EP4157948A1

EP4157948A1 - Anti-ozonant composition for a crosslinked rubber article

Info

Publication number: EP4157948A1
Application number: EP21734197.3A
Authority: EP
Inventors: Sébastien FERREIRA; Gaëlle AVRIL
Original assignee: Compagnie Generale des Etablissements Michelin SCA
Current assignee: Compagnie Generale des Etablissements Michelin SCA
Priority date: 2020-05-29
Filing date: 2021-05-26
Publication date: 2023-04-05
Also published as: WO2021240109A1; US20230212375A1; FR3110911B1; FR3110911A1

Abstract

The invention relates to an anti-ozonant composition for a crosslinked rubber article, said composition being based on at least one chlorinated elastomer, at least one hydrocarbon solvent and at least one aprotic polar solvent. The invention also relates to a rubber article comprising at least one elastomer surface in contact with the air, said surface being entirely or partially coated with said composition.

Description

ANTI-OZONE PROTECTION COMPOSITION FOR A CROSS-LINKED RUBBER ARTICLE

The invention relates to an anti-ozone protection composition for a crosslinked rubber article, the composition being based on at least one chlorinated elastomer, at least one hydrocarbon solvent and at least one aprotic polar solvent.

Crosslinked rubber articles, such as for example pneumatic or non-pneumatic tires, are generally based on diene polymers comprising ethylenic double bonds in their main chain. These polymers are sensitive to the action of ozone due to the presence of these double bonds.

When a crosslinked article made with these polymers is subjected to stress in the presence of ozone, the harmful action of ozone is manifested by the appearance of cracks or cracks which are visible on the surface of the article. These cracks are oriented substantially perpendicular to the direction of said stress, and their propagation under the effect of the persistence of such a stress may ultimately cause a complete rupture of this article.

To limit this degradation, compositions based on diene polymers commonly incorporate anti-ozone chemical compounds as well as waxes. Anti-ozone chemicals slow down the formation and propagation of cracks under static and dynamic conditions. Waxes provide additional static protection by forming a protective coating on the surface.

However, the use of these anti-ozone chemicals and / or waxes results in the appearance of stains on the surface of these rubber articles due to their ability to migrate to the surface. This phenomenon is known under the name of "spotting" (or "blooming" in English). To preserve the surface appearance of tires, there is therefore a tendency to limit the proportion of these compounds in the rubber compositions and consequently their action. Furthermore, the proportions of waxes and anti-ozonating compounds are limited due to the problems of cohesion of the mixture and in order to preserve the properties of the rubber compositions.

However, this limitation of the level of anti-ozonating agents (also called anti-zone agents) and waxes is not very compatible with certain uses of rubber articles, such as for example pneumatic tires especially intended for fitting onto airplanes. In fact, in a known manner, an airplane pneumatic tire must withstand pressure, load and high speed conditions, in particular on landing where they must go from zero speed to very high speed, causing considerable heating and wear. These particular wear conditions do not concern other types of tires such as tires for passenger vehicles, heavy goods vehicles, civil engineering or off-road vehicles. In particular, an airplane tire is subjected to strong stresses during the landing phases (“Touch Down”). The particular conditions of use of pneumatic tires for aircraft have the consequence that the initiation of cracks which are created in the tread under the effect of ozone tend to propagate more and more rapidly than those which would be created on the tread. other types of pneumatic tires such as passenger vehicle tires. These incipient cracks and cracks damage the treads of the pneumatic tire and therefore reduce the service life of said tire. Taking into account their particular conditions of use, pneumatic tires for aircraft therefore need more effective anti-ozone protection than those of other pneumatic tires. Solutions, other than those of limiting anti-ozonants, have been proposed to overcome the aforementioned problem. For example, one solution consists in depositing on the surface to be protected of the tire intended to equip an aircraft one or more layers of an anti-ozone protective coating. Document EP0728810A1 discloses a coating consisting of an aqueous composition based on polymers chosen from the group of acrylic, methacrylic and vinyl esters, a constituent comprising a hydrophilic silica and a polymer whose monomer is chosen from acrylic, methacrylic and vinyl monomers. . However, because this composition exhibits poor adhesion to a rubber surface, it must be deposited in several batches, with very thin layers each time. This restrictive application in several layers results in a coating thickness that is difficult to control and in non-homogeneous distributions of the coating.

Another anti-ozone coating composition for pneumatic tires is also known from document WO2001 / 094453A1. This composition is based on polyurethane polymers. The disadvantage of this composition is a complicated implementation requiring a first step of functionalization of the rubbery support by a functionalization solution, followed by a drying step which can be more or less long, then only then the deposition of the composition. coating. The bond between the elastomer of the tire and the polyurethane is achieved by virtue of the polar functions of the functionalization solution. Its protection efficiency with respect to ozone is therefore dependent on the functionalization step of the support, since this step allows the adhesion of the polyurethane layer to its support.

There is therefore still a need to have an anti-ozone protective composition for a crosslinked rubber article which is simple to use and which provides good protection against attacks from ozone.

An aim of the present invention is to meet this need.

This object is achieved thanks to an anti-ozone protection composition for a crosslinked rubber article, in particular for a crosslinked pneumatic tire, in particular intended to equip airplanes, based on at least one chlorinated elastomer, at least one solvent. hydrocarbon and at least one polar aprotic solvent. This composition is particularly advantageous and easy to use. It is not necessary to functionalize the crosslinked rubber support, it is applied directly to the crosslinked support, in a single step, which has the advantage of being able to produce a layer of uniform thickness.

This composition advantageously makes it possible to form a continuous, flexible coating which adheres to any surface of the pneumatic tire which, by its presence, opposes degradation due to ozone. The rubbery behavior of this composition makes it possible to advantageously resist all the deformations undergone by the crosslinked rubber article. For example, this composition is advantageously used to protect pneumatic tires especially intended for fitting onto airplanes since it is resistant to the deformations undergone after the manufacture of the tires, in particular during the inflation and subsequent use of said tire. It also has the advantage of being able to be applied to any crosslinked rubber surface, and in particular to new or retreaded pneumatic tires.

Another object of the present invention relates to a crosslinked elastomeric article having at least one elastomeric surface in contact with air, said elastomeric surface being wholly or in part coated with an anti-ozone protective composition as defined above. . Advantageously, the crosslinked elastomeric article is chosen from pneumatic tires, non-pneumatic tires, conveyors, gaskets, shoe soles, tracks, hoses, hoses, windshield wipers, ping-pong rackets. and floor coverings. More advantageously still, the crosslinked elastomeric article is a pneumatic or non-pneumatic crosslinked tire of which at least one outer layer is at least partly coated with an anti-ozone protection composition as defined above.

Brief description of the drawings

Figure 1: photograph of a groove in a tread of an airplane tire comprising areas protected by the protective composition according to the invention and areas not protected by the protective composition of the invention.

Line A-A and line B-B delimit the areas which have or have not been protected by the protective composition of the invention. The zone delimited in a rectangle by the lines A-A and B-B has not been the subject of an application of the protective composition according to the invention. Large cracks are visible inside this rectangle. On the other hand in the protected areas, that is to say between the top of the photo and the line A-A and between the line B-B and the bottom of the photo, there are no cracks.

Figure 2: photograph of a groove in a tread of an airplane pneumatic tire; groove in which the protective composition according to the invention has been applied. No cracks are visible. Figure 3: photograph of two grooves in a tread of an airplane pneumatic tire; grooves in which no protective composition according to the invention has been applied. Numerous cracks are visible in the bottom of these furrows.

detailed description

A first subject of the invention relates to an anti-ozone protective composition for a crosslinked rubber article, in particular for a crosslinked pneumatic tire, in particular intended to be fitted to airplanes, the composition being based on at least one chlorinated elastomer, at least one hydrocarbon solvent and at least one polar aprotic solvent.

By “rubber article” or “elastomeric article” is meant an article comprising one or more elastomers, in particular one or more diene elastomers. This rubber article comprises at least one rubber surface (also referred to as an elastomeric surface) in contact with air. For the purposes of the present invention, the term “crosslinked rubber article” means a rubber article which has undergone a crosslinking step, that is to say that the rubber or the elastomers forming this article are in the form of a network. obtained by establishing bridges between the macromolecular chains of the rubber or of said elastomers. The formation of bridges can take place by any known crosslinking agent, such as for example peroxides or else by sulfur. When the crosslinking agent is sulfur, this is referred to as vulcanization.

By “diene elastomer (or rubber indiscriminately)”, whether natural or synthetic, should be understood in a known manner an elastomer consisting at least in part (ie, a homopolymer or a copolymer) of diene monomer units (monomers carrying two carbon-carbon double bonds, conjugated or not). These diene elastomers can be classified into two categories: “essentially unsaturated” or “essentially saturated”. The term “essentially unsaturated” is understood to mean in general 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% (% by moles); it is thus that diene elastomers such as butyl rubbers or copolymers of dienes and alpha-olefins of the EPDM type do not fall within the preceding definition and can in particular be qualified as “essentially saturated” diene elastomers (level of diene. units of weak or very weak diene origin, always less than 15 mol%). By diene elastomer capable of being used in the elastomeric articles in accordance with the invention is particularly understood: any homopolymer of a diene monomer, conjugated or not, having from 4 to 18 carbon atoms; any copolymer of a diene, conjugated or not, having from 4 to 18 carbon atoms and at least one other monomer. By the expression “composition based on” is meant a composition comprising the mixture and / or the in situ reaction product of the various constituents used, some of these constituents being able to react and / or being intended to react with each other, less partially, during the various phases of manufacture of the composition and / or during the use of this composition.

For the purposes of the present invention, the expression “part by weight per hundred parts by weight of elastomer” (or phr) should be understood to mean the part, by mass per hundred parts by mass of elastomer.

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

On the other hand, any interval of values designated by the expression “between a and b” represents the domain of values going from more than a to less than b (that is to say limits a and b excluded) while any range of values designated by the expression “from a to b” signifies the range of values going from a to b (that is to say including the strict limits a and b).

When reference is made to a “predominant” compound, it is understood, within the meaning of the present invention, that this compound is predominant among the compounds of the same type in the composition, that is to say that it is the one which represents the greatest amount by mass among compounds of the same type. Thus, for example, a major elastomer is the elastomer representing the greatest mass relative to the total mass of the elastomers in the composition. Likewise, a so-called majority filler is that representing the greatest mass among the fillers of the composition. By way of example, in a system comprising a single elastomer, the latter is in the majority within the meaning of the present invention; and in a system comprising two elastomers, the majority elastomer represents more than half of the mass of the elastomers.

The compounds mentioned in the description which include carbon can be of fossil origin or biobased. In the latter case, they may be, partially or totally, derived from biomass or obtained from renewable raw materials derived from biomass. This concerns in particular polymers, solvents and additives.

Chlorinated elastomer

The anti-ozone protection composition of the invention comprises at least one chlorinated elastomer. The term “chlorinated elastomer” is understood to mean a polymer which comprises one or more chlorine atoms and which is flexible, deformable, exhibiting elasticity of the rubber type according to the IUPAC definition of elastomers.

Preferably, the chlorine content of the chlorinated elastomer is within a range ranging from 20% to 50% by weight relative to the total weight of the elastomer, more preferably in a range ranging from 25% to 45%, more preferably still ranging from 30% to 37% by weight per relative to the total weight of the elastomer. The level of chlorine in the elastomer is measured according to the usual analysis techniques for elastomers.

Preferably, the chlorinated elastomer has a Mooney ML viscosity index (l + 4) at 100 ° C. within a range ranging from 20 to 100 MU, more preferably ranging from 25 to 60 MU. The Mooney viscosity index is measured according to ASTM D-1646-2015 and is expressed in “Mooney Unit” (MU, with 1 MU = 0.83 N.m).

Among the chlorinated elastomers mentioned above, polychloroprene, chlorosulphonated polyethylene and mixtures of these elastomers may be more specifically suitable. These elastomers are available from suppliers such as Du Pont de Nemours, Lianda, etc.

Preferably, the chlorinated elastomer is a chlorosulfonated polyethylene, in particular having a sulfur content in a range ranging from 0.8% to 2% by weight relative to the total weight of the polyethylene, more particularly in a range ranging from 0, 9% to 1.5% more preferably ranging from 1% to 1.5% by weight. The sulfur content in the elastomer is measured according to the usual analysis techniques for polymers. Chlorosulfonated polyethylenes are made by simultaneous functionalization and modification of polyethylene from chlorine and sulfur dioxide. They are marketed under the name CSM.

Particular embodiments of the present invention may comprise at least one chlorosulfonated polyethylene having a chlorine content ranging from 20% to 50% by weight and a sulfur content ranging from 0.8% to 2% by weight, more preferably can comprise at least one chlorosulfonated polyethylene having a chlorine content in a range ranging from 25% to 45% by weight and a sulfur content in a range ranging from 0.9% to 1, 5%, more preferably still, can comprise at least one chlorosulfonated polyethylene having a chlorine content within a range ranging from 30% to 37% and a sulfur content ranging from a range ranging from 0.8% to 1.2%. The chlorine content and that of sulfur in the elastomer are expressed in% by weight relative to the total weight of the chlorosulfonated polyethylene.

Preferably, the content of the chlorinated elastomer, preferably of polychloroprene and / or of chlorosulfonated polyethylene, in the composition is within a range ranging from 3% to 25% by weight relative to the total weight of the composition, more preferably in a range ranging from 5% to 20% by weight relative to the total weight of the composition. Below 3% by weight of chlorinated elastomer in the composition, the concentration is too low to obtain the desired effects and above 25% by weight the composition becomes very viscous and difficult to apply.

The choice of the chlorinated elastomer concentration depends on the need or not, for the elastomeric surface to be protected, of a significant final thickness of protection and on the conditions of use of this surface. If the rubber article is used in an atmosphere with high ozone concentrations, then the highest chlorinated elastomer concentration will preferably be chosen to reduce the number of layers to be applied and to obtain the best protection.

Hydrocarbon solvent

The anti-ozone protection composition according to the invention comprises at least one hydrocarbon solvent. By “hydrocarbon solvent” is meant a solvent mainly containing carbon atoms and hydrogen atoms. The hydrocarbon solvent is liquid at ambient temperature (20 ° C.) and at atmospheric pressure.

Preferably, the hydrocarbon solvent is a solvent for aliphatic hydrocarbons. It can have a distillation range within a range from 50 ° C to 220 ° C.

Advantageously, the hydrocarbon solvent which can be used in the context of the invention is a solvent for C4-C14 aliphatic hydrocarbons, preferably C5-C10, more preferably still C7-C9.

The hydrocarbon solvent is preferably volatile at room temperature (20 ° C) and has a non-zero vapor pressure at room temperature (20 ° C) and atmospheric pressure, and in particular a vapor pressure ranging from 0.13 Pa to 40,000 Pa , in particular ranging from 1.3 Pa to 13000 Pa, and more particularly ranging from 1.3 Pa to 1300 Pa.

Polar aprotic solvent

The anti-ozone protection composition according to the invention also comprises at least one aprotic polar solvent. For the purposes of the present invention, the term “aprotic polar solvent” means a solvent having a dipole moment without an acidic hydrogen atom, that is to say bonded to a heteroatom. Preferably in the aprotic polar solvent, the heteroatom is an oxygen atom. Preferably, the aprotic polar solvent is chosen from ketone solvents, ester solvents and mixtures of these solvents.

More preferably, the aprotic polar solvent is chosen from dimethylformamide (DMF); acetone, methyl ethyl ketone (also known as butanone), methyl propyl ketone (also known as pentanone-2), methyl isopropyl ketone (also known as 3-methyl-2 -butanone), methyl isobutyl ketone (also known as 4-methyl-2-pentanone), cyclic ketones such as cyclohexanone; tetrahydrofuran (THF); acetonitrile; dimethyl sulfoxide (DMSO) and mixtures thereof. More preferably, the aprotic polar solvent is chosen from acetone, butanone, pentanone-2, 3-methyl-2-butanone, 4-methyl-2-pentanone and their mixture. Preferably, the aprotic polar solvent is acetone.

The polar aprotic solvent, preferably the ketone solvents and the ester solvents, are miscible in the hydrocarbon solvent, in particular in the aliphatic hydrocarbon solvent. In others In other words, the polar aprotic solvent forms a homogeneous and stable mixture (to the naked eye) when it is placed in the presence of said hydrocarbon solvent.

According to one embodiment of the invention, the hydrocarbon solvent is the majority solvent. According to this embodiment; the hydrocarbon solvent is that which represents the largest quantity by mass among the solvents of the composition.

According to another embodiment, the mass ratio of aprotic polar solvent relative to the hydrocarbon solvent is within a range ranging from 15:85 to 85:15 per 100% by mass of solvent, preferably from 30:70 to 70:30. for 100% by mass of solvent, more preferably from 40:60 to 60:40 for 100% by mass of solvent.

According to one embodiment of the invention, the hydrocarbon solvent is a solvent for C4-C14 aliphatic hydrocarbons, preferably C5-C10, more preferably still C7-C9 and the aprotic polar solvent is chosen from acetone , butanone, pentanone-2, methyl-3-butanone, methyl-4-pentanone-2 and a mixture thereof.

According to another embodiment of the invention, the hydrocarbon solvent is a solvent for C5-C10 aliphatic hydrocarbons, more preferably still C7-C9 and the aprotic polar solvent is chosen from butanone, methyl-3-butanone and their mixture.

The anti-ozone protection composition according to the invention may also comprise all or part of the usual additives and processing agents, known to those skilled in the art and usually used in rubber compositions for pneumatic tires, such as by example of plasticizers (such as plasticizing oils and / or plasticizing resins), reinforcing or non-reinforcing fillers, pigments, anti-oxidants, anti-fatigue agents, etc.

Manufacture of the anti-ozone protection composition and its application

The process for obtaining the anti-ozone protection composition is simple. The constituents are brought into contact with each other; they are mixed until a homogeneous solution is obtained, that is to say a solution in which there are no particles in suspension visible to the naked eye. The order in which the constituents of the protective composition are used is irrelevant. Thus, for example, it is possible first of all to bring the chlorinated elastomer in the hydrocarbon solvent into contact to obtain a mixture, this mixture then being brought into contact with the aprotic polar solvent. Another possibility of manufacturing the composition according to the invention is to bring the two solvents into contact together and then to add the chlorinated elastomer. Once the solution has been well homogenized according to the usual techniques, it can be applied to any crosslinked rubber article or crosslinked elastomeric support. This composition can thus be deposited at room temperature (20 ° C.) by any known means and in particular with a brush, a roller or by spraying with a gun. The layer obtained after application is then allowed to dry; the two solvents evaporate, the elastomer thus deposited forms the protective coating. At room temperature (20 ° C), the drying time is in particular of the order of 5 min to 10 min, a time which can be further reduced by operating heating, for example by circulating hot air or by radial heating, which respects maintenance of the surface temperature of the rubber article to be protected below 60 ° C. The dry coating obtained exhibits high mechanical strength, which allows it to remain in place when the tires are stored until they are put into service.

In order to have the desired thickness of the coating formed after the anti-ozone protection composition has dried, it may be advantageous to apply the composition according to the invention in one or more successive layers.

The desired thickness of the dry coating will vary depending on the elastomeric surface where the anti-ozone protection composition is applied. Good results are obtained, for example, with dry coatings having a thickness greater than or equal to 5 μm. Thus, for the furrow bases of the tread patterns of tires in particular intended to equip airplanes (these pneumatic tires crack in particular rapidly under the action of ozone even at rest due to the significant permanent stresses due to the inflation pressure), a thickness within a range ranging from 5 μm to 500 μm will be preferred. On the other hand, for an application for example on the outer surface of the sidewalls of a pneumatic tire, a thickness within a range ranging from 5 μm to 50 μm will be sufficient.

Of course, the protective coating cannot be as effective on the parts of the tire in permanent contact with the ground. Thus, if the anti-ozone protection composition is deposited on the entire surface of the tread, the resulting dry coating makes it possible to protect the tread before its use and continues its action on the parts which are not in contact. contact with the ground therefore in particular the hollow bottoms (grooves) of the sculptures, the coating part covering the tops of the sculptures directly in contact with the ground being rapidly destroyed since it is subject to wear.

Elastomeric article.

The anti-ozone protection composition according to the invention can be applied to any type of crosslinked rubber article, preferably to a crosslinked pneumatic tire in particular intended to be fitted on airplanes.

Thus, another object of the present invention relates to a crosslinked elastomeric article comprising at least one elastomeric surface in contact with air, said elastomeric surface being all or in part coated with an anti-ozone protective composition defined above. .

The term “elastomeric surface” is understood to mean a surface of an article, this surface being based on at least one elastomer, preferably diene elastomer as defined above and another component. Preferably, the elastomeric article can be any known elastomeric article, and preferably chosen from pneumatic tires, in particular those intended to equip airplanes, non-pneumatic tires, conveyors, gaskets, shoe soles, tracks, pipes. , hoses, windshield wipers, table tennis rackets and floor coverings.

By “pneumatic tire” is meant a tire intended to form a cavity by cooperating with a support element, for example a rim, this cavity being able to be pressurized at a pressure greater than atmospheric pressure. In contrast, a non-pneumatic tire is not suitable for being pressurized. Thus, a non-pneumatic tire is a toric body formed by at least one polymeric material, intended to perform the function of a tire but without being subjected to inflation pressure. A non-pneumatic tire can be solid or hollow. A hollow non-pneumatic tire can contain air, but at atmospheric pressure, that is to say it has no pneumatic rigidity provided by an inflation gas at a pressure greater than atmospheric pressure.

The pneumatic tires according to the invention are intended to equip vehicles of any type such as passenger vehicles, two-wheeled vehicles, heavy goods vehicles, agricultural vehicles, civil engineering vehicles or airplanes or, more generally. , on any rolling device. Non-pneumatic tires are intended to be fitted on passenger vehicles or two-wheelers. Preferably, the pneumatic tires according to the invention are intended to equip airplanes.

Preferably, the crosslinked elastomeric article is a pneumatic crosslinked tire, preferably intended to equip an aircraft, or a non-pneumatic tire, at least one outer layer of which has an elastomeric surface at least partly coated with an anti-ozone protective composition. defined above. The term “outer layer” is understood to mean an elastomeric layer which is in contact with air (other than the inflation gas in the context of a pneumatic tire); as opposed to the inner layers which are elastomeric layers in contact with each other or in contact with the inflation gas. The outer layer may be the tread of the pneumatic or non-pneumatic tire, the layer forming the sidewalls of the pneumatic tire or the spokes in the context of a non-pneumatic tire.

More preferably still, the crosslinked elastomeric article is a pneumatic crosslinked tire, in particular intended to equip airplanes comprising a tread and sidewalls, said tread and / or said sidewalls being at least partly coated with a composition of anti-ozone protection defined above. More preferably, this tread can be retreaded.

Example : The aim of this test is to show the protective properties conferred by the compositions of the invention when they are applied to a crosslinked tread of a pneumatic tire for an airplane.

For this, the following compositions C1 to C4 are prepared:

Table 1

(1): chlorosulfonated polyethylene sold by Lianda under the reference “CSM40” having a Mooney viscosity index of 56 UM, a sulfur content equal to 1%, a chlorine content equal to 35%.

(2): C7-C9 aliphatic hydrocarbon solvent, marketed by Total under the reference “Solane 100-155”.

(3): ketone solvent: butanone sold by Fisher Scientific.

Application on a tire

A vulcanized, retreaded airplane tire, PN M05102 / IBE, 4100 mm development, uninflated and not mounted on a rim, is used to test the effectiveness of the protective compositions C1 to C4 in accordance with the invention. The tread of this retreaded tire is conventionally produced from a composition based on natural rubber and carbon black. The sculpture of this tread comprises 4 grooves. On each groove, 5 zones of identical length are materialized and the compositions C1 to C4 are applied using a brush in the manner below on the 2 ^nd and the 4 ^th groove. The ^ier the grooves and furrows 3 ^rd do not include treatment. The first groove is the one located closest to the wheel brake disc, in the direction of rotation of the tire, and the 4 ^th groove is the one that is to farthest from the wheel of the brake disc. After drying at a temperature of 23 ° C., the thickness of the coating is between 0.05 and 0.10 mm.

2 ^'rd and 4 ^th path:

- Zone A: no composition

- Zone B: composition Cl

- Zone C: composition C2

- Zone D: composition C3

- Zone E: composition C4

The tire is then mounted on a rim and is inflated to a pressure of 14.2 bar. Static ozone test

The mounted and inflated tire is then placed in a room thermostatically controlled at 23 ° C. and comprising air in which the ozone concentration is equal to 0.1 ppm (ppm = parts per million). After 1 week, the tire is taken out of the chamber for the evaluation of the number of cracks in the tread groove, then replaced in the same thermostatically controlled chamber, doubling the ozone concentration (0.20 ppm) for a period of other week.

At the end of this second week, the tire is taken out of the chamber for the evaluation of the number of cracks in the tread groove, then replaced for another 2 weeks in the same thermostatically controlled chamber, the ozone concentration of which is increased to 0.4 ppm. After 4 weeks, the tire is taken out of the chamber to assess the number of cracks in the tread grooves.

Airliners fly in an environment that includes a theoretical ozone concentration of 0.1 ppm. The storage of the tires in the thermostatically controlled chamber, beyond the first week under the conditions of the test described above, therefore corresponds to more severe conditions than those that airplanes could encounter in the troposphere (from 2 to 4 times more severe).

The number of cracks is evaluated by visual inspection as follows:

-: no crack;

+: ten cracks or less than ten cracks, each crack having a length of less than 10 mm;

++: at least one crack exceeding 10 mm in length.

The results are presented in Table 2 below

Table 2

It can be seen that zone A, not comprising any protective composition and which corresponds to a control outside the invention, is completely cracked from the first week of storage in contact with ozone. The action of ozone is therefore particularly effective on this zone A of the tread.

On the other hand, surprisingly, on zones B, C, D and E, the surface of the groove of which has been covered respectively by the protective compositions according to the invention C1 to C4, it is observed that no degradation appears, that is to say no cracks when the tire has been stored in contact with ozone for one or two weeks in the thermostatically controlled chamber.

Under very severe storage conditions in the presence of ozone, it is observed that zones D and E still do not exhibit cracks. Compositions C3 and C4 have the advantage of being more protective than compositions C1 and C2 which already have excellent protection against a high ozone concentration (0.4 ppm corresponds to 6 times the average of the ozone concentration. in the troposphere).

The protective compositions in accordance with the invention therefore provide very good anti-ozone protection for atmospheres in which the ozone concentrations are very high.

Claims

1. Anti-ozone protection composition for a crosslinked rubber article, said composition being based on at least one chlorinated elastomer, at least one hydrocarbon solvent and at least one polar aprotic solvent.

2. Anti-ozone protection composition for a crosslinked rubber article according to the preceding claim, in which the hydrocarbon solvent is the predominant solvent.

3. Anti-ozone protection composition for a crosslinked rubber article according to claim 1, wherein the mass ratio of aprotic polar solvent relative to the hydrocarbon solvent is in a range from 15:85 to 85:15 per 100%. mass of solvent, preferably from 30:70 to 70:30 for 100% by mass of solvent, more preferably from 40: 60 to 60:40 for 100% by mass of solvent.

4. Anti-ozone protection composition for a crosslinked rubber article according to any one of the preceding claims, in which the hydrocarbon solvent is a solvent for aliphatic C4-C14, preferably C5-C10, more preferably still. in C7-C9.

5. An anti-ozone protective composition for a crosslinked rubber article according to any preceding claim, wherein the aprotic polar solvent is selected from ketone solvents, ester solvents and mixtures of these solvents.

6. An anti-ozone protective composition for a crosslinked rubber article according to any preceding claim, wherein the aprotic polar solvent is selected from acetone, butanone, 2-pentanone, 3-methyl-butanone. , methyl-4-pentanone-2 and a mixture thereof.

7. An anti-ozone protection composition for a crosslinked rubber article according to any one of the preceding claims, in which the content of the chlorinated elastomer in the composition is within a range ranging from 3% to 25% by weight by weight. relative to the total weight of the composition, more preferably in a range ranging from 5% to 20% by weight relative to the total weight of the composition.

8. An anti-ozone protection composition for a crosslinked rubber article according to any one of the preceding claims, in which the chlorinated elastomer is selected from polychloroprene, chlorosulfonated polyethylene and mixtures of these elastomers.

9. Anti-ozone protection composition for a crosslinked rubber article according to any one of the preceding claims, in which the chlorine content of the chlorinated elastomer is within a range ranging from 20% to 50% by weight relative to to the total weight of the elastomer, plus preferably in a range ranging from 25% to 45% by weight, more preferably in a range ranging from 30% to 37% by weight.

10. Anti-ozone protection composition for a crosslinked rubber article according to any one of the preceding claims, in which the chlorinated elastomer has a Mooney viscosity index comprised in a range ranging from 20 to 100 UM, more preferably ranging from 25 to 60 UM.

11. Anti-ozone protection composition for a crosslinked rubber article according to any one of the preceding claims, in which the chlorinated elastomer is a chlorosulfonated polyethylene elastomer, in particular having a sulfur content in a range ranging from 0.8. % to 2% by weight relative to the total weight of the polyethylene, more particularly within a range ranging from 0.9% to 1.5% by weight, more preferably still from 1% to 1.5 by weight.

12. A crosslinked elastomeric article having at least one elastomeric surface in contact with air, said surface being at least in part coated with an anti-ozone protection composition according to any one of the preceding claims.

13. Crosslinked elastomeric article according to claim 12, the elastomeric article being chosen from pneumatic tires, non-pneumatic tires, conveyors, gaskets, shoe soles, tracks, pipes, hoses, windshield wipers. , table tennis rackets and floor coverings.

14. Pneumatic or non-pneumatic crosslinked tire, at least one outer layer of which is at least partly coated with an anti-ozone protection composition according to any one of claims 1 to 11.

15. Pneumatic or non-pneumatic crosslinked tire according to claim 14, the outer layer of which is a tread.