Patent Application
20250010143
This non-provisional application claims priority under 35 U.S.C. § 119 (a) on Patent Application No. 2023-109792 filed in Japan on Jul. 4, 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 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 a distance for reducing a distance on shots with a driver by long hitters longer, by making a distance for reducing a distance on shots with a driver and an iron by average hitters shorter, reduces an 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, many golf balls have been proposed in which a surface hardness of the ball and an amount of 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) are optimized, and examples thereof include the following Patent Documents 1 to 7.
However, the golf balls proposed above are those for increasing the distance on shots with a driver (W #1) and golf balls focusing on controllability on approach shots, and no golf ball is designed so that the distance for reducing the distance of average hitters is shorter than the distance for reducing the distance of long hitters while reducing the distance on shots with a driver (W #1) by long hitters.
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 a 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 satisfy the needs of professionals or advanced players, instead of simply reducing distance, by making a distance for reducing a distance on shots with a driver (W #1) by average hitters and on shots with an iron shorter, reducing a run on shots with an iron and thus making the ball easy to stop at an intended place, and increasing a level of spin in the short game, while making a distance for reducing a distance on shots with a driver by long hitters longer.
As a result of intensive studies to achieve the above object, the present inventor has 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, and a relationship between a cover material hardness and a midpoint hardness (Cm) between a core surface and a core center satisfies the following condition:
midpoint hardness (Cm) between core surface and core center>cover material hardness
Further, the present inventor has found that where a surface hardness of the ball is not more than 59 on the Shore D hardness scale, 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 2.79 mm, 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, 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 not more than about 45 m/s.
Accordingly, the present invention provides 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, and a relationship between a cover material hardness and a midpoint hardness (Cm) between a core surface and a core center satisfies the following condition:
midpoint hardness (Cm) between core surface and core center>cover material hardness
Further characteristics of the multi-piece solid golf ball are that where a surface hardness of the ball is not more than 59 on the Shore D hardness scale, 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 2.79 mm, 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:
In a preferred embodiment of the multi-piece solid golf ball according to the invention, a volume occupancy ratio VR of the dimples is 0.78 to 0.92%.
In another preferred embodiment of the inventive golf ball, the value of (A2+A3)/2 is from 0.670 to 0.783.
In yet another preferred embodiment, the value of A2 is from 0.635 to 0.750, and the value of A3 is from 0.695 to 0.815.
In still another preferred embodiment, the core has a hardness profile in which, letting the Shore C hardness at the 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 the 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 further preferred embodiment, the core has a hardness profile in which the following two conditions are satisfied:
In a yet further preferred embodiment, the cover material hardness is from 30 to 43 on the Shore D hardness scale.
In a still further preferred embodiment, the cover has a thickness of from 0.6 to 1.2 mm.
In another preferred embodiment, a relationship between a surface hardness of an intermediate layer-encased sphere and the surface hardness of the ball satisfies the following condition:
In yet another preferred embodiment, the core is formed of a rubber composition containing the following components (A) to (D):
In still another preferred embodiment, a weight ratio (D)/(C) of the component (C) to the component (D) is from 0.020 to 0.200.
To address the possibility of there being a change to the rules in the future by the R&A and the USGA to suppress the distance by long hitters by changing the test conditions for the ODS of golf balls, with the golf ball of the present invention, instead of simply reducing distance, making the distance for reducing the distance on shots with a driver by long hitters longer, and making the distance for reducing the distance on shots with a driver (W #1) by average hitters and on shots with an iron shorter may reduce the influence on play other than reducing the distance on shots with a driver by long hitters. In addition, when used by professionals or advanced players, although the golf ball of the present invention has a shorter distance on shots with a driver (W #1) than a conventional tour ball, playability in the short game may be improved by increasing the level of spin rate in the short game. Furthermore, the golf ball of the present invention may satisfy the needs of professionals or advanced players by making the ball easy to stop at an intended place without increasing the run on shots with an iron.
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 the rubber composition, a rebound of the core may become low, and a desired distance may not be attainable on shots with a driver (W #1) by average hitters and on shots with an iron. 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.
Examples of the core are suitably formed of a rubber composition containing, in particular, the following components (A) to (D):
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.
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 representing 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 an 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 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. A 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 an upper limit thereof is preferably not more than 2 parts by weight, and more preferably not more than 1 part by weight.
By including water or a water-containing material as the component (C) directly into the core material, decomposition of the organic peroxide during 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 an amount of active radicals is further reduced, and as a result, a core may be obtained in which crosslink densities at the core center and the core surface differ markedly, and a dynamic viscoelasticity of a core center portion is different.
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.). A 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, although 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.
A weight ratio (D)/(C) of the above components (C) and (D) is preferably at least 0.020, more preferably at least 0.030, and even more preferably at least 0.035. An upper limit thereof is preferably not more than 0.200, more preferably not more than 0.160, and even more preferably not more than 0.120. If the weight ratio deviates from the above numerical ranges, it becomes difficult to achieve an intended core hardness profile, and due to a spin rate-lowering effect on full shots, it may become impossible to achieve both a superior distance on shots with a driver (W #1) by average hitters and on shots with an iron and good durability on repeated impact. The above component (D) means a weight of a sulfur component contained in a sulfur product, not a weight of the sulfur product itself.
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).
The co-crosslinking agent 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 included 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 an upper limit thereof 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, rebound may become low.
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. A 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, 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.
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, 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.
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 are suitably used.
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 the distance on shots with a driver by long hitters may be too long. On the other hand, a 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 0.3 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, and the distance on shots with a driver by average hitters and with an iron by both long hitters and average hitters may be shortened too much.
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 from 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 a rubber core is produced as a plurality of layers of rubber, the layer separation at an interface may arise when the ball is repeatedly struck, possibly leading to cracking at an earlier stage.
A diameter of the core is preferably at least 37.5 mm, more preferably at least 38.0 mm, and even more preferably at least 38.4 mm. An upper limit of the diameter of the core is preferably not more than 40.0 mm, more preferably not more than 39.4 mm, and even more preferably not more than 38.8 mm. If the diameter of the core is too small, an initial velocity of the ball may become too low, or a deflection of the entire ball may become small, so that a 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. 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 is preferably at least 2.5 mm, more preferably at least 2.7 mm, and even more preferably at least 2.9 mm, and an upper limit thereof is preferably not more than 3.9 mm, more preferably not more than 3.7 mm, and even more preferably not more than 3.5 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, or 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, a ball rebound may become too low and a good distance may not be achieved for average hitters, or the feel at impact may be too soft, or the durability to cracking on repeated impact may worsen, and a run on shots with an iron may increase too much.
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 57, more preferably at least 59, and even more preferably at least 61, and an upper limit thereof is preferably not more than 69, 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, a desired distance may not be attainable on shots with a driver (W #1) by average hitters and on shots with an iron, 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 a desired distance on shots with a driver (W #1) by average hitters may not be attainable, or the durability to cracking on repeated impact may worsen, and the run on shots with an iron may increase, which may fail to satisfy the needs of professionals or advanced players.
A hardness (Cc+4) at a position 4 mm outward from the core center is preferably at least 61, more preferably at least 63, and even more preferably at least 65, and an upper limit thereof is preferably not more than 70, more preferably not more than 68, 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 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 is preferably at least 62, more preferably at least 64, and even more preferably at least 66. In addition, an upper limit thereof is not particularly limited, although the upper limit may be 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 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 is preferably at least 61, more preferably at least 63, and even more preferably at least 65. An upper limit thereof is also not particularly limited, but is preferably not more than 70, more preferably not more than 68, 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 center hardness (Cc).
A core surface hardness (Cs) is preferably at least 80, more preferably at least 83, and even more preferably at least 85. An upper limit thereof is preferably not more than 91, more preferably not more than 89, and even more preferably not more than 88. 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 decrease or 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.
A hardness (Cs−4) at a position 4 mm inward from the core surface is preferably at least 75, more preferably at least 76, and even more preferably at least 78, and an upper limit thereof is preferably not more than 85, more preferably not more than 84, and even more preferably not more than 82. 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 is preferably at least 69, more preferably at least 71, and even more preferably at least 73. An upper limit thereof is also not particularly limited, but is preferably not more than 79, more preferably not more than 77, and even more preferably not more than 75. 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, a value of Cs−Cc, is preferably at least 17, more preferably at least 21, and even more preferably at least 22. An upper limit thereof is preferably not more than 32, more preferably not more than 29, and even more preferably not more than 26. If this value is too small, 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. On the other hand, if this value is too large, the rebound may become low, and a desired distance may not be attainable on shots with a driver (W #1) by average hitters and on shots with an iron, or the durability to cracking on repeated impact may worsen.
In addition, it is suitable to optimize a 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 condition represents a ratio of these differences in hardness. The value of (Cs−Cc)/(Cm−Cc) is preferably at least 4.0, more preferably at least 5.0, and even more preferably at least 6.0. An upper limit thereof is preferably not more than 15.0, more preferably not more than 12.0, and even more preferably not more than 10.0. If this value is too small, 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. On the other hand, if this value is too large, the rebound may become low, 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, or the durability to cracking on repeated impact may worsen.
In a core hardness profile, surface areas A to D are defined as follows:
In addition, a value of (surface area C)−(surface area A+surface area B) is preferably at least 4.0, more preferably at least 5.0, and even more preferably at least 6.0, and an upper limit thereof is preferably not more than 20.0, more preferably not more than 15.0, and even more preferably not more than 12.0. If this value is too small, 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. On the other hand, if this value is too large, the rebound may become low, and a desired distance may not be attainable on shots with a driver (W #1) by average hitters and on shots with an iron, or the durability to cracking on repeated impact may worsen.
Furthermore, a value of (surface area D)−(surface area A+surface area B) is preferably at least 4.0, more preferably at least 5.0, and even more preferably at least 6.0, and an upper limit thereof is preferably not more than 20.0, more preferably not more than 15.0, and even more preferably not more than 12.0. If this value is too small, 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. On the other hand, if this value is too large, the rebound may become low, and a desired distance may not be attainable on shots with a driver (W #1) by average hitters and on shots with an iron, or the durability to cracking on repeated impact may worsen.
An initial velocity of the core is preferably at least 75.6 m/s, more preferably at least 76.0 m/s, and even more preferably at least 76.5 m/s. An upper limit thereof is not more than 78.0 m/s, preferably not more than 77.2 m/s, and more preferably not more than 76.9 m/s. If this initial velocity value is too high, the extent to which the distance with respect to a 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 long compared with a standard distance of the new distance rules assumed by the R&A and the USGA. On the other hand, if this 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. 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 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 three hours or more 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), a value of VC/C is preferably at least 17, more preferably at least 19, and even more preferably at least 21. An upper limit thereof is preferably not more than 30, more preferably not more than 28, 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 long compared with the standard distance of the new distance rules assumed by the R&A and the USGA. On the other hand, if the above 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.
When a value of (initial velocity of core×weight of core) is denoted by Ciw, Ciw means a value indicating a rebound of a core material portion in relation to its parts by weight. Ciw is preferably at least 2,600, more preferably at least 2,640, and even more preferably at least 2,670. An upper limit thereof is preferably not more than 2,770, more preferably not more than 2,740, and even more preferably not more than 2,710. If this value deviates from the above ranges, a desired distance may not be attainable on shots with a driver (W #1) by average hitters and on shots with an iron, and the run on shots with an iron may increase too much, which may fail to satisfy the needs of professionals or advanced players.
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), a 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 700, more preferably at least 730, and even more preferably at least 760. An upper limit thereof is preferably not more than 1,000, more preferably not more than 970, and even more preferably not more than 930. If this value deviates from the above ranges, a desired distance may not be attainable on shots with a driver (W #1) by average hitters and on shots with an iron, and the run on shots with an iron may increase too much, which may fail to satisfy the needs of professionals or advanced players.
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, but 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. An upper limit thereof 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 may rise excessively on full shots, or an actual initial velocity on shots may become low, and the distance on shots with a driver (W #1) by average hitters and on shots with an iron 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, and the ball may be less likely to spin on approach shots.
The intermediate layer has a thickness that is preferably at least 0.9 mm, more preferably at least 1.0 mm, and even more preferably at least 1.1 mm. The intermediate layer thickness has an upper limit that is preferably not more than 1.6 mm, more preferably not more than 1.4 mm, and even more preferably not more than 1.3 mm. It is preferable for the intermediate layer to be thicker than the subsequently described cover. If the intermediate layer thickness falls outside of the above ranges or is thinner than that of the cover, the spin rate-lowering effect on shots with a driver (W #1) may be inadequate, and an intended distance on shots with a driver (W #1) by average hitters and on shots with an iron 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 intermediate layer thickness is too thick in comparison with the above ranges, the feel at impact may worsen.
A 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 0.3 mm. An upper limit thereof is preferably not more than 0.8 mm, more preferably not more than 0.6 mm, and even more preferably not more than 0.4 mm. If this value deviates from the above ranges, the spin rate of the ball on full shots rises, the actual initial velocity on shots becomes lower, or the like, and the distance on shots with a driver (W #1) by average hitters and on shots with an iron 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 material 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 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.
The ionomer resin material suitably contains a high-acid ionomer resin having an unsaturated carboxylic acid content (also referred to as “acid content”) of at least 16 wt %.
An amount of high-acid ionomer resin included per 100 wt % of the resin material is preferably at least 25 wt %, more preferably at least 50 wt %, and even more preferably at least 75 wt %. An upper limit thereof is preferably not more than 100 wt %, more preferably not more than 90 wt %, and even more preferably not more than 85 wt %. If the content of this high-acid ionomer resin is too low, the spin rate of the ball on full shots may rise and a good distance may not be attained. On the other hand, when the content of this high-acid ionomer resin is too high, the durability to repeated impact 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 can be included. If these additives are included, the compounding amount thereof is preferably 0.1 parts by weight or more, and more preferably 0.5 parts by weight or more, and an upper limit thereof is preferably 10 parts by weight or less, and more preferably 4 parts by weight or less 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 2.1 mm, more preferably at least 2.3 mm, and even more preferably at least 2.5 mm. An upper limit of the deflection is preferably not more than 3.4 mm, more preferably not more than 3.1 mm, and even more preferably not more than 2.9 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 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 the run increases too much on shots with an iron, it may be difficult to control a 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 that is preferably at least 76.5 m/s, more preferably at least 77.0 m/s, and even more preferably at least 77.3 m/s. An upper limit thereof 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 a 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 long compared with a 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 may not be increased. The value of the initial velocity in this case is measured with the same device and under the same conditions as described above in the measurement of the initial velocity of the core.
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), a value of VM/M is preferably at least 22, more preferably at least 24, and even more preferably at least 26. An upper limit thereof is preferably not more than 36, more preferably not more than 33, and even more preferably not more than 30. 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 long compared with the standard distance of the new distance rules assumed by the R&A and the USGA. On the other hand, if the above value is too small, the distance on shots with a driver (W #1) by average hitters may become too short.
In addition, it is suitable to optimize a 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 an intermediate layer material portion in relation to its parts by weight. The Miw value is preferably at least 2, more preferably at least 3, and even more preferably at least 4. An upper limit thereof is preferably not more than 7, more preferably not more than 6, and even more preferably not more than 5. If this value is too large, the durability on repeated impact may worsen. On the other hand, if the above 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 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 55, and even more preferably at least 61, and an upper limit thereof is preferably not more than 67, more preferably not more than 66, and even more preferably not more than 63. The material hardness on the Shore D hardness scale is preferably at least 30, more preferably at least 34, and even more preferably at least 38, and an upper limit thereof is preferably not more than 43, more preferably not more than 42, and even more preferably not more than 40.
A sphere—that is, the ball—obtained by encasing the intermediate layer-encased sphere with the cover has a surface hardness which, on the Shore C hardness scale, is preferably at least 78, more preferably at least 80, and even more preferably at least 82, and an upper limit thereof is preferably not more than 88, more preferably not more than 86, and even more preferably not more than 84. 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 55, and an upper limit thereof is preferably not more than 59, more preferably not more than 58, and even more preferably not more than 57.
If the material hardness and the surface hardness of the cover are too soft in comparison with the above ranges, the spin rate may rise on full shots, and the distance on shots with a driver (W #1) by average hitters and on shots with an iron 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. In addition, there is a possibility that the distance on shots with a driver (W #1) by long hitters increases too much and does not conform to new ODS rules that may be changed in the future.
The cover has a thickness of preferably at least 0.60 mm, more preferably at least 0.65 mm, and even more preferably at least 0.70 mm. An upper limit of the cover thickness is preferably not more than 1.10 mm, more preferably not more than 0.90 mm, and even more preferably not more than 0.85 mm. If the cover is too thick, the rebound of the ball on full shots is inadequate or the spin rate may rise, and accordingly, the distance on shots with a driver (W #1) by average hitters and on shots with an iron 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 suitable 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 60% or more, and more preferably 70% or more 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 can be used, and are not particularly limited, and examples thereof can 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 can be synthesized.
As the chain extender, those hitherto used in the art related to thermoplastic polyurethanes can 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 can be suitably used, and are not particularly limited. Specifically, one or more selected from a 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 physical properties to be manifested.
As specific examples of the thermoplastic polyurethane serving as the component (I), commercially available products can 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 can 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 can be further improved, and various physical properties required of the golf ball cover material can 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 can 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 can 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 can 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) that is preferably at least 2.00 mm, more preferably at least 2.20 mm, and even more preferably at least 2.30 mm. An upper limit of the deflection is preferably not more than 2.79 mm, more preferably not more than 2.70 mm, and even more preferably not more than 2.60 mm. If the deflection of the golf ball is too small, that is, if the sphere is too hard, the spin rate of the ball rises excessively and the distance on shots with a driver (W #1) by average hitters and on shots with an iron 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 the run increases too much on shots with an iron, it may be difficult to control a desired distance, the feel at impact may be too soft, or the durability to cracking on repeated impact may worsen. Furthermore, the ball may not be receptive to spin on approach shots, and playability in the short game may be inferior.
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. An upper limit thereof 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 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 in the 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) 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 V/B is preferably at least 23, more preferably at least 25, and even more preferably at least 27. An upper limit thereof is preferably not more than 35, more preferably not more than 34, and even more preferably not more than 33. 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 long compared with the standard distance of the new distance rules assumed by the R&A and the USGA. On the other hand, if the above value is too small, the distance on shots with a driver (W #1) by average hitters may become too short.
According to the present invention, it is necessary that a relationship between a hardness at the midpoint between the core surface and the core center (Cm) and the cover material hardness satisfies the following condition:
hardness at midpoint between core surface and core center (Cm)>cover material hardness
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 controllability in the short game and a superior distance on shots with a driver (W #1) by average hitters and on full shots with an iron, the following condition is preferably satisfied:
(surface hardness of ball)<(surface hardness of intermediate layer-encased sphere)
Expressed on the Shore C hardness scale, a value obtained by subtracting the surface hardness of the ball from the surface hardness of the intermediate layer-encased sphere is preferably larger than 0, more preferably at least 4, and even more preferably at least 7. An upper limit thereof is preferably not more than 20, more preferably not more than 17, and even more preferably not more than 15. If the above value is not more than 0, it may be difficult to achieve both a superior distance on full shots with a driver and an iron by average hitters and controllability in the short game. On the other hand, if the above value is too large, the distance on shots with a driver (W #1) by average hitters and on shots with an iron may be shorter than the intended distance.
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 9, and an upper limit thereof is preferably not more than 20, more preferably not more than 17, and even more preferably not more than 14. If this value deviates from the above ranges, 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.
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 27, more preferably at least 30, and even more preferably at least 32, and an upper limit thereof is preferably not more than 43, more preferably not more than 40, and even more preferably not more than 37. If the above value is too small, 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. 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 may become lower and a desired distance may not be attainable on shots with a driver (W #1) by average hitters. In addition, the run on shots with an iron may increase, which may fail to satisfy the needs of professionals or advanced players.
A relationship between the core diameter and a ball diameter, that is, a value of (core diameter)/(ball diameter), is preferably at least 0.878, more preferably at least 0.890, and even more preferably at least 0.899. An upper limit thereof is preferably not more than 0.937, more preferably not more than 0.923, and even more preferably not more than 0.909. If this value is too small, the initial velocity of the ball may become too low, or the deflection of the entire ball becomes small and the ball may become too hard, 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 may be shorter than the intended distance. On the other hand, if the above value is too large, the spin rate of the ball on full shots may rise, the distance on shots with a driver (W #1) by average hitters and on shots with an iron may be shorter than the intended distance, or the durability to cracking on repeated impact may worsen.
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, a value of C−B is preferably at least 0.30 mm, more preferably at least 0.40 mm, and even more preferably at least 0.50 mm. An upper limit thereof is preferably not more than 0.90 mm, more preferably not more than 0.85 mm, and even more preferably not more than 0.80 mm. If this value is too large, the durability to cracking on repeated impact may worsen, the actual initial velocity becomes lower, and a desired distance may not be attainable on shots with a driver (W #1) by average hitters, or the run on shots with an iron may increase too much. On the other hand, if this value is too small, the feel at impact may be too hard, 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.
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, a value of C−M is preferably at least 0.30 mm, more preferably at least 0.35 mm, and even more preferably at least 0.40 mm. An upper limit thereof is preferably not more than 0.70 mm, more preferably not more than 0.65 mm, and even more preferably not more than 0.60 mm. If this value is too large, the durability to cracking on repeated impact may worsen, the actual initial velocity becomes lower, and a desired distance may not be attainable on shots with a driver (W #1) by average hitters. On the other hand, if this value is too small, the feel at impact may be too hard, 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.
When a value of (initial velocity of core×weight of core) is denoted by Ciw and 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, the golf ball of the present invention suitably satisfies a predetermined range. Ciw+Miw means a sum of values indicating the rebound of each portion of the core and the intermediate layer in relation to its parts by weight. A lower limit of Ciw+Miw is at least 2,600, preferably at least 2,630, and more preferably at least 2,680. An upper limit thereof is not more than 2,750, preferably not more than 2,730, and more preferably not more than 2,710. If this value is too large, a distance under shot conditions with a driver (W #1) by long hitters may be too long, or a desired distance may not be attainable on shots with a driver (W #1) by average hitters and on shots with an iron. On the other hand, if the above value is too small, a desired distance may not be attainable on shots with a driver (W #1) by average hitters or on shots with an iron.
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 may be preferably at least 280, more preferably at least 300, and even more preferably at least 310, and an 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 ranges, the distance on shots with a driver (W #1) by average hitters may be shortened.
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.
A dimple coverage ratio of the dimples on a spherical surface of the golf ball, specifically, a ratio (hereinafter, SR value) of a sum of 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 preferably at least 75%, more preferably at least 80%, and even more preferably at least 84%. An upper limit thereof 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 average hitters may be shortened.
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 0.77%, preferably at least 0.79%, and more preferably at least 0.81%. An upper limit thereof is not more than 0.92%, more preferably not more than 0.90%, and even more preferably not more than 0.88%. If this VR value is larger than the above ranges, the distance on shots with a driver (W #1) by long hitters may be too short, 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 may become difficult for the ball to carry, and it may become difficult for the ball to go over a valley or a pond. On the other hand, if the above value is too small, the extent to which the distance is reduced on shots with a driver (W #1) by long hitters is inadequate, and there is a possibility that the distance is too long compared with the standard distance of the new distance rules assumed by the R&A and the USGA.
A value Vo obtained by dividing a 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 even more preferably at least 0.40. An upper limit thereof 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 long hitters and average hitters may be shorter than the intended distance.
In the golf ball of the present invention, 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 dimples are appropriately designed to satisfy the following two conditions:
In the present specification, the lift coefficients (CL1, CL2, CL3) and drag coefficients (CD1, CD2, CD3) are measured in accordance with an Indoor Test Range (ITR) defined by the USGA. The lift coefficients and the drag coefficients may be adjusted by adjusting a 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 an 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 condition (1).
In the above condition (1), p represents a density of a fluid, v represents an average velocity of an object relative to a flow of the fluid, L represents a characteristic length, and u represents a viscosity coefficient of the fluid.
In the present invention, the ratio CL1/CD1 of the lift coefficient CL1 at the Reynolds number of 218,000 and the spin rate of 2,800 rpm to the drag coefficient CD1 is defined as A1, the ratio CL2/CD2 of the lift coefficient CL2 at the Reynolds number of 184,000 and the spin rate of 2,900 rpm to the drag coefficient CD2 is defined as A2, and the ratio CL3/CD3 of the lift coefficient CL3 at the Reynolds number of 158,000 and the spin rate of 3,100 rpm to the drag coefficient CD3 is defined as A3.
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 a long hitter 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.
If a condition of the Reynolds number 184,000 and the spin rate 2,900 rpm under which the lift coefficient CL2 and the drag coefficient CD2 are measured is described, this middle-speed condition corresponds to a condition provided by an average hitter with a driver (W #1) at a head speed (HS) of 45 m/s, this Reynolds number corresponds to the ball speed when the golf ball is driven out at a head speed (HS) of 45 m/s, and the spin rate 2,900 rpm is the average spin condition of a player with a head speed (HS) of 45 m/s.
If a condition of the Reynolds number 158,000 and the spin rate 3,100 rpm under which the lift coefficient CL3 and the drag coefficient CD3 are measured is described, 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 the ball speed when the golf ball is driven out at a head speed (HS) of 40 m/s, and the spin rate 3,100 rpm is the 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 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, an effect of suppressing the distance on shots with a driver (W #1) by long hitters is insufficient and the distance may be too long. On the other hand, if the above value is too small, an actual distance may be shortened too much compared with 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 0.635, more preferably at least 0.645, and even more preferably at least 0.660, and an upper limit thereof is preferably not more than 0.750, more preferably not more than 0.740, and even more preferably not more than 0.730. If this value is too low, it becomes difficult for the ball to carry when hit with a driver (W #1) at a head speed (HS) of 45 m/s, and an intended total distance may not be attainable. On the other hand, if the above value is too high, the ball trajectory is blown up on shots with a driver (W #1) at a head speed (HS) of 45 m/s, and the intended distance may not be attainable.
The ratio between the lift coefficient CL3 and the drag coefficient CD3, that is, the value of CL3/CD3=A3, is preferably at least 0.695, more preferably at least 0.710, and even more preferably at least 0.722, and an 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 for the ball to carry on shots with a driver (W #1) at a head speed (HS) of 40 m/s, and the intended total distance may not be attainable. On the other hand, if the above value is too high, the ball trajectory is blown up on shots with a driver (W #1) at a head speed (HS) of 40 m/s, and the intended distance may not be attainable.
An 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 average hitters, and the intended total distance may not be attainable. On the other hand, if the above value is too high, the ball trajectory is blown up on shots with a driver (W #1) by average hitters, and the intended distance may not be attainable.
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 Example 1 and Comparative Examples 1 to 4, 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 to 4 and Comparative Examples 5 to 9, cores are produced based on the formulations in Table 1 in the same manner as described above.
Details of the above formulations are as follows.
Next, in Example 1 and Comparative Examples 1 to 4, the intermediate layer was formed by injection molding a resin material No. 1 of the intermediate layer shown in Table 2 around the core surface using an injection mold. Next, using a separate injection mold, injection molding was performed with the resin material No. 4 or No. 5 of the cover (outermost layer) shown in Table 2 around the intermediate layer-encased sphere to form the cover. At this time, a predetermined large number of dimples described below were formed on the surface of the cover.
In Examples 2 to 4 and Comparative Examples 5 to 9, 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. Next, using a separate injection mold, injection molding is performed with the resin materials No. 4 to No. 6 of the cover (outermost layer) shown in Table 2 around the intermediate layer-encased sphere to form the cover.
Details of the blending components in Table 2 are as follows.
For the dimples of Examples and Comparative Examples, the following dimples (1) to (4) 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 (4) is shown in
The ratio CL1/CD1=A1 of the lift coefficient CL1 at the Reynolds number of 218,000 and the spin rate of 2,800 rpm to the drag coefficient CD1, the ratio CL2/CD2=A2 of the lift coefficient CL2 at the Reynolds number of 184,000 and the spin rate of 2,900 rpm to the drag coefficient CD2, and the ratio CL3/CD3=A3 of the lift coefficient CL3 at the Reynolds number of 158,000 and the spin rate of 3,100 rpm to the drag coefficient CD3 of the balls with the above dimples (1) to (4) 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 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 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 23±2° C. The numerical values in the table 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 the 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 the position 4 mm inward from the midpoint M, Cm+4 be the Shore C hardness at the 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 the 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 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, 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 a device for measuring COR manufactured by Hye Precision Products of the same type as the R&A. A 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 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 coefficient of restitution (COR) 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.
In the initial velocity measurement of each sphere, the barrel diameter is selected such that the clearance on one side with respect to the 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 all examples. 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, when the value of (initial velocity of core×weight of core) is denoted by Ciw and 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, the value of Ciw+Miw is calculated. Numerical values of each example are shown in Tables 7 and 8, and a graph showing values of Ciw+Miw is shown in
A 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.
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 45 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.
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]
A number six iron (I #6) 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 42 m/s are measured. In addition, a distance (total-carry) of only the run is obtained. 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.
The number six iron (I #6) 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 35 m/s are measured. In addition, a distance (total-carry) of only the run is obtained. 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.
A judgment is made based on the spin rate when a sand wedge is mounted on the golf swing robot and a ball is struck at a head speed (HS) of 20 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.
A judgment is made based on a spin rate when the sand wedge is mounted on the golf swing robot and a ball is struck at an HS of 15 m/s. Similarly, the 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.
As shown in the results in Table 9, the golf balls of Comparative Examples 1 to 9 are inferior to the golf balls according to the present invention (Examples) in the following respects.
In Comparative Example 1, the value of A1 is larger than 0.655, and the surface hardness (Shore D) of the ball is larger than 59. As a result, the distance may not be suppressed with the driver (W #1) at the head speed (HS) of 54 m/s, and the ball does not become a target ball of the present invention.
In Comparative Example 2, the value of A1 is larger than 0.655. As a result, the distance may not be suppressed with the driver (W #1) at the head speed (HS) of 54 m/s, and the ball does not become a target ball of the present invention.
In Comparative Example 3, the surface hardness (Shore D) of the ball is larger than 59. As a result, the spin rate of the ball on approach shots is reduced.
In Comparative Example 4, the surface hardness (Shore D) of the ball is larger than 59. As a result, the spin rate of the ball on approach shots is reduced.
In Comparative Example 5, the value of A1 is smaller than 0.590, the average value of A2 and A3 is smaller than 0.670, the surface hardness (Shore D) of the ball is larger than 59, and the spin rate of the ball on approach shots is reduced.
In Comparative Example 6, the value of A1 is smaller than 0.590, and the average value of A2 and A3 is smaller than 0.670. As a result, the distance of the driver (W #1) is inferior to that in each of the Examples, and in particular, the distance when the ball is struck at the head speed (HS) of 54 m/s is excessively reduced.
In Comparative Example 7, the value of A1 is larger than 0.655, and the deflection of the ball when compressed under a predetermined load is larger than 2.79 mm. As a result, the distance may not be suppressed with the driver (W #1) at the head speed (HS) of 54 m/s, and the ball does not become a target ball of the present invention.
In Comparative Example 8, the deflection of the ball when compressed under the predetermined load is larger than 2.79 mm. As a result, with the 6 iron (I #6), the run when the ball is struck at the head speed (HS) of 42 m/s becomes long, and the spin rate of the ball on approach shots is reduced.
In Comparative Example 9, the deflection of the ball when compressed under the predetermined load is larger than 2.79 mm. As a result, there is an inferior distance with the driver (W #1) at head speeds (HS) of 54 m/s and 45 m/s, the run is longer when the ball is struck with the 6-iron (I #6) at the head speed (HS) of 42 m/s, and the spin rate of the ball on approach shots is reduced.
Japanese Patent Application No. 2023-109792 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 |
|---|---|---|---|
| 2023-109792 | Jul 2023 | JP | national |
