Patent Application
20240399213
This non-provisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2023-090009 filed in Japan on May 31, 2023, the entire contents of which are hereby incorporated by reference.
The present invention relates to a multi-piece solid golf ball composed of three or more layers including a core, an intermediate layer, and a cover.
Many innovations have been made in designing golf balls with a multilayer construction, and many golf balls for professional and skilled amateur golfers with a high head speed have been developed to date. Among them, the most popular golf balls are three-piece solid golf balls composed of a core, an intermediate layer, and a cover (outermost layer). Specifically, there have been many proposals for functional three-piece solid golf balls in which a material hardness of each layer of the intermediate layer and the cover, a surface hardness of the core, and a surface hardness of an intermediate layer-encased sphere are optimized, and some technologies have been proposed to provide high-performance golf balls by designing a core internal hardness in various aspects while focusing on a core hardness profile occupying most of the volume of the ball.
Examples of such technical documents include the three-piece solid golf balls of the following Patent Documents 1 to 7.
However, although some of the proposed golf balls disclose a relationship between initial velocities of layer-encased spheres: the intermediate layer-encased sphere and the ball or a relationship between a deflection when a specific load is applied to the core and a deflection when a specific load is applied to the ball, attention on a relationship between the initial velocity of the intermediate layer-encased sphere and an initial velocity of the core and a specific gravity of the intermediate layer is not sufficient, and there is room for improvement for obtaining a golf ball with higher performance. In addition, for professional golfers who have a high head speed with a driver (W #1) of at least 45 m/s and prefer a moderate hardness and a crisp feel, there is a demand for a ball that increases a distance on shots with the driver (W #1), has a promising feel at impact with a moderate hardness and a crisp feel, is receptive to spin on approach shots to an extent that may be controlled, and further has a sufficient durability to cracking even when repeatedly used by users in a high head speed (HS) region. However, in the proposed golf balls of the conventional technologies, there is no ball that satisfies all of these.
Patent Document 1: JP-A 2004-97802
Patent Document 2: JP-A 2011-120898
Patent Document 3: JP-A 2016-112308
Patent Document 4: JP-A 2017-000183
Patent Document 5: JP-A 2017-000470
Patent Document 6: JP-A 2018-183247
Patent Document 7: JP-A 2019-198465
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a golf ball that has a superior distance on shots with a driver (W #1) and an iron, has good controllability on approach shots, has a good feel at impact, and imparts an excellent durability on repeated impact, mainly when used by professional and skilled amateur golfers having a high head speed.
As a result of intensive studies to achieve the above object, the present inventors have found that in a multi-piece solid golf ball including a core, an intermediate layer, and a cover, a relationship among an initial velocity of the core, an initial velocity of a sphere (intermediate layer-encased sphere) obtained by encasing the core with the intermediate layer, and an initial velocity of a sphere (ball) obtained by encasing the intermediate layer-encased sphere with the cover satisfies the following two conditions:
Further, the present inventors have found that when each sphere of the core and the ball is compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) and the deflections (mm) are denoted by C (mm) and B (mm), respectively, the value of C−B is not more than 1.10 mm, and a relationship between a thickness of the intermediate layer and a diameter of the ball satisfies the following condition:
The present inventors have found that, by satisfying the above conditions, it is possible to increase a distance in a high head speed (HS) region where a head speed with a driver (W #1) is at least 45 m/s, and provide a good feel at impact so that a professional golfer is given a promising feel at impact with a moderate hardness and a crisp feel when using the golf ball, the ball is receptive to spin on approach shots to an extent that may be controlled, and has a sufficient durability to cracking even when repeatedly used by a professional golfer having a high head speed, and thus have completed the present invention.
Accordingly, the present invention provides a multi-piece solid golf ball including
Further characteristics of the multi-piece solid golf ball are that 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 deflections (mm) are denoted by C (mm) and B (mm), respectively, a value of C−B is not more than 1.10 mm, and a relationship between a thickness of the intermediate layer and a diameter of the ball satisfies the following condition:
In a preferred embodiment of the golf ball according to the invention, a specific gravity of the intermediate layer is at least 1.05.
In another preferred embodiment of the inventive golf ball, the resin composition of the intermediate layer contains a high-acid ionomer resin having an acid content of at least 16 wt %.
In yet another preferred embodiment, the intermediate layer contains an inorganic particulate filler.
In still another preferred embodiment, a difference between a specific gravity of the cover and a specific gravity of the intermediate layer, a difference between the specific gravity of the intermediate layer and a specific gravity of the core, and a difference between the specific gravity of the core and the specific gravity of the cover are all within 0.15.
In a further preferred embodiment, the deflection B of the ball has a value of not more than 3.0 mm.
In a yet further preferred embodiment, the following condition is satisfied:
In a still further preferred embodiment, the following condition is satisfied:
where the intermediate layer thickness is 1.02 to 1.45 mm.
In another preferred embodiment, the core has a diameter of from 36.7 to 40.1 mm, and the core has a hardness profile in which, letting the Shore C hardness at a core center be Cc, the Shore C hardness at a position 4 mm outward from the core center be Cc+4, the Shore C hardness at a midpoint M between the core center and a core surface be Cm, the Shore C hardness at a position 4 mm inward from the midpoint M of the core be Cm−4, the Shore C hardness at a position 4 mm outward from the midpoint M of the core be Cm+4, the Shore C hardness at a position 4 mm inward from the core surface be Cs−4, and the Shore C hardness at the core surface be Cs, and defining surface areas A to D as follows:
In yet another preferred embodiment, the following two conditions are satisfied:
With the golf ball according to the present invention, mainly in professional golfers and skilled amateur golfers with a high head speed, a superior distance is obtained on full shots with a driver (W #1), a spin rate on approach shots is high, and playability in the short game is excellent. Furthermore, the golf ball according to the present invention has a good feel at impact with a crisp feel, and has good durability on repeated impact.
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
Layer cover 3 encasing the intermediate layer. The cover 3 is positioned at the outermost layer in the layer construction of the golf ball except for the coating layer. In addition to a single layer as shown in
The core is obtained by vulcanizing a rubber composition containing a rubber material as a chief material. If the core material is not a rubber composition, the rebound of the core becomes low, and as a result, a good distance of the ball may not be achieved. This rubber composition typically contains a base rubber as a chief material, and is obtained with the inclusion of a co-crosslinking agent, a crosslinking initiator, an inert filler, an organosulfur compound, or the like.
As the base rubber, polybutadiene is preferably used. As the type of polybutadiene, a commercially available product may be used, and examples thereof include BR01, BR51, and BR730 (manufactured by JSR Corporation). The proportion of polybutadiene in the base rubber is preferably at least 60 wt %, and more preferably at least 80 wt %. In addition to the polybutadiene, other rubber components are included in the base rubber as long as the effect of the present invention is not impaired. Examples of the rubber component other than the polybutadiene include a polybutadiene other than the polybutadiene described above, and other diene rubbers such as styrene-butadiene rubber, natural rubber, isoprene rubber, and ethylene-propylene-diene rubber.
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 blended in an amount of at least 5 parts by weight, preferably at least 10 parts by weight, and more preferably at least 20 parts by weight, and the upper limit is typically not more than 60 parts by weight, preferably not more than 50 parts by weight, and more preferably not more than 45 parts by weight per 100 parts by weight of the base rubber. If the compounding amount is too large, the core may become too hard, giving the ball an unpleasant feel at impact, and if the compounding amount is too small, the rebound may become low.
As the crosslinking initiator, an organic peroxide is suitably used. Specifically, commercially available organic peroxides 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 compounding amount of the organic peroxide is preferably at least 0.1 parts by weight, more preferably at least 0.3 parts by weight, and even more preferably at least 0.5 parts by weight, and the upper limit 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 2.5 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 suitable feel at impact, durability, and rebound.
As a filler, for example, zinc oxide, barium sulfate, calcium carbonate, or the like may be suitably used. These may be used singly, or two or more may be used in combination. The compounding amount of the filler is preferably at least 1 part by weight, and more preferably at least 3 parts by weight per 100 parts by weight of the base rubber. In addition, the upper limit of the compounding amount is preferably not more than 50 parts by weight, more preferably not more than 40 parts by weight, and even more preferably not more than 30 parts by weight per 100 parts by weight of the base rubber. If the compounding amount is too large or too small, it may not be possible to obtain an appropriate weight and a suitable rebound.
As an antioxidant, for example, commercially available products such as Nocrac NS-6, Nocrac NS-30, Nocrac NS-200, and Nocrac MB (all manufactured by Ouchi Shinko Chemical Industrial Co., Ltd.) may be employed. These may be used singly, or two or more may be used in combination.
The compounding amount of the antioxidant is not particularly limited, although the compounding amount is preferably at least 0.05 parts by weight, and more preferably at least 0.1 parts by weight, and the upper limit is preferably not more than 1.0 part by weight, more preferably not more than 0.7 parts by weight, and even more preferably not more than 0.5 parts by weight per 100 parts by weight of the base rubber. If the compounding amount is too large or too small, a suitable core hardness gradient may not be obtained, and it may not be possible to obtain suitable rebound, durability, and a spin rate-lowering effect on full shots.
Furthermore, an organosulfur compound is included in the rubber composition in order to impart an excellent rebound. Specifically, it is recommended to include thiophenol, thionaphthol, halogenated thiophenol, or a metal salt thereof. More specifically, examples of the organosulfur compound include pentachlorothiophenol, pentafluorothiophenol, pentabromothiophenol, p-chlorothiophenol, a zinc salt of pentachlorothiophenol or the like, and any of the following having 2 to 4 sulfur atoms: diphenylpolysulfide, dibenzylpolysulfide, dibenzoylpolysulfide, dibenzothiazoylpolysulfide, and dithiobenzoylpolysulfide. In particular, the zinc salt of pentachlorothiophenol and diphenyldisulfide are preferably used.
The organosulfur compound is blended in an amount of not more than 5 parts by weight, preferably not more than 4 parts by weight, 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. In addition, the lower limit of the compounding amount is preferably not less than 0.1 parts by weight, more preferably not less than 0.2 parts by weight, and even more preferably not less than 0.3 parts by weight. If the compounding amount is too large, the hardness becomes too soft, and if the compounding amount is too small, the rebound may not be expected to be improved.
Water may be included in the rubber composition. This water, although not particularly limited, may be distilled water or tap water, but it is particularly suitable to employ distilled water free of impurities. The compounding amount of the water included per 100 parts by weight of the base rubber is preferably at least 0.1 parts by weight, and more preferably at least 0.2 parts by weight, and the upper limit is preferably not more than 2 parts by weight, and more preferably not more than 1.5 parts by weight.
By blending the water or a water-containing material directly into the core material, decomposition of the organic peroxide during the core formulation may be promoted. In addition, it is known that the decomposition efficiency of the organic peroxide in the core-forming rubber composition changes depending on temperature, and the decomposition efficiency increases as the temperature becomes higher than a certain temperature. If the temperature is too high, the amount of decomposed radicals becomes too large, and the radicals are recombined or deactivated. As a result, fewer radicals act effectively in crosslinking. Here, when decomposition heat is generated by the decomposition of the organic peroxide at the time of core vulcanization, a temperature near the core surface is maintained at substantially the same level as a temperature of a vulcanization mold, but a temperature around the core center is considerably higher than the mold temperature due to an accumulation of decomposition heat by the organic peroxide decomposing from the outside. If the water or a material containing water is directly included in the core, the water acts to promote the decomposition of the organic peroxide, so that the radical reactions as described above may be changed at the core center and the core surface. That is, the decomposition of the organic peroxide is further promoted near the core center, and the deactivation of radicals is further promoted, so that the amount of active radicals is further reduced, and as a result, a core may be obtained in which the crosslink densities at the core center and the core surface differ markedly.
The core may be manufactured by vulcanizing and curing the rubber composition containing the above components. For example, a molded body may be manufactured by intensively mixing the rubber composition using a mixing apparatus such as a Banbury mixer or a roll mill, subsequently compression molding or injection molding the mixture using a core mold, and curing the resulting molded body by appropriately heating it at a temperature sufficient for the organic peroxide or the co-crosslinking agent to act, such as at a temperature of 100 to 200° C., and preferably at a temperature of 140 to 180° C., for 10 to 40 minutes.
In the present invention, the core is formed as a single layer or a plurality of layers, although it is preferably formed as a single layer. If the rubber core is produced as a plurality of layers of rubber, in the case of a large difference in interface hardness between these rubber layers, layer separation at the interface may arise when the ball is repeatedly struck, possibly leading to a loss in the initial velocity of the ball on full shots.
The diameter of the core is preferably at least 36.7 mm, more preferably at least 37.2 mm, and even more preferably at least 37.6 mm. The upper limit of the diameter of the core is preferably not more than 40.1 mm, more preferably not more than 39.0 mm, and even more preferably not more than 38.1 mm. If the diameter of the core is too small, the initial velocity of the ball may become 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 the intended distance may not be attainable. On the other hand, if the diameter of the core is too large, the spin rate on full shots may rise, and the intended distance may not be attainable, or a durability to cracking on repeated impact may worsen.
The deflection (mm) when the core is compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) is not particularly limited, although the deflection (mm) is preferably at least 2.7 mm, more preferably at least 2.9 mm, and even more preferably at least 3.1 mm, and the upper limit thereof is preferably not more than 4.0 mm, more preferably not more than 3.8 mm, and even more preferably not more than 3.7 mm. If the deflection of the core is too small, that is, the core is too hard, the spin rate of the ball may rise excessively, resulting in a poor flight, or the feel at impact may be too hard. On the other hand, if the deflection of the core is too large, that is, the core is too soft, the ball rebound may become too low, resulting in a poor flight, the feel at impact may be too soft, or the durability to cracking on repeated impact may worsen.
Next, the core hardness profile is described. The hardness of the core described below means Shore C hardness. The Shore C hardness is a hardness value measured with a Shore C durometer conforming to the ASTM D2240 standard.
A core center hardness (Cc) is preferably at least 53, more preferably at least 55, and even more preferably at least 57, and the upper limit is preferably not more than 69, more preferably not more than 67, and even more preferably not more than 65. If this value is too large, the feel at impact becomes hard, or the spin rate on full shots may rise, and the intended distance may not be attainable. On the other hand, if the above value is too small, the rebound may become low and a good distance may not be achieved, or the durability to cracking on repeated impact may worsen.
A hardness (Cc+4) at a position 4 mm outward from the center of the core is not particularly limited, although the hardness (Cc+4) may be preferably at least 55, more preferably at least 57, and even more preferably at least 59. The upper limit is also not particularly limited, although the upper limit may be preferably not more than 71, more preferably not more than 69, and even more preferably not more than 67. Hardnesses that deviate from these values may lead to undesirable results similar to those described above for the core center hardness (Cc).
A hardness (Cm−4) at a position 4 mm inward from a midpoint M of the core is not particularly limited, although the hardness (Cm−4) may be preferably at least 56, more preferably at least 58, and even more preferably at least 60. The upper limit is also 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). Hardnesses that deviate from these values may lead to undesirable results similar to those described above for the core center hardness (Cc).
A cross-sectional hardness (Cm) at the midpoint M of the core is not particularly limited, although the cross-sectional hardness (Cm) may be preferably at least 58, more preferably at least 60, and even more preferably at least 62. The upper limit is also 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 outward toward the core surface (hereinafter, simply referred to as “outward”) from the midpoint M of the core is not particularly limited, although the hardness (Cm+4) may be preferably at least 68, more preferably at least 70, and even more preferably at least 72. The upper limit is also not particularly limited, although the upper limit may be preferably not more than 81, more preferably not more than 79, and even more preferably not more than 77. 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 and a good distance may not be achieved, or the spin rate on full shots may rise, and the intended distance may not be attainable.
A hardness (Cs−4) at a position 4 mm inward from the surface of the core is not particularly limited, although the hardness (Cs−4) may be preferably at least 71, more preferably at least 73, and even more preferably at least 75. The upper limit is also not particularly limited, although the upper limit may be preferably not more than 85, more preferably not more than 83, and even more preferably not more than 81. Hardnesses that deviate from these values may lead to undesirable results similar to those described above for the core position hardness (Cm+4).
A core surface hardness (Cs) is preferably at least 80, more preferably at least 82, and even more preferably at least 84. The upper limit is preferably not more than 91, more preferably not more than 89, and even more preferably not more than 87. Hardnesses that deviate from these values may lead to undesirable results similar to those described above for the core position hardness (Cm+4).
A difference (Cs−Cc) between the surface hardness and the center hardness of the core is not particularly limited, although the difference (Cs−Cc) is preferably at least 18, more preferably at least 19, and even more preferably at least 20. On the other hand, the upper limit is not particularly limited, although the upper limit may be preferably not more than 35, more preferably not more than 30, and even more preferably not more than 27. If this value is too small, the spin rate of the ball on full shots may not be lowered. On the other hand, if this value is too large, the actual initial velocity on full shots may become too low, or the durability to cracking on repeated impact may worsen.
In addition, it is preferable to optimize the value of (Cs−Cc)/(Cm−Cc) for the core hardness profile. The value of (Cs−Cc)/(Cm−Cc) is an index value of a hardness difference from the core surface to the core center with respect to a hardness difference from the core center to the midpoint M. The value of (Cs−Cc)/(Cm−Cc) is preferably at least 4.0, more preferably at least 4.5, and even more preferably at least 5.0. The upper limit is preferably not more than 20.0, more preferably not more than 15.0, 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 the intended distance may not be attainable. On the other hand, if this value is too large, the durability to cracking on repeated impact may worsen.
In the core hardness profile, the surface areas A to D defined as follows:
In addition, the value of (surface area C)−(surface area A+surface area B) is preferably at least 2.0, more preferably at least 4.0, and even more preferably at least 6.0, and the upper limit is preferably not more than 20.0, more preferably not more than 16.0, and even more preferably not more than 13.0. If this value is too large, the durability to cracking on repeated impact may worsen. On the other hand, if this value becomes too small, the spin rate of the ball on full shots may rise, and the intended distance may not be attainable.
Furthermore, the value of (surface area D)−(surface area A +surface area B) is preferably at least 2.0, more preferably at least 4.0, and even more preferably at least 6.0,and the upper limit is preferably not more than 20.0, more preferably not more than 16.0, and even more preferably not more than 13.0. If this value is too large, the durability to cracking on repeated impact may worsen. On the other hand, if this value becomes too small, the spin rate of the ball on full shots may rise, and the intended distance may not be attainable.
An initial velocity of the core is preferably at least 75.8 m/s, more preferably at least 76.3 m/s, and even more preferably at least 76.7 m/s. The upper limit is preferably not more than 78.0 m/s, more preferably not more than 77.5 m/s, and even more preferably not more than 77.0 m/s. If the initial velocity value is too high, the initial velocity of the ball becomes too fast, and it may be against the Rules of Golf. On the other hand, if the initial velocity of the core is too low, the ball rebound on full shots may become low, or the spin rate of the ball may rise, and the intended distance may not be attainable. The value of the initial velocity in this case is a numerical value measured by a device for measuring a coefficient of restitution (COR) (Golf Ball Testing Machine) of the same type as the R&A. Specifically, a Golf Ball Testing Machine manufactured by Hye Precision Products USA is used. As a condition, at the time of measurement, an air pressure is changed in four stages and measured, a relational expression between the incident velocity and the COR is constructed, and the initial velocity at an incident velocity of 43.83 m/s is determined from the relational expression. For a measurement environment of the Golf Ball Testing Machine, a ball temperature-controlled for at least three hours in a thermostatic bath adjusted to 23.9±1° C. is used, and measurement is performed at a room temperature of 23.9±2° C.
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 expressed on the Shore D hardness scale is preferably at least 64, more preferably at least 66, and even more preferably at least 68, and the upper limit is preferably not more than 75, more preferably not more than 72, and even more preferably not more than 70.
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 ball may be excessively receptive to spin on full shots, or the initial velocity of the ball may become low so that the distance may not be increased. On the other hand, if the material hardness and the surface hardness of the intermediate layer are too hard in comparison with the above ranges, the durability to cracking on repeated impact may worsen, or the feel at impact on shots with a putter or on short approaches may become too hard.
The intermediate layer has a thickness which is preferably at least 1.02 mm, more preferably at least 1.11 mm, and even more preferably at least 1.20 mm. The intermediate layer thickness has an upper limit that is preferably not more than 1.45 mm, more preferably not more than 1.37 mm, and even more preferably not more than 1.32 mm. It is preferable for the intermediate layer to be thicker than the subsequently described cover. When the intermediate layer thickness falls outside of the above range or the intermediate layer is thinner than the cover, the ball spin rate-lowering effect on shots with a driver (W #1) may be inadequate, resulting in a poor distance. Also, when the intermediate layer is too thin, the durability to cracking on repeated impact and the low-temperature durability 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 0.20 mm, and even more preferably at least 0.32 mm. The upper limit is preferably not more than 0.62 mm, more preferably not more than 0.58 mm, and even more preferably not more than 0.55 mm. When this value falls outside of the above range, the spin rate of the ball on full shots may rise or the actual initial velocity on shots may become low, as a result of which the intended distance may not be attainable. When this value is too small, the durability to cracking on repeated impact may worsen.
In the present invention, a relationship between the intermediate layer thickness (mm) and the ball diameter (mm), that is, the value of (intermediate layer thickness)/(ball diameter) is between 0.024 and 0.034 inclusive. The lower limit thereof is preferably not less than 0.026, and more preferably not less than 0.028. On the other hand, the upper limit is preferably not more than 0.032, and more preferably not more than 0.031. If this value is too small, it may not be possible to achieve both a moderate hardness and a crisp feel for the feel at impact on full shots so that a professional golfer may not be given a good feel at impact, or the durability to cracking on repeated impact may worsen. On the other hand, if this value is too large, the crisp feel may be weakened so that a professional golfer may not be given a good feel at impact.
As a material of the intermediate layer, it is suitable to employ an ionomer resin as a chief material.
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 20 wt %, more preferably at least 50 wt %, and even more preferably at least 60 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 %. If the compounding amount of the high-acid ionomer resin is too small, the spin rate of the ball on full shots may rise, and the distance may not be increased. On the other hand, if the compounding amount of the high-acid ionomer resin is too large, the durability on repeated impact may worsen.
In addition, when 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 to obtain a desired flight, the durability to cracking on repeated impact at room temperature may worsen, and the durability to cracking at a low temperature (below zero) may worsen.
In the intermediate layer material, an optional additive may be appropriately included depending on the intended use. For example, various additives such as a pigment, a dispersant, an antioxidant, an ultraviolet absorber, and a light stabilizer may be included. If these additives are included, the compounding amount thereof is preferably at least 0.1 part by weight, and more preferably at least 0.5 part by weight, and the upper limit thereof is preferably not more than 10 parts by weight, and more preferably not more than 4 parts by weight per 100 parts by weight of the base resin.
For the intermediate layer material, it is suitable to abrade the surface of the intermediate layer in order to increase the degree of adhesion to a polyurethane suitably used in a cover material described later. Further, it is preferable that a primer (adhesive agent) is applied to the surface of the intermediate layer after the abrasion treatment, or an adhesion reinforcing agent is added to the intermediate layer material.
The material of the intermediate layer may contain an inorganic particulate filler. This inorganic particulate filler is not particularly limited, although zinc oxide, barium sulfate, titanium dioxide, or the like may be appropriately used. Barium sulfate may be preferably used, and particularly preferably, precipitated barium sulfate may be suitably used from the viewpoint of excellent durability to cracking on repeated impact.
The mean particle size of the inorganic particulate filler is not particularly limited, although the mean particle size is preferably from 0.01 to 100 μm, and more preferably from 0.1 to 10 μm. If the mean particle size of the inorganic particulate filler is too small or too large, dispersibility during material preparation may be deteriorated. The mean particle size means a particle size measured by dispersing the particles in an aqueous solution together with an appropriate dispersant and measuring the particles with a particle size distribution measuring device.
The content of the inorganic particulate filler is not particularly limited, although the compounding amount is preferably set to at least 0 part by weight, more preferably at least 10 parts by weight, and even more preferably at least 15 parts by weight, per 100 parts by weight of the base resin of the intermediate layer material. Although there is no particular upper limit, the compounding amount is preferably not more than 50 parts by weight, preferably not more than 40 parts by weight, and more preferably not more than 30 parts by weight. At a content of the inorganic particulate filler that is too low, the durability to cracking on repeated impact may worsen. On the other hand, at a content of the inorganic particulate filler that is too high, the ball rebound may decrease or the spin rate of the ball on full shots may rise, as a result of which the intended distance may not be achieved.
A specific gravity of the intermediate layer is preferably at least 1.05, more preferably at least 1.07, and even more preferably at least 1.09, and the upper limit is preferably not more than 1.25, more preferably not more than 1.20, and even more preferably not more than 1.15. If the specific gravity of the intermediate layer is too small, the durability to cracking on repeated impact may worsen. On the other hand, if the specific gravity of the intermediate layer is too large, the ball rebound may decrease or the spin rate of the ball on full shots may rise, as a result of which the intended distance may not be achieved.
The intermediate layer-encased sphere has an initial velocity which is preferably at least 77.0 m/s, more preferably at least 77.3 m/s, and even more preferably at least 77.5 m/s. The upper limit is preferably not more than 78.5 m/s, more preferably not more than 78.2 m/s, and even more preferably not more than 77.9 m/s. If the initial velocity value is too high, the initial velocity of the ball becomes too fast, and it may be against the Rules of Golf. On the other hand, if the initial velocity is too low, the ball rebound may become low on full shots, or the spin rate may rise, as a result of which the intended distance may not be attainable. The initial velocity in this case is measured with the same device and under the same conditions as described above for measurement of the initial velocity of the core.
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 80, more preferably not more than 74, and even more preferably not more than 70. The material hardness on the Shore D hardness scale is preferably at least 30, more preferably at least 35, and even more preferably at least 40. The upper limit is preferably not more than 53, more preferably not more than 50, and even more preferably not more than 47.
The sphere (ball) obtained by encasing the intermediate layer-encased sphere with the cover—that is, the ball—has a surface hardness which, on the Shore C hardness scale, is preferably at least 73, more preferably at least 78, and even more preferably at least 83, but is preferably not more than 95, more preferably not more than 92, and even more preferably not more than 90. The surface hardness on the Shore D hardness scale is preferably at least 50, more preferably at least 53, and even more preferably at least 56, but is preferably not more than 70, more preferably not more than 65, and even more preferably not more than 60.
If the material hardness and the surface hardness of the cover are too soft in comparison with the above ranges, the spin rate on full shots may rise excessively, and the distance may not be increased. On the other hand, if the material hardness and the surface hardness of the cover are too hard in comparison with the above ranges, the ball may not be fully receptive to spin on approach shots, or a scuff resistance may worsen.
The cover has a thickness of preferably at least 0.3 mm, more preferably at least 0.45 mm, and even more preferably at least 0.6 mm. The upper limit in the cover thickness is preferably not more than 1.2 mm, more preferably not more than 0.9 mm, and even more preferably not more than 0.8 mm. When the cover is too thick, the rebound of the ball on full shots may be inadequate or the spin rate may rise, as a result of which a good distance may not be achieved. 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 a cover material, various types of thermoplastic resin used as a cover material in golf balls may be used, but it is suitable to use a resin material composed primarily of a thermoplastic polyurethane from the viewpoints of spin controllability in the short game and scuff resistance. That is, the cover is suitably formed of a resin blend containing (I) a thermoplastic polyurethane and (II) a polyisocyanate compound as principal components.
The total weight of the components (I) and (II) is recommended to be at least 60%, and more preferably at least 70% with respect to the total amount of the resin composition of the cover. The components (I) and (II) are described in detail below.
Describing the thermoplastic polyurethane (I), the construction of the thermoplastic polyurethane includes a soft segment composed of a polymeric polyol (polymeric glycol), which is a long-chain polyol, and a hard segment composed of a chain extender and a polyisocyanate compound. Here, as the long-chain polyol serving as a starting material, any of those hitherto used in the art related to thermoplastic polyurethane may be used, and are not particularly limited, and examples thereof may include polyester polyol, polyether polyol, polycarbonate polyol, polyester polycarbonate polyol, polyolefin polyol, conjugated diene polymer-based polyol, castor oil-based polyol, silicone-based polyol, and vinyl polymer-based polyol. These long-chain polyols may be used singly, or two or more may be used in combination. Among them, a polyether polyol is preferable from the viewpoint that a thermoplastic polyurethane having a high rebound resilience and excellent low-temperature properties may be synthesized.
As the chain extender, those hitherto used in the art related to thermoplastic polyurethanes may be suitably used, and for example, a low-molecular-weight compound having on the molecule two or more active hydrogen atoms capable of reacting with an isocyanate group and having a molecular weight of 400 or less is preferable. Examples of the chain extender include, but are not limited to, 1,4-butylene glycol, 1,2-ethylene glycol, 1,3-butanediol, 1,6-hexanediol, 2,2-dimethyl-1,3-propanediol, or the like. Among them, the chain extender is preferably an aliphatic diol having from 2 to 12 carbon atoms, and is more preferably 1,4-butylene glycol.
As the polyisocyanate compound, those hitherto used in the art related to thermoplastic polyurethane may be suitably used, and are not particularly limited. Specifically, one or more selected from the group consisting of 4,4′-diphenylmethane diisocyanate, 2,4-toluene diisocyanate (or) 2,6-toluene diisocyanate, p-phenylene diisocyanate, xylylene diisocyanate, 1,5-naphthylene diisocyanate, tetramethylxylene diisocyanate, hydrogenated xylylene diisocyanate, dicyclohexylmethane diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, norbornene diisocyanate, trimethylhexamethylene diisocyanate, and dimer acid diisocyanate may be used. However, it may be difficult to control a crosslinking reaction during injection molding depending on the type of isocyanate. In the present invention, 4,4′-diphenylmethane diisocyanate, which is an aromatic diisocyanate, is most preferable from the viewpoint of providing a balance between stability during production and the physical properties to be manifested.
As specific examples of the thermoplastic polyurethane serving as the component (I), commercially available products may be used such as Pandex T-8295, Pandex T-8290, and Pandex T-8260 (all manufactured by DIC Covestro Polymer, Ltd.).
Although not an essential component, a thermoplastic elastomer other than the thermoplastic polyurethane may be included as a separate component (III) with the components (I) and (II). By including the component (III) in the resin blend, a flowability of the resin blend may be further improved, and various physical properties required of the golf ball cover material may be increased, such as rebound and scuff resistance.
A compositional ratio of the components (I), (II), and (III) is not particularly limited, but in order to sufficiently and effectively exhibit the advantageous effects of the present invention, the compositional ratio (I):(II):(III) is preferably in the weight ratio range of from 100:2:50 to 100:50:0, and more preferably from 100:2:50 to 100:30:8.
Furthermore, various additives other than the components constituting the thermoplastic polyurethane may be included in the resin blend as necessary, and for example, a pigment, a dispersant, an antioxidant, a light stabilizer, an ultraviolet absorber, an internal mold lubricant, or the like may be appropriately included.
The cover has a specific gravity which, although not particularly limited, is preferably at least 1.00, more preferably at least 1.03, and even more preferably at least 1.06. The upper limit is preferably not more than 1.20, more preferably not more than 1.17, and even more preferably not more than 1.14. When the cover specific gravity is lower than the above range, the ratio of low specific gravity materials such as ionomer blended into the cover made chiefly of urethane ends up becoming high, as a result of which the scuff resistance may worsen. On the other hand, when the cover specific gravity is too high, the amount of filler added is high and the rebound may become too low, as a result of which the intended distance may be unattainable.
The manufacture of a multi-piece solid golf ball in which the above-described core, intermediate layer, and cover (outermost layer) are formed as successive layers may be performed by a customary method such as a known injection molding process. For example, an intermediate layer material is injected around the core in an injection mold to obtain an intermediate layer-encased sphere, and finally, a cover material, which is the outermost layer, is injection molded to obtain a multi-piece golf ball. In addition, it is also possible to produce a golf ball by preparing two half-cups pre-molded into hemispherical shapes, enclosing the core and the intermediate layer-encased sphere within the two half cups, and molding the core and the intermediate layer-encased sphere under applied heat and pressure.
The golf ball has a deflection (mm) when compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) which is preferably at least 2.3 mm, more preferably at least 2.4 mm, and even more preferably at least 2.5 mm. The deflection upper limit is preferably not more than 3.0 mm, more preferably not more than 2.9 mm, and even more preferably not more than 2.8 mm. When the golf ball deflection is too small, i.e., when the ball is too hard, the spin rate may rise excessively, resulting in a poor flight, or the feel at impact may be too hard. On the other hand, when the deflection is too large, i.e., when the ball is too soft, the actual initial velocity on full shots with a driver (W #1) or the like may become too low, resulting in a poor flight, the feel at impact may be too soft, or the durability to cracking on repeated impact may worsen.
The ball has an initial velocity which is preferably at least 76.8 m/s, more preferably at least 77.0 m/s, and even more preferably at least 77.2 m/s. The upper limit is preferably not more than 77.724 m/s. A ball initial velocity that is too high may fall outside the range specified in the Rules of Golf. On the other hand, when the ball initial velocity is too low, the ball may not travel well on full shots. The initial velocity in this case is measured with the same device and under the same conditions as described above for measurement of the initial velocities of the core and the intermediate layer-encased sphere.
It is preferable that a relationship between the surface hardness of the intermediate layer-encased sphere and the surface hardness of the ball satisfies the following condition:
Expressed on the Shore C hardness scale, a value obtained by subtracting the surface hardness of the core from the surface hardness of the intermediate layer-encased sphere is preferably at least 1, more preferably at least 6, and even more preferably at least 10, and the upper limit is preferably not more than 25, more preferably not more than 20, and even more preferably not more than 15. If the above value is too large, the durability to cracking on repeated impact may worsen, or the actual initial velocity on shots may become lower, and the intended distance may not be attainable. On the other hand, if the above value is too small, the spin rate of the ball on full shots may rise, and the intended distance may not be attainable.
Expressed on the Shore C hardness scale, a value obtained by subtracting the center hardness of the core from the surface hardness of the intermediate layer-encased sphere is preferably at least 23, more preferably at least 28, and even more preferably at least 33, and the upper limit is preferably not more than 52, more preferably not more than 47, and even more preferably not more than 42. If the above value is too small, the spin rate of the ball on full shots may rise, and the intended distance may not be attainable. On the other hand, if the above value is too large, the durability to cracking on repeated impact may worsen, or the actual initial velocity on shots may become lower, and the intended distance may not be attainable.
It is critical for a relationship among the initial velocity of the core, the initial velocity of the sphere (intermediate layer-encased sphere) obtained by encasing the core with the intermediate layer, and the initial velocity of the sphere (ball) obtained by encasing the intermediate layer-encased sphere with the cover to satisfy the following two conditions:
The value obtained by subtracting the initial velocity of the ball from the initial velocity of the intermediate layer-encased sphere is larger than 0 m/s, preferably at least 0.10 m/s, and more preferably at least 0.30 m/s. The upper limit is preferably not more than 1.00 m/s, more preferably not more than 0.70 m/s, and even more preferably not more than 0.55 m/s. If this value is too large, the spin rate of the ball rises on full shots, the actual initial velocity on shots becomes low, or the like, and the intended distance may not be attainable. On the other hand, if this value is too small due to the cover, the cover becomes hard and the ball is not receptive to spin in the short game, or the durability on repeated impact may be inferior. In addition, if this value is small due to the intermediate layer, the spin rate of the ball rises on full shots, and the intended distance may not be attainable.
The value obtained by subtracting the initial velocity of the core from the initial velocity of the intermediate layer-encased sphere is preferably at least 0.60 m/s, more preferably at least 0.70 m/s, and even more preferably at least 0.75 m/s, and the upper limit is preferably not more than 0.90 m/s, more preferably not more than 0.89 m/s, and even more preferably not more than 0.88 m/s. If this value is too large, the durability to cracking on repeated impact may worsen, the distance may not be increased, or the feel at impact may worsen. On the other hand, if this value is too small, the spin rate on full shots may rise, and the intended distance may not be attainable, or the feel at impact may worsen.
A difference between the specific gravity of the cover and the specific gravity of the intermediate layer, a difference between the specific gravity of the intermediate layer and a specific gravity of the core, and a difference between the specific gravity of the core and the specific gravity of the cover are all typically recommended to be within ±0.15, preferably within ±0.10, and more preferably within ±0.05. That is, if the difference in specific gravity between them is too large, in a case where the intermediate layer material and/or the cover material cannot be molded on a completely concentric circle with these layers and with the layers located inside these layers and is eccentric, the ball hit with a putter may greatly wobble to the left or right.
A relationship between the core diameter and the ball diameter, that is, the value of (core diameter)/(ball diameter) is preferably at least 0.860, more preferably at least 0.870, and even more preferably at least 0.880. On the other hand, the upper limit is preferably not more than 0.940, more preferably not more than 0.910, and even more preferably not more than 0.895. If this value is too small, the initial velocity of the ball becomes low, or the deflection of the entire ball becomes small and the ball becomes hard, the spin rate of the ball on full shots rises, and the intended distance may not be attainable. On the other hand, if the above value is too large, the spin rate of the ball on full shots rises, and the intended distance may not be attainable, 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, the value of C−B is preferably at least 0.64 mm, more preferably at least 0.74 mm, and even more preferably at least 0.84 mm. On the other hand, the upper limit is preferably not more than 1.10 mm, more preferably not more than 1.04 mm, and even more preferably not more than 1.00 mm. If this value is too large, the actual initial velocity on shots with a driver (W #1) may become low and the intended distance may not be attainable, a professional golfer may not be given a good feel at impact, or the durability to cracking on repeated impact may worsen. On the other hand, if this value is too small, a professional golfer may not be given a good feel at impact, or the durability to cracking on repeated impact may worsen.
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 250, more preferably at least 300, and even more preferably at least 320, and the upper limit thereof may be preferably not more than 380, more preferably not more than 350, and even more preferably not more than 340. If the number of dimples is larger than the above range, a ball trajectory may become lower, and a distance traveled by the ball may decrease. On the other hand, if the number of dimples decreases, the ball trajectory may become higher, and the distance traveled by the ball may not increase.
As for the shape of the dimples, one type or a combination of two or more types such as a circular shape, various polygonal shapes, a dewdrop shape, and other oval shapes may be appropriately used. For example, if circular dimples are used, the diameter may be about at least 2.5 mm and not more than 6.5 mm, and the depth may be at least 0.08 mm and not more than 0.30 mm.
A dimple coverage ratio of the dimples on the spherical surface of the golf ball, specifically, a ratio (SR value) of a sum of the individual dimple surface areas, each defined by a flat plane circumscribed by the edge of a dimple, to a ball spherical surface area on the assumption that the ball has no dimples is desirably between 70% and 90% inclusive from the viewpoint of sufficiently exhibiting aerodynamic properties. In addition, 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 suitably between 0.35 and 0.80 inclusive from the viewpoint of optimizing the ball trajectory. Furthermore, a VR value of a sum of the volumes of the individual dimples, formed below the flat plane circumscribed by the edge of a dimple, to a ball spherical volume on the assumption that the ball has no dimples is preferably between 0.6% and 1.0% inclusive. If there is a deviation from the ranges of each numerical value described above, the resulting trajectory may not enable a good distance to be attained, and the ball may fail to travel a sufficiently satisfactory distance.
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 Comparative Example 3 and Comparative Examples 5 to 10, 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 1 to 3 and Comparative Examples 1, 2, 4, 11, and 12, 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 Comparative Example 3 and Comparative Examples 5 to 10, the intermediate layer was formed by injection molding the resin material No. 2, No. 3, or No. 4 of the intermediate layer shown in Table 2 around the core surface using an injection mold. Subsequently, the cover was formed by injection molding the resin material No. 10 of the cover (outermost layer) shown in Table 2 around the intermediate layer-encased sphere using a separate injection mold. At this time, a predetermined large number of dimples common to all Examples and Comparative Examples were formed on the surface of the cover.
In Examples 1 to 3 and Comparative Examples 1, 2, 4, 11, and 12, the intermediate layer is formed by injection molding the resin material No. 1, No. 2, No. 4, or No. 5 of the intermediate layer shown in Table 2 around the core surface using an injection mold. Subsequently, the cover is formed by injection molding the resin material No. 7, No. 8, No. 9, or No. 10 of the cover (outermost layer) shown in Table 2 around the intermediate layer-encased sphere using a separate injection mold. At this time, a predetermined large number of dimples common to all Examples and Comparative Examples are formed on the surface of the cover.
Details of the blending components in the above table are as follows.
Trade names of chief materials mentioned in the table are as follows.
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 initial velocities of each layer-encased sphere are evaluated by the following methods, and are shown in Tables 3 and 4.
The core surface is spherical, but an indenter of a durometer is set substantially perpendicular to the spherical core surface, and a core surface hardness expressed on the Shore C hardness scale is measured in accordance with ASTM D2240. With respect to the core center and a predetermined position of the core, the core is cut into hemispheres to obtain a flat cross-section, the hardness is measured by perpendicularly pressing the indenter of the durometer against the center portion and the predetermined positions shown in Table 3, and the hardness at the center and each position are shown as Shore C hardness values. For the measurement of the hardness, a P2 Automatic Rubber Hardness Tester manufactured by Kobunshi Keiki Co., Ltd. equipped with a Shore C durometer is used. For the hardness value, a maximum value is read. All measurements are carried out in an environment of 23±2° C. The numerical values in the tables are Shore C hardness values.
In addition, in the core hardness profile, letting Cc be the Shore C hardness at the core center, Cc+4 be the Shore C hardness at a position 4 mm outward from the core center, Cm be the Shore C hardness at the midpoint M between the core center and the core surface, Cm−4 be the Shore C hardness at a position 4 mm inward from the midpoint M of the core, Cm+4 be the Shore C hardness at a position 4 mm outward from the midpoint M of the core, Cs−4 be the Shore C hardness at a position 4 mm inward from the core surface, and Cs be the Shore C hardness at the core surface, the surface areas A to D are calculated as follows:
The surface areas A to D in the core hardness profile are described in
In addition,
At a temperature adjusted to 23.9±1° C. for at least three hours or more in a thermostatic bath, five random places on the surface are measured in a room with a temperature of 23.9±2° C., and, using an average value of these measurements as a measured value of each sphere, an average value for the diameter of 10 such spheres is determined.
At a temperature adjusted to 23.9±1° C. for at least three hours or more in a thermostatic bath, a diameter at 15 random dimple-free places is measured in a room at a temperature of 23.9±2° C., and, using an average value of these measurements as a measured value of one ball, an average value for the diameter of 10 balls is determined.
Each subject layer-encased sphere is placed on a hard plate, and a deflection when compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) is measured. The deflection in each case is a measurement value measured in a room at a temperature of 23.9±2° C. after temperature adjustment to 23.9±1° C. for at least three hours in a thermostatic bath. A pressing speed of a 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 was 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 measurement principle for measuring an initial velocity of each sphere using the device for measuring COR manufactured by Hye Precision Products of the same type as the R&A is shown below.
An air pressure is changed to four stages of 35.5 psi, 36.5 psi, 39.5 psi, and 40.5 psi, and a ball is fired at four stages of incident velocity by respective air pressures, collided with a barrier, and its COR (coefficient of restitution) is measured. That is, a correlation equation between the incident velocity and the COR is created by changing the air pressure in four stages. Similarly, a correlation equation between the incident velocity and a contact time is created.
Then, from these correlation equations, the COR (coefficient of restitution) and the contact time (μs) at an incident velocity of 43.83 m/s are determined and substituted into the following initial velocity conversion equation to calculate an initial velocity of each sphere.
In the initial velocity measurement of each sphere, the barrel inner diameter used is 39.88 mm for the cores of Examples 1 to 3 and Comparative Examples 1 to 10, 38.23 mm for the cores of Comparative Examples 11 and 12, 41.53 mm for the intermediate layer-encased spheres of all Examples, and 43.18 mm for the balls of all Examples.
The flight (W #1), the controllability on approach shots, the feel at impact, and the durability on repeated impact of each golf ball are evaluated by the following methods. The results are shown in Table 5.
A driver (W #1) 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 45 m/s are measured. The club used is a JGR/loft angle 9.5° (2016 model) manufactured by Bridgestone Sports Co., Ltd.
The rating criteria are as follows.
A judgment is made based on a spin rate when a sand wedge is mounted on the golf swing robot and a ball is struck at a head speed (HS) of 15 m/s. Similarly, a spin rate immediately after the ball is struck is measured by a device for measuring initial conditions. The sand wedge used is a TOURSTAGE TW-03 (loft angle 57°) 2002 model manufactured by Bridgestone Sports Co., Ltd.
The feel at impact on full shots by a professional golfer at a head speed (HS) of at least 45 m/s with a driver (W #1) is evaluated according to the following criteria.
The evaluation is made based on the number of users who evaluated as having “a crisp feel” and “a moderate hardness”.
A durability of the golf ball is evaluated using an ADC Ball COR Durability Tester produced by Automated Design Corporation (U.S.). The tester fires a golf ball pneumatically and causes it to repeatedly strike two metal plates installed in parallel, and an average value of the number of times of firing required until the ball cracks is regarded as the number of times until cracking of the ball and displayed as an index when an average value of Comparative Example 5 is based at 100. The above average value is a value obtained by preparing 10 balls of the same type and, by firing each ball, averaging the number of times of firing required until each of the 10 balls cracks. The tester is a horizontal COR type, and an incident velocity against the metal plates is set to 43 m/s.
As shown in the results in Table 5, the golf balls of Comparative Examples 1 to 12 are inferior in the following respects to the golf balls according to the present invention (Examples).
In Comparative Example 1, the value of (initial velocity of intermediate layer-encased sphere−initial velocity of core) is larger than 0.90 m/s. As a result, the durability to cracking on repeated impact is poor.
In Comparative Example 2, the value of (deflection of core−deflection of ball) is larger than 1.10 mm. As a result, the feel at impact is not good.
In Comparative Example 3, the value of (deflection of core−deflection of ball) is larger than 1.10 mm. As a result, the feel at impact was not good.
In Comparative Example 4, the value of (deflection of core−deflection of ball) is larger than 1.10 mm. As a result, the feel at impact is not good.
In Comparative Example 5, the value of (deflection of core−deflection of ball) is larger than 1.10 mm, and (initial velocity of intermediate layer-encased sphere−initial velocity of core) is larger than 0.90 m/s. As a result, the golf ball was inferior in the distance when struck at a head speed (HS) of 45 m/s with the driver (W #1), the feel at impact was not good, and the durability to cracking on repeated impact was poor.
In Comparative Example 6, the value of (deflection of core−deflection of ball) is larger than 1.10 mm, and (initial velocity of intermediate layer-encased sphere−initial velocity of core) is larger than 0.90 m/s. As a result, the golf ball was inferior in the distance when struck at a head speed (HS) of 45 m/s with the driver (W #1), the feel at impact was not good, and the durability to cracking on repeated impact was poor.
In Comparative Example 7, the value of (deflection of core−deflection of ball) is larger than 1.10 mm, and (initial velocity of intermediate layer-encased sphere−initial velocity of core) is larger than 0.90 m/s. As a result, the feel at impact was not good, and the durability to cracking on repeated impact was poor.
In Comparative Example 8, the value of (deflection of core−deflection of ball) is larger than 1.10 mm, and (initial velocity of intermediate layer−encased sphere-initial velocity of core) is larger than 0.90 m/s. As a result, the feel at impact was not good, and the durability to cracking on repeated impact was poor.
In Comparative Example 9, the value of (deflection of core−deflection of ball) is larger than 1.10 mm, and (initial velocity of intermediate layer-encased sphere−initial velocity of core) is larger than 0.90 m/s. As a result, the golf ball was inferior in the distance when struck at a head speed (HS) of 45 m/s with the driver (W #1), and the feel at impact was not good.
In Comparative Example 10, the value of (deflection of core−deflection of ball) is larger than 1.10 mm, and (initial velocity of intermediate layer-encased sphere−initial velocity of core) is larger than 0.90 m/s. As a result, the golf ball was inferior in the distance when struck at a head speed (HS) of 45 m/s with the driver (W #1), and the feel at impact was not good.
In Comparative Example 11, the value of (initial velocity of intermediate layer-encased sphere−initial velocity of core) is larger than 0.90 m/s. As a result, the golf ball is inferior in the distance when struck at a head speed (HS) of 45 m/s with the driver (W #1), the spin rate on approach shots is reduced, the feel at impact is not good, and the durability to cracking on repeated impact is poor.
In Comparative Example 12, the value of (initial velocity of intermediate layer-encased sphere−initial velocity of core) is smaller than 0.60 m/s, and the initial velocity of the ball is higher than the initial velocity of the intermediate layer-encased sphere. As a result, the spin rate on approach shots is reduced, and the feel at impact is not good.
Japanese Patent Application No. 2023-090009 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 |
|---|---|---|---|
| 2023-090009 | May 2023 | JP | national |
