Racket string

Abstract

This racket string includes a filament. The filament contains a polymer matrix and carbon nanotubes that are dispersed in the polymer matrix. The polymer matrix is composed of one kind of thermoplastic polymer, or two or more kinds of thermoplastic polymers having compatibility. A racket includes the racket string. A method for producing the racket string includes: a step for mixing and dispersing carbon nanotubes in a first thermoplastic polymer; a step for obtaining a thermoplastic composition by mixing a first thermoplastic polymer, in which the carbon nanotubes are dispersed, and a second thermoplastic polymer having compatibility with the first thermoplastic polymer; and a step for obtaining a filament by melt-spinning the thermoplastic composition.

Description

Racket strings

[0001] The present disclosure relates to strings used in rackets for tennis, soft tennis, squash, badminton, and the like.

[0002] Rackets for tennis, badminton, squash, etc. are equipped with a frame and strings (sometimes called guts). In recent years, strings made of synthetic resin filaments have become increasingly popular.

[0003] The string stretched on the frame is subjected to tensile tension. Therefore, small cracks or notches on the outer surface of the string can become the starting point for fracture. It is known that such fractures are particularly likely to occur in monofilament strings made of a single polymer material or a polymer alloy material. From the standpoint of durability, instead of a simple monofilament structure, strings with a smaller-diameter monofilament wound around the outside of a core monofilament or multifilament, or braided strings, are used.

[0004] Japanese Patent Publication No. 2010-510400 (Patent Document 1) discloses a string composed of a monofilament core wrapped with multiple small-diameter multifilaments, a buffer layer filling gaps between the multifilaments, and an outer coating covering the entire structure. In Patent Document 1, a composite material of nylon and carbon nanotubes is used as the outer coating material. Japanese Patent Publication No. 2007-181553 (Patent Document 2) discloses a racket string having a resin coating layer on its outer surface. The resin coating layer includes a synthetic resin and ultrafine carbon fibers with a solid coaxial multilayer structure in which graphene sheet tubes are stacked concentrically to the center of the tube.

[0005] As proposed in Patent Documents 1 and 2, the surface properties of the string can be changed by coating the outer surface of the string with a resin. However, there is a problem in that the elastic modulus of the string cannot be sufficiently controlled.

[0006] Japanese Patent Laid-Open Publication No. 2023-017526 (Patent Document 3) proposes a racket string made of filaments that are melt-spun from a blend of a thermoplastic polymer in which carbon nanotubes are dispersed and a thermoplastic polymer matrix. The thermoplastic polymer in which carbon nanotubes are dispersed and the thermoplastic polymer matrix are incompatible, with the thermoplastic polymer matrix forming a sea component and the thermoplastic polymer in which carbon nanotubes are dispersed forming island components.

[0007] JP-T-2010-510400A JP-A-2007-181553 JP-A-2023-017526

[0008] According to Patent Document 3, the elastic modulus of the string can be controlled to improve the shot feel and flight performance, but there is still room for improvement in the durability and resilience performance of the string.

[0009] An object of the present disclosure is to provide a racquet string with improved durability and resilience.

[0010] The racquet string comprises filaments containing a polymer matrix and carbon nanotubes dispersed in the polymer matrix, the polymer matrix being composed of one or more compatible thermoplastic polymers.

[0011] The method for manufacturing this racket string includes: (1) a step of mixing and dispersing carbon nanotubes in a first thermoplastic polymer; (2) a step of mixing the first thermoplastic polymer in which the carbon nanotubes have been dispersed with a second thermoplastic polymer that is compatible with the first thermoplastic polymer to obtain a thermoplastic composition; and (3) a step of melt-spinning the thermoplastic composition to obtain filaments.

[0012] According to the present disclosure, it is possible to control the loss factor as well as the modulus of elasticity of the filaments, which are the main components of the string. The racket string according to the present disclosure achieves a balance between shot feel and shot flight, and also has improved durability and resilience.

[0013] Fig. 1 is a front view of a racket according to one embodiment of the present disclosure. Fig. 2 is an enlarged perspective view of a portion of the string of the racket of Fig. 1. Fig. 3 is a cross-sectional view of the string taken along line III-III of Fig. 2. Fig. 4 is a cross-sectional view of a string according to another embodiment of the present disclosure.

[0014] Hereinafter, the present disclosure will be described in detail based on preferred embodiments, with reference to the accompanying drawings. In this specification, the range "X to Y" means "X or more and Y or less." Unless otherwise noted, all test temperatures are room temperature (20°C ± 5°C).

[0015] (Racket String) A racket string according to the present disclosure includes filaments. The filaments contain a polymer matrix and carbon nanotubes dispersed in the polymer matrix. The polymer matrix is ​​composed of one or more compatible thermoplastic polymers. Here, "compatible" refers to a state in which the polymers are miscible with each other at the molecular level. As long as the effects of the present disclosure are obtained, the degree of miscibility is not limited, and the polymers may be completely miscible or partially miscible with each other. In this specification, partial miscibility is sometimes referred to as "partial miscibility." Note that "incompatible" refers to a state in which the polymers are not miscible with each other at the molecular level.

[0016] As a result of extensive research, the present inventors have found that when a sea-island structure is formed in a polymer matrix composed of two or more thermoplastic polymers, the adhesion between the sea region and the island region affects the durability of the string. For example, if the polymers constituting the sea region and the polymers constituting the island region are incompatible, carbon nanotubes will be arranged in the island region, but the sea-island adhesion will be poor, which may result in reduced durability. In contrast, as described above, the filaments provided in the string of the present disclosure have a polymer matrix composed of one or two or more compatible thermoplastic polymers. Therefore, even when a sea-island structure is formed in the polymer matrix, mixing of the polymer components occurs at the molecular level at the interface between the sea region and the island region. As a result, the adhesion between the sea region and the island region is improved, and the durability of the string is improved. Furthermore, the present inventors have unexpectedly found that by constructing a polymer matrix from one or two or more compatible thermoplastic polymers, the loss tangent tan δ of the filament at a predetermined frequency or a predetermined temperature is reduced, significantly improving resilience. By providing filaments in which carbon nanotubes are dispersed in a polymer matrix of this configuration, the elastic modulus of the string can be controlled to obtain a desired feel and ball flight performance. According to the present disclosure, a racket string can be obtained that maintains excellent feel and ball flight performance while also improving durability and resilience.

[0017] 1 shows a racket 2 equipped with a string 10 according to one embodiment of the present disclosure. The racket 2 is a tennis racket. The tennis racket 2 can be used for hard tennis. The string 10 may also be used for rackets for soft tennis, squash, badminton, etc.

[0018] As shown in Figure 1, this tennis racket 2 includes a frame 4 and a grip 6. The frame 4 has a head 12 that defines the outline of a face 14. The front shape of the head 12 is approximately elliptical. The major axis direction of the ellipse coincides with the axial direction Y of the tennis racket 2. The minor axis direction of the ellipse coincides with the width direction X of the tennis racket 2.

[0019] The strings 10 are strung around the head 12. The strings 10 are strung along the width direction X and the axial direction Y. The portions of the strings 10 that extend along the width direction X are called cross strings 10a. The portions of the strings 10 that extend along the axial direction Y are called main strings 10b. The multiple cross strings 10a and the multiple main strings 10b form a face 14. The face 14 is generally aligned along the X-Y plane.

[0020] FIG. 2 shows a string 10. This string 10 has a monofilament structure composed of the filaments described above. FIG. 3 is a cross-sectional view showing a cut surface of the string 10 taken along line III-III in FIG. 2. According to the present disclosure, in addition to the improved durability due to the polymer matrix configuration described above, the suppression effect of microcracks by carbon nanotubes allows a significant improvement in durability to be achieved even with a simple monofilament structure. The string 10 may have a multifilament structure formed by twisting multiple filaments. The string 10 may have a coating on its surface.

[0021] 4 is a cross-sectional view of a racket string 20 according to another embodiment of the present invention. This string 20 includes a core thread 22, multiple skin threads 24 that cover the core thread 22, and a coating resin layer 26 that covers the core thread 22 and the outer surfaces of the multiple skin threads 24. In this specification, the configuration of this string 20 is referred to as a "core-skin structure." In this string 20, either or both of the core thread 22 and the skin threads 24 may be the filaments described above. From the perspective of making it easier to achieve the effects of the present disclosure, it is preferable that at least the core thread 22 be the filament described above.

[0022] The core yarn 22 may have a monofilament structure or a multifilament structure. The fiber diameter of the sheath yarn 24 is preferably smaller than that of the core yarn 22. Multiple sheath yarns 24 may be wound around the outside of the core yarn 22, or may be braided to cover the core yarn 22. From the viewpoint of manufacturing costs, a configuration in which multiple sheath yarns 24 are wound around the outside of the core yarn 22 is preferred.

[0023] As mentioned above, the filaments of the string of the present disclosure include a polymer matrix with dispersed carbon nanotubes. Below, we will explain in more detail two embodiments: A) in which the polymer matrix is ​​composed of one thermoplastic polymer, and B) in which the polymer matrix is ​​composed of two or more compatible thermoplastic polymers.

[0024] (Aspect A) In Aspect A, the polymer matrix is ​​composed of one type of thermoplastic polymer. A so-called sea-island structure is not formed in the polymer matrix of Aspect A. The polymer matrix of Aspect A can contribute to improving the durability and resilience of the string.

[0025] Furthermore, in the polymer matrix of Aspect A, the carbon nanotubes are not uniformly dispersed, but exhibit a non-uniform dispersion state. In other words, a concentration gradient of carbon nanotubes is formed in the polymer matrix of Aspect A. Here, "concentration gradient" means that the concentration changes gradually (or continuously) from a high concentration region to a low concentration region, and refers to a state in which the interface between the high concentration region and the low concentration region is unclear. In Aspect A, the elastic modulus of the filament can be controlled by adjusting the dispersion state of the carbon nanotubes. As long as the effects of the present disclosure are obtained, the polymer matrix of Aspect A may have a region that does not contain carbon nanotubes.

[0026] (Aspect B) In Aspect B, the polymer matrix is ​​composed of two or more thermoplastic polymers. A polymer matrix composed of two or more completely compatible thermoplastic polymers (Aspect B1) does not form a so-called sea-island structure. The polymer matrix of Aspect B1 has a concentration gradient of carbon nanotubes, as described in Aspect A. The polymer matrix of Aspect B1 can contribute to improving the durability and resilience of the string. Furthermore, in Aspect B1, the elastic modulus of the filaments can be controlled by adjusting the dispersion state of the carbon nanotubes.

[0027] In a polymer matrix (Aspect B2) composed of two or more partially compatible thermoplastic polymers, a sea-island structure is formed according to the compatibility of the mixed thermoplastic polymers. Specifically, the sea region and the island regions each contain different types of thermoplastic polymers (polymer components). In this Aspect B2, the polymer component constituting the sea region and the polymer component constituting the island region are compatible. At the interface between the sea region and the island region, the polymer component constituting the sea region and the polymer component constituting the island region are at least partially miscible. In other words, in the polymer matrix of Aspect B2, a sea-island structure is formed in which the polymer component constituting the island region and the polymer component constituting the sea region are miscible at the interface between the island region and the sea region. Here, "miscible" means that the molecular chains of the polymer component in the sea region have penetrated into the island region and / or the molecular chains of the polymer component in the island region have penetrated into the sea region. In this sea-island structure, the sea region and the island region do not easily separate. The adhesion between the sea region and the island region is high. The polymer matrix of embodiment B2 can contribute to improving the durability of the string.

[0028] Furthermore, in the polymer matrix of Aspect B2, most of the carbon nanotubes are contained in the island regions. Preferably, at the interface between the island regions and the sea region, the carbon nanotubes diffuse from the island regions toward the sea region. In other words, a concentration gradient is formed in the polymer matrix of Aspect B2, in which the carbon nanotubes diffuse from the island regions toward the sea region. In Aspect B2, the elastic modulus of the filament can be controlled by adjusting the concentration gradient (diffusion state) of the carbon nanotubes. The concentration gradient (diffusion state) of the carbon nanotubes depends mainly on the degree of compatibility between the polymer components constituting the island regions and the polymer components constituting the sea region. The concentration gradient of the carbon nanotubes can be adjusted by selecting the combination of each polymer component.

[0029] Next, examples of materials constituting the racket string of the present disclosure will be described.

[0030] (Carbon nanotubes) Carbon nanotubes are generally materials having a tube structure in which graphene sheets having a six-membered carbon ring arrangement structure are rolled up into a cylindrical shape. As long as the effects of the present disclosure can be obtained, they may be single-walled carbon nanotubes having one graphene sheet, or multi-walled carbon nanotubes consisting of two or more graphene sheets.

[0031] From the viewpoint of improving dispersibility in thermoplastic polymers, the relative filling amount reduction rate of carbon nanotubes is preferably 4% or less, more preferably 3% or less, and even more preferably 2% or less. Here, the relative filling amount reduction rate (%) is determined by adding 1.64 g of sample carbon nanotubes to a mixed solvent of 180 mL of distilled water and 900 mL of t-butyl alcohol, stirring the mixture at 400 rpm for 15 hours using a stirrer, and then allowing the mixture to stand for two weeks. The volume occupied by the carbon nanotubes before standing is taken as 100%, and the volume occupied by the carbon nanotubes after standing is then taken as the ratio (%) of the volume occupied by the carbon nanotubes after standing.

[0032] The method for producing carbon nanotubes is not particularly limited, and commercially available carbon nanotubes can be appropriately selected and used. From the viewpoint of improving mixing and dispersibility with thermoplastic polymers, crushed carbon nanotubes are preferred. As long as the effects of the present disclosure can be obtained, the crushing method is not particularly limited, and may be a wet method or a dry method. A method of crushing aggregated carbon nanotubes without crushing the carbon nanotubes is preferred, and crushing treatment using a wet method is more preferred.

[0033] An example of a wet method is to subject a slurry of carbon nanotubes to high-speed, high-shear treatment using a wet jet mill or the like by vortex flow. A slurry of carbon nanotubes can be obtained by adding and mixing carbon nanotubes available in powder or flake form to water, an organic solvent, or a mixed solvent of water and an organic solvent. Examples of such organic solvents include t-butyl alcohol, isopropyl alcohol, and N-methylpyrrolidone. An example of a dry method is to crush carbon nanotubes available in powder or flake form using a ball mill or the like.

[0034] From the viewpoint of obtaining a string with a balanced feel and flight performance by controlling the elastic modulus of the filaments, the carbon nanotube content, when the filaments are taken as 100% by mass, is preferably 0.001% by mass or more, more preferably 0.002% by mass or more, even more preferably 0.003% by mass or more, particularly preferably 0.004% by mass or more, and is preferably 1.0% by mass or less, more preferably 0.5% by mass or less, even more preferably 0.1% by mass or less, and particularly preferably 0.01% by mass or less.

[0035] (Thermoplastic polymer) In this specification, "thermoplastic" refers to the property of softening or melting and becoming moldable above a certain temperature, and solidifying when cooled, and "thermoplastic polymer" refers to a polymer having this property. Specific examples of such thermoplastic polymers include polyamide (nylon), polyester, polyolefin, modified polyolefin, etc. Polyamide (nylon) is preferred from the viewpoints of excellent strength and elongation, knot strength, and durability, and, when surface coating is applied, good adhesion to the coating layer.

[0036] Examples of polyamides (nylons) include polyamide 6, polyamide 66, polyamide 11, and polyamide 12. Examples of polyesters include polyethylene terephthalate (PET) and polybutylene terephthalate (PBT). Examples of polyolefins include high-density polyethylene (HDPE), medium-density polyethylene (MDPE), low-density polyethylene (LDPE), low-pressure polyethylene (LIDPE), and polypropylene (PP). Examples of modified polyolefins include copolymers of olefins and unsaturated acids or acid anhydrides, polyolefins grafted with unsaturated acids or acid anhydrides, and copolymers of polyolefins and polyolefins grafted with unsaturated acids or acid anhydrides. A suitable example of modified polyolefin is maleic acid-modified polyethylene. High-density polyethylene (HDPE) and low-pressure polyethylene (LIDPE) can be used as the polyethylene that serves as the base for maleic acid-modified polyethylene.

[0037] Two or more thermoplastic polymers may be used in combination as long as the effects of the present disclosure are achieved. Preferably, the filaments of the string of the present disclosure contain a polymer matrix composed of one or more thermoplastic polymers selected from the group consisting of polyamide 6, polyamide 66, polyamide 11, polyamide 12, and maleic acid-modified polyethylene.

[0038] The thermoplastic polymer constituting the polymer matrix of the above-described embodiment A is preferably one selected from the group consisting of polyamide 6, polyamide 66, polyamide 11, polyamide 12, and maleic acid-modified polyethylene, and polyamide 6 is more preferred.

[0039] The thermoplastic polymer constituting the polymer matrix of the above-mentioned embodiment B is preferably two or more selected from the group consisting of polyamide 6, polyamide 66, polyamide 11, polyamide 12 and maleic acid-modified polyethylene.

[0040] In the sea-island structure formed in the polymer matrix of Aspect B, from the viewpoint of obtaining high adhesion between the sea region and the island region, the absolute value of the difference between the SP value of the thermoplastic polymer constituting the sea region and the SP value of the thermoplastic polymer constituting the island region is preferably 3.0 or less, more preferably 2.5 or less, even more preferably 2.0 or less, and particularly preferably 1.5 or less. The smaller the absolute value of the SP value, the higher the degree of compatibility. Here, the "SP value" is also called the solubility parameter, and can be calculated by the Fedors method or the like with reference to Polymer Handbook (4th Edition, J. Brandrup, E. H. Immergut, published 1999). For example, polyamide 6 (SP value: 12.7), polyamide 66 (SP value: 13.6), polyamide 11 (SP value: 12.3), polyamide 12 (SP value: 12.1), maleic acid-modified polyethylene (SP value: 8.7), and polyethylene (SP value: 7.9).

[0041] In a preferred embodiment, the thermoplastic polymer constituting the sea region is nylon, and the thermoplastic polymer constituting the island region is maleic acid-modified polyethylene. The nylon constituting the sea region may be selected from the group consisting of polyamide 6, polyamide 66, polyamide 11, and polyamide 12.

[0042] In another preferred embodiment, the thermoplastic polymer constituting the sea region is a first nylon, and the thermoplastic polymer constituting the island region is a second nylon, with the first nylon and the second nylon being different combinations. In other words, in this embodiment, the thermoplastic polymer constituting the sea region is a nylon, and the thermoplastic polymer constituting the island region is a different type of nylon from the thermoplastic polymer constituting the sea region. The first nylon and the second nylon may be selected from the group consisting of polyamide 6, polyamide 66, polyamide 11, and polyamide 12. More preferably, the first nylon is polyamide 6, and the second nylon is selected from the group consisting of polyamide 66, polyamide 11, and polyamide 12.

[0043] In Aspect B (particularly Aspect B2), the elastic modulus of the filaments can be controlled by adjusting the ratio of the island regions containing carbon nanotubes to the sea regions. From the viewpoint of obtaining a string with a balanced shot feel and ball flight performance, when the filaments are taken as 100% by mass, the total content of the thermoplastic polymer constituting the island regions and the carbon nanotubes is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, even more preferably 0.3% by mass or more, particularly preferably 0.5% by mass or more, and preferably 10.0% by mass or less, more preferably 9.0% by mass or less, even more preferably 8.0% by mass or less, and particularly preferably 5.0% by mass or less.

[0044] The content of the thermoplastic polymer constituting the sea region is appropriately selected depending on the content of the island region containing carbon nanotubes. From the viewpoint of controlling the elastic modulus of the filament, when the filament is taken as 100 mass%, the total content of the thermoplastic polymer constituting the sea region is preferably 90.0 mass% or more, more preferably 95.0 mass% or more, even more preferably 96.0 mass% or more, particularly preferably 98.0 mass% or more, and is preferably 99.9 mass% or less, more preferably 99.8 mass% or less, even more preferably 99.7 mass% or less, particularly preferably 99.5 mass% or less.

[0045] (Resin Coating Layer) The racket string of the present disclosure may be provided with a resin coating layer that coats its surface. This resin is preferably nylon 6 or nylon 6.12. Nylon 6.12 is a co-condensation product of the amino acids caprolactam (carbon number 6) and lauryllactam (carbon number 12). Nylon 6.12 is said to have approximately half the water absorption of nylon 66. Nylon 12, which has even lower water absorption, may also be used.

[0046] (Method for Manufacturing a Racket String) The method for manufacturing a racket string of the present disclosure includes the steps of mixing and dispersing carbon nanotubes in a first thermoplastic polymer, mixing the first thermoplastic polymer in which the carbon nanotubes are dispersed with a second thermoplastic polymer that is compatible with the first thermoplastic polymer to obtain a thermoplastic composition, and melt-spinning the thermoplastic composition to obtain a filament. This manufacturing method may further include a step of crushing the carbon nanotubes before the step of mixing and dispersing the carbon nanotubes in the first thermoplastic polymer. This manufacturing method may further include a step of resin-coating the surface of the obtained filament. Alternatively, the method may further include a step of using the obtained filament as a core yarn or a skin yarn, arranging multiple skin yarns around the core yarn, and then resin-coating the core yarn and skin yarn so as to cover the core yarn and the skin yarn.

[0047] Hereinafter, a manufacturing method according to an embodiment of the present disclosure will be exemplified and described in detail.

[0048] (1) Process for crushing carbon nanotubes In this process, carbon nanotubes are first mixed with water, an organic solvent, or a mixed solvent of water and an organic solvent to obtain a carbon nanotube slurry. This slurry is subjected to high-speed, high-shear treatment by vortex flow using a wet jet mill to crush the carbon nanotubes. It is preferable to select crushing conditions so that a relative loading reduction rate within the aforementioned range is obtained. The crushed slurry is then dried to obtain crushed carbon nanotubes. Freeze drying or the like is used for drying.

[0049] (2) Step of mixing and dispersing carbon nanotubes in a first thermoplastic polymer In this step, carbon nanotubes (preferably, carbon nanotubes after a crushing treatment) are mixed and dispersed in a first thermoplastic polymer to obtain a carbon nanotube-containing masterbatch.

[0050] When an islands-in-a-sea structure is formed in a polymer matrix, the first thermoplastic polymer is the polymer component that primarily forms the island regions. This first thermoplastic polymer may be selected from the thermoplastic polymers described above. Preferably, the first thermoplastic polymer is selected from the group consisting of polyamide 6, polyamide 66, polyamide 11, polyamide 12, and maleated polyethylene. In one embodiment, a preferred first thermoplastic polymer is maleated polyethylene. In another embodiment, the first thermoplastic polymer may be selected from polyamide 66, polyamide 11, and polyamide 12.

[0051] The method for obtaining the carbon nanotube-containing masterbatch is not particularly limited. For example, crushed and dried carbon nanotubes may be melted and kneaded with a first thermoplastic polymer, dispersed and mixed, and extruded, then cooled to form pellets, or the pellets may be crushed and turned into powder. Alternatively, a slurry containing carbon nanotubes may be crushed and then melt-kneaded with a first thermoplastic polymer without drying. In this case, the carbon nanotubes may be mixed and dispersed in a first thermoplastic polymer while removing water or an organic solvent from the slurry by volatilization or the like, and extruded, then cooled to obtain pellets or powder.

[0052] (3) A step of mixing a first thermoplastic polymer having dispersed carbon nanotubes with a second thermoplastic polymer compatible with the first thermoplastic polymer to obtain a thermoplastic composition. In this step, the carbon nanotube-containing masterbatch obtained in the previous step is mixed with the second thermoplastic polymer to produce a thermoplastic composition. Melt kneading may be used for mixing. Known additives such as fillers, colorants, antioxidants, UV absorbers, and antiaging agents may be added to the thermoplastic composition within a range that achieves the effects of the present disclosure.

[0053] When an islands-in-a-sea structure is formed in a polymer matrix, the second thermoplastic polymer is the polymer component that primarily forms the sea region, and is also referred to herein as the "matrix polymer." This second thermoplastic polymer is selected from the aforementioned thermoplastic polymers so long as it is compatible with the first thermoplastic polymer. Preferably, the second thermoplastic polymer is selected from the group consisting of polyamide 6, polyamide 66, polyamide 11, polyamide 12, and maleic acid-modified polyethylene. In one embodiment, a preferred second thermoplastic polymer is nylon, more preferably selected from the group consisting of polyamide 6, polyamide 66, polyamide 11, and polyamide 12, with polyamide 6 being even more preferred. In another embodiment, the second thermoplastic polymer is preferably selected from the group consisting of polyamide 6, polyamide 66, polyamide 11, and polyamide 12, with polyamide 6 being even more preferred.

[0054] The elastic modulus of the filament can be controlled by adjusting the mixing ratio of the carbon nanotube-containing masterbatch (i.e., the first thermoplastic polymer in which carbon nanotubes are dispersed) and the matrix polymer (i.e., the second thermoplastic polymer). A thermoplastic composition obtained by mixing 0.1% by mass or more and 10% by mass or less of the first thermoplastic polymer in which carbon nanotubes are dispersed and 90% by mass or more and 99.9% by mass or less of the second thermoplastic polymer is preferred.

[0055] From the viewpoint of achieving a balance between the hitting feel and ball flight performance of the resulting string, the amount of the first thermoplastic polymer having dispersed carbon nanotubes is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, even more preferably 0.3% by mass or more, and particularly preferably 0.5% by mass or more, and is preferably 10.0% by mass or less, more preferably 9.0% by mass or less, even more preferably 8.0% by mass or less, and particularly preferably 5.0% by mass or less.

[0056] From the same viewpoint, the amount of the second thermoplastic polymer is preferably 90.0% by mass or more, more preferably 95.0% by mass or more, even more preferably 96.0% by mass or more, particularly preferably 98.0% by mass or more, and is preferably 99.9% by mass or less, more preferably 99.8% by mass or less, even more preferably 99.7% by mass or less, particularly preferably 99.5% by mass or less.

[0057] From the viewpoint of controlling the elastic modulus of the filaments to obtain a favorable hitting feel and ball flight performance, when the thermoplastic composition is taken as 100% by mass, the content of carbon nanotubes is preferably 0.001% by mass or more, more preferably 0.002% by mass or more, even more preferably 0.003% by mass or more, particularly preferably 0.004% by mass or more, and is preferably 1.0% by mass or less, more preferably 0.5% by mass or less, even more preferably 0.1% by mass or less, and particularly preferably 0.01% by mass or less.

[0058] (4) Step of melt-spinning the thermoplastic composition to obtain a filament In this step, the obtained thermoplastic composition is melt-spun to produce a filament. Known methods can be used to produce the filament. Typically, the filament is produced by extruding the heated and molten thermoplastic composition through a die and stretching it while cooling. The carbon nanotube-containing masterbatch and the base polymer may be charged into a known extruder so as to have the above-mentioned mixing ratio, melt-mixed, and then extruded and stretched to produce the filament. The fiber diameter of the filament can be selected appropriately depending on the application.

[0059] (5) Step of Manufacturing a Racquet String Using Filaments In this step, a racket string is manufactured using the filaments obtained by melt spinning. The filaments (monofilaments) obtained by melt spinning may be used as the racket string of the present disclosure as is. Alternatively, a multifilament obtained by twisting multiple filaments after melt spinning may be used as the racket string of the present disclosure. The outer surface of the filament or multifilament may be coated with the above-mentioned coating resin to form the racket string of the present disclosure.

[0060] The racket string of the present disclosure may be a string with a "core-skin structure" obtained by using filaments obtained by melt spinning as the core yarn and / or skin yarn. Typically, a string with a "core-skin structure" is produced by a process of arranging multiple skin yarns on the surface of a core yarn, and a process of applying a resin coating to cover the core yarn and multiple skin yarns.

[0061] (5.1) Step of arranging sheath yarns on the surface of the core yarn In this step, multiple sheath yarns are arranged on the surface of the core yarn. Either or both of the core yarn and the sheath yarn may be the filament described above. It is preferable that at least the core yarn is the filament described above.

[0062] For example, this step may be carried out by using a monofilament having a diameter of 0.40 to 1.00 mm as the core yarn and wrapping sheath yarns having a diameter of 0.10 to 0.20 mm around the surface of the core yarn in an S-twist configuration to form a covering. The number of sheath yarns is preferably 8 to 40, and more preferably 10 to 20. An adhesive may be applied to the surface of the core yarn. For example, nylon phenolic resin or the like can be used as the adhesive.

[0063] (5.2) Step of Resin Coating the Surfaces of the Core Yarn and Sheath Yarns In this step, the surfaces of the core yarn and multiple sheath yarns are resin-coated to form a resin coating layer on the surfaces. The resins used for the resin coating layer are appropriately selected from those described above.

[0064] For example, nylon 6.12 is melt-coated onto the surfaces of the core yarn and multiple sheath yarns. Nylon 6.12 is melted at 200 to 250°C, and the molten liquid is extruded from a nozzle and supplied to the surfaces of the core yarn and multiple sheath yarns, and a predetermined amount is applied by squeezing with a ring. The resulting mixture is then cooled to form a coating resin layer made of nylon 6.12. The amount of coating resin applied is preferably 1.20 to 1.35 g / m, and more preferably 1.28 to 1.32 g / m.

[0065] [Loss tangent tanδ of string] The loss tangent tanδ obtained by dynamic viscoelasticity measurement reflects the resilience of the string. Here, the loss tangent tanδ is measured by temperature dispersion measurement using a dynamic viscoelasticity measuring device (trade name "GABOMER" manufactured by NETZSCH) under conditions of an initial load of 25 kgf, a frequency of 10 Hz, and a temperature range of -50°C to 50°C.

[0066] Specifically, data indicates that the contact time when hitting with a stringed racket is 2 msec to 4 msec, which corresponds to a frequency of 250 to 500 Hz. Assuming that the actual hitting condition is 20°C, Δ10°C corresponds to a single-digit frequency ratio. Considering the difference of two digits in the frequency ratio of the actual hitting frequency of 10 Hz, which is the viscoelasticity measurement condition, the loss tangent tanδ (0°C) at 0°C is compared to a full swing shot. Furthermore, a half swing shot such as a touch shot is compared to the loss tangent tanδ (10°C) at 10°C.

[0067] Since good bite is required for half swing shots and moderate resilience is required for full swing shots, the ratio tan δ(10°C) / tan δ(0°C) is preferably large, more preferably 1.14 or more, even more preferably 1.15 or more, and particularly preferably 1.18 or more. The upper limit of the ratio tan δ(10°C) / tan δ(0°C) is not particularly limited, but is preferably 1.60 or less.

[0068] From the viewpoint of obtaining a favorable repulsion feel, the smaller tan δ (0°C) is the better, and 0.032 or less is more preferable, 0.031 or less is even more preferable, and 0.030 or less is particularly preferable. The lower limit of tan δ (0°C) is not particularly limited, but is preferably 0.022 or more.

[0069] The effects of the present disclosure will be clarified below by examples, but the present disclosure should not be interpreted as being limited based on the description of these examples.

[0070] Example A-1: ​​Crushing of Carbon Nanotubes (1) 20 g of multi-walled carbon nanotubes (trade name "NC7000" manufactured by Nanocyl Corporation, average diameter 9.5 nm, average length 1.5 μm) were added to 2000 mL of distilled water and stirred overnight at 400 rpm using a stirrer to obtain a slurry. (2) The obtained slurry was subjected to high-speed, high-shear treatment using a wet jet mill (manufactured by Joko Co., Ltd., trade name: NAGS100) with three vortex flows at a processing pressure of 100 MPa, thereby crushing the multi-walled carbon nanotubes. (3) 1000 mL of the crushed carbon nanotube slurry was dried in two 500 mL portions using a freeze-drying device (LS-6 freeze-dryer manufactured by Purisu Co., Ltd.) to obtain 6.7 g of crushed carbon nanotube powder.

[0071] <Relative Packing Volume Reduction Rate of Carbon Nanotubes> 1.64 g of the resulting crushed carbon nanotube powder was added to a mixed solvent of 180 mL of distilled water and 900 mL of t-butyl alcohol, and the mixture was stirred at 400 rpm using a stirrer for 15 hours to disperse the powder in the mixed solvent, obtaining a dispersion. This dispersion was transferred to a vial (volume 1,800 ml) and allowed to stand for two weeks. The volume of the carbon nanotubes in the dispersion was measured before and after standing, and the ratio of the volume occupied by the carbon nanotubes after standing to the volume occupied by the carbon nanotubes before standing (relative packing volume reduction rate) was 1%.

[0072] <Mixing and Dispersion of Carbon Nanotubes in Thermoplastic Polymer> (4) Dry Mixing 1.5 g of the disintegrated carbon nanotube powder obtained in (3) and 300 g of modified polyethylene resin pellets (maleic acid-modified polyethylene manufactured by SK Functional Polymers, product name "BONDINE HX8290") were mixed by shaking in a sealed container to obtain a mixture. This mixture was kneaded at a temperature of 150°C in a twin-screw extruder (KZW15TW-45MG-NH(-700) manufactured by Technovel Corporation) to obtain a carbon nanotube / modified polyethylene 0.5 phr masterbatch containing 0.5 parts by mass of carbon nanotubes (CNTs) per 100 parts by mass of modified polyethylene (modified PE).

[0073] (5) Wet Mixing Instead of the dry mixing of (4), a carbon nanotube / modified polyethylene 0.5 phr masterbatch obtained by wet mixing can also be used. In the case of wet mixing, 4000 mL of the slurry of disintegrated carbon nanotubes obtained in (2) and 8000 g of modified polyethylene resin pellets (maleic acid-modified polyethylene manufactured by SK Functional Polymers, trade name "BONDINEHX8290") are mixed at a temperature of 160°C in a twin-screw extruder (TEM-26SS-10 / 2V manufactured by Shibaura Machine Co., Ltd.) to obtain a carbon nanotube / modified polyethylene 0.5 phr masterbatch.

[0074] <Mixing of Masterbatch and Base Polymer> 515 g of the carbon nanotube / modified polyethylene 0.5 phr masterbatch and 51.5 kg of nylon resin pellets (Polyamide 6 manufactured by DSM, product name "1020J"), which is the base polymer, were kneaded in a twin-screw extruder at a temperature of 240°C to obtain a spinning composition (PA6 / modified PE / CNT) having a mass ratio of carbon nanotubes / modified polyethylene / nylon 6 = 0.005 / 1 / 99.

[0075] <Production of Racket String> The resulting spinning composition (PA6 / modified PE / CNT) was extruded at 240°C using a melt spinning apparatus and spun at a draw ratio of 4 and a post-draw shrinkage of 4%, yielding a monofilament with a fiber diameter of 1.26 mm. This monofilament was used as is for the string of Example A-1.

[0076] [Example A-2 and Comparative Example A-2] The strings of Example A-2 and Comparative Example A-2 were obtained in the same manner as in Example A-1, except that the modified polyethylene resin pellets were replaced with nylon resin pellets (Polyamide 12 manufactured by Degussa, trade name "VESTAMID LX9012") and polyethylene resin pellets (Japan Polyethylene Co., Ltd. trade name "Kernel KC580S"), respectively.

[0077] [Comparative Example A-1] 515 g of polyethylene resin pellets (trade name "Kernel KC580S" manufactured by Japan Polyethylene Co., Ltd.) and 51.5 kg of nylon resin pellets (polyamide 6 manufactured by DSM, trade name "1020J"), which is the base polymer, were kneaded in a twin-screw extruder at a temperature of 240°C to obtain a spinning composition (PA6 / PE) with a mass ratio of polyethylene / nylon 6 = 1 / 99. The string of Comparative Example A-1 was obtained by melt spinning in the same manner as in Example A-1, except that this spinning composition (PA6 / PE) was used.

[0078] Example B-1: A spinning composition (PA6 / modified PE / CNT) obtained in the same manner as in Example A-1 was extruded at 240°C using a melt spinning apparatus and spun at a draw ratio of 4x and a post-draw shrinkage of 4%, yielding a core filament with a fiber diameter of 0.88 mm. Separately, separately prepared nylon resin pellets (Polyamide 6, product name "1020J" manufactured by DSM) were similarly melt spun to obtain a sheath filament with a fiber diameter of 0.22 mm. The output rate from the melt spinning apparatus was adjusted to obtain the desired fiber diameter. A phenolic adhesive was applied to the obtained core filament, and 15 sheath filaments were then wound around it, dried, and coated with nylon 66 resin to obtain the string of Example B-1.

[0079] [Comparative Example B-1] A spinning composition (PA6 / PE / CNT) obtained in the same manner as in Comparative Example A-2 was extruded at 240°C in a melt spinning apparatus and spun at a draw ratio of 4 and a post-draw shrinkage of 4%, to obtain a core filament with a fiber diameter of 0.88 mm and a sheath filament with a fiber diameter of 0.22 mm. Using these core filaments and sheath filaments, the string of Comparative Example B-1 was obtained in the same manner as in Example B-2.

[0080] Comparative Example B-2 The string of Comparative Example B-2 was obtained in the same manner as in Comparative Example B-1, except that nylon resin pellets (Polyamide 6 manufactured by DSM, product name "1020J") were used to obtain the sheath filaments.

[0081] [Comparative Example B-3] The string of Comparative Example B-3 was obtained in the same manner as in Comparative Example B-1, except that nylon resin pellets (Polyamide 6 manufactured by DSM, product name "1020J") were used to obtain the core filaments and the sheath filaments.

[0082] [Tensile Properties] Tensile tests were conducted in accordance with JIS L1013 to determine the tensile strength (unit: N), breaking elongation (unit: %), and elastic modulus (unit: GPa) of the strings of the Examples and Comparative Examples. The diameter (fiber diameter) of each string was measured using a micrometer. For the tensile tests, a tensile tester (Shimadzu Corporation's "Autograph AGS-100NX") was used, and measurements were taken under the following conditions. The average values ​​of five measurements are shown in Tables 1 and 2 below. Chuck distance: 254 mm Gauge length: 150 mm Pulling speed: 254 mm / min Plot interval: 100 msec Ambient temperature: 25°C

[0083] [Stiffness and Rebound Rate] A single string was tensioned with a tension of 50 pounds, and both ends were fixed with clamps (grip distance 30 cm). A pendulum hammer was swung down from a fixed position so as to strike the center of the string horizontally at a right angle to the string. The movement (displacement) and stress of the string after the strike were measured at intervals of 1 / 1000 seconds, and the stiffness (unit: pounds / inch) and rebound rate (unit: %) were calculated using the following method: Stiffness (lb / inch) = Maximum stress P (lb) / Maximum displacement L (horizontal, inch) Rebound rate (%) = (S2 / S1) x 100 In the formula, S1 is the area of ​​the portion from the strike to the maximum displacement (forward portion) on the stress-strain (displacement) curve (round trip), and S2 is the area from the maximum displacement position to zero displacement (return portion) on the stress-strain curve.

[0084] The results are shown in Tables 1 and 2 below as stiffness and resilience. A higher stiffness value indicates a harder feel when hit with the string strung on a racket, while a lower value indicates a softer feel when hit. Also, a higher resilience value indicates less energy loss on impact and greater resilience.

[0085] [Holding Feeling] A string was tensioned with 50 pounds and clamped at both ends (grip distance 30 cm). A pendulum hammer was swung from a fixed position so as to strike the center of the string horizontally at a right angle to the string, and the time (unit: seconds) that the hammer was in contact with the string was measured. This contact time is shown as the holding feel in Tables 1 and 2 below.

[0086] [Maximum Displacement] A string was pulled with a tension of 50 pounds and both ends were fixed with clamps (grip distance 30 cm). A pendulum hammer was swung from a fixed position so as to strike the center of the string horizontally at a right angle to the string, and the amount of distortion (movement) of the string at the time of the hammer strike was measured. This distortion (unit: mm) is shown as the maximum displacement in Tables 1 and 2 below.

[0087] [Loss Tangent tanδ] The loss tangent of each string was measured using a dynamic viscoelasticity measuring device (trade name "GABOMETER" manufactured by NETZSCH). Specifically, temperature dispersion measurements were performed under conditions of an initial load of 25 kgf, a frequency of 10 Hz, and temperatures ranging from -50°C to 50°C. The loss tangent tanδ(0°C) at 0°C and the loss tangent tanδ(10°C) at 10°C were measured for each string, and the ratio tanδ(10°C) / tanδ(0°C) was calculated. The results are shown in Tables 1 and 2 below. The larger the ratio tanδ(10°C) / tanδ(0°C), the higher the evaluation, and the smaller the ratio tanδ(0°C), the higher the evaluation.

[0088] [Durability] A soft tennis racket was strung with a string of 40 pounds and left for 24 hours, after which soft tennis balls were hit with the racket (conditions: ball speed 100 km / h, hit interval 15 times / min, hit distance 50 cm, hit angle 40 degrees, hitting four points on the racket in sequence), and the number of hits until the string broke was measured. The average value of a total of three tests is shown in Tables 1 and 2 below as durability. The higher the number, the higher the evaluation.

[0089]

[0090]

[0091] Details of the compounds listed in Tables 1 and 2 are as follows: CNT: Multi-walled carbon nanotubes manufactured by Nanocyl (trade name "NC7000", average diameter 9.5 nm, average length 1.5 μm) that have been crushed PA6: Nylon resin pellets manufactured by DSM (polyamide 6, trade name "1020J"), SP value: 12.7 PA12: Nylon resin pellets manufactured by Degussa (polyamide 12, trade name "VESTAMID LX9012"), SP value: 12.1 PE: Polyethylene resin pellets manufactured by Japan Polyethylene Co., Ltd., trade name "Kernel KC580S", SP value: 7.9 Modified PE: Maleic acid-modified polyethylene resin pellets manufactured by SK Functional Polymers, trade name "BONDINE HX8290", SP value: 8.7

[0092] [Racket Manufacturing and Evaluation] The strings of the Examples and Comparative Examples were strung on tennis rackets of the same weight and balance. A total of 10 adult males, including one professional tennis player, hit tennis balls with each racket and evaluated the results using the scoring system shown in Tables 3 and 4 below for each item. All evaluations were conducted indoors on a hard court. The evaluations were performed using a relative scale ranging from 1 to 5, with the control being given a score of 3.0. The average scores of the 10 panelists are shown in Tables 3 and 4 below. For the monofilament string (Table 3), a commercially available polyester string (Reference Example 1) was used as the control, and for the core-skin string (Table 4), the string of Comparative Example B-1 was used as the control.

[0093]

[0094]

[0095] As shown in Table 1-2, the strings of the examples are more durable than the strings of the comparative examples. Furthermore, the strings of the examples generally have good ball release, do not stick too much, have good repulsion, and transmit vibrations easily. Furthermore, as shown in Table 3-4, the rackets of the examples received higher overall ratings than the rackets of the comparative examples. These evaluation results clearly demonstrate the superiority of the present disclosure.

[0096] Disclosed Items Each of the following items discloses a preferred embodiment.

[0097] [Item 1] A racket string comprising filaments, the filaments including a polymer matrix and carbon nanotubes dispersed in the polymer matrix, the polymer matrix being composed of one or two or more compatible thermoplastic polymers.

[0098] [Item 2] The racket string according to Item 1, wherein the polymer matrix is ​​made of one type of thermoplastic polymer, and a concentration gradient of the carbon nanotubes is formed in the polymer matrix.

[0099] [Item 3] The racket string according to Item 1, wherein the polymer matrix is ​​made of two or more types of thermoplastic polymers, wherein the polymer matrix has a sea-island structure at the interface between the island regions and the sea region in which the polymer components constituting the island regions and the polymer components constituting the sea region are mixed, and wherein a concentration gradient is formed in which the carbon nanotubes diffuse from the island regions toward the sea region.

[0100] [Item 4] A racket string according to any one of Items 1 to 3, wherein the carbon nanotubes have a relative packing volume reduction rate of 4% or less, as determined by the following method: (Method for measuring the relative packing volume reduction rate: 1.64 g of sample carbon nanotubes is placed in a mixed solvent of 180 mL of distilled water and 900 mL of t-butyl alcohol, stirred at 400 rpm using a stirrer for 15 hours, and then allowed to stand for two weeks. The volume occupied by the carbon nanotubes before standing is taken as 100%, and the ratio of the volume occupied by the carbon nanotubes after standing is calculated as the relative packing volume reduction rate (%).)

[0101] [Item 5] The racket string according to any one of Items 1 to 4, wherein the carbon nanotube content is 0.001% by mass or more and 1.0% by mass or less, when the filaments are taken as 100% by mass.

[0102] [Item 6] The racket string according to any one of Items 3 to 5, wherein, when the filaments are taken as 100% by mass, the total content of the thermoplastic polymer forming the island regions and the carbon nanotubes is 0.1% by mass or more and 10.0% by mass or less, and the content of the thermoplastic polymer forming the sea regions is 90.0% by mass or more and 99.9% by mass or less.

[0103] [Item 7] The racket string according to any one of Items 3 to 6, wherein the absolute value of the difference between the SP value of the thermoplastic polymer constituting the sea region and the SP value of the thermoplastic polymer constituting the island region is 3.0 or less.

[0104] [Item 8] The racket string according to any one of Items 3 to 7, wherein the thermoplastic polymer forming the sea regions is nylon, and the thermoplastic polymer forming the island regions is maleic acid-modified polyethylene.

[0105] [Item 9] The racket string according to any one of Items 3 to 8, wherein the thermoplastic polymer forming the sea region is nylon, and the thermoplastic polymer forming the island region is a different type of nylon from the thermoplastic polymer forming the sea region.

[0106] [Item 10] The racket string according to any one of Items 1 to 9, wherein the thermoplastic polymer is selected from the group consisting of polyamide 6, polyamide 66, polyamide 11, polyamide 12, and maleic acid-modified polyethylene.

[0107] [Item 11] A racket string according to any one of Items 1 to 10, wherein the filament is a monofilament and the racket string is constructed from this monofilament.

[0108] [Item 12] A racket string according to any one of Items 1 to 10, comprising a core yarn, a skin yarn covering the core yarn, and a covering resin layer covering the core yarn and the outer surface of the skin yarn, wherein at least one of the core yarn and the skin yarn is the filament.

[0109] [Item 13] A racket equipped with the racket string according to any one of items 1 to 12.

[0110] [Item 14] A method for manufacturing a racket string according to Item 1, comprising the steps of: mixing and dispersing carbon nanotubes in a first thermoplastic polymer; mixing the first thermoplastic polymer in which the carbon nanotubes have been dispersed with a second thermoplastic polymer that is compatible with the first thermoplastic polymer to obtain a thermoplastic composition; and melt-spinning the thermoplastic composition to obtain filaments.

[0111] [Item 15] The method for manufacturing a racket string according to Item 14, wherein the thermoplastic composition is obtained by mixing 0.1% by mass or more and 10.0% by mass or less of the first thermoplastic polymer having dispersed therein carbon nanotubes with 90.0% by mass or more and 99.9% by mass or less of the second thermoplastic polymer.

[0112] [Item 16] The method for manufacturing a racket string according to Item 14 or 15, wherein the content of the carbon nanotubes is 0.001% by mass or more and 1.0% by mass or less when the thermoplastic composition is taken as 100% by mass.

[0113] The racket strings described above are suitable for a variety of sports, including hard tennis, soft tennis, badminton, and squash.

[0114] 2... Tennis racket 4... Frame 6... Grip 10, 20... Strings 10a... Horizontal strings 10b... Longitudinal strings 12... Head 14... Face 22... Core thread 24... Leather thread 26... Coating resin layer

Claims

1. A racquet string comprising filaments, the filaments including a polymer matrix and carbon nanotubes dispersed in the polymer matrix, the polymer matrix being composed of one or more compatible thermoplastic polymers.

2. The racquet string according to claim 1, wherein the polymer matrix is ​​made of one type of thermoplastic polymer, and a concentration gradient of the carbon nanotubes is formed in the polymer matrix.

3. The racket string according to claim 1, wherein the polymer matrix is ​​composed of two or more types of thermoplastic polymers, the polymer matrix has a sea-island structure at the interface between the island regions and the sea region in which the polymer components constituting the island regions and the polymer components constituting the sea region are mixed, and a concentration gradient is formed in which the carbon nanotubes diffuse from the island regions toward the sea region.

4. The racket string according to claim 1, wherein the carbon nanotubes have a relative packing volume reduction rate of 4% or less, as determined by the following method: (Method of measuring the relative packing volume reduction rate: 1.64 g of sample carbon nanotubes is placed in a mixed solvent of 180 mL of distilled water and 900 mL of t-butyl alcohol, stirred at 400 rpm with a stirrer for 15 hours, and then allowed to stand for two weeks. The volume occupied by the carbon nanotubes before standing is taken as 100%, and the ratio of the volume occupied by the carbon nanotubes after standing is determined as the relative packing volume reduction rate (%).) 5. The racket string as set forth in claim 1, wherein the carbon nanotube content is equal to or greater than 0.001% by mass and equal to or less than 1.0% by mass when the filaments are taken as 100% by mass.

6. A racket string as described in claim 3, wherein, when the filaments are taken as 100% by mass, the total content of the thermoplastic polymer constituting the island regions and the carbon nanotubes is 0.1% by mass or more and 10.0% by mass or less, and the content of the thermoplastic polymer constituting the sea regions is 90.0% by mass or more and 99.9% by mass or less.

7. The racket string according to claim 3, wherein the absolute value of the difference between the SP value of the thermoplastic polymer constituting the sea region and the SP value of the thermoplastic polymer constituting the island region is 3.0 or less.

8. The racquet string according to claim 3, wherein the thermoplastic polymer constituting the sea regions is nylon, and the thermoplastic polymer constituting the island regions is maleic acid modified polyethylene.

9. The racquet string according to claim 3, wherein the thermoplastic polymer forming the sea regions is nylon, and the thermoplastic polymer forming the island regions is a different type of nylon from the thermoplastic polymer forming the sea regions.

10. The racquet string of claim 1, wherein said thermoplastic polymer is selected from the group consisting of polyamide 6, polyamide 66, polyamide 11, polyamide 12 and maleated polyethylene.

11. The racquet string of claim 1, wherein said filament is a monofilament and is constructed from said monofilament.

12. The racket string according to claim 1, comprising a core thread, a skin thread covering said core thread, and a resin covering layer covering from said core thread to the outside of said skin thread, wherein at least one of said core thread and said skin thread is said filament.

13. A racquet comprising the racquet string of claim 1.

14. A method for producing a racquet string as claimed in claim 1, comprising the steps of: mixing and dispersing carbon nanotubes in a first thermoplastic polymer; mixing the first thermoplastic polymer in which the carbon nanotubes are dispersed with a second thermoplastic polymer that is compatible with the first thermoplastic polymer to obtain a thermoplastic composition; and melt spinning the thermoplastic composition to obtain filaments.

15. A method for producing a racquet string as described in claim 14, wherein the thermoplastic composition is obtained by mixing 0.1% by mass or more and 10.0% by mass or less of the first thermoplastic polymer having the carbon nanotubes dispersed therein with 90.0% by mass or more and 99.9% by mass or less of the second thermoplastic polymer.

16. The method for manufacturing a racket string as set forth in claim 14, wherein the content of said carbon nanotubes is 0.001% by mass or more and 1.0% by mass or less when the thermoplastic composition is taken as 100% by mass.

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