TIRE AND CROSSLINKABLE ELASTOMERIC COMPOSITION COMPRISING DIATOMITE PARTICLES

Field of the invention

The present invention generally relates to a tire and to a crosslinkable elastomeric composition comprising diatomite particles.

More in particular, the present invention relates to a tire including at least one structural element obtained by crosslinking a crosslinkable elastomeric composition comprising diatomite particles having a relatively high BET surface area and a relatively high average maximum dimension.

Moreover, the present invention also relates to a crosslinkable elastomeric composition comprising diatomite particles having a relatively high BET surface area and a relatively high average maximum dimension, as well as to a crosslinked manufactured product obtained by crosslinking said crosslinkable elastomeric composition.

Background of the invention

In the rubber industry, in particular that of tires manufacturing, it is known practice to use additives with the crosslinkable elastomeric compositions to improve the mechanical properties of the finished products (i.e. the crosslinked manufactured products).

For example, static and dynamic moduli of the elastomeric compositions may be increased by increasing crosslinking density of these compositions by using a large amount of sulfur, or by using a large amount of carbon black, or a very fine and structured carbon black. However, the above ways of increasing static and dynamic moduli may lead to a number of drawbacks.

For example, it is known that the use of a large amount of sulfur may cause remarkable reversion phenomena, which result in modification of the tires performances during use. On the other side, it is known that carbon black gives the crosslinked manufactured products pronounced hysteresis

properties, that is to say an increase in the dissipated heat under dynamic conditions, which results in an increase in the rolling resistance of the tire and the fuel consumption. In addition, a large amount of carbon black causes an increase in the viscosity of the elastomeric composition and, consequently, has a negative impact on the processability and extrudability of the crosslinkable elastomeric composition.

To overcome the drawbacks caused by the use of carbon black, the so-called "white" reinforcing fillers are usually used, in particular silica, in total or partial replacement for the carbon black. However, although the use of said reinforcing fillers leads to good tear resistance, it also entails a series of drawbacks essentially related to the poor affinity of these fillers with respect to the elastomeric polymers commonly used in the production of tires. In particular, to obtain a good degree of dispersion of the silica in the elastomeric polymers, it is necessary to subject the elastomeric compositions to a prolonged thermo mechanical blending action. To increase the affinity of the silica with the elastomeric polymers, it is necessary to use suitable coupling agents, such as, for example, sulfur-containing organosilane products. However, the need to use such coupling agents places a limitation on the maximum temperature which may be reached during the blending and thermo mechanical processing operations of the elastomeric compositions, to avoid the penalty of an irreversible thermal degradation of the coupling agents.

Moreover, the processability of such crosslinkable elastomeric compositions comprising reinforcing fillers such as carbon black and/or silica may require high temperatures, but this implies a reduction of the productivity, an excessive power consumption, and an increased risk of forming defects due to a partial early crosslinking ("scorching phenomena").

Usually, the above mentioned problems have been tackled by the addition of salts of fatty acids with sodium or zinc (soaps) or by the addition of lubricants or oils, that can reduce the viscosity and increase the flowability. However, the use of such ingredients involves the problem of a reduction of the tensile modulus and an increase in hysteresis of the resulting crosslinked elastomeric

compositions.

Recent approaches for improving the processability of crosslinkable elastomeric compositions comprising silica have been directed to reducing or replacing the use of silica coupling agents by employing silica dispersing aids, such as monofunctional silica shielding agents (e.g., silica hydrophobating agents that chemically react with the surface silanol groups on the silica particles but are not reactive with the elastomeric polymers) and agents which physically shield the silanol groups, to prevent reagglomeration (flocculation) of the silica particles after compounding. Silica processing aids useful for such purposes are described, for example, in United States Patent US 6,512,035 disclosing the use of one or more monofunctional alkyl tin compounds, in United States Patent US 6,608,145 disclosing the use of silica dispersing aids, such as alkyl alkoxysilanes, glycols (e.g., diethylene glycol, or polyethylene glycol), fatty acid esters of hydrogenated and non-hydrogenated

C ₅ and C ₆ sugars (e.g., sorbitan oleates), polyoxyethylene derivatives of the fatty acid esters, and fillers such as mica, talc, urea, clay, sodium sulfate, or in United States Patent US 7,041 ,745 disclosing the use of polar additive, such as the polyvinyl acetate) (PVA).

United States Patent US 7,122,090 discloses a tire excellent in performance on ice and snow having a tread comprising a rubber sheet obtained from a rubber composition containing 2 to 50 parts by weight of short fiber or plate- like material based on 100 parts by weight of diene rubber, wherein said short fiber material has an average fiber diameter of 1 to 100 μm and average length of 0.1 to 5 mm and said plate-like material has an average thickness of 1 to 90 μm and average length of 0.1 to 5 mm. The short fiber is preferably organic and/or inorganic short fiber. An example of the organic short fiber is polyester fiber. Examples of the inorganic short fiber are glass fiber, carbon fiber, metal fiber (tungsten, iron, copper, platinum, stainless steel) and potassium titanate fiber. Examples of the plate-like material are aluminum whisker, potassium titanate whisker, aluminum borate whisker, titanate oxide type whisker and zinc oxide wisker.

Japanese Patent Application JP 2002/60553 discloses a rubber composition improving both a frictional force on ice and a wear performance obtained by blending 1 pts.wt to 30 pts.wt. of powder particles consisting essentially of at least one type of a material selected from among silicates, metal carbonates, metal sulfates, and aluminum oxide and has an average particle diameter of 1 μm to 300 μm, with a rubber composition obtained by blending and kneading 20 pts.wt. to 80 pts.wt. of carbon black having at least 70 m ² /g of N ₂ SA and DPB oil absorption of at least 90 ml/100 g, 0 pts.wt. to 50 pts.wt. of precipitated silica, and other general-purpose compounding agents per 100 pts.wt. of diene rubber.

Summary of the invention

The Applicant has faced the problem of improving the processability of the crosslinkable elastomeric compositions comprising reinforcing filler(s) without negatively affecting or even improving the mechanical properties (both static and dynamic) of the obtained crosslinked manufactured products, in particular of the obtained tires.

The Applicant has found that the above mentioned problem may be overcome by adding to the crosslinkable elastomeric compositions which may be advantageously used in the production of crosslinked manufactured products, in particular in the manufacturing of tires, diatomite particles having a BET surface area higher than or equal to about 10 m ² /g and a micrometric average maximum dimension higher than or equal to about 0.3 μm.

In particular, the crosslinkable elastomeric compositions comprising such diatomite particles show low viscosity and good flowability during the manufacturing, in particular during the manufacturing of the green tires. Moreover, the obtained crosslinked manufactured products maintain substantially unchanged or even improved mechanical properties (both static and dynamic).

Furthermore, the Applicant has also found that the obtained crosslinked elastomeric compositions, in particular in the case of the elastomeric

compositions which may be advantageously used in the manufacturing of a tire tread band, show a reduced variation of the hardness and of the dynamic elastic modulus (E') as the temperature increases (namely, a reduced "thermoplastic behavior" of the crosslinked elastomeric compositions, which is of fundamental importance when using said crosslinkable elastomeric compositions in tires manufacturing).

Accordingly, in 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 elastomeric polymer;

(b) from about 1 phr to about 150 phr, preferably from about 5 phr to about 100 phr, of diatomite particles having a BET surface area, measured according to Standard ISO 5794-1 :2005, higher than or equal to about 10 m ² /g, preferably higher than or equal to about 25 m ² /g, more preferably higher than or equal to about 35 m ² /g and an average maximum dimension higher than or equal to about 0.3 μm, preferably lower than or equal to about 35 μm, more preferably lower than or equal to about 15 μm; (c) from about 5 phr to about 120 phr, preferably from about 20 phr to about

90 phr of at least one reinforcing filler.

According to one preferred embodiment, said tire comprises: a carcass structure of a substantially toroidal shape, having opposite lateral edges associated with respective right-hand and left-hand bead structures; a belt structure applied in a radially external position with respect to said carcass structure; a tread band applied in a radially external position with respect to said belt structure; a pair of sidewalls applied laterally on opposite sides with respect to said carcass structure; wherein said structural element is at least one of said tread band, or said pair of sidewalls.

Preferably, said bead structures comprise at least one bead core and at least one bead filler, said bead filler being said structural element.

Preferably, said tire may further comprise: - a tread underlayer applied in a radially internal position with respect to said tread band; and, optionally a pair of sidewall inserts extending radially between each of said bead structures and the corresponding lateral edge of said tread band; and optionally, - a pair of anti-abrasive layers placed in an axially external position with respect to said bead structures; wherein said structural element is at least one of said tread underlayer, or said pair of sidewall inserts, or said pair of anti-abrasive layers.

Even more preferably, said tire may further comprise: at least one first layer of crosslinked elastomeric material applied in a radially internal position with respect to said carcass structure; and optionally at least one second layer of crosslinked elastomeric material applied between said at least one first layer of crosslinked elastomeric material and said carcass structure; wherein said structural element is at least one of said first layer, or of said second layer of crosslinked elastomeric material.

Said at least one first layer of crosslinked elastomeric material is generally known as a "liner" and, in case of tubeless tire, is useful to provide the necessary impermeability to the inflation air of the tire.

Said at least one second layer of crosslinked elastomeric material is generally known as a "under-liner" and, in case of tubeless tire, is useful as an additional element to provide the necessary impermeability to the inflation air of the tire.

In a second aspect, the present invention relates to a crosslinkable elastomeric composition comprising:

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

(b) from about 1 phr to about 150 phr, preferably from about 5 phr to about 100 phr, of diatomite particles having a BET surface area, measured according to Standard ISO 5794-1 :2005, higher than or equal to about 10 m ² /g, preferably higher than or equal to about 25 m ² /g, more preferably higher than or equal to about 35 m ² /g and an average maximum dimension higher than or equal to about 0.3 μm, preferably lower than or equal to about 35 μm, more preferably lower than or equal to about 15 μm; (c) from about 5 phr to about 120 phr, preferably from about 20 phr to about

90 phr of at least one reinforcing filler.

For the purposes of the present description and of the claims which follow, the term "maximum dimension" means the major dimension of a diatomite particle, independently from the measurement direction, and the term "average maximum dimension" means the average of the major dimensions measured by a microscopy technique in a representative sample of diatomite particles.

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).

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

According to one preferred embodiment, said diatomite particles (b) have a residue on a 325 Mesh sieve lower than or equal to about 2.5% by weight, more preferably lower than or equal to about 1 % by weight, with respect to the total weight of the diatomite particles.

According to a further preferred embodiment, said diatomite particles (b) may comprise any desired types of diatomaceous earths, provided that the above mentioned characteristics of BET surface area and average maximum

dimension and, preferably, 325 Mesh sieve residue, are met.

Diatomaceous earth is a light colored, porous sedimentary silica deposit, composed of the fossilized skeletons of diatoms, single celled aquatic plants which accumulate in marine or fresh water environments laid down in the

Miocene period, about 15 million years ago. Diatomaceous earth comprises a honeycomb silica structure comprising a multiplicity of pores having a diameter in the order of some nanometers (10 nm - 100 nm) providing high absorptive capacity and surface area. Diatomaceous earth contains 90% SiO ₂ plus Al, Fe, Ca and Mg oxides. The evolution and different environments in which diatoms are found have resulted in a wide variety of size, shape and appearance in the silica skeletal structure. The diatomite particles useful in the present invention have mainly a rod or acicular shape with one dimension, i.e. the length, prevailing on the other two dimensions, i.e. width and thickness, or a disc or tabular shape with one dimension, i.e. the thickness, shorter than the other two dimensions, i.e. length and width.

Materials consisting, in part or totally, of fragments of diatomite particles, as well as materials consisting of particles having different shape, such as barrel shape, or spherical shape, are also included in the present invention, provided that the above mentioned characteristics of BET surface area, average maximum dimension, and, preferably, 325 Mesh sieve residue, are met.

According to one preferred embodiment, said diatomite particles (b) have a BET surface area, measured according to Standard ISO 5794-1 :2005, in the range of from about 25 m ² /g to about 200 m ² /g, more preferably from about 35 m ² /g to about 100 m ² /g.

According to a further preferred embodiment, said diatomite particles (b) have an average maximum dimension in the range of from about 0.5 μm to about

25 μm, preferably from about 1 μm to about 20 μm, more preferably from about 2 μm to about 15 μm.

According to a further preferred embodiment, said diatomite particles (b) have

a residue on a 325 Mesh sieve lower than or equal to 0.5% by weight, with respect to the total weight of the diatomite particles.

The diatomite particles (b) above reported are commercially available, and may be purchased, for example, from Celite Corporation, or from Shengzhou

Huali Diatomite Products Co., Ltd. Examples of commercial products which may be advantageously used according to the present invention are CelTix™ and Diafil ^® 990 from Celite Corporation; or CD™ 120 from Shengzhou Huali Diatomite Products Co., Ltd.

Without being limited by any theoretical explanation, the Applicant believes that the reinforcing properties of the diatomite particles employed in the present invention are specifically due to the combination of both the relatively high BET surface area and the relatively high dimensions (i.e. the maximum dimension in the micron range) of the individual diatomite particles. Moreover, said relatively high dimensions may reduce the self-affinity of the individual diatomite particles, so reducing aggregation problems between the individual diatomite particles and contributing to easy processability of elastomeric compositions featuring such diatomite particles as reinforcing fillers.

The crosslinkable elastomeric compositions according to the present invention preferably comprise diatomite particles in amounts of from about 1 phr to about 150 phr, more preferably from about 5 phr to about 100 phr. Crosslinkable elastomeric compositions having diatomite particles content of from about 5 phr to about 30 phr, may be particularly advantageous.

According to one preferred embodiment, said at least one elastomeric polymer (a) may be selected, for example, from (ai) 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 (Tg) generally below about 20 ⁰ C, preferably in the range of from about 0 ⁰ C to about -1 10 ⁰ 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 about 60% by weight.

The conjugated diolefins generally contain from about 4 to about 12, preferably from about 4 to about 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 about 8 to about 20, preferably from about 8 to about 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 (ai) may be selected, for example, from: cis-1 ,4-polyisoprene (natural or synthetic, preferably natural rubber), 3,4- polyisoprene, polybutadiene (in particular, polybutadiene with a high 1 ,4-cis content), optionally halogenated isoprene/isobutene copolymers, 1 ,3- butadiene/acrylonitrile copolymers, styrene/1 ,3-butadiene copolymers, styrene/isoprene/1 ,3-butadiene copolymers, styrene/1 ,3-butadiene/acrylonitrile copolymers, or mixtures thereof.

Alternatively, said at least one elastomeric polymer (a) may be selected, for example, from (a ₂ ) 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 about 3 to about 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 about 4 to about 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 (a-i) with the abovementioned elastomeric polymers (a ₂ ), may also be used.

The above reported elastomeric polymers (a) may optionally be functionalized by reaction with suitable terminating agents or coupling agents. In particular, the diene elastomeric polymers (ai) 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 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 one preferred embodiment, said at least one reinforcing filler (c) may be selected from those commonly used for crosslinked manufactured products, in particular for tires, such as, for example, carbon black, silica, alumina, aluminosilicates, calcium carbonate, kaolin, or mixtures thereof. Carbon black, silica and mixture thereof are particularly preferred.

According to one preferred embodiment, said carbon black reinforcing filler may be selected from those having a surface area not lower than or equal to about 20 m ² /g (determined by CTAB absorption as described in Standard ISO 6810:1995).

According to one preferred embodiment, said silica reinforcing filler 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 about 32 m ² /g to about 400 m ² /g, more preferably from about 100 m ² /g to about 250 m ² /g, even more preferably from about 150 m ² /g to about 220 m ² /g. The pH of said silica reinforcing fillers is, generally, of from about 5.5 to about 7.0, preferably from about 5.5 to about 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; or the products known by the name of Ultrasil ^® VN2, Ultrasil ^® VN3, Ultrasil ^® 7000, from Degussa; or the product known under the name of Zeosil ^® 1 165MP from Rhodia.

According to a further preferred embodiment, said at least one reinforcing filler (c) may be selected from nanosized layered materials. Preferably, said nanosized layered materials have an individual layer thickness of from about 0.01 nm to about 30 nm, more preferably from about 0.2 nm to about 15 nm, even more preferably from about 0.5 nm to about 2 nm.

Layered materials which may be advantageously used according to the present invention, 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 (Ca ²⁺ ), potassium (K ⁺ ), magnesium (Mg ²⁺ ), hydroxide (HO ^" ), or carbonate (CO ₃ ^2" ), present at the interlayer surfaces. In order to render said layered materials more compatible with the elastomeric polymer(s) said layered materials may be treated with at least one compatibilizing agent which may be selected, for example, from the quaternary ammonium or phosphonium salts. The treatment of said layered materials 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 compatibilizer: further details are described, for example, in United States Patents US 4,136,103, US 5,747,560, or US 5,952,093.

Examples of layered materials reinforcing fillers 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.

The crosslinkable elastomeric composition of the present invention may advantageously incorporate at least one silane coupling agent (d) capable of interacting with both the diatomite particles (b) and the reinforcing fillers (c) and of linking them to the elastomeric polymer(s) during the vulcanization.

Coupling agents (d) that are preferably used are those based on silane which may be identified, for example, by the following structural formula (I):

(R ₂ ) ₃ Si-C _t H _2t -X (I) wherein the groups R ₂ , 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 R ₂ is an alkoxy or aryloxy group; t is an integer of from about 1 to about 6 extreme included; X is a group selected from: nitroso, mercapto, amino, epoxide, vinyl, imide, chloro, -(S)uCtH ₂ t-Si-(R ₂ ) ₃ or or -S-COR ₂ in which u and t are integers of from about 1 to about 6 extremes included and the groups R ₂ are defined as reported above.

Among the coupling agents that are particularly preferred are bis(3- triethoxysilylpropyl)tetrasulfide or bis(3-triethoxysilylpropyl)disulfide. Said coupling agents 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 crosslinkable elastomeric composition.

The crosslinkable elastomeric composition according to the present invention preferably comprises at least one coupling agent (d) in amounts of from about 0 phr to about 10 phr, more preferably from about 0.5 phr to about 5 phr. Crosslinkable elastomeric composition having coupling agent contents of from about 0.5 phr to about 2 phr may be particularly advantageous.

The crosslinkable elastomeric composition of the present invention may advantageously incorporate at least one condensation catalyst (e) capable of improving the interaction of with both the diatomite particles (b) and the

reinforcing fillers (c) and of linking them to the elastomeric polymer(s) during the vulcanization.

According to one preferred embodiment, said condensation catalyst (e) may be selected, for example, from: metal carboxylates; arylsulphonic acids or derivatives thererof; amines and alkanolamines; strong inorganic acids or bases; organic acids; blocked acids; zeolites modified by reaction with at least one carboxylic acid and/or sulphonic acid; or mixtures thereof. Metal carboxylates are particularly preferred, dibutyltin dilaurate is even particularly preferred.

A more detailed description of said condensation catalysts may be found for example, in European Patent Application EP 1 ,252,230.

The crosslinkable elastomeric composition according to the present invention preferably comprises at least one condensation catalyst (e) in amounts of from about 0 phr to about 5 phr, more preferably from about 0.5 phr to about 2 phr.

The crosslinkable elastomeric composition above reported may be vulcanized according to known techniques, in particular with sulfur-based vulcanizing systems commonly used for elastomeric polymers. To this end, in the elastomeric composition, after one or more steps of thermomechanical processing, a sulfur-based vulcanization agent is incorporated together with vulcanization accelerators. In the final processing step, the temperature is generally kept below 120 ⁰ C and preferably below 100 ⁰ C, so as to avoid any unwanted pre-crosslinking phenomena.

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

Vulcanization activators that are particularly effective are zinc compounds, and in particular ZnO, ZnCOβ, 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, Pb ₃ O ₄ , PbO ₂ , or mixtures thereof.

Vulcanization accelerators that are commonly used may be selected from: dithiocarbamates, guanidine, thiourea, thiazoles, sulfenamides, 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, antiozonants (in particular, of the p-phenylenediamine type), waxes, modifying resins, fibers (for example, Kevlar ^® pulp), or mixtures thereof.

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 of from about 0 phr to about 70 phr, preferably from of about 1 phr to about 30 phr.

The above reported crosslinkable elastomeric composition may be prepared by mixing together the elastomeric polymer(s), the diatomite particles (b) and the reinforcing fillers (c) above reported, with the other additives 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 or multi-screw type. Alternatively, the diatomite particles (b) may be pre-mixed with the elastomeric polymer(s) so as to form a masterbatch which will be subsequently mixed with the remaining components of the crosslinkable elastomeric composition.

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.

Brief description of the drawings

The present invention will now be illustrated in further detail by means of illustrative embodiments, with reference to the attached figures wherein: - Fig. 1 is a view in cross-section of a portion of a tire made according to a first embodiment of the present invention;

Fig. 2 is a view in cross-section of a portion of a tire made according to a further embodiment of 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 (103) comprising at least one bead core (102) and at least one bead filler (104). Said bead filler (104) may comprise an elastomeric composition according to an aspect of the present invention. 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 turned- back 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 fibers, 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 bead core (102) is enclosed in a bead structure (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) which, as reported above, may comprise an elastomeric composition according to an aspect of the present invention.

An anti-abrasive layer (105), which may comprise an elastomeric composition according to an aspect of the present invention, is usually placed in an axially external position relative to the carcass turn-up (101 a).

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), which may comprise an elastomeric composition according to an aspect of 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 ribs and/or 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), which may comprise an elastomeric composition according to an aspect of the present invention, 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 (1 1 1 ), which may comprise an elastomeric composition according to an aspect of the present invention, may be placed between the belt structure (106) and the tread band (109). As represented in Fig. 1 , the tread underlayer (11 1 ) may have uniform thickness. Alternatively, the tread underlayer (11 1 ) 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 (1 11 ) extends over a surface substantially corresponding to the surface of development of said belt structure (106). Alternatively, said tread underlayer (1 1 1 ) 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 (1 10), commonly known as a "mini- sidewaH", 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 first layer of crosslinked elastomeric material (1 12), which may comprise an elastomeric composition according to an aspect of the present invention, 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 ).

Alternatively, a second layer of crosslinked elastomeric material (not shown in Fig. 1 ), which may comprise an elastomeric composition according to an aspect of the present invention, generally known as a "under-liner", may be placed between the liner (1 12) and the carcass ply (101 ).

Fig. 2 shows a tire (100) having a structure as described in Fig. 1 further comprising a sidewall insert (113), which may comprise an elastomeric composition according to an aspect of the present invention. The sidewall insert (1 13) extends radially between the bead structure (103) and the lateral edge of the tread band (109). The sidewall insert (113) is placed in an axially internal or external position with respect to the carcass ply: for example, as represented in Fig. 2, the sidewall insert (113) is placed between the carcass ply (101 ) and the liner (1 12).

Alternatively, in the case more than one carcass ply is present, a sidewall insert (1 13) may be placed between two of said carcass plies (not represented in Fig. 2).

Alternatively, a sidewall insert (113) may be placed between the carcass ply and the sidewall (not represented in Fig. 2).

More than one sidewall insert may be present as disclosed, for example, in United States Patent US 5,238,040, or in European Patent Application EP

943,466.

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 present 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.

The samples of the following examples were evaluated according to the following tests and measurements.

The Mooney viscosity ML(1 +4) at 100 ⁰ C was measured according to Standard

ISO 289-1 :2005, on the non-crosslinked elastomeric compositions obtained as described below.

The tensile modulus (50% Modulus, 100% Modulus, and 300% Modulus), the tensile strength, the elongation at break, as well as the energy at break, were measured according to Standard ISO 37:2005, on samples of the elastomeric compositions described below crosslinked at 170 ⁰ C, for 10 min.

The hardness in IRHD degrees (at 10°C, at 23°C or at 100 ⁰ C) was measured according to Standard ISO 48:2007, on samples of the elastomeric compositions crosslinked at 170°C, for 10 min.

The dynamic mechanical properties were measured using an lnstron dynamic device in the traction-compression mode according to the following methods. A test piece of the crosslinked elastomeric composition (crosslinked at 170 ⁰ C, for 10 min) having a cylindrical form (length = 25 mm; diameter = 14 mm), compression-preloaded up to a 25% longitudinal deformation with respect to the initial length, and kept at the prefixed temperature (23°C, 70 ⁰ 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'). The thermoplastic behavior is evaluated as the difference δE' of the dynamic elastic modulus measured at two reference temperatures selected on the basis of the kind of elastomeric composition and/or its application in the tire.

EXAMPLE 1

Preparation of elastomeric compositions 1 to 3

The elastomeric compositions 1 to 3 given in Table 1 were prepared as follows (the amounts of the various components are given in phr).

All the components, except sulfur, accelerator (TBBS) 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, accelerator (TBBS) and retardant (PVI), were then added and mixing was carried out in an open roll mixer (2 ^nd Step).

TABLE 1

( ^* ): comparison; ( ^λ ): invention.

NR: natural rubber (Standard Thai Rubber STR 20 - Thaiteck Rubber)

BR: polybutadiene (Europrene Neocis ^® - Polimeri Europa)

N550: carbon black;

X50S ^® : 1 :1 mixture of bis[3-(triethoxysilyl)propyl]tetrasulfide and N330 carbon black (X50S ^® - Evonik-Degussa); CelTix™: diatomite particles having a BET surface area of 45 m ² /g, a residue on a 325 Mesh sieve lower than 1 % by weight with respect to the total weight of the diatomite particles, and an average maximum dimension of 10 μm (Celite Corporation); 6-PPD (antioxidant): N-(1 ,3-dimethylbutyl)-N'-phenyl-p-phenylene-diamine

(Santoflex™ 6PPD - Flexsys); TBBS (accelerator): N-tert-butyl-2-benzothiazylsulfenamide (Vulkacit ^®

NZ/EGC - Lanxess); PVI (retardant): N-(cyclohexylthio)phthalimide (Santogard™ PVI - Flexsys).

All the samples were evaluated as described above and the results were summarized in the following Table 2.

TABLE 2

( ^* ): comparison; ( ^λ ): invention.

The samples 2 and 3 according to the present invention showed a viscosity lower than that of sample 1 (comparative). A reduced viscosity in the non- crosslinked state means a better processability. Hardness remain substantially unchanged in all cases and for both temperatures considered.

The static mechanical properties, in particular tensile strength, elongation at break, and energy at break, were greatly improved in samples 2 and 3. The dynamical mechanical properties were not negatively affected in samples 2 and 3.

EXAMPLE 2

Preparation of elastomeric compositions 4 and 5

The elastomeric compositions 4 and 5 given in Table 3 were prepared as follows (the amounts of the various components are given in phr).

All the components, except ZnO, 6-PPD, sulfur and accelerator (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.

After 24 hours, ZnO and 6-PPD were mixed with the 1 ^st step composition in an internal mixer (model Pomini PL 1.6) for about 4 min, up to a temperature of 125±5°C and then the elastomeric composition was discharged (2 ^nd step).

The sulfur and accelerator (CBS), were then added and mixing was carried out in an open roll mixer (3 ^rd Step).

TABLE 3

( ^* ): comparison; ( ^λ ): invention.

S-SBR: solution-prepared styrene/1 ,3-butadiene copolymer having a styrene content of 25% by weight and a vinyl content of 67% by weight, with respect to the total copolymer weight; and containing 36.8 phr of MES oil (Europrene ^® SOL R 72612 - Polimeri Europa); BR: polybutadiene (Europrene Neocis ^® - Polimeri Europa)

Silica: Zeosil ^® 1 165 MP (Rhodia);

X50S ^® : 1 :1 mixture of bis[3-(triethoxysilyl)propyl]tetrasulfide and N330 carbon black (X50S ^® - Evonik-Degussa);

TMQ (anti-aging): polymerized 2,2,4-trimethyl-1 ,2-dihydroquinoline polymer (Vulcanox ^® HS/LG - Lanxess);

CelTix™: diatomite particles having a BET surface area of 45 m ² /g, a residue

on a 325 Mesh sieve lower than 1 % by weight with respect to the total weight of the diatomite particles, and an average maximum dimension of 10 μm (Celite Corporation); 6-PPD (antioxidant): N-(1 ,3-dimethylbutyl)-N'-phenyl-p-phenylene-diamine

(Santoflex™ 6PPD - Flexsys); CBS (accelerator): N-cyclohexyl^-benzothiazyl-sulphenamide (Vulkacit ^®

CZ/EGC - Lanxess).

All the samples were evaluated as described above and the results were summarized in the following Table 4.

TABLE 4

( ^* ): comparison; ( ^λ ): invention.

The sample 5 according to the present invention showed a viscosity lower than that of sample 4 (comparative). A reduced viscosity in the non- crosslinked state means a better processability. Hardness decreases, and more importantly, the difference in hardness between 23°C and 100 ⁰ C decreases, which is an indication of a lower thermoplastic behavior.

The static mechanical properties were improved in sample 5, especially modulus at 100%, and energy. The dynamical mechanical properties of sample 5 were also improved, in particular in terms of reduced variation in E' with temperature (reduced "thermoplasticity", confirming IRHD indication) and of reduced hysteresis (lower Tan delta at 70 ⁰ C), usually taken as indicator of lower rolling resistance of the tire.

EXAMPLE 3

Preparation of elastomeric compositions 6 to 8

The elastomeric compositions 6 to 8 given in Table 5 were prepared as follows (the amounts of the various components are given in phr).

Natural rubber (NR), carbon black (N326), and stearic acid 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.

After 24 hours, ZnO, 6-PPD, silane (X50S ^® ), CelTix ^® , or N326, were mixed with the 1 ^st step composition in an internal mixer (model Pomini PL 1.6) for about 5 min, up to a temperature of 145±5°C and then the elastomeric composition was discharged (2 ^nd Step).

The sulfur, accelerator (TBBS) and retardant (PVI), were then added and mixing was carried out in an open roll mixer (3 ^rd Step).

TABLE 5

( ^* ): comparison; ( ^λ ): invention.

NR: natural rubber (Standard Thai Rubber STR 20 Thaiteck Rubber); N326: carbon black;

X50S ^® : 1 :1 mixture of bis[3-(triethoxysilyl)propyl]tetrasulfide and N330 carbon black (X50S - Evonik-Degussa); CelTix™: diatomite particles having a BET surface area of 45 m ² /g, a residue on a 325 Mesh sieve lower than 1 % by weight with respect to the total weight of the diatomite particles, and an average maximum dimension of 10 μm (Celite Corporation); 6-PPD (antioxidant): N-(1 ,3-dimethylbutyl)-N'-phenyl-p-phenylene-diamine

(Santoflex™ 6PPD Flexsys);

TBBS (accelerator): N-tert-butyl-2-benzothiazylsulfenamide (Vulkacit ^®

NZ/EGC - Lanxess);

PVI (retardant): N-(cyclohexylthio)phthalimide (Santogard™ PVI - Flexsys). All the samples were evaluated as described above and the results were summarized in the following Table 6.

TABLE 6

( ^* ): comparison; ( ^λ ): invention.

The samples 7 and 8 according to the present invention showed a viscosity lower than that of sample 6 (comparative). A reduced viscosity in the non-

crosslinked state means a better processability. The difference in hardness between 23 and 100 ⁰ C greatly decreases, which is an indication of a lower thermoplastic behavior.

The static mechanical properties were improved in samples 7 and 8, especially modulus at 100% and ultimate properties (elongation and energy at break). The dynamical mechanical properties of samples 7 and 8 were also improved, in particular in terms of reduced variation in E' with temperature

(reduced "thermoplasticity", confirming IRHD indication) and of reduced hysteresis (lower Tan delta at 70 ⁰ C), usually taken as indicator of lower rolling resistance of the tire.

The use of a small amount of silane coupling agent in sample 8, leads to further improvements vs. sample 7, except for ultimate properties, which slightly decrease due to higher compound rigidity.

EXAMPLE 4

Preparation of elastomeric compositions 9 and 10

The elastomeric compositions 9 and 10 given in Table 7 were prepared as follows (the amounts of the various components are given in phr).

All the components, except sulfur, accelerator (DCBS) and hexamethoxymethylmelamine (HMMM), 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, accelerator (DCBS) and hexamethoxymethylmelamine (HMMM), were then mixed with the 1 ^st step composition in an open roll mixer (2 ^nd Step).

TABLE 7

( ^* ): comparison; ( ^λ ): invention.

NR: natural rubber (SMR GP - Lee Rubber Group);

N326: carbon black;

X50S ^® : 1 :1 mixture of bis[3-(triethoxysilyl)propyl]tetrasulfide and N330 carbon black (X50S - Evonik-Degussa); CelTix™: diatomite particles having a BET surface area of 45 m ² /g, a residue on a 325 Mesh sieve lower than 1 % by weight with respect to the total weight of the diatomite particles, and an average maximum dimension of 10 μm (Celite Corporation);

6-PPD (antioxidant): N-(1 ,3-dimethylbutyl)-N'-phenyl-p-phenylene-diamine (Santoflex™ 6PPD - Flexsys);

Resorcinol: 80% resorcinol dispersion in polymer binder (Rhenogran resorcinol 80/GE 1323 - Rhein Chemie); HMMM 65%: hexamethoxymethylmelamine (65%) on inert carrier (Cyrez 964

- Cytec); DCBS (accelerator): N,N ^" -dicyclohexyl-2-benzothiazylsulphenamide

(Vulkacit ^® DZ/EGC - Lanxess).

All the samples were evaluated as described above and the results were summarized in the following Table 8.

TABLE 8

( ^* ): comparison; ( ^λ ): invention.

The sample 10 according to the present invention showed a viscosity lower than that of reference sample 9 (comparative). A reduced viscosity in the non- crosslinked state means a better processability. Hardness decreases, and

more importantly the difference in hardness between 23°C and 100 ⁰ C decreases, which is an indication of a lower thermoplastic behavior.

The static mechanical properties were improved in sample 10, especially modulus at 100% and ultimate properties. The dynamical mechanical properties of sample 10 were also improved, in particular in terms of reduced variation in E' with temperature (reduced "thermoplasticity", confirming IRHD indication) and of reduced hysteresis (lower Tan delta at 70 ⁰ C), usually taken as indicator of lower rolling resistance of the tire.