DESCRIPTION FIELD OF THE INVENTION

The present invention relates to a process for preparing a vulcanisable elastomeric composition, in particular a vulcanisable elastomeric composition comprising a combination of a non-functionalised silica and a functionalised silica. In a further aspect, the invention also relates to a vulcanisable elastomeric composition comprising a combination of a non-functionalised silica and a functionalised silica, and to a tyre for vehicle wheels comprising at least one structural element made of a cross-linked elastomeric material obtained by vulcanisation of a vulcanisable elastomeric composition comprising a combination of a non-functionalised silica and a functionalised silica, with improved tyre performance, in particular the balance between rolling resistance, grip in all conditions, and mechanical properties.

PRIOR ART Tyre manufacturers need to make products with improved wet grip features, low rolling resistance, resulting in lower fuel consumption, and good wear and tear resistance at all temperatures.

Among the many solutions proposed, the one most commonly adopted to meet this need consists in replacing carbon black, typically used as a reinforcing filler, in whole or in part, with white reinforcing fillers, typically silica, in the formulations for tyre treads.

In addition to providing excellent reinforcement, silica also imparts superior wet grip and is widely used in tyres for both passenger cars and motorcycles, in summer, winter and all-season applications. For such uses, silicas with different features are commercially available or may be prepared according to known processes. Typically, highly dispersible commercial silicas are used in the elastomeric material of the tyre tread, generally with a high surface area (BET).

However, although the use of these commercial silicas leads to a lower hysteresis with consequent lower rolling resistance, it also implies a reduction of the mechanical properties, in particular the tear resistance, substantially due to the poor affinity of these fillers compared to elastomeric polymers commonly used in the production of tyres.

In order for the elastomeric material of the tyre tread to have the desired properties, it is therefore important that the silica is homogeneously distributed in the elastomeric composition and that it remains so over time, avoiding the formation of agglomerates as much as possible.

The distribution and dispersion of the silica in the elastomeric composition depend both on their chemical nature and on the mechanical energy used to mix them. In particular, a better distribution and dispersion is achieved the more similar their chemical nature is, that is, the more they are compatible, and the greater the mechanical stress applied.

Typically, in rubber compounds, coupling agents, also called compatibilisers, are used to improve the dispersion and compatibilisation between silica, or inorganic fillers having surface hydroxyl groups, and rubber.

Among the most used coupling agents are the polysulphide silane coupling agents, such as for example bis(3-triethoxysilyl-propyl)tetrasulphide TESPT and bis(3-triethoxysilyl-propyl)disulphide TESPD.

These agents have a silane head, capable of reacting with the surface hydroxyl groups of the fillers, and polysulphide units which, upon heating, decompose producing sulphydryl radicals capable of reacting with the elastomer, but with not always optimal results.

It is in fact known that the thermal decomposition of these polysulphide systems is difficult to control, as it may already take place at low temperatures, well before the vulcanisation step (see for example chapter 3, par. 3.17 of the book “Silane coupling, Compounding Precipitated Silica in Elastomers”, Hewitt, Ciullo, William Andrew Publishing, 2007). Furthermore, the radical species thus generated have high reactivity and poor selectivity leading to the formation of mixtures of mono- and disulphides. To homogeneously distribute these polysulphide coupling agents it is necessary to carefully control the internal temperature in the mixers in order to avoid that reactions with the elastomer occur before a satisfactory distribution of the silica and of the coupling agents themselves occurs. In order to overcome these drawbacks, the use of functionalised silicas - which include in their structure functional groups which are able to react with the elastomer - has been proposed.

Some examples of functionalised silicas are described in the patents: · U.S. 6184408 in the name of Dow Corning, which describes silicas modified with sulphurised silanising agents such as organosilanes, organosiloxanes and organo disilazanes, substituted with hydrocarbon radicals having mercapto, disulphide or polysulphide functionality;

• U.S. 7687107 in the name of PPG, which describes silicas modified with sulphurised silanising agents such as bis(alkoxysilylalkyl)polysulphides;

• U.S. 7569107 in the name of PPG, which describes silicas modified with sulphurised silanising agents such as organosilanes functionalised on hydrocarbon residues with sulphide, polysulphide or mercapto groups, in the presence of anionic, non-ionic or amphoteric surfactants; · U.S. 9688784 in the name of PPG, which describes silicas modified with sulphurised silanising agents, in the presence of polymers and anionic, non ionic or amphoteric surfactants;

• U.S. 8846806 in the name of PPG, which describes silicas modified with sulphurised silanising agents such as mercaptosilanes in the presence of anionic, non-ionic or amphoteric surfactants; and

• U.S. 2016326374 in the name of Evonik, which describes silicas modified with sulphurised silanising agents, such as sulphur-containing silanes.

Although the solutions proposed in the art have brought improvements, the tyre industry has shown a continuous interest in finding new solutions suitable for obtaining optimal performance in terms of mechanical properties and hysteresis, while maintaining good stability, workability and vulcanisation kinetics of the elastomeric composition.

SUMMARY OF THE INVENTION The Applicant has undertaken studies to further improve the distribution and dispersion of silica in the production of an elastomeric composition for tyre treads, with the aim of obtaining good hysteresis values at all temperatures, i.e. good grip values in both dry and wet conditions, without penalising the rolling resistance and without affecting the mechanical properties of the vulcanisation product, i.e. of the cross-linked elastomeric material.

Surprisingly, the Applicant has found that through the use of two different types of white reinforcing filler, in particular at least one non-functionalised white reinforcing filler and at least one functionalised silica, added in two distinct steps of the preparation process of a vulcanisable elastomeric composition, it was possible to obtain the desired result.

In particular, during the experimentation, the Applicant observed that the total replacement of the white reinforcing filler with a functionalised silica in the conventional processes of addition and mixing with elastomeric polymers led to obtaining a too rapid vulcanisation kinetics, and to hardness values and static modules not adequate for the objectives set.

At the same time, the Applicant has observed that although the partial replacement of the white reinforcing filler with a functionalised silica achieved an improvement in performance in terms of lower rolling resistance with the same other requirements, it entailed problems of workability, with formation of tears and irregularities during the sheet extrusion of the elastomeric composition.

Continuing with the experimentation, the Applicant has surprisingly observed that the addition and mixing with elastomeric polymers of the two types of white reinforcing filler, in particular a non-functionalised silica and a functionalised silica, at different times allowed the workability problems to be solved, at the same time obtaining an elastomeric composition with better static and dynamic mechanical features, and with hysteresis values predicting a good behaviour of the tyre at all temperatures and conditions of use (dry and wet).

A first aspect of the present invention therefore is a process for the preparation of a vulcanisable elastomeric composition comprising:

• a mixing step (i) in which at least one elastomeric polymer is mixed with one or more additives, except vulcanisation agents, to form a non-vulcanisable elastomeric composition,

• a mixing step (ii) in which the non-vulcanisable elastomeric composition obtained in the mixing step (i) is mixed with a vulcanisation agent, characterised in that said mixing step (i) comprises: - a first mixing step (ia) in which said at least one elastomeric polymer is mixed with a non-functionalised white reinforcing filler and a coupling agent to form a first elastomeric composition, and

- a second mixing step (ib) in which said first elastomeric composition is mixed with a functionalised silica to form said non-vulcanisable elastomeric composition.

In a second aspect, the present invention consists of a vulcanisable elastomeric composition comprising for 100 phr of elastomeric polymer:

(a) 100 phr of at least one diene elastomeric polymer;

(b) 10 phr to 90 phr, preferably 30 phr to 70 phr, of at least one non- functionalised white reinforcing filler; and

(c) 5 phr to 40 phr, preferably 10 phr to 30 phr, of at least one functionalised silica.

In a third aspect, the present invention relates to a structural element of a tyre for vehicle wheels comprising a vulcanisable elastomeric composition according to the second aspect of the present invention.

According to a fourth aspect, the present invention consists of a tyre comprising at least one structural element which includes a cross-linked elastomeric material obtained by cross-linking a vulcanisable elastomeric composition according to the second aspect of the present invention.

DEFINITIONS

For the purposes of the present description and of the following claims, the term “phr” (parts per hundreds of rubber) denotes the number of parts by weight of a given component of the elastomeric composition by 100 parts by weight of the diene elastomeric polymer (vulcanisable polymer). Unless otherwise indicated, all the percentages are expressed as percentages by weight.

In the present description and in the claims, the term “elastomeric polymer” or “rubber” or “elastomer” denotes a vulcanisable natural or synthetic polymer which, after vulcanisation, at room temperature may be stretched repeatedly to at least twice its original length and which, after removal of the tensile load substantially immediately returns with force to approximately its original length (according to the definitions of the ASTM D1566-11 Standard terminology relating to Rubber). The term “diene elastomeric polymer” indicates an elastomeric polymer derived from the polymerization of one or more monomers, of which at least one is a conjugated diene.

In the present description and in the claims, the term “non-vulcanisable elastomeric composition” means the product obtained by mixing and possibly heating at least one elastomeric polymer with at least one of the additives commonly used in the preparation of tyre compounds, with the exception of vulcanisation agents. The non-vulcanisable elastomeric composition is made “vulcanisable” by the presence of a vulcanisation agent, and possibly of the other additives of the vulcanisation package, in the composition itself.

In the present description and in the claims, the term “cross-linked elastomeric material” indicates the material obtained by vulcanisation of a vulcanisable elastomeric composition.

In the present description and in the claims, the term “green” is generally used to indicate a material, a compound, a composition, a structural element or a tyre not yet vulcanised.

In the present description and in the claims, the term “reinforcing filler” indicates a reinforcing material typically used in the art to improve the mechanical properties of tyre rubbers.

The term “vulcanisation” refers to the cross-linking reaction in an elastomeric composition induced for example by a sulphur-based vulcanisation agent.

The term “vulcanisation agent” indicates a product capable of transforming an elastomeric composition into an elastic and resistant material due to the formation of a three-dimensional network of inter- and intra-molecular bonds.

The term “vulcanisation package” means the set of vulcanisation agent and one or more vulcanisation additives selected from vulcanisation activating agents, accelerants and/or retardants.

DETAILED DESCRIPTION OF THE INVENTION

The present invention, in at least one of the aforementioned aspects, may exhibit one or more of the preferred features described below.

Diene elastomeric polymer (a)

According to a preferred embodiment, said at least one diene elastomeric polymer (a) may be selected, for example, among diene elastomeric polymers which are commonly used in sulphur cross-linkable elastomeric compositions, which are particularly suitable for producing tyres, i.e. among elastomeric polymers or elastomeric copolymers with an unsaturated chain having a glass transition temperature (Tg) generally below about 20°C, preferably in the range from about 0°C to about -110°C.

Preferably, the diene elastomeric polymer has a weight average molecular weight higher than 80.000 g/mol.

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 an amount not exceeding 60% by weight.

The conjugated diolefins generally contain from 4 to 12, preferably from 4 to 8 carbon atoms and may 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 mixtures thereof. 1 ,3-butadiene and isoprene are particularly preferred.

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

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

Preferably, the diene elastomeric polymer which may be used in the present invention may be selected, for example, from among: cis-1 ,4-polyisoprene (natural or synthetic, preferably natural rubber), 3,4-polyisoprene, polybutadiene (in particular polybutadiene with a high content of 1 ,4-cis), 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.

Advantageously, the diene elastomeric polymer used in the present invention may be functionalised. The functional group may be introduced into the elastomeric polymer by processes known in the art such as, for example, during the production of the elastomeric polymer by copolymerisation with at least one corresponding functionalised monomer containing at least one ethylene unsaturation; or by subsequent modification of the elastomeric polymer by grafting at least one functionalised monomer in the presence of a free radical initiator (for example, an organic peroxide).

Alternatively, the functionalisation may be introduced by reaction with suitable terminating agents or coupling agents. In particular, the diene elastomeric polymers obtained by anionic polymerization in the presence of an organometallic initiator (in particular, an organolithium initiator) may be functionalised by reacting the residual organometallic groups derived from the initiator with suitable terminating agents or coupling agents such as, for example, amines, amides, imines, carbodiimides, alkyltin halides, substituted benzophenones, alkoxysilanes, aryloxy silanes, alkylthiols, alkyldithiolsilanes, carboxyalkylthiols, carboxyalkylthiolsilanes, and thioglycols.

Useful examples of terminating agents or coupling agents are known in the art and described, for example in patents EP2408626, EP2271682, EP3049447A1 , EP2283046A1 , EP2895515A1 , WO2015/086039A1 and WO2017/211876A1.

Preferably, said at least one functionalised elastomeric polymer is obtained from polybutadiene (in particular polybutadiene with a high 1 ,4-cis content), styrene/1 ,3- butadiene copolymers, styrene/isoprene/1 ,3-butadiene copolymers, styrene/1 ,3- butadiene/acrylonitrile copolymers, and mixtures thereof. Advantageously, said at least one functionalised elastomeric polymer (b) is obtained from styrene/1 ,3- butadiene copolymers. Useful examples of functionalised diene elastomeric polymers are the functionalised styrene butadiene copolymers SPRINTAN™ SLR 3402 and SPRINTAN™ SLR 4602, manufactured and distributed by Trinseo, PA, USA.

Non-functionalised white reinforcing filler (b) The non-functionalised white reinforcing filler (b) may be any conventional white reinforcing filler.

The non-functionalised white reinforcing filler is preferably selected from conventional silica and silicates, in the form of fibres, flakes or granules, such as bentonite, nontronite, beidellite, volkonskoite, hectorite, saponite, sauconite, vermiculite, sericite, sepiolite, paligorskite also known as attapulgite, montmorillonite, alloisite and the like, possibly modified by acid treatment and/or derivatised, and mixtures thereof, more preferably it is silica. Examples of silica are a pyrogenic silica, a precipitated amorphous silica, a wet silica (hydrated silicic acid), or mixtures thereof.

Preferably the non-functionalised white reinforcing filler (b) has a specific surface area (BET) of at least 30 m ² /g, more preferably of at least 50 m ² /g, and even more preferably of at least 80 m ² /g.

Preferably the non-functionalised white reinforcing filler (b) has a specific surface area (BET) of less than 400 m ² /g, more preferably less than or equal to 250 m ² /g, and even more preferably less than or equal to 220 m ² /g.

Advantageously, the non-functionalised white reinforcing filler (b) has a specific surface area (BET) from about 50 m ² /g to about 350 m ² /g, more preferably from about 70 m ² /g to about 240 m ² /g, even more preferably from about 90 m ² /g to about 190 m ² /g.

The elastomeric composition according to the invention comprises said non- functionalised white reinforcing filler (b) in amounts from 10 phr to 90 phr, preferably from 30 phr to 70 phr.

Examples of suitable commercial silicas are products sold under the brand name Hi-Sil® of PPG Industries Chemicals BV (Pittsburgh, Pa), Ultrasil® of Evonik, or Zeosil® of Rhodia, such as the precipitated silica Rhodia Zeosil MP1165 (BET area specific surface area 160 m2/g), Ultrasil® 7000 (BET specific surface area 160 m2/g) and Zeosil 1115 MP (BET specific surface area 95-120 m2/g). Coupling agent

The white reinforcing filler is incorporated into the elastomeric composition with a coupling agent, or compatibiliser, capable of interacting with the silica and binding it to the elastomeric polymer during vulcanisation. The coupling agents preferably used are those based on silane, in particular amino-silanes and sulpho- silanes.

Preferred amino silanes are represented by the following formula (I):

(R) ₃ Si-CnH2n-[X-CmH2m]p-Y (I) wherein the R groups, equal or different from each other, are selected from alkyl or alkoxy groups having from 1 to 4 carbon atoms, provided that at least one of the R groups is an alkoxy group; n and m, equal to or different from each other, are an integer from 1 to 6 inclusive; p is an integer from 0 to 5 inclusive;

X is an -NH- group, and

Y is an -NH2 or NHR’ group, where R’ is an alkyl or cycloalkyl group of 1 to 6 carbon atoms. Preferred sulpho-silanes are represented by the following formula (II):

(R) ₃ Si-CnH2n-X (II) wherein

X is a mercapto group (-SH), or -(S)mCnH2n-Si-(R) ₃ the R groups, equal or different from each other, are selected from alkyl or alkoxy groups having from 1 to 4 carbon atoms, provided that at least one of the R groups is an alkoxy group; and n and m, equal to or different from each other, are an integer from 1 to 6 inclusive.

Amino-silanes which may be used in the present invention represented by formula (I) are 2-aminoethyl-trimethoxysilane, 2-aminoethyl-triethoxysilane, 2- aminoethyl-tripropoxysilane, 2-aminoethyl-tributoxysilane, 3-aminopropyl- trimethoxysilane, 3-aminopropyl-triethoxysilane (APTES), 3-aminopropyl- methyldiethoxysilane, 3-aminopropyl-methyldimethoxysilane, 3-aminopropyl- diisopropylethoxysilane, 3-aminopropyltris-(methoxyethoxyethoxy)silane, 3- aminopropyl-diisopropylethoxy silane, 3-(2-aminomethylamino)propyl- triethoxysilane, 3-(2-(2-aminoethylamino)ethylamino)propyl-trimethoxysilane, 4- aminobutyl-triethoxysilane, 4-aminobuthyldimethyl-methoxysilane, 4-aminobutyl- triethoxysilane, N-(2-aminoethyl)aminomethyl-triethoxysilane, N-(2-aminoethyl)-3- aminopropyl-trimethoxysilane [also known as N-[3- (trimethoxysilyl)propyl]ethylenediamine) (EDTMS)], N-(2-aminoethyl)-3- aminopropyl-triethoxysilane, N-(2-aminoethyl)-3-aminopropyl-tris(2- ethylethoxy)silane, N-(2-aminoethyl)-3-aminopropyl-methyldimethoxysilane, N-(2- aminoethyl)-3-aminopropyl-methyldiethoxysilane, N-(2-aminoethyl)-3- aminoisobutyl-methyldimethoxysilane, N-(6-aminohexyl)-3-aminopropyl- trimethoxysilane, N-(6-aminohexyl)-3-aminopropyl-triethoxysilane, N-2- (vinylbenzylamino)-ethyl-3-aminopropyl-trimethoxysilane, N- cyclohexyl(aminomethyl)methyldietoxysilane, N- cyclohexyl(aminomethyl)triethoxysilane, N-cyclohexyl(aminomethyl) trimethoxysilane, N-cyclohexyl-3-aminopropyl-trimethoxysilane, N-(n-butyl)-3- aminopropyl-trimethoxysilane, N-(n-butyl)-3-aminopropyl-triethoxysilane, N-(n- butyl)-aminomethyl-triethoxysilane, N,N-diethylaminopropyl-trimethoxysilane, N,N- dimethylaminopropyl-trimethoxysilane, N,N-diethylaminomethyl-triethoxysilane.

Sulpho-silanes usable in the present invention represented by formula (I) are bis[3-(trimethoxysilyl)propyl]-tetrasulphane (TESPT), bis[3-(triethoxysilyl)propyl]- disulphane (TESPD), bis[2-(trimethoxysilyl)ethyl]-tetrasulphane, bis[2- (triethoxysilyl)ethyl]-trisulphane, bis[3-(trimethoxysilyl)propyl]-disulphane, (1 - mercaptomethyl)triethoxysilane, (2-mercaptoethyl)triethoxysilane, (3- mercaptopropyl)triethoxysilane, (3-mercaptopropyl)methyldietoxysilane, (3- mercaptopropyl)methyldimethoxysilane, (3-mercaptopropyl)trimethoxysilane, 3- octanoylthio-1 -propyltriethoxysilane and (2-mercaptoethyl)tripropoxysilane.

Preferred compounds represented by the formula (I) and (II) are (i) amino silanes selected from the group consisting of (3-aminopropyl)triethoxysilane (APTES), (3-aminopropyl)trimethoxysilane, N-(2-aminoethyl)-3- aminopropyltrimethoxysilane [also known as N-[3-

(trimethoxysilyl)propyl]ethylenediamine (EDTMS)], and N-(2-aminoethyl)-3- aminopropyltriethoxysilane, and (ii) sulpho-silanes selected from the group consisting of bis[3-(trimethoxysilyl)propyl]-tetrasulphane (TESPT), bis[3- (triethoxysilyl)propyl]-disulphane (TESPD), and (3- mercaptopropyl)trimethoxysilane.

Functionalised silica (c)

The functionalised silica (c) may advantageously comprise a sulphurised silanised silica. The sulphurised silanised silica useful for the purposes of the present invention comprises a sulphur content equal to or greater than 0.1%, preferably equal to or greater than 0.25%. The sulphur content of the sulphurised silanised silica is preferably in the range from 0.5 to 4.0%, more preferably from 0.45 to 2.0%, extremes included.

The sulphurised silanised silica useful for the purposes of the present invention comprises a carbon content equal to or greater than 0.5%, preferably equal to or greater than 1.0%. The carbon content of the sulphurised silanised silica is preferably in the range from 1.0 to 10.0%, more preferably from 2.0 to 8.0%, extremes included.

The sulphurised silanised silica useful for the purposes of the present invention has a pH of between 5 and 8, preferably between 6 and 7.5.

The carbon and sulphur content of sulphurised silanised silica is determined by elemental analysis, using an elemental analyser MACRO Cube Analyzer, manufactured by Elementar. The process involves converting species C and S into CO2 and SO2, respectively, by high temperature combustion, typically higher than 1000°C, adsorption and desorption from a purge and trap column, followed by measurement with a thermal conductivity detector. The pH is measured according to the ISO 787-9 method.

Preferably the sulphurised silanised silica has a specific surface area (BET) of at least 30 m ² /g, more preferably of at least 40 m ² /g, and even more preferably of at least 60 m ² /g.

Preferably, the sulphurised silanised silica has a specific surface area (BET) of less than 300 m ² /g, more preferably less than or equal to 240 m ² /g, and even more preferably less than or equal to 200 m ² /g.

Advantageously, the sulphurised silanised silica has a specific surface area (BET) from about 60 m ² /g to about 260 m ² /g, more preferably from about 80 m ² /g to about 220 m ² /g, even more preferably from about 90 m ² /g to about 180 m ² /g.

Sulphurised silanised silica useful for the purposes of the present invention is a silica prepared by reaction of a silica, such as fumed silica, precipitated amorphous silica, wet silica (hydrated silicic acid), anhydrous silica (anhydrous silicic acid), or mixtures thereof, or of a metal silicate, such as aluminium silicate, sodium silicate, potassium silicate, lithium silicate or mixtures thereof, with at least one sulphurised silanising agent. Typically, the sulphurised silanised silica is more hydrophobic than the starting non-silanised silica.

Preferably, the sulphurised silanised silica is prepared in the presence of surfactants. Sulphurised silanising agents, surfactants and sulphurised silanised silicas suitable for the present purposes are described for example in patents US6184408, US7687107, US7569107, US9688784, US8846806 and

US2016326374, incorporated herein by reference.

The elastomeric composition according to the invention comprises said sulphurised silanised silica in amounts from 5 phr to 40 phr, preferably from 10 phr to 30 phr.

A commercial example of sulphurised silanised silica useful for the purposes of the present invention is Agilon 400 silica from PPG Industries Chemicals BV (Pittsburgh, Pa). For some applications, the vulcanisable elastomeric composition may comprise at least 1 phr, more preferably at least 2 phr, more preferably at least 3 or 4 phr of carbon black.

Carbon black may be selected from those of standard grade for tyres, or having a surface area not smaller than 20 m ² /g, more preferably greater than 50 m ² /g (measured in accordance with the ASTM D6556-16 standard).

Commercial examples of carbon black are N375 or N234 marketed by Birla Group (India) or Cabot Corporation.

Vulcanisation package

The vulcanisation agent (F) is preferably selected from sulphur, or alternatively, sulphur-containing molecules (sulphur donors), such as for example caprolactam disulphide (CLD), bis(trialkoxysilyl)propyl]polysulphides, dithiophosphates, phosphorylpolysulphide (SDT) and mixtures thereof.

Preferably, the vulcanising agent is sulphur preferably selected from soluble sulphur (crystalline sulphur), insoluble sulphur (polymeric sulphur), (iii) oil- dispersed sulphur and mixtures thereof.

Commercial examples of suitable vulcanising agents are the 65% sulphur known under the trade name of Rhenogran of Lanxess, the 67% sulphur known under the trade name of Crystex OT33 of Eastman, the 95% sulphur known under the trade name of Solvay SchwefelKC, the rhombic crystalline sulphur known under the trade name of Sulphur (1% oil and 0.3% silica) of Zolfindustria.

The vulcanisation agent may be present in the vulcanisable elastomeric composition in an overall amount generally of from 0.1 to 15 phr, preferably from 0.5 to 10 phr, even more preferably from 1 to 7 phr.

The vulcanisable elastomeric composition may comprise one or more vulcanisation agents as defined above in mixture.

The vulcanisation agent is preferably used together with adjuvants such as vulcanisation activating agents, accelerants and/or retardants known to the man skilled in the art. The set of vulcanisation activating agents, accelerants and/or retardants constitutes, together with the vulcanisation agent, the so-called “vulcanisation package”.

The vulcanisation activators which are particularly effective are zinc compounds, and in particular ZnO, ZnCC>3, zinc salts of saturated or un saturated fatty acids containing from 8 to 18 carbon atoms, such as,, example, zinc stearate, which are preferably formed in situ in the elastomeric composition from ZnO and fatty acid, as well as BiO, PbO, Pb304, PbO or mixtures thereof. Commercial examples are Wuhan Jinghe's Dispersing Agent FS-200 fatty acid zinc salts, KLK OLEO's Palmera B1810 stearic acid or U.S. Zinc grade 203 zinc oxide. The vulcanisation accelerant agent is preferably selected from dithiocarbamates, guanidines, thioureas, thiazoles, sulphenamides, sulphenimides, thiurams, amines, xanthates and mixtures thereof.

Preferably, the accelerant agent is selected from N-cyclohexyl-2-benzothiazol- sulphenamide (CBS), N-tert-butyl-2-benzothiazol-sulphenamide (TBBS) and mixtures thereof.

A commercial example of a suitable accelerant agent is N-cyclohexyl-2- benzothiazol-sulphenamide Vulkacit® (CBS) marketed by Lanxess.

The vulcanisation accelerant agent may be present in the vulcanisable elastomeric composition in an overall amount generally ranging between 0.05 phr and 10 phr, preferably between 0.1 phr and 5 phr.

The vulcanisable elastomeric composition may comprise one or more vulcanisation accelerants as defined above in mixture. The vulcanisation retardant agent may be selected for example from urea, phthalic anhydride, N-nitrosodiphenylamine N-cyclohexylthiophthalimide (CTP), and mixtures thereof.

A commercial example of a suitable retardant agent is N- cyclohexylthiophthalimide VULKALENT G of Lanxess.

The retardant agent may be present in the vulcanisable elastomeric composition in an amount generally ranging between 0.05 phr and 2 phr.

The vulcanisable elastomeric composition may comprise one or more vulcanisation retardants as defined above in mixture Other additives

The vulcanisable elastomeric composition may comprise other commonly used additives selected on the basis of the specific application for which the elastomeric composition is designed, such as for example antioxidant agents, anti-ageing agents, plasticisers, adhesives, antiozonants (in particular of the p- phenylenediamine type), waxes, modified resins, fibres (e.g. Kevlar ^® pulp), or mixtures thereof.

The antioxidant agent may be selected from the group comprising phenylenediamine, diphenylamine, dihydroquinoline, phenol, benzimidazole, hydroquinone and derivatives thereof, optionally in mixture. The antioxidant agent is preferably selected from N-isopropyl-N'-phenyl-p- phenylenediamine (IPPD), N-(1 ,3-dimethyl-butyl)-n'-phenyl-p-phenylenediamine (6PPD), N,N'-bis-(1 ,4-dimethyl-pentyl)-p-phenylenediamine (77PD), N,N'-bis-(1- ethyl-3-methyl-pentyl)-p-phenylenediamine (DOPD), N,N'-bis-(1 ,4-dimethyl- pentyl)-p-phenylenediamine, N,N'-diphenyl-p-phenylenediamine (DPPD), N,N'- ditolyl-p-phenylenediamine (DTPD), N,N'-di-beta-naphthyl-p-phenylenediamine (DNPD), N,N'-bis(1 -methylheptyl)-p-phenylenediamine, N,N'-Di-sec-butyl-p- phenylenediamine (44PD), N-phenyl-N-cyclohexyl-p-phenylenediamine, N-phenyl- N'-1-methylheptyl-p-phenylenediamine and the like and mixtures thereof, preferably it is N-(1 ,3-dimethyl-butyl)-N’-phenyl-p-phenylenediamine (6-PPD). A commercial example of a suitable antioxidant agent is Solutia/Eastman 6PPD and Lanxess TMQ 2,2,4-trimethyl-1 ,2-dihydroquinoline - Vulkanox ^® HS/LG.

The antioxidant agent may be present in the vulcanisable elastomeric composition in an overall amount generally ranging between 0 phr and 20 phr, preferably between 0.5 phr and 10 phr. The wax may be for example a petroleum wax or a mixture of paraffins.

Commercial examples of suitable waxes are Repsol's N-paraffin mixture and Rhein Chemie's Antilux ^® 654 microcrystalline wax and Ser SpA's RIOWAX BM-01 wax.

The wax may be present in the vulcanisable elastomeric composition in an overall amount generally ranging between 0 phr and 20 phr, preferably between 0.5 phr and 5 phr.

In order to further improve the workability, the vulcanisable elastomeric composition may be admixed with at least one plasticiser agent 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. Commercial example of a plasticizing agent is Nynas NYTEX ^® 4700 naphthenic oil.

The amount of plasticiser generally ranges from 0 phr and 70 phr, preferably from 5 phr to 30 phr.

The above vulcanisable elastomeric composition is prepared according to the preparation process of the present invention which comprises:

• a mixing step (i) in which at least one elastomeric polymer is mixed with one or more additives, except vulcanisation agents, to form a non-vulcanisable elastomeric composition,

• a mixing step (ii) in which the non-vulcanisable elastomeric composition obtained in the mixing step (i) is mixed with a vulcanisation agent, characterised in that said mixing step (i) comprises:

- a first mixing step (ia) in which said at least one elastomeric polymer is mixed with a non-functionalised white reinforcing filler and a coupling agent to form a first elastomeric composition, and

- a second mixing step (ib) in which said first elastomeric composition is mixed with a functionalised silica to form said non-vulcanisable elastomeric composition.

The term “mixing step (i)” or “non-productive step” indicates the step of the preparation process of the vulcanisable elastomeric composition in which one or more additives may be incorporated by mixing and possibly heating, except for the vulcanising agent, which is fed in the mixing step (ii). The term “mixing step (ii)” or “productive step” indicates the next step of the preparation process of the vulcanisable elastomeric composition in which the vulcanising agent and, possibly, the other additives of the vulcanisation package are introduced into the elastomeric composition obtained from the mixing step (i), and incorporated by mixing, at a controlled temperature lower than the vulcanisation temperature, generally at a temperature lower than 120°C, so as to provide the vulcanisable elastomeric composition.

The mixing steps (i) and (ii) may be performed, for example, using a mixer of the cylinder type or an internal mixer of the type with tangential rotors (Banbury ^® ) or with interpenetrating rotors (Intermix ^® ), or in continuous mixers of the Ko- Kneader™ type (Buss ^® ) or of the co-rotating or counter-rotating twin-screw type.

In the first mixing step (ia), one or more elastomeric polymers, one or more non- functionalised white reinforcing fillers and one or more coupling agents are loaded into the mixer, and mixed at a temperature preferably between 100° and 150°C, with a rotation speed of the mixer preferably comprised between 10 and 60 revolutions per minute for a time preferably comprised between 4 and 8 minutes.

In the second mixing step (ib), one or more functionalised silicas are added to the mixer, and the mixing proceeds at a temperature preferably between 100° and 150°C, with a rotation speed of the mixer preferably between 10 and 60 revolutions per minute for a time preferably between 2 and 6 minutes.

Preferably, in the mixing step (i) the other additives described above are added, such as antioxidant agents, anti-ageing agents, plasticisers, adhesives, antiozonants (in particular of the p-phenylenediamine type), waxes, modified resins, fibres (for example Kevlar® paste), or mixtures thereof. The order of addition of the other additives is not particularly limited, and they may be added during step (ia), during step (ib), or partially in step (ia) and partially in step (ib). Similarly, each additive may be added in step (ia), in step (ib), or partially in step (ia) and partially in step (ib). By way of non-limiting example, plasticizing agents, waxes, resins are preferably added in step (ia), while antioxidant, anti-ageing and antiozonants agents are preferably added during step (ib). Generally, in step (i) the vulcanisation activators are also added which will carry out their action later in the mixing step (ii) with the addition of the vulcanisation agent.

In the mixing step (ii), the vulcanisation package consisting of one or more vulcanisation agents together with one or more vulcanisation accelerants and/or retardants, as described above, is added to the mixer. The mixing step (ii) is carried out at a temperature lower than the vulcanisation temperature, typically at a temperature below 100°C, with a rotation speed of the mixer preferably between 30 and 60 revolutions per minute for a time preferably between 1 and 2 minutes.

Thereafter, the vulcanisable elastomeric composition is incorporated in one or more structural elements of the tyre and subjected to vulcanisation, according to known techniques.

A further aspect of the present invention is represented by a structural element of tyre for vehicle wheels comprising, or preferably consisting of, an elastomeric composition according to the invention, preferably selected from the tread band, the underlayer, and the sidewall insert.

The tyre structural element may comprise or preferably may consist of a non- vulcanised elastomeric composition according to the invention (green structural element) or a vulcanised elastomeric composition according to the invention.

A further aspect of the present invention is a tyre for vehicle wheels comprising at least one structural element of a tyre according to the invention.

The tyre for vehicle wheels of the invention may comprise at least one tyre structural element which consists of an elastomeric composition according to the invention not vulcanised (green tyre) or which consists of an elastomeric composition according to the invention vulcanised (vulcanised tyre).

In a preferred embodiment, a tyre for vehicles according to the present invention comprises at least o a carcass structure, having opposite side edges associated with respective bead structures; o a pair of sidewalls, each possibly including a sidewall insert, respectively applied to the side surfaces of the carcass structure in an axially external position; o optionally, a belt structure applied in a radially external position with respect to said carcass structure; o a tread band applied in a radially external position with respect to said carcass structure or, if present, said belt structure, o optionally a layer of elastomeric material, also named underlayer, applied in a radially internal position to said tread band, wherein at least one structural element, preferably the tread band and/or the sidewall insert, comprises, or preferably consists of, the elastomeric composition according to the invention.

In one embodiment, the tyre according to the invention is a tyre for automobile.

In one embodiment, the tyre according to the invention is a tyre for motorcycles wherein at least one structural element comprises, or preferably consists of, the elastomeric composition according to the invention.

In a preferred embodiment, the tyre according to the invention is a tyre for motorcycle wheels, preferably for sports or racing motorcycles.

The tyre according to the invention may be a tyre for two, three or four-wheeled vehicles.

The tyre according to the invention may be for summer or winter use or for all seasons.

In one embodiment, the tyre according to the invention is a tyre for bicycle wheels.

A tyre for bicycle wheels typically comprises a carcass structure turned around a pair of bead cores at the beads and a tread band arranged in a radially outer position with respect to the carcass structure. Preferably, at least the tread band and/or a rubber layer comprises the elastomeric composition according to the invention.

The tyre according to the present invention may be manufactured according to a process which comprises:

- forming one or more structural elements of a green tyre on at least one forming drum;

- shaping, moulding and vulcanising the tyre; wherein forming one or more green tyre structural elements comprises:

- manufacturing at least one green structural element comprising the vulcanisable elastomeric composition of the invention.

DESCRIPTION OF THE DRAWINGS

The description is given hereinafter with reference to the accompanying drawings, provided only for illustrative and, therefore, non-limiting purposes, in which: - Figure 1 shows a cross half-section showing a tyre for motor vehicle wheels according to a first embodiment of the present invention,

- Figure 2 shows the photographs of the sheets of extruded rubber at the end of step 1a of the reference elastomeric composition Fte and of the invention I3, respectively, prepared as described in Example 2,

- Figure 3 shows the photographs of the sheets of extruded rubber at the end of step 1b of the comparative elastomeric composition R2 and of the invention I3, respectively, prepared as described in Example 2

The present description relates by way of example to a tyre for motor vehicle wheels. The Applicant believes that the present invention may also be applied to tyres for different vehicles such as heavy vehicles, motorcycles, bicycles and so on.

In Figure 1 , “a” indicates an axial direction and “x” indicates a radial direction. For simplicity, Figure 1 shows only a portion of the tyre, the remaining portion not shown being identical and arranged symmetrically with respect to the radial direction “x”.

With reference to Figure 1 , the tyre 100 for motor vehicle wheels comprises at least one carcass structure of elastomeric material, comprising at least one carcass layer 101 having respectively opposite end flaps engaged with respective annular anchoring structures 102, referred to as bead cores, possibly associated to a bead filler 104 of elastomeric material. The tyre area comprising the bead core 102 and the filler 104 forms a reinforcing annular structure 103, the so-called bead, intended for anchoring the tyre onto a corresponding mounting rim, not shown. The carcass structure is usually of radial type, i.e. the reinforcing elements of the at least one carcass layer 101 lie on planes comprising the rotational axis of the tyre and substantially perpendicular to the equatorial plane of the tyre. Said reinforcing elements generally consist of textile cords, such as rayon, nylon, polyester (for example polyethylene naphthalate, PEN). Each reinforcing annular structure is associated to the carcass structure by folding back of the opposite lateral edges of the at least one carcass layer 101 around the annular anchoring structure 102 so as to form the so-called carcass flaps 101 a as shown in Figure 1.

In one embodiment, the coupling between the carcass structure and the reinforcing annular structure may be provided by a second carcass layer (not shown in Figure 1) applied in an axially external position with respect to the first carcass layer.

An anti-abrasive strip 105 of elastomeric material is arranged in an external position of each reinforcing annular structure 103. Preferably each anti-abrasive strip 105 is arranged at least in an axially external position to the reinforcing annular structure 103 extending at least between the sidewall 108 and the portion radially below the reinforcing annular structure 103.

Preferably, the anti-abrasive strip 105 is arranged so as to enclose the reinforcing annular structure 103 along the axially internal and external and radially lower areas of the reinforcing annular structure 103 so as to interpose between the latter and the wheel rim when the tyre 100 is mounted to the rim.

The carcass structure is associated to a belt structure 106 of elastomeric material comprising one or more belt layers 106a, 106b placed in radial superposition with respect to one another and with respect to the carcass layer, having typically metallic reinforcing cords. Such reinforcing cords may have crossed orientation with respect to a direction of circumferential extension of the tyre 100. By “circumferential” direction it is meant a direction generally facing in the direction of rotation of the tyre.

At least one zero-degree reinforcing layer 106c, commonly known as a “0° belt”, may be applied in a radially outermost position to the belt layers 106a, 106b, which generally incorporates a plurality of reinforcing cords, typically textile cords, oriented in a substantially circumferential direction, thus forming an angle of a few degrees (such as an angle of between about 0° and 6°) with respect to the equatorial plane of the tyre, and coated with an elastomeric material. A tread band 109 of elastomeric material is applied in a position radially external to the belt structure 106.

Moreover, respective sidewalls 108 of elastomeric material are further applied in an axially external position on the lateral surfaces of the carcass structure, each extending from one of the lateral edges of the tread 109 at the respective reinforcing annular structure 103.

In a radially external position, the tread band 109 has a rolling surface 109a intended to come in 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 over the rolling surface 109a, are generally made on this surface 109a, which for simplicity is represented smooth in Figure 1.

An under-layer 111 of elastomeric material is arranged between the belt structure 106 and the tread band 109. A strip consisting of elastomeric material 110, commonly known as “mini- sidewall”, may optionally be provided in the connecting zone between the sidewalls 108 and the tread band 109, this mini-sidewall being generally obtained by co-extrusion with the tread band 109 and allowing an improvement of the mechanical interaction between the tread band 109 and the sidewalls 108. Preferably, the end portion of sidewall 108 directly covers the lateral edge of the tread band 109.

In the case of tubeless tyres, a layer of elastomeric material 112, generally known as “liner”, which provides the necessary impermeability to the inflation air of the tyre, may also be provided in a radially internal position with respect to the carcass layer 101.

A sidewall insert (not shown) may extend radially between the lateral edge of the tread band 109 and the bead structure 103 in an axially internal or external position with respect to the carcass layer 101 , for example between the carcass layer 101 and the liner 112. The rigidity of the tyre sidewall 108 may be improved by providing the bead structure 103 with a reinforcing layer 120 generally known as “flipper” or additional strip-like insert. The flipper 120 typically comprises a plurality of textile cords incorporated within a layer of elastomeric material.

The flipper 120 is a reinforcing layer which is wound around the respective bead core 102 and the bead filler 104 so as to at least partially surround them, said reinforcing layer being arranged between the at least one carcass layer 101 and the bead structure 103. Usually, the flipper is in contact with said at least one carcass layer 101 and said bead structure 103.

The bead structure 103 of the tyre may comprise a further protective layer which is generally known by the term of “chafer” 121 or protective strip and which has the function of increasing the rigidity and integrity of the bead structure 103.

The chafer 121 usually comprises a plurality of cords incorporated within a layer of elastomeric material. Such cords are generally made of textile materials (such as aramid or rayon) or metal materials (such as steel cords). The elastomeric composition according to the present invention may be advantageously used to make the elastomeric material incorporated in one or more of the structural elements of the tyre selected from the tread band, the tread underlayer, the sidewall insert, and in general any structural element in which silica is used as a reinforcing element, preferably in the tread, even when made in two radially overlapping layers (known as “cap and base” tread) with a radially external portion (“cap”) and a radially internal portion (“base”) comprising different amounts of silica.

The use of the elastomeric composition according to the present invention to make the elastomeric material of the aforesaid structural elements allows a tyre with a lower rolling resistance to be obtained, and consequently a lower development of heat and fuel consumption, at the same time obtaining a good mechanical resistance of the tyre surface, and good handling during use of the same. The building of the tyres 100 as described above may be carried out by assembling respective semi-finished products onto a forming drum, not shown, by at least one assembly device.

At least a part of the structural elements intended to form the carcass structure of the tyre may be built and/or assembled on the forming drum. More particularly, the forming drum is intended to first receive the possible liner, then the carcass structure and the anti-abrasive strip. Thereafter, devices non shown coaxially engage one of the annular anchoring structures around each of the end flaps, position an external sleeve comprising the belt structure and the tread band in a coaxially centred position around the cylindrical carcass sleeve and shape the carcass sleeve according to a substantially toroidal configuration through a radial expansion of the carcass structure, so as to cause the application thereof against a radially internal surface of the external sleeve.

After the building of the green tyre, a moulding and vulcanisation treatment is generally carried out in order to determine the structural stabilisation of the tyre through cross-linking of the elastomeric compositions, as well as to impart a desired tread pattern on the tread band and to impart any distinguishing graphic signs at the sidewalls.

According to an embodiment not shown, the tyre may be a tyre for heavy transport vehicle wheels, such as trucks, buses, trailers, vans, and in general for vehicles in which the tyre is subjected to a high load. Preferably, such a tyre is adapted to be mounted on wheel rims having a diameter equal to or greater than 17.5 inches for directional or trailer wheels.

According to an embodiment not shown, the tyre may be a tyre for motorcycle wheels which is typically a tyre that has a straight section featuring a high tread camber.

According to an embodiment not shown, the tyre may be a tyre for bicycle wheels.

The description of some preparatory and comparative examples according to the invention is given below, provided for illustrative and non-limiting purposes only of the scope of protection of the present invention.

EXPERIMENTAL PART ANALYSIS METHODS MDR rheometric analysis (according to ISO 6502): a rheometer Alpha

Technologies type MDR2000 was used. The 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 minimum torque value (ML), maximum torque (MH), the time required to increase the torque by two units (TS2), and the time necessary to reach different percentages (30, 60 and 90%) of the maximum torque value (MH).

Properties of vulcanised materials

The elastomeric materials prepared in the previous examples were vulcanised to give specimens on which analytical characterisations and the assessment of dynamic mechanical properties were conducted. Unless otherwise indicated, vulcanisation was carried out in a mould, in hydraulic press at 170°C and at a pressure higher than 3.5 Mpa for about 10 minutes.

The IRHD hardness was measured at 23°C on cross-linked elastomeric compositions according to the ISO 48:2007 standard. Static modules: static mechanical properties were measured at 23°C according to the ISO 37:2011 standard. In particular, the tensile stresses at various levels of elongation (100% and 300%, named in the order CA1 and CA3), the load, the elongation and the energy at break (CR, AR and ER, respectively) were measured on ring-shaped samples of vulcanised elastomeric compositions. Dynamic modules: dynamic mechanical properties were measured using an Instron dynamic device in compression and tension operation with the following method. A sample of vulcanised elastomeric cylindrical compositions (height = 25 mm; diameter = 18 mm), preload in compression up to 25% of longitudinal deformation with respect to the initial length and maintained at the predetermined temperature (10°C, 23°C or 70°C) during the test was subjected to a dynamic sinusoidal voltage with amplitude ±3.5% with respect to the length of the preload, at a frequency of 10Hz.

The dynamic mechanical properties are expressed in terms of dynamic elastic modulus (E') and Tan delta (loss factor). The Tan delta value was calculated as the ratio between the viscous dynamic module (E”) and the dynamic elastic modulus (E’).

EXAMPLE 1

The elastomeric materials listed in the following Table 1 were prepared as follows (the amounts of the various components are indicated in phr).

In step (1a), the elastomeric components, the white reinforcing filler and the silanes were mixed in an internal mixer (model Pomini PL 1 ,6) for about 6 minutes up to about 135°C. In step (1b), the zinc-based components and the other additives were added, and the mixing continued for about 4 minutes up to about 135°C. Finally in step (2), sulphur and accelerant (TBBS) were added, mixing for a further 2 minutes up to about 95°C, then the elastomeric composition was discharged.

TABLE 1

< ¹ > SIR20 by ANEKA BUMI PRATAMA, SED

⁽²⁾ functionalised styrene butadiene copolymer - microstructure with 21% styrene and 62.5% vinyl on the butadiene fraction - SPRINT AN™ SLR 4602 - Trinseo < ³ > Tris(2-ethylhexyl Phosphate) super grade - HANGZHOU QIANYANG TECHNOLOGY

⁽⁴⁾ Ultrasil® 7000 (BET specific surface area 160 m ² /g) - Evonik

⁽⁵⁾ Agilon 400 by PPG Industries Chemicals BV (Pittsburgh, Pa)

< ⁶ > bis[3-(triethoxysilyl)propyl]-disulphane (TESPD) JH-S69 by JINGZHOU JIANGHAN FINE CHEM. ⁽⁷⁾ Wuhan Jinghe Dispersing Agent FS-200 fatty acid salt

⁽⁸⁾ U.S. Zinc grade 203 zinc oxide < ⁹ > RIOWAX BM-01 by Ser SpA < ¹⁰ > IMPERA P1504 - EASTMAN ⁽¹¹⁾ Palmera B1810 stearic acid by KLK OLEO < ¹² > carbon black grade ASTM N234 - BIRLA

⁽¹³⁾ TMQ 2,2,4-trimethyl-1 ,2-dihydroquinoline - Vulkanox® HS/LG by Lanxess < ¹⁴ > ANTIOXIDANT 6PPD by SENNICS CO.

⁽¹⁵⁾ N-cyclohexyl-2-benzothiazyl-sulphenamide Vulkacit® (CBS) - Lanxess.

⁽¹⁶⁾ Sulphur (1% oil and 0.3% silica) by Zolfindustria

The elastomeric compositions thus prepared above were evaluated for the behaviour in vulcanisation (170°C, 10 min) and subsequently, in terms of static and dynamic mechanical properties, according to the methods described above. The following Table 2 shows the rheometric, mechanical, dynamic and static features of the compositions of Table 1.

All values were normalized to 100 with respect to the reference Ri. TABLE 2

The elastomeric composition Ci with respect to the reference composition Ri showed a considerable reduction in the energy at break, predicting a poor resistance to tearing, and a too fast vulcanisation kinetics. Furthermore, compared to an improvement in the Tanb value at 10°C, predictive of good behaviour in the wet, the elastomeric composition Ci showed a clear reduction in the E’ value at 23°C, predicting excessive softness of the resulting compound and an increase in the Tanb value at 70°C, predicting greater rolling resistance. The elastomeric compositions of the invention h and I2 showed values in line with the reference Ri, with an improvement in the Tanb value at 10°C, predicting good behaviour in the wet, with the same Tanb values at 70°C and E’ at 23°C.

EXAMPLE 2 The elastomeric materials listed in the following Table 3 were prepared as follows (the amounts of the various components are indicated in phr).

With reference to the compound R2, in step (1a) the elastomeric components, the silanes, the white reinforcing filler, represented by non-functionalised silica and the functionalised silica, and other additives were mixed in an internal mixer with interpenetrating rotors (Intermix model VIC275X) for about 6 minutes up to about 135°C. In step (1b), the zinc-based components and the other protectants were added, and the mixing continued for about 4 minutes up to about 125°C.

In the preparation of compound , in step (1a) only the non-functionalised silica was added, while the functionalised silica was added in step (1 b).

The resulting elastomeric composition was discharged into an internal tangential rotor mixer (Banbury model) to carry out step (2), in which sulphur and accelerant (TBBS) were added, mixing for a further 2 minutes up to about 95°C. Upon completion, the elastomeric composition was discharged. TABLE 3 < ¹ > SIR20 by ANEKA BUMI PRATAMA, SED

⁽²⁾ functionalised styrene butadiene copolymer - microstructure with 21% styrene and

62.5% vinyl on the butadiene fraction - SPRINT AN™ SLR 4602 - Trinseo

< ³ > Tris(2-ethylhexyl Phosphate) super grade - HANGZHOU QIANYANG TECHNOLOGY

⁽⁴⁾ Ultrasil® 7000 (BET specific surface area 160 m ² /g) - Evonik

⁽⁵⁾ Agilon 400 by PPG Industries Chemicals BV (Pittsburgh, Pa)

⁽⁶⁾ bis[3-(triethoxysilyl)propyl]-disulphane (TESPD) JH-S69 by JINGZHOU JIANGHAN FINE CHEM.

⁽⁷⁾ Wuhan Jinghe Dispersing Agent FS-200 fatty acid salt

⁽⁸⁾ U.S. Zinc grade 203 zinc oxide < ⁹ > RIOWAX BM-01 by Ser SpA < ¹⁰ > IMPERA P1504 - EASTMAN

⁽¹¹⁾ Palmera B1810 stearic acid by KLK OLEO < ¹² > carbon black grade ASTM N234 - BIRLA

⁽¹³⁾ TMQ 2,2,4-trimethyl-1 ,2-dihydroquinoline - Vulkanox® HS/LG by Lanxess < ¹⁴ > ANTIOXIDANT 6PPD by SENNICS CO.

⁽¹⁵⁾ N-cyclohexyl-2-benzothiazyl-sulphenamide Vulkacit® (CBS) - Lanxess.

⁽¹⁶⁾ Sulphur (1% oil and 0.3% silica) by Zolfindustria

The elastomeric compositions thus prepared above were evaluated for the behaviour in vulcanisation (170°C, 10 min) and subsequently, in terms of static and dynamic mechanical properties, according to the methods described above. The following Table 4 shows the rheometric, mechanical, dynamic and static features of the compositions of Table 3.

The values were normalized to 100 with respect to the reference R2.

TABLE 4

The images of Figure 2 show the sheets of extruded rubber at the end of step 1a of the elastomeric composition Fte and of the invention I3, respectively. The elastomeric composition R2 clearly showed torn areas and irregularities caused by the high level of reactivity resulting from the simultaneous addition of the reinforcing fillers and the coupling agent. On the other hand, the elastomeric composition of the invention I3 showed a smooth surface without cracks.

The images of Figure 3 show the sheets of extruded rubber at the end of step 1b of the elastomeric composition R2 and of the invention I3, respectively. The same considerations set out above apply to these compositions. The elastomeric composition R2 showed tears and irregularities, while the composition of the invention I3 was smooth and free of cracks.

Confirming the improved workability, the composition I3 shows a clear improvement in the workability index, particularly evident in step 1a. The workability was evaluated by measuring the stress relaxation rate (Slope

[Mu/s]) at the end of a viscosity test carried out using a Mooney viscometer according to the ISO 289-4 standard. The lower this speed in absolute terms, the poorer the workability.

The composition of the invention I3 showed a vulcanisation kinetics in line with the reference and a further marked improvement in the value of the energy at break, predicting an excellent resistance to tearing, with respect to the reference R2, with the same value of Tanb at 10°C and 70°C and E’ at 23°C, in line with the reference R2.

The Applicant has therefore surprisingly observed that the modification to the preparation process, introduced to improve the workability of the elastomeric composition R2, entailed a further improvement in the performance of the resulting compound.