BR112020020053B1 - VULCANIZABLE ELASTOMERIC COMPOSITION FOR TIRES, TIRE COMPONENT FOR VEHICLE WHEELS, AND, TIRE FOR VEHICLE WHEELS - Google Patents

Abstract

VULCANIZABLE ELASTOMERIC COMPOSITION FOR TIRES, TIRE COMPONENT FOR VEHICLE WHEELS, AND TIRE FOR VEHICLE WHEELS. The present invention relates to new elastomeric tire compositions, comprising particular silicas obtained from rice husk ash, and related tires incorporating them, particularly in the tread. These compositions are generally distinguished by good static and dynamic mechanical properties and, unexpectedly, by better resistance to abrasion and tearing, which is reflected in a longer life of the tires that incorporate them.

Description

FIELD OF INVENTION

[001] The present invention relates to new elastomeric compositions for tires, comprising particular silicas obtained from rice husk ash, and related tires that incorporate them, particularly in the tread.

[002] Said compositions are distinguished by good static and dynamic mechanical properties and, unexpectedly, by better resistance to abrasion and tearing.

PREVIOUS TECHNIQUE

[003] In the rubber industry, and more particularly in the tire industry, it is known to add reinforcing fillers to elastomeric compositions in order to improve their mechanical properties.

[004] Due to its high reinforcing power, carbon black is the most commonly used filler. However, it gives strong hysteresis to the articles, that is, it increases the heat dissipated in dynamic conditions. In tires, this results in an unwanted increase in rolling resistance and, above all, in greater fuel consumption, the production of more polluting emissions and higher transport costs.

[005] An improvement in this sense was achieved by the use of so-called “white” reinforcing fillers, such as chalk, talc, kaolin, bentonite, titanium dioxide and especially silica, fillers that can partially or totally replace carbon black in compositions. elastomeric materials, particularly the tread, and provide lower rolling resistance, good grip on wet surfaces and at the same time provide sufficient reinforcement to the tires.

[006] These elastomeric compositions comprising silica can therefore be used with advantage in tires subject to different performances, such as HP tires, summer, all-season or winter tires.

[007] For such uses, silicas with different characteristics are commercially available or can be prepared according to known processes.

[008] Some conventional preparation methods use sand as a raw material, solubilizing crystalline silica in the form of silicates at high temperatures and with strong bases and, finally, reprecipitating it with strong acids, as described, for example, in the article Silicon (2017) 9: 917-922 titled “Preparation and characterization of precipitated silica using sodium silicate prepared from Saudi Arabian desert sand”.

[009] These processes preferably use sodium hydroxide for solubilization and sulfuric acid for subsequent precipitation, with the formation of sodium sulfate, a byproduct of little commercial interest that is generally discarded in wastewater with a non-negligible environmental impact.

[0010] On the other hand, tire and car manufacturers increasingly need more sustainable tires, including raw materials obtained from renewable sources and, possibly, eco-compatible processes.

[0011] The preparation methods were, therefore, developed from rice husk, a renewable source, which operates in milder conditions, mainly at lower temperatures.

[0012] For example, document EP1312581A2 (Goodyear) describes a process for producing silica from rice husk ash, where, however, the precipitation step is in fact still by classical acidification with strong acids, with the disposal problems mentioned above. The description does not contain any specific characterization of the silicas thus obtained nor particular information about the properties of the corresponding tires, but teaches that to improve their dispersibility in elastomeric matrices it is preferable to pre-treat them superficially with silanes.

[0013] Another improvement in terms of ecological compatibility occurred with some silica preparation processes from rice husk ash, where precipitation was carried out with carbon dioxide. These processes lead to the formation of more eco-friendly by-products, in particular sodium carbonate, which can be converted into sodium hydroxide and calcium carbonate, which in turn is broken down into calcium oxide and carbon dioxide. All of these by-products can be completely recycled in the process itself, advantageously avoiding any final disposal.

[0014] For example, document WO2004073600A2 (Ind. Inst. Science) refers to a process for the preparation of silicas from rice husk ash by precipitation with carbon dioxide and its applications in the most diverse sectors such as rubbers, plastics, paints, inks, toothpastes, cosmetics, catalysts, carriers, insulators, stabilizers and desiccants.

[0015] The silicas described therein have a wide range of surface areas (from 50 to 400 m2/g) and density after compaction (compacted density, from 80 to 510 g/l).

[0016] The document states in an entirely generic way that silicas with a density after compaction of more than 200-250 g/l are mainly required by the tire industry, without providing examples of actual incorporation of any particular silica or suggesting any performance improved the same.

[0017] Document WO2017179070A1 (Ind. Inst. Science) describes a process for preparing silica from rice husk ash by carbon dioxide precipitation, improved over that shown in previous document WO2004073600A2. In general, it is stated that silica can be applied in reinforcing rubbers and plastics, in thickening coatings and paints, in printing inks, in plastics and cosmetics, as an antiblocking agent in plastic sheets, as a carrier for pesticides and catalysts. No specific application or any particular advantage is suggested. Silicas obtainable according to the method described here generally have a surface area of 150 to 400 m2/g (page 14), while those exemplified are 87 to 403 m2/g.

SUMMARY OF THE INVENTION

[0018] Current elastomeric tire compositions, in particular tread compositions, generally use conventional silicas, that is, silicas obtained from sand by precipitation with sulfuric acid and possible pretreatment with silanizers.

[0019] The Applicant noted that when these conventional silicas have a high surface area, indicatively greater than 190 m2/g, they are more difficult to process and dispersible in the matrix, possibly due to the increased number of polar silanols that interact poorly with the elastomer.

[0020] Good dispersibility of silica in the elastomeric matrix is an important requirement for obtaining compositions suitable for use in tires. In fact, an inhomogeneous dispersion, with the formation of numerous and/or bulky aggregates, has a negative impact on the performance of the material itself, resulting, for example, in excessive hysteresis or poor rupture behavior.

[0021] Therefore, in commercial elastomeric compositions conventional silicas distinguished by a surface area of less than 190 m2/g, generally between 155 and 185 m2/g, are generally used, precisely because they are more dispersible in the elastomeric matrix.

[0022] Elastomeric tire compositions containing such conventional low surface area silicas can be considered as a reference with regard to mechanical and dynamic properties, in particular with regard to abrasion and tear resistance.

[0023] The Applicant was able to verify that elastomeric compositions comprising eco-compatible silicas from rice husk ash, having conventional values of surface area and density after compaction, show significantly worse tear and abrasion resistance than elastomeric compositions containing silicas conventional.

[0024] However, the Applicant has surprisingly found that certain specific silicas with a larger surface area, which can be prepared from renewable sources, in particular from rice husk ash and precipitated with carbon dioxide, are not only well dispersible, even in the absence of pre-silanization, despite the high surface area and high silanol content, but above all they provide elastomeric compositions by incorporating them with better resistance to abrasion and tearing, without increasing rolling resistance or altering other important properties of the final tires. This increased resistance of elastomeric compositions in abrasion and tear tests translates advantageously into a longer useful life of the tires that incorporate them, in addition to a significant improvement in the eco-compatibility of the tires themselves.

[0025] Therefore, a first aspect of the present invention is a vulcanizable elastomeric composition for tires comprising at least: (a) 100 phr of an elastomeric diene polymer, (b) 1 to 150 phr of a silica having a BET surface area measured according to ISO 18852 greater than 190 m2/g, a density after compaction measured according to the method reported in the description greater than 220 g/l and a total water-soluble salt content measured according to the method reported in the lower description to 0.5% by weight, (c) 0 to 120 phr of an additional reinforcing filler, (d) 0.1 to 15 phr of a vulcanizing agent, and (e) 0 to 20 phr of a coupling agent .

[0026] Without wishing to be limited to any interpretative theory, the Applicant believes that, in addition to the high surface area and high density after compaction, even the low content of water-soluble salts allows eco-compatible silicas to both improve resistance to abrasion and tear resistance of the vulcanized elastomeric composition that incorporates them.

[0027] A second aspect of the present invention relates to a tire component for vehicle wheels comprising a vulcanizable elastomeric composition according to the first aspect or a vulcanized elastomeric composition, obtained by vulcanizing the vulcanizable elastomeric composition according to the first aspect.

[0028] A third aspect of the present invention relates to a vehicle wheel tire comprising at least one tire component according to the second aspect.

DETAILED DESCRIPTION OF THE INVENTION

[0029] For the purposes of the present description and the following claims, the term “phr” (parts per hundreds of rubber) means the parts by weight of a given component of the vulcanizable elastomeric composition per 100 parts by weight of the diene elastomeric polymer .

[0030] Unless otherwise indicated, all percentages are expressed as percentages by weight.

[0031] In the present description, the relative terms “high or greater surface area” and the like, where not otherwise specified, indicate a surface area of the silicas greater than 190 m2/g.

[0032] Likewise, the relative terms “low or lower surface area” and the like, where not otherwise specified, indicate a silica surface area of less than 190 m2/g.

[0033] In the present description, rice husk ash silica is also cited as “eco-compatible” silica as it is prepared from a renewable source and preferably precipitated with carbon dioxide, with the formation of fully recyclable by-products in the process itself. of preparation.

[0034] In the present description, the term “conventional silica” means a silica prepared from sand (fossil sources) and precipitated with strong inorganic acids (such as, for example, sulfuric acid).

[0035] In the present description, the term “green” is used to indicate a material, a composition, a component or a tire that has not yet been vulcanized.

[0036] In the present description, the phrase “composition comprising at least” followed by a list of several ingredients from different categories indicates that there may also be more than one of said ingredients from each category in the mixture (for example, one or more elastomeric polymers diene a), one or more silicas b), one or more reinforcing fillers c), one or more vulcanizing agents d), one or more coupling agents e) etc.).

[0037] According to a first aspect, the present invention relates to a vulcanizable elastomeric composition for tires.

[0038] The vulcanizable elastomeric composition for tires according to the present invention is distinguished by one or more of the following preferred aspects considered alone or in combination with each other.

[0039] The vulcanizable elastomeric composition for tires according to the present invention comprises 100 phr of at least one diene elastomeric polymer (a).

[0040] Preferably, the diene elastomeric polymer (a) that can be used in the present invention can be selected from those commonly used in sulfur vulcanizable elastomeric compositions, which are particularly suitable for the production of tires, that is, from elastomeric polymers or copolymers with an unsaturated chain having a glass transition temperature (Tg) generally below 20°C, preferably in the range of 0°C to -110°C. These polymers or copolymers may be of natural origin or may be obtained by solution polymerization, emulsion polymerization or gas phase polymerization of one or more conjugated diolefins, optionally mixed with at least one comonomer selected from monovinylarenes and/or polar comonomers in a quantity not exceeding 60% by weight.

[0041] Conjugated diolefins generally contain from 4 to 12, preferably from 4 to 8 carbon atoms and can be selected, for example, from the group comprising: 1,3-butadiene, isoprene, 2,3-dimethyl -1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, 3-butyl-1,3-octadiene, 2-phenyl-1,3-butadiene and mixture thereof.

[0042] 1,3-Butadiene and isoprene are particularly preferred.

[0043] Monovinylarenes, which can optionally be used as comonomers, generally contain from 8 to 20, preferably from 8 to 12 carbon atoms and can be selected, for example, from: styrene; 1- vinylnaphthalene; 2-vinylnaphthalene; various alkyl, cycloalkyl, aryl, alkylaryl or arylalkyl derivatives of styrene, such as, for example, α-methylstyrene, 3-methylstyrene, 4-propylstyrene, 4-cyclohexylstyrene, 4-dodecylestyrene, 2-ethyl-4-benzylstyrene , 4-p-tolyl-styrene, 4-(4-phenylbutyl) styrene and mixtures thereof. Styrene is particularly preferred.

[0044] Polar comonomers that can optionally be used can be selected, for example, from: vinylpyridine, vinylquinoline, acrylic acid and alkylacrylic acid esters, nitriles or mixtures thereof, such as, for example, methyl acrylate, acrylate ethyl methacrylate, methyl methacrylate, ethyl methacrylate, acrylonitrile and mixtures thereof.

[0045] Preferably, the diene elastomeric polymer (a) that can be used in the present invention can be selected, for example, from: cis-1,4-polyisoprene (natural or synthetic, preferably natural rubber), 3,4- polyisoprene, polybutadiene (in particular polybutadiene with a high 1,4-cis content), optionally halogenated isoprene/isobutene copolymers, 1,3-butadiene/acrylonitrile copolymers, styrene/1,3-butadiene copolymers , styrene/isoprene/1,3-butadiene copolymers, styrene/1,3-butadiene/acrylonitrile copolymers and mixtures thereof.

[0046] According to a preferred embodiment, said vulcanizable elastomeric composition, preferably for tread, comprises at least 10% by weight, preferably between 20% by weight and 100% by weight of natural rubber, relative to the total weight of said diene elastomeric polymer (a).

[0047] The above vulcanizable elastomeric composition may possibly comprise an elastomeric polymer of one or more monoolefins with an olefinic comonomer or derivatives (a') thereof. Monoolefins can be selected from: ethylene and α-olefins generally containing from 3 to 12 carbon atoms, such as, for example, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene and mixtures thereof. same. The following are preferred: copolymers selected from ethylene and an α-olefin, optionally with a diene; isobutene homopolymers or copolymers thereof with small amounts of a diene, which are optionally at least partially halogenated. The diene possibly present generally contains from 4 to 20 carbon atoms and is preferably selected from: 1,3-butadiene, isoprene, 1,4-hexadiene, 1,4-cyclohexadiene, 5-ethylidene-2-norbornene , 5-methylene-2-norbornene, vinylnorbornene and mixtures thereof. Among them, the following are particularly preferred: ethylene/propylene copolymers (EPR) or ethylene/propylene/diene copolymers (EPDM); polyisobutene; butyl rubber; halobutyl rubbers, in particular chlorobutyl or bromobutyl rubbers; or mixtures thereof.

[0048] A diene elastomeric polymer (a) or an elastomeric polymer (a') functionalized by reaction with suitable terminating agents or coupling agents can also be used. In particular, elastomeric diene polymers obtained by anionic polymerization in the presence of an organometallic initiator (in particular, an organolithium initiator) can be functionalized by reacting the residual organometallic groups derived from the initiator with suitable terminating agents or coupling agents, such as , for example, imines, carbodiimides, alkyltin halides, substituted benzophenones, alkoxysilanes or aryloxysilanes.

[0049] In a preferred embodiment, the diene elastomeric polymer (a) is a functionalized diene elastomeric polymer, preferably functionalized with mercapto groups.

[0050] The present elastomeric composition may comprise one or more diene elastomeric polymers (a) as defined above in a mixture.

[0051] The present vulcanizable elastomeric composition comprises silica (b) distinguished by a BET surface area measured in accordance with ISO 18852 greater than 190 m2/g and a total water-soluble salt content measured in accordance with the method described in the description of less than 0.5% by weight.

[0052] Preferably, the silica (b) is distinguished by a BET surface area greater than 195 m2/g, more preferably greater than 200 m2/g, even more preferably greater than 220 m2/g, 230 m2/g or 240 m2/g.

[0053] Preferably, the silica (b) is distinguished by a BET surface area of less than 300 m2/g, more preferably less than 290 m2/g, even more preferably less than 280 m2/g, 270 m2/g or 260 m2/g.

[0054] Preferably, the silica (b) is distinguished by a BET surface area of between 190 and 300 m2/g, more preferably between 195 and 300 m2/g, even more preferably between 220 and 280 m2/g.

[0055] In a particularly preferred embodiment, the silica (b) is distinguished by a BET surface area between 230 and 260 m2/g.

[0056] The Applicant found that silicas prepared from rice husk ash differ from conventional ones due to the salt content and, in particular, the reduced sodium, sulfur and aluminum content and higher potassium content.

[0057] Preferably, the silica (b) suitable for use in the present invention is distinguished by a total water-soluble salt content of less than 0.3% by weight, more preferably less than 0.2% by weight.

[0058] Preferably, the silica (b) is distinguished by a sulfur, sodium and aluminum content each independently less than 0.2%, more preferably less than 0.1% by weight, measured by X-ray fluorescence. X, as described in the experimental part (XRF analysis)

[0059] Preferably, the silica (b) is distinguished by a potassium content greater than 0.05%, more preferably greater than 0.10% by weight, measured by X-ray fluorescence, as described in the experimental part ( XRF analysis).

[0060] Silica (b) is distinguished by a density after compaction (compacted density) greater than 220 g/l, preferably greater than 230 g/l and/or less than 290 g/l, more preferably less than 280 g/l l.

[0061] Preferably, the silica (b) is distinguished by a density after compaction between 220 and 300 g/l, more preferably between 220 and 290 g/l, even more preferably between 230 and 280 g/l.

[0062] In a particularly preferred embodiment, the silica (b) is distinguished by a density after compaction between 240 and 280 g/l.

[0063] Preferably, the silica (b) is distinguished by a specific pore volume, per unit weight of silica, evaluated in the range of 15 to 45 nm, greater than 0.95 cm3/g, more preferably greater than 0 .98 cm3/g, even more preferably greater than 1.0 cm3/g.

[0064] Preferably, the silica (b) is distinguished by a silanol content of at least 3.0 mmol/g and/or not more than 4.5 mmol/g, more preferably of at least 3.5 mmol/g and /or not exceeding 4.1 mmol/g.

[0065] Preferably, the silica (b) is distinguished by a silanol content between 3.0 mmol/g and 4.5 mmol/g, more preferably between 3.5 mmol/g and 4.1 mmol/g.

[0066] Preferably, the silica (b) is distinguished by a silica (SiO2) content of at least 99.0%, more preferably at least 99.5% by weight.

[0067] In a preferred embodiment, the silica (b) is distinguished by a BET surface area of between 220 and 280 m2/g and a salt content of less than 0.2% by weight.

[0068] In a preferred embodiment, the silica (b) is distinguished by a BET surface area between 220 and 280 m2/g and a density after compaction between 240 and 280 g/l.

[0069] In a preferred embodiment, silica (b) is distinguished by a BET surface area between 220 and 280 m2/g and a specific pore volume greater than 1.0 g/cm3.

[0070] Preferably, the silica (b) is prepared from rice husk ash, more preferably it is prepared from rice husk ash by precipitation with carbon dioxide, adapting the teachings of WO2004073600A2 or WO2017179070A1 to obtain a silica distinguished by the above characteristics.

[0071] The person skilled in the art can easily select the conditions of the preparation process, such as, for example, the basic amount for solubilization, the flow of carbon dioxide, the temperature of the medium and the mixing speed thereof, which are best suited to provide the desired characteristics of silica.

[0072] These characteristics can be measured according to known methods, exemplified in the present experimental part, such as measuring the BET surface area, the total salt and silanol content, the specific pore volume and the density after compaction.

[0073] Optionally, but not necessarily, before incorporation into the elastomeric material, the silica (b) can be subjected to silanization to further improve compatibility.

[0074] The silanization agent can be selected from the silane coupling agents (e) listed below in the present description.

[0075] Preferably, silica (b) is incorporated into the elastomeric material without being silanized. Surprisingly, silica (b), despite the large BET surface area and high silanol content, has excellent dispersibility, even in the absence of silanization, as evidenced by the data reported in the present Table 9 and as corroborated by the good overall performance of the compositions. elastomeric.

[0076] According to the present invention, silica (b) is incorporated into the diene elastomeric polymer together with the other components to produce the vulcanizable elastomeric composition for tires.

[0077] Preferably, the present elastomeric composition comprises at least 5 phr, more preferably at least 10 phr, even more preferably at least 20 phr of silica (b).

[0078] Preferably, the present elastomeric composition comprises 5 to 130 phr, more preferably 10 or 80 phr of silica (b).

[0079] The present elastomeric composition may comprise one or more silicas (b) as defined above in a mixture.

[0080] The vulcanizable elastomeric composition according to the present invention may additionally comprise an additional reinforcing filler (c).

[0081] By “additional reinforcing filler” is meant a reinforcing filler commonly used in the tire industry, preferably selected from carbon black, conventional silica, such as sand silica precipitated with strong acids, preferably amorphous, earth diatomaceous earth, calcium carbonate, titanium dioxide, talc, alumina, aluminosilicates, kaolin, silicate fibers and mixtures thereof.

[0082] The vulcanizable elastomeric composition according to the present invention may not comprise an additional reinforcing filler (c).

[0083] In the case of understanding it, preferably the additional reinforcing filler is selected from carbon black, conventional silica, silicate fibers and mixtures thereof.

[0084] The additional reinforcing filler (c) may be present in the vulcanizable elastomeric composition in an amount generally ranging between 1 phr and 120 phr, preferably between 20 phr and 90 phr.

[0085] Preferably, particularly in the case of a tread composition, the present composition comprises at least 1 phr, more preferably at least 2 phr, more preferably at least 3 or 4 phr of carbon black, which advantageously protects the elastomer from aging caused by the action of ultraviolet radiation.

[0086] The present elastomeric composition may comprise one or more additional reinforcing fillers (c) as defined above in a mixture.

[0087] The vulcanizable elastomeric composition according to the present invention comprises at least one vulcanizing agent (d).

[0088] The most advantageously used vulcanizing agent is sulfur, or, alternatively, sulfur-containing molecules (sulfur donors), with accelerators, activators and/or retardants known to the person skilled in the art.

[0089] Sulfur or derivatives thereof can be advantageously selected, for example, from: (i) soluble sulfur (crystalline sulfur); (ii) insoluble sulfur (polymeric sulfur); (iii) sulfur dispersed in oil (such as 33% sulfur, known by the trade name Crystex OT33 from Eastman); (iv) sulfur donors such as, for example, caprolactam disulfide (CLD), bis[(trialkoxysilyl)propyl] polysulfides, dithiophosphates; and mixtures thereof.

[0090] The vulcanizing agent (d) is present in the vulcanizable elastomeric composition of the invention in an amount generally from 0.1 to 15 phr, preferably from 0.5 to 10 phr, even more preferably from 1 to 7 phr.

[0091] The present elastomeric composition may comprise one or more vulcanizing agents (d) as defined above in a mixture.

[0092] The vulcanizable elastomeric composition according to the present invention may optionally additionally comprise at least one silane coupling agent (e) capable of interacting with the silica and binding it to the diene elastomeric polymer during vulcanization.

[0093] Preferably, the vulcanizable elastomeric composition comprises at least one coupling agent.

[0094] Preferably, the silane coupling agent (e) that can be used in the present invention is selected from those that have at least one hydrolysable silane group, which can be identified, for example, by the following general formula (I): (R)3Si-CnH2n-X (I) where the R groups, which may be the same or different, are selected from alkyl, alkoxy or aryloxy groups or from halogen atoms, provided that at least one of the R groups is an alkoxy group or aryloxy or a halogen; n is an integer from 1 to 6, inclusive; " R groups are as defined above.

[0095] Among silane coupling agents, bis(3-triethoxysilylpropyl) tetrasulfide and bis(3-triethoxysilylpropyl) disulfide are particularly preferred. Said coupling agents may be used as such or in admixture with a suitable inert filler (such as carbon black) in order to facilitate their incorporation into the vulcanizable elastomeric composition.

[0096] Preferably, said silane coupling agent (e) is present in the vulcanizable elastomeric composition in an amount ranging between 0.1 phr and 20 phr, preferably between 0.5 phr and 10 phr.

[0097] The present elastomeric composition may comprise one or more coupling agents (e) as defined above in a mixture.

[0098] Preferably, the vulcanizing agent (d) is used in combination with accelerators (f) and activators (g) known to the person skilled in the art.

[0099] Accelerators (f) that are commonly used can be selected from: dithiocarbamates, guanidine, thiourea, thiazoles, sulfenamides, thiurams, amines, xanthates and mixtures thereof.

[00100] Preferably, vulcanization accelerators are present in the vulcanizable elastomeric composition of the invention in amounts of 0.1 to 8 phr, preferably 0.3 to 6 phr.

[00101] Activators (g) that are particularly effective are zinc compounds, and in particular ZnO, ZnCO3, zinc salts of saturated or unsaturated fatty acids containing 8 to 18 carbon atoms, such as, for example, stearate of zinc, which are preferably formed in situ in the vulcanizable elastomeric composition of ZnO and fatty acid, as well as Bi2O3, PbO, Pb3O4, PbO2 or mixtures thereof.

[00102] Preferably, vulcanization activators are present in the vulcanizable elastomeric composition of the invention in amounts of 0.2 to 15 phr, preferably 0.5 to 10 phr.

[00103] The present elastomeric composition may comprise one or more accelerators (f) and activators (g) as defined above in a mixture.

[00104] Finally, the vulcanizable elastomeric compositions described above may comprise other commonly used additives, selected based on the specific application for which the composition is intended. For example, said materials can be mixed with: antioxidants, anti-aging agents, plasticizers, adhesives, anti-ozone agents, modifying resins or mixtures thereof.

[00105] In particular, in order to further improve processability, said vulcanizable elastomeric composition can be mixed with at least one plasticizer generally selected from mineral oils, vegetable oils, synthetic oils, polymers with a low molecular weight and mixtures thereof. , such as, for example, aromatic oil, naphthenic oil, phthalates, soybean oil and mixtures thereof. The amount of plasticizer generally varies from 0 phr to 70 phr, preferably from 5 phr to 30 phr.

[00106] As shown in the experimental part (Tables 7 and 8), the elastomeric tire composition according to the invention is distinguished by improved resistance to abrasion and tearing.

[00107] In a preferred embodiment, for tread, the present vulcanizable elastomeric composition for tires comprises at least: (a) 100 phr of a diene elastomeric polymer, preferably functionalized, (b) 5 to 130 phr of a silica with a BET surface area measured according to ISO 18852 greater than 190 m2/g and a total water-soluble salt content measured according to the method reported in the present description less than 0.5% by weight, (c) 1 to 120 phr of an additional reinforcing filler, (d) 0.1 to 15 phr of a vulcanizing agent, and (e) 0.4 to 20 phr of a coupling agent.

[00108] The elastomeric composition of the invention can be prepared by mixing the polymeric components with the reinforcing filler and other additives possibly present in accordance with techniques known in the industry. Mixing can be carried out, for example, using an open mixer of the “open mill” type or an internal mixer of the type with tangential rotors (Banbury®) or with interpenetrating rotors (Intermix), or in continuous mixers of the Ko-Tipo type. Kneader™ (Buss®) or twin-screw or multi-screw type.

[00109] A second aspect of the present invention relates to a tire component for vehicle wheels comprising a vulcanizable elastomeric composition as described above (green component) or a vulcanized elastomeric composition, which can be obtained by vulcanizing the same (vulcanized component ).

[00110] The vulcanizable elastomeric compositions of the invention can be vulcanized according to known techniques, due to the presence of sulfur-based vulcanization systems commonly used for diene elastomeric polymers. For this purpose, after one or more thermomechanical treatment steps, a vulcanization agent, preferably sulfur-based, is preferably incorporated into the materials, preferably together with vulcanization accelerators.

[00111] In the final treatment step, the temperature is generally maintained below 120°C and preferably below 100°C, in order to prevent any undesirable pre-crosslinking phenomena. After that, the vulcanizable composition is incorporated into one or more components of the tire and subjected to vulcanization, according to known techniques.

[00112] The tire component according to the invention is preferably selected from the tread, bottom layer, anti-abrasive elongated element, sidewall, sidewall insert, mini sidewall, bottom liner, rubber layers, bead load and sheet, more preferably from between the tread, backsheet and sidewall insert, even more preferably the component is a tread.

[00113] A third aspect of the present invention relates to a tire for vehicle wheels comprising at least one tire component according to the invention, preferably selected from the tread, bottom layer, elongated anti-abrasive element, wall sidewall, sidewall insert, mini sidewall, bottom liner, rubber layers, bead and sheet filler.

[00114] Preferably, in the tire according to the invention, at least the tread comprises or preferably consists of the green or vulcanized elastomeric composition according to the invention.

[00115] Preferably, in the tire according to the invention, at least the tread and at least one component selected from the lower layer, anti-abrasive elongated element, sidewall, sidewall insert, mini sidewall, lower lining, layers of rubber, bead filler and the sheet comprise the elastomeric composition according to the invention.

[00116] A vehicle tire according to the present invention comprises at least - one carcass structure comprising at least one carcass ply having opposing side edges associated with the respective bead structure; - a belt structure applied in a radially external position with respect to the carcass structure, - a tread applied in a radially external position with respect to said belt structure, wherein at least said tread comprises the elastomeric composition according with the invention.

[00117] An embodiment according to the present invention refers to a tire for high-performance vehicles (HP, SUV and UHP), in which at least one component, preferably at least the tread, comprises the elastomeric composition of according to the invention.

[00118] An embodiment according to the present invention relates to a tire for heavy vehicles in which at least one component, preferably at least the tread, comprises the elastomeric composition according to the invention.

[00119] The tire according to the invention can be a tire for two- or four-wheel vehicles.

[00120] The tire according to the invention can be for use in summer or winter or for all seasons.

[00121] The tire according to the present invention can be manufactured according to a process comprising: - constructing components of a green tire in at least one forming drum; - conform, mold and vulcanize the tire; wherein constructing at least one of the components of a green tire comprises: - manufacturing at least one green component comprising the vulcanizable elastomeric composition of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[00122] Figure 1 shows a half radial section of a tire for vehicle wheels, comprising a silica as defined in the first aspect of the invention, preferably in the tread.

[00123] Figure 2 is a graph showing the volumetric distribution of pores when varying the pore radius in conventional silicas (S2, S3), in a low surface rice husk ash silica (S4) and in a silica as defined in the first aspect of the invention (S6). On the graph, the ordinate shows dV/dR (variation in pore volume with variation in radius cm3/g.nm), the abscissa shows the pore radius R (nm).

[00124] Figure 1 shows a half radial section of a tire for vehicle wheels according to the invention.

[00125] In Figure 1, “a” indicates an axial direction and “X” indicates a radial direction, in particular X-X indicates the contour of the equatorial plane. For simplicity, Figure 1 shows only a part of the tire, the remaining part not shown being identical and arranged symmetrically with respect to the “X-X” equatorial plane.

[00126] The four-wheel vehicle tire 100 comprises at least one carcass structure, comprising at least one carcass layer 101 having, respectively, opposing end flaps engaged with respective annular anchor structures 102, referred to as bead cores. , possibly associated with a bead charge 104.

[00127] The carcass layer 101 is optionally made with an elastomeric composition.

[00128] The area of the tire comprising the bead core 102 and the load 104 forms a bead structure 103 intended to anchor the tire to a corresponding mounting rim, not shown.

[00129] The structure of the carcass is generally of the radial type, that is, the reinforcing elements of at least one layer of the carcass 101 lie in planes comprising the axis of rotation of the tire and substantially perpendicular to the equatorial plane of the tire. Said reinforcing elements generally consist of textile cords, such as rayon, nylon, polyester (e.g. polyethylene naphthalate, PEN). Each granule structure is associated with the carcass structure by folding back opposing side edges of at least one carcass layer 101 around the annular anchoring structure 102 so as to form so-called carcass flaps 101a as shown in Figure 1.

[00130] In one embodiment, the coupling between the carcass structure and the bead structure may be provided by a second carcass layer (not shown in Figure 1) applied in an axially external position relative to the first carcass layer.

[00131] An anti-abrasive strip 105 optionally made with an elastomeric composition is disposed in an external position of each granule structure 103.

[00132] The carcass structure is associated with a belt structure 106 comprising one or more belt layers 106a, 106b placed in radial overlap with respect to each other and with respect to the carcass layer, typically having textile reinforcement cords and/or or metals incorporated within a layer of vulcanized elastomeric material.

[00133] Such reinforcing cords may have a cross orientation with respect to a circumferential development direction of the tire 100. By “circumferential” direction is meant a direction generally facing the direction of rotation of the tire.

[00134] At least one zero degree reinforcing layer 106c, commonly known as a “0° belt”, may be applied at a radially outermost position to the belt layers 106a, 106b, which generally incorporate a plurality of reinforcement elements. elongated reinforcement, typically metallic or textile cords, oriented in a substantially circumferential direction, thus forming an angle of a few degrees (such as an angle between about 0° and 6°) with respect to a direction parallel to the equatorial plane of the tire, and coated with vulcanized elastomeric material.

[00135] A tread 109 of vulcanized elastomeric material is applied in a position radially external to the belt structure 106.

[00136] Furthermore, respective sidewalls 108 of vulcanized elastomeric material are applied in an axially external position to the side surfaces of the carcass structure, each extending from one of the side edges of the tread 109 into the respective cord structure 103 .

[00137] In a radially outward position, the tread 109 has a bearing surface 109a intended to come into contact with the ground. Circumferential grooves, which are connected by transverse notches (not shown in Figure 1) so as to define a plurality of blocks of various shapes and sizes distributed along the bearing surface 109a, are generally made on this surface 109a, which for simplicity is represented as smooth in Figure 1.

[00138] A lower layer 111 of vulcanized elastomeric material may be disposed between the belt structure 106 and the tread 109.

[00139] A strip consisting of the elastomeric composition 110, commonly known as a “mini sidewall”, of vulcanized elastomeric material may be optionally provided in the connection zone between the sidewalls 108 and the tread 109, this mini sidewall generally being obtained by coextrusion with the tread 109 and allowing an improvement in the mechanical interaction between the tread 109 and the sidewalls 108. Preferably, the end portion of the sidewall 108 directly covers the lateral edge of the tread 109.

[00140] In the case of tubeless tires, a layer of rubber 112, generally known as a “lining”, which provides the necessary impermeability to tire inflation air, can also be provided in a radially internal position in relation to the carcass layer. 101.

[00141] The stiffness of the tire sidewall 108 can be improved by providing the bead structure 103 with a reinforcing layer 120 generally known as a “pick” or additional strip-shaped insert.

[00142] The vane 120 is a reinforcing layer which is wound around the respective bead core 102 and the bead load 104 so as to at least partially enclose them, said reinforcing layer being disposed between the at least one casing layer 101 and bead structure 103. Typically, the reed is in contact with said at least one casing layer 101 and said bead structure 103.

[00143] The reed 120 typically comprises a plurality of textile cords embedded within a layer of vulcanized elastomeric material.

[00144] The tire bead structure 103 may comprise an additional protective layer which is generally known by the term “lining” 121 or protective strip and which has the function of increasing the rigidity and integrity of the bead structure 103.

[00145] The cover 121 generally comprises a plurality of cords embedded within a rubber layer of vulcanized elastomeric material. These cords are generally made from textile materials (such as aramid or rayon) or metallic materials (such as steel cables).

[00146] A layer or sheet of elastomeric material can be disposed between the belt structure and the carcass structure. The layer may be of uniform thickness. Alternatively, the layer may have a variable thickness in the axial direction. For example, the layer may have a greater thickness near its axially outer edges relative to the central zone (crown).

[00147] Advantageously, the layer or sheet may extend over a surface that substantially corresponds to the extending surface of said belt structure.

[00148] In a preferred embodiment, a layer or sheet of elastomeric material as described above may be placed between said belt structure and said tread, said additional layer or sheet preferably extending on a surface substantially corresponding to the surface length of said belt structure.

[00149] The elastomeric composition according to the present invention can be advantageously incorporated into one or more of the tire components selected from the belt structure, carcass structure, tread, bottom layer, sidewall, mini sidewall, insert of sidewall, bead, vane, lining, sheet and anti-abrasive strip, preferably incorporated at least in the tread and/or in the lower layer.

[00150] According to an embodiment not shown, the tire may be a tire for motorcycle wheels which is typically a tire that has a straight section having a high tread camber.

[00151] According to an embodiment not shown, the tire may be a tire for wheels of heavy transport vehicles, such as trucks, buses, trailers, vans and, in general, for vehicles in which the tire is subject to a load high.

[00152] Preferably, this tire is adapted to be mounted on wheel rims with a diameter equal to or greater than 17.5 inches for directional or trailer wheels.

[00153] The description of some preparative examples of the invention or comparative example, provided for illustrative and non-limiting purposes only, is presented below.

Characterization of silicas

[00154] The silicas used in the comparative or inventive examples described here were distinguished with one or more of the following analytical techniques:

Surface area (BET)

[00155] The BET surface area (m2/g) was measured in accordance with ISO18852 using the Micromeritics TriStar II Plus device. The sample was subjected to a degassing pretreatment at 170°C for 2h under nitrogen flow.

[00156] Table 2 shows the total surface area values (multipoint in the range between P/P00.08 and 0.2) measured for the S1-S6 silicas used here.

Water-soluble salt content

[00157] The content of water-soluble salts (% by weight) of the silicas considered here was determined according to the following internal method: a sample of silica, previously dried in an oven at 105°C until a constant weight of ca. 10 g was weighed and placed in a 250 ml beaker with 100 ml of distilled water under stirring for one hour. It was filtered with a paper filter and 50 ml of the filtrate was placed in a previously dried capsule with constant weight. The water was evaporated in a bath with boiling water, the capsule was cooled in a dryer, the capsule was weighed and the soluble salt residue was calculated, expressed as a percentage by weight in relation to the initial weight.

[00158] Table 2 shows the soluble salt content values of the S2-S6 silicas used here.

Silanol content

[00159] The silanol content (mmol/g) was calculated based on the water loss of the sample measured by thermogravimetry (TGA) according to the following internal method: a first heating was carried out according to a thermal ramp of 25° C to 170°C at 5°C/min and a second from 170°C to 800°C at 10°C/min; the silanol content was calculated by dividing the weight of the sample at the end of the second ramp by the weight of the dry sample (at the end of the first ramp or the initial weight of the sample decreased by the weight of water lost in the heating) and finally dividing by the molecular weight of the silica.

[00160] Table 2 shows the silanol content values for the S2-S6 silicas used here.

Density after compaction (compacted density)

[00161] The density after compaction was determined according to the following method.

[00162] A sufficient amount of product was taken to perform two determinations. The empty cylinder was weighed to the nearest 0.1 g. 200 ± 10 ml of product was added to the cylinder so that no air pockets were formed and the cylinder containing the product was weighed to the nearest 0.1 g. The cylinder containing the product was placed on the support, activating the Quantachrome Instruments Autotap device and performing 2500 strokes. At the end, the volume occupied by the product under test was read on the cylinder. From the final volume and weight values of the sample, the density after compaction was calculated.

[00163] Table 2 shows the density values after compaction for the S2-S6 silicas used here.

pH measurement

[00164] The pH was measured according to an internal method: an aqueous suspension of 5% silica was prepared in a 150 ml beaker, stirred for 5' and the pH was measured with a calibrated electrode, at room temperature and under continuous stirring.

[00165] Table 3 shows the pH values of the aqueous suspensions of silicas S2-S6 used here.

Weight loss by heating

[00166] The weight loss of silica at 105°C was determined according to the following procedure: a known amount of silica was weighed, and the sample was then heated in an oven for 2 hours at 105°C. After cooling in a desiccator, the sample was weighed and the difference between the initial and final weight expressed in % represents the weight loss at 105°C.

[00167] Weight loss by calcination at 900°C was determined by weighing 2 g of silica and calcining the sample in a muffle furnace at 900°C until constant weight. The difference between the initial weight and the weight after calcination in relation to the initial weight expressed in % represents the weight lost by calcination.

[00168] Table 3 shows the % weight loss values at 105°C and 900°C of the silica samples S2-S6 used here.

Specific volume and pore size distribution

[00169] The distribution of the total volume of silica pores was evaluated as a function of its radius expressed in nm, through nitrogen adsorption and desorption across the entire relative pressure range, and applying the BJH calculation system, as described in article “The Determination of Pore Volume and Area Distributions in Porous Substances. I. Computations from Nitrogen Isotherms,” Journal of the American Chemical Society, January 1951, vol. 73, pp. 373-380 (Barrett, Joyner, Halenda). The analysis was performed with the Micromeritics TriStar II Plus device.

[00170] The curves shown in the graph in Figure 2, extrapolated under desorption conditions, show that silica S6, with the requirements for the use of the invention, in the range between 15 and 45 nm, presents a distribution with a greater total volume of pores compared to conventional commercial large surface area silicas (S2, S3) and comparative rice husk ash silica S4.

[00171] Table 3 shows the total pore volume values with radii between 15 and 45 nm for silica samples S2, S3, S4 and S6.

XRF Analysis

[00172] The silica samples were analyzed with a Bruker AXS S4 Pioneer apparatus by X-ray fluorescence with detection of the elements shown in Table 4.

Description and characterization of silicas

[00173] The silicas analyzed and used in the present experimental part are shown in the following Table 1: Table 1 C: comparative (conventional silica or not meeting the requirements of the silica used in the present invention); I: invention (silica having the necessary requirements for use in the present invention).

[00174] Silicas S1-S3 and S7 are conventional commercial silicas, commonly used as reinforcing fillers in elastomeric compositions for tires.

[00175] Silicas S4-S6 are environmentally friendly silicas from rice husk ash produced by the Indian Institute of Science.

[00176] Silicas S1-S7 have the properties detailed in the following Tables 2, 3 and 4: Table 2

[00177] Conventional silicas S1, S2 and S7 have a smaller BET surface area than the silicas used in the invention (with a surface area of at least 190 m2/g).

[00178] S3 silica, although it has a BET surface area in accordance with the requirements of the silicas used in the invention, has a high soluble salt content.

[00179] S4 silica, although it is eco-compatible, does not have a BET surface area in accordance with the requirements of the silicas used in the invention, that is, it does not have a BET surface area greater than 190 m2/g, but less (162 m2/g), according to the area values of commonly used commercial high-dispersibility silicas. It also has a high salt content.

[00180] The eco-compatible silicas S5 and S6, despite the high surface area and high silanol content, showed excellent dispersibility in the elastomeric matrix, as also shown by the values shown below in Table 9. Table 3 * R pore radius: 15 - 45 nm

[00181] The total pore volume values shown in Table 3 correspond to the area underlying the curves shown in the graph in Figure 2.

[00182] As can be seen from this graph, silica S6 presents pores with a more homogeneous volume, in particular it is observed that in S6 pores with radii between 15 and 45 nm prevail while in the other silicas S2, S3 and S4 a different distribution of dimensions of the pores are seen. The prevalence of pores with a radius of 15 to 45 nm in S6 silica may be one of the possible reasons for the unexpected improvement in its dispersibility in the elastomeric matrix. Table 4: XRF analysis (wt%)

[00183] From the values shown in Table 4, it appears that in commercial silicas precipitated with sulfuric acid (S2, S3) the sulfur and sodium content is decidedly higher, even by an order of magnitude, while potassium is most abundant in eco-friendly silicas from carbon dioxide precipitated shells (S5, S6).

Preparation of elastomeric compositions for tread (summer tires)

[00184] The vulcanizable elastomeric compositions of the following examples were prepared according to the methods described here. The amounts of the various components are presented in phr.

[00185] Mixing was carried out in three stages using an internal tangential rotor mixer (Pomini PL 1.6): in the first stage, polymers, fillers, silane, stearic acid and TDAE oil were introduced and mixing was continued for 2-3 minutes , until reaching 140°C ± 5°C, when the composition was discharged. After 12-24 hours, in the second step, carried out using the same mixer, Zn octoate, Zn stearate, alpha-methylstyrene resin, paraffin wax, 6-PPD and TMQ were introduced and mixing was continued for about 3 minutes, until reaching 125°C ± 5°C, when the composition was discharged. After 12-24 hours, in the third stage conducted in the same mixer, TBBS and sulfur were introduced and mixing continued for about 2 minutes, until reaching 95°C ± 5°C, when the composition was discharged.

Example 1

[00186] Conventional sand silicas (S2 and S3, comparative) and eco-compatible rice husk ash (S6 with the requirements according to the use of the invention) were incorporated into elastomeric tread compositions for tire tires. summer, according to the procedure described above.

[00187] In particular, the compositions of Example 1A (comparative) included only silica S2 (commercial silica Ultrasil 7000 sand, precipitated with sulfuric acid, with high dispersibility and low surface area), the composition of Example 1C (comparative) only silica S3 (commercial silica Zeosil Premium 200MP high dispersibility, sand, precipitated with sulfuric acid, surface area and high salt content) while the composition of Example 1B (invention) silica S2 and in its partial replacement (20 phr) silica S6 ( from rice husk ash, precipitated with carbon dioxide, with a high surface area and low salt content), as shown in Table 5 below: Table 5: elastomeric compositions (phr) where NR (natural rubber): SIR20 natural rubber (Indonesia); S-SBR SLR 4602: styrene-butadiene rubber produced by Trinseo, synthesized in solution, containing around 20% styrene, functionalized with sulfur derivatives; Tg of about -25°C; TESPT silane: Bis[3-(triethoxysilyl)propyl] tetrasulfide SI69 produced by Evonik Industries AG; Zinc stearate: Struktol A 50 produced by Struktol Co; Stearic acid: Radiacid 444 produced by Oleon NV; Zinc octoate: Struktol ZEH 75 produced by Struktol Co; Paraffin wax: Riowax bm-01 produced by SER SpA; TDAE: Treated distilled aromatic extract, Vivatec 500 produced by Hansen & Rosenthal KG; Alpha-methylstyrene resin: Impera 1504 produced by Eastmann Chemical Co.; TMQ: Vulkanox HS/LG polymerized 2,2,4-trimethyl-1,2-dihydroquinoline produced by Lanxess GmbH; 6-PPD: phenyl-p-phenylenediamine, Santoflex 6PPD produced by Eastman Chemical Co.; TBBS: N-tert-butyl-2-benzothiazylsulfenamide produced by Rhein Chemie GmbH; Sulfur; Multisperse S-IS70P produced by Omya SpA

Example 2

[00188] Conventional silicas from sand (S2, comparative) or rice husk ash (S4, with low surface area, comparative and S6, with the requirements according to the use of the invention) were incorporated into band compositions. elastomeric tread for summer tires in accordance with the procedure described above.

[00189] In particular, the compositions of Example 2A (comparative) included only silica S2 (commercial silica Ultrasil 7000 sand, precipitated with sulfuric acid, with high dispersibility and low surface area), the composition of Example 2C (comparative) only silica S4 (silica from rice husk ash, precipitated with carbon dioxide, with a low surface area) while the composition of Example 2B (invention), only silica S6 (from rice husk ash, precipitated with carbon dioxide , with a high surface area and low salt content), as shown in the following Table 6: Table 6: Elastomeric compositions (phr) where NR (natural rubber): SIR20 natural rubber (Indonesia); S-SBR SLR 4602: styrene-butadiene rubber produced by Trinseo, synthesized in solution, containing around 20% styrene, functionalized with sulfur derivatives; Tg of about -25°C; TESPT silane: Bis[3-(triethoxysilyl) tetrasulfide SI69 produced by Evonik Industries AG; Zinc stearate: Struktol A 50 produced by Struktol Co.; Stearic acid: Radiacid 444 produced by Oleon NV; Zinc octoate: Struktol ZEH 75 produced by Struktol Co; Paraffin wax: Riowax bm-01 produced by SER SpA; TDAE: Treated Distilled Aromatic Extract, Vivatec 500 produced by Hansen & Rosenthal KG; Alpha-methylstyrene resin: Impera 1504 produced by Eastmann Chemical Co.; TMQ: Vulkanox HS/LG polymerized 2,2,4-trimethyl-1,2-dihydroquinoline produced by Lanxess GmbH; 6-PPD: phenyl-p-phenylenediamine, Santoflex 6PPD produced by Eastman Chemical Co.; TBBS: N-tert-butyl-2-benzothiazylsulfenamide produced by Rhein Chemie GmbH; Sulfur Multisperse S-IS70P produced by Omya SpA

Example 3

[00190] Conventional sand silicas (S2, S3 and S7) were incorporated into the first phase of an elastomeric tread pattern composition, according to the procedure described below.

[00191] Mixing was carried out in a single step using an internal tangential rotor mixer (Pomini PL 1.6): the polymer, filler, silane, stearic acid, TDAE oil and resin were introduced. Mixing continued for 2-3 minutes, until reaching 140°C ± 5°C, when the composition was discharged.

[00192] In particular, composition 3A comprises only silica S7 (commercial silica Zeosil 1115 MP sand, precipitated with sulfuric acid, with high dispersibility and low surface area), composition 3B only silica S2 (commercial silica Ultrasil 7000 GR with high dispersibility), sand, precipitated with sulfuric acid, with an intermediate surface area) and composition 3C only silica S3 (commercial silica Zeosil Premium 200 MP with high dispersibility, precipitated with sulfuric acid, with high surface area), as per illustrated in the following Table 7: Table 7: elastomeric compositions (phr) S-SBR SLR 3402: SBR produced by Trinseo, synthesized in solution, having around 15% styrene, functionalized and Tg of around - 60°C; TESPT silane: Bis[3-(triethoxysilyl)propyl] tetrasulfide SI69 produced by Evonik Industries AG; TDAE: Treated distilled aromatic extract, Vivatec 500 produced by Hansen & Rosenthal KG; Stearic Acid Radiacid 444 produced by Oleon NV; Impera 1504 alpha-methylstyrene resin produced by Eastmann Chemical Co.

Characterization of elastomeric compositions

[00193] The vulcanizable elastomeric compositions (green) of Examples 1 and 2 were subjected to the following evaluations: Mooney ML viscosity (1 + 4) at 100°C: it was measured in accordance with the ISO 289-1:2005 standard.

[00194] MDR rheometric analysis (according to ISO 6502) using an MDR2000 type rheometer from Alpha Technologies, tests were carried out at 170°C for 20 minutes at an oscillation frequency of 1.66 Hz (100 oscillations per minute ) and an oscillation amplitude of ± 0.5°, measuring the time necessary to reach respectively 30% (T30), 60% (T60) and 90% (T90) of the final torque value (Mf). The maximum torque value MH and the minimum torque value ML (dN.m) were also measured.

[00195] The elastomeric compositions of Examples 1 and 2 were subjected after vulcanization at 170°C for 10 minutes to the following evaluations:

Dispersion (automated image analysis)

[00196] From a vulcanized sample of the elastomeric composition, two sections, each 1 micron thick and dimensions 2 mm x 2 mm, were obtained by cold microtomy (-70°C). The sections were stretched on a slide and, with a transmitted light microscope at 100x, 10 images (in the order of 800 x 900 microns) were obtained at different points of the samples. Images are analyzed to assess silica dispersion with Media Cybernetic's Image Pro Plus software. The % undispersed silica was then calculated as the sum of the light areas with dimensions greater than 7 microns compared to the introduced silica.

[00197] The number of aggregates is calculated as a count of light aggregates with dimensions greater than 7 microns.

[00198] Static mechanical properties were measured at 23°C in accordance with ISO 37: 2005.

[00199] Tensile tests were performed on ring specimens (Ring Tensile Test 23°C). In particular, the load was measured at different elongation levels (50%, 100% and 300%, referred to in the sequence as CA05 - CA1 - CA3), the load at break CR and the elongation at break AR.

[00200] Dynamic mechanical properties were measured using an Instron dynamic device in tension-compression mode according to the following methods. A sample of each of the green elastomeric compositions of Examples 1 and 2 vulcanized at 170°C for 10 minutes with a cylindrical shape (length = 25 mm; diameter = 14 mm), preload compression of up to 25% of the longitudinal strain with respect to the initial length and maintained at the predetermined temperature (equal to 10°C, 23°C or 70°C) for the entire duration of the test, it was subjected to a dynamic sinusoidal deformation with an amplitude of ±3.5% with in in relation to length under preload, with a frequency of 100 Hz.

[00201] Dynamic mechanical properties are expressed in terms of dynamic modulus of elasticity (E') and Tan delta (dissipation factor). The Tan delta value was calculated as a ratio between the viscous modulus (E'') and the elastic modulus (E').

Abrasion resistance

[00202] The abrasion resistance of the compositions was measured according to the method of DIN 53516 (volume loss, mm3)

Tear resistance (peel test)

[00203] Tear resistance was evaluated by measuring with a dynamometer the separation force between two sheets of the same composition, green-coupled and co-vulcanized at 170°C for 10'. The samples were conditioned at 100°C (+/- 2°C) for at least 16 hours and subjected to the peeling test on a Zwick Z005 dynamometer, whose clamps were applied to the free section of each leaf. A pulling speed of 260 mm/min (+/- 20 mm/min) was then applied and the peeling force values, expressed in Newton (N), were measured as the average value calculated for the two samples.

[00204] Samples were prepared as described here.

[00205] The non-vulcanized elastomeric composition was calendered to obtain a sheet with a thickness of 3 mm (+/- 0.2 mm). From the sheet thus produced, pieces measuring 220 mm (+/- 1.0 mm) x 220 mm (+/- 1.0 mm) x 3 mm (+/- 0.2 mm) were obtained, marking the calendering direction .

[00206] One surface of each piece was protected with a polyethylene sheet, while on the opposite surface a rubber-reinforced polyamide coated fabric with a thickness of 0.88 mm (+/- 0.05 mm) was applied, orienting the threads in the calendering direction and winding the composite thus assembled in order to obtain good adhesion between the fabric and the non-vulcanized elastomeric composition.

[00207] After cooling, from the composite thus obtained, sheets were produced by cutting and creasing, with dimensions equal to 110 mm (+/- 1.0 mm) x 25 mm (+/- 1.0 mm) x 3.88 mm (+/- 0.05 mm), taking care that the long axis of each sheet is oriented towards the fabric threads.

[00208] A first sheet constituting the first layer and made as described above was placed in a mold with the polyamide layer facing the mold, the polyethylene film was removed, two strips of polyethylene terephthalate (Mylar®) acting as Side separators (0.2 mm thick) were applied laterally and a third strip of Mylar® (0.045 mm thick) was applied to one end of the sheet in order to create a small free stretch non-adherent to the second layer.

[00209] A second sheet constituting the second layer, composed of the same vulcanizable elastomeric composition as the first layer and from which the polyethylene film was previously removed, was then applied to the first sheet in the mold, thus obtaining a sample that was then vulcanized by heating at 170°C for 10 minutes in a press.

[00210] In the following Tables 8 and 9, the results of the analyzes described above for the samples of the compositions according to Examples 1 and 2 are reported.

[00211] The values of the measurements of E', tan d, abrasion resistance and tear resistance were recalculated by setting the values obtained with the composition of Example 1A (containing conventional silica S2) taken as a reference equal to 100. Table 8: properties of compositions of Example 1

[00212] As can be seen from the data reported in Table 8, the tread composition of Example 1B containing silica S6, with the requirements for use in the invention, has static and dynamic mechanical properties in line with the composition of Example 1A containing commercial silica with high dispersibility and low surface area of reference S2, with hysteresis values at 70°C, predictive of rolling resistance, and at 10°C, predictive rather of wet grip, which are comparable.

[00213] The abrasion resistance of the elastomeric composition of the invention (Example 1B) is comparable to that of the standard reference composition (Example 1A), although it is worse for the composition of Example 1C comprising S3 (conventional commercial large surface area silica).

[00214] The tear resistance (peeling) of the composition of Example 1B appears to have been decidedly improved in relation to the reference composition of Example 1A, although in it only 20 phr of the conventional silica S2 was replaced by the silica S6 from rice husk of large surface area according to the invention.

[00215] Finally, the composition of Example 1C, which comprises a conventional silica with a high surface area S3, but with an excessive salt content, is decidedly deteriorating in relation to its abrasion resistance.

[00216] From these data, it can be seen that silicas that are eco-compatible with the requirements selected here (high surface area and lower salt content) are indeed capable of providing better abrasion and tear resistance to elastomeric compositions, even if used in small quantities. Table 9: properties of the compositions of Example 2

[00217] As can be seen from the data reported in Table 9, the tread composition according to the invention of Example 2B, which contains rice husk ash silica S6 with a high surface area, has mechanical properties static and dynamic characteristics generally in line with those of the composition of Example 2A - comprising conventional commercial silica S2 with a lower surface area - and the composition of Example 2C - comprising rice husk ash silica S4 with a lower surface area.

[00218] However, with regard to the comparative compositions of Examples 2A and 2C, the composition of the invention of Example 2B surprisingly has a better resistance to abrasion and tearing and, considering the hysteresis values at 10°C, an adhesion of the tire in predictable wet conditions that is comparable, if not better.

[00219] Furthermore, from the data on the dispersion of silicas in the elastomeric matrix reported above, it can be seen that the rice husk silica S6 selected here has excellent dispersibility, even better than the commercial sand silica S2 - defined as “highly dispersible”, although S6 silica has a greater surface area and higher silanol content than S2 (253 m2/g vs 173 m2/g; 4.1 mmol/g vs 2.5 mmol/g ), characteristics considered detrimental to the compatibility of silica with the small polar elastomeric matrix. Table 10: Processability. of the compositions of Example 3

[00220] Mooney viscosity is a physical property typically used to describe the processability of elastomeric compositions. In the case of the conventional silicas tested here, as can be seen from the data reported in Table 10, there is a direct correlation between the surface area of the silica and the Mooney MS viscosity values (expressed in MU-Mooney Unit): the higher the surface area, the higher (worse) the viscosity values. In particular, the elastomeric composition 3C containing silica S3 (Zeosil Premium 200 MP, with a high surface area) shows high Mooney MS viscosity values, confirming the difficult processability in relation to the other compositions 3A and 3B containing silicas with a lower surface area. and the tendency for viscosity to increase with increasing surface area.

[00221] In conclusion, the elastomeric compositions according to the invention, containing more environmentally friendly specific silicas from rice husks, with high surface area and density, allow the production of tires with general performances similar to those of conventional tires comprising conventional commercial silicas with high dispersibility and lower surface area, in particular tires with comparable rolling resistance but longer service life due to the unexpected improvement in abrasion and tear resistance provided by these silicas.

Claims (15)

1. Vulcanizable elastomeric composition for tires, characterized in that it comprises at least: (a) 100 phr of an elastomeric diene polymer, (b) 1 to 150 phr of a silica having a BET surface area measured in accordance with ISO 18852 greater than 190 m2/g, a density after compaction (compacted density) measured according to the method reported in the description greater than 220 g/l and a total water-soluble salt content measured according to the method reported in the description less than 0 .5% by weight, (c) 0 to 120 phr of an additional reinforcing filler, (d) 0.1 to 15 phr of a vulcanizing agent, and (e) 0 to 20 phr of a coupling agent. 2. Composition according to claim 1, characterized by the fact that the diene elastomeric polymer (a) is a functionalized diene elastomeric polymer. 3. Composition according to claim 2, characterized by the fact that the elastomeric diene polymer (a) is functionalized with mercapto groups. 4. Composition according to any one of the preceding claims, characterized by the fact that the silica (b) is distinguished by a BET surface area greater than 195 m2/g. 5. Composition according to any one of the preceding claims, characterized by the fact that the silica (b) is distinguished by a BET surface area of less than 300 m2/g. 6. Composition according to any one of the preceding claims, characterized by the fact that the silica (b) is distinguished by a total content of water-soluble salts measured according to the method reported in the description of less than 0.3% by weight . 7. Composition according to any one of the preceding claims, characterized by the fact that the silica (b) is distinguished by a density after compaction (compacted density) of less than 290 g/l. 8. Composition according to any one of the preceding claims, characterized by the fact that the silica (b) is distinguished by a specific pore volume, evaluated in the range of 15 to 45 nm, according to the method reported in the description, superior at 0.95 cm3/g. 9. Composition according to any one of the preceding claims, characterized by the fact that the silica (b) is distinguished by a silanol content measured according to the method reported in the description of at least 3.0 mmoles/g and not exceeding 4.5 mmoles/g. 10. Composition according to any one of the previous claims, characterized by the fact that it comprises from 5 to 130 phr of silica (b). 11. Composition according to any one of the preceding claims, characterized by the fact that the additional reinforcing filler (c) is carbon black and is present in quantities of at least 2 phr. 12. Tire component for vehicle wheels, characterized in that it comprises a vulcanizable elastomeric composition as defined in any one of claims 1 to 11 or a vulcanized elastomeric composition, obtained by vulcanizing the vulcanizable elastomeric composition as defined in any one of claims 1 to 11. 13. The tire component of claim 12, wherein said tire component is selected from tread, backsheet, anti-abrasive elongated member, sidewall, sidewall insert, mini sidewall, bottom liner, rubber layers, bead filler and foil. 14. Tire component according to claim 13, characterized in that said component is a tread. 15. Tire for vehicle wheels, characterized in that it comprises at least one tire component as defined in any one of claims 12 to 14.