Tyre comprising a sidewall with at least one high-contrast sidewall element

Abstract

The present invention relates to a vehicle tyre (1), the tyre comprising at least one sidewall (2) with at least one high-contrast sidewall element (3) consisting of a texture having a first luminosity L*1 of at least 1 and at most 15, wherein any adjacent sidewall surface portion (21) has a second luminosity L*2 of at least L*1+5. The invention discloses a rubber composition of the sidewall (2) that exhibits a good trade-off between blooming reduction and ozone attack resistance. According to the invention, the isoprene elastomer content is at least 27.00 wt%, the anti-ozonant wax content is at least 0.60 wt% and at most 1.70 wt%, and a weight ratio of the content of crumb rubber microparticles that are smaller than 74 µm in size to the anti-ozonant wax content, expressed in percentage by weight, is at least 0.50.

Description

Tire comprising a sidewall with at least one high contrast sidewall element

[0001] The present invention relates to a tire for a vehicle, comprising a sidewall with at least one high contrast sidewall element.

[0002] A tire comprises two sidewalls, a sidewall being the portion of the tire connecting one end of the tread, intended to come into contact with the ground, to a bead, intended to be mounted on a rim.

[0003] In the following, the external surface of a sidewall, in contact with atmospheric air, is referred to, more simply, as the "sidewall surface". A sidewall surface generally comprises at least one graphic element and / or, possibly, an aesthetic element. A graphic element, usually called marking and comprising letters, numbers or symbols, is generally intended to communicate technical, commercial or legal information.

[0004] By definition, a high-contrast sidewall element refers to a sidewall surface element consisting of a specific texture different from that of the sidewall surface, which is most often smooth. This texture gives said high-contrast sidewall element a darker appearance than that of any portion of sidewall surface adjacent to said high-contrast sidewall element, such that this high-contrast sidewall element can be visually distinguished from any portion of adjacent sidewall surface. A high-contrast sidewall element may have as its object either a graphic element or an aesthetic element, or a portion of sidewall surface surrounding said graphic or aesthetic element, which makes said graphic or aesthetic element particularly visible on the sidewall surface.

[0005] Thus, whether for the enhancement of graphic elements or aesthetic elements of the sidewall surface, there is a constant concern among tire designers to produce sidewall elements with high contrast.

[0006] The contrast between a high-contrast flank element and a portion of flank surface adjacent to said high-contrast flank element is due to a difference in brightness between the two areas. An adjacent surface portion, which may be smooth or have a different texture, has a brightness greater than that of the texture of said high-contrast flank element, i.e. it appears visually lighter. This texture is consisting of a rubbery material, also called rubber composition or elastomeric composition, identical to that of the portion of the sidewall in contact with atmospheric air, since this texture is made of the same material as the sidewall.

[0007] Brightness can be quantified by luminous luminance, expressed in candela / m 2 , which measures the luminous flux coming from an illuminated surface that is reflected in the observer's eye. But the relationship between luminous luminance and the visual perception of brightness is not linear and is complex. This is why, on a practical level, the International Commission on Illumination (CIE) has defined the luminosity L*, a parameter that characterizes the capacity of a surface to reflect light, from the luminous luminance of the light produced by a primary or secondary source, expressed in candelas per square meter (cd / m 2), relative to the luminous luminance of white taken as a reference. Thus, in the following, the luminosity L* is expressed according to a scale ranging from 0 to 100 in accordance with the L*a*b* colorimetric model adopted in 1976 by the International Commission on Illumination. The value 100 represents white or total reflection and the value 0 represents black or total absorption.

[0008] To calculate the difference between a first brightness L*1 of the texture of the high-contrast flank element and a second brightness L*2 of an adjacent flank surface portion, the first brightness L*1 and the second brightness L*2 must be measured respectively using a spectro-colorimeter, for example a KONICA-MINOLTA CM 700D spectro-colorimeter. To measure the first brightness L*1 of the texture, the spectro-colorimeter is positioned on the texture and this measurement is carried out with the SCI mode (Specular Reflection Included Mode) set at an angle of 8° and with a light setting of type D65 (setting defined according to CIE). Similarly, to measure the second brightness L*2 of an adjacent flank surface portion, the spectro-colorimeter is positioned on said flank surface portion.In order to improve the determination of this second brightness L*2, it is possible to carry out a plurality of brightness measurements on several adjacent portions of flank surface, then to deduce an associated average brightness.

[0009] High contrast flanking elements having a brightness difference substantially less than that of an adjacent flanking surface portion have been described in WO 2016005572 A1 and WO 2011036061 A1 and WO 20174919 A1

[0010] On tire sidewall surfaces, including high-contrast sidewall elements, there has been observed to be a change over time in the contrast between the high-contrast sidewall elements and any adjacent portion of the sidewall surface.

[0011] The evolution of contrast over time results from both the evolution of the texture and that of the visual appearance of the flank surface.

[0012] The evolution of the texture can result from its fouling, its at least partial abrasion or the aging of its constituent material.

[0013] The evolution of the visual appearance of the sidewall surface typically results in an evolution, at least locally, of its coloring (blueing, evolution towards a dark brown color, appearance of whitish spots), an evolution of its brightness (duller appearance) or the appearance of surface scratches or cracks.

[0014] More generally, the aging of the sidewall surface is linked to the elastomeric nature of its material. As is known, common rubber compositions include diene elastomers, natural or synthetic, whose molecular chains have carbon-carbon double bonds. These double bonds are chemically more reactive than a single carbon-carbon bond and are therefore likely to deteriorate more or less quickly after prolonged exposure to the atmosphere, due to known oxidation and ozonolysis mechanisms. The action of ozone promotes the appearance of cracks on the sidewall surface. These degradation mechanisms are further accelerated by the action of heat (thermo-oxidation) or by that of light (photo-oxidation).

[0015] To counteract the chemical degradation of the rubber composition by ozone, it is known to use anti-ozone agents, such as, for example, anti-ozone waxes. These anti-ozone waxes provide static protection by forming a protective coating on the surface. However, these anti-ozone waxes are characterized by their ability to migrate to the sidewall surface and crystallize, which changes the visual appearance of the sidewall surface, causing the appearance of stains or giving the sidewall a dull and gray appearance, or even causing a lighter coloring of the sidewall. This phenomenon is called "blooming". This phenomenon thus causes uneven coloring and makes the sidewall surface, initially black and shiny, gray and dull.

[0016] Thus, non-uniform coloring of the sidewall surface reduces the contrast effect of the high-contrast element and alters the visual and aesthetic appearance of the sidewall.

[0017] It is therefore necessary, in order to obtain a sidewall element with high contrast that lasts throughout the life of the tire, to be able to reduce, or even eliminate, the alteration of the color and / or the brightness of the sidewall surface of the tire, while giving it a good capacity to resist ozone attacks that initiate cracks on the sidewall surface.

[0018] Increasing contrast durability is indeed an important commercial issue for a tire manufacturer. For example, when a user replaces only the tires fitted to the front of their vehicle, they may notice a significant difference between the contrast observed on the new tires fitted to the front of the vehicle and that observed on the used tires fitted to the rear of the vehicle. This difference in contrast between the front and rear tires may be considered unacceptable by the user, especially when their vehicle is a sports or prestige vehicle.

[0019] The inventors therefore set themselves the objective, for a tire comprising a sidewall with at least one high-contrast sidewall element, of increasing the durability over time of the contrast between said high-contrast sidewall element and the adjacent portion of the sidewall surface, using a suitable rubber composition of the sidewall, in particular near the sidewall surface.

[0020] This objective was achieved by a tire for a vehicle, comprising a sidewall with at least one high-contrast sidewall element: - the high contrast flank element being constituted by a texture having a first brightness L*1 at least equal to 1 and at most equal to 15, - any portion of flank surface adjacent to the high-contrast flank element, having a second brightness L*2 at least equal to L*l+5, -the first and second luminosities (L*l, L*2) being expressed according to a scale ranging from 0 to 100 in accordance with the L*a*b* colorimetric model adopted in 1976 by the International Commission on Illumination, -the sidewall comprising a rubber composition based on an elastomer matrix comprising an isoprene elastomer, at least one reinforcing filler, at least one crosslinking system, at least one anti-ozone wax and at least one rubber crumb comprising microparticles having a size of less than 74 pm, -the rate of isoprene elastomer being at least equal to 27.00% by weight, relative to the total weight of the rubber composition, - the anti-ozone wax rate being at least equal to 0.60% by weight and at most equal to 1.70% by weight, relative to the total weight of the rubber composition, -and a weight ratio between the rate of microparticles of rubber crumb having a size less than 74 pm and the rate of anti-ozone wax, these rates being expressed as a percentage by weight, relative to the total weight of the rubber composition, being at least equal to 0.50.

[0021] According to the invention, the high-contrast flank element consists of a texture having a first brightness L* 1 at least equal to 1 and at most equal to 15.

[0022] The lower the brightness of the high-contrast sidewall element in the new condition of the tire, the greater the contrast for a given brightness of an adjacent portion of sidewall surface, and the more significant this contrast will remain over time on the aged tire. Indeed, over time, this first brightness L*1 of the texture of the high-contrast sidewall element tends to increase due, for example, to dust, dirt, or aging of the material. Furthermore, in this brightness range, there is good contrast with any adjacent portion of sidewall surface, which, in standard tire designs, has a brightness most often between 24 and 28. It should be noted that a texture with a first brightness L*1, typically at least equal to 9, is easier to produce, but the contrast is low.

[0023] According to the invention, any portion of flank surface adjacent to the high-contrast flank element has a second brightness L*2 at least equal to L*l+5.

[0024] The greater the difference in brightness between the high-contrast flank element and any adjacent portion of flank surface, the greater the contrast. The greater this difference The more brightness is important on the new tire, the more significant it will remain, over time, on the aged tire.

[0025] Also according to the invention, the sidewall comprises a rubber composition based on an elastomer matrix comprising an isoprene elastomer, at least one reinforcing filler, at least one crosslinking system, at least one anti-ozone wax and at least one rubber crumb comprising microparticles having a size of less than 74 μm.

[0026] The expression "rubber composition based on" means a rubber composition comprising the mixture and / or the in situ reaction product of the different constituents used, some of these constituents being able to react and / or being intended to react with each other, at least partially, during the different phases of manufacture of the rubber composition, the rubber composition thus being able to be in a totally or partially crosslinked state or in a non-crosslinked state.

[0027] A rubber composition comprises at least one and often several elastomers, in particular several diene elastomers. This mixture of elastomers, in particular diene elastomers, is called an elastomer matrix. Most often the elastomer matrix comprises at least two different diene elastomers.

[0028] The term "elastomer" means a polymer, i.e., a homopolymer or copolymer, with elastic properties obtained after crosslinking. The term rubber is a common synonym for elastomer.

[0029] By "diene elastomer" or indistinctly "diene rubber", whether natural or synthetic, we mean an elastomer consisting at least in part of diene monomer units (monomers carrying two carbon-carbon double bonds, conjugated or not). Diene elastomers are non-thermoplastic.

[0030] Diene elastomers can be classified into two categories: "essentially unsaturated" diene elastomers and "essentially saturated" diene elastomers. An "essentially unsaturated" diene elastomer is a diene elastomer derived at least in part from conjugated diene monomers, having a content of units or motifs of diene origin (conjugated dienes) which is greater than 15% (mol %). Thus, diene elastomers such as butyl rubbers or copolymers of dienes and alpha-olefins such as EPDM do not fall within the previous definition and can be described in particular as “essentially saturated” diene elastomers (low or very low level of diene units, always less than 15%).

[0031] The term diene elastomer capable of being used in the rubber compositions in accordance with the invention is understood in particular to mean: a) Any homopolymer of a diene monomer, conjugated or not, having from 4 to 18 carbon atoms; b) Any copolymer of a diene, conjugated or not, having from 4 to 18 carbon atoms and at least one other monomer; the other being able to be ethylene, an olefin or a diene, conjugated or not.

[0032] Suitable conjugated dienes are conjugated dienes having 4 to 12 carbon atoms, in particular 1,3-dienes, such as 1,3-butadiene and isoprene.

[0033] Suitable non-conjugated dienes are non-conjugated dienes with 6 to 12 carbon atoms, such as 1,4-hexadiene, ethylidene norbornene, dicyclopentadiene.

[0034] Suitable olefins are vinylaromatic compounds with 8 to 20 carbon atoms and aliphatic α-monoolefins with 3 to 12 carbon atoms.

[0035] Suitable vinyl aromatic compounds are, for example, styrene, ortho-, meta-, para-methyl styrene, the commercial mixture "vinyl-toluene", para-terti obuty 1 styrene.

[0036] Suitable aliphatic α-monoolefins are, in particular, acy clic aliphatic α-monoolefins having from 3 to 18 carbon atoms.

[0037] More specifically, T diene elastomer is: (a') Any homopolymer of a conjugated diene monomer, in particular 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 vinylaromatic compounds having from 8 to 20 carbon atoms; (c 1 ) Any copolymer obtained by copolymerization of one or more dienes, conjugated or not, with ethylene, an α-monoolefin or their mixture, such as, for example, elastomers obtained from ethylene, propylene with a non-conjugated diene monomer of the aforementioned type.

[0038] By "isoprenic elastomer" is meant, in a known manner, a homopolymer or a copolymer of isoprene. In other words, an isoprene elastomer can be chosen from the group consisting of natural rubber (NR), synthetic polyisoprenes (IR), the various isoprene copolymers and the mixtures of these elastomers. Among the isoprene copolymers, mention will be made in particular of isobutene-isoprene (butyl rubber - IIR), isoprene-styrene (SIR), isoprene-butadiene (BIR) or isoprene-butadiene-styrene (SBIR) copolymers. Preferably, the isoprene elastomer can be chosen from the group consisting of natural rubber, synthetic cis-1,4 polyisoprenes, and their combinations.More preferably still, Isoprene Telastomer is chosen from the group consisting of natural rubber, synthetic polyisoprenes having a rate (mol%) of cis-1,4 bonds greater than 90% (more preferably still greater than 98%), and their combinations.

[0039] A reinforcing filler, intended to reinforce a rubber composition, may be an organic filler such as carbon black, or an inorganic filler such as silica or alumina in combination with a coupling agent between the inorganic filler and the diene elastomer, or a mixture of these types of fillers.

[0040] The crosslinking system may be any type of system known to those skilled in the art in the field of tire rubber compositions. It may in particular be based on sulfur, and / or peroxide and / or bismaleimides. Preferably, the crosslinking system is based on sulfur: this is then referred to as a vulcanization system. The sulfur may be provided in any form, in particular in the form of molecular sulfur, or a sulfur-donating agent. At least one vulcanization accelerator is also preferably present, and, optionally, also preferably, various known vulcanization activators may be used, such as zinc oxide, stearic acid or an equivalent compound such as stearic acid salts and transition metal salts, guanidine derivatives (in particular diphenylguanidine), or known vulcanization retarders. Any compound capable of acting as an accelerator may be used as an accelerator. as an accelerator for the vulcanization of diene elastomers in the presence of sulfur, in particular accelerators of the thiazole type and their derivatives, accelerators of the sulfenamide, thiuram, dithiocarbamate, dithiophosphate, thiourea and xanthate types.

[0041] A plasticizing agent is a common processing agent, known to those skilled in the art and usually used in rubber compositions. A plasticizing agent may be selected from the group consisting of plasticizing oils, plasticizing resins with a high glass transition temperature Tg, and combinations thereof.

[0042] Any extender oil, whether aromatic or non-aromatic and known for its plasticizing properties with respect to elastomers, can be used. At room temperature (23°C), these oils, more or less viscous, are liquids (that is to say, as a reminder, substances having the capacity to eventually take the shape of their container), in contrast in particular to high Tg hydrocarbon resins which are by nature solid at room temperature. The plasticizing oil generally has a glass transition temperature Tg, lower than -20°C, preferably lower than -40°C. The glass transition temperature Tg of the plasticizing oil is measured according to the ASTM D3418 (2008) standard.

[0043] By definition, a high Tg hydrocarbon resin, typically at least equal to 30°C, is solid at room temperature and pressure (23°C, 1 atm), while a plasticizing oil is liquid at room temperature and a low Tg hydrocarbon resin is viscous at room temperature. Hydrocarbon resins, also called hydrocarbon plasticizing resins, are polymers well known to those skilled in the art, essentially based on carbon and hydrogen but which may contain other types of atoms, for example oxygen, which can be used in particular as plasticizing agents or tackifying agents in polymer matrices. They are by nature at least partially miscible (i.e., compatible) at the rates used with the polymer compositions for which they are intended, so as to act as true diluting agents.As is known, these hydrocarbon resins can also be referred to as thermoplastic resins in that they soften upon heating and can thus be molded. The glass transition temperature Tg of the plasticizing resin is measured according to ASTM D3418 (2008).

[0044] As for anti-ozone waxes, they can be, for example, paraffin waxes, microcrystalline waxes or mixtures of paraffin and microcrystalline waxes. They consist of a mixture of linear alkanes and non-linear alkanes (isoalkanes, cycloalkanes, branched alkanes) derived from petroleum refining or from the catalytic hydrogenation of carbon monoxide (Fisher Tropsch process) mainly comprising chains of at least 20 carbon atoms.

[0045] The determination of the distribution of alkanes is carried out by gas chromatography coupled with a flame ionization detector ("GC-FID"). The chromatogram is analyzed according to the EWF ("European Wax Federation") method.

[0046] All known anti-ozone waxes can be used, including natural waxes such as candelilla wax or carnauba wax. These waxes can also be used for cutting.

[0047] Commercially available anti-ozone waxes include, for example, "Varazon 4959", "Varazon 6500" and "Varazon 6810" from Sasol, "Ozoace 0355" from Nippon Seiro, "Negozone 9343" from H&R and "H3841" from Yanggu Huatai.

[0048] Crumb rubber (also called "rubber crumb" in English) comes in the form of granules, possibly formed into a rubber plate.

[0049] Most often, these rubber powders come from grinding or micronizing vulcanized rubber compounds already used for a first application, for example, in a tire, shoe soles, or seals. They are therefore a product of recycling these materials.

[0050] As is known, rubber crumb can be obtained more particularly by reducing used tires into granules from which reinforcing materials such as steel or textile fibers have been removed.

[0051] Rubber crumbs may be prepared by cryogenic grinding of used tires, for example according to the process described in document US 7,445,170, comprising successive and independent steps of granulation, separation of metal and textile reinforcements, cooling and micronization in order to obtain a rough distribution of micron particles of vulcanized mixture (also called microparticles). This micronization can be carried out using a conical impact mill as described in US 7,861,958. The cryogenized input enters the mill (for example, CUM150 mills from Netzsch or CW250 from Alpine can be used), then is transferred by gravity to a rotor rotating at high speed. The cryogenized input is thus projected onto the walls of the rotor chamber multiple times leading to its micronization. The particles can then pass through a series of two vibrating screens of the same size in order to separate the last elements not made up of vulcanized mixture. A rough distribution of micron particles of vulcanized mixture is obtained.By "microparticles" is meant particles which have a size, namely their diameter, in the case of spherical particles, or their largest dimension, in the case of anisometric particles, of a few tens or hundreds of microns. The size of the microparticles can be determined by techniques known to those skilled in the art such as, for example, microscopy. The rubber crumb usable in the present invention comprises in particular microparticles which have a size less than 74 μm and microparticles having a size greater than 74 μm. The distribution of the microparticles of rubber crumb is determined according to the ASTM D5644-01 (2013) standard. The rubber crumbs are commercially available from suppliers such as, for example, the company Lehigh Technology.

[0052] Rubber crumbs can be simple ground or micronized rubber, without any further treatment. However, it is also known that rubber crumbs can undergo treatment to modify them. This treatment can consist of a chemical modification of functionalization or devulcanization. It can also be a thermomechanical, thermochemical, or biological treatment.

[0053] It should be noted that rubber crumb is not considered a reinforcing filler.

[0054] According to the invention, the rate of isoprene elastomer is at least equal to 27.00% by weight, relative to the total weight of the rubber composition.

[0055] Also according to the invention, the anti-ozone wax content is at least equal to 0.60% by weight and at most equal to 1.70% by weight, relative to the total weight of the rubber composition.

[0056] Still according to the invention, a weight ratio between the rate of microparticles of rubber powder having a size less than 74 pm and the rate of anti-ozone wax, these rates being expressed as a percentage by weight, relative to the total weight of the rubber composition, is at least equal to 0.50.

[0057] The inventors were able to verify that the combination of the anti-ozone wax rate and the weight ratio between the rate of microparticles of rubber crumb having a size less than 74 pm and the previous anti-ozone wax rate, in particular for an elastomer matrix with the rate of isoprene elastomer previously described, make it possible to obtain a satisfactory compromise between the reduction of efflorescence and the resistance to attack of the sidewall by ozone.

[0058] Advantageously, the rate of isoprene elastomer is at least equal to 28.00% by weight and at most equal to 34.00% by weight, preferably at least equal to 28.50% by weight and at most equal to 34.00% by weight, relative to the total weight of the rubber composition.

[0059] Advantageously, the level of anti-ozone wax is at least equal to 0.70% by weight and at most equal to 1.68% by weight, preferably at least equal to 0.90% by weight and at most equal to 1.65% by weight, relative to the total weight of the rubber composition.

[0060] Also advantageously the weight ratio between the rate of microparticles of rubber powder having a size less than 74 pm and the rate of anti-ozone wax, these rates being expressed as a percentage by weight, relative to the total weight of the rubber composition, is at least equal to 0.65 and at most equal to 4.00, preferably at least equal to 0.70 and at most equal to 2.50.

[0061] According to an advantageous mode of distribution of the sizes of microparticles of rubber crumb, the rate of microparticles having a size less than 74 μm is at least equal to 0.90% by weight, preferably at least equal to 0.95% by weight, more preferably at least equal to 1.00% by weight, relative to the total weight of the rubber composition.

[0062] According to a first embodiment of the elastomer matrix, the isoprene elastomer is chosen from the group consisting of natural rubber, synthetic polyisoprenes, isoprene copolymers, and mixtures of these elastomers, preferably from the group consisting of natural rubber, synthetic polyisoprenes and mixtures of these elastomers.

[0063] According to a preferred variant of the first embodiment of the elastomer matrix, the isoprene elastomer is chosen from the group consisting of natural rubber, synthetic cis-1,4 polyisoprenes, preferably those having a molar rate of cis-1,4 bonds greater than 90%, preferably greater than 98%.

[0064] According to a second embodiment of the elastomer matrix, the rubber composition comprises a butadiene elastomer.

[0065] By "butadiene elastomer" is meant, in a known manner, a homopolymer or a copolymer of butadiene. In other words, a butadiene elastomer can be chosen from the group consisting of polybutadienes (BR), the different copolymers of butadiene and the mixtures of these elastomers. Among the copolymers of butadiene, mention will be made in particular of copolymers of butadiene-styrene (SBR), or of ethylene-butadiene (EBR). Preferably, the butadiene elastomer can be a cis-1,4 polybutadiene; in particular a polybutadiene having a rate (mol%) of cis-1,4 bonds greater than 90%, more preferably still greater than 96%.

[0066] Advantageously, the butadiene elastomer content is at least equal to 23.00% by weight and at most equal to 31.00% by weight, preferably at least equal to 24.00% by weight and at most equal to 30.00% by weight, more preferably at least equal to 25.00% by weight and at most equal to 29.00% by weight, relative to the total weight of the rubber composition.

[0067] According to a preferred variant of the second embodiment of the elastomer matrix, the butadiene elastomer is chosen from the group consisting of polybutadienes, butadiene copolymers, and combinations of these elastomers, more preferably is a polybutadiene, preferably a polybutadiene having a molar rate of cis-1,4 bonds greater than 90%, preferably greater than 96%.

[0068] According to an advantageous embodiment of the rubber crumb, the rubber crumb is a rubber crumb which has not undergone any modification by a treatment chosen from the group consisting of thermal, mechanical, biological and chemical treatments and their combinations.

[0069] The rubber composition previously described, with all its embodiments, is, in particular, the constituent material of the high-contrast sidewall element, integral with the sidewall and consisting of a texture comprising protuberances, in relief relative to a sidewall surface, in contact with atmospheric air, and / or cavities, hollow relative to the sidewall surface.

[0070] Advantageously, the high-contrast flank element is constituted by a texture having a first brightness L*1 at least equal to 4 and at most equal to 13.

[0071] Also advantageously any portion of flank surface adjacent to the high contrast flank element has a second brightness L*2 at least equal to L*l+10, preferably at least equal to L*l+12.

[0072] Advantageously, any portion of flank surface adjacent to the high-contrast flank element has a second brightness L*2 at least equal to 18, preferably at least equal to 22.

[0073] According to a first and a second preferred embodiment, the high-contrast sidewall element is constituted by a texture comprising protrusions, in relief relative to a sidewall surface, in contact with atmospheric air, and / or cavities, hollow relative to the sidewall surface.

[0074] According to a first variant of the first preferred embodiment, the high-contrast flank element consists of a texture comprising strand-shaped protrusions.

[0075] According to a second variant of the first preferred embodiment, the high-contrast flank element consists of a texture comprising blade-shaped protrusions.

[0076] The texture of a high contrast sidewall element, according to the first and second preferred embodiments, is most often achieved by molding during baking of the tire. The corresponding mold element, intended to produce the texture of the high-contrast sidewall element, is produced, by way of non-exhaustive examples, by machining or by laser engraving. The texture of a high-contrast sidewall element can also be produced directly on the sidewall surface of the tire after curing, for example by laser engraving. The texture is therefore made of the same material as that of the rest of the sidewall.

[0077] The texture of the high-contrast sidewall elements, comprising protrusions in the form of strands or blades, makes it possible to absorb a large portion of the incident light rays, after one or more successive reflections on the walls of the protrusions. This makes it possible to give the texture a blacker appearance and, consequently, to improve its contrast and therefore its visibility compared to any adjacent portion of the sidewall surface. Furthermore, this particular texture makes it possible to obtain a pleasant touch on the sidewall surface, of the "velvet" type. Finally, the texture used has a water-repellent and slightly hydrophobic effect. In a particular embodiment, the texture can be positioned on a surface set back from the sidewall surface, such that it is embedded in the sidewall, which has the advantage of protecting it, for example, against wear caused by scraping the sidewall surface against a pavement.

[0078] Similarly, the texture of the high-contrast sidewall elements, comprising cavities recessed relative to the sidewall surface, makes it possible to absorb a large part of the incident light rays, after one or more successive reflections on the walls of the cavities. This specific texture has the advantage of being set back relative to the sidewall surface, which ensures the durability of said texture by protecting it against wear caused by scraping of the sidewall surface against a pavement. It also has the advantage of not disturbing the aerodynamic flow of air, in the vicinity of the sidewall surface, when the tire is rolling.

[0079] The rubber composition described within the scope of the present invention is illustrated by the following non-limiting examples.

[0080] In order to confirm the properties of the rubber composition of the present invention, twelve rubber compositions (C1, C2, C3, C4 and C5: examples according to the invention, T1: reference, and T2, T3, T4, T5, T6 and T7: comparative examples) were carried out.

[0081] Each rubber composition was produced as follows: the reinforcing filler, the elastomer matrix, the anti-ozone wax, the rubber crumb when present, and the various other ingredients, for example the plasticizing agent, with the exception of the vulcanization system, were successively introduced into an internal mixer having an initial tank temperature equal to 60°C, the internal “Banbury” type mixer being filled to approximately 70% of its volume. The thermomechanical work (non-productive phase) was then carried out in a single step lasting from 3 minutes to 4 minutes, until a maximum “drop” temperature of 165°C was reached.The mixture thus obtained was recovered and cooled, then the vulcanizing agent (sulfur) and the vulcanization accelerator (N-cyclohexyl-2-benzothiazolesulfenamide) of the crosslinking system were incorporated on an external mixer (homo-finisher) at a temperature of 30°C, the whole being mixed (productive phase) for a period of more than 5 minutes and less than 12 minutes.

[0082] The rubber compositions thus obtained were then calendered into sheets for the measurement of their ozone resistance properties and for the measurement of efflorescence according to the protocols below.

[0083] The measurement of ozone resistance is carried out according to the method described below. After curing at 150°C for 40 min in a bell press, then cooling at room temperature (23°C) for one day and then baking at 77°C in air for 28 days, 10 test pieces of each of the rubber compositions to be tested are placed on a trapezoid at different elongations ranging from 10% to 100% in 10% elongation steps. The so-called "B15" test pieces come from an MFTR plate (called Monsanto) whose two beads located at the ends are used to hold the test piece. The so-called "B15" test pieces have the following dimensions: 78.5 mm * 15 mm * 1.5 mm. After 192 hours of exposure to a temperature of 38°C and an ozone level of 50 ppm (parts per hundred million), each facies is noted according to the number and depth of cracks.This subjective rating ranges from 0 to 5 (0: no cracks; 1 to 4: presence of increasingly significant and deep cracks; 5: rupture of the specimen). The average of the ratings of all the deformations is used as the criterion. classification. The lower the average, the better the ozone resistance performance.

[0084] The measurement of the "eflorescence" performance is carried out as follows. After cutting the plates of vulcanized rubber compositions, 2.5 mm thick test pieces are oven-dried at 70°C for 12 hours in air. They are then oven-dried at 40°C in air for 4 weeks. After removal from the oven and exposure to room temperature (23°C) for 15 minutes, a mechanical stimulus is applied to reveal the wax efflorescence. In this case, the mechanical stimulus consists of scraping the test piece with a metal blade. The extent of the efflorescence phenomenon (white coloration of the surface) is then evaluated using a subjective scale of values ​​that is representative of the final appearance of the samples. The values ​​of this subjective scale that were respectively obtained for the tested samples can vary from 0 to 3, and correspond to the "eflorescence rating".These values ​​ranging from 0 to 3 correspond to the following aspects for the samples:. 0 - No efflorescence. The scraped surface remains black. 1 - Slight efflorescence. 2 - Moderate efflorescence. 3 - Total efflorescence. The scraped surface is white.

[0085] The lower the value on the scale, i.e. the lower the efflorescence, the better the efflorescence performance.

[0086] The formulations of the rubber compositions (Cl, C2, C3, C4, C5) are presented in Table 1 below: [Table 1] (1) Natural rubber; (2) cis-1,4-polybutadiene synthesized with a neodymium catalyst having a cis-1,4-linkage rate of at least 98 mol%; (3) Anti-ozone wax marketed by Sasol under the commercial reference “Varazon 4959”; (4) Other ingredients: mixture comprising a carbon black, a TDAE oil marketed by H&R under the commercial reference “VivaTec 500”, ((N-(l,3-dimethylbutyl)-N-phenyl-para-phenylenediamine marketed by Flexsys under the reference “Santoflex 6-PPD”, 2,2,4-trimethyl-l,2-dihydroquinolone marketed by Lanxess; stearic acid marketed by Uniquema under the reference “Pristerene 4931”; zinc oxide: commercial quality, marketed by Umicore; N-dicyclohexyl-2-benzothiazolesulfenamide marketed by Flexsys under the reference “Santocure CBS” and sulfur; (5) Unmodified rubber crumb 1 obtained by recycling (micronization of used tires) marketed by Lehigh Technology, the percentage by weight of crumb microparticles having a particle size less than 74 pm of which is 12%, relative to the total weight of the rubber crumb microparticles, and the percentage by weight of microparticles with a particle size greater than 74 pm of which is 88%, relative to the total weight of the rubber crumb microparticles; the percentage by weight of microparticles is measured according to ASTM D5644-01 (2013); (6) Unmodified rubber crumb 2 obtained by recycling (tire micronization) marketed by Lehigh Technology, the weight percentage of crumb microparticles having a particle size less than 74 pm of which is 24%, relative to the total weight of rubber crumb microparticles, and the weight percentage of microparticles with a particle size greater than 74 pm of which is 76% by weight, relative to the total weight of rubber crumb microparticles; the weight percentage of microparticles is measured according to ASTM D5644-01 (2013); (7) Unmodified rubber crumb 3 obtained by recycling (tire micronization) marketed by Lehigh Technology, the weight percentage of crumb microparticles having a particle size less than 74 pm of which is 100%, relative to the total weight of rubber crumb microparticles; the weight percentage of microparticles is measured according to ASTM D5644-01 (2013).

[0087] The formulations of the rubber compositions (Tl, T2, T3, T4, T5, T6, T7) are presented in Table 2 below: [Table 2] Ingredients (1) to (6) of Table 2 are the same as those mentioned in Table 1. (8) unmodified rubber crumb 4 manufactured by Lehigh Technology Company from micronization of used tires and screening; the rubber crumb not having microparticles having a size less than 74 pm and having a weight percentage of microparticles having a particle size greater than 74 pm and less than 180 pm of 100%, based on the total weight of the rubber crumb microparticles; the weight percentage of microparticles is measured according to ASTM D5644-01 (2013); (9) unmodified rubber crumb 5 manufactured by Lehigh Technology Company from tire micronization and screening; the crumb not having microparticles having a size less than 74 pm and whose weight percentage of microparticles having a particle size greater than 74 pm and less than 850 pm is 100%, relative to the total weight of the rubber crumb microparticles; the weight percentage of microparticles is measured according to ASTM D5644-01 (2013).

[0088] The results of the ozone resistance and efflorescence performance measurements are presented in Tables 3 and 4, as differences between the averages of the ratings of all deformations of each sample and the TL reference. A negative value in Tables 3 and 4 indicates an improvement in performance, either with respect to ozone resistance or efflorescence.

[0089] The results of ozone resistance and bloom performance measurements for rubber compositions (Cl, C2, C3, C4, C5) are shown in Table 3 below: [Table 3]

[0090] The results of ozone resistance and bloom performance measurements for rubber compositions (Tl, T2, T3, T4, T5, T6, T7) are shown in Table 4 below: [Table 4]

[0091] The results in Table 3 show that the compositions (C1, C2, C3, C4, C5) according to the invention make it possible to improve at the same time the efflorescence performance and the ozone resistance performance; compared to the reference composition T1, whereas the comparative compositions (T2, T3, T4, T5, T6, T7), according to the results in Table 4, do not show, compared to the reference composition T1, any improvement in the efflorescence performance and / or an ozone resistance performance which can be improved or degraded.

[0092] In conclusion, the rubber composition according to the invention makes it possible to obtain a sidewall presenting a good compromise of performance properties in terms of efflorescence and ozone resistance, which makes it possible to have a sidewall element with high contrast that is durable over time, throughout the entire service life of the tire.

[0093] The characteristics of a high-contrast flank element according to the invention are illustrated by schematic figures 1 to 5, not shown to scale: -Figure 1: Perspective view of a portion of a tire including a sidewall with high-contrast elements, -Figure 2: Half meridian section of a tire including a sidewall with a high-contrast element, -Figure 3: Texture of a high-contrast element comprising strand-shaped protuberances, according to a first variant of the first preferred embodiment of the texture, -Figure 4: Texture of a high-contrast element comprising blade-shaped protuberances, according to a second variant of the first preferred embodiment of the texture, -Figure 5: Texture of a high-contrast element comprising cavities, according to the second preferred embodiment of the texture.

[0094] Figure 1 is a perspective view of a portion of a tire 1 comprising a sidewall 2 with high-contrast elements 3. Among the high-contrast elements 3 are represented two graphic elements 31, intended to communicate technical, commercial or legal information, and an aesthetic element 32.

[0095] Figure 2 is a half-meridian section of a tire 1 comprising a sidewall 2 with a high-contrast element 3 consisting of a texture comprising protuberances 3, in relief relative to the surface of the sidewall 21. The protuberances 4 have the shape of strands as shown in Figure 3.

[0096] Figure 3 is a texture of a high-contrast element 3 comprising strand-shaped protrusions 4, according to a first variant of the first preferred embodiment of the texture. The strand-shaped protrusions 4, in relief relative to a flank surface, have an average height H4. By average height is meant the arithmetic mean of the heights of all the protrusions. The strand-shaped protrusions 4 are spaced apart by an average pitch P4. The strand-shaped protrusions 4, having a diameter varying over the entire height of the strand, have an average diameter D4. In the embodiment shown, the strand-shaped protrusions 4 have a diameter that decreases from a strand base, interfacing with the flank surface, and a free strand top.

[0097] Figure 4 is a texture of a high-contrast element 3 comprising blade-shaped protrusions 5, according to a second variant of the first preferred embodiment of the texture. The blade-shaped protrusions 5, in relief relative to a flank surface, have an average height H5. By average height is meant the arithmetic mean of the heights of all the protrusions. The blade-shaped protrusions 5 are distributed according to a pitch P5. The blade-shaped protrusions 5, having a width varying over the entire height of the blade, have an average width D5. In the embodiment shown, the blade-shaped protrusions 5 have a width which decreases from a blade base, in interface with the flank surface, and a free blade top.

[0098] Figure 5 is a texture of a high-contrast element 3 comprising cavities 6, according to the second preferred embodiment of the texture. The cavities 6, recessed relative to a flank surface, having an average depth. Average depth means the arithmetic mean of the depths of all the cavities. A cavity 6 is constituted by a cavity interior 62, formed in the thickness of the flank, and an opening 61, opening into the surface of the flank. The openings 61 on the flank surface are spaced apart by a pitch P6. The openings 61 on the flank surface have an average diameter D6. By average diameter, we mean an arithmetic mean of the diameters, not necessarily identical, of the openings on the flank surface.

Claims

Claims 1. Tire (1) for a vehicle comprising a sidewall (2) with at least one high-contrast sidewall element (3): -the high-contrast flank element (3) being constituted by a texture having a first brightness L*1 at least equal to 1 and at most equal to 15, -any portion of flank surface (21) adjacent to the high-contrast flank element (3), having a second brightness L*2 at least equal to L*l+5, -the first and second brightnesses (L*l, L*2) being expressed according to a scale ranging from 0 to 100 in accordance with the colorimetric model L*a*b* adopted in 1976 by the International Commission on Illumination, -the sidewall (2) comprising a rubber composition based on an elastomer matrix comprising an isoprene elastomer, at least one reinforcing filler, at least one crosslinking system, at least one anti-ozone wax and at least one rubber crumb comprising microparticles having a size less than 74 μm, characterized in that the content of isoprene elastomer is at least equal to 27.00% by weight relative to the total weight of the rubber composition, in that the content of anti-ozone wax is at least equal to 0.60% and at most equal to 1.70% by weight relative to the total weight of the rubber composition, and in that a weight ratio between the content of microparticles of rubber crumb having a size less than 74 μm and the content of anti-ozone wax, these contents being expressed as a percentage by weight relative to the total weight of the rubber composition, is at least equal to 0.

50.

2. Tire (1) according to claim 1, in which the level of isoprene elastomer is at least equal to 28.00% by weight and at most equal to 34.00% by weight, preferably at least equal to 28.50% by weight and at most equal to 34.00% by weight, relative to the total weight of the rubber composition.

3. Tire (1) according to one of claims 1 or 2, in which the anti-ozone wax content is at least equal to 0.70% by weight and at most equal to 1.68% by weight, preferably at least equal to 0.90% by weight and at most equal to 1.65% by weight, relative to the total weight of the rubber composition.

4. Tire (1) according to any one of claims 1 to 3, in which the weight ratio between the rate of microparticles of rubber crumb having a size less than 74 pm and the rate of anti-ozone wax, expressed as a percentage by weight relative to the total weight of the rubber composition, is at least equal to 0.65 and at most equal to 4.00, preferably at least equal to 0.70 and at most equal to 2.

50.

5. Tire (1) according to any one of claims 1 to 4, in which the rate of microparticles having a size less than 74 pm is at least equal to 0.90% by weight, preferably at least equal to 0.95% by weight, more preferably at least equal to 1.00% by weight, relative to the total weight of the rubber composition.

6. Tire (1) according to any one of claims 1 to 5, in which the isoprene elastomer is chosen from the group consisting of natural rubber, synthetic polyisoprenes, isoprene copolymers, and mixtures of these elastomers, preferably from the group consisting of natural rubber, synthetic polyisoprenes and mixtures of these elastomers.

7. Tire (1) according to any one of claims 1 to 6, in which the isoprene elastomer is chosen from the group consisting of natural rubber, synthetic cis-1,4 polyisoprenes, preferably those having a molar rate of cis-1,4 bonds greater than 90%, preferably greater than 98%.

8. A tire (1) according to any one of claims 1 to 7, wherein the rubber composition comprises a butadiene elastomer.

9. Tire (1) according to claim 8, in which the content of butadiene elastomer is at least equal to 23.00% by weight and at most equal to 31.00% by weight, preferably at least equal to 24.00% by weight and at most equal to 30.00% by weight, more preferably at least equal to 25.00% by weight and at most equal to 29.00% by weight, relative to the total weight of the rubber composition.

10. A tire (1) according to any one of claims 8 or 9, wherein the butadiene elastomer is chosen from the group consisting of polybutadienes, butadiene copolymers, and combinations of these elastomers, plus preferably is a polybutadiene, preferably a polybutadiene having a molar rate of cis-1,4 bonds greater than 90%, preferably greater than 96%.

11. A tire according to any one of claims 1 to 10, wherein the rubber crumb is a rubber crumb that has not undergone any modification by a treatment chosen from the group consisting of thermal, mechanical, biological and chemical treatments and their combinations.

12. Tire (1) according to any one of claims 1 to 11, in which the high-contrast sidewall element (3) consists of a texture having a first brightness L*1 at least equal to 4 and at most equal to 13.

13. Tire (1) according to any one of claims 1 to 12, wherein any portion of sidewall surface (21) adjacent to the high contrast sidewall element (3) has a second brightness L*2 at least equal to L*1+10, preferably at least equal to L*1+12.

14. Tire (1) according to any one of claims 1 to 13, wherein any portion of sidewall surface (21) adjacent to the high contrast sidewall element (3) has a second brightness L*2 at least equal to 18, preferably at least equal to 22.

15. Tire (1) according to any one of claims 1 to 14, in which the high-contrast sidewall element (3) is constituted by a texture comprising protuberances (4, 5), in relief relative to a sidewall surface (21), in contact with atmospheric air, and / or cavities (6), hollow relative to the sidewall surface (21).

16. A tire (1) according to any one of claims 1 to 15, wherein the high-contrast sidewall element (3) is constituted by a texture comprising strand-shaped protrusions (4).

17. A tire (1) according to any one of claims 1 to 15, wherein the high-contrast sidewall element (3) is constituted by a texture comprising blade-shaped protrusions (4).

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