JP2018094129A - Golf ball - Google Patents

Abstract

To provide a golf ball 2 having excellent flight performance.
A golf ball 2 has a large number of dimples 10 on a surface thereof. Fifteen axes are assumed for the phantom sphere of the golf ball 2. 30240 points in a predetermined region on the surface of the golf ball 2 at the time of backspin about each axis are determined. The length L1 of the perpendicular drawn from each point to the axis is calculated. The 21 lengths L1 calculated based on the 21 vertical lines arranged in the axial direction are summed, and the total length L2 is calculated. Fourier transform is performed on the data group of 1440 total lengths L2 calculated along the rotation direction, and a transform data group is obtained. The peak value and the order of the maximum peak of this converted data group are calculated. The minimum value of the 15 peak values is 95 mm or more.
[Selection] Figure 1

Description

  The present invention relates to a golf ball. Specifically, the present invention relates to a dimple pattern for a golf ball.

  The face of the golf club has a loft angle. When a golf ball is hit with this golf club, backspin caused by the loft angle occurs in the golf ball. Golf balls fly with backspin.

  The golf ball has a large number of dimples on its surface. The dimples disturb the air flow around the golf ball during flight and cause turbulent separation. This phenomenon is called “turbulence”. Due to the turbulent flow, the separation point of air from the golf ball shifts backward, and drag is reduced. The turbulent flow promotes the deviation between the upper peeling point and the lower peeling point of the golf ball due to backspin, and the lift acting on the golf ball is enhanced. The reduction of drag and the improvement of lift are referred to as “dimple effect”. Excellent dimples better disturb the air flow. Excellent dimples produce a great flight distance.

  Various proposals regarding dimples have been made. Japanese Patent Application Laid-Open No. 4-109968 discloses a golf ball in which a hemispherical dimple pattern can be divided into 6 units. Japanese Patent Application Laid-Open No. 2004-243124 discloses a golf ball in which a dimple pattern near the pole is divided into four units and a dimple pattern near the equator can be divided into five units. Japanese Patent Application Laid-Open No. 2011-10667 discloses a golf ball whose parameters depending on the dimple shape are within a predetermined range.

JP-A-4-109968 JP-A-2004-243124 JP 2011-10667 A

  The primary concern of golf players to golf balls is flight performance. The player wants a golf ball with excellent flight performance. From the viewpoint of flight performance, the dimples have room for improvement.

  An object of the present invention is to provide a golf ball having excellent flight performance.

The golf ball according to the present invention has a plurality of dimples on the surface thereof. When the spherical polar coordinates of a point that is located on the surface of the phantom sphere of this golf ball and whose latitude is θ (degree) and longitude is φ (degree) are represented by (θ, φ),
(1) a first axis Ax1 passing through a point Pn1 whose coordinates are (75,270) and a point Ps1 whose coordinates are (−75,90);
(2) a second axis Ax2 passing through a point Pn2 whose coordinates are (60, 270) and a point Ps2 whose coordinates are (-60, 90);
(3) A third axis Ax3 passing through a point Pn3 whose coordinates are (45, 270) and a point Ps3 whose coordinates are (−45, 90),
(4) a fourth axis Ax4 passing through a point Pn4 whose coordinates are (30, 270) and a point Ps4 whose coordinates are (−30, 90);
(5) a fifth axis Ax5 passing through a point Pn5 whose coordinates are (15,270) and a point Ps5 whose coordinates are (-15,90);
(6) a sixth axis Ax6 that passes through the point Pn6 whose coordinates are (75,0) and the point Ps6 whose coordinates are (−75,180);
(7) A seventh axis Ax7 that passes through the point Pn7 whose coordinates are (60, 0) and the point Ps7 whose coordinates are (-60, 180),
(8) An eighth axis Ax8 that passes through the point Pn8 whose coordinates are (45, 0) and the point Ps8 whose coordinates are (−45, 180),
(9) a ninth axis Ax9 that passes through a point Pn9 whose coordinates are (30, 0) and a point Ps9 whose coordinates are (−30, 180);
(10) A tenth axis Ax10 passing through a point Pn10 having coordinates (15, 0) and a point Ps10 having coordinates (-15, 180),
(11) An eleventh axis Ax11 passing through a point Pn11 having coordinates (75, 90) and a point Ps11 having coordinates (−75, 270),
(12) A twelfth axis Ax12 passing through a point Pn12 whose coordinates are (60, 90) and a point Ps12 whose coordinates are (-60, 270),
(13) A thirteenth axis Ax13 passing through a point Pn13 having coordinates (45, 90) and a point Ps13 having coordinates (−45, 270),
(14) A fourteenth axis Ax14 that passes through a point Pn14 whose coordinates are (30, 90) and a point Ps14 whose coordinates are (−30, 270),
And (15) the fifteenth axis Ax15 passing through the point Pn15 whose coordinates are (15, 90) and the point P15s whose coordinates are (-15, 270).
For each of the 15 axes Ax,
(A) a step in which a great circle existing on the surface of the phantom sphere and orthogonal to the axis Ax is assumed;
(B) a step in which two small circles existing on the surface of the phantom sphere, orthogonal to the axis Ax, and having an absolute value of a central angle with the great circle of 30 ° are assumed;
(C) a step of defining a surface of the golf ball by these small circles, and specifying a region sandwiched between the small circles of the surface;
(D) a step in which 30240 points are determined in the above-mentioned region at a central angle of 3 ° in the axial direction and at a central angle of 0.25 ° in the rotational direction;
(E) a step of calculating a length L1 of a perpendicular line drawn from each point to the axis Ax;
(F) A step in which 21 lengths L1 calculated based on 21 vertical lines arranged in the axial direction are summed to calculate a total length L2.
(G) Fourier transform is performed on a data group of 1440 total lengths L2 calculated along the rotation direction to obtain a transformed data group;
(H) The minimum value of the 15 peak values obtained by executing the step of calculating the peak value and the order of the maximum peak of the conversion data group is 95 mm or more. The minimum value of the 15th order obtained by executing these steps (a) to (h) is 27 or more. The maximum value of the 15th order obtained by executing these steps (a) to (h) is 37 or less. The average value of 15 orders obtained by executing these steps (a) to (h) is 30 or more and 34 or less.

  Preferably, the average of 15 peak values obtained by executing these steps (a) to (h) is 200 mm or more.

Preferably, the total volume of the dimples is not less than 450 mm ^{3 and not} more than 750 mm ³ .

  The lift coefficient and drag coefficient when the golf ball according to the present invention is flying are appropriate. This golf ball is excellent in flight performance.

FIG. 1 is a schematic cross-sectional view showing a golf ball according to an embodiment of the present invention. FIG. 2 is an enlarged front view showing the golf ball of FIG. FIG. 3 is a plan view showing the golf ball of FIG. FIG. 4 is an enlarged cross-sectional view showing a part of the golf ball of FIG. FIG. 5 is a schematic view for explaining the golf ball evaluation method of FIG. FIG. 6 is a schematic diagram for explaining the golf ball evaluation method of FIG. FIG. 7 is a schematic cross-sectional view for explaining the golf ball evaluation method of FIG. FIG. 8 is a schematic cross-sectional view for explaining a method for evaluating the golf ball in FIG. FIG. 9 is a graph showing the evaluation results of the golf ball in FIG. FIG. 10 is a graph showing the evaluation results of the golf ball in FIG. FIG. 11 is a schematic diagram for explaining the golf ball evaluation method of FIG. 2. FIG. 12 is a schematic diagram for explaining the golf ball evaluation method of FIG. 2. FIG. 13 is a schematic view for explaining the golf ball evaluation method of FIG. 2. FIG. 14 is a schematic diagram for explaining the golf ball evaluation method of FIG. 2. FIG. 15 is a schematic diagram for explaining the golf ball evaluation method of FIG. 2. FIG. 16 is a schematic diagram for explaining the golf ball evaluation method of FIG. 2. FIG. 17 is a schematic diagram for explaining the golf ball evaluation method of FIG. 2. FIG. 18 is a schematic diagram for explaining the golf ball evaluation method of FIG. 2. FIG. 19 is a schematic diagram for explaining the golf ball evaluation method of FIG. FIG. 20 is a schematic diagram for explaining the golf ball evaluation method of FIG. FIG. 21 is a schematic view for explaining the golf ball evaluation method of FIG. FIG. 22 is a schematic diagram for explaining the golf ball evaluation method of FIG. 2. FIG. 23 is a schematic view for explaining the golf ball evaluation method of FIG. FIG. 24 is a schematic diagram for explaining the golf ball evaluation method of FIG. FIG. 25 is a front view showing a golf ball according to Example 2 of the present invention. FIG. 26 is a plan view showing the golf ball of FIG. FIG. 27 is a front view showing a golf ball according to Example 3 of the present invention. FIG. 28 is a plan view showing the golf ball of FIG. FIG. 29 is a front view showing a golf ball according to Comparative Example 1. FIG. FIG. 30 is a plan view showing the golf ball of FIG. FIG. 31 is a front view showing a golf ball according to Comparative Example 2. FIG. 32 is a plan view showing the golf ball of FIG. FIG. 33 is a front view showing a golf ball according to Comparative Example 3. FIG. 34 is a plan view showing the golf ball of FIG. FIG. 35 is a front view showing a golf ball according to Comparative Example 4. FIG. 36 is a plan view showing the golf ball of FIG.

  Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

  The golf ball 2 shown in FIG. 1 includes a spherical core 4, an intermediate layer 6 located outside the core 4, and a cover 8 located outside the intermediate layer 6. The golf ball 2 has a large number of dimples 10 on the surface thereof. A portion of the surface of the golf ball 2 other than the dimples 10 is a land 12. The golf ball 2 includes a paint layer and a mark layer on the outside of the cover 8, but these layers are not shown.

  The golf ball 2 preferably has a diameter of 40 mm or greater and 45 mm or less. The diameter is particularly preferably equal to or greater than 42.67 mm from the viewpoint that US Golf Association (USGA) standards are satisfied. In light of suppression of air resistance, the diameter is more preferably equal to or less than 44 mm, and particularly preferably equal to or less than 42.80 mm.

  The golf ball 2 preferably has a mass of 40 g or more and 50 g or less. From the viewpoint of obtaining a large inertia, the mass is more preferably 44 g or more, and particularly preferably 45.00 g or more. In light of satisfying the USGA standard, the mass is particularly preferably equal to or less than 45.93 g.

  The core 4 is formed by crosslinking a rubber composition. Examples of the base rubber of the rubber composition include polybutadiene, polyisoprene, styrene-butadiene copolymer, ethylene-propylene-diene copolymer, and natural rubber. Two or more kinds of rubbers may be used in combination. From the viewpoint of resilience performance, polybutadiene is preferred, and high cis polybutadiene is particularly preferred.

  The rubber composition of the core 4 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. It is preferable that the rubber composition contains an organic peroxide together with a 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-butylperoxide). Oxy) hexane and di-t-butyl peroxide.

  The rubber composition of the core 4 may contain additives such as a filler, sulfur, a vulcanization accelerator, a sulfur compound, an anti-aging agent, a colorant, a plasticizer, and a dispersant. The rubber composition may contain a carboxylic acid or a carboxylate. The rubber composition may include a synthetic resin powder or a crosslinked rubber powder.

  The diameter of the core 4 is preferably 30.0 mm or more, and particularly preferably 38.0 mm or more. The diameter of the core 4 is preferably 42.0 mm or less, and particularly preferably 41.5 mm or less. The core 4 may have two or more layers. The core 4 may have a rib on its surface. The core 4 may be hollow.

  The mid layer 6 is made of a resin composition. A preferred base polymer of this resin composition is an ionomer resin. A preferable ionomer resin includes a binary copolymer of an α-olefin and an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms. As another preferable ionomer resin, a ternary copolymer 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 is used. A polymer is mentioned. In this binary copolymer and ternary copolymer, preferred α-olefins are ethylene and propylene, and preferred α, β-unsaturated carboxylic acids are acrylic acid and methacrylic acid. In this binary copolymer and ternary copolymer, some of the carboxyl groups are neutralized with metal ions. Examples of the metal ions for neutralization include sodium ions, potassium ions, lithium ions, zinc ions, calcium ions, magnesium ions, aluminum ions, and neodymium ions.

  Instead of the ionomer resin, the resin composition of the mid layer 6 may contain another polymer. Examples of other polymers include polystyrene, polyamide, polyester, polyolefin, and polyurethane. The resin composition may contain two or more kinds of polymers.

  The resin composition of the intermediate layer 6 includes 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 whitening agent, and the like. But you can. For the purpose of adjusting the specific gravity, the resin composition may contain a powder of a high specific gravity metal such as tungsten or molybdenum.

  The thickness of the mid layer 6 is preferably 0.2 mm or more, and particularly preferably 0.3 mm or more. The thickness of the mid layer 6 is preferably 2.5 mm or less, and particularly preferably 2.2 mm or less. The specific gravity of the mid layer 6 is preferably 0.90 or more, particularly preferably 0.95 or more. The specific gravity of the mid layer 6 is preferably 1.10 or less, particularly preferably 1.05 or less. The intermediate layer 6 may have two or more layers.

  The cover 8 is made of a resin composition. A preferred base polymer of this resin composition is polyurethane. The resin composition may contain a thermoplastic polyurethane or a thermosetting polyurethane. From the viewpoint of productivity, thermoplastic polyurethane is preferred. The thermoplastic polyurethane includes a polyurethane component as a hard segment and a polyester component or a polyether component as a soft segment.

  Polyurethane has a urethane bond in the molecule. This urethane bond can be formed by the reaction of a polyol and a polyisocyanate.

  The polyol which is a raw material of the urethane bond has a plurality of hydroxyl groups. Low molecular weight polyols and high molecular weight polyols can be used.

Examples of the isocyanate of the polyurethane component include alicyclic diisocyanate, aromatic diisocyanate and aliphatic diisocyanate. In particular, alicyclic diisocyanates are preferred. Since the alicyclic diisocyanate does not have a double bond in the main chain, yellowing of the cover 8 is suppressed. As alicyclic diisocyanates, 4,4′-dicyclohexylmethane diisocyanate (H ₁₂ MDI), 1,3-bis (isocyanatomethyl) cyclohexane (H ₆ XDI), isophorone diisocyanate (IPDI) and trans-1,4-cyclohexane Diisocyanate (CHDI) is exemplified. From the viewpoint of versatility and workability, H ₁₂ MDI is preferable.

  Instead of polyurethane, the resin composition of the cover 8 may include other polymers. Examples of other polymers include ionomer resin, polystyrene, polyamide, polyester, and polyolefin. The resin composition may contain two or more kinds of polymers.

  Even if the resin composition of the cover 8 includes 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 whitening agent, and the like. Good.

  The thickness of the cover 8 is preferably 0.2 mm or more, and particularly preferably 0.3 mm or more. The thickness of the cover 8 is preferably 2.5 mm or less, and particularly preferably 2.2 mm or less. The specific gravity of the cover 8 is preferably 0.90 or more, particularly preferably 0.95 or more. The specific gravity of the cover 8 is preferably 1.10 or less, and particularly preferably 1.05 or less. The cover 8 may have two or more layers.

  The golf ball 2 may include a reinforcing layer between the mid layer 6 and the cover 8. The reinforcing layer is firmly attached to the intermediate layer 6 and is also firmly attached to the cover 8. The reinforcing layer suppresses peeling of the cover 8 from the intermediate layer 6. The reinforcing layer is made of a polymer composition. Examples of the base polymer of the reinforcing layer include a two-component curable epoxy resin and a two-component curable urethane resin.

  As shown in FIGS. 2 and 3, the outline of each dimple 10 is a circle. The golf ball 2 includes a dimple A having a diameter of 4.40 mm, a dimple B having a diameter of 4.30 mm, a dimple C having a diameter of 4.15 mm, a dimple D having a diameter of 3.90 mm, Dimple E having a diameter of 3.00 mm. The number of types of dimples 10 is five. The golf ball 2 may have non-circular dimples instead of the circular dimple 10 or together with the circular dimple 10.

  The number of dimples A is 60, the number of dimples B is 158, the number of dimples C is 72, the number of dimples D is 36, and the number of dimples E is 12. The total number of dimples 10 is 338. These dimples 10 and lands 12 form a dimple pattern.

  FIG. 4 shows a cross section of the golf ball 2 along a plane passing through the center of the dimple 10 and the center of the golf ball 2. The vertical direction in FIG. 4 is the depth direction of the dimple 10. In FIG. 4, what is indicated by a two-dot chain line 14 is a virtual sphere. The surface of the phantom sphere 14 is the surface of the golf ball 2 when it is assumed that the dimple 10 does not exist. The diameter of the phantom sphere 14 is the same as the diameter of the golf ball 2. The dimple 10 is recessed from the surface of the phantom sphere 14. The land 12 coincides with the surface of the phantom sphere 14. In the present embodiment, the cross-sectional shape of the dimple 10 is substantially an arc. The radius of curvature of this circular arc is indicated by the symbol CR in FIG.

  In FIG. 4, the diameter of the dimple 10 is indicated by an arrow Dm. This diameter Dm is the distance between one contact point Ed and the other contact point Ed when a common tangent line Tg is drawn on both sides of the dimple 10. The contact point Ed is also an edge of the dimple 10. The edge Ed defines the contour of the dimple 10.

  The diameter Dm of each dimple 10 is preferably 2.0 mm or greater and 6.0 mm or less. The dimple 10 having a diameter Dm of 2.0 mm or more contributes to turbulence. In this respect, the diameter Dm is more preferably equal to or greater than 2.5 mm, and particularly preferably equal to or greater than 2.8 mm. The dimple 10 having a diameter Dm of 6.0 mm or less does not impair the essence of the golf ball 2 that is substantially a sphere. In this respect, the diameter Dm is more preferably equal to or less than 5.5 mm, and particularly preferably equal to or less than 5.0 mm.

  In the case of a non-circular dimple, a circular dimple 10 having the same area as that of the non-circular dimple is assumed. The diameter of the virtual circular dimple 10 is regarded as the diameter of the non-circular dimple.

  In FIG. 4, what is indicated by a double-headed arrow Dp <b> 1 is the first depth of the dimple 10. This first depth Dp1 is the distance between the deepest part of the dimple 10 and the surface of the phantom sphere 14. In FIG. 4, what is indicated by a double-headed arrow Dp2 is the second depth of the dimple 10. This second depth Dp2 is the distance between the deepest part of the dimple 10 and the tangent Tg.

  In light of suppression of hops in the golf ball 2, the first depth Dp1 of the dimple 10 is preferably 0.10 mm or more, more preferably 0.13 mm or more, and particularly preferably 0.15 mm or more. In light of suppression of dropping of the golf ball 2, the first depth Dp1 is preferably equal to or less than 0.65 mm, more preferably equal to or less than 0.60 mm, and particularly preferably equal to or less than 0.55 mm.

The area s of the dimple 10 is an area of a region surrounded by the outline of the dimple 10 when the center of the golf ball 2 is viewed from infinity. In the case of the circular dimple 10, the area S is calculated by the following mathematical formula.
S = (Dm / 2) ² * π

In the golf ball 2 shown in FIGS. 2 and 3, the dimple A has an area of 15.20 mm ² , the dimple B has an area of 14.52 mm ² , and the dimple C has an area of 13.53 mm ^2. The area of D is 11.95 mm ² and the area of the dimple E is 7.07 mm ² .

In the present invention, the ratio of the total area S of all the dimples 10 to the surface area of the phantom sphere 14 is referred to as an occupation ratio. From the viewpoint that sufficient turbulence can be obtained, the occupation ratio is preferably 78% or more, more preferably 80% or more, and particularly preferably 82% or more. The occupation ratio is preferably 95% or less. In the golf ball 2 shown in FIGS. 2 and 3, the total area of the dimples 10 is 4695.4 mm ² . Since the surface area of the phantom sphere 14 of this golf ball 2 is 5728 mm ² , the occupation ratio is 82.0%.

  From the viewpoint that a sufficient occupation ratio is achieved, the total number N of the dimples 10 is preferably 250 or more, more preferably 280 or more, and particularly preferably 300 or more. From the viewpoint that each dimple 10 can contribute to turbulence, the total number N is preferably 450 or less, more preferably 400 or less, and particularly preferably 380 or less.

In the present invention, the “dimple volume V” means the volume of the portion surrounded by the surface of the phantom sphere 14 and the surface of the dimple 10. The total volume TV of the dimple 10 is preferably 450 mm ³ or more and 750 mm ³ or less. In the golf ball 2 having a total volume TV of 450 mm ³ or more, hops during flight are suppressed. In this respect, the total volume of TV is more preferably 480 mm ³ or more, 500 mm ³ or more is particularly preferable. In the golf ball 2 having a total volume TV of 750 mm ³ or less, dropping during flight is suppressed. In this respect, the total volume of TV is more preferably 730 mm ³ or less, 710 mm ³ or less is particularly preferred.

The golf ball 2 according to the present invention has excellent aerodynamic characteristics. This aerodynamic characteristic evaluation method is
(A) a step in which a great circle existing on the surface of the phantom sphere 14 and orthogonal to the axis Ax is assumed;
(B) a step in which two small circles existing on the surface of the phantom sphere 14, orthogonal to the axis Ax, and having an absolute value of the central angle with the great circle of 30 ° are assumed;
(C) a step in which the surface of the golf ball 2 is partitioned by these small circles, and a region sandwiched between these small circles is specified on the surface;
(D) a step in which 30240 points are determined in this region in increments of 3 ° at the central angle in the axial direction and in increments of 0.25 ° at the central angle in the rotational direction;
(E) Step of calculating the length L1 of the perpendicular line drawn from each point to the axis Ax (f) The 21 lengths L1 calculated based on the 21 perpendicular lines arranged in the axial direction are totaled, and the total length The step of calculating the length L2,
(G) Fourier transform is performed on a data group of 1440 total lengths L2 calculated along the rotation direction to obtain a transformed data group;
And (h) a step of calculating the peak value and the order of the maximum peak of the converted data group is executed. Each step is detailed below.

  FIG. 5 is a schematic diagram for explaining this evaluation method. FIG. 5 shows a virtual sphere 14 of the golf ball 2. In FIG. 5, what is indicated by the symbol NP is the north pole. The north pole NP corresponds to the apex of the cavity surface formed by the upper mold for molding the golf ball 2. What is indicated by the symbol SP is the south pole. The south pole SP corresponds to the deepest portion of the cavity surface formed by the lower mold for molding the golf ball 2. What is indicated by a symbol Eq is the equator. With this equator Eq, the phantom sphere 14 can be partitioned into the northern hemisphere NH and the southern hemisphere SH.

  The latitude of the North Pole NP is 90 ° (degree). The latitude θ of the equator Eq is zero. The latitude of the south pole SP is -90 °. The counterclockwise direction when the phantom sphere 14 is viewed from the north pole NP is the positive direction of the longitude φ. The minimum value of φ is zero. The maximum value of φ is 360 °. The spherical polar coordinates of a point existing on the surface of the phantom sphere 14 are represented by (θ, φ). In FIG. 5, the point (0, 0) is located in front.

  In FIG. 5, the symbol Loa indicates the first latitude line. The latitude φ of the first latitude line Loa is 0 ° and 360 °. The phantom sphere 14 has innumerable latitude lines. A latitude line with the maximum number of dimples 10 intersecting the center is defined as a first latitude line Loa. In the dimple 10 that intersects the latitude line at the center, the latitude line passes through the center of gravity of the area of the dimple 10.

  In this evaluation method, the first axis Ax1 is assumed. The first axis Ax1 passes through the point Pn1 and the point Ps1. The point Pn1 and the point Ps1 exist on the surface of the phantom sphere 14. The point Pn1 exists in the northern hemisphere NH. The coordinates of the point Pn1 are (75, 270). The point Ps1 exists in the southern hemisphere SH. The coordinates of the point Ps1 are (−75, 90). The first axis Ax1 is inclined with respect to the ground axis. The angle of inclination is 15 °. The earth axis is a line passing through the north pole NP and the south pole SP.

  In this evaluation method, a first great circle GC1 existing on the surface of the phantom sphere 14 of the golf ball 2 is assumed. The first axis Ax1 is orthogonal to the first great circle GC1. In other words, the first axis Ax1 is orthogonal to the plane including the first great circle GC1. In FIG. 5, the first great circle GC1 is inclined with respect to the equator Eq. The angle of inclination is 15 °. The great circle is a circle that exists on the surface of the phantom sphere and whose diameter is the same as the diameter of the phantom sphere.

  The golf ball 2 rotates about the first axis Ax1. During this rotation, the peripheral speed of the first great circle GC1 is fast. Therefore, the surface roughness of the golf ball 2 in the first great circle GC1 and the vicinity thereof greatly affects the flight performance of the golf ball 2.

  In this evaluation method, two small circles C1 and C2 that exist on the surface of the phantom sphere 14 and are orthogonal to the first axis Ax1 are assumed. FIG. 6 shows these small circles C1 and C2. Each small circle is parallel to the first great circle GC1.

  FIG. 7 schematically shows a partial cross section of the golf ball 2 of FIG. FIG. 7 shows a cross section passing through the center O of the golf ball 2. The left-right direction in FIG. 7 is the direction of the first axis Ax1. As shown in FIG. 7, the absolute value of the central angle between the small circle C1 and the first great circle GC1 is 30 °. Although not shown, the absolute value of the central angle between the small circle C2 and the first great circle GC1 is also 30 °. The golf ball 2 is partitioned by these small circles C1 and C2, and a region sandwiched between these small circles on the surface of the golf ball 2 is specified. Since the first great circle GC1 has a high peripheral speed, the dimples 10 existing in this region have a great influence on the aerodynamic characteristics of the golf ball 2.

  A point P (α) in FIG. 7 is a point located on the surface of the golf ball 2 and having a central angle with the first great circle GC1 of α ° (degree). Point F (α) is a foot of perpendicular line Pe (α) drawn from point P (α) to first axis Ax1. What is indicated by the arrow L1 (α) is the length of the perpendicular line Pe (α). In other words, the length L1 (α) is the distance between the point P (α) and the first axis Ax1. In one cross section, the length L1 (α) is calculated for 21 points P (α). Specifically, −30 °, −27 °, −24 °, −21 °, −18 °, −15 °, −12 °, −9 °, −6 °, −3 °, 0 °, and 3 °. , 6 °, 9 °, 12 °, 15 °, 18 °, 21 °, 24 °, 27 ° and 30 °, the length L1 (α) is calculated. The 21 lengths L1 (α) are summed to obtain a total length L2 (mm). The total length L2 is a parameter depending on the shape of the surface in the cross section shown in FIG.

  FIG. 8 shows a partial cross section of the golf ball 2. In FIG. 8, the direction perpendicular to the paper surface is the direction of the first axis Ax1. In FIG. 8, what is indicated by a symbol β is the rotation angle of the golf ball 2. In the range from 0 ° to less than 360 °, the rotation angle β is set in increments of 0.25 °. The total length L2 is calculated for each rotation angle. As a result, a total length L2 of 1440 is obtained along the rotational direction. The total length L2 is a data group calculated by one rotation of the golf ball 2. This data group is calculated based on 30240 lengths L1.

  FIG. 9 shows a graph in which data groups related to the first axis Ax1 of the golf ball 2 shown in FIGS. 2 and 3 are plotted. In this graph, the horizontal axis is the rotation angle β, and the vertical axis is the total length L2. A Fourier transform is performed on this data group. A frequency spectrum is obtained by Fourier transform. In other words, a Fourier series coefficient represented by the following mathematical formula is obtained by Fourier transform.

The above formula is a combination of two trigonometric functions having different periods. In the above formula, a _n and b _n are Fourier coefficients. The size of each component to be synthesized is determined by these Fourier coefficients. Each coefficient is represented by the following mathematical formula.

In this equation, N is the total number of data in the data group, and F _k is the kth value in the data group. The spectrum is expressed by the following mathematical formula.

  A transform data group is obtained by Fourier transform. A graph in which the conversion data group is plotted is shown in FIG. In this graph, the horizontal axis is the order and the vertical axis is the amplitude. From this graph, the maximum peak is determined. Further, the peak value Pd1 of the maximum peak and the order Fd1 of the maximum peak are determined. The peak value Pd1 and the order Fd1 are numerical values representing aerodynamic characteristics in rotation about the first axis Ax1. In the present embodiment, the peak value Pd1 is 270.2 mm and the order Fd1 is 33.

  FIG. 11 also shows the phantom sphere 14 of the golf ball 2. FIG. 11 shows an equator Eq and a meridian Loa having a longitude φ of zero. In FIG. 11, the point (0, 0) is located in front. In FIG. 11, what is indicated by the symbol Ax2 is the second axis. The second axis Ax2 passes through the point Pn2 and the point Ps2. The point Pn2 and the point Ps2 exist on the surface of the phantom sphere 14. The coordinates of the point Pn2 are (60, 270). The coordinates of the point Ps2 are (−60, 90). The second axis Ax2 is inclined with respect to the ground axis. The angle of inclination is 30 °.

  FIG. 11 shows a second great circle GC2 that exists on the surface of the phantom sphere 14 of the golf ball 2 and in which the second axis Ax2 is orthogonal. The second great circle GC2 is inclined with respect to the equator Eq. The angle of inclination is 30 °.

  Regarding the rotation about the second axis Ax2, the aerodynamic characteristics are evaluated by the same method as the rotation about the first axis Ax1. Specifically, two small circles C1 and C2 are assumed for rotation about the second axis Ax2. The absolute value of the central angle between the small circle C1 and the second great circle GC2 is 30 °. The absolute value of the central angle between the small circle C2 and the second great circle GC2 is also 30 °. A total length L2 of 1440 is calculated in a region sandwiched between these small circles on the surface of the golf ball 2. In other words, a data group for the second axis Ax2 is calculated. Fourier transform is performed on this data group, and a transformed data group is obtained. From the graph in which the conversion data group is plotted, the peak value Pd2 of the maximum peak and the order Fd2 of the maximum peak are determined. The peak value Pd2 and the order Fd2 are numerical values representing aerodynamic characteristics in rotation about the second axis Ax2. In the present embodiment, the peak value Pd2 is 177.9 mm, and the order Fd2 is 37.

  FIG. 12 also shows the phantom sphere 14 of the golf ball 2. FIG. 12 shows an equator Eq and a meridian Loa whose longitude φ is zero. In FIG. 12, the point (0, 0) is located in front. In FIG. 12, what is indicated by the symbol Ax3 is the third axis. The third axis Ax3 passes through the point Pn3 and the point Ps3. The points Pn3 and Ps3 exist on the surface of the phantom sphere 14. The coordinates of the point Pn3 are (45,270). The coordinates of the point Ps3 are (−45, 90). The third axis Ax3 is inclined with respect to the ground axis. The angle of inclination is 45 °.

  FIG. 12 shows a third great circle GC3 that exists on the surface of the phantom sphere 14 of the golf ball 2 and in which the third axis Ax3 is orthogonal. The third great circle GC3 is inclined with respect to the equator Eq. The angle of inclination is 45 °.

  For the rotation about the third axis Ax3, the aerodynamic characteristics are evaluated by the same method as the rotation about the first axis Ax1. Specifically, two small circles C1 and C2 are assumed for rotation about the third axis Ax3. The absolute value of the central angle between the small circle C1 and the third great circle GC3 is 30 °. The absolute value of the central angle between the small circle C2 and the third great circle GC3 is also 30 °. A total length L2 of 1440 is calculated in a region sandwiched between these small circles on the surface of the golf ball 2. In other words, a data group for the third axis Ax3 is calculated. Fourier transform is performed on this data group, and a transformed data group is obtained. From the graph in which the conversion data group is plotted, the peak value Pd3 of the maximum peak and the order Fd3 of the maximum peak are determined. The peak value Pd3 and the order Fd3 are numerical values representing aerodynamic characteristics in rotation about the third axis Ax3. In the present embodiment, the peak value Pd3 is 150.2 mm, and the order Fd3 is 37.

  FIG. 13 also shows the phantom sphere 14 of the golf ball 2. FIG. 13 shows an equator Eq and a meridian Loa whose longitude φ is zero. In FIG. 13, the point (0, 0) is located in front. In FIG. 13, what is indicated by reference numeral Ax4 is the fourth axis. The fourth axis Ax4 passes through the point Pn4 and the point Ps4. The point Pn4 and the point Ps4 exist on the surface of the phantom sphere 14. The coordinates of the point Pn4 are (30, 270). The coordinates of the point Ps4 are (−30, 90). The fourth axis Ax4 is inclined with respect to the ground axis. The angle of inclination is 60 °.

  FIG. 13 shows a fourth great circle GC4 that exists on the surface of the phantom sphere 14 of the golf ball 2 and in which the fourth axis Ax4 is orthogonal. The fourth great circle GC4 is inclined with respect to the equator Eq. The angle of inclination is 60 °.

  For the rotation about the fourth axis Ax4, the aerodynamic characteristics are evaluated by the same method as the rotation about the first axis Ax1. Specifically, two small circles C1 and C2 are assumed for rotation about the fourth axis Ax4. The absolute value of the central angle between the small circle C1 and the fourth great circle GC4 is 30 °. The absolute value of the central angle between the small circle C2 and the fourth great circle GC4 is also 30 °. A total length L2 of 1440 is calculated in a region sandwiched between these small circles on the surface of the golf ball 2. In other words, a data group for the fourth axis Ax4 is calculated. Fourier transform is performed on this data group, and a transformed data group is obtained. From the graph in which the conversion data group is plotted, the peak value Pd4 of the maximum peak and the order Fd4 of the maximum peak are determined. The peak value Pd4 and the order Fd4 are numerical values representing aerodynamic characteristics in rotation about the fourth axis Ax4. In the present embodiment, the peak value Pd4 is 316.4 mm, and the order Fd4 is 34.

  FIG. 14 also shows the phantom sphere 14 of the golf ball 2. FIG. 14 shows an equator Eq and a meridian Loa whose longitude φ is zero. In FIG. 14, the point (0, 0) is located in front. In FIG. 14, what is indicated by reference numeral Ax5 is the fifth axis. The fifth axis Ax5 passes through the point Pn5 and the point Ps5. The point Pn5 and the point Ps5 exist on the surface of the phantom sphere 14. The coordinates of the point Pn5 are (15,270). The coordinates of the point Ps5 are (-15, 90). The fifth axis Ax5 is inclined with respect to the ground axis. The angle of inclination is 75 °.

  FIG. 14 shows a fifth great circle GC5 that exists on the surface of the phantom sphere 14 of the golf ball 2 and in which the fifth axis Ax5 is orthogonal. The fifth great circle GC5 is inclined with respect to the equator Eq. The angle of inclination is 75 °.

  For the rotation about the fifth axis Ax5, the aerodynamic characteristics are evaluated by the same method as the rotation about the first axis Ax1. Specifically, two small circles C1 and C2 are assumed for rotation about the fifth axis Ax5. The absolute value of the central angle between the small circle C1 and the fifth great circle GC5 is 30 °. The absolute value of the central angle between the small circle C2 and the fifth large circle GC5 is also 30 °. A total length L2 of 1440 is calculated in a region sandwiched between these small circles on the surface of the golf ball 2. In other words, a data group for the fifth axis Ax5 is calculated. Fourier transform is performed on this data group, and a transformed data group is obtained. From the graph in which the conversion data group is plotted, the peak value Pd5 of the maximum peak and the order Fd5 of the maximum peak are determined. The peak value Pd5 and the order Fd5 are numerical values representing aerodynamic characteristics in rotation about the fifth axis Ax5. In the present embodiment, the peak value Pd5 is 190.0 mm, and the order Fd5 is 27.

  FIG. 15 also shows a virtual sphere 14 of the golf ball 2. FIG. 15 shows an equator Eq and a meridian Lob having a longitude φ of 90 °. In FIG. 15, the point (0, 90) is located in front. In FIG. 15, what is indicated by reference numeral Ax6 is the sixth axis. The sixth axis Ax6 passes through the point Pn6 and the point Ps6. The point Pn6 and the point Ps6 exist on the surface of the phantom sphere 14. The coordinates of the point Pn6 are (75, 0). The coordinates of the point Ps6 are (−75, 180). The sixth axis Ax6 is inclined with respect to the ground axis. The angle of inclination is 15 °.

  FIG. 15 shows a sixth great circle GC6 that exists on the surface of the phantom sphere 14 of the golf ball 2 and in which the sixth axis Ax6 is orthogonal. The sixth great circle GC6 is inclined with respect to the equator Eq. The angle of inclination is 15 °.

  For the rotation about the sixth axis Ax6, the aerodynamic characteristics are evaluated by the same method as the rotation about the first axis Ax1. Specifically, two small circles C1 and C2 are assumed for rotation about the sixth axis Ax6. The absolute value of the central angle between the small circle C1 and the sixth large circle GC6 is 30 °. The absolute value of the central angle between the small circle C2 and the sixth large circle GC6 is also 30 °. A total length L2 of 1440 is calculated in a region sandwiched between these small circles on the surface of the golf ball 2. In other words, a data group for the sixth axis Ax6 is calculated. Fourier transform is performed on this data group, and a transformed data group is obtained. From the graph in which the conversion data group is plotted, the peak value Pd6 of the maximum peak and the order Fd6 of the maximum peak are determined. The peak value Pd6 and the order Fd6 are numerical values representing aerodynamic characteristics in rotation about the sixth axis Ax6. In the present embodiment, the peak value Pd6 is 270.2 mm and the order Fd6 is 33.

  FIG. 16 also shows the phantom sphere 14 of the golf ball 2. FIG. 16 shows an equator Eq and a meridian Lob whose longitude φ is 90 °. In FIG. 16, the point (0, 90) is located in front. In FIG. 16, what is indicated by reference numeral Ax7 is the seventh axis. The seventh axis Ax7 passes through the point Pn7 and the point Ps7. The points Pn7 and Ps7 exist on the surface of the phantom sphere 14. The coordinates of the point Pn7 are (60, 0). The coordinates of the point Ps7 are (−60, 180). The seventh axis Ax7 is inclined with respect to the ground axis. The angle of inclination is 30 °.

  FIG. 16 shows a seventh great circle GC7 that exists on the surface of the phantom sphere 14 of the golf ball 2 and in which the seventh axis Ax7 is orthogonal. The seventh great circle GC7 is inclined with respect to the equator Eq. The angle of inclination is 30 °.

  Regarding the rotation about the seventh axis Ax7, the aerodynamic characteristics are evaluated by the same method as the rotation about the first axis Ax1. Specifically, two small circles C1 and C2 are assumed for rotation about the seventh axis Ax7. The absolute value of the central angle between the small circle C1 and the seventh great circle GC7 is 30 °. The absolute value of the central angle between the small circle C2 and the seventh great circle GC7 is also 30 °. A total length L2 of 1440 is calculated in a region sandwiched between these small circles on the surface of the golf ball 2. In other words, a data group for the seventh axis Ax7 is calculated. Fourier transform is performed on this data group, and a transformed data group is obtained. From the graph in which the conversion data group is plotted, the peak value Pd7 of the maximum peak and the order Fd7 of the maximum peak are determined. The peak value Pd7 and the order Fd7 are numerical values representing aerodynamic characteristics in rotation about the seventh axis Ax7. In the present embodiment, the peak value Pd7 is 177.9 mm, and the order Fd7 is 37.

  FIG. 17 also shows the phantom sphere 14 of the golf ball 2. FIG. 17 shows an equator Eq and a meridian Lob having a longitude φ of 90 °. In FIG. 17, the point (0, 90) is located in front. In FIG. 17, what is indicated by reference numeral Ax8 is the eighth axis. The eighth axis Ax8 passes through the point Pn8 and the point Ps8. The point Pn8 and the point Ps8 exist on the surface of the phantom sphere 14. The coordinates of the point Pn8 are (45, 0). The coordinates of the point Ps8 are (−45, 180). The eighth axis Ax8 is inclined with respect to the ground axis. The angle of inclination is 45 °.

  FIG. 17 shows an eighth great circle GC8 that exists on the surface of the phantom sphere 14 of the golf ball 2 and in which the eighth axis Ax8 is orthogonal. The eighth great circle GC8 is inclined with respect to the equator Eq. The angle of inclination is 45 °.

  For the rotation about the eighth axis Ax8, the aerodynamic characteristics are evaluated by the same method as the rotation about the first axis Ax1. Specifically, two small circles C1 and C2 are assumed for rotation about the eighth axis Ax8. The absolute value of the central angle between the small circle C1 and the eighth great circle GC8 is 30 °. The absolute value of the central angle between the small circle C2 and the eighth great circle GC8 is also 30 °. A total length L2 of 1440 is calculated in a region sandwiched between these small circles on the surface of the golf ball 2. In other words, a data group for the eighth axis Ax8 is calculated. Fourier transform is performed on this data group, and a transformed data group is obtained. From the graph in which the conversion data group is plotted, the peak value Pd8 of the maximum peak and the order Fd8 of the maximum peak are determined. The peak value Pd8 and the order Fd8 are numerical values representing aerodynamic characteristics in rotation about the eighth axis Ax8. In the present embodiment, the peak value Pd8 is 150.2 mm, and the order Fd8 is 37.

  FIG. 18 also shows the phantom sphere 14 of the golf ball 2. FIG. 18 shows an equator Eq and a meridian Lob whose longitude φ is 90 °. In FIG. 18, the point (0, 90) is located in front. In FIG. 18, what is indicated by reference numeral Ax9 is the ninth axis. The ninth axis Ax9 passes through the point Pn9 and the point Ps9. The point Pn9 and the point Ps9 exist on the surface of the phantom sphere 14. The coordinates of the point Pn9 are (30, 0). The coordinates of the point Ps9 are (−30, 180). The ninth axis Ax9 is inclined with respect to the ground axis. The angle of inclination is 60 °.

  FIG. 18 shows a ninth great circle GC9 that exists on the surface of the phantom sphere 14 of the golf ball 2 and in which the ninth axis Ax9 is orthogonal. The ninth great circle GC9 is inclined with respect to the equator Eq. The angle of inclination is 60 °.

  For the rotation about the ninth axis Ax9, the aerodynamic characteristics are evaluated by the same method as the rotation about the first axis Ax1. Specifically, two small circles C1 and C2 are assumed for rotation about the ninth axis Ax9. The absolute value of the central angle between the small circle C1 and the ninth large circle GC9 is 30 °. The absolute value of the central angle between the small circle C2 and the ninth large circle GC9 is also 30 °. A total length L2 of 1440 is calculated in a region sandwiched between these small circles on the surface of the golf ball 2. In other words, a data group for the ninth axis Ax9 is calculated. Fourier transform is performed on this data group, and a transformed data group is obtained. From the graph in which the conversion data group is plotted, the peak value Pd9 of the maximum peak and the order Fd9 of the maximum peak are determined. The peak value Pd9 and the order Fd9 are numerical values representing aerodynamic characteristics in rotation about the ninth axis Ax9. In the present embodiment, the peak value Pd9 is 316.4 mm, and the order Fd9 is 34.

  FIG. 19 also shows the phantom sphere 14 of the golf ball 2. FIG. 19 shows an equator Eq and a meridian Lob whose longitude φ is 90 °. In FIG. 19, the point (0, 90) is located in front. In FIG. 19, what is indicated by reference numeral Ax10 is the tenth axis. The tenth axis Ax10 passes through the point Pn10 and the point Ps10. The point Pn10 and the point Ps10 exist on the surface of the phantom sphere 14. The coordinates of the point Pn10 are (15, 0). The coordinates of the point Ps10 are (-15, 180). The tenth axis Ax10 is inclined with respect to the ground axis. The angle of inclination is 75 °.

  FIG. 19 shows a tenth great circle GC10 that exists on the surface of the phantom sphere 14 of the golf ball 2 and in which the tenth axis Ax10 is orthogonal. The tenth great circle GC10 is inclined with respect to the equator Eq. The angle of inclination is 75 °.

  For the rotation about the tenth axis Ax10, the aerodynamic characteristics are evaluated by the same method as the rotation about the first axis Ax1. Specifically, two small circles C1 and C2 are assumed for rotation about the tenth axis Ax10. The absolute value of the central angle between the small circle C1 and the tenth large circle GC10 is 30 °. The absolute value of the central angle between the small circle C2 and the tenth large circle GC10 is also 30 °. A total length L2 of 1440 is calculated in a region sandwiched between these small circles on the surface of the golf ball 2. In other words, a data group for the tenth axis Ax10 is calculated. Fourier transform is performed on this data group, and a transformed data group is obtained. From the graph in which the conversion data group is plotted, the peak value Pd10 of the maximum peak and the order Fd10 of the maximum peak are determined. The peak value Pd10 and the order Fd10 are numerical values representing aerodynamic characteristics in rotation about the tenth axis Ax10. In the present embodiment, the peak value Pd10 is 190.0 mm, and the order Fd10 is 27.

  FIG. 20 also shows the phantom sphere 14 of the golf ball 2. FIG. 20 shows an equator Eq and a meridian Loc having a longitude φ of 180 °. In FIG. 20, the point (0, 180) is located in front. In FIG. 20, what is indicated by reference numeral Ax11 is the eleventh axis. The eleventh axis Ax11 passes through the point Pn11 and the point Ps11. The point Pn11 and the point Ps11 exist on the surface of the phantom sphere 14. The coordinates of the point Pn11 are (75, 90). The coordinates of the point Ps11 are (−75, 270). The eleventh axis Ax11 is inclined with respect to the ground axis. The angle of inclination is 15 °.

  FIG. 20 shows an eleventh great circle GC11 that exists on the surface of the phantom sphere 14 of the golf ball 2 and in which the eleventh axis Ax11 is orthogonal. The eleventh great circle GC11 is inclined with respect to the equator Eq. The angle of inclination is 75 °.

  For the rotation about the eleventh axis Ax11, the aerodynamic characteristics are evaluated by the same method as the rotation about the first axis Ax1. Specifically, two small circles C1 and C2 are assumed for rotation about the eleventh axis Ax11. The absolute value of the central angle between the small circle C1 and the eleventh great circle GC11 is 30 °. The absolute value of the central angle between the small circle C2 and the eleventh great circle GC11 is also 30 °. A total length L2 of 1440 is calculated in a region sandwiched between these small circles on the surface of the golf ball 2. In other words, a data group for the eleventh axis Ax11 is calculated. Fourier transform is performed on this data group, and a transformed data group is obtained. From the graph in which the conversion data group is plotted, the peak value Pd11 of the maximum peak and the order Fd11 of the maximum peak are determined. The peak value Pd11 and the order Fd11 are numerical values representing aerodynamic characteristics in rotation about the eleventh axis Ax11. In the present embodiment, the peak value Pd11 is 270.2 mm, and the order Fd11 is 33.

  FIG. 21 also shows the phantom sphere 14 of the golf ball 2. FIG. 21 shows an equator Eq and a meridian Loc having a longitude φ of 180 °. In FIG. 21, the point (0, 180) is located in front. In FIG. 21, what is indicated by reference sign Ax12 is the twelfth axis. The twelfth axis Ax12 passes through the point Pn12 and the point Ps12. The point Pn12 and the point Ps12 exist on the surface of the phantom sphere 14. The coordinates of the point Pn12 are (60, 90). The coordinates of the point Ps12 are (−60, 270). The twelfth axis Ax12 is inclined with respect to the ground axis. The angle of inclination is 30 °.

  FIG. 21 shows a twelfth great circle GC12 that exists on the surface of the phantom sphere 14 of the golf ball 2 and in which the twelfth axis Ax12 is orthogonal. The twelfth great circle GC12 is inclined with respect to the equator Eq. The angle of inclination is 60 °.

  For the rotation about the twelfth axis Ax12, the aerodynamic characteristics are evaluated by the same method as the rotation about the first axis Ax1. Specifically, two small circles C1 and C2 are assumed for rotation about the twelfth axis Ax12. The absolute value of the central angle between the small circle C1 and the twelfth great circle GC12 is 30 °. The absolute value of the central angle between the small circle C2 and the twelfth great circle GC12 is also 30 °. A total length L2 of 1440 is calculated in a region sandwiched between these small circles on the surface of the golf ball 2. In other words, a data group for the twelfth axis Ax12 is calculated. Fourier transform is performed on this data group, and a transformed data group is obtained. The peak value Pd12 of the maximum peak and the order Fd12 of the maximum peak are determined from the graph in which the conversion data group is plotted. The peak value Pd12 and the order Fd12 are numerical values representing aerodynamic characteristics in rotation about the twelfth axis Ax12. In the present embodiment, the peak value Pd12 is 177.9 mm, and the order Fd12 is 37.

  FIG. 22 also shows the phantom sphere 14 of the golf ball 2. FIG. 22 shows an equator Eq and a meridian Loc having a longitude φ of 180 °. In FIG. 22, the point (0, 180) is located in front. In FIG. 22, what is indicated by reference numeral Ax13 is the thirteenth axis. The thirteenth axis Ax13 passes through the point Pn13 and the point Ps13. The point Pn13 and the point Ps13 exist on the surface of the phantom sphere 14. The coordinates of the point Pn13 are (45, 90). The coordinates of the point Ps13 are (−45, 270). The thirteenth axis Ax13 is inclined with respect to the ground axis. The angle of inclination is 45 °.

  FIG. 22 shows a thirteenth great circle GC13 that exists on the surface of the phantom sphere 14 of the golf ball 2 and in which the thirteenth axis Ax13 is orthogonal. The thirteenth great circle GC13 is inclined with respect to the equator Eq. The angle of inclination is 45 °.

  For the rotation about the thirteenth axis Ax13, the aerodynamic characteristics are evaluated by the same method as the rotation about the first axis Ax1. Specifically, two small circles C1 and C2 are assumed for rotation about the thirteenth axis Ax13. The absolute value of the central angle between the small circle C1 and the thirteenth great circle GC13 is 30 °. The absolute value of the central angle between the small circle C2 and the thirteenth great circle GC13 is also 30 °. A total length L2 of 1440 is calculated in a region sandwiched between these small circles on the surface of the golf ball 2. In other words, a data group for the thirteenth axis Ax13 is calculated. Fourier transform is performed on this data group, and a transformed data group is obtained. From the graph in which the conversion data group is plotted, the peak value Pd13 of the maximum peak and the order Fd13 of the maximum peak are determined. The peak value Pd13 and the order Fd13 are numerical values representing aerodynamic characteristics in rotation about the thirteenth axis Ax13. In the present embodiment, the peak value Pd13 is 150.2 mm, and the order Fd13 is 37.

  FIG. 23 also shows the phantom sphere 14 of the golf ball 2. FIG. 23 shows an equator Eq and a meridian Loc having a longitude φ of 180 °. In FIG. 23, the point (0, 180) is located in front. In FIG. 23, what is indicated by reference numeral Ax14 is the fourteenth axis. The fourteenth axis Ax14 passes through the point Pn14 and the point Ps14. The point Pn14 and the point Ps14 exist on the surface of the phantom sphere 14. The coordinates of the point Pn14 are (30, 90). The coordinates of the point Ps14 are (−30, 270). The fourteenth axis Ax14 is inclined with respect to the ground axis. The angle of inclination is 60 °.

  FIG. 23 shows a fourteenth great circle GC14 that exists on the surface of the phantom sphere 14 of the golf ball 2 and in which the fourteenth axis Ax14 is orthogonal. The fourteenth great circle GC14 is inclined with respect to the equator Eq. The angle of inclination is 60 °.

  Regarding the rotation about the fourteenth axis Ax14, the aerodynamic characteristics are evaluated by the same method as the rotation about the first axis Ax1. Specifically, two small circles C1 and C2 are assumed for rotation about the fourteenth axis Ax14. The absolute value of the central angle between the small circle C1 and the fourteenth great circle GC14 is 30 °. The absolute value of the central angle between the small circle C2 and the fourteenth great circle GC14 is also 30 °. A total length L2 of 1440 is calculated in a region sandwiched between these small circles on the surface of the golf ball 2. In other words, a data group for the fourteenth axis Ax14 is calculated. Fourier transform is performed on this data group, and a transformed data group is obtained. From the graph in which the conversion data group is plotted, the peak value Pd14 of the maximum peak and the order Fd14 of the maximum peak are determined. The peak value Pd14 and the order Fd14 are numerical values representing aerodynamic characteristics in rotation about the fourteenth axis Ax14. In the present embodiment, the peak value Pd14 is 316.4 mm, and the order Fd14 is 34.

  FIG. 24 also shows the phantom sphere 14 of the golf ball 2. FIG. 24 shows an equator Eq and a meridian Loc having a longitude φ of 180 °. In FIG. 24, the point (0, 180) is located in front. In FIG. 24, the reference numeral Ax15 indicates the fifteenth axis. The fifteenth axis Ax15 passes through the point Pn15 and the point Ps15. The point Pn15 and the point Ps15 exist on the surface of the phantom sphere 14. The coordinates of the point Pn15 are (15, 90). The coordinates of the point Ps15 are (−15,270). The fifteenth axis Ax15 is inclined with respect to the ground axis. The angle of inclination is 75 °.

  FIG. 24 shows a fifteenth great circle GC15 that exists on the surface of the phantom sphere 14 of the golf ball 2 and in which the fifteenth axis Ax15 is orthogonal. The fifteenth great circle GC15 is inclined with respect to the equator Eq. The angle of inclination is 75 °.

  For the rotation about the fifteenth axis Ax15, the aerodynamic characteristics are evaluated by the same method as the rotation about the first axis Ax1. Specifically, two small circles C1 and C2 are assumed for rotation about the fifteenth axis Ax15. The absolute value of the central angle between the small circle C1 and the fifteenth great circle GC15 is 30 °. The absolute value of the central angle between the small circle C2 and the fifteenth great circle GC15 is also 30 °. A total length L2 of 1440 is calculated in a region sandwiched between these small circles on the surface of the golf ball 2. In other words, a data group for the fifteenth axis Ax15 is calculated. Fourier transform is performed on this data group, and a transformed data group is obtained. From the graph in which the conversion data group is plotted, the peak value Pd15 of the maximum peak and the order Fd15 of the maximum peak are determined. The peak value Pd15 and the order Fd15 are numerical values representing aerodynamic characteristics in rotation about the fifteenth axis Ax15. In the present embodiment, the peak value Pd15 is 190.0 mm, and the order Fd15 is 27.

In this evaluation method,
(1) a first axis Ax1 passing through a point Pn1 whose coordinates are (75,270) and a point Ps1 whose coordinates are (−75,90);
(2) a second axis Ax2 passing through a point Pn2 whose coordinates are (60, 270) and a point Ps2 whose coordinates are (-60, 90);
(3) A third axis Ax3 passing through a point Pn3 whose coordinates are (45, 270) and a point Ps3 whose coordinates are (−45, 90),
(4) a fourth axis Ax4 passing through a point Pn4 whose coordinates are (30, 270) and a point Ps4 whose coordinates are (−30, 90);
(5) a fifth axis Ax5 passing through a point Pn5 whose coordinates are (15,270) and a point Ps5 whose coordinates are (-15,90);
(6) a sixth axis Ax6 that passes through the point Pn6 whose coordinates are (75,0) and the point Ps6 whose coordinates are (−75,180);
(7) A seventh axis Ax7 that passes through the point Pn7 whose coordinates are (60, 0) and the point Ps7 whose coordinates are (-60, 180),
(8) An eighth axis Ax8 that passes through the point Pn8 whose coordinates are (45, 0) and the point Ps8 whose coordinates are (−45, 180),
(9) a ninth axis Ax9 that passes through a point Pn9 whose coordinates are (30, 0) and a point Ps9 whose coordinates are (−30, 180);
(10) A tenth axis Ax10 passing through a point Pn10 having coordinates (15, 0) and a point Ps10 having coordinates (-15, 180),
(11) An eleventh axis Ax11 passing through a point Pn11 having coordinates (75, 90) and a point Ps11 having coordinates (−75, 270),
(12) A twelfth axis Ax12 passing through a point Pn12 whose coordinates are (60, 90) and a point Ps12 whose coordinates are (-60, 270),
(13) A thirteenth axis Ax13 passing through a point Pn13 having coordinates (45, 90) and a point Ps13 having coordinates (−45, 270),
(14) A fourteenth axis Ax14 that passes through a point Pn14 whose coordinates are (30, 90) and a point Ps14 whose coordinates are (−30, 270),
And (15) the fifteenth axis Ax15 passing through the point Pn15 whose coordinates are (15, 90) and the point P15s whose coordinates are (-15, 270).
Steps (a) to (h) are executed for each of the 15 axes Ax. As a result, a peak value of 15 (Pd1-Pd15) and an order of 15 (Fd1-Fd15) are calculated.

  Among the 15 peak values (Pd1-Pd15), the smallest ones are Pd3, Pd8 and Pd13. The minimum value of the peak value Pd is 150.2 mm. According to the knowledge obtained by the present inventors, the minimum value is preferably 95 mm or more. In the golf ball 2 having a minimum value of 95 mm or more, a sufficient dimple effect can be exhibited even when rotating based on any axis Ax. The golf ball 2 has a large flight distance. From this viewpoint, the minimum value of the peak value Pd is more preferably 120 mm or more, and particularly preferably 140 mm or more.

  Among the 15 peak values (Pd1-Pd15), the largest are Pd4, Pd9, and Pd14. The maximum value of the peak value Pd is 316.4 mm. According to the knowledge obtained by the present inventors, the maximum value is preferably 500 mm or less. The golf ball 2 having a maximum value of 500 mm or less is excellent in aerodynamic characteristics. The golf ball 2 has a large flight distance. In this respect, the maximum value of the peak value Pd is more preferably 400 mm or less, and particularly preferably 330 mm or less.

  The average value of 15 peak values (Pd1-Pd15) is preferably 200 mm or more. The golf ball 2 having an average value of 200 mm or more is excellent in aerodynamic characteristics. The golf ball 2 has a large flight distance. In this respect, the average value is more preferably 210 mm or more, and particularly preferably 220 mm or more. The average value is preferably 300 mm or less, and particularly preferably 230 mm or less. In this embodiment, the average value is 220.9 mm.

  The smallest of the 15 orders (Fd1-Fd15) is Fd5, Fd10, and Fd15. The minimum value of the order Fd is 27. According to the knowledge obtained by the present inventors, the minimum value is preferably 27 or more. The golf ball 2 having a minimum value of 27 or more is excellent in aerodynamic characteristics. The golf ball 2 has a large flight distance.

  The largest of the 15 orders (Fd1-Fd15) are Fd2, Fd3, Fd7, Fd8, Fd12 and Fd13. The maximum value of the order Fd is 37. According to the knowledge obtained by the present inventors, the maximum value is preferably 37 or less. The golf ball 2 having a maximum value of 37 or less is excellent in aerodynamic characteristics. The golf ball 2 has a large flight distance.

  The average value of the 15th order (Fd1-Fd15) is preferably 30 or more and 34 or less. The golf ball 2 having an average value within this range is excellent in aerodynamic characteristics. The golf ball 2 has a large flight distance. In the present embodiment, the average value is 33.6.

  In this method, the golf ball 2 is evaluated by 15 peak values Pd based on 15 axes Ax and 15 orders Fd. By this method, the aerodynamic characteristics of the golf ball 2 can be objectively evaluated.

  Hereinafter, the effects of the present invention will be clarified by examples. However, the present invention should not be construed in a limited manner based on the description of the examples.

[Example 1]
100 parts by mass of high-cis polybutadiene (trade name “BR-730” from JSR), 22.5 parts by mass of zinc acrylate, 5 parts by mass of zinc oxide, 5 parts by mass of barium sulfate, 0.5 parts by mass of Diphenyl disulfide and 0.6 parts by mass of dicumyl peroxide were kneaded to obtain a rubber composition. This rubber composition was put into a mold composed of an upper mold and a lower mold each having a hemispherical cavity and heated at 170 ° C. for 18 minutes to obtain a core having a diameter of 38.5 mm.

  50 parts by weight of ionomer resin (trade name “HIMILAN 1605” from Mitsui DuPont Polychemical), 50 parts by weight of other ionomer resin (trade name “HIMIRAN AM7329” from Mitsui DuPont Polychemical) and 4 parts by weight of titanium dioxide. Were kneaded with a twin-screw kneading extruder to obtain a resin composition. This resin composition was coated around the core by an injection molding method to form an intermediate layer. The thickness of this intermediate layer was 1.6 mm.

  A coating composition (trade name “Porin 750LE”, manufactured by Shinto Paint Co., Ltd.) using a two-pack curable epoxy resin as a base polymer was prepared. The curing agent liquid of this coating composition is composed of 40 parts by mass of modified polyamidoamine, 55 parts by mass of solvent, and 5 parts by mass of titanium dioxide. The mass ratio with respect to the curing agent liquid was 1/1, and this coating composition was applied to the surface of the intermediate layer with a spray gun and held at 23 ° C. for 6 hours to obtain a reinforcing layer. The thickness of the reinforcing layer was 10 μm.

  100 parts by mass of a thermoplastic polyurethane elastomer (BASF Japan trade name “Elastolan XNY85A”) and 4 parts by mass of titanium dioxide were kneaded with a twin screw extruder to obtain a resin composition. A half shell was obtained from this resin composition by compression molding. A sphere composed of a core, an intermediate layer and a reinforcing layer was covered with two half shells. These half shells and spheres were both put into a final mold comprising an upper mold and a lower mold having a hemispherical cavity and a large number of pimples on the cavity surface, and a cover was obtained by a compression molding method. The cover thickness was 0.5 mm. A dimple having a shape obtained by inverting the shape of the pimple was formed on the cover. A clear paint based on a two-component curable polyurethane was applied around the cover to obtain a golf ball of Example 1 having a diameter of about 42.7 mm and a mass of about 45.6 g. The dimple pattern of this golf ball is shown in FIGS. The specifications of this golf ball dimple are shown in Table 1 below. The peak value (Pd1-Pd15) and the order (Fd1-Fd15) of this golf ball are shown in Table 3 below.

[Examples 2 and 3 and Comparative Example 1-4]
Golf balls of Examples 2 and 3 and Comparative Example 1-4 were obtained in the same manner as Example 1 except that the dimple specifications were as shown in Tables 1 and 2 below. The peak value (Pd1-Pd15) and the order (Fd1-Fd15) of each golf ball are shown in Table 3 or 4 below.

[Flight test]
A driver having a titanium alloy head (trade name “SRIXON Z-TX” from Dunlop Sports, shaft hardness: X, loft angle: 8.5 °) equipped with a head made of a titanium alloy was attached to a swing machine manufactured by Golf Laboratory. A golf ball was placed on the tee. The golf ball was hit with a head speed of 50 m / sec, a launch angle of about 10 °, and a backspin speed of about 2500 rpm, and the distance from the launch point to the rest point was measured. During the test, there was almost no wind. The average values of the data obtained by 100 measurements are shown in Tables 5 and 6 below. The orientation of the golf ball when placed on the tee was randomly determined. Therefore, the backspin axis was chosen at random.

  As shown in Tables 5 and 6, the golf ball of each example has excellent flight performance. From this evaluation result, the superiority of the present invention is clear.

  The dimple pattern described above is applicable not only to three-piece golf balls, but also to one-piece golf balls, two-piece golf balls, four-piece golf balls, five-piece golf balls, six-piece golf balls, thread-wound golf balls, etc. Can be done.

2 ... Golf ball 4 ... Core 6 ... Intermediate layer 8 ... Cover 10 ... Dimple 12 ... Land 14 ... Virtual sphere

Claims (3)

A golf ball having a plurality of dimples on its surface,
When the spherical polar coordinates of the point located on the surface of the phantom sphere of the golf ball and having latitude θ (degree) and longitude φ (degree) are represented by (θ, φ),
(1) a first axis Ax1 passing through a point Pn1 whose coordinates are (75,270) and a point Ps1 whose coordinates are (−75,90);
(2) a second axis Ax2 passing through a point Pn2 whose coordinates are (60, 270) and a point Ps2 whose coordinates are (-60, 90);
(3) A third axis Ax3 passing through a point Pn3 whose coordinates are (45, 270) and a point Ps3 whose coordinates are (−45, 90),
(4) a fourth axis Ax4 passing through a point Pn4 whose coordinates are (30, 270) and a point Ps4 whose coordinates are (−30, 90);
(5) a fifth axis Ax5 passing through a point Pn5 whose coordinates are (15,270) and a point Ps5 whose coordinates are (-15,90);
(6) a sixth axis Ax6 that passes through the point Pn6 whose coordinates are (75,0) and the point Ps6 whose coordinates are (−75,180);
(7) A seventh axis Ax7 that passes through the point Pn7 whose coordinates are (60, 0) and the point Ps7 whose coordinates are (-60, 180),
(8) An eighth axis Ax8 that passes through the point Pn8 whose coordinates are (45, 0) and the point Ps8 whose coordinates are (−45, 180),
(9) a ninth axis Ax9 that passes through a point Pn9 whose coordinates are (30, 0) and a point Ps9 whose coordinates are (−30, 180);
(10) A tenth axis Ax10 passing through a point Pn10 having coordinates (15, 0) and a point Ps10 having coordinates (-15, 180),
(11) An eleventh axis Ax11 passing through a point Pn11 having coordinates (75, 90) and a point Ps11 having coordinates (−75, 270),
(12) A twelfth axis Ax12 passing through a point Pn12 whose coordinates are (60, 90) and a point Ps12 whose coordinates are (-60, 270),
(13) A thirteenth axis Ax13 passing through a point Pn13 having coordinates (45, 90) and a point Ps13 having coordinates (−45, 270),
(14) A fourteenth axis Ax14 that passes through a point Pn14 whose coordinates are (30, 90) and a point Ps14 whose coordinates are (−30, 270),
And (15) the fifteenth axis Ax15 passing through the point Pn15 whose coordinates are (15, 90) and the point P15s whose coordinates are (-15, 270).
For each of the 15 axes Ax,
(A) a step in which a great circle existing on the surface of the phantom sphere and orthogonal to the axis Ax is assumed;
(B) a step in which two small circles existing on the surface of the phantom sphere, orthogonal to the axis Ax, and having an absolute value of a central angle with the great circle of 30 ° are assumed;
(C) a step of defining a surface of the golf ball by these small circles, and specifying a region sandwiched between the small circles of the surface;
(D) a step in which 30240 points are determined in the above-mentioned region at a central angle of 3 ° in the axial direction and at a central angle of 0.25 ° in the rotational direction;
(E) a step of calculating a length L1 of a perpendicular line drawn from each point to the axis Ax;
(F) A step in which 21 lengths L1 calculated based on 21 vertical lines arranged in the axial direction are summed to calculate a total length L2.
(G) Fourier transform is performed on a data group of 1440 total lengths L2 calculated along the rotation direction to obtain a transformed data group;
And (h) the minimum value of the 15 peak values obtained by executing the step of calculating the peak value and the order of the maximum peak of the conversion data group is 95 mm or more,
The minimum value of the 15th order obtained by executing the steps (a) to (h) is 27 or more,
The maximum value of the 15th order obtained by executing the steps (a) to (h) is 37 or less,
A golf ball having an average value of 15 orders obtained by executing steps (a) to (h) of 30 or more and 34 or less.   The golf ball according to claim 1, wherein an average of 15 peak values obtained by executing steps (a) to (h) is 200 mm or more. The golf ball according to claim 1, wherein a total volume of the dimples is 450 mm ³ or more and 750 mm ³ or less.

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