JP5425329B1 - Golf ball - Google Patents

Abstract

Provided is a golf ball 2 having excellent flight performance and aerodynamic symmetry. A golf ball 2 has a radius change width Rh of 0.4 mm in a zone having a latitude of -10 ° to 10 °. The dimple 8 is as described above. The area Amax of the dimple 8 having the largest area A among the dimples 8 existing in a zone having a latitude of −10 ° to 10 ° is 22.0 mm ² or less. The average value Aave of the area A of the dimples 8 existing in a zone having a latitude of −10 ° to 10 ° is 18.0 mm ² or less. In a zone where the latitude is −10 ° to 10 °, the ratio PE1 of the number NE1 of dimples 8 having a radius variation width Rh of 0.4 mm or more to the total number NE of dimples 8 is 30% or more.
[Selection] Figure 2

Description

  The present invention relates to a golf ball. More specifically, the present invention relates to a method for designing an uneven pattern on the surface of a golf ball.

  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. Turbulent separation shifts the separation point of air from the golf ball backwards, reducing drag. Turbulent separation promotes the deviation between the upper separation point and the lower separation point of the golf ball due to backspin, and increases the lift acting on the golf ball. The reduction of drag and the improvement of lift are referred to as “dimple effect”.

  The ratio of the total area of the dimples to the surface area of the phantom sphere of the golf ball is called an occupation ratio. It is known that occupancy is correlated with flight performance. A golf ball with an increased occupation rate is described in Japanese Patent Laid-Open No. 4-347177. This golf ball has circular dimples.

  In a golf ball in which small circular dimples are arranged in a zone surrounded by a plurality of large circular dimples, a large occupation ratio can be achieved. However, small dimples do not contribute to the flight performance of the golf ball. The dimple effect of a golf ball having a circular dimple has a limit.

  US Pat. No. 7,198,577 describes a golf ball having hexagonal dimples. The occupation ratio of this golf ball is large. This golf ball does not have small dimples. In this golf ball, the dimples are neatly arranged. The dimple effect of this golf ball is insufficient.

  The United States Golf Association (USGA) has established rules regarding the symmetry of golf balls. In this rule, the trajectory during PH rotation and the trajectory during POP rotation are compared. A golf ball having a large difference between the two does not conform to this rule. In other words, a golf ball with poor aerodynamic symmetry does not conform to this rule. A golf ball with poor aerodynamic symmetry is inferior in flight distance due to poor aerodynamic characteristics during PH rotation or aerodynamic characteristics during POP rotation. The rotation axis of PH rotation passes through both pole points of the golf ball. The rotation axis of POP rotation is orthogonal to the rotation axis of PH rotation.

  A golf ball is formed by a mold including an upper mold and a lower mold. This mold has a parting line. The golf ball obtained by this mold has a seam at a position corresponding to the parting line. Due to the molding, burrs are generated in the seam. The burrs are cut and removed. Due to the cutting of burrs, the dimples near the seam are deformed. Furthermore, dimples tend to be arranged in an orderly manner in the vicinity of the seam. The seam coincides with the position of the equator or is located near the equator. The vicinity of the equator is a unique area. Burr cutting impairs the aerodynamic symmetry of the golf ball.

JP-A-4-347177 US Patent No. 7,198,577

  The present inventor proposed in Japanese Patent Application No. 2012-244993 a method for designing an uneven pattern using Voronoi division. With this design method, a pattern with a large occupation rate can be obtained. This design method can further obtain a pattern having distorted dimples. In a pattern having distorted dimples, the dimples are not arranged in an orderly manner. This golf ball is excellent in flight performance.

  In the pattern obtained by Voronoi division, the influence of the deformation of the dimples due to the cutting of burrs appears remarkably. Specifically, a phenomenon in which aerodynamic symmetry is impaired is observed. Furthermore, when the cutting amount varies, there is also a phenomenon that the height of the trajectory during PH rotation varies greatly. The reason for these phenomena seems to be that the volume of the dimple adjacent to the seam is greatly reduced by cutting.

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

The golf ball according to the present invention has a large number of dimples on the surface thereof. This golf ball has dimples whose radius variation width Rh is 0.4 mm or more in a zone whose latitude is −10 ° or more and 10 ° or less. Of the dimples present in a zone having a latitude of −10 ° to 10 °, the area Amax of the dimple having the largest area A is 22.0 mm ² or less. The average value Aave of the area A of the dimples existing in a zone whose latitude is −10 ° to 10 ° is 18.0 mm ² or less.

  Preferably, in a zone where the latitude is −10 ° or more and 10 ° or less, the ratio PE1 of the number NE1 of dimples whose radius variation width Rh is 0.4 mm or more to the total number NE of dimples is 30% or more.

Preferably, the golf ball includes dimples satisfying the following mathematical formula (1) in a zone having a latitude of −10 ° to 10 °.
Rh / Rave ≧ 0.25 (1)
In this equation, Rh represents the radius change width, and Rave represents the average radius. Preferably, in a zone where the latitude is −10 ° to 10 °, the ratio PE2 of the number NE2 of dimples 8 satisfying the formula (1) to the total number NE of dimples is 10% or more.

  Preferably, the difference between the radius change width Rhmax of the dimple having the largest radius change width Rh and the radius change width Rhmin of the dimple having the smallest radius change width Rh is 0.1 mm or more.

Preferably, the golf ball satisfies the following formula (2).
(Rhmax−Rhmin)> (R1−R2) (2)
In this equation, Rhmax represents the radius change width of the dimple having the largest radius change width Rh, Rhmin represents the radius change width of the dimple having the smallest radius change width Rh, and R1 has the largest radius change width Rh. The average radius of the dimples is represented, and R2 represents the average radius of the dimples having the smallest radius change width Rh.

  The golf ball according to the present invention is excellent in flight performance and aerodynamic symmetry.

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 a front view showing a virtual sphere on the surface of which many circles are assumed. FIG. 5 is a plan view showing the phantom sphere of FIG. FIG. 6 is a front view showing a virtual sphere on which a large number of generating points are assumed. FIG. 7 is a plan view showing the phantom sphere of FIG. FIG. 8 is an enlarged view showing the generating point of FIG. 6 together with the Voronoi region. FIG. 9 is a front view showing a mesh used for Voronoi division. FIG. 10 is a front view showing a virtual sphere in which a Voronoi region obtained by a simple method is assumed. FIG. 11 is a plan view showing the phantom sphere of FIG. FIG. 12 is an enlarged view showing the dimples of the golf ball of FIG. FIG. 13 is a graph for explaining a method of calculating the radius change width of the dimple of FIG. FIG. 14 is a front view showing a golf ball according to a comparative example. FIG. 15 is a plan view showing the golf ball of FIG. FIG. 16 is a front view showing a virtual sphere having a loop. FIG. 17 is a plan view showing the phantom sphere of FIG. FIG. 18 is a front view showing a golf ball according to Example 2 of the present invention. FIG. 19 is a plan view showing the golf ball of FIG. FIG. 20 is a front view showing a golf ball according to Example 3 of the present invention. FIG. 21 is a plan view showing the golf ball of FIG. FIG. 22 is a graph showing the evaluation results of the golf ball according to Example 1 of the present invention. FIG. 23 is a graph showing the evaluation results of the golf ball according to Example 2 of the present invention. FIG. 24 is a graph showing the evaluation results of the golf ball according to Example 3 of the present invention. FIG. 25 is a graph showing the evaluation results of the golf ball according to the comparative example. FIG. 26 is a graph showing the evaluation results of the golf ball according to the reference example.

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

  A golf ball 2 shown in FIG. 1 includes a spherical core 4 and a cover 6. A large number of dimples 8 are formed on the surface of the cover 6. A portion of the surface of the golf ball 2 other than the dimples 8 is a land 10. The golf ball 2 includes a paint layer and a mark layer outside the cover 6, but these layers are not shown. An intermediate layer may be provided between the core 4 and the cover 6.

  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. In light of attainment of great inertia, the mass is more preferably equal to or greater than 44 g, and particularly preferably equal to or greater than 45.00 g. 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.

  A co-crosslinking agent may be used for crosslinking the core 4. From the viewpoint of resilience performance, preferred co-crosslinking agents are zinc acrylate, magnesium acrylate, zinc methacrylate and magnesium methacrylate. It is preferable that an organic peroxide is blended with the co-crosslinking agent in the rubber composition. Suitable organic peroxides include dicumyl peroxide, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di (t- Butyl peroxy) hexane and di-t-butyl peroxide.

  Various additives such as sulfur, sulfur compounds, fillers, anti-aging agents, colorants, plasticizers, and dispersants are blended in the rubber composition of the core 4 as necessary. Crosslinked rubber powder or synthetic resin powder may be blended with the rubber composition.

  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 be composed of two or more layers. The core 4 may be provided with ribs on the surface thereof.

  A suitable polymer for the cover 6 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 the 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 the 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.

  Other polymers may be used in place of or in conjunction with the ionomer resin. Examples of other polymers include thermoplastic polyurethane elastomers, thermoplastic styrene elastomers, thermoplastic polyamide elastomers, thermoplastic polyester elastomers, and thermoplastic polyolefin elastomers. From the viewpoint of spin performance, a thermoplastic polyurethane elastomer is preferred.

  If necessary, the cover 6 may contain an appropriate amount of 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, and a fluorescent brightening agent. Blended. For the purpose of adjusting the specific gravity, the cover 6 may be mixed with powder of a high specific gravity metal such as tungsten or molybdenum.

  The thickness of the cover 6 is preferably 0.1 mm or more, and particularly preferably 0.3 mm or more. The thickness of the cover 6 is preferably 2.5 mm or less, and particularly preferably 2.2 mm or less. The specific gravity of the cover 6 is preferably 0.90 or more, particularly preferably 0.95 or more. The specific gravity of the cover 6 is preferably 1.10 or less, and particularly preferably 1.05 or less. The cover 6 may be composed of two or more layers. When the cover 6 has two or more layers, the total thickness of all layers is preferably within the above range. When the cover 6 has two or more layers, the specific gravity of each layer is preferably within the above range.

  FIG. 2 is an enlarged front view showing the golf ball 2 of FIG. FIG. 3 is a plan view showing the golf ball 2 of FIG. As apparent from FIGS. 2 and 3, the golf ball 2 includes a large number of non-circular dimples 8. The dimples 8 and the lands 10 form an uneven pattern on the surface of the golf ball 2.

  Voronoi tessellation is used as a method for designing the uneven pattern. In this design method, a large number of generating points are arranged on the surface of the phantom sphere 12 (see FIG. 1). Based on this generating point, a large number of regions are assumed on the surface of the phantom sphere 12 by Voronoi division. In this specification, this region is referred to as a “Voronoi region”. Based on the outline of the Voronoi region, dimples 8 and lands 10 are assigned. This design method is preferably implemented using a computer and software from the viewpoint of efficiency. Of course, the present invention can also be implemented by hand calculation. The essence of the present invention is not in computer software. Hereinafter, this design method will be described in detail.

  In this design method, as shown in FIGS. 4 and 5, a large number of circles 14 are assumed on the surface of the phantom sphere 12. These assumed methods of the circle 14 are the same as the design method of the dimple pattern having circular dimples. A method for designing a dimple pattern having circular dimples is well known to those skilled in the art. Each circle 14 coincides with the outline of the circular dimple. In the present embodiment, the number of circles 14 is 344.

  Based on the positions of these circles 14, many generating points are assumed on the surface of the phantom sphere 12. In the present embodiment, the center of each circle 14 is assumed as a generating point. These generating points 16 are shown in FIGS. In the present embodiment, since the number of circles 14 is 344, the number of generating points 16 is 344. A point where the center of each circle 14 is projected on the surface of the phantom sphere 12 may be assumed as the generating point 16. This projection is made by light rays emitted from the center of the phantom sphere 12. A generating point may be assumed based on points other than the center. For example, a point on the circumference may be regarded as a generating point.

  Based on these generating points 16, a large number of Voronoi regions are assumed. In FIG. 8, a Voronoi region 18 is shown. In FIG. 8, the generating point 16a is adjacent to the six generating points 16b. What is indicated by reference numeral 20 is a line segment connecting the generating point 16a and the generating point 16b. In FIG. 8, six line segments 20 are shown. What is indicated by reference numeral 22 is a vertical bisector of each line segment 20. The generating point 16 a is surrounded by six vertical bisectors 22. In FIG. 8, a white circle indicates an intersection between the vertical bisector 22 and another vertical bisector 22. The point at which this intersection is projected on the surface of the phantom sphere 12 is the vertex of a spherical polygon (for example, a spherical hexagon). This projection is made by light rays emitted from the center of the phantom sphere 12. This spherical polygon is the Voronoi region 18. The surface of the phantom sphere 12 is divided into a number of Voronoi regions 18. This division method is called Voronoi division. In the present embodiment, since the number of generating points 16 is 344, the number of Voronoi regions 18 is 344.

  The calculations that delineate the Voronoi region 18 based on the vertical bisector 22 are complex. Hereinafter, a method for easily obtaining the Voronoi region 18 will be described. In this method, the surface of the phantom sphere 12 is divided into a number of spherical triangles. The division is based on an advancing front method. The advanced advanced method is disclosed on pages 195 to 197 of “Graduate School of Information Science and Technology 3 Computational Mechanics” (published by Junichi Ito, published by Kodansha). By this division, the mesh 24 shown in FIG. 9 is obtained. In the mesh 24, the number of triangles is 314086 and the number of vertices is 157045. Each vertex is defined as a cell (or cell center). In this mesh 24, the number of cells is 157045. The virtual sphere 12 may be divided by other methods. The number of cells is preferably 10,000 or more, particularly preferably 100,000 or more.

  In this mesh 24, the distance between this cell and all the generating points 16 in each cell is calculated. The same number of distances as the number of generating points 16 are calculated for each cell. The shortest distance is selected from these distances. This cell is associated with the generating point 16 which is the object of the shortest distance. In other words, the generating point 16 closest to this cell is selected. In addition, calculation of the distance with the generating point 16 where it is clear that the distance from the cell is large may be omitted.

  For each generating point 16, a set of cells associated with the generating point 16 is assumed. In other words, a set of cells having the generating point 16 as the closest generating point 16 is assumed. This set is regarded as the Voronoi region 18. A number of Voronoi regions 18 thus obtained are shown in FIGS. 10 and 11, when another cell adjacent to the cell belongs to a Voronoi region 18 different from the Voronoi region 18 to which the cell belongs, the cell is painted black.

  As is clear from FIGS. 10 and 11, the outline of each Voronoi region 18 is zigzag. Smoothing or the like is applied to this contour. A typical smoothing is a moving average. Smoothing by a three-point moving average, a five-point moving average, a seven-point moving average, or the like can be employed.

In the three-point moving average, the coordinates of the following three cells are averaged.
(1) The cell (2) The cell closest to the cell in the clockwise direction (3) The cell closest to the cell in the counterclockwise direction

In the 5-point moving average, the coordinates of the following five cells are averaged.
(1) The cell (2) Cell closest to the cell in the clockwise direction (3) Cell closest to the cell in the counterclockwise direction (4) Cell closest to the cell in the clockwise direction (5) Counterclockwise Cell closest to the cell in

In the 7-point moving average, the coordinates of the following seven cells are averaged.
(1) The cell (2) Cell closest to the cell in the clockwise direction (3) Cell closest to the cell in the counterclockwise direction (4) Cell closest to the cell in the clockwise direction (5) Counterclockwise Cell closest to the cell in (6) cell closest to the cell in the clockwise direction (7) cell closest to the cell in the counterclockwise direction

  A plurality of points having coordinates obtained by moving average are connected by a spline curve. This spline curve provides a loop. When forming a loop, a part of points may be thinned out to form a spline curve. A new loop may be obtained by enlarging or reducing the loop. A land 10 is assigned above or outside the loop. In other words, the land 10 is assigned near the outline of the Voronoi region 18. On the other hand, dimples 8 are allocated inside or on the loop. In this way, the patterns shown in FIGS. 16 and 17 are obtained.

  Hereinafter, an example of a method for assigning the dimples 8 will be described. In this method, the deepest point is determined. Preferably, the deepest point is assumed on the line connecting the center of the loop and the center of the phantom sphere 12. The coordinate of the center of the loop is the average of the coordinates of all the reference points that define this loop. This deepest point is projected onto the surface of the phantom sphere 12. An arc on the surface of the phantom sphere 12 is assumed that passes through this projected point and whose ends are on the loop. A smooth curve that passes through both ends of the arc and the deepest point and protrudes inward in the radial direction of the golf ball 2 is assumed. Preferably, the smooth curve is an arc. This smooth curve and loop are connected by a smooth curved surface. Thereby, the dimple 8 is obtained. The dimple 8 may be obtained by connecting the deepest point and the loop with a smooth curved surface.

In the present specification, the latitude of the golf ball 2 is determined as follows.
North Pole: 90 °
Equator: 0 °
South Pole: -90 °
A zone having a latitude of −10 ° to 10 ° is referred to as an equator vicinity zone. A dimple whose center point is included in the equator vicinity zone is a dimple existing in the equator vicinity zone. A dimple whose center point is not included in the equator vicinity zone is not a dimple existing in the equator vicinity zone.

  Based on the patterns shown in FIGS. 16 and 17, the dimple 8 in the equator vicinity zone is corrected. Specifically, the contour of the dimple 8 is changed so that the area of the dimple 8 is reduced. In this modification, the number of dimples 8 may be increased so that the occupation ratio does not decrease even if the area of the dimples 8 is reduced. The concavo-convex pattern after correction is shown in FIGS. The contours of some of the dimples 8 existing in the equator vicinity zone are changed. The contours of all the dimples 8 existing in the equator vicinity zone may be changed.

Of the dimples 8 existing in the equator vicinity zone, the area Amax of the dimple 8 having the largest area A is 22.0 mm ² or less. In the golf ball 2, it is suppressed that the volume of the dimple 8 is significantly reduced by cutting the seam burr. Furthermore, in this golf ball 8, variation in the volume of the dimple 8 when the cutting depth varies is suppressed. In this golf ball 2, the aerodynamic symmetry is not easily lost by cutting. In this golf ball 2, the variation in flight performance due to cutting is less likely to occur. Area Amax is more preferably 21.0 mm ² or less, 20.0 mm ² or less is particularly preferred. The area Amax is preferably 17.0 mm ² or more.

Prior to the measurement of the area A of each dimple 8, 30 points are assumed on the outline of the dimple 8. These points are assumed such that the angle at the center O is in increments of 12 °. In the measurement of the area A, the dimple 8 is approximately divided into 30 triangles. Each triangle has the following three vertices.
(I) First point assumed on the contour (ii) Second point assumed on the contour and adjacent to the first point (iii) Center point O
The total value of the areas of the 30 triangles is regarded as the area A of the dimple 8.

The average value Aave of the areas A of all the dimples 8 existing in the equator vicinity zone is 18.0 mm ² or less. In the golf ball 2, it is suppressed that the volume of the dimple 8 is significantly reduced by cutting the seam burr. Furthermore, in this golf ball 8, variation in the volume of the dimple 8 when the cutting depth varies is suppressed. In this golf ball 2, the aerodynamic symmetry is not easily lost by cutting. In this golf ball 2, the variation in flight performance due to cutting is less likely to occur. Mean value Aave is more preferably 17.0 mm ² or less, 16.0 mm ² or less is particularly preferred. The average value Aave is preferably 13.0 mm ² or more.

  From the viewpoint of the flight performance of the golf ball 2, the occupation ratio of the dimples 8 is preferably 85% or more, more preferably 90% or more, and particularly preferably 92% or more. From the viewpoint of durability of the golf ball 2, the occupation ratio is preferably 98% or less. In the present embodiment, the occupation ratio is 92%. By adopting Voronoi division, a large occupation ratio can be achieved even if the small dimples 8 are not arranged.

  As is apparent from FIGS. 2 and 3, in this golf ball 2, the dimples 8 are not orderly arranged. The golf ball 2 includes a plurality of types of dimples 8 having different contour shapes. A large dimple effect is achieved by these dimples 8. The number of types of dimples 8 is preferably 50 or more, and more preferably 100 or more. In the present embodiment, each dimple 8 has a contour shape different from the contour shape of any other dimple 8.

  In light of suppression of hops of the golf ball 2, the depth of the dimple 8 is preferably 0.05 mm or more, more preferably 0.08 mm or more, and particularly preferably 0.10 mm or more. From the viewpoint of suppressing the drop of the golf ball 2, the depth is preferably 0.60 mm or less, more preferably 0.45 mm or less, and particularly preferably 0.40 mm or less. The depth is the distance between the deepest point of the dimple 8 and the surface of the phantom sphere 12.

In the present invention, the “dimple volume” means the volume of the portion surrounded by the surface of the phantom sphere 12 and the surface of the dimple 8. The total volume of all the dimples 8 (total volume) is preferably 500 mm ³ or more in terms of rising of the golf ball 2 is suppressed, and more preferably 550 mm ³ or more, 600 mm ³ or more is particularly preferable. In view of dropping of the golf ball 2 is suppressed, the sum is preferably 900 mm ³ or less, more preferably 850 mm ³ or less, particularly preferably 800 mm ³ or less.

  From the viewpoint that the essence of the golf ball 2 that is substantially a sphere is not impaired, the total number of the dimples 8 is preferably 250 or more, more preferably 280 or more, and particularly preferably 340 or more. From the viewpoint that each dimple 8 can contribute to the dimple effect, the total number is preferably 450 or less, more preferably 400 or less, and particularly preferably 370 or less.

As described above, a large number of circles 14 are assumed on the surface of the phantom sphere 12 prior to Voronoi division. From the viewpoint that the dimples 8 can be arranged without deviation, it is preferable that the circle 14 is assumed so that one or more of the conditions shown in the following (1) to (4) are satisfied.
(1) The circle 14 and other circles 14 adjacent to the circle 14 do not intersect. (2) The diameter of the circle 14 is not less than 2.0 mm and not more than 6.0 mm. (3) The number of the circles 14 is 280 or more and 450 or less (4) The ratio of the total area of the circle 14 to the area of the surface of the phantom sphere 12 is preferably 60% or more, preferably (1) to (4) A circle 14 is assumed so that all of the conditions are met.

  The golf ball 2 includes dimples 8 having a radius change width Rh of 0.4 mm or more. A method of calculating the radius change width Rh is shown in FIG. In this method, the coordinates of the center O are determined by averaging the coordinates of all control points on the contour of the dimple 8. Control points are selected from cells on the contour. Typically, cells are selected by thinning. In the present embodiment, the number of control points per dimple 8 is 30. The number of control points is not limited to 30. The number of control points is preferably 10 or more and 50 or less. All cells on the contour of the dimple 8 may be selected as control points.

  After the coordinates of the center O are determined, the distance (that is, the radius R) between the center O and the control point is calculated. The radius R is calculated for all control points. FIG. 13 is a graph in which the radius R is plotted. The horizontal axis of this graph represents the angle of the line connecting the center O and each control point with respect to the meridian direction. As shown in this graph, a value obtained by subtracting the minimum value of the radius R from the maximum value of the radius R is the radius change width Rh. The radius change width Rh is an index indicating the distortion of the dimple 8.

  The radius R may be determined based on a point assumed on the contour of the dimple 8 instead of the control point. Based on 30 points on the contour of the dimple 8, the radius change width Rh is calculated. These points are assumed such that the angle at the center O is in increments of 12 °. The number of assumed points is not limited to 30. The number of assumed points is preferably 10 or more and 50 or less. When the number of assumed points is n, the angle at the center point O is (360 / n) °.

  The radius change width Rh calculated by any one of the calculation methods described above may be 0.4 mm or more.

  In the golf ball 2 provided with the dimples 8 having the radius change width Rh of 0.4 mm or more, the dimples 8 are not arranged in an orderly manner. This golf ball 2 is excellent in flight performance. The ratio P1 of the number N1 of dimples 8 having a radius change width Rh of 0.4 mm or more to the total number N of dimples 8 is preferably 30% or more, more preferably 50% or more, and particularly preferably 70% or more. The ideal ratio P1 is 100%. In the golf ball 2 shown in FIGS. 2 and 3, the ratio P1 is 81%.

  As apparent from FIG. 13, the change in the radius R of the dimple 8 does not have periodicity. In this golf ball 2, the dimples 8 are not orderly arranged. This golf ball 2 is excellent in flight performance.

  From the viewpoint of flight performance, the difference between the radius change width Rhmax of the dimple 8 having the largest radius change width Rh and the radius change width Rhmin of the dimple 8 having the smallest radius change width Rh is preferably 0.1 mm or more. 0.3 mm or more is more preferable, and 0.5 mm or more is particularly preferable.

  From the viewpoint of flight performance, the standard deviation of the radius variation width Rh for all the dimples 8 is preferably 0.10 or more, and particularly preferably 0.13 or more.

The golf ball 2 includes dimples 8 that satisfy the following formula (1).
Rh / Rave ≧ 0.25 (1)
In this equation, Rh represents the radius change width, and Rave represents the average radius. Rave is an average of radii R of all control points of one dimple 8.

  The average radius Rave may be determined based on all cells existing on the contour of the dimple 8 instead of the control point.

  The average radius Rave may be determined based on the points assumed on the contour of the dimple 8. Specifically, the average radius Rave is calculated based on 30 points on the contour of the dimple 8. These points are assumed such that the angle at the center O is in increments of 12 °. The number of assumed points is not limited to 30. The number of assumed points is preferably 10 or more and 50 or less. When the number of assumed points is n, the angle at the center point O is (360 / n) °.

  The formula (1) only needs to be satisfied in the pair of the radius change width Rh and the average radius Rave calculated by any one of the calculation methods described above.

  In the golf ball 2 having the dimples 8 satisfying the above mathematical formula (1), the dimples 8 are not orderly arranged. This golf ball 2 is excellent in flight performance. The ratio P2 of the number N2 of the dimples 8 satisfying the formula (1) to the total number N of the dimples 8 is preferably 10% or more, more preferably 20% or more, and particularly preferably 30% or more. The ideal ratio P2 is 100%. In the golf ball 2 shown in FIGS. 2 and 3, the ratio P2 is 36%.

From the viewpoint of flight performance, the golf ball 2 preferably satisfies the following mathematical formula (2).
(Rhmax−Rhmin)> (R1−R2) (2)
In this equation, Rhmax represents the radius change width of the dimple 8 having the largest radius change width Rh, Rhmin represents the radius change width of the dimple 8 having the smallest radius change width Rh, and R1 has the largest radius change width Rh. Represents the average radius of the dimple 8, and R 2 represents the average radius of the dimple 8 having the smallest radius variation width Rh. The difference between (Rhmax−Rhmin) and (R1−R2) is preferably 0.1 mm or more, more preferably 0.2 mm or more, and particularly preferably 0.3 mm or more. In the golf ball 2 shown in FIGS. 2 and 3, this difference is 0.449 mm.

  From the viewpoint of flight performance during PH rotation, it is preferable that a dimple 8 having a radius variation width Rh of 0.4 mm or more exists in the zone near the equator. The ratio PE1 of the number NE1 of the dimples 8 in which the radius variation width Rh in the equator vicinity zone is 0.4 mm or more to the total number NE of the dimples 8 in the equator vicinity zone is preferably 30% or more, more preferably 50% or more, 70 % Or more is particularly preferable. The ideal ratio PE1 is 100%. In the golf ball 2 shown in FIGS. 2 and 3, the ratio PE1 is 100%.

  From the viewpoint of flight performance during PH rotation, it is preferable that dimples 8 satisfying the above mathematical formula (1) exist in the equator vicinity zone. The ratio PE2 of the number NE2 of the dimples 8 satisfying the above formula (1) in the equator vicinity zone to the total number NE of the dimples 8 in the equator vicinity zone is preferably 10% or more, more preferably 20% or more, and particularly preferably 30% or more. preferable. The ideal ratio PE2 is 100%. In the golf ball 2 shown in FIGS. 2 and 3, the ratio PE2 is 48%.

  The number of dimples 8 in the equator vicinity zone is preferably 30 or more and 90 or less, and particularly preferably 40 or more and 60 or less.

  As described above, in this embodiment, the pattern of the circle 14 is obtained by the same method as the design method of the dimple pattern having circular dimples. The center point of each circle 14 is a generating point 16. The generating point 16 may be obtained by different methods. For example, the generating points 16 may be randomly arranged on the surface of the phantom sphere 12.

One example in which the generating points 16 are randomly arranged is a method using random numbers. This method
(1) generating a random number;
(2) determining coordinates on the surface of the phantom sphere 12 based on the random number;
(3) calculating a distance between a point having this coordinate and a point already existing on the surface of the phantom sphere 12; and (4) if this distance is within a predetermined range, A step of recognizing a point having the base point 16 as a generating point.

The surface-like point of the phantom sphere 12 is represented by spherical coordinates (θ, φ). Here, θ represents latitude and φ represents longitude. The spherical coordinates (θ, φ) can be calculated by the following mathematical formula.
(Θ, φ) = (2 cos ⁻¹ (1-ξ _x ) ^1/2 , 2πξ _y )
In the above formula, ξ _x and ξ _y are real random numbers of 0 or more and 1 or less, respectively.

Random numbers ξ _x and ξ _y are sequentially generated to calculate spherical coordinates (θ, φ), and points having the spherical coordinates (θ, φ) are arranged on the surface of the phantom sphere 12. At this time, if the arrangement is performed indefinitely, a zone where points are concentrated may be generated. In order to avoid the occurrence of this zone, restrictions are placed on the arrangement of points. Specifically, the distance between the point having the spherical coordinates (θ, φ) and the closest base point 16 that already exists on the surface of the phantom sphere 12 and has the spherical coordinates (θ, φ). Is calculated. When this distance is within a predetermined range, a point having spherical coordinates (θ, φ) is recognized as a generating point 16. If the distance between the point having the spherical coordinate (θ, φ) and the point already existing on the surface of the phantom sphere 12 is outside the predetermined range, the point having the spherical coordinate (θ, φ) is , It is not recognized as the mother point 16. Details of a method of randomly arranging points using random numbers are disclosed in Japanese Patent Application No. 2012-220513.

Another example in which the generating points 16 are randomly arranged is a method using a cell automaton method. This method
(1) a step in which a plurality of states are assumed;
(2) a step where a large number of cells are assumed on the surface of the phantom sphere 12;
(3) a step in which any state is given to each cell;
(4) Based on the state of the cell and the state of a plurality of cells located in the vicinity of the cell, any one of inside, outside, and boundary is given as an attribute of the cell,
(5) a step in which a loop is assumed by connecting cells at the boundary; and (6) a step in which 16 generating points are determined based on the loop or another loop obtained based on the loop. Including. Japanese Patent Application No. 2012-220513 discloses details of a method in which points are randomly arranged using the cell automaton method.

[Example 1]
100 parts by weight of polybutadiene (trade name “BR-730” from JSR), 30 parts by weight of zinc acrylate, 6 parts by weight of zinc oxide, 10 parts by weight of barium sulfate, 0.5 parts by weight of diphenyl disulfide and 0.5 parts by mass of dicumyl peroxide was 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 39.7 mm. On the other hand, 50 parts by mass of ionomer resin (trade name “HIMILAN 1605” from Mitsui DuPont Polychemical Co.), 50 parts by mass of other ionomer resins (trade name “HIMILAN 1706” from Mitsui DuPont Polychemical Co., Ltd.) and 3 parts by mass Part of titanium dioxide was kneaded to obtain a resin composition. The core was put into a final mold having a large number of pimples on the inner peripheral surface, and the resin composition was injected around the core by an injection molding method to form a cover having a thickness of 1.5 mm. A large number of dimples having a reversed pimple shape were formed on the cover. Burrs occurred on the surface of the cover. This burr was removed by cutting with a grindstone. The cover was coated with a clear paint based on a two-component curable polyurethane to obtain a golf ball having a diameter of 42.7 mm and a mass of about 45.4 g. The golf ball has a PGA compression of about 85. This golf ball has the dimple pattern shown in FIGS. The occupation ratio of this golf ball is 92%. Details of the dimples are shown in Tables 1 and 2 below. The burr was cut under the following conditions AC.
Condition A: Condition in which the dimple depth is 0.016 mm deeper than Condition B Condition B: Standard condition Condition C: Condition in which the dimple depth is 0.016 mm shallower than Condition B

[Examples 2 and 3]
Golf balls of Examples 2 and 3 were obtained in the same manner as Example 1 except that the final mold was changed. Details of the dimples of this golf ball are shown in Table 1 below.

[Comparative example]
A golf ball of a comparative example was obtained in the same manner as in Example 1 except that the final mold was changed. This golf ball has 339 dimples. This golf ball dimple pattern is shown in FIGS. The dimple pattern of this golf ball is obtained by deleting five dimples from the equator vicinity zone of the dimple pattern of the embodiment. The outline of the dimple adjacent to the deleted dimple is corrected. The occupation ratio of this golf ball is 92%.

[Reference example]
A golf ball of a reference example was obtained in the same manner as in Example 1 except that the final mold was changed. This golf ball has 344 circular dimples. The contour pattern of these circular dimples is shown in FIGS. The occupation ratio of this golf ball is 82%.

[Aerodynamic symmetry test]
Ballistic calculation was performed using the aerodynamic characteristic values obtained in the ITR test. The conditions for this ballistic calculation are as follows.
Ball speed: 78 m / s (255.6 ft / s)
Launch angle: 9.8 °
Backspin speed: 2300 rpm
The difference between the PH rotation and the POP rotation in the flight distance and flight time obtained by this trajectory calculation is shown in Table 1 and FIGS. 22-26. The flight distance is the distance from the launch point to the fall point. In the graph of FIG. 2-26, the horizontal axis represents the flight distance difference (m), and the vertical axis represents the flight time difference (sec). In each graph, golf balls having burrs cut under conditions A, B, and C are plotted.

表１の内容を変更しております。

The contents of Table 1 have been changed.

  Table 1 shows values of Amax, Aave, and occupancy when burr cutting is performed under standard conditions.

  As shown in Table 1 and FIGS. 22-26, the golf ball of each example has a smaller difference between the PH rotation and the POP rotation than the golf ball of the comparative example. Furthermore, the golf ball of each example has less ballistic sensitivity to the burr cutting conditions than the golf ball of the comparative example. From this evaluation result, the superiority of the present invention is clear.

  The dimple pattern described above can be applied not only to a two-piece golf ball but also to a one-piece golf ball, a multi-piece golf ball, and a thread wound golf ball.

2 ... Golf ball 8 ... Dimple 10 ... Land 12 ... Virtual sphere 14 ... Circle 16 ... Generating point 18 ... Voronoi region 22 ... Vertical bisector

Claims (6)

It has many dimples on its surface,
In a zone whose latitude is −10 ° or more and 10 ° or less, a dimple whose radius change width Rh is 0.4 mm or more is provided.
The area Amax of the dimple having the largest area A among the dimples existing in a zone having a latitude of −10 ° to 10 ° is 22.0 mm ² or less,
Latitude Ri der average value Aave is 18.0 mm ² or less of the area A of the dimples present in the zone at -10 ° to 10 °,
Each dimple, the golf ball that have a different contour shapes as any other dimple contour.   The ratio PE1 of the number NE1 of dimples having a radius variation width Rh of 0.4 mm or more to the total number NE of dimples in a zone having a latitude of -10 ° to 10 ° is 30% or more. Golf ball. The golf ball according to claim 1, wherein dimples satisfying the following mathematical formula (1) are included in a zone having a latitude of −10 ° to 10 °.
Rh / Rave ≧ 0.25 (1)
(In this equation, Rh represents the radius change width, and Rave represents the average radius.)   4. The golf ball according to claim 3, wherein, in a zone having a latitude of −10 ° to 10 °, a ratio PE <b> 2 of the number of dimples NE <b> 2 satisfying the formula (1) to the total number of dimples NE is 10% or more.   The difference between the radius change width Rhmax of the dimple having the maximum radius change width Rh and the radius change width Rhmin of the dimple having the minimum radius change width Rh is 0.1 mm or more. The golf ball described. The golf ball according to claim 1, which satisfies the following mathematical formula (2).
(Rhmax−Rhmin)> (R1−R2) (2)
(In this equation, Rhmax represents the radius change width of the dimple having the largest radius change width Rh, Rhmin represents the radius change width of the dimple having the smallest radius change width Rh, and R1 represents the largest radius change width Rh. (The average radius of a dimple is represented, and R2 represents the average radius of a dimple having a minimum radius change width Rh.)

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