Racket

Abstract

Provided is a racket having excellent resilience. The racket is provided with a racket frame 4. The racket frame 4 comprises a racket head 14. The head 14 has a first highly elastic layer 37a and a second highly elastic layer 37b. Each high-elasticity layer 37 is located on the inner side of the head 14 in the thickness direction. The highly elastic layer (37) contains straight reinforcing fibers. The ratio (G2 / G1) of the striking surface stiffness value (G2) to the side pressure stiffness value (G1) in the racket frame (4) is 3.20 or more. The ratio (Tf / Wf) of the thickness (Tf) to the width (Wf) in the frame (4) is preferably 2.0 or more.

Description

TECHNICAL FIELD

[0001] The present specification discloses a racket suitable for tennis, soft tennis, squash, cage tennis, badminton, etc. BACKGROUND

[0002] In tennis, a ball is hit by a racket. By the hit, the kinetic energy of the racket is transmitted to the ball, and the ball flies. A ball hit by a racket having excellent rebound performance can fly at a high speed. A high flying speed is advantageous in a tennis game. Japanese Patent Laid-Open No. 5-15617 discloses a racket having excellent rebound performance. PRIOR ART DOCUMENT PATENT DOCUMENT

[0003] PATENT DOCUMENT 1 Japanese Patent Laid-Open No. 5-15617 SUMMARY PROBLEMS TO BE SOLVED BY THE INVENTION

[0004] A tennis player desires further improvement in rebound performance. The present applicant aims to provide a racket having excellent rebound performance. MEANS FOR SOLVING PROBLEMS

[0005] The racket disclosed in the present specification has a racket frame including a racket head. The ratio (G2 / G1) of the ball hitting surface stiffness value G2 to the side pressure stiffness value G1 in the racket frame is 3.20 or more. EFFECTS OF THE INVENTION

[0006] The racket has excellent rebound performance. A ball hit by the racket can fly at a high speed. BRIEF DESCRIPTION OF DRAWINGS

[0007] Figure 1 Figure 1 is a front view showing a racket according to an embodiment. Figure 2 Figure 2 is a right side view showing the racket of Figure 1 Figure 3 Figure 3 is an exploded view showing a part of the racket of Figure 1 Figure 4 Figure 4 is a perspective view showing a part of a manufacturing process of the racket of Figure 1 Figure 5 Figure 5 is an enlarged sectional view taken along the line V-V of Figure 1 Figure 6 ​​​​​​​​​​​​​​​​Figure 6 is an enlarged sectional view taken along the VI-VI line of Figure 5 . Figure 7 Figure 7 is an enlarged view showing a portion of a pre-preg material of a first fiber-reinforced layer of a head for Figure 6 . Figure 8 Figure 8 is an enlarged view showing a portion of a pre-preg material of a second fiber-reinforced layer of a head for Figure 6 . Figure 9 Figure 9 is a perspective view showing a portion of a high-elasticity layer of a head for Figure 6 . Figure 10 Figure 10 is an enlarged view showing a portion of a pre-preg material of a high-elasticity layer for Figure 9 . Figure 11 Figure 11 is a graph showing a relationship between a side pressure rigidity value and a ball striking face rigidity value of a frame of a tennis racket for Figure 1 . Figure 12 Figure 12 is a front view showing a method of measuring a side pressure rigidity value of a frame of a tennis racket for Figure 1 . Figure 13 Figure 13 (a) is a plan view showing a method of measuring a ball striking face rigidity value of a frame of a tennis racket for Figure 1 , Figure 13 (b) is a front view thereof. [EXPLANATION OF REFERENCE NUMERALS] 2: tennis racket 4: frame 6: grip 10: grommet 12: string 14: head 16: throat 18: shaft 20: face 22: yoke 24: groove 26: wire hole 28: base 30: pipe 32: wire 32a: cross wire​​​​​​​​​​​​​​ 32b: longitudinal line 34: prepreg 34a: first prepreg 34b: second prepreg 34c: third prepreg 36: laminate 37: high-elasticity layer 37a: first high-elasticity layer 37b: second high-elasticity layer 38: fiber-reinforced layer 38a: first fiber-reinforced layer 38b: second fiber-reinforced layer 38c: third fiber-reinforced layer 40: matrix 42a: first reinforcing fiber 42b: second reinforcing fiber 42c: third reinforcing fiber DETAILED DESCRIPTION

[0008] A preferred embodiment will be explained in detail below with appropriate reference to the drawings.

[0009] Figures 1-3 A tennis racket 2 is shown in FIG. 1. The racket 2 has a racket frame 4, a handle skin 6, an end cap 8, a cover 10, and a string 12. The racket 2 can be used for hard tennis. Figure 1 And 2 In FIG. 1, an arrow X indicates a width direction of the racket 2, an arrow Y indicates an axis direction of the racket 2, and a Z direction indicates a thickness direction of the racket 2. Figure 2 In FIG. 1, the illustration of the cover 10 and the string 12 is omitted.

[0010] The racket frame 4 has a head 14, a first neck 16a, a second neck 16b, and a handle 18. The head 14 forms the outline of a face 20 (described below). The head 14 has a generally elliptical shape in plan view. The long diameter direction of the ellipse coincides with the axis direction Y of the racket 2. The short diameter direction of the ellipse coincides with the width direction X of the racket 2. Figure 1 In FIG. 1, a symbol Ch indicates the center of the head 14. The first neck 16a extends from the head 14. The second neck 16b extends from the head 14. The second neck 16b meets the first neck 16a at a position away from the head 14. The handle 18 extends from the meeting point of the two necks 16. The handle 18 is continuous with the necks 16. In the head 14, the portion sandwiched between the two necks 16 is a yoke 22. The racket 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 various reinforcing fibers. The frame 4 contains multiple fiber reinforcement layers. The fiber reinforcement layers are described in detail below.

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

[0013] Examples of reinforcing fibers for the frame 4 include carbon fiber, metal fiber, glass fiber, and aramid fiber. Long carbon fibers are particularly suitable for the frame 4. Multiple fibers can also be used in combination.

[0014] like Figure 2 and 3 As shown, the racket head 14 has a groove 24. The groove 24 is recessed from the outer peripheral surface of the racket head 14. Except for the yoke 22, the groove 24 is formed over almost the entire circumference of the racket head 14. The racket head 14 further has a plurality of wire holes 26. A plurality of wire holes 26 are arranged over almost the entire circumference of the racket head 14.

[0015] The handle 6 is formed by wrapping the handle 18 with adhesive tape. The handle 6 prevents slippage between the player's hand and the racket 2 when swinging the tennis racket 2.

[0016] like Figure 3 As shown, the sheath 10 has a base 28 and a plurality of string tubes 30. The base 28 has a strip shape. Each string tube 30 is integrally formed with the base 28. The string tube 30 stands upright on the base 28. The sheath 10 is typically made of a synthetic resin that is softer than the frame 4. The tennis racket 2 may also have multiple sheaths 10. The number of string tubes 30 in each sheath 10 may also be one.

[0017] The sheath 10 is installed on the racket head 14. With the sheath 10 installed on the racket head 14, the base 28 is received in the groove 24. A portion of the base 28 may also be exposed from the groove 24. Furthermore, with the sheath 10 installed on the racket head 14, the wire sheath 30 passes through the wire hole 26.

[0018] like Figure 1 As shown, the string 12 is tensioned to the head 14. The string 12 is tensioned along the width direction X and the axial direction Y. The string 12 passes through the wire guard 30. A large number of threads 32 are formed through the string 12. The portion of the string 12 extending along the width direction X is called a horizontal thread 32a. The portion of the string 12 extending along the axial direction Y is called a vertical thread 32b. The racket face 20 is formed by the multiple horizontal threads 32a and the multiple vertical threads 32b. The racket face 20 is approximately along the XY plane. Figure 1A portion of the racket face 20 is shown. The racket face 20 may also be formed by two or more strings 12.

[0019] The following is for reference. Figure 4 An example of the manufacturing method for racket 2 will be described below. In this method, a mandrel, a tube, and various prepreg materials 34 are prepared. Each prepreg material 34 is composed of multiple reinforcing fibers and a matrix resin arranged side-by-side. In this method, the mandrel is first inserted into the tube. The prepreg materials 34 are then sequentially wound around the tube. Through winding, the prepreg materials 34 are made into a cylindrical shape. Figure 4 The diagram shows a cylindrical prepreg material 34p and a sheet-like prepreg material 34s. Figure 4 The diagram omits the mandrel and sleeve.

[0020] By rotating the mandrel, prepreg material 34s is wound onto prepreg material 34p. Through this winding, prepreg material 34s takes on a cylindrical shape, resulting in a laminate 36. Other prepreg materials 34 can be further wound onto this laminate 36 as needed. Various sheet-like prepreg materials 34s can also be overlapped and wound onto the mandrel or prepreg material 34p. Figure 4 In the diagram, arrow A1 indicates the length direction of the laminate 36.

[0021] After the mandrel is removed from the sleeve, the sleeve and laminate 36 are placed in a mold. Gas is filled into the sleeve within the mold, causing it to expand. This expansion presses the prepreg material 34 onto the cavity surface of the mold. The prepreg material 34 is heated, causing the matrix resin to cure. Curing yields a molded body. The molded body has a shape with the cavity surface shape reversed.

[0022] The molded body has a string hole 26. Further surface grinding and coating are performed on the molded body to obtain the frame 4. A handle skin 6 and a protective sleeve 10 are then installed on the frame 4. The string 12 is then tensioned onto the frame 4 to complete the tennis racket 2.

[0023] Figure 5 It is along Figure 1 An enlarged cross-sectional view of the VV line. This cross-section is along an axis perpendicular to the frame 4 and passes through the center Ch of the racket head 14. The racket head 14 has a first high-elasticity layer 37a and a second high-elasticity layer 37b (see also [reference]). Figure 2 Each highly elastic layer 37 is located inside the thickness direction in the racket head 14.

[0024] Figure 6 It is along Figure 5 Enlarged cross-sectional view of the VI-VI line. Figure 6The head 14 is shown in FIG. 1. The head 14 has a plurality of fiber reinforced layers 38. In the present embodiment, the head 14 includes a plurality of first fiber reinforced layers 38a, a plurality of second fiber reinforced layers 38b, and a plurality of third fiber reinforced layers 38c. In the present embodiment, the number of the first fiber reinforced layers 38a is 5, the number of the second fiber reinforced layers 38b is 5, and the number of the third fiber reinforced layers 38c is 4. The first fiber reinforced layers 38a and the second fiber reinforced layers 38b are alternately arranged in the thickness direction of the head 14 (the up-down direction in FIG. 1). The first high-elasticity layer 37a is formed by the plurality of third fiber reinforced layers 38c. The first high-elasticity layer 37a is located on the inner side (the lower side in FIG. 1) in the thickness direction of the head 14. Although not shown, the second high-elasticity layer 37b has a shape that is mirror-symmetrical to the shape of the first high-elasticity layer 37a. Figure 6 Figure 6

[0025] Figure 7 A first prepreg 34a for the first fiber reinforced layer 38a is shown in FIG. 1. The first prepreg 34a includes a matrix 40 and a plurality of first reinforcing fibers 42a arranged side by side. Each first reinforcing fiber 42a is inclined with respect to the length direction Al. Figure 7 In FIG. 1, the arrow θa indicates the inclination angle (absolute value) of the first reinforcing fiber 42a with respect to the length direction Al. The inclination angle θa is 30° or more and 60° or less. In the present specification, a reinforcing fiber 42 having an inclination angle of 30° or more and 60° or less is referred to as an “inclined reinforcing fiber”. The first fiber reinforced layer 38a includes the inclined reinforcing fiber.

[0026] Figure 8 A second prepreg 34b for the second fiber reinforced layer 38b is shown in FIG. 1. The second prepreg 34b includes a matrix 40 and a plurality of second reinforcing fibers 42b arranged side by side. Each second reinforcing fiber 42b is inclined with respect to the length direction Al. The inclination direction of the second reinforcing fiber 42b is opposite to the inclination direction of the first reinforcing fiber 42a (refer to FIG. 1). Figure 7 Figure 8 In FIG. 1, the arrow θb indicates the inclination angle (absolute value) of the second reinforcing fiber 42b with respect to the length direction Al. The inclination angle θb is 30° or more and 60° or less. The second reinforcing fiber 42b is an “inclined reinforcing fiber”. The second fiber reinforced layer 38b includes the inclined reinforcing fiber.

[0027] Figure 9 A portion of the high-elasticity layer 37 is shown in FIG. 1. As described above, the high-elasticity layer 37 has four third fiber reinforced layers 38c. These third fiber reinforced layers 38c can be obtained by winding and bending a sheet-shaped third prepreg 34c.

[0028] Figure 10 ​​​A third prepreg material 34c for the high-elasticity layer 37 is shown in FIG. 6. The third prepreg material 34c includes a matrix 40 and a plurality of third reinforcing fibers 42c arranged in parallel. Each third reinforcing fiber 42c extends along the length direction Al. The third reinforcing fiber 42c has an inclination angle (absolute value) of zero with respect to the length direction Al. The third reinforcing fiber 42c can also have a slight inclination with respect to the length direction Al. In the present specification, a reinforcing fiber 42 having an inclination angle (absolute value) of 10° or less with respect to the length direction Al is referred to as a "straight reinforcing fiber". The third fiber-reinforced layer 38c includes straight reinforcing fibers. In other words, the high-elasticity layer 37 includes straight reinforcing fibers.

[0029] Figure 11 The relationship between the side stiffness value G1 and the ball impact surface stiffness value G2 of the racket 4 is shown in a graph in FIG. 7. In the graph, a straight line indicated by the symbol S1 is represented by the following mathematical expression. G2 = 3.20 · G1 On the straight line S1, or in the tennis racket 2 drawn so as to depart from the straight line S1 and above the straight line S1, the ratio (G2 / G1) is 3.20 or more. The racket 2 satisfies the following mathematical expression. G2 > 3.20 · G1 (1) In the tennis racket 2 satisfying the mathematical expression (1), the side stiffness value G1 is relatively small, and the ball impact surface stiffness value G2 is relatively large.

[0030] In the tennis racket 2 satisfying the mathematical expression (1), the side stiffness value G1 is relatively small as described above. According to the finding obtained by the present inventor, in the racket 2, the modal amplitude of the tennis ball is relatively large in the vibration mode excited in the impact with the tennis ball. Therefore, the forward direction speed of the tennis ball at the end of the impact is large. In other words, the rebound performance of the racket 2 having the relatively small side stiffness value G1 is excellent.

[0031] In the tennis racket 2 satisfying the mathematical expression (1), the ball impact surface stiffness value G2 is relatively large as described above. According to the finding obtained by the present inventor, in the racket 2, the modal amplitude of the tennis ball is relatively large in the vibration mode excited in the impact with the tennis ball. Therefore, the forward direction speed of the tennis ball at the end of the impact is large. In other words, the rebound performance of the racket 2 having the relatively large ball impact surface stiffness value G2 is excellent.

[0032] As described above, the high-elasticity layer 37 is located in the thickness direction inside in the head 14. When the ball striking face stiffness value G2 of the tennis racket 2 is measured, a force in the thickness direction (Z direction) is applied to the head 14. Due to the force, the head 14 is bent in the thickness direction with respect to the handle 18. Since the third reinforcing fiber 42c is a straight reinforcing fiber, a large tensile stress is generated in the third reinforcing fiber 42c of the high-elasticity layer 37 due to the bending. The third reinforcing fiber 42c suppresses the bending. The high-elasticity layer 37 contributes to a large ball striking face stiffness value G2.

[0033] When the side pressure stiffness value G1 of the tennis racket 2 is measured, a force in the width direction (X direction) is applied to the head 14. Due to the force, the head 14 is bent in the width direction inside. Due to the bending, a small stress is generated in the third reinforcing fiber 42c. The third reinforcing fiber 42c does not hinder the deformation. In the tennis racket 2 having the high-elasticity layer 37, a small side pressure stiffness value G1 can be achieved.

[0034] Figure 12 A method of measuring the side pressure stiffness value G1 is shown in Fig. 6. Figure 12 In Fig. 6, the tennis racket 2 is placed on a base 44 of a rigid body. The width direction X of the tennis racket 2 coincides with the vertical direction. The axis direction Y of the tennis racket 2 coincides with the horizontal direction. A plate 46 of the rigid body is lowered, and the tennis racket 2 is loaded with a load. The displacement (cm) of the plate 46 from the state where the load is 25 kgf to the state where the load is 50 kgf is measured. The side pressure stiffness value G1 is calculated by dividing the difference between the loads 25 kgf by the displacement (cm). The side pressure stiffness value G1 is measured in the state where the strings 12 are removed from the frame 4.

[0035] From the viewpoint of the rebound performance, the side pressure stiffness value G1 is preferably 90 kgf / cm or less, more preferably 80 kgf / cm or less, and particularly preferably 75 kgf / cm or less. The side pressure stiffness value G1 of the tennis racket 2 which can be practically used is 20 kgf / cm or more.

[0036] Figure 13(a) and (b) show a method of measuring the ball striking face stiffness value G2. In this measurement, first, second and third bars 48a, 48b and 48c are prepared. These bars 48 are made of steel. Each bar 48 has a circular cross sectional shape with a radius of 10.0 mm. The bars 48 extend along the width direction X. The first bar 48a is located at the top of the head 14. The racket 2 is placed on the first bar 48a and the second bar 48b. The width direction X and the axis direction Y of the racket 2 coincide with the horizontal direction. The third bar 48c is lowered to load the racket 2 with a load. The displacement (cm) of the third bar 48c is measured from the state where the load is 25 kgf to the state where the load is 50 kgf. The ball striking face stiffness value G2 is calculated by dividing the difference between the loads (25 kgf) by the displacement (cm). The ball striking face stiffness value G2 is measured in the state where the strings 12 are removed from the frame 4.

[0037] From the viewpoint of the rebound performance, the ball striking face stiffness value G2 is preferably 100 kgf / cm or more, more preferably 200 kgf / cm or more, and particularly preferably 250 kgf / cm or more. The ball striking face stiffness value G2 of the practical racket 2 is 500 kgf / cm or less.

[0038] Figure 2 In the drawing, the arrow Lh indicates the length of the high elasticity layer 37 in the axis direction. In the present embodiment, this length Lh is the distance in the axis direction from the top Pt of the head 14 to the end Ed of the high elasticity layer 37. From the viewpoint of achieving a larger ball striking face stiffness value G2, the length Lh is preferably 170 mm or more, more preferably 250 mm or more, and particularly preferably 340 mm or more.

[0039] Figure 5 In the drawing, the arrow Tf indicates the thickness of the frame 4, and the arrow Wf indicates the width of the frame 4. The ratio (Tf / Wf) of the thickness Tf to the width Wf is preferably 2.0 or more. In the racket 2 in which the ratio (Tf / Wf) is in this range, a larger ratio (G2 / G1) is easily achieved. From this viewpoint, the ratio (Tf / Wf) is more preferably 2.2 or more, further preferably 2.4 or more, and particularly preferably 2.8 or more. The ratio (Tf / Wf) of the practical racket 2 is 4.0 or less.

[0040] From the viewpoint of easily achieving a larger ratio (G2 / G1), the thickness Tf is preferably 20.0 mm or more, more preferably 26.0 mm or more, further preferably 28.5 mm or more, and particularly preferably 33.0 mm or more. The thickness Tf of the practical racket 2 is 40.0 mm or less.

[0041] Figure 11In the graph of FIG. 2, a straight line indicated by a symbol S2 is represented by the following mathematical expression. G2 = 3.55 • G1 On the straight line S2, or in a tennis racket 2 drawn so as to depart from the straight line S2 and above the straight line S2, the ratio (G2 / G1) is 3.55 or more. In the tennis racket 2, the side pressure rigidity value G1 is relatively small, and the ball striking face rigidity value G2 is relatively large. According to the finding obtained by the present inventor, the rebound performance of the tennis racket 2 is further excellent. In other words, the rebound performance of the tennis racket 2 satisfying the following mathematical expression is further excellent. G2 > 3.55 • G1

[0042] Figure 11 In the graph of FIG. 3, a straight line indicated by a symbol S3 is represented by the following mathematical expression. G2 = 3.90 • G1 On the straight line S3, or in a tennis racket 2 drawn so as to depart from the straight line S3 and above the straight line S3, the ratio (G2 / G1) is 3.90 or more. In the tennis racket 2, the side pressure rigidity value G1 is relatively small, and the ball striking face rigidity value G2 is relatively large. According to the finding obtained by the present inventor, the rebound performance of the tennis racket 2 is further excellent. In other words, the rebound performance of the tennis racket 2 satisfying the following mathematical expression is further excellent. G2 > 3.90 • G1

[0043] Figure 11 In the graph of FIG. 4, a straight line indicated by a symbol S4 is represented by the following mathematical expression. G2 = 4.10 • G1 On the straight line S4, or in a tennis racket 2 drawn so as to depart from the straight line S4 and above the straight line S4, the ratio (G2 / G1) is 4.10 or more. In the tennis racket 2, the side pressure rigidity value G1 is relatively small, and the ball striking face rigidity value G2 is relatively large. According to the finding obtained by the present inventor, the rebound performance of the tennis racket 2 is extremely excellent. In other words, the rebound performance of the tennis racket 2 satisfying the following mathematical expression is extremely excellent. G2 > 4.10 • G1

[0044] [Evaluation] [Sample 1] A model of a tennis racket for simulation was produced having the following specifications. Width of the first and second prepreg materials: 250 mm Thickness Tf of the frame: 29.9 mm Elastic modulus of the reinforcing fibers of the high-elasticity layer: 80 tf / mm 2 Thickness of the high-elasticity layer: 0.825 mm

[0045] [Sample 2-120] The racket model of Sample 2-120 was produced in the same manner as Sample 1 except that the specifications shown in Tables 1-6 below were used.

[0046] [Simulation] The lateral stiffness value G1 and the hitting surface stiffness value G2 of each sample were calculated by simulation. Further, the speed of the tennis ball when it bounced off each sample was calculated by simulation. The results are shown in Tables 1-6 below.

[0047] [Table 1] Table 1 Evaluation Results

[0048] [Table 2] Table 2 Evaluation Results

[0049] [Table 3] Table 3 Evaluation Results

[0050] [Table 4] Table 4 Evaluation Results

[0051] [Table 5] Table 5 Evaluation Results

[0052] [Table 6] Table 6 Evaluation Results

[0053] In each sample shown in Table 1, the ratio (G2 / G1) was 4.10 or more. The ball speed of this sample was 5950 mm / s or more.

[0054] In each sample shown in Table 2, the ratio (G2 / G1) was 3.90 or more and less than 4.10. The ball speed of this sample was 5930 mm / s or more and less than 5950 mm.

[0055] In each sample shown in Table 3, the ratio (G2 / G1) was 3.55 or more and less than 3.90. The ball speed of this sample was 5900 mm / s or more and less than 5930 mm.

[0056] In each sample shown in Table 4, the ratio (G2 / G1) was 3.20 or more and less than 3.55. The ball speed of this sample was 5870 mm / s or more and less than 5900 mm.

[0057] The ratio (G2 / G1) in each sample shown in Tables 5 and 6 was less than 3.20. The ball speed of the sample was less than 5870 mm / s.

[0058] From the evaluation results, it was found that the tennis racket having a large ratio (G2 / G1) is advantageous.

[0059] [DISCLOSURE OF INVENTION] The following items are each a disclosure of a preferred embodiment.

[0060] [Item 1] A racket characterized by having a racket frame including a racket head, a ratio (G2 / G1) of a ball striking face stiffness value G2 to a side pressure stiffness value G1 in the racket frame is 3.20 or greater.

[0061] [Item 2] The racket according to item 1, wherein the racket head has a high elasticity layer located inside in a thickness direction and including straight reinforcing fibers.

[0062] [Item 3] The racket according to item 2, wherein the high elasticity layer is present in a cross section along an axis direction perpendicular to the racket frame and passing through a center of the racket head.

[0063] [Item 4] The racket according to any one of items 1 to 3, wherein a ratio (Tf / Wf) of a thickness Tf of the racket frame to a width Wf of the racket frame in a cross section along an axis direction perpendicular to the racket frame and passing through a center of the racket head is 2.0 or greater.

[0064] [Item 5] The racket according to any one of items 1 to 4, wherein the ratio (G2 / G1) is 3.55 or greater.

[0065] [Item 6] The racket according to item 5, wherein the ratio (G2 / G1) is 3.90 or greater.

[0066] [Item 7] The racket according to item 6, wherein the ratio (G2 / G1) is 4.10 or greater.

[0067] [Item 8] The racket according to any one of items 1 to 7, wherein the side pressure stiffness value G1 is 90 kgf / cm or less.

[0068] [Item 9] The racket according to any one of items 1 to 8, wherein the ball striking face stiffness value G2 is 100 kgf / cm or more.

INDUSTRIAL APPLICABILITY

[0069] The racket described above is also suitable for soft tennis, squash, cage tennis, badminton, etc.

Claims

1. A racket characterized in that, It has a frame that includes the racket head. The ratio of the hitting surface stiffness G2 to the lateral compression stiffness G1 in the frame, i.e., G2 / G1, is greater than 3.

20. The units for both G2 and G1 are kgf / cm.

2. A racket according to claim 1, wherein, The racket head has a highly elastic layer located inside the thickness direction and containing straight reinforcing fibers.

3. A racket according to claim 2, wherein, The highly elastic layer exists in a cross section of a plane along an axis perpendicular to the frame and passing through the center of the racket head.

4. A racket according to claim 1 or 2, wherein, In a cross-section along a plane perpendicular to the axis of the frame and passing through the center of the racket head, the ratio of the frame thickness Tf to the frame width Wf, i.e., Tf / Wf, is 2.0 or greater.

5. A racket according to claim 1 or 2, wherein, The ratio G2 / G1 is 3.55 or higher.

6. A racket according to claim 5, wherein, The ratio G2 / G1 is 3.90 or higher.

7. A racket according to claim 6, wherein, The ratio G2 / G1 is 4.10 or higher.

8. The racket according to claim 1 or 2, wherein, The lateral pressure stiffness value G1 is below 90 kgf / cm.

9. The racket according to claim 1 or 2, wherein, The stiffness value G2 of the striking surface is above 100 kgf / cm.

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