A tire comprising a sidewall with at least one high-contrast sidewall element

Abstract

The present invention relates to a tire (1) for a vehicle, comprising at least one sidewall (2) with at least one high-contrast sidewall element (3) consisting of a texture having a first brightness L*1 of at least 1 and at most 15, any adjacent portion of sidewall surface (21) having a second brightness L*2 of at least L*1+5. The invention describes a sidewall rubber composition (2) exhibiting a good compromise between efflorescence reduction and resistance to ozone attack. According to the invention, the isoprene elastomer content is at least 27.00% by weight, the ozone-blocking wax content is at least 0.60% by weight and at most 1.70% by weight, and the weight ratio between the content of rubber powder microparticles having a size less than 74 µm and the content of ozone-blocking wax, expressed as a percentage by weight, is at least 0.50. Figure for the abstract: Fig. 1

Description

Title of the invention: 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, one sidewall being the portion of the tire connecting one end of the tread, intended to come into contact with a ground, to a bead, intended to be mounted on a rim.

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

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

[0005] Thus, whether for the enhancement of graphic elements or aesthetic elements of 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 higher brightness than the texture of said high-contrast flank element; that is, it appears visually brighter. This texture is made of a rubbery material, also called a rubber compound or elastomeric compound, identical to that of the portion of flank in contact with atmospheric air, since this texture is made of the same material as the flank.

[0007] Brightness can be quantified by luminous luminance, expressed in candelas / m², which measures the luminous flux from an illuminated surface that is reflected into the observer's eye. However, the relationship between luminous luminance and the visual perception of brightness is not linear and is complex. Therefore, for practical purposes, the International Commission on Illumination (CIE) defined the luminous intensity L*, a parameter that characterizes a surface's ability to reflect light, based on the luminous intensity of light produced by a primary or secondary source, expressed in candelas per square meter (cd / m²), relative to the luminous intensity of white taken as a reference. Thus, in what follows, the luminous intensity L* is expressed on a scale 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 a 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 performed with the SCI mode (including specular reflection mode) set to 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.To improve the determination of this second brightness L*2, it is possible to perform a plurality of brightness measurements on several adjacent flank surface portions, and then deduce an associated average brightness.

[0009] High-contrast flank elements, having a brightness difference substantially less than that of an adjacent flank surface portion, were described in documents WO 2016005572 A1 and WO 2011036061 A1 and WO 20174919 A1

[0010] It has been observed on tire sidewall surfaces, including high contrast sidewall elements, that there is an evolution over time of the contrast between the high contrast sidewall elements and any adjacent sidewall surface portion.

[0011] The evolution of the 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 may 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 flank surface is typically reflected by an evolution, at least locally, of its colour (blueing, evolution towards a dark brown colour, 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 possess carbon-carbon double bonds. These double bonds are chemically more reactive than a single carbon-carbon bond and are therefore susceptible to deterioration more or less rapidly after prolonged exposure to the atmosphere, due to known oxidation and ozonolysis mechanisms. The action of ozone promotes the formation 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 ozone-blocking agents, such as, for example, ozone-blocking waxes. These ozone-blocking waxes provide static protection by forming a protective coating on the surface. However, these ozone-blocking waxes are characterized by their ability to migrate to the sidewall surface and crystallize, which alters the visual appearance of the sidewall surface, causing stains, a dull, gray appearance, or a lighter coloration. This phenomenon is called "blooming." This phenomenon thus results in uneven coloration and makes the sidewall surface, initially black and shiny, gray and dull.

[0016] Thus, a non-homogeneous coloration of the flank surface reduces the contrast effect of the high-contrast element and alters the visual and aesthetic appearance of the flank.

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

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

[0019] The inventors have 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 sidewall surface portion, using a suitable rubber composition for the sidewall, particularly in the vicinity of the sidewall surface.

[0020] This objective has been achieved by a tire for a vehicle, comprising a sidewall with at least one high-contrast sidewall element: -the high-contrast flank element being made up of a texture having a first luminance L*1 of at least 1 and at most 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 sidewall comprising a rubber composition based on an elastomeric 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 powder comprising microparticles having a size less than 74 pm, -the isoprene elastomer content being at least 27.00% by weight, relative to the total weight of the rubber composition, -the rate of anti-ozone wax 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 rubber powder microparticles 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 of at least 1 and at most 15.

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

[0025] According to the invention, the sidewall comprises a rubber composition based on an elastomeric 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 powder comprising microparticles having a size less than 74 pm.

[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 intended to react with each other, at least partially, during the different phases of manufacturing 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, particularly 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, that is, a homopolymer or a copolymer, exhibiting elastic properties obtained after crosslinking. The term rubber is a common synonym for elastomer.

[0029] The term "diene elastomer" or, interchangeably, "diene rubber," whether natural or synthetic, refers to an elastomer composed at least in part of diene monomer units (monomers bearing 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 proportion of diene motifs or units (conjugated dienes) greater than 15% (mole percent). Thus, diene elastomers such as butyl rubbers or EPDM-type diene-alpha-olefin copolymers do not fall under the preceding definition and can, in particular, be described as diene elastomers. "essentially saturated" (low or very low rate of motifs of diene origin, always less than 15%).

[0031] The term diene elastomer, which can be used in rubber compositions according to the invention, is particularly understood 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 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 T isoprene.

[0033] As unconjugated dienes, unconjugated dienes having 6 to 12 carbon atoms, such as 1,4-hexadiene, ethylidene norbornene, dicyclopentadiene.

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

[0035] Suitable examples of vinylaromatic compounds include styrene, ortho -, meta-, para-methylstyrene, the commercial "vinyl-toluene" mixture, para-tert-butylstyrene.

[0036] As aliphatic α-monoolefins, acyclic aliphatic α-monoolefins having from 3 to 18 carbon atoms are particularly suitable.

[0037] More specifically, Dienic telastomer 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 dienes conjugated together or with one or more vinylaromatic compounds having 8 to 20 carbon atoms; c. 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] The term "isoprene elastomer" is commonly understood to mean a homopolymer or copolymer of isoprene. In other words, an isoprene elastomer can be selected from the group consisting of natural rubber (NR), synthetic polyisoprenes (IR), various isoprene copolymers, and mixtures of these elastomers. Among the isoprene copolymers, particular mention should be made of isobutene-isoprene (butyl rubber - IIR), isoprene-styrene (SIR), isoprene-butadiene (BIR), or isoprene-butadiene-styrene (SBIR). Preferably, the isoprene elastomer may be chosen from the group consisting of natural rubber, synthetic cis-1,4 polyisoprenes, and their combinations. Even more preferably, the isoprene elastomer is chosen from the group consisting of natural rubber, synthetic polyisoprenes having a cis-1,4 linkage percentage (molar %) greater than 90% (even more preferably greater than 98%), and their combinations.

[0039] A reinforcing filler, intended to strengthen a rubber composition, can 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 can be any type of system known to those skilled in the art in the field of tire rubber compounds. It can, in particular, be sulfur-based, and / or peroxide-based, and / or bismaleimide-based. Preferably, the crosslinking system is sulfur-based: this is then referred to as a vulcanization system. The sulfur can be supplied in any form, in particular as molecular sulfur, or as a sulfur-donating agent. At least one vulcanization accelerator is also preferably present, and, optionally and also preferably, various known vulcanization activators can 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 even known vulcanization retardants.Any compound capable of acting as a vulcanization accelerator for diene elastomers in the presence of sulfur can be used as an accelerator, including thiazole-type accelerators and their derivatives, sulfenamide-type accelerators, thiurams, dithiocarbamates, dithiophosphates, thioureas and xanthates.

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

[0042] Any extending oil, whether aromatic or non-aromatic, known for its plasticizing properties with respect to elastomers, is suitable. At room temperature (23°C), these oils, which vary in viscosity, are liquids (that is to say, substances capable of eventually settling into a plasticizer). (form of their container), in contrast to high Tg hydrocarbon resins, which are inherently solid at room temperature. Plasticizing oil generally has a glass transition temperature (Tg) below -20 °C, preferably below -40 °C. The glass transition temperature (Tg) of plasticizing oil is measured according to ASTM D3418 (2008).

[0043] By definition, a high Tg hydrocarbon resin, typically at least 30°C, is solid at ambient temperature and pressure (23°C, 1 atm), while a plasticizing oil is liquid at ambient temperature and a low Tg hydrocarbon resin is viscous at ambient temperature. Hydrocarbon resins, also called hydrocarbon plasticizing resins, are polymers well known to those skilled in the art, essentially carbon- and hydrogen-based but potentially containing other types of atoms, such as oxygen, and are particularly useful as plasticizing or tackifying agents in polymer matrices. By nature, they are 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 diluents.These hydrocarbon resins can also be classified as thermoplastic resins, as 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 regards ozone-blocking waxes, they can be, for example, paraffinic waxes, microcrystalline waxes, or mixtures of paraffinic and microcrystalline waxes. They consist of a mixture of linear and non-linear alkanes (isoalkanes, cycloalkanes, branched alkanes) obtained from petroleum refining or the catalytic hydrogenation of carbon monoxide (Fisher-Tropsch process), comprising predominantly 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 analysis of the chromatogram is carried out according to the EWF (“European Wax Federation”) method.

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

[0047] Anti-ozone waxes are commercially available such as, by way of 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] A rubber powder (also called "crumb rubber" in English) is in the form of granules, possibly in the form of a rubber plate.

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

[0050] In a known manner, rubber powders can be obtained more particularly by reducing used tires into granules from which reinforcing materials such as steels or textile fibers have been removed.

[0051] Rubber powders can be prepared by cryogenic grinding of used tires, for example according to the process described in US patent 7,445,170, comprising successive and independent steps of granulation, separation of metal and textile reinforcements, cooling, and micronization to obtain a coarse distribution of micron-sized particles of vulcanized compound (also called microparticles). This micronization can be carried out using a conical impact mill as described in US patent 7,861,958. The cryogenically cooled incoming material enters the mill (for example, the Netzsch CUM150 or Alpine CW250 mills can be used), and is then transferred by gravity to a high-speed rotating rotor. The cryogenically cooled incoming material is thus repeatedly projected against the walls of the rotor chamber, leading to its micronization.The particles can then pass through a series of two vibrating sieves of the same size to separate any remaining non-vulcanized mixture elements. A crude distribution of micron-sized particles of the vulcanized mixture is obtained. "Microparticles" are defined as particles whose size—namely their diameter in the case of spherical particles, or their largest dimension in the case of anisometric particles—is on the order of tens or hundreds of microns. The size of the microparticles can be determined by techniques known to those skilled in the art, such as microscopy. The rubber powder used in the present invention includes, in particular, microparticles smaller than 74 µm and microparticles larger than 74 µm. The distribution of the rubber powder microparticles is determined according to ASTM D5644-01 (2013).Rubber powders are commercially available from suppliers such as, for example, Lehigh Technology.

[0052] Rubber powders can be simple rubber granules or micronized materials, without further processing. However, it is also known that rubber powders can undergo processing to modify them. This processing can consist of chemical modification through functionalization or devulcanization. It can also involve thermomechanical, thermochemical, or biological treatment.

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

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

[0055] According to the invention, the rate of anti-ozone wax 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] According to the invention, a weight ratio between the rate of rubber powder microparticles having a size less than 74 pm and the rate of antiozone 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 content and the weight ratio between the content of rubber powder microparticles having a size less than 74 pm and the previous anti-ozone wax content, in particular for an elastomer matrix with the previously described isoprene elastomer content, makes it possible to obtain a satisfactory compromise between the reduction of efflorescence and resistance to flank attack by ozone.

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

[0059] Even more advantageously the rate 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 rubber powder microparticles 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 the distribution of the sizes of rubber powder microparticles, the proportion 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.

[0062] According to a first embodiment of the elastomeric matrix, the isoprene elastomer is chosen from the group consisting of natural rubber, synthetic polyisoprenes, isoprene copolymers, and mixtures thereof. 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 ratio 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] The term "butadiene elastomer" is commonly understood to mean a homopolymer or copolymer of butadiene. In other words, a butadiene elastomer can be selected from the group consisting of polybutadienes (BR), various butadiene copolymers, and mixtures of these elastomers. Among the butadiene copolymers, butadiene-styrene (SBR) and ethylene-butadiene (EBR) copolymers are particularly noteworthy. Preferably, the butadiene elastomer can be a cis-1,4 polybutadiene; in particular, a polybutadiene having a cis-1,4 bonding percentage (molar %) greater than 90%, and even more preferably greater than 96%.

[0066] Advantageously the butadiene elastomer content is at least 23.00% by weight and at most 31.00% by weight, preferably at least 24.00% by weight and at most 30.00% by weight, more preferably at least 25.00% by weight and at most 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 ratio of cis-1,4 bonds greater than 90%, preferably greater than 96%.

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

[0069] The rubber composition described above, with all its embodiments, is, in particular, the constituent material of the high-contrast sidewall element, made of material with the sidewall and consisting of a texture comprising protrusions, raised in relation to a sidewall surface, in contact with atmospheric air, and / or cavities, recessed in relation to the sidewall surface.

[0070] Advantageously the high contrast flank element is made up of a texture having a first brightness L*1 of at least 4 and at most 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 of at least 18, preferably at least 22.

[0073] According to a first and second preferred embodiment, the high contrast flank element consists of a texture comprising protrusions, raised in relation to a flank surface, in contact with atmospheric air, and / or cavities, recessed in relation to the flank surface.

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

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

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

[0077] The texture of the high-contrast side elements, comprising strand- or blade-shaped protrusions, absorbs a large portion of the incident light rays after one or more successive reflections off the walls of the protrusions. This gives the texture a darker appearance and, consequently, improves its contrast and therefore its visibility compared to any adjacent portion of the side surface. Furthermore, this particular texture provides a pleasant, velvety feel to the side surface. Finally, the texture used has a water-repellent and slightly hydrophobic effect. In a particular embodiment, the texture can be positioned on a surface recessed from the side surface, so that it is embedded in the side, which has the advantage of protecting it, for example, against wear caused by the side surface rubbing against a curb.

[0078] Similarly, the texture of the high-contrast flank elements, comprising cavities recessed relative to the flank surface, allows for the absorption of a large Part of the incident light rays, after one or more successive reflections off the cavity walls. This specific texture has the advantage of being recessed relative to the sidewall surface, which helps ensure the durability of the texture by protecting it against wear caused by the sidewall rubbing against a curb. It also has the advantage of not disrupting the aerodynamic airflow near the sidewall surface when the tire is rolling.

[0079] The rubber composition described in the context 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 (Cl, C2, C3, C4 and C5: examples according to the invention, T1: reference, and T2, T3, T4, T5, T6 and T7: comparative examples) were produced.

[0081] Each rubber composition was produced as follows: the reinforcing filler, the elastomer matrix, the ozone-blocking wax, the rubber powder (when present), and the various other ingredients, for example, the plasticizing agent, with the exception of the vulcanizing system, were successively introduced into an internal mixer with an initial tank temperature of 60°C, the Banbury-type internal mixer being filled to approximately 70% of its volume. The thermomechanical work (non-productive phase) was then carried out in a single step lasting 3 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 vulcanizing 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 ozone resistance measurement is carried out according to the method described below. After curing at 150°C for 40 minutes in a bell press, then cooling to room temperature (23°C) for one day and subsequently drying at 77°C in air for 28 days, 10 test specimens 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 increments. The specimens referred to as "B15" are taken from an MFTR plate (called Monsanto), the two ridges at the ends of which serve to hold the specimen in place. The specimens referred to as "B15" 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 concentration of 50 ppm (parts per hundred million), each surface is rated 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 large and deep cracks; 5: fracture of the specimen). The average of the ratings for all deformations is used as the classification criterion. The lower the average, the better the ozone resistance performance.

[0084] The "efflorescence" performance measurement is carried out as follows. After cutting the vulcanized rubber composition sheets, 2.5 mm thick test specimens are baked at 70°C for 12 hours in air. They are then baked 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 wax efflorescence. In this case, the mechanical stimulus consists of scraping the test specimen with a metal blade. The extent of the efflorescence phenomenon (white discoloration of the surface) is then assessed using a subjective scale that is representative of the final appearance of the samples. The values ​​on this subjective scale obtained for the tested samples can range from 0 to 3 and correspond to the "efflorescence 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 scale value, 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: [Tables 1] Composition Cl C2 C3 C4 C5 Isoprene elastomer (1) (expressed as % by weight, relative to the total weight of the rubber composition) 30.64 30.64 30.64 30.57 29.18 Butadiene elastomer (2) (expressed as % by weight, relative to the total weight of the rubber composition) 27.18 27.18 27.18 27.11 25.87 Anti-ozone wax (3) (expressed as % by weight, relative to the total weight of the rubber composition) -A 1.32 1.32 1.32 1.56 1.65 Other additives (4) (expressed as % by weight, relative to the total weight of the rubber composition) 31.02 31.02 31.02 30.95 29.54 Rubber powder 1 (5) (expressed as % by weight, relative to the total weight of the rubber composition) 9.83 (-) (-) (-) (-) Rubber powder 2 (6) (expressed as % by weight, relative to the total weight of the rubber composition) (-) 9.83 (-) 9.81 13.76 Rubber powder 3 (7) (expressed as % by weight, relative to the total weight of the rubber composition) (-) (-) 9,83 (-) (-) Microparticle size less than 74 pm in the rubber powder (expressed as % by weight, relative to the total weight of the rubber powder) - B 1.18 2.36 9.83 2.35 3.30 B / A ratio 0.89 1.79 7.45 1.51 2.00 , 1. Natural rubber; 2. Cis-1,4-Polybutadiene synthesized with a neodymium catalyst having a rate cis-1,4 bond strength of at least 98 molar percent; 3. Anti-ozone wax marketed by Sasol under the commercial reference "Varazon 4959"; 4. Other ingredients: mixture comprising carbon black, TDAE oil marketed by H&R under the trade name "VivaTec 500", and ((N-(l,3-dimethylbutyl)-N-phenyl-para-phenylenediamine) marketed by Flexsys under the reference "Santaflex 6-PPD", 2,2,4-trimethyl-1,2-dihydroquinolone marketed by Lanxess; stearic acid marketed by Uniquema under the reference "Pristerene 4931"; zinc oxide: commercial grade, marketed by Umicore; N-dicyclohexyl-2-benzothiazolesulfenamide marketed by Flexsys under the reference "Santocure CBS" and sulfur; 5. Unmodified rubber powder 1 obtained by recycling (micronization of used tires) marketed by Lehigh Technology, the weight percentage of powder microparticles having a particle size less than 74 pm is 12%, relative to the total weight of rubber powder microparticles, and the weight percentage of microparticles with a particle size greater than 74 pm is 88%, relative to the total weight of rubber powder microparticles; the weight percentage of microparticles is measured according to ASTM D5644-01 (2013); 6. Unmodified rubber powder 2 obtained by recycling (tire micronization) marketed by Lehigh Technology, the weight percentage of powder microparticles having a particle size less than 74 pm is 24%, relative to the total weight of rubber powder microparticles, and the weight percentage of microparticles with a particle size greater than 74 pm is 76% by weight, relative to the total weight of rubber powder microparticles; the weight percentage of microparticles is measured according to ASTM D5644-01 (2013); 7. Unmodified rubber powder 3 obtained by recycling (tire micronization) marketed by Lehigh Technology, the weight percentage of powder microparticles having a particle size less than 74 pm is 100%, relative to the total weight of rubber powder microparticles; the weight percentage of microparticles is measured according to ASTM D5644-01 (2013).

[0087] The formulations of the rubber compositions (T1, T2, T3, T4, T5, T6, T7) are presented in Table 2 below: [Tables 2] Composition T1 T2 T3 T4 T5 T6 T7 Isoprene elastomer (1) (expressed as % by weight, relative to the total weight of the rubber composition) 34.05 32.73 30.64 30.64 26.02 30.50 30.87 Butadiene elastomer (2) (expressed as % by weight, relative to the total weight of the rubber composition) 30.20 29.02 27.18 27.18 31.80 27.05 27.38 Anti-ozone wax (3) (expressed as % by weight, relative to the total weight of the rubber composition) -A 1.28 1.42 1.33 1.33 1.33 1.78 0.59 Other additives (4) (expressed as % by weight, relative to the total weight of the rubber composition) (relative to the total weight of the rubber composition) 34.47 33.13 31.02 31.02 31.02 30.89 31.26 Rubber powder 1 (5) (expressed as % by weight, relative to the total weight of the rubber composition) (-) 3.70 (-) (-) (-) (-) (-) Rubber powder 2 (6) (expressed as % by weight, relative to the total weight of the rubber composition) (-) (-) (-) (-) 9.83 9.78 9.90 Rubber powder 4 (8) (expressed as % by weight,relative to the total weight of the rubber composition) (-) (-) 9.83 (-) (-) (-) (-) Rubber powder 5 (9) (expressed as % by weight, relative to the total weight of the rubber composition) (-) (-) (-) 9.83 (-) (-) (-) Microparticle having a size less than 74 pm in the p 0 0.44 0 0 2.36 2.35 2.38 , Rubber dust (expressed as a percentage by weight, relative to the total weight of the rubber composition) - B Ratio B / A (-) 0.31 (-) (-) 1.77 1.32 4.03 Ingredients (1) to (6) in Table 2 are the same as those mentioned in Table 1. (8) unmodified rubber powder 4 manufactured by Lehigh Technology from the micronization of used tires and sieving; the rubber powder not having microparticles having a size less than 74 pm and of which the weight percentage of microparticles having a particle size greater than 74 pm and less than 180 pm is 100%, relative to the total weight of the microparticles of rubber powder; the weight percentage of microparticles is measured according to ASTM D5644-01 (2013); (9) unmodified rubber powder 5 manufactured by Lehigh Technology from tire micronization and sieving; the powder not having microparticles having a size less than 74 pm and of which the 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 powder 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, in the form of differences between the means of the ratings of all the deformations of each sample and the reference TL. A negative value in Tables 3 and 4 indicates an improvement in performance, whether with regard to ozone resistance or efflorescence.

[0089] The results of the ozone resistance and performance measurements efflorescence for rubber compositions (Cl, C2, C3, C4, C5) are presented in Table 3 below: [Tables 3] Composition Cl C2 C3 C4 C5 Ozone resistance performance -0.1 -0.6 -0.8 -0.8 -0.4 Efflorescence performance -2 -2 -2 -1 -2

[0090] The results of the ozone resistance and efflorescence performance measurements for the rubber compositions (T1, T2, T3, T4, T5, T6, T7) are presented in Table 4 below: [Tables 4] Composition T1 T2 T3 T4 T5 T6 T7 O resistance performance zone 0 +0.1 -0.3 -0.2 -0.5 -0.9 +0.4 Efflorescence performance 0 0 0 0 0 0 -2

[0091] The results in Table 3 show that the compositions (Cl, C2, C3, C4, C5) according to the invention make it possible to improve both efflorescence performance and ozone resistance performance; compared to the reference composition Tl, 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 Tl, any improvement in efflorescence performance and / or an ozone resistance performance that can be improved or degraded.

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

[0093] The characteristics of a high-contrast sidewall element according to the invention are illustrated by the schematic Figures 1 to 5, which are not drawn to scale: - [Fig. 1]: Perspective view of a portion of a tire comprising a sidewall with high-contrast elements, -[Fig.2]: Meridional half-section of a tire including a sidewall with a high-contrast element, -[Fig.3]: Texture of a high-contrast element comprising strand-like protuberances, according to a first variant of the first preferred embodiment of the texture, -[Fig.4]: Texture of a high-contrast element comprising blade-like protrusions, according to a second variant of the first preferred embodiment of the texture, -[Fig.5]: Texture of a high-contrast element including cavities, according to the second preferred embodiment of the texture.

[0094] Fig. 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 two graphic elements 31, intended to communicate technical, commercial or legal information, and one aesthetic element 32.

[0095] Figure 2 is a meridional half-section of a tire 1 comprising a sidewall 2 with a high-contrast element 3 consisting of a texture comprising protuberances 3, raised in relation to the surface of flank 21. Protuberances 4 have a strand-like shape as shown in [Fig.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, raised against a flank surface, have an average height H4. Average height is understood to be the arithmetic mean of the heights of all the protrusions. The strand-shaped protrusions 4 are spaced at an average pitch P4. The strand-shaped protrusions 4, having a diameter that varies along 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, at the interface with the flank surface, and a free strand apex.

[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, raised against a flank surface, have an average height H5. Average height is understood to be the arithmetic mean of the heights of all the protrusions. The blade-shaped protrusions 5 are spaced at a pitch P5. The blade-shaped protrusions 5, having a width that varies along the entire height of the blade, have an average width D5. In the embodiment shown, the blade-shaped protrusions 5 have a width that decreases from a blade base, which interfaces with the flank surface, and a free blade apex.

[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 with respect to a flank surface, have an average depth. By average depth, we mean the arithmetic mean of the depths of all the cavities. A cavity 6 consists of a cavity interior 62, formed in the thickness of the flank, and an opening 61, opening onto the surface of the flank. The openings 61 on the flank surface are spaced at 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

Demands

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

50.

2. Pneumatic (1) according to claim 1, wherein the isoprene elastomer content is at least 28.00% by weight and at most 34.00% by weight, preferably at least 28.50% by weight and at most 34.00% by weight, relative to the total weight of the rubber composition.

3. Tire (1) according to claim 1 or 2, wherein the percentage of ozone-reducing wax is at least 0.70% by weight and at most 1.68% by weight, preferably at least 0.90% by weight 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, wherein the weight ratio between the rate of rubber powder microparticles 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. Pneumatic (1) according to any one of claims 1 to 4, wherein 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. Pneumatic (1) according to any one of claims 1 to 5, wherein the isoprene elastomer is selected 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. Pneumatic (1) according to any one of claims 1 to 6, wherein the isoprene elastomer is selected from the group consisting of natural rubber, synthetic cis-1,4 polyisoprenes, preferably those having a molar ratio of cis-1,4 bonds greater than 90%, preferably greater than 98%.

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

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

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

11. Pneumatic according to any one of claims 1 to 10, wherein the rubber powder is a rubber powder that has not undergone any modification by a treatment selected from the group consisting of thermal, mechanical, biological and chemical treatments and combinations thereof.

12. Tire (1) according to any one of claims 1 to 11, wherein the high contrast sidewall element (3) is made up of a texture having a first brightness L*1 of at least 4 and at most 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 of at least 18, preferably at least 22.

15. Pneumatic (1) according to any one of claims 1 to 14, wherein the high contrast sidewall element (3) is made up of a texture comprising protrusions (4, 5), raised in relation to a sidewall surface (21), in contact with atmospheric air, and / or cavities (6), recessed in relation to the sidewall surface (21).

16. Tire (1) according to any one of claims 1 to 15, wherein the high contrast sidewall element (3) is made up of a texture comprising strand-like protrusions (4).

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

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