WO2010018343A1 - String for a racket, particularly for a tennis racket - Google Patents

Abstract

The invention relates to a string for a racket, particularly for a tennis racket, which includes: a central core (2) and a peripheral protective layer (6). Additionally, the string includes an intermediate reinforcing layer (4) made of a composite material and placed between the central core (2) and the peripheral protective layer (6), the hardness of the reinforcing layer (4; 14; 24; 34) being greater than the hardness of the protective layer (6; 16; 26; 36), the reinforcing layer providing a function of increasing the resistance to wear and tear, while the protective layer provides a function of increasing sliding.

Description

 ROPE FOR RACKETS, IN PARTICULAR FOR TENNIS RACKETS

The present invention relates to a racket rope, in particular a rope for a tennis racket.

In racquet sports, a racket with a handle and a frame is used. A rope is stretched longitudinally and transversely across the frame, the rope being intended to undergo the impact of the ball.

It is known to use a rope having a composite structure, the rope comprising a central core encased by a peripheral layer over the entire length of the core.

However, the presence of the peripheral layer is not sufficient to provide satisfactory resistance to abrasion and degradation of the central core. The lifespan of the rope is thus limited.

Also known, in particular from EP-A-1 574 134 or WO-A-2008/061229, ropes having a reinforced peripheral layer. For this purpose, this outer layer includes charges, which are for example carbon nanoparticles, or even glass beads.

This alternative solution, however, does not prove sufficient. Indeed, this type of rope is subject to breakage phenomena, especially at the crossing of the rope strands on the sieve. The peripheral layers create abrasion, and cut very quickly causing premature rupture of the rope.

The object of the present invention is to provide a rope sufficiently resistant to wear and not significantly losing its rope tension value in use.

For this purpose, the subject of the invention is a racket rope, in particular for a tennis racket, comprising:

- a central soul, and

- A peripheral protection layer, characterized in that the rope further comprises an intermediate reinforcing layer of composite material, disposed between the central core and the peripheral protection layer, the hardness of the reinforcing layer being greater than the hardness of the protective layer, the reinforcing layer providing a function of increasing the wear resistance, while the protective layer provides a sliding increase function.

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

the intermediate reinforcing layer is a composite sheath;

the intermediate reinforcing layer comprises a matrix and reinforcing fillers, the fillers representing between 10% and 60% by weight of the reinforcing layer, preferably between 25% and 35%;

- the charges are glass beads;

the glass beads have a larger dimension, in particular a diameter, of between 1 μm and 50 μm, preferably between 5 μm and 20 μm;

the fillers are carbon fibers or ceramic particles;

the matrix comprises polyamide;

the central core consists of a monofilament;

the central core comprises multifilaments arranged in a bonding material; - The central core comprises at least three son twisted helically;

- The central core comprises a central filament of diameter d ₂ around which are arranged filaments of diameter d3 helically, so that 02 is greater than d3; the central core is composed of polyamide;

the peripheral protection layer comprises a base polymer, as well as at least one additive intended to increase the slip;

the base polymer is a plastic material, in particular polyamide, polyurethane, polyester or polypropylene, while the slip additive is silicone or PTFE;

the slip additive is present in the peripheral protection layer between 10% and 60% by weight, preferably between 25% and 30%. the central core has a diameter d ₄ of between 0.5 mm and 1.5 mm;

the reinforcing layer has a radial thickness of between 0.01 mm and 0.5 mm;

the peripheral protection layer has a radial thickness β2 of between 0.01 mm and 0.5 mm;

the reinforcing layer is extruded around the central core;

the protective layer is extruded around the reinforcing layer.

The invention will be better understood on reading the description which follows, given solely by way of non-limiting examples and with reference to the drawings in which:

- Figure 1 is a perspective view of a strand of rope according to a first embodiment of the invention;

- Figure 2 is a front view of the rope strand shown in Figure 1, according to the arrow II;

FIG. 3 is a perspective view of a strand of rope according to a second embodiment of the invention;

- Figure 4 is a front view of the rope strand shown in Figure 3, according to the arrow IV; FIG. 5 is a perspective view of a rope strand according to a third embodiment of the invention;

- Figure 6 is a front view of the rope strand shown in Figure 5, according to the arrow Vl;

FIG. 7 is a perspective view of a strand of rope according to a fourth embodiment of the invention; and

- Figure 8 is a front view of the rope strand shown in Figure 7, according to the arrow VIII.

FIGS. 1 and 2 show a strand of rope 1 comprising a central core 2, coated by an intermediate reinforcing layer 4, itself coated by a peripheral protection layer 6.

The central core 2 constituting a substantially homogeneous central body of the rope strand 1 is a monofilament of thermoplastic material. This monofilament is homogeneous from its periphery to its center. The protective layer 6 is uniformly disposed on the periphery of the rope strand 1. This protective layer 6 is thus arranged around the reinforcing layer 4. The protective layer 6 advantageously comprises a base polymer, which is added at least an additive for increasing slip. Such an additive for increasing the slip is intended to lower the coefficient of friction of this peripheral layer 6, compared with the case where it consists solely of the base polymer.

By way of example, the base polymer may be, for example, polyamide, polyurethane, polyester or polypropylene. In addition, the additive for increasing slip is for example silicone or PTFE (TEFLON).

The first function of the protective layer 6 is to protect the reinforcing layer 4 against premature wear of this layer, causing the rupture of the rope. The second function of the protective layer 6 is related to how the string of a racket frame is made. There are many intersections between two strands of rope on the entire surface of the sieve. The two strands of rope are arranged one above the other and are substantially perpendicular. After the player has made a strike in a tennis ball, both strands of rope 1 tend to move relative to each other. In particular, it is important to ensure that the two strands of rope can both be mobile and return to their original position without breaking near their point of contact. The protective layer 6 allows sliding movements of the rope strands relative to each other. The reinforcing layer 4, disposed between the central core 2 and the protective layer 6, is made of composite material. The reinforcing layer 4 comprises a matrix as well as charges embedded in the matrix.

The fillers have a reinforcing function, the purpose of which is to constitute a contribution in hardness to the reinforcing layer 4. The matrix ensures, at the same time, the cohesion of the structure of the reinforcing layer 4 and the transmission of the forces exerted by the bullet to the charges. The fillers increase the mechanical strength of the reinforcing layer 4. In other words, the function of the layer reinforcement 4 is to protect the central core 2 effectively from abrasion or premature degradation of the racket string.

The reinforcing layer 4 of composite material is a composite sheath uniformly and continuously enveloping the central core 2, as shown in Figure 2. The sheath follows the shape of the central core by surrounding it continuously. This structure for the reinforcing layer 4 makes it possible to increase, more especially, the hardness of the layer and, more generally, the resistance of the rope.

The charges arranged in the reinforcing layer 4 constitute between 10% and 60% by weight of this reinforcing layer 4, preferably between 25% and 35%.

By way of example, the charges may be glass beads, the largest dimension of which, in particular the diameter, may be between 1 μm and 50 μm, preferably between 5 μm and 20 μm.

The applicant has noted an increase of at least 25% in the hardness of the polyamide reinforcing layer 4 comprising 30% by weight of glass beads relative to a reinforcing layer consisting solely of polyamide.

In order to ensure a uniform hardness over the entire periphery of the reinforcing layer 4, the glass beads are distributed substantially evenly in the matrix. The presence of glass beads in the reinforcing layer 4 could cause accelerated shear at the crossing of two strands of rope. The protective layer 6 thus avoids such inconvenience and thus prolongs the life of the rope.

Thus, the hardness of the reinforcing layer 4 is greater than the hardness of the peripheral layer 6. This allows each of these two layers to ensure, in particular, their respective function of increasing the wear resistance for the coating layer. reinforcement 4 and increase of the slip for the protective layer 6.

There is therefore a complementarity between the reinforcing layer and the protective layer, involved in the invention. Thus, the reinforcing layer increases the overall strength, which increases the service life. Moreover, the protective layer makes it possible to avoid an abrasion phenomenon, due to the direct contact between two adjacent hard layers. Under these conditions, the invention overcomes the disadvantages of the prior art, represented for example by WO-A-2008/061229. In this solution using a peripheral reinforcing layer, there is a significant abrasion phenomenon, due to contact between these two adjacent hard layers, which leads to premature wear of the rope. The reinforcing fillers may be, in addition to glass beads, carbon fibers or ceramic particles. The matrix of the reinforcing layer is a thermoplastic material that can be, by way of non-limiting examples, polyamide, polyurethane, polyester or polypropylene.

FIGS. 3 and 4, which differ from FIGS. 1 and 2 by the nature of the core, represent a strand of rope 10 comprising a central core 12 uniformly surrounded by the intermediate reinforcing layer 14, itself uniformly surrounded of the peripheral protection layer 16.

The central core 12 comprises multifilaments of a first type of material arranged in a matrix consisting of a second type of material. By way of example, the multifilaments may consist of polyamide and arranged in a polyurethane matrix. This type of rope, flexible and comfortable, is capable of having a satisfactory life due to the integration of the reinforcing layer 14 between the central core 12 and the protective layer 16. Figures 5 and 6 differ Figures 1 to 4 by the nature of the central soul. They represent a strand of rope 20 comprising a central core 22 reinforced by the reinforcing layer 24 disposed around its entire periphery. The peripheral protection layer 26 is disposed around the reinforcing layer 24. The central core 22 comprises three wires 22 _1; 22 ₂ , 22 ₃ twisted relative to each other helically along a longitudinal axis XX corresponding to the central axis of the rope strand 20. The son 22i, 22 ₂ , 22 ₃ have circular sections each defining a diameter di less than the diameter of the central core 22. These son are embedded in a matrix 25, covered by the reinforcing layer 24. The matrix 25 defines a bonding material. This type of rope is flexible and offers satisfactory strength due to the presence of the reinforcing layer 24. FIGS. 7 and 8, which differ from FIGS. 1 to 6 by the nature of the core, represent a portion of cord 30 provided with a so-called gimped core 32 covered on its periphery by the reinforcing layer 34, itself covered by the protective layer 36. The guiped core 32 comprises a central monofilament 33 of diameter d ₂ , around which are arranged in a helical manner monofilaments 35 of diameter d ₃ . The diameter d ₂ is substantially greater than the diameter d ₃ . The monofilaments 35 constitute hair wraps integrally connected by glue. The presence of the reinforcing layer 34 makes it possible to extend the life of such a rope with a core 32.

The cores 2, 12, 22 and 32 are made of thermoplastic material that can be, by way of non-limiting examples, polyamide, polyurethane, polyester and / or polypropylene.

As a variant not shown, it can be provided a composite core core comprising a central body of a first type of material surrounded by a sheath over its entire periphery made of a second material.

Each central core 2, 12, 22 and 32 has a diameter d ₄ substantially between 0.5 mm and 1.5 mm. Each intermediate reinforcing layer 4, 14, 24 and 34 has a radial thickness ei of between 0.01 mm and 0.5 mm, in particular between 0.05 mm and 0.5 mm. Each peripheral protection layer 6, 16, 26 and 36 has a radial thickness e ₂ of between 0.01 mm and 0.5 mm, in particular between 0.05 mm and 0.5 mm.

A non-limiting example of a method of manufacturing a rope strand 1, 10,

20, 30 according to the present invention is to use an extruder. The central core 2, 12, 22 or 32 passes into an extruder head while the material serving as reinforcing layer 4, 14, 24 or 34 is worked in pressure and temperature to achieve the first sheathing of the core Central.

In a second step, this first cladding then passes into the extruder head. The material used to make the peripheral protection layer 6, 16, 26 or 36 is in turn worked with pressure and temperature to achieve the second cladding around the first cladding.

Such a manufacturing method allows, in a first step, to adhere the reinforcing layer 4, 14, 24 or 34 around the central core in the manner a cladding and then to adhere the protective layer 6, 16, 26 or 36, at the periphery of the reinforcing layer in the manner of a cladding also.

Claims

1. Rope for racket, in particular for tennis racket, comprising: - a central core (2; 12; 22; 32), and - A peripheral protection layer (6; 16; 26; 36), characterized in that the rope further comprises an intermediate reinforcing layer (4; 14; 24; 34) of composite material disposed between the core central (2; 12; 22; 32) and the peripheral protection layer (6; 16; 26; 36), the hardness of the reinforcing layer (4; 14; 24; 34) being greater than the hardness of the layer protective layer (6; 16; 26; 36), the reinforcing layer providing a function of increasing the wear resistance, while the protective layer provides a sliding increase function. 2. Rope according to claim 1, characterized in that the intermediate reinforcing layer (4; 14; 24; 34) is a composite sheath. 3. Rope according to claim 1 or 2, characterized in that the intermediate reinforcing layer (4; 14; 24; 34) comprises a matrix and reinforcing fillers, the fillers representing between 10% and 60% by weight of the reinforcing layer, preferably between 25% and 35%. 4. Rope according to claim 3, characterized in that the charges are glass beads. 5. Rope according to claim 4, characterized in that the glass beads have a larger dimension, in particular a diameter, between 1 micron and 50 microns, preferably between 5 microns and 20 microns. 6. Rope according to any one of claims 3 to 5, characterized in that the fillers are carbon fibers or ceramic particles. 7. Rope according to any one of claims 3 to 6, characterized in that the matrix comprises polyamide. 8. Rope according to any one of the preceding claims, characterized in that the central core (2) consists of a monofilament. 9. Rope according to any one of claims 1 to 7, characterized in that the central core (12) comprises multifilaments arranged in a bonding material. 10. Rope according to any one of claims 1 to 7, characterized in that the central core (22) comprises at least three twisted son (22i, 22 ₂ , 22 ₃ ), helically. 11. Rope according to any one of claims 1 to 7, characterized in that the central core (32) comprises a central filament (33) of diameter d ₂ around which are arranged filaments (35) of diameter d3 so helical, so that d ₂ is greater than d ₃ . 12. Rope according to any one of the preceding claims, characterized in that the central core (2; 12; 22; 32) is composed of polyamide. 13. Rope according to any one of the preceding claims, characterized in that the peripheral protection layer (6; 16; 26; 36) comprises a base polymer, and at least one additive intended to increase the sliding. 14. Rope according to claim 13, characterized in that the base polymer is a plastic material, in particular polyamide, polyurethane, polyester or polypropylene, while the slip additive is silicone or PTFE. 15. Rope according to claim 13 or 14, characterized in that the slip additive is present in the peripheral protection layer between 10% and 60% by weight, preferably between 25% and 35%. 16. Rope according to any one of the preceding claims, characterized in that the central core (2; 12; 22; 32) has a diameter d ₄ of between 0.5 mm and 1.5 mm. 17. Rope according to any one of the preceding claims, characterized in that the reinforcing layer (4; 14; 24; 34) has a radial thickness ei of between 0.01 mm and 0.5 mm. 18. Rope according to any one of the preceding claims, characterized in that the peripheral protection layer (6; 16; 26; 36) has a radial thickness e ₂ of between 0.01 mm and 0.5 mm. 19. Rope according to any one of the preceding claims, characterized in that the reinforcing layer (4; 14; 24; 34) is extruded around the central core (2; 12; 22; 32). 20. Rope according to any one of the preceding claims, characterized in that the protective layer (6; 16; 26; 36) is extruded around the reinforcing layer (4; 14; 24; 34).