Process and device for the manufacture of a string for stringing tennis rackets or the like and string resulting therefrom

Abstract

A process according to which filaments are embedded in a thermoplastic substance. The filaments pass through a chamber which is filled with a thermoplastic substance under pressure and made viscous by heating and the filaments run over a number of return members, thus having the effect of embedding the filaments in a matrix consisting of the thermoplastic. On leaving the chamber, the filaments pass through at least one die with the matrix in which they are embedded. The pseudo monofilament thus formed is subjected to a twist and is coated with a sheath of wear-resistant thermoplastic substance.

I claim: 
     
       1. A process for the manufacture of a tennis string intended for stringing rackets in which filaments are embedded in a thermoplastic substance, wherein the filaments pass through a chamber filled with the thermoplastic substance under pressure and made viscous by heating in which the filaments run over a number of return members, thus having the effect of embedding the filaments in a matrix consisting of the thermoplastic substance, on leaving the chamber the filaments pass through at least one die with the matrix in which they are embedded, thus forming a pseudo monofilament that is subjected to a twist and is coated with a sheath of wear-resistant thermoplastic substance. 
     
     
       2. The process according to claim 1, wherein on leaving the chamber the filaments embedded in the matrix pass successively through a first die, a second chamber filled with the heated thermoplastic substance and finally a second die prior to twisting. 
     
     
       3. The process of claim 1, wherein the pseudo monofilament is wound onto a reel on leaving the at least one die said reel is placed in a rotating unwinder which is used to rotate said reel about its lengthwise axis and about a transverse axis perpendicular to the lengthwise axis, the pseudo monofilament situated thereon is unwound from the reel while applying thereto a rotation about the two above-mentioned orthogonal axes of rotation, which imparts the desired twist to the pseudo monofilament. 
     
     
       4. The process according to claim 3, wherein the pseudo monofilament is subjected to a twist of 30 to 150 turns/m. 
     
     
       5. The process of claim 3, wherein a twist of 60 to 100 turns/m is applied. 
     
     
       6. The process according to claim 4, wherein during the twist the pseudo monofilament passes through a heating tube. 
     
     
       7. The process according to claim 3, wherein the action of twisting the pseudo monofilament occurs over a length of the pseudo monofilament between a roller brake rotating with the unwinder and a stationary roller brake. 
     
     
       8. The process according to claim 1, wherein filaments (32) are employed made of plastic of one of the group consisting of polyester, polyamide, polyamide 4.6, aramid, polyimide, polyester ketone and polyethylene. 
     
     
       9. The process according to claim 1, wherein a plastic of one of the group consisting of polyamide, polyamide 4.6, copolyamide, polyester, polyurethane, polyethylene, polypropylene, hot melt adhesives and elastomers is employed for at least one of embedding the filaments (32) and sheathing the pseudo monofilament (30). 
     
     
       10. The process according to claim 1, wherein a melting point of the embedding matrix is lower than that of the filaments. 
     
     
       11. The process of claim 1, wherein a melting point of the embedding matrix is approximately equal to that of the filaments. 
     
     
       12. The process according to claim 1, wherein a melting point of the thermoplastic substance forming the sheath is lower than that of the filaments. 
     
     
       13. A tennis string obtained by the process according to claim 1. 
     
     
       14. The tennis string according to claim 13, wherein the proportion of filament is approximately between 55 and 90% by weight. 
     
     
       15. The tennis string according to claim 13, wherein the number of pseudo monofilaments is approximately between 700 and 2,800. 
     
     
       16. A device for manufacturing a tennis string, comprising: a chamber intended to receive a thermoplastic substance made viscous by heating and containing return members to divert filaments a number of times within the viscous plastic and embedding the filaments in a matrix consisting of the thermoplastic material; and at least one die downstream from said chamber for forming a pseudo monofilament. 
     
     
       17. The device according to claim 16, wherein at an exit of the chamber is arranged for the filaments embedded in the plastic to pass therethrough. 
     
     
       18. The device according to claim 17, wherein a first die and a second die are arranged at the exit of the chamber. 
     
     
       19. The device according to claim 18, wherein the diameter of the second die is slightly greater than that of the first die. 
     
     
       20. The device according to claim 16, further comprising a rotating unwinder which allows a reel containing the pseudo monofilament to be rotated about its lengthwise axis and about a transverse axis perpendicular to the lengthwise axis and in that this rotating unwinder is also provided with a roller brake rotating therewith, in order to limit a twisting action on said pseudo monofilaments to a length situated downstream of the roller brake. 
     
     
       21. The device according to claim 20, wherein a stationary roller brake is provided, arranged at a certain distance from the rotating roller brake. 
     
     
       22. The device according to claim 20, wherein downstream of the rotating unwinder, a sheathing tool is provided for sheathing the pseudo monofilament with an outer sheath of good mechanical strength. 
     
     
       23. The device according to claim 22, wherein the sheathing tool has a chamber for receiving a molten polymer, an entry opening and an exit die. 
     
     
       24. The device according to claim 23, wherein a vacuum chamber is used in combination with the sheathing tool. 
     
     
       25. The device according to claim 18, wherein a diameter of the second die is greater than that of the first die by 2%-6%.