Sound-insulating tyre for vehicle wheels

Abstract

The invention relates to a soundproof tyre for vehicle wheels, comprising at least one noise reduction element made by vulcanizing a crosslinkable and expandable elastomer compound, the crosslinkable and expandable elastomeric compound comprises at least one diene elastomeric polymer, at least one expanding agent, at least one crosslinked resin, at least one polymer or copolymer of a hydroxy acid, and optionally an agent selected from the group of fatty acid amides.

Description

Technical Field

[0001] The present invention relates to a sound-insulating tire for a vehicle wheel, and more particularly, the present invention relates to a sound-insulating tire that includes at least one noise-reducing element, i.e., capable of reducing the noise perceived in the passenger compartment of a vehicle due to the attenuation of the cavity noise and / or rolling noise of the tire itself. Background Art

[0002] In the automotive industry, there is an increasing demand to improve driver and passenger comfort, particularly to reduce the noise in vehicles, especially in high-end vehicles.

[0003] The automotive industry tends to produce lighter vehicles and / or provide quieter engines - such as electric motors - where, in contrast, road noise is perceived as more of a nuisance.

[0004] Therefore, the problem of reducing cavity noise and / or rolling noise is increasingly being appreciated for both high-end vehicles and sports cars. In high-end vehicles, comfort and particularly sound insulation are important requirements. For sports cars, in fact, reduced weight distribution and particularly rigid damping and drive systems are typical, which substantially do not attenuate the noise that is transmitted from the tire to the passenger compartment almost unchanged.

[0005] To reduce this type of noise, it is known to introduce sound-absorbing material into the internal cavity of the tire, either in free form or by fixing its strips to the inner surface of the liner. The sound-absorbing material can decompose sound waves and convert the energy of the incident sound into heat. The sound-absorbing material is usually composed of foams of heat-resistant expanding polymers, such as polyurethane or foams of elastomeric polymers (natural rubber, butyl rubber, etc.).

[0006] A sound-insulating tire for a vehicle wheel generally includes a noise-reducing element in the cavity, which is preferably fixed to the inner surface of the inner liner in the form of strips.

[0007] In particular, the noise-reducing element can mitigate the so-called cavity noise. The cavity noise is generated during the rolling of the tire on the road. When the air present in the internal annular cavity is in a vibrating state, due to its being cyclically compressed during the tread extrusion step, sound waves amplified by resonance are generated. Then the cavity noise propagates through the rim, hub, suspension, and frame into the passenger compartment of the vehicle and is perceived by the passengers as very annoying.

[0008] The frequency at which air resonates in the cavity is inversely proportional to the tire circumference and also depends in particular on the shape of the cavity itself, on the nature and shape of the material lining the cavity. Indicatively, the resonance frequency can be in the range of about 50 to 400 Hz. For automotive tires with a diameter of about 600 to 800 mm, the resonance frequency can typically be about 180 - 220 Hz, and for tires of heavy vehicles with a diameter of about 750 to 1200 mm, the resonance frequency can be 130 - 150 Hz.

[0009] Sound-insulating tires are known in the art and are described in many patent application publications, such as WO2017163219, WO2016051371, WO2015149959, US20080264539, and US20130087267.

[0010] In particular, US20120247637 describes a sound-insulating tire that includes a noise-reducing element composed of a rubber layer placed on the inner surface of the tire, wherein such a rubber layer is made from a vulcanizable composition that includes an elastomeric polymer (such as natural rubber or butyl rubber), a reinforcing agent (such as silica or carbon black), a blowing agent (such as azodicarbonamide), and a hot-melt agent (such as urea) with a melting point between 70 °C and 150 °C. The latter component is necessary for reducing expansion and controlling the uniformity of the layer thickness during vulcanization and significantly increasing the sound-insulating ability of the resulting vulcanized layer.

[0011] The patent application PCT / IB2022 / 054423 filed on May 12, 2022, describes a noise-reducing element for a tire that is arranged on a lining in the cavity and is obtained from a composition that includes at least one diene elastomeric polymer, at least one reinforcing agent, at least one vulcanizing agent, at least one blowing agent, at least one reagent selected from fatty acid amides, and at least one reagent selected from polymers and copolymers of ε-caprolactone, lactic acid, glycolic acid, and mixtures thereof.

[0012] As an alternative or supplement to being arranged in the cavity, the noise-reducing element can be placed inside the carcass structure.

[0013] For example, WO2015014577A1 describes a sound-insulating tire that includes an expanded noise-reducing element placed inside the carcass structure. The noise-reducing element is obtained by the expansion and vulcanization of a composition that includes one or more elastomeric polymers, a reinforcing agent, a blowing agent (usually a carbonate or bicarbonate), a carboxylic acid that produces carbon dioxide when reacting with the carbonate, a sulfur vulcanizing agent, and an accelerator.

[0014] However, the presence of a significant amount of sulfur vulcanizing agent in these compositions may hinder the expansion of the material and thus hinder sound absorption. Summary of the Invention

[0015] Although the solutions described in the art, especially in US20120247637, have given interesting results, the Applicant has noticed that the use of urea in elastomeric materials for manufacturing tires involves a series of contraindications.

[0016] Firstly, generally speaking, the pKb dissociation constant of urea at 21 °C is 0.1 (Perrin, D.D. (1965) Dissociation constants of Organic Bases in Aqueous Solutions. Butterworth, London), and thus it is a chemical reagent that irritates the skin and eyes, making it difficult to handle in the industrial field.

[0017] In addition, as also described in US6831109, a mixture of urea and / or its derivatives combined with an organic dicarboxylic acid, such as oxalic acid, causes desulfurization of the sulfur lattice S - S, thereby resulting in instability of the material.

[0018] Finally, due to its chemical structure, polarity and molecular size, urea shows a migration phenomenon in tire compounds, thus affecting its vulcanization kinetics and / or causing unsightly surface phenomena on the tire surface.

[0019] In addition, the Applicant wishes the applicability of the noise - reducing element inside the tire to be universal in order to maximize the sound - absorbing effect, and thus it is not limited to use in the inner cavity, but rather or only limited to use in the carcass structure of the tire.

[0020] At this point, the Applicant has noticed that elastomeric compositions, especially those for application in the carcass, will have to meet contradictory requirements. On the one hand, they must ensure high expansion of the vulcanized material to provide sufficient sound insulation, and on the other hand, they must ensure cross - linking that is suitable for ensuring the structural integrity of the element and its durable adhesion to the elastomeric compound, which may not be very compatible even under conditions of strong stress, in order to obtain sufficient structural robustness of the tire. Therefore, the aim of simultaneously imparting expandability and cross - linking to the compound of the sound - absorbing elastomeric material seems somewhat difficult.

[0021] The Applicant has thus conducted research on manufacturing a sound - insulating tire for a vehicle wheel, said sound - insulating tire comprising a noise - reducing element of foamed rubber made by vulcanizing an elastomeric composition that can be vulcanized in the presence of an expanding agent without the help of urea and has universal applicability inside the tire.

[0022] After extensive experimentation, the Applicant has surprisingly found that the use of a combination of crosslinked resins, (co)polymers of hydroxy acids such as polycaprolactone, etc. and optionally fatty acid amides can perform the same function as urea, overcome the contraindications caused by such reagents, and achieve satisfactory results in reducing noise. Using a crosslinking agent as part or all of the replacement for the vulcanizing agent not only prevents separation problems when the element is applied to the carcass and comes into contact with different rubber compounds that are not very compatible but surprisingly do not damage the expansion of the material and its sound absorption effect.

[0023] Accordingly, a first aspect of the present invention is a crosslinkable and expandable elastomeric rubber compound obtained by mixing an elastomeric composition, wherein the elastomeric composition comprises:

[0024] (i) 100 phr of at least one natural or synthetic elastomeric polymer,

[0025] (ii) 10 to 80 phr of at least one reinforcing filler,

[0026] (iii) 0 to 3 phr of at least one vulcanizing agent,

[0027] (iv) 2 to 25 phr of at least one crosslinked resin,

[0028] (v) 5 - 30 phr of at least one swelling agent,

[0029] (vi) 0 to 40 phr of at least one reagent selected from fatty acid amides, and

[0030] (vii) 1 - 20 phr of at least one of the following reagents, which is selected from polymers and copolymers of one or more hydroxy acids, preferably polymers and copolymers of caprolactone, lactic acid, glycolic acid and mixtures thereof.

[0031] Another aspect of the present invention relates to a noise reduction element made by crosslinking and expanding the crosslinkable and expandable elastomeric rubber compound according to the present invention.

[0032] Another aspect of the present invention relates to a sound - insulating tire for a vehicle wheel, which comprises:

[0033] - a carcass structure;

[0034] - a tread, which is located radially outward from the carcass structure;

[0035] - a vulcanized layer (liner) of an air - impermeable elastomeric rubber compound, which is radially arranged inside the carcass structure;

[0036] - at least one noise reduction element made of an expanded elastomeric material;

[0037] wherein the at least one noise reduction element is made by crosslinking and swelling a crosslinkable and swellable elastomeric composition according to the invention.

[0038] Definition

[0039] For the purposes of this specification and the appended claims, the term "phr" (acronym for parts per hundred parts of rubber) means the number of parts by weight of a given elastomeric composition component relative to every 100 parts by weight of elastomeric polymer, and is considered without any extender oil.

[0040] The term "elastomeric composition" means a composition comprising at least one diene elastomeric polymer and one or more additives, which, by mixing and possibly heating, provides an elastomeric composition suitable for tires and their components.

[0041] The components of the elastomeric composition are not generally introduced into the mixer simultaneously, but are usually added in sequence. In particular, vulcanization additives, such as vulcanizing agents and optionally accelerators and retarders, and crosslinking resins, are usually added in a downstream step relative to the incorporation and processing of all other components.

[0042] In a crosslinkable elastomeric composition, the individual components of the elastomeric composition may be completely or partially altered or no longer individually traceable due to interactions with other components, heat, and / or mechanical processing. The term "elastomeric composition" herein means the group of all components used to prepare the elastomeric composition, regardless of whether they are actually present simultaneously, introduced sequentially, or subsequently traceable in the elastomeric composition or the final tire.

[0043] The term "elastomeric polymer" means a natural or synthetic polymer that, after vulcanization, can be repeatedly stretched at room temperature to at least twice its original length and substantially immediately returns to approximately its original length upon removal of the stretching load (as defined by the ASTM D1566-11 standard terminology related to rubber).

[0044] The term "diene polymer" means a polymer or copolymer derived from the polymerization of one or more different monomers, at least one of which is a conjugated diene (conjugated diolefin).

[0045] The term "vulcanizing agent" typically means a sulfur-based crosslinking agent that is capable of converting natural or synthetic rubber into an elastic and resistant material due to the formation of a three-dimensional network of intermolecular and intramolecular bonds. Typical vulcanizing agents are sulfur-based reagents such as elemental sulfur, polymeric sulfur, sulfur donor reagents such as bis[(trialkoxysilyl)propyl] polysulfides, thiurams, dithiodimorpholine, and caprolactam-disulfide. It is well known that other vulcanizing agents, such as peroxides, are also used in the art.

[0046] The term "crosslinking resin" refers to a reactive resin that forms a three-dimensional network of intermolecular and intramolecular bonds in natural or synthetic rubber, which is different from that obtained by the reaction of sulfur-based vulcanizing agents. These differences are discussed, for example, in the article by M. Akiba et al. in Prog. Polym. Sci., Vol. 22, 475 - 521, 1997. Typical crosslinking agents used in the art are, for example, phenol-formaldehyde resins, etc.

[0047] The term "elastomer compound" means a compound obtainable by mixing at least one elastomeric polymer with at least one of the additives commonly used in the preparation of tire compounds and optionally heating.

[0048] The term "crosslinkable and expandable elastomer compound" means an elastomer compound ready for crosslinking and simultaneous expansion, which can be obtained by incorporating all additives (including crosslinking resin, blowing agent, and vulcanizing agent (if present)) into the elastomer compound.

[0049] The term "expanded crosslinked elastomer compound" refers to a material obtained by crosslinking and expanding a crosslinkable and expandable elastomer compound.

[0050] The term "green stock" means a material, compound, composition, part, or tire that has not been crosslinked.

[0051] The term "crosslinking" refers to the formation of a three-dimensional network of intermolecular and intramolecular bonds in natural or synthetic rubber induced by a crosslinking agent.

[0052] The term "vulcanization" refers to the crosslinking reaction in natural or synthetic rubber induced by a vulcanizing agent usually based on sulfur.

[0053] The term "expansion" refers to the increase in volume of a crosslinkable and expandable elastomer compound caused by the generation and capture of gas induced by a blowing agent during the crosslinking process. In this article, the crosslinking and expansion reactions preferably occur in a mold during the vulcanization of a tire.

[0054] The term "blowing agent" refers to a reagent capable of generating gas by heating a crosslinkable and expandable elastomer compound to the crosslinking temperature. Preferably, this temperature is reached or exceeded during the vulcanization of a tire.

[0055] The term "vulcanization accelerator" refers to a reagent capable of reducing the duration and / or operating temperature of the vulcanization process, such as TBBS, general sulfenamides, thiazoles, dithiophosphates, dithiocarbamates, guanidines, and sulfur donors such as thiurams.

[0056] The term "vulcanization activator" means a product capable of further promoting vulcanization so that it occurs in a shorter time and possibly at a lower temperature. Examples of activators are the stearic acid-zinc oxide system.

[0057] The term "vulcanization retarder" denotes a product capable of delaying the onset of the vulcanization reaction and / or inhibiting unwanted secondary reactions, such as N-(cyclohexylthio)phthalimide (CTP).

[0058] The term "vulcanization package" refers to a vulcanizing agent and one or more vulcanization additives selected from vulcanization activators, accelerators, and retarders.

[0059] The term "reinforcing filler" refers to a reinforcing material commonly used in the art to improve the mechanical properties of tire rubber, which is preferably selected from carbon black, conventional silica, such as silica precipitated from sand with a strong acid, preferably amorphous silica, diatomaceous earth, calcium carbonate, titanium dioxide, talc, alumina, aluminosilicate, kaolin, silicate fiber, and mixtures thereof.

[0060] The term "white filler" refers to conventional reinforcing materials used in the art, which are selected from conventional silica and silicates, such as sepiolite, palygorskite (also known as attapulgite), montmorillonite, halloysite, etc., which are optionally modified by acid treatment and / or derivatization. Generally, white fillers have surface hydroxyl groups.

[0061] The term "mixing step (1)" denotes a step of a method for preparing an elastomeric compound, in which, in addition to the vulcanizing agent fed in step (2), one or more additives can be incorporated by mixing and optionally heated. Mixing step (1) is also referred to as a "non-productive step". In the preparation of the compound, there can be several "non-productive" mixing steps, which can be designated as 1a, 1b, etc.

[0062] The term "mixing step (2)" denotes the next step of a method for preparing an elastomeric compound, in which the vulcanizing agent and optionally other additives of the vulcanization package are introduced into the elastomeric compound obtained from step (1) and mixed into the material at a controlled temperature, usually at a temperature of the compound above 120 °C, to provide a crosslinkable and expandable elastomeric compound. Mixing step (2) is also referred to as a "productive step".

[0063] Unless otherwise specified, all percentages are expressed as weight percentages. Detailed Description of the Invention

[0065] The elastomeric compound, noise reduction element, and sound insulation tire according to the present invention can exhibit at least one of the following preferred features individually or in combination with other features.

[0066] The crosslinkable and expandable elastomeric composition of the noise reduction element according to the present invention can be obtained from a composition which may comprise (i) at least one natural or synthetic diene elastomeric polymer, which is derived from the polymerization of one or more monomers, wherein at least one monomer is a conjugated diene, or (ii) at least one elastomeric polymer of one or more monoolefins with an olefin comonomer or its derivative.

[0067] The synthetic diene elastomeric polymer can be obtained by solution polymerization, emulsion polymerization or gas phase polymerization of at least one conjugated diene, which is optionally mixed with at least one comonomer selected from mono-vinyl aromatic hydrocarbons and / or polar comonomers in an amount not exceeding 60% by weight.

[0068] The conjugated diene usually contains 4 to 12 carbon atoms, preferably 4 to 8 carbon atoms, and may be selected from, for example: 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 mixtures thereof, particularly preferably 1,3-butadiene and isoprene.

[0069] The mono-vinyl aromatic hydrocarbon which may optionally be used as a comonomer usually contains 8 to 20, preferably 8 to 12 carbon atoms, and may be selected from, for example: styrene; 1-vinylnaphthalene; 2-vinylnaphthalene; various alkyl, cycloalkyl, aryl, alkaryl or aralkyl derivatives of styrene, such as α-methylstyrene, 3-methylstyrene, 4-propylstyrene, 4-cyclohexylstyrene, 4-dodecylstyrene, 2-ethyl-4-benzylstyrene, 4-p-tolylstyrene, 4-(4-phenylbutyl)styrene and mixtures thereof. Particularly preferably styrene.

[0070] The polar comonomer which may optionally be used may be selected from, for example: vinylpyridine, vinylquinoline, esters, nitriles of acrylic acid and alkylacrylic acid or mixtures thereof, such as methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, acrylonitrile and mixtures thereof.

[0071] Preferably, the diene elastomeric polymers which can be used in the present invention are optionally selected from, for example: cis-1,4-polyisoprene (natural or synthetic, preferably natural rubber), 3,4-polyisoprene, polybutadiene (especially polybutadiene having a high 1,4-cis content), isoprene / isobutene copolymer, 1,3-butadiene / acrylonitrile copolymer, styrene / 1,3-butadiene copolymer, styrene / isoprene / 1,3-butadiene copolymer, styrene / 1,3-butadiene / acrylonitrile copolymer and mixtures thereof.

[0072] The monoolefins may be selected from: ethylene and α-olefins usually containing 3 to 12 carbon atoms, such as propylene, 1-butene, 1-pentene, 1-hexene, 1-octene or mixtures thereof. The following are preferred: copolymers selected from ethylene and α-olefins, optionally with dienes; polyisobutene homopolymers or copolymers thereof with small amounts of dienes, which are optionally at least partially halogenated. The optionally present dienes usually contain 4 to 20 carbon atoms and are preferably selected from: 1,3-butadiene, isoprene, chloroprene, neoprene, 1,4-hexadiene, 1,4-cyclohexadiene, 5-ethylidene-2-norbornene, 5-methylene-2-norbornene, vinyl norbornene or mixtures thereof. Among them, the following are particularly preferred: ethylene / propylene (EPR) copolymers or ethylene / propylene / diene (EPDM) copolymers; polyisobutene; butyl rubber; halogenated butyl rubber, especially chlorinated butyl (CIIR) or brominated butyl (BIIR) rubber; or mixtures thereof.

[0073] Preferably, the natural or synthetic diene elastomer polymer in the elastomer composition of the present invention is selected from natural rubber, synthetic isoprene rubber and mixtures thereof.

[0074] Preferably, the elastomer composition of the present invention contains only natural rubber, synthetic isoprene rubber and mixtures thereof as the natural or synthetic diene elastomer polymer.

[0075] The crosslinkable and expandable elastomer compound in the noise reduction element according to the present invention includes at least one reinforcing filler, and the reinforcing filler is preferably selected from carbon black, conventional silica, such as sand silica precipitated with strong acid, preferably amorphous, diatomaceous earth, calcium carbonate, titanium dioxide, talc, alumina, aluminosilicate, kaolin, silicate fiber and mixtures thereof.

[0076] Preferably, the reinforcing filler is selected from carbon black, conventional silica, silicate fiber, talc and mixtures thereof.

[0077] Commercial examples of the reinforcing filler suitable for the elastomer composition of the present invention are carbon black N326 and N375 from Cabot, carbon black N326 and N375 from Birla, and Mins tron Har layered talc produced by Imerys Talc in France.

[0078] The elastomer composition preferably contains 20 to 60 phr, more preferably 20 to 50 phr of the reinforcing filler.

[0079] The elastomer composition preferably contains at least 30 phr, more preferably at least 40 phr of the reinforcing filler.

[0080] The crosslinkable and expandable elastomeric compound in the noise reduction element according to the present invention may comprise at least one vulcanizing agent, preferably, if present, a sulfur-based vulcanizing agent.

[0081] The vulcanizing agent (if present) is preferably selected from sulfur, sulfur-containing molecules (sulfur donors), preferably in the presence of a reagent containing zinc and fatty acids, or alternatively other conventional vulcanizing agents such as peroxides.

[0082] The vulcanizing agent may be sulfur, which is preferably selected from soluble sulfur (crystalline sulfur), insoluble sulfur (polymeric sulfur), (iii) oil-dispersed sulfur, and mixtures thereof.

[0083] Alternatively, sulfur donor molecules such as caprolactam disulfide (CLD), bis[(trialkoxysilyl)propyl] polysulfide, dithiophosphates, phosphoryl polysulfides (SDT), and mixtures thereof may be used.

[0084] Commercial examples of suitable vulcanizing agents are 65% sulfur known under the trade name Rhenogran (Lanxess), 67% sulfur known under the trade name Crys tex OT33 (Eastman), 95% sulfur known under the trade name Solvay Schwefel KC, and rhombic crystalline sulfur known under the trade name Sulphur (1% oil and 0.3% silica) (Zolfindustria).

[0085] The vulcanizing agent may be present in the elastomeric composition of the present invention in a total amount of less than 3.0 phr, preferably less than 2.5 phr, more preferably less than 2.0 phr or 1.0 phr.

[0086] The vulcanizing agent (if present) is preferably used together with auxiliaries known to those skilled in the art such as vulcanization activators, accelerators, and / or retarders. The group of vulcanization activators, accelerators, and / or retarders together with the vulcanizing agent constitutes the so-called "vulcanization package".

[0087] Preferably, no vulcanizing agent is present.

[0088] In addition to these reagents, the composition of the present invention further comprises an optional sulfur-based vulcanizing agent, or preferably, in their place, comprises at least one crosslinking resin.

[0089] The applicant has observed that the crosslinking resin allows for good crosslinking of the elastomeric material without being detrimental to the expansion of the material, as Figure 4 shown, even for a large amount of crosslinking agent.

[0090] Preferably, the amount of the crosslinking resin is 2-25 phr, more preferably 8-20 phr.

[0091] Typically, a crosslinked resin is a reactive resin containing at least one methylene donor reagent and at least one methylene acceptor reagent.

[0092] The term "methylene donor reagent" refers to formaldehyde or its organic reagent derivatives that can at least partially decompose in situ to release formaldehyde under normal vulcanization conditions, such as hexamethylenetetramine (HMT), hexamethoxymethylmelamine (HMMM), hexahydroxymethylmelamine, N,N'-dimethylolurea, N-hydroxymethyl dicyandiamide, N-allyl dioxazine, N-phenyl dioxazine, N-hydroxymethylacetamide, N-hydroxymethylbutyramide, N-hydroxymethylacrylamide, N-hydroxymethyl succinimide, lauryloxymethylpyridinium chloride, ethoxymethylpyridinium chloride, trioxane hexamethoxymethylmelamine, and hexahydroxymethylmelamine pentamethyl ether (HMPE). The methylene donor reagent can react with the methylene acceptor reagent, usually forming a lattice and remaining wholly or partly incorporated therein.

[0093] The term "methylene acceptor reagent" refers to an aromatic organic reagent that can react with the methylene donor reagent through aromatic electrophilic substitution reaction and form a lattice, such as phenol and its derivatives, resorcinol, cresol, etc.

[0094] The crosslinked resin can be reactive phenol-formaldehyde, resorcinol-formaldehyde, cresol-formaldehyde, or similar resins and their mixtures.

[0095] Commercial examples of suitable phenolic crosslinked resins are those produced by SIGroup with different grades and trade names, such as Elaztobond TM 、SP (such as SP-1045H), BRJ, HRJ, or others from different manufacturers such as Akrochem, Sino Legend, or Kolon.

[0096] Suitably present vulcanization activators are preferably zinc reagents, especially ZnO, ZnCO3, zinc salts of saturated or unsaturated fatty acids containing 8 to 18 carbon atoms, such as zinc stearate, which is preferably formed in situ from ZnO and fatty acids in the elastomer composition, and BiO, PbO, Pb3O4, PbO2, or mixtures thereof. Commercial examples are the zinc salt of fatty acid dispersant FS-200 from Wuhan Jinghe, Palmera B1810 stearic acid from KLK OLEO, or zinc oxide grade 203 from U.S. Zinc.

[0097] In a preferred embodiment, no vulcanization activator is present.

[0098] Optionally present vulcanization accelerators are preferably selected from dithiocarbamates, guanidines, thioureas, thiazoles, sulfenamides, sulfenimides, thiurams, amines, xanthates, and mixtures thereof.

[0099] Preferably, the accelerator is selected from N-cyclohexyl-2-benzothiazole-sulfenamide (CBS), N-tert-butyl-2-benzothiazole-sulfenamide (TBBS), and mixtures thereof.

[0100] A commercial example of a suitable accelerator is N-cyclohexyl-2-benzothiazole-sulfenamide (CBS) sold by Lanxess.

[0101] The total amount of the vulcanization accelerator present in the crosslinkable elastomeric composition can generally be from 0.05 phr to 10 phr, preferably from 0.1 phr to 5 phr.

[0102] The crosslinkable and expandable elastomeric composition may comprise a mixture of one or more of the vulcanization accelerators as defined above.

[0103] Preferably, in the crosslinkable and expandable elastomeric composition of the present invention, no accelerator is present.

[0104] Optional vulcanization retarders may be selected from, for example, urea, phthalic anhydride, N-nitrosodiphenylamine, N-cyclohexylthiophthalimide (CTP), and mixtures thereof.

[0105] A commercial example of a suitable retarder is N-cyclohexylthiophthalimide VULKALENT G from Lanxes s.

[0106] The amount of the retarder present in the crosslinkable and expandable elastomeric composition can generally be from 0.05 phr to 2 phr.

[0107] In a preferred embodiment, no retarder is present.

[0108] The blowing agents preferably used in the crosslinkable and expandable elastomeric compound for the noise reduction element according to the present invention are selected from diazo, dinitrose, hydrazide, carbohydrazide, semicarbazide, tetrazole, carbonate, hydrogencarbonate, citrate reagents, and mixtures thereof, as particularly described in the publication WO2011 / 064128.

[0109] Among them, dinitro-pentane-ethylenetetramine, dinitro-pentane-styrenetetramine, N,N'-dimethyl-N,N'-dinitro-phthalimide, azodicarbonamide, benzenesulfonyl hydrazide, toluenesulfonyl hydrazide, p,p'-oxybis(benzenesulfonyl) hydrazide, p-toluenesulfonyl semicarbazide, p,p'-oxybis(benzenesulfonyl) semicarbazide, and mixtures thereof may be particularly mentioned.

[0110] The blowing agent preferably used in the crosslinkable and expandable elastomeric compound for the noise reduction element according to the present invention is azodicarbonamide.

[0111] The elastomeric composition preferably comprises from 10 phr to 20 phr of said blowing agent.

[0112] The fatty acid amides optionally used in the compositions of the present invention are derived from the corresponding saturated, monounsaturated and polyunsaturated fatty acids by replacing the -OH group of the carboxylic acid with an -NR1R2 group, where R1 and R2 independently of one another represent a hydrogen atom or a straight-chain or branched alkyl group having 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms, preferably methyl, ethyl, propyl, isopropyl, butyl, isobutyl and tert-butyl.

[0113] Saturated fatty acids from which the amides useful in the present invention can be obtained are, for example, butyric acid, valeric acid (pentanoic acid), caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, margaric acid, stearic acid, arachidic acid, behenic acid, lignoceric acid, cerotic acid, montanic acid, melissic acid and laceroic acid.

[0114] Monounsaturated fatty acids from which the amides useful in the present invention can be obtained are, for example, myristoleic acid, palmitoleic acid, sapienic acid, petroselinic acid, oleic acid, elaidic acid, vaccenic acid, trans-vaccenic acid, 11-cis-octadecenoic acid, cis-vaccenic acid, petroselinic acid, cetoleic acid, erucic acid and nervonic acid.

[0115] Polyunsaturated fatty acids from which the amides useful in the present invention can be obtained are, for example, linoleic acid, rumenic acid, α-linolenic acid, γ-linolenic acid, stearidonic acid, arachidonic acid, eicosapentaenoic acid, docosapentaenoic acid and docosahexaenoic acid.

[0116] Fatty acid amides useful in the present invention are, for example, stearamide, oleamide, erucamide, behenamide, lauramide, palmitamide, butyramide, etc.

[0117] Commercial examples of fatty acid amides useful in the present invention are the amides sold by Croda Italia SpA under the trade name Crodamide TM or Incroslip TM such as Crodamide TM SR, Crodamide TM ER, Crodamide TM BR, Crodamide TM ORX, Crodamide TM S, Crodamide TM EBS, Crodamide TM OR and Crodamide TMSRV, and amides sold by Fine Organics under the trade names Finawax S, Finawax S 50, and Finawax S 70.

[0118] The elastomeric composition preferably may comprise from 10 phr to 30 phr, more preferably from 10 phr to 20 phr of said fatty acid amide.

[0119] Without wishing to be bound by any theory, the applicant believes that the use of said fatty acid amide contributes to the uniform dispersion of the polar components, in particular blowing agents, of the composition of the present invention, and thus the gases generated therefrom, in the non-polar elastomeric material, making their distribution uniform and thus improving the properties of the expanded material.

[0120] In the elastomeric composition of the present invention, there are one or more polymers and copolymers of one or more hydroxy acids, which are preferably selected from polymers and copolymers of ε-caprolactone, lactic acid, and glycolic acid and mixtures thereof.

[0121] Without wishing to be bound by any theory, the applicant believes that the use of (co)polymers of hydroxy acids, such as polycaprolactone, etc., imparts gas barrier properties to the expanded compound of the present invention, which advantageously allows it to be retained within the noise reduction element, thereby improving its expansion and sound insulation efficiency.

[0122] Examples of polymers and copolymers useful in the present invention are represented by polycaprolactone (PCL), polylactide (PLA or polylactic acid), polyglycolide (PGA), poly(ε-caprolactone-co-lactide), poly(lactide-co-glycolide) (PLGA), poly(ε-caprolactone-co-glycolide), and mixtures thereof.

[0123] Polycaprolactone useful in the present invention can be obtained by ring-opening polymerization of ε-caprolactone in the presence of an organometallic reagent as a catalyst (such as tetraphenyltin) and a dihydroxy (such as butanediol) or trihydroxy (such as trimethylolpropane) or tetrahydroxy (such as pentaerythritol) reagent as an initiator.

[0124] A commercial example of polycaprolactone useful in the present invention is CAPA sold by Ingevity under the trade name TMPolylactide sold, such as CAPA 2125, CAPA 2045, Capa 2100J, Capa 2101, CAPA 2101A, Capa 2125, CAPA2141A, Capa 2161A, Capa2200J, Capa 2201, CAPA 2201A, Capa 2202AJ, Capa 2203A, Capa2204J, Capa 2205, Capa 2209, Capa 2241A, Capa 2302J, Capa 3022, Capa3041, CAPA 3201, CAPA 6800, Capa 6250 and CAPA 7201A. Further examples of polylactide useful in the present invention are obtained under the trade name TONE, such as TONE 300 and TONE 700 sold by Union Carbide Corporation Danbury, Connecticut.

[0125] Commercial examples of polylactide useful in the present invention are available from Chronopol Inc. (Golden, CO), from NatureWorks LLC under the trade name EcoPLA TM , from Mutsui Chemical under the trade name and from Biomer under the trade name L5000 TM obtained.

[0126] The elastomeric composition preferably comprises 2 phr to 15 phr, more preferably 3 phr to 12 phr of one or more of the above polymers and copolymers of hydroxy acids, preferably polymers and copolymers of caprolactone, lactic acid and glycolic acid.

[0127] The elastomeric composition of the present invention does not contain urea in an amount greater than 0.5 phr, preferably greater than 0.1 phr, and more preferably urea is absent.

[0128] The applicant mainly focuses on applying the rubber compound and noise reduction element of the present invention to the tires of four-wheel vehicles for road use, as tires suitable for equipping medium and high-powered automobiles for transporting people (the maximum chord length dimension is 195 mm to 245 mm). The applicant believes that the present invention is also applicable to tires for small cars or high-performance tires (HP high performance - UHP ultra-high performance) having a maximum chord length dimension of, for example, 145 mm to 355 mm or tires for various vehicles, such as motorcycles or heavy-duty vehicles for transporting people or property.

[0129] The sound-insulating tire can be an HP (High Performance) or UHP (Ultra High Performance) tire, which is designed to equip vehicles mainly for transporting people, such as limousines, minivans, family cars, SUVs (Sports Utility Vehicles) and / or CUVs (Crossover Utility Vehicles), and is usually a tire that allows high-speed driving.

[0130] High-performance and ultra-high-performance tires are particularly those that allow speeds of at least above 160 km / h, above 200 km / h up to over 300 km / h. Examples of such tires are those according to the E.T.R.T.O. standard (European Tyre and Rim Technical Organization standard), especially for four-wheel high-power vehicles, belonging to the "T", "U", "H", "V", "Z", "W", "Y" classes. Tires usually belonging to these classes have a cross-sectional width equal to or greater than 185 mm, preferably not greater than 325 mm, more preferably 195 mm to 325 mm. These tires are preferably mounted on rims with a bead diameter equal to or greater than 15 inches, preferably not greater than 24 inches, more preferably 17 inches to 22 inches. SUVs and CUVs refer to vehicles with an elevated profile, usually four-wheel drive, with a displacement generally greater than or equal to 1800 cc, more preferably 2000 cc to 6200 cc. Preferably, the mass of these vehicles is greater than 1400 kg, more preferably 1500 Kg to 3000 Kg.

[0131] The tire of the present invention can be used as a summer or winter or "all-season" (tires that can be used in all seasons) tire.

[0132] The tire of the present invention can be used as a tire for electric vehicles.

[0133] In the tire of the present invention, at least one noise reduction element made of an expanded elastomeric material can be arranged on at least a part of the radially inner surface of the vulcanized layer (liner) of the airtight elastomeric compound.

[0134] In one embodiment, the noise reduction element is arranged on at least a part of the radially inner surface of the vulcanized layer of the airtight elastomeric compound and axially extends at least at a part of the crown.

[0135] Preferably, at least one noise reduction element is arranged on the radially inner surface of the vulcanized layer of the airtight elastomeric compound, which extends along the entire circumference of the tire and axially extends at least at a part of the crown of the tire, such as 20%, 30%, 40%, 50%, 60%, 70%, 80% or 90% of the tread extension, which is preferably arranged across the equatorial plane.

[0136] Alternatively, at least one noise reduction element may axially extend a width corresponding to 100% or more of the width of the crown, i.e., it may extend in whole or in part on the radially inner surface corresponding to the sidewall of the vulcanized layer of the airtight elastomeric compound, preferably between 10% and 70% of said surface.

[0137] Preferably, the at least one noise reduction element is provided on the radially inner surface of the vulcanized layer of the airtight elastomeric compound, and the vulcanized layer of the airtight elastomeric compound axially extends at a position substantially centered with respect to the equatorial plane of the tire.

[0138] In one embodiment, the tire includes a single noise reduction element in the form of a continuous strip joined at its ends, for example having dimensions of 180 mm × 2 mm and a length equal to the circumference of the tire, and the element is circumferentially arranged at a radially inner position with respect to the vulcanized layer of the airtight elastomeric compound.

[0139] Alternatively, a plurality of noise reduction elements of different sizes and shapes may be arranged side by side, for example in the shape of a square (e.g., measured as 180 mm × 180 mm × 2 mm), as Figure 8A illustrated illustratively, or as rectangles or a plurality of continuous strips placed side by side and joined at their ends, for example as Figure 8B shown.

[0140] Preferably, the number of strips of material is greater than or equal to 1, preferably between 2 and 8, and preferably less than 10.

[0141] In the tire according to the present invention, the noise reduction elements may be circumferentially arranged as a single strip or as a plurality of strips parallel to the equatorial plane on the radially inner surface of the vulcanized layer of the airtight elastomeric compound, or alternatively, inclined at an angle, for example, between + / −30° with respect to this plane. Such strips may be substantially rectangular portions having a width preferably less than the cross-sectional width (maximum chord length) of the tire and lengths equal to or different from each other, preferably including a value between 0.5 and 0.05 developed circumferentially inside the tire; such substantially rectangular portions are preferably arranged at a substantially centered position with respect to the equatorial plane of the tire.

[0142] Preferably, the noise reduction elements are arranged in such a way that the load is distributed as symmetrically as possible so as not to cause an imbalance in the tire attitude.

[0143] Preferably, the noise reduction elements are arranged to avoid overlapping of the end flaps of one or more strips of material.

[0144] Preferably, the coverage of the radially inner surface of the vulcanized layer of the airtight elastomeric compound is less than 100% and preferably greater than 40%, more preferably greater than 50%, and even more preferably greater than 60%.

[0145] In another embodiment, the noise reduction element can be arranged inside the carcass structure.

[0146] In this embodiment, the noise reduction element in the carcass can be arranged at a radially outer position relative to the liner and internally relative to the belt structure. Alternatively, it can be arranged at a radially outer position relative to the belt structure and internally relative to the crown.

[0147] In a preferred embodiment, the noise reduction element in the carcass is arranged in a radially outer position relative to an elastomeric material layer called the "underliner" - the underliner being in a radially outer position and adjacent to the liner - and radially internally relative to the belt structure.

[0148] Advantageously, the noise reduction element arranged in the carcass is better protected against degradation caused by external agents (such as oxygen or ozone); furthermore, it allows the interception of rolling noise and, in particular, if used in combination with another noise reduction element arranged in the cavity, contributes to effective sound insulation.

[0149] The sound-insulating tire according to the invention can include at least one noise reduction element in the cavity, which is arranged in a radially inner position relative to the vulcanized layer of the airtight elastomeric compound and extends axially at least at a part of the crown, or includes at least one noise reduction element arranged inside the carcass structure, or includes at least one noise reduction element in both the cavity and the carcass structure.

[0150] Additional features and advantages will become more apparent from the detailed description of two non-exclusive embodiments of the sound-insulating tire according to the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0151] The attached drawings are provided for illustrative and thus non-limiting purposes only.

[0152] Figure 1 A radial half-section of a sound-insulating tire for a vehicle wheel is schematically shown, which includes a noise reduction element in the cavity.

[0153] Figure 2 A radial half-section of a sound-insulating tire for a vehicle wheel is schematically shown, which includes a noise reduction element in the carcass structure.

[0154] Figure 3 A partial exploded schematic view shows the overlap of the layers constituting the tire according to an embodiment of the invention.

[0155] Figure 4 Photographs of the samples prepared with Compounds B and C of Example 1 after swelling and crosslinking are shown.

[0156] Figure 5The MDR graph and the pressure P / torque S' curve of compound A of Example 1 during the first 10 minutes of crosslinking at 170°C are shown.

[0157] Figure 6 The MDR graph and the pressure P / torque S' curve of compound B of Example 1 during the first 10 minutes of crosslinking at 170°C are shown.

[0158] Figure 7 The MDR diagram and the pressure P / torque S' curve of compound C of Example 1 during the first 10 minutes of crosslinking at 170°C are shown.

[0159] FIG. 8 shows a photograph of a soundproofing tire comprising a noise reduction element according to the invention. Figure 8A and Figure 8B A plurality of noise reduction elements of different shapes (squares in 8A and elongated strips in 8B) are shown applied to the radially inner surface of the cured layer of an air-impermeable elastomeric compound. Figure 8C A photograph of the radially inner surface of a soundproofing tire is shown, the soundproofing tire comprising noise reduction elements in the carcass structure, the noise reduction elements being positioned radially outwards with respect to the liner.

[0160] Reference below Figure 1 , Figure 2 and Figure 3 , the embodiments of the present invention are described, and these drawings are for illustration only and not for limiting purposes, wherein "a" represents the axial direction and "r" represents the radial direction. For simplicity, Figure 1 and Figure 2 Only a portion of the tire is shown, the remaining portions not shown being identical and arranged symmetrically with respect to a radial direction "r".

[0161] Reference numeral 100 is Figure 1 A soundproofing tire for vehicle wheels is shown in the figure, which includes noise reduction elements in the inner cavity. The tire generally comprises a carcass structure including at least one carcass ply or layer 101 having respectively opposite end flaps engaged with corresponding annular anchoring structures 102, called bead cores, optionally associated with bead fillers 104. The tire region including the bead cores 102 and the bead fillers 104 forms a bead structure 103 intended to anchor the tire to a corresponding mounting rim (not shown). Each bead structure 103 is associated with the carcass structure by folding back the opposite side edges of at least one carcass layer 101 around the bead cores 102 so as to form a bead structure such as Figure 1 A so-called carcass wing 101a is shown.

[0162] At least one carcass ply 101 of the carcass structure is optionally associated with a belt structure 106, which includes one or more belt plies 106a, 106b, the one or more belt plies 106a, 106b being placed radially superposed relative to each other and relative to the carcass structure 101, and the belt plies 106a, 106b having metal or fabric reinforcing cords. Such reinforcing cords may have a cross orientation relative to the circumferential extension direction of the tire 100. The "circumferential" direction refers to the direction that is generally facing the direction according to the tire rotation direction, or in any case is slightly inclined relative to the rotation direction of the tire.

[0163] The belt structure 106 further includes at least one radially outer reinforcing ply 106c relative to the belt plies 106a, 106b. The radially outer reinforcing ply 106c includes fabric or metal cords that are disposed at a substantially zero angle relative to the circumferential extension direction of the tire and are immersed in an elastomeric material. Preferably, the cords are substantially parallel and side by side to form a plurality of turns. These turns are substantially oriented according to the circumferential direction (usually having an angle between 0° and 5°), and this direction is usually referred to as "zero-degree" relative to the laying of the equatorial plane X-X of the tire. The "equatorial plane" of the tire refers to the plane perpendicular to the tire rotation axis, which divides the tire into two symmetrically equal parts.

[0164] The crown 109 is disposed in a radially outer position relative to the carcass structure and / or, if present (as in the case shown), relative to the belt structure 106.

[0165] In the radially outer position, the crown 109 has a rolling portion 109a intended to contact the ground. The circumferential grooves are connected by lateral notches ( Figure 1 not shown in the figure) so as to define a plurality of blocks of various shapes and sizes distributed in the rolling portion 109a. The circumferential grooves are generally formed in this rolling portion 109a. For simplicity, this rolling portion 109a is shown as smooth in Figure 1 the figure.

[0166] To optimize the performance of the tread, the crown can be made into a two-layer structure.

[0167] This two-layer structure includes a rolling layer or portion 109a (referred to as the cap) and a substrate 111 (referred to as the base), thus forming a so-called cap-and-base structure. Therefore, an elastomeric material capable of providing low rolling resistance to the cap 109a and at the same time providing high wear resistance and crack formation resistance can be used, while the elastomeric material of the substrate 111 can be specifically targeted at low hysteresis to cooperate with reducing the rolling resistance. The bottom layer 111 of the vulcanized elastomeric compound can be disposed between the belt structure 106 and the rolling portion 109a.

[0168] On the side surface of at least one carcass ply 101 of the carcass structure, the respective sidewalls 108 of the vulcanized elastomeric compound are further arranged in positions axially external to the carcass structure, each sidewall 108 extending from one of the side edges of the crown 109 until the respective bead structure 103.

[0169] In the connection region between the sidewall 108 and the crown 109, a strip made of an elastomeric compound 110 (commonly referred to as a "mini-sidewall") formed of a vulcanized elastomeric compound may optionally be provided. The mini-sidewall is typically obtained by co-extrusion with the crown 109 and allows for an improvement in the mechanical interaction between the crown 109 and the sidewall 108. Preferably, the end of the sidewall 108 directly covers the lateral edge of the crown 109.

[0170] In some specific embodiments, such as the embodiments shown and described herein, the stiffness of the bead 103 may be improved by providing a reinforcing layer 120, commonly referred to as an "outer chafe strip", in the tire bead.

[0171] The outer chafe strip 120 is wound around the respective bead core 102 and bead filler 104 so as to at least partially surround them. The outer chafe strip 120 is provided between the carcass ply 101 and the bead structure 103. Generally, the outer chafe strip 120 is in contact with the carcass ply 101 and the bead structure 103. The outer chafe strip 120 typically includes a plurality of metal or fabric cords incorporated in a vulcanized elastomeric compound.

[0172] In some specific embodiments, such as the embodiments shown and described herein, the bead structure 103 may further include an additional protective layer 121, which is commonly referred to by the term "bead chafe strip" or protective strip and which has the function of increasing the rigidity and integrity of the bead structure 103.

[0173] The bead chafe strip 121 typically includes a plurality of cords incorporated in a vulcanized elastomeric compound; such cords are typically made of textile materials (such as aramids or rayon) or metallic materials (such as steel cords).

[0174] Optionally, a wear-resistant strip 105 is provided so as to wrap around the bead structure 103 along the axially inner and outer regions as well as the radially inner region of the bead structure 103, such that when the tire 100 is mounted on a rim, the wear-resistant strip 105 inserts itself between the bead structure 103 and the wheel rim.

[0175] Furthermore, the radially inner surface of the tire 100 is preferably lined with a layer of substantially airtight elastomeric material or a so-called liner 112.

[0176] Reference Figure 1, a noise reduction element 301 of an expanded elastomeric material made by crosslinking a crosslinkable and expandable elastomeric composition according to the present invention is adhesively attached to the radially inner surface of the airtight elastomeric material layer 112 by co-vulcanization, thereby occupying at least a part of the crown portion of the tire in the axial extension.

[0177] In another embodiment, as Figure 2 shown, at least one noise reduction element 301 may be arranged between at least one carcass ply 101 of the carcass structure and the belt structure 106.

[0178] Alternatively, in Figure 3 another embodiment of a sound-insulating tire schematically shown as a partial exploded view, at least one noise reduction element 301 may be arranged adjacent to at least one ply 101 of the carcass structure, at least for a part of at least one ply 101 of the carcass structure, in a radially outer position relative to the vulcanized layer 112 of the airtight elastomeric compound and the "underlay" 112a. The underlay 112a ( Figure 3 schematically shown) is arranged in a position adjacent to the liner 112 and radially outside the liner 112 and radially inside at least one carcass ply 101 of the carcass structure.

[0179] Preferably, when at least one noise reduction element is arranged adjacent to the carcass structure, the element comprises an elastomeric compound having the same or a similar polymer composition as the compound of the tire element adjacent to the element, so as to ensure the greatest possible compatibility between the layers and prevent their separation during use.

[0180] Preferably but not exclusively, the tire 100 for a motor vehicle is of the HP (High Performance) or UHP (Ultra High Performance) type, i.e., it is a tire capable of withstanding a maximum speed of at least 190 km / h up to over 300 km / h. Examples of such tires are tires belonging to the "T", "U", "H", "V", "Z", "W", "Y" classes.

[0181] According to an embodiment not shown, the tire may be a tire for a motorcycle wheel. The profile of the straight portion of a tire for a motorcycle (not shown) has a high lateral curvature because it must ensure a sufficient contact area under all leaning conditions of the motorcycle. The lateral curvature is defined by the ratio of the distance f between the ridges of the tread measured in the equatorial plane of the tire to the line passing through the transverse opposite ends of the tread itself to the width C defined by the distance between the transverse opposite ends of the tread itself. A tire with a high lateral curvature means a tire whose lateral curvature ratio (f / C) is at least 0.20.

[0182] The construction of the tire 100 as described above is carried out by assembling the corresponding semi-finished products onto a forming drum (not shown) by means of at least one assembling device.

[0183] Construct and / or assemble at least a part of the components intended to form the carcass structure of the tire 100 on the building drum. More specifically, in the case of application on the vulcanized layer (liner 112) of an air-impermeable elastomeric compound ( Figure 1 ), the building drum is adapted to first receive the noise-reducing element 301 made of a crosslinkable and expandable elastomeric compound according to the invention, then receive the liner 112, and subsequently receive the carcass ply or plies 101.

[0184] Conversely, in the case of using a noise-reducing element arranged at least partially adjacent to the carcass structure as shown in Figure 2 、 Figure 3 and Figure 8C , the noise-reducing element 301 made of a crosslinkable and expandable elastomeric compound according to the invention is positioned after the liner 112 and an optional additional "underliner" layer 112a have been applied to the drum.

[0185] Thereafter, a device (not shown) coaxially engages one of the annular anchoring structures 102 surrounding each end flap, positions the outer sleeve including the belt structure 106 and the crown 109 in a coaxial centered position around the cylindrical carcass sleeve, and forms the carcass sleeve according to an annular configuration by radial expansion of at least one carcass ply 101 so as to apply it against the radial inner surface of the outer sleeve.

[0186] After constructing the green tire 100, a molding and vulcanization treatment is generally carried out in order to determine the structural stability of the tire 100 by vulcanization of the elastomeric compound, and to impart the desired tread pattern on the crown 109 and any distinctive graphic symbols at the sidewalls 108.

[0187] After removal from the vulcanization chamber, the vulcanized tire is kept stationary at room temperature for a variable time, for example from about 5 minutes to about 20 minutes, in order to allow the elastomeric material of the noise-reducing element 301 to expand.

[0188] Alternatively, in the embodiment of Figure 2 , the green noise-reducing element 301 is inserted at a position radially external to the carcass structure during the manufacture of the green tire 100 and expands and co-crosslinks during vulcanization in the mold, as described above.

[0189] Alternatively, the tire 100 is manufactured and vulcanized without the noise-reducing element 301. In this case, the noise-reducing element can be applied at a radially internal position to the vulcanized layer (liner) of the air-impermeable elastomeric compound of the finished tire at the green element stage, and expanded and crosslinked there in a subsequent step.

[0190] Alternatively, the noise-reducing element can be applied to the finished tire with a suitable adhesive after having been expanded and crosslinked separately.

[0191] The present invention will be further illustrated by a number of preparation examples, which are for illustrative and non-limiting purposes only. Examples

[0192] Example 1

[0193] Preparation of Expandable Elastomer Compounds A, B and C

[0194] The compositions of expandable elastomer compounds A, B and C are shown in Table 1 below. All values are expressed in phr.

[0195] Table 1: Elastomer Compositions

[0196]

[0197]

[0198] Composition C: According to the teachings of WO2015014577A1 (Table 1C-3).

[0199] NR: Natural rubber (Standard ThaiRubber Str 20 - Thaiteck Rubber);

[0200] IR: Isoprene rubber (SKI 3gr 2 - Aneka Bumi Pratama)

[0201] Carbon black: N234 from Cabot Corporation;

[0202] Silica: from Solvay 1165MP, standard grade, surface area of about 175 m 2 / g;

[0203] Silane: Bis[3-(triethoxysilyl)propyl]tetrasulfide JH - S69 from Chemspec Ltd;

[0204] Silane 2: 50% mixture of bis[3-(triethoxysilyl)propyl]tetrasulfide from Evonik

[0205] Blowing agent: Unicell D200A azodicarbonamide from Tramaco

[0206] Polycaprolactone: Capa 2125 end - capped with polycaprolactone diol from Ingevity

[0207] ZnO: Standard zinc oxide from A - ESSE;

[0208] Vulcanizing agent: 67% insoluble sulfur, Solfotecnica

[0209] Crosslinking resin: Octylphenol - formaldehyde resin with free hydroxymethyl groups, SP - 1045H resin from SIGroup.

[0210] Starting from the elastomeric compositions shown in Table 1, the corresponding elastomeric compounds were prepared according to the following method.

[0211] Using a Banbury, Intermix or Brabender internal mixer, the components were mixed in two steps.

[0212] In the first mixing step (1), all components except the vulcanizing agent and the crosslinking resin were added and mixing was continued for up to 5 minutes to reach a temperature of about 145 °C. Subsequently, in the second mixing step (2), again using the internal mixer, the crosslinking resin and the vulcanizing agent were added separately and mixing was continued for about 4 minutes while maintaining the temperature below 100 °C.

[0213] Then the compound was unloaded and calendered to obtain circular samples with a diameter of about 40 mm and a thickness of about 2 mm. According to the ISO6502 method, using an Alpha Technologies model MDR2000 rheometer, with a pressure cell and a 100% filled vulcanization chamber, MDR rheological analysis was carried out at 170 °C for 10 minutes.

[0214] Compared with the samples obtained with the comparative compound C, the samples obtained with compounds A and B of the present invention showed much greater swelling (about 40% by volume and about 29% by volume respectively) and a higher level of porosity.

[0215] Figure 4 Photographs of the samples obtained with compounds B and C after swelling and crosslinking (with diameters of 6.7 cm and 5.2 cm respectively) are shown, from which the greater swelling of compound B according to the present invention can be seen.

[0216] Figure 5 The MDR (torque S') and pressure (P) graphs obtained with compound A after 10 minutes are shown. The pressure curve shows a rapid and substantially constant pressure increase until a maximum of 7000 kPa is reached, thus demonstrating that compound A is able to effectively retain the gas released inside it, explaining the greater swelling found.

[0217] Figure 6Shows the MDR (torque S’) and pressure (P) graphs obtained with compound B after 10 minutes. The pressure curve shows that the pressure rapidly increases from a minimum of 5700 kPa to a maximum of approximately 7000 kPa, and then decays to approximately 6420 kPa during the final recovery step, thus demonstrating a good pressure increase (approx. 1300 kPa) and consequently compound swelling. In addition, it can be seen from the graph that compound B is able to effectively retain the gas released inside it, explaining the greater swelling detected.

[0218] Figure 7 Shows the MDR (torque S') and pressure (P) graphs obtained with comparative compound C after 10 minutes. The pressure curve clearly shows a pressure increase of only 500 kPa from a minimum of 5700 kPa to a maximum of 6200 kPa (which is significantly lower than that of compound B), followed by a pressure decay up to 5760 kPa, which is very close to the minimum pressure. Based on these data, it is emphasized that compound C does not produce a satisfactory pressure increase, so the compound volume does not increase significantly, and it cannot very effectively retain the gas released inside it, explaining the limited swelling detected.

[0219] Example 2

[0220] Preparation and characterization of tires 1 and 2

[0221] Compound A described in Example 1 was used to prepare a 255 / 40R20 Pirelli P ZERO all-season sound-insulating tire by symmetrically placing a green compound layer with a thickness of approximately 3 mm, a width of approximately 180 mm, and a length equal to the circumference of the tire (tire 1 of the present invention) on the radial inner surface of the backing relative to the equatorial plane. TM The same tire without a sound-insulating compound layer was used as a reference (tire 2).

[0222] Then the green tires were subjected to a conventional vulcanization process. In the finished tire 1, it was observed that the lateral dimension of the noise reduction element remained at approximately 180 mm, and the thickness of the noise reduction element increased by 150% to 200%.

[0223] Then, according to the SAE J2710 method, a noise evaluation test was carried out on the tires by rotating the tires mounted on a rim connected to an engine on a wheel with a rough surface.

[0224] Since the tire rolls on the road wheel surface, vibrations are generated in the tire, and part of this vibration is transmitted into the air and becomes noise measured in dB.

[0225] The test included bringing the wheel to a speed of 150 km / h, making it free, and measuring the noise at speeds up to 20 km / h, with a total noise acquisition of approximately 10 minutes.

[0226] In this test, the tire according to the invention shows a significant reduction in noise compared to the reference tire while maintaining its structural integrity.

Claims

1. A crosslinkable and expandable elastomeric compound obtained by mixing an elastomeric composition, wherein the elastomeric composition comprises: (i) 100 phr of at least one natural or synthetic elastomeric polymer, (ii) 10 to 80 phr of at least one reinforcing filler, (iii) 0 to 3 phr of at least one vulcanizing agent, (iv) 2 to 25 phr of at least one crosslinking resin, (v) 5 to 30 phr of at least one blowing agent, (vi) 0 to 40 phr of at least one reagent selected from fatty acid amides, and (vii) 1 to 20 phr of at least one reagent selected from polymers and copolymers of one or more hydroxy acids.

2. The compound according to claim 1, wherein the elastomeric composition comprises at least one diene elastomeric polymer selected from natural rubber, synthetic isoprene rubber, and mixtures thereof, preferably comprising only natural rubber, synthetic isoprene rubber, and mixtures thereof as natural or synthetic diene elastomeric polymers.

3. The compound according to claim 1 or 2, wherein the elastomeric composition comprises at least 30 phr, preferably at least 40 phr of the reinforcing filler.

4. The compound according to any one of the preceding claims, wherein the elastomeric composition comprises the vulcanizing agent in an amount less than 2.5 phr, preferably less than 2.0 phr or 1.0 phr, more preferably no vulcanizing agent is present.

5. The compound according to any one of the preceding claims, wherein the elastomeric composition comprises at least one crosslinking resin, the crosslinking resin comprising at least one methylene donor agent and at least one methylene acceptor agent, preferably selected from phenol-formaldehyde resins, resorcinol-formaldehyde resins, cresol-formaldehyde resins, and mixtures thereof.

6. The compound according to any one of the preceding claims, wherein the elastomeric composition comprises the crosslinking resin in an amount of 2 to 25 phr, more preferably 8 to 20 phr.

7. The compound according to any one of the preceding claims, wherein the elastomeric composition comprises at least one blowing agent selected from diazo, dinitroso, hydrazide, carbohydrazide, semicarbazide, tetrazole, carbonate, bicarbonate, citrate reagents, and mixtures thereof, preferably the blowing agent is azodicarbonamide.

8. The compound according to any one of the preceding claims, wherein the elastomeric composition comprises polymers and copolymers of one or more hydroxy acids, the polymers and copolymers of one or more hydroxy acids being selected from polymers and copolymers of caprolactone, lactic acid, glycolic acid, and mixtures thereof.

9. The compound according to any one of the preceding claims, wherein the elastomeric composition comprises polymers and copolymers of one or more hydroxy acids in an amount of 2 phr to 15 phr, preferably 3 phr to 12 phr.

10. The compound according to any one of the preceding claims, wherein the elastomeric composition does not contain urea.

11. A noise reduction element made by crosslinking and expanding the crosslinkable and expandable elastomeric compound according to any one of claims 1 to 10.

12. A sound-insulating tire for a vehicle wheel, which comprises: - carcass structure; - tread, said tread being located at a position radially outward from said carcass structure; - a vulcanized layer (liner) of an air-impermeable elastomeric compound, said vulcanized layer being disposed radially inside the carcass structure; - at least one noise-reducing element made of an expanded elastomeric material; wherein said at least one noise-reducing element is made by crosslinking and expanding a crosslinkable and expandable elastomeric compound according to any one of claims 1 to 10.

13. The sound-insulating tire according to claim 12, wherein said at least one noise-reducing element is disposed at a radially inner position of the vulcanized layer of the air-impermeable elastomeric compound, and / or said at least one noise-reducing element is disposed adjacent to said carcass structure.

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