CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2020-017043 filed in Japan on Feb. 4, 2020, the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a golf ball which has at least a core and a cover and is intended for use by amateur golfers lacking a fast head speed.

BACKGROUND ART

Numerous golf balls intended to satisfy the amateur golfer in terms of flight performance and feel at impact have hitherto been developed in the golf ball market for amateur golfers. For example, JP-A H8-280845 describes a golf ball in which the amount of compressive deformation by the ball when subjected to a final load of 5 kgf from an initial load state of 0.2 kgf is used as an indicator of the effects on the ball properties when a small impact force acts upon the ball, this value being set in the range of from 0.26 to 0.40 mm. However, this golf ball is a spin-type ball that is targeted primarily at the spin rate on approach shots and does not fully satisfy the flight performance desired on shots with a driver.

In addition, a variety of functional, multi-piece solid golf balls in which the ball has a multilayer construction and the surface hardnesses of the respective layers—i.e., the core, intermediate layer and cover (outermost layer)—are optimized have been described. These include the multi-piece solid golf balls disclosed in JP-A 2005-211656, JP-A 2007-319666, JP-A 2001-218875, JP-A 2005-218858, JP-A 2008-212682 and JP-A 2009-195670. The golf balls disclosed in these patent publications are three-piece solid golf balls in which a material softer than the cover is used in the intermediate layer, and which provide an excellent flight performance even when used by amateur golfers lacking a fast head speed. However, these prior-art golf balls do not optimize, for example, the amount of compressive deformation when the ball is subjected to a final load of 50 kgf from an initial load state of 5 kgf and the amount of compressive deformation when the ball is subjected to a final load of 90 kgf from an initial load state of 5 kgf. That is, no attention has been paid to how the golf ball properties are affected by the magnitude of the impact forces acting on the ball, and so there remains room for improvement in obtaining a good flight performance and a good feel at impact in golf ball products for the amateur golfer.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a golf ball for amateur golfers which has an excellent flight when hit by the average golfer whose head speed is not very high and which also has a good, soft feel at impact.

As a result of extensive investigations, we have focused on the relationship, in golf balls having a core and a cover, between the magnitude of the impact forces applied to the golf ball and the ball characteristics of flight and feel. We have discovered in particular that by specifying, in the amount of compressive deformation by the golf ball, the compressive deformation B when the ball is subjected to a final load of 50 kgf from an initial load state of 5 kgf and the compressive deformation C when the ball is subjected to a final load of 90 kgf from an initial load state of 5 kgf, and by also specifying the relationships between the Shore C hardnesses at the core center, the core surface and a position 3 mm inside the core surface, a ball can be obtained that enables golfers lacking a high head speed to achieve a satisfactory flight performance on full shots with a driver (W #1) or an iron, that has a good, soft feel at impact, and that moreover has a good durability to cracking.

Accordingly, the invention provides a golf ball having a core and a cover, wherein the ball has a compressive deformation B when subjected to a final load of 50 kgf from an initial load state of 5 kgf that is from 1.30 to 1.80 mm and a compressive deformation C when subjected to a final load of 90 kgf from an initial load state of 5 kgf that is from 2.45 to 2.90 mm, and the core has a hardness profile that satisfies the following conditions:
Cs−Cc≥20  (1)
Cs−Cs−3≤5.0,  (2)
wherein Cs is the Shore C hardness at a surface of the core, Cs−3 is the Shore C hardness at a position 3 mm inside the core surface and Cc is the Shore C hardness at a center of the core.

In a preferred embodiment of the golf ball of the invention, the compressive deformation A of the ball when subjected to a final load of 5 kgf from an initial load state of 0.2 kgf is 0.18 mm or less.

In another preferred embodiment of the inventive golf ball, the compressive deformation D of the ball when subjected to a final load of 130 kgf from an initial load state of 10 kgf is from 3.10 to 3.80 mm.

In yet another preferred embodiment, the compressive deformation E of the ball when subjected to a final load of 30 kgf from an initial load state of 5 kgf is from 0.68 to 1.05 mm.

In still another preferred embodiment, the ratio D/A between compressive deformation D and compressive deformation A is at least 18.0.

In a further preferred embodiment, the ratio DB between compressive deformation D and compressive deformation B is from 2.02 to 2.40.

In a still further preferred embodiment, the ratio D/C between compressive deformation D and compressive deformation C is from 1.20 to 1.31.

In a yet further preferred embodiment, the ratio D/E between compressive deformation D and compressive deformation E is from 3.50 to 4.10.

In another preferred embodiment, the core of the inventive golf ball is formed of a rubber composition containing (a) a base rubber, (b) a co-crosslinking agent which is an α,β-unsaturated carboxylic acid and/or a metal salt thereof, (c) a crosslinking initiator, and (d) a lower alcohol having a molecular weight below 200. In this preferred embodiment, component (d) is included in an amount that may be from 0.5 to 5 parts by weight per 100 parts by weight of the base rubber (a). Component (d) may be a monohydric, dihydric or trihydric alcohol. In particular, component (d) may be butanol, glycerol, ethylene glycol or propylene glycol.

In still another preferred embodiment, the golf ball further includes, between the core and the cover, at least an envelope layer and an intermediate layer, and has a construction of three or more layers that includes the core, the intermediate layer and the cover.

Advantageous Effects of the Invention

The golf ball of the invention has an excellent flight performance when hit by golfers whose head speeds are not that high, a good, soft feel at impact, and moreover a good durability to cracking, making it highly suitable for use by amateur golfers.

