JP6698317B2 - Racket string - Google Patents

Description

  The present invention relates to a racket string used for tennis, badminton, squash, etc., and more particularly to a racket string in which a plurality of side threads are wound around an outer peripheral side of a core thread.

  On rackets for tennis and badminton, strings are stretched like a mesh on the face part. As a string for a racket, a string in which a monofilament to be a core thread or a multifilament is wound around the outside with a monofilament to be a thin side thread is widely used. Such a string is generally called a "monofilament type" when the core yarn is a monofilament and a "multifilament type" when the core yarn is a multifilament.

  As a monofilament type string, as disclosed in Patent Document 1, a structure in which a hollow portion is formed at a central axis position of a core yarn is proposed. By forming such a hollow portion, it is possible to obtain an advantage that the elasticity of the string can be increased and the vibration absorbing performance at the time of hitting the ball can be improved.

JP 2005-237877A

  However, in the string of Patent Document 1, there is a problem that when a force is applied in the radial direction in the cross section, the hollow portion is easily crushed in the radial direction. This crushing of the hollow portion is likely to occur at the intersection of the warp yarn and the weft yarn of the string, and also tends to occur at the time of hitting the ball, and there is a problem that the durability of the string is deteriorated by such crushing.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a racket string that can obtain the advantages of forming a hollow portion and can improve durability.

The racket string of the present invention, in the racket string extending in a predetermined direction, a solid portion formed in a circular region including a central axis position in a cross section, and formed around the solid portion. A plurality of odd-numbered hollow portions extending in the extending direction are provided , and the hollow portions are arranged such that the side on the central axis position side in a cross section is formed in a substantially quadrangular shape extending in the circumferential direction of a circle concentric with the solid portion. The substantially quadrangular shape is provided with two sides that form a substantially right-angled inner angle including the side on the central axis position side and two sides that form an obtuse inner angle on the diagonal side thereof. The plurality of odd-numbered hollow portions are formed in the same shape so as to be pointed toward the outer side in the direction, and are arranged at equal angles around the solid portion . Further, the racket string of the present invention is a racket string comprising a core yarn and a plurality of side yarns wound around an outer peripheral side of the core yarn, wherein the core yarn includes a central axis position in a cross section. A solid portion formed in a circular region and a plurality of odd-numbered hollow portions formed in the periphery of the solid portion and extending in the extending direction of the core yarn are provided, and the hollow portion has a center in a cross section. The side on the axial position side is formed and arranged in a substantially quadrangular shape extending in the circumferential direction of a circle concentric with the solid portion, and the substantially quadrangular shape forms an inner angle of a substantially right angle including the side on the central axis position side. And two sides that form an obtuse internal angle on the opposite side thereof, and are formed in an elongated shape so as to be pointed radially outward of the core yarn, and the plurality of odd-numbered hollow portions are It is characterized in that they are formed in the same shape and are arranged at equal angles around the solid portion .

According to these configurations, the central axis position is the solid portion, and the hollow portion is formed around the solid portion. Direction) It is possible to suppress a strong force from both sides. As a result, it is possible to prevent the hollow portion from being easily crushed, and to obtain an advantage such as a vibration absorbing action at the time of hitting the ball, while avoiding an increase in stress concentration due to crushing and preventing a decrease in durability. .. Further, since a plurality of hollow portions are formed around the solid portion, it is possible to reduce the opening area of each hollow portion while increasing the total opening area of the hollow portions, which also makes it difficult to collapse the hollow portion. can do. Further, it is possible to dispose the hollow portions around the solid portion while preventing the two hollow portions from being aligned in the diameter direction of the string. As a result, even if one of the plurality of hollow portions is crushed by being applied with a diametrical force due to being stretched on the racket, a large diametrical force is prevented from acting on the other hollow portions. can do. As a result, it is possible to prevent the two hollow portions from being crushed at the same time, and the advantages of the hollow portions can be more easily exhibited. Furthermore, even if the circumferential direction of the string changes, the performance of the hollow portion with respect to the hit ball does not change and can be stabilized.

  In addition, in the racket string of the present invention, the number of the hollow portions formed is preferably 3, 5, or 7. With this configuration, the size and layout of the hollow portion can be maintained in a well-balanced manner, stress concentration in the hollow portion can be better alleviated, and durability can be improved, and the hollow portion can be maintained with the hollow portion formed. The advantage of can be exhibited well.

  Further, in the racket string of the present invention, the ratio of the opening area of the hollow portion in the cross section of the entire racket string may be 3.0% or more and 8.0% or less. According to this numerical range, it is possible to satisfactorily achieve both the improvement in cutting durability and the improvement in shot feeling, which are contradictory to each other.

  According to the present invention, since the solid portion is formed at the central axis position and the plurality of hollow portions are formed around the solid portion, the advantage of forming the hollow portion can be obtained and the durability is enhanced. be able to.

It is a cross-sectional view of the string according to the first embodiment. It is a cross-sectional view of a string according to a comparative structure. It is a cross-sectional view of the string which concerns on 2nd Embodiment. It is a graph which shows the hollow ratio of a string, the natural frequency, and the relationship with cutting strength. It is a graph which shows the relationship between the gauge of a string and a natural frequency.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. The string of the present invention can be applied to various rackets such as soft tennis, tennis, badminton, and squash as long as the string is stretched over the frame of the racket to form a face.

[First Embodiment]
FIG. 1 is a cross-sectional view of a string according to the first embodiment. As shown in FIG. 1, a string 10 includes a core yarn 11 that is located at the center and forms a circular outer periphery in cross section, and a plurality of side yarns 12 that are spirally wound around the outer periphery of the core yarn 11. And a resin coating layer 13 formed on the outer circumference thereof, the outer shape is formed in a circular cross section. The core thread 11 and the side thread 12 are integrally bonded with an adhesive.

  As the core yarn 11, a monofilament made of synthetic fiber is used, and it is preferable to use polyamide fibers of nylon 6 and nylon 66. Further, as the side yarn 12, a monofilament, a multifilament or a multimonofilament made of synthetic fiber is used, and it is preferable to use a polyamide fiber such as nylon 6 or nylon 66. The resin coating layer 13 preferably uses a polyamide resin. The core yarn 11 and the side yarns 12 do not prevent the use of polyester (polybutylene terephthalate, polyethylene terephthalate, etc.), polyolefin, polyphenylene sulfide, polyether ether ketone, etc.

  The core yarn 11 includes a solid portion 20 formed in a predetermined region including the central axis position C thereof, and a plurality of hollow portions 21 formed around the solid portion 20. In other words, in the core yarn 11, as shown by the chain double-dashed line in FIG. 1, a region having a substantially circular cross section inside the hollow portions 21 is the solid portion 20. The solid portion 20 and the plurality of hollow portions 21 are each formed so as to extend in the extending direction of the core yarn 11.

  The number of hollow portions 21 formed is odd, and five hollow portions 21 are formed in the first embodiment. The five hollow portions 21 are arranged at equal angles (every 72°) around the solid portion 20. Therefore, all the hollow portions 21 have a positional relationship in which no other hollow portion 21 exists on the line L (dotted line in FIG. 1) connecting the hollow portion 21 and the central axis position C, and which hollow portion 21 is Also, a plurality of core yarns 11 do not line up in the radial direction.

  The five hollow portions 21 are formed to have substantially the same inner peripheral shape, and in the first embodiment, are formed in a substantially quadrangular cross section. Specifically, it is provided with two sides forming a substantially right angle and two sides forming an obtuse inner angle on the opposite side, and is formed in a slender shape so as to be pointed toward the outer side in the radial direction of the core yarn 11. Has been done. Further, the five hollow portions 21 have substantially the same distance from the central axis position C, and the distances from the outer circumference of the core yarn 11 are also set to be substantially the same.

  The ratio of the opening area (total) of all the hollow portions 21 in the cross section of the entire string 10 (hereinafter, referred to as “hollow ratio”) may be set to 3.0% or more and 8.0% or less. Preferably, the reason will be described later.

  Next, the deformation of the hollow portion 21 when the string 10 is stretched will be described in comparison with the comparative structure of FIG.

  When the string 10 is stretched like a mesh on a racket frame (not shown), it receives a pulling force in the extending direction. At the same time, the intersecting portion of the warp yarns and the weft yarns stretched in a mesh shape receives the compressive force from both sides in the diametrical direction in the cross section. Further, even when the ball is hit with a racket, the string 10 receives a compressive force from both diametrical sides in the cross section. Such a compressive force acts on the string 10 from various directions in the diametrical direction in the cross-section due to a change in the circumferential direction of the stretched string 10. Here, as an example, a case where a compressive force acts in the direction of arrow F in FIG. 1 will be considered.

  When such a compressive force acts, the uppermost hollow portion 21 in FIG. 1 is deformed so as to be crushed in the diametrical vertical direction. However, since the other four hollow portions 21 are not located on the line of the arrow F on which the compressive force acts, the compressive force acting becomes extremely weak, and the deformation of the hollow portion 21 can be suppressed. That is, the four hollow portions 21 that are not on the line of the arrow F can maintain the opened state. Even if the diametrical position on which the compressive force acts changes, the two hollow portions 21 are not aligned in the diametrical direction, so that at least four hollow portions 21 can maintain the open state as described above.

  Moreover, in the uppermost hollow portion 21, the compressive force from below acts via the solid portion 20. Therefore, it is presumed that the force for deforming the hollow portion 21 so as to be crushed is dispersed in the solid portion 20 to reduce the deformation amount of crushing. In addition, it is presumed that the solid portion 20 acts like a base to support the uppermost hollow portion 21 against the compressive force from above and the uppermost hollow portion 21 is less likely to be crushed. Therefore, even the uppermost hollow portion 21 is in a state in which it is suppressed from being deformed so as to be crushed.

  Here, the five hollow portions 21 are formed at intervals of about 72° about the axial center position C in the cross section and have the same shape, so that the acting position of the compression force indicated by the arrow F in FIG. When changing every multiple of 72°, the hollow portion 21 is deformed as described above. Depending on the change in the diametrical position on which the compressive force acts, all the hollow parts 21 may not overlap the diametrical position, and in this case, the crush deformation of the hollow part 21 can be better suppressed.

  FIG. 2 is a cross-sectional view of a string according to the comparative structure. In the string 10A according to the comparative structure, the formation position and shape of the hollow portion 21 of the string 10 of the first embodiment are changed, and one hollow portion 21A is formed at the axial center position C of the core yarn 11A. Composed. In the string 10A having such a comparative structure, when a compressive force acts in the direction of the arrow F in the same manner as described above, the hollow portion 21A becomes flat as shown by the chain double-dashed line in the drawing so that its vertical direction (diameter direction). Both sides are crushed. The reason is that the hollow portion 21A is located at the axial center position C and the opening area of the hollow portion 21A is large.

  Stress is concentrated on both the left and right sides of the crushed hollow portion 21A, and there are adverse effects such as cracking from the stress-concentrated portion and deterioration of durability and cutting strength. On the other hand, in the string 10 of the first embodiment, it is possible to reduce the opening area of each hollow portion 21 while increasing the total opening area of the hollow portions 21, and the collapse of each hollow portion 21 is suppressed as described above. It is possible to suppress the stress from being intensively generated as in the comparative structure. As a result, it is possible to avoid the occurrence of cracks in stress-concentrated portions as in the comparative structure, and it is possible to improve the performance with respect to durability and cutting strength. As a result, the life of the string 10 can be extended, high performance can be maintained for a long time, and the replacement frequency can be reduced to reduce the cost burden.

  Here, by forming a plurality of hollow portions 21 in the core yarn 11 like the string 10, the core yarn 11 in which the hollow portions 21 are not formed is a solid string (hereinafter, referred to as “solid string”). Compared with, there are advantages described below.

  By forming the hollow portion 21, the gauge (diameter dimension) can be made thicker without changing the weight per unit length as compared with the solid string. As a result, the contact area between the string 10 and the ball (shuttle) can be increased, the controllability and driveability can be improved, and the strength of the hit ball can be increased. Further, when the string 10 having the same gauge as the solid string is formed, the plurality of hollow portions 21 are formed, so that the string 10 can be easily displaceable to realize high resilience due to the restoration, and is light and sharp. A good shot feeling can be obtained, and the hitting sound can be increased.

  Such an advantage cannot be obtained with a solid string, and is difficult to obtain even when the hollow portion 21A is crushed as in the comparative structure. That is, it can be said that the above-mentioned advantages are peculiar remarkable effects obtained by forming the plurality of hollow portions 21 like the string 10.

[Second Embodiment]
Next, a second embodiment different from the first embodiment will be described with reference to FIG. FIG. 3 is a cross-sectional view of the string according to the second embodiment. In addition, in the second embodiment, the same components as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted.

  In the string 10 according to the second embodiment, the core yarn 11 is formed with three hollow portions 31. The three hollow portions 31 are arranged at equal angle intervals of about 120° with the solid portion 20 as the center. Therefore, also in the second embodiment, all the hollow portions 31 have a positional relationship in which no other hollow portion 31 exists on the line L (dotted line in FIG. 3) connecting the hollow portion 31 and the central axis position C. A plurality of hollow portions 31 do not line up in the radial direction of the core yarn 11.

  The three hollow portions 31 are formed to have substantially the same inner peripheral shape, and in the second embodiment, they are formed to have a substantially triangular cross section. Specifically, it has a substantially isosceles triangular shape, the bottom side is located on the side of the central axis C and is curved concentrically with the core yarn 11, and the other two sides have obtuse internal angles and the core yarn 11 has a radial direction. It is formed so as to be located outside. The three hollow portions 31 have the same distance from the central axis position C, and the distances from the outer circumference of the core yarn 11 are also set to be the same. The three hollow portions 31 are formed closer to the central axis position C and farther from the outer circumference of the core yarn 11 than the hollow portion 21 of the first embodiment.

  The ratio of the opening area (total) of all the hollow portions 31 in the cross section of the entire core yarn 11 is also set to 3.0% or more and 8.0% or less.

  A groove 11a is formed on the outer circumferential surface of the core yarn 11 on the outer side in the radial direction of each hollow portion 31 so as to be cut out in a V shape. The formation of the groove 11a may be omitted, and the core yarn 11 may form the outer periphery of a substantially cylindrical shape.

  According to the second embodiment as described above, the same effect as that of the first embodiment can be obtained, and since the number of the hollow portions 31 formed is reduced, the mold is simplified and the manufacturing is performed. Can be facilitated.

  Next, an experiment conducted to evaluate the feel at impact, the sound at impact, and the durability of the string according to the first embodiment will be described. In the experiment, the strings of the first embodiment shown in FIG. 1 were manufactured as Examples 1 and 2. In Example 1, the hollow ratio of the hollow portion 21 was 4.2%, and in Example 2, 2.3. Set to %. In addition, as a comparative example, a string in which the core yarn 11 is solid was manufactured. The other conditions were the same in each of the examples and comparative examples.

  For the strings of Examples 1 and 2 and the comparative example, in order to evaluate the feel at impact and the sound at impact, an experiment was performed to measure the natural frequency of the strings. Moreover, in order to evaluate the durability of the strings of Examples 1 and 2, an experiment for measuring the cutting strength of the strings was conducted. The measurement results are shown in FIGS. 4A and 4B. 4A and 4B are graphs showing the relationship between the hollow rate of the string and the natural frequency and the cutting strength. FIG. 4A shows the measurement results of the natural frequency and the cutting strength of a string stretched on a hard tennis racket. FIG. 4B shows the measurement results of the natural frequency and the cutting strength of the string stretched on the racket for soft tennis.

  In an experiment for measuring the natural frequency of a string, the strings of Examples 1 and 2 and Comparative Example were stretched on a racket for hard tennis with a tension of 50 pounds, and a racket for soft tennis with a tension of 30 pounds. It was stretched. Then, an acceleration sensor was attached to the grip of the stretched racket, and an FFT analyzer DS-2000 (manufactured by Ono Sokki Co., Ltd.) was used for output analysis of the acceleration sensor. The string intersection was struck with an impulse hammer, the obtained time-axis vibration waveform was Fourier transformed, and the primary natural frequency of the string was measured. The measurement results are shown in FIGS. 4A and 4B.

  In addition, the racket in which the strings of Examples 1 and 2 and the comparative example were stretched was used to evaluate the feel and the sound of the ball when hit by the player. In this evaluation, Example 1 in which the hollow rate is 4.2% is the best, and then Example 2 in which the hollow rate is 2.3% is preferable, and Comparative Example is inferior to Example 1. The amount of change in the natural frequency at which the player who feels the change feels at impact and the sound at impact becomes about 10 Hz or more. In the graphs of FIGS. 4A and 4B, the hollow ratio is about 3% with respect to the value obtained by subtracting 10 Hz from the natural frequency of Example 1 on the straight line obtained by the least square method from the measurement results of the natural frequency. Therefore, when the hollow ratio is 3.0% or more, a good shot feeling can be obtained with a high shot sound. It is assumed that the difference between Examples 1 and 2 is due to the hollowness and not the influence of the number of hollows formed.

  In the experiment for measuring the breaking strength of the strings, the breaking strength of the strings of Examples 1 and 2 was measured with Autograph AGS-J (manufactured by Shimadzu Corporation). The measurement conditions are in accordance with JIS L1013:2010 version “Chemical fiber filament yarn test method”, and the sample gripping interval was 250 mm, the pulling speed was 300 mm/min, and the number of tests was 3 times. The measurement results, which are the average values of three tests, are shown in FIGS. 4A and 4B. The lower limit of cutting strength that can withstand actual use of the string is 300 N. In the graphs of FIGS. 4A and 4B, the hollow ratio is 8% or more when the cutting strength is less than 300 N on the straight line connecting the measurement results of the cutting strength. Therefore, when the hollow ratio is 8.0% or less, good cutting durability can be exhibited. As described above, when the hollow ratio is 3.0% or more and 8.0% or less, it is possible to favorably achieve both the conflicting improvement in cutting durability and the improvement in shot feeling.

  FIG. 5 is a graph showing the relationship between the string gauge and the natural frequency. In order to examine the relationship between the gauge of the string and the presence or absence of a hollow portion in the core yarn, a string of a comparative example having three gauges of 1.15 mm, 1.2 mm and 1.25 mm (core yarn is solid) , And the string of Example 1 having a gauge of 1.25 mm were prepared. Then, in the same manner as above, the natural frequency was measured by stretching the racket for soft tennis. The measurement result is shown in FIG.

  As can be understood from the graph of FIG. 5, compared with the comparative example in which the core yarn is solid under the condition of the gauge of 1.25 mm, the measured natural vibration is in Example 1 in which the hollow portion is formed in the core yarn. The number value increases. Therefore, if the gauge is the same, it is possible to obtain a lighter and sharper hitting feeling by forming the hollow portion, and it is possible to increase the hitting sound.

  Further, in the graph of FIG. 5, a straight line obtained by the least square method from each measurement result of the natural frequency of the comparative example is drawn. On this straight line, the gauge having the same natural frequency as that of Example 1 having a gauge of 1.25 mm is 1.215 mm. That is, if the natural frequency is the same, the gauge can be made thicker in Example 1 in which the hollow portion is formed in the core yarn than in the comparative example in which the core yarn is solid. As a result, the contact area between the string and the ball (shuttle) can be increased while maintaining the feel at impact and the sound at impact.

  The present invention is not limited to the above-mentioned embodiment, but can be implemented with various modifications. In the above-described embodiment, the size, shape, direction, etc. illustrated in the accompanying drawings are not limited to this, and can be appropriately changed within the range where the effect of the present invention is exhibited. Other than the above, the present invention can be appropriately modified and implemented without departing from the scope of the object of the present invention.

  For example, even if the number of hollow portions 21 and 31 formed in the core yarn 11 is seven, the same effect as in each of the above-described embodiments can be obtained. Further, the number of the hollow portions 21 and 31 may be changed to an even number, but if the hollow portions 21 and 31 are arranged at equal angles around the solid portion 20 as an odd number, the two hollow portions 21 in the diameter direction of the core yarn 11 may be formed. , 31 are not aligned and it is advantageous in that it is possible to prevent the two hollow portions from being crushed at the same time. Furthermore, the number of hollow portions 21 and 31 formed may be an odd number of 9 or more, but if the number of formed hollow portions 21 and 31 is 3, 5 and 7, the balance between the size of the hollow portions 21 and 31 and the layout can be improved. It is possible to exhibit excellent durability and hitting performance.

  Further, the opening shape of the hollow portions 21 and 31 is not limited to the illustrated configuration example, and may be changed from the viewpoint of workability, hitting performance, and durability.

  Further, in the string 10, all side threads 12 wound around the core thread 11 may be omitted. In this case, a monofilament made of synthetic fiber is used for the string 10, and polyester is preferably used. However, it does not prevent the use of polyamide fibers such as nylon 6 and nylon 66.

  The racket string of the present invention has an effect that durability can be enhanced while forming a hollow portion.

10 String 11 Core Yarn 12 Side Yarn 20 Solid Part 21 Hollow Part 31 Hollow Part C Center Axis Position

Claims (4)

In the string for the racket that extends in the specified direction,
A solid part formed in a circular region including a central axis position in a transverse section, and a plurality of odd-numbered hollow parts formed in the periphery of the solid part and extending in the extending direction ,
The hollow portion is arranged such that the side on the central axis position side in a cross section is formed in a substantially quadrangular shape extending in the circumferential direction of the concentric circle with the solid portion, and the substantially quadrangular shape is the side on the central axis position side. Including two sides forming a substantially right-angled inner angle and two sides forming an inner angle that is an obtuse angle on the opposite side, and formed in an elongated shape that is sharpened toward the radially outer side of the string,
The racket string, wherein the plurality of odd-numbered hollow portions are formed in the same shape and are arranged at equal angles around the solid portion . In a racket string including a core yarn and a plurality of side yarns wound around the outer peripheral side of the core yarn,
The core yarn includes a solid portion formed in a circular region including a central axis position in a cross section, and a plurality of odd-numbered hollows formed around the solid portion and extending in the extending direction of the core yarn. Section and
The hollow portion is arranged such that the side on the central axis position side in a cross section is formed in a substantially quadrangular shape extending in the circumferential direction of the concentric circle with the solid portion, and the substantially quadrangular shape is the side on the central axis position side. Including two sides that form an inner angle of substantially right angle and two sides that form an inner angle that is an obtuse angle on the opposite side, and are formed in an elongated shape so as to point toward the radially outer side of the core yarn,
The racket string, wherein the plurality of odd-numbered hollow portions are formed in the same shape and are arranged at equal angles around the solid portion . The racket string according to claim 1 or 2 , wherein the number of the hollow portions formed is any one of 3, 5, and 7. The ratio of the opening area of the hollow portion in the cross section of the entire racket string is 3.0% or more and 8.0% or less, and the method according to any one of claims 1 to 3 . Racket string.

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