Multi-piece solid golf ball

Abstract

To provide a golf ball which reduces the distance by which an average hitter loses carry when hitting with a driver and when hitting with an iron, even if the distance by which a long hitter loses carry is increased when hitting with a driver.SOLUTION: The present invention provides a multi-piece solid golf ball including a core, an intermediate layer, and a cover, in which a large number of dimples are formed on an outside surface of the cover, and a relation between a cover material hardness and a midpoint hardness (Cm) between a core surface and a core center satisfies the following condition: midpoint hardness (Cm) between the core surface and the core center>the cover material hardness where hardness means Shore C hardness. Further, a surface hardness of the ball is optimized, a deflection of the ball when compressed under a predetermined load is optimized, and a lift coefficient and a drag coefficient at a predetermined Reynolds number and spin rate of the dimples are set within a predetermined range.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a multi-piece solid golf ball which comprises a core, a mid layer and a cover, the cover having a large number of dimples formed on its outer surface. [Background technology]

[0002] In March 2022, the R&A and the USGA notified golf ball manufacturers that they would begin research to reduce the flying distance of long hitters by changing the test conditions for the overall distance standard (ODS) of golf balls in the future. For this reason, rather than simply reducing the flying distance, it is preferable to create a golf ball that reduces the impact on play other than the reduction in flying distance when hitting with a driver by a long hitter, by increasing the distance by which the flying distance is reduced when hitting with a driver by a long hitter, while reducing the distance by which the flying distance is reduced when hitting with a driver and when hitting with an iron by an average hitter. In addition, it is desirable to design a golf ball so that the spin characteristics of the short game are similar to those of the balls currently used on the tour, so that professionals and advanced players do not feel uncomfortable when using golf balls with reduced flying distance due to the above changes.

[0003] In the past, many golf balls have been proposed that optimize the surface hardness and the amount of deflection when the ball is subjected to an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf). For example, Patent Documents 1 to 7 listed below can be mentioned.

[0004] However, the above proposed golf balls are designed to increase the flight distance when hit with a driver (W#1) or to focus on controllability during approach shots, and none of them are designed to reduce the flight distance when a long hitter hits with a driver (W#1), while making the distance over which an average hitter loses flight distance smaller than the distance over which a long hitter loses flight distance. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2019-198465 A [Patent Document 2] JP 2020-171623 A [Patent Document 3] Patent Publication No. 2023-28455 [Patent Document 4] JP 2023-28456 A [Patent Document 5] JP 2007-282685 A [Patent Document 6] JP 2012-130524 A [Patent Document 7] JP 2013-31640 A Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in consideration of the above circumstances, and in response to the possibility that the rules will be changed to restrict the distance that long hitters can hit by changing the test conditions for the overall distance standard (ODS) of golf balls in the future, the object of the present invention is to provide a golf ball that does not simply reduce the distance, but increases the distance by which the distance is lost when a long hitter hits with a driver, while reducing the distance by which the distance is lost when an average hitter hits with a driver (W#1) and with an iron, and further reduces the run when hit with an iron, making it easier for the ball to stop at the targeted location, and further increases the spin level in the short game, thereby satisfying the needs of professionals and advanced players. [Means for solving the problem]

[0007] As a result of intensive research conducted by the present inventors in order to achieve the above object, it has been found that in a multi-piece solid golf ball having a core, an intermediate layer and a cover, with a large number of dimples formed on the outer surface of the cover, the relationship between the midpoint hardness (Cm) between the surface and center of the core and the hardness of the cover material is expressed by the following formula: Hardness at the midpoint between the surface and center of the core (Cm) > Hardness of the cover material (However, hardness refers to Shore C hardness.) The above conditions are met, the surface hardness of the ball is 59 or less in Shore D hardness, the amount of deflection when the ball is subjected to an initial load of 98N (10kgf) to a final load of 1,275N (130kgf) is 2.79mm or less, and when the ratio CL1 / CD1 of the lift coefficient CL1 to the drag coefficient CD1 at a Reynolds number of 218,000 and a spin rate of 2,800rpm is A1, the ratio CL2 / CD2 of the lift coefficient CL2 to the drag coefficient CD2 at a Reynolds number of 184,000 and a spin rate of 2,900rpm is A2, and the ratio CL3 / CD3 of the lift coefficient CL3 to the drag coefficient CD3 at a Reynolds number of 158,000 and a spin rate of 3,100rpm is A3, the following two equations are satisfied: 0.590≦A1≦0.655, and (A2+A3) / 2≧0.670 By designing a golf ball to satisfy the above, the inventors have found a golf ball conforming to the rules restricting the flying distance of a long hitter, in which even if the distance lost by a long hitter when hitting with a driver becomes large compared to when hitting with a driver, the distance lost by an average hitter when hitting with a driver (W#1) and with an iron is minimized as much as possible, thereby minimizing the impact on play other than the loss of flying distance when hitting with a driver by a long hitter, and have completed the present invention. Furthermore, when used by professionals and advanced players, the golf ball of the present invention has a shorter flying distance when hitting with a driver (W#1) than conventional tour balls, but the level of spin in short games can be increased to improve short game characteristics. Furthermore, the golf ball of the present invention satisfies the needs of professionals and advanced players by making it easier to stop the ball at the target without increasing the run when hitting with an iron.

[0008] In addition, the above-mentioned "long hitter" refers to a user whose head speed when hitting with a driver (W#1) is approximately 50 m / s or more, and the above-mentioned "average hitter" refers to a user whose head speed when hitting with a driver (W#1) is approximately 45 m / s or less.

[0009] Accordingly, the present invention provides a multi-piece solid golf ball as follows: 1. A multi-piece solid golf ball having a core, an intermediate layer, and a cover, the outer surface of which is formed with a number of dimples, the relationship between the midpoint hardness (Cm) between the surface and center of the core and the hardness of the cover material being expressed by the following formula: Hardness at the midpoint between the surface and center of the core (Cm) > Hardness of the cover material (However, hardness refers to Shore C hardness.) The above conditions are met, the surface hardness of the ball is 59 or less in Shore D hardness, the amount of deflection when the ball is subjected to an initial load of 98N (10kgf) and a final load of 1,275N (130kgf) is 2.79mm or less, and when the ball is subjected to a load of 2,800rpm, the ratio CL1 / CD1 of the lift coefficient CL1 to the drag coefficient CD1 at a Reynolds number of 218,000 and a spin rate of 2,800rpm is A1, the ratio CL2 / CD2 of the lift coefficient CL2 to the drag coefficient CD2 at a Reynolds number of 184,000 and a spin rate of 2,900rpm is A2, and the ratio CL3 / CD3 of the lift coefficient CL3 to the drag coefficient CD3 at a Reynolds number of 158,000 and a spin rate of 3,100rpm is A3, the following two equations are satisfied: 0.590≦A1≦0.655, and (A2+A3) / 2≧0.670 A multi-piece solid golf ball comprising: 2. The multi-piece solid golf ball according to the above item 1, wherein the volume fraction VR of the dimples is 0.78 to 0.92%. 3. The multi-piece solid golf ball according to the above 1 or 2, wherein the value of (A2+A3) / 2 is 0.670 to 0.783. 4. The multi-piece solid golf ball according to 1 or 2 above, wherein the value of A2 is 0.635 to 0.750 and the value of A3 is 0.695 to 0.815. 5. In the hardness distribution of the above core, the Shore C hardness at the center of the core is Cc, the Shore C hardness at a position 4 mm outward from the center of the core is Cc+4, the Shore C hardness at the midpoint M between the center and the surface of the core is Cm, the Shore C hardness at a position 4 mm inward from the midpoint M is Cm-4, the Shore C hardness at a position 4 mm outward from the center M is Cm+4, the Shore C hardness at the surface of the core is Cs, and the Shore C hardness at a position 4 mm inward from the surface of the core is Cs-4, then the following areas A to D are ·Area A: 1 / 2×4×(Cc+4-Cc) ·Area B: 1 / 2×4×(Cm-Cm-4) ·Area C: 1 / 2×4×(Cm+4-Cm) ·Area D: 1 / 2×4×(Cs-Cs-4) Regarding (Area C+Area D)-(Area A+Area B)≧2.0 3. A multi-piece solid golf ball according to claim 1 or 2, which satisfies the above requirements. 6. In the hardness distribution of the above core, the following two equations are used (Area C)-(Area A+Area B)≧2.0 (Area D)-(Area A+Area B)≧2.0 6. A multi-piece solid golf ball as described in 5 above which satisfies the above requirements. 7. The multi-piece solid golf ball according to 1 or 2 above, wherein the cover material has a Shore D hardness of 30 to 43. 8. The multi-piece solid golf ball according to 1 or 2 above, wherein the cover has a thickness of 0.6 to 1.2 mm. 9. The relationship between the surface hardness of the intermediate layer-coated sphere and the surface hardness of the ball is expressed by the following formula: (Surface hardness of ball) < (Surface hardness of intermediate layer-coated sphere) (However, hardness refers to Shore C hardness.) 3. A multi-piece solid golf ball according to claim 1 or 2, which satisfies the above requirements. 10. The core comprises the following components (A) to (D): (A) Base rubber (B) Organic peroxide (C)Water (D) Sulfur 3. The multi-piece solid golf ball according to the above 1 or 2, which is formed from a rubber composition containing 11. The multi-piece solid golf ball according to the above 1 or 2, wherein the mass ratio (D) / (C) of the component (C) to the component (D) is 0.020 to 0.200. Effect of the Invention

[0010] According to the golf ball of the present invention, in response to the possibility that the rules will be changed to restrict the distance of long hitters by changing the test conditions for the overall distance standard (ODS) of golf balls in the future, the distance by which the distance is lost for long hitters when hitting with a driver is increased and the distance by which the distance is lost for average hitters when hitting with a driver (W#1) and when hitting with an iron is decreased, rather than simply reducing the distance, thereby reducing the impact on play other than the reduction in the distance of the long hitter's driver shot. Furthermore, when used by professionals and advanced players, the golf ball of the present invention reduces the distance of the driver (W#1) compared to conventional tour balls, but increases the level of spin in the short game, thereby improving the short game characteristics. Furthermore, the golf ball of the present invention satisfies the needs of professionals and advanced players by making it easier to stop the ball at the target without increasing the run when hitting with an iron. [Brief description of the drawings]

[0011] [Figure 1] 1 is a schematic cross-sectional view of a golf ball according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic diagram illustrating areas A to D of the core hardness distribution, using core hardness distribution data of Example 1. [Diagram 3] 2 is a graph showing the core hardness distribution of Examples 1 to 4 and Comparative Examples 1 to 9. [Figure 4]1 is a graph showing values ​​of Ciw+Miw in Examples 1 to 4 and Comparative Examples 1 to 9. [Diagram 5] FIG. 2 shows the arrangement (pattern) of dimples (1) to (4) used in Examples 1 to 4 and Comparative Examples 1 to 9, where (A) shows a plan view of the dimples and (B) shows a side view thereof. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The present invention will now be described in further detail. The multi-piece solid golf ball of the present invention has a core, an intermediate layer, and a cover, and an example thereof is shown in FIG. 1. The golf ball G shown in FIG. 1 has a single-layer core 1, a single-layer intermediate layer 2 covering the core 1, and a single-layer cover 3 covering the intermediate layer. This cover 3 is located at the outermost layer in the layer structure of the golf ball, excluding the paint layer. Each layer of the core and the intermediate layer can be formed as a single layer as shown in FIG. 1, or multiple layers. A large number of dimples D are formed on the surface of the cover (outermost layer) 3 in order to achieve the aerodynamic characteristics targeted by the present invention. In addition, a paint layer is usually formed on the surface of the cover 3, although not shown in the figure. Each of the above layers will be described in detail below.

[0013] The core is obtained by vulcanizing a rubber composition mainly made of rubber material. If the core material is not a rubber composition, the core will have low resilience, and the average hitter may not be able to achieve the desired flight distance when hitting with a driver (W#1) or iron. This rubber composition is usually made mainly of base rubber, and is obtained by compounding a co-crosslinking agent, a crosslinking initiator, an inert filler, an organic sulfur compound, etc.

[0014] The core may be, in particular, the following components (A) to (D): (A) Base rubber (B) Organic peroxide (C)Water (D) Sulfur It is preferable that the rubber composition contains

[0015] The (A) base rubber may contain a diene rubber, such as polybutadiene, natural rubber, isoprene rubber, or ethylene propylene diene rubber.

[0016] As the (B) organic peroxide, it is preferable to use an organic peroxide with a relatively high thermal decomposition temperature. Specifically, an organic peroxide with a high one-minute half-life temperature of about 165 to 185°C is used, and for example, dialkyl peroxides can be mentioned. As dialkyl peroxides, for example, dicumyl peroxide ("Percumyl D" manufactured by NOF Corp.), 2,5-dimethyl-2,5-di(t-butylperoxy)hexane ("Perhexa 25B" manufactured by NOF Corp.), di(2-t-butylperoxyisopropyl)benzene ("Perbutyl P" manufactured by NOF Corp.) can be mentioned, and dicumyl peroxide can be preferably used. These may be used alone or in combination of two or more. The half-life is one of the indicators showing the degree of the decomposition rate of an organic peroxide, and is indicated by the time required for the original organic peroxide to decompose and the amount of active oxygen to be reduced to 1 / 2. The vulcanization temperature of the rubber composition for the core is usually within the range of 120 to 190° C., and within this range, organic peroxides with a high one-minute half-life temperature of about 165° C. to 185° C. undergo thermal decomposition relatively slowly. According to the rubber composition used in the present invention, it is possible to obtain a core, which is a cross-linked rubber product having a specific internal hardness profile described later, by adjusting the amount of free radicals produced, which increases with the passage of vulcanization time.

[0017] The water (C) is not particularly limited and may be distilled water or tap water, but it is particularly preferred to use distilled water that does not contain impurities. The amount of water blended is preferably 0.1 part by mass or more, more preferably 0.2 part by mass or more, per 100 parts by mass of the base rubber, and the upper limit is preferably 2 parts by mass or less, more preferably 1 part by mass or less.

[0018] By directly blending water or a material containing water as component (C) into the core material, the decomposition of the organic peroxide during the core blending can be promoted. It is also known that the decomposition efficiency of the organic peroxide in the rubber composition for the core changes depending on the temperature, and the higher the temperature, the higher the decomposition efficiency. If the temperature is too high, the amount of decomposed radicals becomes too large, and the radicals recombine with each other or become inactivated. As a result, the radicals that work effectively for crosslinking decrease. Here, when the organic peroxide decomposes during the core vulcanization and generates decomposition heat, the temperature near the core surface remains almost the same as that of the vulcanization mold, but the temperature near the core center becomes much higher than the mold temperature because the decomposition heat of the organic peroxide that decomposed from the outside accumulates. When water or a material containing water is directly blended into the core, the water acts to promote the decomposition of the organic peroxide, so the above-mentioned radical reaction can be changed between the core center and the core surface. In other words, the decomposition of the organic peroxide is further promoted near the center of the core, and the inactivation of radicals is further promoted, further reducing the amount of available radicals, making it possible to obtain a core having a significantly different crosslink density between the core center and the core surface, and also a core having different dynamic viscoelastic properties in the center of the core.

[0019] Specific examples of (D) sulfur include products under the trade names "Sunmix S-80N" (manufactured by Sanshin Chemical Industry Co., Ltd.) and "Sulfax-5" (manufactured by Tsurumi Chemical Industry Co., Ltd.). The amount of sulfur may be more than 0, and is preferably 0.005 parts by mass or more, and more preferably 0.01 parts by mass or more, per 100 parts by mass of the base rubber. There is no particular upper limit to the amount of sulfur, but it is preferably 0.1 parts by mass or less, more preferably 0.05 parts by mass or less, and even more preferably 0.03 parts by mass or less. The addition of sulfur can increase the hardness difference of the core. If the amount of sulfur is too large, the resilience may be significantly reduced, or the durability against repeated impact may be reduced.

[0020] The mass ratio (D) / (C) of the above-mentioned (C) component to the (D) component is preferably 0.020 or more, more preferably 0.030 or more, and even more preferably 0.035 or more, and the upper limit is preferably 0.200 or less, more preferably 0.160 or less, and even more preferably 0.120 or less. If the above-mentioned numerical range is exceeded, it becomes difficult to achieve the desired core hardness distribution, and it may become impossible to achieve both an advantageous flight distance when hitting with a driver (W#1) or an iron by an average hitter due to the low spin effect during a full shot and good durability against repeated hitting. Note that the above-mentioned (D) component means the mass of the sulfur component contained in the product, not the mass of the sulfur product itself.

[0021] The rubber composition may contain, as components other than the components (A) to (D), a co-crosslinking agent, a filler, an antioxidant, an organic sulfur compound, and the like.

[0022] 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, and fumaric acid, with acrylic acid and methacrylic acid being particularly preferred. Metal salts of unsaturated carboxylic acids are not particularly limited, but include, for example, those obtained by neutralizing the above-mentioned unsaturated carboxylic acids with desired metal ions. Specific examples include zinc salts and magnesium salts of methacrylic acid and acrylic acid, with zinc acrylate being particularly preferred.

[0023] The unsaturated carboxylic acid and / or metal salt thereof is blended in an amount of usually at least 5 parts by weight, preferably at least 9 parts by weight, and more preferably at least 13 parts by weight, with the upper limit usually not exceeding 60 parts by weight, preferably not exceeding 50 parts by weight, and more preferably not exceeding 40 parts by weight, per 100 parts by weight of the base rubber. If the blended amount is too high, the ball may become too hard, resulting in an unbearable feel on impact, whereas if the blended amount is too low, the resilience may decrease.

[0024] As the filler, for example, zinc oxide, barium sulfate, calcium carbonate, etc. can be suitably used. These may be used alone or in combination of two or more. The amount of the filler is preferably 4 parts by mass or more, more preferably 8 parts by mass or more, and even more preferably 12 parts by mass or more, per 100 parts by mass of the base rubber. The upper limit of the amount is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 30 parts by mass or less, per 100 parts by mass of the base rubber. If the amount is too large or too small, it may not be possible to obtain the appropriate mass and suitable resilience.

[0025] As the antioxidant, for example, commercially available products such as Nocrac NS-6, Nocrac NS-30, Nocrac 200, Nocrac MB (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) can be used. These may be used alone or in combination of two or more kinds.

[0026] The amount of antioxidant is not particularly limited, but is preferably at least 0.05 parts by weight, more preferably at least 0.1 parts by weight, and the upper limit is preferably no more than 1.0 part by weight, more preferably no more than 0.7 parts by weight, and even more preferably no more than 0.5 parts by weight, per 100 parts by weight of base rubber. If the amount is too large or too small, the appropriate core hardness gradient may not be obtained, and suitable resilience, durability, and low spin effect on full shots may not be obtained.

[0027] The organic sulfur compound can be blended in order to control the resilience of the core.Specifically, it is recommended to blend thiophenol, thionaphthol, halogenated thiophenol or their metal salts as the organic sulfur compound.More specifically, it can be pentachlorothiophenol, pentafluorothiophenol, pentabromothiophenol, parachlorothiophenol, zinc salt of pentachlorothiophenol, diphenyl polysulfide, dibenzyl polysulfide, dibenzoyl polysulfide, dibenzothiazoyl polysulfide, dithiobenzoyl polysulfide, etc., which have 2 to 4 sulfurs, and it is particularly preferable to use the zinc salt of pentachlorothiophenol and diphenyl disulfide.

[0028] The upper limit of the amount of the organic sulfur compound is preferably 5 parts by weight or less, more preferably 4 parts by weight or less, even more preferably 3 parts by weight or less, and most preferably 2 parts by weight or less, per 100 parts by weight of the base rubber. If the amount is too high, the core may become too soft, or the core may become too resilient, resulting in too long a flight distance when hit with a driver by a long hitter. On the other hand, the lower limit of the amount is preferably 0.1 parts by weight or more, more preferably 0.2 parts by weight or more, and even more preferably 0.3 parts by weight or more, per 100 parts by weight of the base rubber. If the amount is too low, the core may become too resilient, resulting in too short a flight distance when hit with a driver by an average hitter and when hit with an iron by both a long hitter and an average hitter.

[0029] The core can be produced by vulcanizing and curing a rubber composition containing the above-mentioned components. For example, the rubber composition is kneaded using a kneading machine such as a Banbury mixer or a roll, compression molded or injection molded using a core mold, and the molded body is appropriately heated at a temperature sufficient for the organic peroxide and co-crosslinking agent to act, that is, 100 to 200°C, preferably 140 to 180°C, for 10 to 40 minutes, to cure the molded body.

[0030] In the present invention, the core is formed in a single layer or multiple layers, but is preferably formed in a single layer. If a rubber core is made of multiple layers, peeling may occur at the interface when repeatedly struck, leading to early cracking.

[0031] The diameter of the core is preferably 37.5 mm or more, more preferably 38.0 mm or more, and even more preferably 38.4 mm or more. The upper limit of this diameter is preferably 40.0 mm or less, more preferably 39.4 mm or less, and even more preferably 38.8 mm or less. If the core diameter is too small, the initial velocity of the ball may be too low, or the deflection of the entire ball may be small, and the spin rate of the ball may increase during a full shot, making it impossible for an average hitter to achieve the desired flight distance when hitting with a driver (W#1) or an iron. On the other hand, if the core diameter is too large, the spin rate of the ball may increase during a full shot, making it impossible for an average hitter to achieve the desired flight distance, or the durability against cracking may be poor when hitting repeatedly.

[0032] The deflection (mm) of the core when an initial load of 98N (10kgf) to a final load of 1,275N (130kgf) is applied is not particularly limited, but is preferably 2.5mm or more, more preferably 2.7mm or more, and even more preferably 2.9mm or more, with the upper limit being preferably 3.9mm or less, more preferably 3.7mm or less, and even more preferably 3.5mm or less. If the deflection of the core is too small, i.e., if the core is too hard, the average hitter may not be able to achieve the desired flight distance when hitting with a driver (W#1) or with an iron, or the hitting feel may be too hard. On the other hand, if the deflection of the core is too large, i.e., if the core is too soft, the resilience of the ball may be too low, so that the average hitter cannot fly the ball, or the hitting feel may be too soft, or the cracking durability during repeated hitting may be poor, and the run during hitting with an iron may be too large.

[0033] Next, the hardness distribution of the core will be described. Note that the hardness of the core described below refers to Shore C hardness. This Shore C hardness is a hardness value measured using a Shore C hardness tester conforming to the ASTM D2240 standard.

[0034] The center hardness (Cc) of the core is preferably 57 or more, more preferably 59 or more, and even more preferably 61 or more, with the upper limit being preferably 69 or less, more preferably 67 or less, and even more preferably 66 or less. If this value is too large, the amount of spin increases on a full shot, and the average hitter cannot obtain the desired distance when hitting with a driver (W#1) or with an iron, or the hitting feel may be too hard. On the other hand, if the value is too small, the resilience decreases, and the average hitter cannot obtain the desired distance when hitting with a driver (W#1), or the durability to cracking when hit repeatedly decreases, or the run increases when hitting with an iron, which may not satisfy the needs of professionals or advanced players.

[0035] The hardness (Cc+4) at a position 4 mm outward from the center of the core is preferably at least 61, more preferably at least 63, and even more preferably at least 65, with the upper limit being preferably not more than 70, more preferably not more than 68, and even more preferably not more than 67. Any deviation from these hardness limits may result in the same adverse effects as those described for the center hardness (Cc) of the core.

[0036] The hardness (Cm) at the midpoint M between the center and the surface of the core is not particularly limited, but is preferably at least 62, more preferably at least 64, and even more preferably at least 66. There is also no particular upper limit, but it is preferably not more than 72, more preferably not more than 70, and even more preferably not more than 68. Any deviation from these hardness limits may result in the same adverse effects as those described for the center hardness (Cc) of the core.

[0037] The hardness (Cm-4) at a position 4 mm inward from the middle position M of the core is not particularly limited, but is preferably at least 61, more preferably at least 63, and even more preferably at least 65, and there is no upper limit either, but is preferably not more than 70, more preferably not more than 68, and even more preferably not more than 67. Any deviation from these hardness limits may result in the same adverse effects as those described for the center hardness (Cc) of the core.

[0038] The surface hardness (Cs) of the core is preferably 80 or more, more preferably 83 or more, and even more preferably 85 or more, with the upper limit being preferably 91 or less, more preferably 89 or less, and even more preferably 88 or less. If this value is too large, durability against cracking during repeated impacts may deteriorate, or the hitting feel may be too hard. On the other hand, if this value is too small, the resilience may decrease, or the spin rate during full shots may increase, preventing the average hitter from achieving the desired flying distance when hitting with a driver (W#1) or an iron.

[0039] The hardness (Cs-4) at a position 4 mm inward from the surface of the core is preferably at least 75, more preferably at least 76, and even more preferably at least 78, with the upper limit being preferably not more than 85, more preferably not more than 84, and even more preferably not more than 82. Any deviation from these hardness limits may result in the same adverse effects as those described for the surface hardness (Cs) of the core.

[0040] The hardness (Cm+4) at a position 4 mm outward from the middle position M of the core is not particularly limited, but is preferably at least 69, more preferably at least 71, and even more preferably at least 73, and there is no upper limit either, but is preferably not more than 79, more preferably not more than 77, and even more preferably not more than 75. Any deviation from these hardness limits may result in the same adverse effects as those described for the surface hardness (Cs) of the core.

[0041] The value obtained by subtracting the center hardness from the surface hardness of the core, i.e., the value of Cs-Cc, is preferably 17 or more, more preferably 21 or more, and even more preferably 22 or more, with the upper limit being preferably 32 or less, more preferably 29 or less, and even more preferably 26 or less. If this value is too small, the amount of spin increases when a full shot is made, and the average hitter may not be able to achieve the desired flight distance when hitting with a driver (W#1) or with an iron. On the other hand, if this value is too large, the resilience decreases, and the average hitter may not be able to achieve the desired flight distance when hitting with a driver (W#1) or with an iron, or the durability to cracking during repeated hitting may deteriorate.

[0042] In addition, it is preferable to optimize the value of (Cs-Cc) / (Cm-Cc) for the hardness distribution of the core. The value of (Cs-Cc) indicates the hardness difference between the center and the surface of the core, and the value of (Cm-Cc) indicates the hardness difference between the center of the core and the intermediate position M between the surface of the core and the center of the core, and the above formula represents the ratio of these hardness differences. The value of (Cs-Cc) / (Cm-Cc) is preferably 4.0 or more, more preferably 5.0 or more, and even more preferably 6.0 or more, and the upper limit is preferably 15.0 or less, more preferably 12.0 or less, and even more preferably 10.0 or less. If this value is too small, the spin amount increases when a full shot is made, and the desired flight distance may not be obtained when an average hitter hits with a driver (W#1) or an iron. On the other hand, if this value is too large, the resilience will be low, and the desired distance will not be achieved when an average hitter hits with a driver (W#1) or when both long hitters and average hitters hit with an iron, or the durability to cracking when hit repeatedly may be poor.

[0043] In the above core hardness distribution, the following areas A to D ·Area A: 1 / 2×4×(Cc+4-Cc) ·Area B: 1 / 2×4×(Cm-Cm-4) ·Area C: 1 / 2×4×(Cm+4-Cm) ·Area D: 1 / 2×4×(Cs-Cs-4) Regarding the above, the value of (area C + area D) - (area A + area B) is preferably 4.0 or more, more preferably 7.0 or more, more preferably 10.0 or more, and the upper limit is preferably 35.0 or less, more preferably 30.0 or less, and even more preferably 25.0 or less. If this value is too small, the amount of spin increases when a full shot is made, and the desired flight distance may not be obtained when an average hitter hits the ball with a driver (W#1) or an iron. On the other hand, if this value is too large, the resilience decreases, and the desired flight distance may not be obtained when an average hitter hits the ball with a driver (W#1) or an iron, or the durability to cracking may deteriorate when hit repeatedly.

[0044] Also, the value of (area C)-(area A+area B) is preferably 4.0 or more, more preferably 5.0 or more, and more preferably 6.0 or more, and the upper limit is preferably 20.0 or less, more preferably 15.0 or less, and even more preferably 12.0 or less. If this value is too small, the amount of spin increases when a full shot is made, and the desired flight distance may not be obtained when an average hitter hits the ball with a driver (W#1) or an iron. On the other hand, if this value is too large, the resilience decreases, and the desired flight distance may not be obtained when an average hitter hits the ball with a driver (W#1) or an iron, or the durability to cracking may deteriorate when hit repeatedly.

[0045] Furthermore, the value of (area D)-(area A+area B) is preferably 4.0 or more, more preferably 5.0 or more, and more preferably 6.0 or more, and the upper limit is preferably 20.0 or less, more preferably 15.0 or less, and even more preferably 12.0 or less. If this value is too small, the amount of spin increases when a full shot is made, and the desired flight distance may not be obtained when an average hitter hits the ball with a driver (W#1) or an iron. On the other hand, if this value is too large, the resilience decreases, and the desired flight distance may not be obtained when an average hitter hits the ball with a driver (W#1) or an iron, or the durability to cracking may deteriorate when hit repeatedly.

[0046] 2 is a schematic diagram illustrating areas A to F using the core hardness distribution data of Example 1. Areas A to D are the areas of triangles whose bases are the differences in specific distances and whose heights are the differences in hardness at each position.

[0047] The initial velocity of the core is preferably 75.6 m / s or more, more preferably 76.0 m / s or more, and even more preferably 76.5 m / s or more, with the upper limit being 78.0 m / s or less, preferably 77.2 m / s or less, and more preferably 76.9 m / s or less. If this initial velocity value is too high, the reduction in flight distance compared to the current tour ball may not be sufficient when a long hitter hits the ball with a driver, and the ball may fly longer than the standard distance of the new flight distance rule envisaged by R&A and USGA. On the other hand, if this initial velocity value is too low, the average hitter may not be able to obtain the desired flight distance when hitting the ball with a driver (W#1) or with an iron. The initial velocity value in this case is a value measured by a COR type initial velocity meter of the same type as that of R&A. Specifically, a COR type initial velocity device manufactured by Hye Precision in the United States is used. The conditions for the measurement are as follows: the air pressure is changed in four stages, a relational equation between the incident velocity and COR is constructed, and the initial velocity at an incident velocity of 43.83 m / s is calculated from this relational equation. The measurement environment for the COR type initial velocity device is as follows: a ball that has been kept in a thermostatic chamber adjusted to 23.9±1°C for more than three hours is used, and measurements are taken at room temperature of 23.9±2°C. The barrel diameter is selected so that the clearance on one side between the barrel and the outer diameter of the object being measured is between 0.2 and 2.0 mm.

[0048] The initial velocity of the core is V C (m / s), and the deflection amount C (mm) when the core is loaded with an initial load of 98N (10kgf) to a final load of 1,275N (130kgf), the value of Vc / C is preferably 17 or more, more preferably 19 or more, and even more preferably 21 or more, and the upper limit is preferably 30 or less, more preferably 28 or less, and even more preferably 26 or less. If this value is too large, the reduction in flight distance compared to the current tour ball may not be sufficient when a long hitter hits with a driver, and the ball may fly longer than the standard distance of the new flight distance rule envisaged by the R&A and the USGA. On the other hand, if the value is too small, the average hitter may not be able to obtain the desired flight distance when hitting with a driver (W#1) or with an iron.

[0049] When the value of (initial velocity of core x mass of core) is Ciw, Ciw means a value showing the repulsion of the core material part in relation to its mass part. Ciw is preferably 2600 or more, more preferably 2640 or more, and even more preferably 2670 or more, and the upper limit is preferably 2770 or less, more preferably 2740 or less, and even more preferably 2710 or less. If this value deviates from the above range, the average hitter may not be able to obtain the desired flight distance when hitting with a driver (W#1) or when hitting with an iron, or the run may become too large when hitting with an iron, failing to satisfy the needs of professionals and advanced players.

[0050] When the core is loaded with an initial load of 98N (10kgf) to a final load of 1,275N (130kgf), the deflection (mm) is defined as C (mm). The value of Ciw / C means the distribution amount for a certain deflection in a quantitative index obtained by multiplying the resilience of the core material by its mass. Ciw / C is preferably 700 or more, more preferably 730 or more, and even more preferably 760 or more, and the upper limit is preferably 1000 or less, more preferably 970 or less, and even more preferably 930 or less. If this value deviates from the above range, the average hitter may not be able to obtain the desired flight distance when hitting with a driver (W#1) or with an iron, or the run when hitting with an iron may become too large, failing to satisfy the needs of professionals and advanced players.

[0051] Next, the intermediate layer will be described. The material hardness of the intermediate layer is not particularly limited, but is preferably 90 or more, more preferably 92 or more, and even more preferably 93 or more in Shore C hardness, with the upper limit being preferably 100 or less, more preferably 98 or less, and even more preferably 96 or less. The Shore D hardness is preferably 61 or more, more preferably 63 or more, and even more preferably 65 or more, with the upper limit being preferably 72 or less, more preferably 70 or less, and even more preferably 67 or less.

[0052] The surface hardness of a sphere having a core covered with an intermediate layer (intermediate layer covered sphere) is preferably 95 or more, more preferably 96 or more, and even more preferably 97 or more, in Shore C hardness, with the upper limit being preferably 100 or less, more preferably 99 or less, and even more preferably 98 or less. The surface hardness of a Shore D hardness is preferably 68 or more, more preferably 69 or more, and even more preferably 70 or more, with the upper limit being preferably 78 or less, more preferably 75 or less, and even more preferably 72 or less.

[0053] If the material hardness and surface hardness of these intermediate layers are too softer than the above ranges, the amount of spin may be too much on a full shot, or the initial velocity of the actual shot may be low, resulting in a loss of distance when an average hitter hits with a driver (W#1) or an iron.On the other hand, if the material hardness and surface hardness of the intermediate layers are too hard than the above ranges, the durability against cracking during repeated hits may be poor, or the feel of the shot may be hard when using a putter or on a short approach, or it may be difficult to apply spin when approaching.

[0054] The thickness of the intermediate layer is preferably 0.9 mm or more, more preferably 1.0 mm or more, and even more preferably 1.1 mm or more. On the other hand, the upper limit of the thickness of the intermediate layer is preferably 1.6 mm or less, more preferably 1.4 mm or less, and even more preferably 1.3 mm or less. In addition, it is preferable that the thickness of the intermediate layer is thicker than the cover described below. If the thickness of the intermediate layer is out of the above range or is thinner than the cover, the low spin effect of the ball when hit with a driver (W#1) is insufficient, and the target flight distance may not be achieved when hit with a driver (W#1) or an iron by an average hitter. In addition, if the intermediate layer is too thin, the crack durability during repeated hits may be deteriorated. On the other hand, if the thickness of the intermediate layer is too thicker than the above range, the hitting feeling may be deteriorated.

[0055] The value obtained by subtracting the cover thickness from the intermediate layer thickness is preferably greater than 0 mm, more preferably 0.2 mm or more, and even more preferably 0.3 mm or more, with the upper limit being preferably 0.8 mm or less, more preferably 0.6 mm or less, and even more preferably 0.4 mm or less. If this value is out of the above range, the amount of spin of the ball on a full shot increases, the initial velocity of the actual shot decreases, and the average hitter may not achieve the desired flying distance when hitting with a driver (W#1) or an iron. On the other hand, if this value is too small, the durability against cracking when repeatedly hitting may be poor.

[0056] It is preferable to use an ionomer resin as the main material for the intermediate layer. When using an ionomer resin as the main material, it is preferable to use a mixture of zinc-neutralized ionomer resin and sodium-neutralized ionomer resin as the main material. The blending ratio of zinc-neutralized / sodium-neutralized (mass ratio) is 5 / 95 to 95 / 5, preferably 10 / 90 to 90 / 10, and more preferably 15 / 85 to 85 / 15. If the Zn-neutralized ionomer and the Na-neutralized ionomer are not included in this ratio, the resilience becomes too low and the average hitter may not be able to achieve the desired flight distance when hitting with a driver (W#1) or an iron, and further, the durability against cracking may be deteriorated when hitting repeatedly at room temperature or at low temperatures (below zero).

[0057] In addition, the ionomer resin material preferably contains a high-acid content ionomer resin having an unsaturated carboxylic acid content (also referred to as "acid content") of 16% by mass or more.

[0058] The content of the high acid content ionomer resin is preferably 25% by mass or more, more preferably 50% by mass or more, and even more preferably 75% by mass or more, with the upper limit being preferably 100% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less, based on 100% by mass of the resin material. If the amount of the high acid content ionomer resin is too small, the ball may have a large spin rate upon full shot, resulting in a loss of flight distance. On the other hand, if the amount of the high acid content ionomer resin is too large, the durability against repeated impacts may be poor.

[0059] Any additives can be appropriately blended into the intermediate layer material depending on the application. For example, various additives such as pigments, dispersants, anti-aging agents, UV absorbers, and light stabilizers can be added. When these additives are blended, the blending amount is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and the upper limit is preferably 10 parts by mass or less, more preferably 4 parts by mass or less, relative to 100 parts by mass of the base resin.

[0060] It is preferable to polish the surface of the intermediate layer material to improve adhesion with the polyurethane that is preferably used in the cover material described below. Furthermore, after the polishing process, it is preferable to apply a primer (adhesive) to the intermediate layer surface or to add an adhesion enhancer to the material.

[0061] The deflection (mm) of a ball having a core covered with an intermediate layer (intermediate layer covered ball) when an initial load of 98N (10kgf) to a final load of 1,275N (130kgf) is applied is preferably 2.1mm or more, more preferably 2.3mm or more, and even more preferably 2.5mm or more. On the other hand, the upper limit of the deflection is preferably 3.4mm or less, more preferably 3.1mm or less, and even more preferably 2.9mm or less. If the deflection of the intermediate layer covered ball is too small, that is, if it is too hard, the spin rate increases too much, and the average hitter may not be able to achieve the desired flight distance when hitting with a driver (W#1) and both long hitters and average hitters may not be able to achieve the desired flight distance when hitting with an iron, or the hitting feel may be too hard. On the other hand, if the deflection is too large, i.e., the sphere is too soft, the amount of spin will be reduced and the run will be too long when hit with an iron, making it difficult to control the desired distance, the hitting feel will be too soft, or the durability to cracking when hit repeatedly will be poor.

[0062] The initial velocity of a ball (intermediate layer-coated ball) in which a core is covered with an intermediate layer is preferably 76.5 m / s or more, more preferably 77.0 m / s or more, and even more preferably 77.3 m / s or more, with the upper limit being preferably 78.5 m / s or less, more preferably 78.0 m / s or less, and even more preferably 77.7 m / s or less. If this initial velocity value is too high, the reduction in flight distance compared to the current tour ball may not be sufficient when a long hitter hits with a driver, and the ball may fly longer than the standard distance of the new flight distance rule envisaged by the R&A and the USGA. On the other hand, if this initial velocity is too low, the average hitter may not be able to achieve the flight distance when hitting with a driver (W#1) or with an iron. The initial velocity value in this case is the same as that of the device and conditions used in measuring the initial velocity of the core described above.

[0063] The initial velocity of the intermediate layer-coated sphere is V M (m / s), the deflection amount when the intermediate layer coated sphere is loaded from an initial load of 98N (10kgf) to a final load of 1,275N (130kgf) is M (mm), V MThe value of / M is preferably 22 or more, more preferably 24 or more, and even more preferably 26 or more, with the upper limit being preferably 36 or less, more preferably 33 or less, and even more preferably 30 or less. If this value is too large, the loss in distance compared to current tour balls may not be sufficient when a long hitter hits the ball with a driver, and the ball may fly longer than the standard distance of the new distance rule envisaged by the R&A and USGA. On the other hand, if the value is too small, the average hitter may not be able to achieve the desired distance when hitting the ball with a driver (W#1).

[0064] In addition, it is preferable to optimize the value (Miw) of the relational expression between the initial velocity of the core (m / s), the initial velocity of the intermediate layer-covered sphere (m / s), the mass of the core (g), and the mass of the intermediate layer-covered sphere (g), [(initial velocity of the intermediate layer-covered sphere-initial velocity of the core) x (mass of the intermediate layer-covered sphere-mass of the core)]. This value means a value that indicates the repulsion of the intermediate layer material part in relation to its mass part. The above Miw value is preferably 2 or more, more preferably 3 or more, and even more preferably 4 or more, and the upper limit is preferably 7 or less, more preferably 6 or less, and even more preferably 5 or less. If this value is too large, the durability against repeated impacts may become too poor. On the other hand, if the above value is too small, the amount of spin of the ball when a full shot is made increases, and the average hitter may not be able to achieve the distance when hitting with a driver (W#1) or an iron.

[0065] Next, the cover will be described. The material hardness of the cover is not particularly limited, but the Shore C hardness is preferably 50 or more, more preferably 55 or more, and even more preferably 61 or more, with the upper limit being preferably 67 or less, more preferably 66 or less, and even more preferably 63 or less. The Shore D hardness is preferably 30 or more, more preferably 34 or more, and even more preferably 38 or more, with the upper limit being preferably 43 or less, more preferably 42 or less, and even more preferably 40 or less.

[0066] The surface hardness of a sphere (ball) obtained by covering an intermediate layer-covered sphere with a cover, in Shore C hardness, is preferably 78 or more, more preferably 80 or more, and even more preferably 82 or more, with the upper limit being preferably 88 or less, more preferably 86 or less, and even more preferably 84 or less. The Shore D hardness is preferably 50 or more, more preferably 53 or more, and even more preferably 55 or more, with the upper limit being preferably 59 or less, more preferably 58 or less, and even more preferably 57 or less.

[0067] If the material hardness and surface hardness of these covers are softer than the above ranges, the amount of spin increases on full shots, and the average hitter may not achieve the desired distance when hitting with a driver (W#1) or an iron. On the other hand, if the material hardness and surface hardness of the cover are harder than the above ranges, the spin may not be applied on approaches, or the abrasion resistance may be poor. In addition, the distance may be too long when hitting with a driver (W#1) by a long hitter, and this may not comply with the new overall distance standard (ODS) rules, which may be changed in the future.

[0068] The thickness of the cover is preferably 0.60 mm or more, more preferably 0.65 mm or more, and even more preferably 0.70 mm or more. On the other hand, the upper limit of the cover thickness is preferably 1.10 mm or less, more preferably 0.90 mm or less, and even more preferably 0.85 mm or less. If the cover is too thick, the resilience of the ball may be insufficient on a full shot, or the amount of spin may be increased, resulting in a lack of distance when the average hitter hits the ball with a driver (W#1) or an iron. On the other hand, if the cover is too thin, the abrasion resistance may be poor, or the spin may not be applied on an approach shot, resulting in a lack of controllability.

[0069] As the material for the cover, various urethane resins used in golf ball cover materials can be used from the viewpoints of spin controllability and abrasion resistance in the short game. Furthermore, from the viewpoint of mass production, it is preferable to use a resin material mainly composed of thermoplastic polyurethane. Furthermore, it is preferable to form the cover from a resin blend mainly composed of (I) thermoplastic polyurethane and (II) a polyisocyanate compound.

[0070] The total weight of the above components (I) and (II) is preferably 60% or more, and more preferably 70% or more, based on the total weight of the resin composition of the cover. The above components (I) and (II) are described in detail below.

[0071] Regarding the above (I) thermoplastic polyurethane, the structure of the thermoplastic polyurethane includes a soft segment made of a polymer polyol (polymeric glycol) which is a long-chain polyol, and a hard segment made of a chain extender and a polyisocyanate compound. Here, as the long-chain polyol used as the raw material, any one that has been used in the technology related to thermoplastic polyurethanes can be used, and there is no particular limitation. For example, polyester polyol, polyether polyol, polycarbonate polyol, polyester polycarbonate polyol, polyolefin polyol, conjugated diene polymer polyol, castor oil polyol, silicone polyol, vinyl polymer polyol, etc. can be mentioned. These long-chain polyols may be used alone or in combination of two or more kinds. Among these, polyether polyol is preferred in that it can synthesize a thermoplastic polyurethane with a high resilience modulus and excellent low-temperature properties.

[0072] As the chain extender, those used in conventional techniques related to thermoplastic polyurethanes can be suitably used, and for example, a low molecular weight compound having two or more active hydrogen atoms in the molecule that can react with an isocyanate group and 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, etc. Among these, as the chain extender, an aliphatic diol having 2 to 12 carbon atoms is preferable, and 1,4-butylene glycol is more preferable.

[0073] The polyisocyanate compound may be suitably used in the conventional technology related to thermoplastic polyurethane, and is not particularly limited. Specifically, one or more selected from the group consisting of 4,4'-diphenylmethane diisocyanate, 2,4-(or) 2,6-toluene diisocyanate, p-phenylene diisocyanate, xylylene diisocyanate, naphthylene 1,5-diisocyanate, tetramethyl xylene diisocyanate, hydrogenated xylylene diisocyanate, dicyclohexylmethane diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, norbornene diisocyanate, trimethylhexamethylene diisocyanate, and dimer acid diisocyanate may be used. However, some isocyanate species may be difficult to control the crosslinking reaction during injection molding. In the present invention, from the viewpoint of the balance between stability during production and the physical properties exhibited, 4,4'-diphenylmethane diisocyanate, which is an aromatic diisocyanate, is most preferred.

[0074] Specific examples of thermoplastic polyurethanes that can be used as the component (I) include commercially available products such as Pandex T8295, T8290, and T8260 (all manufactured by DIC Covestro Polymers).

[0075] Although not a required component, a thermoplastic elastomer other than the thermoplastic polyurethane can be blended as component (III) to the above components (I) and (II). By blending component (III) with the resin blend, it is possible to further improve the flowability of the resin blend and to enhance various physical properties required for a golf ball cover material, such as resilience and abrasion resistance.

[0076] There are no particular limitations on the composition ratio of the above components (I), (II) and (III). However, in order to fully and effectively exert the effects of the present invention, the mass ratio is preferably (I):(II):(III)=100:2-50:0-50, and more preferably (I):(II):(III)=100:2-30:8-50 (mass ratio).

[0077] Furthermore, various additives other than the components constituting the thermoplastic polyurethane may be blended into the above-mentioned resin blend as necessary. For example, pigments, dispersants, antioxidants, light resistance stabilizers, ultraviolet absorbers, release agents, etc. may be appropriately blended.

[0078] The manufacturing method of the multi-piece solid golf ball formed by laminating the above-mentioned core, intermediate layer, and cover (outermost layer) can be performed by a conventional method such as a known injection molding method. For example, the intermediate layer material is injected around the core using an injection mold to obtain a sphere covered with the intermediate layer, and finally, the material of the cover, which is the outermost layer, is injection molded to obtain a multi-piece golf ball. Alternatively, a golf ball can be manufactured by preparing two half cups molded into a spherical half shell in advance, encasing the core and the sphere covered with the intermediate layer in these, and molding them under heat and pressure.

[0079] The deflection (mm) of the golf ball when loaded with an initial load of 98N (10kgf) to a final load of 1,275N (130kgf) is preferably 2.00mm or more, more preferably 2.20mm or more, and even more preferably 2.30mm or more. On the other hand, the upper limit of the deflection is preferably 2.79mm or less, more preferably 2.70mm or less, and even more preferably 2.60mm or less. If the deflection of the golf ball is too small, i.e., if the golf ball is too hard, the spin rate increases too much, and the average hitter may not achieve the desired flight distance when hitting with a driver (W#1) or with an iron, or the hitting feel may be too hard. On the other hand, if the deflection is too large, i.e., if the ball is too soft, the spin rate decreases and the run increases too much when hitting with an iron, making it difficult to control the desired distance, the hitting feel may be too soft, or the durability to cracking during repeated hitting may be poor. Furthermore, the approach shot will not have as much spin, which may result in poor short game performance.

[0080] The initial velocity of a sphere (ball) in which a cover is applied to a sphere covered with an intermediate layer is preferably 76.5 m / s or more, more preferably 76.7 m / s or more, and even more preferably 76.9 m / s or more, with the upper limit being 77.724 m / s or less. If this initial velocity value is too high, it will not satisfy the official rules of the R&A and USGA. On the other hand, if this initial velocity is too low, the average hitter may not be able to achieve the desired flight distance when hitting with a driver (W#1) or an iron. The initial velocity value in this case is the same as that of the device and conditions used in measuring the initial velocity of the core and the intermediate layer covered sphere described above.

[0081] If the initial velocity of the ball is V (m / s) and the deflection amount when the ball is loaded with an initial load of 98N (10kgf) to a final load of 1,275N (130kgf) is B (mm), the value of V / B is preferably 23 or more, more preferably 25 or more, and even more preferably 27 or more, and the upper limit is preferably 35 or less, more preferably 34 or less, and even more preferably 33 or less. If this value is too large, the reduction in flight distance compared to the current tour balls may not be sufficient when a long hitter hits with a driver, and the ball may fly longer than the standard distance of the new flight distance rule envisaged by the R&A and USGA. On the other hand, if the value is too small, the flight distance may not be achieved enough when an average hitter hits with a driver (W#1).

[0082] [ Relationship between midpoint hardness (Cm) of core and hardness of cover material 〕 In the present invention, the relationship between the hardness (Cm) at the midpoint between the surface and center of the core and the material hardness of the cover is expressed by the following formula: Hardness at the midpoint between the surface and center of the core (Cm) > Hardness of the cover material (However, hardness refers to Shore C hardness.) It is necessary to satisfy the above. The value obtained by subtracting the hardness of the cover material from the hardness (Cm) of the core midpoint is greater than 0, preferably greater than 1, more preferably greater than 2, and the upper limit is preferably less than 15, more preferably less than 10, and even more preferably less than 6. If the above value is less than 0, it may be difficult for an average hitter to achieve both advantageous flight distance when hitting with a driver and advantageous spin when approaching in a short game. On the other hand, if the above value is too large, the flight distance when hitting with a driver (W#1) by an average hitter and the flight distance when hitting with an iron by all users may decrease.

[0083] [ Relationship between surface hardness of each sphere 〕 In the present invention, the relationship between the surface hardness of the intermediate layer-covered sphere and the surface hardness of the ball is expressed by the following formula, from the viewpoint of achieving both advantageous flight distance in driver (W#1) shots and full iron shots by an average hitter and controllability in the short game. (Surface hardness of ball) < (Surface hardness of intermediate layer-coated sphere) It is preferable that the following condition is satisfied. The value obtained by subtracting the surface hardness of the ball from the surface hardness of the intermediate layer-covered sphere is, in Shore C hardness, preferably greater than 0, more preferably 4 or more, and even more preferably 7 or more, with the upper limit being preferably 20 or less, more preferably 17 or less, and even more preferably 15 or less. If the above value is 0 or less, it may be difficult for an average hitter to achieve both advantageous flight distances in driver and iron full shots and controllability in short games. On the other hand, if the above value is too large, the flight distances of an average hitter when hitting with a driver (W#1) and when hitting with an iron may be shorter than the target distance.

[0084] The surface hardness of the intermediate layer-covered sphere minus the surface hardness of the core is preferably 5 or more, more preferably 7 or more, and even more preferably 9 or more in Shore C hardness, with the upper limit being preferably 20 or less, more preferably 17 or less, and even more preferably 14 or less. If the hardness deviates from the above range, the amount of spin on the ball increases on a full shot, and the average hitter may not be able to achieve the desired flight distance when hitting with a driver (W#1) or an iron.

[0085] The value obtained by subtracting the center hardness of the core from the surface hardness of the intermediate layer-covered sphere is preferably 27 or more, more preferably 30 or more, and even more preferably 32 or more, and the upper limit is preferably 43 or less, more preferably 40 or less, and even more preferably 37 or less. If the above value is too small, the amount of spin of the ball increases during a full shot, and the desired flight distance may not be obtained when an average hitter hits the ball with a driver (W#1) or with an iron. On the other hand, if the above value is too large, the crack resistance may deteriorate when repeatedly hit, or the initial velocity of the actual hit may decrease, and the desired flight distance may not be obtained when an average hitter hits the ball with a driver (W#1). In addition, the run may increase when hitting the ball with an iron, which may not satisfy the needs of professionals and advanced players.

[0086] [ Core diameter and ball diameter〕 The relationship between the core diameter and the ball diameter, i.e., the value of (core diameter) / (ball diameter) is preferably 0.878 or more, more preferably 0.890 or more, and even more preferably 0.899 or more. On the other hand, the upper limit is preferably 0.937 or less, more preferably 0.923 or less, and even more preferably 0.909 or less. If this value is too small, the initial velocity of the ball will be low, or the amount of deflection of the entire ball will be small, making the ball hard, and the spin rate of the ball will increase during a full shot, and the flight distance of an average hitter when hitting with a driver (W#1) or when hitting with an iron may be shorter than the target. On the other hand, if the above value is too large, the spin rate of the ball will increase during a full shot, and the flight distance of an average hitter when hitting with a driver (W#1) or when hitting with an iron may be shorter than the target, or the durability to cracking during repeated hitting may be deteriorated.

[0087] [ Relationship between the amount of deflection of each sphere 〕 When the deflection (mm) of the core and ball when an initial load of 98N (10kgf) to a final load of 1,275N (130kgf) is applied to each sphere is defined as C (mm) and B (mm), respectively. The value of CB is preferably 0.30mm or more, more preferably 0.40mm or more, and even more preferably 0.50mm or more, and the upper limit is preferably 0.90mm or less, more preferably 0.85mm or less, and even more preferably 0.80mm or less. If this value is too large, the durability against cracking during repeated impacts may be poor, the initial velocity of actual impact may be low, and the average hitter may not be able to achieve the desired flight distance when hitting with a driver (W#1), or the run may be too large when hitting with an iron. On the other hand, if this value is too small, the hitting feeling may be too hard, or the amount of spin may be large when hitting a full shot, and the average hitter may not be able to achieve the desired flight distance when hitting with a driver (W#1) or when hitting with an iron.

[0088] When the core and the intermediate layer-covered sphere are subjected to an initial load of 98 N (10 kgf) and a final load of 1,275 N (130 kgf), respectively, the deflection (mm) is defined as C (mm) and M (mm). The value of CM is preferably 0.30 mm or more, more preferably 0.35 mm or more, and even more preferably 0.40 mm or more, and the upper limit is preferably 0.70 mm or less, more preferably 0.65 mm or less, and even more preferably 0.60 mm or less. If this value is too large, the durability against cracking during repeated impacts may deteriorate, or the initial velocity of actual impact may decrease, making it impossible for an average hitter to obtain the desired flight distance when hitting with a driver (W#1). On the other hand, if this value is too small, the hitting feeling may become too hard, or the amount of spin may increase when a full shot is made, making it impossible for an average hitter to obtain the desired flight distance when hitting with a driver (W#1) or with an iron.

[0089] [ Value of Ciw+Miw The golf ball of the present invention preferably satisfies a predetermined range when the value of (initial velocity of core x mass of core) is Ciw and the value of (initial velocity of intermediate layer-initial velocity of core) x (mass of intermediate layer-mass of core) is Miw. Ciw+Miw means the sum of the values ​​of the repulsion of each part of the core and intermediate layer in relation to its mass part. The lower limit of Ciw+Miw is 2600 or more, preferably 2630 or more, more preferably 2680 or more, and the upper limit is 2750 or less, preferably 2730 or less, more preferably 2710 or less. If this value is too large, the ball may fly too far under driver (W#1) hitting conditions of a long hitter, or the desired flight distance may not be obtained when hitting with a driver (W#1) or when hitting with an iron by an average hitter. On the other hand, if the above value is too small, the desired flight distance may not be obtained when hitting with a driver (W#1) or when hitting with an iron by an average hitter.

[0090] A large number of dimples may be formed on the outer surface of the cover. There are no particular limitations on the number of dimples to be arranged on the cover surface, but the number is preferably 280 or more, more preferably 300 or more, and more preferably 310 or more, with the upper limit being preferably 450 or less, more preferably 400 or less, and even more preferably 350 or less. If the number of dimples is outside the above range, the average hitter may experience a short flight distance when hitting with a driver (W#1).

[0091] The shape of the dimples may be one or a combination of two or more of the following shapes: circular, various polygonal, dewdrop, elliptical, etc. For example, when using circular dimples, the diameter may be about 2.5 mm to 6.5 mm, and the depth may be 0.08 mm to 0.30 mm.

[0092] The dimple occupancy rate of the golf ball's spherical surface, specifically, the ratio of the total dimple area defined by the flat surface edges surrounded by the edges of the dimples to the ball's spherical area assuming no dimples (SR value), is preferably 75% or more, more preferably 80% or more, and even more preferably 84% or more, with an upper limit of 90% or less, more preferably 88% or less, and even more preferably 86% or less. If the SR value deviates from the above range, the flight distance when hit with a driver (W#1) by an average hitter may be reduced.

[0093] The VR value, which is the percentage of the total dimple volume formed below the plane surrounded by the dimple edges to the volume of the ball assuming that no dimples exist, is 0.77% or more, preferably 0.79% or more, more preferably 0.81% or more, with the upper limit being 0.92% or less, more preferably 0.90% or less, more preferably 0.88% or less. If this VR value is greater than the above range, the distance traveled by a long hitter when hitting with a driver (W#1) may be too short, or the target distance may not be obtained when hitting with a driver (W#1) by an average hitter. In addition, in this case, the trajectory may be low, making it difficult to achieve a carry and making it difficult to cross valleys or ponds. On the other hand, if the above value is too small, the distance traveled by a long hitter when hitting with a driver (W#1) may not be reduced, and the ball may fly longer than the standard distance of the new distance rule envisaged by the R&A and the USGA.

[0094] The value V0, obtained by dividing the spatial volume of the dimple below the plane surrounded by the edge of each dimple by the volume of a cylinder whose bottom is the plane and whose height is the maximum depth of the dimple from the bottom, is preferably 0.35 or more, more preferably 0.38 or more, and even more preferably 0.40 or more, with the upper limit being 0.80 or less, more preferably 0.70 or less, and even more preferably 0.60 or less. If this V0 value deviates from the above range, the flight distance when hit with a driver (W#1) by long hitters and average hitters may be shorter than the target.

[0095] For the golf ball of the present invention, when the ratio (CL1 / CD1) of the lift coefficient CL1 to the drag coefficient CD1 at a Reynolds number of 218000 and a spin rate of 2800 rpm is A1, the ratio (CL2 / CD2) of the lift coefficient CL2 to the drag coefficient CD2 at a Reynolds number of 184000 and a spin rate of 2900 rpm is A2, and the ratio (CL3 / CD3) of the lift coefficient CL3 to the drag coefficient CD3 at a Reynolds number of 158000 and a spin rate of 3100 rpm is A3, the following two equations can be used to determine the ratio of the lift coefficient CL1 to the drag coefficient CD1 at a Reynolds number of 218000 and a spin rate of 2800 rpm: 0.590≦A1≦0.655, and (A2+A3) / 2≧0.670 The dimples are appropriately designed to satisfy the above.

[0096] In this specification, "lift coefficients (CL1, CL2, CL3) and drag coefficients (CD1, CD2, CD3)" are measured in accordance with the ITR (Indoor Test Range) defined by the USGA (United States Golf Association). The lift coefficient and drag coefficient can be adjusted by adjusting the configuration (arrangement, diameter, depth, volume, number, shape, etc.) of the dimples on the golf ball. The lift coefficient and drag coefficient are independent of the internal configuration of the golf ball. The Reynolds number (Re) is a dimensionless number used in the field of fluid dynamics. The Reynolds number (Re) is calculated by the following formula (1). Re = ρvL / μ (1) In the above equation (1), ρ represents the density of the fluid, v represents the average velocity of the object relative to the fluid flow, L represents the characteristic length, and μ represents the viscosity coefficient of the fluid.

[0097] In the present invention, the ratio CL1 / CD1 of the lift coefficient CL1 to the drag coefficient CD1 at a Reynolds number of 218,000 and a spin rate of 2,800 rpm is defined as A1, the ratio CL2 / CD2 of the lift coefficient CL2 to the drag coefficient CD2 at a Reynolds number of 184,000 and a spin rate of 2,900 rpm is defined as A2, and the ratio CL3 / CD3 of the lift coefficient CL3 to the drag coefficient CD3 at a Reynolds number of 158,000 and a spin rate of 3,100 rpm is defined as A3.

[0098] Regarding the conditions for measuring the above lift coefficient CL1 and drag coefficient CD1, namely a Reynolds number of 218,000 and a spin rate of 2,800 rpm, these high speed conditions correspond to the conditions under which a long hitter hits the ball with a driver (W#1), this Reynolds number corresponds to the ball speed when a golf ball is hit with a head speed (HS) of 54 m / s, and the spin rate of 2,800 rpm corresponds to the average spin condition for a player with a head speed (HS) of 54 m / s.

[0099] Regarding the conditions for measuring the above lift coefficient CL2 and drag coefficient CD2, namely a Reynolds number of 184,000 and a spin rate of 2,900 rpm, these medium speed conditions correspond to the conditions when an average hitter hits the ball with a driver (W#1) at a head speed (HS) of 45 m / s. This Reynolds number corresponds to the ball speed when a golf ball is hit at a head speed (HS) of 45 m / s, and the spin rate of 2,900 rpm is the average spin condition for a player with a head speed (HS) of 45 m / s.

[0100] Regarding the conditions for measuring the above lift coefficient CL3 and drag coefficient CD3, namely a Reynolds number of 158,000 and a spin rate of 3,100 rpm, these low speed conditions correspond to the conditions when an average hitter hits the ball with a driver (W#1) at a head speed (HS) of 40 m / s. This Reynolds number corresponds to the ball speed when a golf ball is hit at a head speed (HS) of 40 m / s, and the spin rate of 3,100 rpm is the average spin condition for a player with a head speed (HS) of 40 m / s.

[0101] The ratio of the lift coefficient CL1 to the drag coefficient CD1, i.e., the value of CL1 / CD1=A1, is 0.590 or more, preferably 0.595 or more, more preferably 0.600 or more, with the upper limit being 0.655 or less, preferably 0.640 or less, more preferably 0.627 or less. If this value is too large, the effect of suppressing the flight distance when a long hitter hits with a driver (W#1) is insufficient, and the flight distance may be too long. On the other hand, if the above value is too small, the actual flight distance may be too short compared to the target flight distance.

[0102] The ratio of the lift coefficient CL2 to the drag coefficient CD2, i.e., the value of CL2 / CD2=A2, is preferably 0.635 or more, more preferably 0.645 or more, and even more preferably 0.660 or more, and the upper limit is preferably 0.750 or less, more preferably 0.740 or less, and even more preferably 0.730 or less. If this value is too low, when the ball is hit with a driver (W#1) at a head speed (HS) of 45 m / s, the carry may not be achieved and the desired total distance may not be obtained. On the other hand, if the value is too high, when the ball is hit with a driver (W#1) at a head speed (HS) of 45 m / s, the ball may fly up and the desired distance may not be obtained.

[0103] The ratio of the lift coefficient CL3 to the drag coefficient CD3, i.e., the value of CL3 / CD3=A3, is preferably 0.695 or more, more preferably 0.710 or more, and even more preferably 0.722 or more, and the upper limit is preferably 0.815 or less, more preferably 0.810 or less, and even more preferably 0.800 or less. If this value is too low, when the ball is hit with a driver (W#1) at a head speed (HS) of 40 m / s, the ball may not carry and the desired total distance may not be obtained. On the other hand, if the value is too high, when the ball is hit with a driver (W#1) at a head speed (HS) of 40 m / s, the ball may fly up and the desired distance may not be obtained.

[0104] The average value of the above A2 and A3 values, i.e., the value of (A2+A3) / 2, is 0.670 or more, preferably 0.680 or more, more preferably 0.690 or more, and the upper limit is preferably 0.783 or less, more preferably 0.775 or less, and even more preferably 0.765 or less. If this value is too low, when an average hitter hits with a driver (W#1), the ball may not carry and the desired total distance may not be obtained. On the other hand, if the above value is too high, when an average hitter hits with a driver (W#1), the ball may fly up and the desired distance may not be obtained.

[0105] The multi-piece solid golf ball of the present invention can be made for competitive use in accordance with the Rules of Golf, with an outer diameter that does not pass through a ring with an inner diameter of 42.672 mm, and a mass preferably ranging from 45.0 to 45.93 g. EXAMPLES

[0106] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0107] [Examples 1 to 4, Comparative Examples 1 to 9] Core formation For Example 1 and Comparative Examples 1 to 4, the rubber compositions shown in Table 1 were prepared, and then vulcanization molding was performed under the vulcanization conditions shown in Table 1 to produce solid cores.

[0108] For Examples 2 to 4 and Comparative Examples 5 to 9, cores were prepared based on the formulations in Table 1 in the same manner as above.

[0109] [Table 1]

[0110] Details of the above formulation are as follows: Polybutadiene: Product name "BR T700" (manufactured by ENEOS Materials) Zinc acrylate: Product name "ZN-DA85S" (manufactured by Nippon Shokubai Co., Ltd.) Zinc stearate: Product name "Zinc Stearate GP" (manufactured by NOF Corporation) Organic peroxide: Dicumyl peroxide, trade name "Percumyl D" (manufactured by NOF Corporation) Sulfur: Product name "Sunmix S-80N" (manufactured by Sanshin Chemical Industry Co., Ltd., containing 80 wt% powdered sulfur for rubber) Water: Pure water (Seiki Pharmaceutical Co., Ltd.) Anti-aging agent A: 2,2-methylenebis(4-methyl-6-butylphenol), product name "Nocrac NS-6" (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) Anti-aging agent B: 2-mercaptobenzimidazole, product name "Nocrac MB" (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) Zinc oxide: Product name "Triple zinc oxide" (manufactured by Sakai Chemical Industry Co., Ltd.) Pentachlorothiophenol zinc salt: Fujifilm Wako Pure Chemical Industries, Ltd.

[0111] Formation of the intermediate layer and cover (outermost layer) Next, for Example 1 and Comparative Examples 1 to 4, an intermediate layer was formed by injection molding around the surface of the core using an injection mold with intermediate layer resin material No. 1 shown in Table 2. Next, a cover was formed by injection molding around the intermediate layer-covered sphere using another injection mold with cover (outermost layer) resin material No. 4 or No. 5 shown in Table 2. At this time, a large number of predetermined dimples, as described below, were formed on the surface of the cover.

[0112] For Examples 2 to 4 and Comparative Examples 5 to 9, an intermediate layer is formed by injection molding the intermediate layer resin material No. 1 or No. 2 shown in Table 2 around the surface of the core using an injection molding die. Next, a cover (outermost layer) resin material No. 4 to No. 6 shown in Table 2 is injection molded around the intermediate layer-covered sphere using another injection molding die to form a cover.

[0113] [Table 2]

[0114] The details of the ingredients in Table 2 are as follows: "Himilan 1605", "Himilan 1557", "Himilan 1706" and "AM7318" are ionomers manufactured by Mitsui Dow Polychemicals. "Trimethylolpropane" (TMP) manufactured by Tokyo Chemical Industry Co., Ltd. "TPU (1)": Trade name "Pandex" manufactured by DIC Covestro Polymer, ether type thermoplastic polyurethane, material hardness (Shore D) "43" "TPU (2)": DIC Covestro Polymer's trade name "Pandex", ether type thermoplastic polyurethane, material hardness (Shore D) "40" "TPU (3)": Trade name "Pandex" manufactured by DIC Covestro Polymer, ether type thermoplastic polyurethane, material hardness (Shore D) "46"

[0115] The dimples used in each of the examples and comparative examples were dimples (1) to (4) below. Each dimple pattern included eight types of circular dimples, No. 1 to No. 8, which differ in diameter and depth. Details are shown in Table 3 below. The arrangement (pattern) of dimples (1) to (4) is shown in Figure 5. Figure 5(A) shows a plan view of the dimples, and Figure 5(B) is a side view of the same.

[0116] [Table 3]

[0117] Definition of a Dimple Edge: The highest point on the cross section passing through the center of the dimple Diameter: The diameter of the plane enclosed by the edge of the dimple Depth: The maximum depth of the dimple from the plane bounded by the dimple edge SR: The ratio of the total dimple area, defined by the plane enclosed by the edges of the dimples, to the area of ​​the ball as if the dimples did not exist. Dimple volume: The volume of the dimple below the plane surrounded by the edge of the dimple Cylinder volume ratio: The ratio of the dimple volume to the volume of a cylinder with the same diameter and depth as the dimple. VR: The ratio of the total volume of the dimples formed below the plane surrounded by the edges of the dimples to the volume of the ball as if the dimples did not exist.

[0118] The following table shows the lift coefficient CL1, drag coefficient CD1, and ratio CL1 / CD1=A1 for a Reynolds number of 218000 and a spin rate of 2800 rpm, the lift coefficient CL2, drag coefficient CD2, and ratio CL2 / CD2=A2 for a Reynolds number of 184000 and a spin rate of 2900 rpm, and the lift coefficient CL3, drag coefficient CD3, and ratio CL3 / CD3=A3 for a Reynolds number of 158000 and a spin rate of 3100 rpm for a ball with the above dimples (1) to (4) formed on the cover surface. These lift coefficients and drag coefficients are measured in accordance with the ITR (Indoor Test Range) defined by the USGA.

[0119] [Table 4]

[0120] For each of the obtained golf balls, various physical properties such as the internal hardness at each position of the core, the outer diameter of the core and each coated sphere, the thickness and material hardness of each layer, the surface hardness of each coated sphere, and the initial velocity of the ball were evaluated by the methods described below. The results are shown in Tables 5 to 8.

[0121] Core hardness distribution The surface of the core is spherical, and the needle of the hardness tester is set almost perpendicular to the spherical surface, and the surface hardness is measured in Shore C hardness according to ASTM D2240. For the center and specified positions of the core, the core is cut into a hemisphere to make the cross section flat, and the needle of the hardness tester is pressed perpendicularly against the center part and the specified positions shown in Tables 5 and 6 to measure the hardness, and the hardness at the center and each position is shown in Shore C hardness values. The hardness is measured using an automatic rubber hardness tester "P2" made by Kobunshi Keiki Co., Ltd., equipped with a Shore C type hardness tester. The hardness value is the maximum value. All measurements are performed in an environment of 23±2°C. The values ​​in the table are Shore C hardness values. In addition, in the hardness distribution of the core, the Shore C hardness Cc at the center of the core, the Shore C hardness Cc+4 at a position 4 mm outward from the center of the core, the Shore C hardness Cm at the midpoint M between the center and the surface of the core, the Shore C hardness Cm-4 at a position 4 mm inward from the midpoint M, the Shore C hardness Cm+4 at a position 4 mm outward from the center M, the Shore C hardness Cs on the surface of the core, and the Shore C hardness Cs-4 at a position 4 mm inward from the surface of the core are shown in the following areas A to D. ·Area A: 1 / 2×4×(Cc+4-Cc) ·Area B: 1 / 2×4×(Cm-Cm-4) ·Area C: 1 / 2×4×(Cm+4-Cm) ·Area D: 1 / 2×4×(Cs-Cs-4) Calculate the values ​​of the following seven formulas. (1)Area A+Area B (2)Area C+Area D (3)(Area C+Area D)-(Area A+Area B) (4)(Area C)-(Area A+Area B) (5)(Area D)-(Area A+Area B)

[0122] To explain areas A to D of the core hardness distribution, a schematic diagram showing areas A to D using the core hardness distribution data of Example 1 is shown in FIG. FIG. 3 shows a graph of the core hardness distribution of Examples 1 to 4 and Comparative Examples 1 to 9.

[0123] The outer diameter of each of the core and intermediate layer-coated spheres The temperature is regulated in a thermostatic chamber at 23.9±1°C for at least three hours, and then measurements are taken at five random points on the surface in a room at 23.9±2°C. The average of these measurements is used as the measurement value for each sphere, and the average value for 10 measurements is calculated.

[0124] Ball diameter The ball is placed in a thermostatic bath at 23.9±1°C for at least three hours, and then 15 randomly selected non-dimpled areas are measured in a room at 23.9±2°C. The average of these measurements is taken as the measurement for one ball. The average of the 10 balls measured is then calculated.

[0125] Deflection of the core, the intermediate layer, and the ball Each covered sphere is placed on a hard plate and the amount of deflection is measured when an initial load of 98N (10kgf) is applied and then a final load of 1275N (130kgf) is applied. Note that the above deflection amount is a value measured in a room at 23.9±2°C after controlling the temperature at 23.9±1°C for at least three hours. The measuring device used is a high-load compression tester manufactured by MU Seiki Co., Ltd., and the down speed of the pressure head compressing the core, each layer of covered sphere, or the ball is 10mm / s.

[0126] Hardness of the intermediate layer and cover material (Shore C hardness, Shore D hardness) The resin material for each layer is formed into a sheet 2 mm thick and left at a temperature of 23±2°C for two weeks. Three sheets are stacked when measuring. Shore C hardness and Shore D hardness are measured using a Shore C hardness tester and a Shore D hardness tester that conform to the ASTM D2240 standard. To measure hardness, an automatic rubber hardness tester "P2" manufactured by Kobunshi Keiki Co., Ltd. equipped with a Shore C type hardness tester or a Shore D type hardness tester is used. The hardness value is read as the maximum value. The measurement method follows the ASTM D2240 standard.

[0127] Surface hardness of each sphere of the intermediate layer coated sphere and the ball Measurements are taken by pressing a needle perpendicularly against the surface of each sphere. The surface hardness of the ball (cover) is measured on the land areas on the ball surface where no dimples are formed. Shore C hardness and Shore D hardness are measured using a Shore C hardness tester and a Shore D hardness tester that comply with the ASTM D2240 standard. To measure hardness, an automatic rubber hardness tester "P2" manufactured by Kobunshi Keiki Co., Ltd. equipped with a Shore C type hardness tester or a Shore D type hardness tester is used. The hardness value is read as the maximum value. The measurement method complies with the ASTM D2240 standard.

[0128] The initial velocity of each sphere The initial velocity of each ball is measured at 23.9±2°C using a COR type initial velocity meter manufactured by Hye Precision Products, the same type as that used by R&A. The measurement principle is as follows. The air pressure is changed to four levels: 35.5, 36.5, 39.5, and 40.5 psi. The ball is shot at four different entry velocities at each air pressure, and the ball is allowed to collide with the barrier, and its COR (coefficient of restitution) is measured. In other words, the air pressure is changed to four levels, and a correlation equation between the entry velocity and COR is created. Similarly, a correlation equation between the entry velocity and contact time is created. Then, from these correlation equations, the COR (coefficient of restitution) and contact time (μs) at an incident velocity of 43.83 m / s are calculated, and substituted into the initial velocity conversion equation below to calculate the initial velocity of each ball. IV=136.8+136.3e+0.019tc (where e is the coefficient of restitution and tc is the contact time (μs) at an impact velocity of 143.8 ft / s (43.83 m / s).) When measuring the initial velocity of each sphere, the barrel diameter is selected so that the clearance between the outer diameter of the measured object and the barrel diameter on one side is between 0.2 and 2.0 mm. For the cores, a barrel diameter of 39.88 mm is selected for all cases. For the intermediate layer coated spheres, a barrel diameter of 41.53 mm is selected for all cases, and for the balls, a barrel diameter of 43.18 mm is selected for all cases.

[0129] Value of Ciw+Miw In each of the examples and comparative examples, the value of Ciw+Miw is calculated by taking the value of (initial velocity of core × mass of core) as Ciw and the value of (initial velocity of intermediate layer-coated sphere − initial velocity of core) × (mass of intermediate layer-coated sphere − mass of core) as Miw. The values ​​of each example are shown in Tables 7 and 8, and a graph showing the values ​​of Ciw+Miw is shown in Figure 4.

[0130] [Table 5]

[0131] [Table 6]

[0132] [Table 7]

[0133] [Table 8]

[0134] The flight (W#1) (I#6) and controllability at the time of approach of each golf ball were evaluated by the following method. The results are shown in Table 9.

[0135] Flight rating (W#1, HS54m / s) A driver club is attached to the golf hitting robot, and the spin rate and flight distance (total) are measured when hitting the ball at a head speed (HS) of 54 m / s. The club used is the Bridgestone Sports TourB XD-5 Driver (2017 model) (loft angle 9.5°), and the evaluation is based on the following criteria. 〔Judgment criteria〕 ⊚ The total compared to Comparative Example 1 is -10.0 m or less and -20.0 m or more. ◯: The total compared to Comparative Example 1 is equal to or smaller than -7.0 m and larger than -10.0 m. △: The total compared to Comparative Example 1 is less than -20.0 m. × The total compared to Comparative Example 1 is greater than -7.0 m.

[0136] Flight rating (W#1, HS45m / s) A driver club is attached to the golf hitting robot, and the amount of spin and the flight distance (total) are measured when hitting the ball at a head speed (HS) of 45 m / s. The club used is the Bridgestone Sports J015 Driver (2016 model) (loft angle 9.5°), and the evaluation is based on the following criteria. 〔Judgment criteria〕 ◯: The total compared to Comparative Example 1 is -5.0 m or more. Δ: The total compared to Comparative Example 1 is equal to or greater than -10.0 m and less than -5.0 m. × The total compared to Comparative Example 1 is less than −10.0 m.

[0137] Flight rating (W#1, HS40m / s) A driver club is attached to the golf hitting robot, and the spin rate and flight distance (total) are measured when hitting the ball at a head speed (HS) of 40 m / s. The club used is the Bridgestone Sports J015 Driver (2016 model) (loft angle 9.5°), and is evaluated according to the following criteria. 〔Judgment criteria〕 ◯: The total compared to Comparative Example 1 is -5.0 m or more. Δ: The total compared to Comparative Example 1 is equal to or greater than -10.0 m and less than -5.0 m. × The total compared to Comparative Example 1 is less than −10.0 m.

[0138] Flight rating (I#6, HS42m / s) A No. 6 iron (I#6) is attached to a golf hitting robot and hit with a head speed (HS) of 42 m / s, and the spin rate and flight distance (total) are measured. The distance of the run alone (total - carry) is also calculated. The club used is the Bridgestone Sports JGR Forged I#6 (2016 model), and is evaluated according to the following criteria. [Judgment criteria / total] ◯: The total compared to Comparative Example 1 is 0 m or more. Δ: The total compared to Comparative Example 1 is equal to or greater than −5.0 m and less than 0 m. × The total compared to Comparative Example 1 is less than −5.0 m. [Criteria / Run] ○ The run is 6.0m or less. × Run is greater than 6.0m.

[0139] Flight rating (I#6, HS35m / s) A No. 6 iron (I#6) is attached to a golf hitting robot and hit with a head speed (HS) of 35 m / s, and the spin rate and flight distance (total) are measured. The distance of the run only (total - carry) is also calculated. The club used is the Bridgestone Sports JGR Forged I#6 (2016 model), and is evaluated according to the following criteria. [Judgment criteria / total] ◯: The total compared to Comparative Example 1 is 0 m or more. Δ: The total compared to Comparative Example 1 is equal to or greater than −5.0 m and less than 0 m. × The total compared to Comparative Example 1 is less than −5.0 m. [Criteria / Run] ○ The run is 6.0m or less. × Run is greater than 6.0m.

[0140] Evaluation of spin rate during approach (SW, HS20m / s) The amount of spin is judged by attaching a sand wedge to a golf hitting robot and hitting it at a head speed (HS) of 20 m / s. The amount of spin is also measured immediately after hitting the ball using an initial condition measuring device. The sand wedge used is the "TourStage TW-03 (loft angle 57°) 2002 model" manufactured by Bridgestone Sports. 〔Judgment criteria〕 〇 ··· Spin rate 6500 rpm or more × Spin rate less than 6500 rpm

[0141] Evaluation of spin rate during approach (SW, HS15m / s) The amount of spin is judged by hitting the ball with a golf hitting robot equipped with a sand wedge at a head speed (HS) of 15 m / s. The amount of spin is measured by using an initial condition measuring device to measure the ball immediately after hitting it. The sand wedge used is the Bridgestone Sports TourStage TW-03 (loft angle 57°) 2002 model. 〔Judgment criteria〕 〇 ··· Spin rate 4800 rpm or more × Spin rate less than 4800 rpm

[0142] [Table 9]

[0143] As shown in the results in Table 9, the golf balls of Comparative Examples 1 to 9 are inferior to the products of the present invention (Examples) in the following respects. In Comparative Example 1, the A1 value was greater than 0.655, and the surface hardness (Shore D) of the ball was greater than 59. As a result, the flight distance at a head speed (HS) of 54 m / s with a driver (W#1) could not be controlled, and the ball was not the target of the present invention. In Comparative Example 2, the A1 value is greater than 0.655. As a result, the flight distance at a head speed (HS) of 54 m / s with a driver (W#1) cannot be controlled, and this is not the ball aimed at by the present invention. In Comparative Example 3, the ball has a surface hardness (Shore D) of greater than 59. As a result, the amount of spin on the ball during approach is small. In Comparative Example 4, the surface hardness (Shore D) of the ball is greater than 59. As a result, the amount of spin on the ball during approach is small. In Comparative Example 5, the value of A1 is smaller than 0.590, the average value of A2 and A3 is smaller than 0.670, the surface hardness (Shore D) of the ball is greater than 59, and the spin amount of the ball on approach is small. In Comparative Example 6, the value of A1 is smaller than 0.590, and the average value of A2 and A3 is smaller than 0.670. As a result, the flight distance of the driver (W#1) is inferior to that of each of the Examples, and the flight distance is too small when hit with a head speed (HS) of 54 m / s in particular. In Comparative Example 7, the A1 value was greater than 0.655, and the deflection of the ball under a given load was greater than 2.79 mm. As a result, the ball could not achieve the distance desired by the present invention when used with a driver (W#1) at a head speed (HS) of 54 m / s. In Comparative Example 8, the deflection of the ball under a given load is greater than 2.79 mm. As a result, the run is large when hit with a No. 6 iron (I#6) at a head speed (HS) of 42 m / s, and the spin amount of the ball on the approach is small. In Comparative Example 9, the deflection of the ball under a given load is greater than 2.79 mm. As a result, the flight distance when using a driver (W#1) with a head speed (HS) of 54 m / s and 45 m / s is poor, and when using a 6-iron (I#6) with a head speed (HS) of 42 m / s is hit, the run is large and the amount of spin of the ball on the approach is small. [Explanation of symbols]

[0144] G Golf ball 1 core 2. Middle Tier 3 Cover D dimple

Claims

1. A multi-piece solid golf ball having a core, an intermediate layer, and a cover, the cover having an outer surface on which a number of dimples are formed, the relationship between the midpoint hardness (Cm) between the surface and center of the core and the hardness of the cover material being expressed by the following formula: Midpoint hardness between the surface and center of the core (Cm) > Hardness of the cover material (However, hardness refers to Shore C hardness.) the surface hardness of the ball is 59 or less in Shore D hardness, the amount of deflection when the ball is subjected to an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf) is 2.79 mm or less, and when the ball is subjected to a load ranging from an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf), the following two equations are satisfied, where A1 is the ratio CL1 / CD1 of the lift coefficient CL1 to the drag coefficient CD1 at a Reynolds number of 218,000 and a spin rate of 2,800 rpm, A2 is the ratio CL2 / CD2 of the lift coefficient CL2 to the drag coefficient CD2 at a Reynolds number of 184,000 and a spin rate of 2,900 rpm, and A3 is the ratio CL3 / CD3 of the lift coefficient CL3 to the drag coefficient CD3 at a Reynolds number of 158,000 and a spin rate of 3,100 rpm: 0.590≦A1≦0.655, and (A2+A3) / 2≧0.670 A multi-piece solid golf ball comprising:

2. 2. The multi-piece solid golf ball according to claim 1, wherein the volume ratio VR of the dimples is 0.78 to 0.92%.

3. 3. The multi-piece solid golf ball according to claim 1, wherein the value of (A2+A3) / 2 is 0.670 to 0.

783.

4. 3. The multi-piece solid golf ball according to claim 1, wherein the value of A2 is 0.635 to 0.750, and the value of A3 is 0.695 to 0.

815.

5. In the hardness distribution of the above core, the Shore C hardness at the center of the core is Cc, the Shore C hardness at a position 4 mm outward from the center of the core is Cc+4, the Shore C hardness at the midpoint M between the center and the surface of the core is Cm, the Shore C hardness at a position 4 mm inward from the midpoint M is Cm-4, the Shore C hardness at a position 4 mm outward from the center M is Cm+4, the Shore C hardness at the surface of the core is Cs, and the Shore C hardness at a position 4 mm inward from the surface of the core is Cs-4, then the following areas A to D are defined. ・Area A: 1 / 2 x 4 x (Cc+4-Cc) ・Area B: 1 / 2 x 4 x (Cm-Cm-4) ・Area C: 1 / 2 x 4 x (Cm+4-Cm) ・Area D: 1 / 2 x 4 x (Cs-Cs-4) Regarding (Area C + Area D) - (Area A + Area B) ≧2.0 3. The multi-piece solid golf ball according to claim 1, wherein the above-mentioned formula (1) is satisfied.

6. In the hardness distribution of the above core, the following two formulas are used: (Area C) - (Area A + Area B) ≧2.0 (Area D) - (Area A + Area B) ≧2.0 6. The multi-piece solid golf ball according to claim 5, which satisfies the above.

7. 3. The multi-piece solid golf ball according to claim 1, wherein the cover has a material hardness of 30 to 43 in Shore D hardness.

8. 3. The multi-piece solid golf ball according to claim 1, wherein the cover has a thickness of 0.6 to 1.2 mm.

9. The relationship between the surface hardness of the intermediate layer-coated sphere and the surface hardness of the ball is expressed by the following formula: (Surface hardness of ball) < (Surface hardness of intermediate layer-coated sphere) (However, hardness refers to Shore C hardness.) 3. The multi-piece solid golf ball according to claim 1, wherein the above-mentioned formula (1) is satisfied.

10. The core comprises the following components (A) to (D): (A) Base rubber (B) Organic peroxide (C) Water (D) Sulfur 3. The multi-piece solid golf ball according to claim 1, which is formed from a rubber composition containing

11. 3. The multi-piece solid golf ball according to claim 1, wherein the mass ratio (D) / (C) of component (C) to component (D) is 0.020 to 0.200.

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