Monofilament string for use in string racket sports

Abstract

A monofilament string for use in string racket sports, wherein the monofilament string comprises: a covering material; a core material embedded in the covering material, wherein the core material comprises: a sea region comprising a thermoplastic elastomer; and a plurality of island regions comprising a thermoplastic plastic doped with one or more doping agents, wherein the plurality of island regions is embedded in the sea region; and wherein a geometry and/or a distribution of the island regions in the sea region is such that a tangent modulus of a stress-strain curve of the monofilament string increases with increasing strain in a playing stress range.

Claims

1. A monofilament string for use in string racket sports, wherein said monofilament string comprises: a covering material; a core material embedded in said covering material, wherein said core material comprises: a sea region comprising a thermoplastic elastomer; and a plurality of island regions comprising a thermoplastic plastic doped with one or more doping agents, wherein said plurality of island regions is embedded in said sea region; and wherein a size shape and/or a distribution of said island regions in said sea region is such that a tangent modulus of a stress-strain curve of said monofilament string increases with increasing strain in a playing stress range.

2. The monofilament string according to claim 1, wherein said distribution of said island regions is such that said island regions are arranged in a geometrical pattern relative to each other and/or to a longitudinal axis of said monofilament string.

3. The monofilament string according to claim 1, wherein said size and shape of said island regions is such that each of said island regions comprises a cross-section with a substantially circular shape and with one surface side facing a surface of said covering material of said monofilament string such that said surface side displays a curvature which lines said curvature of said surface of said covering material of said monofilament string.

4. The monofilament string according to claim 1, wherein said size and shape and said distribution of said island regions are such that each of said island regions comprises a cross-section with a substantially circular shape and with at least one contact side facing at least one contact side of another island region.

5. The monofilament string according to claim 1, wherein said monofilament string comprises three island regions.

6. The monofilament string according to claim 5, wherein each of said island regions comprises one surface side facing a surface of said covering material of said monofilament string such that said surface side displays a curvature which lines said curvature of said surface of said covering material of said monofilament string; and wherein each of said island regions further comprises two contact sides, wherein each contact side of an island region faces a contact side of another island region.

7. The monofilament string according to claim 1, wherein said playing stress range corresponds to a total force applied to said monofilament string comprised between 150 Newton and 400 Newton.

8. The monofilament string according to claim 1, wherein said tangent modulus of said stress-strain curve is comprised between 2000 MPa and 5000 MPa.

9. The monofilament string according to claim 1, wherein a strain is produced when hitting a tennis ball with said monofilament string with a total force comprised between 210 Newton and 250 Newton that is larger than a strain produced when hitting a tennis ball with said monofilament string with a total force comprised between 270 Newton and 320 Newton.

10. The monofilament string according to claim 1, wherein said thermoplastic plastic of said island regions comprises one polymer from the group of thermoplastic polyesters and/or a copolymer and/or a block copolymer and/or a mixture of two or more of these polymers.

11. The monofilament string according to claim 1, wherein said one or more doping agents further comprise a thermoplastic elastomer dispersed in said thermoplastic plastic.

12. The monofilament string according to claim 1, wherein said one or more doping agents comprise a siloxane polymer dispersed in said thermoplastic plastic.

13. A method for manufacturing a monofilament string for use in string racket sports, said method comprising the steps of: providing a covering material; providing a core material; embedding said core material in said covering material by forming a sea region comprising a thermoplastic elastomer and by embedding a plurality of island regions comprising a thermoplastic plastic doped with one or more doping agents in said sea region, thereby forming a monofilament string matrix, and wherein a size, shape and/or a distribution of said island regions in said sea region is such that a tangent modulus of a stress-strain curve of said monofilament string increases with increasing strain in a playing stress range; extruding said monofilament string matrix; cooling said monofilament string matrix; subjecting said monofilament string matrix to a process cycle comprising: stretching said monofilament string matrix, thereby resulting in a stretched monofilament string matrix; annealing said stretched monofilament string matrix; thereby forming said monofilament string.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 schematically illustrates an embodiment of a monofilament string according to the present invention.

(2) FIG. 2 schematically illustrates an embodiment of a stress-strain curve of a monofilament string according to the present invention.

(3) FIG. 3 schematically illustrates an embodiment of a method according to the present invention.

DETAILED DESCRIPTION OF EMBODIMENT(S)

(4) According to an embodiment shown in FIG. 1, a cross-section of a monofilament string 1 along a longitudinal axis 6 is schematically depicted. A monofilament string 1 comprises a covering material 100 and a core material 200 embedded in the covering material 100. The core material 200 comprises a sea region 201. The sea region 201 comprises a thermoplastic elastomer 21. The core material further comprises three island regions 202 which each comprise a thermoplastic plastic 22 doped with one or more doping agents 32. The island regions 202 are embedded in the sea region 201. The island regions 202 are arranged in a geometrical pattern with respect to each other and with respect to a longitudinal axis 6 of the monofilament string 1. The longitudinal axis 6 is traverse to a first axial axis 13 of the monofilament string 1 and is also traverse to a second axial axis 14 traverse to the first axial axis 13. The geometry of the island regions 202 is such that each of the island regions 202 comprises a cross-section with a semi-circular shape and with one surface side 222 leaning close against a surface 110 of the covering material of the monofilament string 1 such the surface side 222 displays a curvature which lines the curvature of the surface 110 of the covering material of the monofilament string. The geometry and the distribution of the island regions 202 are such that each of the island regions 202 comprises a cross-section with a substantially circular shape and with at least one contact side 223 leaning close against at least one contact side 223 of another island region 202. Each of the island regions 202 further comprises two contact sides 223, wherein each contact side 223 of an island region 202 leans close against a contact side 223 of another island region 202. Preferably, the geometry of the island regions 202 is such that each of the island regions 202 comprises a cross-section with a circular shape. As visible on FIG. 1, the three island regions 202 have identical surfaces on the cross-section along the longitudinal axis 6. According to an alternative embodiment, the three island regions 202 have different surfaces on the cross-section along the longitudinal axis 6.

(5) According to an embodiment shown in FIG. 2, a stress 15 versus strain 16 curve 4 of a monofilament string according to the present invention is schematically depicted. The geometry and/or a distribution of the island regions 202 in the sea region 201 is such that a tangent modulus 3 of a stress-strain curve 4 of the monofilament string 1 increases with increasing strain in a playing stress range 5. The playing stress range 5 corresponds to a total force applied to the monofilament string comprised between 150 Newton and 400 Newton. The tangent modulus 3 of the stress-strain curve 4 is comprised between 2000 MPa and 5000 MPa. A soft feeling is produced when hitting a tennis ball with the monofilament string with a total force comprised between 210 Newton and 250 Newton, and a hard feeling is produced when hitting a tennis ball with the monofilament string with a total force comprised between 270 Newton and 320 Newton. The monofilament string demonstrates a larger elasticity than a standard monofilament string 17 and a larger elasticity than a standard monofilament string 18 with ‘islands in the sea’ in a playing stress range 5. The stress-strain curve 4 of the monofilament string demonstrates a positive curvature in the playing stress range 5, while the stress-strain curves of a prior art standard monofilament 17 and a prior art standard monofilament 18 with ‘islands in the sea’ both demonstrate a negative curvature or a constant tangent modulus in the same playing stress range. The geometry and/or a distribution of the island regions in the sea region of the monofilament string is such that a stress-strain curve 4 of the monofilament string comprises a positive curvature, i.e. a positive derivative of the derivative of the stress-strain curve, in a playing stress range 5. In the playing stress range 5 and at constant stress 7, a monofilament string wherein one or more doping agents comprise a siloxane polymer demonstrates a strain 8 that is 4 to 15% larger than a strain 9 demonstrated by a prior art standard monofilament string 18 wherein one or more doping agents comprise a thermoplastic elastomer. A breaking stress 11 of a monofilament string wherein one or more doping agents comprise a siloxane polymer is 10 to 15% larger than a breaking stress 12 of a monofilament string 18 wherein one or more doping agents comprise a thermoplastic elastomer.

(6) An embodiment of the method according to the present invention is depicted in FIG. 3. In step 401, a covering material 100 and a core material 200 are provided. The core material 200 and the covering material 100 are provided in pellets and are melted at a temperature comprised between 260 and 280° C. The core material 200 is embedded in the covering material 100 by forming a sea region comprising a thermoplastic elastomer and by embedding a plurality of island regions comprising a thermoplastic plastic doped with one or more doping agents in the sea region, thereby forming a monofilament string matrix 300. The island regions are formed by embedding a plurality of island regions comprising a thermoplastic plastic doped with one or more doping agents in the sea region corresponds to forming island regions in the sea region wherein the island regions comprise a cross-section with a substantially circular shape and with at least one contact side leaning close against at least one contact side of another island region and with one surface side leaning close against a surface of the covering material of the monofilament string matrix such the surface side displays a curvature which lines the curvature of the surface of the covering material of the monofilament string matrix 300. The monofilament string matrix 300 is extruded in step 401. Although one would expect that the thermoplastic elastomer degrades if it is heated up to a temperature that is too high, it was established that this effect in the monofilament string 1 is negligible and a string with a good strength, tensile strength, consistent characteristics and lifespan is obtained. In consecutive step 402, the monofilament string matrix 300 is quenched and cooled down to a temperature comprised between 30 and 60° C. The monofilament string matrix 300 is then subjected in consecutive steps 403 to 410 to a process cycle 30. The process cycle 30 comprises four times stretching the monofilament string matrix 300, thereby resulting in a stretched monofilament string matrix 300, and four respectively consecutive anneals of the stretched monofilament string matrix 300. The first stretching degree is comprised between 3 and 4 and the first anneal is performed at a temperature comprised between 140 and 190° C. The second stretching degree is comprised between 1.5 and 2.5 and the second anneal is performed at a temperature comprised between 180 and 230° C. The third stretching degree is comprised between 0.8 and 1.2 and the third anneal is performed at a temperature comprised between 180 and 230° C. The fourth stretching degree is comprised between 0.9 and 1.3 and the fourth anneal is performed at a temperature comprised between 100 and 150° C. After the process cycle 30, the monofilament string 1 is formed.

(7) Although the present invention has been illustrated by reference to specific embodiments, it will be apparent to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied with various changes and modifications without departing from the scope thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. In other words, it is contemplated to cover any and all modifications, variations or equivalents that fall within the scope of the basic underlying principles and whose essential attributes are claimed in this patent application. It will furthermore be understood by the reader of this patent application that the words “comprising” or “comprise” do not exclude other elements or steps, that the words “a” or “an” do not exclude a plurality, and that a single element, such as a computer system, a processor, or another integrated unit may fulfil the functions of several means recited in the claims. Any reference signs in the claims shall not be construed as limiting the respective claims concerned. The terms “first”, “second”, third”, “a”, “b”, “c”, and the like, when used in the description or in the claims are introduced to distinguish between similar elements or steps and are not necessarily describing a sequential or chronological order. Similarly, the terms “top”, “bottom”, “over”, “under”, and the like are introduced for descriptive purposes and not necessarily to denote relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and embodiments of the invention are capable of operating according to the present invention in other sequences, or in orientations different from the one(s) described or illustrated above.