Racket string

Abstract

To provide a racket string with improved repulsion performance and durability.SOLUTION: The 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 with each other. A racket includes the racket string. A method of producing the racket string includes: a step of mixing and dispersing carbon nanotubes in a first thermoplastic polymer; a step of 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 of obtaining a filament by melt-spinning the thermoplastic composition.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present disclosure relates to strings used for rackets such as hard tennis, soft tennis, squash, and badminton.

Background Art

[0002] Rackets such as tennis, badminton, and squash include a frame and strings (sometimes referred to as gut). In recent years, strings composed of synthetic resin filaments have been widely used.

[0003] Tension is applied to the strings stretched on the frame. Therefore, small cracks or notches occurring on the outer surface of the strings may serve as a starting point and lead to breakage. In particular, in the case of strings having a monofilament structure made of a single polymer material or a polymer alloy material, it is known that such breakage is likely to occur. From the viewpoint of durability, instead of a simple monofilament structure, for example, a string in which a small-diameter monofilament is wound around a core monofilament or multifilament, or a braided (string-making) string is used.

[0004] Japanese Patent Publication No. 2010-510400 (Patent Document 1) discloses a string composed of a monofilament core wrapped with a plurality of small-diameter multifilaments, a buffer layer filling the gaps between the multifilaments, and an outer coating covering the whole. In Patent Document 1, a composite material of nylon and carbon nanotubes is used as the outer coating material. Japanese Patent Application Laid-Open No. 2007-181553 (Patent Document 2) discloses a racket string having a resin coating layer on the outer peripheral surface. This resin coating layer contains a synthetic resin and ultra-thin carbon fibers having a solid coaxial multilayer structure in which graphene sheets are laminated in a concentric cylindrical shape up to the center of the cylinder.

[0005] According to the techniques proposed in Patent Documents 1 and 2, the surface characteristics of the string can be changed by resin coating the outer surface of the string. However, there has been a problem that the elastic modulus of the string cannot be sufficiently controlled.

[0006] Japanese Patent Application Laid-Open No. 2023-017526 (Patent Document 3) proposes a racket string composed of filaments obtained by blending a thermoplastic polymer in which carbon nanotubes are dispersed and a base thermoplastic polymer and melt-spinning them. The thermoplastic polymer in which carbon nanotubes are dispersed and the base thermoplastic polymer are incompatible, and the base thermoplastic polymer is the sea component and the thermoplastic polymer in which carbon nanotubes are dispersed is the island component.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0008] According to Patent Document 3, the elastic modulus of the string can be controlled to improve the hitting feeling and flying performance. However, there is still room for improvement in the durability and rebound performance of the string.

[0009] An object of the present disclosure is to provide a racket string with improved durability and rebound performance.

Means for Solving the Problems

[0010] The string for a racket is provided with filaments. The filaments include a polymer matrix and carbon nanotubes dispersed in this polymer matrix. The polymer matrix is composed of one type or two or more thermoplastic polymers having compatibility.

[0011] The manufacturing method of this string for a racket is as follows. (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 carbon nanotubes are dispersed and a second thermoplastic polymer having compatibility with this first thermoplastic polymer to obtain a thermoplastic composition. And (3) A step of melt-spinning the thermoplastic composition to obtain filaments. It includes.

Advantages of the Invention

[0012] According to the present disclosure, in addition to the elastic modulus of the filaments which are the main components of the string, the loss coefficient can be controlled. The string for a racket according to the present disclosure has a balanced hitting feeling and hitting flight property, and further, the durability and the repulsion performance are improved.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

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

[0015] (String for racket) The string for a racket according to the present disclosure includes a filament. This filament contains a polymer matrix and carbon nanotubes dispersed in this polymer matrix. The polymer matrix is composed of one type or two or more thermoplastic polymers having compatibility. Here, "compatible" means a state in which the polymers are miscible at the molecular level. As long as the effects of the present disclosure can be obtained, the degree of miscibility is not limited, and they may be completely miscible or partially miscible. In this specification, the case of partial miscibility may be referred to as "partially compatible". Note that "incompatible" means a state that is not compatible, that is, a state in which the polymers are not miscible at the molecular level.

[0016] As a result of intensive studies, 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, when the polymer forming the sea region and the polymer forming the island region are incompatible, although carbon nanotubes are disposed in the island region, the adhesion between the sea and the island is poor, which may cause a reduction in durability. On the other hand, as described above, the filament included in the string of the present disclosure has 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. Further, the present inventors have unexpectedly found that by forming the 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, and the resilience is significantly improved. By providing a filament in which carbon nanotubes are dispersed in a polymer matrix having such a configuration, the elastic modulus of the string can be controlled to obtain a desired hitting feeling and hitting flight property. According to the present disclosure, a racket string with improved durability and resilience can be obtained while maintaining an excellent hitting feeling and hitting flight property.

[0017] FIG. 1 shows a racket 2 provided with a string 10 according to an embodiment of the present disclosure. This racket 2 is a tennis racket. This tennis racket 2 can be used for hard tennis. The string 10 may be used for rackets such as soft tennis, squash, and badminton.

[0018] As shown in FIG. 1, this tennis racket 2 includes a frame 4 and a grip 6. The frame 4 has a head 12 that forms the contour of the face 14. The front shape of the head 12 is substantially 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 string 10 is stretched on the head 12. The string 10 is stretched along the width direction X and the axial direction Y. The portion of the string 10 that extends along the width direction X is referred to as a cross string 10a. The portion of the string 10 that extends along the axial direction Y is referred to as a longitudinal string 10b. The face 14 is formed by a plurality of cross strings 10a and a plurality of longitudinal strings 10b. The face 14 generally lies along the X-Y plane.

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

[0021] FIG. 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 yarn 22, a plurality of sheath yarns 24 that cover the core yarn 22, and a coating resin layer 26 that covers from the core yarn 22 to the outside of the plurality of sheath yarns 24. In this specification, the configuration of this string 20 is referred to as a "core yarn-sheath yarn structure". In this string 20, either one or both of the core yarn 22 and the sheath yarn 24 may be the filaments described above. From the viewpoint of easily obtaining the effects of the present disclosure, it is preferable that at least the core yarn 22 is 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. The plurality of sheath yarns 24 may be wound around the outside of the core yarn 22 or may be coated as a composite. In terms of manufacturing cost, a configuration in which a plurality of sheath yarns 24 are wound around the outside of the core yarn 22 is preferable.

[0023] As described above, the filament included in the string of the present disclosure includes a polymer matrix in which carbon nanotubes are dispersed. Hereinafter, Mode A in which the polymer matrix is composed of one type of thermoplastic polymer and Mode B in which the polymer matrix is composed of two or more compatible thermoplastic polymers will be described in more detail in sequence.

[0024] (Mode A) In Mode 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 Mode A. The polymer matrix of Mode A can contribute to improving the durability and resilience of the string.

[0025] Also, in the polymer matrix of Mode A, the carbon nanotubes are not uniformly dispersed and show a non-uniform dispersion state. In other words, a concentration gradient of carbon nanotubes is formed in the polymer matrix of Mode A. Here, the "concentration gradient" means that the concentration gradually (or continuously) changes from a high-concentration region to a low-concentration region, and means a state where the interface between the high-concentration region and the low-concentration region is unclear. In Mode 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 can be obtained, the polymer matrix of Mode A may have a region that does not contain carbon nanotubes.

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

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

[0028] In the polymer matrix of Aspect B2, many of the carbon nanotubes are included in the island regions. Preferably, at the interface between the island region and the sea region, the carbon nanotubes diffuse from the island region toward the sea region. In other words, in the polymer matrix of Aspect B2, a concentration gradient is formed in which the carbon nanotubes diffuse from the island region 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 mainly depends on the degree of compatibility between the polymer component forming the island region and the polymer component forming the sea region. By selecting the combination of each polymer component, the concentration gradient of the carbon nanotubes can be adjusted.

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

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

[0031] From the viewpoint of improving the dispersibility in the thermoplastic polymer, the relative filling amount reduction rate of the 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 obtained by putting 1.64 g of carbon nanotubes as a sample into a mixed solvent of 180 mL of distilled water and 900 mL of t-butyl alcohol, stirring at 400 rpm for 15 hours using a stirrer, then allowing to stand for 2 weeks, and taking the ratio (%) of the volume occupied by the carbon nanotubes after standing with the volume occupied by the carbon nanotubes before standing as 100%.

[0032] The manufacturing method of carbon nanotubes is not particularly limited, and commercially available carbon nanotubes can be appropriately selected and used. From the viewpoint of improving the mixing and dispersibility with the thermoplastic polymer, 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 a wet method or a dry method may be used. A method of crushing aggregated carbon nanotubes without crushing the carbon nanotubes is preferred, and a crushing treatment by a wet method is more preferred.

[0033] As the wet method, for example, there is a method of subjecting a slurry-like carbon nanotube to high-speed high-shear treatment by a vortex using a wet jet mill or the like. The slurry-like carbon nanotube can be obtained by adding and mixing a powdery or flaky carbon nanotube that can be obtained in water, an organic solvent, or a mixed solvent of water and an organic solvent. Examples of this organic solvent include t-butyl alcohol, isopropyl alcohol, N-methylpyrrolidone, and the like. As the dry method, for example, there is a method of crushing a powdery or flaky carbon nanotube that can be obtained with a ball mill or the like.

[0034] From the viewpoint of controlling the elastic modulus of the filament to obtain a string with a balanced hitting feeling and hitting flight performance, the content of carbon nanotubes when the filament is 100% by mass is preferably 0.001% by mass or more, more preferably 0.002% by mass or more, still more preferably 0.003% by mass or more, particularly preferably 0.004% by mass or more, and preferably 1.0% by mass or less, more preferably 0.5% by mass or less, still more preferably 0.1% by mass or less, and particularly preferably 0.01% by mass or less.

[0035] (Thermoplastic polymer) In this specification, "thermoplastic" means a property of softening or melting to be moldable when exceeding a specific temperature and solidifying when cooled, and "thermoplastic polymer" means a polymer having such a property. Specific examples of such thermoplastic polymers include polyamides (nylons), polyesters, polyolefins, modified polyolefins, etc. From the viewpoints of excellent strength at break, knot strength, and durability, and good adhesiveness with its coating layer when surface-coated, polyamide (nylon) is preferred.

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

[0037] Within the range where the effects of the present disclosure can be obtained, two or more thermoplastic polymers may be used in combination. Preferably, the filament included in the string of the present disclosure comprises 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 aforementioned Aspect 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 aforementioned Aspect 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 forming the sea region and the SP value of the thermoplastic polymer forming the island region is preferably 3.0 or less, more preferably 2.5 or less, still 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 referred to as the solubility parameter and can be calculated by the Fedors method or the like with reference to the Polymer Handbook (4th Edition, authors J. Brandrup, E. H. Immergut, published in 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), polyethylene (SP value: 7.9).

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

[0042] Examples of other preferred embodiments include those in which the thermoplastic polymer forming the sea region is a first nylon, the thermoplastic polymer forming the island region is a second nylon, and the first nylon and the second nylon are different combinations. In other words, in this embodiment, 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. 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 Embodiment B (particularly Embodiment B2), the elastic modulus of the filament can be controlled by adjusting the ratio of the island region containing carbon nanotubes to the sea region. From the viewpoint of obtaining a string with a well-balanced hitting feeling and hitting flight property, when the filament is 100% by mass, the total content of the thermoplastic polymer forming the island region and the carbon nanotubes is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, further 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, further preferably 8.0% by mass or less, particularly preferably 5.0% by mass or less.

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

[0045] (Resin coating layer) The string for a racket of the present disclosure may be provided with a resin coating layer covering its surface. As this resin, nylon 6 or nylon 6.12 is preferable. Nylon 6.12 is a co-condensate of amino acids of caprolactam (6 carbon atoms) and lauryl lactam (12 carbon atoms). Nylon 6.12 is said to have about half the water absorption compared to nylon 66. Further, nylon 12 with even less water absorption may be used.

[0046] (Method for manufacturing a string for a racket) The method for manufacturing a string for a racket of the present disclosure includes a step of mixing and dispersing carbon nanotubes in a first thermoplastic polymer, a step of mixing the first thermoplastic polymer in which the carbon nanotubes are dispersed and a second thermoplastic polymer having compatibility with the first thermoplastic polymer to obtain a thermoplastic composition, and a step of 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. Further, using the obtained filament as a core yarn or a sheath yarn, after arranging a plurality of sheath yarns on the outer periphery of the core yarn, a step of resin-coating so as to cover the core yarn and the sheath yarn may be further included.

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

[0048] (1) Step of crushing carbon nanotubes In this step, first, carbon nanotubes are mixed with water, an organic solvent, or a mixed solvent of water and an organic solvent to obtain a slurry of carbon nanotubes. This slurry is subjected to high-speed high-shear treatment by a vortex using a wet jet mill to crush the carbon nanotubes. It is preferable to select the crushing conditions so as to obtain the relative filling amount reduction rate within the above-described range. Thereafter, the crushed carbon nanotubes are obtained by drying the slurry after the crushing treatment. For drying, freeze-drying or the like is used.

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

[0050] When a sea-island structure is formed in the polymer matrix, the first thermoplastic polymer is a polymer component mainly forming the island region. 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 maleic acid-modified polyethylene. In one embodiment, a preferred first thermoplastic polymer is maleic acid-modified polyethylene. In other embodiments, 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, the crushed and dried carbon nanotubes may be melt-kneaded, dispersed and mixed in a first thermoplastic polymer, extruded, cooled, and made into pellets, and these pellets may be crushed into powder. Also, after the slurry containing carbon nanotubes is crushed, it may be melt-kneaded with a first thermoplastic polymer without drying. In this case, while removing water or an organic solvent in the slurry by volatilization or the like, the carbon nanotubes are mixed and dispersed in the first thermoplastic polymer, extruded, cooled, and pellets or powder can be obtained.

[0052] (3) Step of mixing a first thermoplastic polymer in which carbon nanotubes are dispersed and a second thermoplastic polymer compatible with this first thermoplastic polymer to obtain a thermoplastic composition In this process, a carbon nanotube-containing masterbatch obtained in the previous process and a second thermoplastic polymer are mixed to produce a thermoplastic composition. Melt kneading may be used for the mixing. Known additives such as a filler, a colorant, an antioxidant, an ultraviolet absorber, and an anti-aging agent may be added to the thermoplastic composition as long as the effects of the present disclosure can be obtained.

[0053] When a sea-island structure is formed in the polymer matrix, the second thermoplastic polymer is a polymer component that mainly forms the sea region, and is also referred to as the "base polymer" in this specification. This second thermoplastic polymer is selected from the thermoplastic polymers described above and has compatibility 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, the preferred second thermoplastic polymer is nylon, more preferably selected from the group consisting of polyamide 6, polyamide 66, polyamide 11, and polyamide 12, and polyamide 6 is 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, and polyamide 6 is more preferred.

[0054] 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 base polymer (i.e., the second thermoplastic polymer), the elastic modulus of the filament can be controlled. 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 perspective of balancing the hitting feeling and the flying property of the resulting string, the amount of the first thermoplastic polymer in which carbon nanotubes are dispersed is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, still more preferably 0.3% by mass or more, particularly preferably 0.5% by mass or more. Also, it is preferably 10.0% by mass or less, more preferably 9.0% by mass or less, still more preferably 8.0% by mass or less, particularly preferably 5.0% by mass or less.

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

[0057] From the perspective of controlling the elastic modulus of the filament to obtain a preferable hitting feeling and flying property, when the thermoplastic composition is 100% by mass, the content of the carbon nanotubes is preferably 0.001% by mass or more, more preferably 0.002% by mass or more, still more preferably 0.003% by mass or more, particularly preferably 0.004% by mass or more. Also, it is preferably 1.0% by mass or less, more preferably 0.5% by mass or less, still more preferably 0.1% by mass or less, particularly preferably 0.01% by mass or less.

[0058] (4) A 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 adopted for the production of the filament. Typically, the filament is produced by extruding the heated and melted thermoplastic composition from a die and stretching it while cooling. A carbon nanotube-containing masterbatch and a base polymer may be put into a known extruder so as to have the above-described mixing ratio, melt-mixed, and then extruded and stretched to produce a filament. The fiber diameter of the filament can be appropriately selected according to the application.

[0059] (5) Process of manufacturing a string for a racket using filaments In this process, a string for a racket is manufactured using the filaments obtained by melt spinning. The filaments (monofilaments) obtained by melt spinning may be used as the string for the racket of the present disclosure as they are. Also, after melt spinning, multifilaments obtained by twisting a plurality of filaments may be used as the string for the racket of the present disclosure. A filament or multifilament whose outer surface is coated with the above-described coating resin may be used as the string for the racket of the present disclosure.

[0060] A string having a "core-sheath structure" obtained by using the filaments obtained by melt spinning as the core yarn and / or sheath yarn may be used as the string for the racket of the present disclosure. Typically, a string having a "core-sheath structure" is manufactured by a process of arranging a plurality of sheath yarns on the surface of the core yarn and a process of resin coating so as to cover the core yarn and the plurality of sheath yarns.

[0061] (5.1) Process of arranging sheath yarns on the surface of the core yarn In this process, a plurality of sheath yarns are arranged on the surface of the core yarn. Either one or both of the core yarn and the sheath yarn may be the above-described filaments. It is preferable that at least the core yarn is the above-described filament.

[0062] For example, this process may be carried out by using a monofilament with a diameter of 0.40 to 1.00 mm as the core yarn and winding and coating a sheath yarn with a diameter of 0.10 to 0.20 mm around the surface of the core yarn in an S twist. The number of sheath yarns is preferably 8 to 40, more preferably 10 to 20. An adhesive may be applied to the surface of the core yarn. As the adhesive, for example, nylon phenol resin or the like can be used.

[0063] (5.2) Process of resin coating the surfaces of the core yarn and the sheath yarns In this process, the surfaces of the core yarn and the plurality of sheath yarns are resin coated to form a coating resin layer on the surfaces. The resin described above for the coating resin layer is appropriately selected and used.

[0064] For example, nylon 6·12 is melt-coated on the surface of the core yarn and a plurality of sheath yarns. Nylon 6·12 melts at 200 to 250°C. This melt is extruded from a nozzle and supplied to the surface of the core yarn and the plurality of sheath yarns, and a predetermined amount is adhered by squeezing with a ring. Then, by cooling, a coating resin layer made of nylon 6·12 is formed. The adhesion amount of the coating resin is preferably 1.20 to 1.35 g / m, more preferably 1.28 to 1.32 g / m.

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

[0066] Specifically, there is data showing that the contact time when actually hitting with a racket equipped with a string is 2 msec to 4 msec, which corresponds to a frequency of 250 to 500 Hz. Assuming the actual hitting condition is 20°C, Δ10°C corresponds to one digit of the frequency ratio. Considering the difference in the frequency ratio of two digits of the actual hitting frequency of 10 Hz under the viscoelasticity measurement conditions, the loss tangent tanδ at 0°C (tanδ(0°C)) is compared with the full swing shot. Also, half swing shots such as touch shots are compared with the loss tangent tanδ at 10°C (tanδ(10°C)).

[0067] Since the half swing shot has good bite and the full swing shot requires appropriate resilience, the ratio tanδ(10°C) / tanδ(0°C) is preferably larger, more preferably 1.14 or more, still more preferably 1.15 or more, and particularly preferably 1.18 or more. The upper limit value of the ratio tanδ(10°C) / tanδ(0°C) is not particularly limited, but is preferably 1.60 or less.

[0068] From the viewpoint of obtaining a suitable resilience, the smaller the tanδ(0 °C), the more preferable it is, more preferably 0.032 or less, still more preferably 0.031 or less, and particularly preferably 0.030 or less. The lower limit value of tanδ(0 °C) is not particularly limited, but is preferably 0.022 or more.

Example

[0069] Hereinafter, the effects of the present disclosure will be clarified by examples, but the present disclosure should not be construed in a limited manner 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, average diameter 9.5 nm, average length 1.5 μm) was added to 2000 mL of distilled water, and the mixture was stirred overnight at 400 rpm using a stirrer to obtain a slurry. (2) The obtained slurry was subjected to high-speed high-shear treatment by three vortices at a treatment pressure of 100 MPa using a wet jet mill device (manufactured by Tokuyama Corporation, trade name: NAGS100) to crush the multi-walled carbon nanotubes. (3) 1000 mL of the slurry of the crushed carbon nanotubes was dried in two portions of 500 mL each using a freeze-drying device (LS-6 Freeze Dryer manufactured by Press Corporation) to obtain 6.7 g of crushed carbon nanotube powder.

[0071] <Relative Filling Amount Reduction Rate of Carbon Nanotubes> 1.64 g of the obtained crushed carbon nanotube powder was put into a mixed solvent of 180 mL of distilled water and 900 mL of t-butyl alcohol, and stirred at 400 rpm for 15 hours using a stirrer to disperse it in the mixed solvent, obtaining a dispersion. This dispersion was transferred to a vial (volume 1,800 ml) and allowed to stand for 2 weeks. As a result of measuring the volume occupied by the carbon nanotubes in the dispersion before and after standing, the ratio of the volume occupied by the carbon nanotubes after standing to the volume occupied by the carbon nanotubes before standing (relative filling amount reduction rate) was 1%.

[0072] <Mixing and Dispersion of Carbon Nanotubes in Thermoplastic Polymers> (4) Dry Kneading 1.5 g of the crushed carbon nanotube powder obtained in (3) and 300 g of modified polyethylene resin pellets (maleic acid-modified polyethylene manufactured by SK functional polymer, trade name "BONDINE HX8290") were shaken and mixed in a sealed container to obtain a mixture. This mixture was kneaded at a temperature of 150°C using 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 (CNT) with respect to 100 parts by mass of modified polyethylene (modified PE).

[0073] (5) Wet Kneading Instead of the dry kneading in (4), a carbon nanotube / modified polyethylene 0.5 phr masterbatch obtained by wet kneading can also be used in the same manner. In the case of wet kneading, 4000 mL of the slurry of the crushed carbon nanotubes obtained in (2) and 8000 g of modified polyethylene resin pellets (maleic acid-modified polyethylene manufactured by SK functional polymer, trade name "BONDINE HX8290") are kneaded at a temperature of 160°C using 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 a carbon nanotube / modified polyethylene 0.5 phr masterbatch and 51.5 kg of nylon resin pellets (polyamide 6 manufactured by DSM, trade name "1020J"), which are the base polymer, were kneaded at 240°C using a twin-screw extruder to obtain a spinning composition (PA6 / modified PE / CNT) with a mass ratio of carbon nanotube / modified polyethylene / nylon 6 = 0.005 / 1 / 99.

[0075] <Manufacture of racket strings> The obtained spinning composition (PA6 / modified PE / CNT) was extruded at 240°C using a melt spinning apparatus and spun with a draw ratio of 4 times and a post-draw shrinkage rate of 4% to obtain a monofilament with a fiber diameter of 1.26 mm. This monofilament was used as the string of Example A-1 as it was.

[0076] [Example A-2 and Comparative Example A-2] 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 changed to nylon resin pellets (polyamide 12 manufactured by Degussa, trade name "VESTAMID LX9012") and polyethylene resin pellets (trade name "KERNEL KC580S" manufactured by Nippon Polyethylene Co., Ltd.), respectively.

[0077] [Comparative Example A-1] 515 g of polyethylene resin pellets (trade name "KERNEL KC580S" manufactured by Nippon Polyethylene Co., Ltd.) and 51.5 kg of nylon resin pellets (polyamide 6 manufactured by DSM, trade name "1020J"), which are the base polymer, were kneaded at 240°C using a twin-screw extruder to obtain a spinning composition (PA6 / PE) with a mass ratio of polyethylene / nylon 6 = 1 / 99. A 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] Using the spinning composition (PA6 / modified PE / CNT) obtained in the same manner as in Example A-1, extrusion was carried out at 240 °C using a melt spinning apparatus, and spinning was performed at a draw ratio of 4 times and a shrinkage rate after drawing of 4% to obtain a filament for the core yarn with a fiber diameter of 0.88 mm. Also, using separately prepared nylon resin pellets (polyamide 6 manufactured by DSM, trade name "1020J"), melt spinning was similarly performed to obtain a filament for the sheath yarn with a fiber diameter of 0.22 mm. The discharge amount from the melt spinning apparatus was adjusted so as to obtain a predetermined fiber diameter. After attaching a phenolic adhesive to the obtained filament for the core yarn, 15 filaments for the sheath yarn were wound around and dried, and then coated with nylon 66 resin to obtain the string of Example B-1.

[0079] [Comparative Example B-1] Using the spinning composition (PA6 / PE / CNT) obtained in the same manner as in Comparative Example A-2, extrusion was carried out at 240 °C using a melt spinning apparatus, and spinning was performed at a draw ratio of 4 times and a shrinkage rate after drawing of 4% to obtain a filament for the core yarn with a fiber diameter of 0.88 mm and a filament for the sheath yarn with a fiber diameter of 0.22 mm. Using this filament for the core yarn and the filament for the sheath yarn, in the same manner as in Example B-2, the string of Comparative Example B-1 was obtained.

[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 a filament for the sheath yarn was obtained using nylon resin pellets (polyamide 6 manufactured by DSM, trade name "1020J").

[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 filaments for the core yarn and the sheath yarn were obtained using nylon resin pellets (polyamide 6 manufactured by DSM, trade name "1020J").

[0082] [Tensile properties] Tensile tests were conducted in accordance with JIS L1013 to determine the tensile strength (unit: N), elongation at break (unit: %), and elastic modulus (unit: GPa) of the strings in the examples and comparative examples. The diameter (fiber diameter) of each string was measured using a micrometer. For the tensile test, a tensile testing machine ("Autograph AGS-100NX" manufactured by Shimadzu Corporation) was used and measurements were taken under the following conditions. The average values of the five measurement results are shown in Tables 1 and 2 below. Distance between chucks: 254 mm Gauge length: 150 mm Tensile speed: 254 mm / min Plot interval: 100 msec Ambient temperature: 25 °C

[0083] [Rigidity and bounce rate] One string was pulled with a tension of 50 pounds and both ends were fixed with clamps (grip interval 30 cm). Using a pendulum hammer, it was swung down from a fixed position so as to collide horizontally and at a right angle to the string at the center of the string, and the movement (displacement amount) and stress of the string after the collision were measured at 1 / 1000 second intervals. The rigidity (unit: pounds per inch) and bounce rate (unit: %) were determined by the following method. Rigidity (lb / inch) = maximum stress P (lb) / maximum displacement L (horizontal direction, inch) Bounce rate (%) = (S2 / S1) × 100 In the formula, where S1 is the area of the portion from the collision to the maximum displacement (forward portion) in the stress-strain (displacement amount) curve (round trip), and S2 is the area from the maximum displacement position of the stress-strain curve to zero displacement (return portion).

[0084] The results obtained are shown in Tables 1 and 2 below as rigidity and bounce rate. The higher the numerical value of the rigidity, the harder the hitting feeling when strung on a racket, and the lower the numerical value, the softer the hitting feeling (soft feeling). Also, the higher the numerical value of the bounce rate, the less energy loss in the collision and the greater the bounce.

[0085] [Hold feeling] One string was pulled with a tension of 50 pounds and both ends were fixed with clamps (grip interval 30 cm). Using a pendulum hammer, it was swung from a fixed position so as to collide horizontally at a right angle to the string at the center of the string, and the contact time (unit: second) between the hammer and the string was measured. This contact time is shown in Tables 1 and 2 below as the hold feeling.

[0086] [Maximum displacement] One string was pulled with a tension of 50 pounds and both ends were fixed with clamps (grip interval 30 cm). Using a pendulum hammer, it was swung from a fixed position so as to collide horizontally at a right angle to the string at the center of the string, and how much the string was distorted (moved) at the time of hammer collision was measured. This distortion (unit: mm) is shown in Tables 1 and 2 below as the maximum displacement.

[0087] [Loss tangent tanδ] Using a dynamic viscoelasticity measuring device (trade name "GABOMETER" manufactured by NETZSCH), the loss tangent of the string was measured respectively. Specifically, under the conditions of an initial load of 25 kgf, a frequency of 10 Hz, and -50°C to 50°C, temperature dispersion measurement was performed to measure the loss tangent tanδ(0°C) and the loss tangent tanδ(10°C) of each string at 0°C, and the ratio tanδ(10°C) / tanδ(0°C) was calculated. The obtained 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 tanδ(0°C), the higher the evaluation.

[0088] [Durability] The string was installed on a soft tennis racket at 40 pounds and left for 24 hours. Then, a soft tennis ball was hit out of this racket (conditions: ball speed 100 km / h, hitting interval 15 times / minute, hitting distance 50 cm, hitting angle 40 degrees, and hitting the four points of the racket in sequence), and the number of hits until the string was cut was measured. The average value in a total of 3 tests is shown in Tables 1 and 2 below as the durability. The larger the value, the higher the evaluation.

[0089]

Table 1

[0090]

Table 2

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

[0092] [Manufacture and Evaluation of Rackets] The strings of the examples and comparative examples were strung on rigid tennis rackets with the same weight and balance. Using each racket, a total of 10 adult men including 1 professional tennis player were made to hit a hard tennis ball, and were evaluated by a scoring method for each item shown in Tables 3 and 4 below. All evaluations were carried out indoors on a hard court. The evaluation method was a relative evaluation in the range of 1 to 5 points with the control standard product set at 3.0 points. The average value of the evaluation scores of 10 people is shown in Tables 3 and 4 below. For the strings with a monofilament structure (Table 3), a commercially available polyester string (Reference Example 1) was used as the control standard product, and for the strings with a core yarn-sheath yarn structure (Table 4), the string of Comparative Example B-1 was used as the control standard product.

[0093]

Table 3

[0094]

Table 4

[0095] As shown in Table 1-2, the string of the example is superior in durability compared to the string of the comparative example. Furthermore, it can be seen that the string of the example generally has good ball release, does not bite too much, has good repulsion, and the vibration is easily transmitted. Also, as shown in Table 3-4, the racket of the example has a higher overall evaluation compared to the racket of the comparative example. From this evaluation result, the superiority of the present disclosure is clear.

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

[0097] [Item 1] Comprising a filament, The above filament includes a polymer matrix and carbon nanotubes dispersed in the polymer matrix, The above polymer matrix is composed of one type or two or more compatible thermoplastic polymers, a string for a racket.

[0098] [Item 2] The above polymer matrix is composed of one type of thermoplastic polymer, A concentration gradient of the above carbon nanotubes is formed in the above polymer matrix, the string for a racket according to Item 1.

[0099] [Item 3] The above polymer matrix is composed of two or more thermoplastic polymers, In the above polymer matrix, an island-sea structure is formed at the interface between the island region and the sea region, where the polymer component forming the island region and the polymer component forming the sea region are miscible. The string for a racket according to item 1, wherein a concentration gradient is formed in which the carbon nanotubes diffuse from the island region toward the sea region.

[0100] [Item 4] The string for a racket according to any one of items 1 to 3, wherein the carbon nanotubes have a relative filling amount reduction rate of 4% or less as determined by the following method. (Method for measuring the relative filling amount reduction rate: 1.64 g of carbon nanotubes as a sample was added to a mixed solvent of 180 mL of distilled water and 900 mL of t-butyl alcohol, and stirred at 400 rpm for 15 hours using a stirrer, then allowed to stand for 2 weeks. Taking the volume occupied by the carbon nanotubes before standing as 100%, the ratio of the volume occupied by the carbon nanotubes after standing is determined as the relative filling amount reduction rate (%).)

[0101] [Item 5] The string for a racket according to any one of items 1 to 4, wherein when the filament is 100% by mass, the content of the carbon nanotubes is 0.001% by mass or more and 1.0% by mass or less.

[0102] [Item 6] The string for a racket according to any one of items 3 to 5, wherein when the filament is 100% by mass, the total content of the thermoplastic polymer forming the island region 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 region is 90.0% by mass or more and 99.9% by mass or less.

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

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

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

[0106] [Item 10] The racquet 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] The racquet string according to any one of Items 1 to 10, wherein the above filament is a monofilament and is composed of this monofilament.

[0108] [Item 12] Including a core yarn, a sheath yarn covering the above core yarn, and a coating resin layer covering from the core yarn to the outside of the sheath yarn, The racquet string according to any one of Items 1 to 10, wherein at least one of the above core yarn and the above sheath yarn is the above filament.

[0109] [Item 13] A racquet provided with the racquet string according to any one of Items 1 to 12.

[0110] [Item 14] A step of mixing and dispersing carbon nanotubes in a first thermoplastic polymer, A step of obtaining a thermoplastic composition by mixing a first thermoplastic polymer in which the carbon nanotubes are dispersed and a second thermoplastic polymer compatible with the first thermoplastic polymer. A step of melt-spinning the thermoplastic composition to obtain filaments. The method for manufacturing a string for a racket according to item 1, comprising the above steps.

[0111] [Item 15] The method for manufacturing a string for a racket according to item 14, wherein 0.1% by mass or more and 10.0% by mass or less of the first thermoplastic polymer in which the carbon nanotubes are dispersed and 90.0% by mass or more and 99.9% by mass or less of the second thermoplastic polymer are mixed to obtain the thermoplastic composition.

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

Industrial Applicability

[0113] The string for a racket described above is suitable for various sports such as hard tennis, soft tennis, badminton, and squash.

Explanation of Symbols

[0114] 2 ··· Tennis racket 4 ··· Frame 6 ··· Grip 10, 20 ··· String 10a ··· Horizontal string 10b ··· Vertical string 12 ··· Head 14 ··· Face 22 ··· Core yarn 24 ··· Cover yarn 26 ··· Coating resin layer

Claims

1. Comprising a filament, The filament includes a polymer matrix and carbon nanotubes dispersed in the polymer matrix, The polymer matrix is a string for a racket composed of one type or two or more compatible thermoplastic polymers.

2. The polymer matrix is composed of one type of thermoplastic polymer, The string for a racket according to claim 1, wherein a concentration gradient of the carbon nanotubes is formed in the polymer matrix.

3. The polymer matrix is composed of two or more thermoplastic polymers, In the polymer matrix, a sea-island structure is formed at the interface between the island region and the sea region, where the polymer component forming the island region and the polymer component forming the sea region are miscible, The string for a racket according to claim 1, wherein a concentration gradient is formed in which the carbon nanotubes diffuse from the island region toward the sea region.

4. The string for a racket according to claim 1, wherein the carbon nanotubes have a relative filling amount reduction rate of 4% or less determined by the following method. (Measurement method of relative filling amount reduction rate: 1.64 g of carbon nanotubes as a sample was added to a mixed solvent of 180 mL of distilled water and 900 mL of t-butyl alcohol, stirred at 400 rpm for 15 hours using a stirrer, then allowed to stand for 2 weeks. Taking the volume occupied by the carbon nanotubes before standing as 100%, the ratio of the volume occupied by the carbon nanotubes after standing is determined as the relative filling amount reduction rate (%).)

5. The string for a racket according to claim 1, wherein when the filament is 100% by mass, the content of the carbon nanotubes is 0.001% by mass or more and 1.0% by mass or less.

6. The string for a racket according to claim 3, wherein when the filament is 100% by mass, the total content of the thermoplastic polymer forming the island region 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 region is 90.0% by mass or more and 99.9% by mass or less.

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

8. The thermoplastic polymer forming the sea region is nylon, The thermoplastic polymer forming the island region is maleic acid-modified polyethylene, The string for a racket according to claim 3.

9. The thermoplastic polymer forming the sea region is nylon, The thermoplastic polymer forming the island region is a different type of nylon from the thermoplastic polymer forming the sea region, The string for a racket according to claim 3.

10. The thermoplastic polymer is selected from the group consisting of polyamide 6, polyamide 66, polyamide 11, polyamide 12, and maleic acid-modified polyethylene, The string for a racket according to claim 1.

11. The filament is a monofilament, and is composed of this monofilament, The string for a racket according to claim 1.

12. Including a core yarn, a skin yarn covering the core yarn, and a coating resin layer covering from the core yarn to the outside of the skin yarn, At least one of the core yarn and the skin yarn is the filament, The string for a racket according to claim 1.

13. A racket provided with the string for a racket according to claim 1.

14. A step of mixing and dispersing carbon nanotubes in a first thermoplastic polymer, A step of mixing the first thermoplastic polymer in which the carbon nanotubes are dispersed and a second thermoplastic polymer compatible with the first thermoplastic polymer to obtain a thermoplastic composition, A step of melt-spinning the thermoplastic composition to obtain a filament, The method for manufacturing a string for a racket according to claim 1, including.

15. 0.1% by mass or more and 10.0% by mass or less of the first thermoplastic polymer in which the carbon nanotubes are dispersed and 90.0% by mass or more and 99.9% by mass or less of the second thermoplastic polymer are mixed to obtain the thermoplastic composition, The method for manufacturing a string for a racket according to claim 14.

16. When the thermoplastic composition is 100% by mass, the content of the carbon nanotubes is 0.001% by mass or more and 1.0% by mass or less, The method for manufacturing a string for a racket according to claim 14.

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