GOLF BALL
20250269242 ยท 2025-08-28
Assignee
Inventors
Cpc classification
International classification
Abstract
A golf ball includes a core and a cover, in which a large number of dimples are formed on an outside surface of the cover, the cover is formed using an ionomer resin as a chief material, an initial velocity of the ball is set within a predetermined range, a deflection when a predetermined load is applied to the ball is set within a predetermined range, a relationship of a ratio to a lift coefficient/drag coefficient at a Reynolds number of 218,000 and a spin rate of 2,800 rpm, a lift coefficient/drag coefficient at a Reynolds number of 184,000 and a spin rate of 2,900 rpm, and a lift coefficient/drag coefficient at a Reynolds number of 158,000 and a spin rate of 3,100 rpm is specified, and a volume occupancy ratio of the dimples is set within a predetermined range.
Claims
1. A golf ball comprising a core and a cover, wherein a large number of dimples are formed on an outside surface of the cover, the cover is formed of an ionomer resin as a chief material, an initial velocity of the ball is from 76.0 to 77.724 m/s, and a deflection when the ball is compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) is not more than 3.8 mm, and when a ratio CL1/CD1 of a lift coefficient CL1 at a Reynolds number of 218,000 and a spin rate of 2,800 rpm to a drag coefficient CD1 is denoted by A1, a ratio CL2/CD2 of a lift coefficient CL2 at a Reynolds number of 184,000 and a spin rate of 2,900 rpm to a drag coefficient CD2 is denoted by A2, and a ratio CL3/CD3 of a lift coefficient CL3 at a Reynolds number of 158,000 and a spin rate of 3,100 rpm to a drag coefficient CD3 is denoted by A3, the following two conditions are satisfied:
2. The golf ball according to claim 1, wherein a value of A1 is from 0.590 to 0.613, a value of A2 is from 0.635 to 0.668, and a value of A3 is from 0.695 to 0.734.
3. The golf ball according to claim 1, wherein a value of A1 is from 0.614 to 0.655, a value of A2 is from 0.669 to 0.750, and a value of A3 is from 0.735 to 0.815.
4. The golf ball according to claim 1, wherein a value of (A2+A3)/2 is from 0.670 to 0.783.
5. The golf ball according to claim 1, wherein when a total volume of the dimples is denoted by D (mm.sup.3), and a deflection when the ball is compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) is denoted by B (mm), the following condition is satisfied:
6. The golf ball according to claim 1, wherein the core has a hardness profile in which, letting Shore C hardness at a core center be Cc, Shore C hardness at a midpoint M between the core center and a core surface be Cm, Shore C hardnesses at positions 2 mm, 4 mm, and 6 mm inward from the midpoint M be Cm2, Cm4, and Cm6 respectively, Shore C hardnesses at positions 2 mm, 4 mm, and 6 mm outward from the midpoint M be Cm+2, Cm+4, and Cm+6 respectively, and Shore C hardness at the core surface be Cs, and defining surface areas A to F as follows: surface area A: 2(Cm4Cm6) surface area B: 2(Cm2Cm4) surface area C: 2(CmCm2) surface area D: 2(Cm+2Cm) surface area E: 2(Cm+4Cm+2) surface area F: 2(Cm+6Cm+4) the following condition is satisfied:
7. The golf ball according to claim 6, wherein the core has a hardness profile in which the following condition is satisfied:
8. The golf ball according to claim 6, wherein the core has a hardness profile in which the following condition is satisfied:
9. The golf ball according to claim 6, wherein the core has a hardness profile in which the following condition is satisfied: surface area E>surface area D>surface area C.
10. The golf ball according to claim 1, wherein the core is formed of a rubber composition containing the following components (A) to (D): (A) a base rubber, (B) an organic peroxide, (C) water or a monocarboxylic acid metal salt, and (D) sulfur.
11. The golf ball according to claim 1, wherein a relationship between a surface hardness of the core and a surface hardness of the ball satisfies the following condition: (ball surface hardness)>(core surface hardness) (where hardness means Shore C hardness).
12. The golf ball according to claim 1, wherein a difference between a specific gravity of the core and a specific gravity of the cover is within 0.10.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0058]
[0059]
[0060]
[0061]
[0062]
[0063]
DETAILED DESCRIPTION OF THE INVENTION
[0064] Hereinafter, the present invention is described in more detail.
[0065] A golf ball according to the present invention has a core and a cover, and an example thereof is shown in
[0066] 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, the rebound of the core may become low, and a desired distance on shots with a driver (W #1) and an iron by amateur users may not be attainable. The rubber composition typically contains a base rubber as the chief material, and is obtained with the inclusion of a co-crosslinking agent, a co-crosslinking initiator, an inert filler, an organosulfur compound, or the like.
[0067] In particular, the core is suitably formed of a rubber composition containing the following components (A) to (D): [0068] (A) a base rubber, [0069] (B) an organic peroxide, [0070] (C) water or a monocarboxylic acid metal salt, and [0071] (D) sulfur.
[0072] The base rubber (A) may include a diene rubber. Examples of the diene rubber include polybutadiene, natural rubber, isoprene rubber, and ethylene propylene diene rubber.
[0073] As the organic peroxide (B), an organic peroxide having a relatively high thermal decomposition temperature is suitably used. Specifically, a high-temperature organic peroxide having a one-minute half-life temperature of about 165 to 185 C. is used, and examples thereof include dialkyl peroxides. Examples of the dialkyl peroxides include a dicumyl peroxide (Percumyl D manufactured by NOF Corporation), a 2,5-dimethyl-2,5-di(t-butylperoxy) hexane (Perhexa 25B manufactured by NOF Corporation), and a di(2-t-butylperoxyisopropyl) benzene (Perbutyl P manufactured by NOF Corporation), and a dicumyl peroxide may be suitably used. These may be used singly, or two or more may be used in combination. The half-life is one of the indices indicating a degree of a decomposition rate of the organic peroxide, and is indicated by a time required for the original organic peroxide to be decomposed and its active oxygen amount to reach . A vulcanization temperature in the core-forming rubber composition is typically within a range of from 120 to 190 C., and in that range, an organic peroxide having a one-minute half-life temperature of a high temperature, which is about 165 to 185 C., is thermally decomposed relatively slowly. With the rubber composition used in the present invention, by adjusting the amount of free radicals produced, which increases with the lapse of a vulcanization time, it is possible to obtain a core that is a rubber cross-linked product having a specific internal hardness shape described later.
[0074] 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.
[0075] 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, but 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 outside. If the water or a 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 can 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.
[0076] 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 a chemical formula [CH.sub.2CHCOO].sub.2Zn. 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 a powder, a 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 of the base rubber. If the compounding amount of the monocarboxylic acid metal salt is too small, it may be 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.
[0077] As the carboxylic acid, an acrylic acid, a methacrylic acid, a maleic acid, a fumaric acid, a stearic acid, or the like may be used. Examples of a substitute metal include Na, K, Li, Zn, Cu, Mg, Ca, Co, Ni, and Pb, and Zn is preferably used. Specific examples thereof include a zinc monoacrylate and a zinc monomethacrylate, and it is particularly preferable to use a zinc monoacrylate.
[0078] Specific examples of the sulfur (D) include trade names SANMIX S-80N (manufactured by Sanshin Chemical Industry Co., Ltd.) and SULFAX-5 (manufactured by Tsurumi Chemical Industry Co., Ltd.). The compounding amount of the sulfur may exceed 0, and may be preferably at least 0.005 parts by weight, and even more preferably at least 0.01 parts by weight per 100 parts by weight of the base rubber. In addition, an upper limit of the compounding amount is not particularly limited, but the upper limit is preferably not more than 0.1 parts by weight, more preferably not more than 0.05 parts by weight, and even more preferably not more than 0.03 parts by weight. The addition of the sulfur may increase a difference in hardness of the core. If the compounding amount of the sulfur is too large, rebound may be greatly reduced, or a durability on repeated impact may worsen.
[0079] In the rubber composition, a co-crosslinking agent, a filler, an antioxidant, an organosulfur compound, and the like may be included as components other than the components (A) to (D).
[0080] The co-crosslinking agent is an ,-unsaturated carboxylic acid and/or a metal salt thereof. Specific examples of the unsaturated carboxylic acid include acrylic acid, methacrylic acid, maleic acid, fumaric acid, or the like, and in particular, acrylic acid and methacrylic acid are suitably used. The metal salt of the unsaturated carboxylic acid is not particularly limited, and examples thereof include those obtained by neutralizing the unsaturated carboxylic acid with a desired metal ion. Specific examples thereof include zinc salts and magnesium salts such as methacrylic acid and acrylic acid, and in particular, zinc acrylate is suitably used.
[0081] The unsaturated carboxylic acid and/or the metal salt thereof is typically blended in an amount of at least 5 parts by weight, preferably at least 9 parts by weight, and even more preferably at least 13 parts by weight, and the upper limit is typically not more than 60 parts by weight, preferably not more than 50 parts by weight, and even more preferably not more than 40 parts by weight per 100 parts by weight of the base rubber. If the compounding amount is too large, the core may become too hard, giving the ball an unpleasant feel at impact, and if the compounding amount is too small, the rebound may become low.
[0082] As a filler, for example, zinc oxide, barium sulfate, calcium carbonate, or the like may be suitably used. These may be used singly, or two or more may be used in combination. The compounding amount of the filler may be preferably at least 4 parts by weight, more preferably at least 8 parts by weight, and even more preferably at least 11 parts by weight per 100 parts by weight of the base rubber. In addition, an upper limit of the compounding amount is preferably not more than 50 parts by weight, more preferably not more than 40 parts by weight, and even more preferably not more than 30 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 an appropriate weight and a suitable rebound.
[0083] As an antioxidant, for example, commercially available products such as Nocrac NS-6, Nocrac NS-30, Nocrac NS-200, and Nocrac MB (all manufactured by Ouchi Shinko Chemical Industrial Co., Ltd.) may be employed. These may be used singly, or two or more may be used in combination.
[0084] The compounding amount of the antioxidant is not particularly limited, but is preferably 0.05 parts by weight or more, and more preferably 0.1 parts by weight or more, and the upper limit is preferably 1.0 part by weight or less, more preferably 0.7 parts by weight or less, and even more preferably 0.5 parts by weight or less per 100 parts by weight of the base rubber. If the compounding amount is too large or too small, a suitable core hardness gradient cannot be obtained, and it may not be possible to obtain suitable rebound, durability, and a spin rate-lowering effect on full shots.
[0085] The organosulfur compound may be included in order to control the rebound of the core so that it is increased. As the organosulfur compound, specifically, it is recommended to include thiophenol, thionaphthol, halogenated thiophenol, or a metal salt thereof. More specifically, examples of the organosulfur compound include zinc salts such as pentachlorothiophenol, pentafluorothiophenol, pentabromothiophenol, p-chlorothiophenol, and pentachlorothiophenol, and any of the following having 2 to 4 sulfur atoms: diphenylpolysulfide, dibenzylpolysulfide, dibenzoylpolysulfide, dibenzothiazoylpolysulfide, and dithiobenzoylpolysulfide. In particular, diphenyldisulfide and the zinc salt of pentachlorothiophenol is preferably used.
[0086] An upper limit of a compounding amount of the organosulfur compound 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 parts by weight per 100 parts by weight of the base rubber. If the compounding amount is too large, the core hardness becomes too soft or the rebound of the core becomes too high, and a distance on shots with a driver by the longest hitters may be too long.
[0087] The core can be manufactured by vulcanizing and curing the rubber composition containing the above components. For example, a molded body can be manufactured by intensively mixing the rubber composition using a mixing apparatus such as a Banbury mixer or a roll mill, subsequently compression molding or injection molding the mixture using a core mold, and curing the resulting molded body by appropriately heating it at a temperature sufficient for the organic peroxide or the co-crosslinking agent to act, such as at a temperature of from 100 to 200 C., and preferably at a temperature of from 140 to 180 C., for 10 to 40 minutes.
[0088] In the present invention, the core is formed as a single layer or a plurality of layers, although it is preferably formed as a single layer. If a rubber core is produced as a plurality of layers of rubber, layer separation at an interface may arise when the ball is repeatedly struck, possibly leading to cracking at an earlier stage.
[0089] The diameter of the core is preferably at least 37.7 mm, more preferably at least 38.1 mm, and even more preferably at least 38.7 mm. The upper limit of the diameter of the core is preferably not more than 40.7 mm, more preferably not more than 39.9 mm, and even more preferably not more than 39.3 mm. If the core diameter is too small, an initial velocity of the ball may become too low, or a deflection of an entire ball may become small, a spin rate of the ball on full shots may increase, and the desired distance on full shots by amateur users may not be attainable. On the other hand, if the core diameter is too large, the spin rate on full shots increases, and the desired distance may not be attainable by amateur users, or a durability to cracking on repeated impact may worsen.
[0090] The 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) is not particularly limited, but is preferably at least 2.5 mm, more preferably at least 2.8 mm, and even more preferably at least 3.0 mm, and the upper limit thereof is preferably not more than 4.5 mm, more preferably not more than 4.0 mm, and even more preferably not more than 3.5 mm. If the deflection of the core is too small, that is, if the core is too hard, the spin rate on full shots increases excessively, the distance on shots with a driver (W #1) and an iron by amateur users may not be sufficiently increased, and the feel at impact may be too hard. On the other hand, if the deflection of the core is too large, that is, if the core is too soft, an actual initial velocity becomes too low, so that the distance on shots with a driver (W #1) by the longest hitters and amateur users may be too short, the feel at impact may become too soft, and the durability to cracking on repeated impact may become too poor.
[0091] Next, the core hardness profile is described. Note that the hardness of the core described below means Shore C hardness. The Shore C hardness is a hardness value measured with a Shore C durometer conforming to the ASTM D2240 standard.
[0092] A core center hardness (Cc) is preferably at least 57, more preferably at least 59, and even more preferably at least 61, and the upper limit is preferably not more than 68, more preferably not more than 67, and even more preferably not more than 66. If this value is too large, the spin rate of the ball on full shots may rise, the desired distance may not be attainable on shots with a driver (W #1) and an iron by amateur users, or the feel at impact may be too hard. On the other hand, if the above value is too small, the rebound may become low, and the desired distance for amateur users may not be attainable, or the durability to cracking on repeated impact may worsen.
[0093] A hardness (Cm6) at a position 6 mm inward from a point M (hereinafter, also referred to as midpoint M) between the core center and the core surface is not particularly limited, but the hardness may be preferably at least 57, more preferably at least 59, and even more preferably at least 61, and the upper limit is also not particularly limited, and may be preferably not more than 68, more preferably not more than 67, and even more preferably not more than 66. Hardnesses that deviate from these values may lead to undesirable results similar to those described above for the core center hardness (Cc).
[0094] A hardness (Cm4) at a position 4 mm inward from the midpoint M between the core center and the core surface is not particularly limited, but the hardness may be preferably at least 57, more preferably at least 59, and even more preferably at least 61, and the upper limit is also not particularly limited, and may be preferably not more than 68, more preferably not more than 67, and even more preferably not more than 66. Hardnesses that deviate from these values may lead to undesirable results similar to those described above for the core center hardness (Cc).
[0095] A hardness (Cm2) at a position 2 mm inward from the midpoint M of the core is not particularly limited, but the hardness may be preferably at least 57, more preferably at least 59, and even more preferably at least 61. The upper limit is also not particularly limited, and may be preferably not more than 69, more preferably not more than 67, and even more preferably not more than 66. Hardnesses that deviate from these values may lead to undesirable results similar to those described above for the core center hardness (Cc).
[0096] A cross-sectional hardness (Cm) at the midpoint M of the core is not particularly limited, but may be preferably at least 58, more preferably at least 60, and even more preferably at least 62. In addition, the upper limit is not particularly limited, but may be preferably not more than 70, more preferably not more than 68, and even more preferably not more than 66. Hardnesses that deviate from these values may lead to undesirable results similar to those described above for the core center hardness (Cc).
[0097] A core surface hardness (Cs) is preferably at least 80, more preferably at least 82, and even more preferably at least 84. The upper limit is preferably not more than 91, more preferably not more than 90, and even more preferably not more than 89. If this value is too large, the durability to cracking on repeated impact may worsen, or the feel at impact may be too hard. On the other hand, if the above value is too small, the rebound may become low or the spin rate of the ball on full shots may rise, and the desired distance may not be attainable on shots with a driver (W #1) and an iron by amateur users.
[0098] A hardness (Cm+2) at a position 2 mm outward from the midpoint M of the core toward the core surface is not particularly limited, although the hardness may be preferably at least 60, more preferably at least 62, and even more preferably at least 64, and an upper limit thereof is not particularly limited, and may be preferably not more than 71, more preferably not more than 69, and even more preferably not more than 67. Hardnesses that deviate from these values may lead to undesirable results similar to those described above for the core surface hardness (Cs).
[0099] A hardness (Cm+4) at a position 4 mm outward from the midpoint M of the core is not particularly limited, but the hardness may be preferably at least 65, more preferably at least 67, and even more preferably at least 69. The upper limit is also not particularly limited, and may be preferably not more than 76, more preferably not more than 74, and even more preferably not more than 72. Hardnesses that deviate from these values may lead to undesirable results similar to those described above for the core surface hardness (Cs).
[0100] A hardness (Cm+6) at a position 6 mm outward from the midpoint M of the core is not particularly limited, but the hardness may be preferably at least 70, more preferably at least 72, and even more preferably at least 74. The upper limit is also not particularly limited, and may be preferably not more than 82, more preferably not more than 80, and even more preferably not more than 78. Hardnesses that deviate from these values may lead to undesirable results similar to those described above for the core surface hardness (Cs).
[0101] A value obtained by subtracting the core center hardness from the core surface hardness, that is, the value of Cs-Cc, is preferably at least 20, more preferably at least 21, and even more preferably at least 22, and an upper limit thereof is preferably not more than 30, more preferably not more than 27, and even more preferably not more than 24. If this value is too small, the spin rate of the ball on full shots may rise, the desired distance may not be attainable on shots with a driver (W #1) and an iron by amateur users, or the feel at impact may be too hard. On the other hand, if this value is too large, the rebound may become low, and the desired distance may not be attainable on shots with a driver (W #1) and an iron by amateur users, or the durability to cracking on repeated impact may worsen.
[0102] In addition, it is preferable to optimize the value of (CsCc)/(CmCc) for the core hardness profile. The value of (CsCc) indicates a difference in hardness between the core center and the core surface, and the value of (CmCc) indicates a difference in hardness between the core center and the midpoint between the core surface and the core center, and the above expression represents the ratio of these differences in hardness. The value of (CsCc)/(CmCc) is preferably at least 3.0, more preferably at least 4.0, and even more preferably at least 5.0. If this value is too small, the spin rate of the ball on full shots may rise, and the desired distance may not be attainable on shots with a driver (W #1) and an iron by amateur users.
[0103] In the core hardness profile, surface areas A to F are defined as follows: [0104] surface area A: 2(Cm4Cm6) [0105] surface area B: 2(Cm2Cm4) [0106] surface area C: 2(CmCm2) [0107] surface area D: 2(Cm+2Cm) [0108] surface area E: 2(Cm+4Cm+2) [0109] surface area F: 2(Cm+6Cm+4) [0110] and are characterized in that a value of (surface area D+surface area E)(surface area A+surface area B) is preferably at least 4.0, more preferably at least 4.5, and even more preferably at least 5.0, and the upper limit is preferably not more than 15.0, more preferably not more than 10.0, and even more preferably not more than 7.0. If this value is too small, the spin rate of the ball on full shots may rise, and the desired distance may not be attainable on shots with a driver (W #1) and an iron by amateur users. On the other hand, if this value is too large, the rebound may become low, and the desired distance may not be attainable on shots with a driver (W #1) and an iron by amateur users, or the durability to cracking on repeated impact may worsen.
[0111] A value of (surface area D+surface area E)(surface area B+surface area C) is preferably at least 3.5, more preferably at least 4.0, and even more preferably at least 4.5, and the upper limit is preferably not more than 15.0, more preferably not more than 10.0, and even more preferably not more than 7.0. If this value is too small, the spin rate of the ball on full shots may rise, and the desired distance may not be attainable on shots with a driver (W #1) and an iron by amateur users. On the other hand, if this value is too large, the rebound may become low, and the desired distance may not be attainable on shots with a driver (W #1) and an iron by amateur users, or the durability to cracking on repeated impact may worsen.
[0112] A value of {(surface area D+surface area E)(surface area A+surface area B)}(CsCc) is preferably at least 100, more preferably at least 120, and even more preferably at least 140, and the upper limit is preferably not more than 400, more preferably not more than 250, and even more preferably not more than 180. In addition, a value of {(surface area D+surface area E)(surface area B+surface area C)}(CsCc) is preferably at least 80, more preferably at least 90, and even more preferably at least 100, and the upper limit is preferably not more than 400, more preferably not more than 250, and even more preferably not more than 180. In addition, if these values are too small, the spin rate of the ball on full shots may rise, and the desired distance may not be attainable on shots with a driver (W #1) and an iron by amateur users. On the other hand, if these values are too large, the rebound may become low, and the desired distance may not be attainable on shots with a driver (W #1) and an iron by amateur users, or the durability to cracking on repeated impact may worsen.
[0113] A relationship between the surface areas calculated from the hardness profile described above is preferably surface area E>surface area C>surface area A, more preferably surface area F>surface area E>surface area C>surface area A, and even more preferably surface area F>surface area E>surface area C>(surface area A+surface area B). If these relational expressions are not satisfied, the spin rate of the ball on full shots may rise, and the desired distance may not be attainable on shots with a driver (W #1) and an iron by amateur users.
[0114]
[0115] Next, the cover is described.
[0116] The cover has a material hardness on the Shore C hardness scale which, although not particularly limited, is preferably at least 83, more preferably at least 89, and even more preferably at least 93, and the upper limit is preferably not more than 100, more preferably not more than 97, and even more preferably not more than 95. The material hardness on the Shore D hardness scale is preferably at least 55, more preferably at least 60, and even more preferably at least 63, and the upper limit is preferably not more than 75, more preferably not more than 70, and even more preferably not more than 68.
[0117] A surface hardness of the ball (whole sphere) including the core and the cover is preferably at least 90, more preferably at least 93, and even more preferably at least 95, and the upper limit thereof is preferably not more than 100, more preferably not more than 99, and even more preferably not more than 98 on the Shore C hardness scale. The surface hardness on the Shore D hardness scale is preferably at least 62, more preferably at least 67, and even more preferably at least 70, and the upper limit thereof is preferably not more than 76, more preferably not more than 74, and even more preferably not more than 72.
[0118] If the material hardness and the surface hardness of the cover are too soft in comparison with the above ranges, the spin rate of the ball on full shots may rise, and the distance on shots with a driver (W #1) and an iron by amateur users may not be increased. In addition, the launch angle on approach shots may become low, and the ball may be felt by amateur users to be difficult to handle. On the other hand, if the material hardness and the surface hardness of the cover are too hard in comparison with the above ranges, the feel at impact may become too hard, the durability to cracking on repeated impact may worsen, and the distance on shots by the longest hitters may become too long.
[0119] The cover has a thickness of preferably at least 1.0 mm, more preferably at least 1.4 mm, and even more preferably at least 1.7 mm. On the other hand, the upper limit of the cover thickness is preferably not more than 2.5 mm, more preferably not more than 2.3 mm, and even more preferably not more than 2.0 mm. If the cover is too thin, the durability to cracking on repeated impact may worsen, or it may be difficult to mold the cover and mass productivity may be deteriorated. On the other hand, if the cover is too thick, the feel at impact may become too hard, the rebound may become low, and it may be difficult for the distance on shots by amateur users to increase. In addition, if the cover thickness deviates from the above ranges, the spin rate of the ball on full shots may rise, and a good distance may not be increased on shots by amateur users.
[0120] As the material of the cover, a resin material containing an ionomer resin as the chief material is used. If the cover has a plurality of layers, the outermost layer is made of the resin material containing an ionomer resin as the chief material. If a urethane material is used as the cover material, since the material is not a hard material, the launch angle on approach shots may become low, and the ball may be felt by amateur users to be difficult to handle. In addition, even if a material having the hardest grade among the types of urethane materials is selected, the rebound may be lower than that of an ionomer material having the same hardness, and the distance on shots by amateur users may not reach a target. In addition, when the cover is formed, from the viewpoint of mass productivity, it is preferable to adopt a method of encasing the core or an intermediate layer-encased sphere with the cover by injection molding.
[0121] If an ionomer resin is employed as the chief material, an aspect that uses in admixture a zinc-neutralized ionomer resin and a sodium-neutralized ionomer resin as the chief materials is desirable. The blending ratio in terms of zinc-neutralized ionomer resin/sodium-neutralized ionomer resin (weight ratio) is from 5/95 to 95/5, preferably from 20/80 to 90/10, and more preferably from 30/70 to 70/30. If the zinc-neutralized ionomer and the sodium-neutralized ionomer are not included in this ratio, the rebound may become too low to obtain a desired flight, the durability to cracking on repeated impact at room temperature may worsen, and the durability to cracking at a low temperature (below zero) may worsen.
[0122] The material of the cover may contain an inorganic particulate filler. This inorganic particulate filler is not particularly limited, but zinc oxide, barium sulfate, titanium dioxide, or the like can be appropriately used. Barium sulfate can be preferably used, and particularly preferably, precipitated barium sulfate can be suitably used from the viewpoint of excellent durability to cracking on repeated impact.
[0123] The mean particle size of the inorganic particulate filler is not particularly limited, but is preferably from 0.01 to 100 m, and more preferably from 0.1 to 10 m. If the mean particle size of the inorganic particulate filler is too small or too large, dispersibility during material preparation may be deteriorated. Note that the mean particle size means a particle size measured by dispersing the particles in an aqueous solution together with an appropriate dispersant and measuring the particles with a particle size distribution measuring device.
[0124] The compounding amount of the inorganic particulate filler is not particularly limited, although the compounding amount may be preferably set to at least 0 parts by weight, more preferably at least 10 parts by weight, and even more preferably at least 15 parts by weight per 100 parts by weight of the ionomer resin, which is the base resin of the cover material. Although there is no particular upper limit, the content is preferably not more than 50 parts by weight, more preferably not more than 40 parts by weight, and even more preferably not more than 30 parts by weight. At an inorganic filler content that is too low, the durability to cracking on repeated impact may worsen. On the other hand, at a compounding amount of the inorganic particulate filler that is too high, the ball rebound may become low, or the spin rate of the ball on full shots by amateur users may rise, and an intended distance may not be increased.
[0125] A specific gravity of the cover is preferably at least 1.05, more preferably at least 1.07, and even more preferably at least 1.09, and the upper limit thereof is preferably not more than 1.25, more preferably not more than 1.20, and even more preferably not more than 1.15. If the specific gravity of the cover is too small, the durability to cracking on repeated impact may worsen. On the other hand, if the specific gravity of the cover is too large, the ball rebound becomes low, or the spin rate of the ball on full shots by amateur users rises, and the intended distance may not be attained.
[0126] Various additives may be appropriately included in the cover material as necessary, for example, a pigment, a dispersant, an antioxidant, a light stabilizer, an ultraviolet absorber, an internal mold lubricant, or the like.
[0127] A method for manufacturing the golf ball of the present invention may be performed by a customary method such as a known injection molding method. For example, the golf ball may be obtained by injection molding the material of the cover around the core. In addition, it is also possible to produce the golf ball by preparing two half-cups (cover materials) pre-molded into hemispherical shapes, enclosing the core within the two half cups, and molding the core under applied heat and pressure.
[0128] The golf ball has a deflection (mm) when compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) which is preferably at least 2.0 mm, more preferably at least 2.4 mm, and even more preferably at least 2.7 mm. On the other hand, an upper limit of the deflection is preferably not more than 3.8 mm, more preferably not more than 3.4 mm, and even more preferably not more than 3.0 mm. If the deflection of the golf ball is too small, the spin rate of the ball on full shots increases excessively, and the distance on shots with a driver (W #1) and an iron by amateur users may not be increased, or the feel at impact may be too hard. On the other hand, if the deflection is too large, the actual initial velocity becomes too low, so that the distance on shots with a driver (W #1) by the longest hitters and amateur users may be too short, the feel at impact may become too soft, or the durability to cracking on repeated impact may become too poor.
[0129] The initial velocity of the ball is preferably at least 76.0 m/s, more preferably at least 76.5 m/s, and even more preferably at least 77.0 m/s. An upper limit thereof is not more than 77.724 m/s. If this initial velocity value is too high, the official rules of R&A and USGA are not satisfied. On the other hand, if the initial velocity is too low, the actual initial velocity may become low and the desired distance may not be attainable under all striking conditions on full shots. The value of the initial velocity in this case is a numerical value measured by a device for measuring a coefficient of restitution (COR) (Golf Ball Testing Machine) of the same type as the R&A. Specifically, a device for measuring a COR manufactured by Hye Precision USA is used. As a condition, at the time of measurement, an air pressure is changed in four stages and measured, a relational expression between the incident velocity and the COR is constructed, and the initial velocity at an incident velocity of 43.83 m/s is determined from the relational expression. For a measurement environment of the device for measuring a COR, a ball temperature-controlled for at least three hours in a thermostatic bath adjusted to 23.91 C. is used, and measurement is performed at a room temperature of 23.92 C. In addition, a barrel diameter is selected such that a clearance on one side with respect to an outer diameter of the object being measured is from 0.2 to 2.0 mm.
[0130] A value obtained by dividing the initial velocity of the ball by the deflection of the ball is preferably at least 20, more preferably at least 23, and even more preferably at least 26, and the upper limit is preferably not more than 32, more preferably not more than 30, and even more preferably not more than 29. This value has a meaning of measuring a magnitude of the actual initial velocity of the ball. If this value is too large, the distance on shots by the longest hitters becomes too long, and it may be impossible to conform to the new ODS rules. On the other hand, if this value is too small, the spin rate of the ball on full shots may increase, or the actual initial velocity may become lower, and the desired distance may not be attainable under all striking conditions.
[0131] Expressed on the Shore C hardness scale, a value obtained by subtracting the core surface hardness from the ball surface hardness is preferably at least 2, more preferably at least 4, and even more preferably at least 8, and an upper limit thereof is preferably not more than 25, more preferably not more than 20, and even more preferably not more than 15. Expressed on the Shore C hardness scale, a value obtained by subtracting the core center hardness from the ball surface hardness is preferably at least 15, more preferably at least 17, and even more preferably at least 21, and an upper limit thereof is preferably not more than 38, more preferably not more than 33, and even more preferably not more than 28. If these values are too large, the durability to cracking on repeated impact may worsen, the actual initial velocity may become low, and the distance on all shots with a driver (W #1) may be shorter than the desired distance. On the other hand, if these values are too small, the spin rate of the ball on full shots may rise, and the desired distance on shots with a driver (W #1) and an iron by amateur users may not be attainable.
[0132] Letting each deflection (mm) when each sphere of the core and the ball is compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) be C (mm) and B (mm) respectively, a value of CB is preferably at least 0.30 mm, more preferably at least 0.35 mm, and even more preferably at least 0.40 mm, and an upper limit thereof is preferably not more than 0.65 mm, more preferably not more than 0.60 mm, and even more preferably not more than 0.55 mm. In addition, a value of C/B is preferably at least 1.08, more preferably at least 1.11, and even more preferably at least 1.14, and the upper limit thereof is preferably not more than 1.30, more preferably not more than 1.25, and even more preferably not more than 1.20. If these values are too large, the durability to cracking on repeated impact may worsen, the actual initial velocity becomes lower, and the distance on all shots with a driver (W #1) may be shorter than the desired distance. On the other hand, if these values are too small, the spin rate of the ball on full shots may rise, and the desired distance on shots with a driver (W #1) and an iron by amateur users may not be attainable.
[0133] Regarding a specific gravity relationship between the core and the cover, it is desirable that a difference in specific gravity between both members is as small as possible. Specifically, the difference between the core specific gravity and the cover specific gravity is within 0.10, preferably within 0.08, more preferably within 0.05, and even more preferably within 0.03. If this difference in specific gravity deviates from the above ranges, when the core is eccentrically molded, the ball may swerve and fly on full shots, or may not roll straight on shots with a putter.
[0134] A relationship between the core diameter and a ball diameter, that is, a value of (core diameter)/(ball diameter), is preferably at least 0.883, more preferably at least 0.892, and even more preferably at least 0.906. On the other hand, an upper limit thereof is preferably not more than 0.953, more preferably not more than 0.934, and even more preferably not more than 0.920. If this value is too small, the initial velocity of the ball becomes low, or the deflection of the entire ball becomes small and the ball becomes hard, the spin rate of the ball on full shots increases, and the desired distance on full shots by amateur users may not be attainable. On the other hand, if the above value is too large, the spin rate of the ball on full shots increases, the desired distance on full shots by amateur users may not be attainable, and the durability to cracking on repeated impact may worsen.
[0135] The golf ball of the present invention includes the core and the cover described above, and an intermediate layer may be interposed between the core and the cover as necessary. This intermediate layer is not limited to one layer, and may be two or more layers. As the intermediate layer, a known resin material for golf balls such as an ionomer resin or a polyester-based elastomer may be suitably employed.
[0136] Numerous dimples may be formed on the outside surface of the cover. Although not particularly limited, the number of dimples arranged on the surface of the cover is preferably at least 280, preferably at least 300, and more preferably at least 310, and the upper limit thereof can be preferably not more than 450, more preferably not more than 400, and even more preferably not more than 350. If the number of dimples deviates from the above ranges, the distance on shots with a driver (W #1) by amateur users may be shortened.
[0137] As for the shape of the dimples, one type or a combination of two or more types such as a circular shape, various polygonal shapes, a dewdrop shape, and other oval shapes can be appropriately used. For example, if circular dimples are used, the diameter can be about 2.5 mm or more and 6.5 mm or less, and the depth can be 0.08 mm or more and 0.30 mm or less.
[0138] A dimple coverage ratio of the dimples on the spherical surface of the golf ball, specifically, a ratio (surface area coverage ratio, hereinafter, SR value) of a sum of the individual dimple surface areas, each defined by a flat plane circumscribed by an edge of a dimple, to a ball spherical surface area on the assumption that the ball has no dimples is preferable at least 75%, more preferably at least 80%, and even more preferably at least 84%. The upper limit is not more than 90%, more preferably not more than 88%, and even more preferably not more than 86%. If the SR value deviates from the above ranges, the distance on shots with a driver (W #1) by amateur users may be shortened.
[0139] A VR value of a sum of volumes of the individual dimples formed below the flat plane circumscribed by the edge of a dimple to a ball spherical volume on the assumption that the ball has no dimples is at least 0.75%, preferably at least 0.78%, and more preferably at least 0.80%. An upper limit thereof is not more than 0.89%, more preferably not more than 0.88%, and even more preferably not more than 0.86%. If this VR value is larger than the above ranges, the distance on shots with a driver (W #1) by the longest hitters may be too short, or the intended distance on shots with a driver (W #1) by amateur users may not be attainable. In addition, in this case, a ball trajectory may become lower, it becomes difficult to carry, and it may become difficult to go over a valley or a pond. On the other hand, if the above value is too small, the distance on shots with a driver (W #1) by the longest hitters does not decrease, and there is a possibility that the ball flies too much further than an upper limit distance of the new ODS rules.
[0140] A total volume of the dimples means the sum of volumes of the individual dimples formed below the flat plane circumscribed by the edge of the dimple in all the dimples formed on one ball. The total volume of the dimples is not particularly limited, but the total volume is preferably at least 306 mm.sup.3, more preferably at least 318 mm.sup.3, and even more preferably at least 326 mm.sup.3, and the upper limit thereof is preferably not more than 363 mm.sup.3, more preferably not more than 359 mm.sup.3, and even more preferably not more than 351 mm.sup.3. If the value of this total volume of the dimples is larger than the above ranges, the distance on shots with a driver (W #1) by the longest hitters may be too short, or the intended distance on shots with a driver (W #1) by amateur users may not be attainable. In addition, in this case, a ball trajectory may become lower, it becomes difficult to carry, and it may become difficult to go over a valley or a pond. On the other hand, if the above value is too small, the distance on shots with a driver (W #1) by the longest hitters does not decrease, and there is a possibility that the ball flies too much further than an upper limit distance of the new ODS rules.
[0141] A value V.sub.0 obtained by dividing the spatial volume of the dimples below the flat plane circumscribed by the edge of each dimple by a volume of a cylinder whose base is the flat plane and whose height is a maximum depth of the dimple from the base is preferably at least 0.35, more preferably at least 0.38, and further preferably at least 0.40. The upper limit is not more than 0.80, more preferably not more than 0.70, and even more preferably not more than 0.60. If the Vo value deviates from the above ranges, the distance on shots with a driver (W #1) by the longest hitters and amateur users may be shorter than the intended distance.
[0142] In the golf ball of the present invention, when a ratio (CL1/CD1) of a lift coefficient CL1 at a Reynolds number of 218000 and a spin rate of 2800 rpm to a drag coefficient CD1 is denoted by A1, a ratio (CL2/CD2) of a lift coefficient CL2 at a Reynolds number of 184000 and a spin rate of 2900 rpm to a drag coefficient CD2 is denoted by A2, and a ratio (CL3/CD3) of a lift coefficient CL3 at a Reynolds number of 158000 and a spin rate of 3100 rpm to a drag coefficient CD3 is denoted by A3, the dimples are designed to satisfy the following two conditions:
[0143] In the present specification, the lift coefficients (CL1, CL2, CL3), drag coefficients (CD1, CD2, CD3) are measured in accordance with the Indoor Test Range (ITR) defined by the USGA (United States Golf Association). The lift coefficients and the drag coefficients can be adjusted by adjusting the configuration of the dimples of the golf ball (arrangement, diameter, depth, volume, number, shape, and the like). The lift coefficients and the drag coefficients are independent of the internal configuration of the golf ball. The Reynolds number (Re) is a dimensionless number used in the field of hydrodynamics. The Reynolds number (Re) is calculated by the following equation (1).
[0144] In Equation (1) above, represents the density of a fluid, v represents the average velocity of an object relative to the flow of the fluid, L represents a characteristic length, and represents the viscosity coefficient of the fluid.
[0145] In the present invention, when a ratio CL1/CD1 of a lift coefficient CL1 at a Reynolds number of 218000 and a spin rate of 2800 rpm to a drag coefficient CD1 is defined as A1, a ratio CL2/CD2 of a lift coefficient CL2 at a Reynolds number of 184000 and a spin rate of 2900 rpm to a drag coefficient CD2 is defined as A2, and a ratio CL3/CD3 of a lift coefficient CL3 at a Reynolds number of 158000 and a spin rate of 3100 rpm to a drag coefficient CD3 is defined as A3.
[0146] If a condition of the Reynolds number 218,000 and the spin rate 2,800 rpm under which the lift coefficient CL1 and the drag coefficient CD1 are measured is described, this high-speed condition corresponds to a condition provided by the longest hitters with a driver (W #1), this Reynolds number corresponds to a ball speed when the golf ball is driven out at a head speed (HS) of 54 m/s, and the spin rate 2,800 rpm is an average spin condition of a player with a head speed (HS) of 54 m/s.
[0147] If a condition under which the lift coefficient CL2 and the drag coefficient CD2 are measured is described, that is, a Reynolds number of 184,000 and a spin rate of 2,900 rpm, this middle-speed condition corresponds to a condition on shots with a driver (W #1) by amateur users at a head speed (HS) of 45 m/s, this Reynolds number corresponds to the ball speed when the golf ball is struck at a head speed (HS) of 45 m/s, and the spin rate of 2,900 rpm is the average spin condition of a player with a head speed (HS) of 45 m/s.
[0148] If a condition under which the lift coefficient CL3 and the drag coefficient CD3 are measured is described, that is, a Reynolds number of 158,000 and a spin rate of 3,100 rpm, this low-speed condition corresponds to a condition on shots with a driver (W #1) by amateur users at a head speed (HS) of 40 m/s, this Reynolds number corresponds to a ball speed when the golf ball is struck at a head speed (HS) of 40 m/s, and the spin rate of 3,100 rpm is the average spin condition of a player with a head speed (HS) of 40 m/s.
[0149] The ratio between the lift coefficient CL1 and the drag coefficient CD1, that is, the value of CL1/CD1=A1 is at least 0.590, preferably at least 0.595, and more preferably at least 0.600, and an upper limit thereof is not more than 0.655, preferably not more than 0.640, and more preferably not more than 0.627. If this value is too large, the distance on shots with a driver (W #1) by the longest hitters does not decrease, and there is a possibility that the ball flies too much further than the upper limit distance of the new ODS rules. On the other hand, if the above value is too small, the distance may become too short compared to the intended distance under all striking conditions.
[0150] When the value of A1 is from 0.590 to 0.613, the ratio between the lift coefficient CL2 and the drag coefficient CD2, that is, a value of CL2/CD2=A2, is preferably at least 0.635, more preferably at least 0.645, and even more preferably at least 0.655, and an upper limit thereof is preferably not more than 0.668, more preferably not more than 0.666, and even more preferably not more than 0.664. When the value of A1 is from 0.614 to 0.655, the value of A2 is preferably at least 0.669, more preferably at least 0.671, and even more preferably at least 0.673, and an upper limit thereof is preferably not more than 0.750, more preferably not more than 0.725, and even more preferably not more than 0.700. If the above value deviates from the above ranges, under all striking conditions, the ball may blow up, there may be a trajectory in which the ball does not carry, and an intended total distance may not be attainable.
[0151] When the value of A1 is from 0.590 to 0.613, the ratio between the lift coefficient CL3 and the drag coefficient CD3, that is, a value of CL3/CD3=A3, is preferably at least 0.695, more preferably at least 0.705, and even more preferably at least 0.715, and an upper limit thereof is preferably not more than 0.734, more preferably not more than 0.731, and even more preferably not more than 0.728. In addition, when the value of A1 is 0.614 to 0.655, the value of A3 is preferably at least 0.735, more preferably at least 0.738, and even more preferably at least 0.741, and an upper limit thereof is preferably not more than 0.815, more preferably not more than 0.780, and even more preferably not more than 0.760. If the above valuc deviates from the above ranges, under all striking conditions, the ball may blow up, there may be a trajectory in which the ball does not carry, and an intended total distance may not be attainable.
[0152] The average value of the above A2 and A3, that is, the value of (A2+A3)/2 is at least 0.670, preferably at least 0.680, and more preferably at least 0.690, and an upper limit thereof is preferably not more than 0.783, more preferably not more than 0.775, and even more preferably not more than 0.765. If this value is too low, it becomes difficult for the ball to carry on shots with a driver (W #1) by amateur users, and the intended total distance may not be attainable. On the other hand, if the above value is too high, the ball trajectory may be blown up on shots with a driver (W #1) by amateur users, and the intended distance may not be attainable.
[0153] When the total volume of the dimples is denoted by D (mm.sup.3), and a deflection when the ball is compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) is denoted by B (mm), a value of D/B is preferably not more than 140, more preferably not more than 135, and even more preferably not more than 130. On the other hand, a lower limit thereof is preferably at least 100, more preferably at least 105, and even more preferably at least 110. This D/B means an index in which an appropriate distance suppression effect is produced on shots with a driver (W #1) by the longest hitters, and a good distance is casily obtained on shots by amateur users. If this value deviates from the above ranges, the intended distance may not be attainable on shots with a driver (W #1) by the longest hitters and by amateur users.
[0154] The golf ball of the present invention may be made to conform to the Rules of Golf for play. The inventive ball may be formed to a diameter which is such that the ball does not pass through a ring having an inner diameter of 42.672 mm and to a weight which is preferably between 45.0 and 45.93 g.
EXAMPLES
[0155] Hereinafter, the present invention is specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.
Examples 1 to 4 and Comparative Examples 1 to 12
[Formation of Core]
[0156] In Comparative Examples 5, 7, and 9 to 11, a rubber composition of each Example shown in Table 1 was prepared, and then vulcanization molding was performed under vulcanization conditions according to each Example shown in Table 1 to produce a solid core.
[0157] In Examples 1 to 4 and Comparative Examples 1 to 4, 6, 8, and 12, cores are produced based on formulations in Table 1 in the same manner as described above.
TABLE-US-00001 TABLE 1 Core formulation Example Comparative Example (pbw) 1 2 3 4 1 2 3 4 5 Polybutadiene A 100 100 100 100 35 100 100 100 100 Polybutadiene B Polybutadiene C Isoprene rubber Styrene-butadiene 65 rubber Zinc acrylate 32.5 32.5 32.5 30.7 27.4 32.5 32.5 26.0 37.0 Zinc methacrylate 1.0 1.0 Methacrylic acid Zinc stearate 2.0 2.0 2.0 2.0 2.0 2.0 5.0 Organic peroxide A 1.0 1.0 1.0 1.0 1.0 1.0 1.0 0.6 1.0 Organic peroxide B 0.6 Sulfur 0.025 0.025 0.025 0.025 0.025 0.025 Water 0.2 0.2 0.2 0.2 0.4 0.2 0.2 0.4 Antioxidant 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Zinc oxide 11.8 11.8 11.8 12.6 13.3 11.8 11.8 18.8 14.8 Barium sulfate Zinc salt of 1.0 1.0 pentachlorothiophenol Vulcani- Temp. 150 150 150 150 150 150 150 160 150 zation ( C.) conditions Time 19 19 19 19 19 19 19 11 19 (min) Core formulation Comparative Example (pbw) 6 7 8 9 10 11 12 Polybutadiene A 100 100 100 35 95 Polybutadiene B 20 20 Polybutadiene C 80 80 Isoprene rubber 5 Styrene-butadiene 65 rubber Zinc acrylate 37.0 37.0 37.0 33.5 33.5 26.9 Zinc methacrylate 1.0 1.0 1.0 1.0 Methacrylic acid 23.5 Zinc stearate 2.0 2.0 Organic peroxide A 1.0 1.0 1.0 1.0 1.0 1.0 1.2 Organic peroxide B Sulfur 0.025 0.025 Water 0.4 0.4 0.4 0.6 0.6 0.4 Antioxidant 0.1 0.1 0.1 0.1 0.1 0.1 0.2 Zinc oxide 14.8 14.8 14.8 19.3 19.3 16.5 23.5 Barium sulfate 1.0 Zinc salt of 1.0 1.0 1.0 0.6 0.6 pentachlorothiophenol Vulcani- Temp. 150 150 150 160 160 150 163 zation ( C.) conditions Time 19 19 19 14 14 19 21 (min)
[0158] Details of the above formulations are as follows. [0159] Polybutadiene A: Trade name BR 01, (manufactured by ENEOS Materials Corporation) [0160] Polybutadiene B: Trade name Diene 645 (Firestone Polymers) [0161] Polybutadiene C: Trade name BUDENE 1224 G (Goodyear Tire & Rubber Company) [0162] Isoprene rubber: Trade name IR 2200 (manufactured by ENEOS Materials Corporation) [0163] Styrene-butadiene rubber: Trade name SBR 1507 (manufactured by ENEOS Materials Corporation) [0164] Zinc acrylate: Trade name ZN-DA85S (manufactured by Nippon Shokubai Co., Ltd.) [0165] Zinc methacrylate: Trade name ZDA-90 (manufactured by Asada Chemical Industry Co., Ltd.) [0166] Zinc stearate: Trade name BR-3T (manufactured by Akrochem Corporation) [0167] Organic peroxide A: Dicumyl peroxide, trade name Percumyl D (manufactured by NOF Corporation) [0168] Organic peroxide B: A mixture of 1,1-di (t-butylperoxy) cyclohexane and silica, trade name Perhexa C-40 (manufactured by NOF Corporation) [0169] Sulfur: Trade name SANMIX S-80N (manufactured by Sanshin Chemical Industry Co., Ltd., containing sulfur powder for rubber in an amount of 80 wt %) [0170] Water: Pure water (manufactured by Seiki Co., Ltd.) [0171] Antioxidant: 2,2-methylenebis (4-methyl-6-butylphenol), trade name Nocrac NS-6 (manufactured by Ouchi Shinko Chemical Industrial Co., Ltd.) [0172] Zinc oxide: Trade name Grade 3 Zinc Oxide (manufactured by Sakai Chemical Industry Co., Ltd.) [0173] Zinc salt of pentachlorothiophenol: Manufactured by FUJIFILM Wako Pure Chemical Corporation
[Formation of Intermediate Layer and Cover (Outermost Layer)]
[0174] Next, in Comparative Examples 5, 7, and 9 to 11, the intermediate layer was formed by injection molding a resin material No. 1 or No. 2 of the intermediate layer shown in Table 2 around the core surface using an injection mold. Subsequently, the cover was formed by injection molding the resin material No. 3 of the cover (outermost layer) shown in Table 2 around the intermediate layer-encased sphere using a separate injection mold. At this time, a predetermined large number of dimples described below were formed on the surface of the cover.
[0175] In Examples 1 to 4 and Comparative Examples 1 to 4 and 12, the cover is formed by injection molding the resin material No. 4, No. 5, or No. 6 of the cover shown in Table 2 around the core surface using an injection mold. In Comparative Examples 6 and 8, the intermediate layer is formed by injection molding the resin material No. 2 of the intermediate layer shown in Table 2 around the core surface using an injection mold. Subsequently, the cover is formed by injection molding the resin material No. 3 of the cover (outermost layer) shown in Table 2 around the intermediate layer-encased sphere using a separate injection mold. At this time, a large number of predetermined dimples described below are formed on the cover surface.
TABLE-US-00002 TABLE 2 Resin material (pbw) No. 1 No. 2 No. 3 No. 4 No. 5 No. 6 Himilan 1605 50 50 Himilan 1601 37.5 Himilan 1557 15 37.5 Himilan 1706 35 15 50 AM7318 85 AN4319 25 Titanium oxide 3 3 4 4 Barium sulfate 20 Magnesium stearate 1 Trimethylolpropane 1.1 1.1 TPU (1) 100 TPU (2) 100
[0176] Details of the blending components in Table 2 are as follows. [0177] Himilan 1605, Himilan 1601, Himilan 1557, Himilan 1706, and AM7318 ionomer resins manufactured by Dow-Mitsui Polychemicals Co., Ltd. [0178] AN4319 NUCREL manufactured by Dow-Mitsui Polychemicals Co., Ltd. [0179] Barium sulfate Trade name Precipitated Barium Sulfate 300 barium sulfate manufactured by Sakai Chemical Industry Co., Ltd. [0180] Magnesium stearate Trade name Magnesium stearate G magnesium stearate manufactured by NOF Corporation [0181] Trimethylolpropane (TMP) manufactured by Tokyo Chemical Industry Co., Ltd. [0182] TPU(1) Trade name Pandex ether-type thermoplastic polyurethane, material hardness (Shore D) 50, manufactured by DIC Covestro Polymer Ltd. [0183] TPU(2) Trade name Pandex ether-type thermoplastic polyurethane, material hardness (Shore D) 47, manufactured by DIC Covestro Polymer Ltd.
[0184] For the dimples of the Examples and Comparative Examples, the following dimples (1) to (5) were used. Each dimple mode includes eight types of circular dimples of No. 1 to No. 8 having different diameters and depths. Details thereof are listed in Table 3 below. In addition, an arrangement mode (pattern) of the dimples (1) to (5) is illustrated in
TABLE-US-00003 TABLE 3 Cylinder Total volume Diameter Depth Volume volume ratio SR VR of dimples Type Quantity (mm) (mm) (mm.sup.3) Vo (%) (%) (mm.sup.3) Dimple (1) No. 1 12 4.63 0.122 1.009 0.491 84 0.68 278 No. 2 198 4.50 0.119 0.919 0.486 No. 3 36 3.92 0.115 0.655 0.472 No. 4 12 2.87 0.086 0.245 0.442 No. 5 36 4.49 0.126 0.965 0.483 No. 6 24 3.92 0.124 0.711 0.473 No. 7 6 3.31 0.133 0.550 0.479 No. 8 6 3.21 0.132 0.457 0.430 Total 330 Dimple (2) No. 1 12 4.69 0.144 1.220 0.493 86 0.81 331 No. 2 198 4.54 0.140 1.100 0.486 No. 3 36 3.96 0.134 0.766 0.467 No. 4 12 2.92 0.109 0.322 0.441 No. 5 36 4.54 0.146 1.141 0.485 No. 6 24 3.96 0.144 0.827 0.468 No. 7 6 3.36 0.136 0.590 0.491 No. 8 6 3.22 0.127 0.433 0.421 Total 330 Dimple (3) No. 1 12 4.69 0.146 1.236 0.490 86 0.83 338 No. 2 198 4.54 0.143 1.122 0.484 No. 3 36 3.96 0.137 0.790 0.470 No. 4 12 2.92 0.106 0.310 0.438 No. 5 36 4.54 0.149 1.162 0.482 No. 6 24 3.96 0.147 0.846 0.467 No. 7 6 3.38 0.138 0.608 0.493 No. 8 6 3.28 0.132 0.470 0.423 Total 330 Dimple (4) No. 1 12 4.70 0.149 1.252 0.487 86 0.85 345 No. 2 198 4.55 0.146 1.144 0.483 No. 3 36 3.97 0.140 0.815 0.472 No. 4 12 2.91 0.103 0.298 0.435 No. 5 36 4.55 0.152 1.183 0.480 No. 6 24 3.97 0.150 0.864 0.467 No. 7 6 3.40 0.140 0.627 0.495 No. 8 6 3.33 0.138 0.510 0.426 Total 330 Dimple (5) No. 1 12 4.68 0.164 1.391 0.493 85 0.93 378 No. 2 198 4.53 0.161 1.258 0.485 No. 3 36 3.95 0.154 0.883 0.468 No. 4 12 2.90 0.114 0.331 0.440 No. 5 36 4.53 0.168 1.294 0.480 No. 6 24 3.95 0.165 0.949 0.470 No. 7 6 3.36 0.154 0.663 0.487 No. 8 6 3.26 0.152 0.538 0.426 Total 330
[Definition of Dimple]
[0185] Edge: highest point in cross section passing through center of a dimple [0186] Diameter: diameter of the flat plane circumscribed by the edge of a dimple [0187] Depth: maximum depth of a dimple from the flat plane circumscribed by the edge of the dimple [0188] SR: a ratio of a sum of the individual dimple surface areas, each defined by a flat plane circumscribed by an edge of a dimple, to a ball spherical surface area on the assumption that the ball has no dimples [0189] Dimple volume: a dimple volume under a flat plane circumscribed by an edge of a dimple Cylinder volume ratio: a ratio of the dimple volume to the cylinder volume having the same diameter as the dimple [0190] VR: a sum of the volumes of the individual dimples formed below the flat plane circumscribed by the edge of the dimple to the ball spherical volume on the assumption that the ball has no dimples
[0191] The ratio CL1/CD1=A1 of the lift coefficient CL1 at a Reynolds number of 218,000 and a spin rate of 2,800 rpm to the drag coefficient CD1, the ratio CL2/CD2=A2 of the lift coefficient CL2 at a Reynolds number of 184,000 and a spin rate of 2,900 rpm to the drag coefficient CD2, and the ratio CL3/CD3=A3 of the lift coefficient CL3 at a Reynolds number of 158,000 and a spin rate of 3,100 rpm to the drag coefficient CD3 of the balls with the above dimples (1) to (5) formed on their cover surfaces are listed in the table below. These lift coefficients and drag coefficients are measured in accordance with the Indoor Test Range (ITR) defined by USGA.
TABLE-US-00004 TABLE 4 Dimple (1) Dimple (2) Dimple (3) Dimple (4) Dimple (5) CL1 0.151 0.147 0.146 0.145 0.143 CD1 0.230 0.237 0.238 0.239 0.244 CL1/CD1 = A1 0.657 0.620 0.613 0.607 0.586 CL2 0.168 0.162 0.161 0.160 0.156 CD2 0.233 0.240 0.241 0.242 0.246 CL2/CD2 = A2 0.721 0.675 0.668 0.661 0.634 CL3 0.190 0.182 0.181 0.179 0.173 CD3 0.242 0.245 0.246 0.247 0.250 CL3/CD3 = A3 0.785 0.743 0.734 0.725 0.692
[0192] For each resulting golf ball, various physical properties such as internal hardnesses at various positions of the core, outer diameters of the core and each layer-encased sphere, thicknesses and material hardnesses of each layer, surface hardnesses of each layer-encased sphere, and ball initial velocities are evaluated by the following methods, and are shown in Tables 5 to 8.
[Core Hardness Profile]
[0193] The core surface is spherical, but an indenter of a durometer is set substantially perpendicular to the spherical core surface, and a core surface hardness expressed on the Shore C scale is measured in accordance with ASTM D2240. With respect to the core center and a predetermined position of the core, the core is cut into hemispheres to obtain a flat cross-section, the hardness is measured by perpendicularly pressing the indenter of the durometer against a center portion and the predetermined positions shown in Tables 5 and 6, and the hardnesses at the center and each position are shown as Shore C hardness values. For the measurement of the hardness, a P2 Automatic Rubber Hardness Tester manufactured by Kobunshi Keiki Co., Ltd. equipped with a Shore C durometer is used. For the hardness value, a maximum value is read. All measurements are carried out in an environment of 232 C. It is noted that the numerical values in the table are Shore C hardness values.
[0194] In addition, in the core hardness profile, letting the Shore C hardness at the core center be Cc, the Shore C hardness at the midpoint M between the core center and the core surface be Cm, the respective Shore C hardnesses at positions 2 mm, 4 mm, and 6 mm inward from the midpoint M be Cm2, Cm4, and Cm6, the respective Shore C hardnesses at positions 2 mm, 4 mm, and 6 mm outward from the midpoint M be Cm+2, Cm+4, and Cm+6, and the Shore C hardness at the core surface be Cs, the surface areas A to F are calculated as follows: [0195] surface area A: 2(Cm4Cm6) [0196] surface area B: 2(Cm2Cm4) [0197] surface area C: 2(CmCm2) [0198] surface area D: 2(Cm+2Cm) [0199] surface area E: 2(Cm+4Cm+2) [0200] surface area F: 2(Cm+6Cm+4) [0201] and the values of the following seven expressions are determined.
Surface area A+surface area B (1)
Surface area B+surface area C (2)
Surface area D+surface area E (3)
(Surface area D+surface area E)(surface area A+surface area B) (4)
(Surface area D+surface area E)(surface area B+surface area C) (5)
{(Surface area D+surface area E)(surface area A+surface area B)}(CsCc) (6)
{(Surface area D+surface area E)(surface area B+surface area C)}(CsCc) (7)
[0202] The surface areas A to F in the core hardness profile are described in
[0203] In addition,
[Diameters of Core and of Intermediate Layer-Encased Sphere]
[0204] At a temperature adjusted to 23.91 C. for at least three hours or more in a thermostatic bath, five random places on the surface are measured in a room with a temperature of 23.92 C., and, using an average value of these measurements as a measured value of each sphere, an average value for the diameter of 10 such spheres is determined.
[Ball Diameter]
[0205] At a temperature adjusted to 23.91 C. for at least three hours or more in a thermostatic bath, a diameter at 15 random dimple-free places is measured in a room at a temperature of 23.92 C., and, using an average value of these measurements as a measured value of one ball, an average value for the diameter of 10 balls is determined.
[Deflections of Core and Ball]
[0206] Each subject layer-encased sphere of the core or the ball is placed on a hard plate, and the deflection when compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) is measured. It is noted that the deflection in each case is a measurement value measured in a room at a temperature of 23.92 C. after temperature adjustment to 23.91 C. for at least three hours or more in a thermostatic bath. As a measuring device, a high-load compression tester manufactured by MU Instruments Trading Corp. is used, and a down speed of a pressure head that compresses the core or the ball is set to 10 mm/s.
[Material Hardnesses of Intermediate Layer and Cover (Shore C and Shore D Hardnesses)]
[0207] The resin material of each layer is molded into a sheet having a thickness of 2 mm and left at a temperature of 232 C. for two weeks. At the time of measurement, three such sheets are stacked together. The Shore C hardness and the Shore D hardness are each measured with a Shore C durometer and a Shore D durometer conforming to the ASTM D2240 standard. For the measurement of the hardness, the P2 Automatic Rubber Hardness Tester manufactured by Kobunshi Keiki Co., Ltd. to which a Shore C durometer or a Shore D durometer is mounted is used. For the hardness value, a maximum value is read. The measurement method is in accordance with the ASTM D2240 standard.
[Surface Hardnesses of Intermediate Layer-Encased Sphere and of Ball]
[0208] A measurement is performed by perpendicularly pressing the indenter against the surface of each sphere. It is noted that a surface hardness of a ball (cover) is a measured value at a dimple-free area (land) on the surface of the ball. The Shore C hardness and the Shore D hardness are each measured with a Shore C durometer and a Shore D durometer conforming to the ASTM D2240 standard. For the measurement of the hardness, the P2 Automatic Rubber Hardness Tester manufactured by Kobunshi Keiki Co., Ltd. to which a Shore C durometer or a Shore D durometer is mounted is used. For the hardness value, a maximum value is read. The measurement method is in accordance with the ASTM D2240 standard.
[Initial Velocity of Ball]
[0209] The initial velocity of each sphere is measured at a temperature of 23.92 C. using a device for measuring COR manufactured by Hye Precision Products of the same type as the R&A. The measurement principle is as follows.
[0210] An air pressure is changed to four stages of 35.5 psi, 36.5 psi, 39.5 psi, and 40.5 psi, and a ball is fired at four stages of incident velocity by respective air pressures, collided with a barrier, and its COR is measured. That is, a correlation equation between the incident velocity and the COR is created by changing the air pressure in four stages. Similarly, a correlation equation between the incident velocity and a contact time is created.
[0211] Then, from these correlation equations, the COR (coefficient of restitution) and the contact time (us) at an incident velocity of 43.83 m/s are determined and substituted into the following initial velocity conversion equation to calculate an initial velocity of each sphere.
[Here, e is a coefficient of restitution, and te is a contact time (us) at a collision speed of 143.8 ft/s (43.83 m/s).]
[0212] In the initial velocity measurement of the balls of all examples, a barrel diameter of 43.18 mm is selected.
TABLE-US-00005 TABLE 5 Example Comparative Example 1 2 3 4 1 2 3 4 Ball structure (piece) 2P 2P 2P 2P 2P 2P 2P 2P Core Outer diameter (mm) 39.30 39.30 39.30 39.30 39.30 39.30 39.30 39.70 Weight (g) 35.83 35.83 35.83 35.83 35.83 35.83 35.83 37.74 Specific gravity 1.127 1.127 1.127 1.127 1.127 1.127 1.127 1.152 Deflection (mm) 3.12 3.12 3.12 3.48 3.12 3.12 3.12 4.50 Cs [surface] (Shore C) 88.3 88.3 88.3 84.6 79.4 88.3 88.3 76.0 Cm + 6 (Shore C) 77.5 77.5 77.5 74.7 77.7 77.5 77.5 66.5 Cm + 4 (Shore C) 71.1 71.1 71.1 69.1 77.5 71.1 71.1 64.9 Cm + 2 (Shore C) 66.1 66.1 66.1 64.1 74.9 66.1 66.1 63.4 Cm [intermediate] (Shore C) 65.4 65.4 65.4 62.5 71.3 65.4 65.4 62.9 Cm 2 (Shore C) 64.5 64.5 64.5 61.0 67.3 64.5 64.5 62.4 Cm 4 (Shore C) 64.6 64.6 64.6 61.0 65.4 64.6 64.6 61.3 Cm 6 (Shore C) 64.7 64.7 64.7 61.5 63.8 64.7 64.7 59.7 Cc [center] (Shore C) 65.2 65.2 65.2 62.3 61.8 65.2 65.2 56.2 Cs Cc (Shore C) 23.1 23.1 23.1 22.3 17.6 23.1 23.1 19.8 (Cs Cc)/(Cm Cc) 115.5 115.5 115.5 111.5 1.9 115.5 115.5 3.0 Surface area A 0.1 0.1 0.1 0.5 1.6 0.1 0.1 1.6 Surface area B 0.1 0.1 0.1 0.0 1.9 0.1 0.1 1.1 Surface area C 0.9 0.9 0.9 1.5 4.0 0.9 0.9 0.5 Surface area D 0.7 0.7 0.7 1.6 3.6 0.7 0.7 0.5 Surface area E 5.0 5.0 5.0 5.0 2.6 5.0 5.0 1.5 Surface area F 6.4 6.4 6.4 5.6 0.2 6.4 6.4 1.6 Surface area A + surface area B 0.2 0.2 0.2 0.5 3.5 0.2 0.2 2.7 Surface area B + surface area C 0.8 0.8 0.8 1.5 5.9 0.8 0.8 1.6 Surface area D + surface area E 5.7 5.7 5.7 6.6 6.2 5.7 5.7 2.0 (Surface areas: D + E) (surface areas: A + B) 5.9 5.9 5.9 7.1 2.7 5.9 5.9 0.7 (Surface areas: D + E) (surface areas: B + C) 4.9 4.9 4.9 5.1 0.3 4.9 4.9 0.4 {(Surface areas: D + E) (surface areas: 136 136 136 158 48 136 136 14 A + B)} (Cs Cc) {(Surface areas: D + E) (surface areas: 113 113 113 114 5 113 113 8 B + C)} x (Cs Cc)
TABLE-US-00006 TABLE 6 Comparative Example 5 6 7 8 9 10 11 12 Ball structure (piece) 3P 3P 3P 3P 3P 3P 3P 2P Core Outer diameter (mm) 38.65 38.65 38.65 38.65 38.06 38.06 38.64 39.80 Weight (g) 35.09 35.09 35.09 35.09 33.83 33.83 35.10 36.99 Specific gravity 1.161 1.161 1.161 1.161 1.172 1.172 1.162 1.121 Deflection (mm) 2.92 2.92 2.92 2.92 4.13 4.13 2.93 2.63 Cs [surface] (Shore C) 87.4 87.4 87.4 87.4 86.3 86.3 81.5 84.3 Cm + 6 (Shore C) 80.4 80.4 80.4 80.4 74.1 74.1 80.5 79.0 Cm + 4 (Shore C) 75.8 75.8 75.8 75.8 65.9 65.9 79.0 75.9 Cm + 2 (Shore C) 70.8 70.8 70.8 70.8 61.3 61.3 76.2 72.8 Cm [intermediate] (Shore C) 66.3 66.3 66.3 66.3 61.0 61.0 72.3 70.8 Cm 2 (Shore C) 65.6 65.6 65.6 65.6 61.4 61.4 68.4 69.8 Cm 4 (Shore C) 64.9 64.9 64.9 64.9 61.0 61.0 66.9 68.4 Cm 6 (Shore C) 63.3 63.3 63.3 63.3 60.1 60.1 65.4 66.3 Cc [center] (Shore C) 62.6 62.6 62.6 62.6 57.9 57.9 62.7 60.7 Cs Cc (Shore C) 24.8 24.8 24.8 24.8 28.4 28.4 18.8 23.6 (Cs Cc)/(Cm Cc) 6.7 6.7 6.7 6.7 9.2 9.2 2.0 2.3 Surface area A 1.6 1.6 1.6 1.6 0.9 0.9 1.5 2.1 Surface area B 0.7 0.7 0.7 0.7 0.4 0.4 1.5 1.4 Surface area C 0.7 0.7 0.7 0.7 0.4 0.4 3.9 1.0 Surface area D 4.5 4.5 4.5 4.5 0.3 0.3 3.9 2.0 Surface area E 5.0 5.0 5.0 5.0 4.6 4.6 2.8 3.1 Surface area F 4.6 4.6 4.6 4.6 8.2 8.2 1.5 3.1 Surface area A + surface area B 2.3 2.3 2.3 2.3 1.3 1.3 3.0 3.5 Surface area B + surface area C 1.4 1.4 1.4 1.4 0.0 0.0 5.4 2.4 Surface area D + surface area E 9.5 9.5 9.5 9.5 4.9 4.9 6.7 5.1 (Surface areas: D + E) (surface areas: A + B) 7.2 7.2 7.2 7.2 3.6 3.6 3.7 1.6 (Surface areas: D + E) (surface areas: B + C) 8.1 8.1 8.1 8.1 4.9 4.9 1.3 2.7 {(Surface areas: D + E) (surface areas: 179 179 179 179 102 102 70 38 A + B)} (Cs Cc) {(Surface areas: D + E) (surface areas: 201 201 201 201 139 139 24 64 B + C)} (Cs Cc)
TABLE-US-00007 TABLE 7 Example Comparative Example 1 2 3 4 1 2 3 4 Intermediate Material layer Thickness (mm) Weight (g) Material hardness (Shore C) Material hardness (Shore D) Intermediate Outer diameter (mm) layer-encased Weight (g) sphere Surface hardness (Shore C) Surface hardness (Shore D) Cover Material No. 5 No. 5 No. 5 No. 5 No. 5 No. 5 No. 5 No. 6 Thickness (mm) 1.70 1.70 1.70 1.70 1.70 1.70 1.70 1.50 Specific gravity 1.100 1.100 1.100 1.100 1.100 1.100 1.100 0.980 Material hardness (Shore C) 94 94 94 94 94 94 94 84 Material hardness (Shore D) 65 65 65 65 65 65 65 56 Dimple Type (2) (3) (4) (2) (1) (1) (5) (4) Quantity 330 330 330 330 330 330 330 330 Surface area coverage ratio: SR (%) 86 86 86 86 84 84 85 86 Volume occupancy ratio: VR (%) 0.81 0.83 0.85 0.81 0.68 0.68 0.93 0.85 Total volume of dimples (mm.sup.3) 331 338 345 331 278 278 378 345 A1: CL1/CD1 0.620 0.613 0.607 0.620 0.657 0.657 0.586 0.607 A2: CL2/CD2 0.675 0.668 0.661 0.675 0.721 0.721 0.634 0.661 A3: CL3/CD3 0.743 0.734 0.725 0.743 0.785 0.785 0.692 0.725 Average value of A2 and A3 0.709 0.701 ).693 0.709 0.753 0.753 0.663 0.693 Ball Outer diameter (mm) 42.70 42.70 42.70 42.70 42.70 42.70 42.70 42.70 Weight (g) 45.50 45.50 45.50 45.50 45.50 45.50 45.50 45.40 Deflection (mm) 2.71 2.71 2.71 2.95 2.71 2.71 2.71 4.00 Initial velocity (m/s) 77.0 77.0 77.0 77.0 74.1 77.0 77.0 77.0 Initial velocity/deflection 28.4 28.4 28.4 26.1 27.3 28.4 28.4 19.3 Surface hardness (Shore C) 98 98 98 98 98 98 98 92 Surface hardness (Shore D) 71 71 71 71 71 71 71 62 Total volume of dimples/deflection of ball (mm.sup.2) 122 125 127 112 103 103 140 86 Ball surface hardness 10 10 10 13 19 10 10 16 core surface hardness (Shore C) Ball surface hardness 33 33 33 36 36 33 33 36 core center hardness (Shore C) Deflection of core deflection of ball (mm) 0.41 0.41 0.41 0.53 0.41 0.41 0.41 0.50 Deflection of core/deflection of ball 1.15 1.15 1.15 1.18 1.15 1.15 1.15 1.13 Core specific gravity cover specific gravity 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.17 Core diameter/ball diameter 0.920 0.920 0.920 0.920 0.920 0.920 0.920 0.930
TABLE-US-00008 TABLE 8 Comparative Example 5 6 7 8 9 10 11 12 Intermediate Material No. 2 No. 2 No. 2 No. 2 No. 1 No. 1 No. 2 layer Thickness (mm) 1.17 1.17 1.17 1.17 1.47 1.47 1.21 Weight (g) 5.54 5.54 5.54 5.54 6.82 6.82 5.71 Material hardness (Shore C) 94 94 94 94 94 94 94 Material hardness (Shore D) 67 67 67 67 65 65 67 Intermediate Outer diameter (mm) 40.99 40.99 40.99 40.99 41.00 41.00 41.06 layer-encased Weight (g) 40.63 40.63 40.63 40.63 40.65 40.65 40.81 sphere Surface hardness (Shore C) 97 97 97 97 97 97 97 Surface hardness (Shore D) 71 71 71 71 71 71 71 Cover Material No. 3 No. 3 No. 3 No. 3 No. 3 No. 3 No. 3 No. 4 Thickness (mm) 0.85 0.85 0.85 0.85 0.84 0.84 0.81 1.46 Specific gravity 1.084 1.091 1.098 1.091 1.119 1.093 1.101 1.139 Material hardness (Shore C) 71 71 71 71 71 71 71 67 Material hardness (Shore D) 50 50 50 50 50 50 50 47 Dimple Type (4) (2) (1) (5) (1) (4) (1) (2) Quantity 330 330 330 330 330 330 330 330 Surface area coverage ratio: SR (%) 86 86 84 85 84 86 84 86 Volume occupancy ratio: VR (%) 0.85 0.81 0.68 0.93 0.68 0.85 0.68 0.81 Total volume of dimples (mm.sup.3) 345 331 278 378 278 345 278 331 A1: CL1/CD1 0.607 0.620 0.657 0.586 0.657 0.607 0.657 0.620 A2: CL2/CD2 0.661 0.675 0.721 0.634 0.721 0.661 0.721 0.675 A3: CL3/CD3 0.725 0.743 0.785 0.692 0.785 0.725 0.785 0.743 Average value of A2 and A3 0.693 0.709 0.753 0.663 0.753 0.693 0.753 0.709 Ball Outer diameter (mm) 42.69 42.69 42.69 42.69 42.68 42.69 42.68 42.72 Weight (g) 45.49 45.52 45.55 45.52 45.60 45.52 45.51 45.66 Deflection (mm) 2.37 2.35 2.32 2.35 2.96 2.98 2.38 2.51 Initial velocity (m/s) 77.0 77.1 77.2 77.1 76.9 77.0 73.1 73.4 Initial velocity/deflection 32.5 32.6 33.3 32.8 26.0 25.8 30.7 29.2 Surface hardness (Shore C) 87 87 87 87 86 86 87 79 Surface hardness (Shore D) 61 61 61 61 60 60 61 53 Total volume of dimples/deflection of ball (mm.sup.2) 145 141 120 161 94 116 117 132 Ball surface hardness 0 0 0 0 0 0 6 5 core surface hardness (Shore C) Ball surface hardness 24 24 24 24 28 28 24 18 core center hardness (Shore C) Deflection of core deflection of ball (mm) 0.55 0.57 0.60 0.57 1.17 1.15 0.55 0.12 Deflection of core/deflection of ball 1.23 1.24 1.26 1.24 1.40 1.39 1.23 1.05 Core specific gravity cover specific gravity 0.08 0.07 0.06 0.07 0.05 0.08 0.06 0.02 Core diameter/ball diameter 0.905 0.905 0.905 0.905 0.892 0.892 0.905 0.932
[0213] The flight (W #1 and I #6) and the controllability on approach shots of each golf ball are evaluated by the following methods. The results are shown in Table 9.
[Evaluation of Flight (W #1, HS 54 m/s)]
[0214] A driver is mounted on a golf swing robot, and a spin rate and a distance traveled (total) by a ball when struck at a head speed (HS) of 54 m/s are measured. The club used is a TOUR B XD-5 Driver/loft angle 8.5 (2017 model) manufactured by Bridgestone Sports Co., Ltd. and is evaluated according to the following rating criteria.
[Rating Criteria]
[0215] Good: Total compared to Comparative Example 7 is not more than 8.0 m, and at least 14.0 m. [0216] Fair: Total compared to Comparative Example 7 is less than 14.0 m. [0217] NG: Total compared to Comparative Example 7 is more than 8.0 m.
[Evaluation of Flight (W #1, HS 40 m/s)]
[0218] The driver is mounted on the golf swing robot, and the spin rate and the distance traveled (total) by a ball when struck at a head speed (HS) of 40 m/s are measured. The club used is a J015 Driver/loft angle 9.5 (2016 model) manufactured by Bridgestone Sports Co., Ltd. and is evaluated according to the following rating criteria.
[Rating Criteria]
[0219] Good: Total compared to Comparative Example 7 is at least 0 m. [0220] Fair: Total compared to Comparative Example 7 is at least 5.0 m and less than 0 m. [0221] NG: Total compared to Comparative Example 7 is less than 5.0 m.
[Evaluation of Flight (I #6, HS 42 m/s)]
[0222] When a number six iron (I #6) is mounted on the golf swing robot and a ball is struck at an HS of 42 m/s, a spin rate and a distance traveled (total) are measured. The club used is a JGR Forged I #6 (2016 model) manufactured by Bridgestone Sports Co., Ltd. and is evaluated according to the following rating criteria.
[Rating Criteria]
[0223] Good: Total compared to Comparative Example 7 is at least 0 m. [0224] Fair: Total compared to Comparative Example 7 is at least 5.0 m and less than 0 m. [0225] NG: Total compared to Comparative Example 7 is less than 5.0 m.
[Evaluation of Flight (I #6, HS 35 m/s)]
[0226] When a number six iron (I #6) is mounted on the golf swing robot and a ball is struck at an HS of 35 m/s, a spin rate and a distance traveled (total) are measured. The club used is a JGR Forged I #6 (2016 model) manufactured by Bridgestone Sports Co., Ltd. and is evaluated according to the following rating criteria.
[Rating Criteria/Total]
[0227] Good: Total compared to Comparative Example 7 is at least 0 m. [0228] Fair: Total compared to Comparative Example 7 is at least 5.0 m and less than 0 m. [0229] NG: Total compared to Comparative Example 7 is less than 5.0 m.
[Evaluation of Spin Rate on Approach Shots]
[0230] A judgment is made based on a launch angle when a sand wedge is mounted on the golf swing robot and a ball is struck at a head speed (HS) of 15 m/s. Similarly, a spin rate immediately after the ball is struck is measured by a device for measuring initial conditions. The sand wedge used is a TOURSTAGE TW-03 (loft angle 57) 2002 model manufactured by Bridgestone Sports Co., Ltd.
[Rating Criteria]
[0231] Good: Launch angle is at least 35.0. [0232] NG: Launch angle is less than 35.0.
TABLE-US-00009 TABLE 9 Example Comparative Example 1 2 3 4 1 2 3 4 5 Flight W#1 Spin rate 2,423 2,423 2,423 2,376 2,573 2,423 2,423 2,479 2,801 HS (rpm) 54 m/s Total (m) 270.4 269.5 268.6 269.5 271.3 278.6 256.7 267.0 271.5 Total (m) 11.1 12.0 12.9 12.0 10.3 2.9 24.8 14.5 10.0 compared to Comp. Ex. 7 Rating Good Good Good Good Good NG Fair Fair Good W#1 Spin rate 2,754 2,754 2,754 2,651 2,854 2,754 2,754 2,692 3,177 HS (rpm) 40 m/s Total (m) 199.1 199.6 200.0 199.3 187.9 197.9 198.2 198.1 200.4 Total (m) 0.8 1.3 1.7 1.0 10.5 0.4 0.1 0.2 2.1 compared to Comp. Ex. 7 Rating Good Good Good Good NG Fair Fair Fair Good I#6 Spin rate 5,271 5,271 5,271 5,146 5,671 5,271 5,271 5,143 5,780 HS (rpm) 42 m/s Total (m) 183.9 183.6 183.2 184.2 168.4 180.7 179.8 184.3 180.6 Total (m) 5.8 5.5 5.1 6.1 9.7 2.6 1.7 6.2 2.5 compared to Comp. Ex. 7 Rating Good Good Good Good NG Good Good Good Good I#6 Spin rate 5,139 5,139 5,139 4,893 5,439 5,139 5,139 4,933 5,448 HS (rpm) 35 m/s Total (m) 141.8 142.9 143.9 142.2 133.4 142.1 144.3 144.8 141.9 Total (m) 1.7 2.8 3.8 2.1 6.7 2.0 4.2 4.7 1.8 compared to Comp. Ex. 7 Rating Good Good Good Good NG Good Good Good Good Approach SW Launch 41.1 41.1 41.1 41.2 40.1 41.1 41.1 36.7 32.5 HS angle () 15 m/s Rating Good Good Good Good Good Good Good Good NG Comparative Example 6 7 8 9 10 11 12 Flight W#1 Spin rate 2,794 2,786 2,794 2,542 2,545 2,981 3,149 HS (rpm) 54 m/s Total (m) 273.3 281.5 259.6 276.1 268.8 269.3 259.8 Total (m) 8.2 0.0 21.9 5.4 12.7 12.2 21.7 compared to Comp. Ex. 7 Rating NG NG Fair NG Good Good Fair W#1 Spin rate 3,166 3,154 3,166 2,912 2,900 3,372 3,629 HS (rpm) 40 m/s Total (m) 199.5 198.3 198.6 199.5 200.4 184.9 179.0 Total (m) 1.2 0.0 0.3 1.2 2.1 13.4 19.3 compared to Comp. Ex. 7 Rating Good Good Good Good Good NG NG I#6 Spin rate 5,751 5,721 5,751 4,948 5,039 6,249 6,354 HS (rpm) 42 m/s Total (m) 181.3 178.1 177.2 184.4 186.6 163.4 167.1 Total (m) 3.2 0.0 0.9 6.3 8.5 14.7 11.0 compared to Comp. Ex. 7 Rating Good Good Fair Good Good NG NG I#6 Spin rate 5,468 5,487 5,468 4,724 4,807 5,881 6,067 HS (rpm) 35 m/s Total (m) 139.8 140.1 142.3 144.7 146.0 129.8 131.1 Total (m) 0.3 0.0 2.2 4.6 5.9 10.3 9.0 compared to Comp. Ex. 7 Rating Fair Good Good Good Good NG NG Approach SW Launch 32.5 32.6 32.5 32.8 32.8 31.5 32.6 HS angle () 15 m/s Rating NG NG NG NG NG NG NG
[0233] As shown in the results in Table 9, the golf balls of Comparative Examples 1 to 12 are inferior in the following respects to the golf balls according to the present invention (Examples).
[0234] In Comparative Example 1, the dimple volume occupancy ratio VR is smaller than 0.75%, and A1 is larger than 0.655. In addition, the initial velocity of the ball is lower than 76.0 m/s. As a result, the distance on shots with a driver (W #1) at a head speed (HS) of 40 m/s is inferior, and the distance on shots with a number six iron (I #6) is inferior.
[0235] In Comparative Example 2, the dimple volume occupancy ratio VR is smaller than 0.75%, and A1 is larger than 0.655. As a result, the distance on shots with a driver (W #1) at a head speed (HS) of 54 m/s is longer, and does not conform to the new ODS rules.
[0236] In Comparative Example 3, the dimple volume occupancy ratio VR is larger than 0.89%. In addition, A1 is smaller than 0.590, and (A2+A3)/2 is smaller than 0.670. As a result, the distance is inferior under striking conditions with a driver (W #1) at head speeds (HS) of both 54 m/s and 40 m/s.
[0237] In Comparative Example 4, the deflection of the ball when compressed under a load of 10 to 130 kgf is larger than 3.8 mm. As a result, the actual initial velocity on shots with a driver (W #1) becomes low, and thus the distance is inferior under striking conditions with a driver (W #1) at head speeds (HS) of both 54 m/s and 40 m/s.
[0238] In Comparative Example 5, the cover material is made of a urethane material. As a result, the launch angle on approach shots was too low, and the ball was difficult for an amateur.
[0239] In Comparative Example 6, the cover material is made of a urethane material. As a result, the launch angle on approach shots is too low, and the ball is difficult for an amateur.
[0240] Comparative Example 7 is one of the embodiments used by male professionals in which the cover material is a urethane material. The dimple volume occupancy ratio VR is smaller than 0.75%, and A1 is larger than 0.655. As a result, the distance on shots with a driver (W #1) at a head speed (HS) of 54 m/s was increased, the ball did not conform to the new ODS rules, the launch angle on approach shots was too low, and the ball was difficult for an amateur.
[0241] In Comparative Example 8, the cover material is made of a urethane material, and the dimple volume occupancy ratio VR is larger than 0.89%. In addition, A1 is smaller than 0.590, and (A2+A3)/2 is smaller than 0.670. As a result, the distance on shots with a driver at a head speed (HS) of 54 m/s is too short, the launch angle on approach shots is excessively low, and the ball is difficult for an amateur.
[0242] In Comparative Example 9, the cover material is made of a urethane material, the dimple volume occupancy ratio VR is smaller than 0.75%, and A1 is larger than 0.655. As a result, the distance on shots with a driver (W #1) at a head speed (HS) of 54 m/s was long, the ball did not conform to the new ODS rules, the launch angle on approach shots was too low, and the ball was difficult for an amateur.
[0243] In Comparative Example 10, the cover material is made of a urethane material. As a result, the launch angle on approach shots was too low, and the ball was difficult for an amateur.
[0244] In Comparative Example 11, the cover material is made of a urethane material, the initial velocity of the ball is lower than 76.0 m/s, the dimple volume occupancy ratio VR is smaller than 0.75%, and A1 is larger than 0.655. As a result, the actual initial velocity was low under all striking conditions. The distance was good on shots with a driver (W #1) at a head speed (HS) of 54 m/s, but the distance decreased under other striking conditions. In addition, the launch angle on approach shots was too low, and the ball was difficult for an amateur.
[0245] Comparative Example 12 corresponds to a golf ball having a two-piece structure for a driving range, the initial velocity of the ball is less than 76.0 m/s, and the cover material is made of urethane. As a result, the actual initial velocity decreases under all striking conditions. On shots with a driver (W #1) at a head speed (HS) of 54 m/s, the distance is fairly good, but the distance decreases under other striking conditions. In addition, the launch angle on approach shots is too low, and the ball is difficult for an amateur.
[0246] Japanese Patent Application No. 2024-025235 is incorporated herein by reference. Although some preferred embodiments have been described, many modifications and variations may be made thereto in light of the above teachings. It is therefore to be understood that the invention may be practiced otherwise than as specifically described without departing from the scope of the appended claims.