Patent Application
20240299811
This non-provisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2023-035600 filed in Japan on Mar. 8, 2023, the entire contents of which are hereby incorporated by reference.
The present invention relates to a multi-piece solid golf ball including a core, an intermediate layer, and a cover, wherein a large number of dimples are formed on an outside surface of the cover.
In March 2022, manufacturers of golf balls were notified by the Royal and Ancient Golf Club of St Andrews (hereinafter, R&A) and the United States Golf Association (hereinafter, USGA) that they would start research to suppress the distance by long hitters by changing test conditions for the Overall Distance Standard (hereinafter, ODS) of golf balls in the future. For this reason, it is preferable to provide a golf ball that does not simply reduce distance, but while making the distance for reducing the distance on shots with a driver by long hitters larger, by making the distance for reducing the distance on shots with a driver and an iron by average hitters smaller, reduces the influence on play other than reducing the distance on shots with a driver by long hitters. In addition, due to the above changes, it is desirable to design the ball so that its spin characteristics in the short game have a similar performance to those of the ball used in the current tour so that a sense of discomfort does not occur for professionals or advanced players when using the golf ball with the reduced distance.
In the past, some golf balls in which an initial velocity of the ball is restricted to not more than 76.5 m/s have been proposed. Examples of such technical documents include the following Patent Documents 1 to 5.
However, each of the proposed golf balls is a practice ball for a driving range that is simply designed so as not to have a larger distance than a game ball. Therefore, the golf ball is not designed such that while reducing the distance on shots with a driver (W #1) by long hitters, the distance for reducing the distance by average hitters is made smaller than the distance for reducing the distance by long hitters.
Further, Patent Documents 6 to 14 listed below each disclose a golf ball in which, as for dimples formed on the ball surface, a sum of the 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, that is, a dimple volume occupancy ratio VR, is specified within a predetermined value, whereby a superior distance may be obtained in the low head speed (HS) range while reducing the distance in the high HS range.
However, with the golf balls proposed above, the distance on shots with the driver (W #1) by long hitters is reduced, and a desired distance on shots with an iron by both long hitters and average hitters is not attainable. Therefore, it is desirable to prevent the distance on shots with the iron from being reduced for both long hitters and average hitters as much as possible.
The present invention has been made in view of the above circumstances, and to address the possibility of there being a change to the rules in the future to suppress the distance by long hitters by changing the test conditions for the ODS of golf balls, an object of the present invention is to provide a golf ball that is intended to reduce the influence on play other than reducing the distance on shots with a driver by long hitters, instead of simply reducing distance, while making the distance for reducing the distance on shots with a driver by long hitters larger, by making the distance for reducing the distance on shots with a driver (W #1) by average hitters and with an iron by both long hitters and average hitters smaller.
As a result of intensive studies to achieve the above object, the present inventors have found that in a multi-piece solid golf ball including a core, an intermediate layer, and a cover, in which a large number of dimples are formed on an outside surface of the cover, a relationship between a surface hardness of an intermediate layer-encased sphere and a surface hardness of the ball satisfies the following condition:
Further, the present inventors have found that when an initial velocity of the ball is set to from 76.5 to 77.724 m/s, a deflection is set to at least 2.7 mm when the ball is compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf), and a value of (initial velocity of core×weight of core) is denoted by Ciw, a value of [(initial velocity of intermediate layer-encased sphere-initial velocity of core)×(weight of intermediate layer-encased sphere-weight of core)] is denoted by Miw, and a value of [(initial velocity of ball-initial velocity of intermediate layer-encased sphere)×(weight of ball-weight of intermediate layer-encased sphere)] is denoted by CViw, the following condition is satisfied:
Further, the present inventors have found that 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, and a ratio CL2/CD2 of a lift coefficient CL2 at a Reynolds number of 158000 and a spin rate of 3100 rpm to a drag coefficient CD2 is denoted by A2, by designing the golf ball to satisfy the following two conditions:
The above “long hitters” mean users whose head speed on shots with a driver (W #1) is at least about 50 m/s, and the above “average hitters” mean users whose head speed on shots with a driver (W #1) is less than about 45 m/s.
Accordingly, the present invention provides a multi-piece solid golf ball including
Further characteristics of the multi-piece solid golf ball are that when an initial velocity of the ball is from 76.5 to 77.724 m/s, a deflection is at least 2.7 mm when the ball is compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf), and a value of (initial velocity of core×weight of core) is denoted by Ciw, a value of [(initial velocity of intermediate layer-encased sphere-initial velocity of core)×(weight of intermediate layer-encased sphere-weight of core)] is denoted by Miw, and a value of [(initial velocity of ball-initial velocity of intermediate layer-encased sphere)×(weight of ball-weight of intermediate layer-encased sphere)] is denoted by CViw, the following condition is satisfied:
In a preferred embodiment of the multi-piece solid golf ball according to the invention, when an initial velocity of the core is denoted by Vc (m/s), and a deflection is denoted by C (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), the following condition is satisfied:
In another preferred embodiment of the inventive golf ball, a relationship between a surface hardness of the core and the surface hardness of the intermediate layer-encased sphere satisfies the following condition:
In yet another preferred embodiment, when each sphere of the core, the intermediate layer-encased sphere, and the ball is compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) and deflections (mm) are denoted by C (mm), M (mm), and B (mm) respectively, the following two conditions are satisfied:
In still another preferred embodiment, when a deflection (mm) is denoted by C (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), the following condition is satisfied:
In a further preferred embodiment, the core has a hardness profile in which, letting the Shore C hardness at a core center be Cc, the Shore C hardness at a position 4 mm outward from the core center be Cc+4, the Shore C hardness at a midpoint M between the core center and a core surface be Cm, the Shore C hardness at a position 4 mm inward from the midpoint M be Cm−4, the Shore C hardness at a position 4 mm outward from the midpoint M be Cm+4, the Shore C hardness at the core surface be Cs, and the Shore C hardness at a position 4 mm inward from the core surface be Cs−4, and defining surface areas A to D as follows:
In a yet further preferred embodiment, the core has a hardness profile in which the following condition is satisfied:
In a still further preferred embodiment, the core has a hardness profile in which the following condition is satisfied:
In another preferred embodiment, the core has a hardness profile in which the following condition is satisfied:
In yet another preferred embodiment, the core has a hardness profile in which the following condition is satisfied:
In still another preferred embodiment, a volume occupancy ratio VR of the dimples is from 0.75 to 0.89%.
In a further preferred embodiment, a value of A2 is from 0.695 to 0.815.
To address the possibility of there being a change to the rules in the future to suppress the distance by long hitters by the R&A and the USGA by changing the test conditions for the ODS of golf balls, with the golf ball according to the present invention, instead of simply reducing distance, making the distance for reducing the distance on shots with a driver by long hitters larger, and making the distance for reducing the distance on shots with a driver (W #1) by average hitters and the distance on shots with an iron by both long hitters and average hitters smaller can reduce an influence on play other than reducing the distance on shots with a driver by long hitters. In addition, the golf ball of the present invention has a similar performance to the ball used in the current tour with respect to its spin characteristics in the short game so that a sense of discomfort does not occur for professionals or advanced players when using the golf ball.
Hereinafter, the present invention is described in more detail.
A multi-piece solid golf ball according to the present invention has a core, an intermediate layer, and a cover, and an example thereof is shown in
The core is obtained by vulcanizing a rubber composition containing a rubber material as a chief material. If the core material is not a rubber composition, the rebound of the core may become low, and a desired distance may not be attainable on shots with a driver (W #1) and an iron by average hitters and on shots with an iron by long hitters. This rubber composition typically contains a base rubber as a chief material, and is obtained with the inclusion of a co-crosslinking agent, a crosslinking initiator, an inert filler, an organosulfur compound, or the like.
Examples of the core are preferably formed of a rubber composition containing, in particular, the following components (A) to (E):
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.
The co-crosslinking agent (B) is an α,β-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.
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.
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 parts by weight, and more preferably at least 0.2 parts by weight, and the upper limit is preferably not more than 2 parts by weight, and more preferably not more than 1 part by weight.
By blending the water or a water-containing material as the component (C) directly into the core material, 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 a 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 may be changed at the core center and the core surface. That is, the decomposition of the organic peroxide is further promoted near the core center, and the deactivation of radicals is further promoted, so that the amount of active radicals is further reduced, and as a result, a core may be obtained in which the crosslink densities at the core center and the core surface differ markedly, and the dynamic viscoelasticity of the core center portion is different.
In addition, a monocarboxylic acid metal salt may be employed instead of the water. In the monocarboxylic acid metal salt, it is presumed that a carboxylic acid is coordinate-bonded to the metal salt, and the monocarboxylic acid metal salt is distinguished from a dicarboxylic acid metal salt such as zinc diacrylate of [CH2═CHCOO]2Zn in a chemical formula. The monocarboxylic acid metal salt brings water into the rubber composition by subjecting the monocarboxylic acid metal salt to 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 in the rubber composition as powder, the working process may be simplified, and it is easy to uniformly disperse the monocarboxylic acid metal salt in the rubber composition. In order to effectively perform the above reaction, it is necessary to use a mono-salt. The compounding amount of the monocarboxylic acid metal salt included per 100 parts by weight of the base rubber is preferably at least 1 part by weight, and more preferably at least 3 parts by weight. As the 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. If the compounding amount of the monocarboxylic acid metal salt is too small, it is difficult to obtain an appropriate crosslink 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.
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.
As the organic peroxide (D), an organic peroxide having a relatively high thermal decomposition temperature is preferably 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 ½. 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° C. 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.
The organosulfur compound (E) is 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.
The upper limit of the compounding amount of the organosulfur compound is preferably not more than 5 parts by weight, more preferably not more than 4 parts by weight, further 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 and the rebound of the core becomes too high, and the distance on shots with a driver by long hitters may be too large. On the other hand, the lower limit of the compounding amount is preferably at least 0.1 parts by weight, more preferably at least 0.2 parts by weight, and even more preferably at least 0.5 parts by weight per 100 parts by weight of the base rubber. If the compounding amount is too small, the rebound of the core may be too low, so that the distance on shots with a driver by average hitters and with an iron by both long hitters and average hitters may be largely lowered.
In the rubber composition, a filler, an antioxidant, and the like may be blended as components other than the components (A) to (E).
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 12 parts by weight per 100 parts by weight of the base rubber. In addition, the 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.
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.
The compounding amount of the antioxidant is not particularly limited, although the compounding amount is preferably at least 0.05 parts by weight, and more preferably at least 0.1 parts by weight, and the upper limit is preferably not more than 1.0 part by weight, more preferably not more than 0.7 parts by weight, and even more preferably not more than 0.5 parts by weight per 100 parts by weight of the base rubber. If the compounding amount is too large or too small, a suitable core hardness gradient may not be obtained, and it may not be possible to obtain suitable rebound, durability, and a spin rate-lowering effect on full shots.
The core may be manufactured by vulcanizing and curing the rubber composition containing the above components. For example, a molded body may 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 100 to 200° C., and preferably at a temperature of 140 to 180° C., for 10 to 40 minutes.
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 the rubber core is produced as a plurality of layers of rubber, layer separation at the interface may arise when the ball is repeatedly struck, possibly leading to a cracking in earlier timing.
The diameter of the core is preferably at least 36.7 mm, more preferably at least 37.3 mm, and even more preferably at least 37.9 mm. The upper limit of the diameter of the core is preferably not more than 40.0 mm, more preferably not more than 39.2 mm, and even more preferably not more than 38.5 mm. If the diameter of the core is too small, the initial velocity of the ball may become too low, or a deflection of the entire ball may become small, so that the spin rate of the ball on full shots may rise, and a desired distance may not be attainable on shots with a driver (W #1) by average hitters and on shots with an iron by both average hitters and long hitters. On the other hand, if the diameter of the core is too large, the spin rate on full shots may rise, and the desired distance of average hitters may not be attainable, or a durability to cracking on repeated impact may worsen.
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, although the deflection (mm) is preferably at least 3.5 mm, more preferably at least 3.7 mm, and even more preferably at least 4.0 mm. The upper limit is preferably not more than 5.0 mm, more preferably not more than 4.7 mm, and even more preferably not more than 4.5 mm. If the deflection of the core is too small, that is, the core is too hard, a desired distance may not be attainable on shots with a driver (W #1) by average hitters and on shots with an iron by both average hitters and long hitters, or the feel at impact may be excessively hard. On the other hand, if the deflection of the core is too large, that is, if the core is too soft, the ball rebound may become too low and a good distance may not be achieved on shots with a driver (W #1) by average hitters, or the feel at impact may be too soft, or the durability to cracking on repeated impact may worsen.
Next, the core hardness profile is described. 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.
A core center hardness (Cc) is preferably at least 49, more preferably at least 51, and even more preferably at least 53, and the upper limit is preferably not more than 62, more preferably not more than 60, and even more preferably not more than 58. If this value is too large, the spin rate on full shots may rise, so that a desired distance may not be attainable on shots with a driver (W #1) by average hitters and on shots with an iron by both average hitters and long hitters, or the feel at impact may be excessively hard. On the other hand, if the above value is too small, the rebound may become low and the desired distance of average hitters may not be attainable, or the durability to cracking on repeated impact may worsen.
A hardness (Cc+4) at a position 4 mm outward from the core center is preferably at least 51, more preferably at least 53, and even more preferably at least 55, and the upper limit is preferably 65 or less, more preferably 63 or less, and even more preferably 61 or less. Hardnesses that deviate from these values may lead to undesirable results similar to those described above for the core center hardness (Cc).
A hardness (Cm) at a midpoint M between the core center and the core surface is not particularly limited, although the hardness (Cm) is preferably at least 54, more preferably at least 56, and even more preferably at least 58. In addition, the upper limit is also not particularly limited, although the upper limit is preferably not more than 65, more preferably not more than 63, and even more preferably not more than 61. Hardnesses that deviate from these values may lead to undesirable results similar to those described above for the core center hardness (Cc).
A hardness (Cm−4) at a position 4 mm inward from the midpoint M of the core is not particularly limited, although the hardness (Cm−4) is preferably at least 52, more preferably at least 54, and even more preferably at least 56. The upper limit is also not particularly limited, although the upper limit is preferably not more than 65, more preferably not more than 63, and even more preferably not more than 61. Hardnesses that deviate from these values may lead to undesirable results similar to those described above for the core center hardness (Cc).
A core surface hardness (Cs) is preferably at least 76, more preferably at least 78, and even more preferably at least 80, and the upper limit is preferably not more than 90, more preferably not more than 88, and even more preferably not more than 86. 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 this value is too small, the rebound may become low or the spin rate on full shots may rise, so that a desired distance may not be attainable on shots with a driver (W #1) by average hitters and on shots with an iron by both average hitters and long hitters.
A hardness (Cs−4) at a position 4 mm inward from the core surface is preferably at least 67, more preferably at least 69, and even more preferably at least 71, and the upper limit is preferably not more than 78, more preferably not more than 76, and even more preferably not more than 74. Hardnesses that deviate from these values may lead to undesirable results similar to those described above for the core surface hardness (Cs).
A hardness (Cm+4) at a position 4 mm outward from the midpoint M of the core is not particularly limited, although the hardness (Cm+4) is preferably at least 61, more preferably at least 63, and even more preferably at least 65. The upper limit is also not particularly limited, although the upper limit is preferably not more than 72, more preferably not more than 70, and even more preferably not more than 68. Hardnesses that deviate from these values may lead to undesirable results similar to those described above for the core surface hardness (Cs).
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 22, more preferably at least 24, and even more preferably at least 26. The upper limit is preferably not more than 35, more preferably not more than 32, and even more preferably not more than 29. If this value is too small, the spin rate on full shots may rise, so that a desired distance may not be attainable on shots with a driver (W #1) by average hitters and on shots with an iron by both average hitters and long hitters. On the other hand, if this value is too large, the rebound may become low, so that a desired distance may not be attainable on shots with a driver (W #1) by average hitters and on shots with an iron by both average hitters and long hitters, or the durability to cracking on repeated impact may worsen.
In addition, it is preferable to optimize the value of (Cs−Cc)/(Cm−Cc) for the core hardness profile. The value of (Cs−Cc) indicates a difference in hardness between the core center and the core surface, and the value of (Cm−Cc) indicates a difference in hardness between the core center and the midpoint M between the core surface and the core center. The above expression represents the ratio of these differences in hardness. The value of (Cs−Cc)/(Cm−Cc) is preferably at least 3.0, more preferably at least 4.0, and even more preferably at least 5.0. The upper limit is preferably not more than 12.0, more preferably not more than 11.0, and even more preferably not more than 9.5. If this value is too small, the spin rate on full shots may rise, so that a desired distance may not be attainable on shots with a driver (W #1) by average hitters and on shots with an iron by both average hitters and long hitters. On the other hand, if this value is too large, the rebound may become low, so that a desired distance may not be attainable on shots with a driver (W #1) by average hitters and on shots with an iron by both average hitters and long hitters, or the durability to cracking on repeated impact may worsen.
In the core hardness profile, the surface areas A to D defined as follows:
In addition, the value of (surface area C+surface area D)/(surface area A+surface area B) is preferably at least 2.0, more preferably at least 3.0, and even more preferably at least 4.0, and the upper limit is preferably not more than 15.0, more preferably not more than 12.0, and even more preferably not more than 8.0.
In addition, the relationship of each surface area calculated from the core hardness profile preferably satisfies the following condition:
The value of (surface area D-surface area A) is preferably at least 2.0, more preferably at least 4.0, and even more preferably at least 6.0, and the upper limit is preferably not more than 33.0, more preferably not more than 28.0, and even more preferably not more than 23.0.
The value of (surface area C-surface area B) is preferably at least 2.0, more preferably at least 5.0, and even more preferably at least 8.0, and the upper limit is preferably not more than 20.0, more preferably not more than 17.0, and even more preferably not more than 15.0.
Further, it is preferable to optimize the value of the following condition:
This value is at least 100, preferably at least 200, and more preferably at least 400. The upper limit is preferably not more than 1500, more preferably not more than 1200, and even more preferably not more than 1000. If this value is too small, the spin rate on full shots may rise, so that a desired distance may not be attainable on shots with a driver (W #1) by average hitters and on shots with an iron by both average hitters and long hitters. On the other hand, if this value is too large, the rebound may become low, so that a desired distance may not be attainable on shots with a driver (W #1) by average hitters and on shots with an iron by both average hitters and long hitters, or the durability to cracking on repeated impact may worsen.
The initial velocity of the core is preferably at least 75.0 m/s, more preferably at least 75.8 m/s, and even more preferably at least 76.2 m/s. The upper limit is not more than 78.0 m/s, preferably not more than 77.2 m/s, and more preferably not more than 76.6 m/s. If this initial velocity value is too high, the extent to which the distance with respect to the current tour ball is reduced on shots with a driver by long hitters is inadequate, and there is a possibility that the distance is too large compared with the standard distance of the new distance rules assumed by the R&A and the USGA. On the other hand, if the initial velocity is too low, a desired distance may not be attainable on shots with a driver (W #1) by average hitters and on shots with an iron by both average hitters and long hitters. 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 Golf Ball Testing Machine manufactured by Hye Precision Products 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 Golf Ball Testing Machine, a ball temperature-controlled for at least three hours in a thermostatic bath adjusted to 23.9±1° C. is used, and measurement is performed at a room temperature of 23.9±2° 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.
When the initial velocity of the core is denoted by Vc (m/s), and the deflection is denoted by C (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), the value of Vc/C is preferably at least 15, more preferably at least 16, and even more preferably at least 17. The upper limit is preferably not more than 25, more preferably not more than 23, and even more preferably not more than 20. If this value is too large, the extent to which the distance with respect to the current tour ball is reduced on shots with a driver by long hitters is inadequate, and there is a possibility that the distance is too large compared with the standard distance of the new distance rules assumed by the R&A and the USGA. On the other hand, if the value is too small, a desired distance may not be attainable on shots with a driver (W #1) by average hitters and on shots with an iron by both average hitters and long hitters.
When the value of (initial velocity of core×weight of core) is denoted by Ciw, Ciw means a value indicating the rebound of the core material portion in relation to its parts by weight. Ciw is preferably at least 2490, more preferably at least 2520, and even more preferably at least 2550. The upper limit is preferably not more than 2650, more preferably not more than 2630, and even more preferably not more than 2600. If this value is too large, the distance on shots with a driver (W #1) by long hitters may be larger than the intended distance, or the distance on shots with an iron may be smaller than the intended distance. On the other hand, if this value is too small, the distance on shots with a driver (W #1) by average hitters may be smaller than the intended distance.
When the deflection (mm) is denoted by C (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), the value of Ciw/C means a distribution amount with respect to a certain deflection in a quantitative index obtained by multiplying the rebound of the core material portion and its parts by weight. Ciw/C is preferably at least 400, more preferably at least 500, and even more preferably at least 550. The upper limit is preferably not more than 850, more preferably not more than 750, and even more preferably not more than 650. If this value is too large, the distance on shots with a driver (W #1) by long hitters may be larger than the intended distance, or the distance on shots with an iron may be smaller than the intended distance. On the other hand, if this value is too small, the distance on shots with a driver (W #1) by average hitters may be smaller than the intended distance.
Next, the intermediate layer is described.
The intermediate layer has a material hardness on the Shore C hardness scale which, although not particularly limited, is preferably at least 90, more preferably at least 92, and even more preferably at least 93. The upper limit is preferably not more than 100, more preferably not more than 98, and even more preferably not more than 96. The material hardness on the Shore D hardness scale is preferably at least 61, more preferably at least 63, and even more preferably at least 65. The upper limit is preferably not more than 72, more preferably not more than 70, and even more preferably not more than 67.
The sphere obtained by encasing the core with the intermediate layer (intermediate layer-encased sphere) has a surface hardness which, on the Shore C hardness scale, is preferably at least 95, more preferably at least 96, and even more preferably at least 97. The upper limit is preferably not more than 100, more preferably not more than 99, and even more preferably not more than 98. The surface hardness on the Shore D hardness scale is preferably at least 68, more preferably at least 69, and even more preferably at least 70. The upper limit is preferably not more than 78, more preferably not more than 75, and even more preferably not more than 72.
If the material hardness and the surface hardness of the intermediate layer are too soft in comparison with the above ranges, the spin rate on full shots may rise excessively, or an actual initial velocity on shots may become low, so that the distance on shots with a driver (W #1) by average hitters and an iron by both average hitters and long hitters may not be increased. On the other hand, if the material hardness and the surface hardness of the intermediate layer are too hard in comparison with the above ranges, the durability to cracking on repeated impact may worsen, or the feel at impact on shots with a putter or on short approaches may become too hard.
The intermediate layer has a thickness which is preferably at least 1.0 mm, more preferably at least 1.2 mm, and even more preferably at least 1.4 mm. The intermediate layer thickness has an upper limit that is preferably not more than 2.0 mm, more preferably not more than 1.8 mm, and even more preferably not more than 1.6 mm. It is preferable for the intermediate layer to be thicker than the subsequently described cover. When the intermediate layer thickness falls outside of the above range or the intermediate layer is thinner than the cover, the ball spin rate-lowering effect on shots with a driver (W #1) may be inadequate, and the intended distance on full shots by average hitters and on shots with an iron by both long hitters and average hitters may not be increased. Also, if the intermediate layer is too thin, the durability to cracking on repeated impact may worsen. On the other hand, if the thickness of the intermediate layer is too thick in comparison with the above range, the feel at impact may worsen.
The value obtained by subtracting the cover thickness from the intermediate layer thickness is preferably larger than 0 mm, more preferably at least 0.2 mm, and even more preferably at least 0.4 mm. The upper limit is preferably not more than 1.2 mm, more preferably not more than 0.9 mm, and even more preferably not more than 0.7 mm. When this value falls outside of the above range, the spin rate of the ball on full shots may rise or the actual initial velocity on shots may become low, as a result of which the distance on shots with a driver (W #1) by average hitters and on shots with an iron by both average hitters and long hitters may not be increased. On the other hand, if this value is too small, the durability to cracking on repeated impact may worsen.
As a material of the intermediate layer, it is suitable to employ an ionomer resin as a chief material. 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 10/90 to 90/10, and more preferably from 15/85 to 85/15. If the zinc-neutralized ionomer and the sodium-neutralized ionomer are not included in this ratio, the rebound may become too low and the distance on shots with a driver (W #1) by average hitters and on shots with an iron by both long hitters and average hitters may not be increased. Further, 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.
In the intermediate layer material, an optional additive may be appropriately included depending on the intended use. For example, various additives such as a pigment, a dispersant, an antioxidant, an ultraviolet absorber, and a light stabilizer may be included. If these additives are included, the compounding amount thereof is preferably at least 0.1 parts by weight, and more preferably at least 0.5 parts by weight, and the upper limit thereof is preferably not more than 10 parts by weight, and more preferably not more than 4 parts by weight per 100 parts by weight of the base resin.
For the intermediate layer material, it is suitable to abrade the surface of the intermediate layer in order to increase the degree of adhesion to a polyurethane suitably used in a cover material described later. Further, it is preferable that a primer (adhesive agent) is applied to the surface of the intermediate layer after the abrasion treatment, or an adhesion reinforcing agent is added to the intermediate layer material.
When the sphere (intermediate layer-encased sphere) in which the core is encased with the intermediate layer is compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf), the deflection (mm) is preferably at least 2.6 mm, more preferably at least 2.8 mm, and even more preferably at least 3.0 mm. The deflection upper limit is preferably not more than 4.2 mm, more preferably not more than 3.9 mm, and even more preferably not more than 3.6 mm. If the deflection of the intermediate layer-encased sphere is too small, that is, if the sphere is too hard, the spin rate of the ball rises and the distance on shots with a driver (W #1) by average hitters and on shots with an iron by both long hitters and average hitters may not be increased, or the feel at impact may be too hard. On the other hand, if the deflection is too large, that is, if the sphere is too soft, the spin rate decreases and a run increases too much on shots with an iron, it may be difficult to control the desired distance, the feel at impact may be too soft, or the durability to cracking on repeated impact may worsen.
The sphere (intermediate layer-encased sphere) in which the core is encased with the intermediate layer has an initial velocity which 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. The upper limit is preferably not more than 78.5 m/s, more preferably not more than 78.0 m/s, and even more preferably not more than 77.7 m/s. If this initial velocity value is too high, the extent to which the distance with respect to the current tour ball is reduced on shots with a driver by long hitters is inadequate, and there is a possibility that the distance is too large compared with the standard distance of the new distance rules assumed by the R&A and the USGA. On the other hand, if the initial velocity is too low, the distance on shots with a driver (W #1) by average hitters and on shots with an iron by both long hitters and average hitters may not be increased. The value of the initial velocity in this case is the same as the device and conditions used in the measurement of the initial velocity of the core described above.
When the initial velocity of the intermediate layer-encased sphere is denoted by VM (m/s), and the deflection is denoted by M (mm) when the intermediate layer-encased sphere is compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf), the value of VM/M is preferably at least 17, more preferably at least 19, and even more preferably at least 21. The upper limit is preferably not more than 29, more preferably not more than 27, and even more preferably not more than 25. If this value is too large, the extent to which the distance with respect to the current tour ball is reduced on shots with a driver by long hitters is inadequate, and there is a possibility that the distance is too large compared with the standard distance of the new distance rules assumed by the R&A and the USGA. On the other hand, if this value is too small, the distance on shots with a driver (W #1) by average hitters may become too small.
In addition, it is preferable to optimize the value (Miw) of [(initial velocity of intermediate layer-encased sphere-initial velocity of core)×(weight of intermediate layer-encased sphere-weight of core)], which is a relational expression of the initial velocity (m/s) of the core, the initial velocity (m/s) of the intermediate layer-encased sphere, the weight (g) of the core, and the weight (g) of the intermediate layer-encased sphere. This value means a value indicating a rebound of the intermediate layer material portion in relation to its parts by weight. The Miw value is preferably at least 1, more preferably at least 4, and even more preferably at least 7. The upper limit is preferably not more than 15, more preferably not more than 13, and even more preferably not more than 10. If this value is too large, the durability on repeated impact may worsen. On the other hand, if this value is too small, the spin rate of the ball on full shots may rise, and the distance on shots with a driver (W #1) by average hitters and on shots with an iron by both average hitters and long hitters may not be increased.
Next, the cover is described.
The cover has a material hardness on the Shore C hardness scale which, although not particularly limited, is preferably at least 50, more preferably at least 57, and even more preferably at least 63. The upper limit is preferably not more than 86, more preferably not more than 74, and even more preferably not more than 71. The material hardness on the Shore D hardness scale is preferably at least 30, more preferably at least 35, and even more preferably at least 40. The upper limit is preferably not more than 57, more preferably not more than 53, and even more preferably not more than 50.
The sphere (ball) obtained by encasing the intermediate layer-encased sphere with the cover—that is, the ball—has a surface hardness which, on the Shore C hardness scale, is preferably at least 73, more preferably at least 78, and even more preferably at least 83, but is preferably not more than 95, more preferably not more than 92, and even more preferably not more than 90. The surface hardness on the Shore D hardness scale is preferably at least 50, more preferably at least 53, and even more preferably at least 56, but is preferably not more than 70, more preferably not more than 65, and even more preferably not more than 60.
If the material hardness and the surface hardness of the cover are too soft in comparison with the above ranges, the spin rate on full shots may rise, and the distance on shots with a driver (W #1) by average hitters and on shots with an iron by both average hitters and long hitters may not be increased. 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 ball may not be fully receptive to spin on approach shots, or a scuff resistance may worsen.
The cover has a thickness of preferably at least 0.3 mm, more preferably at least 0.5 mm, and even more preferably at least 0.6 mm. The upper limit in the cover thickness is preferably not more than 1.2 mm, more preferably not more than 0.9 mm, and even more preferably not more than 0.8 mm. When the cover is too thick, the rebound of the ball on full shots may be inadequate or the spin rate may rise, as a result of which the distance on shots with a driver (W #1) by average hitters and on shots with an iron by both average hitters and long hitters may not be increased. On the other hand, when the cover is too thin, the scuff resistance may worsen or the ball may not be receptive to spin on approach shots and may thus lack sufficient controllability.
As the cover material, various urethane resins used as a cover material in golf balls may be used from the viewpoints of spin controllability and scuff resistance in the short game. Furthermore, from the viewpoint of mass productivity, it is preferable to use a resin material mainly composed of a thermoplastic polyurethane. Further, the cover is suitably formed of a resin blend containing (I) a thermoplastic polyurethane and (II) a polyisocyanate compound as principal components.
The total weight of the components (I) and (II) is recommended to be at least 60%, and more preferably at least 70% with respect to the total amount of the resin composition of the cover. The components (I) and (II) are described in detail below.
Describing the thermoplastic polyurethane (I), the construction of the thermoplastic polyurethane includes a soft segment composed of a polymeric polyol (polymeric glycol), which is a long-chain polyol, and a hard segment composed of a chain extender and a polyisocyanate compound. Here, as the long-chain polyol serving as a starting material, any of those hitherto used in the art related to thermoplastic polyurethane may be used, and are not particularly limited, and examples thereof may include polyester polyol, polyether polyol, polycarbonate polyol, polyester polycarbonate polyol, polyolefin polyol, conjugated diene polymer-based polyol, castor oil-based polyol, silicone-based polyol, and vinyl polymer-based polyol. These long-chain polyols may be used singly, or two or more may be used in combination. Among them, a polyether polyol is preferable from the viewpoint that a thermoplastic polyurethane having a high rebound resilience and excellent low-temperature properties may be synthesized.
As the chain extender, those hitherto used in the art related to thermoplastic polyurethanes may be suitably used, and for example, a low-molecular-weight compound having on the molecule two or more active hydrogen atoms capable of reacting with an isocyanate group and having a molecular weight of 400 or less is preferable. Examples of the chain extender include, but are not limited to, 1,4-butylene glycol, 1,2-ethylene glycol, 1,3-butanediol, 1,6-hexanediol, 2,2-dimethyl-1,3-propanediol, or the like. Among them, the chain extender is preferably an aliphatic diol having from 2 to 12 carbon atoms, and is more preferably 1,4-butylene glycol.
As the polyisocyanate compound, those hitherto used in the art related to thermoplastic polyurethane may be suitably used, and are not particularly limited. Specifically, one or more selected from the group consisting of 4,4′-diphenylmethane diisocyanate, 2,4-toluene diisocyanate (or) 2,6-toluene diisocyanate, p-phenylene diisocyanate, xylylene diisocyanate, 1,5-naphthylene diisocyanate, tetramethylxylene diisocyanate, hydrogenated xylylene diisocyanate, dicyclohexylmethane diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, norbornene diisocyanate, trimethylhexamethylene diisocyanate, and dimer acid diisocyanate may be used. However, it may be difficult to control a crosslinking reaction during injection molding depending on the type of isocyanate. In the present invention, 4,4′-diphenylmethane diisocyanate, which is an aromatic diisocyanate, is most preferable from the viewpoint of providing a balance between stability during production and the physical properties to be manifested.
As specific examples of the thermoplastic polyurethane serving as the component (I), commercially available products may be used such as Pandex T-8295, Pandex T-8290, and Pandex T-8260 (all manufactured by DIC Covestro Polymer, Ltd.).
Although not an essential component, a thermoplastic elastomer other than the thermoplastic polyurethane may be included as a separate component (III) with the components (I) and (II). By including the component (III) in the resin blend, a flowability of the resin blend may be further improved, and various physical properties required of the golf ball cover material may be increased, such as rebound and scuff resistance.
A compositional ratio of the components (I), (II), and (III) is not particularly limited, but in order to sufficiently and effectively exhibit the advantageous effects of the present invention, the compositional ratio (I):(II):(III) is preferably in the weight ratio range of from 100:2:50 to 100:50:0, and more preferably from 100:2:50 to 100:30:8.
Furthermore, various additives other than the components constituting the thermoplastic polyurethane may be included in the resin blend as necessary, and for example, a pigment, a dispersant, an antioxidant, a light stabilizer, an ultraviolet absorber, an internal mold lubricant, or the like may be appropriately included.
The manufacture of a multi-piece solid golf ball in which the above-described core, intermediate layer, and cover (outermost layer) are formed as successive layers may be performed by a customary method such as a known injection molding process. For example, an intermediate layer material is injected around the core in an injection mold to obtain an intermediate layer-encased sphere, and finally, a cover material, which is the outermost layer, is injection molded to obtain a multi-piece golf ball. In addition, it is also possible to produce a golf ball by preparing two half-cups pre-molded into hemispherical shapes, enclosing the core and the intermediate layer-encased sphere within the two half cups, and molding the core and the intermediate layer-encased sphere under applied heat and pressure.
The golf ball has a deflection 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 2.7 mm, more preferably at least 2.8 mm, and even more preferably at least 2.9 mm. The deflection upper limit is preferably not more than 3.7 mm, more preferably not more than 3.5 mm, and even more preferably not more than 3.3 mm. When the golf ball deflection is too small, i.e., when the ball is too hard, the spin rate may rise excessively, and the distance on shots with a driver (W #1) by average hitters and on shots with an iron by both long hitters and average hitters may not be increased, or the feel at impact may be too hard. On the other hand, if the deflection is too large, that is, if the sphere is too soft, the spin rate decreases and a run increases too much on shots with an iron, it may be difficult to control the desired distance, the feel at impact may be too soft, or the durability to cracking on repeated impact may worsen.
The initial velocity of the sphere (ball) in which the intermediate layer-encased sphere is encased with the cover is preferably at least 76.5 m/s, more preferably at least 76.7 m/s, and even more preferably at least 76.9 m/s. The upper limit is not more than 77.724 m/s. If this initial velocity value is too high, the official rules of the R&A and the USGA are not satisfied. On the other hand, if the initial velocity is too low, the distance on shots with a driver (W #1) by average hitters and on shots with an iron by both long hitters and average hitters may not be increased. The initial velocity value in this case is measured with the same device and under the same conditions as described above for measurement of the initial velocities of the core and the intermediate layer-encased sphere.
When the initial velocity of the ball is denoted by V (m/s), and the deflection (mm) is denoted by B (mm) when the ball is compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf), the value of V/B is preferably at least 20, more preferably at least 21, and even more preferably at least 23. The upper limit is preferably not more than 28, more preferably not more than 27, and even more preferably not more than 26. If this value is too large, the extent to which the distance with respect to the current tour ball is reduced on shots with a driver by long hitters is inadequate, and there is a possibility that the distance is too large compared with the standard distance of the new distance rules assumed by the R&A and the USGA. On the other hand, if this value is too small, the distance on shots with a driver (W #1) by average hitters may become too small.
In addition, it is preferable to optimize the value (CViw) of [(initial velocity of ball—initial velocity of intermediate layer-encased sphere)×(weight of ball-weight of intermediate layer-encased sphere)], which is a relational expression of the initial velocity (m/s) of the intermediate layer-encased sphere, the initial velocity (m/s) of the ball, the weight (g) of the intermediate layer-encased sphere, and the weight (g) of the ball. This value means a value indicating a rebound of the cover material portion in relation to its parts by weight. The CViw value is preferably at least −5, more preferably at least −4, and even more preferably at least −3. The upper limit is preferably not more than 0, more preferably not more than −1, and even more preferably not more than −2. If this value is too large, the controllability in the short game may be insufficient. On the other hand, if this value is too small, the spin rate of the ball on full shots may rise, and the distance on shots with a driver (W #1) by average hitters and on shots with an iron by both average hitters and long hitters may become too small.
In the present invention, from the viewpoint that a relationship between the surface hardness of the intermediate layer-encased sphere and the surface hardness of the ball is compatible with a superior distance on shots with a driver (W #1) by average hitters and on full shots with an iron by long hitters and the controllability in the short game, the following condition needs to be satisfied:
Expressed on the Shore C hardness scale, a value obtained by subtracting the core surface hardness from the surface hardness of the intermediate layer-encased sphere is preferably at least 5, more preferably at least 7, and even more preferably at least 10. The upper limit is preferably not more than 28, more preferably not more than 25, and even more preferably not more than 20. If this value deviates from the above range, the spin rate of the ball on full shots may rise, so that a desired distance may not be attainable on shots with a driver (W #1) by average hitters and on shots with an iron by both average hitters and long hitters.
Expressed on the Shore C hardness scale, a value obtained by subtracting the core center hardness from the surface hardness of the intermediate layer-encased sphere is preferably at least 30, more preferably at least 35, and even more preferably at least 38. The upper limit is preferably not more than 53, more preferably not more than 48, and even more preferably not more than 45. If the value is too small, the spin rate of the ball on full shots may rise, so that a desired distance may not be attainable on shots with a driver (W #1) by average hitters and on shots with an iron by both average hitters and long hitters. On the other hand, if the above value is too large, the durability to cracking on repeated impact may worsen, or the actual initial velocity on shots may become lower, so that a desired distance may not be attainable on shots with a driver (W #1) by average hitters.
A relationship between the core diameter and the ball diameter, that is, the value of (core diameter)/(ball diameter) is preferably at least 0.859, more preferably at least 0.874, and even more preferably at least 0.888. The upper limit is preferably not more than 0.937, more preferably not more than 0.918, and even more preferably not more than 0.902. If this value is too small, the initial velocity of the ball may become too low, or the deflection of the entire ball may become small and the ball may become too hard, so that the spin rate on full shots may rise, and the distance on shots with a driver (W #1) by average hitters and on shots with an iron by both average hitters and long hitters may be shorter than the intended distance. On the other hand, if the value is too large, the spin rate of the ball on full shots may rise, and the distance on shots with a driver (W #1) by average hitters and on shots with an iron by both average hitters and long hitters may be shorter than the intended distance, or the durability to cracking on repeated impact may worsen.
[Relationships between Deflections of Each Sphere]
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) and the deflections (mm) are denoted by C (mm) and B (mm), respectively, the value of C−B is preferably at least 1.00 mm, more preferably at least 1.05 mm, and even more preferably at least 1.10 mm. The upper limit is preferably not more than 1.50 mm, more preferably not more than 1.40 mm, and even more preferably not more than 1.30 mm. If the above value is too large, the durability to cracking on repeated impact may worsen, or the actual initial velocity on shots may become lower, and a desired distance may not be attainable on shots with a driver (W #1) by average hitters. If this value is too small, the feel at impact may become too hard, or the spin rate on full shots may rise, so that a desired distance may not be attainable on shots with a driver (W #1) by average hitters and on shots with an iron by both average hitters and long hitters.
When each sphere of the core and the intermediate layer-encased sphere is compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) and the deflections (mm) are denoted by C (mm) and M (mm), respectively, the value of C-M is preferably at least 0.65 mm, more preferably at least 0.80 mm, and even more preferably at least 0.90 mm. The upper limit is preferably not more than 1.15 mm, more preferably not more than 1.10 mm, and even more preferably not more than 1.00 mm. If the above value is too large, the durability to cracking on repeated impact may worsen, or the actual initial velocity on shots may become lower, and a desired distance may not be attainable on shots with a driver (W #1) by average hitters. If this value is too small, the feel at impact may become too hard, or the spin rate on full shots may rise, so that a desired distance may not be attainable on shots with a driver (W #1) by average hitters and on shots with an iron by both average hitters and long hitters.
In the golf ball of the present invention, when the value of (initial velocity of core×weight of core) is denoted by Ciw, the value of [(initial velocity of intermediate layer-encased sphere-initial velocity of core)×(weight of intermediate layer-encased sphere −weight of core)] is denoted by Miw, and the value of [(initial velocity of ball-initial velocity of intermediate layer-encased sphere)×(weight of ball-weight of intermediate layer-encased sphere)] is denoted by CViw, the following condition needs to be satisfied:
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 may 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 range, the distance on shots with a driver (W #1) by average hitters may be lowered.
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 may be appropriately used. For example, if circular dimples are used, the diameter may be about at least 2.5 mm and not more than 6.5 mm, and the depth may be at least 0.08 mm and not more than 0.30 mm.
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 the 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 range, the distance on shots with a driver (W #1) by average hitters may be lowered.
A ratio (VR value) of a sum of the 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%. The upper limit 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 higher than the above range, there is a case where the distance on shots with a driver (W #1) by long hitters may be too small, or the intended distance on shots with a driver (W #1) by average hitters 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 value is too small, the extent of reducing the distance on shots with a driver (W #1) by long hitters is inadequate, and there is a possibility that the distance is too large compared with the standard distance of the new distance rules assumed by the R&A and the USGA.
A value V0 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 V0 value deviates from the above range, the distance on shots with a driver (W #1) by long hitters and average hitters may be lowered.
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, and a ratio (CL2/CD2) of a lift coefficient CL2 at a Reynolds number of 158000 and a spin rate of 3100 rpm to a drag coefficient CD2 is denoted by A2, the dimples are designed to satisfy the following two conditions:
In the present specification, the “lift coefficients (CL1, CL2), drag coefficients (CD1, CD2)” 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 may 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).
In Equation (1) above, p represents the density of a fluid, ν represents the average velocity of an object relative to the flow of the fluid, L represents a characteristic length, and μ represents the viscosity coefficient of the fluid.
In the present invention, the ratio CL1/CD1 of the lift coefficient CL1 at a Reynolds number of 218000 and a spin rate of 2800 rpm to the drag coefficient CD1 is defined as A1, and the ratio CL2/CD2 of the lift coefficient CL2 at a Reynolds number of 158000 and a spin rate of 3100 rpm to the drag coefficient CD2 is defined as A2.
The condition under which the lift coefficient CL1 and the drag coefficient CD1 are measured is described, that is, Reynolds number 218000 and spin rate 2800 rpm. This high-speed condition corresponds to a condition provided by a long hitter with a driver (W #1), this Reynolds number corresponds to a ball speed when a golf ball is driven out at a head speed (HS) of 54 m/s, and the spin rate 2800 rpm is an average spin condition of a player with a head speed (HS) of 54 m/s.
The condition under which the lift coefficient CL2 and the drag coefficient CD2 are measured is described, that is, Reynolds number 158000 and spin rate 3100 rpm. This low-speed condition corresponds to a condition provided by an average hitter with a driver (W #1) at a head speed (HS) of 40 m/s, this Reynolds number corresponds to a ball speed when a golf ball is driven out at a head speed (HS) of 40 m/s, and the spin rate 3100 rpm is an average spin condition of a player with a head speed (HS) of 40 m/s.
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 the 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 effect of reducing the distance made by a long hitter with a driver (W #1) is insufficient, and the distance may be too large. On the other hand, if the above value is too small, the actual distance may be lower than the intended distance.
The ratio between the lift coefficient CL2 and the drag coefficient CD2, that is, the value of CL2/CD2=A2 is preferably at least 0.695, more preferably at least 0.710, and even more preferably at least 0.722, and the upper limit thereof is preferably not more than 0.815, more preferably not more than 0.810, and even more preferably not more than 0.800. If this value is too low, it becomes difficult to carry when hit with a driver (W #1) at a head speed (HS) of 40 m/s, and the intended total distance may not be obtained. On the other hand, if the above value is too high, the ball trajectory is blown up when hit with a driver (W #1) at a head speed (HS) of 40 m/s, and the intended distance may not be obtained.
The multi-piece solid golf ball of the invention can 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.
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.
In Examples 1 and 3 and Comparative Examples 1 to 4, 6, and 8, 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.
In Examples 2 and 4 and Comparative Examples 5, 7, and 9, cores are produced based on the formulations in Table 1 in the same manner as described above.
Next, in Examples 1 and 3 and Comparative Examples 1 to 4, 6, and 8, the intermediate layer was formed by injection molding the 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.
In Examples 2 and 4 and Comparative Examples 5 and 7, the intermediate layer is formed by injection molding the 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 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. In Comparative Example 9, the cover is formed by injection molding the resin material No. 4 shown in Table 2 around the core surface using an injection mold. At this time, a predetermined large number of dimples described below are formed on the surface of the cover.
For the dimples of Examples and Comparative Examples, the following dimple modes (1) to (6) 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 shown in Table 3 below [dimples (1) to (6)]. In addition, an arrangement mode (pattern) of the dimples (1) to (5) is illustrated in
The ratio CL1/CD1=A1 of the lift coefficient CL1 at a Reynolds number of 218000 and a spin rate of 2800 rpm to the drag coefficient CD1, and the ratio CL2/CD2=A2 of the lift coefficient CL2 at a Reynolds number of 158000 and a spin rate of 3100 rpm to the drag coefficient CD2 of the balls with the above dimples (1) to (5) formed on their cover surfaces are listed in Table 4 below. These lift coefficients and drag coefficients are measured in accordance with the Indoor Test Range (ITR) defined by the USGA.
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.
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 hardness 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 the center portion and the predetermined positions shown in Tables 5 and 6, and the hardness 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 23±2° C. The numerical values in the tables are Shore C hardness values.
In addition, in the core hardness profile, letting Cc be the Shore C hardness at the core center, Cc+4 be the Shore C hardness at a position 4 mm outward from the core center, Cm be the Shore C hardness at the midpoint M between the core center and the core surface, Cm−4 be the Shore C hardness at a position 4 mm inward from the midpoint M, Cm+4 be the Shore C hardness at a position 4 mm outward from the midpoint M, Cs be the Shore C hardness at the core surface, and Cs−4 be the Shore C hardness at a position 4 mm inward from the core surface, the surface areas A to D are calculated as follows:
The surface areas A to D in the core hardness profile are described in
In addition,
At a temperature adjusted to 23.9±1° 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 23.9±2° 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.
At a temperature adjusted to 23.9±1° 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 23.9±2° 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.
Each subject layer-encased sphere is placed on a hard plate, and a deflection when compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) is measured. The deflection in each case is a measurement value measured in a room at a temperature of 23.9±2° C. after temperature adjustment to 23.9±1° C. for at least three hours in a thermostatic bath. As a measuring device, a high-load compression tester manufactured by MU Instruments Trading Corp. is used, and the down speed of the pressure head that compresses the core, the layer-encased sphere of each layer, or the ball is set to 10 mm/s.
The resin material of each layer is molded into a sheet having a thickness of 2 mm and left at a temperature of 23±2° 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.
A measurement is performed by perpendicularly pressing the indenter against the surface of each sphere. 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.
The initial velocity of each sphere is measured at a temperature of 23.9±2° C. using the device for measuring COR manufactured by Hye Precision Products of the same type as the R&A. The measurement principle is as follows.
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 (coefficient of restitution) 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.
Then, from these correlation equations, the COR (coefficient of restitution) and the contact time (μs) 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 tc is a contact time (μs) at a collision speed of 143.8 ft/s (43.83 m/s).]
In the initial velocity measurement of each sphere, 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. For the core, a barrel diameter of 39.88 mm is selected in Examples 1 to 4 and Comparative Examples 1 to 8, and a barrel diameter of 41.53 mm is selected in Comparative Example 9. A barrel of 41.53 mm in all examples is selected for the intermediate layer-encased sphere, and a barrel of 43.18 mm in all examples is selected for the ball.
In each example of the Examples and the Comparative Examples, a value of Ciw+Miw+CViw is calculated by assuming that a value of (initial velocity of core×weight of core) is denoted by Ciw, a value of [(initial velocity of intermediate layer-encased sphere −initial velocity of core)×(weight of intermediate layer-encased sphere-weight of core)] is denoted by Miw, and a value of [(initial velocity of ball-initial velocity of intermediate layer-encased sphere)×(weight of ball-weight of intermediate layer-encased sphere)] is denoted by CViw. The numerical values of each example are shown in Tables 7 and 8, and a graph showing the values of Ciw+Miw+CViw is shown in
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)]
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 9.5° (2017 model) manufactured by Bridgestone Sports Co., Ltd. and evaluation is performed according to the following rating criteria.
A driver is mounted on the golf swing robot, and a spin rate and a distance traveled (total) by a ball when struck at a head speed (HS) of 40 m/s are measured. The club used is a JGR Driver/loft angle 9.5° (2016 model) manufactured by Bridgestone Sports Co., Ltd. and evaluation is performed according to the following rating criteria.
A number six iron (I #6) is mounted on the golf swing robot, and a spin rate and a distance traveled (total) by a ball when struck at a head speed (HS) of 42 m/s are measured. The club used is a JGR Forged I #6 (2016 model) manufactured by Bridgestone Sports Co., Ltd. and evaluation is performed according to the following rating criteria.
A number six iron (I #6) is mounted on the golf swing robot, and a spin rate and a distance traveled (total) by a ball when struck at a head speed (HS) of 35 m/s are measured. The club used is a JGR Forged I #6 (2016 model) manufactured by Bridgestone Sports Co., Ltd. and evaluation is performed according to the following rating criteria.
A judgment is made based on a spin rate 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 57º) 2002 model manufactured by Bridgestone Sports Co., Ltd.
As shown in the results in Table 9, the golf balls of Comparative Examples 1 to 9 are inferior in the following respects to the golf balls according to the present invention (Examples).
In Comparative Example 1, the value of A1 is larger than 0.655, the initial velocity of the ball is smaller than 76.5 m/s, and the value of Ciw+Miw+CViw is smaller than 2500. As a result, each distance on shots with a driver (W #1, HS 40 m/s), a number six iron (I #6, HS 42 m/s), or a number six iron (I #6, HS 35 m/s) is inferior.
In Comparative Example 2, the value of A1 is larger than 0.655, the initial velocity of the ball is smaller than 76.5 m/s, and the value of Ciw+Miw+CViw is smaller than 2500. As a result, each distance on shots with a driver (W #1, HS 40 m/s), a number six iron (I #6, HS 42 m/s), or a number six iron (I #6, HS 35 m/s) is inferior.
In Comparative Example 3, the value of A1 is larger than 0.655, the initial velocity of the ball is smaller than 76.5 m/s, and the value of Ciw+Miw+CViw is smaller than 2500. As a result, each distance on shots with a driver (W #1, HS 40 m/s), a number six iron (I #6, HS 42 m/s), or a number six iron (I #6, HS 35 m/s) is inferior.
In Comparative Example 4, the value of A1 is larger than 0.655. As a result, a distance on shots with a driver (W #1, HS 54 m/s) is inferior.
In Comparative Example 5, the value of A1 is smaller than 0.590, and the value of A2 is smaller than 0.695. As a result, a distance on shots with a driver (W #1, HS 54 m/s) is excessively reduced, and a distance on shots with a driver (W #1, HS 40 m/s) is also reduced.
Comparative Example 6 is one embodiment of a tour ball currently used by professionals or advanced players. The value of A1 is larger than 0.655, the deflection of the ball is smaller than 2.7 mm, and the value of Ciw+Miw+CViw is larger than 2650. As a result, a distance on shots with a driver (W #1, HS 54 m/s) is too large, and each distance on shots with a driver (W #1, HS 40 m/s), a number six iron (I #6, HS 42 m/s), and a number six iron (I #6, HS 35 m/s) is inferior to those in the examples.
In Comparative Example 7, the deflection of the ball is smaller than 2.7 mm, and the value of Ciw+Miw+CViw is larger than 2650. As a result, each distance on shots with a driver (W #1, HS 40 m/s), a number six iron (I #6, HS 42 m/s), or a number six iron (I #6, HS 35 m/s) is inferior to those in the examples.
In Comparative Example 8, the value of A1 is larger than 0.655, the deflection of the ball is smaller than 2.7 mm, and the initial velocity of the ball is smaller than 76.5 m/s. As a result, each distance on shots with a driver (W #1, HS 40 m/s), a number six iron (I #6, HS 42 m/s), or a number six iron (I #6, HS 35 m/s) is inferior.
Comparative Example 9 corresponds to a practice ball having a two-piece structure for a driving range, in which the deflection of the ball is smaller than 2.7 mm, the initial velocity of the ball is smaller than 76.5 m/s, and the value of Ciw+Miw+CViw is larger than 2650. As a result, a distance on shots with a driver (W #1, HS 54 m/s) is excessively reduced, and each distance on shots with a driver (W #1, HS 40 m/s), a number six iron (I #6, HS 42 m/s), and a number six iron (I #6, HS 35 m/s) is also reduced.
Japanese Patent Application No. 2023-035600 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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2023-035600 | Mar 2023 | JP | national |
