String for racket

Abstract

To provide a string for rackets having balanced shot feeling at impact and ball flight by controlling an elastic modulus.SOLUTION: A string 2 for rackets is composed of thermoplastic synthetic fiber filaments 3 and 4. The filaments 3 and 4 are melt-spun by blending a thermoplastic polymer with dispersed carbon nanotubes (CNT) and a thermoplastic polymer of a base material, where the thermoplastic polymer with dispersed CNT and the thermoplastic polymer of the base material are immiscible, the thermoplastic polymer of the base material is a sea component and the thermoplastic polymer with dispersed CNT is an island component. When the filaments are 100 mass%, the carbon nanotubes are 0.0001-0.1 mass%.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a synthetic string for rackets (also called gut) used in hard tennis, soft tennis, squash, badminton, etc.

Background Art

[0002] Conventionally, as synthetic strings for rackets such as tennis, badminton, and squash, strings in which a monofilament or multifilament serving as a core is wound with a thin monofilament on the outside or braided (strung) strings have been proposed. Patent Document 1 proposes arranging a thin filament on the outside of a core monofilament and coating the surface with a composite material of nylon and carbon nanotubes. Patent Document 2 proposes coating as a resin coating layer by mixing a synthetic resin and ultrafine carbon fibers of a solid coaxial multilayer structure type in which graphene sheet cylinders contained in this synthetic resin are laminated concentrically up to the center of the cylinder.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, a conventional racket string formed with a resin coating layer containing carbon nanotubes can change surface characteristics, but there are problems in controlling the elastic modulus, and this improvement has been demanded.

[0005] In order to solve the above - mentioned conventional problems, the present invention provides a racket string with a controlled elastic modulus that balances the hitting feeling and the flying property of the hit ball.

Means for Solving the Problems

[0006] The present invention is a string for a racket composed of filaments made of a thermoplastic synthetic fiber, wherein the filaments are obtained by blending and melt-spinning a thermoplastic polymer in which carbon nanotubes are dispersed and a base thermoplastic polymer, the thermoplastic polymer in which carbon nanotubes are dispersed and the base thermoplastic polymer are incompatible, the base thermoplastic polymer forms a sea component, and the thermoplastic polymer in which carbon nanotubes are dispersed forms an island component, The thermoplastic polymer in which the carbon nanotubes are dispersed is a copolymer of ethylene and an α-olefin, and the thermoplastic polymer of the base material is nylon. when the filaments are taken as 100% by mass, the carbon nanotubes are 0.0001 to 0.1% by mass.

Advantages of the Invention

[0007] The string for a racket of the present invention is composed of filaments made of a thermoplastic synthetic fiber, and is obtained by blending and melt-spinning a thermoplastic polymer in which carbon nanotubes are dispersed and a base thermoplastic polymer. The thermoplastic polymer in which carbon nanotubes are dispersed and the base thermoplastic polymer are incompatible, the base thermoplastic polymer forms a sea component, and the thermoplastic polymer in which carbon nanotubes are dispersed forms an island component. When the filaments are taken as 100% by mass, the carbon nanotubes are 0.0001 to 0.1% by mass. Therefore, it is possible to provide a string for a racket in which the elastic modulus is controlled to balance the hitting feeling and the hitting flight property. Further, when the filaments are taken as 100% by mass, since the carbon nanotubes are 0.0001 to 0.1% by mass, it is possible to control the elastic modulus with a small amount of addition and balance the hitting feeling and the hitting flight property. This is presumably because the carbon nanotubes are in a small amount and do not get entangled and are easily oriented in the fiber axis direction.

Brief Description of the Drawings

[0008]

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DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention is a string for a racket composed of filaments made of a thermoplastic synthetic fiber. The filament made of a thermoplastic synthetic fiber is obtained by blending and melt-spinning a thermoplastic polymer in which carbon nanotubes (also referred to as CNTs) are dispersed and a base thermoplastic polymer. The thermoplastic polymer in which CNTs are dispersed and the base thermoplastic polymer are incompatible with each other, and the base thermoplastic polymer forms a sea-island structure in which the base thermoplastic polymer is the sea component and the thermoplastic polymer in which CNTs are dispersed is the island component. As the base thermoplastic polymer, synthetic fibers such as nylon and polyester can be used, among which nylon is preferable, and nylon 6 (also referred to as PA6) is more preferable. Nylon 6 has good strength at break, knot strength, durability, and adhesiveness to the resin coating layer on the surface.

[0010] The filament is a combination in which the two constituent polymers are incompatible and separated, with the thermoplastic polymer of the base material being the sea component and the thermoplastic polymer with CNTs dispersed and mixed being the island component. This results in a filament with a sea-island structure. For example, the sea component is nylon and the island component is polyethylene or an ethylene copolymer. Among these, a copolymer of ethylene and α-olefin is preferred. The polyethylene or ethylene copolymer becomes the island component and is stretched within the nylon, and CNTs are arranged therein. The polyethylene or ethylene copolymer has a low melting point, good operability during blending, and is hydrophobic, so it is easy to mix CNTs. As the polyethylene or ethylene copolymer, high-density polyethylene, low-pressure process polyethylene or its copolymer can be used. These are used for fibers.

[0011] When CNTs are dispersed in the polymer of the island component, the elastic modulus can be controlled, and a string for a racket that balances the hitting feeling and the flying property of the hit ball can be provided. This balance between the hitting feeling and the flying property of the hit ball refers to the properties intermediate between a string made of nylon 6 (PA6) and a string made of polyethylene terephthalate (PET). That is, the PA6 string has a problem that although the bounce is lower than that of the PET string, it is soft and easy to control the ball, while the PET string has good bounce but is hard. The string of the present invention has properties intermediate between the PA6 string and the PET string.

[0012] The filament is obtained by blending and melt-spinning a thermoplastic polymer with CNTs dispersed therein and the thermoplastic polymer of the base material. The reason for separating the thermoplastic polymer with CNTs dispersed therein and the thermoplastic polymer of the base material is to increase the dispersibility of CNTs and to mix and disperse CNTs in the thermoplastic polymer in advance using a masterbatch.

[0013] The CNT is preferably crushed such that the relative filling amount reduction rate, which represents the reduction rate of the volume occupied by the CNT in the liquid after standing for 12 hours or more after being dispersed in water, is 4% or less. When the CNT available in the form of powder, flakes, etc. is crushed and then kneaded with the thermoplastic polymer, the dispersibility of the CNT can be improved. If the CNT is crushed during the crushing process, the function of the CNT may not be effectively exhibited in the thermoplastic polymer. Therefore, it is desirable to crush the aggregated CNT without crushing it. As such a treatment, as described later, a slurry in which the CNT raw material is dissolved in an organic solvent such as water, t-butyl alcohol, isopropyl alcohol, N-methylpyrrolidone, or a mixed solvent of water and an organic solvent is preferably subjected to high-speed high-shear treatment by a vortex using a wet jet mill, but those crushed by a dry pulverization method using a ball mill or the like may also be used.

[0014] When the string is 100% by mass, it is preferable to blend 0.001 to 0.01% by mass of CNT. A more preferable blending amount of CNT is 0.002 to 0.005% by mass. Thereby, a racket string with controlled elastic modulus and balanced hitting feeling and hitting flight property can be provided. This is presumably because the amount of carbon nanotubes is very small and they do not get entangled and are easily oriented in the fiber axis direction. When the string is 100% by mass, the thermoplastic polymer of the masterbatch in which the CNT is dispersed is preferably 0.1 to 10% by mass, more preferably 0.2 to 9% by mass, and still more preferably 0.3 to 8% by mass. The rest is the base polymer. Thereby, a racket string with controlled elastic modulus and balanced hitting feeling and hitting flight property can be provided.

[0015] The string may be a monofilament alone, or may be formed of a core yarn, a sheath yarn covering the core yarn, and a coating resin layer covering from the core yarn to the outside of the sheath yarn. When formed of a core yarn and a sheath yarn, the CNT is added to at least one selected from the core yarn and the sheath yarn. The core yarn may be a monofilament or a multifilament. A monofilament is preferred from the viewpoint of durability. The sheath yarn is preferably a filament thinner than the core yarn, and preferably a plurality of sheath yarns are arranged outside the core yarn. The sheath yarn is preferably wound around the outside of the core yarn. As another means, the sheath yarn can be coated as a composition outside the core yarn, but winding is cheaper in terms of manufacturing cost.

[0016] The coating resin layer is preferably nylon 6 or nylon 6·12. 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 of nylon 66.

[0017] A method for manufacturing a filament made of a thermoplastic synthetic fiber according to an embodiment of the present invention will be described. (1) Crushing of CNT A slurry in which a CNT material is dissolved in water, an organic solvent, or a mixed solvent of water and an organic solvent is subjected to high-speed high-shear treatment by a vortex using a wet jet mill, crushed, and subjected to a drying treatment such as freeze-drying. (2) Mixing and dispersion of CNT into a thermoplastic polymer by the masterbatch method The crushed and dried CNT is melt-kneaded and dispersed in a thermoplastic polymer, extruded, cooled, and made into pellets or pulverized. Alternatively, without performing the drying treatment of the crushed CNT, it may be melt-kneaded in a thermoplastic polymer, dispersed, extruded, and cooled while removing the solvent by volatilization or the like to make pellets or pulverized. (3) Mixing of the masterbatch method polymer and the base polymer and melt spinning The pellets of the masterbatch method polymer and the pellets of the base polymer are mixed, melt-extruded by an extruder, spun, and drawn to produce a filament.

[0018] A method for manufacturing a string for a racket according to an embodiment of the present invention will be described. 1. In the case of a monofilament Use the monofilament as it is. 2. In the case of a core yarn and a sheath yarn (1) Step of coating the surface of the core yarn with the sheath yarn First, a monofilament such as nylon 6 with a diameter of 0.40 to 1.00 mm is used as the core yarn, and a sheath yarn with a diameter of 0.10 to 0.20 mm is wound around the surface of the core yarn, for example, in an S twist and coated. The sheath yarn is arranged on the surface of the core yarn with 8 to 40 filaments, preferably 10 to 20 filaments, of a filament such as nylon 6. At this time, it is preferable to bond the core yarn and the sheath yarn with a nylon phenolic resin or the like. (2) Step of coating the surface of the core yarn and the sheath yarn with a coating resin The surfaces of the core yarn and the sheath yarn are melt-coated with nylon 6.12. Nylon 6.12 melts at 200 to 250 °C, and this melt is extruded from a nozzle and supplied to the surfaces of the core yarn and the sheath yarn, and is squeezed with a ring to adhere a predetermined amount. Then it is cooled. The preferable adhesion amount of the coating resin is 1.20 to 1.35 g / m, and more preferably 1.28 to 1.32 g / m.

[0019] Next, it will be described with reference to the drawings. FIG. 1 is a cross-sectional view of a string for a racket 1 made of a single monofilament according to an embodiment of the present invention. This string for a racket 1 is also referred to as a "monofilament type". FIG. 2 is a cross-sectional view of a string for a racket in which a sheath yarn is arranged on the surface of a core yarn according to another embodiment of the present invention. This string for a racket 2 is composed of a core yarn 3 made of a synthetic fiber filament, a sheath yarn 4 made of a synthetic fiber filament that coats the core yarn 3, and a coating resin layer 5 from the surface of the core yarn 3 to the outside of the sheath yarn 4. This string for a racket 3 is also referred to as a "multifilament type".

Examples

[0020] It will be specifically described using the following examples. Note that the present invention is not limited to the following examples. In the following examples, the evaluation was performed by the following method.

[0021] <Tensile strength characteristics> The tensile strength and elongation at break of the string were measured using a tensile testing machine (Shimadzu Corporation, Autograph AGS-100NX) in accordance with JIS L1013. The diameter was measured using a micrometer. The measured number represents the average value of N = 5. <Rigidity and coefficient of restitution> One string was pulled with a tension of 50 pounds and both ends were fixed with clamps (grip interval 30 cm). Using a pendulum-type hammer, it was swung down from a fixed position so as to collide with the center of the string at a right angle and horizontally to the string, and the movement (displacement amount) and stress of the string after the collision were measured at intervals of 1 / 1000 second. The rigidity (pounds per inch) and coefficient of restitution (%) were determined by the following method. Rigidity (pounds per inch) = maximum stress P (pounds) / maximum displacement amount L (horizontal direction, inches) Coefficient of restitution (%) = (S2 / S1) × 100 However, S1: the area of the portion from the collision to the maximum displacement (forward portion) in the stress-strain (displacement amount) curve (round trip). S2: the area from the maximum displacement position of the stress-strain curve to zero displacement (return portion). The higher the numerical value of the rigidity value, the harder the hitting feeling when strung on a racket, and the lower the numerical value, the softer (softer feeling). The higher the numerical value of the coefficient of restitution, the less the energy loss in the collision and the greater the resilience. The coefficient of restitution and the rigidity ratio are described in detail in the reference; Rod Cross "Laboratory testing of tennis string" Sports Engineering (2000) 3, 219-230). <Holding feeling, maximum displacement> Holding 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-type hammer, it was swung from a fixed position so as to collide with the center of the string at a right angle and horizontally to the string, and the contact time (seconds) between the hammer and the string was measured. This contact time was regarded as the holding feeling. Maximum displacement: Pull one string with a tension of 50 pounds and fix both ends with clamps (grip interval 30 cm). Using a pendulum hammer, swing it from a fixed position so as to collide horizontally at a right angle to the string at the center of the string, and measure how much the string is distorted (moved) when the hammer collides. This distortion (unit: mm) was taken as the maximum displacement.

[0022] (Example 1) <CNT Crushing> (1) Add 20 g of multi-walled CNT NC7000 (average diameter 9.5 nm, average length 1.5 μm) manufactured by Nanocyl to 2000 mL of distilled water, and stir the slurry overnight at 400 rpm using a stirrer. (2) Using a wet jet mill device (manufactured by Tsunehiro Co., Ltd., product name: NAGS100), the slurry was subjected to high-speed high-shear treatment by three vortices at a processing pressure of 100 MPa to perform a crushing treatment on the multi-walled CNT. The obtained CNT slurry was allowed to stand for 24 hours, and the relative filling amount reduction rate of CNT from before standing was measured, and it was 1%. (3) 1000 mL of the above-mentioned crushed CNT slurry was dried in two portions of 500 mL each using a freeze-drying device (LS-6 Freeze Dryer manufactured by Press Co., Ltd.) to obtain 6.7 g of crushed CNT powder. <Mixing and Dispersion of CNT in Thermoplastic Polymer by Masterbatch Method> (4) Dry Kneading Mix 3.0 g of the above-mentioned crushed CNT powder and 600 g of a copolymer resin pellet of ethylene and α-olefin (manufactured by Nippon Polyethylene Co., Ltd., product name "KERNEL KC580S") in a sealed container by shaking, and knead at a temperature of 150 °C using a twin-screw extruder (KZW15TW-45MG-NH(-700) manufactured by Technovel Co., Ltd.) to obtain a 0.5 phr masterbatch of CNT / ethylene copolymer. <Mixing of Masterbatch Method Polymer and Base Polymer and Melt Spinning> 515 g of the CNT / ethylene copolymer 0.5 phr masterbatch obtained in (4) above and 51.5 kg of nylon resin pellets (1020J manufactured by DSM) were kneaded at 240°C using a twin-screw extruder to obtain a polymer composition for spinning having a ratio of CNT / ethylene copolymer / nylon 6 = 0.005 / 1 / 99. <Manufacture of String for Racquet> Using the above polymer composition for spinning, extrusion was carried out at 240°C using a melt spinning apparatus, and spinning was performed with a draw ratio of 4 times and a shrinkage ratio after drawing of 4% to obtain a string. The discharge amount from the extruder was adjusted so that the monofilament type had a fiber diameter of 1.25 mm, the core yarn of the multifilament type had a fiber diameter of 0.88 mm, and the sheath yarn had a fiber diameter of 0.22 mm. For the production of the multifilament type string, a phenolic adhesive was attached to the core yarn, and then 15 sheath yarns were wound around and dried, and then coated with nylon 66 resin to obtain a string. <Measurement of Physical Properties of String> Tensile strength and elongation were measured in accordance with JIS L1013 using an autograph AGS-X manufactured by Shimadzu Corporation. Dynamic viscoelasticity was measured using a GABOMETER manufactured by NETZSCH in a state where an initial load of 25 kgf was applied assuming the load applied to the string. Temperature dispersion measurement was carried out from -50°C to 50°C at a frequency of 10 Hz. There are data showing that the contact time during actual hitting is 2 msec to 4 msec, which corresponds to 250 to 500 Hz in terms of frequency. Assuming that the actual hitting condition is 20°C, since Δ10°C corresponds to one digit of the frequency ratio, considering the difference of two digits of the frequency ratio of the actual hitting frequency at a viscoelasticity measurement condition of 10 Hz, attention was paid to the data at 0°C. Also, assuming shots with half swings such as touch shots, data at 10°C was also extracted. For half swing shots, the bite is good, and for full swing shots, appropriate resilience is required. It is preferable that the difference in tanδ(10°C) / tanδ(0°C) is larger, and preferably 1.14 times or more. Furthermore, considering the biting feeling, it is preferable that the value of tanδ at 10°C is 0.04 or more. Figure 3 shows a graph of the dynamic viscoelasticity of the monofilament type, and Figure 4 shows a graph of the dynamic viscoelasticity of the multifilament type. Also, the tensile stress-strain curve of the monofilament type is shown in FIG. 5, and the tensile stress-strain curve of the multifilament type is shown in FIG. 6. The physical properties of the strings are summarized in Table 1 below.

[0023] [Table 1]

[0024] <Evaluating by stringing the strings on a racket> The obtained strings were strung on a rigid tennis racket with the same weight and balance, and a trial hit evaluation was conducted by a total of 10 adult men including 1 professional tennis player. The evaluation of each item was performed by a scoring method. The evaluation was carried out on an indoor hard court. When evaluating, the control standard product was set at 3.0 points, and relative evaluation was performed in the range of 1 to 5 points. The average value of the evaluation scores of the 10 people was used as the evaluation score for each item. The trial hit evaluation results (monofilament type) are shown in Table 2 and FIG. 7 below, and the trial hit evaluation results (multifilament type) are shown in Table 3 and FIG. 8.

[0025] [Table 2]

[0026] [Table 3]

[0027] From the above results, it was confirmed that the racket string of this example is a racket string that controls the elastic modulus and balances the hitting feeling, hitting flight property, and other properties for both the monofilament type and the multifilament type.

Industrial Applicability

[0028] The racket string of the present invention can be applied to hard tennis, soft tennis, badminton, squash, etc.

Explanation of Signs

[0029] String for 1,2 rackets 3 Core yarn 4 Cover yarn 5 Coating resin layer

Claims

1. A string for a racket composed of filaments made of a thermoplastic synthetic fiber, wherein the filaments are 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 the carbon nanotubes are dispersed and the base thermoplastic polymer are incompatible, the base thermoplastic polymer forms a sea component, and the thermoplastic polymer in which the carbon nanotubes are dispersed forms an island component, the thermoplastic polymer in which the carbon nanotubes are dispersed is a copolymer of ethylene and an α-olefin, and the base thermoplastic polymer is nylon, A string for a racket, characterized in that when the filaments are 100% by mass, the carbon nanotubes are 0.0001 to 0.1% by mass.

2. The string for a racket according to claim 1, wherein the carbon nanotubes are crushed so that the relative filling amount reduction rate, which represents the reduction rate of the volume occupied by the carbon nanotubes in the liquid after being dispersed in water and left standing for 12 hours or more, is 4% or less.

3. The string for a racket according to claim 1 or 2, wherein when the filaments are 100% by mass, the carbon nanotubes are 0.001 to 0.01% by mass.

4. The string for a racket according to any one of claims 1 to 3, wherein when the filaments are 100% by mass, the thermoplastic polymer of the masterbatch in which the carbon nanotubes are dispersed and mixed is 0.1 to 10% by mass, and the base thermoplastic polymer is 90 to 99.9% by mass.

5. The string for a racket according to any one of claims 1 to 4, wherein the string is a monofilament.

6. The string for a racket according to any one of claims 1 to 5, wherein the string includes a core yarn, a sheath yarn covering the core yarn, and a coating resin layer covering from the core yarn to the outside of the sheath yarn, and the carbon nanotubes are added to at least one selected from the core yarn and the sheath yarn.

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