Multi-piece solid golf ball

Abstract

To provide a golf ball which decreases a reduction in distance on shots with a driver and an iron by average hitters while increasing a reduction in distance on shots with a driver by long hitters.SOLUTION: A golf ball includes a core, an intermediate layer, and a cover. A relationship between surface hardness of an intermediate layer-encased sphere and surface hardness of the ball satisfies a predetermined relational expression. When an initial velocity of the ball and deflection under a predetermined load applied to the ball are optimized, a value of (an initial velocity of the core×weight of the core) is Ciw, a value of [(the initial velocity of the intermediate layer-encased sphere-the initial velocity of the core)×(weight of the intermediate layer-encased sphere-the weight of the core)] is Miw, and a value of [(the initial velocity of the ball-the initial velocity of the intermediate layer-encased sphere)×(the weight of the ball-the weight of the intermediate layer-encased sphere)] is CViw, the following expression is satisfied:2600≤Ciw+Miw+CViw≤2715. A prescribed Reynolds number of dimples and a coefficient lift and a drag coefficient at a spin rate are set in a prescribed range.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a multi-piece solid golf ball comprising a core, an intermediate layer and a cover, wherein a large number of dimples are formed on the outer surface of the cover. [Background Art]

[0002] In March 2022, the R&A and the USGA notified golf ball manufacturers that they would start research to restrict the flight distance of long hitters by changing the test conditions for the Overall Distance Standard (ODS) of golf balls in the future. For this reason, it is preferable to provide a golf ball that, rather than simply reducing flight distance, increases the reduction in flight distance when a long hitter hits with a driver, while reducing the reduction in flight distance when an average hitter hits with a driver and when hitting with an iron, thereby minimizing the impact on play other than the reduction in flight distance for long hitters using a driver. It is also desired to design the ball such that, even when the flight distance-reduced golf ball resulting from the above change is used by professionals and advanced players, no uncomfortable feeling occurs, and the spin performance in short games approximates that of balls currently used on tour.

[0003] It should be noted that in the past, several golf balls have been proposed that restrict the initial ball velocity to 76.5 m / s or less, which is lower than that of ordinary game balls. Examples of such technical documents include Patent Documents 1 to 5 below.

[0004] However, all of the above-proposed golf balls are practice balls for driving ranges that are simply designed to travel shorter distances than regular game balls. Therefore, none of these golf balls are designed to reduce the flight distance when a long hitter hits with a driver (W#1), while making the reduction in flight distance for average hitters smaller than the reduction in flight distance for long hitters.

[0005] Furthermore, regarding dimples formed on the surface of the ball, the sum of the dimple volumes formed downward from the plane surrounded by the edges of the dimples is specified within a predetermined range to represent the ball volume assuming no dimples exist, i.e., the dimple volume occupancy rate VR. This allows for a golf ball that suppresses distance in the high head speed (HS) range while achieving superior distance in the low HS range, as described in the following Patent Documents 6 to 14.

[0006] However, with the proposed golf balls, the distance an average hitter could hit with an iron sometimes decreased significantly. Also, the ball would sometimes roll too much when hit with an iron, making it difficult to stop it where intended. Therefore, it is desirable to develop a golf ball that minimizes the impact on play, aside from a decrease in distance for long hitters when hitting with a driver. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2012-228470 [Patent Document 2] Japanese Patent Publication No. 2014-069045 [Patent Document 3] Japanese Patent Publication No. 2013-138857 [Patent Document 4] Japanese Patent Publication No. 2013-138839 [Patent Document 5] Japanese Patent Publication No. 2013-138840 [Patent Document 6] Japanese Patent Publication No. 2011-218160 [Patent Document 7] Japanese Patent Publication No. 2011-218161 [Patent Document 8] Japanese Patent Publication No. 2011-218162 [Patent Document 9] Japanese Patent Publication No. 2011-240122 [Patent Document 10] Japanese Patent Publication No. 2011-240123 [Patent Document 11] Japanese Patent Publication No. 2011-240124 [Patent Document 12] Japanese Patent Publication No. 2011-240125 [Patent Document 13] Japanese Patent Publication No. 2011-240126 [Patent Document 14] Japanese Patent Publication No. 2011-240127 [Overview of the project] [Problems that the invention aims to solve]

[0008] This invention was made in view of the above circumstances, and in response to the possibility that the rules may be changed in the future to restrict the distance of long hitters by changing the test conditions for the standard total distance (ODS) of golf balls, the present invention aims to provide a golf ball that can satisfy the needs of professionals and advanced players by not simply reducing the distance, but by increasing the distance reduced when long hitters hit with their drivers, while reducing the distance reduced when average hitters hit with their drivers (W#1) and irons, and further reducing the roll when hitting with irons so that the ball can stop more easily where it is aimed. [Means for solving the problem]

[0009] The inventors have conducted diligent studies to achieve the above objective and have found that in a multi-piece solid golf ball comprising a core, an intermediate layer, and a cover, with numerous dimples formed on the outer surface of the cover, the relationship between the surface hardness of the intermediate layer-coated sphere and the surface hardness of the ball is given by the following formula (Surface hardness of the ball) < (Surface hardness of the sphere coated with an intermediate layer) (However, hardness refers to Shore C hardness.) When the following conditions are met, and the initial velocity of the ball is set to 76.5-77.724 m / s, and the amount of deflection when an initial load of 98 N (10 kgf) is applied to the ball and a final load of 1,275 N (130 kgf) is set to less than 2.7 mm, and when the value of (initial velocity of the core × mass of the core) is Ciw, the value of [(initial velocity of the intermediate layer-coated sphere - initial velocity of the core) × (mass of the intermediate layer-coated sphere - mass of the core)] is Miw, and the value of [(initial velocity of the ball - initial velocity of the intermediate layer-coated sphere) × (mass of the ball - mass of the intermediate layer-coated sphere)] is CViw, then the following formula 2600 ≤ Ciw + Miw + CViw ≤ 2715 Furthermore, if the following conditions are met, and if the ratio 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 CL1 / CD1, then A1 is the ratio 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 CL2 / CD2, and A3 is the ratio 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 CL3 / CD3, then the following two equations apply: 0.590 ≤ A1 ≤ 0.655, and (A2+A3) / 2≧0.670 By designing a golf ball to satisfy the requirements, and in a golf ball that complies with the rules that restrict the distance of long hitters, even if the distance reduced is greater for long hitters' driver shots, the distance reduced for average hitters' driver (W#1) and iron shots is kept to a minimum. This has led to the discovery of a golf ball that minimizes the impact on play other than the reduction in distance for long hitters' driver shots, and thus the present invention was realized. Furthermore, the golf ball of the present invention has spin characteristics in the short game that are close to those of balls currently used on tour, so that professionals and advanced players do not feel any discomfort when using it. Moreover, the golf ball of the present invention can satisfy the needs of professionals and advanced players by making it easier to stop the ball where you intend without increasing the roll when hitting an iron.

[0010] It should be noted that the above "long hitters" refer to users with a head speed of about 50 m / s or more when hitting with a driver (W#1), and the above "average hitters" refer to users with a head speed of about 45 m / s or less when hitting with a driver (W#1).

[0011] Accordingly, the present invention provides the following multi-piece solid golf ball described below. 1. A multi-piece solid golf ball comprising a core, an intermediate layer and a cover, wherein a large number of dimples are formed on the outer surface of the cover, wherein the relationship between the surface hardness of the intermediate layer-coated sphere and the surface hardness of the ball satisfies the following formula (Ball surface hardness) < (Surface hardness of intermediate layer-coated sphere) (provided that the hardness means Shore C hardness.) is satisfied, the initial velocity of the ball is 76.5 to 77.724 m / s, the deflection amount of the ball when loaded from an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf is less than 2.7 mm, and when the value of (core initial velocity × core mass) is defined as Ciw, the value of [(initial velocity of intermediate layer-coated sphere - initial velocity of core) × (mass of intermediate layer-coated sphere - mass of core)] is defined as Miw, and the value of [(initial velocity of the ball - initial velocity of intermediate layer-coated sphere) × (mass of the ball - mass of intermediate layer-coated sphere)] is defined as CViw, the following formula 2600≦Ciw+Miw+CViw≦2715 is satisfied, further, 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 defined as 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 defined as 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 defined as A3, the following two formulas 0.590≦A1≦0.655, and (A2+A3) / 2≧0.670 A multi-piece solid golf ball characterized by satisfying the above conditions. 2. The multi-piece solid golf ball described in item 1 above, wherein the volume occupancy rate (VR) of the dimples is 0.77 to 0.92%. 3. A multi-piece solid golf ball as described in 1 or 2 above, wherein the value of (A2+A3) / 2 is between 0.670 and 0.783. 4. A multi-piece solid golf ball as described in 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. The relationship between the surface hardness of the core and the surface hardness of the intermediate layer-coated sphere is given by the following formula: (Surface hardness of the intermediate layer-coated sphere) ≥ (Surface hardness of the core) (However, hardness refers to Shore C hardness.) A multi-piece solid golf ball as described in 1 or 2 above, which satisfies the requirements. 6. When the initial velocity of the core is Vc (m / s) and the deflection amount C (mm) is applied to the core from an initial load of 98N (10kgf) to a final load of 1,275N (130kgf), the following formula 20 ≤ Vc / C ≤ 30 A multi-piece solid golf ball as described in 1 or 2 above, which satisfies the requirements. 7. When the deflection amounts (mm) of the core, intermediate layer coated sphere, and ball are applied from an initial load of 98N (10kgf) to a final load of 1,275N (130kgf), respectively, let C (mm), M (mm), and B (mm), then the following two equations apply. 0.30 ≤ CB ≤ 0.90 0.30 ≤ CM ≤ 0.65 A multi-piece solid golf ball as described in 1 or 2 above, which satisfies the requirements. 8. When the deflection (mm) of the core is applied from an initial load of 98N (10kgf) to a final load of 1,275N (130kgf), the following formula is used: 700 ≤ Ciw / C ≤ 1000 A multi-piece solid golf ball as described in 1 or 2 above, which satisfies the requirements. 9. In the hardness distribution of the core described above, the Shore C hardness at the center of the core is Cc, and the Shore C hardness at the midpoint M between the center of the core and the surface is C mWhen the Shore C hardness at positions 2mm, 4mm, and 6mm inward from the midpoint M is Cm-2, Cm-4, and Cm-6 respectively, and the Shore C hardness at positions 2mm, 4mm, and 6mm outward from the center M is Cm+2, Cm+4, and Cm+6 respectively, and the Shore C hardness of the core surface is Cs, then the following areas A to F ·Area A: 1 / 2×2×(Cm-4-Cm-6) ·Area B: 1 / 2×2×(Cm-2-Cm-4) ·Area C: 1 / 2×2×(Cm-Cm-2) ·Area D: 1 / 2×2×(Cm+2-Cm) ·Area E: 1 / 2×2×(Cm+4-Cm+2) ·Area F: 1 / 2×2×(Cm+6-Cm+4) Regarding the following formula {(Area D+Area E)-(Area A+Area B)}≧4.0 A multi-piece solid golf ball as described in 1 or 2 above, which satisfies the requirements. 10. In the hardness distribution of the above core, the following formula (Cs-Cc)≧22 A multi-piece solid golf ball as described in item 9 above that satisfies the requirements. 11. In the hardness distribution of the above core, the following formula (Cs-Cc) / (Cm-Cc)≧4.0 A multi-piece solid golf ball as described in item 9 above that satisfies the requirements. 12. In the hardness distribution of the above core, the following formula Area E > Area D > Area C A multi-piece solid golf ball as described in item 9 above that satisfies the requirements. [Effects of the Invention]

[0012] With the golf ball of the present invention, in response to the possibility that the R&A and USGA may change the rules in the future to restrict the distance of long hitters by altering the standard total distance (ODS) test conditions for golf balls, instead of simply reducing the distance, the present invention increases the distance reduction for long hitters' driver shots, while decreasing the distance reduction for average hitters' driver (W#1) and iron shots. This minimizes the impact on play other than the reduction in driver distance for long hitters. Furthermore, the golf ball of the present invention has spin characteristics in the short game that are close to those of balls currently used on tour, so that it does not cause any discomfort to professionals and advanced players. Moreover, it can satisfy the needs of professionals and advanced players by reducing the roll during iron shots and making it easier to stop the ball where intended. [Brief explanation of the drawing]

[0013] [Figure 1] This is a schematic cross-sectional view of a golf ball, which is one embodiment of the present invention. [Figure 2] This is a schematic diagram illustrating the core hardness distribution areas A to F, using the core hardness distribution data from Example 1. [Figure 3] This graph shows the core hardness distribution for Examples 1-3 and Comparative Examples 1-6. [Figure 4] This graph shows the core hardness distribution for comparative examples 7-10. [Figure 5] This graph shows the Ciw+Miw+CViw values ​​for Examples 1-3 and Comparative Examples 1-10. [Figure 6] The arrangement patterns (patterns) of the dimples (1) to (4) used in Examples 1 to 3 and Comparative Examples 1 to 9 are shown, with (A) being a plan view of the dimples and (B) being a side view thereof. [Figure 7] The arrangement (pattern) of the dimples (5) used in Comparative Example 10 is shown in (A), a plan view of the dimples, and (B), a side view thereof.

[0014] The present invention will be described in more detail below. The multi-piece solid golf ball of the present invention has a core, an intermediate layer, and a cover, and an example is shown in Figure 1. The golf ball G shown in Figure 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 the outermost layer in the layer structure of the golf ball, excluding the paint layer. Each layer of the core and intermediate layer can be a single layer as shown in Figure 1, or multiple layers. In addition, the surface of the cover (outermost layer) 3 usually has many dimples D formed on it to improve aerodynamic properties. Also, although not specifically shown in the figures, a paint layer is usually formed on the surface of the cover 3. The above layers will be described in detail below.

[0015] The above core is obtained by vulcanizing a rubber composition mainly composed of rubber material. If the core material is not a rubber composition, the core's rebound properties will be low, and the desired distance may not be achieved when an average hitter hits a driver (W#1) and an iron. This rubber composition usually consists mainly of a base rubber, to which co-crosslinking agents, crosslinking initiators, inert fillers, organic sulfur compounds, etc., are blended to obtain the rubber composition.

[0016] The core components mentioned above include, in particular, the following components (A) to (E). (A) Base rubber (B) Cocrosslinking agent (C) Water or metal monocarboxylate salt (D)Organic peroxide (E)Organic sulfur compounds It is preferable that the rubber composition be formed from a rubber composition containing [the specified substance].

[0017] (A) The base rubber may include diene rubber. Examples of diene rubber include polybutadiene, natural rubber, isoprene rubber, and ethylene propylene diene rubber.

[0018] (B) The cocrosslinking agent is an α,β-unsaturated carboxylic acid and / or a metal salt thereof. Specific examples of unsaturated carboxylic acids include acrylic acid, methacrylic acid, maleic acid, fumaric acid, etc., with acrylic acid and methacrylic acid being particularly preferred. The metal salt of the unsaturated carboxylic acid is not particularly limited, but examples include those obtained by neutralizing the above unsaturated carboxylic acid with a desired metal ion. Specific examples include zinc salts and magnesium salts of methacrylic acid, acrylic acid, etc., with zinc acrylate being particularly preferred.

[0019] The above-mentioned unsaturated carboxylic acid and / or its metal salt are usually blended in an amount of 5 parts by mass or more, preferably 9 parts by mass or more, more preferably 13 parts by mass or more, with an upper limit of 60 parts by mass or less, preferably 50 parts by mass or less, and more preferably 40 parts by mass or less, per 100 parts by mass of the base rubber. If the blending amount is too high, it may become too hard and the feel of hitting it may become unbearable, and if the blending amount is too low, the rebound may decrease.

[0020] (C) There are no particular restrictions on the water used; distilled water or tap water may be used, but it is preferable to use distilled water that does not contain impurities. The amount of water to be added is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, with an upper limit of preferably 2 parts by mass or less, and more preferably 1 part by mass or less, per 100 parts by mass of the base rubber.

[0021] By directly incorporating water or a water-containing material as component (C) into the core material, the decomposition of organic peroxides in the core compound can be promoted. It is also known that the decomposition efficiency of organic peroxides in core rubber compositions changes with temperature, with the decomposition efficiency increasing as the temperature rises above a certain point. If the temperature is too high, the amount of decomposed radicals becomes too large, leading to recombination and inactivation of the radicals. As a result, the number of radicals that effectively work for crosslinking decreases. Here, when decomposition heat is generated as organic peroxides decompose during core vulcanization, the temperature near the core surface remains at approximately the same level as the vulcanization mold, but the temperature near the core center becomes considerably higher than the mold temperature because the decomposition heat of organic peroxides that decomposed from the outside accumulates. When water or a water-containing material is directly incorporated into the core, water promotes the decomposition of organic peroxides, thus altering the radical reactions described above in the core center and on the core surface. In other words, near the core center, the decomposition of organic peroxides is further promoted, and the inactivation of radicals is further accelerated, resulting in a further reduction in the amount of effective radicals. This makes it possible to obtain cores with significantly different crosslinking densities between the core center and the core surface, as well as cores with different dynamic viscoelastic properties at the core center.

[0022] Alternatively, a monocarboxylate metal salt can be used instead of water. Monocarboxylate metal salts are presumed to have a carboxylic acid coordinate bond to the metal salt and are distinguished from dicarboxylate metal salts such as zinc diacrylate, which is represented by the chemical formula [CH2=CHCOO]2Zn. Monocarboxylate metal salts introduce water into the rubber composition through a dehydration condensation reaction, thus providing the same effect as water. Furthermore, since monocarboxylate metal salts can be incorporated into the rubber composition as a powder, the work process can be simplified, and it is easy to uniformly disperse them in the rubber composition. It should be noted that a monosalt is necessary for the above reaction to be carried out effectively. The amount of monocarboxylate metal salt to be incorporated is preferably 1 part by mass or more, and more preferably 3 parts by mass or more, per 100 parts by mass of base rubber. As an upper limit, the amount of monocarboxylate metal salt to be incorporated is preferably 60 parts by mass or less, and more preferably 50 parts by mass or less. If the amount of monocarboxylate metal salt is too small, it may be difficult to obtain an appropriate crosslinking density, and the low-spin effect of the golf ball may not be sufficiently obtained. Furthermore, if the amount of compound is too high, the core may become too hard, making it difficult to maintain a proper feel when hitting the ball.

[0023] The carboxylic acid mentioned above can be acrylic acid, methacrylic acid, maleic acid, fumaric acid, stearic acid, etc. Suitable substitution metals include Na, K, Li, Zn, Cu, Mg, Ca, Co, Ni, Pb, etc., but Zn is preferably used. Specific examples include zinc monoacrylate and zinc monomethacrylate, with zinc monoacrylate being particularly preferred.

[0024] (D) As the organic peroxide, it is preferable to use an organic peroxide with a relatively high thermal decomposition temperature. Specifically, it is preferable to use an organic peroxide with a high temperature of approximately 165 to 185°C with a half-life temperature of about 1 minute. Examples of dialkyl peroxides include dicumyl peroxide (NOF Corporation's "Permyl D"), 2,5-dimethyl-2,5-di(t-butylperoxy)hexane (NOF Corporation's "Perhexa 25B"), and di(2-t-butylperoxyisopropyl)benzene (NOF Corporation's "Perbutyl P"), and dicumyl peroxide can be suitably used. These may be used individually or in combination of two or more. Half-life is one of the indicators that represents the degree of the decomposition rate of the organic peroxide, and is indicated by the time required for the original organic peroxide to decompose and its amount of reactive oxygen species to be halved. The vulcanization temperature for core rubber compositions is typically in the range of 120 to 190°C. Within this range, organic peroxides with a high half-life temperature of approximately 165°C to 185°C decompose relatively slowly. According to the rubber composition used in the present invention, by adjusting the amount of free radicals generated, which increases with the progression of vulcanization time, a core that is a rubber crosslinked material having a specific internal hardness shape, as described later, can be obtained.

[0025] (E) Organic sulfur compounds can be added to control the core's resilience. Specifically, it is recommended to add thiophenols, thionaphthols, halogenated thiophenols, or metal salts thereof as organic sulfur compounds. More specifically, zinc salts of pentachlorothiophenol, pentafluorothiophenol, pentabromothiophenol, parachlorothiophenol, pentachlorothiophenol, etc., diphenyl polysulfide with 2 to 4 sulfur atoms, dibenzyl polysulfide, dibenzoyl polysulfide, dibenzothiazoyl polysulfide, dithiobenzoyl polysulfide, etc., but zinc salts of pentachlorothiophenol and diphenyl disulfide can be used particularly favorably.

[0026] The upper limit for the amount of organic sulfur compound is preferably 5 parts by mass or less, more preferably 4 parts by mass or less, even more preferably 3 parts by mass or less, and most preferably 2 parts by mass or less, per 100 parts by mass of the base rubber. If the amount is too high, the core may become too soft, or the core's rebound may become too high, resulting in excessive distance when a long hitter hits a driver. On the other hand, the lower limit for the amount is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, and even more preferably 0.5 parts by mass or more, per 100 parts by mass of the base rubber. If the amount is too low, the core's rebound may become too low, resulting in excessively short distances when an average hitter hits a driver and when both long hitters and average hitters hit irons.

[0027] The above rubber composition may contain components other than those listed in (A) to (E), such as fillers and antioxidants.

[0028] Suitable fillers include, for example, zinc oxide, barium sulfate, and calcium carbonate. These may be used individually or in combination of two or more. The amount of filler added 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 this 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 high or too low, it may not be possible to obtain the appropriate mass and suitable rebound properties.

[0029] As an anti-aging agent, commercially available products such as Nocrack NS-6, NS-30, NS-200, and MB (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) can be used. These may be used individually or in combination of two or more.

[0030] There are no particular restrictions on the amount of antioxidant added, but it is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, with an upper limit of preferably 1.0 part by mass or less, more preferably 0.7 parts by mass or less, and even more preferably 0.5 parts by mass or less, per 100 parts by mass of base rubber. If the amount added is too much or too little, it may not be possible to obtain an appropriate core hardness gradient, and the desired rebound properties, durability, and low spin effect during full shots may not be obtained.

[0031] The above-mentioned core can be manufactured by vulcanizing and curing a rubber composition containing the above-mentioned components. For example, it can be manufactured by kneading using a kneader such as a Banbury mixer or roll, compression molding or injection molding using a core mold, and then curing the molded body by appropriately heating it at a temperature of 100 to 200°C, preferably 140 to 180°C, for 10 to 40 minutes, which is sufficient for the organic peroxide and co-crosslinking agent to act.

[0032] In this invention, the core is formed as a single layer or multiple layers, but it is preferable to form it as a single layer. If a multi-layered rubber core is made, delamination may occur at the interface when repeatedly struck, and it may crack prematurely.

[0033] The core diameter 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 ball initial velocity may become too low, or the amount of deflection of the entire ball may decrease, increasing the amount of spin on the ball during a full shot, which may prevent average hitters from achieving their desired distance when hitting with a driver (W#1) and irons. On the other hand, if the core diameter is too large, the amount of spin on a full shot may increase, preventing average hitters from achieving their desired distance, or the durability against cracking after repeated impacts may decrease.

[0034] The amount of deflection (mm) of the core when an initial load of 98N (10kgf) is applied to a final load of 1,275N (130kgf) 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 an upper limit of preferably 3.9mm or less, more preferably 3.6mm or less, and even more preferably 3.3mm or less. If the amount of deflection of the core is too small, i.e., the core is too hard, the desired distance may not be obtained when an average hitter hits a driver (W#1) or an iron, or the feel may become too hard. On the other hand, if the amount of deflection of the core is too large, i.e., the core is too soft, the rebound of the ball may become too low, resulting in a lack of distance for an average hitter, or the feel may become too soft, or the durability against cracking during repeated impacts may worsen, and the roll may become too large when hitting with an iron.

[0035] Next, the hardness distribution of the core described above will be explained. Note that the hardness of the core described below refers to Shore C hardness. This Shore C hardness is the hardness value measured using a Shore C hardness tester compliant with the ASTM D2240 standard.

[0036] The core's central hardness (Cc) is preferably 57 or higher, more preferably 59 or higher, and even more preferably 61 or higher, with an upper limit of preferably 67 or lower, more preferably 65 or lower, and even more preferably 63 or lower. If this value is too high, the amount of spin when hitting a full shot will increase, making it difficult for average hitters to achieve their desired distance when hitting with a driver (W#1) and irons, or the feel may become too hard. On the other hand, if the above value is too low, the rebound effect will be low, making it difficult for average hitters to achieve their desired distance, or the durability against cracking after repeated impacts will be poor, resulting in more roll when hitting with irons, which may not satisfy the needs of professionals and advanced players.

[0037] The positional hardness (Cm-6) at a distance of 6 mm inward from the intermediate position M between the center and the surface of the core (hereinafter also referred to as "intermediate position M") is not particularly limited, but is preferably 58 or higher, more preferably 60 or higher, and even more preferably 62 or higher. There is also no particular upper limit to this, but is preferably 68 or lower, more preferably 66 or lower, and even more preferably 64 or lower. If these hardness values ​​are deviated from, it may lead to unfavorable results similar to those described for the central hardness (Cc) of the core.

[0038] The positional hardness (Cm-4) at a distance of 4 mm inward from the midpoint M between the center and the surface of the core (hereinafter also referred to as "intermediate position M") is not particularly limited, but is preferably 60 or higher, more preferably 62 or higher, and even more preferably 64 or higher. There is also no particular upper limit, but is preferably 69 or lower, more preferably 67 or lower, and even more preferably 65 or lower. If these hardness values ​​are deviated from, it may lead to unfavorable results similar to those described for the central hardness (Cc) of the core.

[0039] The positional hardness (Cm-2) of the core at a distance of 2 mm inward from the intermediate position M is not particularly limited, but is preferably 61 or higher, more preferably 63 or higher, and even more preferably 65 or higher. There is also no particular upper limit, but it is preferably 70 or lower, more preferably 68 or lower, and even more preferably 66 or lower. If these hardness values ​​are exceeded, it may lead to unfavorable results similar to those described for the central hardness (Cc) of the core.

[0040] The cross-sectional hardness (Cm) at the intermediate position M of the core described above is not particularly limited, but is preferably 62 or higher, more preferably 64 or higher, and even more preferably 66 or higher. Similarly, the upper limit is not particularly limited, but is preferably 71 or lower, more preferably 69 or lower, and even more preferably 67 or lower. Deviating from these hardness levels may lead to unfavorable consequences similar to those described for the central hardness (Cc) of the core.

[0041] The surface hardness (Cs) of the core is preferably 80 or higher, more preferably 82 or higher, and even more preferably 84 or higher, with an upper limit of preferably 91 or lower, more preferably 89 or lower, and even more preferably 87 or lower. If this value is too high, the crack resistance when repeatedly struck will be poor, or the feel may become too hard. On the other hand, if the above value is too low, the rebound will be low, or the amount of spin during a full shot will be high, and the desired distance may not be achieved when an average hitter hits a driver (W#1) or an iron.

[0042] The positional hardness (Cm+2) at a distance of 2 mm outward from the intermediate position M of the core toward the core surface (hereinafter simply referred to as "outside") is not particularly limited, but is preferably 66 or higher, more preferably 68 or higher, and even more preferably 70 or higher. There is also no particular upper limit, but is preferably 75 or lower, more preferably 73 or lower, and even more preferably 71 or lower. If these hardness values ​​are deviated from, it may lead to unfavorable results similar to those described for the surface hardness (Cs) of the core.

[0043] The positional hardness (Cm+4) of the core at a distance of 4 mm from the intermediate position M is not particularly limited, but is preferably 71 or higher, more preferably 73 or higher, and even more preferably 75 or higher. There is also no particular upper limit, but it is preferably 80 or lower, more preferably 78 or lower, and even more preferably 76 or lower. If these hardness values ​​are exceeded, it may lead to unfavorable results similar to those described for the surface hardness (Cs) of the core.

[0044] The positional hardness (Cm+6) of the core at a distance of 6 mm from the intermediate position M is not particularly limited, but is preferably 75 or higher, more preferably 77 or higher, and even more preferably 79 or higher. There is also no particular upper limit, but it is preferably 85 or lower, more preferably 83 or lower, and even more preferably 81 or lower. If these hardness values ​​are exceeded, it may lead to unfavorable results similar to those described for the surface hardness (Cs) of the core.

[0045] The value obtained by subtracting the core hardness from the surface hardness of the core, i.e., the Cs-Cc value, is preferably 22 or higher, more preferably 23 or higher, and even more preferably 24 or higher, with an upper limit of preferably 32 or lower, more preferably 29 or lower, and even more preferably 26 or lower. If this value is too low, the amount of spin when hitting a full shot will increase, and the desired distance may not be obtained when an average hitter hits a driver (W#1) or an iron. On the other hand, if this value is too high, the rebound effect will be low, and the desired distance may not be obtained when an average hitter hits a driver (W#1) or an iron, or the crack resistance when repeatedly hit may be poor.

[0046] Furthermore, it is preferable to optimize the (Cs-Cc) / (Cm-Cc) value for the hardness distribution of the core. The (Cs-Cc) value indicates the hardness difference between the center and surface of the core, and the (Cm-Cc) value indicates the hardness difference between the midpoint between the core surface and the core center and the core center. The above formula represents the ratio of these hardness differences. The (Cs-Cc) / (Cm-Cc) value is preferably 4.0 or higher, more preferably 5.0 or higher, and even more preferably 6.0 or higher. The upper limit is preferably 12.0 or lower, more preferably 11.0 or lower, and even more preferably 9.5 or lower. If this value is too small, the amount of spin when hitting a full shot will increase, and the desired distance may not be obtained when an average hitter hits a driver (W#1) or an iron. On the other hand, if this value is too high, the rebound effect will decrease, which may prevent average hitters from achieving the desired distance when hitting with a driver (W#1) and when both long hitters and average hitters hit with irons, or it may worsen the durability against cracking when repeatedly hitting the ball.

[0047] In the above core hardness distribution, the following areas A to F ·Area A: 1 / 2×2×(Cm-4-Cm-6) ·Area B: 1 / 2×2×(Cm-2-Cm-4) ·Area C: 1 / 2×2×(Cm-Cm-2) ·Area D: 1 / 2×2×(Cm+2-Cm) ·Area E: 1 / 2×2×(Cm+4-Cm+2) ·Area F: 1 / 2×2×(Cm+6-Cm+4) Regarding this, the value of (Area D + Area E) - (Area A + Area B) is preferably 4.0 or greater, more preferably 5.0 or greater, and more preferably 6.0 or greater. The upper limit is preferably 12.0 or less, more preferably 10.0 or less, and even more preferably 8.0 or less. If this value is too small, the amount of spin when taking a full shot will increase, and the desired distance may not be achieved when an average hitter hits a driver (W#1) or an iron. On the other hand, if this value is too large, the rebound effect will be low, and the desired distance may not be achieved when an average hitter hits a driver (W#1) or an iron, or the crack resistance when repeatedly hit may be poor.

[0048] Furthermore, the relationship between each area calculated from the hardness distribution of the core is given by the following formula Area E > Area D > Area C It is preferable that this condition is satisfied. If this relationship is not satisfied, the amount of spin when hitting a full shot will increase, and the desired distance may not be achieved when an average hitter hits a driver (W#1) or an iron.

[0049] Furthermore, the following formula It is preferable to optimize the value of {(Area D + Area E) - (Area A + Area B)} × (Cs - Cc). This value should be 120 or more, preferably 130 or more, more preferably 140 or more, with an upper limit of preferably 220 or less, more preferably 200 or less, and even more preferably 190 or less. If this value is too small, the amount of spin when hitting a full shot will be too large, and the desired distance may not be obtained when an average hitter hits a driver (W#1) or an iron. On the other hand, if this value is too large, the rebound will be too low, and the desired distance may not be obtained when an average hitter hits a driver (W#1) or an iron, or the crack resistance when repeatedly hit may be poor.

[0050] Figure 2 shows a schematic diagram illustrating areas A to F using the core hardness distribution data from Example 1. As shown, areas A to F are the areas of triangles whose bases are the differences in each specific distance and whose heights are the differences in hardness at each position.

[0051] The initial velocity of the core is preferably 75.6 m / s or higher, more preferably 76.0 m / s or higher, and even more preferably 76.4 m / s or higher, with an upper limit of 78.0 m / s or lower, preferably 77.2 m / s or lower, and more preferably 76.8 m / s or lower. If this initial velocity is too high, the reduction in distance compared to the current tour ball may not be sufficient for long hitters' driver swings, and the ball may fly beyond the standard distance of the new distance rules envisioned by the R&A and USGA. On the other hand, if this initial velocity is too low, the desired distance may not be achieved for average hitters' driver (W#1) and iron swings. The initial velocity values ​​mentioned above are measured using a COR-type initial velocity meter of the same type as those used by the R&A. Specifically, a COR-type initial velocity device manufactured by Hye Precision in the United States is used. The conditions for measurement are as follows: during measurement, the air pressure is changed in four stages, a relationship equation between the incident velocity and COR is constructed, and the initial velocity at an incident velocity of 43.83 m / s is determined from this relationship equation. The measurement environment for the above COR-type initial velocity device uses a ball that has been temperature-controlled for more than 3 hours in a constant temperature chamber adjusted to 23.9 ± 1°C, and the measurement is performed 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.

[0052] The initial velocity of the core is V C (m / s) When the deflection amount C (mm) is applied to the core from an initial load of 98N (10kgf) to a final load of 1,275N (130kgf), the value of Vc / C is preferably 19 or more, more preferably 21 or more, and even more preferably 23 or more, with an upper limit of preferably 31 or less, more preferably 29 or less, and even more preferably 27 or less. If this value is too large, the reduction in distance compared to the current tour ball may not be sufficient for long hitters' driver swings, and the ball may fly beyond the standard distance of the new distance rules envisioned by the R&A and USGA. On the other hand, if the above value is too small, the desired distance may not be obtained for average hitters' driver (W#1) swings and iron swings.

[0053] When Ciw is defined as the value (initial velocity of the core × mass of the core), Ciw represents the rebound of the core material portion in relation to its mass portion. Preferably, Ciw is 2600 or more, more preferably 2640 or more, and even more preferably 2670 or more, with an upper limit of 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 desired distance may not be obtained when an average hitter hits a driver (W#1) or an iron, or the run when hitting an iron may become too large, failing to satisfy the needs of professionals and advanced players.

[0054] When the core is subjected to a load ranging from an initial load of 98N (10kgf) to a final load of 1,275N (130kgf), the deflection amount (mm) is defined as C (mm). The Ciw / C value represents the distribution of a certain amount of deflection in a quantitative index obtained by multiplying the rebound of the core material portion by its mass portion. Preferably, Ciw / C is 700 or more, more preferably 760 or more, and even more preferably 820 or more. 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 desired distance may not be obtained when an average hitter hits a driver (W#1) or an iron, or the roll when hitting an iron may become too large, failing to satisfy the needs of professionals and advanced players.

[0055] Next, I will explain the middle class. The material hardness of the intermediate layer is not particularly limited, but in terms of Shore C hardness, it is preferably 90 or higher, more preferably 92 or higher, and even more preferably 93 or higher, with an upper limit of preferably 100 or less, more preferably 98 or less, and even more preferably 96 or less. In terms of Shore D hardness, it is preferably 61 or higher, more preferably 63 or higher, and even more preferably 65 or higher, with an upper limit of preferably 72 or less, more preferably 70 or less, and even more preferably 67 or less.

[0056] The surface hardness of a sphere with a core covered by an intermediate layer (intermediate layer-covered sphere) is preferably 95 or higher, more preferably 96 or higher, and even more preferably 97 or higher on the Shore C hardness scale, with an upper limit of preferably 100 or less, more preferably 99 or less, and even more preferably 98 or less. On the Shore D hardness scale, it is preferably 68 or higher, more preferably 69 or higher, and even more preferably 70 or higher, with an upper limit of preferably 78 or less, more preferably 75 or less, and even more preferably 72 or less.

[0057] If the material hardness and surface hardness of these intermediate layers are too soft compared to the above range, it may result in excessive spin or low initial ball speed when hitting a full shot, potentially reducing the distance an average hitter can achieve with a driver (W#1) and irons. On the other hand, if the material hardness and surface hardness of the intermediate layers are too hard compared to the above range, it may result in poor crack resistance during repeated impacts, a hard feel when putting or making short approaches, or difficulty in generating spin during approach shots.

[0058] 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 1.2 mm or less. Furthermore, it is preferable that the thickness of the intermediate layer be thicker than the cover described later. If the thickness of the intermediate layer is outside the above range or is thinner than the cover, the low-spin effect on the ball when hitting with a driver (W#1) may be insufficient, and the target distance when hitting with a driver (W#1) and irons may not be achieved for average hitters. Also, if the intermediate layer is too thin, its durability against cracking when repeatedly hitting may be poor. On the other hand, if the thickness of the intermediate layer is too thick compared to the above range, the feel of the ball may be poor.

[0059] 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. The upper limit is 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 deviates from the above range, the amount of spin on the ball during a full shot may increase, or the initial ball speed may decrease, resulting in a loss of distance for average hitters when hitting with a driver (W#1) and irons. On the other hand, if this value is too small, the crack resistance when repeatedly hit may be poor.

[0060] For the intermediate layer material, it is preferable to use ionomer resin as the main material. When using ionomer resin as the main material, it is desirable to use a mixture of zinc-neutralized ionomer resin and sodium-neutralized ionomer resin as the main material. The mixing ratio of zinc-neutralized type / sodium-neutralized type (mass ratio) is 5 / 95 to 95 / 5, preferably 10 / 90 to 90 / 10, and more preferably 15 / 85 to 85 / 15. If Zn-neutralized ionomer and Na-neutralized ionomer are not included in this ratio, the rebound may become too low, resulting in a loss of distance when hitting with a driver (W#1) and irons for average hitters. Furthermore, the crack resistance during repeated impacts at room temperature may be poor, as may the crack resistance at low temperatures (below freezing).

[0061] Furthermore, the ionomer resin material preferably contains a high acid content ionomer resin with an unsaturated carboxylic acid content (also called "acid content") of 16% by mass or more.

[0062] Furthermore, 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, based on 100% by mass of the resin material, with an upper limit of preferably 100% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less. If the amount of the high-acid-content ionomer resin is too low, the amount of spin on the ball during a full shot may increase, resulting in a loss of distance. On the other hand, if the amount of the high-acid-content ionomer resin is too high, the durability of repeated impacts may deteriorate.

[0063] The intermediate layer material can be appropriately blended with any additives depending on the application. For example, various additives such as pigments, dispersants, antioxidants, UV absorbers, and light stabilizers can be added. When these additives are blended, the amount blended is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and preferably 10 parts by mass or less, and more preferably 4 parts by mass or less, per 100 parts by mass of the base resin.

[0064] For the intermediate layer material, it is preferable to polish the surface of the intermediate layer in order to improve adhesion with the polyurethane, which is suitably used in the cover material described later. Furthermore, it is preferable to apply a primer (adhesive) to the surface of the intermediate layer after the polishing treatment, or to add an adhesion-enhancing agent to the material.

[0065] When a sphere with an intermediate layer covering the core (intermediate-layer coated sphere) is subjected to an initial load of 98N (10kgf) and a final load of 1,275N (130kgf), the deflection amount (mm) is preferably 2.0mm or more, more preferably 2.2mm or more, and even more preferably 2.4mm or more. On the other hand, the upper limit of the above deflection amount is preferably 3.4mm or less, more preferably 3.1mm or less, and even more preferably 2.8mm or less. If the deflection amount of the intermediate-layer coated sphere is too small, i.e., too hard, the amount of spin will increase too much, which may reduce the distance when an average hitter hits a driver (W#1) or iron, or the feel may become too hard. On the other hand, if the above deflection amount is too large, i.e., the sphere is too soft, the amount of spin will decrease when hitting an iron, resulting in too much roll, making it difficult to control the desired distance, or the feel may become too soft, or the durability against cracking during repeated impacts may be poor.

[0066] The initial velocity of a sphere with an intermediate layer covering the core (intermediate layer-covered sphere) is preferably 76.5 m / s or higher, more preferably 77.0 m / s or higher, and even more preferably 77.3 m / s or higher, with an upper limit of preferably 78.5 m / s or lower, more preferably 78.0 m / s or lower, and even more preferably 77.7 m / s or lower. If this initial velocity is too high, the reduction in distance compared to the current tour ball may not be sufficient for long hitters' driver shots, and the ball may fly beyond the standard distance of the new distance rules envisioned by the R&A and USGA. On the other hand, if this initial velocity is too low, the distance for average hitters' driver (W#1) and iron shots may be reduced. In this case, the above initial velocity values ​​are the same as those used for measuring the initial velocity of the core as described above.

[0067] The initial velocity of the intermediate layer-coated sphere is V. M (m / s), when an intermediate layer covering sphere is subjected to a load from an initial load of 98N (10kgf) to a final load of 1,275N (130kgf), the deflection is M (mm), V MThe value of / M is preferably 23 or higher, more preferably 25 or higher, and even more preferably 27 or higher, with an upper limit of preferably 36 or lower, more preferably 34 or lower, and even more preferably 32 or lower. If this value is too high, the reduction in distance compared to the current tour ball may not be sufficient for long hitters' driver swings, and the ball may fly too far beyond the standard distance of the new distance rules envisioned by the R&A and USGA. On the other hand, if the above value is too low, the distance for average hitters' driver (W#1) swings may be reduced too much.

[0068] Furthermore, it is preferable to optimize the value (Miw) of the relationship between the initial velocity of the core (m / s), the initial velocity of the intermediate layer-coated sphere (m / s), the mass of the core (g), and the mass of the intermediate layer-coated sphere (g), namely, [(initial velocity of intermediate layer-coated sphere - initial velocity of core) × (mass of intermediate layer-coated sphere - mass of core)]. This value represents the rebound of the intermediate layer material in relation to its mass. The above Miw value is preferably 2 or more, more preferably 3 or more, and even more preferably 4 or more, with an upper limit of 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 on the ball when taking a full shot may increase, and the distance of the driver (W#1) and iron shots for average hitters may decrease.

[0069] Next, I will explain the cover. The hardness of the cover material is not particularly limited, but is preferably 50 or higher, more preferably 57 or higher, and even more preferably 63 or higher on the Shore C hardness scale, with an upper limit of preferably 86 or lower, more preferably 74 or lower, and even more preferably 71 or lower. On the Shore D hardness scale, it is preferably 30 or higher, more preferably 35 or higher, and even more preferably 40 or higher, with an upper limit of preferably 57 or lower, more preferably 53 or lower, and even more preferably 50 or lower.

[0070] The surface hardness of the sphere (ball) with the intermediate layer coated sphere covered with a cover is preferably 73 or higher, more preferably 78 or higher, and even more preferably 83 or higher on the Shore C hardness scale, with an upper limit of preferably 95 or lower, more preferably 92 or lower, and even more preferably 90 or lower. On the Shore D hardness scale, it is preferably 50 or higher, more preferably 53 or higher, and even more preferably 56 or higher, with an upper limit of preferably 70 or lower, more preferably 65 or lower, and even more preferably 61 or lower.

[0071] If the material hardness and surface hardness of these covers are too soft compared to the above range, the amount of spin on full shots may increase, resulting in reduced distance for average hitters when using drivers (W#1) and irons. On the other hand, if the material hardness and surface hardness of the covers are too hard compared to the above range, spin on approach shots may be reduced, or scratch resistance may be poor.

[0072] The thickness of the cover is preferably 0.3 mm or more, more preferably 0.5 mm or more, and even more preferably 0.6 mm or more. On the other hand, the upper limit of the cover thickness is preferably 1.2 mm or less, more preferably 0.9 mm or less, and even more preferably 0.8 mm or less. If the cover is too thick, the ball may not have enough rebound during full shots, or the amount of spin may increase, resulting in a decrease in distance when an average hitter hits a driver (W#1) or iron. On the other hand, if the cover is too thin, the scratch resistance may be poor, or spin may not be applied during approach shots, resulting in a lack of control.

[0073] As for the material of the above cover, various urethane resins used for golf ball covers can be used from the viewpoint of spin control and scratch 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. Moreover, it is preferable to form it with a resin compound mainly composed of (I) thermoplastic polyurethane and (II) polyisocyanate compounds.

[0074] The total mass of components (I) and (II) mentioned above is recommended to be 60% or more, and more preferably 70% or more, of the total amount of the resin composition of the cover. Components (I) and (II) are described in detail below.

[0075] Regarding the thermoplastic polyurethane described in (I) above, the structure of the thermoplastic polyurethane includes a soft segment made of a high-molecular-weight polyol (polymeric glycol), which is a long-chain polyol, and a hard segment made of a chain extender and a polyisocyanate compound. Here, any long-chain polyol that has been conventionally used in thermoplastic polyurethane technology can be used as a raw material, and there are no particular restrictions, but examples include polyester polyols, polyether polyols, polycarbonate polyols, polyester polycarbonate polyols, polyolefin polyols, conjugated diene polymer polyols, castor oil polyols, silicone polyols, and vinyl polymer polyols. One type of these long-chain polyol may be used, or two or more types may be used in combination. Among these, polyether polyols are preferred because they can synthesize thermoplastic polyurethanes with a high rebound modulus and excellent low-temperature properties.

[0076] As the chain extender, those used in conventional thermoplastic polyurethane technologies can be suitably used, and for example, it is preferable to use a low molecular weight compound with a molecular weight of 400 or less that has two or more active hydrogen atoms in the molecule that can react with an isocyanate group. Examples of chain extenders include, but are not limited to, 1,4-butylene glycol, 1,2-ethylene glycol, 1,3-butanediol, 1,6-hexanediol, and 2,2-dimethyl-1,3-propanediol. Among these, aliphatic diols having 2 to 12 carbon atoms are preferred as chain extenders, and 1,4-butylene glycol is more preferred.

[0077] As the polyisocyanate compound, those used in conventional thermoplastic polyurethane technology can be suitably used, and there are no particular restrictions. Specifically, one or more selected from the group consisting of 4,4'-diphenylmethane diisocyanate, 2,4-(or)2,6-toluene diisocyanate, p-phenylenediisocyanate, xylylene diisocyanate, naphthylene 1,5-diisocyanate, tetramethylxylylene diisocyanate, hydrogenated xylylene diisocyanate, dicyclohexylmethane diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, norbornene diisocyanate, trimethylhexamethylene diisocyanate, and dimer acid diisocyanate can be used. However, depending on the isocyanate species, it may be difficult to control the crosslinking reaction during injection molding. In the present invention, from the viewpoint of balancing stability during production with the physical properties that are exhibited, 4,4'-diphenylmethanediisocyanate, an aromatic diisocyanate, is most preferred.

[0078] The specific thermoplastic polyurethane component (I) can be a commercially available product, such as Pandex T8295, T8290, and T8260 (all manufactured by DIC Covestropolymer Co., Ltd.).

[0079] Although not an essential component, a thermoplastic elastomer other than the thermoplastic polyurethane can be added to components (I) and (II) above as component (III). By adding this component (III) to the resin compound, it is possible to further improve the fluidity, resilience, abrasion resistance, and other physical properties required for a golf ball cover material.

[0080] There are no particular restrictions on the composition ratio of components (I), (II), and (III) above, but in order to fully exert the effects of the present invention, it is preferable that the mass ratio of (I):(II):(III) = 100:2 to 50:0 to 50, and more preferably (I):(II):(III) = 100:2 to 30:8 to 50 (mass ratio).

[0081] Furthermore, the above resin formulation may contain various additives other than the components that make up the thermoplastic polyurethane, as needed. For example, pigments, dispersants, antioxidants, light stabilizers, UV absorbers, mold release agents, etc., can be added as appropriate.

[0082] A multi-piece solid golf ball, formed by laminating the core, intermediate layer, and cover (outermost layer) described above, can be manufactured by conventional methods such as known injection molding. For example, an intermediate layer material can be injected around the core using an injection molding die to obtain an intermediate layer-coated sphere, and finally, the outermost layer, the cover material, can be injection-molded to obtain a multi-piece golf ball. Alternatively, a golf ball can be manufactured by preparing two half-cups molded into a semi-spherical shape in advance, wrapping the core and intermediate layer-coated sphere with them, and then heat-pressure-molding them.

[0083] When a golf ball is subjected to an initial load of 98N (10kgf) and a final load of 1,275N (130kgf), the amount of deflection (mm) is preferably 2.0mm or more, more preferably 2.2mm or more, and even more preferably 2.3mm or more. On the other hand, the upper limit of the above deflection must be less than 2.7mm, preferably 2.6mm or less, and more preferably 2.5mm or less. If the amount of deflection of the golf ball is too small, i.e., too hard, the amount of spin will increase too much, which may reduce the distance when an average hitter hits a driver (W#1) or iron, or the feel may become too hard. On the other hand, if the amount of deflection is too large, i.e., the sphere is too soft, the amount of spin will decrease when hitting an iron, resulting in too much roll, making it difficult to control the desired distance, or the feel may become too soft, or the durability against cracking during repeated impacts may be poor.

[0084] The initial velocity of the sphere (ball) with a cover over the intermediate layer-coated sphere is preferably 76.5 m / s or higher, more preferably 76.7 m / s or higher, and even more preferably 76.9 m / s or higher, with an upper limit of 77.724 m / s or lower. If this initial velocity is too high, it will not meet the R&A and USGA approved rules. On the other hand, if this initial velocity is too low, the distance of an average hitter's driver (W#1) and iron shots may be reduced. In this case, the above initial velocity values ​​are the same as those used for measuring the initial velocity of the core and intermediate layer-coated sphere described above using the same equipment and conditions.

[0085] When the initial velocity of the ball is V (m / s) and 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 B (mm), the value of V / B is preferably 27 or more, more preferably 29 or more, and even more preferably 31 or more, with an upper limit of 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 distance when a long hitter hits with a driver may not be sufficient compared to the current tour ball, and the ball may fly too far, exceeding the standard distance of the new distance rules envisioned by the R&A and USGA. On the other hand, if the above value is too small, the distance when an average hitter hits with a driver (W#1) may be reduced too much.

[0086] Furthermore, it is preferable to optimize the value (CViw) of the relationship between the initial velocity of the intermediate layer-covered sphere (m / s), the initial velocity of the ball (m / s), the mass of the intermediate layer-covered sphere (g), and the mass of the ball (g), which is given by [(initial velocity of the ball - initial velocity of the intermediate layer-covered sphere) × (mass of the ball - mass of the intermediate layer-covered sphere)]. This value represents the rebound of the cover material portion in relation to its mass portion. The above CViw value is preferably -5 or higher, more preferably -4 or higher, and even more preferably -3 or higher, and the upper limit is preferably 0 or lower, more preferably -1 or lower, and even more preferably -2 or lower. If this value is too high, controllability during short games may be insufficient. On the other hand, if the above value is too low, the amount of spin on the ball may increase during full shots, or the rebound of the ball may decrease, resulting in a significant loss of distance when an average hitter hits a driver (W#1) or iron.

[0087] [ Relationship between the surface hardness of each sphere ] The present invention relates the surface hardness of the intermediate layer-coated sphere to the surface hardness of the ball, and in order to achieve both superior distance during driver (W#1) shots and full iron shots for average hitters, and controllability during short game shots, the following formula (Surface hardness of the ball) < (Surface hardness of the sphere coated with an intermediate layer) The following conditions must be met. The value obtained by subtracting the surface hardness of the ball from the surface hardness of the intermediate layer coated sphere is preferably greater than 0, more preferably 4 or higher, and even more preferably 7 or higher in Shore C hardness, with an upper limit of preferably 20 or less, more preferably 16 or less, and even more preferably 12 or less. If the above value is 0 or less, it may become difficult for average hitters to achieve both superior distance when hitting with a driver and full iron shots and controllability in the short game. On the other hand, if the above value is too high, the distance when hitting with a driver (W#1) and irons for average hitters may be lower than the target distance.

[0088] The difference between the surface hardness of the core and the surface hardness of the intermediate layer-coated sphere is preferably 5 or higher, more preferably 7 or higher, and even more preferably 9 or higher on the Shore C hardness scale. The upper limit is preferably 20 or lower, more preferably 17 or lower, and even more preferably 14 or lower. If the value deviates from the above range, the amount of spin on the ball when hitting a full shot will increase, and the desired distance may not be achieved when an average hitter hits a driver (W#1) or an iron.

[0089] The value obtained by subtracting the core's center hardness from the surface hardness of the intermediate layer-coated sphere is preferably 27 or higher, more preferably 30 or higher, and even more preferably 33 or higher in Shore C hardness, with an upper limit of preferably 43 or lower, more preferably 40 or lower, and even more preferably 37 or lower. If the above value is too low, the amount of spin on the ball will increase during a full shot, and the desired distance may not be achieved when an average hitter hits a driver (W#1) or an iron. On the other hand, if the above value is too high, the crack resistance when repeatedly hit will be poor, or the actual initial ball speed will be low, and the desired distance may not be achieved when an average hitter hits a driver (W#1). Also, the roll may increase when hitting an iron, and the needs of professionals and advanced players may not be satisfied.

[0090] [ Regarding 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 higher, more preferably 0.890 or higher, and even more preferably 0.899 or higher. On the other hand, the upper limit is preferably 0.937 or lower, more preferably 0.923 or lower, and even more preferably 0.909 or lower. If this value is too low, the initial ball speed will be low, or the amount of deflection of the entire ball will be small, making the ball harder, which may increase the amount of spin on the ball during a full shot, and the distance the average hitter will achieve with a driver (W#1) and an iron may be lower than intended. On the other hand, if the above value is too high, the amount of spin on the ball during a full shot may increase, which may also result in the distance the average hitter will achieve with a driver (W#1) and an iron, or the crack resistance after repeated impacts may be poor.

[0091] [ Regarding the relationship between the amount of deflection of each sphere ] When the deflection amounts (mm) of the core and ball spheres are applied from an initial load of 98N (10kgf) to a final load of 1,275N (130kgf), respectively, C (mm) and B (mm), the value of CB is preferably 0.30mm or more, more preferably 0.40mm or more, and even more preferably 0.50mm or more, with an upper limit of preferably 0.90mm or less, more preferably 0.80mm or less, and even more preferably 0.70mm or less. If this value is too large, the crack resistance when repeatedly struck will be poor, the actual initial ball speed will be low, and the desired distance when hitting with a driver (W#1) will not be obtained for average hitters, or the roll will be too large when hitting with an iron. On the other hand, if this value is too small, the feel will be too hard, or the amount of spin when hitting with a full shot will be too high, and the desired distance when hitting with a driver (W#1) and an iron will not be obtained for average hitters.

[0092] When an initial load of 98N (10kgf) is applied to each sphere of the core and intermediate layer covering spheres, and the deflection amount (mm) is applied from an initial load of 98N (10kgf) to a final load of 1,275N (130kgf), respectively, C (mm) and M (mm) are used. The value of CM is preferably 0.30mm or more, more preferably 0.35mm or more, and even more preferably 0.40mm or more. The upper limit is preferably 0.65mm or less, more preferably 0.60mm or less, and even more preferably 0.55mm or less. If this value is too large, the crack resistance when repeatedly struck will be poor, and the actual initial ball speed will be low, which may prevent average hitters from achieving the desired distance when hitting with a driver (W#1). On the other hand, if this value is too small, the feel may become too hard, and the amount of spin when hitting with a full shot may increase, which may prevent average hitters from achieving the desired distance when hitting with a driver (W#1) and irons.

[0093] [ [Values ​​of Ciw + Miw + CViw] The golf ball of the present invention, when Ciw is the value of (initial velocity of the core × mass of the core), Miw is the value of [(initial velocity of the intermediate layer covering sphere - initial velocity of the core) × (mass of the intermediate layer covering sphere - mass of the core)], and CViw is the value of [(initial velocity of the ball - initial velocity of the intermediate layer covering sphere) × (mass of the ball - mass of the intermediate layer covering sphere)], then the following formula 2600 ≤ Ciw + Miw + CViw ≤ 2715 The following conditions must be met. Ciw+Miw+CViw represents the sum of the values ​​indicating the rebound of the core, intermediate layer material, and cover material in relation to their mass. By designing a golf ball to satisfy the above formula, it is possible to reduce the distance a long hitter will hit with a driver (W#1), while reducing the distance an average hitter will lose with a driver (W#1) or long iron than a long hitter. The lower limit of Ciw+Miw+CViw is 2600 or more, preferably 2630 or more, more preferably 2660 or more, and the upper limit is 2715 or less, preferably 2705 or less, more preferably 2695 or less. If this value is too large, the ball may fly too far under the conditions of a long hitter hitting with a driver (W#1), or the desired distance may not be achieved when an average hitter hits with a driver (W#1) or an iron. On the other hand, if the above value is too small, an average hitter may not be able to achieve the desired distance when hitting with a driver (W#1) or an iron.

[0094] Numerous dimples can be formed on the outer surface of the cover. There are no particular restrictions on the number of dimples arranged on the cover surface, but preferably there are 280 or more, preferably 300 or more, more preferably 310 or more, and as an upper limit, preferably 450 or less, more preferably 400 or less, and even more preferably 350 or less. If the number of dimples deviates from the above range, the distance of the driver (W#1) hit by an average hitter may decrease.

[0095] The dimple shape can be one or more types, such as circular, various polygons, dewdrop shapes, or elliptical shapes, and can be used as appropriate. For example, when using a circular dimple, the diameter can be approximately 2.5 mm to 6.5 mm, and the depth can be 0.08 mm to 0.30 mm.

[0096] The ratio of dimples to the spherical surface of a golf ball, specifically the ratio of the total dimple area defined by the plane edges surrounded by the edges of the dimples to the ball's spherical surface assuming no dimples (SR value), is preferably 75% or more, more preferably 80% or more, and even more preferably 84% or more. The upper limit is 90% or less, more preferably 88% or less, and even more preferably 86% or less. If this SR value deviates from the above range, the distance an average hitter can achieve with a driver (W#1) may decrease.

[0097] The VR value (Vision Rating) of the total dimple volume formed below the plane surrounded by the edges of the dimples, relative to the ball volume assuming no dimples exist, is 0.77% or more, preferably 0.79% or more, more preferably 0.81% or more, with an upper limit of 0.92% or less, more preferably 0.89% or less, and more preferably 0.86% or less. If this VR value is greater than the above range, the distance of a long hitter's driver (W#1) shot may drop too much, or an average hitter's driver (W#1) shot may not achieve the desired distance. In this case, the trajectory may be lower, making it difficult to achieve carry distance and making it difficult to clear valleys and water hazards. On the other hand, if the above value is too small, the distance of a long hitter's driver (W#1) shot may not drop, and the ball may fly too far, exceeding the standard distance of the new distance rules assumed by the R&A and USGA.

[0098] The value V0, obtained by dividing the spatial volume of the dimples beneath the plane surrounded by the edges of each dimple by the volume of a cylinder with the plane as its base and the maximum depth of the dimples from this base as its height, is preferably 0.35 or more, more preferably 0.38 or more, and even more preferably 0.40 or more, with an upper limit of 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 distance of the driver (W#1) hit by long hitters and average hitters may be lower than intended.

[0099] For the golf ball of the present invention, when the ratio 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 (CL1 / CD1) is A1, the ratio 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 (CL2 / CD2) is A2, and the ratio 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 (CL3 / CD3) is A3, the following two equations apply: 0.590 ≤ A1 ≤ 0.655, and (A2+A3) / 2≧0.670 The dimples are designed as appropriate to satisfy the requirements.

[0100] In this specification, the "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 coefficients and drag coefficients can be adjusted by adjusting the configuration (arrangement, diameter, depth, volume, number, shape, etc.) of the golf ball's dimples. The lift coefficients and drag coefficients do not depend on 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 equation (1). Re = ρvL / μ (1) In equation (1) above, ρ represents the fluid density, 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.

[0101] In this invention, A1 is defined as 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 defined as 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 defined as 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.

[0102] To explain the conditions under which the above-mentioned lift coefficient CL1 and drag coefficient CD1 are measured—a Reynolds number of 218,000 and a spin rate of 2,800 rpm—this high-speed condition corresponds to the conditions under which a long hitter hits a golf 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 a spin rate of 2,800 rpm is the average spin condition for a player with a head speed (HS) of 54 m / s.

[0103] To explain the conditions under which the above-mentioned lift coefficient CL2 and drag coefficient CD2 are measured—a Reynolds number of 184,000 and a spin rate of 2,900 rpm—this medium-speed condition corresponds to the conditions under which an average hitter hits a golf 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 a spin rate of 2,900 rpm is the average spin condition for a player with a head speed (HS) of 45 m / s.

[0104] To explain the conditions under which the lift coefficient CL3 and drag coefficient CD3 are measured, namely a Reynolds number of 158,000 and a spin rate of 3,100 rpm, these low-speed conditions correspond to the conditions under which an average hitter hits a golf ball with a driver (W#1) at a head speed (HS) of 40 m / s. The 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.

[0105] The ratio of the lift coefficient CL1 to the drag coefficient CD1, i.e., CL1 / CD1=A1, is 0.590 or greater, preferably 0.595 or greater, more preferably 0.600 or greater, with an upper limit of 0.655 or less, preferably 0.640 or less, and more preferably 0.627 or less. If this value is too large, the effect of suppressing the distance when a long hitter hits with a driver (W#1) may be insufficient, resulting in excessive distance. On the other hand, if the above value is too small, the actual distance may be too low compared to the intended distance.

[0106] 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 higher, more preferably 0.645 or higher, and even more preferably 0.660 or higher. The upper limit is preferably 0.750 or lower, more preferably 0.740 or lower, and even more preferably 0.730 or lower. If this value is too low, when hitting with a driver (W#1) at a head speed (HS) of 45 m / s, the carry distance may not be sufficient, and the target total distance may not be achieved. On the other hand, if the above value is too high, when hitting with a driver (W#1) at a head speed (HS) of 45 m / s, the trajectory may balloon, and the target distance may not be achieved.

[0107] 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 higher, more preferably 0.710 or higher, and even more preferably 0.722 or higher. The upper limit is preferably 0.815 or lower, more preferably 0.810 or lower, and even more preferably 0.800 or lower. If this value is too low, when hitting with a driver (W#1) at a head speed (HS) of 40 m / s, the carry distance may not be sufficient, and the target total distance may not be achieved. On the other hand, if the above value is too high, when hitting with a driver (W#1) at a head speed (HS) of 40 m / s, the trajectory may balloon, and the target distance may not be achieved.

[0108] The average value of A2 and A3, i.e., (A2+A3) / 2, is 0.670 or higher, preferably 0.680 or higher, more preferably 0.690 or higher, and the upper limit is preferably 0.783 or lower, more preferably 0.775 or lower, and even more preferably 0.765 or lower. If this value is too low, an average hitter may not get enough carry when hitting with a driver (W#1), and may not achieve the target total distance. On the other hand, if the above value is too high, an average hitter may get a ballooning trajectory when hitting with a driver (W#1), and may not achieve the target distance.

[0109] Furthermore, the multi-piece solid golf ball of the present invention can be used in competition and comply with the rules of golf. The outer diameter of the ball is such that it does not pass through a ring with an inner diameter of 42.672 mm, and the mass can preferably be formed to 45.0 to 45.93 g. [Examples]

[0110] 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.

[0111] [Examples 1-3, Comparative Examples 1-10] Core formation For Example 1 and Comparative Examples 1, 3-5, and 7-9, solid cores were prepared by preparing the rubber compositions shown in Table 1 and then vulcanizing them under the vulcanization conditions shown in Table 1.

[0112] For Examples 2 and 3 and Comparative Examples 2, 6, and 10, cores were prepared based on the formulations shown in Table 1, in the same manner as described above.

[0113] [Table 1]

[0114] Details regarding the above formulation are as follows: • Polybutadiene A: Product name "BR01" (manufactured by JSR Corporation) • Polybutadiene B: Product name "Diene645" (Firestone Polymers) • Polybutadiene C: Product name "BUDENE 1224G" (Goodyear Tire & Rubber Company) • Isoprene rubber: Product name "IR2200" (manufactured by JSR Corporation) • Styrene-butadiene rubber: Product name "SBR1507" (manufactured by JSR Corporation) • Zinc acrylate: Product name "ZN-DA85S" (manufactured by Nippon Shokubai Co., Ltd.) • Zinc methacrylate: Product name "ZDA-90" (manufactured by Asada Chemical Industries Co., Ltd.) • Zinc stearate: Product name "BR-3T" (manufactured by Akrochem) • Organic peroxide: Dicumyl peroxide, trade name "Perkmyl 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: Purified water (manufactured by Masaki Pharmaceutical Co., Ltd.) • Anti-aging agent: 2,2-methylenebis(4-methyl-6-butylphenol), trade name "Nocrac NS-6" (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: Manufactured by Wako Pure Chemical Industries, Ltd.

[0115] Formation of the intermediate layer and cover (outermost layer) Next, for Example 1 and Comparative Examples 1, 3-5, 7-9, an intermediate layer was formed by injection molding using an injection mold with the intermediate layer resin material No. 1 or No. 2 shown in Table 2 around the core surface. Then, using a different injection mold, a cover was formed by injection molding using the cover (outermost layer) resin material No. 3 shown in Table 2 around the intermediate layer-covered sphere. At this time, a predetermined number of dimples described below were formed on the cover surface.

[0116] For Examples 2 and 3 and Comparative Examples 2, 6, and 10, an intermediate layer is formed by injection molding of the intermediate layer resin material No. 1 or No. 2 shown in Table 2 around the core surface using an injection molding die. Then, using another injection molding die, a cover is formed by injection molding of the cover (outermost layer) resin material No. 3 shown in Table 2 around the intermediate layer-covered sphere. For Comparative Example 10, a cover is formed by injection molding of the resin material No. 4 shown in Table 2 around the core surface using an injection molding die. At this time, a predetermined number of dimples described below are formed on the cover surface.

[0117] [Table 2]

[0118] The details of the ingredients listed in Table 2 are as follows. "Hymiran 1605," "Hymiran 1557," "Hymiran 1706," and "AM7318" are ionomers manufactured by Mitsui Dow Polychemicals. Trimethylolpropane (TMP), manufactured by Tokyo Chemical Industry Co., Ltd. "TPU(1)" is a product name "Pandex" manufactured by DIC Covestropolymer, Inc., an ether-type thermoplastic polyurethane, with a material hardness (Shore D) of "50". "TPU(2)" is a product name "Pandex" manufactured by DIC Covestropolymer, an ether-type thermoplastic polyurethane, with a material hardness (Shore D) of "47".

[0119] For each example and comparative example, the following dimples (1) to (5) were used. Each dimple configuration includes eight types of circular dimples, No. 1 to No. 8, with different diameters and depths. Details are shown in Table 3 below. The arrangement patterns (designs) of dimples (1) to (4) are shown in Figure 6. Figure 6(A) is a plan view of the dimples, and Figure 6(B) is a side view thereof. The arrangement pattern (design) of dimple (5) is shown in Figure 7. Figure 7(A) is a plan view of the dimples, and Figure 7(B) is a side view thereof.

[0120] [Table 3]

[0121] Definition of a dimple Edge: The highest point in the cross-section passing through the center of the dimple. Diameter: The diameter of the plane surrounded by the rim of the dimple. Depth: Maximum depth of the dimple from the plane surrounded by the edges of the dimple. SR: The ratio of the total dimple area, defined by the plane enclosed by the edges of the dimples, to the ball's surface area assuming no dimples exist. Dimple volume: The volume of the dimple beneath the plane surrounded by the edges of the dimple. Cylinder volume ratio: The ratio of the volume of a dimple to the volume of a cylinder with the same diameter and depth as the dimple. VR: The sum of the dimple volumes formed downward from the plane surrounded by the edges of the dimples is the ball volume assuming no dimples exist.

[0122] Furthermore, the following table shows the lift coefficient CL1, drag coefficient CD1, and ratio CL1 / CD1=A1 for a ball with the above-mentioned dimples (1) to (5) formed on its cover surface at a Reynolds number of 218,000 and a spin rate of 2,800 rpm; the lift coefficient CL2, drag coefficient CD2, and ratio CL2 / CD2=A2 for a Reynolds number of 184,000 and a spin rate of 2,900 rpm; and the lift coefficient CL3, drag coefficient CD3, and ratio CL3 / CD3=A3 for a Reynolds number of 158,000 and a spin rate of 3,100 rpm. These lift and drag coefficients are measured in accordance with the ITR (Indoor Test Range) defined by the USGA.

[0123] [Table 4]

[0124] For each golf ball obtained, 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 ball velocity were evaluated using the method described below and are shown in Tables 5 to 8.

[0125] Core hardness distribution The core surface is spherical, and the hardness is measured using the Shore C hardness scale according to ASTM D2240 by setting the needle of the hardness tester nearly perpendicular to the spherical surface. For the center and designated positions of the core, the core is cut into a hemispherical shape to create a flat cross-section, and the hardness is measured by pressing the needle of the hardness tester perpendicularly against the center and the designated positions shown in Table 3. The hardness of the center and each position is shown as a Shore C hardness value. For hardness measurement, an automatic rubber hardness tester "P2" manufactured by Polymer Instruments Co., Ltd., equipped with a Shore C hardness tester, is used. The hardness value is read as the maximum value. All measurements are performed in an environment of 23±2℃. The values ​​in the table are Shore C hardness values. Furthermore, in the core hardness distribution, the Shore C hardness Cc at the center of the core and the Shore C hardness C at the midpoint M between the center of the core and the surface are also included. m The Shore C hardness at positions 2mm, 4mm, and 6mm inward from the midpoint M is Cm-2, Cm-4, and Cm-6; the Shore C hardness at positions 2mm, 4mm, and 6mm outward from the center M is Cm+2, Cm+4, and Cm+6; and the Shore C hardness Cs of the core surface is measured in the following areas A to F. ·Area A: 1 / 2×2×(Cm-4-Cm-6) ·Area B: 1 / 2×2×(Cm-2-Cm-4) ·Area C: 1 / 2×2×(Cm-Cm-2) ·Area D: 1 / 2×2×(Cm+2-Cm) ·Area E: 1 / 2×2×(Cm+4-Cm+2) ·Area F: 1 / 2×2×(Cm+6-Cm+4) Calculate the following and find the values ​​of the four formulas below. (1)Area A+Area B (2)Area D+Area E (3)(Area D+Area E)-(Area A+Area B) (4){(Area D+Area E)-(Area A+Area B)}×(Cs-Cc)

[0126] Figure 2 shows a schematic diagram illustrating areas A to F of the core hardness distribution, using the core hardness distribution data from Example 1. Furthermore, graphs of the core hardness distribution for Examples 1-3 and Comparative Examples 1-10 are shown in Figures 3 and 4.

[0127] Outer diameter of each sphere in the core and intermediate layer covering spheres The temperature of the spheres is controlled in a constant temperature bath at 23.9±1℃ for at least 3 hours. Then, in a room at 23.9±2℃, measurements are taken at 5 arbitrary points on the surface, and the average value of these measurements is taken as the measurement value for each sphere. The average value for all 10 measured spheres is then calculated.

[0128] Ball diameter The balls are kept at a constant temperature of 23.9±1℃ for at least 3 hours. Then, in a room at 23.9±2℃, 15 measurements are taken at arbitrary non-dimpled areas, and the average value is taken as the measurement value for one ball. The average value for 10 measured balls is then calculated.

[0129] Deflection of the core, intermediate layer covering sphere, and ball Each target coated 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. The above deflection amounts were measured in a room at 23.9±2℃ after the temperature was controlled in a constant temperature chamber at 23.9±1℃ for at least 3 hours. A high-load compression tester manufactured by Mu Seiki Co., Ltd. was used as the measuring instrument, and the down speed of the pressure head that compresses the core, each layer of coated spheres, or balls was set to 10mm / s.

[0130] Material hardness of the intermediate layer and cover (Shore C hardness, Shore D hardness) Each layer of resin material is molded into a 2mm thick sheet and left at a temperature of 23±2℃ for two weeks. Three sheets are stacked together for measurement. Shore C hardness and Shore D hardness are measured using a Shore C hardness tester and a Shore D hardness tester compliant with the ASTM D2240 standard. For hardness measurement, an automatic rubber hardness tester "P2" manufactured by Polymer Instruments Co., Ltd., equipped with a Shore C or Shore D hardness tester, is used. The maximum value is read. The measurement method follows the ASTM D2240 standard.

[0131] Surface hardness of each sphere in the intermediate layer coated sphere and the ball The hardness of each sphere is measured by pressing the needle perpendicularly against its surface. The surface hardness of the ball (cover) is measured on the land portion of the ball surface where no dimples are formed. Shore C hardness and Shore D hardness are measured using Shore C and Shore D hardness testers compliant with the ASTM D2240 standard. For hardness measurement, an automatic rubber hardness tester "P2" manufactured by Polymer Instruments Co., Ltd., equipped with either a Shore C or Shore D hardness tester, is used. The maximum value is read. The measurement method follows the ASTM D2240 standard.

[0132] Initial velocity of each sphere The initial velocity of each sphere will be measured at 23.9±2°C using a COR-type velocometer manufactured by Hye Precision Products, the same type used by the 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. A ball is launched at four different incident velocities according to the air pressure, collides with a barrier, and the coefficient of restitution (COR) is measured. In other words, a correlation equation between incident velocity and COR is created by changing the air pressure in four stages. Similarly, a correlation equation between incident velocity and contact time is created. Then, using these correlation equations, the coefficient of restitution (COR) and contact time (μs) at an incident velocity of 43.83 m / s are determined, and these values ​​are substituted into the initial velocity conversion formula below to calculate the initial velocity of each sphere. IV = 136.8 + 136.3e + 0.019tc [Here, e is the coefficient of restitution, and tc is the contact time (μs) at a collision velocity of 143.8 ft / s (43.83 m / s).] In measuring the initial velocity of each sphere, 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. For the core, a barrel diameter of 39.88 mm is selected for Examples 1-3 and Comparative Examples 1-9, and 41.53 mm for Comparative Example 10. For the intermediate layer coated spheres, a barrel of 41.53 mm is selected for all cases, and for the balls, a barrel of 43.18 mm is selected for all cases.

[0133] Values ​​of Ciw + Miw + CViw In each example and comparative example, the value of Ciw + Miw + CViw is calculated, where Ciw is the value of (initial velocity of the core × mass of the core), Miw is the value of [(initial velocity of the intermediate layer coated sphere - initial velocity of the core) × (mass of the intermediate layer coated sphere - mass of the core)], and CViw is the value of [(initial velocity of the ball - initial velocity of the intermediate layer coated sphere) × (mass of the ball - mass of the intermediate layer coated sphere)]. The values ​​for each example are listed in Tables 7 and 8, and a graph showing the value of Ciw + Miw + CViw is shown in Figure 5.

[0134] [Table 5]

[0135] [Table 6]

[0136] [Table 7]

[0137] [Table 8]

[0138] The flight distance (W#1)(I#6) and controllability during approach shots for each golf ball were evaluated using the following method. The results are shown in Table 9.

[0139] Flight evaluation (W#1, HS54m / s) A golf swing robot will be fitted with a driver club and hit the ball at a head speed (HS) of 54 m / s. The spin rate and total distance will be measured. The club used will be a Bridgestone Sports "TourB XD-5 Driver (2017 model)" (loft angle 8.5°), and the results will be evaluated according to the following criteria. 〔Judgment criteria〕 ○ ··· The total compared to Comparative Example 1 is -8.0m or less, or -20.0m or more. △ ··· The total compared to Comparative Example 1 is less than -20.0m. × ··· The total compared to Comparative Example 1 is greater than -8.0m.

[0140] Flight evaluation (W#1, HS45m / s) A golf swing robot will be fitted with a driver club and struck at a head speed (HS) of 45 m / s to measure spin rate and total distance. The club used will be a Bridgestone Sports "J015 Driver (2016 model)" (loft angle 9.5°), and will be evaluated according to the following criteria. 〔Judgment criteria〕 ○ ··· The total compared to Comparative Example 1 is -5.0m or more. △ ··· The total compared to Comparative Example 1 is -10.0m or more and less than -5.0m. × ··· The total compared to Comparative Example 1 is less than -10.0m.

[0141] Flight evaluation (W#1, HS40m / s) A golf hitting robot will be fitted with a driver club and hit the ball at a head speed (HS) of 40 m / s. The spin rate and total distance will be measured. The club used will be a Bridgestone Sports "J015 Driver (2016 model)" (loft angle 9.5°), and the results will be evaluated according to the following criteria. 〔Judgment criteria〕 ○ ··· The total compared to Comparative Example 1 is -5.0m or more. △ ··· The total compared to Comparative Example 1 is -10.0m or more and less than -5.0m. × ··· The total compared to Comparative Example 1 is less than -10.0m.

[0142] Flight evaluation (I#6, HS42m / s) A golf hitting robot will be fitted with a 6-iron (I#6) and hit at a head speed (HS) of 42 m / s. The spin rate and total distance will be measured. The distance of the roll only (total - carry) will also be calculated. The club used will be a Bridgestone Sports "JGR Forged I#6 (2016 model)" and will be evaluated according to the following criteria. [Evaluation Criteria / Total] ○ ··· The total compared to Comparative Example 1 is 0m or more. △ ··· The total compared to Comparative Example 1 is -5.0m or more and less than 0m. × ··· The total compared to Comparative Example 1 is less than -5.0m. [Judgment Criteria / Run] ○ ··· The run is 6.0m or less. × ··· The run is larger than 6.0m.

[0143] Flight evaluation (I#6, HS35m / s) A golf swing robot will be fitted with a 6-iron (I#6) and hit at a head speed (HS) of 35 m / s. The spin rate and total distance will be measured. The distance of the roll only (total - carry) will also be calculated. The club used will be a Bridgestone Sports "JGR Forged I#6 (2016 model)" and will be evaluated according to the following criteria. [Evaluation Criteria / Total] ○ ··· The total compared to Comparative Example 1 is 0m or more. △ ··· The total compared to Comparative Example 1 is -5.0m or more and less than 0m. × ··· The total compared to Comparative Example 1 is less than -5.0m. [Judgment Criteria / Run] ○ ··· The run is 6.0m or less. × ··· The run is larger than 6.0m.

[0144] Evaluating spin rate during approach shots The spin rate will be determined by the amount of spin produced when a golf swing robot is hit with a sand wedge at a head speed (HS) of 15 m / s. The spin rate will be similarly measured using an initial condition measurement device immediately after impact. The sand wedge used will be a Bridgestone Sports "TourStage TW-03 (loft angle 57°) 2002 model". 〔Judgment criteria〕 ○ ··· Spin rate of 4500 rpm or more × ··· Spin rate less than 4500 rpm

[0145] [Table 9]

[0146] As shown in the results in Table 9, the golf balls of Comparative Examples 1 to 10 are inferior to the present invention (example) in the following respects. Comparative Example 1 is one embodiment of a tour ball currently used by professionals and advanced players, in which the A1 value is greater than 0.655. As a result, the distance is excessive when using a driver (W#1) with a head speed (HS) of 54 m / s. In Comparative Example 2, the value of A1 is less than 0.590, and the value of (A2+A3) / 2 is less than 0.670. As a result, the distance when hitting with a driver (W#1) at a head speed (HS) of 54 m / s is too low, and the distance when hitting with a driver (W#1) at a head speed (HS) of 45 m / s is also inferior. In Comparative Example 3, the value of A1 is greater than 0.655, the amount of ball deflection under a specified load is greater than 2.7 mm, and the value of Ciw+Miw+CViw is less than 2600. As a result, the distance of the ball when hit with a driver (W#1) at a head speed (HS) of 54 m / s is excessive, and the roll of the ball when hit with a 6-iron (I#6) is also excessive. Comparative Example 4 shows that the ball deflection under a predetermined load is greater than 2.7 mm, and Ciw+Miw+CViw is less than 2600. As a result, the distance when hitting with a driver (W#1) at a head speed (HS) of 45 m / s is reduced, and the roll when hitting with a 6-iron (I#6) is increased. Comparative Example 5 has an A1 value greater than 0.655, a ball initial velocity less than 76.5 m / s, and Ciw+Miw+CViw less than 2600. As a result, the distance of shots with the driver (W#1) at head speeds (HS) of 45 m / s and 40 m / s is inferior, as is the distance of shots with the 6-iron (I#6). Comparative Example 6 has a ball speed less than 76.5 m / s, and the Ciw+Miw+CViw value is less than 2600. As a result, the distance of the driver (W#1) at a head speed (HS) of 54 m / s is too low, and the distance of the driver (W#1) at head speeds (HS) of 45 m / s and 40 m / s is also inferior, as is the distance of the 6-iron (I#6). Comparative Example 7 has an A1 value greater than 0.655, a ball deflection greater than 2.7 mm under a specified load, a ball initial velocity less than 76.5 m / s, and Ciw+Miw+CViw less than 2600. As a result, the distance when hitting with a driver (W#1) at a head speed (HS) of 45 m / s is reduced, and the roll is increased when hitting with a 6-iron (I#6) at a head speed (HS) of 35 m / s. Comparative Example 8 has an A1 value greater than 0.655, a ball deflection greater than 2.7 mm under a predetermined load, a ball initial velocity less than 76.5 m / s, and Ciw+Miw+CViw less than 2600. As a result, the distance of shots with the driver (W#1) at head speeds (HS) of 45 m / s and 40 m / s, and with the 6-iron (I#6), is inferior, and the roll of the ball is increased when hitting with the 6-iron (I#6) at a head speed (HS) of 42 m / s. Comparative Example 9 has an A1 value greater than 0.655, a ball deflection greater than 2.7 mm under a predetermined load, a ball initial velocity less than 76.5 m / s, and Ciw+Miw+CViw less than 2600. As a result, the distance of shots with a driver (W#1) at a head speed (HS) of 45 m / s and with a 6-iron (I#6) is inferior, and the roll of the ball is increased when hitting with a 6-iron (I#6) at a head speed (HS) of 35 m / s. Comparative Example 10 is a two-piece golf ball designed for practice ranges, with a ball speed less than 76.5 m / s and a Ciw+Miw+CViw value greater than 2715. As a result, the distance of the ball when hit with a driver (W#1) at a head speed (HS) of 54 m / s is too low, and the distance of the ball when hit with a driver (W#1) at head speeds (HS) of 45 m / s and 40 m / s, and with a 6-iron (I#6), is also inferior. [Explanation of Symbols]

[0147] G Golf Balls 1 core 2. Middle class 3 Cover D-dimple

Claims

1. A multi-piece solid golf ball comprising a core, an intermediate layer, and a cover, wherein numerous dimples are formed on the outer surface of the cover, and the relationship between the surface hardness of the intermediate layer-covered sphere and the surface hardness of the ball is given by the following formula (Surface hardness of the ball) < (Surface hardness of the sphere coated with an intermediate layer) (However, hardness refers to Shore C hardness.) When the following conditions are met, the initial velocity of the ball is 76.5 to 77.724 m / s, and the deflection of the ball when an initial load of 98 N (10 kgf) is applied to the ball and a final load of 1,275 N (130 kgf) is applied is less than 2.7 mm, and when the value of (initial velocity of the core × mass of the core) is Ciw, the value of [(initial velocity of the intermediate layer-coated sphere - initial velocity of the core) × (mass of the intermediate layer-coated sphere - mass of the core)] is Miw, and the value of [(initial velocity of the ball - initial velocity of the intermediate layer-coated sphere) × (mass of the ball - mass of the intermediate layer-coated sphere)] is CViw, then the following formula 2600≦Ciw+Miw+CViw≦2715 Furthermore, when the following conditions are met, and the ratio 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 CL1 / CD1, A1 is the ratio 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 CL2 / CD2, A2 is the ratio 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 CL3 / CD3, then the following two equations 0.590 ≤ A1 ≤ 0.655, and (A2+A3) / 2≧0.670 A multi-piece solid golf ball characterized by satisfying the following conditions.

2. The multi-piece solid golf ball according to claim 1, wherein the volume occupancy rate VR of the dimples is 0.77 to 0.92%.

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

783.

4. The multi-piece solid golf ball according to claim 1 or 2, wherein the value of A2 is 0.635 to 0.750 and the value of A3 is 0.695 to 0.

815.

5. The relationship between the surface hardness of the core and the surface hardness of the intermediate layer-coated sphere is given by the following formula: (Surface hardness of the intermediate layer-coated sphere) ≥ (Surface hardness of the core) (However, hardness refers to Shore C hardness.) A multi-piece solid golf ball according to claim 1 or 2 that satisfies the requirements.

6. When the initial velocity of the core is Vc (m / s) and the deflection amount C (mm) is applied to the core from an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf), the following formula is used: 20 ≤ Vc / C ≤ 30 A multi-piece solid golf ball according to claim 1 or 2 that satisfies the requirements.

7. When the deflection amounts (mm) of the core, intermediate layer coated sphere, and ball are applied from an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf), respectively, C (mm), M (mm), and B (mm), then the following two equations apply: 0.30 ≤ C - B ≤ 0.90 0.30 ≤ C - M ≤ 0.65 A multi-piece solid golf ball according to claim 1 or 2 that satisfies the requirements.

8. When the deflection (mm) of the core is applied from an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf), the following formula is used: 700 ≤ Cw / C ≤ 1000 A multi-piece solid golf ball according to claim 1 or 2 that satisfies the requirements.

9. In the hardness distribution of the core described above, the Shore C hardness at the center of the core is Cc, and the Shore C hardness at the midpoint M between the center of the core and the surface is C m When the Shore C hardness at positions 2 mm, 4 mm, and 6 mm inward from the midpoint M is Cm-2, Cm-4, and Cm-6 respectively, and the Shore C hardness at positions 2 mm, 4 mm, and 6 mm outward from the center M is Cm+2, Cm+4, and Cm+6 respectively, and the Shore C hardness of the core surface is Cs, then the following areas A to F ・Area A: 1 / 2 x 2 x (Cm-4-Cm-6) ・Area B: 1 / 2×2×(Cm-2-Cm-4) ・Area C: 1 / 2×2×(Cm-Cm-2) ・Area D: 1 / 2 x 2 x (Cm+2-Cm) ・Area E: 1 / 2 x 2 x (Cm+4-Cm+2) ・Area F: 1 / 2 x 2 x (Cm+6-Cm+4) Regarding the following formula {(Area D+Area E)-(Area A+Area B)}≧4.0 A multi-piece solid golf ball according to claim 1 or 2 that satisfies the requirements.

10. In the hardness distribution of the above core, the following formula (Cs-Cc)≧22 A multi-piece solid golf ball according to claim 9 that satisfies the requirements.

11. In the hardness distribution of the above core, the following formula (Cs-Cc) / (Cm-Cc)≧4.0 A multi-piece solid golf ball according to claim 9 that satisfies the requirements.

12. In the hardness distribution of the above core, the following formula Area E > Area D > Area C A multi-piece solid golf ball according to claim 9 that satisfies the requirements.

Images