Golf ball

Abstract

To provide a golf ball suitable for a golf player who can achieve a sufficiently high trajectory by an initial element and also suitable for a golf player who cannot achieve the sufficiently high trajectory by the initial element.SOLUTION: The golf ball includes a core 6, a cover 8, and a paint layer 14. The golf ball has variable dimples 10 on the surface thereof. The cover 8 has a hole 20. A space S1 is formed by the hole 20. Immediately below the dimple 10, the cover 8 and the paint layer 14 are not joined to each other. A space S2 is formed between the cover 8 and the paint layer 14. The volume of the space S2 is varied by centrifugal forces caused by the backspin.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] This specification discloses a golf ball. In particular, this specification discloses a golf ball having improved dimples. [Background technology]

[0002] A golf ball has many dimples on its surface. The dimples disrupt the airflow around the golf ball during flight, causing turbulent separation. This phenomenon is called "turbulence." Turbulence shifts the separation point of the air from the golf ball backward, reducing drag. Turbulence promotes the misalignment of the upper and lower separation points of the golf ball caused by backspin, increasing the lift acting on the golf ball.

[0003] Japanese Patent Application Laid-Open No. 61-284264 discloses a golf ball with dimples, which has regions containing dimples with large volumes and regions containing dimples with small volumes. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 61-284264 Summary of the Invention [Problem to be solved by the invention]

[0005] A golf ball with an appropriate flight time when hit can achieve a long flight distance. A golf ball with an appropriate trajectory height achieves an appropriate flight time. Trajectory height is closely correlated with flight distance.

[0006] Factors that affect the trajectory height include: (1) Initial elements, and (2) Flight elements Examples include:

[0007] As the initial element (1), (1-1) Initial ball speed, (1-2) Launch angle, and (1-3) Initial spin speed Examples include:

[0008] As a flight element (2), (2-1) Gravity, (2-2) Lift, and (2-3) Drag force Examples include:

[0009] The trajectory height is particularly affected by lift (2-2). This lift is particularly affected by the initial spin rate (1-3). A flight with a high initial spin rate generates a large amount of lift, resulting in a high trajectory.

[0010] For golf players who are unable to achieve a sufficiently high trajectory with the initial element (1), a golf ball having a flight element (2) that can contribute to a high trajectory is suitable. Specifically, a golf ball having dimples that can generate sufficient lift is suitable for such players.

[0011] A golf ball having a flight element (2) that can suppress an excessively high trajectory is suitable for a golf player who can achieve a sufficiently high trajectory with the initial element (1). Specifically, a golf ball having dimples that do not generate excessive lift is suitable for this golf player.

[0012] When a golf ball suitable for a golf player who is unable to achieve a sufficiently high trajectory due to initial factors is hit by a golf player who is able to achieve a sufficiently high trajectory due to initial factors, the golf ball flies with an excessively high trajectory, and the flight distance of this golf ball is insufficient.

[0013] When a golf ball suitable for a golf player who can achieve a sufficiently high trajectory with initial elements is hit by a golf player who cannot achieve a sufficiently high trajectory with initial elements, the golf ball flies with an excessively low trajectory, and the flight distance of this golf ball is insufficient.

[0014] Golf ball manufacturers must develop and manufacture golf balls for golf players who can achieve a sufficiently high trajectory with initial elements and golf balls for golf players who cannot achieve a sufficiently high trajectory with initial elements, which increases the manufacturing costs of golf balls.

[0015] A golf player needs to select and purchase a golf ball that matches his or her initial factors. This selection is not easy. Initial factors can vary depending on the golf club, the player's physical condition, the weather, etc. This variation makes selecting a golf ball even more difficult.

[0016] The applicant's intention is to provide a golf ball that is suitable for golf players who can achieve a sufficiently high trajectory with initial elements, and is also suitable for golf players who cannot achieve a sufficiently high trajectory with initial elements. [Means for solving the problem]

[0017] The golf ball disclosed herein has a plurality of dimples on its surface, including one or more variable dimples, each of which has a structure that causes its shape in flight to differ from its shape at rest. [Effects of the Invention]

[0018] When this golf ball is hit, a great distance can be achieved regardless of the initial factors. [Brief explanation of the drawings]

[0019] [Figure 1]FIG. 1 is a partially cutaway cross-sectional view showing a golf ball according to one embodiment. [Figure 2] FIG. 2 is an enlarged cross-sectional view of a portion of a golf ball at rest. [Figure 3] FIG. 3 is a cross-sectional view showing a further enlarged portion of the golf ball of FIG. [Figure 4] FIG. 4 is an enlarged cross-sectional view of a portion of a golf ball in flight. [Figure 5] FIG. 5 is a cross-sectional view showing a further enlarged portion of the golf ball of FIG. [Figure 6] FIG. 6 is an enlarged cross-sectional view of another portion of the golf ball of FIG. [Figure 7] FIG. 7 is an enlarged cross-sectional view of a portion of a golf ball in flight. [Figure 8] FIG. 8 is a cross-sectional view showing a further enlarged portion of the golf ball of FIG. [Figure 9] FIG. 9 is a cross-sectional view showing a golf ball according to another embodiment. [Figure 10] FIG. 10 is an enlarged cross-sectional view of a portion of a golf ball at rest. [Figure 11] FIG. 11 is a cross-sectional view showing a further enlarged portion of the golf ball of FIG. [Figure 12] FIG. 12 is an enlarged cross-sectional view of another portion of the golf ball of FIG. [Figure 13] FIG. 13 is an enlarged cross-sectional view of a portion of a golf ball in flight. [Figure 14] FIG. 14 is an enlarged cross-sectional view of another portion of the golf ball of FIG. [Figure 15] FIG. 15 is a cross-sectional view showing a part of the golf ball according to Sample 1. As shown in FIG. [Figure 16] FIG. 16 is a front view showing the golf ball according to Sample 1 together with a laser displacement meter. [Figure 17]FIG. 17 is a graph showing the measurement results of the golf ball according to Sample 1. [Figure 18] FIG. 18 is a graph showing the measurement results of the golf ball according to Sample 1. [Figure 19] FIG. 19 is a graph showing the measurement results of the golf ball according to Sample 1. [Figure 20] FIG. 20 is a graph showing the measurement results of the golf ball according to Sample 2. [Figure 21] FIG. 21 is a graph showing the measurement results of the golf ball according to Sample 2. [Figure 22] FIG. 22 is a perspective view showing a golf ball used in an experiment for the golf ball of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, preferred embodiments will be described in detail with reference to the drawings as appropriate.

[0021] [Preliminary experiment] Figure 22 is a perspective view of a golf ball 2 used in an experiment conducted by the inventor. In Figure 22, the symbol AX is the axis of rotation of the backspin of this golf ball 2. The arrow X represents the direction of the rotation axis AX. Figure 22 also shows the North Pole NP, the South Pole SP, the equator EQ, the parallel NL at 30° north latitude, and the parallel SL at 30° south latitude when this rotation axis AX is considered to be the Earth's axis. The rotation axis AX passes through the North Pole NP and the South Pole SP.

[0022] The area of ​​the surface of golf ball 2 sandwiched between latitude line NL and latitude line SL is called the near-equator area. The areas of the surface of golf ball 2 other than the near-equator area are called pole near areas. This golf ball 2 has one near-equator area and two pole near areas. Although not shown in FIG. 22 , multiple dimples are arranged in the near-equator area, and multiple dimples are also arranged in each pole near area.

[0023] The axis of rotation AX is determined depending on the impact point when the golf ball 2 collides with the golf club. The near-equator region and the near-pole region are determined depending on this axis of rotation AX. In other words, for one golf ball 2, the position of the near-equator region is indefinite, and the position of the near-pole region is also indefinite.

[0024] The distance from the rotation axis AX of dimples in the near-equator region is large. The peripheral speed during spin of dimples in the near-equator region is large. The distance from the rotation axis AX of dimples in the pole vicinity region is small. The peripheral speed during spin of dimples in the pole vicinity region is small.

[0025] The inventors prepared three types of golf ball samples. The lift coefficients of these samples were measured in accordance with the ITR standard established by the United States Golf Association (USGA). The total volume VS (mm ) of all dimples present in the near-equator region of each sample was 3 ), the total volume VP (mm 3 ), the lift coefficient CL1 under the first condition and the lift coefficient CL2 under the second condition were as follows: The volume of the dimples was adjusted by changing the depth of the dimples. VS VP CL1 CL2 Sample A1 170 168 0.1690 0.2319 Sample A2 170 188 0.1565 0.2222 Sample A3 190 168 0.1747 0.2482 First condition Ball speed: 40m / s Spin speed: 1770 rpm Second condition Ball speed: 40m / s Spin speed: 2830 rpm

[0026] As is clear from a comparison of Samples A1 and A2, golf balls with a larger volume VP of dimples in the extreme vicinity region (dimples located a short distance from the axis of rotation AX) had a smaller lift coefficient. As is clear from a comparison of Samples A1 and A3, golf balls with a larger volume VS of dimples in the equatorial vicinity region (dimples located a long distance from the axis of rotation AX) had a larger lift coefficient. Based on these findings, the inventors have completed a golf ball that can achieve a long flight distance regardless of the initial factors.

[0027] [First embodiment] FIG. 1 shows a golf ball 4 according to one embodiment. The golf ball 4 has a spherical core 6 and a cover 8 positioned on the outside of the core 6. The golf ball 4 has a large number of dimples 10 on its surface. The portion of the surface of the golf ball 4 other than the dimples 10 is land 12. The golf ball 4 has a paint layer and a mark layer on the outside of the cover 8, but these layers are not shown in FIG. 1. The golf ball 4 may have one or more intermediate layers between the core 6 and the cover 8.

[0028] The diameter of the golf ball 4 is preferably 40 mm or greater and 45 mm or less. From the viewpoint of satisfying the standards of the United States Golf Association (USGA), the diameter is particularly preferably 42.67 mm or greater. From the viewpoint of suppressing air resistance, the diameter is more preferably 44 mm or less, and particularly preferably 42.80 mm or less.

[0029] The mass of the golf ball 4 is preferably 40 g or greater and 50 g or less. From the viewpoint of obtaining a large inertia, the mass is more preferably 44 g or greater, and particularly preferably 45.00 g or greater. From the viewpoint of satisfying the USGA standard, the mass is particularly preferably 45.93 g or less.

[0030] [core] The core 6 is formed by crosslinking a rubber composition. Examples of base rubber for the rubber composition include polybutadiene, polyisoprene, styrene-butadiene copolymer, ethylene-propylene-diene copolymer, and natural rubber. Two or more types of rubber may be used in combination. From the viewpoint of resilience performance, polybutadiene is preferred, and high-cis polybutadiene is particularly preferred.

[0031] The rubber composition of the core 6 contains a co-crosslinking agent. From the viewpoint of resilience performance, preferred co-crosslinking agents are zinc acrylate, magnesium acrylate, zinc methacrylate, and magnesium methacrylate. The rubber composition preferably contains an organic peroxide together with the co-crosslinking agent. Preferred organic peroxides include dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and di-t-butyl peroxide.

[0032] The rubber composition of the core 6 may contain additives such as fillers, sulfur, vulcanization accelerators, sulfur compounds, antioxidants, colorants, plasticizers, and dispersants. The rubber composition may also contain carboxylic acids or carboxylate salts. The rubber composition may also contain synthetic resin powder or crosslinked rubber powder.

[0033] The diameter of the core 6 is preferably 30.0 mm or more, more preferably 37.0 mm or more, and particularly preferably 38.0 mm or more. The diameter of the core 6 is preferably 42.0 mm or less, more preferably 41.5 mm or less, and particularly preferably 41.0 mm or less. The core 6 may have two or more layers. The core 6 may have ribs on its surface. The core 6 may be hollow.

[0034] [cover] The cover 8 is made of a resin composition. A preferred base polymer for this resin composition is an ionomer resin. A preferred ionomer resin is a binary copolymer of an α-olefin and an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms. Another preferred ionomer resin is a terpolymer of an α-olefin, an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms, and an α,β-unsaturated carboxylic acid ester having 2 to 22 carbon atoms. In these binary and terpolymers, preferred α-olefins are ethylene and propylene, and preferred α,β-unsaturated carboxylic acids are acrylic acid and methacrylic acid. In these binary and terpolymers, a portion of the carboxyl groups is neutralized with a metal ion. Examples of metal ions for neutralization include sodium ions, potassium ions, lithium ions, zinc ions, calcium ions, magnesium ions, aluminum ions, and neodymium ions.

[0035] The resin composition of the cover 8 may contain another polymer instead of or in addition to the ionomer resin. Examples of the other polymer include polyurethane, polystyrene, polyamide, polyester, and polyolefin. The resin composition may contain two or more types of polymers.

[0036] The resin composition of cover 8 may contain a colorant such as titanium dioxide, a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent agent, a fluorescent brightener, etc. For the purpose of adjusting the specific gravity, this resin composition may also contain powder of a high specific gravity metal such as tungsten or molybdenum.

[0037] The thickness of the cover 8 is preferably 0.3 mm or more, more preferably 1.0 mm or more, and particularly preferably 1.5 mm or more. The thickness of the cover 8 is preferably 2.5 mm or less, more preferably 2.2 mm or less, and particularly preferably 2.0 mm or less. The specific gravity of the cover 8 is preferably 0.90 or more and 1.10 or less. The cover 8 may have two or more layers.

[0038] [dimple] Figure 2 shows a cross section of the golf ball 4 taken along a plane passing through the center of the dimple 10 and the center of the golf ball 4. Figure 2 shows the golf ball 4 in a stationary state. Figure 2 also shows the core 6, cover 8, and paint layer 14. The core 6 and cover 8 form a main portion 16 of the golf ball 4. The paint layer 14 covers the main portion 16.

[0039] The up-down direction in Figure 2 is the depth direction of the dimple 10. In Figure 2, the two-dot chain line 18 indicates a phantom sphere. The surface of the phantom sphere 18 is the surface of the golf ball 4 if the dimple 10 were not present. The diameter of the phantom sphere 18 is the same as the diameter of the golf ball 4. The dimple 10 is recessed from the surface of the phantom sphere 18. The land 12 coincides with the surface of the phantom sphere 18.

[0040] As shown in Figure 1, in this embodiment, the outline shape of each dimple 10 is a circle. In Figure 2, the arrow Dm indicates the diameter of the dimple 10. This diameter Dm is the distance between one point of contact Ed and the other point of contact Ed when a tangent line Tg common to both sides of the dimple 10 is drawn. The point of contact Ed is also the edge of the dimple 10. The edge Ed defines the outline of the dimple 10.

[0041] 2, the double-headed arrow Dp indicates the depth of the dimple 10. This depth Dp is the distance between the deepest part of the dimple 10 and the surface of the phantom sphere 18.

[0042] The total number of dimples 10 is preferably 250 or greater and 450 or less. The total number is more preferably 270 or greater, and particularly preferably 280 or greater. The total number N is more preferably 432 or less, and particularly preferably 380 or less.

[0043] In this specification, the "volume of a dimple" refers to the volume of the space surrounded by the dimples 10 and a plane that includes the tangent line Tg and is perpendicular to the depth direction. The total volume V of all the dimples 10 is 250 mm 3 Over 450mm3 The total volume V is preferably 250 mm 3 In the golf ball 4 having the above structure, hopping during flight is suppressed. From this viewpoint, the total volume V is 280 mm 3 More than 300mm is more preferable. 3 The above is particularly preferable. The total volume V is 450 mm 3 In the golf ball 4, the total volume V is 400 mm or less, and the drop during flight is suppressed. 3 Less than 380mm is preferable 3 The following are particularly preferred:

[0044] If the contour shape of the dimple 10 is not a circle, the volume of the area surrounded by the surface of the phantom sphere 18 and the surface of the dimple 10 is used as the volume of the dimple 10. In this case, the total volume V is 450 mm 3 More than 750mm 3 It is preferable that the total volume V is 450 mm 3 In the golf ball 4 having the above structure, hopping during flight is suppressed. From this viewpoint, the total volume V is 480 mm 3 More than 500mm is preferable. 3 The above is particularly preferable. The total volume V is 750 mm 3 In the golf ball 4, which has a total volume V of 700 mm or less, drop during flight is suppressed. 3 Less than 670mm is preferable 3 The following are particularly preferred:

[0045] As shown in FIG. 3, the cover 8 has a hole 20. The hole 20 forms a space S1. A fluid is contained in the space S1. In other words, the golf ball 4 has a fluid between the main portion 16 and the paint layer 14. The fluid may be a gas or a liquid. A compressible fluid is preferred. A particularly preferred fluid in this embodiment is a gas. A typical fluid is air. In this embodiment, the pressure of the air is substantially the same as atmospheric pressure.

[0046] The paint layer 14 covers the cover 8. The paint layer 14 abuts against the cover 8 in places other than the holes 20. Therefore, the distance between the cover 8 and the paint layer 14 is zero except for the area directly above the holes 20. The paint layer 14 is not bonded to the cover 8 directly below the dimples 10. The paint layer 14 is bonded to the cover 8 directly below the lands 12 (see Figure 2). Prior to forming the paint layer 14, a release substance may be applied to the surface of the dimples 10 to prevent the paint layer 14 from bonding to the cover 8 directly below the dimples 10.

[0047] Figures 4 and 5 show a dimple 10E on a golf ball 4 during flight. The golf ball 4 is flying with backspin. Arrow X in Figures 4 and 5 indicates the direction of the axis of rotation AX. The dimple 10E is located in the vicinity of the equator. Therefore, the distance from the axis of rotation AX of the dimple 10E is large. The peripheral speed of the dimple 10E during spin is high. A large centrifugal force acts on the dimple 10E. As mentioned above, the paint layer 14 is not bonded to the cover 8 directly below the dimple 10E. Due to centrifugal force, the paint layer 14 is separated from the cover 8. The distance between the cover 8 and the paint layer 14 is greater than zero. In addition to space S1, a space S2 is generated between the paint layer 14 and the cover 8. In other words, air, which is a fluid, is expanding. The pressure of this air is lower than atmospheric pressure.

[0048] In Figure 5, arrow Dp1E indicates the depth of dimple 10E. As is clear from a comparison of Figures 3 and 5, the depth Dp1E in flight is smaller than the depth Dp at rest. In other words, the volume of dimple 10E in flight is smaller than the volume of dimple 10E at rest. The shape of dimple 10E in flight is different from the shape at rest. A dimple 10 having a structure that makes the shape in flight different from the shape at rest is referred to in this specification as a "variable dimple."

[0049] FIG. 6 shows a dimple 10P on a golf ball 4 during flight. This dimple 10P is located in the immediate vicinity region. If this dimple 10P is located at the North Pole NP or the South Pole SP, the distance of this dimple 10P from the axis of rotation AX is zero. If this dimple 10P is located at a position other than the North Pole NP or the South Pole SP, the distance of this dimple 10P from the axis of rotation AX is small. The peripheral speed of this dimple 10P during spin is zero or small. No centrifugal force or a relatively small centrifugal force acts on this dimple 10P. Although this dimple 10P is a variable dimple 10, the paint layer 14 is attached to the cover 8 because the centrifugal force is small.

[0050] In Figure 6, the arrow Dp1P indicates the depth of the dimple 10P. As is clear from a comparison of Figures 3 and 6, the depth Dp1P in flight is the same as the depth Dp at rest. In other words, the volume of this dimple 10P in flight is the same as the volume at rest. If a small centrifugal force acts on the dimple 10P, the depth Dp1P in flight may be slightly smaller than the depth Dp at rest.

[0051] 7 and 8 show a dimple 10E of a golf ball 4 in flight. This golf ball 4 is flying with backspin. The axis of rotation of this backspin coincides with the axis of rotation in the state shown in FIGS. 4 and 5. The backspin speed in the state shown in FIGS. 7 and 8 is greater than that in the state shown in FIGS. 4 and 5. Therefore, an extremely large centrifugal force acts on this dimple 10E. This centrifugal force causes the paint layer 14 to be significantly separated from the cover 8. In addition to the space S1, a space S3 is generated between the paint layer 14 and the cover 8. Because the centrifugal force is extremely large, the space S3 is larger than the space S2 (see FIG. 5).

[0052] In Figure 8, arrow Dp2E indicates the depth of dimple 10E. As is clear from a comparison of Figures 5 and 8, depth Dp2E is smaller than depth Dp1E. In other words, the volume of dimple 10E when flying with a high backspin rate is smaller than the volume of dimple 10E when flying with a low backspin rate.

[0053] Even when the golf ball 4 flies with a high backspin rate, the centrifugal force acting on the dimple 10P (see FIG. 6) in the immediate vicinity is zero or small. Therefore, the depth of this dimple 10P is the same as the depth Dp at rest. In other words, the volume of this dimple 10P in flight is the same as the volume at rest. The depth at flight may be slightly smaller than the depth Dp at rest.

[0054] The initial spin rate of a golf ball 4 hit with a golf club by a powerful player is generally higher than that of a golf ball hit with an equivalent golf club by a less powerful player. In a golf ball 4 after being hit by a powerful player, a large centrifugal force acts on the dimple 10E in the region near the equator. The volume of this dimple 10E during flight is smaller than its volume at rest. On the other hand, the centrifugal force acting on the dimple 10P in the region near the pole is small. The volume of this dimple 10E during flight is the same as or slightly smaller than its volume at rest. With this golf ball 4, lift during flight can be suppressed. The trajectory height of this golf ball 4 is appropriate. This golf ball 4 can achieve a long flight distance.

[0055] The initial spin rate of a golf ball 4 hit with a golf club by a less powerful player is generally lower than that of a golf ball hit with an equivalent golf club by a more powerful player. After being hit by a less powerful player, the centrifugal force acting on the dimple 10E in the region near the equator of the golf ball 4 is small. The volume of this dimple 10E during flight is not too small compared to its volume at rest. Sufficient lift is generated in this golf ball 4. The trajectory height of this golf ball 4 is appropriate. This golf ball 4 can achieve a long flight distance.

[0056] The golf ball 4 is suitable for golf players who can achieve a sufficiently high trajectory with initial factors. The golf ball 4 is also suitable for golf players who cannot achieve a sufficiently high trajectory with initial factors. The golf ball 4 is highly versatile.

[0057] During flight, the spin decays. As this decay occurs, the fluid gradually contracts. As this contraction occurs, the volume of the dimple 10E increases. The dimple 10E on the golf ball 4 that has fallen to rest has the shape shown in FIGS. 2 and 3.

[0058] The volume change rate Pv of the variable dimple 10 is calculated by the following formula. Pv = (V2 - V1) / V1 100 In this formula, V1 represents the volume of the dimple 10 in its shape at rest, and V2 represents the volume of the dimple 10 in its shape in flight. When measuring V2, the spin rate is 2500 rpm. When measuring V2, the dimple 10 being measured is positioned on the equator EQ. From the standpoint of versatility, the absolute value of the volume change rate Pv is preferably 5% or greater, more preferably 8% or greater, and particularly preferably 10% or greater. The upper limit of the absolute value of the volume change rate Pv for a practical golf ball 4 is 100%.

[0059] From the viewpoint of versatility, the ratio of the number of variable dimples 10 to the total number of dimples 10 is preferably 50% or more, more preferably 70% or more, and particularly preferably 80% or more. This ratio may be 100%.

[0060] In golf, players cannot touch the golf ball 4 except on the tee and green. Players cannot select the axis of rotation AX of the backspin on shots other than tee shots. From the viewpoint of reducing the dependence of the trajectory on the position of the axis of rotation AX, it is preferable that the variable dimples 10 are evenly arranged on the surface of the golf ball 4.

[0061] Symmetry A typical golf ball 4 is formed in a mold having an upper and lower mold. When the upper mold and the lower mold are mated, a parting line is formed at the boundary between them. Molds with circular parting lines exist. Molds with zigzag parting lines also exist. The portion of the surface of the golf ball 4 that corresponds to the parting line is called a "seam." Golf balls 4 with circular seams also exist. Golf balls 4 with zigzag seams also exist.

[0062] The USGA has standards for a symmetry test regarding the flight performance of a golf ball 4. This test compares the flight performance of a golf ball 4 during PH rotation and POP rotation. The axis of rotation AX of the PH rotation is a line connecting a point on the surface of the golf ball 4 corresponding to the top of the upper die and a point on the surface of the golf ball 4 corresponding to the bottom of the lower die. The axis of rotation AX of the POP rotation is a line perpendicular to the axis of rotation AX of the PH rotation. On the surface of the golf ball 4, the seam and its vicinity are unique regions. The trajectory height during PH rotation tends to be lower than the trajectory height during POP rotation due to the influence of the seam. The seam can disrupt the symmetry of the golf ball 4.

[0063] From the viewpoint of improving symmetry, a golf ball 4 is preferred in which non-variable dimples 10 are primarily present in the seams and their adjacent regions, and variable dimples 10 are primarily present in other regions. During PH rotation of this golf ball 4, non-variable dimples 10 are primarily present in regions that are a large distance from the axis of rotation AX. Even when centrifugal force acts on these non-variable dimples 10, the volume of these non-variable dimples 10 does not decrease. These non-variable dimples 10 generate sufficient lift during PH rotation. During POP rotation of this golf ball 4, variable dimples 10 and non-variable dimples 10 are present in regions that are a large distance from the axis of rotation AX. When centrifugal force acts on these variable dimples 10, the volume of these variable dimples 10 decreases. These variable dimples 10 suppress the lift of the POP rotation. These variable dimples 10 bring the trajectory height during POP rotation closer to the trajectory height during PH rotation. This golf ball 4 can comply with USGA standards. The golf ball 4 has a small variation in trajectory depending on the impact point.

[0064] [Relationship with golf clubs] The loft angle of the short iron is large. When hit with this short iron, the golf ball 4 flies with a high spin rate. This spin rate suppresses the run (roll) of the golf ball after it lands. A high spin rate is advantageous for a player who wants the golf ball 4 to stop at the target point.

[0065] When the golf ball 4 is hit with a short iron, a large centrifugal force acts on the variable dimple 10E due to the spin rate. Therefore, the volume of the variable dimple 10E is relatively small. Despite the high spin rate of this golf ball 4, the lift force is relatively small. With this golf ball 4, the trajectory height can be suppressed. The trajectory of this golf ball 4 is less affected by wind.

[0066] The loft angle of the driver (W#1) is small. When hit with this driver, the golf ball 4 flies with a small spin rate. This spin rate can contribute to a long flight distance.

[0067] When the golf ball 4 is hit with a driver, the spin rate is low, so the centrifugal force acting on the variable dimple 10E is relatively small. Therefore, the volume of the variable dimple 10E is relatively large. With this golf ball 4, a large lift is generated on a driver shot despite the low spin rate. With this golf ball 4, a high trajectory and a long distance are achieved on a driver shot.

[0068] In this golf ball 4, (1) When using short irons, the trajectory is less affected by the wind. (2) Run is reduced on short iron shots. and (3) Achieving great distance on driver shots can be achieved.

[0069] [Relationship with the ballistic field] The golf ball 4 rises from the impact point to the apex of its trajectory. This region is referred to herein as the "ascending region." The golf ball 4 falls from this apex to the landing point. This region is referred to herein as the "descending region." The spin of the golf ball 4 decreases from impact to landing. The spin rate in the ascending region is generally high, and the spin rate in the descending region is generally low. The centrifugal force acting on the dimple 10E in the ascending region is high, and the centrifugal force acting on the dimple 10E in the descending region is low. The volume of the variable dimple 10E in the ascending region is relatively small. The volume of the variable dimple 10E in the descending region is relatively large.

[0070] The direction of the lift is perpendicular to the direction of travel of the golf ball 4. The lift in the ascending region includes a vertically upward component and a horizontally backward component. Because the volume of the variable dimple 10E in the ascending region is small, the lift acting on this golf ball 4 is not excessive. In this golf ball 4, the horizontally backward component in the ascending region is not excessive. This golf ball 4 has excellent flight performance.

[0071] The lift force in the descending region includes a vertically upward component and a horizontally forward component. Because the volume of variable dimple 10E in the descending region is large, sufficient lift force acts on this golf ball 4. In this golf ball 4, the horizontally forward component in the descending region is sufficiently large. This golf ball 4 has excellent flight performance.

[0072] [Second embodiment] FIG. 9 shows a golf ball 22 according to another embodiment. This golf ball 22 has a spherical core 24 and a cover 26 positioned on the outside of this core 24. The core 24 and the cover 26 form a main portion 30. This golf ball 22 has a paint layer and a marking layer on the outside of the cover 26, but these layers are not shown in the figure. The core 24 may have two or more layers. The cover 26 may have two or more layers. The golf ball 22 may have one or more intermediate layers between the core 24 and the cover 26. The diameter, mass, and materials of this golf ball 22 are the same as those of the golf ball 4 shown in FIG. 1.

[0073] This golf ball 22 has a large number of dimples 32 on its surface. The portion of the surface of the golf ball 22 other than the dimples 32 is land 34. The number of dimples 32 is the same as the number of dimples 10 on the golf ball 4 shown in FIG. 1. The diameter, depth, and volume of each dimple 32 are the same as those of the dimples 10 shown in FIG. 2. These dimples 32 include a first dimple 32E and a second dimple 32P. In FIG. 9, arrow X indicates the direction of the rotation axis of backspin. When the golf ball 22 flies with spin, the first dimple 32E belongs to the equator-near region, and the second dimple 32P belongs to the pole-near region.

[0074] As shown in Figure 9, the golf ball 22 has a passageway 36. This passageway 36 penetrates the core 24 and also penetrates the cover 26 in two places. The golf ball 22 has multiple passageways 36. In Figure 9, one passageway 36 is shown, and the other passageways 36 are not shown. The passageway 36 shown in Figure 9 passes through the center of the golf ball 22. The golf ball may have a passageway 36 that does not pass through the center.

[0075] 10 and 11 show the vicinity of the first dimple 32E of the golf ball 22 in a stationary state. The paint layer 38 is also shown in these figures. The golf ball 22 has a first chamber 40E directly below the first dimple 32E. This first chamber 40E is sandwiched between the cover 26 and the paint layer 38. This first chamber 40E is connected to the passage 36. A fluid 42 is contained in the first chamber 40E and the passage 36. An incompressible fluid is preferred. A particularly preferred fluid 42 in this embodiment is a liquid with low viscosity and high specific gravity. The paint layer 38 is bonded to the cover 26 directly below the land 34.

[0076] 12 shows the vicinity of the second dimple 32P of the golf ball 22 in a stationary state. The golf ball 22 has a second chamber 40P directly below the second dimple 32P. This second chamber 40P is sandwiched between the cover 26 and the paint layer 38. This second chamber 40P is connected to the passage 36. The passage 36 connects the first chamber 40E and the second chamber 40P. The second chamber 40P contains the same fluid 42 as the first chamber 40E.

[0077] FIG. 13 shows the first dimple 32E of the golf ball 22 during flight. The golf ball 22 is flying with backspin. Because the distance of the first dimple 32E from the axis of rotation AX is large, the peripheral speed of the first dimple 32E during spin is high. A large centrifugal force acts on the first dimple 32E. As is clear from a comparison of FIGS. 11 and 13, the centrifugal force separates the paint layer 38 from the cover 26. As a result, the fluid 42 flows into the first chamber 40E. The amount of fluid 42 in the first chamber 40E in FIG. 13 is greater than that in FIG. 11.

[0078] In Figure 13, the arrow DpE indicates the depth of the first dimple 32E. As is clear from a comparison between Figures 11 and 13, the depth DpE during flight is smaller than the depth Dp at rest. In other words, the volume of the first dimple 32E during flight is smaller than the volume of the first dimple 32E at rest. The first dimple 32E is called a "variable dimple."

[0079] The amount of fluid 42 flowing into the first chamber 40E varies depending on the strength of the centrifugal force acting on the first dimple 32E. In other words, the amount of fluid 42 flowing into the first chamber 40E varies depending on the spin rate of the golf ball 22. The amount of fluid 42 flowing into the first chamber 40E is greater when the spin rate is high than when the spin rate is low. Therefore, the depth DpE of the dimple 32E when the spin rate is high is smaller than when the spin rate is low. The volume of the dimple 32E when the spin rate is high is smaller than when the spin rate is low.

[0080] FIG. 14 shows the second dimple 32P of the golf ball 22 during flight. Because the distance of this second dimple 32P from the rotation axis AX is small, the peripheral speed of this second dimple 32P during spin is small. The centrifugal force acting on the second dimple 32P is small. As described above, the fluid 42 moves toward the first chamber 40E. As this movement occurs, the fluid 42 flows out of the second chamber 40P. The amount of fluid 42 in the second chamber 40P decreases. In the example shown in FIG. 14, all of the fluid 42 in the second chamber 40P has moved toward the passage 36 or the first chamber 40E. Therefore, the paint layer 38 is in contact with the cover 26. A small amount of fluid 42 may be present in the second chamber 40P.

[0081] In Figure 14, the arrow DpP indicates the depth of the second dimple 32P. As is clear from a comparison between Figures 12 and 14, the depth DpP during flight is greater than the depth Dp during rest. In other words, the volume of the second dimple 32P during flight is greater than the volume of the second dimple 32P during rest. The second dimple 32P is called a "variable dimple."

[0082] The amount of fluid 42 flowing out of the second chamber 40P varies depending on the amount of fluid 42 flowing into the first chamber 40E. In other words, the amount of fluid 42 flowing out of the second chamber 40P varies depending on the spin rate of the golf ball 22. The amount of flowing out when the spin rate is high is greater than when the spin rate is low. Therefore, the depth DpP of the dimple 32P when the spin rate is high is greater than when the spin rate is low. The volume of the dimple 32P when the spin rate is high is greater than when the spin rate is low.

[0083] The initial spin rate of a golf ball 22 hit by a powerful player with a golf club is generally higher than that of a golf ball hit by a less powerful player with an equivalent golf club. In the golf ball 22 after being hit by a powerful player, a large centrifugal force acts on the first dimple 32E. The volume of this first dimple 32E during flight is smaller than its volume at rest. On the other hand, the centrifugal force acting on the second dimple 32P is small. The volume of this second dimple 32P during flight is larger than its volume at rest. With this golf ball 22, lift during flight can be suppressed. The trajectory height of this golf ball 22 is appropriate. With this golf ball 22, a long flight distance can be achieved.

[0084] The initial spin rate of a golf ball 22 hit with a golf club by a less powerful player is generally lower than that of a golf ball hit with an equivalent golf club by a more powerful player. In a golf ball 22 hit by a less powerful player, the centrifugal force acting on the first dimple 32E is small. In the golf ball 22 after being hit, the amount of fluid 42 flowing into the first chamber 40E is small. The volume of this first dimple 32E during flight is not too small compared to its volume at rest. Because the amount of fluid 42 flowing out of the second chamber 40P is small, the volume of the second dimple 32P during flight is not too large compared to its volume at rest. This golf ball 22 generates sufficient lift. The trajectory height of this golf ball 22 is appropriate. This golf ball 22 can achieve a long flight distance.

[0085] This golf ball 22 is suitable for golf players who can achieve a sufficiently high trajectory with initial factors. This golf ball 22 is also suitable for golf players who cannot achieve a sufficiently high trajectory with initial factors. This golf ball 22 is highly versatile.

[0086] During flight, the spin decays. As the spin decays, the fluid 42 flows out of the first dimple 32E and into the second dimple 32P. When the golf ball 22 falls to rest, the first dimple 32E has the shape shown in FIG. 11, and the second dimple 32P has the shape shown in FIG. 12.

[0087] In this golf ball 22, the absolute value of the volume change rate Pv in the variable dimples 32 is preferably 5% or greater, more preferably 8% or greater, and particularly preferably 10% or greater. The upper limit of the absolute value of the volume change rate Pv for a practical golf ball 22 is 100%.

[0088] This golf ball 22 has a plurality of variable dimples 32 in addition to the first dimple 32E and the second dimple 32P. This golf ball 22 has a chamber 40 directly below each variable dimple 32. This chamber 40 is connected to the passage 36. The golf ball 22 may have variable dimples 32 that are connected to the passage 36 and variable dimples that are not connected to the passage 36. An example of a variable dimple that is not connected to the passage 36 is the dimple 10 shown in FIG. 3.

[0089] From the standpoint of versatility, the ratio of the number of variable dimples 32 to the total number of dimples 32 is preferably 50% or more, more preferably 70% or more, and particularly preferably 80% or more. This ratio may even be 100%. It is preferable that the variable dimples 32 are arranged evenly on the surface of the golf ball 22.

[0090] [experiment] [Sample B1] A golf ball without a paint layer was prepared. This golf ball had 338 dimples. One depression was formed in the core and cover of this golf ball using a tool, as shown in FIG. 15 . The depression had a diameter of 2.5 mm and a depth of approximately 2 mm. The center of this depression coincided with the center of one of the dimples. A disk-shaped weight was prepared. The weight had a diameter of 1.0 mm and a thickness of 0.2 mm. Furthermore, a laminate was prepared. This laminate had a film with a diameter of 4.0 mm and a thickness of 30 μm, and an adhesive layer. The weight was attached to this adhesive layer. The laminate was attached to the dimple. This attachment was achieved by the adhesive in the adhesive layer. The center of the weight coincided with the center of the dimple. The laminate adhered to the surface of the dimple except for the depression. A space surrounded by the depression and the laminate was present on the golf ball. Air was present in this space. In this dimple, the distance between the laminate and the bottom of the depression could vary due to deformation of the laminate. In other words, this dimple was a variable dimple. The number of variable dimples on this golf ball was one. None of the remaining dimples were variable dimples. Hereinafter, dimples that are not variable dimples will be referred to as "normal dimples."

[0091] The golf ball was set in the device shown in Figure 16. This device had two chucks. The golf ball was clamped between these chucks. The chucks rotated around the axis indicated by the line AX in Figure 16. The rotation of the chucks caused the golf ball to rotate as well. A laser was emitted from a laser displacement meter (Keyence Corporation's LK-H022 & LK-G5000) toward the golf ball. The reflected light of this laser measured the displacement of the golf ball's surface (the change in distance from the laser displacement meter to the golf ball's surface).

[0092] The measurement results when the golf ball rotation speed was 500 rpm are shown in the graph of Figure 17. In this graph, the horizontal axis represents the rotation angle of the golf ball, and the vertical axis represents the height (i.e., displacement). In this graph, the displacement of the variable dimple and the displacement of the normal dimple adjacent to this variable dimple were measured consecutively. In this graph, arrow D1 represents the depth of the variable dimple, and arrow D2 represents the depth of the normal dimple.

[0093] Similarly, displacement was measured when the golf ball's rotation speed was 1,000 rpm, 3,000 rpm, and 5,000 rpm. The results are shown in the graph of FIG. 18. In this graph, the vertical axis represents dimple depth, and the horizontal axis represents rotation speed. In this graph, the depth of the variable dimples is shown by a solid line, and the depth of the normal dimples is shown by a dotted line. For the variable dimples, the higher the rotation speed, the smaller the dimple depth. On the other hand, for the normal dimples, the dimple depth was independent of the rotation speed. With the variable dimples, centrifugal force generated by rotation acts on the laminate and weight, which presumably moves the laminate and weight radially outward on the golf ball, thereby reducing the dimple depth. From the graph of FIG. 18, it can be seen that the difference between the dimple depth at a rotation speed of 500 rpm and that at a rotation speed of 5,000 rpm is approximately 50 μm. A difference of 50 μm can significantly affect the aerodynamic characteristics of the dimple.

[0094] Figure 19 is a graph showing the dimple depth of a variable dimple. In this graph, the vertical axis is dimple depth and the horizontal axis is the square of the rotation speed. The four points plotted on this graph are roughly on a straight line. In other words, the square of the rotation speed and the dimple depth have a relationship that can be expressed by a linear equation. This suggests that the change in dimple depth of a variable dimple depends on centrifugal force. This is because centrifugal force is proportional to the square of the rotation speed.

[0095] [Sample B2] A golf ball was obtained in the same manner as Sample B1, except that the diameter of the depressions was 2.0 mm and the diameter of the laminate was 3.0 mm. This golf ball was evaluated in the same manner as the golf ball of Sample B1. The results are shown in the graphs of Figures 20 and 21. In the graph of Figure 20, the depth of the variable dimples is shown by the solid line, and the depth of the normal dimples is shown by the dotted line. For the variable dimples, the higher the rotation speed, the smaller the dimple depth. On the other hand, for the normal dimples, the dimple depth was independent of the rotation speed. For the variable dimples, centrifugal force generated by rotation acts on the laminate and weight, which presumably moves the laminate and weight radially outward on the golf ball, thereby reducing the dimple depth. As is clear from the graph of Figure 21, the square of the rotation speed and the dimple depth of the variable dimples are related by a linear equation. This suggests that the change in dimple depth of the variable dimples depends on centrifugal force. This is because the centrifugal force is proportional to the square of the rotational speed.

[0096] 19 and 21, the variable dimple depth of sample B1 has a greater dependency on rotation speed than sample B2. This is presumably because the diameter of the dimples in sample B1 is larger than the diameter of the dimples in sample B2.

[0097] The above experimental results demonstrate that it is possible to create a golf ball with dimples that have a structure that allows the shape of the ball to differ in flight from the shape of the ball at rest. The dependence of the depth of the variable dimples on the rotation speed is as follows: (1) Weight mass (2) Film thickness (3) Film material and properties and (4) Size of the recess can be adjusted by

[0098] [Disclosure items] Each of the following sections discloses a preferred embodiment.

[0099] [Item 1] A golf ball having a plurality of dimples on its surface, These dimples include one or more variable dimples, A golf ball in which each variable dimple has a structure that causes the shape in flight to differ from the shape at rest.

[0100] [Item 2] Item 1. The golf ball according to item 1, wherein the transition from the rest shape to the flight shape is achieved by centrifugal force resulting from the spin of the golf ball.

[0101] [Item 3] 3. The golf ball according to item 1 or 2, wherein a volume V2 of the variable dimple in the in-flight shape is different from a volume V1 of the variable dimple in the rest shape.

[0102] [Item 4] Item 4. The golf ball according to item 3, wherein the volume V2 in the in-flight configuration is smaller than the volume V1 in the rest configuration.

[0103] [Item 5] a first variable dimple, the volume V2 in the in-flight configuration being smaller than the volume V1 in the rest configuration; and a second variable dimple, the volume V2 in the in-flight configuration being greater than the volume V1 in the rest configuration; 4. The golf ball according to item 3, comprising:

[0104] [Item 6] 6. The golf ball according to any one of items 3 to 5, including the variable dimples, wherein the absolute value of the volume change rate Pv calculated by the following formula is 5% or more. Pv = (V2 - V1) / V1 100 (In this formula, V1 represents the volume of the dimple in the rest configuration, and V2 represents the volume of the dimple in the in-flight configuration when the spin rate is 2500 rpm.)

[0105] [Item 7] The golf ball has a main portion and a film covering the main portion, the surface of the film has a plurality of dimples including the variable dimples and lands that are portions other than the dimples, 7. The golf ball according to any one of items 1 to 6, wherein the distance between the main portion of the film and the area directly below the variable dimple is variable.

[0106] [Item 8] Item 8. The golf ball according to item 7, wherein a fluid is present between the membrane and the main portion directly below the variable dimple, and the distance between the membrane and the main portion can vary due to expansion or contraction of this fluid.

[0107] [Item 9] Item 8. The golf ball according to item 7, wherein a fluid is present between the film and the main portion directly below the variable dimple, and an increase or decrease in this fluid can change the distance between the film and the main portion.

[0108] [Item 10] a first variable dimple having the fluid directly underneath between the membrane and the main portion; a second variable dimple immediately below the second variable dimple, the second variable dimple having the fluid between the membrane and the main portion; and a passage that allows the fluid present immediately below the second variable dimple to move to immediately below the first variable dimple; Item 10. The golf ball according to item 9, having

[0109] [Item 11] 11. The golf ball according to any one of items 1 to 10, wherein the ratio Ps of the number of variable dimples to the total number of dimples is 50% or greater. [Industrial Applicability]

[0110] The golf balls described above are suitable for shots with a variety of golf clubs. [Explanation of symbols]

[0111] 4. Golf balls 6 cores 8···Cover 10 dimples 10E···Dimple 10P···Dimple 12.0 ... 14. Paint layer 16. Main part 18. Imaginary sphere 20...hole 22. Golf balls 24 cores 26···Cover 30...Main part 32 dimples 32E···First dimple 32P...Second dimple 34... rand 36... aisle 38...Paint layer 40... Chamber 40E First chamber 40 40P...Second chamber 40 42 Fluid

Claims

1. A golf ball having a plurality of dimples on its surface, The dimples include one or more variable dimples, A golf ball in which each variable dimple has a structure that causes the shape in flight to differ from the shape at rest.

2. 10. The golf ball of claim 1, wherein the transition from the rest shape to the in-flight shape is accomplished by centrifugal forces resulting from spin of the golf ball.

3. 3. The golf ball according to claim 1, wherein a volume V2 of the variable dimple in the in-flight configuration is different from a volume V1 of the variable dimple in the rest configuration.

4. 4. The golf ball of claim 3, wherein the volume V2 in the in-flight configuration is smaller than the volume V1 in the rest configuration.

5. a first variable dimple, the volume V2 in the in-flight configuration being smaller than the volume V1 in the rest configuration; and a second variable dimple, the volume V2 in the in-flight configuration being greater than the volume V1 in the stationary configuration; The golf ball of claim 3 , comprising:

6. 4. The golf ball according to claim 3, comprising the variable dimples, the absolute value of which is 5% or greater for the volume change rate Pv calculated by the following formula: Pv = (V2 - V1) / V1 ・100 (In this formula, V1 represents the volume of the dimple in the rest configuration, and V2 represents the volume of the dimple in the in-flight configuration when the spin rate is 2500 rpm.)

7. The golf ball has a main portion and a film covering the main portion, the surface of the film has a plurality of dimples including the variable dimples and lands that are portions other than the dimples, 3. The golf ball according to claim 1, wherein the distance between the main portion of the film and the area directly below the variable dimple is variable.

8. 8. The golf ball according to claim 7, wherein a fluid is provided between the film and the main portion directly below the variable dimple, and the distance between the film and the main portion can be changed by expansion or contraction of the fluid.

9. 8. The golf ball according to claim 7, wherein a fluid is present between the film and the main portion directly below the variable dimple, and the distance between the film and the main portion can be varied by increasing or decreasing the amount of the fluid.

10. a first variable dimple having the fluid directly underneath between the membrane and the main portion; a second variable dimple immediately below the second variable dimple, the second variable dimple having the fluid between the membrane and the main portion; and a passage that allows the fluid present immediately below the second variable dimple to move to immediately below the first variable dimple; The golf ball of claim 9 , having

11. 3. The golf ball according to claim 1, wherein a ratio Ps of the number of the variable dimples to the total number of the dimples is 50% or greater.

Images