WO2008145155A1

WO2008145155A1 - Tire and crosslinkable elastomeric composition

Info

Publication number: WO2008145155A1
Application number: PCT/EP2007/004759
Authority: WO
Inventors: Maurizio Galimberti; Massimiliano Guglielmone; Luca Napolitano
Original assignee: Pirelli Tyre S.P.A.; Politecnico Di Milano
Priority date: 2007-05-30
Filing date: 2007-05-30
Publication date: 2008-12-04

Abstract

Tire comprising at least one structural element including a crosslinked elastomeric material obtained by crosslinking a crosslinkable elastomeric composition comprising: (a) 100 phr of at least one solid elastomeric polymer having a Mooney viscosity, measured at 100°C, of from 30 to 90, preferably of from 40 to 75; (b) from 3 phr to 33 phr, preferably of from 5 phr to 15 phr, of at least one liquid elastomeric polymer having a number average molecular weight (Mn) of from 1000 to 20000, preferably of from 3000 to 15000 and an amount of vinyl unsaturations in the butadiene part, of from 15% to 100%, preferably of from 30% to 90%; (c) from 5 phr to 120 phr, preferably from 20 phr to 90 phr of at least one silica reinforcing filler; (d) from 0.1 phr to 10 phr, preferably from 0.5 phr to 8 phr, of at least one coupling agent containing at least one mercapto group. Preferably, said at least one structural element is a tread band. Preferably, said at least one structural element is a tread band.

Description

"TIRE AND CROSSLINKABLE ELASTOMERIC COMPOSITION"

Field of the invention

The present invention relates to a tire, to a tire tread band and to a crosslinkable elastomeric composition.

More in particular the present invention relates to a tire including at least one structural element obtained by crosslinking a crosslinkable elastomeric composition comprising at least one solid elastomeric polymer, at least one liquid elastomeric polymer, at least one silica reinforcing filler, at least one coupling agent containing at least one mercapto group.

Moreover, the present invention also relates to a tire tread band including a crosslinkable elastomeric composition comprising at least one solid elastomeric polymer, at least one liquid elastomeric polymer, at least one silica reinforcing filler, at least one coupling agent containing at least one mercapto group.

Furthermore, the present invention also relates to a crosslinkable elastomeric composition comprising at least one solid elastomeric polymer, at least one liquid elastomeric polymer, at least one silica reinforcing filler, at least one coupling agent containing at least one mercapto group, as well as to a crosslinked manufactured article obtained by crosslinking said crosslinkable elastomeric composition.

Background of the invention In the rubber industry, in particular that of tires manufacturing, it is known to add rubber processing oil to both natural and synthetic elastomeric polymers, for a number of reasons such as, for example, to reduce the mixing temperatures during processing, to decrease the viscosity of the elastomeric polymers and thereby facilitate milling, extruding and general workability of the crosslinkable elastomeric compositions which may contain other components, to reduce mill and calendering shrinkage, to aid the dispersion of fillers, to modify the physical properties of the crosslinked elastomeric compositions.

However, the addition of said processing oils may show some drawbacks. For example, while increasing the processing oils contents of a tread band elastomeric composition usually increases its dry traction, it also usually reduces its lifetime as evidenced by a reduction of one of more of tensile modulus at 300% elongation (300% Modulus), stress at break, elongation at break, and/or abrasion resistance.

Attempts have been already made in the art in order to overcome said drawbacks.

For example, United States Patent US 6,242,523 relates to a rubber composition comprised of, based upon its rubber component, (A) 100 parts by weight (phr) of at least one solid, sulfur vulcanizable, diene-based elastomer selected from homopolymers and copolymers of conjugated diene and copolymers of at least one conjugated diene with a vinyl aromatic compound selected from styrene and α- methylstyrene; wherein said elastomers have a glass transition temperature (T₉) of lower than +10⁰C and wherein at least 50% by weight of said elastomers have a glass transition temperature (T₉) above -40⁰C; and (B) from about 5 phr to about 50 phr of a liquid polymer of high vinyl polybutadiene, characterized by being a pourable liquid at a temperature in a range of about 20⁰C to about 25°C, having a vinyl (1 ,2-) content in a range of about 40% to 95% and a glass transition temperature (T₉) in a range of about -5°C to about -40°C. A tire having a tread made of said rubber composition is also disclosed. The abovementioned rubber composition is said to be advantageously used for a tire tread in order to improve dry traction (increased hysteresis) while maintaining durability and treadwear in high performance tires which are intended to be driven at relatively high speeds.

Canadian Patent Application CA 2,544,592 relates to a sulfur-vulcanizable rubber mixture, especially for the treads of tires, which comprises at least one diene rubber; liquid polybutadiene having a molecular weight of from 1500 g/mol to 10000 g/mol and a vinyl content of from 15% to 50%; at least one polar filler; at least one high- structure carbon black having a iodine absorption number of from 115 g/kg to 200 g/kg and a DBP number of from 125 ml/100 g to 160 ml/100 g; and at least one glyceride and/or factice. The abovementioned rubber composition is said to give tires having good abrasion characteristics, good wet traction, good traction on ice and snow and good dry braking.

Summary of the invention However, the Applicant has noticed that the use of the above disclosed liquid elastomeric polymers may show some drawbacks.

In particular, the Applicant has noticed that the crosslinked elastomeric compositions including the above disclosed liquid elastomeric polymers, as well as the tires so obtained, may show the following drawbacks: a reduction of one or more of the static mechanical properties, in particular a reduction of the tensile modulus at 300% elongation (300% Modulus) and, consequently, a reduced lifetime of the obtained tires; an increased variation of the dynamic elastic modulus (E') as the temperature increases (namely, an increased "thermoplastic behaviour" of the crosslinked elastomeric compositions, consequently, the crosslinked elastomeric compositions may not be able to maintain essentially constant elastic performance qualities over a wide temperature range which is of fundamental importance when using the compositions in tires manufacturing); - an increase in the Tan delta (loss factor) values (in particular, at 70⁰C) and, consequently, an increased rolling resistance of the obtained tire; a reduction of abrasion resistance and, consequently, a reduced lifetime of the obtained tires.

More in particular, the Applicant has noticed that tires (e.g., high-performance tires) showing a good balance between wet grip, rolling resistance and abrasion resistance, may not be obtained.

The Applicant has faced the problem of providing a tire showing a good balance between wet grip, rolling resistance and abrasion resistance.

The Applicant has now found that it is possible to obtain a tire having the abovementioned properties, by adding at least one coupling agent containing at least one mercapto group to crosslinkable elastomeric compositions comprising at least one solid elastomeric polymer, at least one liquid elastomeric polymer and at least one silica reinforcing filler.

Moreover, the Applicant has also found that the amount of said at least one solid elastomeric polymer may be reduced. The use of a reduced amount of said at least one solid elastomeric polymer may allow to obtain crosslinkable elastomeric compositions having a relatively low viscosity (Mooney viscosity) which, consequently, may be more easily processed in conventional rubber processing apparatus, including internal rubber mixers and various rubber extruders.

Furthermore, the Applicant has also found that, the amount of processing oils which is usually added to crosslinkable elastomeric compositions may be reduced. The use of a reduced amount of said processing oils may allows to avoid a decrease in tensile modulus which often occurs in the crosslinked elastomeric composition so obtained. Moreover, a reduced amount of said processing oils, which often are aromatic oils, have a positive effect on the environment (pollution problems are avoided).

Moreover, the Applicant has also found that the amount of silane coupling agents, in particular the amount of those containing a sequence of sulfur atoms, other than said coupling agent containing at least one mercapto group, which is usually used in crosslinkable elastomeric compositions comprising silica reinforcing fillers, may be reduced or even eliminated. The reduced amount of said silane coupling agents allows to avoid the limitation on the maximum temperature which may be reached during the blending and thermomechanical processing operations of the crosslinkable elastomeric compositions comprising the same, which is usually necessary in order to avoid the penalty of an irreversible thermal degradation of the silane coupling agents.

According to a first aspect, the present invention relates to a tire comprising at least one structural element including a crosslinked elastomeric material obtained by crosslinking a crosslinkable elastomeric composition comprising:

(a) 100 phr of at least one solid elastomeric polymer having a Mooney viscosity, measured at 100⁰C, of from 30 to 90, preferably of from 40 to 75;

(b) from 3 phr to 33 phr, preferably of from 5 phr to 15 phr, of at least one liquid elastomeric polymer having a number average molecular weight (M_n) of from

1000 to 20000, preferably of from 3000 to 15000, and an amount of vinyl unsaturations in the butadiene part, of from 15% to 100%, preferably of from 30% to 90%;

(c) from 5 phr to 120 phr, preferably from 20 phr to 90 phr, of at least one silica reinforcing filler; (d) from 0.1 phr to 10 phr, preferably from 0.5 phr to 8 phr, of at least one coupling agent containing at least one mercapto group.

According to a second aspect, the present invention relates to a tire comprising at least one structural element including a crosslinked elastomeric material obtained by crosslinking a crosslinkable elastomeric composition comprising: (a) from 75 phr to 95 phr, preferably of from 85 phr to 90 phr, of at least one solid elastomeric polymer having a Mooney viscosity, measured at 100⁰C, of from 30 to 90, preferably of from 40 to 75; (b) from 5 phr to 25 phr, preferably of from 10 phr to 15 phr, of at least one liquid elastomeric polymer having a number average molecular weight (M_n) of from 1000 to 20000, preferably of from 3000 to 15000, and an amount of vinyl unsaturations in the butadiene part, of from 15% to 100%, preferably of from 30% to 90%; the sum of (a) + (b) being 100 phr;

(c) from 5 phr to 120 phr, preferably from 20 phr to 90 phr, of at least one silica reinforcing filler;

(d) from 0.1 phr to 10 phr, preferably from 0.5 phr to 8 phr, of at least one coupling agent containing at least one mercapto group.

Said Mooney viscosity [ML(1+4)] is measured according to Standard ISO 289- 1 :1994.

Said number average molecular weight (M_n) may be measured according to techniques known in the art such as, for example, by gel permeation chromatography (GPC).

Said vinyl unsaturations may be measured according to techniques known in the art such as, for example, by ¹H-NMR spectroscopy or ¹³C-NMR spectroscopy.

For the purposes of the present description and of the claims which follow, the term "phr" means the parts by weight of a given component of the crosslinkable elastomeric composition per 100 parts by weight of the elastomeric polymer(s).

For the purpose of the present description and of the claims which follow, except where otherwise indicated, all numbers expressing amounts, quantities, percentages, and so forth, are to be understood as being modified in all instances by the term "about". Also, all ranges include any combination of the maximum and minimum points disclosed and include any intermediate ranges therein, which may or may not be specifically enumerated herein.

According to a further aspect, the present invention relates to a tire tread band including a crosslinkable elastomeric composition comprising:

(b) from 3 phr to 33 phr, preferably of from 5 phr to 15 phr, of at least one liquid elastomeric polymer having a number average molecular weight (M_n) of from 1000 to 20000, preferably of from 3000 to 15000, and an amount of vinyl unsaturations in the butadiene part, of from 15% to 100%, preferably of from 30% to 90%;

(a) from 75 phr to 95 phr, preferably of from 85 phr to 90 phr, of at least one solid elastomeric polymer having a Mooney viscosity, measured at 100⁰C, of from 30 to 90, preferably of from 40 to 75;

(b) from 5 phr to 25 phr, preferably of from 10 phr to 15 phr, of at least one liquid elastomeric polymer having a number average molecular weight (M_n) of from 1000 to 20000, preferably of from 3000 to 15000, and an amount of vinyl unsaturations in the butadiene part, of from 15% to 100%, preferably of from 30% to 90%; the sum of (a) + (b) being 100 phr;

(d) from 0.1 phr to 10 phr, preferably from 0.5 phr to 8 phr, of at least one coupling agent containing at least one mercapto group. According to a further aspect, the present invention relates to a crosslinkable elastomeric composition comprising:

(a) 100 phr of at least one solid elastomeric polymer having a Mooney viscosity, measured at 100⁰C, of from 30 to 90, preferably of from 40 to 75; (b) from 3 phr to 33 phr, preferably of from 5 phr to 15 phr, of at least one liquid elastomeric polymer having a number average molecular weight (M_n) of from

1000 to 20000, preferably of from 3000 to 15000, and an amount of vinyl unsaturations in the butadiene part, of from 15% to 100%, preferably of from

30% to 90%; (c) from 5 phr to 120 phr, preferably from 20 phr to 90 phr, of at least one silica reinforcing filler; (d) from 0.1 phr to 10 phr, preferably from 0.5 phr to 8 phr, of at least one coupling agent containing at least one mercapto group.

According to a further aspect, the present invention relates to a crosslinkable elastomeric composition comprising:

(a) from 75 phr to 95 phr, preferably of from 85 phr to 90 phr, of at least one solid elastomeric polymer having a Mooney viscosity, measured at 100⁰C, of from 30 to 90, preferably of from 40 to 75; (b) from 5 phr to 25 phr, preferably of from 10 phr to 15 phr, of at least one liquid elastomeric polymer having a number average molecular weight (M_n) of from 1000 to 20000, preferably of from 3000 to 15000, and an amount of vinyl unsaturations in the butadiene part, of from 15% to 100%, preferably of from 30% to 90%; the sum of (a) + (b) being 100 phr;

According to a further aspect, the present invention relates to a crosslinked manufactured article obtained by crosslinking a crosslinkable elastomeric composition above reported.

The present invention, in at least one of the abovementioned aspects, may show one or more of the preferred characteristics hereinafter described.

According to a further preferred embodiment, said crosslinkable elastomeric composition may further comprise (e) at least one silane coupling agent, other than said at least one coupling containing at least one mercapto group (d).

According to a further preferred embodiment, said crosslinkable elastomeric composition may further comprise (f) at least one layered material having an individual layer thickness of from 0.01 nm to 30 nm, preferably of from 0.2 nm to 15 nm, more preferably of from 0.5 nm to 2 nm. The addition of said at least one layered material (T) may allow to improve, in particular, the abrasion resistance of the crosslinked elastomeric composition so obtained and, consequently, the lifetime of the tire so obtained,

According to one preferred embodiment, said at least one solid elastomeric polymer (a) may be selected, for example, from Ca₁) diene elastomeric polymers which are commonly used in sulfur-crosslinkable elastomeric compositions, that are particularly suitable for producing tires, that is to say from elastomeric polymers or copolymers with an unsaturated chain having a glass transition temperature (T₉) generally below 20⁰C, preferably in the range of from 0⁰C to -110°C. These polymers or copolymers may be of natural origin or may be obtained by solution polymerization, emulsion polymerization or gas-phase polymerization of one or more conjugated diolefins, optionally blended with at least one comonomer selected from monovinylarenes and/or polar comonomers. Preferably, the obtained polymers or copolymers contain said at least one comonomer selected from monovinylarenes and/or polar comonomers in an amount of not more than 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: 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, or mixtures thereof. 1 ,3-butadiene, or 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, α- methylstyrene, 3-methylstyrene, 4-propylstyrene, 4-cyclohexylstyrene, 4- dodecylstyrene, 2-ethyl-4-benzylstyrene, 4-p-tolylstyrene, 4-(4-phenylbutyl)styrene, or mixtures thereof. Styrene is particularly preferred.

Polar comonomers which 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, or mixtures thereof.

Preferably, said diene elastomeric polymer (a^ may be selected, for example, from: cis-1 ,4-polyisoprene (natural or synthetic cis-1 ,4-polyisoprene, preferably natural cis-1,4-polyisoprene, i.e. natural rubber), 3,4-polyisoprene, polybutadiene (in particular, polybutadiene with a high 1 ,4-cis content), optionally halogenated isoprene/isobutene copolymers, 1 ,3-butadiene/acrylonitrile copolymers, styrene/1 ,3- butadiene copolymers, styrene/isoprene/1 ,3-butadiene copolymers, styrene/1 ,3- butadiene/acrylonitrile copolymers, or mixtures thereof. Styrene/1 , 3-butadiene copolymers, styrene/isoprene/1 , 3-butadiene copolymers, styrene/1 ,3- butadiene/acrylonitrile copolymers, or mixtures thereof, are particualrly preferred.

Alternatively, said at least one solid elastomeric polymer (a) may be selected, for example, from (a₂) elastomeric polymers of one or more monoolefins with an olefinic comonomer or derivatives thereof. The monoolefins may be selected, for example, from: ethylene and α-olefins generally containing from 3 to 12 carbon atoms, such as, for example, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, or mixtures thereof. The following are preferred: copolymers between ethylene and an α-olefin, optionally with a diene; isobutene homopolymers or copolymers thereof with small amounts of a diene, which are optionally at least partially halogenated. The diene optionally present generally contains from 4 to 20 carbon atoms and is preferably selected from: 1 , 3-butadiene, isoprene, 1 ,4-hexadiene, 1 ,4-cyclohexadiene, 5- ethylidene-2-norbornene, 5-methylene-2-norbornene, vinylnorbornene, or mixtures thereof. Among these, the following are particularly preferred: ethylene/propylene copolymers (EPR) or ethylene/propylene/diene copolymers (EPDM); poly-isobutene; butyl rubbers; halobutyl rubbers, in particular chlorobutyl or bromobutyl rubbers; or mixtures thereof.

Mixtures of the abovementioned diene elastomeric polymers (ai) with the abovementioned elastomeric polymers (a₂), may also be used.

According to one preferred embodiment, said crosslinkable elastomeric composition may comprise at least 10% by weight, preferably from 20% by weight to 100% by weight, with respect to the total weight of the at least one solid elastomeric polymer (a), of styrene/1 ,3-butadiene copolymers, in particular of styrene/1 ,3-butadiene copolymers having a high amount of vinyl unsaturation (e.g., higher than or equal to 40% in the butadiene part).

The above reported solid elastomeric polymers (a) may optionally be functionalized by reaction with suitable terminating agents or coupling agents. In particular, the diene elastomeric polymers Ca₁) obtained by anionic polymerization in the presence of an organometallic initiator (in particular an organolithium initiator) may be functionalized by reacting the residual organometallic groups derived from the initiator with suitable terminating agents or coupling agents such as, for example, imines, carbodiimides, alkyltin halides, substituted benzophenones, alkoxysilanes or aryloxysilanes (see, for example, European Patent EP 451 ,604, or United States Patents US 4,742,124, or US 4,550,142).

The above reported solid elastomeric polymers (a) may optionally include at least one functional group which may be selected, for example, from: carboxylic groups, carboxylate groups, anhydride groups, ester groups, epoxy groups, or mixtures thereof.

According to one preferred embodiment, said at least one liquid elastomeric polymer (b) may be selected, for example, from liquid elastomeric polymers having a Brookfield viscosity, measured at 45°C, not higher than 150000 cPs, preferably of from 10000 cPs to 100000 cPs.

According to a further preferred embodiment, said at least one liquid elastomeric polymer (b), may be selected, for example, from liquid elastomeric polymers having a glass transition temperature (T₉) of from -5°C to -120⁰C, preferably of from -1O⁰C to -8O⁰C.

Advantageously, said at least one liquid elastomeric polymer may be pourable at a temperature of from 20⁰C to 25°C. Said polymer is preferably administered within such temperature, although it might be used at a temperature above or below such temperature range.

According to one preferred embodiment, said at least one liquid elastomeric polymer (b), may be selected, for example, from homopolymers or copolymers of conjugated diolefins containing from 4 to 12, preferably from 4 to 8, carbon atoms, such as, 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, or mixtures thereof. 1 ,3- Butadiene homopolymers, or 1 ,3-butadiene-isoprene copolymers, are particularly preferred.

According to a further preferred embodiment, said at least one liquid elastomeric polymer (b), may be selected, for example, from copolymers of 1 ,3-butadiene with at least one monovinylarene containing from 8 to 20, preferably from 8 to 12 carbon atoms, said monovinylarene being selected, for example from: styrene; 1-vinylnaphthalene; 2-vinylnaphthalene; various alkyl, cycloalkyl, aryl, alkylaryl or arylalkyl derivatives of styrene such as, for example, α-methylstyrene, 3- methylstyrene, 4-propylstyrene, 4-cyclohexylstyrene, 4-dodecylstyrene, 2-ethyl-4- benzylstyrene, 4-p-tolylstyrene, 4-(4-phenylbutyl)styrene, or mixtures thereof. Styrene/1 ,3-butadiene copolymers are preferred, styrene/1 ,3-butadiene random copolymers are particularly preferred.

Alternatively, epoxydized poly(butadienes), maleic poly(butadienes), acrylated poly(butadienes), acrylonitrile/1 ,3-butadiene copolymers, may be advantageously used.

Examples of liquid elastomeric polymers which may be used according to the present invention and are available commercially are the following products: poly(butadienes) (Ricon 130, 131 , 134, 142, 150, 152, 153, 154, 156, 157, P30D) available from Sartomer Company, Inc; styrene/1 ,3-butadiene random copolymers (Ricon 100, 181 , 184) available from Sartomer Company Inc.; maleinized poly(butadienes) (Ricon 130MA8, 130MA13, 130MA20, 131 MA5, 131 MA10, 131 MA17, 131 MA20, 156MA17) available from Sartomer Company, Inc.; acrylated poly(butadienes) (CN302, NTX6513, CN301 , NTX6039, PRO6270, Ricacryl 3100, Ricacryl 3500) available from Sartomer Inc.; epoxydized poly(butadienes) (Polybd 600, 605) available from Sartomer Company. Inc., or Epolead PB3600 available from Daicel Chemical Industries, Ltd; acrylonitrile/1 ,3-butadiene copolymers (Hycar CTBN series, ATBN series, VTBN series and ETBN series) available from Hanse Chemical.

According to one preferred embodiment, said at least one silica reinforcing filler (c) may be selected, for example, from: pyrogenic silica, precipitated amorphous silica, wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), fumed silica, calcium silicate, or mixtures thereof. Other suitable fillers include aluminum silicate, magnesium silicate, or mixtures thereof. Among these, precipitated amorphous wet- process, hydrated silicas are preferred. These silicas are so-called because they are produced by a chemical reaction in water, from which they are precipitated as ultrafine, spherical particles. These primary particles strongly associate into aggregates, which in turn combine less strongly into agglomerates. The BET surface area, as measured according to Standard ISO 5794-1 :2005, gives the best measure of the reinforcing character of different silicas. Silica reinforcing fillers which may be advantageously used according to the present invention, preferably have a surface area of from 32 m²/g to 400 m²/g, more preferably of from 100 m²/g to 250 m²/g, still more preferably of from 150 m²/g to 220 m²/g. The pH of said silica reinforcing fillers is, generally, of from 5.5 to 7.0, preferably of from 5.5 to 6.8.

Examples of silica reinforcing fillers which may be used according to the present invention and are available commercially are the products known by the name of Hi- Sil^® 190, Hi-Sil^® 210, Hi-Sil^® 215, Hi-Sil^® 233, Hi-Sil^® 243, from PPG Industries (Pittsburgh, Pa.); or the products known by the name of Ultrasil^® VN2, Ultrasil^® VN3 from Degussa; or the product known under the name of Zeosil^® 1165MP from Rhodia.

According to one preferred embodiment, said at least one coupling agent containing at least one mercapto group (d), may be selected, for example, from compounds having the following general formula (I): HS (CH) _a — (X) _b— (CH) _c -γ ( D

I I

R R wherein: a + c is an integer of from 1 to 36, extremes included;

R represents a hydrogen atom; a linear or branched C₁-C₆ alkyl group; a COOH group;

X represents an oxygen atom; a sulfur atom; a NH group; when X represent an oxygen atom or a NH group, b is O or 1 ; when X represents a sulfur atom, b is O, or an integer of from 1 to 4, extremes included; - Y represents a polar group which is selected from: silane groups; acid groups; ester groups; amide groups; imide groups; nitro groups; hydroxy groups; mercapto groups; on condition that, when Y represents a mercapto group, at least one of the R substituents is a COOH group.

According to a further preferred embodiment, said at least one coupling agent containing at least one mercapto group (d) may be selected from mercaptosilanes, mercaptans, or mixtures thereof. Mercaptosilanes are particularly preferred.

According to a further preferred embodiment, said mercaptosilanes may be selected, for example, from compounds having the following general formula (II):

(R " ) n

HS ( ( I I )

n wherein: a, b, c, R and X, have the same meanings as above disclosed;

R" represents a halogen atom such as, for example, chlorine, bromine, iodine, preferably chlorine; or a Ci-C₁₀ alkoxy group;

R', which may be equal or different from each other, are selected from: C₁-C₃₆ alkyl groups; C₆-C₂₀ aryl groups; C₇-C₃₀ alkylaryl or arylalkyl groups; C₅-C₃₀ cycloaliphatic groups; n is an integer of from 1 to 3, extremes included.

Preferably, R" represents a C₁-C₃ alkoxy group; R represents a hydrogen atom; b is 0; a + c is 3; and n is 3.

Specific examples of mercaptosilanes having general formula (II) which may be advantageously used according to the present invention are: 1-mercapto- methyltriethoxysilane, 2-mercaptoethyltriethoxysilane, 3-mercaptopropyltriethoxy- silane, 3-mercaptopropylmethyldiethoxysilane, 2-mercaptoethyltripropoxysilane, 18- mercaptooctadecyldiethoxychlorosilane, or mixture thereof. 3-Mercaptopropyl- triethoxysilane is particularly preferred.

According to a further preferred embodiment, said mercaptanes may be selected, for example, from compounds having the following general formula (III):

HS ( CH) _a — (X ) _b — ( CH) _c COR ¹ " ( m )

I I

R R wherein: a, b, c, R and X, have the same meanings as above disclosed; - R'" represents: a OR_a group, wherein R_a represents a hydrogen atom; a metal such as, for example, lithium, sodium, potassium, magnesium, calcium; a linear or branched or cyclic C₁-C₃₆ alkyl group; a C₆-C₂₀ aryl group; a C₇-C₃₀ alkylaryl or arylalkyl group; a C₅-C₃₀ cycloaliphatic group; an ammonium ion; a NRiR₂ group, wherein Ri and R₂, represents a linear or branched or cyclic Ci-C₃₆ alkyl group; a C₆-C₂₀ aryl group; a C₇-C₃₀ alkylaryl or arylalkyl group; a C₅-C₃₀ cycloaliphatic group.

Preferably, R is a hydrogen atom; b is 0; a + c is an integer of from 3 to 12, extremes included; R'" represent a OR_a wherein R_a is a hydrogen atom.

Specific example of mercaptans having general formula (III) which may be advantageously used according to the present invention are: thioglycolic acid, 2- mercaptopropionic acid (thiolactic acid), 3-mercaptopropionic acid, 4- mercaptobutyric acid, mercaptoundecanoic acid, mercaptooctadecanoic acid, 2- mercaptosuccinic acid, 3,4-dimercaptosuccinic acid, 3-(3-mercaptopropyl- sulfanyl)propionic acid, 3-(3-mercaptopropyloxy)propionic acid, alkali, alkaline earth or ammonium salts thereof, or mixtures thereof. Mercaptoundecanoic acid is preferred.

As disclosed above, said crosslinkable elastomeric composition may further comprise (e) at least one silane coupling agent, other than said at least one coupling agent containing at least one mercapto group (d).

According to one preferred embodiment, said at least one silane coupling agent (e) may be selected from those having at least one hydrolizable silane group which may be identified, for example, by the following general formula (IV): (Rs)₃Si-C_nH_2n-R₆ (IV) wherein the groups Rs, which may be equal or different from each other, are selected from: alkyl, alkoxy or aryloxy groups or from halogen atoms, on condition that at least one of the groups R₅ is an alkoxy or aryloxy group; n is an integer of from 1 to 6, extremes included; R₆ is a group selected from: nitroso, amino, epoxide, vinyl, imide, chloro, -(S)₀₁C_nH_2n-Si-(Rs)₃, or -S-COR₅, in which m and n are integers of from 1 to 6, extremes included and the groups R₅ are defined as above.

Among the silane coupling agents (e) that are particularly preferred are bis(3- triethoxysilyl-propyl)tetrasulphide or bis(3-triethoxysilylpropyl)-disulphide. Said silane coupling agents (e) may be used as such or as a suitable mixture with an inert filler (for example carbon black) so as to facilitate their incorporation into the elastomeric polymer(s).

According to one preferred embodiment, said at least one silane coupling agent (e) may be present in the crosslinkable elastomeric composition in an amount of from 0 phr to 10 phr, preferably of from 0.5 phr to 5 phr.

As disclosed above, said crosslinkable elastomeric composition may further comprise (f) at least one layered material.

According to one preferred embodiment, said at least one layered material (f) may be selected, for example, from: phyllosilicates such as, for example, smectites, for example, montmorillonite, bentonite, nontronite, beidellite, volkonskoite, hectorite, saponite, sauconite; vermiculite; halloisite; sericite; aluminate oxides; hydrotalcite; or mixtures thereof. Montmorillonite is particularly preferred. These layered material generally contains exchangeable ions such as sodium (Na⁺), calcium (Ca²⁺), potassium (K⁺), magnesium (Mg²⁺), hydroxide (HO^"), or carbonate (CO₃ ^2'), present at the interlayer surfaces.

In order to render the layered material (f) more compatible with the elastomeric polymer(s) said at least one layered material (f) may be treated with at least one compatibilizing agent. Said compatibilizing agent is capable of undergoing ion exchange reactions with the ions present at the interlayers surfaces of the layered material.

According to one preferred embodiment, said at least one compatibilizing agent may be selected, for example, from the quaternary ammonium or phosphonium salts having the following general formula (V):

wherein:

Yi represents N or P;

R₁, R₂, R₃ and R₄, which may be equal or different from each other, represent a linear or branched C₁-C_2O alkyl or hydroxyalkyl group; a linear or branched C₁-C₂₀ alkenyl or hydroxyalkenyl group; a group -R₅-SH or -R₅-NH wherein R₅ represents a linear or branched C₁-C₂O alkylene group; a C₆-C₁₈ aryl group; a C₇-C₂₀ arylalkyl or alkylaryl group; a C₅-C₁₈ cycloalkyl group, said cycloalkyl group possibly containing hetero atom such as oxygen, nitrogen or sulfur; X₁"^" represents an anion such as the chloride ion, the sulphate ion or the phosphate ion; - n represents 1 , 2 or 3.

Said layered material (f) may be treated with the compatibilizing agent before adding it to the elastomeric polymer(s). Alternatively, said layered material (f) and the compatibilizing agent may be separately added to the elastomeric polymer(s). The treatment of the layered material (T) with the compatibilizing agent may be carried out according to known methods such as, for example, by an ion exchange reaction between the layered material and the compatibilizing agent: further details about said methods may be found, for example, in United States Patents US 4,136,103, US 5,747,560, or US 5,952,093.

According to one preferred embodiment, said at least one layered material (f) may be present in the crosslinkable elastomeric composition in an amount of from 0 phr to 20 phr, preferably from 2 phr to 10 phr.

Examples of layered material (f) which may be used according to the present invention and are available commercially are the products known by the name of Dellite^® 67G, Dellite^® 72T, Dellite^® 43B, from Laviosa Chimica Mineraria S.p.A.; Cloisite^® 25A, Cloisite^® 10A, Cloisite^® 15A, Cloisite^® 2OA, from Southern Clays; Nanofil^® 5, Nanofil^® 8, Nanofil^® 9, from Sϋd Chemie; Bentonite^® AG/3 from DaI Cin S.p.A.

At least one additional reinforcing filler may be advantageously added to the above reported crosslinkable elastomeric composition, in an amount generally of from 0 phr to 70 phr, preferably of from 20 phr to 50 phr. The reinforcing filler may be selected from those commonly used for crosslinked manufactured articles, in particular for tires, such as, for example, carbon black, calcium carbonate, kaolin, or mixtures thereof.

The types of carbon black which may be used according to the present invention may be selected from those conventionally used in tires manufacturing, and generally have a surface area of not less than 20 m²/g (determined by CTAB absorption as described in Standard ISO 6810:1995).

The crosslinkable elastomeric composition above reported may be vulcanized according to known techniques, in particular with sulfur-based vulcanizing systems commonly used for elastomeric polymer(s). To this end, in the crosslinkable elastomeric composition, after one or more steps of thermomechanical processing, a sulfur-based vulcanizing agent is incorporated together with vulcanization accelerators. In the final processing step, the temperature is generally kept below 140°C, so as to avoid any undesired pre-crosslinking phenomena.

The vulcanizing agent most advantageously used is sulfur, or molecules containing sulfur (sulfur donors), with accelerators and activators known to those skilled in the art.

Activators that are particularly effective are zinc compounds, and in particular ZnO, ZnCO₃, zinc salts of saturated or unsaturated fatty acids containing from 8 to 18 carbon atoms, such as, for example, zinc stearate, which are preferably formed in situ in the elastomeric composition from ZnO and fatty acid, and also BiO, PbO, Pb₃O₄, PbO₂, or mixtures thereof.

Accelerators that are commonly used may be selected from: dithiocarbamates, guanidine, thiourea, thiazoles, sulphenamides, thiurams, amines, xanthates, or mixtures thereof.

Said crosslinkable elastomeric composition may comprise other commonly used additives selected on the basis of the specific application for which the composition is intended. For example, the following may be added to said crosslinkable elastomeric composition: antioxidants, anti-ageing agents, plasticizers, adhesives, anti-ozone agents, modifying resins, or mixtures thereof.

In particular, for the purpose of further improving the processability, a plasticizer generally selected from mineral oils, vegetable oils, synthetic oils, or mixtures thereof, such as, for example, aromatic oil, naphthenic oil, phthalates, soybean oil, or mixtures thereof, may be added to said crosslinkable elastomeric composition. The amount of plasticizer generally ranges from O phr to 50 phr, preferably from of 5 phr to 30 phr.

The above reported crosslinkable elastomeric composition may be prepared by mixing together the solid elastomeric polymer(s), the liquid elastomeric polymer(s), and the coupling agent(s) containg at least one mercapto group, with the silica reinforcing filler and the other compounds optionally present, according to techniques known in the art. The mixing may be carried out, for example, using an open mixer of open-mill type, or an internal mixer of the type with tangential rotors (Banbury) or with interlocking rotors (Intermix), or in continuous mixers of Ko- Kneader type (Buss), or of co-rotating or counter-rotating twin-screw type.

Brief description of the drawing The present invention will now be illustrated in further detail by means of illustrative embodiments, with reference to the attached Fig. 1 which is a view in cross-section of a portion of a tire made according to the present invention.

Detailed description of the preferred embodiments With reference to Fig. 1 , "a" indicates an axial direction and "r" indicates a radial direction. For simplicity, Fig. 1 shows only a portion of the tire, the remaining portion not represented being identical and symmetrically arranged with respect to the radial direction "r".

The tire (100) comprises at least one carcass ply (101), the opposite lateral edges of which are associated with respective bead structures comprising at least one bead core (102) and at least one bead filler (104). The association between the carcass ply (101 ) and the bead core (102) is achieved here by turning back the opposite lateral edges of the carcass ply (101 ) around the bead core (102) so as to form the so-called carcass turn-up (101a) as shown in Fig. 1.

Alternatively, the conventional bead core (102) may be replaced with at least one annular insert formed from rubberized wires arranged in concentric coils (not represented in Fig. 1 ) (see, for example, European Patent Applications EP 928,680 or EP 928,702). In this case, the carcass ply (101) is not tumed-up around said annular inserts, the coupling being provided by a second carcass ply (not represented in Fig. 1 ) applied externally over the first.

The carcass ply (101) usually comprises a plurality of reinforcing cords arranged parallel to each other and at least partially coated with a layer of a crosslinked elastomeric composition. These reinforcing cords are usually made of textile fibres, for example rayon, nylon or polyethylene terephthalate, or of steel wires stranded together, coated with a metal alloy (for example copper/zinc, zinc/manganese, zinc/molybdenum/cobalt alloys, and the like). The carcass ply (101) is usually of radial type, i.e. it incorporates reinforcing cords arranged in a substantially perpendicular direction relative to a circumferential direction.

The core (102) is enclosed in a bead (103), defined along an inner circumferential edge of the tire (100), with which the tire engages on a rim (not represented in Fig. 1 ) forming part of a vehicle wheel. The space defined by each carcass turn-up (101a) contains a bead filler (104) usually made of a crosslinked elastomeric composition.

An antiabrasive strip (105) is usually placed in an axially external position relative to the carcass turn-up (101a).

A belt structure (106) is applied along the circumference of the carcass ply (101). In the particular embodiment of Fig. 1 , the belt structure (106) comprises two belt strips (106a, 106b) which incorporate a plurality of reinforcing cords, typically metal cords, which are parallel to each other in each strip and intersecting with respect to the adjacent strip, oriented so as to form a predetermined angle relative to a circumferential direction. On the radially outermost belt strip (106b), at least one zero-degree reinforcing layer (106c) may optionally be applied, commonly known as a "0° belt", which generally incorporates a plurality of reinforcing cords, typically textile cords, arranged at an angle of a few degrees relative to a circumferential direction, usually coated with a crosslinked elastomeric composition.

A tread band (109), according to the present invention, whose lateral edges are connected to the side walls (108), is applied circumferentially in a position radially external to the belt structure (106). Externally, the tread band (109) has a rolling surface (109a) designed to come into contact with the ground. Circumferential grooves which are connected by transverse notches (not represented in Fig. 1 ) so as to define a plurality of blocks of various shapes and sizes distributed over the rolling surface (109a) are generally made in this surface (109a), which is represented for simplicity in Fig. 1 as being smooth.

A sidewall (108) is also applied externally onto the carcass ply (101 ), this sidewall extending, in an axially external position, from the bead (103) to the end of the belt structure (106).

A tread underlayer (111) is placed between the belt structure (106) and the tread band (109).

As represented in Fig. 1 , the tread underlayer (111) may have uniform thickness.

Alternatively, the tread underlayer (111) may have a variable thickness in the transversal direction. For example, the thickness may be greater near its outer edges than at a central zone.

In Fig. 1 , said tread underlayer (111 ) extends over a surface substantially corresponding to the surface of development of said belt structure (106). Alternatively, said tread underlayer (111) extends only along at least one portion of the development of said belt structure (106), for instance at opposite side portions of said belt structure (106) (not represented in Fig. 1).

A strip made of elastomeric material (110), commonly known as a "mini-sidewall", may optionally be present in the connecting zone between the sidewalls (108) and the tread band (109), this mini-sidewall generally being obtained by co-extrusion with the tread band and allowing an improvement in the mechanical interaction between the tread band (109) and the side walls (108). Alternatively, the end portion of the side wall (108) directly covers the lateral edge of the tread band (109).

In the case of tubeless tires, a rubber layer (112) generally known as a liner, which provides the necessary impermeability to the inflation air of the tire, may also be provided in an inner position relative to the carcass ply (101 ).

The process for producing the tire according to the present invention may be carried out according to techniques and using apparatus that are known in the art, said process including manufacturing a green tire, and subsequently moulding and vulcanizing the green tire.

The tire according to the present invention may be suitable for running at high speeds. In particular, said tire may be a high performance tire commonly referred to as "HP" ("High Performance"), i.e. a tire capable of sustaining a maximum speed of at least 210 Km/h, preferably of from 210 Km/h and 240 Km/h. Examples of said tires are those belonging to the classes "H" and "V".

Although the present invention has been illustrated specifically in relation to a tire, other crosslinked elastomeric manufactured products that may be produced according to the invention may be, for example, conveyor belts, drive belts, or hoses.

The present invention will be further illustrated below by means of a number of preparation examples, which are given for purely indicative purposes and without any limitation of this invention.

EXAMPLES 1-3 Preparation of the elastomeric compositions

The elastomeric compositions given in Table 1 were prepared as follows (the amounts of the various components are given in phr).

All the components, except sulfur and accelerators (DPG80 and CBS), were mixed together in an internal mixer (model Pomini PL 1.6) for about 5 min (1^st Step). As soon as the temperature reached 145±5°C, the elastomeric composition was discharged. The sulfur and accelerators (DPG and CBS), were then added and mixing was carried out in an open roll mixer (2^nd Step).

TABLE 1

(^*): comparative.

S-SBR: solution-prepared styrene/1 ,3-butadiene copolymer having a styrene content of 25% by weight and an amount of vinyl unsaturations in the butadiene part of 67%; and having a Mooney viscosity, measured at 100⁰C, of

48 (Europrene^® SOL R 76612 - Polimeri Europa); NR: cis-1 ,4-polyisoprene having a Mooney viscosity, measured at 100⁰C, of 60

(SMR GP - Lee Rubber Group); BR: solution prepared high-cis polybutadiene having a Mooney viscosity, measured at 100⁰C, of 44 (Buna^® CB 25 - Lanxess); Ricon^® 100: butadiene-styrene random copolymer having an amount of vinyl unsaturations in the butadiene part of 70%; a number average molecular weight (M_n) of 4500; a Brookfield viscosity, measured at 45°C, of 40000±12000 cps; a glass transition temperature (T₉) of -30⁰C;

Silquest^® A-1891 Silane: 3-mercaptopropyltriethoxysilane (GE Silicones); TESPD: bis(3-triethoxysilylpropyl)disulphide (Degussa-Hϋls); Antioxidant: phenyl-p-phenylenediamine (6-PPD - Akzo Nobel); Silica: Zeosil^® 1165 MP (Rhodia);

DPG80 (accelerator): diphenyl guanidine (Rhenogran^® DPG80 - Rhein Chemie); CBS (accelerator): N-cyclohexyl^-benzothiazyl-sulphenamide (Vulkacit^® CZ/C - Lanxess).

The modulus (100% Modulus and 300% Modulus), the stress at break, as well as the elongation at break, were measured according to Standard ISO 37:2005 on samples of the abovementioned elastomeric compositions vulcanized at 17O⁰C, for 10 min. The results obtained are given in Table 2.

The hardness in IRHD degrees (at 23°C and at 7O⁰C) according to Standard ISO 48:1994 were measured on samples of the abovementioned elastomeric compositions vulcanized at 17O⁰C, for 10 min. The results obtained are given in Table 2.

Table 2 also shows the dynamic mechanical properties, measured using an lnstron dynamic device in the traction-compression mode according to the following methods. A test piece of the crosslinked elastomeric composition (vulcanized at 170°C, for 10 min) having a cylindrical form (length = 25 mm; diameter = 12 mm), compression-preloaded up to a 25% longitudinal deformation with respect to the initial length, and kept at the prefixed temperature (10⁰C, 23°C, and 70°C) for the whole duration of the test, was submitted to a dynamic sinusoidal strain having an amplitude of ±3.5% with respect to the length under pre-load, with a 100 Hz frequency. The dynamic mechanical properties are expressed in terms of dynamic elastic modulus (E') and Tan delta (loss factor) values. The Tan delta value is calculated as a ratio between viscous modulus (E") and elastic modulus (E').

Moreover, Table 2 also show the DIN abrasion: the data (expressed in mm³) correspond to the amount of elastomeric composition removed by operating under the standard conditions given in Standard DIN 53516. TABLE 2

(^*): comparative.

EXAMPLES 4-6

Preparation of the elastomeric compositions

The elastomeric compositions given in Table 3 were prepared as follows (the amounts of the various components are given in phr).

TABLE 3

(^*): comparative.

S-SBR: solution-prepared styrene/1 ,3-butadiene copolymer having a styrene content of 25% by weight and an amount of vinyl unsaturations in the butadiene part of 67%; and having a Mooney viscosity, measured at 100°C, of 48 (Europrene^® SOL R 76612 - Polimeri Europa);

NR: cis-1 ,4-polyisoprene having a Mooney viscosity, measured at 100⁰C, of 72

(SKI - Nizhnekamskneftechim Export); Ricon^® 100: butadiene-styrene random copolymer having an amount of vinyl unsaturations in the butadiene part of 70%; a number average molecular weight (M_n) of 4500; a Brookfield viscosity, measured at 45⁰C, of

40000±12000 cps; a glass transition temperature (T₉) of -30⁰C; Silquest^® A-1891 Silane: 3-mercaptopropyltriethoxysilane (GE Silicones); TESPD: bis(3-triethoxysilylpropyl)disulphide (Degussa-Hϋls); Antioxidant: phenyl-p-phenylenediamine (6-PPD - Akzo Nobel); Silica: Zeosil^® 1165 MP (Rhodia);

The modulus (100% Modulus and 300% Modulus), the stress at break, the elongation at break, the hardness in IRHD degrees (at 23⁰C and at 70⁰C), the dynamic mechanical properties, as well as the DIN abrasion, were measured as reported in Examples 1-3. The results obtained are given in Table 4.

TABLE 4

(*): comparative.

EXAMPLES 7-9

Preparation of the elastomeric compositions

The elastomeric compositions given in Table 5 were prepared as follows (the amounts of the various components are given in phr).

All the components, except sulfur, accelerators (DPG and CBS), and retardant (PVI), were mixed together in an internal mixer (model Pomini PL 1.6) for about 5 min (1^st Step). As soon as the temperature reached 145±5°C, the elastomeric composition was discharged. The sulfur, accelerators (DPG and CBS), and retardant (PVI), were then added and mixing was carried out in an open roll mixer (2^nd Step).

TABLE 5

(^*): comparative.

48 (Europrene^® SOL R 76612 - Polimeri Europa);

NR: cis-1 ,4-polyisoprene having a Mooney viscosity, measured at 100⁰C, of 60

Silquest^® A-1891 Silane: 3-mercaptopropyltriethoxysilane (GE Silicones);

TESPD: bis(3-triethoxysilylpropyl)disulphide (Degussa-Hϋls);

Dellite^® 67G: montmorillonite belonging to the smectite family modified with quaternary ammonium salt (Laviosa Chimica Mineraria S.p.A.); Antioxidant: phenyl-p-phenylenediamine (6-PPD - Akzo Nobel); Silica: Zeosil^® 1165 MP (Rhodia);

PVI: N-(cyclohexylthio)phthalimide (Santogard^® PVI - Flexsys); CBS (accelerator): N-cyclohexyl-2-benzothiazyl-sulphenamide

(Vulkacit^® CZ/C - Lanxess); DPG80 (accelerator): diphenyl guanidine (Rhenogran^® DPG80 - Rhein Chemie);

The modulus (100% Modulus and 300% Modulus), the stress at break, the elongation at break, the hardness in IRHD degrees (at 23°C and at 70°C), the dynamic mechanical properties, as well as the DIN abrasion, were measured as reported in Examples 1-3. The results obtained are given in Table 6.

TABLE 6

(^*): comparative.

The results above reported (Tables 2, 4 and 6) clearly show that the addition of a coupling agent containing at least one mercapto group (Examples 3, 6 and 9) allows to obtain crosslinked elastomeric compositions showing a good balance between their wet grip, rolling resistance and abrasion resistance. In particular, said crosslinked elastomeric compositions show: - higher tensile modulus at 300% elongation (300% Modulus); reduced variation of said dynamic elastic modulus (E') as the temperatures increases (low ΔE'); reduced rolling resistance (i.e. lower Tan delta at 7O⁰C); good or even improved abrasion resistance; good wet grip (i.e. higher Tan delta at 10⁰C).

Claims

1. Tire comprising at least one structural element including a crosslinked elastomeric material obtained by crosslinking a crosslinkable elastomeric composition comprising: (a) 100 phr of at least one solid elastomeric polymer having a Mooney viscosity, measured at 100°C, of from 30 to 90;

(b) from 3 phr to 33 phr of at least one liquid elastomeric polymer having a number average molecular weight (M_n) of from 1000 to 20000 and an amount of vinyl unsaturations in the butadiene part, of from 15% to 100%;

(c) from 5 phr to 120 phr of at least one silica reinforcing filler;

(d) from 0.1 phr to 10 phr of at least one coupling agent containing at least one mercapto group.

2. Tire according to claim 1 , wherein said at least one liquid elastomeric polymer (b) is present in the crosslinkable elastomeric composition in an amount of from 5 phr to 15 phr.

3. Tire comprising at least one structural element including a crosslinked elastomeric material obtained by crosslinking a crosslinkable elastomeric composition comprising: (a) from 75 phr to 95 phr of at least one solid elastomeric polymer having a

Mooney viscosity, measured at 100⁰C, of from 35 to 90;

(b) from 5 phr to 25 phr of at least one liquid elastomeric polymer having a number average molecular weight (M_n) of from 1000 to 20000 and an amount of vinyl unsaturations in the butadiene part, of from 15% to 100%; the sum of (a) + (b) being 100 phr;

(c) from 5 phr to 120 phr of at least one silica reinforcing filler;

4. Tire according to claim 3, wherein said at least one solid elastomeric polymer

(a) is present in the crosslinkable elastomeric composition in an amount of from 85 phr to 90 phr, the sum of (a) + (b) being 100 phr.

5. Tire according to claim 4, wherein said at least one liquid elastomeric polymer

(b) is present in the crosslinkable elastomeric composition in an amount of from 10 phr to 15 phr, the sum of (a) + (b) being 100 phr.

6. Tire according to any one of the preceding claims, wherein said at least one solid elastomeric polymer (a) has a Mooney viscosity, measured at 100⁰C, of from 40 to 75.

7. Tire according to any one of the preceding claims, wherein said at least one liquid elastomeric polymer (b) has a number average molecular weight (M_n) of from 3000 to 15000.

8. Tire according to any one of the preceding claims, wherein said at least one liquid elastomeric polymer (b) has an amount of vinyl unsaturations in the butadiene part of from 30% to 90%.

9. Tire according to any one of the preceding claims, wherein said at least one silica reinforcing filler (c) is present in the crosslinkable elastomeric composition in an amount of from 20 phr to 90 phr.

10. Tire according to any one of the preceding claims, wherein said at least one coupling agent (d) containing at least one mercapto group is present in the crosslinkable elastomeric composition in an amount of from 0.5 phr to 8 phr.

11. Tire according to any one of the preceding claims, comprising: a carcass structure of a substantially toroidal shape, having opposite lateral edges terminating in respective bead structures; a belt structure applied in a radially external position with respect to said carcass structure; a tread band radially superimposed on said belt structure; a pair of sidewalls applied laterally on opposite sides with respect to said carcass structure; wherein said structural element is a tread band.

12. Tire according to any one of the preceding claims, wherein said at least one solid elastomeric polymer (a) is selected from diene elastomeric polymer Ca₁) having a a glass transition temperature below 2O⁰C.

13. Tire according to claim 12, wherein said diene elastomeric polymer fa ) is selected from: natural or synthetic cis-1 ,4-polyisoprene, 3,4-polyisoprene, polybutadiene, optionally halogenated . isoprene/isobutene copolymers, 1 ,3- butadiene/acrylonitrile copolymers, styrene/1 ,3-butadiene copolymers, styrene/isoprene/1 ,3-butadiene copolymers, styrene/1 ,3-butadiene/acrylonitrile copolymers, or mixtures thereof.

14. Tire according to any one of claims 1 to 11 , wherein said at least one solid elastomeric polymer (a) is selected from elastomeric polymers of one or more monoolefins with an olefinic comonomer or derivatives thereof (a₂).

15. Tire according to claim 14, wherein said elastomeric polymers (a₂) are selected from: ethylene/propylene copolymers (EPR) or ethylene/propylene/diene copolymers (EPDM); polyisobutene; butyl rubbers;

5 halobutyl rubbers; or mixtures thereof.

16. Tire according to any one of the preceding claims, wherein said at least one liquid elastomeric polymer (b) is selected from liquid elastomeric polymers having a Brookfield viscosity, measured at 45°C, not higher than 150000 cPs.

17. Tire according to claim 16, wherein said at least one liquid elastomeric 10 polymer (b) is selected from liquid elastomeric polymers having a Brookfield viscosity, measured at 45°C, of from 10000 cPs to 100000 cPs.

18. Tire according to any one of the preceding claims, wherein said at least one liquid elastomeric polymer (b) is selected from liquid elastomeric polymers having a glass transition temperature (T₉) of from -5°C to -120⁰C.

15 19. Tire according to claim 18, wherein said at least one liquid elastomeric polymer (b) is selected from liquid elastomeric polymers having a glass transition temperature (T₉) of from -10⁰C to -80°C.

20. Tire according to any one of the preceding claims, wherein said at least one liquid elastomeric polymer (b) is selected from homopolymers or copolymers

20 of conjugated diolefins containing from 4 to 12 carbon atoms, such as: 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, or mixtures thereof.

21. Tire according to any one of claims 1 to 19, wherein said at least one liquid elastomeric polymer (b) is selected from copolymers of 1 ,3-butadiene with at

25 least one monovinylarene containing from 8 to 20 carbon atoms, said monovinylarene being selected from: styrene; 1-vinylnaphthalene; 2- vinylnaphthalene; various alkyl, cycloalkyl, aryl, alkylaryl or arylalkyl derivatives of styrene such as α-methylstyrene, 3-methylstyrene, 4-propylstyrene, 4-cyclohexylstyrene, 4-dodecylstyrene, 2-ethyl-4-

30 benzylstyrene, 4-p-tolylstyrene, 4-(4-phenylbutyl)styrene, or mixtures thereof.

22. Tire according to any one of the preceding claims, wherein said at least one silica reinforcing filler (c) is selected from: pyrogenic silica, precipitated amorphous silica, wet silica (hydrated silicic acid), dry silica (anhydrous silicic acid), fumed silica, calcium silicate, or mixtures thereof.

35 23. Tire according to any one of the preceding claims, wherein said at least one coupling agent containing at least one mercapto group (d) is selected from compounds having the following general formula (I):

HS ( CH) _a — (X) _b — ( CH) _c -γ ( I )

I I

R R wherein: 5 - a + c is an integer of from 1 to 36, extremes included;

R represents a hydrogen atom; a linear or branched C₁-C₆ alkyl group; a

COOH group;

X represents an oxygen atom; a sulfur atom; a NH group; when X represent an oxygen atom or a NH group, b is O or 1; 10 - when X represents a sulfur atom, b is 0, or an integer of from 1 to 4, extremes included;

Y represents a polar group which is selected from: silane groups; acid groups; ester groups; amide groups; imide groups; nitro groups; hydroxy groups; mercapto groups; on condtion that, when Y represents a 15 mercapto group, at least one of the R substituents is a COOH group.

24. Tire according to any one of the preceding claims, wherein said at least one coupling agent containing at least one mercapto group (d) is selected from mercaptosilanes, mercaptans, or mixtures thereof.

25. Tire according to claim 24, wherein said mercaptosilanes are selected from 20 compounds having the following general formula (II):

/

HS ( CH) _a — (X ) _b — ( CH) _C — S i ( I I )

I I \

R R (R ¹ I ₃ . ,, wherein: a, b, c, R and X, have the same meanings as above disclosed;

R" represents a halogen atom such as chlorine, bromine, iodine; or a C₁- 25 C₁₀ alkoxy group;

R', which may be equal or different from each other, are selected from:

C₁-C₃₆ alkyl groups; C₆-C₂₀ aryl groups; C₇-C₃₀ alkylaryl or arylalkyl groups; C₅-C₃₀ cycloaliphatic groups; n is an integer of from 1 to 3, extremes included.

30 26. Tire according to claim 25, wherein said mercaptosilanes having general formula (II) are: 1-mercaptomethyltriethoxysilane, 2-mercaptoethyltriethoxy- silane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropylmethyldiethoxy- silane, 2-mercaptoethyltripropoxysilane, 18-mercaptooctadecyldiethoxy- chlorosilane, or mixture thereof.

27. Tire according to claim 24, wherein said mercaptanes are selected from

5 compounds having the following general formula (III):

HS (CH) _a — (X) _b — (CH) _c COR ' ' ' ( m )

I I

R R wherein: a, b, c, R and X, have the same meanings as above disclosed; R'" represents:

10 - a OR_a group, wherein R₃ represents a hydrogen atom; a metal such as lithium, sodium, potassium, magnesium, calcium; a linear or branched or cyclic C₁-C₃₆ alkyl group; a C₆-C_2O aryl group; a C₇- C₃₀ alkylaryl or arylalkyl group; a C₅-C₃₀ cycloaliphatic group; an ammonium ion;

15 - a NR₁R₂ group, wherein R₁ and R₂, represents a linear or branched or cyclic C₁-C₃₆ alkyl group; a C₆-C₂₀ aryl group; a C₇-C₃₀ alkylaryl or arylalkyl group; a C₅-C₃₀ cycloaliphatic group.

28. Tire according to claim 27, wherein said mercaptans having general formula (III) are: thioglycolic acid, 2-mercaptopropionic acid (thiolactic acid), 3-

20 mercaptopropionic acid, 4-mercaptobutyric acid, mercaptoundecanoic acid, mercaptooctadecanoic acid, 2-mercaptosuccinic acid, 3,4-dimercaptosuccinic acid, 3-(3-mercaptopropylsulfanyl)propionic acid, 3-(3- mercaptopropyloxy)propionic acid, alkali, alkaline earth or ammonium salts thereof, or mixtures thereof.

25 29. Tire according to any one of the preceding claims, wherein said crosslinkable elastomeric composition further comprises (e) at least one silane coupling agent, other than said at least one coupling agent containing at least one mercapto group (d).

30. Tire according to claim 29, wherein said at least one silane coupling agent (e)

30 is selected from those having at least one hydrolizable silane group which are identified by the following general formula (IV):

(Rs)₃Si-C_nH_2n-R₆ (IV) wherein the groups R₅, which may be equal or different from each other, are selected from: alkyl, alkoxy or aryloxy groups or from halogen atoms, on condition that at least one of the groups R₅ is an alkoxy or aryloxy group; n is an integer of from 1 to 6, extremes included; R₆ is a group selected from: nitroso, amino, epoxide, vinyl, imide, chloro, -(S)_n)C_nH_2n-Si-(Rs)₃, or -S-

COR₅, in which m and n are integers of from 1 to 6, extremes included and the groups R₅ are defined as above.

31. Tire according to claim 29 or 30, wherein said at least one silane coupling agent (e) is present in the crosslinkable elastomeric composition in an amount of from O phr to 10 phr.

32. Tire according to any one of the preceding claim, wherein said crosslinakble elastomeric composition further comprises (f) at least one layered material having an individual layer thickness of from 0.01 nm to 30 nm.

33. Tire according to claim 31 , wherein said at least one layered material (f) is selected from: phyllosilicates such as smectites, such as montmorillonite, bentonite, nontronite, beidellite, volkonskoite, hectorite, saponite, sauconite; vermiculite; halloisite; sericite; aluminate oxides; hydrotalcite; or mixtures thereof.

34. Tire according to claim 32 or 33, wherein said at least one layered material (f) is treated with at least one compatibilizing agent which is selected from the quaternary ammonium or phosphonium salts having the following general formula (V):

wherein:

Y₁ represents N or P;

R₁, R₂, R₃ and R₄, which may be equal or different from each other, represent a linear or branched C₁-C₂₀ alkyl or hydroxyalkyl group; a linear or branched C₁-C₂₀ alkenyl or hydroxyalkenyl group; a group -R₅- SH or -R₅-NH wherein R₅ represents a linear or branched C₁-C₂₀ alkylene group; a C₆-Ci₈ aryl group; a C₇-C₂₀ arylalkyl or alkylaryl group; a C₅-C₁₈ cycloalkyl group, said cycloalkyl group possibly containing hetero atom such as oxygen, nitrogen or sulfur; X₁"^" represents an anion such as the chloride ion, the sulphate ion or the phosphate ion; n represents 1 , 2 or 3.

35. Crosslinkable elastomeric composition comprising: (a) 100 phr of at least one solid elastomeric polymer having a Mooney viscosity, measured at 100⁰C, of from 30 to 90;

(b) from 3 phr to 33 phr, of at least one liquid elastomeric polymer having a number average molecular weight (M_n) of from 1000 to 20000 and an amount of vinyl unsaturations in the butadiene part, of from 15% to 100%;

(c) from 5 phr to 120 phr of at least one silica reinforcing filler;

36. Crosslinkable elastomeric composition according to claim 35, wherein said at least one liquid elastomeric polymer (b) is present in an amount of from 5 phr to 15 phr.

37. Crosslinkable elastomeric composition comprising:

(a) from 75 phr to 95 phr of at least one solid elastomeric polymer having a

Mooney viscosity, measured at 100⁰C, of from 30 to 90; (b) from 5 phr to 25 phr of at least one liquid elastomeric polymer having a number average molecular weight (M_n) of from 1000 to 20000 and an amount of vinyl unsaturations in the butadiene part, of from 15% to 100%; the sum of (a) + (b) being 100 phr; (c) from 5 phr to 120 phr of at least one silica reinforcing filler;

38. Crosslinkable elastomeric composition according to claim 37, wherein said at least one solid elastomeric polymer (a) is present in an amount of from 85 phr to 90 phr, the sum of (a) + (b) being 100 phr.

39. Crosslinkable elastomeric composition according to claim 38, wherein said at least one liquid elastomeric polymer (b) is present in an amount of from 10 phr to 15 phr, the sum of (a) + (b) being 100 phr.

40. Crosslinkable elastomeric composition according to any one of claims 35 to 36, wherein said at least one solid elastomeric polymer has a Mooney viscosity, measured at 100⁰C₁ of from 40 to 75.

41. Crosslinkable elastomeric composition according to any one of claims 35 to 38, wherein said at least one liquid elastomeric polymer has a number average molecular weight (M_n) of from 3000 to 15000.

5 42. Crosslinkable elastomeric composition according to any one of claims 35 to 39 wherein said at least one liquid elastomeric polymer has an amount of vinyl unsaturations in the butadiene part of from 30% to 90%.

43. Crosslinkable elastomeric composition according to any one of claims 35 to

42, wherein said at least one silica reinforcing filler is present in an amount of 10 from 20 phr to 90.

44. Crosslinkable elastomeric composition according to any one of claims 35 to

43, wherein said at least one coupling agent containing at least one mercapto group is present in an amount of from 0.5 phr to 8 phr.

45. Crosslinkable elastomeric composition according to any one of claims 35 to 15 44, wherein said at least one solid elastomeric polymer (a) is defined according to any one of claims 12 to 15.

46. Crosslinkable elastomeric composition according to any one of claims 35 to

45, wherein said at least one liquid elastomeric polymer (b) is defined according to any one of claims 16 to 21.

20 47. Crosslinkable elastomeric composition according to any one of claims 35 to

46, wherein said at least one silica reinforcing filler is defined according to claim 22.

48. Crosslinkable elastomeric composition according to any one of claims 35 to

47, wherein said at least one coupling agent containing at least one mercapto 25 group is defined according to any one of claims 23 to 28.

49. Crosslinkable elastomeric composition according to any one of claims 35 to

48, comprising (e) at least one silane coupling agent, other than said at least one coupling agent containing at least one mercapto group (d), which is defined according to claim 30 or 31.

30 50. Crosslinkable elastomeric composition according to any one of claims 35 to

49, comprising (f) at least one layered material (f) which is defined according to any one of claims 32 to 34.

51. Tire tread band including a crosslinkable elastomeric composition, said crosslinkable elastomeric composition being defined according to any one of 35 claims 35 to 50.

52. Crosslinked manufactured article obtained by crosslinking a crosslinkable elastomeric composition defined according to any one of claims 35 to 50.