Golf Ball

This non-provisional application claims priority under 35 U.S.C. § 119 (a) on Patent Application No. 2024-050918 filed in Japan on Mar. 27, 2024, the entire contents of which are hereby incorporated by reference.

The present invention relates to a golf ball including a core and a cover.

Many innovations have been made in designing golf balls with a multilayer construction, and many balls that satisfy not only professional golfers but also general amateur golfers from beginners to advanced players have been developed to date. Among them, the most popular golf balls are three-piece solid golf balls composed of a core, an intermediate layer, and a cover (outermost layer). Specifically, there have been many proposals for functional three-piece solid golf balls in which a material hardness and a core surface hardness of each layer of the intermediate layer and the cover, and a surface hardness of an intermediate layer-encased sphere are optimized, and some technologies have been proposed to provide high-performance golf balls by designing a core internal hardness in various aspects while focusing on a core hardness profile occupying most of the volume of the ball.

Examples of such technical documents include the three-piece solid golf balls of the following Patent Documents 1 to 11.

However, although some of the proposed golf balls disclose a relationship between an initial velocity of each of the intermediate layer-encased sphere and each encased sphere of the ball, or a relationship between a deflection when a predetermined load is applied to the core and the deflection when a predetermined load is applied to the ball, none of the proposed golf balls has been invented so as to obtain a superior distance on full shots with clubs from a driver to an iron and to improve a golf ball having controllability on approach shots, a good feel at impact, and excellent striking durability. In particular, for an average golfer whose head speed is not so fast, there is a demand for a golf ball capable of obtaining a superior distance not only on shots with a driver but also on full shots with a utility club and an iron.

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 allows an average golfer whose head speed is not so fast to obtain a superior distance not only on shots with a driver but also on full shots with a utility club and an iron.

As a result of intensive studies to achieve the above object, the present inventor has found that in a golf ball including a core and a cover, the core has a hardness profile in which, letting a Shore C hardness at a core center be H, a Shore C hardness at a position where a distance from the core center is 12.5% of a core radius be H, a Shore C hardness at a position where the distance from the core center is 25% of the core radius be H, a Shore C hardness at a position where the distance from the core center is 37.5% of the core radius be H, a Shore C hardness at a position where the distance from the core center is 50% of the core radius be H, a Shore C hardness at a position where the distance from the core center is 62.5% of the core radius be H, a Shore C hardness at a position where the distance from the core center is 75% of the core radius be H, a Shore C hardness at a position where the distance from the core center is 87.5% of the core radius be H, and a Shore C hardness at a core surface be H, and defining differences in hardness between the respective positions as follows:

The present inventor has found that, by satisfying the above conditions, for an average golfer, not only on shots with a driver but on full shots with a utility club and an iron, it is possible to obtain a superior distance, excellent durability on repeated impact, controllability in the short game, and a soft and comfortable feel at impact, and has completed the present invention.

It is noted that an “average golfer” as defined in the present specification is an amateur golfer with a low handicap who places importance on controllability in the short game, but has a head speed that is not as fast as that of a professional. The head speed of such a golfer on shots with a driver (W #1) is in the region of approximately 35 to 44 m/s.

Accordingly, the present invention provides a golf ball including

Further characteristics of the golf ball are that letting a deflection (mm) when the core is compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) be C (mm), the following condition is satisfied:

In a preferred embodiment of the golf ball according to the invention, the following condition (IV) is satisfied:

In another preferred embodiment of the inventive golf ball, the following condition (V) is satisfied:

In yet another preferred embodiment, the following condition (VI) is satisfied:

In still another preferred embodiment, the following condition (VII) is satisfied:

In a further preferred embodiment, the following condition (VIII) is satisfied:

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

In a still further preferred embodiment, a content ratio of the components (D) and (C) is from 0.005 to 0.100 in a weight ratio of (D)/(C).

In another preferred embodiment, an intermediate layer is formed between the core and the cover.

In yet another preferred embodiment, the intermediate layer contains an inorganic particulate filler.

In still another preferred embodiment, a specific gravity of the intermediate layer is at least 1.05.

In a further preferred embodiment, letting a deflection (mm) when the ball is compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) be B (mm), the following two conditions are satisfied:

2.80 and

-1.00.

In a yet further preferred embodiment, a relationship between a core surface hardness, a surface hardness of a sphere (intermediate layer-encased sphere) in which the core is encased with the intermediate layer, and a surface hardness of a sphere (ball) in which the intermediate layer-encased sphere is encased with the cover satisfies the following condition:

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

In a still further preferred embodiment, a difference between a specific gravity of the cover and a specific gravity of the intermediate layer is not more than 0.15, and a difference between the specific gravity of the intermediate layer and a specific gravity of the core is not more than 0.15.

In another preferred embodiment, a relationship between an initial velocity of the entire core, an initial velocity of a sphere (intermediate layer-encased sphere) in which the core is encased with the intermediate layer, and an initial velocity of a sphere (ball) in which the intermediate layer-encased sphere is encased with the cover satisfies the following two conditions:

(initial velocity of ball)<(initial velocity of intermediate layer-encased sphere)

0.65≤(initial velocity of intermediate layer-encased sphere)−(initial velocity of entire core)≤0.98 (m/s).

With the golf ball of the present invention, even for an average golfer whose head speed is not so fast, a superior distance may be obtained not only on shots with a driver but also on full shots with a utility club and an iron. Furthermore, the golf ball of the present invention has good controllability in the short game, provides a soft and comfortable feel at impact, and has excellent durability on repeated impact.

Hereinafter, the present invention is described in more detail.

A golf ball of the present invention has a core and a cover, and an example thereof is shown in, for example. A golf ball G shown inhas a single-layer core 1, a single-layer intermediate layer 2 encasing the core 1, and a single-layer cover 3 encasing the intermediate layer. The cover 3 is positioned at the outermost layer in the layer construction of the golf ball except for the coating layer. The core is formed in a single layer as shown in. The cover is formed in a single layer. In addition, a single layer or a plurality of surrounding layers may be formed between the core 1 and the intermediate layer 2. A large number of dimples D are typically formed on the surface of the cover (outermost layer) 3 in order to improve the aerodynamic properties of the ball. In addition, although not particularly illustrated, a coating layer is typically formed on the surface of the cover 3. Hereinafter, each of the above layers is described in detail.

The core is obtained by vulcanizing a rubber composition containing a rubber material as a chief material. If the core material is not the rubber composition, a core rebound becomes low, and a desired distance may not be attainable on shots by an average golfer whose head speed is not so high. This rubber composition typically contains a base rubber as a chief material, and is obtained with the inclusion of a co-crosslinking agent, a crosslinking initiator, an inert filler, an organosulfur compound, or the like.

In particular, the core is preferably formed of a rubber composition containing the following components (A) to (D):

As the base rubber (A), polybutadiene is preferably used. As the type of polybutadiene, a commercially available product may be used, and examples thereof include BR01, BR51, and BR730 (manufactured by JSR Corporation). The proportion of polybutadiene in the base rubber is preferably at least 60 wt %, and more preferably at least 80 wt %. In addition to the polybutadiene, other rubber components are included in the base rubber as long as the effect of the present invention is not impaired. Examples of the rubber component other than the polybutadiene include a polybutadiene other than the polybutadiene described above, and other diene rubbers such as styrene-butadiene rubber, natural rubber, isoprene rubber, and ethylene-propylene-diene rubber.

The organic peroxide (B) is suitably used as a co-crosslinking initiator. Specifically, commercially available organic peroxides may be used, and for example, Percumyl D, Perhexa C-40, Perhexa 3M (all manufactured by NOF Corporation), and Luperco 231XL (manufactured by AtoChem Corporation) may be suitably used. These may be used singly, or two or more may be used in combination. The compounding amount of the organic peroxide is preferably at least 0.1 parts by weight, more preferably at least 0.3 parts by weight, and even more preferably at least 0.5 parts by weight, and the upper limit is preferably not more than 5 parts by weight, more preferably not more than 4 parts by weight, even more preferably not more than 3 parts by weight, and most preferably not more than 2.5 parts by weight per 100 parts by weight of the base rubber. If the compounding amount is too large or too small, it may not be possible to obtain suitable feel at impact, durability, and rebound.

The water (C), although not particularly limited, may be distilled water or tap water, but it is particularly suitable to employ distilled water free of impurities. The compounding amount of the water included per 100 parts by weight of the base rubber is preferably at least 0.1 part by weight, and more preferably at least 0.2 parts by weight, and an upper limit thereof is preferably not more than 2 parts by weight, and more preferably not more than 1 part by weight.

By blending the water or a material containing water as the component (C) directly into the core material, a decomposition of the organic peroxide during the core formulation may be promoted. In addition, it is known that the decomposition efficiency of the organic peroxide in the core-forming rubber composition changes depending on temperature, and the decomposition efficiency increases as the temperature becomes higher than a certain temperature. If the temperature is too high, the amount of decomposed radicals becomes too large, and the radicals are recombined or deactivated. As a result, fewer radicals act effectively in crosslinking. Here, when decomposition heat is generated by the decomposition of the organic peroxide at the time of core vulcanization, a temperature near the core surface is maintained at substantially the same level as a temperature of a vulcanization mold, although the temperature around the core center is considerably higher than the mold temperature due to an accumulation of decomposition heat by the organic peroxide decomposing from the outer side. If the water or the material containing water is directly included in the core, the water acts to promote the decomposition of the organic peroxide, so that the radical reactions as described above may be changed at the core center and the core surface. That is, the decomposition of the organic peroxide is further promoted near the core center, and the deactivation of radicals is further promoted, so that the amount of active radicals is further reduced, and as a result, a core may be obtained in which the crosslink densities at the core center and the core surface differ markedly, and the dynamic viscoelasticity of the core center portion is different.

In addition, a monocarboxylic acid metal salt may be employed instead of the water. In the monocarboxylic acid metal salt, it is presumed that a carboxylic acid is coordinate-bonded to the metal salt, and the monocarboxylic acid metal salt is distinguished from a dicarboxylic acid metal salt such as zinc diacrylate, which is represented by chemical formula [CH═CHCOO]Zn. The monocarboxylic acid metal salt brings water into the rubber composition by a dehydration condensation reaction, so that the same effect as that of the water may be obtained. In addition, since the monocarboxylic acid metal salt may be blended into the rubber composition as powder, the working process may be simplified, and it is easy to uniformly disperse the monocarboxylic acid metal salt in the rubber composition. In order to effectively perform the above reaction, it is necessary to use a mono-salt. The compounding amount of the monocarboxylic acid metal salt is preferably at least 1 part by weight, and more preferably at least 3 parts by weight per 100 parts by weight of the base rubber. As an upper limit thereof, the compounding amount of the monocarboxylic acid metal salt is preferably not more than 60 parts by weight, and more preferably not more than 50 parts by weight per 100 parts by weight of the base rubber. If the compounding amount of the monocarboxylic acid metal salt is too small, it is difficult to obtain an appropriate crosslinking density, and it may not be possible to obtain an adequate golf ball spin rate-lowering effect. In addition, if the compounding amount is too large, the core becomes too hard, so that it may be difficult to maintain an appropriate feel at impact.