Golf ball

Abstract

To provide a golf ball allowing average golfers with not-so-fast head speeds to achieve a superior carry when hitting with a driver as well as when hitting full shot with a utility club or an iron club.SOLUTION: A golf ball includes a core and a cover, where the core is formed in a single layer from a rubber composition, the cover is formed from a resin composition, and hardness distribution of the core has a specific cross-sectional hardness distribution. When an amount of deflection (mm) in a case where the core is subjected to an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf) is C (mm), the Shore C hardness at the core center is H0, and the Shore C hardness of the core surface is H100, the golf ball satisfies the following formula: C×(H100-H0)≥125.0.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a golf ball having a core and a cover. [Background technology]

[0002] Many efforts have been made to design balls with multi-layer structures, and many balls have been developed to satisfy not only professional golfers but also general amateur golfers from beginners to advanced players. Among these, three-piece solid golf balls consisting of a core, an intermediate layer, and a cover (outermost layer) have been developed. Specifically, many proposals have been made for functional three-piece solid golf balls in which the material hardness of each layer of the intermediate layer and cover, the surface hardness of the core, and the surface hardness of the intermediate layer-covered sphere are optimized. Furthermore, several technologies have been proposed that focus on the core hardness distribution, which accounts for the majority of the ball's volume, and design various modes of core internal hardness to provide high-performance golf balls.

[0003] Examples of such technical documents include the three-piece solid golf balls of Patent Documents 1 to 11 below.

[0004] However, although some of the above-mentioned proposed golf balls disclose the relationship between the initial velocity of the intermediate layer-covered sphere and each covered sphere of the ball, or the relationship between the amount of deflection when a specific load is applied to the core and the amount of deflection when a specific load is applied to the ball, none have been invented to improve a golf ball that provides superior distance on full shots from a driver to an iron, as well as controllability on approaches, a good feel on impact, and excellent durability on impact. In particular, average golfers who do not have a particularly fast head speed are looking for a golf ball that provides superior distance not only on driver shots but also on full shots with a utility club and an iron. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-097802 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-120898 [Patent Document 3] Japanese Patent Application Laid-Open No. 2013-230365 [Patent Document 4] Japanese Patent Application Laid-Open No. 2015-047502 [Patent Document 5] Japanese Patent Application Laid-Open No. 2016-112308 [Patent Document 6] Japanese Patent Application Laid-Open No. 2017-000183 [Patent Document 7] Japanese Patent Application Laid-Open No. 2017-000470 [Patent Document 8] Japanese Patent Application Publication No. 2018-183247 [Patent Document 9] Japanese Patent Application Publication No. 2019-198465 [Patent Document 10] Japanese Patent Application Publication No. 2019-198467 [Patent Document 11] Japanese Patent Publication No. 2020-175021 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in consideration of the above circumstances, and aims to provide a golf ball that allows average golfers with a relatively low head speed to achieve advantageous distances not only when hitting with a driver but also when hitting full shots with a utility club or iron. [Means for solving the problem]

[0007] As a result of extensive research into achieving the above object, the inventors of the present invention have discovered a golf ball having a core and a cover, in which the hardness distribution of the core is such that the Shore C hardness at the center of the core is H0 and the Shore C hardness at a position 12.5% ​​of the core radius from the center of the core is H 12.5, the Shore C hardness at a position 25% of the core radius from the core center is H 25 , the Shore C hardness at a position 37.5% of the core radius from the core center is H 37.5 , the Shore C hardness at the position 50% of the core radius from the core center is H 50 , the Shore C hardness at the position where the distance from the core center is 62.5% of the core radius is H 62.5 , the Shore C hardness at the position 75% of the core radius from the core center is H 75 , the Shore C hardness at the position where the distance from the core center is 87.5% of the core radius is H 87.5 , the Shore C hardness of the core surface is H 100 When the hardness difference between the following positions is A: H 100 -H 87.5 B: H 87.5 -H 75 C: H 75 -H 62.5 D: H 62.5 -H 50 E: H 50 -H 37.5 F: H 37.5 -H 25 G: H 25 -H 12.5 H: H 12.5 -H0 Regarding the following two formulas (I) and (II), (E+F+G+H)<(C+D) ···(I) (H 100 -H0)≧30.0 (II) The above condition is satisfied, and the deflection (mm) when the core is loaded from an initial load of 98N (10kgf) to a final load of 1,275N (130kgf) is C (mm). The following formula is satisfied: C×(H 100 -H0)≧125.0 (III) By satisfying the above requirements, the average golfer can obtain superior distance performance not only when hitting with a driver but also when hitting full shots with a utility club and an iron, as well as excellent durability against repeated hitting, controllability in short games, and a soft and comfortable hitting feel, which has led to the present invention.

[0008] The term "average golfer" as defined in this specification refers to an amateur golfer with a low handicap who does not have as fast a head speed as a professional golfer, but who also places importance on control during the short game. The head speed of this golfer when hitting with a driver (W#1) is generally in the range of 35 to 44 m / s.

[0009] Accordingly, the present invention provides the following golf balls. 1. A golf ball having a core and a cover, wherein the core is formed as a single layer from a rubber composition and the cover is formed from a resin composition, and the hardness distribution of the core is such that the Shore C hardness at the center of the core is H0, the Shore C hardness at a position 12.5% ​​of the core radius from the center of the core is H 12.5 , the Shore C hardness at a position 25% of the core radius from the core center is H 25 , the Shore C hardness at a position 37.5% of the core radius from the core center is H 37.5 , the Shore C hardness at the position 50% of the core radius from the core center is H 50 , the Shore C hardness at a position 62.5% of the core radius from the core center is H 62.5 , the Shore C hardness at the position where the distance from the core center is 75% of the core radius is H 75 , the Shore C hardness at the position where the distance from the core center is 87.5% of the core radius is H 87.5 , the Shore C hardness of the core surface is H 100 When the hardness difference between the following positions is A: H 100 -H 87.5 B: H 87.5 -H 75 C: H 75 -H62.5 D: H 62.5 -H 50 E: H 50 -H 37.5 F: H 37.5 -H 25 G: H 25 -H 12.5 H: H 12.5 -H0 Regarding the following two formulas (I) and (II), (E+F+G+H)<(C+D) ···(I) (H 100 -H0)≧30.0 (II) The above condition is satisfied, and the deflection (mm) when the core is loaded from an initial load of 98N (10kgf) to a final load of 1,275N (130kgf) is C (mm). The following formula is satisfied: C×(H 100 -H0)≧125.0 (III) A golf ball characterized by satisfying the above. 2. Formula (IV) below (E+F+G+H)<(A+B) (IV) 1. A golf ball that satisfies the above requirement. 3. Formula (V) below (E+F+G+H)<(C+D)<(A+B) ···(V) 3. The golf ball according to 1 or 2 above, which satisfies the above. 4. Formula (VI) below {(C+D)-(E+F+G+H)}≧3.0 (VI) 3. The golf ball according to 1 or 2 above, which satisfies the above. 5. Formula (VII) below {(H 100 -H0) / (H 50 -H0)}≧5.0 (VII) 3. The golf ball according to 1 or 2 above, which satisfies the above. 6. The following formula (VIII) {(H 87.5 -H0) / (H 50-H0)}≧3.0 (VIII) 3. The golf ball according to 1 or 2 above, which satisfies the above. 7. The core comprises the following components (A) to (D): (A) Base rubber (B) Organic peroxide (C) Water or a metal monocarboxylate (D) Sulfur 3. The golf ball according to 1 or 2 above, which is formed from a rubber composition containing 8. The golf ball according to the above item 7, wherein the content ratio of components (D) and (C) is 0.005 to 0.100 in terms of a mass ratio of (D) / (C). 9. The golf ball according to 1 or 2 above, wherein an intermediate layer is formed between the core and the cover. 10. The golf ball according to claim 9, wherein the intermediate layer contains an inorganic granular filler. 11. The golf ball according to claim 9, wherein the specific gravity of the intermediate layer is 1.05 or more. 12. When a ball is subjected to an initial load of 98N (10kgf) and a final load of 1,275N (130kgf), the deflection (mm) is B (mm). B≧2.80 CB≧1.00 3. The golf ball according to 1 or 2 above, which satisfies the above. 13. The relationship between the surface hardness of the core, the surface hardness of a sphere with a core covered with an intermediate layer (an intermediate-layer-covered sphere), and the surface hardness of a sphere with an intermediate layer covered with a cover (a golf ball) is expressed by the following formula: Ball surface hardness <Surface hardness of mid-layer coated ball> Core surface hardness (However, the surface hardness of each sphere mentioned above means Shore C hardness.) 9. A golf ball as described above that satisfies the above requirements. 14. The golf ball according to claim 9, wherein the difference between the specific gravity of the cover and the specific gravity of the intermediate layer is within 0.15, and the difference between the specific gravity of the intermediate layer and the specific gravity of the core is within 0.15. 15. The relationship between the initial velocity of the entire core, the initial velocity of a sphere with a core covered with an intermediate layer (an intermediate-layer-covered sphere), and the initial velocity of a sphere (a ball) with an intermediate layer covered with a cover is expressed by the following two equations. (Initial velocity of ball)<(Initial velocity of intermediate layer-coated sphere) 0.65≦(initial velocity of intermediate layer coated sphere)-(initial velocity of entire core)≦0.98(m / s) 9. A golf ball as described above that satisfies the above requirements. [Effects of the Invention]

[0010] The golf ball of the present invention enables average golfers with a moderate head speed to achieve superior distance not only on driver shots but also on full shots with utilities and irons. Furthermore, the golf ball of the present invention provides good controllability during short games, a soft and comfortable feel, and excellent durability against repeated shots. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic cross-sectional view of a golf ball according to one embodiment of the present invention. [Figure 2] FIG. 1 is a schematic diagram illustrating the hardness differences A to H between positions in the core hardness distribution, using the core hardness distribution data of Example 1. [Figure 3] 1 is a graph showing the core hardness distributions of Examples 1 to 5 and Comparative Examples 1 and 2. [Figure 4] 1 is a graph showing the core hardness distribution of Comparative Examples 3 to 7. [Figure 5] 1 is a graph showing the relationship between the amount of deflection of the core and the difference in hardness between the surface and the center of the core for each example and comparative example.

[0012] The present invention will be described in more detail below. The golf ball of the present invention has a core and a cover, an example of which is shown in FIG. 1. The golf ball G shown in FIG. 1 has 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. This cover 3 is the outermost layer in the layer structure of the golf ball, excluding the paint layer. The core is formed as a single layer as shown in FIG. 1. The cover is formed as a single layer. A single or multiple surrounding layers can be formed between the core 1 and the intermediate layer 2. A large number of dimples D are usually formed on the surface of the cover (outermost layer) 3 to improve aerodynamic characteristics. Although not specifically shown, a paint layer is usually formed on the surface of the cover 3. Each of the above layers will be described in detail below.

[0013] The core is obtained by vulcanizing a rubber composition mainly composed of rubber material. If the core material is not a rubber composition, the core's resilience will be low, and the desired flight distance may not be achieved when hitting with an average golfer who does not have a particularly fast head speed. This rubber composition is usually obtained by compounding a base rubber as the main component with a co-crosslinking agent, a crosslinking initiator, an inert filler, an organic sulfur compound, etc.

[0014] The core may particularly comprise the following components (A) to (D): (A) Base rubber (B) Organic peroxide (C) Water or a metal monocarboxylate (D) Sulfur It is preferable that the rubber composition contains the above-mentioned compound.

[0015] Polybutadiene is preferably used as the base rubber (A). Commercially available polybutadienes can be used, such as BR01, BR51, and BR730 (manufactured by JSR Corporation). The proportion of polybutadiene in the base rubber is preferably 60% by mass or more, and more preferably 80% by mass or more. Rubber components other than the polybutadiene may be blended into the base rubber within a range that does not impair the effects of the present invention. Examples of rubber components other than polybutadiene include polybutadienes other than the polybutadienes mentioned above, and other diene rubbers, such as styrene-butadiene rubber, natural rubber, isoprene rubber, and ethylene-propylene-diene rubber.

[0016] (B) Organic peroxide is used as a crosslinking initiator. Specifically, commercially available organic peroxides can be used, such as Percumyl D (manufactured by Nippon Oil & Fats Co., Ltd.), Perhexa C-40, Perhexa 3M (manufactured by Nippon Oil & Fats Co., Ltd.), and Luperco 231XL (manufactured by Atochem). These can be used alone or in combination. The amount of organic peroxide added is preferably 0.1 parts by weight or more, more preferably 0.3 parts by weight or more, and even more preferably 0.5 parts by weight or more, per 100 parts by weight of the base rubber. The upper limit is preferably 5 parts by weight or less, more preferably 4 parts by weight or less, even more preferably 3 parts by weight or less, and most preferably 2.5 parts by weight or less. If the amount added is too high or too low, it may be difficult to achieve a satisfactory feel, durability, and resilience.

[0017] The water (C) is not particularly limited and may be distilled water or tap water, but it is particularly preferred to use distilled water that does not contain impurities. The amount of water blended is preferably 0.1 part by weight or more, more preferably 0.2 part by weight or more, per 100 parts by weight of the base rubber, and the upper limit is preferably 2 parts by weight or less, more preferably 1 part by weight or less.

[0018] By directly blending water or a water-containing material as component (C) into the core material, the decomposition of organic peroxides during core compounding can be accelerated. It is known that the decomposition efficiency of organic peroxides in core rubber compositions varies with temperature, with the decomposition efficiency increasing as the temperature rises. If the temperature is too high, too many radicals are decomposed, leading to recombination and inactivation of the radicals. As a result, the number of radicals available for crosslinking is reduced. When the organic peroxide decomposes during core vulcanization and generates heat, the temperature near the core surface remains roughly the same as the vulcanization mold temperature. However, the temperature near the core center rises significantly higher than the mold temperature due to the accumulation of heat from the decomposition of the organic peroxide decomposed from the outside. When water or a water-containing material is directly blended into the core, the water promotes the decomposition of the organic peroxide, thereby altering the radical reaction described above between the core center and the core surface. That is, near the core center, the decomposition of the organic peroxide is further promoted, and the deactivation of radicals is further promoted, further reducing the amount of effective radicals. This makes it possible to obtain cores with significantly different crosslink densities between the core center and the core surface, and cores with different dynamic viscoelastic properties in the core center.

[0019] Alternatively, a monocarboxylate metal salt can be used instead of the water described above. It is believed that a carboxylic acid is coordinately bonded to the metal salt in a monocarboxylate metal salt, and it is distinct from dicarboxylate metal salts such as zinc diacrylate, which has the chemical formula [CH₂=CHCOO]₂Zn. A monocarboxylate metal salt introduces water into the rubber composition through a dehydration condensation reaction, thereby achieving the same effects as water. Furthermore, a monocarboxylate metal salt can be incorporated into the rubber composition as a powder, simplifying the processing steps and facilitating uniform dispersion throughout the rubber composition. To effectively carry out the reaction, a monosalt is required. The amount of the monocarboxylate metal salt is preferably 1 part by weight or more, more preferably 3 parts by weight or more, per 100 parts by weight of the base rubber. The upper limit of the amount of the monocarboxylate metal salt is preferably 60 parts by weight or less, more preferably 50 parts by weight or less. If the amount of the monocarboxylate metal salt is too small, it may be difficult to achieve an appropriate crosslink density, which may result in an insufficient golf ball spin reduction effect. On the other hand, if the blending amount is too high, the core becomes too hard, which may make it difficult to maintain an appropriate feel on impact.

[0020] Examples of the carboxylic acid that can be used include acrylic acid, methacrylic acid, maleic acid, fumaric acid, and stearic acid. Examples of the substituting metal include Na, K, Li, Zn, Cu, Mg, Ca, Co, Ni, and Pb, with Zn being preferred. Specific examples include zinc monoacrylate and zinc monomethacrylate, with zinc monoacrylate being particularly preferred.

[0021] The use of (D) sulfur can increase the difference in hardness between the inner and outer cores. Specific examples of (D) sulfur include products such as "Sunmix S-80N" (manufactured by Sanshin Chemical Industry Co., Ltd.) and "Sulfax-5" (manufactured by Tsurumi Chemical Industry Co., Ltd.). The amount of sulfur added per 100 parts by weight of the base rubber can be greater than 0, preferably 0.005 parts by weight or more, and more preferably 0.01 parts by weight or more. There is no particular upper limit to the amount added, but it is preferably 0.1 parts by weight or less, more preferably 0.05 parts by weight or less, and even more preferably 0.03 parts by weight or less. Note that excessive sulfur content can significantly reduce resilience and durability against repeated impacts.

[0022] The content ratio of the above components (D) and (C), expressed as the mass ratio (D) / (C), is preferably 0.005 or more, more preferably 0.008 or more, and even more preferably 0.010 or more, with the upper limit being preferably 0.100 or less, more preferably 0.060 or less, and even more preferably 0.030 or less. Outside of this range, it may be difficult to achieve the desired core hardness distribution, and it may become impossible to achieve both advantageous distance due to low spin on full shots and good durability against repeated impacts. Note that the above component (D) refers to the mass (effective mass) of the sulfur component contained in the product, not the mass of the sulfur product itself.

[0023] Examples of rubber compounding components other than the above components (A) to (D) include a co-crosslinking agent, an inert filler, an antioxidant, and an organic sulfur compound.

[0024] The co-crosslinking agent is an α,β-unsaturated carboxylic acid and / or a metal salt thereof. Specific examples of unsaturated carboxylic acids include acrylic acid, methacrylic acid, maleic acid, and fumaric acid, with acrylic acid and methacrylic acid being particularly preferred. Metal salts of unsaturated carboxylic acids are not particularly limited, but examples include those obtained by neutralizing the above-mentioned unsaturated carboxylic acids with desired metal ions. Specific examples include zinc salts and magnesium salts of methacrylic acid, acrylic acid, and the like, with zinc acrylate being particularly preferred.

[0025] The unsaturated carboxylic acid and / or metal salt thereof is blended in an amount of typically 5 parts by weight or more, preferably 9 parts by weight or more, and more preferably 13 parts by weight or more, per 100 parts by weight of the base rubber, with the upper limit typically being 60 parts by weight or less, preferably 50 parts by weight or less, and more preferably 40 parts by weight or less. If the blended amount is too high, the ball may become too hard, resulting in an unbearable feel at impact, while if the blended amount is too low, the resilience may decrease.

[0026] Suitable fillers include, for example, zinc oxide, barium sulfate, and calcium carbonate. These may be used alone or in combination. The amount of filler 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. The upper limit of the amount is preferably no more than 50 parts by weight, more preferably no more than 40 parts by weight, and even more preferably no more than 30 parts by weight, per 100 parts by weight of the base rubber. If the amount is too high or too low, it may not be possible to obtain the appropriate mass and appropriate resilience.

[0027] As the antioxidant, for example, commercially available products such as Nocrac NS-6, Nocrac NS-30, Nocrac 200, Nocrac MB (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) can be used. These may be used alone or in combination of two or more.

[0028] The amount of antioxidant blended is not particularly limited, but is preferably at least 0.05 part by weight, more preferably at least 0.1 part by weight, and preferably not more than 1.0 part by weight, more preferably not more than 0.7 part by weight, and even more preferably not more than 0.5 part by weight, per 100 parts by weight of base rubber. If the blended amount is too high or too low, the appropriate core hardness gradient may not be obtained, and favorable resilience, durability, and spin reduction effect on full shots may not be achieved.

[0029] An organic sulfur compound can be blended to control the core's resilience in a direction that increases it.Specific examples of the organic sulfur compound include thiophenol, thionaphthol, halogenated thiophenol, or metal salts thereof.More specific examples include zinc salts of pentachlorothiophenol, pentafluorothiophenol, pentabromothiophenol, parachlorothiophenol, pentachlorothiophenol, and the like; diphenyl polysulfide, dibenzyl polysulfide, dibenzoyl polysulfide, dibenzothiazoyl polysulfide, dithiobenzoyl polysulfide, and the like, each of which has 2 to 4 sulfur atoms; and particularly, the zinc salt of pentachlorothiophenol and diphenyl disulfide can be preferably used.

[0030] The organic sulfur compound is blended in an amount of no more than 5 parts by weight, preferably no more than 4 parts by weight, more preferably no more than 3 parts by weight, and even more preferably no more than 2 parts by weight per 100 parts by weight of the base rubber. The lower limit of the blended amount is typically at least 0.1 parts by weight, preferably at least 0.2 parts by weight, and even more preferably at least 0.4 parts by weight. If the blended amount is too high, the core may become too soft, making it impossible to achieve the desired core hardness distribution. On the other hand, if the blended amount is too low, the core's resilience may be too low, making it impossible to achieve the desired distance.

[0031] The core can be produced by vulcanizing and curing a rubber composition containing the above components. For example, the core can be produced by kneading the rubber composition using a kneader such as a Banbury mixer or a roll, compression molding or injection molding using a core mold, and curing the molded product by appropriately heating the molded product at a temperature sufficient for the organic peroxide and co-crosslinking agent to act, 100 to 200°C, preferably 140 to 180°C, for 10 to 40 minutes.

[0032] In the present invention, the core is preferably formed of a single layer, since if the core is formed of multiple layers, repeated impacts can cause the core to crack prematurely from the interface between the layers.

[0033] The core diameter is preferably 36.7 mm or more, more preferably 37.2 mm or more, and even more preferably 37.6 mm or more. The upper limit of this diameter is preferably 40.1 mm or less, more preferably 39.0 mm or less, and even more preferably 38.2 mm or less. If the core diameter is too small, the initial velocity of the ball will be low or the overall deflection of the ball will be small, increasing the spin rate of the ball on full shots and preventing the desired distance from being achieved. On the other hand, if the core diameter is too large, the spin rate will be high on full shots, preventing the desired distance from being achieved, or the durability to cracking upon repeated impacts may be poor.

[0034] The deflection (mm) of the core when subjected to an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf) is not particularly limited, but is preferably at least 3.8 mm, more preferably at least 4.0 mm, and even more preferably at least 4.2 mm, with the upper limit being preferably at most 6.0 mm, more preferably at most 5.4 mm, and even more preferably at most 5.0 mm. If the deflection of the core is too small, i.e., if the core is too hard, the ball may have too much spin, resulting in a loss of flight distance, or the feel on impact may be too hard. On the other hand, if the deflection of the core is too large, i.e., if the core is too soft, the ball may have too little resilience, resulting in a loss of flight distance, a too soft feel, or poor durability to cracking upon repeated impact.

[0035] Next, the hardness distribution of the core will be described. Note that the hardness of the core described below refers to Shore C hardness. This Shore C hardness is a hardness value measured using a Shore C hardness tester conforming to ASTM D2240 standard.

[0036] The center hardness (H0) of the core is not particularly limited, but is preferably 47 or more, more preferably 49 or more, and even more preferably 51 or more, with the upper limit being preferably 58 or less, more preferably 56 or less, and even more preferably 54 or less. If this value is too high, the feel on impact may be too hard, or the spin rate on full shots may increase, preventing the desired flight distance from being achieved. On the other hand, if this value is too low, the resilience may be reduced, resulting in a loss of flight distance, or the durability to cracking when hit repeatedly may be reduced.

[0037] The hardness (H 12.5 ) is not particularly limited, but is preferably 48 or greater, more preferably 50 or greater, and even more preferably 52 or greater. There is no upper limit to the hardness, but it is preferably 59 or less, more preferably 57 or less, and even more preferably 55 or less. If these hardnesses are exceeded, the same adverse effects as those described above for the center hardness (H0) of the core may occur.

[0038] The hardness (H 25 ) is not particularly limited, but is preferably 49 or greater, more preferably 51 or greater, and even more preferably 53 or greater. There is no upper limit to the hardness, but it is preferably 60 or less, more preferably 58 or less, and even more preferably 56 or less. If these hardnesses are exceeded, the same adverse effects as those described above for the center hardness (H0) of the core may occur.

[0039] The hardness (H 37.5 ) is not particularly limited, but is preferably 50 or greater, more preferably 52 or greater, and even more preferably 54 or greater. Its upper limit is also not particularly limited, but is preferably 61 or less, more preferably 59 or less, and even more preferably 57 or less. Deviation from these hardness ranges may result in the same adverse effects as those described above for the center hardness (H0) of the core.

[0040] The hardness (H 50 ), i.e., the hardness at the midpoint between the center and the surface of the core, is not particularly limited, but is preferably at least 50, more preferably at least 52, and even more preferably at least 54. The upper limit of the hardness is also not particularly limited, but is preferably at most 62, more preferably at most 60, and even more preferably at most 58. Deviation from these hardness limits may result in the same adverse effects as those described above for the center hardness (H0) of the core.

[0041] The hardness (H 62.5) is not particularly limited, but is preferably 54 or more, more preferably 56 or more, and even more preferably 58 or more. Its upper limit is also not particularly limited, but is preferably 64 or less, more preferably 62 or less, and even more preferably 60 or less. If this value is too large, durability to cracking when repeatedly hit may be poor, or the feel on impact may be too hard. On the other hand, if this value is too small, the resilience may be low, resulting in a loss of distance, or the amount of spin on a full shot may be so high that the desired distance cannot be achieved.

[0042] The hardness (H 75 ) is not particularly limited, but is preferably 61 or more, more preferably 63 or more, and even more preferably 65 or more. There is no particular upper limit to the hardness, but it is preferably 71 or less, more preferably 69 or less, and even more preferably 67 or less. If the hardness deviates from these limits, the position hardness (H 62.5 ) may result in adverse consequences similar to those described above.

[0043] The hardness (H 87.5 ) is not particularly limited, but is preferably 67 or more, more preferably 69 or more, and even more preferably 71 or more. There is no particular upper limit, but it is preferably 77 or less, more preferably 75 or less, and even more preferably 73 or less. If the hardness deviates from these limits, the position hardness (H 62.5 ) may result in adverse consequences similar to those described above.

[0044] The hardness (H 100), i.e., the surface hardness of the core, is not particularly limited, but is preferably 79 or more, more preferably 81 or more, and even more preferably 83 or more. There is no particular upper limit to the surface hardness, but it is preferably 91 or less, more preferably 89 or less, and even more preferably 87 or less. If the hardness deviates from these limits, the position hardness (H 62.5 ) may result in adverse consequences similar to those described above.

[0045] The core hardness distribution in the present invention is determined by the hardness difference between the following positions: A: H 100 -H 87.5 B: H 87.5 -H 75 C: H 75 -H 62.5 D: H 62.5 -H 50 E: H 50 -H 37.5 F: H 37.5 -H 25 G: H 25 -H 12.5 H: H 12.5 -H0 Regarding the following two formulas (I) and (II), (E+F+G+H)<(C+D) ···(I) (H 100 -H0)≧30.0 (II) The core hardness distribution in the present invention is designed so that the difference in hardness between the center and surface of the core is sufficiently large, and the hardness gradient from the center of the core to the midpoint between the surface and the center is gentle, and then the hardness gradient from there to the surface becomes steep, as shown in the core hardness distribution data for Example 1 in Figure 2. This hardness distribution is expressed mathematically in the above formulas (I) and (II).

[0046] In the above formula (I), the value of (C+D)-(E+F+G+H) is greater than 0, preferably 3.0 or greater, more preferably 4.5 or greater, with the upper limit being preferably 16.0 or less, more preferably 13.0 or less, and even more preferably 10.0 or less. If this value is too small, the ball will have a high spin rate on full shots, which may prevent the desired flight distance from being achieved. On the other hand, if this value is too large, the ball will have poor durability to cracking when hit repeatedly, or the initial velocity on full shots will be low, which may prevent the desired flight distance from being achieved.

[0047] Also, the following formula (IV) (E+F+G+H)<(A+B) (IV) It is preferable that the following condition be satisfied. The value of (A+B)-(E+F+G+H) in the above formula (IV) is greater than 0, preferably 4.0 or greater, more preferably 8.0 or greater, with the upper limit being preferably 30.0 or less, more preferably 24.0 or less, and even more preferably 20.0 or less. If this value is too small, the amount of spin of the ball on a full shot increases, which may prevent the desired flight distance from being achieved. On the other hand, if this value is too large, the durability to cracking when repeatedly hit may be poor, or the initial velocity on a full shot may be low, which may prevent the desired flight distance from being achieved.

[0048] Furthermore, the following formula (V) (E+F+G+H)<(C+D)<(A+B) ···(V) If the above formula (V) is not satisfied, the amount of spin increases when a full shot is made, and the desired flight distance may not be achieved.

[0049] In the core hardness distribution of the present invention, the difference in hardness between the surface and the center (H 100-H0) is 30.0 or more, preferably 31.0 or more, more preferably 33.0 or more, with the upper limit being 40.0 or less, more preferably 37.0 or less, and even more preferably 35.0 or less. If this value is too small, the amount of spin on a full shot increases, and the desired flight distance may not be achieved. On the other hand, if this value is too large, the durability to cracking may be poor when repeatedly hit, and the resilience may be low, making it impossible to achieve the desired flight distance.

[0050] The hardness distribution of the core is calculated by the following formula (VII): {(H 100 -H0) / (H 50 -H0)}≧5.0 (VII) In the above formula (VII), (H 100 -H0) indicates the difference in hardness between the center and surface of the core, and (H 50 The value of (H -H0) indicates the difference in hardness between the midpoint and the center of the core, and means that the difference in hardness from the midpoint to the surface of the core is set to be greater than the difference in hardness from the center to the midpoint. 100 -H0) / (H 50 The value of (H0) is preferably 5.0 or more, more preferably 6.5 or more, and even more preferably 8.0 or more, with the upper limit being preferably 16.0 or less, more preferably 14.0 or less, and even more preferably 12.0 or less. If this value is too small, the amount of spin on a full shot increases, which may prevent the desired flight distance from being achieved. On the other hand, if this value is too large, the durability to cracking when repeatedly hit may be poor, or the initial velocity on a full shot may be low, which may prevent the desired flight distance from being achieved.

[0051] Also, the following formula (VIII) {(H 87.5 -H0) / (H 50 -H0)}≧3.0 (VIII) In the above formula (VIII), (H 87.5 -H0) / (H 50The value of (H0) is preferably 3.0 or more, more preferably 4.0 or more, and even more preferably 5.0 or more, with the upper limit being preferably 13.0 or less, more preferably 11.0 or less, and even more preferably 9.0 or less. If this value is too small, the amount of spin on a full shot increases, which may prevent the desired flight distance from being achieved. On the other hand, if this value is too large, the durability to cracking when repeatedly hit may be poor, or the initial velocity on a full shot may be low, which may prevent the desired flight distance from being achieved.

[0052] In the present invention, when the core is subjected to an initial load of 98 N (10 kgf) and a final load of 1,275 N (130 kgf), the deflection (mm) is defined as C (mm), and the following formula is used: C×(H 100 -H0)≧125.0 (III) That is, C×(H 100 A large value of C×(H −H0) means that the amount of deflection of the core when a predetermined load is applied is large, and the value obtained by subtracting the center hardness from the surface hardness of the core is larger than that of conventional cores. Specifically, as shown in Figure 5, if the amount of deflection when a predetermined load is applied is the same in each example and comparative example, it can be seen that the difference between the surface hardness and the center hardness of the core in each example is sufficiently higher than in each comparative example. 100 The value of (H0) is preferably 125.0 or more, more preferably 130.0 or more, and even more preferably 135.0 or more, with the upper limit being preferably 200.0 or less, more preferably 180.0 or less, and even more preferably 160.0 or less. If this value is too small, the amount of spin on a full shot may increase, making it impossible to achieve the desired distance. On the other hand, if this value is too large, the durability to cracking may decrease when hit repeatedly, or the resilience may decrease, making it impossible to achieve the desired distance.

[0053] The initial velocity of the core is preferably 75.8 m / s or greater, more preferably 76.3 m / s or greater, and even more preferably 76.6 m / s or greater. The upper limit is preferably 77.5 m / s or less, more preferably 77.2 m / s or less, and even more preferably 76.9 m / s. If this initial velocity value is too high, the initial velocity of the ball will be too high and may violate the rules. On the other hand, if the initial velocity of the core is too low, the ball's resilience may be reduced or the amount of spin may be increased on full shots, resulting in an inability to achieve the desired distance. The initial velocity values ​​in this case are values ​​measured using a COR-type initial velocity meter, the same type as that used by R&A. Specifically, a COR-type initial velocity device manufactured by Hye Precision in the United States was used. The measurement conditions were as follows: air pressure was varied in four stages, and a relationship between the incident velocity and COR was established. From this relationship, the initial velocity at an incident velocity of 43.83 m / s was calculated. The measurement environment for the COR-type initial velocity device is such that a ball that has been kept in a thermostatic chamber at 23.9±1°C for at least three hours is used, and measurements are taken at a room temperature of 23.9±2°C. The barrel diameter set when measuring with the COR-type initial velocity device is selected so that the clearance on one side between the outer diameter of the object being measured is between 0.2 and 2.0 mm.

[0054] Next, the intermediate layer will be described. The material hardness of the intermediate layer is not particularly limited, but is preferably 90 or more, more preferably 92 or more, and even more preferably 93 or more in Shore C hardness, with the upper limit being preferably 100 or less, more preferably 98 or less, and even more preferably 96 or less.The Shore D hardness is preferably 64 or more, more preferably 66 or more, and even more preferably 67 or more, with the upper limit being preferably 75 or less, more preferably 72 or less, and even more preferably 70 or less.

[0055] The surface hardness of a sphere in which the core is covered with an intermediate layer (intermediate layer-covered sphere) is preferably 95 or more, more preferably 96 or more, and even more preferably 97 or more on the Shore C scale, with the upper limit being preferably 100 or less, more preferably 99 or less, and even more preferably 98 or less.The surface hardness of a sphere in which the core is covered with an intermediate layer is preferably 68 or more, more preferably 69 or more, and even more preferably 70 or more, with the upper limit being preferably 78 or less, more preferably 75 or less, and even more preferably 72 or less on the Shore D scale.

[0056] If the material hardness and surface hardness of these intermediate layers are too soft, the spin rate on full shots may increase too much, resulting in a loss of distance, or the initial velocity of the ball may decrease, resulting in a loss of distance.On the other hand, if the material hardness and surface hardness of the intermediate layer are too hard, the durability to cracking caused by repeated impacts may decrease, or the feel on impact with a putt or on short approaches may become too hard.

[0057] The thickness of the intermediate layer is preferably 1.00 mm or more, more preferably 1.25 mm or more, and even more preferably 1.45 mm or more. The upper limit of the thickness of the intermediate layer is preferably 1.80 mm or less, more preferably 1.65 mm or less, and even more preferably 1.55 mm or less. If the thickness of the intermediate layer is outside the above range, the ball may not have sufficient spin-reducing effect when hit with a driver (W#1), resulting in a loss of distance. Furthermore, if the intermediate layer is too thin, the resistance to cracking due to repeated impacts and the durability at low temperatures may be poor.

[0058] It is preferable to use an ionomer resin as the main material for the mid layer.

[0059] The ionomer resin material may include a high-acid content ionomer resin having an unsaturated carboxylic acid content (also referred to as "acid content") of 16% by mass or more.

[0060] The content of the high-acid-content ionomer resin is typically greater than 0% by mass, preferably at least 30% by mass, and more preferably at least 60% by mass, relative to 100% by mass of the resin material. The upper limit is preferably at most 100% by mass, more preferably at most 90% by mass, and even more preferably at most 85% by mass. If the amount of the high-acid-content ionomer resin is too small, the ball may have a high spin rate on full shots, resulting in a loss of distance. On the other hand, if the amount of the high-acid-content ionomer resin is too large, the durability to repeated impacts may be impaired.

[0061] Furthermore, when an ionomer resin is used as the primary material, a desirable embodiment is one in which a zinc-neutralized ionomer resin and a sodium-neutralized ionomer resin are mixed and used as the primary material. The blending ratio, zinc-neutralized / sodium-neutralized (by mass), is 5 / 95 to 95 / 5, preferably 10 / 90 to 90 / 10, and more preferably 15 / 85 to 85 / 15. If the zinc-neutralized ionomer and sodium-neutralized ionomer are not included within this ratio, the resilience may be too low to achieve the desired distance, and crack resistance may be poor during repeated impacts at room temperature and even at low temperatures (below freezing).

[0062] Any additives can be added to the intermediate layer material depending on the application. For example, various additives such as pigments, dispersants, antioxidants, UV absorbers, and light stabilizers can be added. When these additives are added, the amount of the additives added is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and preferably 10 parts by mass or less, more preferably 4 parts by mass or less, per 100 parts by mass of the base resin.

[0063] It is preferable to polish the surface of the intermediate layer material to improve adhesion with the polyurethane that is preferably used in the cover material described below. After the polishing process, it is also preferable to apply a primer (adhesive) to the surface of the intermediate layer or to add an adhesion enhancer to the material.

[0064] The material for the intermediate layer may contain an inorganic granular filler. This inorganic granular filler is not particularly limited, but zinc oxide, barium sulfate, titanium dioxide, etc. can be used as appropriate. From the viewpoint of excellent resistance to cracking due to repeated impacts, barium sulfate is preferably used, and precipitated barium sulfate is particularly preferably used.

[0065] The average particle size of the inorganic granular filler is not particularly limited, but is preferably 0.01 to 100 μm, and more preferably 0.1 to 10 μm. If the average particle size of the inorganic granular filler is too small or too large, dispersibility during material preparation may be impaired. The average particle size refers to the particle size measured by a particle size distribution analyzer after dispersing the filler in an aqueous solution together with an appropriate dispersing agent.

[0066] The amount of inorganic granular filler is not particularly limited, but is preferably 0 parts by weight or more, more preferably 10 parts by weight or more, and even more preferably 15 parts by weight or more per 100 parts by weight of the base resin of the mid layer material. The upper limit is also not particularly limited, but is 50 parts by weight or less, preferably 40 parts by weight or less, and even more preferably 30 parts by weight or less. If the amount of inorganic granular filler is too low, the durability against cracking due to repeated impacts may be poor. On the other hand, if the amount of inorganic granular filler is too high, the resilience of the ball may be reduced or the spin rate of the ball may be increased on full shots, resulting in a loss of the desired flight distance.

[0067] The specific gravity of the intermediate layer is preferably 1.05 or more, more preferably 1.07 or more, and even more preferably 1.09 or more, with the upper limit being preferably 1.25 or less, more preferably 1.20 or less, and even more preferably 1.15 or less. If the specific gravity of the intermediate layer is too low, the durability against cracking due to repeated impacts may be poor. On the other hand, if the specific gravity of the intermediate layer is too high, the resilience of the ball may be reduced or the amount of spin on the ball on full shots may be increased, resulting in a failure to achieve the desired distance.

[0068] The deflection (mm) of the intermediate layer-covered sphere when subjected to an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf) is not particularly limited, but is preferably at least 2.90 mm, more preferably at least 3.10 mm, and even more preferably at least 3.25 mm, with the upper limit being preferably at most 4.10 mm, more preferably at most 3.90 mm, and even more preferably at most 3.70 mm. If the deflection of the intermediate layer-covered sphere is too small, i.e., if the intermediate layer-covered sphere is too hard, the ball may have too much spin, resulting in a loss of flight distance, or the feel on impact may be too hard. On the other hand, if the deflection of the intermediate layer-covered sphere is too large, i.e., if the intermediate layer-covered sphere is too soft, the ball may have too little resilience, resulting in a loss of flight distance, a too soft feel on impact, or poor durability to cracking upon repeated impact.

[0069] The initial velocity of a ball consisting of a core covered with an intermediate layer (intermediate layer-covered ball) is preferably 77.0 m / s or greater, more preferably 77.3 m / s or greater, and even more preferably 77.5 m / s or greater. The upper limit is preferably 78.5 m / s or less, more preferably 78.2 m / s or less, and even more preferably 77.9 m / s. If this initial velocity is too high, the ball's initial velocity may be too high and violate the rules. On the other hand, if this initial velocity is too low, the ball's resilience may be reduced or the amount of spin may be too high on full shots, preventing the desired flight distance. The initial velocity in this case is measured using the same equipment and conditions as those used to measure the initial velocity of the core described above.

[0070] Next, the cover will be described. The cover material hardness is not particularly limited, but is preferably 50 or greater, more preferably 55 or greater, and even more preferably 59 or greater in Shore C hardness, with the upper limit being preferably 80 or less, more preferably 74 or less, and even more preferably 70 or less. The cover material hardness is preferably 30 or greater, more preferably 35 or greater, and even more preferably 38 or greater, with the upper limit being preferably 53 or less, more preferably 48 or less, and even more preferably 45 or less in Shore D hardness.

[0071] The surface hardness of a sphere (ball) obtained by covering a sphere covered with an intermediate layer, in Shore C hardness, is preferably 73 or more, more preferably 78 or more, and even more preferably 81 or more, with an upper limit of preferably 94 or less, more preferably 91 or less, and even more preferably 88 or less. The Shore D hardness is preferably 50 or more, more preferably 53 or more, and even more preferably 56 or more, with an upper limit of preferably 70 or less, more preferably 65 or less, and even more preferably 60 or less.

[0072] If the cover material hardness and surface hardness are too softer than the above ranges, the spin rate on full shots may increase too much, resulting in a loss of distance, whereas if the cover material hardness and surface hardness are too hard, the spin rate on approaches may decrease or the abrasion resistance may be poor.

[0073] The cover thickness is preferably 0.3 mm or more, more preferably 0.4 mm or more, and even more preferably 0.6 mm or more. The upper limit of the cover thickness is preferably 1.2 mm or less, more preferably 0.9 mm or less, and even more preferably 0.8 mm or less. If the cover is too thick, the ball may not have sufficient resilience on full shots or may generate too much spin, resulting in a loss of distance. On the other hand, if the cover is too thin, the abrasion resistance may be poor, or the ball may not generate enough spin on approaches, resulting in a lack of controllability.

[0074] The cover can be made of a polyurethane resin, which provides excellent spin control and abrasion resistance during the short game. Furthermore, a resin material primarily composed of thermoplastic polyurethane is preferred for its mass-productivity. That is, the cover is preferably made of a resin blend primarily composed of (I) thermoplastic polyurethane and (II) a polyisocyanate compound.

[0075] The total mass of the components (I) and (II) is preferably 60% or more, and more preferably 70% or more, of the total mass of the resin composition of the cover. Components (I) and (II) are described in detail below.

[0076] Regarding the above-mentioned (I) thermoplastic polyurethane, the structure of the thermoplastic polyurethane includes a soft segment composed of a long-chain polyol (polymeric glycol) and a hard segment composed of a chain extender and a polyisocyanate compound. The long-chain polyol used as the raw material can be any of those conventionally used in thermoplastic polyurethane-related technologies, and is not particularly limited. Examples of such long-chain polyols include polyester polyols, polyether polyols, polycarbonate polyols, polyester polycarbonate polyols, polyolefin polyols, conjugated diene polymer polyols, castor oil polyols, silicone polyols, and vinyl polymer polyols. These long-chain polyols may be used alone or in combination. Among these, polyether polyols are preferred because they can synthesize thermoplastic polyurethanes with high rebound resilience and excellent low-temperature properties.

[0077] The chain extender may be any of those used in conventional thermoplastic polyurethane technologies, and is preferably a low-molecular-weight compound having two or more active hydrogen atoms in the molecule that can react with isocyanate groups and a molecular weight of 400 or less. Examples of the chain extender include, but are not limited to, 1,4-butylene glycol, 1,2-ethylene glycol, 1,3-butanediol, 1,6-hexanediol, and 2,2-dimethyl-1,3-propanediol. Of these, aliphatic diols having 2 to 12 carbon atoms are preferred, and 1,4-butylene glycol is more preferred.

[0078] The polyisocyanate compound may be any of those used in conventional thermoplastic polyurethane technologies, and is not particularly limited. Specifically, one or more compounds selected from the group consisting of 4,4'-diphenylmethane diisocyanate, 2,4-(or) 2,6-toluene diisocyanate, p-phenylene diisocyanate, xylylene diisocyanate, naphthylene 1,5-diisocyanate, tetramethylxylene diisocyanate, hydrogenated xylylene diisocyanate, dicyclohexylmethane diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, norbornene diisocyanate, trimethylhexamethylene diisocyanate, and dimer acid diisocyanate may be used. However, some isocyanate species may make it difficult to control the crosslinking reaction during injection molding. From the viewpoint of the balance between stability during production and the physical properties that are exhibited, 4,4'-diphenylmethane diisocyanate, which is an aromatic diisocyanate, is most preferred.

[0079] Specific thermoplastic polyurethanes of component (I) may be commercially available products, such as Pandex T8295, T8290, and T8260 (all manufactured by DIC Covestro Polymers).

[0080] Although not a required component, a thermoplastic elastomer other than the thermoplastic polyurethane may be blended as component (III) in addition to components (I) and (II). By blending component (III) in the resin blend, it is possible to further improve the flowability of the resin blend and enhance the various physical properties required of a golf ball cover material, such as resilience and abrasion resistance.

[0081] The composition ratio of the above components (I), (II), and (III) is not particularly limited, but is preferably (I):(II):(III)=100:2-50:0-50 by mass, and more preferably (I):(II):(III)=100:2-30:8-50 (by mass).

[0082] Furthermore, various additives other than the components constituting the thermoplastic polyurethane may be blended into the resin blend as needed. For example, pigments, dispersants, antioxidants, light resistance stabilizers, ultraviolet absorbers, mold release agents, etc. may be blended as appropriate.

[0083] The specific gravity of the cover is not particularly limited, but is preferably 1.00 or higher, more preferably 1.03 or higher, and even more preferably 1.06 or higher, with the upper limit being preferably 1.20 or lower, more preferably 1.17 or lower, and even more preferably 1.14 or lower. If the specific gravity of the cover is lower than the above range, the proportion of low-specific-gravity materials such as ionomer blended into the main urethane cover will be high, which may result in poor abrasion resistance. On the other hand, if the specific gravity of the cover is too high, the amount of filler added will be too high, which may result in too low resilience and make it difficult to achieve the desired distance.

[0084] The golf ball formed by laminating the above-mentioned core, intermediate layer, and cover (outermost layer) can be manufactured by a conventional method such as a known injection molding method. For example, a multi-piece golf ball can be obtained by injecting the intermediate layer material around the core using an injection mold to obtain an intermediate layer-covered sphere, and finally, injection molding the material for the cover, which is the outermost layer. Alternatively, a golf ball can be manufactured by preparing two half-shelled spherical half cups in advance, encasing the core and intermediate layer-covered sphere in these, and then molding them under heat and pressure.

[0085] The deflection (mm) of the golf ball when subjected to an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf) is preferably 2.80 mm or more, more preferably 2.90 mm or more, and even more preferably 3.00 mm or more. The upper limit of the deflection is preferably 3.80 mm or less, more preferably 3.60 mm or less, and even more preferably 3.40 mm or less. If the golf ball's deflection is too small, i.e., too hard, the spin rate may increase too much, resulting in a loss of flight distance, or the feel on impact may be too hard. On the other hand, if the deflection is too large, i.e., the golf ball is too soft, the resilience of the ball may be too low, resulting in a loss of flight distance, the feel may be too soft, or the durability to cracking upon repeated impact may be poor.

[0086] The initial velocity of a ball (a sphere formed by encasing a sphere covered with an intermediate layer and a cover) is preferably 76.5 m / s or more, more preferably 77.0 m / s or more, and even more preferably 77.2 m / s or more, with the upper limit being 77.724 m / s or less. If this initial velocity is too high, the ball's initial velocity will be too high and will be outside the rules. On the other hand, if this initial velocity is too low, the ball may not fly as far on a full shot. The initial velocity in this case is determined using the same equipment and conditions as those used to measure the initial velocity of the core and intermediate layer-covered sphere described above.

[0087] [ Regarding the relationship between the surface hardness of each sphere 〕 The surface hardness of the intermediate layer-covered sphere minus the surface hardness of the core is, in Shore C hardness, preferably greater than 0, more preferably at least 8, and even more preferably at least 10, with the upper limit being preferably no greater than 32, more preferably no greater than 25, and even more preferably no greater than 20. If the value deviates from this range, the amount of spin on the ball will increase on full shots, which may prevent the desired flight distance from being achieved.

[0088] The surface hardness of the intermediate layer-covered sphere minus the center hardness of the core is preferably 40 or more, more preferably 41 or more, and even more preferably 42 or more, in Shore C hardness, with the upper limit being preferably 53 or less, more preferably 50 or less, and even more preferably 47 or less. If this value is too small, the ball's spin rate increases on full shots, which can result in the ball not achieving the desired distance. On the other hand, if this value is too large, the ball's durability to cracking after repeated impacts may be reduced, or the initial velocity may be low, preventing the desired distance from being achieved.

[0089] The surface hardness of the ball minus the surface hardness of the intermediate layer-covered sphere is preferably greater than 0, more preferably greater than 4, and even more preferably greater than 6, in Shore C hardness. The upper limit is preferably 25 or less, more preferably 17 or less, and even more preferably 14 or less. If this value is too small and is due to the cover hardness, controllability in the short game may be impaired. Furthermore, if the intermediate layer hardness is the cause, the spin rate on full shots may increase, making it impossible to achieve the desired distance. On the other hand, if this value is too large and is due to the cover hardness, the spin rate on full shots may increase, making it impossible to achieve the desired distance. Furthermore, if the intermediate layer hardness is the cause, the ball may be less durable to cracking when hit repeatedly, or may have poor spin controllability in the short game.

[0090] [ Regarding the initial velocity of each sphere 〕 The relationship between the initial velocity of a ball with a core covered with an intermediate layer (an intermediate-layer-covered ball) and the initial velocity of a ball with a cover covered with an intermediate layer (a ball) is calculated using the following formula: (Initial velocity of ball)<(Initial velocity of intermediate layer-coated sphere) It is preferable that the following condition be satisfied. The value obtained by subtracting the initial velocity of the ball from the initial velocity of the intermediate layer-covered sphere is greater than 0 m / s, preferably 0.10 m / s or greater, and more preferably 0.30 m / s or greater, with the upper limit being preferably 1.00 m / s or less, more preferably 0.70 m / s or less, and even more preferably 0.50 m / s or less. If this value is too large, the ball may have an increased spin rate on full shots or a lower initial velocity, making it impossible to achieve the desired distance. On the other hand, if this value is too small, the ball may have an increased spin rate on full shots, making it impossible to achieve the desired distance.

[0091] The initial velocity of the intermediate layer-covered sphere minus the initial velocity of the core is preferably 0.65 m / s or more, more preferably 0.72 m / s or more, and even more preferably 0.80 m / s or more, with the upper limit being preferably 0.98 m / s or less, more preferably 0.95 m / s or less, and even more preferably 0.92 m / s or less. If this value is too high, the durability to cracking when hit repeatedly may be poor. On the other hand, if this value is too low, the amount of spin increases on full shots, which may prevent the desired distance from being achieved.

[0092] [ Specific gravity relationship between the middle layer and the cover 〕 It is recommended that the difference in specific gravity between the intermediate layer and the cover be within ±0.15, preferably ±0.10, and more preferably ±0.05. That is, the value of (specific gravity of the cover) minus (specific gravity of the intermediate layer material) is typically at least -0.15, preferably at least -0.10, and more preferably at least -0.05, with the upper limit typically being 0.15 or less, preferably 0.10 or less, and more preferably 0.05 or less. If the difference in specific gravity between these layers is too large, the intermediate layer material and / or the cover material may not be molded perfectly concentrically with the layer located inside them, resulting in eccentricity, which may result in significant left-right deviation when the ball is hit with a putter.

[0093] [ The specific gravity relationship between the middle layer and the core 〕 It is recommended that the difference between the specific gravity of the intermediate layer and the specific gravity of the core be within ±0.15, preferably ±0.10, and more preferably ±0.05. That is, the value of (intermediate layer specific gravity) - (core specific gravity) is typically -0.15 or more, preferably -0.10 or more, and more preferably -0.05 or more, with the upper limit typically being 0.15 or less, preferably 0.10 or less, and more preferably 0.05 or less. If the difference in specific gravity between these layers is too large, and the intermediate layer material is not molded perfectly concentrically with the core layer and ends up eccentric, the ball may experience significant left-right deviation when hit with a putter.

[0094] [ Core diameter and ball diameter 〕 The relationship between the core diameter and the ball diameter, i.e., the value of (core diameter) / (ball diameter), is preferably 0.860 or greater, more preferably 0.870 or greater, and even more preferably 0.880 or greater. The upper limit, on the other hand, is preferably 0.940 or less, more preferably 0.910 or less, and even more preferably 0.895 or less. If this value is too small, the initial velocity of the ball will be low, or the overall deflection of the ball will be small, making the ball harder. This may increase the spin rate of the ball on full shots, preventing the desired distance from being achieved. On the other hand, if this value is too large, the spin rate of the ball will be high, preventing the desired distance from being achieved, or the durability to cracking during repeated impacts may be poor.

[0095] [ Difference in deflection between the core and the ball 〕 When the core and ball are subjected to an initial load of 98 N (10 kgf) and a final load of 1,275 N (130 kgf), the deflection (mm) is defined as C (mm) and B (mm), respectively. The value of CB is preferably 1.00 mm or more, more preferably 1.20 mm or more, and even more preferably 1.30 mm or more, with the upper limit being preferably 1.80 mm or less, more preferably 1.70 mm or less, and even more preferably 1.60 mm or less. If this value is too small, the spin rate on full shots may increase, making it difficult to achieve the desired distance. On the other hand, if this value is too large, the initial velocity on actual impact may decrease, making it difficult to achieve the desired distance when hit with a driver (W#1), and may result in poor durability to cracking when hit repeatedly.

[0096] [Relationship between the thickness of the intermediate layer and the cover] The value obtained by subtracting the cover thickness from the intermediate layer thickness is preferably at least -0.1 mm, more preferably at least 0.2 mm, and even more preferably at least 0.4 mm, with the upper limit being preferably at most 1.0 mm, more preferably at most 0.8 mm, and even more preferably at most 0.7 mm. If this value deviates from the above range, the amount of spin on the ball on full shots may increase, the initial velocity may decrease, and the desired flight distance may not be achieved. If this value is too small, the durability to cracking may decrease when hit repeatedly.

[0097] A large number of dimples can be formed on the outer surface of the cover. There are no particular restrictions on the number of dimples to be arranged on the cover surface, but the number is preferably 250 or more, preferably 300 or more, more preferably 320 or more, with the upper limit being preferably 380 or less, more preferably 350 or less, and even more preferably 340 or less. If the number of dimples exceeds the above range, the ball's trajectory may be lowered, resulting in a shorter flight distance. On the other hand, if the number of dimples is lower, the ball's trajectory may be higher, resulting in a shorter flight distance.

[0098] The dimples may be of one or a combination of two or more shapes, such as circular, polygonal, dewdrop, or elliptical. For example, if circular dimples are used, the diameter may be approximately 2.5 mm to 6.5 mm, and the depth may be 0.08 mm to 0.30 mm.

[0099] The dimple coverage (SR value), which is the ratio of the total dimple area defined by the planes surrounded by the dimple edges to the ball's area assuming no dimples, is preferably 70% to 90% in order to fully demonstrate aerodynamic characteristics. Furthermore, V0, the value obtained by dividing the spatial volume of each dimple below the plane surrounded by the dimple edges by the volume of a cylinder whose base is the plane and whose height is the maximum depth of the dimple from the bottom, is preferably 0.35 to 0.80 in order to optimize the ball's trajectory. Furthermore, the VR value, which is the ratio of the total dimple volume below the planes surrounded by the dimple edges to the ball's area assuming no dimples, is preferably 0.6% to 1.0%. Any deviation from the above-mentioned ranges may result in a poor trajectory and an insufficient flight distance.

[0100] The golf ball of the present invention can be made to conform to the Rules of Golf for competitive use, with an outer diameter that does not pass through a ring with an inner diameter of 42.672 mm, and a mass preferably ranging from 45.0 to 45.93 g. [Example]

[0101] EXAMPLES The present invention will be specifically explained below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0102] [Examples 1 to 5, Comparative Examples 1 to 7] Core formation For Examples 1 and 3 and Comparative Examples 1 to 7, the rubber compositions shown in Table 1 were prepared, and then vulcanized and molded under the vulcanization conditions shown in Table 1 to produce solid cores.

[0103] For Examples 2, 4, and 5, cores were prepared based on the formulations in Table 1 in the same manner as above.

[0104] [Table 1]

[0105] Details of the above formulation are as follows: Polybutadiene: Product name "BR730" (manufactured by ENEOS Materials Co., Ltd.) Zinc acrylate: Product name "ZN-DA85S" (manufactured by Nippon Shokubai Co., Ltd.) Organic peroxide A: Dicumyl peroxide, trade name "Percumyl D" (manufactured by NOF Corporation) Organic peroxide B: a mixture of 1,1-di(t-butylperoxy)cyclohexane and silica, trade name "Perhexa C-40" (manufactured by NOF Corporation) Sulfur: Product name: "Sunmix S-80N" (manufactured by Sanshin Chemical Industry Co., Ltd., containing 80 wt% powdered sulfur for rubber) Water: Pure water (Seiki Pharmaceutical Co., Ltd.) Antioxidant A: 2,2-methylenebis(4-methyl-6-butylphenol), product name "Nocrac NS-6" (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) Antioxidant B: 2-mercaptobenzimidazole, product name "Nocrac MB" (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) Zinc stearate: Product name "Zinc Stearate GP" (NOF Corporation) Zinc oxide: Product name "Triple Zinc Oxide" (manufactured by Sakai Chemical Industry Co., Ltd.) Pentachlorothiophenol zinc salt: Fujifilm Wako Pure Chemical Industries, Ltd.

[0106] Formation of the intermediate layer and cover (outermost layer) Next, for Examples 1 and 3 and Comparative Examples 1 to 7, an intermediate layer was formed by injection molding the intermediate layer resin material No. 1 or No. 2 shown in Table 2 around the surface of the core using an injection mold. Next, a cover (outermost layer) resin material No. 3 shown in Table 2 was injection molded around the intermediate layer-covered sphere using another injection mold to form a cover. At this time, a predetermined number of dimples common to all Examples and Comparative Examples were formed on the surface of the cover.

[0107] For Examples 2, 4, and 5, an intermediate layer was formed by injection molding the intermediate layer resin material No. 1 or No. 2 shown in Table 2 around the surface of the core using an injection mold. Next, a cover (outermost layer) resin material No. 3 shown in Table 2 was injection molded around the intermediate layer-covered sphere using another injection mold to form a cover. At this time, a predetermined number of dimples common to all Examples and Comparative Examples were formed on the surface of the cover.

[0108] [Table 2]

[0109] The details of the ingredients in the above table are as follows: The trade names of the main materials listed in the table are as follows: "Himilan 1605", "Himilan 1557", "Himilan 1706", "AM7318" Ionomers manufactured by Mitsui Dow Polychemicals "Barium sulfate" "Precipitated Barium Sulfate 300" manufactured by Sakai Chemical Industry Co., Ltd. "Trimethylolpropane" (TMP) manufactured by Tokyo Chemical Industry Co., Ltd. "TPU" is a trade name "Pandex" manufactured by DIC Covestro Polymer, an ether-type thermoplastic polyurethane with a material hardness (Shore D) of 42.

[0110] For each of the resulting golf balls, various physical properties such as the internal hardness at each position of the core, the outer diameter of the core and each coated sphere, the thickness and material hardness of each layer, the surface hardness of each coated sphere, and the initial velocity of each coated sphere were evaluated using the methods described below, and the results are shown in Tables 3 and 4.

[0111] Core hardness distribution The core's surface is spherical, and the needle of a hardness tester is set nearly perpendicular to the spherical surface, and the surface hardness is measured in Shore C hardness in accordance with ASTM D2240. For the center and specified positions of the core, the core is cut into a hemisphere, the cross section is flattened, and the needle of the hardness tester is pressed perpendicularly against the center and the specified positions shown in Table 3. The hardness at the center and each position is shown in Shore C hardness. Hardness measurements are performed using an automatic rubber hardness tester "P2" manufactured by Kobunshi Keiki Co., Ltd., equipped with a Shore C hardness tester. The maximum hardness value is read. All measurements are performed in an environment of 23±2°C. The values ​​in the table are Shore C hardness values. Regarding the hardness distribution of the core, The Shore C hardness of the core center is H0. The Shore C hardness at a distance of 12.5% ​​of the core radius from the core center is H 12.5 , The Shore C hardness at a distance of 25% of the core radius from the core center is H 25 , The Shore C hardness at a distance of 37.5% of the core radius from the core center is H 37.5 , The Shore C hardness at the point 50% of the core radius from the center of the core is H 50 , The Shore C hardness at a distance of 62.5% of the core radius from the core center is H 62.5 , The Shore C hardness at the position 75% of the core radius from the center of the core is H 75 , The Shore C hardness at a distance of 87.5% of the core radius from the core center is H 87.5 , The Shore C hardness of the core surface is H 100 The hardness difference between the following positions is defined as: A: H 100 -H87.5 B: H 87.5 -H 75 C: H 75 -H 62.5 D: H 62.5 -H 50 E: H 50 -H 37.5 F: H 37.5 -H 25 G: H 25 -H 12.5 H: H 12.5 -H0 and finally calculate the values ​​of the following two formulas. (1) (C+D)-(E+F+G+H) (2) (A+B)-(E+F+G+H)

[0112] FIG. 2 is a schematic diagram illustrating the hardness differences A to H between positions in the core hardness distribution, using the core hardness distribution data of Example 1. Graphs of the core hardness distributions of Examples 1 to 5 and Comparative Examples 1 to 7 are shown in FIGS.

[0113] The outer diameter of each core and intermediate layer coated sphere The temperature is adjusted to 23.9±1°C in a thermostatic chamber for at least 3 hours, and then measurements are taken at any 5 points on the surface in a room at 23.9±2°C. The average value is used as the measurement value for one sphere, and the average value for 10 measurements is calculated.

[0114] Ball diameter The ball is placed in a thermostatic chamber at 23.9±1°C for at least three hours, and then 15 randomly selected non-dimpled areas are measured in a room at 23.9±2°C. The average of these measurements is used as the measurement value for one ball, and the average value for 10 balls is calculated.

[0115] Deflection of the core, the mid-layer covered sphere, and the ball Each covered sphere is placed on a hard plate and the amount of deflection is measured when an initial load of 98 N (10 kgf) is applied and a final load of 1275 N (130 kgf) is applied. The above deflection is measured in a room at 23.9 ± 2°C after being regulated at 23.9 ± 1°C for at least three hours. The head compression speed for compressing the core, each layer of covered sphere, or the ball is 10 mm / s. FIG. 5 is a graph showing the relationship between the amount of deflection of the core and the difference in hardness between the surface hardness and the center hardness of the core for each example and comparative example.

[0116] Mid layer and cover material hardness (Shore C hardness, Shore D hardness) The resin material for each layer was molded into a 2 mm thick sheet and left to stand at a temperature of 23 ± 2°C for two weeks. Three sheets were stacked together during measurement. The Shore C hardness and Shore D hardness were measured using a Shore C hardness tester and a Shore D hardness tester, respectively, in accordance with the ASTM D2240 standard. To measure hardness, an automatic rubber hardness tester "P2" manufactured by Kobunshi Keiki Co., Ltd., equipped with a Shore C or Shore D hardness tester, was used. The hardness value was read as the maximum value. The measurement method followed the ASTM D2240 standard.

[0117] Surface hardness of the intermediate layer coated sphere and each ball Measurements are taken by pressing a needle perpendicularly against the surface of each sphere. The surface hardness of the ball (cover) is measured on the land area on the ball surface where no dimples are formed. Shore C hardness and Shore D hardness are measured using a Shore C hardness tester and a Shore D hardness tester, respectively, that comply with the ASTM D2240 standard. To measure hardness, an automatic rubber hardness tester "P2" manufactured by Kobunshi Keiki Co., Ltd., equipped with a Shore C or Shore D hardness tester, is used. The hardness value is read as the maximum value. The measurement method complies with the ASTM D2240 standard.

[0118] The initial velocity of each sphere The initial velocity of each ball is measured at 23.9±2°C using a COR type initial velocity meter manufactured by Hye Precision Products, the same type as that used by the R&A. The measurement principle is as follows. The air pressure is changed to four levels: 35.5, 36.5, 39.5, and 40.5 psi. The ball is launched at four different entry velocities at each air pressure, and the ball is allowed to collide with the barrier, measuring its COR (coefficient of restitution). In other words, the air pressure is changed to four levels, and a correlation equation is created between entry velocity and COR. Similarly, a correlation equation is created between entry velocity and contact time. Then, from these correlation equations, the COR (coefficient of restitution) and contact time (μs) at an incident velocity of 43.83 m / s are calculated, and substituted into the initial velocity conversion formula below to calculate the initial velocity of each ball. IV=136.8+136.3e+0.019tc (Where e is the coefficient of restitution and tc is the contact time (μs) at an impact velocity of 143.8 ft / s (43.83 m / s).) When measuring the initial velocity of each sphere, the barrel diameter was selected to provide a clearance between 0.2 and 2.0 mm on one side of the diameter of the object being measured. The cores used in the present examples and comparative examples were all 39.88 mm, the intermediate layer-covered spheres were all 41.53 mm, and the balls were all 43.18 mm.

[0119] [Table 3]

[0120] [Table 4]

[0121] The distance (driver), (utility), (I#6), and (I#8) of each golf ball, its controllability during approach shots, and its durability against repeated shots were evaluated using the following methods. The results are shown in Table 5.

[0122] Distance rating (W#1, HS40m / s) A driver club is attached to the golf hitting robot, and the spin rate and total distance are measured when hitting the ball at a head speed (HS) of 40 m / s. The club used is the Bridgestone Sports "JGR Driver (2016 model)" (loft angle 9.5°), and evaluation is based on the following criteria. 〔Judgment criteria〕 Total distance over 209.0m Total distance less than 209.0m ×

[0123] Distance rating (W#1, HS35m / s) A driver club is attached to the golf hitting robot, and the spin rate and total distance are measured when hitting the ball at a head speed (HS) of 35 m / s. The club used is the Bridgestone Sports "JGR Driver (2016 model)" (loft angle 9.5°), and evaluation is based on the following criteria. 〔Judgment criteria〕 Total distance over 178.5m Total flight distance is less than 178.5m... ×

[0124] Distance rating (utility) A utility club is attached to the golf hitting robot, and the spin rate and flight distance (total) are measured when hitting the ball at a head speed (HS) of 38 m / s. The club used is the Bridgestone Sports JGR H2 (2016 model). The evaluation criteria are as follows: 〔Judgment criteria〕 Total distance over 160.0m Total flight distance is less than 160.0m ×

[0125] Distance rating (I#6, HS40m / s) A 6-iron (I#6) is attached to the golf hitting robot, and when it hits the ball at a head speed (HS) of 40 m / s, the spin rate and flight distance (total) are measured and judged according to the following criteria. The club used is the Bridgestone Sports JGR Forged I#6 (2016 model). 〔Judgment criteria〕 Total distance over 168.0m Total distance less than 168.0m ×

[0126] Distance rating (I#6, HS35m / s) A 6-iron (I#6) is attached to the golf hitting robot, and when it hits the ball at a head speed (HS) of 35 m / s, the spin rate and flight distance (total) are measured and judged according to the following criteria. The club used is the Bridgestone Sports JGR Forged I#6 (2016 model). 〔Judgment criteria〕 Total distance over 146.0m Total flight distance is less than 146.0m ×

[0127] Flight rating (I#8) An 8-iron (I#8) is attached to the golf hitting robot, and when it hits the ball at a head speed (HS) of 35 m / s, the spin rate and flight distance (total) are measured and judged according to the following criteria. The club used is the Bridgestone Sports JGR Forged I#8 (2016 model). 〔Judgment criteria〕 Total distance over 131.0m Total distance less than 131.0m ×

[0128] Evaluating spin rate during approach The sand wedge is attached to a golf hitting robot and hit at a head speed (HS) of 15 m / s, and the amount of spin is measured. The amount of spin is also measured immediately after hitting the ball using an initial condition measuring device. The sand wedge used is the "TourStage TW-03 (loft angle 57°) 2002 model" manufactured by Bridgestone Sports. 〔Judgment criteria〕 ○ Spin rate of 4400 rpm or more × Spin rate less than 4400 rpm

[0129] Resistance to cracking due to repeated impacts Ball durability was evaluated using an ADC Ball COR Durability Tester manufactured by Automated Design Corporation in the United States. A golf ball was fired using air pressure and then collided continuously with two parallel metal plates. The average number of shots required for the ball to break was taken as the durability. In this case, the average value was calculated by preparing 10 identical balls, firing each ball, and averaging the number of shots required for each of the 10 balls to break. The tester was a horizontal COR, and the incident speed on the metal plates was 43 m / s. 〔Judgment criteria〕 ○ Average value: 160 times or more × Average value 159 times or less

[0130] [Table 5]

[0131] As shown in the results in Table 5, the golf balls of Comparative Examples 1 to 7 are inferior to the products of the present invention (Examples) in the following respects. In Comparative Example 1, the difference in hardness between the surface and the center of the core (H 100 -H0) is less than 30.0, and is calculated by multiplying the "amount of deflection of the core when a specified load is applied" by the "difference in hardness between the surface and center of the core" using the formula "C × (H 100-H0) is less than 125.0. As a result, the distance is not achieved when hitting with a driver (W#1, HS40m / s), 6-iron (I#6, HS40m / s) or 8-iron. In Comparative Example 2, the difference in hardness between the surface and center of the core (H 100 -H0) is less than 30.0. As a result, the distance is not achieved when hitting with a driver (W#1, HS40m / s), utility club, or 6-iron. In Comparative Example 3, the difference in hardness between the surface and center of the core (H 100 -H0) is smaller than 30.0, and "C × (H 100 -H0) is less than 125.0. As a result, the distance is not achieved when hitting with a utility club or a 6-iron (I#6, HS40m / s). In Comparative Example 4, the difference in hardness between the surface and the center of the core (H 100 -H0) is less than 30.0. As a result, the distance is not achieved when hitting with a driver (W#1, HS40m / s), utility club, 6-iron (I#6, HS40m / s), or 8-iron. In Comparative Example 5, the difference in hardness between the surface and center of the core (H 100 -H0) is smaller than 30.0, and "C × (H 100 The value of "C + D - H0" is less than 125.0. Furthermore, in the core hardness distribution, the value of (C + D) is not greater than the value of (E + F + G + H). As a result, the golfer does not achieve the desired distance when hitting with a driver (W#1, HS40m / s), driver (W#1, HS35m / s), utility club, 6-iron, or 8-iron. In Comparative Example 6, the difference in hardness between the surface and the center of the core (H 100 -H0) is smaller than 30.0, and "C × (H 100 The value of "C + D" is less than 125.0. Furthermore, in the core hardness distribution, the value of (C + D) is not greater than the value of (E + F + G + H). As a result, the clubhead does not achieve the desired distance when hit with a driver (W#1, HS35m / s) or a 6-iron (I#6, HS40m / s). In Comparative Example 7, the difference in hardness between the surface and the center of the core (H 100The value of "C x (H100 - H0)" is less than 30.0, and the value of "C x (H100 - H0)" is less than 125.0. Furthermore, in the core hardness distribution, the value of (C + D) is not greater than the value of (E + F + G + H). As a result, the club does not achieve the desired distance when hit with a driver (W#1, HS40m / s) or a 6-iron (I#6, HS40m / s). [Explanation of symbols]

[0132] G Golf Ball 1 core 2. Middle class 3 Cover D dimple

Claims

1. A golf ball having a core and a cover, the core being formed as a single layer from a rubber composition, and the cover being formed from a resin composition, wherein the hardness distribution of the core is such that the Shore C hardness at the center of the core is H 0 , the Shore C hardness at a position 12.5% ​​of the core radius from the core center is H 12.5 , the Shore C hardness at a position 25% of the core radius from the core center is H 25 , the Shore C hardness at a position 37.5% of the core radius from the core center is H 37.5 , the Shore C hardness at a position 50% of the core radius from the core center is H 50 , the Shore C hardness at a position 62.5% of the core radius from the core center is H 62.5 , the Shore C hardness at a position 75% of the core radius from the core center is H 75 , the Shore C hardness at a position 87.5% of the core radius from the core center is H 87.5 , the Shore C hardness of the core surface is H 100 When the hardness difference between the following positions is ・A: H 100 -H 87.5 ・B: H 87.5 -H 75 ・C: H 75 -H 62.5 ・D: H 62.5 -H 50 ・E: H 50 -H 37.5 ・F: H 37.5 -H 25 ・G: H 25 -H 12.5 ・H: H 12.5 -H 0 Regarding the following two formulas (I) and (II), (E+F+G+H)<(C+D)...(I) () 100  0 ≧!\0 ･･･(I) and the deflection (mm) when the core is loaded from an initial load of 98N (10kgf) to a final load of 1,275N (130kgf) is C (mm), the following formula is satisfied. C×(H 100 -H 0 )≧125.0 ・・・(III) A golf ball characterized by satisfying the above.

2. Formula (IV) below (E+F+G+H)<(A+B)...(IV) 2. The golf ball of claim 1, wherein the above formula satisfies the above formula.

3. The following formula (V) (E+F+G+H)<(C+D)<(A+B)...(V) 3. The golf ball of claim 1, wherein the above formula satisfies the above formula.

4. Formula (VI) below {(C+D)-(E+F+G+H)}≧3.0...(VI) 3. The golf ball of claim 1, wherein the above formula satisfies the above formula.

5. Formula (VII) below { () 100  0 ))() 50  0 )? 3. The golf ball of claim 1, wherein the above formula satisfies the above formula.

6. The following formula (VIII): { () 87.5  0 ))() 50  0 )? 3. The golf ball of claim 1, wherein the above formula satisfies the above formula.

7. The core comprises the following components (A) to (D): (A) Base rubber (B) Organic peroxide (C) Water or a metal monocarboxylate (D) sulfur 3. The golf ball of claim 1, which is formed from a rubber composition containing:

8. 8. The golf ball of claim 7, wherein the content ratio of components (D) and (C) is 0.005 to 0.100 in terms of a mass ratio of (D) / (C).

9. 3. The golf ball according to claim 1, wherein an intermediate layer is formed between the core and the cover.

10. 10. The golf ball of claim 9, wherein the intermediate layer contains an inorganic particulate filler.

11. 10. The golf ball of claim 9, wherein the specific gravity of the intermediate layer is 1.05 or greater.

12. When the ball is subjected to an initial load of 98N (10kgf) and a final load of 1,275N (130kgf), the deflection (mm) is B (mm). B≧2.80 C-B≧1.00 3. The golf ball of claim 1, wherein the above formula satisfies the above formula.

13. The relationship between the surface hardness of the core, the surface hardness of a sphere with a core covered with an intermediate layer (an intermediate-layer-covered sphere), and the surface hardness of a sphere with an intermediate layer covered with a cover (a golf ball) is expressed by the following formula: Ball surface hardness (surface hardness of mid-layer coated ball) Core surface hardness (However, the surface hardness of each sphere mentioned above means Shore C hardness.) 10. The golf ball of claim 9, which satisfies the following:

14. 10. The golf ball of claim 9, wherein the difference between the specific gravity of the cover and the specific gravity of the intermediate layer is within 0.15, and the difference between the specific gravity of the intermediate layer and the specific gravity of the core is within 0.

15.

15. The relationship between the initial velocity of the entire core, the initial velocity of a sphere with a core covered with an intermediate layer (an intermediate-layer-covered sphere), and the initial velocity of a sphere (a ball) with an intermediate layer covered with a cover is expressed by the following two equations: (Initial velocity of ball) < (Initial velocity of intermediate layer-coated sphere) 0.65≦(initial velocity of intermediate layer-coated sphere)−(initial velocity of entire core)≦0.98 (m / s) 10. The golf ball of claim 9, which satisfies the following:

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