BACKGROUND OF THE INVENTION It is known that elements for winding any type of thread or yarn, such as cops for spinners or twisters, must be at the same time both very light, so they can be handled easily, and also very strong, so they can support very high stresses, even in the range of several hundred bar, due to the greater or lesser elasticity of the threads or yarns themselves.

Until now, to manufacture cops for spinners, twisters or suchlike, either light but very resistant metals have been used, such as aluminum and its alloys, or plastic materials such as polycarbonate (PC), polyethylene terephtalate (PET), polypropylene (PP), possibly reinforced with fiber glass.

However, if on the one hand the metals allow to obtain relatively light winding elements of a limited thickness, they have the disadvantage that they are very costly,

especially due to the mechanical processes required to produce them, on the other hand the plastic materials used until now have shown a rather limited mechanical resistance, so that, as a consequence, the winding elements are rather thick.

In the case of cops for yarns, which have a standardized height and inner diameter, so that they are interchangeable with the corresponding spindles of different textile machines, the thickness is a very important factor, because it directly affects the quantity of yarn which can be wound thereon, considering that the outer diameter of the bobbin of yarn is also standardized.

For example, a cop T for textile yarns (fig. 1) of known type, made of PC, shaped like a truncated cone, with height H of 210 mm, a through longitudinal hole F with the lower inner diameter A of 20 mm, has a thickness S1, substantially constant, of 3.5 mm, so that the lower outer diameter B1 is 27 mm. The upper outer diameter C, which must necessarily be more than the lower inner diameter A, so as to prevent two cops from being inserted one inside the other, is 21 mm. Consequently, the upper inner diameter D1 is 14 mm.

One purpose of the present invention is to perfect a method for manufacturing winding elements for the textile field, such as cops for spinners, twisters or suchlike, using plastic materials which have already been on the market for a long time, which are relatively inexpensive and which at the same time have high mechanical characteristics, such as to allow to reduce the thickness of the winding elements.

In this way, the outer diameter of the winding element can be reduced, at least for a good part of its height, without likewise reducing the mechanical resistance, so

that the quantity of thread or yarn, which can be wound on every individual winding element, can be increased, with the same outer diameter of the bobbin.

A second purpose of the present invention is to obtain winding elements such as cops for spinners, twisters or suchlike which are certainly new and lead to the expected advantages, yet which can be interchangeable with those already in use.

In this case, said new winding elements must have, at least in the lower part, both the same inner diameter of the hole by means of which they are able to couple with the corresponding spindle or other positioning/drawing element, and also the upper outer diameter greater than the afore- said lower inner diameter, especially in the case of cops for winding yarns or threads.

A further purpose of the present invention is to manufacture cops for spinners, twisters or suchlike which, thanks to their low specific weight, allow to reduce the energy needed to make them rotate.

In accordance with the above purposes and to overcome the shortcomings of the state of the art, the Applicant has devised and perfected the method according to the present invention.

SUMMARY OF THE INVENTION The method according to the present invention for manufacturing winding elements for the textile field, such as cops for spinners, twisters and suchlike, and the winding elements thus achieved, are set forth and characterized in the main claims, while the dependent claims describe other innovative characteristics of the present invention.

In accordance with the above purposes, the method according to the present invention provides that the

winding elements for the textile field are manufactured by using one or more semi-crystalline thermoplastic polymers.

Said polymers are syndiotactic polystyrene (SPS) resins, obtained from a styrene monomer by means of metallocene catalysis. Said resins, according to a first embodiment, are reinforced with fiber glass, or similar or equivalent material, to a quantity of between about 15% and 25%, advantageously 20%, of the total.

According to a variant, substances which make the final product antistatic are added to said resins, reinforced or not with fiber glass, or similar or equivalent material.

Said resins have been known for a long time, like for example the resin distributed commercially under the name Questra of the Ashland Company@ of Dow Chemical Company, but until now they have never been prepared for the production of cops for winding yarns.

With respect to a state of the art winding element, made with other plastic materials, such as for example PC, PET or PP, the use of SPS resins, given the same inner diameter and mechanical resistance, allows to reduce the thickness of the walls of the winding element by about 1/3.

In this way it is possible to obtain much thinner cops, and consequently increase the quantity of yarn or thread which can be wound on each of them.

To give an example, in the case of a cop to make bobbins of thread or yarns, the thickness can be reduced, at least for a good part of its height, from 3.5 to 2.5 mm, and even less, so that the quantity of yarn wound on the cop can be more by 6-10%, and even more, with respect to that wound on a known cop, according to the thickness of the thread or yarn and to the outer diameter of the cop.

Moreover, according to the present invention,

considering that the outer diameter of the cop is reduced, but that we want to maintain the characteristics of interchangeability with known cops, and also to prevent one cop from penetrating another, at least the upper part of each cop is shaped so that its outer diameter is substantially equal to that of the cops in the same category.

In order to do this, according to operating and constructional requirements, the taper of the cop can be slightly modified, or the upper part of the cop can be made substantially cylindrical, or slightly flared outwards, or an annular or radial protrusion can be made, which increases the diameter only of the upper end of the cop.

In order to strengthen the cop in its lower part too, the thickness of the end of the latter can be increased, until the outer diameter of this end is taken to the value of the corresponding cops of a known type.

Another advantage of the cops for spinners, twisters or suchlike manufactured in accordance with the present invention, is that they require less energy, with respect to state of the art cops, to be made to rotate, thus obtaining also an energy saving in the range of about 5- 10%.

BRIEF DESCRIPTION OF THE DRAWINGS These and other characteristics of the present invention will become apparent from the following description of some preferential forms of embodiment, given as a non-restrictive example, with reference to the attached drawings wherein: - fig. 1 is a longitudinal section of a cop made according to the state of the art; - fig. 2a is a longitudinal section of a cop made according to the present invention in accordance with a first form

of embodiment; - fig. 2b is a longitudinal section of a cop made according to the present invention in accordance with a second form of embodiment; - fig. 3 shows an enlarged detail of a first variant of the cop in fig. 2b; - fig. 4 shows an enlarged detail of a second variant of the cop in fig. 2b; - fig. 5 shows an enlarged detail of a third variant of the cop in fig. 2b.

DETAILED DESCRIPTION OF SOME PREFERENTIAL FORMS OF EMBODIMENT OF THE INVENTION Fig. 2a shows a longitudinal section of a cop 10 for spinners, twisters or suchlike, manufactured according to the present invention, that is to say, using syndiotactic polystyrene (SPS) resins, obtained from a styrene monomer by means of metallocene catalysis, possibly reinforced with fiber glass or other equivalent materials.

According to the present invention, in a hot molding step, the mold to manufacture the cop 10 is kept at a temperature of between about 90°C and about 170°C, advantageously about 160°C.

According to the present invention, the above resins, to which about 10-25% of fiber glass or other similar or equivalent material has been added, are injected at a temperature of between about 270°C and about 315°C, advantageously about 295°C.

According to the present invention, the injection pressure, in the case of cops 10 having a wall thickness of about 1 mm, varies from about 90 MPa to about 110 MPa, and is advantageously 100 Mpa, whereas, in the case of cops 10 having a wall thickness of about 4 mm, it varies from about 45 MPa to about 55 MPa, and is advantageously 50 MPa.

The cop 10 is shaped substantially like a truncated cone, with an upper part 10a and a lower part 10b, and is provided with a longitudinal hole 11, by means of which it is able to couple with a corresponding spindle, of a known type and not shown in the drawings.

Some sizes of the cop 10 according to the present invention are equal to those of a corresponding cop T of a known type, such as the height H which is 210 mm, the lower inner diameter A of the hole 11, which is 20 mm, and the outer diameter C of the upper part 10a, which is 21 mm.

According to one characteristic of the present invention, the thickness S2 of the lower part 10b of the cop 10 is less than the corresponding thickness S1 of the cop T of a known type. In this case, the thickness S2 is 2.5 mm. As a consequence, the outer diameter B2 of the lower part 10b is 25 mm, that is, 2 mm less than the corresponding outer diameter B1 of the known cop T. The thickness S1 of the upper part 10a of the cop 10 and the corresponding inner diameter D1, on the contrary, are equal to those of the known cop T. Therefore, the taper of the inner hole 11 of the cop 10 is also equal to that of the hole F of the cop T. In this embodiment, moreover, the thickness of the cop 10, along its height H, is variable and between the value S2 at the bottom and the value S1 at the top.

In accordance with a second form of embodiment, shown in fig. 2b, the thickness S2 of the cop 10 is constant for the whole height H, so that, since the upper outer diameter C is constant, as a consequence the upper inner diameter D2 is greater than the corresponding upper inner diameter D1 of the known cop T.

In this second embodiment, the taper of the cop 10 and of its hole 11 is therefore less accentuated than that of

the corresponding known cop T and of the corresponding hole F.

Fig. 3 shows a variant of fig. 2b wherein, in order to keep in the cop 10 the same taper as the corresponding known cop T and a thickness S2 substantially constant for almost all the height H, the upper part 10a is substantially cylindrical in shape, or slightly flared outwards.

In the variant shown in fig. 4, the same objectives are achieved by creating an annular protrusion 12 on the upper end of the part 10a. Alternatively, this annular protrusion 12 can be replaced by one or more radial protrusions, not shown in the drawings.

In accordance with a third variant, shown in fig. 5, in order to strengthen the cop 10 in its lower part 10b too, the thickness of the end 13 of the latter is increased to the value S1. In this way, and advantageously only in correspondence with said end 13, an annular protrusion is achieved having an outer diameter B2 substantially equal to the outer diameter B1 of a corresponding known cop T.

It is clear, however, that some steps can be added to or modified in the method as described heretofore, without departing from the field and scope of the present invention.

It is also clear that, although the present invention has been described with reference to some specific examples, a person of skill in the art shall be able to perfect many other equivalent methods, all of which shall come within the field and scope of the present invention.

Moreover, the cops which can be manufactured with the method according to the present invention can be of the most diverse types.