strings for rackets

Abstract

To provide a racket string that offers a good balance between a hitting feel and durability.SOLUTION: A method for producing a racket string 10 includes the steps of: (A) preparing an untreated string with a loss elastic modulus E" at 25°C of less than 500 Pa and (B) irradiating the untreated string with radiation ray to increase the loss elastic modulus E" at 25°C to 500 Pa or more. Preferably, the untreated string is irradiated with γ-rays. A preferable irradiance is 250 kGy or more and 2000 kGy or less. A preferable material of the untreated string is a resin composition composed of polyester.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to strings for tennis rackets, badminton rackets, squash rackets, and the like. [Background technology]

[0002] A tennis racket has a frame and strings. In the past, natural gut was mainly used as the strings. Natural gut is made from sheep intestines. Natural gut is less durable. It is also expensive. On the other hand, natural gut provides an excellent feel when hitting the ball.

[0003] In recent years, strings have become mainstream and are made of synthetic resin. Strings made of synthetic resin are highly durable. Strings made of resin compositions with polyester or nylon as the base material are widely used. A string made of polyester is disclosed in JP 2009-226107 A. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2009-226107 A Summary of the Invention [Problem to be solved by the invention]

[0005] Players who hit a tennis ball with a tennis racket with polyester strings feel that it is hard. Nylon strings provide a better feel than polyester strings, but they still provide a harder feel than natural gut strings.

[0006] An object of the present invention is to provide a racket string that provides an excellent shot feeling. [Means for solving the problem]

[0007] The racket string according to the present invention has a loss modulus E" at 25°C of 500 Pa or more. Preferably, the string is made of a resin composition based on polyester.

[0008] According to another aspect, the racket of the present invention comprises a frame having a head, and a string strung on the head. The string has a loss modulus E" of 500 Pa or greater at 25°C. Preferably, the string is made of a resin composition based on polyester.

[0009] According to yet another aspect, a method for manufacturing a racket string according to the present invention comprises the steps of: (A) providing an untreated string having a loss modulus E" at 25°C of less than 500 Pa; and (B) irradiating the untreated string with radiation to increase the loss modulus E" at 25°C to 500 Pa or more. Includes.

[0010] Preferably, in step (B), the untreated string is irradiated with gamma rays. Preferably, in step (B), the untreated string is irradiated with radiation of 250 kGy to 2000 kGy. Preferably, the material of the string prepared in step (A) is a resin composition based on polyester.

[0011] Preferably, the change ΔE″ calculated by the following formula is 30 Pa or more. ΔE” = E”2 - E”1 In this formula, E"1 represents the loss modulus of the untreated string and E"2 represents the loss modulus of the string. [Effects of the Invention]

[0012] The racket string according to the present invention provides an excellent shot feeling. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a front view showing a tennis racket according to an embodiment of the present invention. [Figure 2] FIG. 2 is an enlarged perspective view of a portion of the strings of the tennis racket of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, the present invention will be described in detail based on preferred embodiments, with appropriate reference to the drawings.

[0015] 1 shows a tennis racket 2. This tennis racket 2 has a frame 4, a grip 6, an end cap 8, and strings 10. This tennis racket 2 can be used for playing tennis.

[0016] The frame 4 has a head 12, two throats 14, and a shaft 16. The head 12 forms the outline of the face 18. 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. One end of each throat 14 is continuous with the head 12. This throat 14 joins with another throat 14 near the other end. The throat 14 extends from the head 12 to the shaft 16. The shaft 16 extends from the point where the two throats 14 join. The shaft 16 is formed continuously and integrally with the throat 14. The portion of the head 12 sandwiched between the two throats 14 is a yoke 20.

[0017] The frame 4 is made of a pipe. In other words, the frame 4 is hollow. The material of the pipe is a fiber-reinforced resin. The matrix resin of the fiber-reinforced resin is a thermosetting resin. A typical thermosetting resin is an epoxy resin. A typical fiber of the fiber-reinforced resin is a carbon fiber. The fiber is a long fiber.

[0018] The grip 6 is formed by a tape wound around the shaft 16. The grip 6 prevents slippage between the player's hand and the tennis racket 2 when the tennis racket 2 is swung.

[0019] The string 10 is strung on the head 12. The string 10 is strung along a width direction X and an axial direction Y. The portions of the string 10 that extend along the width direction X are called horizontal threads 10a. The portions of the string 10 that extend along the axial direction Y are called vertical threads 10b. The multiple horizontal threads 10a and the multiple vertical threads 10b form a face 18. This face 18 is generally aligned along the XY plane.

[0020] 2 shows a string 10. The string 10 is a monofilament type. The string 10 may be formed by twisting multiple filaments. The string 10 may have multiple layers. The string 10 may have a coating on its surface.

[0021] The preferred material for the string 10 is a resin composition. A preferred base resin for this resin composition is a thermoplastic resin. The resin composition may contain various additives in addition to the base resin. Specific examples of additives include ultraviolet absorbers, softeners, plasticizers, and colorants.

[0022] Polyester is a specific example of a thermoplastic resin suitable for the string 10. A string 10 made of polyester has superior durability compared to natural gut. Even if the string 10 is repeatedly hit against a tennis ball, the string 10 is less likely to break.

[0023] A method for manufacturing the string 10 will be described below. In this manufacturing method, an untreated string is first prepared. The untreated string refers to a string that has not been irradiated with radiation, which will be described later. The loss modulus E" of the untreated string is less than 500 Pa.

[0024] Known methods can be used to prepare the untreated string. A typical method is drawing. In this drawing, a base resin is heated and melted. Additives are added to this base resin to obtain a molten resin composition. This molten resin composition is cooled while being drawn out from a die to obtain a bus bar. This bus bar is stretched to obtain an untreated string.

[0025] Next, the untreated string is irradiated with radiation. Examples of radiation include α-rays, β-rays, γ-rays, and X-rays. γ-rays are preferred because of their industrial proven track record. γ-rays have been used for the purpose of killing insects and sterilizing packaged foods. Furthermore, γ-rays have been used for the purpose of preventing the germination of agricultural crops such as potatoes. γ-rays are generated due to the phenomenon in which energy is released when the energy level of an atomic nucleus transitions from an unstable state to a stable state. Typically, cobalt-60 γ-rays are used.

[0026] The radiation may be applied on the drawing equipment immediately after the drawing process is completed. The radiation may also be applied to the untreated string in a wound state after the drawing process is completed. The radiation may also be applied to the untreated string that has been cut to a predetermined size and packaged. One untreated string may be irradiated multiple times.

[0027] The loss modulus E" is increased by radiation exposure, and string 10 is obtained. The loss modulus E" of string 10 is 500 Pa or more. It is presumed that radiation exposure increases branching in the resin molecules. Furthermore, it is presumed that radiation exposure causes scission of molecular chains. It is presumed that the increased branching and molecular chain scission increase the viscosity of the resin, and increase the loss modulus E".

[0028] When a tennis ball is hit with the racket 2 using this string 10, the player feels that the hitting feel of the racket 2 is "soft." This string 10 can contribute to the hitting feel of the racket 2. This string 10 can also reduce damage to the player's joints.

[0029] In light of the shot feel, the loss modulus E" of the string 10 is more preferably 520 Pa or greater, and particularly preferably 550 Pa or greater. The loss modulus E" is preferably 800 Pa or less.

[0030] In the present invention, the change amount ΔE″ is calculated by the following formula: ΔE” = E”2 - E”1 In this formula, E"1 represents the loss modulus of the untreated string, and E"2 represents the loss modulus of the string 10. The change ΔE" is preferably 30 Pa or more, more preferably 50 Pa or more, and particularly preferably 70 Pa or more.

[0031] The loss modulus E" is measured by a dynamic viscoelasticity measuring device. A specific example of this device is the "EPLEXOR 4000N" manufactured by Netsch (GABO). The measurement conditions are as follows: Initial applied strain: 0.1% Mode: Sine wave tension Temperature range: -50℃ to 50℃ Heating rate: 2°C / min Measurement temperature: 25℃ Excitation frequency: 10Hz Distortion: 0.05%

[0032] As mentioned above, polyester is a preferred base resin from the viewpoint of durability. Irradiating an untreated string containing polyester can provide a shot feel similar to that of a nylon string. This irradiation does not significantly impair durability. A string 10 obtained by irradiating a string containing polyester as a base resin is excellent in both durability and shot feel.

[0033] The radiation dose is preferably 250 kGy or more and 2000 kGy or less. A manufacturing method using an irradiation dose of 250 kGy or more can produce a string 10 with an excellent shot feel. From this perspective, an irradiation dose of 350 kGy or more is more preferable, and 400 kGy or more is particularly preferable. Irradiation with an irradiation dose of 2000 kGy or less can be carried out at low cost. From this perspective, an irradiation dose of 1600 kGy or less is more preferable, and 1400 kGy or less is particularly preferable. When multiple irradiations are repeated on a single untreated string, it is preferable that the total of each irradiation dose be within the above range. [Example]

[0034] The effects of the present invention will be clarified below by examples, but the present invention should not be construed as being limited based on the descriptions of these examples.

[0035] [Example 1] A commercially available string I was prepared. The base resin of this string I was polyester. This string I was placed in an aluminum-coated bag. An oxygen scavenger was further placed in the bag, and the bag was sealed. This state was maintained for two days to remove oxygen. This string I was irradiated with cobalt-60 gamma rays. The irradiation dose was 500 kGy. This irradiation was performed twice. The total irradiation dose was 1000 kGy.

[0036] [Comparative Examples 1 and 2] Strings of Comparative Examples 1 and 2 were obtained in the same manner as in Example 1, except that the radiation doses were as shown in Table 1 below.

[0037] [Example 2] A commercially available string II was prepared. The base resin of this string II was polyester. This string II was irradiated with cobalt 60 gamma rays in the same manner as in Example 1. The irradiation dose was 500 kGy.

[0038] [Comparative Example 3 and Example 3] Strings of Comparative Example 3 and Example 3 were obtained in the same manner as in Example 2, except that the radiation doses were as shown in Table 1 below.

[0039] Comparative Example 4 A commercially available string III was prepared. The base resin of this string III was polyester.

[0040] [Ball feel] The strung tennis rackets were used by players to evaluate the impact. The results are shown in Table 1 below as an index, with the hitting feel of Comparative Example 1 used as the standard. The smaller the value, the smaller the impact, and therefore the better the hitting feel.

[0041] [Table 1]

[0042] As shown in Table 1, the strings according to each example have an excellent shot feeling. The superiority of the present invention is clear from these evaluation results. [Industrial Applicability]

[0043] The string according to the present invention is suitable for a variety of sports such as tennis, soft tennis, squash, and badminton. [Explanation of symbols]

[0044] 2. Tennis rackets 4. Frame 6. Grip 10 strings 10a Horizontal thread 10b Vertical thread 12 heads 18...face

Claims

1. (A) providing an untreated string having a loss modulus E" of less than 500 Pa at 25°C, the untreated string being made of a polyester-based resin composition; and (B) irradiating the untreated string with radiation to increase the loss modulus E" at 25°C to 500 Pa or more. A method for manufacturing a racket string, comprising:

2. The method according to claim 1, wherein the untreated string is irradiated with gamma rays in step (B).

3. 3. The method according to claim 1, wherein in step (B), the untreated string is irradiated with radiation of 250 kGy to 2000 kGy.

4. The method according to any one of claims 1 to 3, wherein the change ΔE″ calculated by the following formula is 30 Pa or more. ΔE" = E"2 - E"1 (In this formula, E"1 represents the loss modulus of the untreated string and E"2 represents the loss modulus of the string.)

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