The present invention relates to a process and a plant for building tyres for vehicle wheels. In particular, the present invention relates to a process and a plant for building tyres for racing or high performance vehicle. The present invention also relates to a green tyre and a tyre obtained with said building process.

Tyre production cycles envisage a building process, wherein the various components of the tyre itself are made and/or assembled in one or more building lines, followed by a moulding and vulcanization process, in a suitable vulcanization line, adapted for defining the tyre structure according to a desired geometry and tread pattern.

A tyre generally comprises a toroidally ring-shaped carcass structure including one or more carcass plies, strengthened with reinforcing cords lying in substantially radial planes (a radial plane contains the rotation axis of the tyre). Each carcass ply has its ends integrally associated with at least one metal reinforcing annular structure, known as bead core, constituting the reinforcing at the beads, i.e. at the radially inner ends of the tyre, having the function of enabling the assembling of the tyre with a corresponding mounting rim.

Placed on the carcass is a crown structure formed by a reinforcing structure, generally known as belt structure, whereon a band of elastomeric material, called tread band, is applied, within which, at the end of the moulding and vulcanization steps, a raised pattern is formed for ground contact. The tread band is formed by a segment closed up on itself the two free ends whereof are made integral to one another by a joint. The belt structure usually comprises, in the case of tyres for cars, at least two radially overlapped strips of rubber fabric provided with reinforcing cords, usually of metal, arranged parallel to each other in each strip and crossed with the cords of the adjacent strip, preferably symmetrical to the equatorial plane of the tyre. Preferably, the belt structure further comprises in radially outer position, at least on the ends of the underlying belt strips, also a third layer of textile or metal cords, arranged circumferentially (at 0 degrees).

Finally, in tyres of the tubeless type, a radially inner layer, called liner, is present which has imperviousness features for ensuring the air-tightness of the tyre itself.

To the aims of the present invention and in the following claims, by the term "elastomeric material" it is intended a composition comprising at least one elastomeric polymer and at least one reinforcing filler. Preferably, such composition further comprises additives such as cross-linking and/or plasticizing agents. By virtue of the cross-linking agents, such material may be cross-linked by heating, so as to form the final manufactured article.

In the present description and following claims, the terms "radial" and "axial" and the expressions "radially inner/outer" are used with reference to the radial direction and to the axial direction of a forming support, that is, of a tyre mounted on a wheel. The terms "circumferential" and "circumferentially" are used in the direction of the extension of the tyre periphery, that is, the direction of rotation thereof, both in use and in the forming processes.

To the aims of the present scope, by the term "green tyre" it is meant a tyre obtained by the building process and not yet vulcanized.

For the deposition of the tread band, normally, segments of elastomeric material with even composition and suitable length (corresponding to the extension for a complete revolution on the belt structure) are arranged on special devices, wherefrom they are picked up for the application on the belt structure.

Document EP 1398182 describes tread bands with a so-called "cap and base" (tread and underlayer) structure, wherein the tread provides the running surface of the tread band whereas the underlayer offers a transition zone between the tread and the belt structure of the tyre. The different layers have differentiated mechanical properties and elastomeric compositions. In the embodiment, a shaped component of non vulcanized rubber is arranged with conventional means (for example extrusion).

Document EP 0105822 shows a tyre, in particular for earth moving vehicles, wherein the tread band comprises at least one inner layer with good heat resistance properties and at least one outer layer with good wear, cut and tear resistance properties. For the deposition, the compositions of the layers are combined and calendered in a single sheet, prior to the application to the carcass.

Document WO 2004/096583 describes a tyre with a tread band that includes at least one radially inner layer and one radially outer layer having different compression elasticity modulus; the radially inner layer comprises a plurality of circumferential abutment elements extended radially in the radially outer layer and axially distributed along the cross development of the tread band. Each of the two layers is formed by an elongated element laid forming a plurality of windings axially side by side and/or radially overlapped for forming the circumferential abutment elements.

Document GB 1372254 describes a tread band with layered structure, formed by the overlapping of a finite number of segments of sheet material or by the spiral winding of a single segment; the sheet material is picked up from a feeding roll where it is stored wound interleaved with a polyethylene sheet or foil. Before being subject to vulcanization, the tread band is formed by a large number of overlapped layers.

The Applicant has checked that the discontinuity unavoidably introduced in the tread band by the joint may sometimes cause problems, especially in high performance or racing vehicles.

The Applicant has therefore perceived that it would be advantageous to eliminate the same joint or at least reduce the extent of the discontinuity present on the tread band.

The Applicant has thus understood that it is possible to reduce the impact of the joint on the tyre performance, reducing the dimensions thereof and in particular the thickness.

The Applicant has then found that making the tread band with a plurality of layers, suitably hot-deposited, it is possible to minimise the discontinuities introduced in the tread band by the need of closing the same tread band on itself.

More in particular, in accordance with a first aspect thereof, the invention relates to a process for building tyres, comprising:

- building a carcass structure,

- building a crown structure comprising a belt structure and a tread band;

- association of the carcass structure with the crown structure;

wherein the building of the crown structure envisages the building of said belt structure on a drum and the deposition of said tread band in a position radially outside said belt structure;

wherein the deposition of said tread band comprises:

- provision of a predetermined elastomeric material in a hot-extrusion device,

- from said extrusion device, extrusion of a band of elastomeric material having a width equal to the predetermined width of the tread band and a thickness smaller than the predetermined thickness of the tread band,

- hot-deposition of said band onto the belt structure in at least two overlapping layers.

The Applicant believes that with this process it is possible to minimise the discontinuities introduced in the tread band. In fact, due to the reduced thickness of each layer, it is possible to prevent joints of such dimensions as to introduce considerable discontinuities.

More in particular, in accordance with a second aspect thereof, the invention relates to a green tyre comprising:

- a carcass structure,

- a crown structure radially overlapped to said carcass structure, comprising a belt structure and a tread band,

wherein the tread band comprises at least two radially overlapping layers of a band of elastomeric material having a width equal to the width of the tread band, extruded and hot-deposited in a radially outer position on said belt structure.

In accordance with a third aspect thereof, the invention relates in particular to a tyre according to the second aspect of the invention, moulded and vulcanized.

The Applicant believes that the discontinuities introduced in the tread band are minimised in this tyre.

More in particular, in accordance with a fourth aspect thereof, the invention relates to a plant for building a tyre, comprising:

- at least one workstation for building of a carcass structure;

- at least one workstation for building a crown structure comprising a belt structure and a tread band;

- at least one workstation for the association of the carcass structure with the crown structure;

wherein the workstation for building of the crown structure comprises:

- a forming drum, for supporting and rotating the crown structure being processed,

- a device for feeding at least one belt strip onto said forming drum to form said belt structure;

- a hot-extrusion device, for feeding, with heat, an extruded band having a width equal to a predetermined width of the tread band and a thickness smaller than a predetermined thickness of the tread band, in a radially outer position on the belt structure supported by the forming drum.

The Applicant believes that since this plant implements a process according to the first aspect of the invention, it allows minimising the discontinuities in the tread band of the manufactured tyres.

The present invention, in accordance with one of said aspects, may exhibit one or more of the preferred features described hereinafter.

According to a preferred embodiment, there is provided a guide of said band of elastomeric material towards said belt structure. I n another preferred embodiment, it is also provided for the deposition of the extruded band to take place directly, without the interposition of any guiding means.

Preferably, a cut of said band in a predetermined position is provided.

Even more preferably, the cut is provided to take place during deposition, whilst a first leading portion of the band downstream of the cut has already been deposited and a second trailing portion downstream of the cut is still to be deposited.

A preferred embodiment comprises a guiding of said band of elastomeric material towards said belt structure, wherein the cut takes place during the guiding.

Even more preferably, the cut takes place before the deposition starts and the guiding comprises an acceleration of the band downstream of the cut, after cutting. Advantageously, this implies that the band is deposited on the belt structure at a higher speed than the speed at which it is extruded, thus subjecting the band to a certain longitudinal traction that improves the adhesion thereof to the belt structure.

According to a preferred embodiment, during the guide it is comprised:

- further cut of said band in a predetermined position, with separation from the band of a waste portion of predetermined length,

- discard of the waste portion.

Preferably, the guiding comprises:

- temporary arrangement of the band on a transfer device, so as to carry out the deposition on said belt structure in a position relatively remote from said extrusion device.

Preferably, the thickness of the band is comprised between 0.5 and 2.0 mm. More preferably, said thickness of the band is comprised between 0.8 and 1.5 mm. Even more preferably, said thickness of the band is equal to about 1.0 mm. According to a preferred embodiment, said at least two layers of the band of elastomeric material have all the same length. Advantageously, the building is thus simplified.

According to another preferred embodiment, said at least two layers of the band of elastomeric material have different widths to one another, decreasing in the radial direction, from the inside outwards. Advantageously, a tapered section is thus directly obtained, substantially trapezoidal, of the tread band.

According to a preferred embodiment, the band is deposited wound at least twice around, with formation of said at least two overlapping layers. Advantageously, the tread band is thus free from joints.

Even more preferably, there is provided a rolling of the deposited band, to level off, with heat, an end part of the deposited band. Advantageously, the step at the end part of the deposited band is thus chamfered and moulding and vulcanization are thus simplified.

Preferably, said band is deposited in single revolutions, on top of one another with formation of at least two overlapping layers, each of said layers having its own joint formed therein.

Even more preferably, said deposition is carried out so that the joints of the distinct single layers are in distinct angular positions, angularly distributed along the circumferential direction of a tyre being processed.

According to another preferred embodiment, the band deposition provides for:

- first deposition of a first portion of said band on said belt structure for a first revolution, with formation of a first of said at least two overlapping layers, and formation of a first joint between a final edge and an initial edge of the first portion,

- second deposition of a second portion of said band on the first layer for a second revolution, with formation of a second of said at least two overlapping layers, and formation of a second joint between a final edge and an initial edge of the second portion,

- optionally, one or more further depositions of further portions of said band of the last layer previously deposited for further revolutions, with formation of further overlapping layers, and formation of a further joint between a final edge and an initial edge of each further portion.

Advantageously, the tread band thus obtained has multiple joints, which have reduced dimensions and are regularly distributed in circumferential direction. As a consequence, the structure of the tread band is substantially free from the problems due to the discontinuity of a single large sized joint.

Even more preferably, at least two between said first portion, said second portion, said optional further portions are made with a band of a different elastomeric material. Advantageously, it is thus possible to differentiate the features of the tread band in radial direction, for example for obtaining differentiated performance during the useful life of the tyre, or for imparting specific properties to specific radial zones of the tread band.

According to a preferred embodiment, said at least two layers of the band of elastomeric material have different widths to one another, decreasing in the radial direction, from the inside outwards.

According to a different preferred embodiment, said at least two overlapping layers are formed by a deposited band wound at least twice around.

According to another preferred embodiment, said at least two overlapping layers are formed by corresponding band portions, deposited one onto the other and each closed by a joint.

Preferably, the joints are in distinct angular positions, angularly distributed along the circumferential direction of the tyre.

Even more preferably, said two band portions are made from different elastomeric material.

Preferably, a cutting device is provided to cut said hot-extruded band.

Preferably, a transfer device is provided to support and transport the hot- extruded band from the extruder device to the crown structure.

Even more preferably, the transfer device comprises its own motorised devices, to accelerate the supported band. Further features and advantages of invention will appear more clearly from the following description of some preferred examples of processes, green tyres, tyres and plants according to the invention, made by way of an indicative non- limiting example with reference to the annexed drawings, wherein:

- fig. 1 is a schematic partly cross-sectional view of a tyre according to a first embodiment of the invention;

- fig. 2 is a schematic cross-sectional view of the tread band of the tyre of fig. 1 according to a plane perpendicular to the tyre axis;

- fig. 3 is a schematic cross-sectional view of the tread band of the tyre of fig. 1 according to a radial plane, passing by the tyre axis;

- fig. 4 is a schematic cross-sectional view of a variant of embodiment of the tread band of the tyre of fig. 1 according to a radial plane, passing by the tyre axis;

- fig. 5 is a schematic partly cross-sectional view of a tyre according to a second embodiment of the invention;

- fig. 6 is a schematic cross-sectional view of the tread band of the tyre of fig. 5 according to a plane perpendicular to the tyre axis;

- fig. 7 is a schematic cross-sectional view of the tread band of the tyre of fig. 5 according to a radial plane, passing by the tyre axis;

- fig. 8 is a schematic cross-sectional view of a variant of embodiment of the tread band of the tyre of fig. 5 according to a radial plane, passing by the tyre axis;

- fig. 9 is a functional diagram of a plant for building a tyre according to the invention;

- fig. 10 is a schematic view of a workstation of the plant of fig. 9;

- fig. 11 is an enlarged scale view of a portion of the workstation of fig. 10.

With reference to figures 1 to 3, reference numeral 100 globally denotes a tyre according to a first embodiment of the invention.

Tyre 100 comprises a carcass structure 110 and a crown structure 130, radially overlapped to the carcass structure 110 and in turn comprising at least one belt structure 140 and a tread band 150.

The carcass structure 110 (per se known) comprises at least one carcass ply 111 , which is folded outwards at the ends thereof around respective annular reinforcing structures, in particular respective bead cores 112 and annular inserts 113, so as to form beads 114 for mounting tyre 100 on a rim.

The carcass ply 111 is preferably internally coated with a sealing layer 115, or the so-called "liner", essentially consisting of a layer of airtight elastomeric material adapted to ensure the seal of tyre 100 once inflated.

A further layer of elastomeric material (not shown in the figures) generally called "underliner" with features of mechanical resistance to breakout and good chemical features of weldability in vulcanization, may in turn be interposed between the liner and the carcass ply 111 for preventing the escape of the cords of the carcass ply 1 1 inside the tyre during the shaping step and for ensuring the liner weldability to the same carcass ply.

The belt structure 140 (per se known as well) comprises belt strips, for example three strips 141 , 142, 143.

The tread band 150 comprises at least two radially overlapping layers of a band of elastomeric material, in the example shown for example three layers 151 , 152, 153, The three layers 151 , 152, and 153 have a width equal to the width of the tread band 150 and are extruded from a same band of elastomeric material, hot-deposited in a radially outer position on said belt structure 140.

Preferably, the thickness of each one of layers 151 , 152 and 153 is comprised between 0.5 and 2.0 mm, more preferably between 0.8 and 1.5 mm and even more preferably equal to about 1.0 mm.

Layers 151 , 152 and 153 are formed by the same band, deposited wound by a number of turns equal to the number of layers, that is, in tyre 100 by three turns on the belt structure 140, as better shown in figure 2.

Finally, tyre 100 exhibits respective sidewalls 116 of elastomeric material on the side surfaces of the carcass structure 110, each extending from one of the side edges of the tread band 150 up to the respective annular reinforcing structure to beads 114.

According to the preferred embodiment, shown in figures 1 to 3, layers 151 , 153, 153 have all the same width.

Figure 4 shows a tread band 150' according to a version of the first embodiment of the invention. Tread band 150' is similar to tread band 150, and like that one it comprises three layers 151 ', 152' and 153', which have each a width equal to tread band 150', but they exhibit a width differing from each other, decreasing in radial direction, from the inside outwards of the tyre: layer 152' is narrower than layer 153' and larger than layer 151'. In this case, the indication that layers 151', 152' and 153' have a width equal to the tread band 150' is to be understood as referred to each position in radial direction: the width of tread band 150' in fact varies as the radial position varies, so that the tread band 150' is larger in the radially inner portion thereof, corresponding to layer 151 ', narrower in the radially intermediate portion thereof, corresponding to layer 152', and even narrower in the radially outer portion thereof, corresponding to layer 153'.

The different width of layers 151', 152' and 153' may be obtained with a band of elastomeric material in turn having a decreasing width, in a continuous manner or step-wise.

More precisely, the width-wise adjustment of said band may be obtained with different methods.

According to first preferred embodiment, such adjustment is obtained by extrusion from a single die or mouth having adjustable width; said adjustment may in turn be continuous or discontinuous.

As an alternative, it is possible to perform an extrusion by dies or mouths of different widths.

A further preferred method for said adjustment may be performed with a setup of the band by knife trimming.

A different preferred adjustment method may finally be performed by stretching the elastomeric material the band is made of, controlling the latter between the extrusion point and the application point.

With reference to figures 5 to 7, reference numeral 200 globally denotes a tyre according to a second embodiment of the invention.

Tyre 200, similar to tyre 100, comprises a carcass structure 210 and a crown structure 230, radially overlapped to the carcass structure 210 and in turn comprising at least one belt structure 240 and a tread band 250.

The carcass structure 210 (per se known and equal to the carcass structure 110 of the first embodiment) comprises at least one carcass ply 211 , which is folded outwards at the ends thereof around respective annular reinforcing structures, in particular respective bead cores 212 and annular inserts 213, so as to form beads 214 for mounting tyre 200 on a rim.

The carcass ply 211 is preferably internally coated with a sealing layer 215, or the so-called "liner", essentially consisting of a layer of airtight elastomeric material adapted to ensure the seal of tyre 200 once inflated. Also in this case, the presence of a underliner is preferably provided, interposed between liner and carcass ply 211.

The belt structure 240 (per se known as well) comprises belt strips, for example three strips 241 , 242, 243.

The tread band 250 comprises at least two radially overlapping layers of a band of elastomeric material, in the example shown for example three layers 251 , 252, 253, The three layers 251 , 252, and 253 have a width equal to the width of the tread band 250 and are extruded from a same band of elastomeric material, hot-deposited in a radially outer position on said belt structure 240.

Preferably, the thickness of each one of layers 251 , 252 and 253 is comprised between 0.5 and 2.0 mm, more preferably between 0.8 and 1.5 mm and even more preferably equal to about 1.0 mm.

Layers 251 , 252 and 253 are formed by corresponding band portions, deposited on top of each other and closed each by a respective joint 261 , 262, 263; joints 261 , 262, 263 are in different angular positions, angularly distributed along 360° relative to the tyre axis Z; in the example shown, therefore, the three joints 254, 255, 256 are arranged at 120° from one another.

Similar to tyre 100, tyre 200 exhibits respective sidewalls 216 of elastomeric material on the side surfaces of the carcass structure 210, each extending from one of the side edges of the tread band 250 up to the respective annular reinforcing structure to beads 214.

According to the preferred embodiment, shown in figures 5 to 7, layers 251 , 252, 253 have all the same width.

Figure 8 shows a tread band 250' according to a version of the second embodiment of the invention. Tread band 250' is similar to tread band 250, and like that one it comprises three layers 251', 252' and 253', which have each a width equal to tread band 250', but they exhibit a width differing from each other, decreasing in radial direction, from the inside outwards of the tyre: layer 252' is narrower than layer 253' and larger than layer 251 '. In this case, the indication that layers 251', 252' and 253' have a width equal to the tread band 250' is to be understood as referred to each position in radial direction: the width of tread band 250' in fact varies as the radial position varies, so that the tread band 250' is larger in the radially inner portion thereof, corresponding to layer 251', narrower in the radially intermediate portion thereof, corresponding to layer 252', and even narrower in the radially outer portion thereof, corresponding to layer 253'.

The different width of layers 251', 252' and 253' may be obtained with a band of elastomeric material in turn having a decreasing width, in a continuous manner or step-wise.

In said tread bands 150, 150', 250, 250', according to a preferred feature of the invention, the single layers 151-153, 151'-153', 251-253, 251 '-253', are all made of the same elastomeric material using any formulation suitable for producing tread bands.

According to another preferred feature, the single layers 151-153 in tread band 150, 151'-153' in tread band 150', 251-253 in tread band 250, 251 '-253' in tread band 250', are made of elastomeric materials differing from one another. According to a preferred embodiment, the hardness of the materials used for producing adjacent layers must differ by at least 4 IRHD at room temperature, measured according to the ISO 48 standard, with hardness between inner layers and outer layers sorted in an increasing or decreasing manner according to the required performance.

Tyres 100 and 200, once built as green tyres, are then moulded and vulcanized so that the desired tread pattern 159, 259 remains steadily impressed therein.

Figures 9 and 10 show a plant 500 according to the fourth aspect of the invention, suitable for carrying out a process according to the first aspect of the invention for building tyres 100 and 200 according to the second aspect of the invention.

Plant 500 comprises at least one workstation 510 for building a carcass structure 110, 210, at least one workstation 520 for building a crown structure 130, 230 comprising at least one belt structure 140, 240 and a tread band 150, 250, and at least one workstation 525 for the association of the carcass structure 110, 210 with the crown structure 130, 230.

The workstation 520 for building of the crown structure 130, 230 comprises: a forming drum 521 , for supporting and rotating the crown structure 130, 230 being processed, a device 522 for feeding at least one belt strip 141-143, 241- 243 on the forming drum 521 for forming the belt structure 140, 240; a hot- extrusion device 530, for feeding, with heat, an extruded band 531 having a width equal to a predetermined width of the tread band 150, 250 and a thickness smaller than a predetermined thickness of the tread band 150, 250, in a radially outer position on the belt structure 140, 240 supported by the forming drum 521.

Preferably, workstation 520 of plant 500 further comprises a cutting device 540, to cut the hot-extruded band 531.

Preferably, workstation 520 of plant 500 further comprises a transfer device 550, to support and transport the hot-extruded band 530 from the extruder device 530 to the crown structure 130, 230 being processed.

Preferably, the transfer device 550 comprises its own motorised devices 551 , to accelerate band 531 supported thereon.

With reference to the building plant 500 illustrated in figures 9 and 10, and to tyres 100 and 200 illustrated in figures 1 to 8, a preferred embodiment of a process for building a tyre according to the invention shall now be described. Such process provides:

- building the carcass structure 110, 210,

- building a crown structure 130, 230 comprising at least one belt structure 140, 240 and a tread band 150, 250,

- the association of the carcass structure 110, 210 with the crown structure 130, 230.

The building of the crown structure 130, 230 envisages the building of the belt structure 140, 240 on a drum 521 and the deposition of the tread band 150 250 in a position radially outside the belt structure 140, 240.

The deposition of the tread band 150, 250 comprises:

- the provision of a predetermined elastomeric material in a hot-extrusion device 530,

- from said extrusion device 530, the extrusion of a band 531 of elastomeric material having a width equal to the predetermined width of the tread band 150, 250 and a thickness smaller than the predetermined thickness of the tread band 150, 250,

- the hot-deposition of band 531 onto the belt structure 140, 240 in at least two overlapping layers 151-153, 251-253.

Preferably, the process provides guiding of band 531 of elastomeric material towards the belt structure 140, 240.

Preferably, the process provides the cut of band 531 in a predetermined position.

Preferably, the cut takes place during deposition, whilst a first leading portion 531a of band 531 downstream of the cut has already been deposited and a second trailing portion 531 b downstream of the cut is still to be deposited. Preferably, the process further provides guiding of band 531 of elastomeric material towards the belt structure 140, 240 and the cut takes place during the guiding.

Preferably, the cut takes place before the deposition starts and the guiding comprises an acceleration of the band downstream of the cut, after cutting.

Preferably, during the guiding, the process also provides a further cut of band 531 in a predetermined position, with separation from band 531 of a waste portion 531c of predetermined length, and the discard of the waste portion 531c.

Preferably, the guiding comprises the temporary arrangement of band 531 on a transfer device 550, so as to carry out the deposition on the belt structure 140, 240 in a position relatively remote from the extrusion device 530.

In a preferred embodiment, which leads to the building of tyre 100, band 531 is deposited wound by three turns, with formation of the overlapping layers 151- 153. In this case, preferably, the process provides the rolling of the deposited band 531 , to level off, with heat, an end part thereof.

In an alternative preferred embodiment, which leads to the building of tyre 200, band 531 is deposited wound in single turns, overlapping one another, with formation of the overlapping layers 251-253. In each one of layers 251-253, an own joint 261-263 is formed and the deposition is carried out so that joints 261- 263 of the distinct single layers 251-253 are in distinct angular positions, angularly distributed along the circumferential direction of the tyre.

More preferably, the deposition of band 531 provides:

- the deposition of a first portion of band 531 on the belt structure 240, for a first revolution, with formation of the first one 251 of the overlapping layers, and formation of a first joint 261 between a final edge and an initial edge of the first portion;

- the deposition of a second portion of band 531 on the first layer 251 for a second revolution, with formation of the second one 252 of the overlapping layers, and formation of a second joint 262 between a final edge and an initial edge of the second portion;

- the further deposition of a further portion of band 531 of the last layer 252 previously deposited for a further revolution, with formation of a further overlapping layer, and formation of a further joint 263 between a final edge and an initial edge of the further portion.

Finally, it should be noted that thanks to the invention it is possible to obtain tyres wherein the tread band is more regular than in known tyres, thanks to the absence of any joint or to the presence of small sized joints regularly distributed circumferentially along the circumferential direction of the tyre.

Within the scope of the present description and in the following claims, all numerical values indicating amounts, parameters, percentages and the like are to always be deemed as preceded by the term "about", if not otherwise stated. Moreover, all numerical value ranges include all possible combinations of the maximum and minimum numerical values and all possible intermediate ranges, besides those specifically indicated in the text.

It is clear that a man skilled in the art may make further changes and variants to the invention described hereinbefore in order to meet specific and incidental application requirements, changes and variants in any case falling within the scope of protection defined in the following claims.