Golf ball

Abstract

To provide a golf ball for reducing only a flying distance when being hit with a driver (W#1) at a high head speed and also achieving sufficient stabilization of a ball trajectory.SOLUTION: There is provided a golf ball with a large number of dimples formed on a ball surface, where, when edge angles at points of 10%, 20% and 30% of the depth in the cross-section of one dimple are respectively, ED1, ED2 and ED3, the dimples whose cross-sectional shape satisfies the following formula (1): ED1<ED2>ED3...(1) account for 10% or more of the total number of dimples, and where a ratio (A1) of a lift coefficient to a drag coefficient at a Reynolds number of 218,000 and a spin rate of 2,800 rpm, a ratio (A2) of a lift coefficient to a drag coefficient at a Reynolds number of 184,000 and a spin rate of 2,900 rpm, and a ratio (A3) of a lift coefficient to a drag coefficient at a Reynolds number of 158,000 and a spin rate of 3,100 rpm are optimized.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a golf ball having a large number of dimples formed on the ball surface. More specifically, by focusing on the aerodynamic characteristics and the unique cross-sectional shape of the dimples formed on the ball surface, the present invention relates to a golf ball that achieves both reduction of flight distance only at high head speeds and stabilization of the trajectory.

Background Art

[0002] In order to improve the flight distance of a golf ball, it is generally well known that the air resistance during flight is reduced by the dimples formed on the ball surface to improve the aerodynamic characteristics. For example, the golf ball described in Patent Document 1 proposes that by optimizing the shape of the wall surface close to the bottom in the dimple cross-section, the trajectory of the hit ball is optimized and the flight distance is increased. Patent Document 2 discloses a golf ball in which the dimples are formed by at least two or more different cross-sectional shapes and the three-dimensional dimple shape is optimized, thereby dramatically improving the aerodynamic characteristics. However, these golf balls are technologies that focus on improving the flight distance and do not pay attention to the fact that the trajectory of the ball is stable and a stable flight performance can be obtained.

[0003] Also, Patent Document 3 describes that in order to reduce the variation in flight and improve the aerodynamic performance, the change amount ΔH of the depth every 20% of the above distance is optimized in the depth ratio in the dimple region from the dimple edge to the dimple center, which is 20 to 100% of the distance. However, this technology does not focus on the edge angle with respect to the dimple depth, and although it shows that the flight distance of the ball increases, it does not show that the trajectory is stabilized.

[0004] In March 2022, the R&A and USGA notified golf ball manufacturers that they would start research to suppress the flight distance of long hitters by changing the test conditions for the standard overall distance (ODS) of golf balls in the future. Therefore, rather than simply reducing the flight distance, it is preferable to make a golf ball that reduces the distance of long hitters during driver shots while increasing the distance reduction during driver shots of average hitters, thereby minimizing the impact on play other than the reduction of the flight distance of long hitters during driver shots.

[0005] Patent Documents 4 to 7 below propose a golf ball that combines a low-trajectory dimple design on the ball surface to greatly reduce the flight distance of the ball at high clubhead speeds, while minimizing the reduction in flight distance at low clubhead speeds compared to the reduction at high clubhead speeds.

[0006] However, the golf balls in Patent Documents 4 to 7 reduce the flight distance too much during driver shots at high clubhead speeds and do not sufficiently achieve ballistic stabilization.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] The present invention has been made in view of the above circumstances, and an object thereof is to provide a golf ball that reduces only the flight distance when struck by a driver (W#1) at a high head speed and sufficiently stabilizes the trajectory of the ball after being struck by the driver (W#1).

MEANS FOR SOLVING THE PROBLEMS

[0009] As a result of intensive studies to achieve the above object, the present inventors focused on optimizing the balance between the regulation of the edge angle in the dimple cross section of the golf ball and the aerodynamic characteristics of the dimple. As a specific means, attention was paid to specifying the optimum shape of the edge angle with respect to the dimple depth in the dimple cross-sectional shape. Specifically, in the cross section of one dimple, when the edge angles at the points of 10%, 20%, and 30% of the depth are ED1, ED2, and ED3, respectively, the cross-sectional shape is represented by the following formula (1), ED1 < ED2 > ED3 ···(1) Dimples satisfying the above are made to be 10% or more of the total number of dimples formed on the ball surface. Also, when the ratio CL1 / CD1 of the lift coefficient CL1 to the drag coefficient CD1 at a Reynolds number of 218000 and a spin rate of 2800 rpm is A1, the ratio CL2 / CD2 of the lift coefficient CL2 to the drag coefficient CD2 at a Reynolds number of 184000 and a spin rate of 2900 rpm is A2, and the ratio CL3 / CD3 of the lift coefficient CL3 to the drag coefficient CD3 at a Reynolds number of 158000 and a spin rate of 3100 rpm is A3, the following two formulas 0.590 ≦ A1 ≦ 0.655, and (A2 + A3) / 2 ≧ 0.670 By satisfying the above, when a long hitter strikes a driver, the distance by which the flight distance is reduced is increased, and the flight distance when an average hitter strikes a driver can be made smaller than the distance by which the long hitter's distance drops. Also, it has been found that the aerodynamic performance stability due to the dimple effect can be improved to ensure the stability of the flight, and thus the present invention has been made.

[0010] Note that the above "long hitter" refers to a user with a head speed of about 50 m / s or more when hitting a driver (W#1), and the above "average hitter" refers to a user with a head speed of about 45 m / s or less when hitting a driver (W#1).

[0011] Therefore, the present invention provides the following golf ball. 1. A golf ball having a plurality of dimples formed on the ball surface. When the edge angles at the 10%, 20%, and 30% depth points in the cross-section of one dimple are ED1, ED2, and ED3 respectively, the cross-sectional shape satisfies the following formula (1): ED1 < ED2 > ED3 ···(1) Dimples satisfying the above are 10% or more of the total number of dimples. Also, when the ratio CL1 / CD1 of the lift coefficient CL1 to the drag coefficient CD1 at a Reynolds number of 218000 and a spin rate of 2800 rpm is A1, the ratio CL2 / CD2 of the lift coefficient CL2 to the drag coefficient CD2 at a Reynolds number of 184000 and a spin rate of 2900 rpm is A2, and the ratio CL3 / CD3 of the lift coefficient CL3 to the drag coefficient CD3 at a Reynolds number of 158000 and a spin rate of 3100 rpm is A3, the following two formulas: 0.590 ≦ A1 ≦ 0.655, and (A2 + A3) / 2 ≧ 0.670 A golf ball characterized by satisfying the above. 2. The golf ball according to the above 1, wherein the dimples satisfying the above formula (1) are 50% or more of the total number of dimples. 3. In the dimples satisfying the above formula (1), when the edge angle at the 40% depth point is further defined as ED4, the following formula: ED3 ≥ ED1 ≥ ED4 The golf ball according to the above item 1 or 2, which satisfies the above condition. 4. In the dimple that satisfies the above formula (1), when the edge angle at the 50% depth point is defined as ED5, the following formula ED1 / ED5 ≥ 1.35 The golf ball according to the above item 1 or 2, which satisfies the above condition. 5. In the dimple that satisfies the above formula (1), when the edge angle at the 50% depth point is defined as ED5, the following formula ED2 / ED5 ≥ 1.35 The golf ball according to the above item 1 or 2, which satisfies the above condition. 6. In the dimple that satisfies the above formula (1), when the edge angle at the 50% depth point is defined as ED5, the following formula ED3 / ED5 ≥ 1.35 The golf ball according to the above item 1 or 2, which satisfies the above condition. 7. In the dimple that satisfies the above formula (1), when the edge angle at the 60% depth point is defined as ED6, the following formula ED2 / ED6 ≥ 2.0 The golf ball according to the above item 1 or 2, which satisfies the above condition. 8. In the dimple that satisfies the above formula (1), when the edge angles at the 50% and 60% depth points are defined as ED5 and ED6 respectively, the golf ball according to the above item 1 or 2, wherein ED1, ED2, ED3, ED5 and ED6 are all 90 degrees or less. 9. The multi-piece solid golf ball according to the above item 1 or 2, wherein the value of (A2 + A3) / 2 is 0.670 to 0.783. 10. The multi-piece solid golf ball according to the above item 1 or 2, wherein the value of A2 is 0.635 to 0.750 and the value of A3 is 0.695 to 0.815. 11. The golf ball according to the above item 1 or 2, wherein there are three or more types of dimples that satisfy the above formula (1). 12. The golf ball according to the above item 1 or 2, wherein the number of dimples that satisfy the above formula (1) is 250 to 500. 13. The golf ball according to the above item 1 or 2, wherein the occupancy rate of the dimples that satisfy the above formula (1) is 60 to 90%. 14. The total volume of the above dimples is 300 to 500 mm 3 The golf ball according to the above 1 or 2, wherein the total volume is as described above.

Advantages of the Invention

[0012] The golf ball of the present invention does not simply reduce the flight distance, but increases the distance by which the flight distance is reduced during driver strikes by long hitters, and the flight distance during driver strikes by average hitters is made smaller than the distance by which long hitters' flight distance drops. Thus, while reducing the flight distance during driver strikes by long hitters, the impact on the overall play can be minimized. Further, the golf ball of the present invention can provide a stable trajectory and improve the stability of the flight.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0014] Hereinafter, the present invention will be described in more detail. The golf ball of the present invention is characterized in that a large number of dimples are formed on the ball surface, and as will be described later, one of the features is to define the change in the edge angle of the dimple cross-section.

[0015] Dimples are usually formed on the surface of the cover (outermost layer) of the ball simultaneously with the molding such as injection molding of the resin material of the cover. Further, usually, a paint is applied to the surface of the cover to complete the golf ball. The dimples in the present invention mean the dimples formed on the surface of the completed golf ball. Therefore, the numerical values such as the diameter and depth of the dimples described below are the numerical values of the dimples in the completed golf ball.

[0016] The number of the above dimples is not particularly limited, but preferably 250 or more, preferably 300 or more, and as an upper limit, preferably 500 or less, more preferably 450 or less.

[0017] Regarding the shape of the dimple as viewed from the plane of the dimple (planar view shape), a circle, various polygons, a dumbbell shape, an ellipse, other non-circular shapes, etc., can be appropriately used alone or in combination of two or more types. In the present invention, it is particularly preferable to use a combination of three or more types of dimples.

[0018] The diameter of the dimple (diagonal length in the case of a polygon) is not particularly limited, but it is preferably 2.0 mm or more, more preferably 2.5 mm or more. Also, the upper limit thereof is not particularly limited, but it is preferably 6.0 mm or less, more preferably 5.5 mm or less.

[0019] The depth at the deepest point of the dimple is not particularly limited, but it is preferably 0.05 to 0.5 mm, more preferably 0.09 to 0.4 mm.

[0020] The arrangement method of the dimples is not particularly limited, but a method using a geometric arrangement pattern of a regular polyhedron such as a regular octahedron, a regular dodecahedron, a regular icosahedron, etc., or a method of arranging the dimples so as to be rotationally symmetric about the poles of the ball such as three-fold symmetry, four-fold symmetry, five-fold symmetry, six-fold symmetry, etc. can be preferably adopted.

[0021] The ratio (dimple surface occupancy rate) SR value (%) of the total surface area of the virtual spherical surface surrounded by the edges of each dimple is usually 60% or more, preferably 80% or more, and the upper limit value is preferably 90% or less. If the SR value is outside the above range, an appropriate trajectory may not be obtained, and the flight distance may decrease.

[0022] The total volume of the dimple space formed downward from the plane surrounded by the edges of the dimples is preferably 300 to 500 mm 3 The ratio (dimple space occupancy rate) VR of the total volume of the dimple space to the volume of the virtual sphere assuming that there are no dimples on the ball surface is not particularly limited, but is usually 0.7% or more, preferably 0.75% or more, and more preferably 0.8% or more. The upper limit is also not particularly limited, but can be 1.5% or less, preferably 1.45% or less, and more preferably 1.4% or less. By setting the dimple space occupancy rate VR within the above range, it is possible to prevent excessive blow-up of the hit ball or the ball from not rising and dropping when hitting the ball with a club that gains flight distance such as a driver.

[0023] In the present invention, when the edge angles at the 10%, 20%, and 30% depth points in the cross-section of one dimple are ED1, ED2, and ED3, respectively, the cross-sectional shape is represented by the following formula (1), ED1 < ED2 > ED3 ···(1) The dimples satisfying this are included. Thus, in the present invention, a stable trajectory can be obtained by specifying the optimal shape of the edge angle with respect to the dimple depth.

[0024] Here, the above-mentioned "cross-section of the dimple" means the cross-sectional plane when the dimple is vertically cut so as to pass through the deepest part (the center of the bottom) of the dimple.

[0025] The above-mentioned edge angle is defined as follows. That is, as shown in FIG. 1, on the dimple D, a spherical surface Q of the golf ball before dimple formation (the spherical surface of the golf ball without dimples) is assumed. Further, when the depth DP of the dimple D is set to 100%, a tangent line T is drawn on the wall portion P of the dimple D at a position where the depth is n%. Let the point where this tangent line T intersects the above-mentioned virtual spherical surface Q be Q1. Then, the angle θ formed by the horizontal line in the horizontal direction of this Q1 (the line segment connecting the points Q1 and Q1 in the figure) and the tangent line T is defined as the edge angle. In FIG. 1, the points E and E are the outer peripheral edges of the dimple, the distance between them is the diameter DM of the dimple D, and the depth DP of the dimple D is the distance between the center of the bottom portion and the line segment EE.

[0026] Specifically, FIG. 2 is an explanatory diagram of ED1, ED2, and ED3. The measurement method of ED1 is as follows. First, draw a tangent line (T1) at the point P1 where the dimple depth is 10%, find the intersection point of this tangent line and the virtual spherical surface Q, and draw a line in the horizontal direction from this intersection point (straight line E1). ED1 is the angle formed by the tangent line T1 and the straight line E1. The measurement method of ED2 is as follows. First, draw a tangent line (T2) at the point P2 where the dimple depth is 20%, find the intersection point of this tangent line and the virtual spherical surface Q, and draw a line in the horizontal direction from this intersection point (straight line E2). ED2 is the angle formed by the tangent line T2 and the straight line E2. The measurement method of ED3 is as follows. First, draw a tangent line (T3) at the point P2 where the dimple depth is 30%, find the intersection point of this tangent line and the virtual spherical surface Q, and draw a line in the horizontal direction from this intersection point (straight line E3). ED3 is the angle formed by the tangent line T3 and the straight line E3.

[0027] The ratio of the dimples having a cross-sectional shape satisfying the above formula (1) is 10% or more, preferably 30% or more, more preferably 50% or more, and still more preferably 80% or more with respect to 100% of the total number of dimples formed on the ball surface.

[0028] It is preferable that there are three or more types of dimples having a cross-sectional shape satisfying the above formula (1). Even if the cross-sectional shapes are the same, those having different diameters and depths are regarded as different types of dimples if they are included.

[0029] As shown in the above formula (1), the edge angle ED2 at the point of 20% of the dimple depth is larger than the edge angles ED1 and ED3 at the points of 10% and 30% of the dimple depth. This is presumably because, in the dimple cross-sectional shape, the effect of the dimple is likely to be stably exerted due to the action of smoothing the flow of air entering the dimple, the variation in the ball trajectory is reduced, and a more stable trajectory is obtained.

[0030] In order to further improve the stability of the trajectory, it is preferable that the edge angle ED3 at the point of 30% of the dimple depth is larger than the edge angle ED1 at the point of 10% of the dimple depth. Also, it is preferable that the edge angles ED1, ED2, and ED3 are all 90 degrees or less.

[0031] When the edge angle at the point of 40% of the dimple depth is ED4, the following formula ED1≧ED4 is preferably satisfied.

[0032] Furthermore, in order to further improve the stability of the trajectory, when the edge angle at the point of 50% of the dimple depth is ED5, it is preferable that the edge angle ED5 is 90 degrees or less and satisfies at least one of the following three formulas. ED1 / ED5≧1.35 ED2 / ED5≧1.35 ED3 / ED5≧1.35

[0033] When the edge angle at the point of 60% of the dimple depth is ED6, it is preferable that the edge angle ED6 is 90 degrees or less and satisfies the following formula. ED2 / ED6≧2.0

[0034] As described above, the present invention focuses on the change in the dimple edge angle within the range where the dimple depth is 10 to 60%, and in particular, by optimizing the shape of the dimple edge angle at 10%, 20%, and 30% in the range relatively close to the edge of the dimple, it aims to stabilize the aerodynamic performance due to the action of the dimple, and thus stabilize the trajectory.

[0035] Also, regarding the golf ball of the present invention, when the ratio (CL1 / CD1) of the lift coefficient CL1 to the drag coefficient CD1 at a Reynolds number of 218000 and a spin rate of 2800 rpm is A1, the ratio (CL2 / CD2) of the lift coefficient CL2 to the drag coefficient CD2 at a Reynolds number of 184000 and a spin rate of 2900 rpm is A2, and the ratio (CL3 / CD3) of the lift coefficient CL3 to the drag coefficient CD3 at a Reynolds number of 158000 and a spin rate of 3100 rpm is A3, the following two equations 0.590 ≦ A1 ≦ 0.655, and (A2 + A3) / 2 ≧ 0.670 The dimples are appropriately designed to satisfy these conditions.

[0036] In this specification, the "lift coefficients (CL1, CL2, CL3) and drag coefficients (CD1, CD2, CD3)" are measured in accordance with the ITR (Indoor Test Range) defined by the USGA (United States Golf Association). The lift coefficient and the drag coefficient can be adjusted by adjusting the configuration (arrangement, diameter, depth, volume, number, shape, etc.) of the dimples of the golf ball. The lift coefficient and the drag coefficient do not depend on the internal configuration of the golf ball. The Reynolds number (Re) is a dimensionless number used in the field of fluid mechanics. The Reynolds number (Re) is calculated by the following formula (1). Re = ρvL / μ (1) In the above formula (1), ρ represents the density of the fluid, v represents the relative average velocity of the object with respect to the flow of the fluid, L represents the characteristic length, and μ represents the viscosity coefficient of the fluid.

[0037] In the present invention, the ratio CL1 / CD1 of the lift coefficient CL1 to the drag coefficient CD1 at a Reynolds number of 218000 and a spin rate of 2800 rpm is defined as A1, the ratio CL2 / CD2 of the lift coefficient CL2 to the drag coefficient CD2 at a Reynolds number of 184000 and a spin rate of 2900 rpm is defined as A2, and the ratio CL3 / CD3 of the lift coefficient CL3 to the drag coefficient CD3 at a Reynolds number of 158000 and a spin rate of 3100 rpm is defined as A3.

[0038] Regarding the Reynolds number of 218000 and the spin rate of 2800 rpm, which are the conditions under which the lift coefficient CL1 and the drag coefficient CD1 are measured, this high-speed condition corresponds to the condition under which a long hitter hits with a driver (W#1). This Reynolds number corresponds to the ball speed when a golf ball is hit at a head speed (HS) of 54 m / s, and the spin rate of 2800 rpm is the average spin condition of a player with a head speed (HS) of 54 m / s.

[0039] Regarding the Reynolds number of 184000 and the spin rate of 2900 rpm, which are the conditions under which the lift coefficient CL2 and the drag coefficient CD2 are measured, this medium-speed condition corresponds to the condition under which an average hitter hits with a driver (W#1) at a head speed (HS) of 45 m / s. This Reynolds number corresponds to the ball speed when a golf ball is hit at a head speed (HS) of 45 m / s, and the spin rate of 2900 rpm is the average spin condition of a player with a head speed (HS) of 45 m / s.

[0040] Regarding the Reynolds number of 158000 and the spin rate of 3100 rpm, which are the conditions under which the lift coefficient CL3 and the drag coefficient CD3 are measured, this low-speed condition corresponds to the condition under which an average hitter hits with a driver (W#1) at a head speed (HS) of 40 m / s. This Reynolds number corresponds to the ball speed when a golf ball is hit at a head speed (HS) of 40 m / s, and the spin rate of 3100 rpm is the average spin condition of a player with a head speed (HS) of 40 m / s.

[0041] The ratio of the above lift coefficient CL1 to the drag coefficient CD1, that is, the value of CL1 / CD1 = A1 is 0.590 or more, preferably 0.595 or more, more preferably 0.600 or more, and the upper limit value is 0.655 or less, preferably 0.640 or less, more preferably 0.627 or less. If this value is too large, the effect of suppressing the flight distance when a long hitter hits with a driver (W#1) may be insufficient and the flight distance may be too long. On the other hand, if the above value is too small, the actual flight distance may be much lower than the targeted flight distance.

[0042] The ratio of the above lift coefficient CL2 to the drag coefficient CD2, that is, the value of CL2 / CD2 = A2 is preferably 0.635 or more, more preferably 0.645 or more, still more preferably 0.660 or more, and the upper limit value is preferably 0.750 or less, more preferably 0.740 or less, still more preferably 0.730 or less. If this value is too low, the carry may not occur when hitting with a driver (W#1) at a head speed (HS) of 45 m / s, and the targeted total flight distance may not be obtained. On the other hand, if this value is too high, the trajectory will soar when hitting with W#1 at HS 45 m / s, and the targeted flight distance may not be obtained.

[0043] The ratio of the above lift coefficient CL3 to the drag coefficient CD3, that is, the value of CL3 / CD3 = A3 is preferably 0.695 or more, more preferably 0.710 or more, still more preferably 0.722 or more, and the upper limit value is preferably 0.815 or less, more preferably 0.810 or less, still more preferably 0.800 or less. If this value is too low, the carry may not occur when hitting with a driver (W#1) at a head speed (HS) of 40 m / s, and the targeted total flight distance may not be obtained. On the other hand, if this value is too high, the trajectory will soar when hitting with W#1 at HS 40 m / s, and the targeted flight distance may not be obtained.

[0044] The average value of the values of A2 and A3 above, that is, the value of (A2 + A3) / 2, is 0.670 or more, preferably 0.680 or more, more preferably 0.690 or more, and the upper limit value is preferably 0.783 or less, more preferably 0.775 or less, still more preferably 0.765 or less. If this value is too low, when an average hitter hits with a driver (W#1), there may be no carry and the target total flight distance may not be obtained. On the other hand, if the above value is too high, when an average hitter hits with W#1, the trajectory will be a pop-up trajectory, and the target flight distance may not be obtained.

[0045] Regarding the production of the mold for forming the above dimples, 3DCAD·CAM can be used, and methods such as directly cutting out the entire surface shape in three dimensions for the reverse master mold and directly cutting out the cavity part (inner wall surface) of the molding die in three dimensions can be adopted.

[0046] In addition, on the ball surface, various coatings such as white enamel coating, epoxy coating, and clear coating can be applied in the same manner as a normal golf ball. In this case, it is desirable to apply the coating evenly without unevenness so that the cross-sectional shape of the above dimples is not impaired.

[0047] The golf ball of the present invention has no particular limitation regarding the internal structure, and can be a solid golf ball such as a one-piece golf ball, a two-piece golf ball, or a multi-piece golf ball having a three-layer structure or more, or a wound golf ball, and can be applied to all types of golf balls.

[0048] Ball specifications such as the mass and diameter of the golf ball can be appropriately set according to the golf rules.

Examples

[0049] Hereinafter, examples and comparative examples will be shown to specifically explain the present invention, but the present invention is not limited to the following examples.

[0050] 〔Examples 1 to 3, Comparative Examples 1 to 3〕 A core with a diameter of 38.6 mm is produced. The formulations of the cores were all common in the examples and comparative examples. As the base rubber, 20 parts by mass of polybutadiene A (trade name "BR51" manufactured by ENEOS MATERIALS), 80 parts by mass of polybutadiene B (trade name "BR730" manufactured by ENEOS MATERIALS), 29.5 parts by mass of zinc acrylate (manufactured by Wako Pure Chemical Industries, Ltd.), 0.6 parts by mass of dicumyl peroxide (trade name "Perk Mill D" manufactured by NOF Corporation) as an organic peroxide, 0.1 parts by mass of 2,2-methylenebis(4-methyl-6-butylphenol) (trade name "No Crack NS-6" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) as an antioxidant, 19.3 parts by mass of zinc oxide (trade name "Three Kinds of Zinc Oxide" manufactured by Sakai Chemical Industry Co., Ltd.), and 0.3 parts by mass of zinc pentachlorothiophenolate (manufactured by Wako Pure Chemical Industries, Ltd.) as an organic sulfur compound are each blended. The vulcanization of the rubber composition is carried out under the conditions of a temperature of 155 °C and a time of 15 minutes. The compounding specific gravity is 1.138.

[0051] Formation of the intermediate layer Next, a resin material for the intermediate layer is injection molded around the core with a diameter of 38.6 mm to produce an intermediate layer-coated sphere having an intermediate layer with a thickness of 1.25 mm. The resin materials for the intermediate layer are all common in the examples and comparative examples, and the trade names "Himilan 1605", "Himilan 1557", and "Himilan 1706" (all ionomer resins manufactured by Mitsui Dow Chemical Co., Ltd.) are blended at 50:12:38 (mass ratio), respectively. For a total of 100 parts by mass of this ionomer resin, 1.1 parts by mass of trimethylolpropane (manufactured by Tokyo Chemical Industry Co., Ltd.) is blended.

[0052] Formation of the cover (outermost layer) Next, as the resin material for the cover (outermost layer), an ether-type thermoplastic polyurethane (trade name "Pandex" manufactured by DIC Covestro Polymer, Shore D hardness "43" and rebound resilience "61%") is used. Using another injection mold, the above resin material is injection molded around the above intermediate layer-coated sphere to produce a three-piece golf ball with a diameter of 42.7 mm having an outermost layer with a thickness of 0.8 mm. At this time, a predetermined number of dimples described below are formed on the cover surface.

[0053] Formation of the paint layer (coating film) Next, in the paint formulation shown in Table 1 below, a paint composition containing polyester polyol (main agent) and isocyanate curing agent is applied by an air spray gun onto the surface of the outermost layer where numerous dimples are formed, to produce golf balls for each example in which a paint layer (coating film) with a thickness of 15 μm is formed.

[0054] Dimple Regarding the details of the dimples in each example and comparative example, as shown in FIG. 3, based on four types of cross-sectional types, namely type A, type B, type C, and type D, the diameter and depth were appropriately changed to obtain the dimple details of Examples 1 to 3 and Comparative Examples 1 to 3 shown in Tables 1 to 6. The dimple details (data) in each of these tables were obtained by analyzing a golf ball with paint applied to the surface of the cover using a laser device ("LT-8010" manufactured by Keyence Corporation) to calculate the dimple diameter, depth, edge angle, etc. Also, the dimple arrangement patterns (patterns) in each of these examples are all common, and are a combination of multiple types of dimples that are circular in plan view. The arrangement pattern is shown in FIG. 4. FIG. 4(A) shows a plan view of the dimples, and FIG. 4(B) is a view of (A) seen slightly obliquely. In the figure, the symbol D indicates a dimple and O indicates a pole point. Since FIG. 4(B) is a view of (A) seen slightly obliquely, the pole point O can be seen in the foreground.

[0055]

Table 1

[0056]

Table 2

[0057]

Table 3

[0058]

Table 4

[0059]

Table 5

[0060]

Table 6

[0061] Definition of dimple · Edge: The highest point in the cross-section passing through the center of the dimple · Diameter: The diameter of the plane surrounded by the edge of the dimple · Depth: The maximum depth of the dimple from the plane surrounded by the edge of the dimple · Edge angle: As shown in Fig. 1, draw a tangent line T at point P with a specific dimple depth, find the intersection point of this tangent line and the virtual spherical surface Q, and draw a line horizontally from this intersection point (straight line E1). The edge angle is the angle formed by the tangent line T and the straight line E. · Total area: The total of the dimple areas defined by the planes surrounded by the edges of the dimples · Area occupancy ratio (SR): The ratio (%) of the total of the dimple areas defined by the planes surrounded by the edges of the dimples to the spherical surface area of the ball assuming no dimples · Total volume: The total of the dimple volumes under the planes surrounded by the edges of the dimples

[0062] Also, the lift coefficient CL1, drag coefficient CD1, ratio CL1 / CD1 = A1 at a Reynolds number of 218,000 and a spin rate of 2,800 rpm, the lift coefficient CL2, drag coefficient CD2, ratio CL2 / CD2 = A2 at a Reynolds number of 184,000 and a spin rate of 2,900 rpm, and the lift coefficient CL3, drag coefficient CD3, ratio CL3 / CD3 = A3 at a Reynolds number of 158,000 and a spin rate of 3,100 rpm for the balls with dimples formed on the cover surface in Examples 1 to 3 and Comparative Examples 1 to 3 are shown in Table 7 below. These lift coefficients and drag coefficients are measured in accordance with the ITR (Indoor Test Range) defined by the USGA.

[0063]

Table 7

[0064] Jump evaluation (1) (W#1, HS54m / s) Attach the club of the driver to the golf hitting robot and measure the flight distance (total) when hitting at a head speed (HS) of 54 m / s. The club used is the "TourB XD-5 driver (2017 model)" (loft angle 9.5°) manufactured by Bridgestone Sports Co., Ltd., and it is evaluated according to the following criteria. 〔Judgment Criteria〕 ○ ··· The total compared to Comparative Example 1 is -20.0 m or more and -8.0 m or less △ ··· The total compared to Comparative Example 1 is less than -20.0 m × ··· The total compared to Comparative Example 1 is greater than -8.0 m

[0065] Also, measure the standard deviation of the above flight distance (total) and evaluate it according to the following criteria. 〔Judgment Criteria〕 ○ ··· The total standard deviation is less than 3.4 m △ ··· The total standard deviation is 3.4 m or more and less than 3.7 m × ··· The total standard deviation is 3.7 m or more

[0066] Jump evaluation (2) (W#1, HS45m / s) Attach a driver club to a golf hitting robot and measure the total flight distance when hitting at a head speed (HS) of 45 m / s. The club used is the "J015 Driver (2016 model)" (loft angle 9.5°) manufactured by Bridgestone Sports Co., Ltd., and it is evaluated according to the following criteria. 〔Judgment Criteria〕 ○ ··· The total compared to Comparative Example 1 is -5.0 m or more △ ··· The total compared to Comparative Example 1 is -10.0 m or more and less than -5.0 m × ··· The total compared to Comparative Example 1 is less than -10.0 m

[0067] Also, measure the standard deviation of the above total flight distance and evaluate it according to the following criteria. 〔Judgment Criteria〕 ○ ··· The total standard deviation is less than 2.4 m △ ··· The total standard deviation is 2.4 m or more and less than 2.7 m × ··· The total standard deviation is 2.7 m or more

[0068] Jump evaluation (3) (W#1, HS40m / s) Attach a driver club to a golf hitting robot and measure the total flight distance when hitting at a head speed (HS) of 40 m / s. The club used is the "J015 Driver (2016 model)" (loft angle 9.5°) manufactured by Bridgestone Sports Co., Ltd., and it is evaluated according to the following criteria. 〔Judgment Criteria〕 ○ ··· The total compared to Comparative Example 1 is -5.0 m or more △ ··· The total compared to Comparative Example 1 is -10.0 m or more and less than -5.0 m × ··· The total compared to Comparative Example 1 is less than -10.0 m

[0069] Also, measure the standard deviation of the above total flight distance and evaluate it according to the following criteria. 〔Judgment Criteria〕 ○ ··· The total standard deviation is less than 1.6 m △ ··· The total standard deviation is 1.6 m or more and less than 1.9 m × ··· The total standard deviation is 1.9 m or more

[0070] Score In each of the above determinations, "○" was counted as 2 points, "△" as 1 point, and "×" as 0 point, and the total score was obtained as the comprehensive evaluation

[0071]

Table 8

[0072] As shown in Table 8, the golf balls of Examples 1 to 3 can sufficiently reduce the reduction in flight distance during driver (W#1) strikes in the high head speed region compared to each comparative example, and can maintain the flight distance well during driver (W#1) strikes in the low head speed region. Further, the golf balls of Examples 1 to 3 can reduce the standard deviation of the flight distance of the golf ball after hitting compared to each comparative example, and can achieve flight stabilization

Explanation of symbols

[0073] D Dimple P Specified dimple wall surface Q Virtual spherical surface E Outer peripheral edge of the dimple DM Dimple diameter DP Dimple depth ED1 Angle formed by tangent T1 and straight line E1 ED2 Angle formed by tangent T2 and straight line E2 ED3 Angle formed by tangent T3 and straight line E3

Claims

**Claim 1** A golf ball having a plurality of dimples formed on its surface, wherein when the edge angles at the 10%, 20%, and 30% depth points in the cross-section of one dimple are ED1, ED2, and ED3 respectively, the cross-sectional shape satisfies the following formula (1): ED1 < ED2 > ED3... (1) where the dimples satisfying the formula (1) account for 10% or more of the total number of dimples, and when the ratio CL1 / CD1 of the lift coefficient CL1 to the drag coefficient CD1 at a Reynolds number of 218000 and a spin rate of 2800 rpm is A1, the ratio CL2 / CD2 of the lift coefficient CL2 to the drag coefficient CD2 at a Reynolds number of 184000 and a spin rate of 2900 rpm is A2, and the ratio CL3 / CD3 of the lift coefficient CL3 to the drag coefficient CD3 at a Reynolds number of 158000 and a spin rate of 3100 rpm is A3, the following two formulas 0.590 ≤ A1 ≤ 0.655, and (A2 + A3) / 2 ≥ 0.670 A golf ball characterized by satisfying the above conditions. **Claim 2** The golf ball according to claim 1, wherein the dimples satisfying the above formula (1) account for 50% or more of the total number of dimples. **Claim 3** In the dimples satisfying the above formula (1), when the edge angle at the 40% depth point is further defined as ED4, the following formula ED3 ≥ ED1 ≥ ED4 The golf ball according to claim 1 or 2, which satisfies the above conditions. **Claim 4** In the dimples satisfying the above formula (1), when the edge angle at the 50% depth point is further defined as ED5, the following formula ED1 / ED5 ≥ 1.35 The golf ball according to claim 1 or 2, which satisfies the above conditions. **Claim 5** In the dimples satisfying the above formula (1), when the edge angle at the 50% depth point is further defined as ED5, the following formula ED2 / ED5 ≥ 1.35 The golf ball according to claim 1 or 2, which satisfies the above conditions. **Claim 6** In the dimples satisfying the above formula (1), when the edge angle at the 50% depth point is further defined as ED5, the following formula ED3 / ED5 ≥ 1.35 The golf ball according to claim 1 or 2, which satisfies the above conditions. **Claim 7** In the dimples satisfying the above formula (1), when the edge angle at the 60% depth point is further defined as ED6, the following formula ED2 / ED6 ≥ 2.0 The golf ball according to claim 1 or 2, which satisfies the above conditions. **Claim 8** In the dimple satisfying the above formula (1), when the edge angles at the points of 50% and 60% of the depth are ED5 and ED6 respectively, the golf ball according to claim 1 or 2, wherein ED1, ED2, ED3, ED5 and ED6 are all 90 degrees or less.

9. The multi-piece solid golf ball according to claim 1 or 2, wherein the value of (A2 + A3) / 2 is 0.670 to 0.

783.

10. The multi-piece solid golf ball according to claim 1 or 2, wherein the value of A2 is 0.635 to 0.750 and the value of A3 is 0.695 to 0.

815.

11. The golf ball according to claim 1 or 2, wherein there are three or more types of dimples satisfying the above formula (1).

12. The golf ball according to claim 1 or 2, wherein the number of dimples satisfying the above formula (1) is 250 to 500.

13. The golf ball according to claim 1 or 2, wherein the occupancy rate of the dimples satisfying the above formula (1) is 60 to 90%.

14. The total volume of the above dimples is 300 to 500 mm 3 The golf ball according to claim 1 or 2, wherein the total volume of the dimples is 300 to 500 mm

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