Multi-Piece Solid Golf Ball

This non-provisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2024-047427 filed in Japan on Mar. 25, 2024, the entire contents of which are hereby incorporated by reference.

The present invention relates to a multi-piece solid golf ball that has a good flight and rises easily on approach shots by amateur users, and seeks to make the game of golf easy, while seeking to comply with new Overall Distance Standard (ODS) rules applicable from January 2028.

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 they would start research to suppress a distance by the longest hitters by changing test conditions for the Overall Distance Standard (hereinafter, ODS) of golf balls in the future. Further, the R&A and the USGA specifically announced the following in December 2023.

“Club head speeds in ODS for rule compliance will be increased from the current 54 m/s to 56 m/s. That is, an influence of 13 to 15 yards (11.9 to 13.7 m) is predicted under striking conditions of the longest hitters.”

This test change is to be implemented from January 2028, but it is said that the current test conditions may be used until Jan. 1, 2030 for recreational golf, which is non-competitive.

Therefore, under the striking conditions of the longest hitters having a high head speed, a time is approaching when the ball as described above with a suppressed distance compared to the current ball is required. On the other hand, as a golf ball for amateur users, it is desired that even a ball in which the above-described distance is suppressed has as long a distance as possible under striking conditions at a head speed of amateur users. In addition, since it is difficult for the ball to rise on approach shots by an amateur user who is non-competitive, making it easy for the ball to rise on approach shots, that is, raising a launch angle, makes it easy for the ball to be regarded as “a ball that makes approach shots easy”. Moreover, while striking the ball softly, amateur users prefer a feel at impact with a sense of bounce and a sense that the ball will fly. It is desirable to develop a ball that satisfies all these characteristics simultaneously for amateur users.

In addition, in the past, some golf balls in which an initial velocity of the ball is set lower than that of a normal game ball have been proposed. Examples of such technical documents include the following Patent Documents 1 to 5.

However, each of the proposed golf balls is a practice ball for a driving range that is simply designed so as not to have a longer distance than the game ball. Therefore, in each of the above-mentioned Patent Documents, good distance performance on shots by amateur users, and the ball rising easily and the feel at impact on approach shots are not considered at all.

Further, Patent Documents 6 to 14 listed below each disclose a golf ball in which, as for dimples formed on the ball surface, a sum of the volumes of the individual dimples, formed below the flat plane circumscribed by the edge of a dimple, to a ball spherical volume on the assumption that the ball has no dimples, that is, a dimple volume occupancy ratio VR, is specified within a predetermined range, whereby a superior distance may be obtained in the low head speed (HS) range while reducing the distance in the high HS range.

However, with respect to the proposed golf balls, the reducing of the distance in the high head speed range is too great, and a distance on full shots by amateur users may not be satisfactory. Further, in each of the above Patent Documents, the ball rising easily and the feel at impact on approach shots are not considered at all.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a multi-piece solid golf ball for complying with new ODS rules applicable from January 2028, in which not only suppression of a distance on shots by the longest hitters is caused to at least a specific level, but also a distance on full shots with a driver (W #1) and an iron by amateur users may be favorably maintained without decreasing, and moreover, a launch angle on approach shots by amateur users becomes high, the ball rises easily, and there is a sense of bounce and a sense that the ball will fly in the feel at impact.

As a result of intensive studies to achieve the above object, the present inventor has found that in a multi-piece solid golf ball including a core, a surrounding layer, an intermediate layer, and a cover, in which a large number of dimples are formed on an outside surface of the cover, the core is formed of a rubber material, the surrounding layer, the intermediate layer, and the cover are formed of a resin material, a relationship between a surface hardness of each sphere of the ball, a surrounding layer-encased sphere, and an intermediate layer-encased sphere satisfies the following conditions (1-a) and (1-b):

(surface hardness of ball)>(surface hardness of surrounding layer-encased sphere)   (1-a)

(surface hardness of ball)>(surface hardness of intermediate layer-encased sphere)   (1-b)

(surface hardness of surrounding layer-encased sphere)<(surface hardness of core)   (2-a)

(surface hardness of intermediate layer-encased sphere)<(surface hardness of core)   (2-b).

Further, when an initial velocity of the ball is set to a range of from 75.0 to 77.724 m/s, 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 following two conditions are satisfied:

The present inventor has found that by designing the multi-piece solid golf ball so as to satisfy the conditions described above, new ODS rules may be complied with, that is, a suppression of a distance on shots by the longest hitters is caused to at least a specific level, a distance on full shots with a driver (W #1) and an iron by amateur users does not decrease, and conversely, the distance on full shots with a driver (W #1) and an iron by amateur users increases. In addition, the present inventor has found that in the above-described designed multi-piece solid golf ball, a launch angle of the ball is increased on approach shots by amateur users, the ball rises easily, the ball becomes a ball that is “easy on approach shots”, and further, on full shots by amateur users, the ball has a feel at impact that has softness, a sense of bounce, and a sense that the ball will fly, and has completed the present invention.

The above “longest hitters” refers to golfers whose head speed on shots with a driver (W #1) is at least 50 m/s, and the above “non-competitive amateur golfers” refers to golfers who have a head speed with a driver (W #1) of not more than 45 m/s and a handicap of approximately 30 or more.

Accordingly, the present invention provides a multi-piece solid golf ball including

a core, a single-layer or multiple-layer surrounding layer, a single-layer intermediate layer, and a single-layer cover, wherein a large number of dimples are formed on an outside surface of the cover, the core is formed of a rubber material, the surrounding layer, the intermediate layer, and the cover are formed of a resin material, a relationship between a surface hardness of each sphere of the ball, a surrounding layer-encased sphere, and an intermediate layer-encased sphere satisfies the following conditions (1-a) and (1-b):

(surface hardness of ball)>(surface hardness of surrounding layer-encased sphere)   (1-a)

(surface hardness of ball)>(surface hardness of intermediate layer-encased sphere)   (1-b)

(surface hardness of surrounding layer-encased sphere)<(surface hardness of core)   (2-a)

(surface hardness of intermediate layer-encased sphere)<(surface hardness of core)   (2-b)

Further, when an initial velocity of the ball is from 75.0 to 77.724 m/s, 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 following two conditions are satisfied:

A further characteristic of the multi-piece solid golf ball is that when a volume occupancy ratio VR of the dimples is from 0.75 to 0.89%, a total volume of the dimples is denoted by D (mm), and a deflection when the ball is compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) is denoted by B (mm), the following condition is satisfied:

In a preferred embodiment of the multi-piece solid golf ball according to the invention, a value of A1 is from 0.590 to 0.613, a value of A2 is from 0.635 to 0.668, and a value of A3 is from 0.695 to 0.734.

In another preferred embodiment of the inventive golf ball, a value of A1 is from 0.614 to 0.655, a value of A2 is from 0.669 to 0.750, and a value of A3 is from 0.735 to 0.815.

In yet another preferred embodiment, a value of (A2+A3)/2 is from 0.670 to 0.783.

In still another preferred embodiment, the cover is formed of an ionomer resin as a chief material.

In a further preferred embodiment, the relationship between the surface hardness of each sphere satisfies the following condition:

(surface hardness of ball)>(surface hardness of intermediate layer-encased sphere)>(surface hardness of surrounding layer-encased sphere)<(surface hardness of core)

In a yet further preferred embodiment, the core has a hardness profile in which, letting the Shore C hardness at a core center be Cc, the Shore C hardness at a midpoint M between the core center and a core surface be Cm, the Shore C hardnesses at positions 2 mm, 4 mm, and 6 mm inward from the midpoint M be Cm-2, Cm-4, and Cm-6 respectively, the Shore C hardnesses at positions 2 mm, 4 mm, and 6 mm outward from the midpoint M be Cm+2, Cm+4, and Cm+6 respectively, and the Shore C hardness at the core surface be Cs, and defining surface areas A to F as follows:

In a still further preferred embodiment, the core has a hardness profile in which the following condition is satisfied:

In another preferred embodiment, the core has a hardness profile in which the following condition is satisfied:

In yet another preferred embodiment, the core has a hardness profile in which the following condition is satisfied:

surface area E >surface area D>surface area C.

In still another preferred embodiment, the core is formed of a rubber composition containing the following components (A) to (D):

Advantageous Effects of the Invention

The multi-piece solid golf ball according to the present invention is a golf ball which is intended to comply with new ODS rules applicable from January 2028, and may increase the distance on full shots with a driver (W #1) and an iron by amateur users while reducing the distance on shots with a driver by the longest hitters. In addition, with the golf ball of the present invention, the launch angle of the ball becomes high on approach shots by amateur users, the ball rises easily, and easiness can be felt on approach shots. Furthermore, the golf ball of the present invention has a feel at impact that combines softness and a sense that the ball will fly on full shots by amateur users.