Racket

Abstract

To provide a racket with an excellent balance of rebound performance, spin performance, and face stability.SOLUTION: A racket 2 includes a frame 4, a grip 6, a grommet 10, and strings 12. In the racket 2, an in-plane rigidity index Gi, defined as a ratio of a top-pressure rigidity value Git (kgf / cm) to a side-pressure rigidity value Gis (kgf / cm), is 1.40 or greater. An out-of-plane rigidity index Go, defined as a product of a throat rigidity value Gos (kgf / cm) and a hitting-surface rigidity value Goh (kgf / cm), is between 60000 and 85000. A moment of inertia Mi about an axis of the racket 2 is between 13500 g cm2 and 15000 g cm2. An inertia index Ii, calculated by the formula Ii=Mi / (Wr Lc), is 0.150 or greater, where Wr represents the weight (g) of the racket and Lc represents the distance (mm) from the grip end to the center of gravity of the racket.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This specification discloses a racket suitable for tennis, soft tennis, squash, padel, badminton, etc. [Background technology]

[0002] In tennis, a ball is hit with a racket. This hit transfers the kinetic energy of the racket to the ball, causing it to fly. A ball hit with a tennis racket with excellent resilience can fly at a high speed. A high flight speed is advantageous in tennis. Japanese Patent Application Laid-Open No. 5-15617 discloses a tennis racket with excellent resilience. Japanese Patent Application Laid-Open No. 2001-61996 discloses a tennis racket with excellent resilience and hitting feel. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 5-15617 [Patent Document 2] JP 2001-61996 A Summary of the Invention [Problem to be solved by the invention]

[0004] Tennis players require not only repulsion performance but also spin performance and surface stability from their tennis rackets. The applicant's intention is to provide a racket that has an excellent balance of repulsion performance, spin performance, and surface stability. [Means for solving the problem]

[0005] In the racket disclosed in this specification, the in-plane stiffness index Gi, which is the ratio of the top pressure stiffness value Git (kgf / cm) to the side pressure stiffness value Gis (kgf / cm), is 1.40 or more. The out-of-plane stiffness index Go, which is the product of the throat stiffness value Gos (kgf / cm) and the hitting surface stiffness value Goh (kgf / cm), is 60,000 or more and 85,000 or less. The moment of inertia Mi about the axis of this racket is 13,500 g cm 2 More than 15000g cm 2 The inertia index Ii calculated by the following formula is 0.150 or more. Ii = Mi / (Wr Lc) In this formula, Wr represents the mass of the racket (g), and Lc represents the distance (mm) from the grip end to the center of gravity of the racket. [Effects of the Invention]

[0006] This racket has an excellent balance of resilience, spin and surface stability. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a front view showing a tennis racket according to an embodiment. [Figure 2] FIG. 2 is a side view of the tennis racket of FIG. [Figure 3] FIG. 3 is an exploded view showing a portion of the tennis racket of FIG. 1 on an enlarged scale. [Figure 4] FIG. 4 is an enlarged cross-sectional view taken along line IV-IV in FIG. [Figure 5] FIG. 5 is a perspective view showing a part of the manufacturing process of the racket of FIG. [Figure 6] FIG. 6 is an enlarged view of a portion of the prepreg for the tennis racket of FIG. [Figure 7] FIG. 7 is an enlarged view showing a portion of another prepreg for the tennis racket of FIG. [Figure 8] FIG. 8 is an enlarged view showing a portion of yet another prepreg for the tennis racket of FIG. [Figure 9] FIG. 9(a) is a front view showing a method for measuring the top pressure stiffness value of the tennis racket of FIG. 1, and FIG. 9(b) is a side view thereof. [Figure 10] FIG. 10 is a front view showing a method for measuring the side pressure stiffness value of the tennis racket of FIG. [Figure 11] FIG. 11(a) is a plan view showing a method for measuring the throat stiffness value of the tennis racket of FIG. 1, and FIG. 11(b) is a front view thereof. [Figure 12] FIG. 12(a) is a plan view showing a method for measuring the stiffness value of the ball-striking surface of the tennis racket of FIG. 1, and FIG. 12(b) is a front view thereof. [Figure 13] FIG. 13 is a front view showing a method for measuring the moment of inertia of the tennis racket of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0008] Preferred embodiments will be described in detail below with reference to the drawings as appropriate.

[0009] [Tennis racket elements] A tennis racket 2 is shown in Figures 1-4. The racket 2 has a frame 4, a grip 6, an end cap 8, grommets 10, and strings 12. The racket 2 can be used for playing tennis. In Figures 1, 2, and 4, arrow X indicates the width direction of the racket 2, arrow Y indicates the axial direction of the racket 2, and direction Z indicates the thickness direction of the racket 2. The grommets 10 and strings 12 are not shown in Figure 2.

[0010] The frame 4 has a head 14, a first throat 16a, a second throat 16b, and a shaft 18. The head 14 forms the outline of a face 20 (described in detail later). The front shape of the head 14 is approximately elliptical. The major axis direction of the ellipse coincides with the axial direction Y of the racket 2. The minor axis direction of the ellipse coincides with the width direction X of the racket 2. The first throat 16a extends from the head 14. The second throat 16b extends from the head 14. The second throat 16b joins the first throat 16a at a position away from the head 14. The shaft 18 extends from the point where the two throats 16 join. The shaft 18 is continuous with the throats 16. The portion of the head 14 sandwiched between the two throats 16 is a yoke 22. The frame 4 is hollow.

[0011] The main material of the frame 4 is fiber-reinforced resin. This fiber-reinforced resin has a resin matrix and a large number of reinforcing fibers. The frame 4 includes a plurality of fiber-reinforced layers. The fiber-reinforced resin will be described in detail later.

[0012] Examples of the base resin for the frame 4 include thermosetting resins such as epoxy resin, bismaleimide resin, polyimide and phenolic resin, and thermoplastic resins such as polyetheretherketone, polyethersulfone, polyetherimide, polyphenylene sulfide, polyamide and polypropylene. A resin particularly suitable for the frame 4 is epoxy resin.

[0013] Examples of reinforcing fibers for the frame 4 include carbon fibers, metal fibers, glass fibers, and aramid fibers. Carbon long fibers are particularly suitable for the frame 4. Multiple types of fibers may be used in combination.

[0014] 2 and 3, the head 14 has a groove 24. This groove 24 is recessed from the outer peripheral surface of the head 14. The groove 24 is formed around almost the entire circumference of the head 14, excluding the yoke 22. The head 14 further has a plurality of holes 26. The plurality of holes 26 are arranged along the circumferential direction of the head 14.

[0015] The grip 6 is wound around the shaft 18. The grip 6 is formed of tape. The grip 6 prevents slippage between the player's hand and the racket 2 when the tennis racket 2 is swung.

[0016] As shown in FIG. 3, the grommet 10 has a base 28 and a plurality of pipes 30. The base 28 has a belt shape. Each pipe 30 is formed integrally with the base 28. The pipes 30 stand upright from the base 28. The grommet 10 is typically made of a synthetic resin that is softer than the frame 4. The tennis racket 2 may have a plurality of grommets 10. The number of pipes 30 in each grommet 10 may be one.

[0017] The grommet 10 is attached to the head 14. When the grommet 10 is attached to the head 14, the base 28 is housed in the groove 24. A portion of the base 28 may protrude from the groove 24. Furthermore, when the grommet 10 is attached to the head 14, the pipe 30 passes through the hole 26.

[0018] As shown in FIG. 1 , strings 12 are strung on a head 14. The strings 12 are strung along the width direction X or the axial direction Y. The strings 12 pass through a pipe 30. The strings 12 form a number of threads 32. Portions of the strings 12 that extend along the width direction X are referred to as horizontal threads 32a. Portions of the strings 12 that extend along the axial direction Y are referred to as vertical threads 32b. The multiple horizontal threads 32a and the multiple vertical threads 32b form a face 20. The face 20 generally extends along the XY plane. The face 20 may be formed from two or more strings 12.

[0019] [Manufacturing method] An example of a method for manufacturing a tennis racket 2 will now be described with reference to FIG. 5. In this manufacturing method, a mandrel, a tube, and a plurality of prepregs 34 are prepared. Each prepreg 34 is made of a plurality of parallel reinforcing fibers and a matrix resin. In this manufacturing method, a mandrel is first inserted into a tube. The prepregs 34 are sequentially wound around this tube. By being wound, the prepregs 34 assume a cylindrical shape. FIG. 5 shows a cylindrical prepreg 34p and a sheet-like prepreg 34s. The mandrel and tube are not shown in FIG. 5.

[0020] As the mandrel is rotated, prepreg 34s is wound onto prepreg 34p. This winding causes prepreg 34s to assume a cylindrical shape. This winding results in a laminate 36. In FIG. 5, arrow A1 indicates the longitudinal direction of laminate 36. Another prepreg 34 is wound onto this laminate 36 as needed.

[0021] After the mandrel is removed from the tube, the tube and laminate 36 are set in a mold. Inside the mold, the tube is filled with gas, causing it to expand. This expansion presses the prepreg 34 against the cavity surface of the mold. The prepreg 34 is heated, causing the matrix resin to harden. This hardening results in a molded body. The molded body has a shape that is the inverse of the shape of the cavity surface.

[0022] Holes 26 are drilled in this molded body. This molded body is then subjected to further surface polishing, painting, and other processes to obtain the frame 4. A grip 6, grommets 10, and the like are attached to this frame 4. Strings 12 are then strung on this frame 4 to complete the tennis racket 2. This racket 2 has multiple fiber-reinforced layers.

[0023] [Prepreg] FIG. 6 shows a first prepreg 34a. This first prepreg 34a includes a matrix 40 and a plurality of first reinforcing fibers 42a arranged in parallel. Each of the first reinforcing fibers 42a is inclined with respect to the longitudinal direction A1. In FIG. 6, an arrow θa indicates the inclination angle (absolute value) of the first reinforcing fiber 42a with respect to the longitudinal direction A1. The inclination angle θa is 20° or more and 60° or less. In this specification, reinforcing fibers 42 having an inclination angle of 20° or more and 60° or less are referred to as "bias-type reinforcing fibers."

[0024] FIG. 7 shows a second prepreg 34b. This second prepreg 34b includes a matrix 40 and a plurality of second reinforcing fibers 42b arranged in parallel. Each second reinforcing fiber 42b is inclined with respect to the longitudinal direction A1. The inclination direction of the second reinforcing fibers 42b is opposite to the inclination direction of the first reinforcing fibers 42a (see FIG. 6). In FIG. 7, an arrow θb indicates the inclination angle (absolute value) of the second reinforcing fibers 42b with respect to the longitudinal direction A1. The inclination angle θb is equal to or greater than 20° and equal to or less than 60°. The second reinforcing fibers 42b are "bias-type reinforcing fibers."

[0025] 8 shows a third prepreg 34c. This third prepreg 34c includes a matrix 40 and a plurality of third reinforcing fibers 42c arranged in parallel. Each of the third reinforcing fibers 42c extends along the longitudinal direction A1. The inclination angle (absolute value) of the third reinforcing fibers 42c with respect to the longitudinal direction A1 is zero. The third reinforcing fibers 42c may be slightly inclined with respect to the longitudinal direction A1. In this specification, reinforcing fibers 42 having an inclination angle (absolute value) with respect to the longitudinal direction A1 of 10 degrees or less are referred to as "straight-type reinforcing fibers."

[0026] The frame 4 has a fiber reinforced layer containing bias type reinforcing fibers and a fiber reinforced layer containing straight type reinforcing fibers.

[0027] [In-plane stiffness index Gi] This tennis racket 2 has an appropriate in-plane stiffness index Gi. The in-plane stiffness index Gi is the ratio of the top pressure stiffness value Git (kgf / cm) to the side pressure stiffness value Gis (kgf / cm). The in-plane stiffness index Gi is calculated using the following formula. Gi = Git / Gis

[0028] FIG. 9 shows a method for measuring the top pressure stiffness value Git. In FIG. 9, the tennis racket 2 is fixed to a support 44. The support 44 has a spacer 46, and the yoke 22 is placed on this spacer 46. The width direction X of the racket 2 coincides with the horizontal direction. The axial direction Y of the racket 2 coincides with the vertical direction. A rigid plate 48 abuts against the top of the racket 2. The plate 48 descends, and a load is applied to the racket 2. The displacement (cm) of the plate 48 from a state where the load is 25 kgf to a state where the load is 50 kgf is measured. The load difference, 25 kgf, is divided by the displacement (cm) to calculate the side pressure stiffness value Gis (kgf / cm). The side pressure stiffness value Gis is measured with the strings 12 removed from the frame 4.

[0029] From the viewpoint of resilience performance, the apex pressure stiffness value Git is preferably 60 kgf / cm or more, more preferably 70 kgf / cm or more, and particularly preferably 80 kgf / cm or more. From the viewpoint of controllability, the apex pressure stiffness value Git is preferably 110 kgf / cm or less, more preferably 100 kgf / cm or less, and particularly preferably 90 kgf / cm or less.

[0030] FIG. 10 shows a method for measuring the lateral pressure stiffness value Gis. In FIG. 10, a tennis racket 2 is placed on a rigid base 50. The width direction X of the racket 2 coincides with the vertical direction. The axial direction Y of the racket 2 coincides with the horizontal direction. A rigid plate 52 descends, and a load is applied to the racket 2. The displacement (cm) of the plate 52 from a state where the load is 25 kgf to a state where the load is 50 kgf is measured. The load difference, 25 kgf, is divided by the displacement (cm) to calculate the lateral pressure stiffness value Gis (kgf / cm). The lateral pressure stiffness value Gis is measured with the strings 12 removed from the frame 4.

[0031] From the viewpoint of resilience performance, the lateral pressure stiffness value Gis is preferably 45 kgf / cm or more, more preferably 50 kgf / cm or more, and particularly preferably 60 kgf / cm or more. From the viewpoint of controllability, the lateral pressure stiffness value Gis is preferably 100 kgf / cm or less, more preferably 90 kgf / cm or less, and particularly preferably 80 kgf / cm or less.

[0032] The in-plane rigidity index Gi is preferably 1.40 or greater. A tennis racket 2 with an in-plane rigidity index Gi of 1.40 or greater has excellent spin performance. It is presumed that the reason this racket 2 has excellent spin performance is that deflection of the head 14 in the axial direction Y is suppressed upon impact with a tennis ball. It is presumed that in a head 14 with little deflection in the axial direction Y, the real axial length of the longitudinal threads 32b upon impact is large. It is presumed that the deformation and restoration of these longitudinal threads 32b upon impact imparts a large rotational force to the tennis ball. From the viewpoint of spin performance, the in-plane rigidity index Gi is more preferably 1.45 or greater, and particularly preferably 1.50 or greater. The upper limit of the range of the in-plane rigidity index Gi of a tennis racket 2 that can be used in practice is 1.80.

[0033] [Out-of-plane stiffness index Go] This tennis racket 2 has an appropriate out-of-plane stiffness index Go. The out-of-plane stiffness index Go is the product of the throat stiffness value Gos (kgf / cm) and the hitting surface stiffness value Goh (kgf / cm). The out-of-plane stiffness index Go is calculated using the following formula. Go = Gos × Goh

[0034] 11(a) and (b) show a method for measuring the throat stiffness value Gos. For this measurement, a first bar 54a, a second bar 54b, and a third bar 54c are prepared. These bars 54 are made of steel. Each bar 54 has a circular cross-sectional shape with a radius of 5.0 mm. The bars 54 extend along the width direction X. The axial distance between the first bar 54a and the third bar 54c is 100 mm, and the axial distance between the third bar 54c and the second bar 54b is 100 mm. The first bar 54a is located closer to the head 14 than one end P1 of the throat 16. The second bar 54b is located closer to the grip 6 than the other end P2 of the throat 16. The racket 2 is placed on the first bar 54a and the second bar 54b. The width direction X and the axial direction Y of the racket 2 are aligned horizontally. The third bar 54c descends, and a load is applied to the racket 2. The displacement (cm) of the third bar 54c is measured when the load changes from 25 kgf to 50 kgf. The difference in load, 25 kgf, is divided by the displacement (cm) to calculate the throat stiffness value Gos (kgf / cm). The throat stiffness value Gos is measured with the string 12 removed from the frame 4.

[0035] From the viewpoint of resilience performance, the throat stiffness value Gos is preferably 350 kgf / cm or more, more preferably 370 kgf / cm or more, and particularly preferably 400 kgf / cm or more. From the viewpoint of controllability, the throat stiffness value Gos is preferably 480 kgf / cm or less, more preferably 460 kgf / cm or less, and particularly preferably 440 kgf / cm or less.

[0036] 12(a) and (b) show a method for measuring the ball-striking surface stiffness value Goh. For this measurement, a first bar 56a, a second bar 56b, and a third bar 56c are prepared. These bars 56 are made of steel. Each bar 56 has a circular cross-sectional shape with a radius of 10.0 mm. The bars 56 extend along the width direction X. The axial distance between the first bar 56a and the third bar 56c is 170 mm, and the axial distance between the third bar 56c and the second bar 56b is also 170 mm. The first bar 56a is located at the top Pt of the head 14. The racket 2 is placed on the first bar 56a and the second bar 56b. The width direction X and the axial direction Y of the racket 2 are aligned with the horizontal. The third bar 56c is lowered, and a load is applied to the racket 2. The displacement (cm) of the third bar 56c is measured as the load changes from 25 kgf to 50 kgf. The load difference of 25 kgf is divided by the displacement (cm) to calculate the ball-striking surface stiffness value Goh (kgf / cm). The ball-striking surface stiffness value Goh is measured with the strings 12 removed from the frame 4.

[0037] From the viewpoint of resilience performance, the stiffness value Goh of the ball-striking surface is preferably 100 kgf / cm or more, more preferably 110 kgf / cm or more, and particularly preferably 120 kgf / cm or more. From the viewpoint of control performance, the stiffness value Goh of the ball-striking surface is preferably 170 kgf / cm or less, more preferably 160 kgf / cm or less, and particularly preferably 150 kgf / cm or less.

[0038] The out-of-plane rigidity index Go is preferably 60,000 or greater and 85,000 or less. A tennis racket 2 having an out-of-plane rigidity index Go of 60,000 or greater has excellent resilience performance. From this viewpoint, the out-of-plane rigidity index Go is more preferably 65,000 or greater, and particularly preferably 70,000 or greater. A tennis racket 2 having an out-of-plane rigidity index Go of 85,000 or less has excellent shot feel and controllability. From this viewpoint, the out-of-plane rigidity index Go is more preferably 83,000 or less, and particularly preferably 80,000 or less.

[0039] [Moment of inertia Mi] In this tennis racket 2, the moment of inertia Mi about the axis Y is appropriate. Figure 13 shows a method for measuring this moment of inertia Mi. In this measurement, the racket 2 is fixed to a string 58 at a position 15 mm from the grip end. The racket 2 is suspended from this string 58. The axial direction Y of the racket 2 coincides with the vertical direction. The racket 2 is rotated around the axis of the vertical direction Y. The period Tc (sec) of this rotation is measured, and the moment of inertia Mi (g cm) is calculated based on the following formula: 2 ) is calculated. Mi = 254458 · (Tc / π) 2 - 8357 The moment of inertia Mi is measured with the strings 12 removed from the frame 4.

[0040] The moment of inertia Mi is 13,500 g cm 2 More than 15000g cm 2 The following is preferable: Moment of inertia Mi is 13500g·cm 2 In the tennis racket 2 described above, when a tennis ball hits a location other than the sweet spot, the change in the angle of the face 20 is small. In other words, this racket 2 has excellent face stability. From this perspective, the moment of inertia Mi is 13800 g cm 2 More than 14000g·cm is preferable. 2 The moment of inertia Mi is 15000g cm or more. 2 Tennis racket 2, which has a moment of inertia of 14900 g cm, provides a sharp feel when hitting the ball. 2 Less than 14800 g·cm is preferable. 2 The following are particularly preferred:

[0041] [Inertia index II] The index of inertia Ii is appropriate for this tennis racket 2. The index of inertia Ii is calculated by the following formula. Ii = Mi / (Wr Lc) In this formula, Wr represents the mass (g) of the racket 2, and Lc represents the distance (mm) from the end of the grip 6 to the center of gravity of the racket 2.

[0042] The index of inertia Ii is preferably 0.150 or greater. A tennis racket 2 with an index of inertia Ii of 0.150 or greater has excellent surface stability. From this perspective, the index of inertia Ii is more preferably 0.152 or greater, and particularly preferably 0.153 or greater. The upper limit of the range of the index of inertia Ii of a tennis racket 2 that can be used in practical use is 0.180.

[0043] [mass] The mass of the tennis racket 2 is preferably 260 g or more and 320 g or less. A racket 2 with a mass of 260 g or more has excellent resilience performance. From this viewpoint, the mass is more preferably 270 g or more, and particularly preferably 285 g or more. A racket 2 with a mass of 320 g or less has excellent spin performance. From this viewpoint, the mass is more preferably 310 g or less, and particularly preferably 305 g or less. The mass is measured with the strings 12 removed from the frame 4.

[0044] [Tennis racket performance] This tennis racket 2 has an in-plane stiffness index Gi of 1.40 or more, an out-of-plane stiffness index Go of 60,000 or more and 85,000 or less, and a stiffness of 3,500 g cm 2 More than 15000g cm 2 The moment of inertia Mi is 0.150 or less, and the index of inertia Ii is 0.150 or more. This tennis racket 2 has an excellent balance of repulsion performance, spin performance, and surface stability.

[0045] As described above, the tennis racket 2 includes bias-type reinforcing fibers. These bias-type reinforcing fibers can contribute to an in-plane stiffness index Gi of 1.40 or greater and an out-of-plane stiffness index Go of 60,000 or greater and 85,000 or less. In particular, reinforcing fibers 42 having an absolute value of an inclination angle (θa or θb) of 40° or greater and 50° or less can contribute to the in-plane stiffness index Gi and the out-of-plane stiffness index Go. The proportion of reinforcing fibers 42 having an absolute value of an inclination angle of 40° or greater and 50° or less to all reinforcing fibers 42 included in the frame 4 is preferably 8% by mass or greater, more preferably 10% by mass or greater, and particularly preferably 12% by mass or greater. This proportion is preferably 30% by mass or less, more preferably 25% by mass or less, and particularly preferably 20% by mass or less.

[0046] By adjusting the material, thickness, density, etc. of the reinforcing fibers 42, an in-plane stiffness index Gi of 1.40 or more and an out-of-plane stiffness index Go of 60,000 or more and 85,000 or less can be achieved. [Example]

[0047] The effects of the racket according to the example will be explained below, but the scope of the disclosure in this specification should not be construed as being limited based on the description of this example.

[0048] [Example 1] A tennis racket was manufactured. The frame of this racket had multiple fiber-reinforced layers. The ratio of the mass of the reinforcing fibers with an absolute value of the inclination angle (θa or θb) of 40° or more and 50° or less to the total mass of the reinforcing fibers was 14%. The face area of ​​this racket was 100 in 2 The mass of this racket, including the grip, cap, and grommets but excluding the strings, was 300 g. The overall length of this racket was 686 mm. The distance Lc from the grip end to the center of gravity of this racket was 320 mm. The in-plane stiffness index Gi, measured with the grip, cap, and grommets but excluding the strings, of this racket was 1.57, the out-of-plane stiffness index Go was 75548, and the moment of inertia Mi was 14713 g cm 2and the inertia index Ii was 0.153.

[0049] [Examples 2-4 and Comparative Examples 1-6] Tennis rackets were obtained in Examples 2-4 and Comparative Examples 1-6, the specifications of which are shown in Tables 1 and 2 below.

[0050] [Ball speed and spin rate] Two advanced tennis players were asked to play a rally using each tennis racket. The velocity (initial velocity) and spin rate of the tennis ball were measured immediately after impact. The averages of multiple measurements are shown in Tables 1 and 2 below.

[0051] [Ball feel] The tennis players were asked to rate the surface stability performance during the rallies according to the following criteria. A: Good B: Not bad C: Bad The results are shown in Tables 1 and 2 below.

[0052] [Table 1]

[0053] [Table 2]

[0054] As is clear from Tables 1 and 2, the tennis rackets of the examples have an excellent balance of repulsion performance, spin performance, and surface stability. These evaluation results clearly demonstrate the superiority of these rackets.

[0055] [Disclosure items] Each of the following sections discloses a preferred embodiment.

[0056] [Item 1] The in-plane stiffness index Gi, which is the ratio of the apex pressure stiffness value Git (kgf / cm) to the side pressure stiffness value Gis (kgf / cm), is 1.40 or more; The out-of-plane stiffness index Go, which is the product of the throat stiffness value Gos (kgf / cm) and the ball-hitting surface stiffness value Goh (kgf / cm), is 60,000 or more and 85,000 or less; The moment of inertia Mi about that axis is 13500 g cm 2 More than 15000g cm 2 is as follows: A racket having an inertia index Ii calculated by the following formula of 0.150 or more. Ii = Mi / (Wr Lc) (In this formula, Wr represents the mass of the racket (g), and Lc represents the distance from the grip end to the center of gravity of the racket (mm).)

[0057] [Item 2] Item 1. The racket according to item 1, wherein the mass Wr is equal to or greater than 285 g and equal to or less than 305 g.

[0058] [Item 3] It has a frame, The material of the frame is a fiber reinforced resin containing a plurality of reinforcing fibers, 3. The racket according to item 1 or 2, wherein the ratio of reinforcing fibers having an absolute value of an inclination angle of 40° or more and 50° or less to all reinforcing fibers contained in the frame is 8% by mass or more and 30% by mass or less. [Industrial Applicability]

[0059] The aforementioned racket is also suitable for soft tennis, squash, padel, badminton, etc. [Explanation of symbols]

[0060] 2. Tennis rackets 4. Frame 6. Grip 10 Grommet 12 strings 14...head 16. Throat 18. Shaft 20...face 22. York 24...Groove 26...hole 28...Base 30... pipe 32...threads 32a Horizontal thread 32b Vertical thread 34 Prepreg 34a···First prepreg 34b Second prepreg 34c···Third prepreg 36...Laminate 40...Matrix 42a···First reinforced fiber 42b Second reinforcing fiber 42c···Third reinforcement fiber

Claims

1. The in-plane stiffness index Gi, which is the ratio of the apex pressure stiffness value Git (kgf / cm) to the side pressure stiffness value Gis (kgf / cm), is 1.40 or more, an out-of-plane stiffness index Go, which is the product of the throat stiffness value Gos (kgf / cm) and the ball-striking surface stiffness value Goh (kgf / cm), is 60,000 or greater and 85,000 or less; The moment of inertia Mi around that axis is 13,500 g cm ２ More than 15000g・cm ２ is as follows: A racket having an inertia index Ii calculated by the following formula of 0.150 or more. Ii = Mi / (Wr・Lc) (In this formula, Wr represents the mass of the racket (g), and Lc represents the distance (mm) from the grip end to the center of gravity of the racket.)

2. 2. The racket according to claim 1, wherein the mass Wr is equal to or greater than 285 g and equal to or less than 305 g.

3. It has a frame, The material of the frame is a fiber reinforced resin containing a plurality of reinforcing fibers, 3. The racket according to claim 1, wherein the ratio of reinforcing fibers having an absolute value of an inclination angle of 40° or more and 50° or less to all reinforcing fibers contained in the frame is 8% by mass or more and 30% by mass or less.

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