Patent Application
20250041673
This non-provisional application claims priority under 35 U.S.C. § 119 (a) on Patent Application No. 2023-124517 filed in Japan on Jul. 31, 2023, the entire contents of which are hereby incorporated by reference.
The present invention relates to a multi-piece solid golf ball including a two-layer core (entire core) including an inner layer and an outer layer, an intermediate layer, and a cover, in which a large number of dimples are formed on an outer 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 (herein after, 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 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 an iron 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 set spin characteristics of the ball in the short game to a high level so that a sense of discomfort does not occur even for professionals or advanced players when using the golf ball with the reduced distance.
In the past, as a golf ball having a two-layer core including an inner layer and an outer layer, the following Patent Documents 1 to 3 can be cited. In addition, a golf ball is proposed in the following Patent Documents 4 to 7 in which, by combining a design of low-trajectory dimples with a ball surface, the distance of the ball is greatly reduced at high head speeds, and at low head speeds, a decrease in the distance is suppressed as much as possible in spite of the reduction at high head speeds.
However, the golf balls of Patent Documents 1 to 3 are intended to increase the distance on shots with a driver (W #1), and are not intended to suppress the distance of long hitters. In addition, the golf balls of Patent Documents 4 to 7 have an excessively reduced distance with respect to shots with a driver at high head speeds, and a design of a golf ball focusing on the distance on shots with an iron is not made.
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 test conditions for the ODS of golf balls, an object of the present invention is to provide a golf ball that, instead of simply reducing distance, makes a distance for reducing a distance on shots with a driver by long hitters longer, but has superiority in a distance on shots with an iron.
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 outer surface of the cover, the core is formed in two layers of an inner layer core and an outer layer core, the inner layer core and the outer layer core are formed of a rubber composition, the intermediate layer and the cover are formed of a resin composition, and a relationship between a surface hardness of an intermediate layer-encased sphere and a ball surface hardness satisfies the following condition:
(ball surface hardness)< (surface hardness of intermediate layer-encased sphere) (where hardness means Shore D hardness).
Further, when a Shore C hardness value obtained by subtracting a center hardness of an entire core from a surface hardness of the entire core is set to at least 25, and regarding aerodynamic properties of the golf ball, 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:
The present inventor has found that, by designing the golf ball so as to satisfy the requirements described above, a distance for reducing a distance on shots with a driver (W #1) by long hitters is increased, but a distance on shots with an iron may be made superior, thereby achieving the present invention.
That is, the present invention relates to a multi-piece solid golf ball including a two-layer core (entire core) made of rubber, an intermediate layer, and a cover, and provides a multi-piece solid golf ball having at least four layers, with a spin-type multilayer construction in which a surface of an intermediate layer-encased sphere is harder than a ball surface hardness, a hardness difference between a surface and a center of the entire core is set to be relatively large, and by a special dimple design, a distance on shots with a driver (W #1) by long hitters is suppressed, but a distance on shots with an iron is superior.
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
Further, when a value obtained by subtracting a center hardness of the entire core from a surface hardness of the entire core is at least 25 on the Shore C hardness scale, 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 from 0.78 to 0.89%.
In another preferred embodiment of the inventive golf ball, the value of A1 is from 0.590 to 0.613, the value of A2 is from 0.635 to 0.668, and the value of A3 is from 0.695 to 0.734.
In yet another preferred embodiment, the value of A1 is from 0.614 to 0.655, the value of A2 is from 0.669 to 0.750, and the value of A3 is from 0.735 to 0.815.
In still another preferred embodiment, the value of (A2+A3)/2 is from 0.670 to 0.783.
In a further preferred embodiment, the entire core has a hardness profile in which, letting the Shore C hardness at the center of the entire core be Cc, the Shore C hardnesses at positions 3 mm, 6 mm, and 9 mm outward from the center of the entire core be C3, C6, and C9 respectively, the Shore C hardness at the surface of the entire core be Cs, and the Shore C hardnesses at positions 3 mm and 6 mm inward from the surface of the entire core be Cs-3 and Cs-6 respectively, and defining the surface areas A to E as follows:
the following condition is satisfied:
In a yet further preferred embodiment, the entire core has a hardness profile in which
the following condition is satisfied:
In a still further preferred embodiment, the entire core has a hardness profile in which
the following condition is satisfied:
In another preferred embodiment, the entire core has a hardness profile in which the following condition is satisfied:
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, the distance for reducing the distance on shots with a driver by long hitters is made longer, but the distance on shots with an iron is superior.
Hereinafter, the present invention is described in more detail.
As shown in
In the present invention, the entire core is formed in two layers of the inner layer core and the outer layer core. In the following description, the entire core including the inner layer core and the outer layer core may be simply referred to as the “core”.
Both the inner layer core and the outer layer core are obtained by vulcanizing a rubber composition containing a rubber material as a chief material. The inner layer core is desirably a blend of rubber compositions suitable for achieving high rebound and an intended hardness profile of the present invention.
The rubber material of the outer layer core surrounding the inner layer core may be the same kind as or a different kind from the material of the inner layer rubber. Each of the inner layer core and the outer layer core contains a base rubber as a chief material, and a co-crosslinking agent, an organic peroxide, an inert filler, an organosulfur compound, or the like may be blended with the base rubber to prepare the rubber composition.
The base rubber may include a diene rubber. Examples of the diene rubber include polybutadiene, natural rubber, isoprene rubber, and ethylene propylene diene rubber. As the base rubber, polybutadiene is preferably used.
The polybutadiene as a component of the rubber suitably has at least 60 wt %, preferably at least 80 wt %, more preferably at least 90 wt %, and most preferably at least 95 wt % of a cis-1,4 bond in a polymer chain thereof. If the cis-1,4 bond occupying a bond in a molecule is too small, rebound may be reduced.
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.
In a case of the inner layer core, the unsaturated carboxylic acid and/or the metal salt thereof is blended in an amount of typically at least 7 parts by weight, preferably at least 10 parts by weight, and even more preferably at least 13 parts by weight, and an upper limit thereof is typically not more than 25 parts by weight, preferably not more than 20 parts by weight, and even more preferably not more than 16 parts by weight per 100 parts by weight of the base rubber. If the compounding amount is too large, the ball becomes too hard, spin may increase on shots with an iron, and an intended distance may not be attainable. On the other hand, if the compounding amount is too small, rebound may be reduced, or a durability to cracking on repeated impact may worsen. In a case of the outer layer core, the unsaturated carboxylic acid and/or the metal salt thereof is blended in an amount of typically at least 30 parts by weight, preferably at least 35 parts by weight, and even more preferably at least 38 parts by weight, and an upper limit thereof is typically not more than 50 parts by weight, preferably not more than 45 parts by weight, and even more preferably not more than 42 parts by weight per 100 parts by weight of the base rubber. If the compounding amount is too large, the resin composition becomes too hard, the feel at impact may worsen, and the durability to cracking on repeated impact may worsen. On the other hand, if the compounding amount is too small, the spin may rise on shots with an iron, and the intended distance may not be attainable.
As the organic peroxide, commercially available products may be used, and for example, Percumyl D, Perhexa C-40, Perhexa 3M (all manufactured by NOF Corporation), and Luperco 231XL (manufactured by AtoChem Corporation) may be suitably used. These may be used singly, or two or more may be used in combination.
The organic peroxide is blended in an amount of preferably at least 0.1 parts by weight, more preferably at least 0.3 parts by weight, even more preferably at least 0.5 parts by weight, and most preferably at least 0.7 parts by weight, and an upper limit thereof 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 or too small, it may not be possible to obtain a suitable feel at impact, durability, and rebound.
As the inert 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 5 parts by weight per 100 parts by weight of the base rubber. In addition, an upper limit of the compounding amount may be preferably not more than 50 parts by weight, more preferably not more than 40 parts by weight, and even more preferably not more than 35 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.
Furthermore, an antioxidant may be included as necessary. For example, Nocrac NS-6, Nocrac NS-30, Nocrac NS-200, and Nocrac MB (all manufactured by Ouchi Shinko Chemical Industrial Co., Ltd.), and YOSINOX 425 (manufactured by Yoshitomiyakuhin Corporation) may be employed as commercially available products. These may be used singly, or two or more may be used in combination.
Although not particularly limited, a compounding amount of the antioxidant is preferably at least 0.05 parts by weight and more preferably at least 0.1 parts by weight, and an upper limit thereof is preferably not more than 3 parts by weight, more preferably not more than 2 parts by weight, even more preferably not more than 1 part by weight, and most 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, an appropriate core hardness gradient may not be attainable, and it may not be possible to obtain suitable rebound and durability.
The organosulfur compound may be blended in order to impart good rebound to both or one of the inner layer core and the outer layer core. 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.
A compounding amount of the organosulfur compound is preferably at least 0.05 parts by weight and more preferably at least 0.1 parts by weight, and an upper limit thereof is preferably not more than 5 parts by weight, more preferably not more than 3 parts by weight, and even more preferably not more than 2.5 parts by weight per 100 parts by weight of the base rubber. If the compounding amount is too large, an effect of improving the rebound (in particular, on shots with a driver (W #1)) may not be expected any more, the core may be too soft, and the feel at impact may worsen. On the other hand, if the compounding amount is too small, the effect of improving the rebound may not be expected.
The inner layer core may be manufactured by vulcanizing and curing the rubber composition containing the above components. For example, a molded body can be manufactured by intensively mixing the rubber composition using a mixing apparatus such as a Banbury mixer or a roll mill, subsequently compression molding or injection molding the mixture using a core mold, and curing the resulting molded body by appropriately heating it at a temperature sufficient for the organic peroxide or the co-crosslinking agent to act, such as at a temperature of from 100 to 200° C., and preferably at a temperature of from 140 to 180° C., for 10 to 40 minutes.
A diameter of the inner layer core is typically at least 21 mm, preferably at least 22 mm, and more preferably at least 23 mm. The diameter has an upper limit that is preferably not more than 30 mm and more preferably not more than 25 mm. If the diameter of the inner layer core is too small, an actual initial velocity on full shots may become low, a spin rate-lowering effect may be insufficient, and the intended distance on shots with an iron may not be attainable. On the other hand, if the diameter of the inner layer core is too large, the durability to cracking on repeated impact may worsen, the spin rate-lowering effect on full shots may be insufficient, and the intended distance may not be attainable.
Although not particularly limited, a deflection (mm) when the inner layer core is compressed under a final load of 1,275N (130 kgf) from an initial load of 98 N (10 kgf) is preferably at least 5.0 mm, more preferably at least 5.5 mm, and even more preferably at least 6.0 mm, and an upper limit thereof is preferably not more than 7.2 mm, more preferably not more than 6.8 mm, and even more preferably not more than 6.3 mm. If the deflection of the inner layer core is too small, that is, if the inner layer core is too hard, the spin rate on full shots increases excessively, the distance on shots with an iron may be too short, and the feel at impact may be too hard. On the other hand, if the deflection of the inner layer core is too large, that is, if the inner layer core is too soft, the feel at impact on full shots may become too soft, and the durability to cracking on repeated impact may worsen.
The component of the rubber material of the outer layer core encasing the inner layer core may be the same kind as or a different kind from the material of the inner layer core. However, since the inner layer core and the outer layer core have different intended hardnesses, component ratios of the inner layer core and the outer layer core are different.
A thickness of the outer layer encasing the inner layer core is preferably at least 4.2 mm and more preferably at least 6.7 mm in order to obtain the intended hardness profile of the present invention. An upper limit thereof is preferably not more than 8.8 mm, more preferably not more than 8.5 mm, and even more preferably not more than 8.0 mm.
Although a method for manufacturing the inner layer core is not particularly limited, according to a customary method, the inner layer core may be molded by a method such as heat compression at 140 to 180° C. for 8 to 30 minutes to form a spherical shape. As a method of forming the outer layer core on a surface of the inner layer core, a method can be adopted of forming a pair of half-cups using sheet-like unvulcanized rubber, placing the inner layer core in the cups, further encapsulating the inner layer core, and molding the inner layer core under applied pressure and heat. For example, a method can be suitably employed in which primary vulcanization (semi-vulcanization) is performed to produce a pair of hemispherical cup bodies, secondary vulcanization (total vulcanization) is performed in a state in which the inner layer core encased with the outer layer core produced in advance is placed on one hemispherical cup body, and then the other hemispherical cup body is further encased with the inner layer core, or a method can be suitably employed in which a rubber composition is formed into a sheet shape in an unvulcanized state to form a pair of sheets for the outer layer core, the sheets are imprinted with a half mold provided with hemispherical protrusions to produce an unvulcanized hemispherical cup body, and then the pair of hemispherical cup bodies is covered with the inner layer core produced in advance and heat compressed at 140 to 180° C. for 8 to 30 minutes to form a spherical shape, whereby the vulcanizing step is divided into two stages.
A diameter of the core (entire core) is typically at least 37.5 mm, preferably at least 38.0 mm, and more preferably at least 38.4 mm. The 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 core diameter is too small, an initial velocity of the ball may become too low, a hardness of the entire ball may become hard (a deflection may become small), and a desired distance on shots with an iron may not be attainable. On the other hand, if the core diameter is too large, the spin rate on full shots increases, the desired distance on shots with an iron may not be attainable, and the durability to cracking on repeated impact may worsen.
Next, a 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 an upper limit thereof is preferably not more than 61, more preferably not more than 59, and even more preferably not more than 57. If this value is too large, the spin rate on full shots may rise, the desired distance on shots with an iron may not be attainable, or the feel at impact may be too hard. On the other hand, if the above value is too small, the rebound may become low and the intended distance on shots with an iron may not be attainable, or the durability to cracking on repeated impact may worsen, and a run on shots with an iron may increase, which may fail to satisfy the needs of professionals or advanced players.
A hardness (C3) at a position 3 mm outward from the core center is preferably at least 50, more preferably at least 52, and even more preferably at least 54, and an upper limit thereof is preferably not more than 62, more preferably not more than 60, and still more preferably not more than 58. Hardnesses that deviate from these values may lead to undesirable results similar to those described above for the core center hardness (Cc).
A hardness (C6) at a position 6 mm outward from the core center is preferably at least 52, more preferably at least 54, and even more preferably at least 56, and an upper limit thereof 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 (C9) at a position 9 mm outward from the core center 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 67, more preferably not more than 65, and even more preferably not more than 63. 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 84, more preferably at least 86, and even more preferably at least 88. An upper limit thereof is preferably not more than 95, more preferably not more than 93, and even more preferably not more than 91. If this value is too large, the durability to cracking on repeated impact may worsen, or the feel at impact may be too hard. On the other hand, if the above value is too small, the rebound may become low, or the spin rate on full shots may rise, and the desired distance on shots with an iron may not be attainable.
The core surface hardness (Cs) on the Shore D hardness scale is preferably at least 56, more preferably at least 58, and even more preferably at least 60. An upper limit thereof is preferably not more than 67, more preferably not more than 65, and even more preferably not more than 63.
A hardness (Cs-3) at a position 3 mm inward from the core surface is preferably at least 73, more preferably at least 75, and even more preferably at least 77, and an upper limit thereof is preferably not more than 85, more preferably not more than 82, and even more preferably not more than 79. Hardnesses that deviate from these values may lead to undesirable results similar to those described above for the core surface hardness (Cs).
A hardness (Cs-6) at a position 6 mm inward from the core surface is preferably at least 68, more preferably at least 70, and even more preferably at least 72, and an upper limit thereof is preferably not more than 81, more preferably not more than 78, 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).
In the present invention, a value obtained by subtracting the core center hardness from the core surface hardness, that is, a value of Cs-Cc, is preferably set to at least 25, more preferably at least 29, and even more preferably at least 33. An upper limit thereof is preferably not more than 42, more preferably not more than 40, and even more preferably not more than 38. If this value is too small, the spin rate on full shots may rise, and the desired distance on shots with an iron may not be attainable. On the other hand, if this value is too large, the rebound may become low and the desired distance on shots with an iron may not be attainable, or the durability to cracking on repeated impact may worsen.
In addition, it is suitable to optimize a value of (C5C8-6)/(C6-Cc) for the core hardness profile. The value of (C5C8-6) indicates a hardness difference between the core surface and a position 6 mm inward therefrom, the value of (C6-Cc) indicates a hardness difference between the core center and a position 6 mm outward therefrom, and the above expression represents a ratio of these hardness differences. The value of (Cs−Cs−6)/(C6-Cc) is preferably at least 3.0, more preferably at least 4.0, and even more preferably at least 4.5. 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 on full shots may rise, and the desired distance on shots with an iron may not be attainable. On the other hand, if this value is too large, the rebound may become low, the desired distance on shots with an iron may not be attainable, or the durability to cracking on repeated impact may worsen.
In the core hardness profile, when surface areas A to E are defined as follows:
a value of (surface area D+surface area E)-(surface area A+surface area B+surface area C) is preferably at least 5.0, more preferably at least 7.5, and even more preferably at least 10.0, and an upper limit thereof is preferably not more than 25.0, more preferably not more than 22.0, and even more preferably not more than 20.0. If this value is too small, the spin rate on full shots may rise, and the desired distance on shots with an iron may not be attainable. On the other hand, if this value is too large, the rebound may become low, the desired distance on shots with an iron may not be attainable, or the durability to cracking on repeated impact may worsen.
In addition, a value of (surface area E)-(surface area A+surface area B+surface area C) is preferably larger than 0.0, more preferably at least 2.0, and even more preferably at least 4.0, and 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 on full shots may rise, and the desired distance on shots with an iron may not be attainable. On the other hand, if this value is too large, the rebound may become low, the desired distance on shots with an iron may not be attainable, 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 larger than 0.0, more preferably at least 1.0, and even more preferably at least 2.0, and an upper limit thereof is preferably not more than 10.0, more preferably not more than 7.0, and even more preferably not more than 5.0. If this value is too small, the spin rate on full shots may rise, and the desired distance on shots with an iron may not be attainable. On the other hand, if this value is too large, the rebound may become low, the desired distance on shots with an iron may not be attainable, or the durability to cracking on repeated impact may worsen.
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 may rise excessively on full shots and the actual initial velocity may become low, so that the distance 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 which is preferably at least 0.9 mm, more preferably at least 1.0 mm, and even more preferably at least 1.1 mm. An upper limit of the intermediate layer thickness 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 the intermediate layer is thinner than the cover, the ball spin rate-lowering effect on full shots may be insufficient, and the intended distance on shots with an iron may not be increased. Also, when 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 thicker than 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 0.3 mm. The upper limit 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 may increase and the actual initial velocity becomes lower, or the like, so that the intended distance 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 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 may not be increased, and 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 %.
The 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 %. The upper limit is preferably not more than 100 wt %, more preferably not more than 90 wt %, and even more preferably not more than 85 wt %. When the compounding amount 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 compounding amount 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 at least 0.1 parts by weight, and more preferably at least 0.5 parts by weight, and an 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), a deflection (mm) is preferably at least 1.8 mm, more preferably at least 2.0 mm, and even more preferably at least 2.2 mm. An upper limit of the deflection is preferably not more than 3.0 mm, more preferably not more than 2.7 mm, and even more preferably not more than 2.5 mm. If the deflection of the intermediate layer-encased sphere is too small, that is, if the sphere is too hard, the spin rate increases excessively and the distance 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 feel at impact may become too soft, or the durability to cracking on repeated impact may worsen.
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 surface 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 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. The upper limit 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. The upper limit is preferably not more than 70, more preferably not more than 65, and even more preferably not more than 61.
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 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 excessively and does not conform to new ODS rules that may be changed in the future.
The cover has a thickness of preferably at least 0.3 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. If the cover is too thick, the rebound of the ball on full shots may be insufficient or the spin rate may rise, or the like, as a result of which the distance on shots with an iron may not be increased. On the other hand, if 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 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 not more than 400 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) which is preferably at least 2.0 mm, more preferably at least 2.1 mm, and even more preferably at least 2.2 mm. An upper limit of the deflection is preferably not more than 2.7 mm, more preferably not more than 2.6 mm, and even more preferably not more than 2.5 mm. If the deflection of the golf ball is too small, that is, if the golf ball is too hard, the spin rate may rise excessively and the distance 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 on shots with an iron, the run increases, 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 77.0 m/s. An upper limit thereof is not more than 77.724 m/s. If this initial velocity value is too high, the official rules of R&A and USGA are not satisfied. On the other hand, if the initial velocity is too low, the distance on shots with an iron may not be increased. The value of the initial velocity in this case is a numerical value measured by a device for measuring a coefficient of restitution (COR) (Golf Ball Testing Machine) of the same type as the R&A. Specifically, a device for measuring a COR manufactured by Hye Precision USA is used. As a condition, at the time of measurement, an air pressure is changed in four stages and measured, a relational expression between the incident velocity and the COR is constructed, and the initial velocity at an incident velocity of 43.83 m/s is determined from the relational expression. For a measurement environment of the device for measuring a COR, a ball temperature-controlled for at least three hours in a thermostatic bath adjusted to 23.9+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.
In the present invention, from a viewpoint that a relationship between the surface hardness of the intermediate layer-encased sphere and the ball surface hardness is compatible with a superior distance on full shots with an iron and controllability in the short game, the following condition is preferably satisfied:
(ball surface hardness)< (surface hardness of intermediate layer-encased sphere) Expressed on the Shore D hardness scale, a value obtained by subtracting the ball surface hardness 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 the superior distance on full shots with an iron and controllability in the short game. On the other hand, if the above value is too large, the distance on shots with an iron may be shorter than the intended distance. If this is caused by the hardness of the intermediate layer, the durability to repeated impact may worsen, the spin rate in the short game may decrease, and controllability in the short game may worsen.
Expressed on the Shore D 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 4, more preferably at least 6, and even more preferably at least 8, 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 there is a deviation from the above ranges, the spin rate of the ball on full shots may rise, and the desired distance on shots with an iron may not be attainable.
A relationship between the core diameter (diameter of entire core) 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 low, or a deflection of the entire ball becomes small and the ball may become too hard, the spin rate of the ball on full shots may increase, and the distance 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 increases, the distance on shots with an iron 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 inner layer 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 IC (mm) and B (mm) respectively, a value of IC-B is preferably at least 3.0 mm, more preferably at least 3.5 mm, and even more preferably at least 3.9 mm. An upper limit thereof is preferably not more than 4.5 mm, more preferably not more than 4.3 mm, and even more preferably not more than 4.1 mm. If this value deviates from the above ranges, the rebound of the ball may become too low, the spin rate on full shots may rise, the distance on shots with a driver (W #1) by long hitters may become too short, and the desired distance on shots with an iron may be unattainable.
A deflection ratio (B/IC) between the inner layer core and the ball is preferably at least 0.30, more preferably at least 0.32, and even more preferably at least 0.34, and an upper limit thereof is preferably not more than 0.50, more preferably not more than 0.45, and still more preferably not more than 0.40. If this ratio value is too large, the rebound may become too low, and the distance on shots with a driver (W #1) by long hitters may become too short. On the other hand, if this ratio value is too large, the spin rate on full shots may rise, and the desired distance on shots with an iron may not be attainable.
When the core (entire core) is compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) and the deflection (mm) is denoted by C (mm), a deflection ratio (C/IC) between the inner layer core and the core (entire core) is preferably at least 0.40, more preferably at least 0.45, even more preferably at least 0.47, and an upper limit thereof is preferably not more than 0.75, more preferably not more than 0.65, even more preferably not more than 0.55. If this ratio value is too large, the rebound may become too low, and the distance on shots with a driver (W #1) by long hitters may become too short. On the other hand, if this ratio value is too small, the spin rate on full shots may rise, and the desired distance on shots with an iron may not be attainable.
When each sphere of the core (entire 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 0.35 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 0.80 mm, more preferably not more than 0.75 mm, and even more preferably not more than 0.70 mm. If this value deviates from the above ranges, the rebound of the ball may become too low, the spin rate on full shots may rise, the distance on shots with a driver (W #1) by long hitters may become too short, and the desired distance on shots with an iron may be unattainable.
A deflection ratio (M/C) between the core (entire core) and the intermediate layer-encased sphere is preferably at least 0.68, more preferably at least 0.72, and even more preferably at least 0.75, and an upper limit thereof is preferably not more than 0.90, more preferably not more than 0.86, and even more preferably not more than 0.82. If this ratio value is too large, the rebound may become too low, and the distance on shots with a driver (W #1) by long hitters may become too short. On the other hand, if this ratio value is too small, the spin rate on full shots may rise, and the desired distance on shots with an iron may not be attainable.
Numerous dimples may be formed on the outside surface of the cover. Although not particularly limited, the number of dimples arranged on the surface of the cover is preferably at least 280, preferably at least 300, and more preferably at least 310, and the upper limit thereof can be preferably not more than 450, more preferably not more than 400, and even more preferably not more than 350. If the number of dimples deviates from the above ranges, the distance on shots with an iron may become shorter.
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 at least 2.5 mm and not more than 6.5 mm, and the depth can 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 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%. The upper limit is not more than 90%, more preferably not more than 88%, and even more preferably not more than 86%. If the SR value deviates from the above ranges, the distance on shots with a driver (W #1) by average hitters may become shorter, and the distance on shots with an iron may become shorter.
A VR value of a sum of volumes of the individual dimples formed below the flat plane circumscribed by the edge of the dimple to a ball spherical volume on the assumption that the ball has no dimples is at least 0.78%, preferably at least 0.79%, and more preferably at least 0.81%. An upper limit thereof is not more than 0.89%, more preferably not more than 0.88%, and even more preferably not more than 0.87%. If this VR value is larger than the above ranges, the distance on shots with a driver (W #1) by long hitters may be excessively reduced. In addition, in this case, a ball trajectory may become lower, it becomes 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 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 this V0 value deviates from the above ranges, the distance on shots with a driver (W #1) by long hitters and average hitters and on shots with an iron 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 218000 and a spin rate of 2800 rpm to a drag coefficient CD1 is denoted by A1, a ratio (CL2/CD2) of a lift coefficient CL2 at a Reynolds number of 184000 and a spin rate of 2900 rpm to a drag coefficient CD2 is denoted by A2, and a ratio (CL3/CD3) of a lift coefficient CL3 at a Reynolds number of 158000 and a spin rate of 3100 rpm to a drag coefficient CD3 is denoted by A3, the dimples are designed to satisfy the following two conditions:
In the present specification, the “lift coefficients (CL1, CL2, CL3), drag coefficients (CD1, CD2, CD3)” are measured in accordance with the Indoor Test Range (ITR) defined by the USGA (United States Golf Association). The lift coefficients and the drag coefficients can be adjusted by adjusting the configuration of the dimples of the golf ball (arrangement, diameter, depth, volume, number, shape, and the like). The lift coefficients and the drag coefficients are independent of the internal configuration of the golf ball. The Reynolds number (Re) is a dimensionless number used in the field of hydrodynamics. The Reynolds number (Re) is calculated by the following equation (1).
In Equation (1) above, p represents the density of a fluid, v represents the average velocity of an object relative to the flow of the fluid, L represents a characteristic length, and u represents the viscosity coefficient of the fluid.
In the present invention, when a ratio CL1/CD1 of a lift coefficient CL1 at a
Reynolds number of 218000 and a spin rate of 2800 rpm to a drag coefficient CD1 is defined as A1, a ratio CL2/CD2 of a lift coefficient CL2 at a Reynolds number of 184000 and a spin rate of 2900 rpm to a drag coefficient CD2 is defined as A2, and a ratio CL3/CD3 of a lift coefficient CL3 at a Reynolds number of 158000 and a spin rate of 3100 rpm to a drag coefficient CD3 is defined as A3.
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 184000 and spin rate 2900 rpm. 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 a ball speed when a golf ball is driven out at a head speed (HS) of 45 m/s, and the spin rate 2900 rpm is an average spin condition of a player with a head speed (HS) of 45 m/s.
The condition under which the lift coefficient CL3 and the drag coefficient CD3 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 an upper limit thereof is not more than 0.655, preferably not more than 0.640, and more preferably not more than 0.627. If this value is too large, the 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.
When the value of A1 is 0.590 to 0.613, the ratio between the lift coefficient CL2 and the drag coefficient CD2, that is, a value of CL2/CD2=A2, is preferably at least 0.635, more preferably at least 0.645, and even more preferably at least 0.655, and an upper limit thereof is preferably not more than 0.668, more preferably not more than 0.666, and even more preferably not more than 0.664. When the value of A1 is 0.614 to 0.655, the value of A2 is preferably at least 0.669, more preferably at least 0.671, and even more preferably at least 0.673, and an upper limit thereof is preferably not more than 0.750, more preferably not more than 0.725, and even more preferably not more than 0.700. If the above value deviates from the above ranges, on shots with an iron, the ball may blow up, there may be a trajectory in which the ball does not carry, and an intended total distance may not be attainable.
When the value of A1 is from 0.590 to 0.613, the ratio between the lift coefficient CL3 and the drag coefficient CD3, that is, a value of CL3/CD3=A3, is preferably at least 0.695, more preferably at least 0.705, and even more preferably at least 0.715, and an upper limit thereof is preferably not more than 0.734, more preferably not more than 0.731, and even more preferably not more than 0.728. In addition, when the value of A1 is from 0.614 to 0.655, the value of A3 is preferably at least 0.735, more preferably at least 0.738, and even more preferably at least 0.741, and an upper limit thereof is preferably not more than 0.815, more preferably not more than 0.780, and even more preferably not more than 0.760. If the above value deviates from the above ranges, on shots with an iron, the ball may blow up, there may be a trajectory in which the ball does not carry, and an intended total distance may not be attainable.
The average value of the above A2 and A3, that is, the value of (A2+A3)/2 is at least 0.670, preferably at least 0.680, and more preferably at least 0.690, and an upper limit thereof is preferably not more than 0.783, more preferably not more than 0.775, and even more preferably not more than 0.765. If this value is too low, it becomes difficult for the ball to carry on shots with an iron and the intended total distance may not be attainable. On the other hand, if the above value is too high, the ball trajectory may blow up on shots with an iron, and the intended distance may not be attainable.
The multi-piece solid golf ball of the present 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 to 3 and Comparative Examples 1, 2, and 5, the rubber composition of each Example shown in Table 1 is prepared, and then vulcanization molding is performed under vulcanization conditions according to each Example shown in Table 1 to produce the inner layer core.
In Comparative Examples 3 and 4, single-layer cores were produced based on the formulations in Table 1 in the same manner as described above.
In Examples 1 to 3 and Comparative Examples 1 and 2, after the production of the inner layer core, the rubber material for the outer layer core is placed in an outer layer core mold, sandwiched between the outer layer core mold and a convex mold having the same radius as the inner layer core, heated at 145° C. for three minutes to perform primary vulcanization, and then removed from the mold to produce a pair of half-cup-shaped outer layer cores. These outer layer cores are used to cover the inner layer core, which has been previously vulcanized and molded, and vulcanization molding is performed at 145° C. for 13 minutes to prepare the entire core (inner layer core+outer layer core) of each Example. Then, after the core is removed from the mold, the core surface is polished.
In Examples 1 to 3 and Comparative Examples 1, 2, and 5, the intermediate layer is formed by injection molding a resin material No. 1 of the intermediate layer shown in Table 2 around the core surface using the injection mold. Subsequently, the cover is formed by injection molding a resin material No. 2 of the cover (outermost layer) shown in Table 2 around the intermediate layer-encased sphere using a separate injection mold. At this time, a large number of predetermined dimples described below are formed on the cover surface.
In Comparative Examples 3 and 4, the intermediate layer and the cover were formed in the same manner as described above.
Details of the blending components in Table 2 are as follows. “Himilan 1706” and “AM7318” ionomer resins manufactured by Dow-Mitsui Polychemicals Co., Ltd. “Trimethylolpropane” (TMP) manufactured by Tokyo Chemical Industry Co., Ltd. Trade name “Pandex” ether-type thermoplastic polyurethane (TPU), material hardness (Shore D) 46, manufactured by DIC Covestro Polymer Ltd.
For the dimples of the 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, arrangement modes (patterns) of the dimples (1) to (4) is illustrated 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 ball with the above dimples (1) to (4) formed on its cover surface are listed in the table below. These lift coefficients and drag coefficients are measured in accordance with the Indoor Test Range (ITR) defined by USGA.
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 and deflections of each layer-encased sphere, and initial velocities of the ball are evaluated by the following methods, and are shown in Tables 5 and 6.
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 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. Note that 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, C3, C6, and C9 be the Shore C hardnesses at positions 3 mm, 6 mm, and 9 mm outward from the core center, Cs be the Shore C hardness at the core surface, and Cs−3 and Cs−6 be the Shore C hardnesses at positions 3 mm and 6 mm inward from the core surface, the surface areas A to E are calculated as follows:
and the values of the following three expressions are determined.
The surface areas A to E 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. It is noted that a surface hardness of a ball (cover) is a measured value at a dimple-free area (land) on the surface of the ball. The Shore C hardness and the Shore D hardness are each measured with a Shore C durometer and a Shore D durometer conforming to the ASTM D2240 standard. For the measurement of the hardness, the P2 Automatic Rubber Hardness Tester manufactured by Kobunshi Keiki Co., Ltd. to which a Shore C durometer or a Shore D durometer is mounted is used. For the hardness value, a maximum value is read. The measurement method is in accordance with the ASTM D2240 standard.
The initial velocity of the ball 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 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 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 the initial velocity of the ball.
[Here, e is a coefficient of restitution, and the is a contact time (μs) at a collision speed
of 143.8 ft/s (43.83 m/s).]
In the measurement of the initial velocity of the ball, the barrel diameter is selected such that a clearance on one side with respect to the outer diameter of the object being measured is from 0.2 to 2.0 mm, although in this Example, all the barrel diameters are set to 1.700 inches (43.18 mm).
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 7.
[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 B-Limited 415 Driver/loft angle 9.0° (2022 model) manufactured by Bridgestone Sports Co., Ltd. and is evaluated according to the following rating criteria.
(Rating criteria)
Very good: Total compared with Comparative Example 5 is not more than −10.0 m and at least −20.0 m.
Good: Total compared with Comparative Example 5 is not more than −7.0 m and more than −10.0 m.
Fair: Total compared with Comparative Example 5 is less than −18.0 m.
NG: Total compared with Comparative Example 5 is more than −7.0 m.
[Evaluation of Flight (I #6, HS 42 m/s)]
When a number six iron (I #6) is mounted on the golf swing robot and a ball is struck at an HS of 42 m/s, a spin rate and a distance traveled (total) are measured. The club used is a JGR Forged I #6 (2016 model) manufactured by Bridgestone Sports Co., Ltd. and is evaluated according to the following rating criteria.
(Rating criteria)
Very good: Total compared with Comparative Example 5 is at least 5.0 m.
Good: Total compared with Comparative Example 5 is at least 0 m and less than +5.0 m. Fair: Total compared with Comparative Example 5 is at least −5.0 m and less than 0 m.
NG: Total compared with Comparative Example 5 is less than −5.0 m.
[Evaluation of Flight (I #6, HS 38 m/s)]
When the number six iron (I #6) is mounted on the golf swing robot and a ball is struck at an HS of 38 m/s, the spin rate and the distance traveled (total) are measured. The club used is a JGR Forged I #6 (2016 model) manufactured by Bridgestone Sports Co., Ltd. and is evaluated according to the following rating criteria.
[Evaluation of Flight (I #6, HS 35 m/s)]
When a number six iron (I #6) is mounted on the golf swing robot and a ball is struck at an HS of 35 m/s, a spin rate and a distance traveled (total) are measured. The club used is a JGR Forged I #6 (2016 model) manufactured by Bridgestone Sports Co., Ltd. and is evaluated according to the following rating criteria.
[Evaluation of Spin Rate on Approach Shots (SW, HS 20 m/s)]
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 an 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.
[Evaluation of Spin Rate on Approach Shots (SW, HS 15 m/s)]
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 an HS of 15 m/s. Similarly, a spin rate immediately after the ball is struck is measured by a device for measuring initial conditions. The sand wedge used is a TOURSTAGE TW-03 (loft angle 57°) 2002 model manufactured by Bridgestone
As shown in the results in Table 7, the golf balls of Comparative Examples 1 to 5 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 less than 0.590, the average value of A2 and A3 is less than 0.670, and the distance when a ball is struck at the head speed (HS) of 54 m/s is excessively reduced.
In Comparative Example 2, the value of A1 is larger than 0.655, the distance at the head speed (HS) of 54 m/s cannot be suppressed with a driver (W #1), and the ball does not become a target ball of the present invention.
Comparative Example 3 is a ball having a three-piece structure in which the core is made of a single layer of rubber, and a difference in hardness between the surface and the center of the entire core is smaller than 25 on the Shore C hardness scale. As a result, the distance when a ball was struck with the number six iron (I #6) was inferior to that of the Examples, the rating (score) was lower than that of the Examples, and performance was totally inferior.
Comparative Example 4 is a ball having the three-piece structure in which the core is made of the single layer of rubber, and the difference in hardness between the surface and the center of the entire core is smaller than 25 on the Shore C hardness scale. As a result, the distance when a ball was struck with the number six iron (I #6) was inferior to that of the Examples, the rating (score) was lower than that of the Examples, and performance was totally inferior.
In Comparative Example 5, a ball has the three-piece structure in which the core is made of the single layer of rubber, the difference in hardness between the surface and the center of the entire core is smaller than 25 on the Shore C hardness scale, and the value of A1 is larger than 0.655, so that the distance at the head speed (HS) of 54 m/s cannot be suppressed with a driver (W #1), and the ball is not the target ball of the present invention.
Japanese Patent Application No. 2023-124517 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 |
|---|---|---|---|
| 2023-124517 | Jul 2023 | JP | national |
