EP2482937A1

EP2482937A1 - Core for racket string, racket string comprising such a core and corresponding manufacturing method

Info

Publication number: EP2482937A1
Application number: EP10777049A
Authority: EP
Inventors: Jean-Philippe Onnis; Rosemonde Maillet; Catherine Tartivel
Original assignee: Babolat VS SA
Current assignee: Babolat VS SA
Priority date: 2009-10-01
Filing date: 2010-09-30
Publication date: 2012-08-08
Also published as: FR2950816B1; WO2011039482A1; US8613184B2; FR2950816A1; JP2013506476A; US20120240547A1; CN102725035A

Abstract

This core (2) for a racket string, in particular for a tennis racket string, comprises a thermoplastic matrix (24) in which filaments (22) are embedded, at least one of these filaments being of natural origin and the thermoplastic matrix (24) being made of a material which, at a temperature lower than a threshold temperature, at which the filaments (22) are not substantially damaged, has a viscosity making it suitable for an extrusion process. The matrix (24) comprises a plurality of strands that are helically twisted in a first direction, each of the strands comprising a plurality of filaments (22) of natural origin that are helically twisted in a second direction, which is or is not opposite to the first direction.

Description

Soul for racket rope, racket rope comprising such a core and corresponding method of manufacture

The present invention relates to a racquet string core, in particular for tennis racket string, a racket string comprising such a core, and a method of manufacturing such a core.

In the field of ropes used especially in racket sports, we seek to integrate natural materials in order to preserve as much as possible the environment. In addition, natural filaments, such as those of silk, have a mechanical strength suitable for application as tennis string, as well as superior elasticity to synthetic filaments. To do this, it is known to want to integrate into a rope a plurality of silk filaments. This type of filament from the silkworm is entirely natural.

GB 600424 discloses a method according to which, once the plurality of silk filaments have been gathered together, the yarn thus obtained passes into an extruder head fed with a thermoplastic polymer. The polymer matrix then constitutes a sheathing of the natural yarn. However, the method described in this document proves difficult to industrialize. In addition, the soul thus produced does not have characteristics that make it suitable for use as a racket rope. It is also known from US Pat. No. 4,707,977 to make the matrix of a thermoplastic material whose melting temperature is lower than the deterioration temperature of the yarns and whose viscosity allows satisfactory impregnation of the yarns.

That being said, the present invention aims to provide a racquet string core which has characteristics adapted for use as a racket string. The present invention also aims at providing a method of manufacturing this core, which can be implemented simply and reliably.

For this purpose, the subject of the invention is a racquet string core, in particular for a tennis racket string, comprising a thermoplastic matrix in which filaments are embedded, at least one of these filaments being of natural origin, and the thermoplastic matrix being produced in a material which, at a temperature below a threshold temperature, for which the filaments are substantially not degraded, has a viscosity rendering it suitable for an extrusion process. This racquet string core is characterized in that the die comprises a plurality of helically twisted strands in a first direction, each of the strands including a plurality of naturally occurring filaments helically twisted in a second, opposing or opposite direction. not in the first sense.

According to other advantageous features of the core according to the invention, taken separately or in any technically possible combination:

the threshold temperature is less than 130 °, in particular equal to 110 °;

the threshold temperature defines the maximum value of a range of working temperatures, the minimum value of which corresponds to a threshold viscosity below which the material is adapted to said extrusion process.

- the minimum temperature is greater than 70Ό, in particular equal to

90 ^< C;

the threshold viscosity is less than 2500 Pa.s, in particular equal to 1500 Pa.s at 100 °, this viscosity being measured according to the ISO 1133 standard;

the viscosity of the material of the thermoplastic matrix is greater than 500 Pa.s at 100 °, this viscosity being measured according to the ISO 1 133 standard;

the threshold viscosity is less than 180 Pa.s, in particular equal to 50 Pa.s, this viscosity being measured according to DIN 53018;

the matrix comprises a single thermoplastic material;

the matrix comprises a mixture of thermoplastic materials;

the or at least one of the thermoplastic materials is polyamide or polyurethane;

at least one of the filaments of natural origin is a silk filament;

the core comprises at least one protective protective sheath.

Another object of the present invention is a racket string comprising at least one core as described above.

Another object of the present invention is a method of manufacturing a racquet string core, particularly for tennis racket rope, the soul comprising a plurality of filaments, the method comprising the steps of:

twisting a plurality of filaments helically in a first direction, and then twisting a plurality of strands, comprising a plurality of twisted filaments, helically in a second opposite or opposite direction,

passing the plurality of filaments comprising at least one filament of natural origin into a preparation bath comprising a first thermoplastic material dissolved in a solvent at ambient temperature and at atmospheric pressure, and

passing of the plurality of filaments into an extruder head fed with a second thermoplastic material which, at a temperature below a threshold temperature, for which the filaments are not substantially degraded, has a viscosity rendering it suitable for an extrusion process; 'extrusion.

According to an advantageous characteristic, the speed of the filaments during the passage in the bath is adapted to allow impregnation of the first thermoplastic material in each of the filaments.

Various other features and advantages of the invention will emerge from the description which follows, given solely by way of nonlimiting example and with reference to the drawings in which:

- Figure 1 is a schematic view of an assembly for the manufacture of a racquet string core according to the present invention;

FIG. 2 is a section of a racquet string core according to a first embodiment of the present invention;

FIG. 3 is a section of a racquet string core according to a second embodiment of the present invention; and

- Figure 4 is a graph, illustrating the variation of the viscosity as a function of temperature, for different materials.

Figure 1 shows an assembly 1 for the manufacture of a core 2 for racket rope. The assembly 1 comprises eight coils 4. Around each of these coils is wound a plurality 6 of filaments which may be called "multifilament" or elementary wire. In what follows, for the sake of simplicity, we will talk about wire 6. It is possible to envisage using a number of coils different from that illustrated. We can then vary the diameter of the core 2. The entirety of the filaments of the wire 6 is of natural origin. It is also possible to provide that one or more of these filaments are of natural origin. Advantageously, these filaments may be silk, the silk may be produced by a silkworm, a spider or a genetically modified animal capable of producing silk. In this respect, it will be noted that spider genes have been grafted onto a goat and a silkworm.

For the purposes of the invention, filament of natural origin is understood to mean a filament essentially made of silk of plant or animal origin, whether or not transformed, extracts of animal tissues or animal secretions, whether or not transformed, of vegetable fibers, especially of cotton, flax or other plants.

The naturally occurring material may have been mechanically or chemically processed, for example braiding or by acid treatment.

To manufacture such a wire 6, it is possible to provide a bundle of several filaments of natural origin by bringing them together. A helical twist is then performed in a given direction with respect to the central axis of the filament bundle thus defined. This results in a strand whose mechanical strength is essentially provided by the torsion.

It is also possible to assemble a plurality of strands in the form of a beam. Their cohesion is then ensured by a helical twist in a direction opposite to the twisting performed previously. By first producing a so-called S twist and then, in a second step, a so-called Z-twist, ie in an opposite direction with respect to the twist S, the cohesion and the hold of the wire 6 are thus increased. for example, the strands can comprise between 5 and 15 filaments of natural origin, and preferably between 7 and 10 filaments. In the same way, one can choose to assemble between 5 and 15 strands, preferably between 7 and 10. It can be expected to perform both twists in the same direction.

The assembly 1 also comprises a tank 10, which contains a preparation bath made from a protective thermoplastic material dissolved in a solvent, at room temperature and at atmospheric pressure. Advantageously, this material may be a polyurethane or a polyamide. The son 6, which are admitted in the tray 10, emerge from the latter being covered and / or impregnated with the protective thermoplastic material. These treated yarns, thus coated and / or impregnated, are assigned to the reference 11.

The assembly 1 further comprises an extruder head 12, having a guide 14 dug eight holes. Each of the holes allows the passage of each of the eight treated son 1 1. The head 12, which comprises at the outlet a die 16, is connected to a sleeve 18 in which an extrusion screw 20 is arranged. The latter cooperates with a thermoplastic sheathing material, which may be polyamide or polyurethane, whose properties will be explained in what follows.

FIG. 4 is a graph illustrating the evolution of the viscosity V as a function of the temperature T at atmospheric pressure. In this graph, the curve C relating to a material that can be used by the invention has been reported. It is noted that, in the usual way, the viscosity decreases with the temperature that is, the higher the temperature increases and the material considered becomes fluid.

In this figure 4, T _{M is} a threshold temperature, beyond which the filaments of natural origin, described above, are likely to be degraded. Note also V _s , the threshold viscosity, above which the material is not suitable for the extrusion process. This threshold value V _s corresponds to a temperature, denoted T _m .

It is conceivable that, on reading the curve, it is possible to delimit a working zone represented by a hatched quadrilateral. Outside this working zone Z, the method according to the invention can not be implemented. Indeed, for a temperature above the threshold temperature, or maximum T _M , the extrusion process will lead to the destruction of naturally occurring filaments.

On the other hand, for a temperature below T _m , namely a viscosity greater than V _s , the extrusion process can not give satisfactory results on an industrial scale. Indeed, the son can not be properly impregnated with the material, since the latter is not fluid enough.

In other words, the thermoplastic sheathing material used by the invention has a threshold viscosity value for a temperature value below the maximum temperature alone. This is to be compared with other materials, in particular of the polyethylene type, for which curve C has been drawn in FIG. It is noted that for the temperature T _M , the viscosity of this material is greater than the threshold viscosity, so that it is not suitable for the extrusion process. Thus, if it is desired to implement this extrusion with this material, it will be necessary to increase the temperature up to a value denoted T ', which is greater than that T _M. In other words, using this material for the extrusion process will lead to the destruction of natural filaments.

Typically, the threshold temperature, beyond which the filaments are degraded, is advantageously less than 1 30Ό, more preferably equal to 1 10Ό. Moreover, the threshold viscosity V _s is advantageously less than 2500 Pa.s, preferably equal to 1500 Pa.s. The viscosity V is also greater than a low value V _m , advantageously equal to 500 Pa.s, below which the matrix is too liquid and does not allow satisfactory impregnation of the filaments. These viscosity values are calculated according to ISO 1133 (100 * 0 / 2.16 kg). Finally, the minimum temperature T _m of the working zone, corresponding to this threshold viscosity, is advantageously greater than 70 ° C., in particular equal to 90 ° C.

According to one variant, the threshold viscosity V _s is advantageously less than 180 Pa.s, preferably equal to 50 Pa.s. The viscosity V is also greater than a low value V _M advantageously equal to 50 Pa .s. These viscosity values are calculated according to DIN 53018, Brookfield, needle 29.

In operation, the eight coils 4 are unwound at a speed that can be between 1 and 8 meters per minute, preferably between 2 and 5 meters per minute. The son 6 then bathe in the tank 10. The speed defined above is adapted to advantageously allow the thermoplastic material to cover and / or impregnate each son.

This impregnation is facilitated because it is performed in the presence of a thermoplastic material, dissolved in a solvent. Indeed, the presence of solvent makes it easier to convey this material between the filaments. Each treated wire 1 1 thus has mechanical characteristics, which are substantially identical to those of the wire 6 formed by the various filaments of natural origin.

Each of the treated wires 11 is introduced into the extruder head 12 through the holes of the guide 14. By the extrusion process, the treated wires 11 are thus coated. with the thermoplastic sheath material. At the exit of the die 16, the core 2 is thus obtained. Due to the melting temperature, relative to the thermoplastic cladding material, the filaments of natural origin are substantially not damaged during the various stages of their treatment process, described above.

Figure 2 illustrates a section, showing a core 2 according to the invention. This racquet string core comprises a plurality of silk filaments 22 embedded in a thermoplastic matrix 24 comprising a mixture of the thermoplastic material coming from the tank 10 and the thermoplastic material coming from the extruder head 12. This constituent material of this matrix presents characteristics that are substantially similar to those of the thermoplastic material described above, used for the extrusion step. In particular, this matrix 24 can be associated with a viscosity-temperature curve which corresponds substantially to that C, illustrated and described with reference to FIG.

It is advantageously possible to perform a twisting of the core 2, with respect to its central axis, at the exit of the extruder head 12. A core having a better cohesion as well as a better resistance is then obtained. mechanical. Advantageously, this twist can be between 50 and 100 revolutions per minute.

In Figure 3 is shown the core 2 around which is disposed a sheath 26 of protection. To do this, the core 2 passes into the head of an additional extruder, not shown, while the protective sheath material 26 is worked in pressure and temperature in a sheath of this extruder.

In the same way, provision may be made around the sheath 26 at least one additional sheath by a similar manufacturing process.

Furthermore, the speed of passage of the core 2 in a head of this additional extruder may be higher than the rate of passage of the treated son 1 1 in the extruder head 12. Preferably, this speed can be between 50 meters per minute and 100 meters per minute.

The process according to the invention can be applied to debased silk filaments, that is to say emptied of their protein, as well as undecorated silk filaments. In this respect, it will be noted that, by way of nonlimiting example, the installation treatment shown in the figures may comprise an additional tray not shown. The latter can ensure, in a manner known per se, an operation such as debase or de-enzyme.

From the soul 2, we can make a racket rope. The soul can be used directly and thus serve to string a racket frame. Alternatively, one can provide to assemble several cores 2, for example by torsion, then use this set in other applications. It is also possible to provide a protective sheath around this assembly.

Claims

1. - Soul (2) for racket rope, in particular for tennis racket rope, comprising a thermoplastic matrix (24) in which filaments (22) are embedded, at least one of these filaments being of natural origin and the matrix thermoplastic (24) being made of a material which, at a temperature below a threshold temperature (T _M ), for which the filaments (22) are not substantially degraded, has a viscosity rendering it suitable for an extrusion process, characterized in that the die (24) comprises a plurality of helically twisted strands in a first direction, each of the strands including a plurality of naturally occurring filaments (22) twisted helically in a second direction, opposite or otherwise in the first sense.

2. A core according to claim 1, characterized in that the threshold temperature (T _M ) is less than 130 ° C, in particular equal to 1 1 0 ° C.

3. Soul according to one of claims 1 and 2, characterized in that said threshold temperature defines the maximum value (T _M ) of a range of working temperatures, the minimum value (T _m ) corresponds to a viscosity only, below which the material is adapted to said extrusion process.

4. - Soul according to revendication 3, characterized in that the minimum temperature (T _m ) is greater than 70 ° C, in particular equal to 90 ° C.

5. Core according to one of claims 3 and 4, characterized in that the viscosity only is less than 2500 Pa .s, in particular equal to 1500 Pa .s at 100 ° C, this viscosity being measured according to ISO standard 1,133.

6. - Soul according to one of the preceding claims, characterized in that the viscosity of the material of the thermoplastic matrix is greater than 500 Pa.s, the viscosity being measured according to ISO 1133.

7. - Soul according to one of claims 3 and 4, characterized in that the viscosity only is less than 1 80 Pa .s, in particular equal to 50 Pa .s, this viscosity being measured according to DIN 53018 .

8. Soul according to one of the preceding claims, characterized in that the matrix (24) comprises a single thermoplastic material.

9. A core according to one of claims 1 to 8, characterized in that the matrix (24) comprises a mixture of several thermoplastic materials.

10. - Soul according to one of claims 8 or 9, characterized in that the or a m o n n o n d m ate ri a u x th ermo p l astiq ues is polyamide or polyurethane.

1 1. Soul according to any one of the preceding claims, characterized in that at least one of the filaments (22) of natural origin is a silk filament.

12- Soul according to any one of the preceding claims, characterized in that it comprises at least one protective outer sheath (26).

13. Rope for racket, comprising at least one core according to any one of the preceding claims.

14. A method of manufacturing a core (2) for racket rope, in particular for tennis racket rope, the core comprising a plurality of filaments (22), the method comprising the following steps:

twisting a plurality of filaments (22) in a helical manner in a first direction, and then twisting a plurality of strands, comprising a plurality of twisted filaments (22) helically in a second direction, opposite or not in the first sense,

passing the plurality of filaments (22) comprising at least one filament of natural origin, into a preparation bath comprising a first thermoplastic material dissolved in a solvent, at ambient temperature and at atmospheric pressure, and

passing the plurality of filaments (22) into an extruder head (18) impregnated with a second thermoplastic material which at a temperature below a threshold temperature (T _M ), for which the filaments (22) do not are substantially not degraded, has a viscosity making it suitable for an extrusion process.

15. A process according to claim 14, characterized in that the speed of the filaments (22) during passage into the bath is adapted to allow impregnation of the first thermoplastic material in each of the filaments.