FR3078336A1 - USE OF MAGNESIUM OXIDE IN THE MANUFACTURE OF TIRES - Google Patents

Abstract

The invention relates to a tire comprising a rubber composition based on at least one elastomer, an organic peroxide, and magnesium oxide, the ratio of the mass quantity of magnesium oxide to the mass quantity of organic peroxide being greater than or equal to 1. The invention also relates to the use of magnesium oxide to increase the crosslinking speed and / or the crosslinking density of at least one elastomer, in the manufacture of all or part of a tire. including the manufacture of treads, sidewalls, linings, carcass plies, beads, and / or crown plies.

Description

FIELD OF THE INVENTION

The present invention relates to a new use of magnesium oxide in the crosslinking of crosslinkable polymers, in particular elastomers, for the preparation of tires, as well as a tire comprising such a magnesium oxide.

TECHNICAL BACKGROUND

In the field of tires, and in particular treads, specific properties are sought, such as, for example, reduced rolling resistance. The latter depends on the elastic properties of the rubber making up the tire. The crosslinking of the rubber compositions makes it possible to confer such elastic properties. The crosslinking of crosslinkable polymers also gives advantageous properties to other products such as pipes, gaskets, belts, sporting goods or insulation.

Document CN 104795149 describes a process for manufacturing sheaths for communication cables in coal mines comprising the vulcanization of a composition containing in particular chloroprene rubber, chlorinated polyethylene, ethylene-butylene rubber, magnesium oxide, dicumyl peroxide, 2,5-dimethyl-2,5-bis (tert-butylperoxy) hexane and zinc acrylate.

Document CN 103772743 discloses compositions comprising ethylene-propylene-diene rubber monomer (EPDM), dicumyl peroxide or diisopropylbenzene peroxide, zinc methacrylate and magnesium oxide, subjected to vulcanization.

Document JP 2002306637 relates to the manufacture of golf balls. It discloses vulcanized rubber compositions comprising a metal salt of α, β-unsaturated carboxylic acid, an organic peroxide, and zinc oxide or magnesium oxide, zinc acrylate being preferred among the salts. of α, β-unsaturated carboxylic acid.

Document US Pat. No. 6,057,395 discloses compositions containing a hydrogenated butadiene-acrylonitrile rubber (HNBR) or a butadiene-acrylonitrile rubber (NBR) or a styrene-butadiene copolymer (SBR) or a polybutadiene (BR) or a natural rubber (NR) or of EPDM, zinc methacrylate, magnesium oxide and a peroxide (1,3-bis (tertbutylperoxyisopropyl) benzene). These rubber compositions are vulcanized and can be used for rollers, belts, seals, tires, vibration isolators and pipes.

Document US Pat. No. 4,843,114 describes vulcanizable compositions for tracks of military tanks containing nitrilated polymers, a metal oxide chosen from zinc oxide and magnesium oxide, a zinc methylmethacrylate or dimethylmethacrylate resin and a hardening agent chosen from dicumyl peroxide, its derivatives, sulfur and a sulfur donor.

Document FR 3012147 describes compositions for tires comprising a diene elastomer, a derivative of zinc diacrylate and a peroxide.

The speed of crosslinking is important for the production and optimal curing of tires, while the density of crosslinking ensures properties after baking. There is therefore a need to provide crosslinking systems of rubber composition or the like which make it possible to obtain a crosslinking density and / or an improved crosslinking speed for the manufacture of tires.

SUMMARY OF THE INVENTION

The invention relates firstly to a tire comprising a rubber composition based on:

- at least one elastomer,

- an organic peroxide, and

- magnesium oxide., the ratio of the mass quantity of magnesium oxide to the mass quantity of organic peroxide being greater than or equal to 1.

According to embodiments, the elastomer is free from chlorine functional groups and from carboxylic acid functional groups, preferably free from halogen functional groups and carboxylic acid functional groups.

According to embodiments, which elastomer is chosen from the group consisting of diene elastomers, saturated polyolefins, silicones, fluorinated elastomers, ethylene-vinyl acetate copolymers, ethylene- (meth ) methyl acrylate, ethylene-glycidyl methacrylate copolymers and / or mixtures thereof.

According to embodiments, the elastomer is chosen from the group consisting of polybutadienes, synthetic polyisoprenes, natural rubber, butadiene copolymers, in particular butadiene and styrene copolymers and butadiene and copolymers acrylonitrile, isoprene copolymers, in particular isoprene and styrene copolymers, and mixtures of these elastomers.

According to embodiments, the organic peroxide is chosen from dicumyl peroxide, aryl or diaryl peroxides, diacetyl peroxide, benzoyl peroxide, dibenzoyl peroxide, ditertbutyl peroxide, tertbutylcumyl peroxide , 2,5-bis (tertbutylperoxy) -2,5dimethylhexane, n-butyl-4,4'-di (tert-butylperoxy) valerate, OO- (t-butyl) -O (2-ethylhexyl) monoperoxycarbonate, tert-butyl peroxyisopropylcarbonate, tert-butyl peroxybenzoate, letert-butyl peroxy-3,5,5-trimethylhexanoate, 1,3 (4) -bis (tert-butylperoxyisopropyl) benzene and mixtures thereof.

According to embodiments, the organic peroxide is used in a mass amount of 0.1 to 10 phr, preferably from 0.4 to 6 phr.

According to embodiments, the magnesium oxide has a BET specific surface ranging from 1 to 200 m ² / g, preferably from 5 to 170 m ² / g.

According to embodiments, the magnesium oxide has a BET specific surface greater than 25 m ² / g.

According to embodiments, the magnesium oxide is used in a mass quantity of from 1 to 50 phr, preferably from 2 to 30 phr.

According to embodiments, the composition also comprises a crosslinking co-agent chosen from the group consisting of (meth) acrylate compounds, maleimide compounds, allylic compounds, vinyl compounds and their mixtures.

According to embodiments, the crosslinking co-agent comprises a (meth) acrylate compound, in the form of a metal salt, or of an ester or in a polymeric form.

According to embodiments, the crosslinking co-agent comprises a (meth) acrylate compound in the form of a metal salt.

According to embodiments, the metal salt is a zinc salt of formula (I):

in which Ri, R ₂ , R3, R4, Rs and R6 independently represent a hydrogen atom or a C1-C7 hydrocarbon group chosen from linear, branched or cyclic alkyl groups, aralkyl groups, alkylaryl groups and groups aryls, and possibly interrupted by one or more heteroatoms, R ₂ and R3 on the one hand and R5 and R6 on the other hand which can independently form a non-aromatic ring.

According to embodiments, the metal salt is a zinc salt of formula (II):

r ₂ oor ₂

in which Ri, R ₂ and R3 independently represent a hydrogen atom or a C1-C7 hydrocarbon group chosen from linear, branched or cyclic alkyl groups, aralkyl groups, alkylaryl groups and aryl groups, and optionally interrupted by one or more heteroatoms, R ₂ and R3 can form a non-aromatic ring.

According to embodiments, Ri, R ₂ , R3, R4, Rs and R6 in formula (I) or Ri, R ₂ , Rs in formula (II) independently represent a hydrogen atom or a methyl group.

According to embodiments, the metal salt is zinc diacrylate or zinc dimethacrylate.

According to embodiments, the co-agent is used in a mass amount of 5 to 50 phr, preferably from 10 to 30 phr.

According to embodiments:

the ratio of the mass quantity of organic peroxide to the mass quantity of crosslinking co-agent in the composition is less than or equal to 0.09, preferably less than or equal to 0.05, more preferably less than or equal to 0, 04 and even more preferably less than or equal to 0.03; and or

- The ratio of the mass quantity of co-agent to the mass quantity of magnesium oxide in the composition is from 0.5 to 5, preferably from 0.8 to 2, and more particularly from 1 to 1 5.

According to embodiments, the composition also comprises a reinforcing filler, preferably chosen from the group consisting of carbon black, silica and their mixtures.

According to embodiments, the mass quantity of reinforcing filler in the composition is from 5 to 45 phr, preferably from 10 to 40 phr, more particularly preferably from 15 to 35 phr.

According to embodiments, the ratio of the mass quantity of reinforcing filler to the mass quantity of crosslinking co-agent in the composition is less than or equal to 2, and preferably is equal to 0.3 to 2, even more preferably of 0.7 to 1.3.

According to embodiments, the ratio of the mass quantity of magnesium oxide to the mass quantity of organic peroxide in the composition is from 5 to 60, preferably from 10 to 40, and more particularly from 15 to 30 .

According to embodiments, the composition also comprises one or more compounds chosen from the group consisting of plasticizers, processing agents, antioxidants, and stabilizers.

According to embodiments, the composition is that of at least all or part of a layer of the tire chosen from a tread, a sidewall, an interior coating, a carcass ply, a bead, or a crown ply.

The invention also relates to the use of magnesium oxide to increase the crosslinking speed and / or the crosslinking density of at least one elastomer, in a rubber composition, for the manufacture of all or part of a tire. , in particular the manufacture of treads, sidewalls, interior coatings, carcass plies, beads, and / or crown plies.

According to embodiments, the rubber composition is as defined above.

According to embodiments, the use according to the invention makes it possible to obtain a crosslinking density greater than 1.5 times, preferably 2 times, 3 times, 5 times, 10 times, 20 times, 50 times or 100 times the crosslinking density obtained under the same crosslinking conditions but in the absence of magnesium oxide.

According to embodiments, the use according to the invention makes it possible to obtain a crosslinking speed greater than 1.1 times, preferably 1.2 times, 1.3 times, 1.4 times, 1.5 times, 1.8 times or 2 times the speed of crosslinking obtained under the same crosslinking conditions but in the absence of magnesium oxide.

The present invention meets the need expressed above. It more particularly provides a crosslinking system having one or both of the following advantages: an increase in the crosslinking density and an increase in the crosslinking speed. Such a system makes it possible to obtain end products with advantageous mechanical properties, and in particular an increase in the modulus of elasticity in traction, very particularly with relatively low elongation (such as an elongation of 10%, or 50%, or 100%, or 200%).

It also accelerates crosslinking and thus saves time in the manufacture of finished or semi-finished products.

This is accomplished through the use of magnesium oxide during crosslinking. It has surprisingly been found that a very significant increase in the crosslinking density and / or the crosslinking speed has been obtained by the addition of magnesium oxide in a crosslinking process, this effect not being observed with, for example, the addition of zinc oxide in the same process.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 represents the rheometric curves obtained by an RPA 2000 rheometer, at 160 ° C., during the crosslinking of composition no. 1 and of composition no. 7 described in example 1. The time (in h: min : s) appears on the abscissa and the couple S ', in dN m, appears on the ordinate.

FIG. 2 represents the rheometric curves obtained by an RPA 2000 rheometer, at 160 ° C., during the crosslinking of compositions n ° 7, n ° 8 and n ° 2 described in example 1. The time (in h: min : s) appears on the abscissa and the couple S ', in dN m, appears on the ordinate.

FIG. 3 represents the rheometric curves obtained by an RPA 2000 rheometer, at 160 ° C., during the crosslinking of compositions n ° 3, n ° 4, n ° 5, n ° 6, n ° 7, n ° 8, n ° 9, n ° 10, n ° 11, and n ° 12 described in example 1. Time (in h: min: s) appears on the abscissa and the couple S ', in dN m, appears on the ordinate.

FIG. 4 represents the rheometric curves obtained by an RPA2000 rheometer, at 160 ° C., during the crosslinking of compositions n ° 15, n ° 16, n ° 17, n ° 18 and n ° 19 described in example 2. Time (in h: min: s) appears on the abscissa and the couple S ', in dN m, appears on the ordinate.

FIG. 5 represents the rheometric curves obtained by an RPA 2000 rheometer, at 160 ° C., during the crosslinking of compositions n ° 7, n ° 8, n ° 13 and n ° 14 described in examples 1. The time ( in h: min: s) appears on the abscissa and the couple S ', in dN m, appears on the ordinate.

FIG. 6 represents the rheometric curves obtained by an MDR rheometer, at 160 ° C., during the crosslinking of compositions n ° 26, n ° 27, n ° 28 and n ° 29 described in example 3. The time (in h: min: s) appears on the abscissa and the couple S ', in dN m, appears on the ordinate.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The invention is now described in more detail and without limitation in the description which follows.

In the present description, unless expressly indicated otherwise, all the percentages (%) indicated are percentages by mass.

In the present application, the expression “pce” means in known manner parts by weight per hundred parts by weight of elastomers (or other crosslinkable polymers). The quantity by weight of the constituents of the compositions is thus expressed relative to the total quantity of elastomers (or other crosslinkable polymers) by weight considered by convention at the value hundred.

The invention relates to the use of magnesium oxide to increase the crosslinking speed and / or the crosslinking density of at least one crosslinkable polymer, in particular of at least one elastomer, for the manufacture of all or part a tire, in particular the manufacture of treads, sidewalls, interior coatings, carcass plies, beads, and / or crown plies.

The invention also relates to a tire comprising a rubber composition based on at least one crosslinkable polymer, in particular at least one elastomer, an organic peroxide, and magnesium oxide, the ratio of the mass amount of magnesium oxide on the mass quantity of organic peroxide being greater than or equal to 1.

By the expression “composition based on” is meant a composition comprising the mixture and / or the in situ reaction product of the various basic constituents used, some of these constituents being able to react and / or being intended to react with each other, at least partially, during the various stages of manufacturing the composition, or during subsequent cooking, modifying the composition as it is prepared at the start. Thus, the compositions as used for the invention may be different in the non-crosslinked state and in the crosslinked state. In an equivalent manner, the invention preferably relates to a tire comprising a composition as defined above, in which the composition is in the non-crosslinked state or in the crosslinked state.

Thus, in an equivalent manner, the invention relates to a tire comprising a rubber composition comprising at least one crosslinkable polymer, in particular at least one elastomer, an organic peroxide, and magnesium oxide, the ratio of the mass quantity d magnesium oxide on the mass quantity of organic peroxide being greater than or equal to 1.

By “crosslinking” is meant the formation of a three-dimensional network by the creation of bonds between the molecules of crosslinkable polymers. The use according to the invention is therefore preferably carried out in the context of a crosslinking process, during which the crosslinking takes place.

Crosslinkable polymers

Preferably, the crosslinkable polymer is an elastomer.

Preferably, the crosslinkable polymer is chosen from the group consisting of diene elastomers, saturated polyolefins (in particular linear low density polyethylenes, low density polyethylenes, high density polyethylenes, ethylenepropylene copolymers), silicones , fluorinated elastomers, ethylene vinyl acetate copolymers, ethylene-methyl (meth) acrylate copolymers, ethylene-glycidyl methacrylate copolymers and / or mixtures thereof.

Preferably the crosslinkable polymer, in particular the elastomer, comprises or is a diene elastomer.

By diene elastomer is meant an elastomer (or more) derived at least in part (homopolymer or copolymer) from diene monomers (monomers carrying two carbon-carbon double bonds, conjugated or not).

A distinction is made between diene elastomers having functional groups -Cl or -COOH (carboxylic acid), such as polychloroprene, and diene elastomers lacking such functional groups.

Diene elastomers lacking such functional groups are preferred. It is therefore preferred that the composition used in the context of the invention is devoid of diene elastomer having functional groups -Cl or -COOH. More generally, it is preferred that the composition used in the context of the invention is devoid of diene elastomer having halogen or -COOH functional groups.

Magnesium oxide is capable of acting as a crosslinking agent as such on diene elastomers provided with such functional groups, which act as crosslinking sites. Therefore, preferably, in the context of the invention, magnesium oxide is not used as a crosslinking agent as such. For the invention, the crosslinking agent is an organic peroxide, possibly combined with a co-agent as discussed below.

Diene elastomers can also be classified in a known manner into two categories, those called essentially unsaturated and those called essentially saturated. These two categories of diene elastomers can be envisaged in the context of the invention.

An essentially saturated diene elastomer has a low or very low level of units or units of diene origin (conjugated dienes) of less than 15% (in moles). For example, butyl rubbers or copolymers of dienes and alpha-olefins such as EPDM are included in the definition of essentially saturated diene elastomers.

Conversely, by essentially unsaturated diene elastomer is meant a diene elastomer derived at least in part from conjugated diene monomers, having a proportion of units or units of diene origin (conjugated dienes) which is greater than 15% (in moles). In the category of essentially unsaturated diene elastomers, the term “highly unsaturated diene elastomer” is understood to mean in particular a diene elastomer having a content of units of diene origin (conjugated dienes) which is greater than 50% (in moles).

The term “diene elastomer capable of being used in the invention” is more particularly understood:

(a) any homopolymer obtained by polymerization of a conjugated diene monomer having from 4 to 12 carbon atoms;

(b) any copolymer obtained by copolymerization of one or more dienes conjugated together or with one or more vinyl aromatic compounds having from 8 to 20 carbon atoms;

(c) any ternary copolymer obtained by copolymerization of ethylene, of an α-olefin having from 3 to 6 carbon atoms with a non-conjugated diene monomer having from 6 to 12 carbon atoms, such as for example the elastomers obtained from ethylene, propylene with a non-conjugated diene monomer of the aforementioned type such as in particular 1,4-hexadiene, ethylidene norbornene, dicyclopentadiene; such polymers are described in particular in documents WO 2004/035639 and US 2005/0239639;

(d) any copolymer of isobutene and isoprene (butyl rubber), as well as the halogenated versions, in particular chlorinated or brominated, of this type of copolymers.

Diene elastomers of the highly unsaturated type, in particular of the type (a) or (b) above are preferred.

As conjugated dienes, 1,3-butadiene, 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, 2methyl-3-ethyl-1,3-butadiene, 2-methyl-3-isopropyl-1,3- butadiene, an aryl-

1,3-butadiene, 1,3-pentadiene, 2,4-hexadiene. Suitable vinyl aromatic compounds are, for example, styrene, ortho-, meta-, paramethylstyrene, vinyl toluene, para-tertiobutylstyrene, methoxystyrenes, chlorostyrenes, vinyl mesitylene, divinylbenzene, vinylnaphthalene.

The copolymers can contain between 99% and 20% by weight of diene units and between 1% and 80% by weight of vinyl aromatic units. The elastomers can have any microstructure which is a function of the polymerization conditions used, in particular the presence or absence of a modifying and / or randomizing agent and the quantities of randomizing modifying agent used. The elastomers can be, for example, block, random, sequenced, microsequenced, and be prepared in dispersion, in emulsion or in solution; they can be coupled and / or starred or functionalized with a coupling and / or star-forming or functionalizing agent. For coupling to carbon black, there may be mentioned for example functional groups comprising a C-Sn bond or amino functional groups such as aminobenzophenone for example; for coupling to a reinforcing inorganic filler such as silica, mention may, for example, be made of silanol or polysiloxane functional groups having a silanol end (as described for example in documents FR 2740778, US 6,013,718 and WO 2008/141702), alkoxysilane groups (as described for example in documents FR 2765882 or US 5,977,238), carboxylic groups (as described for example in documents WO 01/92402 or US 6,815,473, WO 2004/096865 or US 2006/0089445) or also polyether groups (as described for example in documents EP 1127909, US 6,503,973, WO 2009/000750 and WO 2009/000752). As other examples of functionalized elastomers, mention may also be made of elastomers, such as isoprene-styrene copolymers (SBR), polybutadienes (BR), natural rubber (NR) or synthetic polyisoprenes (IR), epoxidized type.

These functionalized elastomers can be used in combination with one another or with non-functionalized elastomers. For example, it is possible to use a functionalized silanol or polysiloxane elastomer having a silanol end, in mixture with an elastomer coupled and / or starred with tin (described in the document WO 2011/042507), the latter representing a level of 5 to 50% by mass, for example from 25 to 50%.

Polybutadienes are suitable and in particular those having a content (molar%) in units -1,2 of between 4% and 80% or those having a content (molar%) of cis-1,4 greater than 80%, polyisoprenes, butadiene-styrene copolymers and in particular those having a glass transition temperature (Tg) of between 0 ° C and -70 ° C and more particularly between -10 ° C and -60 ° C, a styrene content of between 5 % and 60% by weight and more particularly between 20% and 50%, a content (molar%) of -1,2 bonds of the butadiene part of between 4% and 75%, a content (molar%) of trans- 1.4 between 10% and 80%, butadiene-isoprene copolymers and in particular those having an isoprene content between 5% and 90% by weight and a Tg of -40 ° C to -80 ° C, the copolymers isoprene-styrene and in particular those having a styrene content of between 5% and 50% by weight and a Tg of between -5 ° C and -60 ° C. In the case of butadiene-styrene-isoprene copolymers, especially those having a styrene content of between 5% and 50% by weight and more particularly between 10% and 40%, an isoprene content of between 15% and 60 are suitable. % by weight and more particularly between 20% and 50%, a butadiene content between 5% and 50% by weight and more particularly between 20% and 40%, a content (molar%) in units -1.2 of the butadiene part between 4% and 85%, a content (molar%) in trans units -1.4 of the butadienic part between 6% and 80%, a content (molar%) in units -1.2 more - 3.4 of the isoprene part between 5% and 70% and a content (molar%) in trans units -1.4 of the isoprene part between 10% and 50%, and more generally any butadiene-styrene-isoprene copolymer having a Tg of between -20 ° C and -70 ° C.

Throughout the present application, the Tg is measured according to standard ASTM D3418.

In summary, the diene elastomer in the composition is preferably chosen from the group of highly unsaturated diene elastomers constituted by polybutadienes (BR), synthetic polyisoprenes (IR), natural rubber (NR), butadiene copolymers, isoprene copolymers and mixtures of these elastomers. The copolymers are more preferably chosen from the group consisting of butadiene-styrene copolymers (SBR), isoprene butadiene copolymers (BIR), isoprene-styrene copolymers (SIR), isoprene-butadiene-styrene copolymers (SBIR), butadiene-acrylonitrile copolymers (NBR), butadiene-styrene-acrylonitrile copolymers (NSBR) or a mixture of two or more of these compounds.

According to a particular embodiment, the composition comprises from 50 to 100 phr of an SBR elastomer, whether it is an SBR prepared in emulsion (ESBR) or an SBR prepared in solution (SSBR).

According to another particular embodiment, the diene elastomer is an SBR / BR blend (mixture).

According to other possible embodiments, the diene elastomer is an SBR / NR (or SBR / IR), BR / NR (or BR / IR), or even SBR / BR / NR (or SBR / BR / IR) blend. ).

In the case of an SBR elastomer (ESBR or SSBR), use is in particular of an SBR having an average styrene content, for example between 20% and 35% by weight, or a high styrene content, for example from 35 to 45% by weight, a content (molar%) of vinyl bonds in the butadiene part of between 15% and 70%, a content (molar%) of trans-1,4 bonds between 15% and 75% and a Tg included between 10 ° C and -55 ° C. Such an SBR can advantageously be used in admixture with a BR preferably having more than 90% (mol%) of cis-1,4 bonds.

In the case of an NBR elastomer, use is made in particular of an NBR having an acrylonitrile content of between 15% and 40% by weight, a content (molar%) of vinyl bonds in the butadiene part of between 15% and 70%, a content (mol%) of trans-1,4 bonds of between 15% and 75%.

According to a particular embodiment of the invention, the composition comprises a cut of one (one or more) diene elastomer called "high

Tg "having a Tg between -70 ° C and 0 ° C and one (or more) diene elastomer called" low Tg "between -110 ° C and -80 ° C, more preferably between -105 ° C and -90 ° C. The high Tg elastomer is preferably chosen from the group consisting of SSBR, ESBR, natural rubber, synthetic polyisoprenes (having a rate (molar%) of cis-1,4 chains preferably greater than 95 %), BIRs, SIRs, SBIRs, and mixtures of these elastomers. The low Tg elastomer preferably comprises butadiene units at a rate (mol%) at least equal to 70%; it preferably consists of a polybutadiene (BR) having a rate (molar%) of cis-1,4 chains greater than 90%.

According to another particular embodiment of the invention, the composition comprises for example between 30 and 90 phr, in particular between 40 and 90 phr, of a high Tg elastomer in combination with a low Tg elastomer.

According to another particular embodiment of the invention, the diene elastomer comprises a cutting of a BR (as a low Tg elastomer) having a rate (molar%) of cis-1,4 chains greater than 90%, with one or more SSBR or ESBR (as high Tg elastomer (s)).

Organic peroxide

The composition useful in the invention contains an organic peroxide.

By "organic peroxide" is meant an organic compound, that is to say containing carbon, comprising a group -O-O- (two oxygen atoms linked by a single covalent bond).

During the crosslinking process, the organic peroxide breaks down at its 0-0 unstable bond into free radicals. These free radicals allow the creation of crosslinking bonds.

According to one embodiment, the organic peroxide is chosen from the group consisting of dialkyl peroxides, monoperoxycarbonates, diacyl peroxides, peroxyketals or peroxyesters.

Preferably, the dialkyl peroxides are chosen from the group consisting of dicumyl peroxide, di-t-butyl peroxide, t-butylcumyl peroxide, 2,5-dimethyl-2,5-di (t-butylperoxy ) hexane, 2,5-dimethyl-2,5-di (t-amylperoxy) -hexane, 2,5-dimethyl-2,5-di (tbutylperoxy) hexyne-3, 2,5-dimethyl-2,5 -di (t-amylperoxy) hexyne-3, α, α'-di [(t-butyl-peroxy) isopropyl] benzene, oc, oc'-di - [(t-amyl-peroxy) isopropyl] benzene, di-t-amyl peroxide, 1,3,5-tri - [(t butylperoxy) isopropyl] benzene, 1,3-dimethyl-3- (t-butylperoxy) butanol, and

1,3-dimethyl-3- (t -amylperoxy) butanol.

A mixture of dicumyl peroxide and of 1,3 and 1,4-isopropylcumyl cumyl peroxide (sold for example by Arkema under the trade name Luperox® DC60) is also interesting.

Certain monoperoxycarbonates such as 00-tert-butyl-0- (2-ethylhexyl) monoperoxycarbonate, OO-tert-butyl-O-isopropyl monoperoxycarbonate and OO-tert-amyl-O-2-ethyl hexyl monoperoxycarbonate, can also be used.

Among the diacyl peroxides, the preferred peroxide is benzoyl peroxide.

Among the peroxyketals, the preferred peroxides are chosen from the group consisting of

1.1- di- (t-butylperoxy) -3,3,5-trimethylcyclohexane, 4,4-di- (t-butylperoxy) n-butyl valerate, 3,3-di- (t-butylperoxy) butyrate d 'ethyl, the

2.2- di- (t-amylperoxy) -propane, 3,6,9-triethyl-3,6,9-trimethyl-1,4,7- triperoxynonane (or methyl ethyl ketone cyclic trimer peroxide), on 3, 3,5,7,7-pentamethyl-1,2,4-trioxepane, 4,4-bis (t-amylperoxy) nbutyl valerate, 3,3-di (t-amylperoxy) ethyl butyrate, 1,1-di (tbutylperoxy) cyclohexane, 1,1-di (t-amylperoxy) cyclohexane and their mixtures. Preferably, the peroxyesters are chosen from the group consisting of tert-butylperoxybenzoate, tert-butyleperoxy-2ethylhexanoate and tert-butyleperoxy-3,5,5-trimethylhexanoate.

In a particularly preferred manner, the organic peroxide is chosen from the group consisting of dicumyl peroxide, aryl or diaryl peroxides, diacetyl peroxide, benzoyl peroxide, dibenzoyl peroxide, ditertbutyl peroxide, tert-butylcumyl peroxide, 2,5-bis (tert-butylperoxy) -2,5-dimethylhexane, n-butyl-4,4'-di (tert-butylperoxy) valerate, OO- (t-butyl) -O- (2- ethylhexyl) monoperoxycarbonate, tert-butyl peroxyisopropylcarbonate, tert-butyl peroxybenzoate, tert-butyl peroxy-3,5,5-trimethylhexanoate, 1,3 (4) -bis (tert-butylperoxyisopropyl) benzene and mixtures of these, more preferably in the group consisting of dicumyl peroxide, n-butyl-4,4'-di (tert-butylperoxy) -valerate, OO- (t-butyl) O- (2-ethylhexyl) monoperoxycarbonate, tert-butyl peroxyisopropylcarbonate, tert-butyl peroxybenzoate, tert-butyl peroxy-3,5,5-trimethylhexanoate, 1,3 (4) bis (tert-butylperox yisopropyl) benzene and mixtures thereof.

Preferably, the mass amount of organic peroxide in the composition is less than or equal to 10 phr. More preferably, the amount of organic peroxide in the composition is within a range ranging from 0.1 to 10 phr, even more preferably from 0.4 to 6 phr. Even more preferably, the amount of organic peroxide is in a range from 0.8 to 4 phr.

In a variant also preferred, the mass amount of organic peroxide in the composition may be less than or equal to 3 phr, preferably from 0.1 to 3 phr, more particularly preferably from 0.2 to 2 phr, and more preferably still from 0.25 to 1 pce.

Organic peroxide crosslinking co-agent

The composition relating to the invention preferably contains a crosslinking coagent.

The co-agents can be classified according to their mode of action, of type 1 or 2, or also according to their chemical nature, and include in particular the (meth) acrylate compounds, in the form of salts such as zinc diacrylates or dimethacrylates ( Zn) (such as the compounds of formula I or II below), magnesium (Mg) or calcium (Ca); in the form of an ester such as polyfunctional acrylates or methacrylates; in polymeric form such as polybutadiene diacrylate; maleimide compounds such as bismaleimides or biscitraconimides; allyl compounds such as allyl cyanurate and triallyl isocyanurate, or vinyl compounds such as low molecular weight polymers with high vinyl content.

A single co-agent or a mixture of several co-agents can be used. When a mixture of several co-agents is used, they may be of the same or different type and of an identical or different chemical nature.

The table below gives examples of these co-agents.

Cross-linking co-agents Acronym Type 1 or 2 Trimethylolpropane triacrylate TMPTA Type 1 T rimethylolpropane trimethacrylate TMPTMA Type 1 Ethylene glycol dimethacrylate EGDA Type 1 Ethylene glycol diacrylate EGDMA Type 1 N, N'-m-phenylene dimaleimide PDM Type 1 Zinc diacrylate ZDA Type 1 Zinc dimethacrylate ZDMA Type 1 triallyl TAC Type 2

triallyl TAIC Type 2 90% vinyl polybutadiene HVPBd Type 2 70% vinyl styrene-butadiene copolymer HVSBR Type 2

Preferably for the invention, the co-agent will comprise at least one compound chosen from the group consisting of (meth) acrylate compounds, maleimide compounds, allylic compounds, vinyl compounds and their mixtures.

Preferably, the co-agent comprises a (meth) acrylate compound, in the form of a metal salt, or of an ester or in a polymeric form.

Preferably for the invention, the co-agent comprises a (meth) acrylate compound in the form of a monovalent or bivalent metal salt of an unsaturated alpha or beta carboxylic acid, preferably having 2 to 8 carbon atoms. In a particularly preferred manner, the metal compound of the metal salt is chosen from the group consisting of zinc, aluminum, magnesium and calcium, preferably zinc.

The metal compound can be in the form of oxide, hydroxide or peroxide.

Even more preferably, the metal salt is a zinc salt of formula (I):

in which Ri, R ₂ , R3, R4, Rs and R6 independently represent a hydrogen atom or a C1-C7 hydrocarbon group chosen from linear, branched or cyclic alkyl groups, aralkyl groups, alkylaryl groups and groups aryls, and possibly interrupted by one or more heteroatoms, R ₂ and R3 on the one hand and R5 and R6 on the other hand which can independently form a non-aromatic ring.

By cyclic alkyl group is meant an alkyl group comprising one or more rings.

The term “hydrocarbon group interrupted by one or more heteroatoms” means a group comprising one or more heteroatoms, each heteroatom being between two carbon atoms of said group, or between a carbon atom of said group and another heteroatom of said group or between two others heteroatoms of said group. The heteroatom (s) may be a nitrogen, sulfur or oxygen atom.

The addition of a metal co-agent containing several unsaturations and in which the zinc is linked to the rest of the molecule by ionic and non-covalent bonds (metal salt) makes it possible to increase the efficiency of the peroxide during the crosslinking process. and to confer certain particular properties on the crosslinked compositions.

According to a particular embodiment, Ri, R ₂ R3, R4, Rs and R6 independently represent a hydrogen atom or a methyl group.

According to one embodiment, the metal salt is a compound of formula (II):

in which Ri, R ₂ and R3 independently represent a hydrogen atom or a C1-C7 hydrocarbon group chosen from linear, branched or cyclic alkyl groups, aralkyl groups, alkylaryl groups and aryl groups, and optionally interrupted by one or more heteroatoms, R ₂ and R3 can form a non-aromatic ring.

According to a particular embodiment, Ri, R ₂ and R3 independently represent a hydrogen atom or a methyl group.

Advantageously, R ₂ and R3 represent a hydrogen atom. According to a particular embodiment, Ri is a methyl group.

Preferably, the metal salt is zinc diacrylate or zinc dimethacrylate.

By way of example, mention may be made of zinc diacrylate (ZDA) DIMALINK® 633 from the company CRAY VALLEY or zinc dimethacrylate (ZDMA) DIMALINK® 634 from the company CRAY VALLEY.

Alternatively, the crosslinking co-agent may comprise a vinyl compound, for example chosen from the group consisting of transstilbene, divinylbenzene, trans, trans-2,6-dimethyl-2,4,6-octatriene, dicyclopentadiene, 3,7-dimethyl-1,3,6-octatriene (OCIMENE), the compounds represented by the general formula (III):

in which R ^x represents a hydrogen atom or an alkyl group of 1 to 9 carbon atoms and n is an integer between 1 and 3, and the compounds represented by the general formula (IV):

CTI

O 3

I

wherein R ^y and R ^z may be the same or different and represent an alkyl group of 1 to 4 carbon atoms.

As compounds represented by the general formula (III), mention may be made of Ι'α-methyl styrene, ortho, meta, para diisopropenyl benzene, 1,2,4triisopropenyl benzene, 1,3,5-triisopropenyl benzene, 3-isopropyl-ortho diisopropenyl benzene, 4-isopropyl-ortho diisopropenyl benzene, 4isopropyl-m-diisopropenyl benzene, 5-isopropyl-m-diisopropenyl benzene, 2-isopropyl-p-diisopropenyl benzene.

As compounds represented by the general formula (IV), mention may be made of 2,4-di (3-isopropylphenyl) -4-methyl-1 pentene, 2,4-di (4-iso propylphenyl) 4-methyl-1 pentene, 2- (3-isopropylphenyl) -4- (4isopropylphenyl) -4-methyl-1 -pentene, 2- (4-isopropylphenyl) -4- (3isopropylphenyl) -4-methyl-1 -pentene, 2 , 4-di (3-methyl-phenyl) -4-methyl-1 pentene, 2,4-di (4-methylphenyl) -4-methyl-1 pentene.

Methyl methacrylate, lauryl methacrylate, allyl methacrylate, trimethylolpropane triacrylate, triallyl cyanurate (TAC), triallyl isocyanurate (TAIC), triallyl phosphate, tetraallyloxyethane, carbonate allyIdiglycol, triallyl trimellate, triallyl citrate, diallyl adipate, diallyl terephalate, diallyl oxalate, diallyl fumarate, ethylene glycol dimethacrylate and 2-hydroxyethyl methacrylate, may also suitable as a crosslinking co-agent.

May also be suitable as crosslinking agent maleimide compounds such as those represented by the general formula (X):

in which n is equal to 1 or 2 and R is divalent or trivalent and is chosen from the group formed by acyclic aliphatic groups having from 2 to 16 carbon atoms, cyclic aliphatic groups having from 5 to 20 carbon atoms, aromatic groups having 6 to 18 carbon atoms and alkyl aromatic (alkylaryl) groups having 7 to 24 carbon atoms, and these divalent or trivalent groups may contain one or more heteroatoms of oxygen, nitrogen and / or sulfur instead of one or more carbon atoms and each R4 is identical and represents a hydrogen atom or an alkyl group having from 1 to 18 carbon atoms.

Among the compounds of general formula (X), the bismaleimides and the biscitraconimides are advantageously chosen.

As bismaleimide there may be mentioned bismaleimide of N, N'-mphenylene, bismaleimide of Ν, Ν'-ethylene, bismaleimide of N, N'hexamethylene, bismaleimide of Ν, Ν'-dodecamethylene, bismaleimide of N, N '- ( 2,2,4-trimethylhexamethylene), bismaleimide of N, N '- (oxydipropylene), bismaleimide of N, N' - (aminodipropylene), bismaleimide of N, N '(ethylenedioxydipropylene), bismaleimide of N, N' (1, 4-cyclohexylene), bismaleimide N, N '(1,3-cyclohexylene), bismaleimide N, N' - (methylene 1,4dicyclohexylene), bismaleimide N, N '- (isopropylidene-1,4-dicyclohexylene, bismaleimide N, N '- (oxy-1,4-dicyclohexylene), bismaleimide of N, N'-p (phenylene), bismaleimide of N, N' - (o-phenylene), bismaleimide of N, N '- (1, 3naphthylene), bismaleimide of N, N '- (1,4-naphthylene), bismaleimide of N, N' (1,5-naphthylene), bismaleimide of N, N '- (3,3'dimethyl- (4,4 -diphenylene), bismaleimide of N, N '- (3,3-dichloro-4,4 biphenylene), bismaleimide of N, N' (2,4-pyridyl), bismalei mide of N, N '- (2,6-pyridyl), bismaleimide of N, N' - (1,4 anthraquinonediyl), bismaleimide of N, N '- (m-tolylene), bismaleimide of N, N' (p -tolylene), bismaleimide of N, N '- (4,6-dimethyl-1,3-phenylene), bismaleimide of N, N' - (2,3-dimethyl-1,4-phenylene), bismaleimide of N, N '- (4,6-dichloro-1,3phenylene), bismaleimide of N, N' - (5-chloro-1,3-phenylene), bismaleimide of

N, N '- (5-hydroxy-1,3-phenylene), bismaleimide of N, N' - (5-methoxy-1,3phenylene), bismaleimide of N, N '- (m-xylylene), bismaleimide of N , N '- (pxylylene), bismaleimide of N, N' - (methylenedi-p-phenylene), bismaleimide of N, N '- (isopropylidene-p-phenylene), bismaleimide of N, N' - (oxydi-pphenylene) , bismaleimide of N, N '- (thiodi-p-phenylene), bismaleimide of N, N' (dithiodi-p-phenylene), bismaleimide of N, N '- (sulfodi-p-phenylene), bismaleimide of N, N '- (carbonyldi-p-phenylene), a, a'-bis- (4maleimodophenyl) -meta-diisopropylbenzene, bismaleimide of a, a'-bis- (4-pphenylene) and a, a'-bis- (4- maleimidophenyl) -para-diisopropylbenzene.

As biscitraconimides, mention may be made of 1,2-N biscitraconimide, N'dimethylene, 1,2-N, N'-trimethylene biscitraconimide, 1,5-N, N '- (2-methyl- pentamethylene) and the biscitraconimide of N, N'methylphenylene).

The mass amount of co-agent is preferably within a range from 5 to 50 phr. Ranges of 10 to 50 phr, from 10 to 30 phr, and from 20 to 30 phr are preferred. Such amounts allow good dispersion of the co-agent in the composition; in addition, the properties of the crosslinked composition obtained are less degradable and the effect of the co-agent is notable on the stiffening and strengthening of the crosslinked composition.

Advantageously, the ratio of the mass quantity of organic peroxide to the mass quantity of co-agent is less than 0.5, preferably less than 0.2. Such a low ratio is favorable in terms of synergy between the organic peroxide and the co-agent, which has a positive effect on the rheometry and the elongation at break of the composition (which is particularly advantageous in the case of a composition intended for example for the manufacture of treads for tires).

In certain preferred embodiments, the ratio of the mass amount of peroxide to the mass amount of co-agent is less than or equal to 0.09, or 0.05, more preferably less than or equal to 0.04 and more preferably less than or equal to 0.03.

Magnesium oxide

According to one embodiment, the magnesium oxide is used in a mass amount of from 1 phr to 50 phr, preferably from 2 phr to 30 phr, more preferably from 5 to 15 phr.

When a crosslinking co-agent is present, the ratio of the mass quantity of co-agent to the mass quantity of magnesium oxide in the composition is preferably from 0.5 to 5, more preferably from 0.8 to 2, and even more preferably from 1 to 1.5.

According to embodiments, the ratio of the mass quantity of magnesium oxide to the mass quantity of organic peroxide in the composition is from 5 to 60, preferably from 10 to 40, and more particularly from 15 to 30 .

Advantageously, the magnesium oxide has a BET specific surface ranging from 1 to 200 m ² / g. More preferably, the magnesium oxide has a BET specific surface ranging from 5 to 170 m ² / g. The BET specific surface area of magnesium oxide is measured according to ISO 9277: 2010.

In a particularly advantageous manner, the magnesium oxide has a BET specific surface greater than 25 m ² / g.

According to particular embodiments, the magnesium oxide has a BET specific surface ranging from 1 to 60 m ² / g, from 60 to 120 m ² / g or from 120 to 200 m ² / g; or from 1 to 20 m ² / g, from 20 to 25 m ² / g, from 20 to 26 m ² / g, from 25 to 30 m ² / g, from 26 to 30 m ² / g, from 30 to 40 m ² / g, from 40 to 60 m ² / g, from 40 to 90 m ² / g, from 60 to 90 m ² / g, from 90 to 120 m ² / g, from 90 to 140 m ² / g, from 90 to 170 m ² / g, from 120 to 170 m ² / g, from 140 to 170 m ² / g, or from 170 to 200 m ² / g.

According to the invention, the presence of magnesium oxide in the composition has the effect of increasing the crosslinking density and / or the crosslinking speed of the crosslinkable polymer, in particular of the elastomer.

The crosslinking density is linked to the number of bridge bonds per constituent unit of the polymer. It can be determined by a rheometric measurement, for example using a rheometer. For example, it can be determined according to ASTM standard D 5289A using an RPA 2000 or MDR type rheometer, at a temperature of 160 ° C., with an oscillation amplitude of 0.5 °, a frequency d oscillation of 1.667 Hz, from discs of the test sample with a diameter of 3.5 cm and a volume of 4.8 cm ³ .

Depending on the crosslinking systems, adjusting the temperature to a different value may be appropriate.

The measurement is carried out during the crosslinking of the test sample which is initiated at the same time as the measurement, by placing the sample in a preheated test cavity. It makes it possible to obtain a rheometric curve representing the evolution of the viscoelastic couple resulting from the deformation imposed on the composition to be tested as a function of time. In the context of the present application, the crosslinking density is defined directly by the difference between the maximum torque MH and the minimum torque ML, and is expressed in dN m.

The minimum torque ML corresponds to the minimum value of the torque measured during crosslinking (at the start of the test).

The maximum torque MH corresponds to the value of the torque at the end of the measurement. Preferably, the duration of the test is adjusted so that the crosslinking is essentially completed at the end of this duration, the couple then reaching a plateau. An appropriate duration for the test is for example 60 minutes. However, this duration can be adapted as a function of the actual duration planned for the manufacture of a given part, from the crosslinkable polymer composition, and at a given temperature.

The crosslinking speed is evaluated by the value T’90 corresponding to the time necessary to reach 90% of the maximum torque, which is obtained using the rheometric measurement described above. The lower the T’90, the higher the cross-linking speed.

According to a particular embodiment, the crosslinking density obtained is greater than the crosslinking density which is obtained under the same conditions but without the use of magnesium oxide. Preferably, the crosslinking density obtained is greater than 1.5 times, 2 times, 3 times, 5 times, 10 times, 20 times, 50 times or 100 times the crosslinking density which is obtained under the same conditions but without use magnesium oxide.

By “same conditions but without the use of magnesium oxide”, is meant a crosslinking carried out with the same parameters (the same duration, the same temperature, etc.) and from the same composition, with the exception of the presence of magnesium oxide, as for the crosslinking according to the invention carried out in the presence of magnesium oxide.

In this embodiment, the crosslinking densities obtained with and without magnesium oxide can be measured in the same way, according to the procedure described above.

According to a particular embodiment, the crosslinking speed obtained is greater than the crosslinking speed which is obtained under the same conditions but without the use of magnesium oxide. Preferably, the crosslinking speed during the crosslinking process is greater than 1.1 times, 1.2 times, 1.3 times, 1.4 times, 1.5 times, 1.8 times or 2 times the speed of crosslinking which is obtained under the same conditions but without the use of magnesium oxide.

The crosslinking rates obtained with and without magnesium oxide can be measured in the same way, according to the procedure described above.

Other additives in the composition

The composition relating to the invention may also include a reinforcing filler.

The physical state in which the reinforcing filler is present is immaterial, whether in the form of powder, microbeads, granules, beads or any other suitable densified form.

It is possible, for example, to use an organic filler such as carbon black, an inorganic reinforcing filler such as silica, or alternatively a blend of these two types of filler, in particular a blend of carbon black and silica.

As other reinforcing fillers, it is also possible to use cellulosic fillers, talc, calcium carbonate, mica or wollastonite, glass or metal oxides or hydrates, with the exception of magnesium oxide.

As carbon blacks, all carbon blacks are suitable, in particular so-called pneumatic grade blacks. Among the latter, there may be mentioned more particularly the reinforcing carbon blacks of the 100, 200 or 300 series (ASTM grades), such as, for example, the blacks N115, N134, N234, N326, N330, N339, N347, N375, or even, depending on the intended applications, the blacks of higher series (for example N660, N683, N772). The carbon blacks could for example already be incorporated into an isoprene elastomer in the form of a masterbatch (see for example documents WO 97/36724 or WO 99/16600).

As examples of organic fillers other than carbon blacks, mention may be made of organic fillers of functionalized polyvinyl as described in documents WO 2006/069792, WO 2006/069793, WO 2008/003434 and WO 2008/003435.

The composition can also contain a type of silica or a blend of several silicas. The silica used can be any reinforcing silica known to those skilled in the art, in particular any precipitated or pyrogenic silica having a BET surface as well as a CTAB specific surface, both less than 450 m ² / g, preferably from 5 to 400 m ² / g. The BET specific surface is determined according to ISO 9277: 2010 and the CTAB specific surface is measured according to ISO 6810: 1995. As highly dispersible precipitated silicas (called HDS), mention may be made, for example, of the Ultrasil 7000 and Ultrasil 7005 silicas from the company Degussa, the Zeosil 1165MP, 1135MP and 1115MP silicas from the company Rhodia, the Hi-Sil EZ150G silica from the PPG, the Zeopol 8715, 8745 and 8755 silicas from the Huber company, treated precipitated silicas such as for example the aluminum doped silicas described in application EP 0735088 or the silicas with high specific surface as described in the application WO 03/16837.

The silica preferably has a BET surface of between 45 and 400 m ² / g, more preferably between 60 and 300 m ² / g.

One can also use a reinforcing filler of another nature, in particular organic, covered with a layer of silica, or else would have on its surface functional sites, in particular hydroxyls.

The volume fraction of reinforcing filler in the composition is defined as being the ratio of the volume of the reinforcing filler to the volume of all the constituents of the composition, it being understood that the volume of all the constituents is calculated by adding the volume of each of the constituents of the composition. The volume fraction of reinforcing filler in a composition is therefore defined as the ratio of the volume of the reinforcing filler to the sum of the volumes of each of the constituents of the composition, and preferably, this volume fraction is between 5% and 20%, preferably between 5% and 15%. In an equivalent preferential manner, the mass quantity of total reinforcing filler (for example carbon black and / or silica) is less than 50 phr, preferably from 5 to 45 phr, more preferably from 10 to 40 phr and so very preferable, from 15 to 35 pce.

Preferably, the ratio of the mass quantity of filler to the mass quantity of the co-agent is less than or equal to 2. More preferably, this ratio is within a range ranging from 0.3 to 2, preferably from 0.7 at 1.3. Preferably, the composition according to the invention comprises predominantly carbon black as a reinforcing filler.

By majority reinforcing filler is meant that which has the highest rate among the reinforcing fillers present in the composition. In particular, the term “reinforcing filler” is understood to mean any reinforcing filler which represents at least 50% by weight of the reinforcing fillers present, preferably more than 50% and more preferably more than 60%.

The composition may optionally also contain, in addition to reinforcing fillers, coupling agents, coupling activators, agents for recovery of inorganic charges or, more generally, agents for aid in implementation which are capable in known manner, thanks to an improvement. of the dispersion of the filler in the matrix of crosslinkable polymers, in particular of elastomers, and to a lowering of the viscosity of the composition, to improve the ability to be used in the raw state, these agents being for example hydrolysable silanes such as alkylalkoxysilanes, polyols, fatty acids, polyethers, primary, secondary or tertiary amines, hydroxylated or hydrolyzable polyorganosiloxanes.

As coupling agent, it is possible in particular to use polysulphurized silanes, said to be symmetrical or asymmetrical according to their particular structure, known to those skilled in the art, such as those described for example in documents WO 03/002648 and WO 03/002649.

In the composition according to the invention, the content of coupling agent is preferably between 2 and 15 phr, more preferably between 3 and 13 phr and even more preferably between 5 and 10 phr.

The composition can also comprise an implementing agent, in particular zinc oxide or calcium oxide, preferably zinc oxide.

Preferably, the composition relating to the invention does not contain a vulcanization system, which is one of the advantages of the invention since this makes it possible to simplify the formula and the preparation of the composition. If, however, a vulcanization system is present in the composition, it is preferably present in small quantities explained below.

The actual vulcanization system is usually based on sulfur (or a sulfur-donating agent) and a primary vulcanization accelerator. To this basic vulcanization system are added, incorporated during the first non-productive phase and / or during the productive phase as described later, various secondary accelerators or known vulcanization activators such as oxide zinc, stearic acid or equivalent compounds, guanidine derivatives (in particular diphenylguanidine).

Molecular sulfur (or equivalent molecular sulfur donor agents), when used, is at a rate preferably less than 0.5 phr, preferably less than 0.3 phr, more preferably at a rate less than 0.1 pce. Very preferably, the composition is devoid of molecular sulfur.

The vulcanization system can also include one or more additional accelerators, for example the compounds of the thiuram family, zinc dithiocarbamate derivatives, sulfenamides, guanidines or thiophosphates. It is possible in particular to use any compound capable of acting as an accelerator for vulcanization of polymers in the presence of sulfur, in particular accelerators of the thiazole type as well as their derivatives, accelerators of the thiuram type, zinc dithiocarbamates. These accelerators are more preferably chosen from the group consisting of 2-mercaptobenzothiazyl disulfide (abbreviated MBTS), N-cyclohexyl-2-benzothiazyle sulfenamide (abbreviated CBS), N, Ndicyclohexyl-2-benzothiazyle sulfenamide (abbreviated DCBS), N-tert-butyl2-benzothiazyle sulfenamide (abbreviated TBBS), N-tert-butyl-2benzothiazyle sulfenimide (abbreviated TBSI), zinc dibenzyldithiocarbamate (abbreviated as ZBEC) and mixtures of these compounds. Preferably, a primary accelerator of the sulfenamide type is used.

Preferably, the composition is devoid of any vulcanization accelerator (other than the co-agent and magnesium oxide).

The composition according to the invention can also comprise additives such as petroleum fractions, solvents, plasticizing agents, whether the latter are of aromatic or non-aromatic nature, pigments and / or dyes, tackifying resins, aids for processing aids, lubricants, anti-radiation additives (anti-UV), protective agents such as anti-ozone waxes (such as Cone Ozone C32 ST), anti-ozonants chemicals, antioxidants (such as 6paraphenylenediamine), anti-fatigue agents, reinforcing resins, acceptors (for example phenolic novolak resin) or methylene donors (for example HMT or H3M) as described for example in the document WO 02/10269, as well as adhesion promoters (cobalt salts for example).

In particular, the composition may include a plasticizer, an antioxidant, a stabilizer or a mixture thereof.

According to one embodiment, the composition is devoid of plasticizer.

According to another embodiment, the composition according to the invention comprises a plasticizing agent. Preferably, this plasticizing agent is a solid hydrocarbon resin (or plasticizing resin), an extension oil (or plasticizing oil), or a mixture of the two.

When it is included in the composition, the level of total plasticizing agent is preferably greater than or equal to 5 phr, more preferably from 5 to 100 phr, in particular from 10 to 80 phr, for example from 15 to 70 phr.

Use / crosslinking process

The use of magnesium oxide according to the invention involves adding magnesium oxide to the composition comprising the crosslinkable polymer, in particular the elastomer, and then crosslinking thereof.

In a particularly preferred manner, the composition also comprises a co-agent and an organic peroxide, and therefore the use of magnesium oxide is carried out in the presence of a co-agent, and of an organic peroxide.

The use according to the invention provides for implementing the crosslinking of a composition as described above, in a crosslinking process. This process can be implemented as follows.

The composition can be manufactured in a suitable mixer, using two successive preparation phases well known to those skilled in the art: a first working phase or thermo-mechanical kneading (sometimes referred to as a non-productive phase) at high temperature, up to '' at a maximum temperature between 110 ° C and 190 ° C, preferably between 130 ° C and 180 ° C, followed by a second mechanical working phase (sometimes referred to as the productive phase) at a lower temperature, typically below 110 ° C, for example between 60 ° C and 100 ° C, finishing phase during which is incorporated the crosslinking or vulcanization system and in particular the peroxide; such phases have been described for example in documents EP 0501227, EP 0735088, EP 0810258, WO 00/05300 or WO 00/05301.

The first (non-productive) phase is preferably carried out in several thermomechanical stages. During a first step, the polymers and the reinforcing fillers (and optionally the coupling agents and / or other ingredients) are introduced into a suitable mixer such as a conventional internal mixer, at a temperature between 20 ° C and 100 ° C, preferably between 25 ° C and 100 ° C.

After a few minutes, preferably from 0.5 to 2 min and a rise in temperature from 90 ° C to 100 ° C, the other ingredients (that is to say, those that remain if not all of them have been started) ) are added all at once or in parts, with the exception of the crosslinking system and in particular organic peroxide during mixing ranging from 20 seconds to a few minutes. The total duration of the kneading, in this non-productive phase, is preferably between 2 and 10 minutes at a temperature less than or equal to 180 ° C., and preferably less than or equal to 170 ° C.

After the mixture thus obtained has cooled, the crosslinking system, and in particular the peroxide, is then incorporated at low temperature (typically less than 100 ° C.), generally in an external mixer such as a cylinder mixer. The whole is then mixed (productive phase) for a few minutes, for example between 5 and 15 min.

The composition thus obtained is then calendered, for example in the form of a sheet or a plate, in particular for a characterization in the laboratory, or else extruded, to form for example a rubber profile used for the manufacture of semi-finished products in order to obtain finished products.

The crosslinking (or baking) is carried out in a known manner at a temperature generally between 130 ° C and 200 ° C, under pressure, for a sufficient time which can vary for example between 5 and 90 min depending in particular on the baking temperature. , the crosslinking system adopted and the crosslinking kinetics of the composition considered

According to one embodiment, the crosslinking method is implemented for the manufacture of all or part of a tire, in particular the manufacture of treads, sidewalls, interior coatings, carcass plies, beads, and / or top layers.

The invention also relates to the products obtained at the end of the crosslinking process, in particular tire parts such as treads, as well as tires comprising such parts.

EXAMPLES

The following examples illustrate the invention without limiting it.

Example 1

The crosslinking density and the crosslinking speed of different compositions were evaluated. The following compositions were prepared:

Composition No. 1 2 3 4 5 6 BR (pce) 100 100 100 100 100 100 Carbon black N234 (pc) 25 25 25 25 25 25

Composition No. 1 2 3 4 5 6 Zinc dimethacrylate (pce) 20 20 20 20 20 20 Zinc oxide (pce) 2 2 2 2 2 2 Dicumyl peroxide (pce) 0.9 - - - - - Luperox 230XL40-SP (Phr) 1.45 Luperox® TBEC (pce) - - 0.89 - - - Luperox TBICM75 (pce) - - - 0.82 - - Luperox® 270 (Pce) - - - - 0.81 - Luperox® P (pce) - - - - - 0.69 Magnesium oxide (pce) 15 15 15 15 15 15

Composition No. 7 8 9 10 11 12 13 14 BR (pce) 100 100 100 100 100 100 100 100 Carbon black N234 (pce) 25 25 25 25 25 25 25 25 Zinc dimethacrylate (pce) 20 20 20 20 20 20 20 20 Zinc oxide (pce) 2 2 2 2 2 2 2 2 Dicumyl peroxide (pce) 0.9 - - - - - 0.9 Luperox 230XL40-SP (Phr) 1.45 1.45 Luperox® TBEC (pce) - - 0.89 - - -

Composition No. 7 8 9 10 11 12 13 14 Luperox TBICM75 (Phr) 0.82 Luperox® 270 (Pce) - - - - 0.81 - Luperox® P (pce) - - - - - 0.69 N, N-phenylene bismaleimide (pce) 0.5 0.5 Magnesium oxide (pce)

BR = polybutadiene

Luperox® 230XL40-SP = n-butyl-4,4‘-di (tert-butylperoxy) valerate

Luperox® TBEC = OO- (t-butyl) -O- (2-ethylhexyl) monoperoxycarbonate Luperox® TBICM75 = tert-butyl peroxyisopropylcarbonate

Luperox® 270 = tert-butyl peroxy-3,5,5-trimethylhexanoate

Luperox® P = tertio butyl peroxybenzoate

The compositions were prepared using an internal Brabender 350S mixer (maximum capacity: 350 ml). The parameters are the following 10:

- Initial temperature: 22 ° C (room temperature);

- Rotor rotation speed: 50 rpm (rotations per minute);

- Order and time of introduction of raw materials:

0 BR 5 minutes Carbon black N234 10 minutes Zinc dimethacrylate 12 mins Zinc oxide 14 mins crosslinking system (peroxide possibly followed by MgO possibly followed by the crosslinking co-agent) 16 mins Falling out of the mixture

Final temperature (fall of the mixture): maximum 80 ° C.

The mixtures were homogenized in an open mixer of the Gumix brand at room temperature to obtain plates approximately 5 mm thick, which were allowed to cool to room temperature and then tested the day after the day of production.

Compositions 1 to 6 illustrate the use according to the invention, compositions 7 to 14 correspond to comparative examples.

The crosslinking density and the crosslinking speed are evaluated as follows:

A disc about 3.5 cm in diameter is cut from the mixing plate to be tested. It is placed between two sheets of Mylar type polymer then the assembly is placed in the test cavity of the RPA 2000 rheometer already preheated to the test temperature and adjusted according to the following parameters:

- Temperature: 160 ° C;

- Amplitude of oscillation: 0.5 °;

- Oscillation frequency: 1.667 Hz;

- Time: 60 min.

The test is immediately started and the measurements are automatically recorded by the computer connected to the instrument.

The results are summarized in Figures 1,2, 3 and 5, as well as in the tables below:

Composition No. 1 2 3 4 5 6 ML (dN m) 1,956 2.04 2,544 2,512 2,236 2,384 MH (dN m) 87.69 52.25 23.3 24.24 22.98 21,33 T’90 (h: min: s) 0:18:12 0:24:11 0:37:14 0:36:03 0:33:32 0:30:47 Ts2 (h: min: s) 0:00:39 0:00:42 0:00:43 0:00:42 00: 0046 0:00:45 MH-ML (dN m) 85.7 50.2 20.8 21.7 20.7 18.9

Composition No. 7 8 9 10 11 12 13 14 ML (dN m) 2,003 1,988 - - - - 1.95 1,961 MH (dN m) 35.7 17.45 - - - - 41.28 19.8 T’90 (h: min: s) 0:25:02 0:22:12 - - - - 0:27:09 0:21:16 Ts2 (h: min: s) 0:02:15 0:02:38 - - - - 0:02:02 0:02:03 MH-ML (dN m) 33.7 15.5 - - - - 39.3 17.8

The value Ts2 corresponds to the roasting time, that is to say the time necessary to reach an increase in viscosity of 2 units from the minimum torque ML.

It is found that the compositions containing magnesium oxide (compositions Nos. 1 and 2) have a higher crosslinking density than the same compositions without magnesium oxide (compositions Nos. 7 and 8) or that the same compositions containing Ν, Ν-phenylene bismaleimide as crosslinking co-agent (compositions no. 13 and 14). Ν, Ν-phenylene bismaleimide is a cross-linking co-agent conventionally used and well known to those skilled in the art.

The T’90 obtained with composition No. 1 is lower than that observed with compositions No. 7 and No. 13 (same composition without magnesium oxide or with Ν, Ν-phenylene bismaleimide as crosslinking agent). On the other hand, the T’90 obtained with composition n ° 2 is higher than that observed with compositions n ° 8 and n ° 14.

The roasting time Ts2 of the composition n ° 1 and that of the composition n ° 2 are lower than that of the compositions n ° 7 and n ° 13 and that of the compositions n ° 8 and n ° 14 respectively.

It may also be noted that compositions no. 9, 10, 11 and 12 do not crosslink and that the addition of magnesium oxide in these compositions allows crosslinking of these compositions (compositions no. 3, 4, 5 and 6 ).

Example 2

In this example, compositions having a lower amount of carbon black were tested.

The following compositions were prepared:

Composition No. 15 16 17 18 19 BR (pce) 100 100 100 100 100 Carbon black N234 (Phr) 3 3 3 3 3 Zinc dimethacrylate (pce) 20 20 20 20 20 Zinc oxide (pce) 2 2 2 2 2 Dicumyl peroxide (pce) 0.9 - 0.4 0.8 -

Composition No. 15 16 17 18 19 TBEC (pce) - 0.89 - - 0.89 Magnesium oxide (pce) 15 15 - - -

The compositions were prepared in the same manner as in Example 1.

Compositions 15 and 16 illustrate the use of magnesium oxide according to the invention, compositions 17 to 19 correspond to comparative examples.

The crosslinking density and the crosslinking speed are evaluated in the same way as in Example 1.

The results are summarized in Figure 4, as well as in the table below:

Composition No. 15 16 17 18 19 ML (dN m) 1.35 1.59 1,252 1,218 1,318 MH (dN m) 78.69 19.34 13,12 30.43 3.98 T’90 (h: min: s) 0:27:44 0:33:47 0:35:53 0:33:20 0:36:02 Ts2 (h: min: s) 0:00:49 0:00:46 0:07:44 0:03:29 0:25:07 MH-ML (dN m) 77.3 17.8 11.9 29.2 2.7

The crosslinking speed and the crosslinking density are increased by the addition of magnesium oxide even when the amount of carbon black is low.

Example 3

In this example, the effect of magnesium oxide on the density and speed of crosslinking was compared with that of zinc oxide. The following compositions were prepared:

Composition No. 26 27 28 29 BR (pce) 100 100 100 100 Carbon black N234 (pce) 25 25 25 25 Zinc dimethacrylate (pce) 20 20 20 20 Zinc oxide (pce) - 2 15 - Dicumyl peroxide (pce) 0.9 0.9 0.9 0.9

Composition No. 26 27 28 29 Magnesium oxide (pce) 15 15 - -

The compositions were prepared in the same manner as in Example 1.

Compositions 26 and 27 illustrate the use of magnesium oxide according to the invention, compositions 28 to 29 correspond to comparative examples.

The density and the speed of crosslinking are evaluated as follows.

A disc about 3.5 cm in diameter is cut from the mixing plate to be tested. It is placed between two sheets of Mylar type polymer then the assembly is placed in the test cavity of the MDR rheometer already preheated to the test temperature and adjusted according to the following parameters:

- Temperature: 160 ° C;

- Amplitude of oscillation: 0.5 °;

- Oscillation frequency: 1.667 Hz;

- Time: 60 min.

The test was immediately started and the measurements were automatically saved by the computer connected to the instrument.

The results are summarized in Figure 6, as well as in the table below:

Composition No. 26 27 28 29 ML (dN m) 3,447 3,437 2,246 2,012 MH (dN m) 88.23 85.51 58.92 53.95 T’90 (h: min: s) 0:19:36 0:18:07 0:20:57 0:21:19 Ts2 (h: min: s) 0:00:19 0:00:24 0:00:43 0:00:47 MH-ML (dN m) 84.8 82.1 56.7 51.9

Compositions containing magnesium oxide have an increased density and crosslinking speed compared to the composition containing zinc oxide. In particular, composition 26 makes it possible to obtain a higher crosslinking density and a higher crosslinking speed compared with composition 28 which corresponds to the same composition as composition 26 but with zinc oxide instead of l 'magnesium oxide (in the same proportion).

It can also be noted that the addition of zinc oxide (composition 28) slightly increases the crosslinking density and the speed of crosslinking compared to the same composition without metallic oxide (composition 29). However, this very weak effect is probably only due to a reinforcing effect of zinc oxide.

Claims (28)

1. A tire comprising a rubber composition based on: - at least one elastomer, - an organic peroxide, and - magnesium oxide, the ratio of the mass quantity of magnesium oxide to the mass quantity of organic peroxide being greater than or equal to 1. 2. A tire according to claim 1, in which the elastomer is free of chlorine functional groups and of carboxylic acid functional groups, preferably free of halogen functional groups and carboxylic acid functional groups. 3. A tire according to any one of claims 1 or 2, in which the elastomer is chosen from the group consisting of diene elastomers, saturated polyolefins, silicones, fluorinated elastomers, ethylene vinyl acetate copolymers, ethylene- (meth) acrylate copolymers, ethylene-glycidyl methacrylate copolymers and / or mixtures thereof. 4. Tire according to any one of the preceding claims, in which the elastomer is chosen from the group consisting of polybutadienes, synthetic polyisoprenes, natural rubber, butadiene copolymers, in particular butadiene and styrene copolymers and butadiene and acrylonitrile copolymers, isoprene copolymers, in particular isoprene and styrene copolymers, and mixtures of these elastomers. 5. Tire according to any one of the preceding claims, in which the organic peroxide is chosen from dicumyl peroxide, aryl or diaryl peroxides, diacetyl peroxide, benzoyl peroxide, dibenzoyl peroxide, ditertbutyl peroxide, tertbutylcumyl peroxide, 2,5-bis (tertbutylperoxy) -2,5-dimethylhexane, n-butyl-4,4'-di (tert-butylperoxy) valerate, 00- (t-butyl ) -0- (2ethylhexyl) monoperoxycarbonate, tert-butyl peroxyisopropylcarbonate, tertio-butyl peroxybenzoate, tertbutyl peroxy-3,5,5-trimethylhexanoate, 1,3 (4) -bis (tertbutylperoxyisopropyl) benzene and mixtures of these latter. 6. Tire according to any one of the preceding claims, in which the organic peroxide is used in a mass amount of 0.1 to 10 phr, preferably from 0.4 to 6 phr. 7. Tire according to any one of the preceding claims, in which the magnesium oxide has a BET specific surface ranging from 1 to 200 m ² / g, preferably from 5 to 170 m ² / g. 8. Tire according to any one of the preceding claims, in which the magnesium oxide has a BET specific surface greater than 25 m ² / g. 9. Tire according to any one of the preceding claims, in which the magnesium oxide is used in a mass amount of from 1 to 50 phr, preferably from 2 to 30 phr. 10. A tire according to any one of the preceding claims, in which the composition also comprises a crosslinking co-agent chosen from the group consisting of (meth) acrylate compounds, maleimide compounds, allyl compounds, vinyl compounds and their mixtures. 11. Tire according to claim 10, in which the crosslinking co-agent comprises a (meth) acrylate compound, in the form of a metal salt, or of an ester or in a polymeric form. 12. A tire according to claim 10 or 11, in which the crosslinking coagent comprises a (meth) acrylate compound in the form of a metal salt. 13. A tire according to claim 11 or 12, in which the metal salt is a zinc salt of formula (I): in which Ri, R ₂ , R3, R4, Rs and R6 independently represent a hydrogen atom or a C1-C7 hydrocarbon group chosen from linear, branched or cyclic alkyl groups, aralkyl groups, alkylaryl groups and groups aryls, and possibly interrupted by one or more heteroatoms, R ₂ and R3 on the one hand and R5 and R6 on the other hand which can independently form a non-aromatic ring. 14. A tire according to any one of claims 11 to 13, in which the metal salt is a zinc salt of formula (II): hydrogen atom or a C1-C7 hydrocarbon group chosen from linear, branched or cyclic alkyl groups, aralkyl groups, alkylaryl groups and aryl groups, and optionally interrupted by one or more heteroatoms, R ₂ and R3 may form a non-aromatic cycle. 15. A tire according to any one of claims 13 or 14, in which Ri, R ₂ , R3, R4, Rs and R6 in formula (I) or Ri, R ₂ , R 3 in formula (II) independently represent a hydrogen atom or a methyl group. 16. A tire according to any one of claims 11 to 15, in which the metal salt is zinc diacrylate or zinc dimethacrylate. 17. A tire according to any one of claims 10 to 16, in which the co-agent is used in a mass amount of 5 to 50 phr, preferably from 10 to 30 phr. 18. A tire according to any one of claims 10 to 17, in which: the ratio of the mass quantity of organic peroxide to the mass quantity of crosslinking co-agent in the composition is less than or equal to 0.09, preferably less than or equal to 0.05, more preferably less than or equal to 0.04 and even more preferably less than or equal to 0.03; and / or the ratio of the mass quantity of co-agent to the mass quantity of magnesium oxide in the composition is from 0.5 to 5, preferably from 0.8 to 2, and more particularly from 1 at 1.5. 19. A tire according to any one of the preceding claims, in which the composition also comprises a reinforcing filler, preferably chosen from the group consisting of carbon black, silica and their mixtures. 20. A tire according to claim 19, in which the mass quantity of reinforcing filler in the composition is from 5 to 45 phr, preferably from 10 to 40 phr, more particularly from 15 to 35 phr. 21. A tire according to claim 19 or 20, in which the ratio of the mass quantity of reinforcing filler to the mass quantity of crosslinking co-agent in the composition is less than or equal to 2, and preferably is 0.3 to 2, even more preferably from 0.7 to 1.3. 22. Tire according to any one of the preceding claims, in which the ratio of the mass quantity of magnesium oxide to the mass quantity of organic peroxide in the composition is from 5 to 60, preferably from 10 to 40, and more particularly preferably from 15 to 30. 23. A tire according to any one of the preceding claims, in which the composition further comprises one or more compounds chosen from the group consisting of plasticizers, implementing agents, antioxidants, and stabilizers. 24. Tire according to any one of the preceding claims, in which the composition is that of at least all or part of a layer of the tire chosen from a tread, a sidewall, an inner coating, a carcass ply, a bead, or a top layer. 25. Use of magnesium oxide to increase the crosslinking rate and / or the crosslinking density of at least one elastomer, in a rubber composition, for the manufacture of all or part of a tire, in particular the manufacture of treads, sidewalls, interior coverings, carcass plies, beads, and / or crown plies. 26. Use according to claim 25, in which the rubber composition is as defined in any one of claims 1 to 24. 27. Use according to one of claims 25 or 26, making it possible to obtain a crosslinking density greater than 1.5 times, preferably 2 times, 3 times, 5 times, 10 times, 20 times, 50 times or 100 times. the crosslinking density obtained under the same crosslinking conditions but in the absence of magnesium oxide. 28. Use according to one of claims 25 to 27, making it possible to obtain a crosslinking speed greater than 1.1 times, preferably 1.2 times, 1.3 times, 1.4 times, 1.5 times, 1.8 times or 2 times the speed of crosslinking obtained under the same conditions of 5 crosslinking but in the absence of magnesium oxide.