JP2006314481A - Golf ball - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a golf ball 2 with excellent flying performance. <P>SOLUTION: A dimple 8 of the golf ball has an upper wall face 14, a side wall face 16, a first slope face 18, a second slope face 20 and a bottom face 22. The upper wall face 14, the side wall face 16, and the first and second slope faces 18 and 20 are ring-shaped, while the bottom face 22 is bowl-shaped. The side wall face 16 makes contact with the upper wall face 14 at the point P1, and the side wall face 16 is a downward projecting curved face. The first slope face 18 makes contact with the side wall face 16 at the point P2, and the cross section of the first slope face 18 is linear. The second slope face 20 is continued from the first slope face 18 at the point P3, and the cross section of the second slope face 20 is linear. The bottom face 22 makes contact with the second slope face 20 at the point P4, and the bottom face 22 is a downward projecting curved face. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a golf ball. More specifically, the present invention relates to an improvement in golf ball dimples.

  The golf ball includes a cover and a paint layer positioned on the surface of the cover. The role of the paint layer is to improve the appearance, protect the mark layer, and protect the cover. There are golf balls having a paint layer composed of a white layer and a clear layer, and golf balls having only a clear layer.

  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 difference between the upper and lower separation points of the golf ball due to backspin, and increases the lift acting on the golf ball. Such a role of the dimple is called a “dimple effect”. Excellent dimples better disturb the air flow.

  Various proposals regarding the cross-sectional shape of dimples have been made for the purpose of improving flight performance. Japanese Patent Application Laid-Open No. 5-96026 discloses a dimple having a shape in which the slope surface near the edge is steeper than the slope surface at the bottom. Japanese Unexamined Patent Application Publication No. 2004-166725 discloses a dimple having a large ratio of the curvature radius of the bottom to the curvature radius near the edge.

Japanese Patent Application Laid-Open No. 9-70449 discloses a dimple whose cross-sectional shape is double radius. This double radius dimple has an annular side wall surface and a bowl-shaped bottom surface. The cross-sectional shape of the side wall surface and the bottom surface is an arc shape. The side wall surface has a small radius of curvature and the bottom surface has a large radius of curvature. In this double radius dimple, the direction of air flow abruptly changes at the contact point between the side wall surface and the bottom surface. Thereby, the flow of air is disturbed. Double radius dimples have excellent dimple effects.
Japanese Patent Laid-Open No. 5-96026 JP-A-9-70449 JP 2004-166725 A

  The coating layer is obtained by applying a liquid paint on the surface of the cover and curing the paint. The paint immediately after painting can flow on the surface of the cover. In the double radius dimple, the paint tends to accumulate near the contact point between the side wall surface and the bottom surface due to flow. When the paint accumulates, a coating layer that is thick in the vicinity of the contact and thin in other portions is obtained. This paint layer relaxes the change in radius of curvature at the contact. Thereby, the dimple effect is inhibited. 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 large number of dimples on the surface thereof. This dimple is
(1) Side wall surface having a circular cross section and convex downward;
(2) a first slope surface that is in contact with the side wall surface at the lower end P2 of the side wall surface and is inclined downward toward the center of the dimple;
(3) a second slope surface which is continuous with the first slope surface at the lower end P3 of the first slope surface, and which slopes downward toward the center of the dimple more gently than the first slope surface; The lower slope P4 of the second slope surface is in contact with the second slope surface, has a circular cross section, and has a bowl-shaped bottom surface located at the center of the dimple.

  Preferably, the ratio of the depth d2 to the dimple depth d0 is not less than 50% and not more than 85%. The depth d2 is the depth of the contact P2 between the side wall surface and the first slope surface. Preferably, the ratio of the depth d4 to the dimple depth d0 is not less than 50% and not more than 85%. The depth d4 is the depth of the contact point P4 between the second slope surface and the bottom surface.

  Preferably, the ratio of the difference (d4−d2) between the depth d4 and the depth d2 to the dimple depth d0 is not less than 10% and not more than 30%. Preferably, the arc whose side wall surface is extended and the arc whose bottom surface is extended are in contact at the contact point P5. The ratio of the depth d5 of the contact P5 to the dimple depth d0 is 50% or more and 85% or less.

Preferably, the ratio (Rb / Ra) of the curvature radius Rb of the bottom surface and the curvature radius Ra of the side wall surface is 5 or more and 55 or less.

  The present invention is particularly suitable for a golf ball having a coating layer having an average thickness of 6 μm or more.

  In this golf ball, the air flow from the land toward the center of the dimple is disturbed in the vicinity of the intersection P3 between the first slope surface and the second slope surface. In this golf ball, the air flow from the center of the dimple toward the land is also disturbed in the vicinity of the intersection P3 between the first slope surface and the second slope surface. This golf ball is excellent in flight performance.

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

  FIG. 1 is a schematic cross-sectional view showing a golf ball 2 according to an embodiment of the present invention. The golf ball 2 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.

  The golf ball 2 has a diameter of 40 mm to 45 mm. The diameter is preferably 42.67 mm or more from the viewpoint that the American Golf Association (USGA) standard is satisfied. In light of suppression of air resistance, the diameter is preferably equal to or less than 44 mm, and more preferably equal to or less than 42.80 mm. The golf ball 2 has a mass of 40 g or more and 50 g or less. From the viewpoint of obtaining large inertia, the mass is preferably 44 g or more, particularly preferably 45.00 g or more. From the viewpoint that the USGA standard is satisfied, the mass is 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.

  For crosslinking of the core 4, a co-crosslinking agent is preferably used. 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.

  In the rubber composition of the core 4, various additives such as a filler, a sulfur compound, an anti-aging agent, a colorant, a plasticizer, and a dispersant are blended in appropriate amounts as necessary. Crosslinked rubber powder or synthetic resin powder may be blended with the rubber composition.

  The diameter of the core 4 is 30.0 mm or more, particularly 38.0 mm or more. The diameter of the core 4 is 42.0 mm or less, particularly 41.5 mm or less. The core 4 may be composed of two or more layers. An intermediate layer may be provided between the core 4 and the cover 6.

  A suitable polymer for the cover 6 is an ionomer resin. In particular, it is preferable that a carboxylic acid in a copolymer of an α-olefin and an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms is neutralized with a metal ion. Preferred α-olefins are ethylene and propylene. Preferred α, β-unsaturated carboxylic acids are acrylic acid and methacrylic acid. 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. Neutralization may be performed with two or more metal ions. Particularly suitable metal ions from the viewpoint of resilience performance and durability of the golf ball 2 are sodium ion, zinc ion, lithium ion and magnesium ion.

  Other polymers may be used in place of or in conjunction with the ionomer resin. Examples of other polymers include thermoplastic styrene elastomers, thermoplastic polyurethane elastomers, thermoplastic polyamide elastomers, thermoplastic polyester elastomers, and thermoplastic polyolefin elastomers.

  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 cover 6 has a thickness of 0.5 mm or more, particularly 0.8 mm or more. The cover 6 has a thickness of 2.5 mm or less, particularly 2.2 mm or less. The specific gravity of the cover 6 is 0.90 or more, particularly 0.95 or more. The specific gravity of the cover 6 is 1.10 or less, particularly 1.05 or less. The cover 6 may be composed of two or more layers.

  FIG. 2 is an enlarged plan view showing the golf ball 2 of FIG. 1, and FIG. 3 is a front view thereof. As is apparent from FIGS. 2 and 3, the planar shape of all the dimples 8 is a circle. In FIG. 2, the types of the dimples 8 are indicated by reference signs A to D in one unit when the surface of the golf ball 2 is partitioned into ten equivalent units. This golf ball 2 includes a dimple A having a diameter of 4.1 mm, a dimple B having a diameter of 3.6 mm, a dimple C having a diameter of 3.4 mm, and a dimple D having a diameter of 3.2 mm. I have. The number of dimples A is 132, the number of dimples B is 180, the number of dimples C is 60, and the number of dimples D is 60. The total number of dimples 8 of this golf ball 2 is 432 pieces.

  FIG. 4 is an enlarged cross-sectional view showing a part of the golf ball 2 of FIG. FIG. 4 shows a cross section along the plane passing through the center of gravity of the dimple 8 and the center of the golf ball 2. The vertical direction in FIG. 4 is the depth direction of the dimple 8. The depth direction is a direction from the center of gravity of the dimple 8 toward the center of the golf ball 2. In FIG. 4, what is indicated by a two-dot chain line 12 is a virtual sphere. The surface of the phantom sphere 12 is the surface of the golf ball 2 when it is assumed that the dimple 8 does not exist. The dimple 8 is recessed from the phantom sphere 12. The land 10 coincides with the phantom sphere 12.

  In FIG. 4, what is indicated by a double-pointed arrow Di is the diameter of the dimple 8. The diameter Di is a distance between one contact point Ed and the other contact point Ed when a common tangent line T is drawn on both sides of the dimple 8. The contact point Ed is also an edge of the dimple 8. The edge Ed defines the contour of the dimple 8. The diameter Di is preferably 2.00 mm or greater and 6.00 mm or less. By setting the diameter Di to be 2.00 mm or more, a large dimple effect can be obtained. From this viewpoint, the diameter Di is more preferably 2.20 mm or more, and particularly preferably 2.40 mm or more. By setting the diameter Di to 6.00 mm or less, the original characteristic of the golf ball 2 that is substantially a sphere is maintained. In this respect, the diameter Di is more preferably equal to or less than 5.80 mm, and particularly preferably equal to or less than 5.60 mm.

  In FIG. 4, what is indicated by a double-headed arrow d0 is the depth of the dimple 8. The depth d0 is a distance between the tangent line T and the deepest part of the dimple 8. In light of suppression of hops in the golf ball 2, the depth d0 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 d0 is preferably 0.60 mm or less, more preferably 0.45 mm or less, and particularly preferably 0.40 mm or less.

  FIG. 5 is an enlarged cross-sectional view showing a part of the dimple 8 of the golf ball 2 of FIG. In this figure, an unpainted golf ball 2 is shown. The dimple 8 includes an upper wall surface 14, a side wall surface 16, a first slope surface 18, a second slope surface 20, and a bottom surface 22. The upper wall surface 14, the side wall surface 16, the first slope surface 18 and the second slope surface 20 are ring-shaped. The bottom surface 22 has a bowl shape.

  The upper wall surface 14 extends from the edge Ed to the point P1. The upper wall surface 14 is a curved surface convex upward. The air that has passed through the land 10 first flows along the upper wall surface 14.

  The side wall surface 16 is located on the bottom side of the upper wall surface 14. The side wall surface 16 extends from the point P1 to the point P2. Side wall surface 16 is continuous with upper wall surface 14 at point P1. Side wall surface 16 is in contact with upper wall surface 14 at point P1. The side wall surface 16 is a curved surface convex downward. The cross-sectional shape of the side wall surface 16 is an arc shape. In FIG. 5, what is indicated by an arrow Ra is the radius of curvature of the side wall surface 16.

  The first slope surface 18 is located on the bottom side of the side wall surface 16. The first slope surface 18 extends from the point P2 to the point P3. The first slope surface 18 is continuous with the side wall surface 16 at the point P2. The first slope surface 18 is in contact with the side wall surface 16 at the point P2. The cross-sectional shape of the first slope surface 18 is linear. The first slope surface 18 is inclined downward toward the center of the dimple 8.

  The second slope surface 20 is located on the bottom side of the first slope surface 18. The second slope surface 20 extends from the point P3 to the point P4. The second slope surface 20 is continuous with the first slope surface 18 at the point P3. Point P3 is an intersection of the first slope surface 18 and the second slope surface 20. The cross-sectional shape of the second slope surface 20 is linear. The second slope surface 20 is inclined downward toward the center of the dimple 8. The slope of the second slope surface 20 is gentler than the slope of the first slope surface 18. Therefore, the angle formed by the first slope surface 18 and the second slope surface 20 is an acute angle above the point P3.

  The bottom surface 22 is located at the center of the dimple 8. The bottom surface 22 extends from the point P4 to the other point P4 (see FIG. 4). The bottom surface 22 is continuous with the second slope surface 20 at the point P4. The bottom surface 22 is in contact with the second slope surface 20 at the point P4. The bottom surface 22 is a curved surface that protrudes downward. The cross-sectional shape of the bottom surface 22 is an arc shape. In FIG. 5, what is indicated by an arrow Rb is the radius of curvature of the bottom surface 22.

  The arc 24 with the side wall surface 16 extended and the arc 26 with the bottom surface 22 extended contact each other at a point P5. As is apparent from FIG. 5, the point P3 is located below the point P5. The surface of the dimple 8 is recessed in the vicinity of the point P3.

  In the golf ball 2, the air from the land 10 toward the center of the dimple 8 flows along the upper wall surface 14, the side wall surface 16, the first slope surface 18, the second slope surface 20, and the bottom surface 22. The air flow direction changes rapidly in the vicinity of the point P3. A large dimple effect is obtained by this change. In the golf ball 2, the air from the center of the dimple 8 toward the land 10 flows along the bottom surface 22, the second slope surface 20, the first slope surface 18, the side wall surface 16, and the upper wall surface 14. The air flow direction changes rapidly in the vicinity of the point P3. A large dimple effect is obtained by this change.

  When the paint is applied, the paint accumulates in the vicinity of the point P3 due to the flow. By this accumulation, a thin coating layer is formed in the vicinity of the point P3 and thick in other areas. This coating layer reduces changes in the direction of air flow. However, since the vicinity of the point P3 is recessed, there is less inhibition of the dimple effect than the conventional double radius dimple. This golf ball 2 is excellent in flight performance. A coating layer having a large average thickness tends to inhibit the dimple effect. In the golf ball 2 having a coating layer having an average thickness of 6 μm or more, particularly 8 μm or more, the depression at the point P3 is effective. The average thickness is calculated based on the paint layer thickness measured at 20 randomly extracted lands.

  The ratio (Rb / Ra) between the curvature radius Rb of the bottom surface 22 and the curvature radius Ra of the side wall surface 16 is preferably 5 or more. By setting the ratio (Rb / Ra) to 5 or more, the air flow direction changes greatly, and a large dimple effect is obtained. From the viewpoint of the dimple effect, the ratio (Rb / Ra) is more preferably 7 or more, and particularly preferably 30 or more. From the viewpoint of the dimple effect, the ratio (Rb / Ra) is preferably 55 or less.

  The curvature radius Ra is preferably 1.0 mm or greater and 1.5 mm or less. By setting the curvature radius Ra to be 1.0 mm or more, damage to the cover 6 at the time of impact is suppressed. In this respect, the curvature radius Ra is more preferably 1.1 mm or more. A large dimple effect can be obtained by setting the curvature radius Ra to 1.5 mm or less. In this respect, the curvature radius Ra is more preferably 1.4 mm or less.

  The curvature radius Rb is preferably 10.0 mm or greater and 50.0 mm or less. By setting the curvature radius Rb within the above range, a large dimple effect can be obtained. In this respect, the curvature radius Rb is more preferably 20.0 mm or more. The curvature radius Rb is more preferably 40.0 mm or less.

  In FIG. 5, what is indicated by the double arrow d1 is the depth of the point P1, what is indicated by the double arrow d2 is the depth of the point P2, and what is indicated by the double arrow d3 The depth of the point P3 is indicated by the double arrow d4, and the depth of the point P4 is indicated by the double arrow d5.

  From the viewpoint of the dimple effect, the ratio of the depth d2 to the depth d0 (see FIG. 4) is preferably 50% or more and 85% or less. By setting this ratio to 50% or more, the side wall surface 16 and the first slope surface 18 greatly contribute to the dimple effect. From this viewpoint, the ratio is more preferably 55% or more. By setting the ratio to 85% or less, the second slope surface 20 and the bottom surface 22 greatly contribute to the dimple effect. From this viewpoint, the ratio is more preferably 65% or less.

  From the viewpoint of the dimple effect, the ratio of the depth d4 to the depth d0 (see FIG. 4) is preferably 50% or more and 85% or less. By setting this ratio to 50% or more, the side wall surface 16 and the first slope surface 18 greatly contribute to the dimple effect. From this viewpoint, the ratio is more preferably 65% or more. By setting the ratio to 85% or less, the second slope surface 20 and the bottom surface 22 greatly contribute to the dimple effect. In this respect, the ratio is more preferably equal to or less than 80%.

  From the viewpoint of the dimple effect, the ratio of the depth d5 to the depth d0 is preferably 50% or more and 85% or less. By setting the ratio to 50% or more, the side wall surface 16 greatly contributes to the dimple effect. From this viewpoint, the ratio is more preferably 60% or more. By setting this ratio to 85% or less, the bottom surface 22 greatly contributes to the dimple effect. In this respect, the ratio is more preferably equal to or less than 80%, and particularly preferably equal to or less than 70%.

  The ratio of the difference (d4−d2) to the depth d0 of the dimple 8 is preferably 10% or more and 30% or less. By setting this ratio to 10% or more, a large dimple effect can be obtained. From this viewpoint, the ratio is more preferably 15% or more. The dimple 8 having this ratio of 30% or less is excellent in appearance. From this viewpoint, the ratio is more preferably 25% or less.

  The upper wall surface 14 is formed for the convenience of manufacturing the golf ball 2. The ratio of the depth d1 to the depth d0 is preferably 10% or less, particularly preferably 5% or less. The dimple 8 may not have the upper wall surface 14. In this case, the ratio of the depth d1 to the depth d0 is zero.

  From the viewpoint of the dimple effect, the ratio of the difference (d2-d1) to the depth d0 of the dimple 8 is preferably 30% to 70%, and the ratio of the difference (d3-d2) to the depth d0 of the dimple 8 is 5% or more. The ratio of the difference (d4−d3) to the depth d0 of the dimple 8 is preferably 5% or more and 20% or less, and the ratio of the difference (d0−d4) to the depth d0 of the dimple 8 is 35% or more. 15% or less is preferable.

The area s of the dimple 8 is an area of a region surrounded by a contour line when the center of the golf ball 2 is viewed from infinity. In the case of the circular dimple 8, the area s is calculated by the following mathematical formula.
s = (Di / 2) ²・ π
In the golf ball 2 shown in FIGS. 2 and 3, the area of the dimple A is 13.20 mm ² , the area of the dimple B is 10.18 mm ² , and the area of the dimple C is 9.08 mm ² , The area of the dimple D is 8.04 mm ² .

In the present invention, the ratio of the total area s of all the dimples 8 to the surface area of the phantom sphere 12 is referred to as an occupation ratio. From the viewpoint of obtaining a sufficient dimple effect, the occupation ratio is preferably 70% or more, more preferably 72% or more, and particularly preferably 74% or more. The occupation ratio is preferably 90% or less. In the golf ball 2 shown in FIGS. 2 and 3, the total area of the dimples 8 is 4602.0 mm ² . Since the surface area of the phantom sphere 12 of this golf ball 2 is 5728.0 mm ² , the occupation ratio is 80.3%.

In the present invention, the “dimple volume” means a volume of a portion surrounded by a plane including the outline of the dimple 8 and the surface of the dimple 8. From the viewpoint of rising of the golf ball 2 is suppressed, the total volume of the dimples 8 is preferably 250 mm ³ or more, more preferably 260 mm ³ or more, 270 mm ³ or more is particularly preferable. In view of dropping of the golf ball 2 is suppressed, the total volume is preferably 400 mm ³ or less, more preferably 390 mm ³ or less, 380 mm ³ or less is particularly preferred.

  From the viewpoint of obtaining a sufficient dimple effect, the total number of dimples 8 is preferably 200 or more, more preferably 240 or more, and particularly preferably 260 or more. From the viewpoint that each dimple 8 can have a sufficient diameter, the total number is preferably 500 or less, more preferably 480 or less, and particularly preferably 460 or less.

The dimple 8 shown in FIG.
(1) Side wall surface 16 whose cross section is arcuate and convex downward;
(2) a first slope surface 18 that is in contact with the side wall surface 16 at the lower end P2 of the side wall surface 16 and is inclined downward toward the center of the dimple 8;
(3) The second slope surface which is continuous with the first slope surface 18 at the lower end P3 of the first slope surface 18 and is inclined downward toward the center of the dimple 8 more gently than the first slope surface 18. 20
And (4) a bowl-shaped bottom surface 22 which is in contact with the second slope surface 20 at the lower end P4 of the second slope surface 20 and has a circular cross section and is located at the center of the dimple 8.
Have The ratio of the number of dimples 8 having (1) to (4) to the total number of dimples 8 is preferably 50% or more, and more preferably 70% or more. This ratio is ideally 100%.

  In the present invention, the size of each part of the dimple 8 is measured in the golf ball 2 to which no paint is applied. In the golf ball 2 after the paint layer is removed, the size of each part may be measured.

  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 weight of polybutadiene (trade name “BR-18” 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., Ltd.), 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 mold having a large number of protrusions on the inner peripheral surface, and the resin composition was injected around the sphere by an injection molding method to form a cover having a thickness of 1.5 mm. A large number of dimples having a shape in which the shape of the protrusion was inverted were formed on the cover. A clear paint based on a two-component curable polyurethane was applied to this cover to obtain a golf ball of Example 1 having a diameter of 42.7 mm and a mass of about 45.4 g. The thickness of the coating layer on the side wall surface was 10 μm, the coating layer thickness just above the point P3 was 15 μm, and the thickness of the coating layer on the bottom surface was 9 μm. The average thickness of the coating layer was 10 μm. In this golf ball, the total dimple volume was about 320 mm ³ . This golf ball has the dimple pattern shown in FIGS. The dimples of this golf ball have the cross-sectional shape shown in FIGS. Details of the dimple specifications are shown in Table 1 below.

[Examples 2 to 5]
Golf balls of Examples 2 to 5 were obtained in the same manner as in Example 1 except that the depth d2 and the depth d4 were set as shown in Tables 1 and 2 below.

[Examples 6 and 7]
Golf balls of Examples 6 and 7 were obtained in the same manner as in Example 1 except that the curvature radius Ra of the side wall surface and the curvature radius Rb of the bottom surface were changed as shown in Tables 1 and 2 below.

[Comparative example]
A comparative golf ball was obtained in the same manner as in Example 1 except that the dimple had a double radius cross section. The dimple has an upper wall surface, a side wall surface, and a bottom surface. The side wall surface and the bottom surface are in contact with each other.

[Flight distance test]
A driver with a titanium head (trade name “XXIO”, Sumitomo Rubber Industries Ltd., shaft hardness: X, loft angle: 9 °) equipped with a titanium head was attached to a swing machine manufactured by Tsurutemper. A golf ball was hit under the condition that the head speed was 49 m / sec, and the distance from the launch point to the rest point was measured. Average values of 20 measurements are shown in Tables 1 and 2 below.

  As shown in Tables 1 and 2, the golf balls of the examples are excellent in flight performance. From this evaluation result, the superiority of the present invention is clear.

  The present invention 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.

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 plan view showing the golf ball of FIG. FIG. 3 is a front 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 an enlarged cross-sectional view showing a part of the dimple of the golf ball of FIG.

Explanation of symbols

2 ... Golf ball 4 ... Core 6 ... Cover 8 ... Dimple 10 ... Land 12 ... Virtual sphere 14 ... Upper wall surface 16 ... Side wall surface 18 ... First Slope surface 20 ... Second slope surface 22 ... Bottom surface

Claims (6)

It has many dimples on its surface,
This dimple is
(1) Side wall surface having a circular cross section and convex downward;
(2) a first slope surface that is in contact with the side wall surface at the lower end P2 of the side wall surface and is inclined downward toward the center of the dimple;
(3) a second slope surface which is continuous with the first slope surface at the lower end P3 of the first slope surface, and which slopes downward toward the center of the dimple more gently than the first slope surface; A golf ball in contact with the second slope surface at the lower end P4 of the second slope surface, having a circular cross section and having a bowl-shaped bottom surface located at the center of the dimple.   2. The golf ball according to claim 1, wherein when the depth of the contact point P <b> 2 between the side wall surface and the first slope surface is d <b> 2, the ratio of the depth d <b> 2 to the dimple depth d <b> 0 is 50% or more and 85% or less.   The golf according to claim 1 or 2, wherein when the depth of the contact point P4 between the second slope surface and the bottom surface is d4, the ratio of the depth d4 to the dimple depth d0 is 50% or more and 85% or less. ball.   4. The golf ball according to claim 1, wherein a ratio of a difference (d4-d2) between the depth d4 and the depth d2 to the depth d0 of the dimple is 10% or more and 30% or less.   5. The golf ball according to claim 1, wherein a ratio (Rb / Ra) of a curvature radius Rb of the bottom surface and a curvature radius Ra of the side wall surface is 5 or more and 55 or less.   The golf ball according to claim 1, further comprising a coating layer on a surface thereof, and an average thickness of the coating layer being 6 μm or more.

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