Golf ball

This application claims priority on Patent Application No. 2004-280930 filed in JAPAN on Sep. 28, 2004, the entire contents of which are hereby incorporated by reference.

1. Field of the Invention

The present invention relates to golf balls. More particularly, the present invention relates to improvement of dimples of a golf ball.

2. Description of the Related Art

Golf balls have numerous dimples on the surface thereof. The dimples disrupt the air flow around the golf ball during the flight, thereby causing turbulent flow separation. By causing the turbulent flow separation, a separating point of air from the golf ball shifts backwards leading to the reduction of drag. The turbulent flow separation promotes the differentia between the separating points at the upper and lower sides of the golf ball, which results from the backspin, thereby enhancing the lift force that acts upon the golf ball. Such a role of the dimple is referred to as a “dimple effect”. Excellent dimples disturb the air flow more efficiently.

A variety of proposals with respect to the dimple shape have been made in an attempt to improve the flight performance. U.S. Pat. No. 5,338,039 discloses a dimple having double slopes. U.S. Pat. No. 5,536,013 discloses a dimple having a projection at the center. U.S. Pat. No. 5,735,757 discloses a dimple having a double radius shape. JP-A No. 2002-336337 discloses a dimple having a sub-dimple formed inside thereof.

Top concern to golf players for golf balls is the travel distance. In light of elevation of the travel distance, there remains room for improvement of the dimple. An object of the present invention is to provide a golf ball that is excellent in the flight performance.

The golf ball according to the present invention has numerous dimples with a contour being circular, on the surface thereof. This dimple has a first curved face, a second curved face, a third curved face, a circular first edge that is a boundary between a land and the first curved face, a circular second edge that is a boundary between the first curved face and the second curved face, and a circular third edge that is a boundary between the second curved face and the third curved face. The second edge and the third edge are disposed concentrically with the first edge. According to this golf ball, the air flow is disrupted by the edge formed inside of the dimple. This golf ball is excellent in the flight performance.

Preferably, the first curved face is inclined downward toward the dimple center; the second curved face is inclined upward toward the dimple center; and the third curved face is inclined downward toward the dimple center.

Preferably, the dimple further has a fourth curved face, and a fourth edge that is a boundary between the third curved face and the fourth curved face. This fourth edge is disposed concentrically with the first edge.

Preferably, the dimple further has a fifth curved face, and a fifth edge that is a boundary between the fourth curved face and the fifth curved face. This fifth edge is disposed concentrically with the first edge.

Preferably, the dimple further has a sixth curved face, and a sixth edge that is a boundary between the fifth curved face and the sixth curved face. This sixth edge is disposed concentrically with the first edge.

Preferably, the dimple further has a seventh curved face, and a seventh edge that is a boundary between the sixth curved face and the seventh curved face. This seventh edge is disposed concentrically with the first edge.

Preferably, all the curved faces included in the dimple are not protruded upward from the plane including the first edge. Preferably, the first curved face makes a part of a phantom spherical surface, and is inclined downward toward the dimple center. All the curved faces included in the dimple are not protruded downward from this phantom spherical surface.

Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:

FIG. 1 is a schematic cross-sectional view illustrating a golf ball according to one embodiment of the present invention;

FIG. 2 is an enlarged plan view illustrating the golf ball shown in FIG. 1 ;

FIG. 3 is a front view illustrating the golf ball shown in FIG. 2 ;

FIG. 4( a ) is an enlarged plan view illustrating a part of the golf ball shown in FIG. 1 ;

FIG. 4( b ) is an enlarged cross-sectional view illustrating a part of the golf ball shown in FIG. 1 ;

FIG. 5( a ) a plan view illustrating a part of a golf ball according to another embodiment of the present invention;

FIG. 5( b ) is a cross-sectional view illustrating the golf ball shown in FIG. 5( a );

FIG. 6( a ) is a plan view illustrating a part of a golf ball according to still another embodiment of the present invention;

FIG. 6( b ) is a cross-sectional view illustrating the golf ball shown in FIG. 6( a );

FIG. 7( a ) is a plan view illustrating a part of a golf ball according to yet another embodiment of the present invention;

FIG. 7( b ) is a cross-sectional view illustrating the golf ball shown in FIG. 7( a );

FIG. 8( a ) is a plan view illustrating a part of a golf ball according to yet another embodiment of the present invention;

FIG. 8( b ) is a cross-sectional view illustrating the golf ball shown in FIG. 8( a );

FIG. 9( a ) is a plan view illustrating a part of a golf ball according to Comparative Example 1;

FIG. 9( b ) is a cross-sectional view illustrating the golf ball shown in FIG. 9( a );

FIG. 10( a ) is a plan view illustrating a part of a golf ball according to Comparative Example 2; and

FIG. 10( b ) is a cross-sectional view illustrating the golf ball shown in FIG. 10( a ).

The present invention is hereinafter described in detail with appropriate references to the accompanying drawing according to the preferred embodiments of the present invention.

A golf ball 2 illustrated in FIG. 1 has a spherical core 4 and a cover 6 . Numerous dimples 8 are formed on the surface of the cover 6 . Of the surface of the golf ball 2 , a part except for the dimples 8 is a land 10 . This golf ball 2 has a paint layer and a mark layer to the external side of the cover 6 , although these layers are not shown in the Figure.

This golf ball 2 has a diameter of from 40 mm to 45 mm. From the standpoint of conformity to a rule defined by the United States Golf Association (USGA), the diameter is preferably equal to or greater than 42.67 mm. In light of suppression of the 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 weight of this golf ball 2 is 40 g or greater and 50 g or less. In light of attainment of great inertia, the weight is preferably equal to or greater than 44 g, and particularly preferably equal to or greater than 45.00 g. From the standpoint of conformity to a rule defined by the USGA, the weight is preferably equal to or less than 45.93 g.

The core 4 is formed through crosslinking of a rubber composition. Illustrative examples of the base rubber for use in the rubber composition include polybutadienes, polyisoprenes, styrene-butadiene copolymers, ethylene-propylene-diene copolymers and natural rubbers. Two or more kinds of the rubbers may be used in combination. In light of the resilience performance, polybutadienes are preferred, and particularly, high-cis polybutadienes are preferred.

For crosslinking of the core 4 , a co-crosslinking agent is usually used. Preferable examples of the co-crosslinking agent in light of the resilience performance include zinc acrylate, magnesium acrylate, zinc methacrylate and magnesium methacrylate. Into the rubber composition, an organic peroxide may be preferably blended together with the co-crosslinking agent. Examples of suitable organic peroxide include dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane and di-t-butyl peroxide.

Various kinds of additives such as a filler, a sulfur compound, an anti-aging agent, a coloring agent, a plasticizer, a dispersant and the like may be blended at an appropriate amount into the rubber composition of the core 4 as needed. Crosslinked rubber powder or synthetic resin powder may be also blended into the rubber composition.

The core 4 has a diameter of equal to or greater than 30.0 mm, and particularly equal to or greater than 38.0 mm. The core 4 has a diameter of equal to or less than 42.0 mm, and particularly equal to or less than 41.5 mm. The core 4 may be composed of two or more layers.

Polymer that is suitable for the cover 6 is an ionomer rein. In particular, a copolymer of α-olefin and an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms in which a part of the carboxylic acid is neutralized with a metal ion is suitable. Examples of preferable α-olefin include ethylene and propylene. Examples of preferable α,β-unsaturated carboxylic acid include acrylic acid and methacrylic acid. Illustrative examples of the metal ion for use in the neutralization include sodium ion, potassium ion, lithium ion, zinc ion, calcium ion, magnesium ion, aluminum ion and neodymium ion. The neutralization may also be carried out with two or more kinds of the metal ions. In light of the resilience performance and durability of the golf ball 2 , examples of suitable metal ion include sodium ion, zinc ion, lithium ion and magnesium ion.

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

Into the cover 6 may be blended a coloring agent such as titanium dioxide, a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorbent, a light stabilizer, a fluorescent agent, a fluorescent brightening agent and the like in an appropriate amount as needed. The cover 6 may be also blended with powder of a highly dense metal such as tungsten, molybdenum or the like for the purpose of adjusting the specific gravity.

The cover 6 has a thickness of equal to or greater than 0.2 mm, and particularly equal to or greater than 0.8 mm. The cover 6 has a thickness of equal to or less than 2.5 mm, and particularly equal to or less than 2.2 mm. The cover 6 has a specific gravity of equal to or greater than 0.90, and particularly equal to or greater than 0.95. The cover 6 has a specific gravity of equal to or less than 1.10, and particularly equal to or less than 1.05. The cover 6 may be composed of two or more layers.

FIG. 2 is an enlarged plan view illustrating the golf ball 2 shown in FIG. 1 ; and FIG. 3 is a front view illustrating the golf ball 2 shown in FIG. 2 . As is clear from FIG. 2 and FIG. 3 , the contour shape of all the dimples 8 is circular. In FIG. 2 , types of the dimples 8 are illustrated by symbols of A to E in one unit, provided when the surface of the golf ball 2 is comparted into six equivalent units. This golf ball 2 has dimples A having a diameter of 5.50 mm, dimples B having a diameter of 4.80 mm, dimples C having a diameter of 4.46 mm, dimples D having a diameter of 3.40 mm and dimples E having a diameter of 3.00 mm.

In the golf ball 2 shown in FIG. 2 and FIG. 3 , the number of the dimples A is 18; the number of the dimples B is 126; the number of the dimples C is 72; the number of the dimples D is 60; and the number of the dimples E is 24. Total number of the dimples 8 of this golf ball 2 is 300.

FIG. 4( a ) is an enlarged plan view illustrating a part of the golf ball 2 shown in FIG. 1 ; and FIG. 4( b ) is an enlarged cross-sectional view illustrating a part of the golf ball 2 shown in FIG. 1 . In this FIG. 4( b ), a cross section along a plane passing through the deepest site of the dimple 8 and the center of the golf ball 2 is shown. A top-to-bottom direction in FIG. 4( b ) is an in-depth direction. What is indicated by a chain double-dashed line 12 in FIG. 4( b ) is a ball phantom sphere 12 . The surface of the ball phantom sphere 12 corresponds to a surface of the golf ball 2 when it is postulated that there is no dimple 8 existed. The dimple 8 is recessed from the ball phantom sphere 12 . The land 10 agrees with the ball phantom sphere 12 .

The dimple 8 has a first curved face S 1 , a second curved face S 2 , a third curved face S 3 , a first edge E 1 , a second edge E 2 and a third edge E 3 . The first edge E 1 is a boundary between the land 10 and the first curved face S 1 . The second edge E 2 is a boundary between the first curved face S 1 and the second curved face S 2 . The third edge E 3 is a boundary between the second curved face S 2 and the third curved face S 3 . The first edge E 1 , the second edge E 2 and the third edge E 3 are circular. As is clear from FIG. 4( a ), the second edge E 2 and the third edge E 3 are disposed concentrically with the first edge E 1 .

The first curved face S 1 makes a part of a first phantom spherical surface P 1 . The first curved face S 1 is convex downward. The first curved face S 1 is ring-shaped. The first curved face S 1 is inclined downward from the first edge E 1 toward the center of the dimple 8 . The second curved face S 2 makes a part of a second phantom spherical surface P 2 . The second curved face S 2 is convex upward. The second curved face S 2 is ring-shaped. The second curved face S 2 is inclined upward from the second edge E 2 toward the center of the dimple 8 . The third curved face S 3 makes a part of a third phantom spherical surface P 3 . The third curved face S 3 is convex downward. The third curved face S 3 is bowl-shaped. The third curved face S 3 is inclined downward from the third edge E 3 toward the center of the dimple 8 .

According to this dimple 8 , the air that flows toward the center of the dimple 8 collides with the third edge E 3 . Due to this collision, the air flow is disrupted. According to the golf ball 2 having this type of dimple 8 , the drag is suppressed. This golf ball 2 is excellent in the flight performance.

In this dimple 8 , the first curved face S 1 , the second curved face S 2 and the third curved face S 3 are not protruded upward from the plane including the first edge E 1 . In addition, the first curved face S 1 , the second curved face S 2 and the third curved face S 3 are not protruded downward from the first phantom spherical surface P 1 . According to this dimple 8 , the air in a sufficient amount flows in toward the center thereof. This dimple 8 is responsible for the flight performance.

In FIG. 4( a ), what is indicated by a two-headed arrow D 1 is the diameter of the first edge E 1 ; what is indicated by a two-headed arrow D 2 is the diameter of the second edge E 2 ; and what is indicated by a two-headed arrow D 3 is the diameter of the third edge E 3 . The diameter D 1 is also a diameter of the dimple 8 . The diameter D 1 is greater than the diameter D 2 . The diameter D 2 is greater than diameter D 3 .

What is indicated by a two-headed arrow L 1 in FIG. 4( b ) is the depth of the first phantom spherical surface P 1 . Herein, the depth L 1 is defined as a distance between the plane including the first edge E 1 and the deepest point of the first phantom spherical surface P 1 . What is indicated by a two-headed arrow L 2 in FIG. 4( b ) is the height of the second phantom spherical surface P 2 . Herein, the height L 2 is defined as a distance between the plane including the second edge E 2 and the top of the second phantom spherical surface P 2 . What is indicated by a two-headed arrow L 3 in FIG. 4( b ) is the depth of the third phantom spherical surface P 3 . Herein, the depth L 3 is defined as a distance between the plane including the third edge E 3 and the deepest point of the third phantom spherical surface P 3 . In light of possible air flow in a sufficient amount toward the center of the dimple 8 , it is preferred that the height L 2 is smaller than the depth L 1 , and the depth L 3 is smaller than the depth L 1 .

The dimple 8 has three circular edges E 1 , E 2 and E 3 . The golf ball 2 may also have other dimple in addition to the dimple 8 having three or more circular edges. In this instance, proportion of the number of the dimples 8 having three or more circular edges to total number of the dimples is preferably equal to or greater than 50%, and more preferably equal to or greater than 70%. Ideally, this proportion is 100%.

In light of the dimple effect, the diameter D 1 of the dimple 8 is preferably equal to or greater than 2.0 mm, more preferably equal to or greater than 2.2 mm, and particularly preferably equal to or greater than 2.4 mm. In light of possibility in keeping a fundamental feature of the golf ball 2 which is substantially a sphere, the diameter D 1 is preferably equal to or less than 6.0 mm, more preferably equal to or less than 5.8 mm, and particularly preferably equal to or less than 5.6 mm.

When the total number of the dimples 8 is too small, the dimple effect is hardly achieved. In light of the dimple effect, the total number is preferably equal to or greater than 200, more preferably equal to or greater than 240, and particularly preferably equal to or greater than 260. When the total number is too large, the dimple effect is hardly achieved due to small size of the individual dimples 8 . In light of the dimple effect, the total number is preferably equal to or less than 500, more preferably equal to or less than 480, and particularly preferably equal to or less than 460.

Herein, the term “dimple volume” means a volume of a part surrounded by a plane including the contour of the dimple 8 , and the surface of the dimple 8 . In light of suppression of hopping trajectory, total volume of the dimples 8 is preferably equal to or greater than 250 mm 3 , more preferably equal to or greater than 260 mm 3 , and particularly preferably equal to or greater than 270 mm 3 . In light of suppression of dropping trajectory, the total volume is preferably equal to or less than 400 mm 3 , more preferably equal to or less than 390 mm 3 , and particularly preferably equal to or less than 380 mm 3 .

In the present invention, ratio of total area of all the dimples 8 occupying the surface area of the ball phantom sphere is referred to as occupation ratio. In light of achievement of sufficient dimple effect, the occupation ratio is preferably equal to or greater than 75%, more preferably equal to or greater than 77%, and particularly preferably equal to or greater than 79%. The occupation ratio is preferably equal to or less than 90%.

FIG. 5( a ) is a plan view illustrating a part of a golf ball according to another embodiment of the present invention; and FIG. 5( b ) is a cross-sectional view of the same. In this FIG. 5 , a dimple 14 is depicted. What is indicated by a chain double-dashed line 16 in FIG. 5( b ) is a ball phantom sphere.

This dimple 14 has a first curved face S 1 , a second curved face S 2 , a third curved face S 3 , a fourth curved face S 4 , a first edge E 1 , a second edge E 2 , a third edge E 3 and a fourth edge E 4 . The first edge E 1 is a boundary between a land 18 and the first curved face S 1 . The second edge E 2 is a boundary between the first curved face S 1 and the second curved face S 2 . The third edge E 3 is a boundary between the second curved face S 2 and the third curved face S 3 . The fourth edge E 4 is a boundary between the third curved face S 3 and the fourth curved face S 4 . The first edge E 1 , the second edge E 2 , the third edge E 3 and the fourth edge E 4 are circular. As is clear from FIG. 5( a ), the second edge E 2 , the third edge E 3 and the fourth edge E 4 are disposed concentrically with the first edge E 1 .

The first curved face S 1 makes a part of a first phantom spherical surface P 1 . The first curved face S 1 is convex downward. The first curved face S 1 is ring-shaped. The first curved face S 1 is inclined downward from the first edge E 1 toward the center of the dimple 14 . The second curved face S 2 makes a part of a second phantom spherical surface P 2 . The second curved face S 2 is convex upward. The second curved face S 2 is ring-shaped. The second curved face S 2 is inclined upward from the second edge E 2 toward the center of the dimple 14 . The third curved face S 3 makes a part of a third phantom spherical surface P 3 . The third curved face S 3 is convex downward. The third curved face S 3 is ring-shaped. The third curved face S 3 is inclined downward from the third edge E 3 toward the center of the dimple 14 . The fourth curved face S 4 makes a part of a fourth phantom spherical surface P 4 . The fourth curved face S 4 is convex upward. The fourth curved face S 4 is hill-shaped. The fourth curved face S 4 is inclined upward from the fourth edge E 4 toward the center of the dimple 14 .

According to this dimple 14 , the air that flows toward the center of the dimple 14 collides with the third edge E 3 and the fourth curved face S 4 . Due to this collision, the air flow is disrupted. According to the golf ball having this type of dimple 14 , the drag is suppressed. This golf ball is excellent in the flight performance.

In this dimple 14 , the first curved face S 1 , the second curved face S 2 , the third curved face S 3 and the fourth curved face S 4 are not protruded upward from the plane including the first edge E 1 . In addition, the first curved face S 1 , the second curved face S 2 , the third curved face S 3 and the fourth curved face S 4 are not protruded downward from the first phantom spherical surface P 1 . According to this dimple 14 , the air in a sufficient amount flows in toward the center thereof. This dimple 14 is responsible for the flight performance.

In FIG. 5( a ), what is indicated by a two-headed arrow D 1 is the diameter of the first edge E 1 ; what is indicated by a two-headed arrow D 2 is the diameter of the second edge E 2 ; what is indicated by a two-headed arrow D 3 is the diameter of the third edge E 3 ; what is indicated by a two-headed arrow D 4 is the diameter of the fourth edge E 4 . The diameter D 1 is greater than the diameter D 2 . The diameter D 2 is greater than the diameter D 3 . The diameter D 3 is greater than the diameter D 4 .

What is indicated by a two-headed arrow L 4 in FIG. 5( b ) is the height of the fourth phantom spherical surface P 4 . Herein, the height L 4 is defined as a distance between the plane including the fourth edge E 4 and the top of the fourth phantom spherical surface P 4 . In light of possible air flow in a sufficient amount toward the center of the dimple 14 , it is preferred that the height L 4 is smaller than the depth L 1 (see, FIG. 4) .

FIG. 6( a ) is a plan view illustrating a part of a golf ball according to still another embodiment of the present invention; and FIG. 6( b ) is a cross-sectional view of the same. In this FIG. 6 , a dimple 20 is depicted. What is indicated by a chain double-dashed line 22 in FIG. 6( b ) is a ball phantom sphere.

This dimple 20 has a first curved face S 1 , a second curved face S 2 , a third curved face S 3 , a fourth curved face S 4 , a fifth curved face S 5 , a first edge E 1 , a second edge E 2 , a third edge E 3 , a fourth edge E 4 and a fifth edge E 5 . The first edge E 1 is a boundary between a land 24 and the first curved face S 1 . The second edge E 2 is a boundary between the first curved face S 1 and the second curved face S 2 . The third edge E 3 is a boundary between the second curved face S 2 and the third curved face S 3 . The fourth edge E 4 is a boundary between the third curved face S 3 and the fourth curved face S 4 . The fifth edge E 5 is a boundary between the fourth curved face S 4 and the fifth curved face S 5 . The first edge E 1 , the second edge E 2 , the third edge E 3 , the fourth edge E 4 and the fifth edge E 5 are circular. As is clear from FIG. 6( a ), the second edge E 2 , the third edge E 3 , the fourth edge E 4 and the fifth edge E 5 are disposed concentrically with the first edge E 1 .

The first curved face S 1 makes a part of a first phantom spherical surface P 1 . The first curved face S 1 is convex downward. The first curved face S 1 is ring-shaped. The first curved face S 1 is inclined downward from the first edge E 1 toward the center of the dimple 20 . The second curved face S 2 makes a part of a second phantom spherical surface P 2 . The second curved face S 2 is convex upward. The second curved face S 2 is ring-shaped. The second curved face S 2 is inclined upward from the second edge E 2 toward the center of the dimple 20 . The third curved face S 3 makes a part of a third phantom spherical surface P 3 . The third curved face S 3 is convex downward. The third curved face S 3 is ring-shaped. The third curved face S 3 is inclined downward from the third edge E 3 toward the center of the dimple 20 . The fourth curved face S 4 makes a part of a fourth phantom spherical surface P 4 . The fourth curved face S 4 is convex upward. The fourth curved face S 4 is ring-shaped. The fourth curved face S 4 is inclined upward from the fourth edge E 4 toward the center of the dimple 20 . The fifth curved face S 5 makes a part of a fifth phantom spherical surface P 5 . The fifth curved face S 5 is convex downward. The fifth curved face S 5 is bowl-shaped. The fifth curved face S 5 is inclined downward from the fifth edge E 5 toward the center of the dimple 20 .

According to this dimple 20 , the air that flows toward the center of the dimple 20 collides with the third edge E 3 and the fifth edge E 5 . Due to this collision, the air flow is disrupted. According to the golf ball having this type of dimple 20 , the drag is suppressed. This golf ball is excellent in the flight performance.

In this dimple 20 , the first curved face S 1 , the second curved face S 2 , the third curved face S 3 , the fourth curved face S 4 and the fifth curved face S 5 are not protruded upward from the plane including the first edge E 1 . In addition, the first curved face S 1 , the second curved face S 2 , the third curved face S 3 , the fourth curved face S 4 and the fifth curved face S 5 are not protruded downward from the first phantom spherical surface P 1 . According to this dimple 20 , the air in a sufficient amount flows in toward the center thereof. This dimple 20 is responsible for the flight performance.

In FIG. 6( a ), what is indicated by a two-headed arrow D 1 is the diameter of the first edge E 1 ; what is indicated by a two-headed arrow D 2 is the diameter of the second edge E 2 ; what is indicated by a two-headed arrow D 3 is the diameter of the third edge E 3 ; what is indicated by a two-headed arrow D 4 is the diameter of the fourth edge E 4 ; and what is indicated by a two-headed arrow D 5 is the diameter of the fifth edge E 5 . The diameter D 1 is greater than the diameter D 2 . The diameter D 2 is greater than the diameter D 3 . The diameter D 3 is greater than the diameter D 4 . The diameter D 4 is greater than the diameter D 5 .

What is indicated by a two-headed arrow L 5 in FIG. 6( b ) is the depth of the fifth phantom spherical surface P 5 . Herein, the depth L 5 is defined as a distance between the plane including the fifth edge E 5 and the deepest point of the fifth phantom spherical surface P 5 . In light of possible air flow in a sufficient amount toward the center of the dimple 20 , it is preferred that the height L 5 is smaller than the depth L 1 (see, FIG. 4) .

FIG. 7( a ) is a plan view illustrating a part of a golf ball according to yet another embodiment of the present invention; and FIG. 7( b ) is a cross-sectional view of the same. In this FIG. 7 , a dimple 26 is depicted. What is indicated by a chain double-dashed line 28 in FIG. 7( b ) is a ball phantom sphere.

This dimple 26 has a first curved face S 1 , a second curved face S 2 , a third curved face S 3 , a fourth curved face S 4 , a fifth curved face S 5 , a sixth curved face S 6 , a first edge E 1 , a second edge E 2 , a third edge E 3 , a fourth edge E 4 , a fifth edge E 5 and a sixth edge E 6 . The first edge E 1 is a boundary between a land 30 and the first curved face S 1 . The second edge E 2 is a boundary between the first curved face S 1 and the second curved face S 2 . The third edge E 3 is a boundary between the second curved face S 2 and the third curved face S 3 . The fourth edge E 4 is a boundary between the third curved face S 3 and the fourth curved face S 4 . The fifth edge E 5 is a boundary between the fourth curved face S 4 and the fifth curved face S 5 . The sixth edge E 6 is a boundary between the fifth curved face S 5 and the sixth curved face S 6 . The first edge E 1 , the second edge E 2 , the third edge E 3 , the fourth edge E 4 , the fifth edge E 5 and the sixth edge E 6 are circular. As is clear from FIG. 7( a ), the second edge E 2 , the third edge E 3 , the fourth edge E 4 , the fifth edge E 5 and the sixth edge E 6 are disposed concentrically with the first edge E 1 .

The first curved face S 1 makes a part of a first phantom spherical surface P 1 . The first curved face S 1 is convex downward. The first curved face S 1 is ring-shaped. The first curved face S 1 is inclined downward from the first edge E 1 toward the center of the dimple 26 . The second curved face S 2 makes a part of a second phantom spherical surface P 2 . The second curved face S 2 is convex upward. The second curved face S 2 is ring-shaped. The second curved face S 2 is inclined upward from the second edge E 2 toward the center of the dimple 26 . The third curved face S 3 makes a part of a third phantom spherical surface P 3 . The third curved face S 3 is convex downward. The third curved face S 3 is ring-shaped. The third curved face S 3 is inclined downward from the third edge E 3 toward the center of the dimple 26 . The fourth curved face S 4 makes a part of a fourth phantom spherical surface P 4 . The fourth curved face S 4 is convex upward. The fourth curved face S 4 is ring-shaped. The fourth curved face S 4 is inclined upward from the fourth edge E 4 toward the center of the dimple 26 . The fifth curved face S 5 makes a part of a fifth phantom spherical surface P 5 . The fifth curved face S 5 is convex downward. The fifth curved face S 5 is ring-shaped. The fifth curved face S 5 is inclined downward from the fifth edge E 5 toward the center of the dimple 26 . The sixth curved face S 6 makes a part of a sixth phantom spherical surface P 6 . The sixth curved face S 6 is convex upward. The sixth curved face S 6 is hill-shaped. The sixth curved face S 6 is inclined upward from the sixth edge E 6 toward the center of the dimple 26 .

According to this dimple 26 , the air that flows toward the center of the dimple 26 collides with the third edge E 3 , the fifth edge E 5 and the sixth curved face S 6 . Due to this collision, the air flow is disrupted. According to the golf ball having this type of dimple 26 , the drag is suppressed. This golf ball is excellent in the flight performance.

In this dimple 26 , the first curved face S 1 , the second curved face S 2 , the third curved face S 3 , the fourth curved face S 4 , the fifth curved face S 5 and the sixth curved face S 6 are not protruded upward from the plane including the first edge E 1 . In addition, the first curved face S 1 , the second curved face S 2 , the third curved face S 3 , the fourth curved face S 4 , the fifth curved face S 5 and the sixth curved face S 6 are not protruded downward from the first phantom spherical surface P 1 . According to this dimple 26 , the air in a sufficient amount flows in toward the center thereof. This dimple 26 is responsible for the flight performance.

In FIG. 7( a ), what is indicated by a two-headed arrow D 1 is the diameter of the first edge E 1 ; what is indicated by a two-headed arrow D 2 is the diameter of the second edge E 2 ; what is indicated by a two-headed arrow D 3 is the diameter of the third edge E 3 ; what is indicated by a two-headed arrow D 4 is the diameter of the fourth edge E 4 ; what is indicated by a two-headed arrow D 5 is the diameter of the fifth edge E 5 ; and what is indicated by a two-headed arrow D 6 is the diameter of the sixth edge E 6 . The diameter D 1 is greater than the diameter D 2 . The diameter D 2 is greater than the diameter D 3 . The diameter D 3 is greater than the diameter D 4 . The diameter D 4 is greater than the diameter D 5 . The diameter D 5 is greater than the diameter D 6 .

What is indicated by a two-headed arrow L 6 in FIG. 7( b ) is the height of the sixth phantom spherical surface P 6 . Herein, the height L 6 is defined as a distance between the plane including the sixth edge E 6 and the top of the sixth phantom spherical surface P 6 . In light of possible air flow in a sufficient amount toward the center of the dimple 26 , it is preferred that the height L 6 is smaller than the depth L 1 (see, FIG. 4) .

FIG. 8( a ) is a plan view illustrating a part of a golf ball according to yet another embodiment of the present invention; and FIG. 8( b ) is a cross-sectional view of the same. In this FIG. 8 , a dimple 32 is depicted. What is indicated by a chain double-dashed line 34 in FIG. 8( b ) is a ball phantom sphere.

This dimple 32 has a first curved face S 1 , a second curved face S 2 , a third curved face S 3 , a fourth curved face S 4 , a fifth curved face S 5 , a sixth curved face S 6 , a seventh curved face S 7 , a first edge E 1 , a second edge E 2 , a third edge E 3 , a fourth edge E 4 , a fifth edge E 5 , a sixth edge E 6 and a seventh edge E 7 . The first edge E 1 is a boundary between a land 36 and the first curved face S 1 . The second edge E 2 is a boundary between the first curved face S 1 and the second curved face S 2 . The third edge E 3 is a boundary between the second curved face S 2 and the third curved face S 3 . The fourth edge E 4 is a boundary between the third curved face S 3 and the fourth curved face S 4 . The fifth edge E 5 is a boundary between the fourth curved face S 4 and the fifth curved face S 5 . The sixth edge E 6 is a boundary between the fifth curved face S 5 and the sixth curved face S 6 . The seventh edge E 7 is a boundary between the sixth curved face S 6 and the seventh curved face S 7 . The first edge E 1 , the second edge E 2 , the third edge E 3 , the fourth edge E 4 , the fifth edge E 5 , the sixth edge E 6 and the seventh edge E 7 are circular. As is clear from FIG. 8( a ), the second edge E 2 , the third edge E 3 , the fourth edge E 4 , the fifth edge E 5 , the sixth edge E 6 and the seventh edge E 7 are disposed concentrically with the first edge E 1 .

The first curved face S 1 makes a part of a first phantom spherical surface P 1 . The first curved face S 1 is convex downward. The first curved face S 1 is ring-shaped. The first curved face S 1 is inclined downward from the first edge E 1 toward the center of the dimple 32 . The second curved face S 2 makes a part of a second phantom spherical surface P 2 . The second curved face S 2 is convex upward. The second curved face S 2 is ring-shaped. The second curved face S 2 is inclined upward from the second edge E 2 toward the center of the dimple 32 . The third curved face S 3 makes a part of a third phantom spherical surface P 3 . The third curved face S 3 is convex downward. The third curved face S 3 is ring-shaped. The third curved face S 3 is inclined downward from the third edge E 3 toward the center of the dimple 32 . The fourth curved face S 4 makes a part of a fourth phantom spherical surface P 4 . The fourth curved face S 4 is convex upward. The fourth curved face S 4 is ring-shaped. The fourth curved face S 4 is inclined upward from the fourth edge E 4 toward the center of the dimple 32 . The fifth curved face S 5 makes a part of a fifth phantom spherical surface P 5 . The fifth curved face S 5 is convex downward. The fifth curved face S 5 is ring-shaped. The fifth curved face S 5 is inclined downward from the fifth edge E 5 toward the center of the dimple 32 . The sixth curved face S 6 makes a part of a sixth phantom spherical surface P 6 . The sixth curved face S 6 is convex upward. The sixth curved face S 6 is ring-shaped. The sixth curved face S 6 is inclined upward from the sixth edge E 6 toward the center of the dimple 32 . The seventh curved face S 7 makes a part of a seventh phantom spherical surface P 7 . The seventh curved face S 7 is convex downward. The seventh curved face S 7 is bowl-shaped. The seventh curved face S 7 is inclined downward from the seventh edge E 7 toward the center of the dimple 32 .

According to this dimple 32 , the air that flows toward the center of the dimple 32 collides with the third edge E 3 , the fifth edge E 5 and the seventh edge E 7 . Due to this collision, the air flow is disrupted. According to the golf ball having this type of dimple 32 , the drag is suppressed. This golf ball is excellent in the flight performance.

In this dimple 32 , the first curved face S 1 , the second curved face S 2 , the third curved face S 3 , the fourth curved face S 4 , the fifth curved face S 5 , the sixth curved face S 6 and the seventh curved face S 7 are not protruded upward from the plane including the first edge E 1 . In addition, the first curved face S 1 , the second curved face S 2 , the third curved face S 3 , the fourth curved face S 4 , the fifth curved face S 5 , the sixth curved face S 6 and the seventh curved face S 7 are not protruded downward from the first phantom spherical surface P 1 . According to this dimple 32 , the air in a sufficient amount flows in toward the center thereof. This dimple 32 is responsible for the flight performance.

In FIG. 8( a ), what is indicated by a two-headed arrow D 1 is the diameter of the first edge E 1 ; what is indicated by a two-headed arrow D 2 is the diameter of the second edge E 2 ; what is indicated by a two-headed arrow D 3 is the diameter of the third edge E 3 ; what is indicated by a two-headed arrow D 4 is the diameter of the fourth edge E 4 ; what is indicated by a two-headed arrow D 5 is the diameter of the fifth edge E 5 ; what is indicated by a two-headed arrow D 6 is the diameter of the sixth edge E 6 ; and what is indicated by a two-headed arrow D 7 is the diameter of the seventh edge E 7 . The diameter D 1 is greater than the diameter D 2 . The diameter D 2 is greater than the diameter D 3 . The diameter D 3 is greater than the diameter D 4 . The diameter D 4 is greater than the diameter D 5 . The diameter D 5 is greater than the diameter D 6 . The diameter D 6 is greater than the diameter D 7 .

What is indicated by a two-headed arrow L 7 in FIG. 8( b ) is the depth of the seventh phantom spherical surface P 7 . Herein, the depth L 7 is defined as a distance between the plane including the seventh edge E 7 and the deepest point of the seventh phantom spherical surface P 7 . In light of possible air flow in a sufficient amount toward the center of the dimple 32 , it is preferred that the depth L 7 is smaller than the depth L 1 (see, FIG. 4) .

A rubber composition was obtained by kneading 100 parts by weight of polybutadiene (trade name “BR-11”, available from JSR Corporation), 24.5 parts by weight of zinc diacrylate, 10 parts of zinc oxide, 15 parts by weight of barium sulfate and 0.8 part by weight of dicumyl peroxide. This rubber composition was placed into a mold having upper and lower mold half each having a hemispherical cavity, and heated at 160° C. for 20 minutes to obtain a core having a diameter of 38.1 mm. On the other hand, a resin composition was obtained by kneading 50 parts by weight of an ionomer resin (trade name “Himilan 1605”, available from Du Pont-MITSUI POLYCHEMICALS Co., Ltd.), 50 parts by weight of another ionomer resin (trade name “Himilan 1706”, available from Du Pont-MITSUI POLYCHEMICALS Co., Ltd.) and 3 parts of titanium dioxide. The aforementioned core was placed into a mold having numerous pimples on the inner surface, followed by injection of the aforementioned resin composition around the core according to injection molding to form a cover having a thickness of 2.3 mm. Numerous dimples having a shape inverted from the shape of the pimple were formed on the cover. Paint was applied on this cover to give a golf ball of Example 1 having a diameter of 42.7 mm and a weight of about 45.4 g. This golf ball had a compression (ATTI) of about 85. Specifications of the dimples of this golf ball are presented in Table 2 below.

Examples 2 to 4 and Comparative Examples 1 to 2

In a similar manner to Example 1 except that the mold was changed to alter specifications of the dimples as presented in Table 1 to Tale 5 below, golf balls of Examples 2 to 4 and Comparative Examples 1 to 2 were obtained.

[Flight Distance Test]

A driver having a metal head (trade name “XXIO”, available from Sumitomo Rubber Industries, Ltd.; shaft hardness: X, loft angle: 9°) was attached to a swing machine, available from True Temper Co. Then the golf ball was hit under the condition of the head speed being 49 m/sec, the launch angle being approximately 11° and giving the initial spin rate of approximately 3000 rpm. Accordingly, distance from the launching point to the point where the ball stopped was measured. Under the condition during the test, it was almost windless. Mean values of 20 times measurement are shown in Table 6 below.

As is shown in Table 6, the golf balls of Examples are excellent in the flight performance. Therefore, advantages of the present invention are clearly suggested by these results of evaluation.

The dimples as described hereinabove are suitable for not only two-piece golf balls, but also one-piece golf balls, multi-piece golf balls and wound golf balls. The foregoing description is just for an illustrative example, therefore, various modifications can be made in the scope without departing from the principles of the present invention.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.