood on reading the following description of several exemplary embodiments of the invention, given by way of illustration and not limitation.

Experimental techniques used for the characterization of the polymers obtained:

a) The SEC technique (size exclusion chromatography) was used to determine the molecular weight distributions relating to samples of these polymers. From standard products whose characteristics are described in Example 1 of European patent document EP-A-692 493, this technique made it possible to evaluate for a sample a number molecular mass which has a relative value, at the difference from that determined by osmometry, as well as a weight average molecular mass (Mw). We deduced the polydispersity index (Ip = Mw / Mn) from this sample.

According to this technique, 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 and 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 μl. 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".

b) In order to calculate the rate of COOH functions (in meq / kg of polymer) and the number of corresponding functional units per polymer chain, an assay method was used according to the 1 H NMR technique, after esterification with an excess diazomethane, reagent known to react with the COOH functions. More specifically, this method consists in obtaining, using diazomethane, methyl ester functions from the COOH functions which have been fixed on the elastomer, with a view to indirectly and quantitatively accessing the rates of COOH functions by 1 H NMR.

(i) 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.

(ii) A sample of the elastomer having been washed and dried in a specific manner is dissolved in toluene, so that it can be characterized analytically.

(iii) This specific preparation consists in treating the elastomer by three successive solutions in toluene, respectively followed by coagulations in a mixture which consists of acetone and water and which is acidified to pH = 2 with l hydrochloric acid, in order to eliminate all possible traces of acid compounds (stopper, antioxidant, residues catalytic, by-products such as isovaleric acid, in particular). The elastomer thus treated is then dried in an oven at 50 ° C., under vacuum and under a nitrogen atmosphere.

(iv) The ethereal solution containing the diazomethane is then added thereto, so that there is an excess of reagent with respect to the COOH functions. The polymer thus treated is subsequently coagulated in methanol. The polymer is then dried in an oven at room temperature and under high vacuum, using a vane pump.

(v) A ^λ H NMR analysis is then carried out in the following manner.

A sample of the polymer thus esterified is dissolved in carbon sulphide. We use for the analysis of the NMR signal ^! H a spectrometer marketed under the name BRUKER AC200. The characteristic signal of the three methyl protons of COOCH ₃ allows quantitative access to the initial rate of COOH functions of the functional polymer.

In some cases, 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.

c) For polymers and rubber compositions, the Mooney viscosities

ML (1 + 4) at 100 ° C are measured according to standard ASTM D-1646.

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. The Mooney plasticity (ML 1 + 4) is expressed in “Mooney unit” (MU, with 1 MU = 0.83 N.m).

d) The glass transition temperatures Tg of the polymers are measured using a differential scanning calorimeter. Example 1: Introduction of COOH groups on solutions of elastomers treated by grafting of 3-mercaptopropionic acid up to 40 meq / kg

1) Starting elastomer used:

Copolymer of styrene and butadiene (SBR) 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%.

This SBR has a Tg of -37 ° C (with ΔT = 7) and a Mooney viscosity ML (l + 4) of 33.6.

2) Treatments conforming or not to the invention applied to this starting elastomer:

a) 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). b) 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:

45 g of 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.

In parallel, 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.

Following this, 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 reaction medium is then stripped in the presence of 10 ml of 37% hydrochloric acid (pH = 2). 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

2), these are carried out after re-solution in toluene (37.5 mL / g) with an acetone / HCl water mixture at 35% in the proportions: 1/4/1 by volume.

Table 1 below details the results obtained for these syntheses, in terms of Mooney viscosity ML (l + 4), of average molecular mass in number Mn (SEC technique), of polydispersity index Ip (SEC technique), of rate of COOH functions (IR technique) and yield. Table 1

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. However, it is found that the yield of the grafting reaction is better in the absence of the antioxidant comprising an aromatic amine function. Through these results, it also appears that in order to reach a functional level close to 40 meq / kg, it is necessary to introduce mercaptan more into the reaction medium when an antioxidant comprising an aromatic amino function is present. ,

We have also sought to evaluate the incidence of stripping and coagulation treatments carried out after the grafting reaction, for the SBRs which have been grafted in the presence or in the absence of the antioxidant comprising an aromatic amine function. Table 2 below specifies the value in meq. / Kg of the rate of COOH functions determined by NMR for each of the two grafted elastomers having been “stripped” or else “stripped” and coagulated 1 or 2 times.

Table 2:

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.

In this example, 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):

Elastomer 100

Silica (1) 80 Aromatic oil ("ENERDEX 65") (5) 39.5

Liaison officer (2) 6.4

ZnO 2.5

Stearic acid 2

Antioxidant (3) 1.9 Anti-ozone wax “C32ST” (6) 1.5

Sulfur 1.2

Sulfenamide (4) 2

Diphenylguanidine 1.5

With:

(1) = Silica "Zeosil. 1165 MP" from the company Rhodia,

(2) = Liaison agent "Si69" from Degussa,

(3) = N- (1,3-dimethylbutyl) -N'-phenyl-p-phenylenediamine,

(4) = N-cyclohexyl-2-benzothiazylsulfenamide,

(5) = Aromatic oil from the company Hansen & Rosenthal European. (6) = Anti-ozone wax from Repsol Each of the following compositions is produced, in a first time of thermomechanical work, by two stages separated by a cooling phase, then, in a second time of finishing, by mechanical work.

Is successively introduced into an internal laboratory mixer of the "Banbury 'type, whose capacity is 400 cm ³ , which is filled to 70% and whose initial temperature is approximately

90 ° C, the elastomer, two thirds of the reinforcing filler, the coupling agent, diphenylguanidine and stearic acid, then, approximately one minute later, the rest of the reinforcing filler, the aromatic oil and the anti-ozone wax “C32ST”.

The first stage of 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.

Then a second 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.

The first aforementioned 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 and the sulfenamide are added at 30 ° C., mixing everything again for a period of 3 to 4 minutes (second time aforementioned mechanical work).

The 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.

The results are reported in Table 3 below.

Table 3:

Composition No. 1 No. 2 No. 3a

Elastomer SBR n ° l SBR n ° 2 SBR n ° 3a

ML (1 + 4) at 100 ° C (gum) 30 49 38

Uncrosslinked properties

ML (1 + 4) at 100 ° C 49 74 68

("Mooney mix")

Cross-linked properties

Shore A 67.7 59.5 59.6

MA10 5.56 3.53 3.59

MAY 00 1.87 2.05 2.10

MA300 2.04 2.75 2.76

MA300 / MA100 1.09 1.34 1.31

Scott breaking index at 20 ° C Fr (MPa) 18.5 20.91 20.01

Ar (%) 527 484 487

Losses 60 ° C 33.57 19.87 20.2

Dynamic properties as a function of deformation

Delta G * (MPa) at 23 ° C 4.34 0.29 0.32 Tan (δ) max at 23 ° C. 0.338 0.145 0.149 Concerning the properties in the crosslinked state, it will be noted, on the one hand, that the ratio

MA300 / MA100 relating to compositions n ° 2 and n ° 3a (based respectively on SBR n ° 2 and SBR 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.

Note that 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.

In other words, 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.

The starting SBR used is the same as that of Example 1 (ML (l + 4) = 33.6) 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 procedure followed is the same as that described in Example 1, unless otherwise indicated concerning the nature and the quantities of the products added or the method of introduction of the mercaptan. The mercaptan was in fact added directly to the polymer solution as in Example 1 or to the peroxide solution. The operating conditions are summarized in table 4

Table 4:

The results of these grafts are summarized in Table 5 Table 5

The results of this table confirm that 6-PPD does not interfere with grafting and that, whatever the mercaptoacid used, it avoids the evolution of macrostructure, all the more so since it is in significant quantity (SBR n ° 4a has a less degraded macrostructure than SBR n ° 5a for which the antioxidant was added in unusual proportions of only 0.2 phr, in order to demonstrate the influence of the amount of antioxidant on grafting). Through these results, it is verified that the grafting yield is higher the lower the rate of 6-PPD (SBR No. 4a has a worse grafting yield than SBR No. 5a).

The comparison of SBR No. 4a with SBR No. 3 of Example 1 shows that the mode of introduction of mercaptan has a negligible influence on the efficiency of grafting.

These results also show that grafting is possible without peroxide for the benefit of the macrostructure but that the yield is greatly penalized (SBR No. 5b has a less good grafting yield than SBR No. 5a). Example 3:

Tests for grafting of COOH groups with 3-mercaptopropionic acid on different polymers.

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 procedure followed for grafting is the same as that described in Example 1, unless otherwise indicated concerning the quantities of products added. The characteristics of the starting polymers and the operating conditions are summarized in Table 6.

Table 6

Table 7 brings together all the results of these grafting reactions:

Table 7

It appears from this table that the grafting applies to a wide range of polymers. These results demonstrate the existence of a relationship between the microstructure and the efficiency of grafting: the yield is higher the higher the vinyl content, regardless of the antioxidant present in the reaction medium. during grafting (aromatic amine alone or associated with a phenol). In this example, 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.

Each of these compositions No. 6 and No. 7 has the following formulation (expressed in phr: parts per hundred parts of elastomer):

Elastomer 75

PB113 25 Silica (1) 80

Aromatic oil ("ENERDEX 65") (5) 37

Liaison officer (2) 6.4

ZnO 2.5

Stearic acid 2

Antioxidant (3) 1.9

Anti-ozone wax "C32ST" (6) 1.5

Sulfur 1.2

Sulfenamide (4) 2

Diphenylguanidine 1.5

With:

(1) = Silica "Zeosil 1165 MP" from the company Rhodia,

(2) = Liaison agent "Si69" from Degussa,

(3) = N- (1,3-dimethylbutyl) -N'-phenyl-p-phenylenediamine,

(4) = N-cyclohexyl-2-benzothiazylsulfenamide, (5) = Aromatic oil from Hansen & Rosenthal European

(6) = Anti-ozonizing wax from Repsol

Each of these compositions no. 8 and no. 9b has the following formulation (expressed in pce: parts per hundred parts of elastomer):

Elastomer 100

Silica (1) 50

Liaison officer (2) 8

ZnO 2.5

Stearic acid 2

Antioxidant (3) 2

Paraffin 1

Sulfur 1.2

Sulfenamide (4) 1.2

Diphenylguanidine 1

ZBEC (5) 0.2

With:

(1) = Silica "Zeosil 1165 MP" from the company Rhodia,

(2) = Liaison agent “Si69” supported on black from the company Degussa, (3) = N- (1,3-dimethylbutyl) -N'-phenyl-p-phenylenediamine,

(4) = N-cyclohexyl-2-benzothiazylsulfenamide,

(5) = Zinc dibenzyldithiocarbamate Each of these compositions no. 10 and no. 11 has the following formulation (expressed in phr: parts per hundred parts of elastomer):

Elastomer 100

Silica (1) 50

Liaison officer (2) 8

ZnO 2.5

Stearic acid 2

Antioxidant (3) 2

Paraffin 1

Sulfur 1.2

Sulfenamide (4) 1.2

Diphenylguanidine 1

ZBEC (5) 0.2

With:

(1) = Silica "Zeosil 1165 MP" from the company Rhodia,

(2) = Liaison agent "Si69" supported on black by Degussa,

(3) = N- (1,3-dimethylbutyl) -N'-phenyl-p-phenylenediamine,

(4) = N-cyclohexyl-2-benzothiazylsulfenamide,

(5) = Zinc dibenzyldithiocarbamate Each of these compositions No. 12 and No. 13 has the following formulation (expressed in phr: parts per hundred parts of elastomer):

Elastomer 100

Silica (1) 80 Aromatic oil ("ENERDEX 65") (5) 39.5

Liaison officer (2) '6.4

ZnO 2.5

Stearic acid 2 Antioxidant (3) 1.9

Anti-ozone wax "C32ST" (6) 1.5

Sulfur 1.2

Sulfenamide (4) 2

Diphenylguanidine 1.5

With:

(1) = Silica "Zeosil 1165 MP" from the company Rhodia,

(2) = Liaison agent "Si69" from Degussa,

(3) = N- (1,3-dimethylbutyl) -N'-phenyl-p-phenylenediamine,

(4) = N-cyclohexyl-2-benzothiazylsulfenamide, (5) = Aromatic oil from the company Hansen & Rosenthal European

(6) = Anti-ozonizing wax from Repsol

Each of the following 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.

Is successively introduced into an internal laboratory mixer of the 'Banbury' type, whose capacity is 400 cm ³ , which is filled to 70%> and whose initial temperature is approximately

90 ° C, the elastomer, two thirds of the reinforcing filler, the coupling agent, diphenylguanidine and stearic acid, then, approximately one minute later, the rest of the reinforcing filler, the aromatic oil and anti-ozone wax "C32ST" or paraffin 6266. The first stage of 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.

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).

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. 6, no. 7, no. 8 , n ° 9, n ° 10, n ° l 1, n ° 12 and n ° 13 crosslinkable.

The results are reported in Tables 8, 9, 10 and 11 below. Table 8:

Composition n ° 6 n ° 7

Elastomer SBR n ° 6 SBR n ° 7b ML (1 + 4) at 100 ° C (gum) 5O0 54

Uncrosslinked properties

ML (l + 4) at l00 ° C. 58 56

("Mooney mix")

Properties in crosslinked state Shore A 62.3 56.3

MA10 4.44 3.03

MAY 00 1.64 1.59

MA300 2.03 2.19

^• MA300 / MA100 1.24 1.37 Scott breaking index at 20 ° C

Fr (MPa) 18.97 21.76

Ar (%) 512,576

Losses, 60 ° C 26.28 21.17

Dynamic properties as a function of the deformation Delta G * (MPa) at 23 ° C 3.46 0.44

Tan (δ) max at 23 ° C 0.348 0.174

Concerning the properties in the crosslinked state, it will be noted, on the one hand, that the ratio

MA300 / MA100 relating to composition n ° 7 (based on SBR n ° 7b) is superior to that relating to composition n ° 6 and, on the other hand, that the hysteretic properties (with weak and strong deformations) are strongly improved compared to those presented by said composition No. 6. In other words, 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.

Table 9:

Composition n ° 8 n ° 9

Elastomer SBR n ° 8 SBR n ° 9b

ML (1 + 4) at 100 ° C (gum) 55.0 58.0

Properties in the non-crosslinked state ML (1 + 4) at 100 ° C 56 74 ("Mooney mixture")

P Prroopprriiééttéss à à l''ététatt rrééttiicciulf: "

S Shhoorree AA 6 699..55 66.0

MA10 7.28 5.91

MAY 00 2.67 2.74

MA300 3.43 4.06

MA300 / MA100 1.28 1.48

Scott breaking index at 20 ° C

Fr (MPa) 21.56 23.69

Ar (%) 385,371

Losses 60 ° C 23.17 18.10

Dynamic properties as a function of the deformation Delta G * (MPa) at 23 ° C 2.87 0.53

Tan (δ) max at 23 ° C 0.195 0.103 Concerning the properties in the crosslinked state, it will be noted, on the one hand, that the ratio

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.

In other words, 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.

Table 10:

Composition No. 10 No. l l

Elastomer SBR n ° 10 SBR n ° 11b ML (1 + 4) at 100 ° C (gum) 54 ^ 5 60.0

Uncrosslinked properties

MS (l + 4) at l00 ° C 53.3 76.4 ("Mooney mixture")

Properties in the crosslinked state Shore A 69.2 66.6

MA10 6.69 5.47

MA100 2.14 2.25

MA300 2.72 3.27

MA300 / MA100 1.27 1.45 Scott breaking index at 20 ° C

Fr (MPa) 26.26 20.41

Ar (%) 475,347

Losses 60 ° C 292 24.1

Dynamic properties as a function of the deformation Delta G * (MPa) at 23 ° C 3.37 0.73

Tan (δ) ma at 23 ° C 0.233 0.140 Concerning the properties in the crosslinked state, it will be noted, on the one hand, that the ratio

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.

In other words, the 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.

Table 11:

Composition No. 12 No. 13

Elastomer BR n ° 12 BR n ° 13 ML (1 + 4) at 100 ° C (gum) 3O0. 39.5

Uncrosslinked properties

ML (1 + 4) at 100 ° C 80.4 95.1

("Mooney mix")

Properties in the crosslinked state Shore A 61.9 58.0

MA10 4.59 3.72

MAY 00 1.47 1.49

MA300 1.47 1.67

MA300 / MA100 1.00 1.12 Scott breaking index at 20 ° C

Fr (MPa) 17.99 17.17

Ar (%) 628,523

Losses 60 ° C 23/7 20.6

Dynamic properties as a function of the deformation Delta G * (MPa) at 23 ° C 3.05 0.69

Tan (δ) max at 23 ° C 0.254 0.133 Concerning the properties in the crosslinked state, it will be noted, on the one hand, that the ratio

MA300 / MA100 relating to composition no. 13 (based on BR 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.

In other words, composition no. 13, based on BR no. 13 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.

Example 4: Tests for grafting of COOH groups with mass 3-mercaptoundecanoic acid.

The starting SBR used is the same as SBR n ° 6 of Example 3 (ML (1 + 4) = 50).

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:

The 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.

40 g of gum are added and preheated on the mixer for 2 minutes. The lauroyl peroxide (when there is one) is then added as it is (in powder), followed by the addition of mercaptoundecanoic acid, also in powder. These two reagents are added in variable proportions according to the tests (see Table 12). The reaction mixture is kneaded for 5 minutes then the Brabender is stopped and the gum recovered, cooled and then analyzed.

The characteristics of the gums obtained are described in Table 13.

Table 12

Table 13

These results show that the grafting can be carried out in bulk, at 40 ° C. as at 100 ° C., with or without peroxide. In the absence of peroxide, it is necessary to charge more in mercaptoacid to achieve the same level of function as a test carried out with peroxide as shown in SBR No. 14b and 14c. As with solution grafting, degradation of the macrostructure is less pronounced in the absence of peroxide. It also appears from these tables that the macrostructural evolution is all the more pronounced the higher the reaction temperature (the viscosity variation is greater for SBR n ° 14c than for SBR n ° 14b, whereas the latter is made with six times more mercaptoacid).

Claims

1) Process for obtaining a grafted diene elastomer comprising functional groups along its chain, said process comprising a radical grafting reaction which is carried out in solution or in bulk by means of a reagent of mercaptan type and which is intended to graft said groups on the chain of the starting elastomer, characterized in that said method comprises an antioxidant treatment step before said radical grafting reaction, by means of an antioxidant agent comprising at least one aromatic amino function .

2) Method according to claim 1, characterized in that said antioxidant agent is chosen from the group consisting of naphthylamines, diphenylamines, p-phenylenediamines and mixtures of these compounds.

3) Method according to claims 1 or 2, characterized in that said antioxidant agent further comprises at least one phenol function.

4) Method according to claims 1 or 2, characterized in that at least one second antioxidant is used which comprises at least one phenol function.

5) Method according to claim 4, characterized in that said second antioxidant is chosen from the group consisting of trialkyl phenols, hydroquinones, polyphenols and mixtures of such compounds.

6) Method according to any one of claims 1 to 5, characterized in that the total amount of antioxidant (s) is within a range of 0.2 phr to 1.0 phr (phr: parts by weight percent parts of said starting diene elastomer). 7) Process according to any one of claims 1 to 6, characterized in that said mercaptan type reagent comprises a functional group chosen from the group consisting of hydroxyl, carbonyl, ether, amine, nitrile and silane groups, so that said grafted elastomer optionally has, along its chain, hydroxyl, carbonyl, ether, amine, nitrile or silane groups, respectively.

8) Method according to claim 7, characterized in that said reagent of mercaptan type comprises a carbonyl functional group belonging to the family consisting of carboxylic acid, carboxylic acid ester, amide and ketone groups, so that said grafted elastomer comprises at choice along its chain of carboxylic acid, carboxylic acid ester, amide or ketone groups.

9) Method according to claim 8, characterized in that said reagent of mercaptan type, such as a mercaptopropionic or mercaptoundecanoic acid, comprises a carboxylic acid functional group, so that said grafted elastomer comprises along its chain of carboxylic acid groups.

10) Method according to any one of claims 1 to 9, characterized in that said grafting reaction is carried out in the presence of a radical initiator.

11) Method according to claim 10, characterized in that the radical initiator is a peroxide.

12) Process for obtaining a grafted diene elastomer according to one of the preceding claims, characterized in that said starting elastomer comprises a molar ratio of units derived from conjugated dienes greater than 30%>.

13) Process for obtaining a grafted diene elastomer according to claim 12, characterized in that said starting elastomer is: 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 solution copolymerization of one or more dienes conjugated together and / or with one or more vinyl aromatic compounds having 8 to 20 carbon atoms, such as a butadiene / vinyl aromatic or butadiene / vinyl aromatic / isoprene copolymer.

14) Process for obtaining a grafted diene elastomer according to any one of claims 1 to 13, characterized in that a second antioxidant treatment step is carried out after the radical grafting reaction.

15) grafted diene elastomer comprising functional groups along its chain, capable of being obtained by a process according to any one of claims 1 to 14.

16) Crosslinkable or crosslinked rubber composition which can be used to form a tire tread, comprising at least one reinforcing inorganic filler and a grafted diene elastomer capable of being obtained by a process according to any one of claims 12 to 14.

17) Composition according to claim 16, characterized in that said functional groups that comprises said grafted elastomer belong to the family consisting of hydroxyl, carbonyl, ether, amino, nitrile and silane groups.

18) Composition according to claim 16, characterized in that said functional groups are of carbonyl type and belong to the family consisting of the carboxylic acid, carboxylic acid ester, amide and ketone groups.

19) Composition according to claim 16, characterized in that said functional groups are of carboxylic acid type. 20) Composition according to any one of Claims 16 to 19, characterized in that the said grafted elastomer is obtained:

- of 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 - of a copolymer obtained by solution copolymerization of one or more dienes conjugated together and / or with one or more vinylaromatic compounds having 8 to 20 carbon atoms, such as a butadiene / vinylaromatic or butadiene / vinylaromatic / isoprene copolymer.

21) Composition according to claim 20, characterized in that said grafted elastomer is derived from a butadiene / vinylaromatic copolymer prepared in solution.

22) Rubber composition according to any one of claims 16 to 21, characterized in that said grafted elastomer has a number average molecular weight Mn which is greater than 100,000 g / mol.

23) Rubber composition according to one of claims 16 to 22, characterized in that it is based on an elastomer matrix comprising mainly said grafted elastomer.

24) Rubber composition according to one of claims 16 to 23, characterized in that it comprises an elastomer matrix consisting of said grafted elastomer.

25) Rubber composition according to one of claims 16 to 24, said composition comprising a reinforcing filler comprising said reinforcing inorganic filler, characterized in that said reinforcing inorganic filler is present in said reinforcing filler according to a mass fraction greater than 50% ι and ranging up to 100%>.

26) Method for preparing a crosslinkable composition according to any one of claims 16 to 25, characterized in that it comprises: (i) the preparation of a grafted diene elastomer capable of being obtained by a process according to any one of claims 12 to 14;

(ii) carrying out, at a maximum temperature of ^"between 130 ° C and 200 ° C, a first thermo-mechanical working of the components of said composition comprising said grafted elastomer and a reinforcing inorganic filler, with the exception of a crosslinking system and 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.

27) Tire tread, characterized in that it comprises a crosslinkable or crosslinked rubber composition according to any one of claims 16 to 25.

28) Tire tread according to claim 27, characterized in that it consists of said crosslinkable or crosslinked rubber composition.

29) A tire with reduced rolling resistance, characterized in that it comprises a tread according to claims 27 or 28.