Golf ball

Abstract

The invention provides a golf ball having a core and a cover of at least one layer. The cover includes an outermost layer and at least one intermediate layer interposed between the outermost layer and the core. The core has a cross-sectional hardness which, letting R (mm) be the radius of the core, A be the JIS-C hardness at the center of the core, B be the JIS-C hardness at a position R / 3 mm from the core center, C be the JIS-C hardness at a position R / 1.8 mm from the core center, D be the JIS-C hardness at a position R / 1.5 mm from the core center, and E be the JIS-C hardness at the surface of the core, satisfies formulas (1) B−A<D−B, (2) C−A≦8, and (3) E−B≧15. The intermediate layer and the outermost layer have a hardness relationship therebetween which satisfies the formula “material hardness of intermediate layer≧material hardness of outermost layer.”

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]This application is a continuation-in-part of copending application Ser. No. 13 / 461,187 filed on May 1, 2012, the entire contents of which are hereby incorporated by reference.BACKGROUND OF THE INVENTION[0002]The present invention relates to a golf ball having a core and a cover of at least one layer, which cover includes an outermost layer and at least one intermediate layer interposed between the outermost layer and the core. More specifically, the invention relates to a golf ball which achieves satisfactory distances both on shots with drivers and on shots with middle irons used by professional golfers and skilled amateurs, and which also has an excellent durability to cracking when repeatedly struck.[0003]Solid golf balls have a relatively simple inner structure composed of a core and a cover, although various golf ball properties such as rebound, feel, spin on approach shots and durability depend to a large degree on synergy between t...

AI Technical Summary

Benefits of technology

[0006]It is therefore an object of the present invention to provide a golf ball which achieves satisfactory distances both on shots with drivers and on shots with middle irons used by professional golfers and skilled amateurs, and which also has an excellent durability to cracking when repeatedly struck.

[0007]As a result of extensive investigations aimed at achieving the above objects, the inventor has developed golf ball cores having cross-sectional hardnesses like those shown in FIGS. 3 and 4 of working examples of the invention; that is, cores which, in the cross-sectional hardness profiles thereof, have a cross-sectional hardness from the core center to a position at a given distance therefrom that is relatively soft and free of large fluctuations in hardness, and have a cross-sectional hardness thereafter up to the core surface that rises at a steep gradient. The inventor has found that golf balls having a core with such a cross-sectional hardness achieve in particular satisfactory distances, both on shots with drivers and on shots with middle irons such as a number six iron (I#6) used by professional golfers and skilled amateurs, and also exhibit an improved durability to cracking when repeatedly struck.

[0008]Among recent golf balls in particular, three-piece solid golf balls and four-piece solid golf balls featuring a urethane cover are widely used by professional golfers and skilled amateurs. The present invention, by optimizing the internal hardness profile of the core in the above ball, improves not only the distance achieved on shots with drivers used by professionals and skilled amateurs, but also the distance achieved with middle irons such as a number six iron (I#6) used by such golfers. Moreover, the invention provides a ball which, along with improving the distance performance, has an excellent durability to cracking when repeatedly struck and is capable of withstanding harsh conditions of use.

Problems solved by technology

Lately, research and development on golf balls has been especially intense.

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