Patent Application
20250170455
This non-provisional application claims priority under 35 U.S.C. § 119 (a) on Patent Application No. 2023-201378 filed in Japan on Nov. 29, 2023, the entire contents of which are hereby incorporated by reference.
The present invention relates to a golf ball in which a large number of dimples are formed on a ball surface, and more specifically, relates to a golf ball that achieves both reduction of a distance only at high head speeds and stabilization of a trajectory by focusing on aerodynamic properties and a unique cross-sectional shape of the dimples formed on the ball surface.
In order to improve a distance of a golf ball, it is generally well known that air resistance during flight is reduced by dimples formed on a ball surface to improve aerodynamic properties. For example, a golf ball described in Patent Document 1 proposes that a shape of a wall surface close to a bottom portion in a dimple cross-section is optimized to optimize a trajectory of the ball when hit and increase the distance. Patent Document 2 discloses a golf ball in which dimples are formed by at least two different cross-sectional shapes, and the dimple shape is three-dimensionally optimized to dramatically improve aerodynamic properties. However, these golf balls are related to technologies focusing on improvement of the distance, and do not focus on the fact that the trajectory of the ball is stabilized and stable flight performance is obtained.
In addition, Patent Document 3 describes that a change amount ΔH of a depth every 20% of a distance from a dimple edge to a center of the dimple is optimized at a ratio of a depth in a dimple region of from 20 to 100% of the above distance in order to reduce variation of the flight and improve aerodynamic performance. However, this technique does not focus on an edge angle with respect to the dimple depth, and although it is shown that the distance of the ball increases, it is not shown that the trajectory is stabilized.
In March 2022, manufacturers of golf balls were notified by the Royal and Ancient Golf Club of St Andrews (hereinafter, R & A) and the United States Golf Association (hereinafter, USGA) that the R & A and USGA would start research to suppress a distance by long hitters by changing test conditions for the Overall Distance Standard (hereinafter, ODS) of golf balls in the future. For this reason, it is preferable to provide a golf ball that does not simply reduce distance, but while making a distance for reducing a distance on shots with a driver by long hitters longer, by making a distance for reducing a distance on shots with a driver by average hitters shorter, reduces an influence on play other than reducing the distance on shots with a driver by long hitters.
A golf ball is proposed in the following Patent Documents 4 to 7 in which, by combining a design of low-trajectory dimples with the ball surface, the distance of the ball is greatly reduced at high head speeds, and at low head speeds, a decrease in the distance is suppressed as much as possible in spite of the reduction at high head speeds.
However, the golf ball of Patent Documents 4 to 7 has a distance that is reduced excessively compared to shots with a driver at high head speeds, and has not been able to sufficiently stabilize the trajectory.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a golf ball that reduces only a distance of the ball on shots with a driver (W #1) at high head speeds, and sufficiently stabilizes a trajectory of the ball after shots with a driver (W #1).
As a result of intensive studies to achieve the above object, the present inventors have focused on optimizing a balance between a definition of an edge angle in a dimple cross-section of the golf ball and aerodynamic properties of dimples. As a specific means thereof, the inventors have focused attention on designating an optimum shape of the edge angle with respect to a dimple depth in a dimple cross-sectional shape, and specifically, when edge angles at points where depths are 10%, 20%, and 30% in the cross-section of one dimple are denoted by ED1, ED2, and ED3, respectively, dimples with the cross-sectional shape satisfying the following condition (1):
The present inventors have found that a distance for reducing a distance on shots with a driver by long hitters may be increased, a distance for reducing a distance on shots with a driver by average hitters may be made shorter than the reduced distance on shots with a driver by long hitters, and stability of aerodynamic performance due to a dimple action may be improved to ensure stability of flight, and thus have completed the present invention.
The above “long hitters” mean users whose head speed on shots with a driver (W #1) is at least about 50 m/s, and the above “average hitters” mean users whose head speed on shots with a driver (W #1) is not more than about 45 m/s.
Accordingly, the present invention provides a golf ball in which a large number of dimples are formed on a ball surface, and when edge angles at points where depths are 10%, 20%, and 30% in a cross-section of one dimple are denoted as ED1, ED2, and ED3, respectively, dimples with a cross-sectional shape satisfying the following condition (1):
In a preferred embodiment of the golf ball according to the invention, the dimples satisfying the above condition (1) account for at least 50% of the total number of dimples.
In another preferred embodiment of the inventive golf ball, in the dimples satisfying the above condition (1), when an edge angle at a point where the depth is 40% is further denoted by ED4, the following condition is satisfied:
In yet another preferred embodiment of the inventive golf ball, in the dimples satisfying the above condition (1), when an edge angle at a point where the depth is 50% is further denoted by ED5, the following condition is satisfied:
In still another preferred embodiment of the inventive golf ball, in the dimples satisfying the above condition (1), when an edge angle at a point where the depth is 50% is further denoted by ED5, the following condition is satisfied:
In a further preferred embodiment of the inventive golf ball, in the dimples satisfying the above condition (1), when an edge angle at a point where the depth is 50% is further denoted by ED5, the following condition is satisfied:
In a yet further preferred embodiment of the inventive golf ball, in the dimples satisfying the above condition (1), when an edge angle at a point where the depth is 60% is further denoted by ED6, the following condition is satisfied:
In still another preferred embodiment of the inventive golf ball, in the dimples satisfying the above condition (1), when edge angles at points where the depth is 50% and 60% are denoted by ED5 and ED6, respectively, ED1, ED2, ED3, ED5, and ED6 are all not more than 90 degrees.
In another preferred embodiment of the inventive golf ball, the value of (A2+A3)/2 is from 0.670 to 0.783.
In yet another preferred embodiment of the inventive golf ball, the value of A2 is from 0.635 to 0.750, and the value of A3 is 0.695 to 0.815.
In still another preferred embodiment of the inventive golf ball, the number of types of the dimples satisfying the above condition (1) is at least three.
In a further preferred embodiment of the inventive golf ball, the number of the dimples satisfying the above condition (1) is from 250 to 500.
In a yet further preferred embodiment of the inventive golf ball, a coverage ratio of the dimples satisfying the above condition (1) is from 60 to 90%.
In yet another preferred embodiment of the inventive golf ball, a total volume of the dimples is from 300 to 500 mm3.
The golf ball of the present invention does not simply reduce distance, but while making the distance for reducing the distance on shots with a driver by long hitters longer, by making the distance for reducing a distance on shots with a driver by average hitters shorter than the reduced distance by long hitters, may reduce an influence on play overall while reducing the distance on shots with a driver by long hitters. In addition, the golf ball of the present invention may provide a stable trajectory and may improve the stability of flight.
Hereinafter, the present invention is described in more detail.
One of the characteristics of the golf ball of the present invention is that a large number of dimples are formed on a ball surface to define a change in an edge angle of a dimple cross-section, as described later.
The dimples are usually formed on a surface of a cover (outermost layer) of the ball simultaneously with molding such as injection molding of a resin material of the cover. Further, usually, a coating is applied to the surface of the cover to complete the golf ball. The dimples in the present invention mean dimples formed on the surface of this completed golf ball. Therefore, numerical values such as a diameter and a depth of the dimples described later are numerical values of the dimples in the completed golf ball.
The number of the above dimples is not particularly limited, although the number of the dimples is preferably at least 250 and more preferably at least 300, and the upper limit is preferably not more than 500 and more preferably not more than 450.
As a shape of the dimples as viewed from a flat plane (shape in plan view), one type or a combination of at least two types such as a circular shape, various polygonal shapes, a dewdrop shape, an ellipse, and other non-circular shapes may be appropriately used. In the present invention, it is particularly preferable to use at least three types of dimples in combination.
The diameter of the dimples (diagonal length in a polygon) is not particularly limited, although the diameter may be preferably at least 2.0 mm, and more preferably at least 2.5 mm. The upper limit is also not particularly limited, although the upper limit may be preferably not more than 6.0 mm, and more preferably not more than 5.5 mm.
The depth at a deepest point of the dimples is not particularly limited, although the depth may be preferably from 0.05 to 0.5 mm, and more preferably from 0.09 to 0.4 mm.
A method of arranging the dimples is not particularly limited, although a method using a geometric arrangement pattern of regular polyhedrons such as a regular octahedron, a regular 12-hedron, and a regular 20-hedron, or a method of arranging the dimples so as to be rotationally symmetric about a pole point of the ball such as three-fold symmetry, four-fold symmetry, five-fold symmetry, and six-fold symmetry may be suitably employed.
A ratio (dimple surface coverage ratio) SR value (%) of a total surface area of a virtual spherical surface circumscribed by an edge portion of each dimple is usually at least 60% and preferably at least 80%, and the upper limit is preferably not more than 90%. If the SR value falls outside of the above range, an appropriate trajectory may not be attainable and a distance may decrease.
A total dimple space volume formed downward from a flat plane circumscribed by the edge of the dimple is preferably from 300 to 500 mm3. In addition, a ratio (volume occupancy ratio) VR of the total dimple space volume to a volume of a virtual sphere assuming that no dimple exists on the ball surface is not particularly limited, although the ratio may be usually at least 0.7%, preferably at least 0.75%, and more preferably at least 0.8%. The upper limit is also not particularly limited, although the upper limit may be not more than 1.5%, preferably not more than 1.45%, and more preferably not more than 1.4%. By setting the dimple space occupancy ratio VR within the above ranges, it is possible to prevent the ball from being blown up too much when the ball is hit with a club such as a driver that gains distance, and to prevent the ball from dropping without rising.
In the present invention, when the edge angles at points where the depths are 10%, 20%, and 30% in the cross-section of one dimple are denoted by ED1, ED2, and ED3, respectively, dimples having a cross-sectional shape satisfying the following condition (1):
are included. As described above, in the present invention, a stable trajectory may be obtained by specifying optimum shapes of the edge angles with respect to the dimple depth.
Here, the above-described “cross-section of a dimple” means a cross-section when the dimple is vertically cut so as to pass through the deepest portion (bottom central portion) of the dimple.
The above-described edge angles are defined as follows. That is, as illustrated in
Specifically,
In a measurement method of ED1, first, a tangent (T1) at a point P1 having a dimple depth of 10% is drawn, an intersection between the tangent and the virtual spherical surface Q is obtained, and a line is drawn in a horizontal direction from the intersection (straight line E1). ED1 is an angle formed by the tangent line T1 and the straight line E1.
In a measurement method of ED2, first, a tangent (T2) at a point P2 having a dimple depth of 20% is drawn, an intersection between the tangent and the virtual spherical surface Q is obtained, and a line is drawn in the horizontal direction from the intersection (straight line E2). ED2 is an angle formed by the tangent line T2 and the straight line E2.
In a measurement method of ED3, first, a tangent (T3) at a point P3 having a dimple depth of 30% is drawn, an intersection between the tangent and the virtual spherical surface Q is obtained, and a line is drawn in the horizontal direction from the intersection (straight line E3). ED3 is an angle formed by the tangent line T3 and the straight line E3.
A ratio of the dimples having a cross-sectional shape satisfying the above condition (1) is at least 10%, preferably at least 30%, more preferably at least 50%, and even more preferably at least 80% with respect to 100% of a total number of the dimples formed on the ball surface.
The number of types of dimples having a cross-sectional shape satisfying the above condition (1) is preferably at least three. Even if the cross-sectional shapes are the same, if those having different diameters and depths are included, they are treated as different types of dimples.
As shown in the above condition (1), the edge angle ED2 at the point where the dimple depth is 20% is larger than the edge angles ED1 and ED3 at the points where the dimple depths are 10% and 30%. It is estimated that, in the dimple cross-sectional shape, an effect of the dimple is easily exhibited stably by an action of smoothing a flow of air entering the inside of the dimple, variation in the ball trajectory is reduced, and a more stable trajectory is obtained.
The edge angle ED3 at the point where the dimple depth is 30% is preferably larger than the edge angle ED1 at the point where the dimple depth is 10% in order to further stabilize the trajectory. In addition, each of the above edge angles ED1, ED2, and ED3 is preferably not more than 90 degrees.
Further, when the edge angle at a point where the dimple depth is 40% is denoted by ED4, the following condition is preferably satisfied:
ED1≥ED4.
Furthermore, in order to further stabilize the trajectory, when the edge angle at a point where the dimple depth is 50% is denoted by ED5, the edge angle ED5 is preferably not more than 90 degrees, and at least one of the following three conditions is preferably satisfied.
Further, when the edge angle at a point where the dimple depth is 60% is denoted by ED6, the edge angle ED6 is preferably not more than 90 degrees, and the following condition is preferably satisfied.
As described above, the present invention focuses on the change in the dimple edge angle within a range where the dimple depth is from 10 to 60%, and in particular, the optimum shapes of the dimple edge angles of 10%, 20%, and 30% in a range relatively close to the edge of the dimple are achieved, whereby aerodynamic performance is stabilized by an action of the dimple, and eventually the trajectory is stabilized.
In the golf ball of the present invention, when a ratio (CL1/CD1) of a lift coefficient CL1 at a Reynolds number of 218,000 and a spin rate of 2,800 rpm to a drag coefficient CD1 is denoted by A1, a ratio (CL2/CD2) of a lift coefficient CL2 at a Reynolds number of 184,000 and a spin rate of 2,900 rpm to a drag coefficient CD2 is denoted by A2, and a ratio (CL3/CD3) of a lift coefficient CL3 at a Reynolds number of 158,000 and a spin rate of 3,100 rpm to a drag coefficient CD3 is denoted by A3, the dimples are appropriately designed to satisfy the following two conditions:
In Equation (I) above, ρ represents the density of a fluid, v represents the average velocity of an object relative to the flow of the fluid, L represents a characteristic length, and μ represents the viscosity coefficient of the fluid.
In the present invention, when a ratio CL1/CD1 of a lift coefficient CL1 at a Reynolds number of 218000 and a spin rate of 2800 rpm to a drag coefficient CD1 is defined as A1, a ratio CL2/CD2 of a lift coefficient CL2 at a Reynolds number of 184000 and a spin rate of 2900 rpm to a drag coefficient CD2 is defined as A2, and a ratio CL3/CD3 of a lift coefficient CL3 at a Reynolds number of 158000 and a spin rate of 3100 rpm to a drag coefficient CD3 is defined as A3.
The condition under which the lift coefficient CL1 and the drag coefficient CD1 are measured is described, that is, Reynolds number 218000 and spin rate 2800 rpm. This high-speed condition corresponds to a condition provided by a long hitter with a driver (W #1), this Reynolds number corresponds to a ball speed when a golf ball is driven out at a head speed (HS) of 54 m/s, and the spin rate 2800 rpm is an average spin condition of a player with a head speed (HS) of 54 m/s.
The condition under which the lift coefficient CL2 and the drag coefficient CD2 are measured is described, that is, Reynolds number 184000 and spin rate 2900 rpm. This middle-speed condition corresponds to a condition provided by an average hitter with a driver (W #1) at a head speed (HS) of 45 m/s, this Reynolds number corresponds to a ball speed when a golf ball is driven out at a head speed (HS) of 45 m/s, and the spin rate 2900 rpm is an average spin condition of a player with a head speed (HS) of 45 m/s.
The condition under which the lift coefficient CL3 and the drag coefficient CD3 are measured is described, that is, Reynolds number 158000 and spin rate 3100 rpm. This low-speed condition corresponds to a condition provided by an average hitter with a driver (W #1) at a head speed (HS) of 40 m/s, this Reynolds number corresponds to a ball speed when a golf ball is driven out at a head speed (HS) of 40 m/s, and the spin rate 3100 rpm is an average spin condition of a player with a head speed (HS) of 40 m/s.
The ratio between the lift coefficient CL1 and the drag coefficient CD1, that is, the value of CL1/CD1=A1 is at least 0.590, preferably at least 0.595, and more preferably at least 0.600, and an upper limit thereof is not more than 0.655, preferably not more than 0.640, and more preferably not more than 0.627. If this value is too large, the effect of reducing the distance made by a long hitter with a driver (W #1) is insufficient, and the distance may be too large. On the other hand, if the above value is too small, the actual distance may be lower than the intended distance.
The ratio between the lift coefficient CL2 and the drag coefficient CD2, that is, the value of CL2/CD2=A2, is preferably at least 0.635, more preferably at least 0.645, and even more preferably at least 0.660, and an upper limit thereof is preferably not more than 0.750, more preferably not more than 0.740, and even more preferably not more than 0.730. If this value is too low, it becomes difficult for the ball to carry on shots with a driver (W #1) at a head speed (HS) of 45 m/s, and an intended total distance may not be attainable. On the other hand, if this value is too high, the trajectory may blow up on shots with a driver (W #1) at a head speed of 45 m/s, and the intended distance may not be attainable.
The ratio between the lift coefficient CL3 and the drag coefficient CD3, that is, the value of CL3/CD3=A3, is preferably at least 0.695, more preferably at least 0.710, and even more preferably at least 0.722, and an upper limit thereof is preferably not more than 0.815, more preferably not more than 0.810, and even more preferably not more than 0.800. If this value is too low, it becomes difficult for the ball to carry on shots with a driver (W #1) at a head speed (HS) of 40 m/s, and the intended total distance may not be attainable. On the other hand, if this value is too high, the trajectory may blow up on shots with a driver (W #1) at a head speed of 40 m/s, and the intended distance may not be attainable.
The average value of the above A2 and A3, that is, the value of (A2+A3)/2 is at least 0.670, preferably at least 0.680, and more preferably at least 0.690, and an upper limit thereof is preferably not more than 0.783, more preferably not more than 0.775, and even more preferably not more than 0.765. If this value is too low, it becomes difficult for the ball to carry on shots with a driver (W #1) by average hitters, and the intended total distance may not be attainable. On the other hand, if the above value is too high, the trajectory may be blown up on shots with a driver (W #1) by average hitters, and the intended distance may not be attainable.
For preparation of a mold for forming the above dimple, a method of directly three-dimensionally cutting out an entire surface shape in a reversing master mold using 3DCAD/CAM, a method of directly three-dimensionally cutting out a cavity portion (inner wall surface) of the mold for molding, or the like may be adopted.
Similarly to a normal golf ball, the ball surface may be subjected to various types of coating, such as white enamel coating, epoxy coating, and clear coating. In this case, it is desirable to perform coating uniformly without unevenness so that the cross-sectional shape of the above dimple is not impaired.
The golf ball of the present invention is not particularly limited in terms of its internal structure, and may be a solid golf ball such as a one-piece golf ball, a two-piece golf ball, or a multi-piece golf ball having a structure of at least three layers, or may be a wound golf ball, and may be applied to any type of golf ball.
Ball specifications such as the weight and the diameter of the golf ball may be appropriately set according to the Rules of Golf.
Hereinafter, the present invention is specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.
A core having a diameter of 38.6 mm is prepared. Compounding of the cores is common to all Examples and Comparative Examples. As a base rubber, 20 parts by weight of polybutadiene A (trade name “BR51” manufactured by ENEOS Materials Corporation), 80 parts by weight of polybutadiene B (trade name “BR730” manufactured by ENEOS Materials Corporation), 29.5 parts by weight of zinc acrylate (manufactured by Wako Pure Chemical Corporation), 0.6 parts by weight of dicumyl peroxide (trade name “Percumyl D” manufactured by NOF Corporation) as an organic peroxide, 0.1 parts by weight of 2,2-methylenebis(4-methyl-6-butylphenol) (trade name “Nocrac NS-6” manufactured by Ouchi Shinko Chemical Industrial Co., Ltd.) as an antioxidant, 19.3 parts by weight of zinc oxide (trade name “Grade 3 Zinc Oxide” manufactured by Sakai Chemical Industry Co., Ltd.), and 0.3 parts by weight of pentachlorothiophenol zinc salt (manufactured by Wako Pure Chemical Corporation) as an organosulfur compound are blended. A rubber composition is vulcanized at a temperature of 155° C. for a time of 15 minutes. A specific gravity of the blend is 1.138.
Next, a resin material for an intermediate layer is injection molded around the core having a diameter of 38.6 mm to prepare an intermediate layer-encased sphere having the intermediate layer having a thickness of 1.25 mm. The resin material of the intermediate layer is common to all Examples and Comparative Examples, and trade names “Himilan 1605”, “Himilan 1557”, and “Himilan 1706” (ionomer resins manufactured by Dow-Mitsui Polychemicals Co., Ltd.) are blended at 50:12:38 (weight ratio) respectively, and 1.1 parts by weight of trimethylolpropane (manufactured by Tokyo Chemical Industry Co., Ltd.) is blended per 100 parts by weight of a total of the ionomer resins.
Next, an ether-type thermoplastic polyurethane (trade name “PANDEX” manufactured by DIC Covestro Polymer Ltd., Shore D hardness 43, and rebound resilience 61%) is used as the resin material of the cover (outermost layer). Using another mold for injection molding, the above-described resin material is injection-molded around the above-described intermediate layer-encased sphere to prepare a three-piece golf ball having a diameter of 42.7 mm and the outermost layer having a thickness of 0.8 mm. At this time, a large number of predetermined dimples described below are formed on the cover surface.
Next, a golf ball of each Example in which a coating layer (coating film) having a thickness of 15 μm is formed is prepared by using an air spray gun to apply a coating composition containing a polyester polyol (main component) and an isocyanate curing agent to the surface of the outermost layer on which a large number of dimples are formed in a coating formulation listed in Table 1 below.
As for details of the dimples of the Examples and Comparative Examples, as shown in
In addition, Table 7 below shows the ratio CL1/CD1=A1 of the lift coefficient CL1 at the Reynolds number of 218,000 and the spin rate of 2,800 rpm to the drag coefficient CD1, the ratio CL2/CD2=A2 of the lift coefficient CL2 at the Reynolds number of 184,000 and the spin rate of 2,900 rpm to the drag coefficient CD2, and the ratio CL3/CD3=A3 of the lift coefficient CL3 at the Reynolds number of 158,000 and the spin rate of 3,100 rpm to the drag coefficient CD3 of the balls with the dimples formed on their cover surface in Examples 1 to 3 and Comparative Examples 1 to 3. These lift coefficients and drag coefficients are measured in accordance with the Indoor Test Range (ITR) defined by USGA.
[Evaluation of Flight (1) (W #1, HS 54 m/s)]
A driver is mounted on a golf swing robot, and a distance traveled (total) by a ball when struck at a head speed (HS) of 54 m/s is measured. The club used is a TOUR B XD-5 Driver/loft angle 9.5° (2017 model) manufactured by Bridgestone Sports Co., Ltd. and is evaluated according to the following rating criteria.
In addition, a standard deviation of the above distance (total) is measured and
A driver is mounted on the golf swing robot, and the distance traveled (total) by the ball when struck at a head speed (HS) of 45 m/s is measured. The club used is a J015 Driver/loft angle 9.5° (2016 model) manufactured by Bridgestone Sports Co., Ltd. and is evaluated according to the following rating criteria.
In addition, a standard deviation of the above distance (total) is measured and evaluated according to the following rating criteria.
A driver is mounted on the golf swing robot, and the distance traveled (total) by the ball when struck at a head speed (HS) of 40 m/s is measured. The club used is a J015 Driver/loft angle 9.5° (2016 model) manufactured by Bridgestone Sports Co., Ltd. and is evaluated according to the following rating criteria.
In addition, a standard deviation of the above distance (total) is measured and evaluated according to the following rating criteria.
In each of the above ratings, a total score is obtained as a comprehensive evaluation by calculating two points for “Good”, one point for “Fair”, and zero points for “NG”.
As shown in Table 8, with the golf balls of Examples 1 to 3, as compared with each of the Comparative Examples, the distance on shots with a driver (W #1) in a high head speed region may be sufficiently reduced, and the distance with on shots with a driver (W #1) in a low head speed region may be well maintained. In addition, with the golf balls of Examples 1 to 3, the standard deviation of the distances of the golf balls after striking may be made lower than with each of the Comparative Examples, and the flight may be stabilized.
Japanese Patent Application No. 2023-201378 is incorporated herein by reference. Although some preferred embodiments have been described, many modifications and variations may be made thereto in light of the above teachings. It is therefore to be understood that the invention may be practiced otherwise than as specifically described without departing from the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2023-201378 | Nov 2023 | JP | national |
