The present invention relates to a method of manufacturing a tyre, the tyre comprising a tread portion comprising a rubber polymer and a carcass comprising a polyurethane polymer, wherein the tread portion is directly bonded to the carcass. The invention also relates to such a tyre. Pneumatic tyres employing polyurethane materials are generally known in the art. EP 1 437 371 Al for instance discloses a pneumatic tyre comprising a skin layer which is formed by curing a polyurethane resin composition comprising a compound having active hydrogen atoms and an organic polyisocyanate compound, has an oxygen permeation coefficient at 23 °C under a relative humidity of 60% of 2.0 ml.mm/m ² .day.MPa or smaller and comprises 20% by weight or more of a skeleton structure represented by a given general formula is provided. It is stated that since the tyre has the skin layer formed with the polyurethane resin composition and having an excellent barrier property to gases, the weight of the tyre can be decreased, durability can be improved and quiet driving can be achieved while the internal pressure is retained even when the gas filling the tyre is the air, and the tyre is more economical than tyres filled with nitrogen gas. Unlike other tyres using other materials having the barrier property to gases to decrease the weight, no adhesives are necessary for disposing the skin layer. Thus, the process can be simplified and the cost can be reduced in the production.

While polyurethane has advantages over rubber material for tyres with respect to rolling resistance, the grip of a polyurethane tread on the road surface is less favourable than the grip of a rubber tread. Therefore, hybrid tyres have been developed which attempt to combine the advantages of both polyurethane and rubber materials in one tyre.

WO 2008/127091 describes a method for mutually adhering a first moulded article of an at least partially vulcanized rubber polymer and a second moulded article of a polymer. The method comprises at least the steps of providing a first moulded article of a rubber polymer which comprises a compound containing carboxylic acid anhydride; providing a second moulded article of a polymer; providing an adhesive composition comprising at least a polyisocyanate, a polyol and a catalyst; arranging an adhesive layer of the adhesive composition on the surface for adhesion of at least one moulded article; bringing the surfaces for adhesion together under pressure; and polymerizing at least the adhesive layer at a suitable temperature. NL 2003748 Al discloses a tyre comprising a carcass of a polyurethane polymer and a tread portion of a rubber polymer. The tread portion is moulded with the carcass by providing, between the tread portion and the carcass, a first intermediate layer of a rubber polymer comprising a compound containing carboxylic acid anhydride, and a second intermediate layer of a composition comprising at least a polyisocyanate, a polyol and a catalyst, and polymerizing at least the second intermediate layer. The publication further relates to a method for manufacturing the tyre. The tyre according to the publication has a relatively low rolling resistance and a good grip on the road.

A different approach regarding the use of polyurethane material in tyre applications has been taken in US 2013/0276968 Al. This patent application concerns a process for forming a solid polyurethane an airless solid core tyre with a wheel rim bonded thereto where the tyre bonding takes place during the tyre casting or moulding process where a wheel rim area, that includes a circumferential trough, is etched, treated with a primer and, after drying, receives an adhesive coating applied thereto, and the wheel is positioned in a mould to receive a mixture of polyurethane materials passed into the mould to form the airless solid core tyre that is permanently bonded onto the wheel rim. WO 2007/139657A1 discloses vacuum forming apparatus for forming a tyre, wheel, or other item in a mould having a cavity with the shape of the item to be cast that is contained in the apparatus. The vacuum forming apparatus utilizes a bell shaped outer cover arranged to seal along its lower edge to a mould base plate, and includes a canister maintained under a deep vacuum and arranged in or connected to the apparatus as a reservoir to receive a mixture of urethane constituents, with the deep vacuum removing air from that mixture, and the air free mixture is passed through a valve and into the mould cavity. A low level vacuum is pulled through a vent valve in the bell shaped outer cover to pull the flow of urethane material through the cavity, filling the mould. With the cavity filled, the canister valve is shut and the vent valve in the bell shaped outer cover is closed, allowing the urethane material in the mould cavity to cure, and the mould is broken open and the cast item is removed from the cavity.

A urethane wheel having a metal core is described in WO 2006/118613. The urethane wheel is manufactured by moulding, casting, or vacuum forming methods in a mould having a wheel shaped cavity that a wheel core formed from a rigid material such as steel or aluminium has been supported in to receive a flow of a urethane material directed therearound, encapsulating the entire wheel core and forming a wheel capable of supporting a car or light truck traveling at highway speeds.

US 6,165,397 and US 5,906,836 disclose spin casting methods for manufacturing polyurethane tyres.

It would be desirable to simplify the structure of a polyurethane/rubber tyre and hence simplify its manufacture. For this, a flexible but durable bond between a polyurethane carcass and a rubber tread is needed. The present invention has the object of providing such a manufacturing method and such a tyre.

This object is achieved by a method of manufacturing a tyre, the tyre comprising: a tread portion comprising a rubber polymer and a carcass comprising a polyurethane polymer; the tread portion being directly bonded to the carcass; wherein the method comprises the steps of:

A) providing:

Al) a vulcanized tread portion with an outward facing surface and an inward facing surface, the tread portion furthermore comprising a compound with hydroxyl groups, amino groups, isocyanate groups and/or carboxylic acid anhydride groups; or

A2) an at most partially vulcanized tread portion precursor with an outward facing surface and an inward facing surface, the tread portion precursor furthermore comprising a compound with hydroxyl groups, amino groups, isocyanate groups and/or carboxylic acid anhydride groups;

B) contacting the inward facing surface of the vulcanized tread portion of step Al) or the inward facing surface of the at most partially vulcanized tread portion precursor of step A2) with a polyurethane reaction mixture comprising a polyol, a polyisocyanate and a catalyst; C) curing the polyurethane reaction mixture of step B), thereby forming the carcass of the tyre.

Rubber polymers frequently applied in the rubber industry, for instance natural rubber, styrene- butadiene rubber, butadiene rubber and ethylene -propylene -diene rubber, are apolar. Simply moulding such rubbers with other polar polymers, such as the polyurethane polymer of the carcass, easily leads to a poor bond and therefore to delamination during use. It has surprisingly been found that the method according to the invention provides tyres with a strong bonding between the carcass and the tread without the need for intermediate layers or adhesion layers. This is to be understood as a direct bonding between the tread portion and the carcass. It is also within the scope of the invention that the tread and/or the carcass have inner structures such as an outer part of the tread and a cushioning inner part of the tread. In particular, the peeling force needed to separate the polyurethane carcass from the rubber tread in the finished tyre as determined by a T-peel test (ASTM D1876) may exceed 70 N. In some instances, the rubber or polyurethane material fractured before the bond between rubber and polyurethane showed signs of failure.

The tyres produced by the method according to the invention benefit from the good road traction properties of the rubber tread and the low rolling resistance properties of polyurethane polymers. Rolling resistance relates to the force resisting relative movement of a tyre and the road. As the tyre rotates under the weight of the vehicle, it experiences repeated cycles of deformation and recovery. Since the rubber in a tyre exhibits hysteresis, the tyre will dissipate the hysteresis energy loss as heat. Hysteresis is the main cause of energy loss associated with rolling resistance and is attributed to the viscoelastic characteristics of the rubber.

Step A) of the method according to the invention generally concerns providing a tread portion onto which the polyurethane carcass will be bonded. It is possible that the tread portion is vulcanized (Al) or is a partially vulcanized or un vulcanized tread portion precursor (A2).

According to the invention, the tread portion or precursor comprise a compound with OH groups, amino groups, NCO groups and/or carboxylic acid anhydride groups. The compound may be present as a physical mixture in the rubber or chemically bonded to the vulcanized or unvulcanized rubber. The chemical bonding is preferred.

Suitable compounds with hydroxyl groups include unsaturated mono- and poly alcohols such as alkenols, butadienols, polybutadieneols and furthermore unsaturated OH terminated urethane prepolymers.

Suitable compounds with amino groups include primary and secondary amines, preferably allyl amine, diallyl amine, ethylene diamine, ethanolamine and/or triethanolamine.

Suitable compounds with isocyanate groups include unsaturated mono- and polyisocyanates such as α,α-dimethyl meta-isopropenyl benzyl isocyanate and furthermore unsaturated NCO terminated urethane prepolymers.

Suitably applicable compounds containing carboxylic acid anhydride are at least monoiunctional relative to the polyurethane of the carcass. Monoiunctional is understood to mean in the context of this application that the compound containing carboxylic acid anhydride will react mainly via the anhydride functionality with the polyurethane reaction mixture of the carcass, and/or via the diacid functionality formed after hydrolysis of the anhydride.

This does not preclude that the carboxylic acid anhydride containing compound possibly comprises other reactive groups, although the reactivity of these groups will preferably be lower than the reactivity of the polyurethane of the carcass with the carboxylic acid anhydride group. Compounds suitable for application are for instance saturated aliphatic (di)carboxylic acid anhydrides, such as for instance succinic acid anhydride, glutaric acid anhydride, adipinic acid anhydride and so forth.

Also suitable are cycloaliphatic dicarboxylic acid anhydrides, such as for instance cyclohexane- dicarboxylic acid anhydride. Application of cycloaliphatic dicarboxylic acid anhydrides has the additional advantage that discoloration as a result of for instance sunlight is prevented. In addition, dicarboxylic acid anhydride containing compounds which comprise ethylenic unsaturations are preferably suitable. An example of such an ethylenic unsaturated compound is maleic acid anhydride (MAA). Also suitable are compounds comprising an aromatic unsaturation, such as for instance phthalic acid anhydride and/or trimellitic acid anhydride.

The reaction products of compounds with hydroxyl groups, amino groups, isocyanate groups and/or carboxylic acid anhydride groups with vulcanized or at most partially vulcanized rubber are also within the scope of the present invention.

In step B) of the method according to the invention the inward facing surface of the tread or precursor, i.e. the surface which is opposed to the surface to contact the road, is contacted with a polyurethane reaction mixture.

Suitable polyisocyanates include toluene diisocyanates, m-phenylene diisocyanate, 4-chloro-l,3- phenylene diisocyanate, 4,4'tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 1,10- decamethylene diisocyanate, 1,4-cyclohexylene diisocyanate, 4,4'-methylene bis cyclohexane diisocyanate, 1,4-cyclohexane bis methyl isocyanate, isophorone diisocyanate, 1,5- tetrahydronaphthalene diisocyanate, p-xylene diisocyanate, m-xylene diisocyanate and polymers, such as dimers and trimers of such polyisocyanates.

Suitable polyols, and in particular diols, comprise aliphatic diols such as for instance ethylene glycol, propane-1 ,2-diol, propane -1 ,3-diol, butane-1 ,2-diol, butane -1 ,4-diol, butane-l,3-diol, 2,2- dimethyl propanediol-1,3 (= neopentyl glycol), hexane-2,5-diol, hexane-l,6-diol, 2,2-bis(4- hydroxycyclohexyl) -propane (hydrogenated bisphenol-A), 1,4-dimethylolcyclohexane, diethylene glycol, dipropylene glycol and 2,2-bis[4-2-hydroxyethoxy)-phenyl propane. It is also possible to apply aromatic polyalcohols and/or relatively small quantities, such as less than about 4% by weight, but preferably less than 2% by weight, of trifunctional alcohols. Suitable catalysts for polyurethane reactions can be nucleophilic (tertiary amines, weak acids) such as triethylene diamine or N-ethylmorpholine, or electrophilic (organometallic compounds) such as tin octoate. A combination of catalysts can also be used.

All catalysts known for polyurethane reactions, such as for instance metal complexes, are in principle applicable in the adhesive composition. The quantity of catalyst generally lies between 0.1 and 10% by weight relative to the overall weight of the polyurethane composition, although other contents are possible. The surfaces of the tread portion and/or the carcass may be pre-treated, for instance by roughening, sanding, degreasing and/or providing the surfaces with radicals. The latter can for instance take place by irradiating the surfaces with radiation of suitable wavelength, for instance UV light, if desired laser radiation. It is also possible to subject the surfaces to an additional plasma treatment. In step C) of the method according to the invention the polyurethane reaction mixture cures and thereby forms the shape of the carcass of the tyre. Of course, this preferably takes place in a suitable shaped mould. Furthermore, at least the OH groups, amine groups, NCO groups and/or carboxylic acid anhydride groups located on the surface of the tread or tread precursor also participate in the reaction leading to the polyurethane carcass. Without wishing to be bound by theory, it is believed that this leads to the strong bonding between tread and carcass.

In case an at most partially vulcanized tread portion precursor as mentioned in step A2) is employed, a vulcanization step is additionally performed during or after step C). The heat transferred into the polyurethane reaction system may increase the reaction speed and lead to a wider diffusion of reaction components into the tread precursor. In summary, the bond strength between carcass and tread may be increased even more.

The base rubber composition from which the tread portion is obtained can be prepared in a manner known to the skilled person. Any known method of mixing polymers, fillers and other additives is in principle suitable for this purpose. It is thus possible to mix the rubber composition with the compound with hydroxyl groups, amine groups, isocyanate groups and/or carboxylic acid anhydride groups and optionally supplement them if desired with additives and/or other polymers, using an internal mixer or Banbury mixer, a single or double-screw extruder apparatus, a blade kneader, a Buss co-kneader, a roller and the like.

Suitable temperatures during mixing are substantially determined by the rheological properties of the relevant rubber polymer. In general these rubbers have a glass transition temperature T _g lower than -10 °C, although this is not essential. Rubbers suitable for application are for instance chosen from the group of natural rubbers, isoprene rubbers, butadiene rubbers, styrene butadiene copolymer rubbers, acrylonitrile butadiene copolymer rubbers, if desired copolymerized with styrene, butadiene isoprene copolymer rubbers, chloroprene rubbers, butyl and acryl rubbers, and ethylene propylene copolymers which, if desired, comprise a third copolymerizable diene monomer such as for instance 1,4-hexadiene, dicyclopentadiene, dicyclooctadiene, methylene norbornene, ethylidene norbornene and tetrahydroindene.

If desired, the rubber composition also comprises a minor quantity of natural rubber and/or elastomer, which is preferably composed of 1,3 -diene compounds such as for instance butadiene and/or isoprene and/or 2,3-dimethyl butadiene. The rubber composition applied in the method for example comprises an ethylene-propylene rubber, a natural rubber, a butadiene rubber, and a styrene butadiene copolymer rubber.

The rubber compositions may be sulfur-vulcanizable and/or peroxide-vulcanizable. Other vulcanization systems may also be used. If desired, additives can be added to the rubber polymer and the polyurethane polymer. Examples of usual additives are stabilizers, antioxidants, lubricants, fillers, dyes, pigments, flame retardants, conductive fibres and reinforcing fibres. The rubber composition can particularly also comprise an oil as additive. It is also possible to add petroleum plasticizers.

If desired, the rubber composition can also comprise a coupling agent. Suitable coupling agents comprise silane compounds. Particularly suitable silane compounds comprise di- and tetrasulphides. Preferably the rubber composition for the tread portion is provided with a conductive filler to make it at least partially conductive.

Other embodiments and further aspects of the present invention will be described below. They may be combined freely unless the context clearly indicates otherwise. In one embodiment of the method according to the invention step B) is at least partially performed as a spin casting step. In spin casting, a centrifugal force is used to produce castings from a mould. The casting is preferably continued until the polyurethane reaction mixture has cured, i.e. step C) is also performed under spin casting conditions.

Spin casting has the advantage that air bubbles can be expelled from the polyurethane reaction mixture and hence the structural integrity of the carcass is increased.

In another embodiment of the method according to the invention step B) is at least partially performed under vacuum conditions. The vacuum is preferably maintained until the polyurethane reaction mixture has cured, i.e. step C) is also performed under vacuum conditions.

For example, step B) may be at least partially performed in a vacuum forming apparatus for manufacturing a transport tyre containing a core of plies, belts and beads from an elastomeric material comprising, a mould formed from an inner mould that includes a mandrel whereon a transport tyre core of plies, belt and beads are laid-up on, with said core maintained in an annular area of said mould between said inner mould and an outer mould that is arranged for mounting to said inner mould; means for sealing said annular area from an air flow from outside of said mould; a canister that is open through its top to pass a flow of elastomeric material and has a valve means fitted into said canister for providing a controlled flow therefrom of said elastomeric material into said annular area where said core of plies, belt and beads is positioned; passage means from said valve means into said annular area between said inner mould and outer mould; a first port means mounted into said canister for connection to a high level vacuum source for pulling air therethrough; a cover arranged for mounting onto said outer mould that has an open interior area that is connected to receive a flow from said annular area; and a second port means mounted into said cover for connection to a low level vacuum source. In another embodiment of the method according to the invention the vulcanized tread portion of step Al) is prepared by combining a polybutadiene comprising isocyanate groups, hydroxyl groups, amino groups and/or carboxylic anhydride groups with an uncured rubber composition and curing the resulting mixture.

In another embodiment of the method according to the invention the vulcanized tread portion of step Al) is prepared by combining a polyisoprene comprising isocyanate groups, hydroxyl groups, amino groups and/or carboxylic anhydride groups with an uncured rubber composition and curing the resulting mixture.

In another embodiment of the method according to the invention the vulcanized tread portion of step Al) is prepared by combining a styrene butadiene copolymer comprising isocyanate groups, hydroxyl groups, amino groups and/or carboxylic anhydride groups with an uncured rubber composition and curing the resulting mixture.

The respective functional groups may be terminal functional groups or located on side chains of the polybutadiene.

Particularly preferred are OH terminated polybutadienes such as di-(2-hydroxypropyl)- polybutadienes of the general formula HO-C(CH ₃ )H-(CH ₂ -CH=CH-CH ₂ )„-CH ₂ -C(CH ₃ )H-OH with n taking a value of 2 to 210, preferably 30 to 100. Their number average molecular weight may be in a range of 1800 to 2500 g/mol, 2500 to 3500 g/mol, 4500 to 5500 g/mol or 9000 to 11000 g/mol. Their content of OH groups may be in a range of 0.73 to 1.11 mmol/g, 0.52 to 0.80 mmol/g, 0.33 to 0.44 mmol/g or 0.16 to 0.22 mmol/g. Their OH number may be in a range of 41.0 to 62.3 mg KOH/g, 29.2 to 44.9 mg KOH/g, 18.6 to 24.9 mg KOH/g or 8.9 to 12.5 mg KOH/g.

Also preferred are NCO terminated polybutadienes which are obtained by reacting the above- mentioned OH terminated polybutadienes with polyisocyanates. For example, a di-(2- hydroxypropyl)polybutadiene with a number average molecular weight of 1800 to 2500 g/mol and a hydroxyl number of 41.0 to 62.3 mg KOH/g (referred to as "polyol" in the following table) may be employed in the synthesis of NCO terminated prepolymers with the following formulations (amounts given are parts per weight):

Polyol 100 100 100 100

4,4' -MDI 23.70 28.22 33.86 45.15 NCO/OH ratio 2.10 2.50 3.00 4.00

NCO content 3.5% 4.4% 5.7% 8.0%

By way of another example, a di-(2-hydroxypropyl)polybutadiene with a number average molecular weight of 2500 to 3500 g/mol and a hydroxyl number of 29.2 to 44.9 mg KOH/g (referred to as "polyol" in the following table) may be employed in the synthesis of NCO terminated prepolymers with the following formulations (amounts given are parts per weight):

It is believed that the polybutadiene-based functional compounds are covalently incorporated into the rubber during the curing step via their C=C double bonds.

In another embodiment of the method according to the invention the at most partially vulcanized tread portion of step A2) is prepared by combining a polybutadiene comprising isocyanate groups, hydroxyl groups, amino groups and/or carboxylic anhydride groups with an uncured rubber composition.

In another embodiment of the method according to the invention the at most partially vulcanized tread portion of step A2) is prepared by combining a polyisoprene comprising isocyanate groups, hydroxyl groups, amino groups and/or carboxylic anhydride groups with an uncured rubber composition. In another embodiment of the method according to the invention the at most partially vulcanized tread portion of step A2) is prepared by combining a styrene butadiene copolymer comprising isocyanate groups, hydroxyl groups, amino groups and/or carboxylic anhydride groups with an uncured rubber composition.

The respective functional groups may be terminal functional groups or located on side chains of the polybutadiene.

Particularly preferred are OH terminated polybutadienes such as di-(2-hydroxypropyl)- polybutadienes of the general formula HO-C(CH ₃ )H-(CH ₂ -CH=CH-CH ₂ )„-CH ₂ -C(CH ₃ )H-OH with n taking a value of 2 to 210, preferably 30 to 100. Their number average molecular weight may be in a range of 1800 to 2500 g/mol, 2500 to 3500 g/mol, 4500 to 5500 g/mol or 9000 to 11000 g/mol. Their content of OH groups may be in a range of 0.73 to 1.11 mmol/g, 0.52 to 0.80 mmol/g, 0.33 to 0.44 mmol/g or 0.16 to 0.22 mmol/g. Their OH number may be in a range of 41.0 to 62.3 mg KOH/g, 29.2 to 44.9 mg KOH/g, 18.6 to 24.9 mg KOH/g or 8.9 to 12.5 mg KOH/g. Also preferred are NCO terminated polybutadienes which are obtained by reacting the above- mentioned OH terminated polybutadienes with polyisocyanates. For example, a di-(2- hydroxypropyl)polybutadiene with a number average molecular weight of 1800 to 2500 g/mol and a hydroxyl number of 41.0 to 62.3 mg KOH/g (referred to as "polyol" in the following table) may be employed in the synthesis of NCO terminated prepolymers with the following formulations (amounts given are parts per weight):

By way of another example, a di-(2-hydroxypropyl)polybutadiene with a number average molecular weight of 2500 to 3500 g/mol and a hydroxyl number of 29.2 to 44.9 mg KOH/g (referred to as "polyol" in the following table) may be employed in the synthesis of NCO terminated prepolymers with the following formulations (amounts given are parts per weight):

It is believed that the polybutadiene-based functional compounds are covalently incorporated into the rubber during the curing step via their C=C double bonds.

In another embodiment of the method according to the invention the uncured rubber composition comprises a natural rubber and/or a butadiene rubber and/or a styrene-butadiene copolymer rubber. For example, the tread base rubber composition may comprise 75 parts per hundred rubber (phr) of a SBR and 25 phr of a polybutadiene rubber (BR). Alternatively, natural rubber or a blend of SBR, BR and natural rubber may be used as a base rubber composition. The base rubber composition may further comprise 80 phr of silica, about 45 phr of usual additives such as oil, zinc oxide and stearic acid, and about 1.4 phr of sulfur for vulcanization.

In another embodiment of the method according to the invention the rubber composition comprises the following components:

0-100 phr, preferably 40-90 phr, for instance 50 phr of natural rubber;

0-100 phr, preferably 10-40 phr, for instance 25 phr of a butadiene rubber;

0-100 phr, preferably 10-40 phr, for instance 25 phr of a styrene butadiene rubber, the phr of all rubbers adding up to 100 phr;

0-100 phr, preferably 50-90 phr, for instance 75 phr of filler such as carbon black or silica; 0-5 phr, preferably 1-4 phr, for instance 2.5 phr of zinc oxide;

0-3 phr, preferably 1-2 phr, for instance 1.5 phr of stearic acid;

0-30 phr, preferably 10-20 phr, for instance 15 phr of oil;

0-5 phr, preferably 1-4 phr, for instance 2 phr of suitable accelerator;

0.1-5 phr, preferably 1-4 phr, for instance 2 phr of sulphur; and

0-30 phr, preferably 10-20 phr, for instance 15 phr of a compound with hydroxyl groups and/or amino groups and/or isocyanate groups and/or carboxylic acid anhydride groups.

In another embodiment of the method according to the invention in the vulcanized tread portion of step Al) or in the at most partially vulcanized tread portion precursor of step A2) the isocyanate group content is > 0.5 weight- to < 15 weight or the hydroxyl group content is > 0.05 weight- to < 5 weight or the amino group content is > 0.05 weight-% to < 5 weight-% or the carboxylic acid anhydride group content is > 5 weight-% to < 35 weight%. The weight percentages are based on the total weight of the vulcanized tread portion of step Al) or the total weight of the at most partially vulcanized tread portion precursor of step A2). Preferred is an isocyanate group content of > 1 weight-% to < 5 weight% or a hydroxyl group content of > 0.1 weight-% to < 1 weight% or an amino group content of > 0.1 weight-% to < 1 weight-% or a carboxylic acid anhydride group content of > 10 weight-% to < 25 weight%.

In another embodiment of the method according to the invention between step B) and step C) the step B') is undertaken: B') mechanically introducing the polyurethane reaction mixture of step B) into the vulcanized tread portion of step Al) or into the at most partially vulcanized tread portion precursor of step A2).

This step has the effect of increasing the contact area between tread or precursor and the polyurethane reaction mixture. Instead of a two-dimensional bonding surface, a three-dimensional bonding area is created. Mechanical means for introducing the PUR reaction mixture include spiked rotary drums.

A further aspect of the present invention is a tyre comprising: a tread portion comprising a rubber polymer and a carcass comprising a polyurethane polymer, wherein the tread portion is directly bonded to the carcass via urethane and/or urea linkages without additional intermediate or adhesive layers. Due to its polyurethane carcass, the tyre may exhibit a rolling resistance according to ISO 28580 as low as 3.2 kg/ton.

A tyre generally may comprise several parts. Typical parts include the tread portion, the shoulders, the sidewalls, the bead, carcass, belt and inner liner. The tread portion is that part that comes in direct contact with the road when driving. The shoulders are located between the tread and the sidewalls, and act to protect the tyre against impact loads, for which reason they are usually the thickest rubber part in the tyre.

The flexible sidewalls are located between the shoulder and bead, protect the carcass and enhance the ride. They are also used to indicate the type, size, structure, pattern, manufacturing company, product name and the like of the tyre.

The bead is the part of the tyre that attaches the tyre to the rim and wraps the end of the tyre's cord fabric. Comprised of the bead wire, core, flipper and other parts, the bead is generally designed to be slightly tight around the rim so that in the case of a sudden drop in inflation pressure, the tyre will not fall off the rim. The carcass represents the tyre structural framework and acts to support air pressure, vertical load and absorb shocks. The breaker is a cord layer placed between the carcass and the tread in order to protect the carcass of a bias tyre. The breaker reduces shocks, prevents rips or injury of the tread from reaching the carcass directly while also stopping the separation between the rubber layer and the carcass. The belt is a strong reinforcement found between the tread and the carcass in a radial or belted bias tyre. It functions much like the breaker but also increases tread rigidity by tightly winding about the carcass.

The inner liner finally is made of a layer of rubber that resists air diffusion and replaces the inner tube within a tyre. Generally made of a (halogenated) butyl rubber, the inner liner maintains the air inside the tyre.

The tyre according to the invention may be obtained by a method according to the invention. Hence, all details of the composition and structure in particular for the carcass and tread as outlined above also apply. In the interest of avoiding repetition, they will not be discussed again. It shall merely be mentioned that the urethane and/or urea linkages are the result of the reaction of a polyurethane reaction mixture which will form the carcass with a compound with hydroxyl groups, isocyanate groups and/or carboxylic acid anhydride groups present in the tread portion (or a tread precursor). In a preferred embodiment of the tyre according to the invention the bonding strength between the tread portion and the carcass as determined by a T-peel test (ASTM D1876) is greater than the bonding strength within the material of the tread portion and/or the bonding strength within the material of the carcass. This means that the failure mode during the T-peel test lies for example in the rubber component and/or the polyurethane component, not on the interface between the polyurethane and rubber layer. By way of example, the bonding strength between the tread portion and the carcass as determined by a T-peel test (ASTM D1876) may be > 70 N. This exceeds the fracture strength of certain rubber compositions.

The present invention will be described in more detail with reference to the following figure and examples without wishing to be limited by them.

FIG. 1 shows a perspective view of a tyre cross-section according to the invention

FIG. 2 shows a perspective view of another tyre cross-section according to the invention

FIG. 1 shows a perspective view of a tyre cross-section according to the invention. The tyre comprises a carcass 10 of a polyurethane polymer and a tread portion of a rubber compound. A typical tread portion base rubber compound is for instance given in Table 1 of EP 0 501 227 Al as compound 1.

The tread portion of the tyre shown comprises an outer part 20, provided with longitudinal grooves and transverse grooves (not shown), and an inner part 30 that acts as cushion for part 20. The longitudinal and transverse grooves define profiled elements. At the central part 40 of the tread portion, the rubber composition for the tread portion may be provided with a conductive filler to make it at least partially conductive. At the sides of the tread portion, wing tips 50 are provided.

In the carcass, a core layer 80 of metal and/or polymeric cords is embedded. This divides the carcass into an outer layer 60 and an inner layer 70. If desired, the tyre may be provided with an inner liner to further improve air tightness. However, this is rarely needed. The outer layer 60 of the carcass is firmly bonded to the wing tips 50 and the inner part 30 of the tread without additional adhesives. This is effected by the presence of a compound with hydroxyl groups and/or amino groups and/or isocyanate groups and/or carboxylic acid anhydride groups in the rubber of the wing tips 50 and the inner part 30 of the tread which reacts with the polyurethane reaction mixture during the forming of the carcass. A preferred compound is Krasol NN-3A, the composition of which is described in the experimental section.

FIG. 2 shows a perspective view of a tyre cross-section according to another embodiment of the invention. The tyre comprises a carcass 10 of a polyurethane polymer and a tread portion of a rubber compound. A typical tread portion base rubber compound is for instance given in Table 1 of EP 0 501 227 Al as compound 1.

The tread portion 20 of the tyre shown is provided with longitudinal grooves and transverse grooves (not shown). The longitudinal and transverse grooves define profiled elements. At the central part 40 of the tread portion, the rubber composition for the tread portion may be provided with a conductive filler to make it at least partially conductive.

In the carcass, a core layer 80 of metal and/or polymeric cords is embedded. This divides the carcass into an outer layer 60 and an inner layer 70. If desired, the tyre may be provided with an inner liner to further improve air tightness. However, this is rarely needed. The outer layer 60 of the carcass is firmly bonded to the tread part 20 without additional adhesives. This is effected by the presence of a compound with hydroxyl groups and/or amino groups and/or isocyanate groups and/or carboxylic acid anhydride groups in the rubber of the tread part which reacts with the polyurethane reaction mixture during the forming of the carcass. A preferred compound is Krasol NN-3A, the composition of which is described in the experimental section. Examples

The samples were analysed according to a strip test as outlined by ASTM D1876 with a width of 15 mm and measured at 23 °C.

The rubber part of the sample had the following composition: natural rubber/polybutadiene rubber: 70/30 phr; carbon black: 60 phr; zinc oxide: 5 phr ; stearic acid: 1 phr; vulcanization system: 4 phr. The polyurethane reaction mixture was prepared from an 100 parts by weight of an NCO terminated prepolymer, 26 parts by weight of a polyol and 5 parts by weight of a catalyst.

In order to prepare the samples, a rubber strip with the above-mentioned basic composition was placed in a mould and the polyurethane reaction mixture was poured onto the strip. After the PUR had cured, the force necessary to peel the PUR layer from the rubber strip was measured. Comparative examples:

1. A previously prepared PUR strip was bonded to a rubber strip using the adhesive Cilbond 48. This adhesive is described by the manufacturer as "a fast drying one-coat bonding system capable of bonding both hot and cold cast polyurethane systems to a variety of substrates including metals, polyamides and other engineering thermoplastics". However, the adhesion force measured was 0 N, meaning that no adhesion has taken place. 2. In a sample prepared from a rubber with the basic composition and the PUR reaction mixture the adhesion also was 0 N.

Example according to the invention:

1. To the base rubber composition was added 30 weight- , based on the total weight of the resulting composition, the NCO terminated prepolymer Krasol NN-3A (Cray Valley). Krasol NN-3A is the reaction product of a hydroxylated terminated polybutadiene (Krasol LBH 2000) and a modified methylenediphenyl diisocyanate (MDI). The NCO content of Krasol NN-3A according to the manufacturer is 0.95 to 1.30 mmol/g. This rubber composition was then contacted with the PUR reaction mixture and after curing the PUR, a peel test was undertaken. As a result of the test, the adhesion force was 70 N and the fracture was in the rubber - meaning that the adhesion bond was not the limiting factor.