Golf club shaft

Abstract

To provide a light-weight shaft that is easily swung, and is suppressed in the excessive bending rigidity of a portion largely deformed due to whipping while the portion is reinforced.SOLUTION: A hollow shaft 6 includes a hoop layer, and a shaft weight is 50 g or less. The shaft 6 has a bending rigidity EI (N m2) and a shaft thickness t (mm). In a first region R1 having a distance from a tip end Tp of 200-300 mm, EI / t is 10 or more and 40 or less. In a second region R2 having a distance from the tip end Tp of 800-900 mm or less, EI / t is 45 or more and 80 or less. The hoop layer includes a partial hoop layer s6 partially arranged relative to the full length of the shaft 6. The partial hoop layer s6 includes a specific butt hoop layer s6 which does not exist in the first region R1 but is arranged in the whole of the second region R2. A thickness of the specific butt hoop layer s6 is 0.05 mm or more.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a golf club shaft.

Background Art

[0002] A lightweight shaft is advantageous for improving flight distance. In particular, shafts for average golfers tend to be lightweight. Japanese Patent Application Laid-Open No. 2014-171582 discloses a shaft that is lightweight based on the configuration of a bias layer.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In order to pursue weight reduction, it is necessary to make the entire shaft thinner. However, if the entire shaft is made thinner, the strength is insufficient in the region from the grip end to the middle part of the shaft, where it deforms greatly due to deflection during swinging. Therefore, it is conceivable to selectively reinforce this region. However, it has been found that this reinforcement increases the bending rigidity of this region for average golfers with a relatively low clubhead speed, making it impossible to obtain an appropriate feeling of deflection and reducing swingability.

[0005] An example of the present disclosure provides a lightweight shaft that is easy to swing, in which a portion that deforms greatly due to deflection is reinforced while suppressing an increase in the bending rigidity of the portion.

Means for Solving the Problems

[0006] In one aspect, a golf club shaft is formed by a plurality of fiber reinforced resin layers. The shaft has a tip end and a butt end. The shaft is hollow. The shaft weight is 50 g or less. At each axial position, it has a flexural rigidity EI (N·m 2 ) and a shaft wall thickness t (mm). In a first region where the distance from the tip end is 200 mm or more and 300 mm or less, EI / t is 10 or more and 40 or less. In a second region where the distance from the tip end is 800 mm or more and 900 mm or less, EI / t is 45 or more and 80 or less. The plurality of fiber reinforced resin layers include a straight layer, a bias layer, and a hoop layer. The straight layer includes a full-length straight layer disposed over the entire length of the shaft and a partial straight layer disposed partially with respect to the entire length of the shaft. The hoop layer includes a full-length hoop layer disposed over the entire length of the shaft and a partial hoop layer disposed partially with respect to the entire length of the shaft. The partial hoop layer includes a specific butt hoop layer that does not exist in the first region and is disposed over the entire second region. The thickness of the specific butt hoop layer is 0.05 mm or more.

Advantages of the Invention

[0007] As one aspect, it is possible to provide a lightweight shaft that is easy to swing, in which a portion with a large deformation due to bending is reinforced while an increase in the flexural rigidity of the portion is suppressed.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments will be described in detail with reference to the drawings as appropriate.

[0010] In the present application, the terms "layer" and "sheet" are used. "Layer" is the name after winding, while "sheet" is the name before winding. A "layer" is formed by winding a "sheet". That is, the wound "sheet" forms a "layer".

[0011] In the present application, the same reference numerals are used for the layer and the sheet. For example, the layer formed by the sheet s1 is referred to as layer s1.

[0012] In the present application, the axial direction means the axial direction of the shaft. This axial direction is the direction of the center line Z of the shaft. In the present application, the circumferential direction means the circumferential direction of the shaft. In the present application, the radial direction means the radial direction of the shaft. Unless otherwise specified, the length in the present application means the axial length. Unless otherwise specified, the distance in the present application means the axial distance. Unless otherwise specified, the position in the present application means the axial position.

[0013] FIG. 1 shows a golf club 2 including a golf club shaft 6 according to the present disclosure. The golf club 2 includes a head 4, a shaft 6, and a grip 8. The head 4 is provided at the tip portion of the shaft 6. The grip 8 is provided at the butt portion of the shaft 6. The shaft 6 is a shaft for a wood club. The golf club 2 is a driver (1-wood). The shaft 6 is a shaft for a driver.

[0014] Note that the head 4 and the grip 8 are not limited. Examples of the head 4 include a wood-type head, a utility-type head, an iron-type head, and a putter head. In the present embodiment, the head 4 is a wood-type head. The head 4 is a driver head.

[0015] The shaft 6 is formed of a plurality of fiber-reinforced resin layers. The type of fiber is not limited. In the present embodiment, as the fiber-reinforced resin layers, a carbon fiber-reinforced resin layer and a glass fiber-reinforced resin layer are used. The enlarged portion of FIG. 1 is a cross-sectional view of the shaft 6. As shown in this cross-sectional view, the shaft 6 is a tubular body. The shaft 6 has a hollow structure. The shaft 6 has a tip end Tp and a butt end Bt. In the golf club 2, the tip end Tp is located inside the head 4. In the golf club 2, the butt end Bt is located inside the grip 8.

[0016] The shaft 6 has a wall thickness t (see the enlarged portion of FIG. 1). The wall thickness t is the distance between the inner surface and the outer surface of the shaft 6. The wall thickness t is measured along the radial direction. The wall thickness t can be calculated by dividing the difference between the outer diameter and the inner diameter of the shaft 6 by 2. The wall thickness t is equal to the total thickness of the plurality of prepregs laminated. Depending on the axial position, the wall thickness t can vary. Note that in the present application, "t" meaning the value of the wall thickness of the shaft is also used as a drawing reference numeral.

[0017] In FIG. 1, what is indicated by the double-headed arrow Ls is the length of the shaft 6. The length Ls is the length from the tip end Tp to the butt end Bt. This length Ls is measured along the direction of the center line Z of the shaft 6. That is, this length Ls is measured along the axial direction.

[0018] The shaft 6 is formed by winding a plurality of prepreg sheets. In these prepreg sheets, the fibers are substantially oriented in one direction. Such a prepreg in which the fibers are substantially oriented in one direction is also referred to as a UD prepreg. "UD" is an abbreviation for unidirectional. Note that prepregs other than the UD prepreg may be used. For example, in the prepreg sheet, the fibers may be woven. In the present application, the prepreg sheet is also simply referred to as a sheet.

[0019] The prepreg sheet has fibers and a resin. This resin is also referred to as a matrix resin. Examples of such fibers include carbon fibers and glass fibers. Typically, this matrix resin is a thermosetting resin.

[0020] Examples of the matrix resin of the prepreg sheet include thermosetting resins and thermoplastic resins. From the viewpoint of shaft strength, as the matrix resin, a thermosetting resin is preferable, and an epoxy resin is more preferable.

[0021] The shaft 6 is manufactured by a sheet winding method. In the prepreg, the matrix resin is in a semi-cured state. In the shaft 6, the prepreg sheet is wound and cured. This curing means that the matrix resin in the semi-cured state is cured. This curing is achieved by heating. The manufacturing process of the shaft 6 includes a heating process. This heating cures the matrix resin of the prepreg sheet.

[0022] Figure 2 is a developed view of the prepreg sheets that make up the shaft 6. Figure 2 shows the sheets that make up the shaft 6. The shaft 6 is composed of a plurality of sheets. In the embodiment of Figure 2, the shaft 6 is composed of 12 sheets. The shaft 6 has sheets from the first sheet s1 to the twelfth sheet s12. This developed view shows the sheets that make up the shaft in order from the inner side in the radial direction of the shaft. They are wound in order starting from the sheet located on the upper side in Figure 2. In Figure 2, the left-right direction of the drawing coincides with the axial direction. In Figure 2, the right side of the drawing is the tip side of the shaft. In Figure 2, the left side of the drawing is the butt side of the shaft.

[0023] Figure 2 shows not only the winding order but also the arrangement in the axial direction. For example, in Figure 2, one end of the sheet s1 is located at the tip end Tp.

[0024] The shaft 6 has a straight layer, a bias layer, and a hoop layer. Figure 2 shows the fiber orientation angles of each sheet. The sheet marked "0°" is a straight sheet. The straight sheets constitute the straight layer.

[0025] The straight layer is a layer in which the fiber orientation is substantially 0° with respect to the axial direction. Due to errors during winding etc., the fiber orientation may not be completely parallel to the shaft axis direction. In the straight layer, the absolute angle of the fiber with respect to the shaft axis is 10° or less. The absolute angle is the absolute value of the angle (fiber angle) formed by the shaft axis and the fiber direction. That is, the absolute angle being 10° or less means that the fiber angle is -10 degrees or more and +10 degrees or less.

[0026] In the embodiment of Figure 2, the sheets (straight sheets) that make up the straight layer are the sheet s1, the sheet s5, the sheet s7, the sheet s8, the sheet s10, the sheet s11, and the sheet s12. The straight layer contributes significantly to the bending rigidity and bending strength.

[0027] The bias layer is a layer in which the orientation of the fibers is substantially inclined with respect to the axial direction. The bias layer significantly contributes to the torsional rigidity and torsional strength. Preferably, the bias layer is formed by a pair of two sheets in which the orientation of the fibers is inclined in opposite directions to each other. Preferably, this pair of sheets includes a layer with a fiber angle of -60° or more and -30° or less and a layer with a fiber angle of 30° or more and 60° or less. That is, preferably, in the bias layer, the absolute angle is 30° or more and 60° or less.

[0028] In the shaft 6, the sheets (bias sheets) constituting the bias layer are the sheet s2 and the sheet s4. The sheet s2 and the sheet s4 constitute a pair of sheets. This pair of sheets is wound in a state of being bonded to each other.

[0029] In FIG. 2, the fiber angle is described for each sheet. The plus (+) and minus (-) in the fiber angle indicate the inclination direction of the fibers. In the pair of sheets, the sheet with a plus fiber angle and the sheet with a minus fiber angle are combined. In each pair of sheets, the fibers are inclined in opposite directions to each other. In FIG. 2, although the fiber orientation directions of the sheet s2 and the sheet s4 are the same, since the sheet s4 is turned over and bonded to the sheet s2, the fiber directions are opposite to each other.

[0030] The hoop layer is a layer in which the fibers are arranged substantially along the circumferential direction of the shaft. Preferably, in the hoop layer, the absolute angle of the fibers is substantially 90° with respect to the shaft axis. However, due to errors during winding or the like, the fiber orientation may not be exactly 90° with respect to the shaft axis direction. Usually, in this hoop layer, the absolute angle of the fibers is 80° or more and 90° or less.

[0031] The hoop layer significantly contributes to the crushing rigidity and crushing strength of the shaft. The crushing rigidity is the rigidity against crushing deformation. The crushing deformation is the deformation caused by a force that presses the shaft inward in the radial direction. In a typical crushing deformation, the shaft cross-section changes from circular to elliptical. The crushing strength is the strength against crushing deformation.

[0032] In the embodiment of FIG. 2, the prepreg sheets for the hoop layer (hoop sheets) are sheet s3, sheet s6, and sheet s9. Hoop layer s3 is sandwiched between bias layer s2 and bias layer s4. Hoop layer s6 is sandwiched between straight layer s5 and straight layer s7. Hoop layer s9 is sandwiched between straight layer s8 (or straight layer s7) and straight layer s10.

[0033] In the production of the shaft 6 shown in FIG. 2, a combined sheet is used. The combined sheet is formed by bonding a plurality of sheets together.

[0034] In the embodiment of FIG. 2, three sets of combined sheets are used. The first combined sheet is a combination of sheet s2, sheet s3, and sheet s4. The second combined sheet is a combination of sheet s6 and sheet s7. The third combined sheet is a combination of sheet s9 and sheet s10.

[0035] As described above, in the present application, sheets and layers are classified according to the fiber orientation angle. In addition, in the present application, sheets and layers are classified according to the axial length.

[0036] Layers disposed over the entire axial direction are referred to as full-length layers. Sheets disposed over the entire axial direction are referred to as full-length sheets. The wound full-length sheets form full-length layers. On the other hand, layers disposed partially in the axial direction are referred to as partial layers. Sheets disposed partially in the axial direction are referred to as partial sheets. The wound partial sheets form partial layers.

[0037] Full-length layers that are bias layers are referred to as full-length bias layers. Full-length layers that are straight layers are referred to as full-length straight layers. Full-length layers that are hoop layers are referred to as full-length hoop layers.

[0038] In the embodiment of FIG. 2, the full-length bias layers are sheets s2 and s4. The full-length straight layers are sheets s5, s7, and s10. The shaft 6 has a plurality of full-length straight layers s5, s7, s10. The full-length hoop layers are sheets s3 and s9. The shaft 6 has a partial hoop layer s6 sandwiched between the full-length straight layers s5, s7.

[0039] A partial layer that is a bias layer is referred to as a partial bias layer. A partial layer that is a straight layer is referred to as a partial straight layer. A partial layer that is a hoop layer is referred to as a partial hoop layer.

[0040] The embodiment of FIG. 2 does not have a partial bias layer. The partial straight layers are sheets s1, s8, s11, and s12. The partial hoop layer is sheet s6. Except for the partial hoop layer s6, no partial hoop layer is provided.

[0041] Sheet s6 is a bat partial hoop layer. The bat partial hoop layer s6 is disposed at the rear end portion of the shaft 6. One end of the bat partial hoop layer s6 is located at the bat end Bt. Except for the bat partial hoop layer s6, no bat partial hoop layer is provided.

[0042] Sheets s1, s11, and s12 are chip partial straight layers. The chip partial straight layers are disposed at the front end portion of the shaft 6. One end of the chip partial straight layers s1, s11, s12 is located at the chip end Tp.

[0043] Sheet s8 is a bat partial straight layer. The bat partial straight layer s8 is disposed at the rear end portion of the shaft 6. One end of the bat partial straight layer s8 is located at the bat end Bt. Except for the bat partial straight layer s8, no bat partial straight layer is provided.

[0044] The general manufacturing process of this shaft 6 is described below.

[0045] [Outline of Shaft Manufacturing Process]

[0046] (1) Cutting process In the cutting process, the prepreg sheet is cut into a desired shape. By this process, each sheet shown in FIG. 2 is cut out.

[0047] Note that the cutting may be performed by a cutting machine or manually. In the case of manual work, for example, a cutter knife is used.

[0048] (2) Laminating process In this process, a plurality of sheets are laminated to produce the combined sheet described above. In the laminating process, heating and / or pressing may be used.

[0049] (3) Winding process In the winding process, a mandrel is prepared. A typical mandrel is made of metal. A release agent is applied to this mandrel. Further, an adhesive resin is applied to this mandrel. This resin is also referred to as a tacking resin. The cut sheet is wound around this mandrel. This tacking resin facilitates the attachment of the sheet end to the mandrel.

[0050] By this winding process, a wound body is obtained. In this wound body, the prepreg sheet is wound around the outside of the mandrel. This winding is performed, for example, by rolling the winding object on a plane. This winding may be performed manually or by a machine. This machine is referred to as a rolling machine.

[0051] (4) Taping process In the taping process, a tape is wound around the outer peripheral surface of the wound body. This tape is also referred to as a wrapping tape. This wrapping tape is wound spirally without gaps while tension is applied. By this wrapping tape, pressure is applied to the wound body. This pressure contributes to the reduction of voids.

[0052] (5) Curing process In the curing process, the wound body after taping is heated. Due to this heating, the matrix resin cures. During this curing process, the matrix resin temporarily becomes fluidized. Due to this fluidization of the matrix resin, air between or within the sheets can be discharged. The tightening force of the wrapping tape promotes the discharge of this air. As a result of this curing, a cured laminate is obtained.

[0053] (6) Mandrel withdrawal process and wrapping tape removal process After the curing process, a mandrel withdrawal process and a wrapping tape removal process are performed. Preferably, after the mandrel withdrawal process, the wrapping tape removal process is performed.

[0054] (7) Both-end cutting process In this process, both ends of the cured laminate are cut. This cutting makes the end faces of the chip end Tp and the butt end Bt flat.

[0055] (8) Polishing process In this process, the surface of the cured laminate is polished. On the surface of the cured laminate, spiral irregularities remain as traces of the wrapping tape. By polishing, these irregularities disappear and the surface becomes smooth.

[0056] (9) Coating process The cured laminate after the polishing process is coated.

[0057] The shaft 6 has bending rigidity at each position in the axial direction. This bending rigidity (or its value) is also referred to as EI. In the present application, the unit of EI is "N·m 2 ".

[0058] Figure 3 shows the measurement method of EI. As a measuring device, a universal material testing machine of the 2020 type (maximum load 500 kg) manufactured by Intesco can be used. The shaft 6 is supported from below by the first support point T1 and the second support point T2. While maintaining this support, a load F1 is applied from above to the measurement point T3. The direction of the load F1 is vertically downward. The distance between the point T1 and the point T2 is 200 mm. The position of the measurement point T3 is the position that bisects the distance between the point T1 and the point T2. The deflection amount H when the load F1 is applied is measured. The load F1 is applied by the pressure element D1. The tip of the pressure element D1 is a cylindrical surface with a curvature radius of 5 mm. The downward movement speed of the pressure element D1 is 5 mm / min. When the load F1 reaches 196 N, the movement of the pressure element D1 ends, and the deflection amount H at that time is measured. The deflection amount H is the displacement amount of the point T3 in the vertical direction. EI is calculated by the following formula.

[0059] EI (N·m 2 ) = F1 × L 3 / (48 × H) However, F1 is the maximum load (N), L is the distance between the support points (m), and H is the deflection amount (m). The maximum load F1 is 196 N, and the distance between the support points L is 0.2 m.

[0060] The strength at each position of the shaft 6 can be measured by the SG three-point bending strength test. This test is a test for golf club shafts defined by the Product Safety Association of Japan (CPSA number 0098). In this test, measurements at points T, A, B, and C are specified, but in this application, this strength test can also be applied to other positions other than the above four positions. In the measurement at these other positions, as much as possible, the measurement methods at points A, B, and C (span 300 mm) are adopted. At the tip and rear end of the shaft 6, where a span of 300 mm cannot be secured, the measurement method at point T (span 150 mm) is adopted.

[0061] As shown in FIG. 2, the shaft 6 has a first region R1 and a second region R2. The first region R1 is a region where the distance from the chip end Tp is 200 mm or more and 300 mm or less. The second region R2 is a region where the distance from the chip end Tp is 800 mm or more and 900 mm or less.

[0062] The shaft 6 has a point P2 that is 200 mm away from the chip end Tp, a point P3 that is 300 mm away from the chip end Tp, a point P8 that is 800 mm away from the chip end Tp, and a point P9 that is 900 mm away from the chip end Tp. The first region R1 is the region from point P2 to point P3. The second region R2 is the region from point P8 to point P9.

[0063] As described above, the shaft 6 includes a partial hoop layer s6 that is partially arranged with respect to the total length Ls of the shaft 6. As shown in FIG. 2, the partial hoop layer s6 is a partial hoop layer arranged over the entire second region R2. This partial hoop layer is also referred to as a specific bat hoop layer. The specific bat hoop layer s6 is arranged from a position closer to the chip side than point P8 to the bat end Bt. The chip-side end of the specific bat hoop layer s6 is located between point P3 and point P8. The bat-side end of the specific bat hoop layer s6 is located on the bat side of point P9. In the present embodiment, the bat-side end of the specific bat hoop layer s6 is located at the bat end Bt. The bat-side end of the specific bat hoop layer s6 may not be located at the bat end Bt. The specific bat hoop layer s6 does not exist in the first region R1. In the shaft 6, the partial hoop layer is only the specific bat hoop layer s6

[0064] As described above, the shaft 6 includes a partial straight layer s8. The partial straight layer s8 is a bat partial straight layer. As shown in FIG. 2, the chip-side end of the partial straight layer s8 is located on the bat side of point P9. The partial straight layer s8 does not exist in the second region R2. The partial straight layer s8 is arranged from a position on the bat side of point P9 to the bat end Bt.

[0065] In this application, the bat portion straight layer disposed on the bat side of the second region R2 is also referred to as the specific bat straight layer. The partial straight layer s8 is the specific bat straight layer. The specific bat straight layer s8 does not exist in the second region R2. In the shaft 6, there is no partial straight layer in the second region R2. In the shaft 6, the bat portion straight layer is only the specific bat straight layer s8.

[0066] The shaft 6 has chip portion straight layers s1, s11 on the chip side of the first region R1. The length of the chip portion straight layer s1 is 200 mm or less. The bat-side end of the chip portion straight layer s1 is located on the chip side of the point P2. The length of the chip portion straight layer s11 is 200 mm or less. The bat-side end of the chip portion straight layer s11 is located on the chip side of the point P2.

[0067] The shaft 6 has a chip portion straight layer s12 existing in the first region R1. The length of the chip portion straight layer s12 is greater than 200 mm. The bat-side end of the chip portion straight layer s12 is located on the bat side of the point P2. The bat-side end of the chip portion straight layer s12 is located between the point P2 and the point P3.

[0068] At each position of the shaft 6, EI / t can be calculated. EI / t is the ratio of the bending rigidity EI (N·m 2 ) to the shaft wall thickness t (mm).

[0069] In the shaft 6, in the second region R2, EI / t is suppressed. The second region R2 has large bending deformation during swinging. Also, since the second region R2 is close to the golfer's grip position, the deflection in the second region R2 is likely to be felt by the golfer. From the viewpoint of increasing strength while being lightweight, it is preferable to selectively reinforce the second region R2, which is a part with large deformation. However, when this reinforcement is carried out, especially for an average golfer with a relatively slow clubhead speed, the bending rigidity of the second region R2 becomes excessive. As a result, it has been found that no deflection is felt and the feeling during swinging deteriorates. In the second region R2, by increasing the wall thickness t while preventing the bending rigidity EI from becoming excessive, it is possible to ensure easy swinging and strength. From this viewpoint, EI / t in the second region R2 is preferably 80 or less, more preferably 70 or less, and even more preferably 60 or less. If EI / t is too small, the bending rigidity EI may be too small resulting in excessive deflection, or the wall thickness t may be too large making weight reduction difficult. From this viewpoint, EI / t in the second region R2 is preferably 45 or more, more preferably 46 or more, and even more preferably 47 or more.

[0070] Note that an average golfer with a relatively slow clubhead speed is a golfer with a clubhead speed of about 30 - 42 m / s with a driver.

[0071] From the viewpoint of easy swinging, EI in the second region R2 is preferably 45 (N·m 2 ) or less, more preferably 40 (N·m 2 ) or less, and even more preferably 35 (N·m 2 ) or less. If the second region R2 is excessively deformed, the strength may decrease or it may become difficult to swing. From this viewpoint, EI in the second region R2 is preferably 15 (N·m 2 ) or more, more preferably 20 (N·m 2 ) or more, and even more preferably 25 (N·m 2 ) or more.

[0072] From the viewpoint of the strength of the second region R2, the wall thickness t in the second region R2 is preferably 0.50 mm or more, more preferably 0.52 mm or more, still more preferably 0.54 mm or more, and even more preferably 0.56 mm or more. From the viewpoint of weight reduction of the shaft 6, the wall thickness t in the second region R2 is preferably 0.68 mm or less, more preferably 0.66 mm or less, still more preferably 0.64 mm or less, and even more preferably 0.62 mm or less.

[0073] If the bending rigidity of the first region R1 is excessive, the deflection of the tip of the shaft 6 may be insufficient and the head speed may decrease. From the viewpoint of ensuring the wall thickness t and increasing the strength while suppressing the bending rigidity from becoming excessive, EI / t in the first region R1 is preferably 40 or less, more preferably 35 or less, and still more preferably 30 or less. If EI / t is too small, the bending rigidity EI may be too small and the deflection may be excessive, or the wall thickness t may be too large and it may be difficult to reduce the weight. From this viewpoint, EI / t in the first region R1 is preferably 10 or more, more preferably 15 or more, and still more preferably 20 or more.

[0074] From the viewpoint of the head speed, EI in the first region R1 is preferably 30 (N·m 2 ) or less, more preferably 25 (N·m 2 ) or less, and still more preferably 20 (N·m 2 ) or less. If the first region R1 is excessively deformed, the strength may decrease or the springback may be insufficient and the head speed may decrease. From this viewpoint, EI in the first region R1 is preferably 8 (N·m 2 ) or more, more preferably 10 (N·m 2 ) or more, and still more preferably 12 (N·m 2 ) or more.

[0075] Note that springback is a phenomenon in which the deflection of the shaft where the head lags behind in the direction of swing progress returns. The head speed increases due to the springback in the downswing.

[0076] From the perspective of the strength of the first region R1, the wall thickness t in the first region R1 is preferably 0.52 mm or more, more preferably 0.54 mm or more, still more preferably 0.56 mm or more, and even more preferably 0.58 mm or more. From the perspective of weight reduction of the shaft 6, the wall thickness t in the first region R1 is preferably 0.78 mm or less, more preferably 0.76 mm or less, still more preferably 0.74 mm or less, and even more preferably 0.72 mm or less.

[0077] By arranging the specific bat hoop layer s6 in the second region R2, it is possible to suppress an increase in the bending rigidity EI and ensure appropriate deflection while reinforcing the second region R2. Therefore, a shaft 6 that is lightweight, has sufficient strength, and is easy to swing can be achieved.

[0078] From the perspective of reinforcing the entire second region R2, the axial length of the specific bat hoop layer s6 is preferably 350 mm or more, more preferably 400 mm or more, and still more preferably 450 mm or more. From the perspective of weight reduction of the shaft 6, the axial length of the specific bat hoop layer s6 is preferably 650 mm or less, more preferably 600 mm or less, and still more preferably 550 mm or less.

[0079] The thickness of the specific bat hoop layer s6 is larger than that of a normal hoop layer. The specific bat hoop layer s6 is thicker than the full-length hoop layer s3. The specific bat hoop layer s6 is thicker than the full-length hoop layer s9. The thickness of the specific bat hoop layer s6 is 1.8 times or more the thickness of the full-length hoop layers s3 and s9.

[0080] It has been found that by increasing the thickness of the specific bat hoop layer s6, an increase in the bending rigidity E1 in the second region R2 is suppressed while the strength of the second region R2 is further increased. From this perspective, the thickness of the specific bat hoop layer s6 is preferably 0.05 mm or more, more preferably 0.06 mm or more, still more preferably 0.07 mm or more, and even more preferably 0.08 mm or more. From the perspective of weight reduction of the shaft 6, the thickness of the specific bat hoop layer s6 is preferably 0.11 mm or less, more preferably 0.10 mm or less, and still more preferably 0.09 mm or less.

[0081] The thickness of the specific butt hoop layer s6 is Ta (mm), and the thickness of the full-length hoop layers s3 and s9 is Tb (mm). Tb is the maximum value of the thickness of the full-length hoop layers. For example, in the shaft 6, when the thickness of the full-length hoop layer s3 and the thickness of the full-length hoop layer s9 are different, the larger thickness is taken as Tb. From the viewpoint of increasing the strength of the second region R2 while suppressing an increase in the bending rigidity E1 in the second region R2, and from the viewpoint of making the shaft 6 lighter by thinning the full-length hoop layer, Ta / Tb is preferably 1.6 or more, more preferably 1.8 or more, and still more preferably 2.0 or more. If the thickness Ta is excessive, the weight of the shaft 6 increases. From this viewpoint, Ta / Tb is preferably 3.0 or less, more preferably 2.8 or less, and still more preferably 2.6 or less.

[0082] The shaft 6 has a full-length straight layer with a resin content of 20 mass% or less. This full-length straight layer is also referred to as a low-resin full-length straight layer. In the shaft 6, the layers s5 and s7 are low-resin full-length straight layers. From the viewpoint of available materials, the resin content of the low-resin full-length straight layer is preferably 18 mass% or more.

[0083] As shown in FIG. 2, the low-resin full-length straight layer s5 is in contact with the inside of the specific butt hoop layer s6. This low-resin full-length straight layer s5 is also referred to as the first low-resin full-length straight layer. The low-resin full-length straight layer s7 is in contact with the outside of the specific butt hoop layer s6. This low-resin full-length straight layer s7 is also referred to as the second low-resin full-length straight layer. The specific butt hoop layer s6 is sandwiched between the first low-resin full-length straight layer s5 and the second low-resin full-length straight layer s7. The resin content of the specific butt hoop layer s6 is larger than that of the low-resin full-length straight layers s5 and s7.

[0084] The two-layer low-resin full-length straight layer contributes to the weight reduction of the shaft 6. On the other hand, in the layer with a low resin content, the adhesive force with the adjacent layer may decrease. By interposing a specific butt hoop layer s6 with a wall thickness t of 0.05 mm or more and a resin content higher than 20% by mass between the low-resin layers s5 and s7, a decrease in the interlayer adhesive force in the second region R2 can be prevented. As a result, the strength of the second region R2 can be improved. From this perspective, the resin content of the specific butt hoop layer s6 is preferably 22% by mass or more, more preferably 23% by mass or more, and even more preferably 24% by mass or more. From the perspective of reducing the weight of the shaft 6, the resin content of the specific butt hoop layer s6 is preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 30% by mass or less. In the present application, the resin content of a certain layer is regarded as the resin content of the prepreg forming that layer.

[0085] As shown in FIG. 2, the shaft 6 has a tip portion straight layer s1 and a tip portion straight layer s12. The tip portion straight layer s1 is located inside the full-length bias layers s2 and s3. The tip portion straight layer s1 is the innermost layer of the shaft 6. The tip portion straight layer s12 is located outside the full-length bias layers s2 and s3. The tip portion straight layer s12 is the outermost layer of the shaft 6. The tip portion straight layer s12 is longer than the tip portion straight layer s1. The fiber elastic modulus of the tip portion straight layer s12 is larger than the fiber elastic modulus of the tip portion straight layer s1. The tip portion straight layer s1 does not reach the first region R1. The tip portion straight layer s1 does not exist in the first region R1. The tip portion straight layer s12 reaches the first region R1. The tip portion straight layer s12 has a portion existing in the first region R1. With such a configuration of the layers s1 and s12, the bending deformation can be effectively dispersed from the tip of the shaft 6 to the first region R1, and the stress concentration at the joint portion between the shaft 6 and the head 4 can be alleviated.

[0086] The fiber elastic modulus of the tip portion straight layer s1 is 10 t / mm 2The following is preferable. In this case, without making the bending rigidity of the tip portion of the shaft 6 excessive, the impact absorption energy of the tip portion can be increased. From this viewpoint, the fiber elastic modulus of the tip portion straight layer s1 is 10 t / mm 2 or less is preferable, 9 t / mm 2 or less is more preferable, 8 t / mm 2 or less is more preferable. From the viewpoint of the strength of the fiber, the fiber elastic modulus of the tip portion straight layer s1 is 3 t / mm 2 or more is preferable, 4 t / mm 2 or more is more preferable, 5 t / mm 2 or more is more preferable.

[0087] The tip portion straight layer may include a glass fiber reinforced layer reinforced with glass fibers. In the shaft 6, the tip portion straight layer s1 is a glass fiber reinforced layer. By using glass fibers, it is possible to increase the impact absorption energy while suppressing the bending rigidity.

[0088] In the second region R2, there is no end of the partial straight layer. At the end of the partial straight layer, since the change in bending rigidity is large, stress concentration may occur. By not having the end of the partial straight layer in the second region R2, the strength of the second region R2 can be improved.

[0089] As described above, the partial straight layer s8 is a specific butt straight layer that does not reach the second region R2. The specific butt straight layer s8 reinforces the portion grasped by the golfer and its vicinity, and does not increase the bending rigidity of the second region R2. Therefore, the shaft 6 has an appropriate flexural feeling and is easy to swing for an average golfer with a relatively slow head speed. Further, since the specific butt straight layer s8 does not reach the second region R2, it is short and contributes to the weight reduction of the shaft 6.

[0090] The fiber elastic modulus of the specific butt straight layer s8 is 10 t / mm 2It is preferably as follows. In this case, the strength can be increased without excessive bending rigidity at the rear end portion of the shaft 6. From this viewpoint, the fiber elastic modulus of the specific butt straight layer s8 is 10 t / mm 2 or less, preferably 9 t / mm 2 or less, more preferably 8 t / mm 2 or less, even more preferably. From the viewpoint of fiber strength, the fiber elastic modulus of the specific butt straight layer s8 is preferably 3 t / mm 2 or more, preferably 4 t / mm 2 or more, more preferably 5 t / mm 2 or more, even more preferably.

[0091] The specific butt straight layer s8 may be a glass fiber reinforced layer reinforced with glass fibers. By using glass fibers, the bending rigidity can be suppressed while reinforcing the rear end portion of the shaft 6.

[0092] From the viewpoint of suppressing an increase in bending rigidity in the second region R2, the axial length of the specific butt straight layer s8 is preferably 300 mm or less, more preferably 250 mm or less, even more preferably 200 mm or less. From the viewpoint of reinforcing the portion gripped by the golfer, the axial length of the specific butt straight layer s8 is preferably 140 mm or more, more preferably 160 mm or more, even more preferably 180 mm or more.

[0093] The shaft 6 has a tip portion straight layer s1 which is a glass fiber reinforced layer and a butt portion straight layer s8 which is a glass fiber reinforced layer. Glass fibers have a larger specific gravity than carbon fibers. By disposing glass fiber reinforced layers at both end portions of the shaft 6, the moment of inertia of the shaft 6 becomes large. As a result, the behavior of the shaft 6 during swinging can be stabilized. When the behavior of the shaft 6 is stabilized, the shot is stabilized. The rotation axis of this moment of inertia is a straight line passing through the center of gravity of the shaft 6 and perpendicular to the center line Z.

[0094] From the perspective of weight reduction, the shaft weight is preferably 50 g or less, more preferably 48 g or less, still more preferably 46 g or less, still more preferably 44 g or less, and still more preferably 42 g or less. From the perspective of strength, the shaft weight is preferably 34 g or more, more preferably 36 g or more, and still more preferably 38 g or more.

[0095] In the present disclosure, a shaft in which the deformation of the second region R2 is likely to increase during swinging is preferred. From this perspective, the length Ls of the shaft 6 is preferably 1100 mm or more, more preferably 1120 mm or more, and still more preferably 1140 mm or more. From the same perspective, the length Ls of the shaft 6 is preferably 1210 mm or less, more preferably 1200 mm or less, and still more preferably 1190 mm or less.

[0096] In the present disclosure, a shaft in which the deformation of the second region R2 is likely to increase during swinging is preferred. From this perspective, the length from the center position of the second region R2 to the tip end Tp is preferably 67% or more, more preferably 68% or more, and still more preferably 69% or more with respect to the length Ls of the shaft 6. From the same perspective, the length from the center position of the second region R2 to the tip end Tp is preferably 78% or less, more preferably 77% or less, and still more preferably 76% or less with respect to the length Ls of the shaft 6. The center position of the second region R2 is a position 850 mm away from the tip end Tp.

[0097] Tables 1 and 2 below are examples of prepregs that can be used for the shafts of the present disclosure. These prepregs are commercially available.

[0098] [Table 1]

[0099] [Table 2] [Examples]

[0100] [Examples] According to the manufacturing process of the shaft described above, a shaft identical to the shaft 6 of the above embodiment was fabricated. The sheet configuration of this shaft was made as shown in FIG. 2. The length Ls of the shaft was 1168 mm. The chip portion straight layer s1 and the specific butt straight layer s8 were made of a glass fiber reinforced layer. The product name "3255S-10" manufactured by Toray Industries, Inc. was used as the specific butt hoop layer s6. The shaft weight was 41 g.

[0101] [Comparative Example] A comparative example shaft was obtained in the same manner as in Example 1, except that the specific butt hoop layer s6 was replaced with a partial straight layer. The prepreg of this partial straight layer was the same as the specific butt hoop layer s6 of Example 1, i.e., "3255S-10".

[0102] [Measurement of Bending Rigidity EI] The bending rigidity EI was measured by the method described above. As shown in FIGS. 3 and 4 below, EI was measured every 50 mm. The measured values in the examples, together with the wall thickness t, are shown in Table 3 below. The measured values in the comparative example, together with the wall thickness t, are shown in Table 4 below. At all positions, the wall thickness t in the examples is the same as that in the comparative example.

[0103]

Table 3

[0104]

Table 4

[0105] FIG. 4 is a graph showing the distribution of the wall thickness t in the examples and the comparative example. The horizontal axis of this graph is the distance from the chip end Tp (unit: mm). The vertical axis of this graph is the wall thickness t (unit: mm).

[0106] FIG. 5 is a graph showing the distribution of EI / t in the embodiment. The horizontal axis of this graph is the distance from the chip end Tp (unit: mm). The vertical axis of this graph is EI / t (unit: N·m 2 / mm).

[0107] FIG. 6 is a graph showing the distribution of EI / t in the comparative example. The horizontal axis of this graph is the distance from the chip end Tp (unit: mm). The vertical axis of this graph is EI / t (unit: N·m 2 / mm).

[0108] As can be seen from Tables 3 and 4, in the embodiment, an excessive increase in the bending rigidity EI in the second region R2 is suppressed. Therefore, for an average golfer with a relatively slow head speed, appropriate deflection can be obtained in the second region R2, and swingability is achieved. Also, as can be seen from FIGS. 5 and 6, in the embodiment, since EI / t is in an appropriate range, it is lightweight yet excellent in strength and appropriate deflection can be obtained.

[0109] Referring to FIG. 4, the portion where the wall thickness t is minimum does not exist in the second region R2. The portion where the wall thickness t is minimum is located closer to the chip side than the second region R2. The portion where the wall thickness t is minimum is located between the first region R1 and the second region R2. In particular, in the present embodiment, the portion where the wall thickness t is minimum is located in the region where the distance from the chip end Tp is 450 to 650 mm. By making the portion where the wall thickness t is minimum closer to the chip side than the second region R2, the bending deformation in the second region R2 during swinging is alleviated. As a result, the load in the second region R2 is reduced.

[0110] As shown in FIG. 5, in the embodiment, in the region from 600 mm to 900 mm from the chip end Tp, EI / t increases as it is farther from the chip end Tp.

[0111] As shown in FIG. 5, in the embodiment, the variation rate of EI / t has little variation. Therefore, in the embodiment, the stress generated by the bending of the second region R2 can be dispersed and the strength can be improved. Further, since this variation rate is small, it is possible to suppress EI / t in the second region R2 from becoming excessive. From these viewpoints, it is preferable to reduce the variation rate of EI / t in the second region R2 and the region 600 to 800 mm from the chip end Tp adjacent thereto. Specifically, in a graph where the horizontal axis is the distance (mm) from the chip end and the vertical axis is EI / t (N·m 2 / mm), the variation rates of the six regions determined every 50 mm between 600 mm and 900 mm from the chip end are preferably all 0.20 or less, more preferably 0.15 or less, still more preferably 0.13 or less, and even more preferably 0.11 or less. From the viewpoint of suppressing the variation of the variation rate of EI / t and the viewpoint of appropriately ensuring EI / t in the second region R2, in a graph where the horizontal axis is the distance (mm) from the chip end and the vertical axis is EI / t (N·m 2 / mm), the variation rates of the six regions determined every 50 mm between 600 mm and 900 mm from the chip end are preferably all 0.020 or more, more preferably 0.025 or more, and still more preferably 0.030 or more.

[0112] This variation rate is the slope of the straight line connecting adjacent points in a line graph as shown in FIG. 5. These six regions are (1) the region where the distance from the chip end Tp is 600 to 650 mm, (2) the region where the distance from the chip end Tp is 650 to 700 mm, (3) the region where the distance from the chip end Tp is 700 to 750 mm, (4) the region where the distance from the chip end Tp is 750 to 800 mm, (5) the region where the distance from the chip end Tp is 800 to 850 mm, and (6) the region where the distance from the chip end Tp is 850 to 900 mm. Referring to Table 3, for example, the variation rate of the region where the distance from the chip end Tp is 600 to 650 mm is (39 - 36) / 50 = 0.06.

[0113] <Measurement of Strength> The three-point bending strength was measured at a point 850 mm from the tip Tp of the chip, which is the center position of the second region R2. The method for measuring the three-point bending strength is as described above. The measurement was made with a span of 300 mm.

[0114] The three-point bending strength at a point 850 mm from the tip Tp of the chip was 95 kgf in the example and 97 kgf in the comparative example. Generally, the straight layer has a large contribution to the bending strength, while the hoop layer has a small contribution to the bending strength. However, in the example, substantially the same strength as that of the comparative example in which the hoop layer was replaced with the straight layer was obtained. Also, the strength of the example exceeded 137% of the strength standards (40 kgf) at points A, B, and C determined by the Product Safety Association, and was 2.37 times or more of the strength standard. Thus, by using a thick specific bat hoop layer, the bending rigidity of the second region R2 was suppressed while ensuring the strength of the second region R2.

[0115] The following appendices are part of the invention included in the present disclosure. [Appendix 1] A hollow golf club shaft formed of a plurality of fiber-reinforced resin layers and having a tip end and a butt end, wherein the shaft weight is 50 g or less, at each axial position, having a bending rigidity EI (N·m 2 ) and a shaft wall thickness t (mm), in a first region where the distance from the tip end is 200 mm or more and 300 mm or less, EI / t is 10 or more and 40 or less, in a second region where the distance from the tip end is 800 mm or more and 900 mm or less, EI / t is 45 or more and 80 or less, wherein the plurality of fiber-reinforced resin layers includes a straight layer, a bias layer, and a hoop layer, the straight layer includes a full-length straight layer disposed over the entire length of the shaft and a partial straight layer disposed partially with respect to the entire length of the shaft, the hoop layer includes a full-length hoop layer disposed over the entire length of the shaft and a partial hoop layer disposed partially with respect to the entire length of the shaft, The partial hoop layer includes a specific butt hoop layer that does not exist in the first region and is disposed across the entire second region. A golf club shaft in which the thickness of the specific butt hoop layer is 0.05 mm or more. [Appendix 2] The partial straight layer includes a tip partial straight layer provided at the tip of the shaft and a butt partial straight layer provided at the rear end of the shaft. The golf club shaft according to Appendix 1, wherein the butt partial straight layer includes a specific butt straight layer disposed on the butt side of the second region and not present in the second region. [Appendix 3] The fiber elastic modulus of the specific butt straight layer is 10 t / mm 2 or less. The golf club shaft according to Appendix 2. [Appendix 4] The golf club shaft according to Appendix 3, wherein the specific butt straight layer is reinforced with glass fibers. [Appendix 5] The tip partial straight layer includes a glass fiber reinforced layer reinforced with glass fibers. The golf club shaft according to Appendix 4, wherein the glass fiber reinforced layer is disposed on the tip side of the first region and not present in the first region. [Appendix 6] The butt partial straight layer is only the specific butt straight layer. The golf club shaft according to any one of Appendices 2 to 5, wherein the partial hoop layer is only the specific butt hoop layer. [Appendix 7] The full-length straight layer includes a low-resin full-length straight layer having a resin content of 20% by mass or less. The resin content of the specific butt hoop layer is greater than 20% by mass. The golf club shaft according to any one of Appendices 1 to 6, wherein the low-resin full-length straight layer includes a first low-resin full-length straight layer in contact with the inside of the specific bat hoop layer and a second low-resin full-length straight layer in contact with the outside of the specific bat hoop layer. [Appendix 8] The golf club shaft according to any one of Appendices 1 to 7, wherein the thickness of the specific bat hoop layer is greater than the thickness of the full-length hoop layer. [Appendix 9] In a graph where the horizontal axis is the distance (mm) from the tip end and the vertical axis is EI / t (N·m 2 / mm), the rate of change in 6 regions determined every 50 mm between 600 mm and 900 mm from the tip end is all 0.20 or less. The golf club shaft according to any one of Appendices 1 to 7.

Explanation of Signs

[0116] 2 ··· Golf club 4 ··· Head 6 ··· Shaft 8 ··· Grip s1~s12 ··· Prepreg sheet (layer) R1 ··· First region R2 ··· Second region t ··· Wall thickness of the shaft Bt ··· Butt end Tp ··· Tip end

Claims

1. A hollow golf club shaft formed by a plurality of fiber reinforced resin layers and having a tip end and a butt end, wherein the shaft weight is 50 g or less, At each position in the axial direction, it has a bending rigidity EI (N·m ２ ), and a shaft wall thickness t (mm), and in a first region where the distance from the tip end is 200 mm or more and 300 mm or less, EI / t is 10 or more and 40 or less, in a second region where the distance from the tip end is 800 mm or more and 900 mm or less, EI / t is 45 or more and 80 or less, wherein the plurality of fiber reinforced resin layers include a straight layer, a bias layer, and a hoop layer, the straight layer includes a full-length straight layer disposed over the entire length of the shaft and a partial straight layer disposed partially with respect to the entire length of the shaft, the hoop layer includes a full-length hoop layer disposed over the entire length of the shaft and a partial hoop layer disposed partially with respect to the entire length of the shaft, the partial hoop layer does not exist in the first region and includes a specific butt hoop layer disposed over the entire second region, the thickness of the specific butt hoop layer is 0.05 mm or more, the partial straight layer includes a tip partial straight layer provided at the tip end of the shaft and a butt partial straight layer provided at the rear end of the shaft, the butt partial straight layer includes a specific butt straight layer disposed on the butt side rather than in the second region and not existing in the second region, a golf club shaft.

2. The fiber elastic modulus of the specific butt straight layer is 10 t / mm ２ The golf club shaft according to claim 1, wherein the fiber elastic modulus is 10 t / mm or less.

3. The golf club shaft according to claim 1 or 2, wherein the specific butt straight layer is reinforced with glass fibers.

4. the tip partial straight layer includes a glass fiber reinforced layer reinforced with glass fibers, the golf club shaft according to any one of claims 1 to 3, wherein the glass fiber reinforced layer is disposed on the tip side rather than in the first region and does not exist in the first region.

5. the butt partial straight layer is only the specific butt straight layer, the golf club shaft according to any one of claims 1 to 4, wherein the partial hoop layer is only the specific butt hoop layer.

6. the full-length straight layer includes a low-resin full-length straight layer having a resin content of 20% by mass or less, the resin content of the specific butt hoop layer is greater than 20% by mass, The golf club shaft according to any one of claims 1 to 5, wherein the low resin full-length straight layer includes a first low resin full-length straight layer in contact with the inside of the specific butt hoop layer and a second low resin full-length straight layer in contact with the outside of the specific butt hoop layer.

7. The golf club shaft according to any one of claims 1 to 6, wherein the thickness of the specific butt hoop layer is greater than the thickness of the full-length hoop layer.

8. In a graph where the horizontal axis is the distance (mm) from the tip of the chip and the vertical axis is EI / t (N·m ２ / mm), the change rate of six regions determined every 50 mm between 600 mm and 900 mm from the tip of the chip is 0.20 or less in each case. The golf club shaft according to any one of claims 1 to 7.

9. The golf club shaft according to any one of claims 1 to 8, wherein the shaft wall thickness t in the second region is 0.50 mm or more.

10. The golf club shaft according to any one of claims 1 to 9, wherein the thickness of the specific butt hoop layer is 0.06 mm or more.

11. The golf club shaft according to any one of claims 1 to 10, wherein when the thickness of the specific butt hoop layer is Ta (mm) and the thickness of the full-length hoop layer is Tb (mm), Ta / Tb is 1.6 or more and 3.0 or less.

12. The shaft weight is 42 g or less, the shaft wall thickness t in the second region is 0.56 mm or more, the thickness of the specific butt hoop layer is 0.08 mm or more, and the bending rigidity EI in the second region is 35 (N·m2) or less. The golf club shaft according to any one of claims 1 to 11.

Images