EP3758956A1

EP3758956A1 - Use of magnesium oxide in tyre manufacture

Info

Publication number: EP3758956A1
Application number: EP19715151.7A
Authority: EP
Inventors: Alfredo Defrancisci; Leonard Palys; Peter Dluzneski
Original assignee: Compagnie Generale des Etablissements Michelin SCA; Arkema France SA
Current assignee: Compagnie Generale des Etablissements Michelin SCA; Arkema France SA
Priority date: 2018-02-27
Filing date: 2019-02-27
Publication date: 2021-01-06
Also published as: FR3078336A1; WO2019166739A1; FR3078336B1

Abstract

The invention relates to a tyre comprising a rubber composition based on at least one elastomer, an organic peroxide and magnesium oxide, the ratio of the weight amount of magnesium oxide to the weight amount of organic peroxide being greater than or equal to 1. The invention also relates to the use of magnesium oxide for increasing the rate of crosslinking and/or the crosslinking density of at least one elastomer, in the manufacture of all or part of a tyre, in particular the manufacture of treads, of sidewalls, of internal coatings, of carcass plies, of beads and/or of crown plies.

Description

USE OF MAGNESIUM OXIDE IN MANUFACTURING

OF PNEUMATIC

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, and 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 component of the tire. The crosslinking of the rubber compositions makes it possible to impart such elastic properties. Cross-linking of crosslinkable polymers also provides advantageous properties for other products such as pipes, joints, belts, sporting goods or insulators.

CN 104795149 discloses a method of manufacturing sheaths for communication cables of coal mines comprising vulcanizing 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.

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

JP 2002306637 relates to the manufacture of golf balls.

It discloses vulcanized rubber compositions comprising a metal salt of a, b-unsaturated carboxylic acid, an organic peroxide, and zinc oxide or magnesium oxide, zinc acrylate being preferred among the metal salts of α, β-unsaturated carboxylic acid.

US 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 EPDM, zinc methacrylate, magnesium oxide and peroxide (1,3-bis (tert-butylperoxyisopropyl) benzene). These rubber compositions are vulcanized and can be used for rollers, belts, gaskets, tires, vibration isolators and hoses.

US 4,843,114 discloses vulcanizable compositions for military tank crawlers containing nitrilated polymers, a metal oxide selected from zinc oxide and magnesium oxide, a zinc methacrylate or zinc dimethylmethacrylate resin, and an agent curing agent selected from dicumyl peroxide, its derivatives, sulfur and a sulfur donor.

FR 3012147 discloses tire compositions comprising a diene elastomer, a zinc diacrylate derivative and a peroxide.

The rate of crosslinking is important for optimum manufacturing and cooking of the tires, while the crosslinking density makes it possible to ensure the properties after firing. There is therefore a need to provide rubber composition crosslinking systems or the like which makes 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 of chlorine functional groups and carboxylic acid functional groups, preferably free of halogen functional groups and carboxylic acid functional groups. According to embodiments, the elastomer is chosen from the group consisting of diene elastomers, saturated polyolefins, silicones, fluorinated elastomers, ethylene-vinyl acetate copolymers, and ethylene- (meth) copolymers. ) methyl acrylate, copolymers of ethylene-glycidyl methacrylate and / or mixtures thereof.

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

According to embodiments, the organic peroxide is selected 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) -O- (2-ethylhexyl) ) monoperoxycarbonate, tert-butyl peroxyisopropylcarbonate, tert-butyl peroxybenzoate, tert-butylperoxy-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 quantity of 0.1 to 10 phr, preferably of 0.4 to 6 phr.

According to embodiments, the magnesium oxide has a BET specific surface area 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 area 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 further comprises a crosslinking co-agent selected from the group consisting of (meth) acrylate compounds, maleimide compounds, allyl compounds, vinyl compounds and mixtures thereof.

According to embodiments, the crosslinking co-agent comprises a (meth) acrylate compound, in the form of a metal salt, or an ester or in 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 R 1, R ₂ , R 3, R ₄ , R ₅ and R 6 independently represent a hydrogen atom or a C 1 -C 7 hydrocarbon-based group chosen from linear, branched or cyclic alkyl groups, aralkyl groups, alkylaryl groups and aryl groups, and optionally interrupted by one or more heteroatoms, R2 and R3 on the one hand and R5 and R6 on the other hand can independently form a non-aromatic ring.

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

wherein R 1, R 2 and R 3 independently represent a hydrogen atom or a C 1 -C 7 hydrocarbon group selected from linear, branched or cyclic alkyl groups, aralkyl groups, alkylaryl groups and aryl groups, and optionally interrupted by a or more heteroatoms, R2 and R3 may form a non-aromatic ring.

According to embodiments, R 1, R ₂ , R 3, R ₄ , R ₅ and R 6 in formula (I) or R 1, R ₂ , R ₅ in formula (II) independently represent a hydrogen atom or a methyl group.

In some embodiments, the metal salt is zinc diacrylate or zinc dimethacrylate.

According to embodiments, the co-agent is used in a mass quantity of 5 to 50 phr, preferably 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 preferably from 1 to 1; 5.

According to embodiments, the composition further comprises a reinforcing filler, preferably selected from the group consisting of carbon black, silica and mixtures thereof.

According to embodiments, the amount by weight of reinforcing filler in the composition is from 5 to 45 phr, preferably from 10 to 40 phr, more preferably from 15 to 35 phr.

According to embodiments, the ratio of the mass amount of reinforcing filler to the mass quantity of crosslinking co-agent in the composition is less than or equal to 2, and preferably ranges from 0.3 to 2, even more preferably from 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 preferably from 15 to 30. .

In embodiments, the composition further comprises one or more compounds selected 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 selected from a tread, a sidewall, an inner lining, a carcass ply, a bead, or a crown ply.

The invention also relates to the use of magnesium oxide for increasing the rate of crosslinking and / or the crosslinking density of at least one elastomer, in a rubber composition, for the manufacture of all or part of a tire. including the manufacture of treads, sidewalls, linings, 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 twice, 3 times, 5 times, 10 times, 20 times, 50 times or 100 times. the crosslinking density obtained under the same conditions of crosslinking but in the absence of magnesium oxide.

According to embodiments, the use according to the invention makes it possible to obtain a crosslinking rate greater than 1, 1 time, preferably 1, 2 times, 1, 3 times, 1, 4 times, 1, 5 times, 1, 8 times or 2 times the crosslinking rate obtained under the same crosslinking conditions but in the absence of magnesium oxide.

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

It also makes it possible to accelerate the 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 large increase in the crosslinking density and / or in the crosslinking rate 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 composition No. 7 described in Example 1. The time (in h: min: s) is shown on the abscissa and the pair 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 the compositions No. 7, No. 8 and No. 2 described in Example 1. The time (in h: min: s) is shown on the abscissa and the pair 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 the compositions No. 3, No. 4, No. 5, No. 6, No. 7 and No. 8, No. 9, No. 10, No. 11, and No. 12 described in Example 1. The time (in h: min: s) is shown on the abscissa and the pair S ', in dN m, appears on the ordinate. FIG. 4 represents the rheometric curves obtained by an RPA 2000 rheometer at 160 ° C. during the crosslinking of the compositions No. 15, No. 16, No. 17, No. 18 and No. 19 described in Example 2 The time (in h: min: s) is shown on the abscissa and the pair S ', in dN m, is shown on the ordinate.

FIG. 5 represents the rheometric curves obtained by an RPA 2000 rheometer at 160 ° C. during the crosslinking of the compositions No. 7, No. 8, No. 13 and No. 14 described in Example 1. The time (in h: min: s) is shown on the abscissa and the pair 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 the compositions No. 26, No. 27, No. 28 and No. 29 described in Example 3. The time (in h: min: s) is shown on the abscissa and the pair S ', in dN m, is 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 term "phr" 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 in relation to the total amount of elastomers (or other crosslinkable polymers) by weight conventionally considered to be the hundred value.

The invention relates to the use of magnesium oxide for increasing the crosslinking rate and / or the crosslinking density of at least one crosslinkable polymer, in particular at least one elastomer, for the manufacture of all or part of a tire, in particular the manufacture of treads, sidewalls, internal linings, 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 quantity of magnesium oxide on the mass quantity of organic peroxide being greater than or equal to 1.

By the term "composition based on" is meant a composition comprising the mixture and / or the reaction product in situ of the various basic constituents used, some of these constituents being able to react and / or being intended to react with one another, at least partially, during different phases of manufacture of the composition, or during the subsequent firing, modifying the composition as it was initially prepared. Thus, the compositions as implemented for the invention may be different in the uncrosslinked 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 uncrosslinked 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 of 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 crosslinkable polymer molecules. 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 (especially linear low density polyethylenes, low density polyethylenes, high density polyethylenes, ethylene-propylene 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) of diene monomers (monomers bearing two carbon-carbon double bonds, conjugated or otherwise).

Diene elastomers having functional groups -Cl or -COOH (carboxylic acid), such as polychloroprene, and diene elastomers lacking such functional groups are distinguished. 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 broadly, it is preferred that the composition used in the context of the invention is devoid of diene elastomer having halogen functional groups or -COOH.

The 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, the magnesium oxide is not used as a crosslinking agent as such. For the invention, the crosslinking agent is an organic peroxide, optionally associated with a co-agent as discussed below.

The diene elastomers can also be classified in known manner into two categories, those said to be essentially unsaturated and those said to be essentially saturated. These two categories of diene elastomers can be envisaged within the scope of the invention.

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

By contrast, essentially unsaturated diene elastomer is understood to mean a diene elastomer derived at least in part from conjugated diene monomers having a level 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 degree of units of diene origin (conjugated dienes) which is greater than 50% (in moles).

More particularly, the term "diene elastomer" may be used in the invention:

(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 conjugated dienes with each other or with one or more vinyl aromatic compounds having from 8 to 20 carbon atoms; (c) any ternary copolymer obtained by copolymerization of ethylene, an α-olefin having from 3 to 6 carbon atoms with a non-conjugated diene monomer having from 6 to 12 carbon atoms, for example elastomers obtained from ethylene, propylene with a nonconjugated diene monomer of the aforementioned type such as in particular hexadiene-1,4, ethylidene norbornene, dicyclopentadiene; such polymers are described in particular in WO 2004/035639 and US 2005/0239639;

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

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

By way of conjugated dienes 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-di (C 1 -C 5) alkyl-1,3-butadienes, such as, for example, 2 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, aryl-1,3-butadiene, 1,3-pentadiene, 2,4-hexadiene. Suitable vinyl aromatic compounds are, for example, styrene, ortho-, meta-, para-methylstyrene, vinyl-toluene, para-tertiarybutylstyrene, methoxystyrenes, chlorostyrenes, vinylmesitylene, divinylbenzene and vinylnaphthalene.

The copolymers may contain between 99% and 20% by weight of diene units and between 1% and 80% by weight of vinylaromatic units. The elastomers 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 amounts of randomizing modifying agent used. The elastomers may be, for example, block, random, sequenced or microsequential, and may be prepared in dispersion, in emulsion or in solution; they may be coupled and / or starred or functionalized with a coupling agent and / or starring or functionalization. For coupling with 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 with a reinforcing inorganic filler such as silica, mention may be made, for example, 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), groups carboxylic acids (as described for example in the documents WO 01/92402 or US 6,815,473, WO 2004/096865 or US 2006/0089445) or polyether groups (as described for example in the documents EP 1 127909, US 6,503,973, WO 2009/000750 and WO 2009/000752). Other examples of functionalized elastomers that may be mentioned include elastomers, such as isoprene-styrene copolymers (SBR), polybutadienes (BR), natural rubber (NR) or synthetic polyisoprenes (IR), Epoxy type.

These functionalized elastomers may be used in a blend with each other or with unfunctionalized elastomers. For example, a functionalized silanol or polysiloxane elastomer having a silanol end, in admixture with a coupled and / or tin-starred elastomer (described in WO 201 1/042507), may be used, the latter representing a rate of 5 to 50% by weight, for example 25 to 50%.

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

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

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

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

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

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

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

According to a particular embodiment of the invention, the composition comprises a blend of one (or more) diene elastomers known as "high Tg "having a Tg between -70 ° C and 0 ° C and a (one or more) diene elastomer called" low Tg "between -1 10 ° C and -80 ° C, more preferably between -105 ° C and -90 ° C. The high Tg elastomer is preferably selected from the group consisting of SSBR, ESBR, natural rubber, synthetic polyisoprenes (having a content (mol%) of cis-1, 4 chains preferably of greater than 95 %), BIRs, SIRs, SBIRs, and mixtures of these elastomers. The low Tg elastomer preferably comprises butadiene units at a level (mol%) of at least 70%; it consists preferably of a polybutadiene (BR) having a content (mol%) 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 blending with a low Tg-elastomer.

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

Organic peroxide

The composition useful for the invention contains an organic peroxide.

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

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

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

Preferably, the dialkyl peroxides are selected 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 (t-butylperoxy) hexyne-3, 2,5-dimethyl -2,5-di (t-amylperoxy) hexyne-3, α, α'-di- [(t-butyl-peroxy) isopropyl] benzene, α, α'-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 1, 3 and 1, 4-isopropylcumyl cumyl peroxide (marketed for example by Arkema under the trade name Luperox ^® DC60) is also interesting.

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

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

Of the peroxyketals, the preferred peroxides are selected 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) ethyl butyrate, the

2,2-di- (t-amylperoxy) -propane, 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxynonane (or cyclic methyl ethyl ketone peroxide), 3, 3,5,7,7-pentamethyl-1,2,4-trioxepane, 4,4-bis (t-amylperoxy) n-butyl valerate, ethyl 3,3-di (t-amylperoxy) butyrate 1,1-di (t-butylperoxy) cyclohexane, 1,1-di (t-amylperoxy) cyclohexane, and mixtures thereof. Preferably, the peroxyesters are selected from the group consisting of tert-butylperoxybenzoate, tert-butylperoxy-2-ethylhexanoate and tert-butylperoxy-3,5,5-trimethylhexanoate.

Particularly preferably, the organic peroxide is selected from the group consisting of 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) -O- ( 2-ethylhexyl) monoperoxycarbonate, tert-butylperoxyisopropylcarbonate, tert-butyl peroxybenzoate, tert-butylperoxy-3,5,5-trimethylhexanoate, 1,3 (4) -bis (tert-butylperoxyisopropyl) benzene and mixtures thereof. of these, still 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-buty lperoxyisopropyl) benzene and mixtures thereof. Preferably, the mass quantity 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 in a range from 0.1 to 10 phr, 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 which is also preferred, the mass quantity of organic peroxide in the composition may be less than or equal to 3 phr, preferably from 0.1 to 3 phr, more preferably from 0.2 to 2 phr, and more preferably still 0.25 to 1 phr.

Co-agent for the crosslinking of organic peroxide

The composition relating to the invention preferentially contains a co-crosslinking agent.

The co-agents may be classified according to their mode of action, type 1 or 2, or 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 ester form such as polyfunctional acrylates or methacrylates; in polymeric form such as polybutadiene diacrylate; maleimide compounds such as bismaleimides or biscitraconimides; allyl compounds such as allylcyanurate and triallyl isocyanurate, or vinyl compounds such as low molecular weight polymers with a high vinyl content.

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

The table below gives examples of these co-agents.

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

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

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

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

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

in which R 1, R ₂ , R 3, R ₄ , R ₅ and R 6 independently represent a hydrogen atom or a C 1 -C 7 hydrocarbon-based 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 R 3 on the one hand and R ₅ and R 6 on the other hand can independently form a non-aromatic ring.

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

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 one carbon atom of said group and another heteroatom of said group or between two other 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 bonded to the rest of the molecule by ionic and non-covalent bonds (metal salt) makes it possible to increase the effectiveness of the peroxide during the crosslinking process. and imparting certain particular properties to the crosslinked compositions.

According to a particular embodiment, R 1, R ₂ , R 3, R ₄ , R ₅ and R 6 independently represent a hydrogen atom or a methyl group.

According to one embodiment, the metal salt is a compound of formula

According to a particular embodiment, R 1, R 2 and R 3 independently represent a hydrogen atom or a methyl group.

Advantageously, R2 and R3 represent a hydrogen atom.

According to a particular embodiment, R 1 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 CRAY VALLEY or zinc dimethacrylate (ZDMA) DIMALINK® 634 from CRAY VALLEY.

Alternatively, the crosslinking co-agent may comprise a vinyl compound, for example selected from the group consisting of trans-stilbene, 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):

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 Ga-methyl styrene, ortho, meta, para-diisopropenyl benzene, 1,2,4-triisopropenyl benzene, 1,3,5-triisopropenyl benzene, 3-isopropyl ortho diisopropenyl benzene, 4-isopropyl ortho diisopropenyl benzene, 4-isopropyl-m-diisopropenyl benzene, 5-isopropyl-m-diisopropenyl benzene, 2-isopropyl-p-diisopropenyl benzene.

As compounds represented by the general formula (IV), there may be mentioned 2,4-di (3-isopropylphenyl) -4-methyl-1-pentene, 2,4-di (4-isopropylphenyl) 4-methyl-1 pentene, 2- (3-isopropylphenyl) -4- (4-isopropylphenyl) -4-methyl-1-pentene, 2- (4-isopropylphenyl) -4- (3-isopropylphenyl) -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, tetra-allyloxyethane, carbonate allyldiglycol, triallyl trimellate, triallyl citrate, diallyl adipate, diallyl terephalate, diallyl oxalate, diallyl fumarate, ethylene glycol dimethacrylate and 2-hydroxyethyl methacrylate , may also be suitable as co-crosslinking agent.

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

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

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

As bismaleimide, mention may be made of N, N'-m-phenylene bismaleimide, N, N'-ethylene bismaleimide, N, N'-hexamethylene bismaleimide, N, N'-dodecamethylene bismaleimide and N, N bismaleimide. N, N '- (oxydipropylene), N, N' - (aminodipropylene) bismaleimide, bismaleimide, N, N'- (ethylenedioxydipropylene) bismaleimide, N, N '- (aminodipropylene) bismaleimide, N, N N, N '(1,3-cyclohexylene) N, N' (1,3-cyclohexylene), N, N '- (methylene 1,4-dicyclohexylene) bismaleimide, N, N' - (isopropylidene-1) bismaleimide, 4-dicyclohexylene, N, N '- (oxy-1,4-dicyclohexylene) bismaleimide, N, N'-p- (phenylene) bismaleimide, N, N' - (o-phenylene) bismaleimide, N-bismaleimide N, N '- (1,4-naphthylene), N', N '- (1,3-naphthylene) bismaleimide, N, N'- (1,5-naphthylene) bismaleimide, N, N' - bismaleimide 3,3'-dimethyl- (4,4-diphenylene), N, N '- (3,3-dichloro-4,4-biphenylene) bismaleimide, N, N'- ( 2,4-pyridyl), N, N '- (2,6-pyridyl) bismaleimide, N, N' - (1,4-anthraquinonediyl) bismaleimide, N, N '- (m-tolylene) bismaleimide, bismaleimide of N, N '(p-tolylene), N, N' - (4,6-dimethyl-1,3-phenylene) bismaleimide, N, N '- (2,3-dimethyl-1,4-bismaleimide) phenylene), N, N '- (4,6-dichloro-1,3-phenylene) bismaleimide, N, N' - (5-chloro-1,3-phenylene) bismaleimide, bismaleimide of N, N '- (5-hydroxy-1,3-phenylene), N, N' - (5-methoxy-1,3-phenylene) bismaleimide, N, N '- (m-xylylene) bismaleimide, bismaleimide of N, N '- (p-xylylene), N, N' - (methylenedi-p-phenylene) bismaleimide, N, N '- (isopropylidene-p-phenylene) bismaleimide, N, N' - oxidi-p-phenylene), N, N '- (thiodi-p-phenylene) bismaleimide, N, N'- (dithiodi-p-phenylene) bismaleimide, N, N' - (sulfodi-p-phenylene) bismaleimide ), N, N '- (carbonyldi-p-phenylene) bismaleimide, α, α'-bis (4-maleimodophenyl) -meta-diisopropylbenzene, α, α'-bis (4-p-phenylene) bismaleimide and α, α'-bis- (4-maleimidophenyl) -para-diisopropylbenzene.

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

The mass amount of co-agent is preferably in a range from 5 to 50 phr. Ranges of 10 to 50 phr, 10 to 30 phr, and 20 to 30 phr are preferred. Such amounts allow a 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 noticeable 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 elongation at break of the composition (which is particularly advantageous in the case of a composition intended for example for the manufacture of tire treads).

In certain preferred embodiments, the ratio of the mass quantity of peroxide to the mass quantity of co-agent is less than or equal to 0.09, or to 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 quantity of from 1 phr to 50 phr, preferably from 2 phr to 30 phr, more preferably from 5 to 15 phr.

When a co-crosslinking 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.

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

Particularly advantageously, the magnesium oxide has a BET specific surface area greater than 25 m ² / g.

According to particular embodiments, the magnesium oxide has a BET specific surface area 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 the magnesium oxide in the composition has the effect of increasing the crosslinking density and / or the crosslinking rate of the crosslinkable polymer, in particular the elastomer.

The crosslinking density is related 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 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 of 1. 667 Hz oscillation from discs of the test sample 3.5 cm in diameter and 4.8 cm ³ in volume.

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

The measurement is made 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 torque 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 the crosslinking (at the beginning 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 substantially completed at the end of this period, the torque then reaching a plateau. A suitable duration for the test is for example 60 minutes. However, this time can be adapted according to the actual duration expected for the manufacture of a given part, from the crosslinkable polymer composition, and at a given temperature.

The crosslinking rate is evaluated by the value T'90 corresponding to the time required to reach 90% of the maximum torque, which is obtained using the rheometric measurement described above. The lower T'90, the higher the rate of crosslinking.

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, 2, 3, 5, 10, 20, 50 or 100 times the crosslinking density which is obtained under the same conditions but without use. of 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, only 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 rate which is obtained under the same conditions but without the use of magnesium oxide. Preferably, the crosslinking rate during the crosslinking process is greater than 1, 1, 1, 2, 1, 3, 1, 4, 1, 5, 1, 8, or 2 times the rate of cure. 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 of the composition

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

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

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

Carbon blacks are suitable for all carbon blacks, especially so-called pneumatic grade blacks. Among these, the reinforcing carbon blacks of the 100, 200 or 300 series (ASTM grades), for example blacks N 15, N134, N 234, N 326, N330, N 339, N 347 or N375, or even more particularly , depending on the intended applications, 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, WO 97/36724 or WO 99/16600).

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

The composition may also contain a type of silica or a blend of several silicas. The silica used may be any reinforcing silica known to those skilled in the art, especially any precipitated or fumed silica having a BET surface and a CTAB specific surface both less than 450 m ² / g, preferably from 5 to 400 m ² / g. The BET surface area is determined according to ISO 9277: 2010 and the CTAB surface area is measured according to ISO 6810: 1995. As silicas highly dispersible precipitates (known as HDS), there may be mentioned, for example, the silicas Ultrasil 7000 and Ultrasil 7005 from the company Degussa, the silicas Zeosil 1 165MP, 1 135MP and 1 1 15MP from the company Rhodia, the silica Hi-Sil EZ150G from the PPG company, the Zeopol 8715, 8745 and 8755 silicas of the Huber Company, treated precipitated silicas such as, for example, the aluminum-doped silicas described in the application EP 0735088 or the silicas with a high specific surface area as described in the application WO 03/16837.

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

It is also possible to use a reinforcing filler of another nature, in particular organic, covered with a layer of silica, or else comprise on its surface functional sites, in particular hydroxyl sites.

The volume fraction of reinforcing filler in the composition is defined as 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 a preferentially equivalent manner, the mass quantity of total reinforcing filler (for example carbon black and / or silica) is less than 50 phr, preferably 5 to 45 phr, more preferably 10 to 40 phr, and more preferably very preferential, from 15 to 35 phr.

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 in a range from 0.3 to 2, preferably 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 "majority reinforcing filler" means 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 the reinforcing fillers, coupling agents, coupling promoters, inorganic charge-covering agents or, more generally, processing aids which can be used in a known manner, by improving the dispersion of the filler in the matrix of crosslinkable polymers, in particular elastomers, and at a lowering of the viscosity of the composition, to improve the ability to implement in the green state, these agents being for example hydrolysable silanes such as alkylalkoxysilanes, polyols, fatty acids, polyethers primary, secondary or tertiary amines, hydroxyl or hydrolyzable polyorganosiloxanes.

As coupling agent, it is possible to use in particular polysulfurized 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 the 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 may also comprise an agent for processing, 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 it 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 in low amounts explained below.

The vulcanization system itself is usually based on sulfur (or a sulfur-donor 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 known secondary accelerators or vulcanization activators such as zinc, stearic acid or equivalent compounds, guanidine derivatives (especially diphenylguanidine).

The molecular sulfur (or equivalently the molecular sulfur donor agents), when it is used, is at a level preferably less than 0.5 phr, preferably less than 0.3 phr, more preferably at a rate less than 0.1 phr. Most preferably, the composition is free of molecular sulfur.

The vulcanization system may also comprise one or more additional accelerators, for example the compounds of the family thiurams, zinc dithiocarbamate derivatives, sulfenamides, guanidines or thiophosphates. In particular, any compound capable of acting as an accelerator for the vulcanization of polymers in the presence of sulfur, in particular thiazole type accelerators and their derivatives, accelerators of the thiuram type, zinc dithiocarbamates, may be used in particular. These accelerators are more preferably selected from the group consisting of 2-mercaptobenzothiazyl disulfide (abbreviated MBTS), N-cyclohexyl-2-benzothiazyl sulfenamide (CBS abbreviated), N, N-dicyclohexyl-2-benzothiazyl sulfenamide ( abbreviated DCBS), N-tert-butyl-2-benzothiazyl sulfenamide (abbreviated TBBS), N-tert-butyl-2-benzothiazyl sulfenimide (abbreviated as 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 co-agent and magnesium oxide).

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

In particular, the composition may comprise 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 plasticizer. Preferably this plasticizer is a solid hydrocarbon resin (or plasticizing resin), an extender oil (or plasticizing oil), or a mixture of both.

When it is included in the composition, the level of total plasticizer is preferably greater than or equal to 5 phr, more preferably 5 to 100 phr, in particular 10 to 80 phr, for example 15 to 70 phr. Use / Crosslinking process

The use of the magnesium oxide according to the invention involves adding the magnesium oxide to the composition comprising the crosslinkable polymer, in particular the elastomer, and then cross-linking it.

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

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

The composition may be manufactured in a suitable mixer, using two successive preparation phases well known to those skilled in the art: a first phase of work or thermomechanical mixing (sometimes called non-productive phase) at high temperature, until at a maximum temperature of between 110.degree. C. and 190.degree. C., preferably between 130.degree. C. and 180.degree. C., followed by a second phase of mechanical work (sometimes referred to as a productive phase) at a lower temperature, which is typically lower at 110.degree. C., for example between 60.degree. C. and 100.degree. C., a finishing phase during which the crosslinking or vulcanization system and in particular the peroxide is incorporated; such phases have been described for example in the 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 steps. In 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 of between 20.degree. ° 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, those that remain if not all initially) are added at once or in portions, with the exception of the crosslinking system and especially the organic peroxide during a mixing ranging from 20 seconds to a few minutes. The total mixing time, in this non-productive phase, is preferably between 2 and 10 minutes at a temperature of less than or equal to 180 ° C, and preferably less than or equal to 170 ° C. After cooling the mixture thus obtained, the crosslinking system and in particular the peroxide are then incorporated at low temperature (typically below 100 ° C.), generally in an external mixer such as a roll mill. 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 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 conducted in a known manner at a temperature generally between 130 ° C and 200 ° C, under pressure, for a sufficient time which may vary for example between 5 and 90 min depending in particular on the cooking temperature of the crosslinking system adopted and the kinetics of crosslinking of the composition considered

According to one embodiment, the crosslinking process is implemented for the manufacture of all or part of a tire, in particular the manufacture of treads, sidewalls, internal linings, carcass plies, beads, and / or tablecloths.

The invention also relates to the products obtained from the crosslinking process, including tire parts such as treads, and tires comprising such parts.

EXAMPLES

The following examples illustrate the invention without limiting it.

Example 1

The crosslinking density and the crosslinking rate of different compositions were evaluated. The following compositions have been prepared:

BR = polybutadiene

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

Luperox® TBEC = 00- (t-butyl) -O- (2-ethylhexyl) monoperoxycarbonate Luperox® TBICM75 = tert-butyl peroxyisopropylcarbonate

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

Luperox® P = tertiary butyl peroxybenzoate

The compositions were prepared using a Brabender 350S internal mixer (maximum capacity: 350 ml). The parameters are as follows:

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

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

- Order and timing of introduction of raw materials:

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

The blends were homogenized in a Gumix open blender at room temperature to obtain plates about 5 mm thick, which were allowed to cool to room temperature and then tested the day after the day of production.

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

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

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

- Temperature: 160 ° C;

- Oscillation amplitude: 0.5 °;

Oscillation frequency: 1.667 Hz;

- Time: 60 min.

The test is started immediately 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:

The value Ts2 corresponds to the roasting time, that is to say the time necessary to achieve 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 N, N-phenylene bismaleimide as co-crosslinking agent (compositions 13 and 14). N, N-phenylene bismaleimide is a crosslinking co-agent conventionally used and well known to those skilled in the art.

The T'90 obtained with the composition No. 1 is lower than that observed with the compositions No. 7 and No. 13 (same composition without magnesium oxide or with N, N-phenylene bismaleimide as crosslinking agent). In contrast, the T'90 obtained with the composition No. 2 is higher than that observed with the compositions No. 8 and No. 14.

The roasting time Ts 2 of the composition No. 1 and that of the composition No. 2 are lower than that of the compositions No. 7 and No. 13 and that of the compositions No. 8 and No. 14, respectively.

It may also be noted that the compositions Nos. 9, 10, 11 and 12 do not crosslink and that the addition of magnesium oxide in these compositions makes it possible to crosslink these compositions (compositions Nos. 3, 4, 5 and 6 ).

Example 2

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

The following compositions have been prepared:

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 rate are evaluated in the same manner as in Example 1.

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

The crosslinking rate 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 rate of crosslinking was compared with that of zinc oxide. The following compositions have been prepared:

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 rate of crosslinking are evaluated as follows.

A disk about 3.5 cm in diameter is cut in the mixing plate to be tested. It is placed between two sheets of Mylar-type polymer and 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;

- Oscillation amplitude: 0.5 °;

Oscillation frequency: 1.667 Hz;

- Time: 60 min.

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

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

The magnesium oxide containing compositions have an increased density and rate of crosslinking relative to the zinc oxide containing composition. In particular, the composition 26 makes it possible to obtain a higher crosslinking density and a higher rate of crosslinking with respect to the composition 28 which corresponds to the same composition as the composition 26 but with zinc oxide in place of the magnesium oxide (in the same proportion). It may also be noted that the addition of zinc oxide (composition 28) slightly increases the crosslinking density and crosslinking rate with respect to the same composition without metal oxide (composition 29). However, this effect, very low, is probably due to a reinforcing effect of zinc oxide.

Claims

A tire comprising a rubber composition based on:

at least one elastomer,

an organic peroxide, and

magnesium oxide,

The tire of claim 1, wherein the elastomer is free of chlorine functional groups and 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, wherein the elastomer is selected from the group consisting of diene elastomers, saturated polyolefins, silicones, fluorinated elastomers, ethylene-vinyl acetate copolymers. copolymers of ethylene methyl (meth) acrylate, copolymers of ethylene-glycidyl methacrylate and / or mixtures thereof.

4. A tire according to any one of the preceding claims, wherein the elastomer is selected from the group consisting of polybutadienes, synthetic polyisoprenes, natural rubber, butadiene copolymers, in particular copolymers of butadiene and styrene. and copolymers of butadiene and acrylonitrile, copolymers of isoprene, in particular copolymers of isoprene and styrene, and mixtures of these elastomers.

A tire according to any one of the preceding claims, wherein the organic peroxide is selected 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) -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 thereof.

6. A tire according to any one of the preceding claims, wherein the organic peroxide is used in a mass amount of 0.1 to 10 phr, preferably 0.4 to 6 phr.

A tire according to any one of the preceding claims, wherein the magnesium oxide has a BET specific surface area of from 1 to 200 m ² / g, preferably from 5 to 170 m ² / g.

A tire according to any one of the preceding claims, wherein the magnesium oxide has a BET specific surface area greater than 25 m ² / g.

9. A tire according to any one of the preceding claims, wherein the magnesium oxide is used in a mass amount of 1 to 50 phr, preferably 2 to 30 phr.

A tire according to any one of the preceding claims, wherein the composition further comprises a crosslinking co-agent selected from the group consisting of (meth) acrylates, maleimide compounds, allyl compounds, vinyl compounds and their mixtures.

11. A tire according to claim 10, wherein the co-crosslinking agent comprises a (meth) acrylate compound, in the form of a metal salt, or an ester or in polymeric form.

Tire according to claim 10 or 11, wherein the co-crosslinking agent comprises a (meth) acrylate compound in the form of a metal salt.

Tire according to claim 11 or 12, wherein the metal salt is a zinc salt of formula (I):

wherein R 1, R 2, R 3, R ₄ , R 5 and R 6 independently represent a hydrogen atom or a C 1 -C 7 hydrocarbon group selected from linear, branched or cyclic alkyl groups, aralkyl groups, alkylaryl groups and groups. aryls, and optionally interrupted by one or more heteroatoms, R2 and R3 on the one hand and R5 and R6 on the other hand 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):

15. A tire according to any one of claims 13 or 14, wherein R 1, R 2, R 3, R 4, R 5 and R 6 in formula (I) or R 1, R ₂ , R 3 in the formula (II) independently represent a hydrogen atom or a methyl group.

16. A tire according to any one of claims 11 to 15, wherein the metal salt is zinc diacrylate or zinc dimethacrylate.

17. A tire according to any one of claims 10 to 16, wherein the co-agent is used in a mass quantity of 5 to 50 phr, preferably 10 to 30 phr.

18. A tire according to any one of claims 10 to 17, wherein:

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

19. A tire according to any one of the preceding claims, wherein the composition further comprises a reinforcing filler, preferably selected from the group consisting of carbon black, silica and mixtures thereof.

20. A tire according to claim 19, wherein the mass amount of reinforcing filler in the composition is 5 to 45 phr, preferably 10 to 40 phr, more preferably 15 to 35 phr.

21. A tire according to claim 19 or 20, wherein the ratio of the mass amount of reinforcing filler to the mass quantity of crosslinking co-agent in the composition is less than or equal to 2, and preferably ranges from 0.3 to 2, still more preferably from 0.7 to 1, 3.

22. A tire according to any one of the preceding claims, wherein 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 from more particularly preferably from 15 to 30.

A tire according to any one of the preceding claims, wherein the composition further comprises one or more compounds selected from the group consisting of plasticizers, processing agents, antioxidants, and stabilizers.

24. A tire according to any one of the preceding claims, wherein the composition is that of at least all or part of a tire layer selected from a tread, a sidewall, an inner lining, a carcass ply, a bead, or a tablecloth.

Use of magnesium oxide to increase the rate of crosslinking and / or crosslinking density of at least one elastomer in a rubber composition for the manufacture of all or part of a tire, including the manufacture of treads, sidewalls, linings, carcass plies, beads, and / or crown plies.

The use of claim 25, wherein the rubber composition is as defined in any one of claims 1 to 24.

27. Use according to one of claims 25 or 26, for obtaining 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, for obtaining a crosslinking rate greater than 1, 1 time, preferably 1, 2 times, 1, 3 times, 1, 4 times, 1, 5 times, 1, 8 times or 2 times the crosslinking rate obtained under the same crosslinking conditions but in the absence of magnesium oxide.