JP2022161528A - Racket string - Google Patents

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

The present invention relates to strings for tennis rackets, badminton rackets, squash rackets and the like.

A tennis racket has a frame and strings. In the past, strings were mainly made of natural gut. The raw material for natural gut is sheep intestines. Natural gut is inferior in durability. Furthermore, natural gut is expensive. On the other hand, the natural gut has excellent feel at impact.

Most of strings in recent years are made of synthetic resin. Strings made of synthetic resin are excellent in durability. Strings made of a resin composition whose base material is polyester or nylon are widely used. A string using polyester is disclosed in JP-A-2009-226107.

Japanese Patent Application Laid-Open No. 2009-226107

A player hitting a tennis ball with a tennis racquet having polyester strings feels stiff. The feel at impact of a nylon string is superior to that of a polyester string, but the feel at impact is still harder than that of a natural gut.

SUMMARY OF THE INVENTION An object of the present invention is to provide a racket string that provides an excellent feel at impact.

The racket string according to the present invention has a loss elastic modulus E″ at 25° C. of 500 Pa or more. Preferably, the material of this string is a polyester-based resin composition.

According to another aspect, a racket according to the present invention has a frame having a head and a string strung on the head. The loss elastic modulus E″ of this string at 25° C. is 500 Pa or more. Preferably, the material of this string is a resin composition based on polyester.

According to still another aspect, the method for manufacturing a racket string according to the present invention comprises:
(A) providing a green string having a loss modulus E″ at 25° C. of less than 500 Pa;
and (B) irradiating the untreated string to increase the loss modulus E″ at 25° C. to 500 Pa or more.

Preferably, in step (B), the green string is irradiated with gamma rays. Preferably, in step (B), the untreated string is irradiated with radiation of 250 kGy or more and 2000 kGy or less. Preferably, the material of the string prepared in step (A) is a polyester-based resin composition.

Preferably, the amount of change ΔE″ calculated by the following formula is 30 Pa or more.
ΔE″ = E″2 − E″1
In this equation, E″1 represents the loss modulus of the untreated string and E″2 represents the loss modulus of the string.

The racket string according to the present invention has excellent feel at impact.

FIG. 1 is a front view showing a tennis racket according to one embodiment of the present invention. 2 is an enlarged perspective view showing a portion of the string of the tennis racket of FIG. 1; FIG.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

A tennis racket 2 is shown in FIG. This tennis racket 2 has a frame 4 , a grip 6 , end caps 8 and strings 10 . This tennis racket 2 can be used for hard tennis.

Frame 4 has head 12 , two throats 14 and shaft 16 . Head 12 defines the contour of face 18 . 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 matches the width direction X of the tennis racket 2 . One end of each throat 14 is continuous with the head 12 . This throat 14 merges with another throat 14 near the other end. Throat 14 extends from head 12 to shaft 16 . A shaft 16 extends from where the two throats 14 meet. Shaft 16 is formed continuously and integrally with throat 14 . A yoke 20 is a portion of the head 12 sandwiched between the two throats 14 .

This frame 4 consists of a pipe. In other words, this frame 4 is hollow. The material of this pipe is fiber reinforced resin. The matrix resin of this fiber reinforced resin is a thermosetting resin. A typical thermosetting resin is an epoxy resin. A typical fiber for fiber-reinforced resin is carbon fiber. This fiber is a long fiber.

The grip 6 is formed by tape wrapped around the shaft 16 . The grip 6 suppresses slippage between the player's hand and the tennis racket 2 when the tennis racket 2 is swung.

A string 10 is strung on a head 12 . The string 10 is stretched along the width direction X and the axial direction Y. As shown in FIG. A portion of the string 10 extending along the width direction X is referred to as a transverse thread 10a. The portion of string 10 that extends along axial direction Y is referred to as longitudinal thread 10b. A face 18 is formed by a plurality of horizontal threads 10a and a plurality of vertical threads 10b. This face 18 is generally along the XY plane.

A string 10 is shown in FIG. This string 10 is of the monofilament type. String 10 may be formed by twisting a plurality of filaments. String 10 may have multiple layers. String 10 may have a coating on its surface.

A 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 UV absorbers, softeners, plasticizers, colorants, and the like.

A specific example of a thermoplastic resin suitable for the string 10 is polyester. The string 10 using polyester is superior in durability to natural gut. Even if the string 10 repeatedly hits a tennis ball, the string 10 is less likely to break.

A method for manufacturing the string 10 will be described below. In this manufacturing method, first, a green string is prepared. An untreated string means 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 500Pa.

Known methods may be employed to prepare the raw string. A typical method is stretching. In this stretching process, the 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 pulled out from the die to obtain a bus bar. This bus bar is stretched to obtain a raw string.

The raw string is then irradiated. Radiation includes alpha rays, beta rays, gamma rays and X-rays. γ-rays are preferable from the viewpoint of having an industrial track record. Gamma rays have been put to practical use for the purpose of insecticide and sterilization of food after packaging. Furthermore, γ-rays have been put into practical use for the purpose of preventing germination of crops such as potatoes. γ-rays are generated due to the phenomenon that energy is released when the energy level of atomic nuclei transitions from an unstable state to a stable state. Cobalt 60 gamma rays are typically used.

Radiation can be applied on the drawing equipment immediately after the drawing process is finished. Radiation may be applied to the untreated string that has been wound after the stretching step. The raw string that has been cut to size and wrapped may be irradiated. Multiple exposures may be given to a single untreated string.

The loss elastic modulus E″ is increased by irradiation with radiation, and the string 10 is obtained. The loss elastic modulus E″ of the string 10 is 500 Pa or more. It is speculated that branching in the resin molecules increases due to irradiation with radiation. Furthermore, it is presumed that irradiation of radiation causes scission of molecular chains. It is speculated that the increased branching and chain scission increase the viscosity of the resin and increase the loss modulus E″.

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

From the viewpoint of feel at impact, the loss modulus E″ of the string 10 is more preferably 520 Pa or more, particularly preferably 550 Pa or more. The loss modulus E″ is preferably 800 Pa or less.

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

The loss elastic modulus E″ is measured by a dynamic viscoelasticity measuring device. A specific example of this device is “EPLEXOR 4000N” manufactured by Netsch (GABO). The measurement conditions are as follows.
Initial applied strain: 0.1%
Mode: Sinusoidal tension Temperature range: -50°C to 50°C
Heating rate: 2°C/min Measurement temperature: 25°C
Excitation frequency: 10Hz
Strain: 0.05%

As described above, the preferred base resin is polyester from the viewpoint of durability. By irradiating an untreated string containing polyester, the feel at impact can approach that of a string made of nylon. This irradiation does not significantly impair durability. The string 10 having a base resin made of polyester and obtained by irradiation with radiation is excellent in both durability and feel at impact.

The dose of radiation is preferably 250 kGy or more and 2000 kGy or less. A string 10 with excellent feel at impact can be obtained by a manufacturing method in which the irradiation dose is 250 kGy or more. From this point of view, the irradiation dose is more preferably 350 kGy or more, particularly preferably 400 kGy or more. Irradiation with a dose of 2000 kGy or less can be done at low cost. From this point of view, the irradiation dose is more preferably 1600 kGy or less, particularly preferably 1400 kGy or less. When multiple irradiations are repeated for one untreated string, it is preferable that the total of each irradiation dose is within the above range.

The effects of the present invention will be clarified by examples below, but the present invention should not be construed in a limited manner based on the description of these examples.

[Example 1]
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. The oxygen scavenger was added to the bag and the bag was sealed. This state was maintained for 2 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.

[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 dose of radiation was changed as shown in Table 1 below.

[Example 2]
A commercial 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.

[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 dose of radiation was changed as shown in Table 1 below.

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

[feeling at impact]
A stringed tennis racket was used by the player and evaluated for impact. The results are shown in Table 1 below as an index when the feel at impact of Comparative Example 1 is used as a reference. The smaller the numerical value, the smaller the impact, and thus the better the feel at impact.

As shown in Table 1, the strings according to each example have excellent feel at impact. From this evaluation result, the superiority of the present invention is clear.

Strings according to the present invention are suitable for various sports such as tennis, soft tennis, squash, and badminton.

2 tennis racket 4 frame 6 grip 10 string 10a horizontal thread 10b vertical thread 12 head 18 face

Claims (9)

A racket string having a loss elastic modulus E″ at 25° C. of 500 Pa or more. 2. The racket string according to claim 1, wherein the material is a polyester-based resin composition. comprising a frame having a head and a string strung on the head,
A racket, wherein the loss elastic modulus E″ of the string at 25° C. is 500 Pa or more. 4. The racket according to claim 3, wherein the material of the string is a polyester-based resin composition. (A) providing a green string having a loss modulus E″ at 25° C. of less than 500 Pa;
and (B) a method for producing a racket string, comprising the step of irradiating the untreated string with radiation to increase the loss elastic modulus E″ at 25° C. to 500 Pa or more. 6. The manufacturing method according to claim 5, wherein in the step (B), the untreated string is irradiated with gamma rays. 7. The manufacturing method according to claim 5 or 6, wherein in the step (B), the untreated string is irradiated with radiation of 250 kGy or more and 2000 kGy or less. 8. The manufacturing method according to any one of claims 5 to 7, wherein the material of the string prepared in the step (A) is a resin composition based on polyester. 9. The manufacturing method according to any one of claims 5 to 8, wherein the amount of 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 10.)

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