WO2008135061A1

WO2008135061A1 - Tire comprising an elastomeric polymer including a functional group and crosslinkable elastomeric composition

Info

Publication number: WO2008135061A1
Application number: PCT/EP2007/003935
Authority: WO
Inventors: Michela Caprio; Marco Nahmias Nanni; Mario Martin; Paola Luciana Pinacci
Original assignee: Pirelli Tyre S.P.A.
Priority date: 2007-05-04
Filing date: 2007-05-04
Publication date: 2008-11-13

Abstract

A tire for heavy load vehicles comprising: - a carcass structure; - a belt structure applied in a radially external position with respect to said carcass structure; - a tread band in a radially external position with respect to said belt structure; - a pair of sidewalls laterally applied on opposite sides with respect to said carcass structure; - at least one structural element selected from said tread band and said sidewalls being obtained by crosslinking a crosslinkable elastomeric composition comprising: (a) at least about 50 phr of at least one functionalized elastomeric polymer including from about 0.05% by weight to about 10% by weight, with respect to the total weight of the elastomeric polymer, of at least one functional group selected from carboxylic groups, carboxylate groups, anhydride groups, ester groups; (b) from ' about 10 phr to about 70 phr of at least one carbon black reinforcing filler; (c) less than 50% by weight relative to said carbon black reinforcing filler of an additional reinforcing filler.

Description

TIRE COMPRISING AN ELASTOMERIC POLYMER INCLUDING A FUNCTIONAL GROUP AND CROSSLINKABLE ELASTOMERIC COMPOSITION

DESCRIPTION

Background of the invention

The present invention relates to a tire 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 elastomeric polymer including at least one functional group.

Moreover, the present invention also relates to a crosslinkable elastomeric composition comprising at least one elastomeric polymer including at least one functional group.

Known art

Modern tires, and particularly tires for heavy load vehicles such as trucks, lorries, and buses, should meet a number of demanding requirements. Thus, tires for heavy load vehicles should exhibit excellent wear properties, low rolling resistance, low hysteresis, and good strength properties. However, it is difficult to achieve certain of these properties without sacrificing or diminishing some of the other properties.

Thus, for example, lower rolling resistance and hysteresis is often accompanied by lower wear properties and viceversa.

More particularly, tires for heavy load vehicles need to have a high stiffness and a low deformability of the elements of the tread, i.e., blocks and ribs, to avoid excessive mobility of the tread elements which would result in an increase of wear of ribs and blocks. The crosslinked elastomeric composition having such requirements need to have high hardness and high tensile modulus.

Heavy duty large size tires for trucks and buses frequently running on non-paved road, particularly rock-exposed rough road, or off-the-road tires have a frequent chance of subjecting their tread and sidewall portions to tear failure. Therefore, tire treads and sidewalls require to use a elastomeric composition having excellent tear resistance. The crosslinked elastomeric composition having such requirements need to have high resistance to peeling.

Further, heavy duty large size tires for trucks and buses are often used for long times and long distances and the degree of heat build-up in use can be such that thick sections in the treads are degraded to the point of failure, resulting in separations and delaminations, often to the extent that the entire tread peels off the tire. Additionally, a high degree of heat build-up in use increase the rolling resistance and the fuel consumption. It is therefore desirable to obtain crosslinked elastomeric composition which generate less heat under operating conditions. The crosslinked elastomeric composition having such requirements need to have low-hysteresis characteristics.

There are known in the art several approaches to solve the above mentioned problems.

US 4,154,277 discloses a pneumatic tire having a tread formed of a rubber composition consisting essentially of 100 parts by weight of natural rubber or synthetic polyisoprene rubber and 30-60 parts by weight of highly reinforcing carbon black having an iodine adsorbability of 130-150 mg/g, a dibutyl phthalate absorbability of 80- 105 ml/100 g and a tinting strength of at least 240%. The disclosed pneumatic tire is told to have excellent cut resistance, chipping resistance, wear resistance and resistance against heat build-up, and to be excellent in the running durability on both of paved road and off road.

US 5,225,011 discloses a tire having superior cut resistance and less belt separation comprising a tread with steel cord belts in which a center rubber for middle part of the tread and a side rubber for both sides thereof are respectively formed of different rubber compositions, and in which at least an inner portion of the center rubber is composed of a rubber composition of superior cut resistance wherein either a natural rubber of a SBR blended natural rubber is compounded with carbon black of large iodine absorption number, silica and silane coupling agent having a specific formula, while the side rubber is composed of a rubber composition having small heat build up.

" US 6,211,271 discloses a process for producing a vulcanizable rubber composition containing silica and carbon black, comprises the step of intimately mixing at a temperature of from 130° to 180° at least a first cross-linkable unsaturated chain polymer with a first carbon black-based reinforcing filler, so as to obtain a first rubber composition capable of allowing a subsequent effective dispersion of a second silica- based reinforcing filler and of a second cross-linkable unsaturated chain polymer. The rubber composition thus obtained shows a homogeneous dispersion of the reinforcing fillers, in particular of the silica-based reinforcing filler, constant physical-mechanical characteristics, and improved drawability, and is particularly suitable for the manufacture of tire treads with low rolling resistance.

US 7,019,084 discloses a rubber compositions, especially provided for heavy load tire treads and sidewalls, reinforced with precipitated silica and selected carbon black in specified amounts and prepared with a prescribed order of addition to the rubber composition and composed of elastomers as a specific combination of high trans styrene-butadiene rubber with natural or synthetic cis 1,4-polyisoprene rubber and cis 1 ,4-polybutadiene rubber.

US 7,073,549 discloses a rubber composition for base tread having reduced heat build-up characteristics and excellent reinforcing property, and a pneumatic tire using the rubber composition for the base tread, wherein the rubber composition comprises 30 to 40 parts by weight of carbon black having iodine adsorption amount of at least 115 mg/g, 5 to 10 parts by weight of silica and 1.2 to 2.2 parts by weight of sulfur based on 100 parts by weight of a rubber component, and wherein the total amount of the carbon black and the silica is at most 45 parts by weight.

The use of functionalized elastomers comprising carboxylic groups along the chain for the preparation of rubber compositions useful in tires is generally known in the art for coupling silica with the rubber composition.

US 5,494,091 discloses a composition comprising (a) from about 25 to 55 parts by weight of polyisoprene; (b) from about 75 to 45 parts by weight of a diene polymer selected from the group consisting of homopolymers of conjugated diene monomers and copolymers thereof with monoolefϊn monomers and EPDM terpolymers to total 100 parts by weight of rubber polymer; and (c) from about 50 to 70 parts by weight of a reinforcing filler, per 100 parts by weight wherein at least a portion of at least one of the rubber polymers is grafted with a polymeric metal salt of an α,/3-ethylenically unsaturated carboxylic acid to form an uncured graft rubber copolymer and at least about 4 parts by weight of a curative selected from the group consisting of sulfur and sulfur donors, per 100 parts by weight of rubber. The composition is told to be useful in internal reinforcement for tire sidewalls having high module, low hysteresis and high compressive flex fatigue and to provide run flat operation.

US2003/0195288 discloses a rubber composition usable to constitute a tread for a tire comprising: (a) a reinforcing filler comprising a reinforcing inorganic filler, wherein the mass fraction of said reinforcing inorganic filler in said reinforcing filler is greater than 50%; and (b) at least one diene elastomer having a molar ratio of units originating from conjugated dienes which is greater than 30% and comprising carboxylic acid functions along its chain. The composition is told to provide reduced hysteresis losses in the cross-linked state and improved processing properties in the cross-linkable state.

WO2005/118695 discloses a tire wherein at least one structural element selected from bead filler, sidewall insert, and tread underlayer is obtained by crosslinking a crosslinkable elastomeric composition comprising: (a) a crosslinkable elastomeric base comprising at least about 30 phr, preferably from about 50 phr to about 100 phr, of at least one elastomeric polymer including from about 0.05% by weight to about 10% by weight, preferably from about 0.1% by weight to about 5% by weight, with respect to the total weight of the elastomeric polymer, of at least one functional group selected from carboxylic groups, carboxylate groups, anhydride groups, ester groups; (b) from about 2 phr to about 50 phr, preferably from about 5 phr to about 30 phr, of at least one layered inorganic material.

The Applicant has perceived that in spite of the efforts known in the art, there is still the need to obtain an elastomeric composition having improved overall properties, in particular in the manufacturing of outer structural elements of a tire for heavy load vehicles, and especially for the manufacturing of tire treads for heavy load vehicles.

The Applicant has now found that it is possible to obtain crosslinkable elastomeric compositions that may be advantageously used in the production of crosslinked manufactured products, in particular in the manufacturing of tires, more in particular in the manufacturing of outer structural elements of a tire for heavy load vehicles, and most particularly in the manufacturing of tire treads for heavy load vehicles, by using at least one elastomeric polymer preferably selected from natural or synthetic isoprene rubber including at least one functional group selected from carboxylic groups, carboxylate groups, anhydride groups, ester groups. The tires of the invention exhibit an excellent balance of overall properties while providing for improved wear resistance, lower rolling resistance and better hysteresis properties.

The crosslinked elastomeric compositions have shown improved elastic modulus without affecting the viscous or loss modulus. The improvement of elastic modulus resulted in improved hysteresis properties, and, as a consequence, in a reduction of the rolling resistance and the fuel consumption. In addition, the crosslinked elastomeric compositions have shown improved tear resistance (peeling), and accordingly, an improved resistance to tear failure. Said improvements have been obtained without negatively affecting the mechanical properties, such as tensile modulus, tensile strength, elongation at break and hardness.

Accordingly, the Applicant has found that a tire for heavy load vehicles comprising outer structural elements, in particular tread and sidewalls, and more particularly tread, manufactured with the crosslinked elastomeric composition of the present invention shows a lower rolling resistance and a reduced fuel consumption together with a lower wear of the tread and with an improved resistance to tear failure of the elements of the tread, such as blocks and ribs. The same composition of the present invention was proved to be good also for the construction of sidewalls of tyres, particularly tyres for heavy load vehicles.

For the purpose of the present invention, the term "heavy load vehicles" means vehicles of categories M2-M3, N2-N3 and O2~O4 according to ECE Consolidated Resolution on the Construction of Vehicles (R.E.3), Annex 7, "Classification and definition of power-driven vehicles and trailers", such as, for example, truck, tractor- trailers, lorries, buses, large vans, and other similar vehicles.

According to a first aspect, the present invention relates to a tire for heavy load vehicles comprising:

- a carcass structure;

- a belt structure applied in a radially external position with respect to said carcass structure;

- a tread band in a radially external position with respect to said belt structure;

- a pair of sidewalls laterally applied on opposite sides with respect to said carcass structure;

- at least one structural element selected from said tread band and said sidewalls being obtained by crosslinking a crosslinkable elastomeric composition comprising:

(a) at least about 50 phr, preferably from about 70 phr to about 100 phr, most preferably from about 90 phr to about 100 phr, of at least one functionalized elastomeric polymer including from about 0.05% by weight to about 10% by weight, preferably from about 0.1% by weight to about 5% by weight, with respect to the total weight of the functionalized elastomeric polymer, of at least one functional group selected from carboxylic groups, carboxylate groups, anhydride groups, ester groups;

(b) from about 10 phr to about 70 phr, preferably from about 20 phr to about

60 phr, of at least one carbon black reinforcing filler;

(c) less than 50% by weight relative to said carbon black reinforcing filler of at least one additional reinforcing filler.

The amount of functional groups present on the functionalized elastomeric polymer may be determined according to known techniques such as, for example, by Infrared ATR- spectroscopy analysis: further details about said techniques will be reported in the examples which follow.

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

(a) at least about 50 phr, preferably from about 70 phr to about 100 phr, most preferably from about 90 phr to about 100 phr, of at least one functionalized elastomeric polymer selected from natural and synthetic isoprene rubber including from about 0.05% by weight to about 10% by weight, preferably from about 0.1% by weigth to about 5% by weight, with respect to the total weight of the functionalized elastomeric polymer, of at least one functional group selected from carboxylic groups, carboxylate groups, anhydride groups, ester groups;

(b) from about 10 phr to about 70 phr, preferably from about 20 phr to about 60 phr, of at least one carbon black reinforcing filler;

According to a further preferred embodiment, said functionalized elastomeric polymer including at least one functional group has a weight average molecular weight

(M_w) not lower than about 80,000, preferably of from about 100,000 to about 1,000,000. Said weight average molecular weight (M_w) may be determined according to known techniques such as, for example, by gel permeation cromatography (GPC). The functional group may be introduced into the functionalized elastomeric polymer by means of processes known in the art such as, for example, during the production of the functionalized elastomeric polymer by co-polymerization with at least one corresponding functionalized monomer containing at least one ethylenic unsaturation; or by subsequent modification of the elastomeric polymer by grafting said at least one functionalized monomer, optionally in the presence of a free radical initiator (for example, an organic peroxide).

Said functionalized elastomeric polymer including at least one functional group may be obtained in the form of a continuous ribbon or, alternatively, in the form of a subdivided product.

Functionalized monomers which may be advantageously used include, for example, monocarboxylic or dicarboxylic acids containing at least one ethylenic unsaturation or derivatives thereof, in particular salts, anhydride or esters.

Examples of monocarboxylic or dicarboxylic acids containing at least one ethylenic unsaturation or derivatives thereof are: maleic acid, fumaric acid, citraconic acid, itaconic acid, acrylic acid, methacrylic acid, and salts, anhydrides or esters derived therefrom, or mixtures thereof. Maleic anhydride is particularly preferred.

According to one preferred embodiment, the elastomeric polymer which may be utilized in the production of the functionalized elastomeric polymer including at least one functional group, may be selected from those commonly used in sulphur- 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 (T_g) generally below 2O⁰C, preferably in the range of from about -80°C to O⁰C. 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. The conjugated diolefins generally contain from 4 to 12, preferably from 4 to 8 carbon atoms, and may be selected, for example, from the group comprising: 1,3-butadiene, isoprene, 2,3-dimethyl-l,3- butadiene, 1,3-pentadiene, 1,3-hexadiene, 3-butyl-l,3-octadiene, 2 -phenyl- 1,3- butadiene, or mixtures thereof.

Preferably, the elastomeric polymer may be selected, for example, from: cis-1,4- polyisoprene (natural or synthetic, preferably natural rubber), 3,4-polyisoprene, or mixtures thereof. As disclosed above, said crosslinkable elastomeric composition comprises (b) from about 10 phr to about 70 phr, preferably from about 20 phr to about 60 phr, of at least one carbon black reinforcing filler.

According to one preferred embodiment, the carbon black reinforcing filler which may be used in the present invention may be selected from those having a surface area higher than about 20 m²/g (determined by CTAB absorption as described in Standard ISO 6810: 1995).

As disclosed above, said crosslinkable elastomeric composition comprises (c) at least one additional reinforcing filler in an amount generally of less than 50% by weight relative to the carbon black reinforcing filler. The reinforcing filler may be selected from those commonly used for crosslinked manufactured products, in particular for tires, such as, for example, silica, alumina, aluminosilicates, calcium carbonate, kaolin, or mixtures thereof.

The silica which may be used in the present invention may generally be a pyrogenic silica or, preferably, a precipitated silica, with a BET surface area (measured according to ISO standard 5794/1) of from about 50 m²/g to about 500 m²/g, preferably of from about 70 m²/g to about 200 m²/g.

When a reinforcing filler comprising silica is present, the crosslinkable elastomeric composition may advantageously incorporate a silane coupling agent capable of interacting with the silica and of linking it to the elastomeric polymer during the vulcanization. Examples of silane coupling agent which may be used in the crosslinkable elastomeric composition of the present invention may be selected from those having at least one hydrolizable silane group which may be identified, for example, by the following general formula (II):

(R)₃Si-C_nH_2n-X (II)

wherein the groups R, which may be identical or different, are selected from: alkyl, alkoxy or aryloxy groups or from halogen atoms, on condition that at least one of the groups R is an alkoxy or aryloxy group; n is an integer between 1 and 6 inclusive; X is a group selected from: nitroso, mercapto, amino, epoxide, vinyl, imide, chloro, - (S)₁₁₁C_nH_2n-Si-(R)₃, or -S-COR, in which m and n are integers between 1 and 6 inclusive and the groups R are defined as above.

Among the silane coupling agents that are particularly preferred are bis(3- triethoxysilyl-propyl)tetrasulphide and bis(3-triethoxysilylpropyl)-disulphide. 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 base (a).

According to one preferred embodiment, said silane coupling agent is present in the crosslinkable elastomeric composition in an amount of from about 0 phr to about 10 phr, preferably of from about 0.5 phr to about 5 phr.

The crosslinkable elastomeric composition may further comprises at least one additional elastomeric polymer in an amount lower than about 50 phr, more preferably lower than 30 phr, and most preferably lower than 10 phr. Said elastomeric polymer may be selected from the elastomeric polymers or copolymers reported above or, alternatively, from the elastomeric polymers of one or more monoolefins with an olefinic comonomer or derivatives thereof. Among those, the preferred additional elastomeric polymer is:

- cis-l,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;

- ethylene/propylene copolymers (EPR) or ethylene/propylene/diene copolymers

(EPDM); polyisobutene; butyl rubbers; halobutyl rubbers, in particular chlorobutyl or bromobutyl rubbers; or mixtures thereof.

The crosslinkable elastomeric composition above reported may be vulcanized according to known techniques, in particular with sulphur-based vulcanizing systems commonly used for elastomeric polymers. To this end, in the composition, after one or more stages of thermomechanical processing, a sulphur-based vulcanizing agent is incorporated together with vulcanization accelerators. In the final processing stage, the temperature is generally kept below about 130°C and preferably below about 110°C, so as to avoid any unwanted pre-crosslinking phenomena.

The vulcanizing agent most advantageously used is sulphur, or molecules containing sulphur (sulphur 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, for example, 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 elastomeric composition: antioxidants, anti-ageing agents, plasticizers, adhesives, anti-ozone agents, modifying resins, fibres (for example Kevlar^® pulp), 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 about O phr to about 70 phr, preferably from about 5 phr to about 30 phr.

The above reported crosslinkable elastomeric composition may be prepared by mixing together the crosslinkable elastomeric base, with the reinforcing filler and 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 type.

Brief description of the drawings

The present invention will now be illustrated in further detail by means of an illustrative embodiment, with reference to the attached Fig. 1, which represents a view in cross section of a portion of a tire made according to the invention. In the drawing figure, "a" indicates an axial direction and "r" indicates a radial direction.

Detailed description of preferred embodiments

The tire (100) comprises at least one carcass ply (10), the opposite lateral edges of which are associated with respective bead structures comprising at least one bead core (20) and at least one bead filler (25). The association between the carcass ply (10) and the bead core (20) is achieved here by turning up the opposite lateral edges of the carcass ply (10) around the bead core (20) so as to form the so-called carcass turn-up (30) as shown in Fig. 1.

The carcass ply (10) generally comprises a plurality of reinforcing cords arranged parallel to each other and at least partially coated with a layer of elastomeric composition. These reinforcing cords are usually made of steel wires stranded together, coated with a metal alloy (for example copper/zinc, zinc/manganese, zinc/molybdenum/cobalt alloys and the like), or of textile fibres, for example rayon, nylon or polyethylene terephthalate.

The carcass ply (10) 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 (20) is enclosed in a bead (35), defined along an inner circumferential edge of the tire (100), with which the tire engages on a rim (c) forming part of a vehicle wheel. The space defined by each carcass turn-up (30) contains a bead filler (25), wherein the bead core (20) is embedded. An antiabrasive strip (40) is usually placed in an axially external position relative to the carcass turn-up (30).

A belt structure (50) is applied along the circumference of the carcass ply (10). In the particular embodiment in Fig. 1, the belt structure (50) comprises two belt strips (50a, 50b) 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 (50b), at least one zero-degree reinforcing layer (55), commonly known as a "0° belt", may optionally be applied. The zero-degree reinforcing layer (55) generally incorporates a plurality of reinforcing cords, typically metal cords, arranged at an angle of a few degrees relative to a circumferential direction, and coated and welded together by means of an elastomeric material.

A sidewall (60), which may be made according to the present invention, is also applied externally onto the carcass ply (10), this side wall extending, in an axially external position, from the bead (35) to the belt structure (50).

A tread band (70), which may be made according to the present invention, is applied circumferentially in a position radially external to the belt structure (50). Externally, the tread band (70) has a rolling surface designed to come into contact with the ground. Circumferential grooves (75) which are connected by transverse notches (not represented in Fig. 1) so as to define a plurality of blocks (75a) of various shapes and sizes distributed over the rolling surface are generally made in this surface.

A tread underlayer (80) can optionally be placed between the belt structure (50) and the tread band (70). The tread underlayer may have uniform thickness.

Alternatively, the tread underlayer 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.

The tread band (70) can also be made with a cap and base construction. More in particular, the tread band (70) can comprise a radially inner layer or tread base (not shown) and a radially outer layer or tread cap (not shown). When the tread band is made with a cap and base constructions both the tread base and the tread cap may be made according to the present invention. Preferably, the tread cap may be made according to the present invention. The tread base can have a uniform thickness. In any case, the thickness of the tread base may also be not uniform but, for example, greater near its outer edges and/or at the central zone thereof.

In the case of tubeless tires, a rubber layer generally known as a liner (90), which provides the necessary impermeability to the inflation air of the tire, may also be provided in a radially internal position relative to the carcass ply (10).

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, as described, for example, in patents EP 199,064, US 4,872,822, US 4,768,937, said process including at least one stage of manufacturing the green tire and at least one stage of vulcanizing this tire.

More particularly, the process for producing the tire comprises the steps of preparing, beforehand and separately from each other, a series of semi-finished products corresponding to the various structural elements of the tire (carcass plies, belt structure, bead wires, fillers, sidewalls and tread band) which are then combined together using a suitable manufacturing machine.

The step of preparing the abovementioned semi-finished products will be preceded by a step of preparing and moulding the various crosslikable elastomeric compositions, of which said semi-finished products are made, according to conventional techniques. Next, the subsequent vulcanization step welds the abovementioned semifinished products together to give a monolithic block, i.e. the finished tire. To this end, a vulcanization mould is used which is designed to receive the green tire being processed inside a moulding cavity having walls which are countermoulded to define the outer surface of the tire when the vulcanization is complete.

At this point, the step of vulcanizing the green tire is carried out. To this end, the outer wall of the vulcanization mould is placed in contact with a heating fluid (generally steam) such that the outer wall reaches a maximum temperature generally of from about 100°C to about 230°C. Simultaneously, the inner surface of the tire is heated to the vulcanization temperature using the same pressurized fluid used to press the tire against the walls of the moulding cavity, heated to a maximum temperature of from about 100⁰C to about 250°C. The time required to obtain a satisfactory degree of vulcanization throughout the mass of the elastomeric material may vary in general from about 3 min to about 90 min and depends mainly on the dimensions of the tire. When the vulcanization is complete, the tire is removed from the vulcanization mould.

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.

EXAMPLE 1

Preparation of the elastomeric polymer including a functional group in a twin-screw extruder

The amounts of the compounds used are given in Table 1 (the amounts of the various components are given in phr).

TABLE 1

ER: cis-l,4-polyisoprene (SKB - Nizhnekamskneftechim Export);

maleic anhydride: commercial product from Lonza Milano SrI, Caravaggio, Italy;

antioxidant: Irganox 1010, a penta-erythrityl-tetrakis-(3,5-di-tert-butyl-4- hydroxyphenyl) propionate manufactured by Ciba

The cis-l-4-polyisoprene was obtained in the form of granules having an average particles size diameter of about 3 mm - 20 mm, by means of a rubber grinder. The so obtained granules and maleic anhydride, also in a granular form, were fed to the feed hopper of a co-rotating twin-screw extruder Mans TM40HT having a nominal screw diameter of about 40 mm and a L/D ratio of about 48. The maximum temperature in the extruder was about 220°C. The extrusion head was kept at a temperature of about 100°C.

The obtained elastomeric polymer was discharged from the extruder in the form of a continuous strand, was cooled at room temperature in a cooling device and granulated. A sample of the obtained elastomeric polymer was subjected to Infrared ATR-Spectroscopy analysis below reported in order to evaluate the amount of the grafted maleic anhydride.

IR analysis

The elastomeric polymer obtained as above disclosed was subjected to Infrared ATR-Spectroscopy analysis.

A thin plate of the elastomeric polymer (0.5 g weight) was obtained by pressure die-casting, under vacuum, at about 70⁰C, the elastomeric polymer obtained as above disclosed.

The obtained thin plate was put in a Soxhlet apparatus in order to extract the non-grafted maleic anhydride: the extraction was carried out in a toluene:ethanol (70:30) solvent mixture, for about 8 hours, at the reflux temperature of the solvent.

The amount of the grafted maleic anhydride was calculated by means of a calibration curve.

The signals used are the following: the signal at 1780 cm^'1 which refers to the C=O stretching of the acid form of the carbonyl group of the maleic anhydride (open form of the maleic anhydride) and the signal at 840 cm^"1 which refers to the bending of the C=C group of cis-l,4-polyisoprene. The amount of the grafted maleic anhydride was calculated from the ratio between the area of the signal corresponding to maleic anhydride and the area of the signal corresponding to cis-l,4-polyisoprene by means of a calibration curve.

The elastomeric polymer was found to include about 0.6% by weight of grafted maleic anhydride with respect to the total weight of the elastomeric polymer.

EXAMPLE 2

The amounts of the compounds used are given in Table 2 (the amounts of the various components are given in phr).

TABLE 2

NRl : natural rubber (STR20 - Thaiteck Rubber, Thailand)

maleic anhydride: commercial product from Lonza Milano SrI, Caravaggio, Italy;

The natural rubber was obtained in the form of granules having an average particles size diameter of about 3 mm - 20 mm, by means of a rubber grinder. The so obtained granules and maleic anhydride, also in a granular form, were fed to the feed hopper of a co-rotating twin-screw extruder Maris TM40HT having a nominal screw diameter of about 40 mm and a L/D ratio of about 48. The maximum temperature in the extruder was about 220°C. The extrusion head was kept at a temperature of about 100°C. The obtained elastomeric polymer was discharged from the extruder in the form of a continuous strand, was cooled at room temperature in a cooling device and granulated. A sample of the obtained elastomeric polymer was subjected to Infrared

ATR-Spectroscopy analysis below reported in order to evaluate the amount of the grafted maleic anhydride.

IR analysis

A thin plate of the ealstomeric polymer (0.5 g weight) was obtained by pressure die-casting, under vacuum, at about 70°C, the elastomeric polymer obtained as above disclosed.

The signals used are the following: the signal at 1780 cm^"1 which refers to the C=O stretching of the acid form of the carbonyl group of the maleic anhydride (open form of the maleic anhydride) and the signal at 840 cm^"1 which refers to the bending of the C=C group of cis- 1 ,4-polyisoprene.

The amount of the grafted maleic anhydride was calculated from the ratio between the area of the signal corresponding to maleic anhydride and the area of the signal corresponding to natural rubber by means of a calibration curve.

The elastomeric polymer was found to include about 0.8% by weight of grafted maleic anhydride with respect to the total weight of the elastomeric polymer.

EXAMPLE 3

The amounts of the compounds used are given in Table 3 (the amounts of the various components are given in phr).

TABLE 3

NR2: natural rubber (RSS3 - Grand Rubber, Thailand,);

maleic anhydride: commercial product from Lonza Milano SrI, Caravaggio, Italy;

The natural rubber was obtained in the form of granules having an average particles size diameter of about 3 mm - 20 mm, by means of a rubber grinder. The so obtained granules and maleic anhydride, also in a granular form, were fed to the feed hopper of a co-rotating twin-screw extruder Mans TM40HT having a nominal screw diameter of about 40 mm and a L/D ratio of about 48. The maximum temperature in the extruder was about 180°C. The extrusion head was kept at a temperature of about 40°C.

The obtained elastomeric polymer was discharged from the extruder in the form of a continuous strand, was cooled at room temperature in a cooling device and granulated. A sample of the obtained elastomeric polymer was subjected to Infrared

IR analysis

The elastomeric polymer obtained as above disclosed was subjected to Infrared ATR-Spectroscopy analysis. A thin plate of the ealstomeric polymer (0.5 g weight) was obtained by pressure die-casting, under vacuum, at about 70°C, the elastomeric polymer obtained as above disclosed.

The signals used are the following: the signal at 1780 cm^"1 which refers to the C=O stretching of the acid form of the carbonyl group of the maleic anhydride (open form of the maleic anhydride) and the signal at 840 cm^"1 which refers to the bending of the C=C group of cis-l,4-polyisoprene.

EXAMPLES 4-8

Preparation of the elastomeric compositions

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

All the components, except sulphur and accelerator (TBBS), 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 sulphur and the accelerator were then added and mixing was carried out in an open roll mixer (2^nd Step). TABLE 4

(*): comparative.

IR: cis-l,4-polyisoprene (SKI3 - Nizhnekamskneftechim Export);

NRl: natural rubber (STR20 - Thaiteck Rubber, Thailand)

NR2: natural rubber (RSS3 - Grand Rubber, Thailand);

IR-g-MAH: functionalized cis-l,4-polyisoprene obtained in Example 1 ;

NRl-g-MAH: functionalized natural rubber obtained in Example 2;

NR2-g-MAH: functionalized natural rubber obtained in Example 3;

X50S: silane coupling agent comprising 50% by weight of carbon black and 50% by weight of bis(3-triethoxysilylpropyl) tetrasulphide (Degussa-Huls);

Antioxidant: phenyl-p-phenylenediamine;

TBBS (accelerator): N-t-butyl-2-benzothiazolesulfenamide;

The static mechanical properties according to Standard ISO 37:1994 as well as hardness in IRHD degrees at 23°C according to ISO standard 48:1994, were measured on samples of the abovementioned elastomeric compositions vulcanized at 150°C for 30 min. The results obtained are given in Table 5.

Table 5 also shows the dynamic mechanical properties, measured using an Instron dynamic device in the traction-compression mode according to the following methods. A test piece of the crosslinked elastomeric composition (vulcanized at 150°C for 30 min) having a cylindrical form (length = 25 mm; diameter = 12 mm), compression-preloaded up to a 10% longitudinal deformation with respect to the initial length, and kept at the prefixed temperature (0° or 23°C or 70°C) for the whole duration of the test, was submitted to a dynamic sinusoidal strain having an amplitude of ±7.5% 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').

Finally, the peeling force values were measured on samples of the above mentioned elastomeric compositions by superimposing two layers of the same non- crosslinked elastomeric composition, followed by crosslinking at 150°C for 30 minutes. In detail, the test pieces were prepared as follows. Each elastomeric composition was calendered so as to obtain a sheet with a thickness equal to 3 mm ± 0.2 mm. From the sheet thus produced were obtained plates with dimensions equal to 220 mm (± 1.0 mm) x 220 mm (± 1.0 mm) x 3 mm (± 0.2 mm), marking the direction of the calendering. One side of each plate was protected with a polyethylene sheet, while a reinforcing fabric made of rubberized polyamide with a thickness of 0.88 mm ± 0.05 mm was applied to the opposite side, orienting the strands in the direction of calendering and rolling the composite thus assembled so as to achieve good adhesion between the fabric and the non-crosslinked elastomeric compositon. After cooling, sheets were produced from the composite thus obtained, by punching, these sheets having dimensions equal to 110 mm (± 1.0 mm) x 25 mm (± 1.0 mm) x 3.88 mm (± 0.05 mm), taking care to ensure that the major axis of each sheet was oriented in the direction of the strands of the fabric.

A first sheet made of the crosslinkable elastomeric composition obtained as disclosed above (i.e., the crosslinkable elastomeric composition obtained in Examples 4 to 8) constituting the first layer was placed in a mould, the polyethylene film was removed, two Mylar^® strips acting as lateral separators (thickness = 0.2 mm) were applied laterally and a third strip again made of Mylar^® (thickness = 0.045 mm) was applied to one extremity of the sheet in order to create a short free section not adhering to the second layer. A second sheet made of the same crosslinkable elastomeric composition (i.e., the crosslinkable elastomeric composition obtained in Examples 4 to 8) above disclosed, from which the polyethylene film was previuosly removed, was then applied to the first sheet thus prepared, constituting the second layer (the first layer and the second layer being made of the same crosslinkable elastomeric composition), thus obtaining a test piece which was then crosslinked by heating at 150°C for 30 minutes in a press.

Subsequently, the test pieces crosslinked as described above were conditioned at room temperature (23°C ± 2°C) for at least 16 hours and were then subjected to the peel test using a Zwick Z005 dynamometer, the clamps of which were applied to the free section of each layer. A traction speed equal to 260 mm/min ± 20 mm/min was then applied and the peel force values thus measured, expressed in Newtons (N), are given in

Table 5 and are each the average value calculated for 4 test pieces. The same tests were carried out on the test pieces crosslinked as described above and conditioned at 100⁰C for at least 16 hours: the obtained results were given on Table 5 and are each the average value calculated for 4 test pieces. TABLE 5

(*): comparative.

As shown in Table 5 above, the crosslinked elastomeric compositions 6 to 8 of the invention have shown improved elastic modulus without affecting the viscous or loss modulus. The improvement of elastic modulus resulted in improved hysteresis properties, and, as a consequence, in a reduction of the rolling resistance and the fuel consumption. In addition, the crosslinked elastomeric compositions 6 to 8 of the invention have shown improved tear resistance (peeling), in particular at high temperatures, and accordingly, an improved resistance to tear failure. Said improvements have been obtained without negatively affecting the mechanical properties, such as tensile modulus and hardness.

Claims

1. A tire for heavy load vehicles comprising:

- a carcass structure;

(a) at least about 50 phr of at least one functionalized elastomeric polymer including from about 0.05% by weight to about 10% by weight, with respect to the total weight of the elastomeric polymer, of at least one functional group selected from carboxylic groups, carboxylate groups, anhydride groups, ester groups;

(b) from about 10 phr to about 70 phr of at least one carbon black reinforcing filler;

(c) less than 50% by weight relative to said carbon black reinforcing filler of an additional reinforcing filler.

2. Tire according to claim 1, wherein said crosslinkable elastomeric composition comprises from about 70 phr to about 100 phr of said functionalized elastomeric polymer.

3. Tire according to claim 1, wherein said crosslinkable elastomeric composition comprises from about 90 phr to about 100 phr of said functionalized elastomeric polymer.

4. Tire according to claims 1 to 3, wherein said functionalized elastomeric polymer includes from about 0.1% by weight to about 5% by weight, with respect to the total weight of the elastomeric polymer, of at least one functional group selected from carboxylic groups, carboxylate groups, anhydride groups, ester groups.

5. Tire according to any one of the preceding claims, wherein said functionalized elastomeric polymer including at least one functional group has a weight average molecular weight (M_w) not lower than about 80,000.

6. Tire according to claim 5, wherein said functionalized elastomeric polymer including at least one functional group has a weight average molecular weight (M_w) of from about 100,000 to about 1,000,000.

7. Tire according to any one of the preceding claims, wherein said functional group is introduced into the elastomeric polymer during the production of said functionalized elastomeric polymer by co-polymerization with at least one corresponding functionalized monomer containing at least one ethylenic unsaturation; or by subsequent modification of said elastomeric polymer by grafting said at least one functionalized monomer, optionally in the presence of a free radical initiator.

8. Tire according to claim 7, wherein said functionalized monomer containing at least one ethylenic unsaturation is selected from monocarboxylic or dicarboxylic acids containing at least one ethylenic unsaturation or derivatives thereof, in particular salts, anhydride or esters.

9. Tire according to claim 8, wherein said monocarboxylic or dicarboxylic acids containing at least one ethylenic unsaturation or derivatives thereof are: maleic acid, fumaric acid, citraconic acid, itaconic acid, acrylic acid, methacrylic acid, and salts, anhydrides or esters derived therefrom, or mixtures thereof.

10. Tire according to any one of the preceding claims, wherein the elastomeric polymer utilized in the production of said functionalized elastomeric polymer including at least one functional group is selected from natural or synthetic sulphur-crosslinkable elastomeric polymer or copolymers with an unsaturated chain having a glass transition temperature below about 20°C.

11. Tire according to claim 10, wherein the elastomeric polymer utilized in the production of said functionalized elastomeric polymer including at least one functional group is selected from: natural or synthetic cis-l,4-polyisoprene, 3,4-polyisoprene, or mixtures thereof.

12. Tire according to any one of the preceding claims, wherein said crosslinkable elastomeric composition comprises from about 20 phr to about 60 phr of at least one carbon black reinforcing filler.

13. Tire according to any one of the preceding claims, wherein said carbon black reinforcing filler has a surface area higher than about 20 m²/g.

14. Tire according to any one of the preceding claims, wherein said crosslinkable elastomeric composition comprises less than 40% by weight relative to said carbon black reinforcing filler of said additional reinforcing filler.

15. Tire according to any one of the preceding claims, wherein said additional reinforcing filler is silica.

16. Tire according to claim 15, wherein said silica is selected from pyrogenic silica and precipitated silica having a BET surface area of from about 50 m²/g to about 500 m²/g.

17. Tire according to any one of the preceding claims, wherein said crosslinkable elastomeric composition comprises an additional elastomeric polymer in an amount lower than about 50 phr.

18. Tire according to any one of the preceding claims, wherein said crosslinkable elastomeric composition comprises an additional elastomeric polymer in an amount lower than about 30 phr.

19. Tire according to any one of the preceding claims, wherein said crosslinkable elastomeric composition comprises an additional elastomeric polymer in an amount lower than about 10 phr.

20. Tire according to any one of the preceding claims, wherein said additional elastomeric polymer is selected from:

- natural or synthetic cis-l,4-polyisoprene, 3,4-polyisoprene, polybutadiene, optionally halogenated isoprene/isobutene copolymers, 1,3-butadiene/acrylonitrile copolymers, styrene/l,3-butadiene copolymers, styrene/isoprene/ 1,3 -butadiene copolymers, styrene/l,3-butadiene/acrylonitrile copolymers, or mixtures thereof;

- ethylene/propylene copolymers (EPR) or ethylene/propylene/diene copolymers (EPDM); polyisobutene; butyl rubbers; halobutyl rubbers, in particular chlorobutyl or bromobutyl rubbers; or mixtures thereof.

21. Tire according to any one of the preceding claims, wherein said crosslinkable elastomeric composition comprises at least one silane coupling agent.

22. Tire according to claim 21, wherein said silane coupling agent is selected from those having at least one hydrolizable silane group which may be identified by the following general formula (II):

(R)₃Si-C_nH_2n-X (II)

wherein the groups R, which may be identical or different, are selected from: alkyl, alkoxy or aryloxy groups or from halogen atoms, on condition that at least one of the groups R is an alkoxy or aryloxy group; n is an integer between 1 and 6 inclusive; X is a group selected from: nitroso, mercapto, amino, epoxide, vinyl, imide, chloro, - (S)₀₁C_nH_2n-Si-(R)₃ or -S-COR in which m and n are integers between 1 and 6 inclusive and the groups R are defined as above.

23. Tire according to claim 20 or 21, wherein said silane coupling agent is present in the crosslinkable elastomeric composition in an amount of from about 0 phr to 10 phr.

24. Tire for vehicle wheels according to any one of the preceding claims, wherein said at least one structural element is said tread band.

25. A crosslinkable elastomeric composition comprising:

(a) at least about 50 phr of at least one functionalized elastomeric polymer selected from natural and synthetic isoprene rubber including from about 0.05% by weight to about 10% by weight with respect to the total weight of the functionalized elastomeric polymer, of at least one functional group selected from carboxylic groups, carboxylate groups, anhydride groups, ester groups;

26. The crosslinkable elastomeric composition according to claim 25, wherein said at least one functionalized elastomeric polymer is comprised in an amount ranging from about 70 phr to about 100 phr.

27. The crosslinkable elastomeric composition according to claim 25, wherein said at least one functionalized elastomeric polymer is comprised in an amount ranging from about 90 phr to about 100 phr

28. The crosslinkable elastomeric composition according to any of claims 25 to 27, wherein said functionalized elastomeric polymer includes from about 0.1% by weight to about 5% by weight with respect to the total weight of the elastomeric polymer, of at

5 least one functional group selected from carboxylic groups, carboxylate groups, anhydride groups, ester groups.

29. The crosslinkable elastomeric composition according to any one of claims 25 to 28, wherein said functionalized elastomeric polymer including at least one functional group has a weight average molecular weight (M_w) not lower than about 80,000.

10 30. The crosslinkable elastomeric composition according to claim 29, wherein said functionalized elastomeric polymer including at least one functional group has a weight average molecular weight (M_w) of from about 100,000 to about 1,000,000.

31. The crosslinkable elastomeric composition according to any one of claims 25 to

30. wherein said functional group is introduced into the elastomeric polymer during the 15 production of said functionalized elastomeric polymer by co-polymerization with at least one corresponding functionalized monomer containing at least one ethylenic unsaturation; or by subsequent modification of said elastomeric polymer by grafting said at least one functionalized monomer, optionally in the presence of a free radical initiator. 0 32. The crosslinkable elastomeric composition according to claim 31, wherein said functionalized monomer containing at least one ethylenic unsaturation is selected from monocarboxylic or dicarboxylic acids containing at least one ethylenic unsaturation or derivatives thereof, in particular salts, anhydride or esters.

33. The crosslinkable elastomeric composition according to claim 32, wherein said 5 monocarboxylic or dicarboxylic acids containing at least one ethylenic unsaturation or derivatives thereof are: maleic acid, fumaric acid, citraconic acid, itaconic acid, acrylic acid, methacrylic acid, and salts, anhydrides or esters derived therefrom, or mixtures thereof.

34. The crosslinkable elastomeric composition according to any one of claims 25 to 0 33, wherein the elastomeric polymer utilized in the production of said functionalized elastomeric polymer including at least one functional group is selected from natural or synthetic sulphur-crosslinkable isoprene rubber having a glass transition temperature below about 20°C.

35. The crosslinkable elastomeric composition according to claim 34, wherein the elastomeric polymer utilized in the production of said functionalized elastomeric polymer including at least one functional group is selected from: natural or synthetic cis-l,4-polyisoprene, 3,4-polyisoprene, or mixtures thereof.

5 36. The crosslinkable elastomeric composition according to any one of claims 25 to

35, wherein said crosslinkable elastomeric composition comprises from about 20 phr to about 60 phr of at least one carbon black reinforcing filler.

37. The crosslinkable elastomeric composition according to any one of claims 25 to

36, wherein said carbon black reinforcing filler has a surface area higher than about 20 10 m²/g.

38. The crosslinkable elastomeric composition according to any one of claims 25 to

37, wherein said crosslinkable elastomeric composition comprises less than 40% by weight relative to said carbon black reinforcing filler of said additional reinforcing filler.

15 39. The crosslinkable elastomeric composition according to any one of claims 25 to

38, wherein said additional reinforcing filler is silica.

40. The crosslinkable elastomeric composition according to claim 39, wherein said silica is selected from pyrogenic silica and precipitated silica having a BET surface area of from about 50 m²/g to about 500 m²/g. 0 41. The crosslinkable elastomeric composition according to any one of claims 25 to

40, wherein said crosslinkable elastomeric composition comprises an additional elastomeric polymer in an amount lower than about 50 phr.

42. The crosslinkable elastomeric composition according to any one of claims 25 to

41, wherein said crosslinkable elastomeric composition comprises an additional 5 elastomeric polymer in an amount lower than about 30 phr.

43. The crosslinkable elastomeric composition according to any one of claims 25 to

42, wherein said crosslinkable elastomeric composition comprises an additional elastomeric polymer in an amount lower than about 10 phr.

44. The crosslinkable elastomeric composition according to any one of claims 25 to 0 43, wherein said additional elastomeric polymer is selected from:

- natural or synthetic cis-l,4-polyisoprene, 3,4-polyisoprene, polybutadiene, optionally halogenated isoprene/isobutene copolymers, 1,3-butadiene/acrylonitrile copolymers, styrene/ 1,3 -butadiene copolymers, styrene/isoprene/l,3-butadiene copolymers, styrene/l,3-butadiene/acrylonitrile copolymers, or mixtures thereof;

45. The crosslinkable elastomeric composition according to any one of claims 25 to 44, wherein said crosslinkable elastomeric composition comprises at least one silane coupling agent.

46. The crosslinkable elastomeric composition according to claim 45, wherein said silane coupling agent is selected from those having at least one hydrolizable silane group which may be identified by the following general formula (II):

(R)₃Si-C_nH_2n-X (II)

wherein the groups R, which may be identical or different, are selected from: alkyl, alkoxy or aryloxy groups or from halogen atoms, on condition that at least one of the groups R is an alkoxy or aryloxy group; n is an integer between 1 and 6 inclusive; X is a group selected from: nitroso, mercapto, amino, epoxide, vinyl, imide, chloro, - (S)_1T1C_nH_2n-Si-(R)₃ or -S-COR in which m and n are integers between 1 and 6 inclusive and the groups R are defined as above.

47. The crosslinkable elastomeric composition according to claim 45 or 46, wherein said silane coupling agent is present in the crosslinkable elastomeric composition in an amount of from about 0 phr to 10 phr.

48. The crosslinkable elastomeric composition according to any of claims 45 or 46, wherein said silane coupling agent is present in the crosslinkable elastomeric composition in an amount of from about 0.5 phr to about 5 phr.