Golf ball

Abstract

To provide a golf ball which is designed not to compete excessively for superiority in terms of a distance when a golfer with a high head speed (HS) and an ordinary golfer use the same ball.SOLUTION: A golf ball in this invention includes a core and a cover, the cover is formed primarily of polyurethane, the ball has a diameter of at least 42.8 mm and a mass of the ball of 44.9 g or less, and in an impact test (a head speed of 40 m / s) carried out by hitting the ball with a driver, the sum (t1+t2) of the time (t1) required from initial contact of the driver with the ball for deformation of the ball to the maximum deformation of the ball and the time (t2) required for the ball and driver to separate from the state of maximum deformation is not more than 660 μ sec.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a golf ball having two or more layers including at least a core and a cover.

Background Art

[0002] Conventionally, various golf balls have been proposed to increase the flight distance and obtain a good feel. Many of these golf balls are optimized for players with a head speed of around 45 m / sec. However, when a player with a head speed of around 40 m / sec uses such a golf ball, the flight distance and feel are not satisfactory. Also, many golf balls optimized for players with a head speed of around 40 m / sec have problems such as difficulty in stopping on the green during an iron shot or issues during a short game. Originally, golf should be a sport that competes in the skills of players. If the difference in flight distance due to the difference in the head speed of golf players becomes too large, it means competing in the difference in power of the players, which is not preferable.

[0003] As a design of a golf ball having a two-layer structure or more with a core and a cover, devices such as making the ball diameter larger than normal, reducing the weight of the ball, and further adjusting the total dimple volume have been made. Examples of such technical documents include the following Patent Documents 1 to 34.

[0004] However, the proposed golf ball has a sufficiently large difference in flight distance when struck with a driver (W#1) between golfers with high clubhead speed and those without, and is disadvantageous for players without high clubhead speed or power when competing with the same ball. Also, it cannot be said to be a golf ball sufficient for competing in scores based on the accuracy of a golfer's shot or approach technique. Further, in order to compete in scores based on the skill of each shot of a golfer without relying on power, it is fair and preferable to increase the spin amount in the short game to enhance controllability without increasing the run, which is the difference between the total flight distance and carry during iron shots, in order to compete in scores based on the skill of a golfer. Therefore, it is necessary to develop a golf ball that is fair and appropriate for each player with the above aims while following the original golf rules.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Patent Document 8

Patent Document 9

Patent Document 10

Patent Document 11

[0006] The present invention has been made in view of the above circumstances, and by using the same ball for a person with a high club head speed and a person without it, it does not compete for excessive superiority in flight distance, and can compete fairly and appropriately by using the same ball for skills in iron shots and short games. An object of the present invention is to provide a golf ball. [Means for Solving the Problems]

[0007] As a result of intensive studies to achieve the above object, regarding a golf ball having a core and a cover, the cover is formed mainly of polyurethane, the ball diameter is designed to be 42.8 mm or more, and the ball mass is designed to be 44.9 g or less. In a driving test (club head speed: 40 m / s) using a driver, the time (t1) required for the deformation amount of the golf ball to become the largest from the start of contact between the driver and the golf ball, and the golf ball from the state where the deformation amount of the golf ball becomes the largest until the golf ball and the driver are separated. It has been found that a golf ball in which the total (t1 + t2) of the time (t2) required for this is 660 μsec or less can provide a golf ball in which the difference in flight distance at the time of hitting a driver (W#1) between a golfer with a high club head speed and a golfer without it does not become too large, the run at the time of iron hitting is not large, and the spin amount is large and the controllability is high in a short game, and the present invention has been completed.

[0008] Note that the golfer with a high club head speed mentioned above refers to a person with a club head speed (HS) of 45 m / s or more, and the golfer with a low club head speed refers to a person with a club head speed (HS) of less than 45 m / s. The same meaning applies hereinafter in the text.

[0009] Therefore, the present invention provides the following golf ball. 1. A golf ball comprising a core and a cover, wherein the cover is formed mainly of polyurethane, the ball diameter is 42.8 mm or more, the ball mass is 44.9 g or less, Hitting a golf ball with a driver under the condition of a head speed of 40 m / s In a hitting test, the total time (t1 + t2) from the start of contact between the driver and the golf ball until the deformation amount of the golf ball becomes the largest and the time (t2) from the state where the deformation amount of the golf ball becomes the largest until the golf ball and the driver are separated is 660 μsec or less. Further, an intermediate layer made of a resin material is formed between the core and the cover, and the surface hardness of the spherical body (intermediate layer-coated spherical body) in which the core is coated with the intermediate layer is 70 or more in Shore D hardness A golf ball characterized by the above. 2. The golf ball according to item 1 above, wherein the specific gravity of the ball is 1.02 to 1.10. 3. The golf ball according to item 1 or 2 above, wherein the specific gravity relationship between the core and the cover is core specific gravity ≤ cover specific gravity. 4. The golf ball according to any one of items 1 to 3 above, wherein the ratio (t2 / t1) of the time (t2) to the time (t1) is 1.28 or less. 5. The golf ball according to item 1 or 2 above, wherein the deflection amount (mm) from an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf) applied to the ball is 3.2 mm or less. 6. The diameter of the core is 37.0 mm or more, and in the hardness distribution of the core, when the Shore C hardness at the center of the core is Cc, the Shore C hardness at the midpoint M between the center and the surface of the core is Cm, the Shore C hardness at positions 2 mm, 4 mm, 6 mm, 8 mm inward from the midpoint M is Cm-2, Cm-4, Cm-6, Cm-8 respectively, and the Shore C hardness at positions 2 mm, 4 mm, 6 mm outward from the center M is Cm+2, Cm+4, Cm+6 respectively, and the Shore C hardness at the surface of the core is Cs, the following areas A to F · Area X: 1 / 2 × 2 × (Cm-6 - Cm-8) · 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 20.0 ≧ (Area D + Area E + Area F) - (Area A + Area B + Area C) > 0 The golf ball according to any one of 1 to 5 above that satisfies the above formula 7. Regarding Areas A to F, X of the core hardness distribution above, the following formula 20.0 ≧ (Area D + Area E + Area F) - (Area X + Area A + Area B + Area C) > 0 The golf ball according to any one of 1 to 6 above that satisfies the above formula 8. Regarding Areas A to E of the core hardness distribution above, the following formula 14.0 ≧ (Area D + Area E) - (Area A + Area B + Area C) ≧ 1 The golf ball according to the above 6 description that satisfies the above formula 9. Regarding Areas A to E, X of the core hardness distribution above, the following formula 14.0 ≧ (Area D + Area E) - (Area X + Area A + Area B + Area C) > 0 The golf ball according to the above 6 description that satisfies the above formula 10. Regarding Areas A to F of the core hardness distribution above, core center hardness Cc, and core surface hardness Cs, the following formula 0 < 〔(Area: D + E + F) - (Area: A + B + C)〕 / (Cs - Cc) ≦ 1.00 The golf ball according to 6 above that satisfies the above formula 11. The golf ball according to the above 6 description where the value of core surface hardness (Cs) - core center hardness (Cc) is 20 or more 12. From the amount of deflection E (mm) when a load 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 value E - B (mm) obtained by subtracting the amount of deflection B (mm) when a load is applied to the ball from an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf) is 0.3 to 1.2 mm, and the golf ball according to any one of 1 to 11 above.

Advantages of the Invention

[0010] According to the golf ball of the present invention, excessive differences in flight distance due to differences in head speed (HS) when each player hits with a driver (W#1) are reduced, and there are few runs in an iron full shot, and good spin and high controllability are obtained in a short game.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Modes for Carrying Out the Invention

[0012] Hereinafter, the present invention will be described in more detail. The golf ball of the present invention comprises a core and a cover. One or more intermediate layers may be interposed between the core and the cover. For example, in FIG. 1, there is a golf ball G having a three-layer structure including a core 1, an intermediate layer 2 covering the core 1, and a cover 3 covering the intermediate layer. Note that the cover 3, excluding the coating film layer, is located in the outermost layer of the layer structure of the golf ball. A large number of dimples D are usually formed on the surface of the cover (outermost layer) 3 to improve the aerodynamic characteristics. Further, a coating film layer is usually formed on the surface of the cover 3, but is not shown in FIG. 1. Hereinafter, each of the above layers will be described in detail.

[0013] As the material of the core, a rubber material is mainly used. Specifically, a rubber composition can be prepared by using a base rubber as the main component and blending a co-crosslinking agent, an organic peroxide, an inert filler, an organic sulfur compound, etc. with this. As the base rubber, it is preferable to use polybutadiene.

[0014] As the type of polybutadiene, commercially available products can be used, for example, BR01, BR51, BR730 (manufactured by JSR Corporation), etc. Further, the proportion of polybutadiene in the base rubber is preferably 60% by mass or more, more preferably 80% by mass or more. Other rubber components can be blended with the base rubber within a range that does not impair the effects of the present invention in addition to the above polybutadiene. Examples of the rubber components other than the above polybutadiene include polybutadiene other than the above polybutadiene, other diene rubbers, for example, styrene-butadiene rubber, natural rubber, isoprene rubber, ethylene-propylene-diene rubber, etc.

[0015] Examples of the co-crosslinking agent include unsaturated carboxylic acids, metal salts of unsaturated carboxylic acids, etc. Specific examples of the unsaturated carboxylic acid include acrylic acid, methacrylic acid, maleic acid, fumaric acid, etc., and acrylic acid and methacrylic acid are particularly preferably used. The metal salt of the unsaturated carboxylic acid is not particularly limited, but examples thereof 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., and zinc acrylate is particularly preferably used.

[0016] The above unsaturated carboxylic acid and / or its metal salt is usually formulated in an amount of 20 parts by mass or more, preferably 25 parts by mass or more, more preferably 30 parts by mass or more, and usually 60 parts by mass or less, preferably 50 parts by mass or less, more preferably 40 parts by mass or less, based on 100 parts by mass of the base rubber. If the compounding amount is too large, it may become too hard and have a difficult-to-endure hitting feeling. If the compounding amount is too small, the resilience may decrease.

[0017] Commercially available products can be used as the above organic peroxide. For example, Parkmyl D (manufactured by NOF Corporation), Perhexa C-40, Perhexa 3M (manufactured by NOF Corporation), Luperco 231XL (manufactured by Atochem), etc. can be preferably used. These may be used alone or in combination of two or more. The compounding amount of the organic peroxide is preferably 0.1 part by mass or more, more preferably 0.3 part by mass or more, further preferably 0.5 part by mass or more, and preferably 5 parts by mass or less, more preferably 4 parts by mass or less, further preferably 3 parts by mass or less, and most preferably 2.5 parts by mass or less, based on 100 parts by mass of the base rubber. If the compounding amount is too large or too small, it may not be possible to obtain a suitable hitting feeling, durability, and resilience.

[0018] In addition, examples of the compounding agents compounded with the base rubber include inert fillers, and for example, zinc oxide, barium sulfate, calcium carbonate, etc. can be preferably used. These may be used alone or in combination of two or more. The compounding amount of the inert filler is preferably 1 part by mass or more, more preferably 3 parts by mass or more, preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and still more preferably 12 parts by mass or less with respect to 100 parts by mass of the base rubber. If the compounding amount is too large or too small, appropriate mass and suitable resilience may not be obtained.

[0019] Furthermore, an anti-aging agent can be compounded as needed. For example, commercially available products include No Crack NS-6, NS-30 (manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.), Yoshinox 425 (manufactured by Yoshitomi Pharmaceutical Industries, Ltd.), etc. These may be used alone or in combination of two or more.

[0020] The compounding amount of the anti-aging agent is preferably 0 part by mass or more, more preferably 0.05 part by mass or more, particularly preferably 0.1 part by mass or more, preferably 3 parts by mass or less, more preferably 2 parts by mass or less, particularly preferably 1 part by mass or less, and most preferably 0.5 part by mass or less with respect to 100 parts by mass of the base rubber. If the compounding amount is too large or too small, suitable resilience and durability may not be obtained.

[0021] In addition, in order to impart good resilience to the core, an organic sulfur compound can be compounded. The organic sulfur compound is not particularly limited as long as it can improve the resilience of the golf ball. Examples thereof include thiophenols, thionaphthols, halogenated thiophenols, or metal salts thereof. More specifically, pentachlorothiophenol, pentafluorothiophenol, pentabromothiophenol, parachlorothiophenol, zinc salt of pentachlorothiophenol, zinc salt of pentafluorothiophenol, zinc salt of pentabromothiophenol, zinc salt of parachlorothiophenol, diphenyl polysulfide, dibenzyl polysulfide, dibenzoyl polysulfide, dibenzothiazoyl polysulfide, dithiobenzoyl polysulfide, etc. having 2 to 4 sulfur atoms can be mentioned. In particular, the zinc salt of pentachlorothiophenol is preferably used. The compounding amount of the organic sulfur compound is preferably 0 parts by mass or more, more preferably 0.05 parts by mass or more, still more preferably 0.1 parts by mass or more, and as the upper limit, preferably 5 parts by mass or less, more preferably 3 parts by mass or less, still more preferably 2.5 parts by mass or less, based on 100 parts by mass of the base rubber. If the compounding amount is too large, the improvement effect on resilience (particularly, the impact by W#1) cannot be expected any more, and the core may become too soft or the hitting feeling may deteriorate. On the other hand, if the compounding amount is too small, the improvement effect on resilience cannot be expected.

[0022] More specifically, by directly adding water (materials containing water) to the above core material, the decomposition of the organic peroxide during core compounding can be promoted. It is known that the decomposition efficiency of the organic peroxide in the core rubber composition changes with temperature, and the higher the temperature above a certain level, the higher the decomposition efficiency. However, if the temperature is too high, the amount of decomposed radicals becomes excessive, and the radicals recombine or become inactivated with each other. As a result, the amount of radicals effectively working for crosslinking decreases. Here, when heat of decomposition is generated by the decomposition of the organic peroxide during core vulcanization, the temperature near the core surface is maintained at approximately the same level as the temperature of the vulcanization mold, but near the core center, the heat of decomposition of the organic peroxide decomposed from the outside accumulates, so it becomes significantly higher than the mold temperature. When water (materials containing water) is directly added to the core, since water has the function of promoting the decomposition of the organic peroxide, the radical reaction as described above can be changed at the core center and the core surface. That is, near the core center, the decomposition of the organic peroxide is further promoted, and the inactivation of radicals is further accelerated, resulting in a further decrease in the amount of effective radicals. Therefore, a core with a significantly different crosslink density between the core center and the core surface can be obtained, and a core with different dynamic viscoelastic properties at the core center can be obtained.

[0023] There are no particular restrictions on the water added to the above core material, and it may be distilled water or tap water. In particular, it is preferably adopted to use distilled water containing no impurities. The amount of water added is preferably 0.1 part by mass or more, more preferably 0.3 part by mass or more, based on 100 parts by mass of the base rubber. The upper limit is preferably 5 parts by mass or less, more preferably 4 parts by mass or less.

[0024] The above core can be manufactured by vulcanizing and curing a rubber composition containing the above components. For example, knead using a kneader such as a Banbury mixer or a roll, and perform compression molding or injection molding using a mold for the core. Heat the molded body appropriately at a temperature sufficient for an organic peroxide or a co-crosslinking agent to act, at 100 to 200 °C, preferably 140 to 180 °C, for 10 to 40 minutes, whereby the molded body can be cured and manufactured.

[0025] In addition, the above core can be formed not only in a single layer but also in multiple layers. As a specific example, a two-layer structure of an inner core and an outer core can be mentioned. When the core is formed into two layers of an inner core and an outer core, as the materials of the inner and outer cores, any of the above-mentioned rubber materials can be used as the main material. Also, the rubber material of the outer core covering the inner core may be of the same type or different type from the material of the inner core. Specifically, it is the same as described for each component of the rubber material of the above core.

[0026] The diameter of the core is preferably 37.0 mm or more, more preferably 38.0 mm or more, still more preferably 38.8 mm or more, and the upper limit is preferably 41.2 mm or less, more preferably 40.3 mm or less, still more preferably 39.4 mm or less. If the diameter of the core is too small, the amount of spin increases when hitting with a driver (W#1), and the desired flight distance may not be obtained for a golfer with a slow head speed. On the other hand, if the diameter of the core is too large, the repeated impact durability may deteriorate or the hitting feel may become poor.

[0027] With respect to the core, the amount of deflection (mm) from an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf) is not particularly limited, but is preferably 2.5 mm or more, more preferably 2.7 mm or more, still more preferably 2.9 mm or more, and as the upper limit value, is preferably 3.9 mm or less, more preferably 3.7 mm or less, still more preferably 3.5 mm or less. If the amount of deflection of the core is too small, i.e., the core is too hard, the spin of the ball will increase too much, and the ball may not fly even for golfers with a high head speed, and not only for golfers with a high head speed but also for golfers with a low head speed, and the hitting feeling 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 resilience of the ball will become too low, and the ball may not fly even for golfers with a high head speed, and not only for golfers with a high head speed but also for golfers with a low head speed, and the hitting feeling may become too soft, or the crack durability during repeated hitting may deteriorate.

[0028] Next, the hardness distribution of the core will be described. Note that the hardness of the core described below means the Shore C hardness. This Shore C hardness is a hardness value measured with a Shore C hardness tester conforming to ASTM D2240 standard.

[0029] The core center hardness (Cc) is not particularly limited, but can preferably be 56 or more, more preferably 58 or more, still more preferably 60 or more. Also, the upper limit thereof is not particularly limited, but can preferably be 67 or less, more preferably 65 or less, still more preferably 63 or less. If this value is too large, the hitting feeling may become hard, or the spin may increase in a full shot and the desired flight distance may not be obtained. On the other hand, if the above value is too small, the resilience may decrease and the desired flight distance may not be obtained, or the crack durability during repeated hitting may deteriorate. Note that the above core center hardness (Cc) means the hardness measured at the center of the cross-section obtained by cutting the core in half (so as to pass through the center).

[0030] The hardness (Cm-8) at a position 8 mm inward from the position M (hereinafter also referred to as the "intermediate position M") in the middle between the center and the surface of the above core is not particularly limited, but is preferably 56 or more, more preferably 58 or more, and still more preferably 60 or more. Also, the upper limit thereof is not particularly limited, and can be preferably 68 or less, more preferably 66 or less, and still more preferably 64 or less.

[0031] The hardness (Cm-6) at a position 6 mm inward from the position M (hereinafter also referred to as the "intermediate position M") in the middle between the center and the surface of the above core is not particularly limited, but is preferably 57 or more, more preferably 59 or more, and still more preferably 61 or more. Also, the upper limit thereof is not particularly limited, and can be preferably 69 or less, more preferably 67 or less, and still more preferably 65 or less.

[0032] The hardness (Cm-4) at a position 4 mm inward from the position M (hereinafter also referred to as the "intermediate position M") in the middle between the center and the surface of the above core is not particularly limited, but is preferably 59 or more, more preferably 61 or more, and still more preferably 63 or more. Also, the upper limit thereof is not particularly limited, and can be preferably 70 or less, more preferably 68 or less, and still more preferably 66 or less.

[0033] The hardness (Cm-2) at a position 2 mm inward from the intermediate position M of the above core is not particularly limited, but is preferably 60 or more, more preferably 62 or more, and still more preferably 64 or more. Also, the upper limit thereof is not particularly limited, and can be preferably 71 or less, more preferably 69 or less, and still more preferably 67 or less. If these hardness values deviate, there is a risk of causing the same adverse results as those described for the center hardness (Cc) of the above core.

[0034] The cross-sectional hardness (Cm) at the intermediate position M of the above core is not particularly limited, but it can preferably be 60 or more, more preferably 62 or more, and still more preferably 64 or more. Also, the upper limit thereof is not particularly limited, but it can preferably be 72 or less, more preferably 70 or less, and still more preferably 68 or less. If these hardness values deviate, there is a risk of causing the same adverse results as those described for the core center hardness (Cc) of the above core.

[0035] The hardness (Cm+2) at a position 2 mm outward from the intermediate position M of the above core toward the core surface (hereinafter simply referred to as "outward") is not particularly limited, but it can preferably be 63 or more, more preferably 65 or more, and still more preferably 67 or more. Also, the upper limit thereof is not particularly limited, and it can preferably be 77 or less, more preferably 75 or less, and still more preferably 73 or less. If this value is too large, the crack durability upon repeated impact may deteriorate, or the hitting feeling may become too hard. On the other hand, if the above value is too small, the repulsion may become too low, or the spin during a full shot may increase and the desired flying distance may not be obtained.

[0036] The hardness (Cm+4) at a position 4 mm outward from the intermediate position M of the above core is not particularly limited, but it can preferably be 69 or more, more preferably 71 or more, and still more preferably 73 or more. Also, the upper limit thereof is not particularly limited, and it can preferably be 82 or less, more preferably 80 or less, and still more preferably 78 or less. If these hardness values deviate, there is a risk of causing the same adverse results as those described for the hardness (Cm+2) at a position 2 mm away from the intermediate position M of the above core.

[0037] The hardness (Cm+6) at a position 6 mm outward from the intermediate position M of the above core is not particularly limited, but is preferably 73 or more, more preferably 75 or more, and still more preferably 77 or more. Also, the upper limit thereof is not particularly limited, and can be preferably 85 or less, more preferably 83 or less, and still more preferably 81 or less. If these hardness values deviate, there is a risk of causing the same adverse results as those described for the hardness (Cm+2) at a position 2 mm away from the intermediate position M of the above core.

[0038] The surface hardness (Cs) of the above core is not particularly limited, but can be preferably 80 or more, more preferably 82 or more, and still more preferably 84 or more. Also, the upper limit thereof is not particularly limited, and can be preferably 91 or less, more preferably 89 or less, and still more preferably 87 or less. If this value is too large, the hitting feeling may become hard, or the spin may increase in a full shot and the desired flying distance may not be obtained. Note that the above surface hardness (Cs) means the hardness measured on the surface (spherical surface) of the above core.

[0039] In order to increase the hardness difference between the inside and outside of the core, the hardness difference between the center and the surface of the core is optimized. That is, the value of the core surface hardness (Cs) - the core center C hardness (Cc) is preferably 20 or more in Shore C hardness, more preferably 22 or more, and still more preferably 23 or more. Also, the upper limit thereof is not particularly limited, and can be preferably 30 or less, more preferably 28 or less, and still more preferably 25 or less. If the above hardness difference is too small, the flying distance of a golfer with a low spin effect during driver (W#1) hitting and a low head speed may not be achieved. On the other hand, if the above hardness difference is too large, the initial hitting speed may be low, and the flying distance of a golfer with a low head speed may not be achieved, or the crack durability during repeated hitting may deteriorate.

[0040] In the above core hardness distribution in the present invention, the following areas A to F, X · Area X: 1 / 2 × 2 × (Cm - 6 - Cm - 8) · 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, it is preferable that the value of (Area D + Area E + Area F) - (Area A + Area B + Area C) exceeds 0, more preferably 2.0 or more, still more preferably 4.0 or more, and the upper limit value is preferably 20.0 or less, more preferably 16.0 or less, still more preferably 12.0 or less. If this value is too small, the flight distance may not be achieved for golfers with a fast head speed but insufficient low spin effect when hitting with the driver (W#1). On the other hand, if the above value is large, the initial hitting speed may be low and the flight distance may not be achieved for golfers with a fast head speed, or the crack durability during repeated hitting may deteriorate.

[0041] Regarding the above Areas A to F and X, the value of (Area D + Area E + Area F) - (Area X + Area A + Area B + Area C) is not particularly limited, but it is preferably more than 0, more preferably 2.0 or more, still more preferably 4.0 or more, and the upper limit value is preferably 20.0 or less, more preferably 16.0 or less, still more preferably 12.0 or less. If it deviates from the above range, there is a risk of causing the same adverse results as those described for the value of (Area D + Area E + Area F) - (Area A + Area B + Area C).

[0042] Regarding the above areas A to E, the value of (Area D + Area E) - (Area A + Area B + Area C) is not particularly limited, but it is preferably 1.0 or more, more preferably 2.0 or more, and even more preferably 3.0 or more. As the upper limit value, it is preferably 14.0 or less, more preferably 11.0 or less, and even more preferably 8.0 or less. If it deviates from the above range, there is a risk of causing the same adverse results as those described for the value of (Area D + Area E + Area F) - (Area A + Area B + Area C).

[0043] Regarding the above areas A to E, X, the value of (Area D + Area E) - (Area X + Area A + Area B + Area C) is not particularly limited, but it is preferably more than 0, more preferably 1.0 or more, and even more preferably 2.0 or more. As the upper limit value, it is preferably 14.0 or less, more preferably 11.0 or less, and even more preferably 8.0 or less. If it deviates from the above range, there is a risk of causing the same adverse results as those described for the value of (Area D + Area E + Area F) - (Area A + Area B + Area C).

[0044] Regarding the above areas A to F, core center hardness Cc and core surface hardness Cs, the following formula 0 < 〔(Area: D + E + F) - (Area: A + B + C)〕 / (Cs - Cc) ≤ 1.00 is preferably satisfied, and more preferably, 0.10 ≤ 〔(Area D + E + F) - (Area A + B + C)〕 / (Cs - Cc) ≤ 0.80, and even more preferably, 0.20 ≤ 〔(Area D + E + F) - (Area A + B + C)〕 / (Cs - Cc) ≤ 0.60.

[0045] Note that Fig. 2 shows a schematic diagram explaining areas A to F, X using the core hardness distribution data of Example 1. Thus, areas A to F, X are the areas of each triangle having the difference in each specific distance as the base and the difference in hardness at each position as the height.

[0046] Next, the intermediate layer will be described. The material hardness of the intermediate layer is not particularly limited, but in terms of Shore D hardness, it is preferably 60 or more, more preferably 62 or more, still more preferably 64 or more, and as the upper limit value, it is preferably 72 or less, more preferably 70 or less, still more preferably 68 or less. Further, the surface hardness of the sphere coated with the intermediate layer (intermediate layer-coated sphere) is, in terms of Shore D hardness, preferably 66 or more, more preferably 68 or more, still more preferably 70 or more, and as the upper limit value, it is preferably 78 or less, more preferably 76 or less, still more preferably 74 or less. If the material hardness and surface hardness of these intermediate layers are too soft compared to the above ranges, even for a person with a low club head speed, the amount of spin during a full shot may increase too much and the carry distance may not be achieved, or the initial speed of the ball may be low and the carry distance may not be achieved during a full shot. On the other hand, if the material hardness and surface hardness of the intermediate layer are too hard compared to the above ranges, the crack durability due to repeated impacts may deteriorate, or the feel of hitting may deteriorate.

[0047] In addition, when the material hardness of the intermediate layer is expressed in terms of Shore C hardness, it is preferably 88 or more, more preferably 89 or more, still more preferably 92 or more, and as the upper limit value, it is preferably 98 or less, more preferably 96 or less, still more preferably 94 or less. Further, the surface hardness of the intermediate layer-coated sphere, when expressed in terms of Shore C hardness, is preferably 92 or more, more preferably 94 or more, still more preferably 96 or more, and as the upper limit value, it is preferably 100 or less, more preferably 99 or less, still more preferably 98 or less.

[0048] The thickness of the intermediate layer is preferably 0.9 mm or more, more preferably 1.1 mm or more, still more preferably 1.2 mm or more. On the other hand, as the upper limit value of the thickness of the intermediate layer, it is preferably 1.8 mm or less, more preferably 1.6 mm or less, still more preferably 1.4 mm or less. If the intermediate layer is too thin, the crack durability due to repeated impacts may deteriorate, or the spin may increase during an iron full shot and the carry distance may not be achieved. On the other hand, if the intermediate layer is too thick, the initial speed may decrease and even a golfer with a low club head speed may not achieve the carry distance, or the feel of hitting may deteriorate.

[0049] As for the material of the intermediate layer, it is preferable to adopt an ionomer resin as the main material.

[0050] As the ionomer resin material, it is preferable to blend a high acid content ionomer resin with an unsaturated carboxylic acid content (also referred to as "acid content") of 16% by mass or more into a normal ionomer resin and use it. By this blending, low spin and high resilience during a full shot can be realized, so that a golfer with a slow clubhead speed can ensure the desired flight distance.

[0051] The content (acid content) of the unsaturated carboxylic acid contained in the high acid content ionomer resin is usually 16% by mass or more, preferably 17% by mass or more, more preferably 18% by mass or more, and as the upper limit value, preferably 22% by mass or less, more preferably 21% by mass or less, still more preferably 20% by mass or less. If this value is too small, the spin may increase during a full shot, and the desired flight distance may not be obtained. On the contrary, if the above value is too large, the hitting feeling may become too hard, or the crack durability during repeated hitting may deteriorate.

[0052] Also, the high acid content ionomer resin is preferably 10% by mass or more, more preferably 30% by mass or more, still more preferably 60% by mass or more based on 100 mass of the resin material. If the blending amount of the above high acid content ionomer resin is too small, the spin may increase when hitting a driver (W#1), and the flight distance may not be achieved.

[0053] Any additives can be appropriately blended into the intermediate layer material according to the application. For example, various additives such as pigments, dispersants, anti-aging agents, ultraviolet absorbers, and light stabilizers can be added. When blending these additives, the blending amount is preferably 0.1 part by mass or more, more preferably 0.5 part by mass or more, and as the upper limit, preferably 10 parts by mass or less, more preferably 4 parts by mass or less based on 100 parts by mass of the base resin.

[0054] Regarding the intermediate layer material, it is preferable to polish the surface of the intermediate layer in order to enhance the adhesion with the polyurethane, which is preferably used as the cover material described later. Further, it is preferable to apply a primer (adhesive) to the surface of the intermediate layer after the polishing treatment, or to add an adhesion enhancer to the material.

[0055] The specific gravity of the intermediate layer material is preferably 0.90 or more, more preferably 0.93 or more, and even more preferably 0.95 or more. The upper limit value is preferably 1.08 or less, more preferably 1.05 or less, and even more preferably 1.00 or less. If the above specific gravity is too large, it may inhibit low spin during a full shot, and it may not be possible to ensure the target flight distance for a golfer with a low head speed. On the other hand, if the above specific gravity is too small, for example, in order to take measures such as foaming the resin to provide air bubbles inside, the repeated impact durability may deteriorate, the resilience may decrease, and the flight distance may not be achieved even for a golfer with a low head speed.

[0056] Next, the cover (outermost layer) will be described. The material hardness of the cover is not particularly limited, but in terms of Shore D hardness, it is preferably 35 or more, more preferably 40 or more, and even more preferably 45 or more. As the upper limit value, it is preferably 60 or less, more preferably 55 or less, and even more preferably 50 or less. Also, the surface hardness of the sphere (ball surface hardness) with the intermediate layer-coated sphere covered with the cover is, in terms of Shore D hardness, preferably 50 or more, more preferably 53 or more, and even more preferably 56 or more. As the upper limit value, it is preferably 70 or less, more preferably 67 or less, and even more preferably 64 or less. If the material hardness of these covers and the ball surface hardness are too soft compared to the above ranges, the spin will increase during an iron full shot, and the flight distance may not be achieved under any hitting conditions. On the other hand, if the material hardness of the above covers and the ball surface hardness are too hard compared to the above ranges, the spin may not be generated during an approach, or the scratch resistance may deteriorate.

[0057] In addition, when the material hardness of the cover is expressed in Shore C hardness, it is preferably 57 or more, more preferably 63 or more, still more preferably 70 or more, and as the upper limit value, it is preferably 89 or less, more preferably 83 or less, still more preferably 76 or less. Further, when the surface hardness of the ball is expressed in Shore C hardness, it is preferably 75 or more, more preferably 80 or more, still more preferably 85 or more, and as the upper limit value, it is preferably 95 or less, more preferably 92 or less, still more preferably 90 or less.

[0058] The thickness of the cover is preferably 0.3 mm or more, more preferably 0.45 mm or more, still more preferably 0.6 mm or more. On the other hand, as the upper limit value of the thickness of the cover, it is preferably 1.2 mm or less, more preferably 1.15 mm or less, still more preferably 1.0 mm or less. If the cover is too thick, there may be insufficient rebound or excessive spin during an iron full shot, resulting in no flying distance. On the other hand, if the cover is too thin, the scratch resistance may deteriorate, or insufficient spin may be generated during approach, resulting in insufficient controllability.

[0059] The total thickness of the intermediate layer and the cover is not particularly limited, but is preferably 1.4 mm or more, more preferably 1.7 mm or more, still more preferably 2.0 mm or more, and as the upper limit value, it is preferably 2.8 mm or less, more preferably 2.5 mm or less, still more preferably 2.3 mm or less. If the total thickness is less than the above range, the crack durability due to repeated impacts may deteriorate, or the hitting feeling may deteriorate. On the other hand, if the total thickness is greater than the above range, the amount of spin during a full shot increases, and not only for players with a high head speed but also for players with a low head speed, the flying distance may not be achieved.

[0060] As the material of the cover, various thermoplastic resins used for golf ball covers can be added. However, from the viewpoints of controllability and abrasion resistance, a urethane resin is used as the main material. That is, in the golf ball of the present invention, a cover made of urethane resin is required in order to reduce the run in an iron shot and stop on the green, and to enhance the controllability in a short game. In particular, from the viewpoint of mass productivity of ball products, it is preferable to use a material mainly composed of thermoplastic polyurethane. More preferably, it can be formed from a resin composition mainly composed of (I) thermoplastic polyurethane and (II) polyisocyanate compound.

[0061] It is recommended that the total mass of the above components (I) and (II) combined is 60% or more, more preferably 70% or more, based on the total amount of the resin composition of the cover. The above components (I) and (II) will be described in detail below.

[0062] Regarding the above (I) thermoplastic polyurethane, the structure of the thermoplastic polyurethane includes a soft segment composed of a high molecular polyol (polymeric glycol) which is a long-chain polyol, and a hard segment composed of a chain extender and a polyisocyanate compound. Here, as the long-chain polyol as a raw material, any of those conventionally used in the technology related to thermoplastic polyurethane can be used and is not particularly limited. For example, polyester polyol, polyether polyol, polycarbonate polyol, polyester polycarbonate polyol, polyolefin-based polyol, conjugated diene polymerization-based polyol, castor oil-based polyol, silicone-based polyol, vinyl polymerization-based polyol, etc. can be mentioned. These long-chain polyols may be used alone or in combination of two or more. Among these, polyether polyol is preferable in that a thermoplastic polyurethane having a high resilience modulus and excellent low-temperature characteristics can be synthesized.

[0063] As the chain extender, those used in the technology related to conventional thermoplastic polyurethanes can be preferably used. For example, it is preferably a low molecular compound having a molecular weight of 400 or less and having two or more active hydrogen atoms capable of reacting with isocyanate groups in the molecule. Examples of the chain extender include 1,4-butylene glycol, 1,2-ethylene glycol, 1,3-butanediol, 1,6-hexanediol, 2,2-dimethyl-1,3-propanediol, etc., but are not limited thereto. Among these, aliphatic diols having 2 to 12 carbon atoms are preferred as the chain extender, and 1,4-butylene glycol is more preferred.

[0064] As the polyisocyanate compound, those used in the technology related to conventional thermoplastic polyurethanes can be preferably used, and there is no particular limitation. Specifically, one or more selected from the group consisting of 4,4'-diphenylmethane diisocyanate, 2,4-(or)2,6-toluene diisocyanate, p-phenylene diisocyanate, xylylene diisocyanate, naphthylene 1,5-diisocyanate, tetramethylxylylene diisocyanate, hydrogenated xylylene diisocyanate, dicyclohexylmethane diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, norbornene diisocyanate, trimethylhexamethylene diisocyanate, 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 the balance between the stability during production and the physical properties expressed, 4,4'-diphenylmethane diisocyanate, which is an aromatic diisocyanate, is most preferred.

[0065] As the specific thermoplastic polyurethane of component (I), commercially available products can also be used. For example, Pandex T8295, T8290, T8260 (all manufactured by DIC Covestro Polymer Co., Ltd.) etc. can be mentioned.

[0066] Although not an essential component, a thermoplastic elastomer other than the above thermoplastic polyurethane can be blended as another component (III) with the above components (I) and (II). By blending this component (III) into the above resin composition, various physical properties required for a golf ball cover material, such as further improvement in the fluidity, resilience, and scratch resistance of the resin composition, can be enhanced.

[0067] Regarding the composition ratio of the above components (I), (II), and (III), there is no particular limitation. However, in order to fully and effectively exhibit the effects of the present invention, it is preferably (I):(II):(III) = 100:2 to 50:0 to 50 by mass ratio, and more preferably (I):(II):(III) = 100:2 to 30:8 to 50 (mass ratio).

[0068] Furthermore, various additives other than the components constituting the above thermoplastic polyurethane can be blended into the above resin composition as necessary. For example, pigments, dispersants, antioxidants, light stabilizers, ultraviolet absorbers, mold release agents, etc. can be appropriately blended.

[0069] Regarding the manufacturing method of a golf ball formed by laminating each of the above-described core, intermediate layer, and cover (outermost layer), it can be carried out by a conventional method such as a known injection molding method. For example, a multi-piece golf ball can be obtained by injecting an intermediate layer material with an injection molding die around the core to obtain each coated sphere, and then injecting the material of the cover, which is the outermost layer. Also, as each coated layer, a golf ball can be produced by wrapping the coated sphere with two half cups pre-formed into a semi-shell shape and performing heat and pressure molding.

[0070] 〔 Hardness relationship of each layer 〕 The intermediate layer-coated sphere has a higher surface hardness than the surface of the core, and the difference in these surface hardnesses is, in Shore C hardness, preferably 1 or more, more preferably 5 or more, still more preferably 10 or more, and as the upper limit, preferably 30 or less, more preferably 20 or less, still more preferably 15 or less. If the above value is too small, even for a golfer with increased spin in a full shot and a low clubhead speed, the flying distance may not be achieved. If the above value is too large, the crack durability when repeatedly struck may deteriorate.

[0071] The intermediate layer-coated sphere has a higher surface hardness than the surface of the ball, and the difference in these surface hardnesses is, in Shore C hardness, preferably 1 or more, more preferably 5 or more, still more preferably 9 or more, and as the upper limit, preferably 20 or less, more preferably 17 or less, still more preferably 15 or less. When the above value is small, if the small value is due to the material hardness of the intermediate layer, even for a player with a low clubhead speed, the spin in a full shot may increase and the aimed flying distance may not be achieved. When the small value is due to the material hardness of the cover, the spin controllability in a shot game may deteriorate or the scratch resistance may deteriorate. On the other hand, when the above value is large, if the large value is due to the material hardness of the intermediate layer, the crack durability due to repeated strikes may deteriorate or the feel may become too hard. When the large value is due to the material hardness of the cover, even for a player with a low clubhead speed, the spin in a full shot may increase and the aimed flying distance may not be achieved.

[0072] Deflection amount relationship between the core and the ball ​​From the deflection amount E (mm) of the core from the initial load of 98 N (10 kgf) to the final load of 1,275 N (130 kgf), the value E - B (mm) obtained by subtracting the deflection amount B (mm) of the ball from the initial load of 98 N (10 kgf) to the final load of 1,275 N (130 kgf) is preferably 0.3 mm or more, more preferably 0.5 mm or more, and even more preferably 0.6 mm or more. As the upper limit value, it is preferably 1.2 mm or less, more preferably 1.0 mm or less, and even more preferably 0.8 mm or less. If this value is too small, the spin at full shot may increase, and the flight distance may not be achieved even for a golfer with a slow head speed. On the other hand, if the above value is too large, the crack durability during repeated strikes may deteriorate, or there may be too much run during an iron shot.

[0073] The ratio of the deflection amount of the ball to the core, that is, the value of B / E, is preferably 0.70 or more, more preferably 0.73 or more, and even more preferably 0.78 or more. As the upper limit value, it is preferably 0.84 or less, more preferably 0.82 or less, and even more preferably 0.80 or less. If this value is too small, the crack durability during repeated strikes may deteriorate, or there may be too much run during an iron shot. On the other hand, if the above value is too large, the spin at full shot may increase, and the target flight distance may not be achieved even for a golfer with a slow head speed.

[0074] Specific gravity relationship between the core and the cover ​​Regarding the relationship between the specific gravity of the core and the specific gravity of the cover, it is preferable to satisfy Core Specific Gravity ≤ Cover Specific Gravity. That is, the value obtained by subtracting the core specific gravity from the cover specific gravity is preferably 0 or more, more preferably 0.01 or more, and even more preferably 0.02 or more. Also, the upper limit value of this value is preferably 0.09 or less, more preferably 0.07 or less, and even more preferably 0.05 or less. If this value is too small, in the case of being caused by the cover specific gravity, since a cover with a small specific gravity such as ionomer is used, the cover may be easily damaged. In the case of being caused by the core specific gravity, the rebound of the ball becomes low, and it may become impossible to obtain the desired flight distance even for a person with a slow head speed, or it becomes difficult to make the ball mass (weight) 45.93 g or less, which is recognized as an R&A approved ball. On the other hand, if this value is too large, in the case of being caused by the cover specific gravity, a filler is added to the cover, so the cover may be easily damaged. In the case of being caused by the core specific gravity, something other than zinc oxide, barium sulfate, calcium carbonate, etc. is used as the filler, the rebound of the ball becomes low, and it may become impossible to obtain the desired flight distance even for a person with a slow head speed. Also, when using zinc oxide, barium sulfate, calcium carbonate, etc. as the filler, it becomes difficult to make the ball mass (weight) 45.93 g or less, which is recognized as an R&A approved ball.

[0075] In the present invention, in a hitting test using a driver (head speed: 40 m / s), the time (t1) required from the start of contact between the driver and the golf ball until the deformation amount of the golf ball becomes the largest, and the time (t2) required from the state where the deformation amount of the golf ball becomes the largest until the golf ball and the club face of the driver are separated, the ratio (t2 / t1) is preferably 1.28 or less.

[0076] Specifically, a driver (W#1) made of a metal head, the product name "TourB XD-5" (loft angle 9.5°) manufactured by Bridgestone Sports Co., Ltd., is attached to the golf hitting robot, and a golf ball is hit under the condition of a head speed (HS) of 40 m / s. For the golf ball during the hit, it is photographed using a high-speed video camera (FASTCAM SA-Z manufactured by Photron), the photographed image is analyzed, and the times of (t1) and (t2) above are obtained. Note that, using an image photographed from directly side of the hit, the time point when the diameter of the golf ball in the flight direction is the smallest from the contact surface between the club face and the golf ball is set as the time point when the deformation amount of the golf ball is the largest.

[0077] Regarding the above (t1) time, that is, in the hitting test using the driver (head speed 40 m / s), the time required from the start of contact between the driver and the golf ball until the deformation amount of the golf ball becomes the largest is preferably 260 μsec or more, more preferably 270 μsec or more, still more preferably 275 μsec or more, and the upper limit value is preferably 300 μsec or less, more preferably 295 μsec or less, still more preferably 285 μsec or less. If the above value is too small, especially in the case of an iron full shot, the spin may become too much and the flying distance may not be achieved, or the hitting feeling may deteriorate. On the other hand, if the above value is too large, the initial velocity may become low, and especially in the hitting conditions of the driver (W#1), the flying distance may not be achieved, or there may be too much run during the iron shot.

[0078] Regarding the above-mentioned time (t2), that is, in the hitting test using a driver (head speed: 40 m / s), the time required from the state where the deformation amount of the golf ball is the largest until the golf ball and the driver separate is preferably 295 μsec or more, more preferably 305 μsec or more, still more preferably 315 μsec or more, and the upper limit value is preferably 365 μsec or less, more preferably 355 μsec or less, still more preferably 345 μsec or less. If the above value is too small, especially in an iron full shot, the spin may become too much and the flying distance may not be achieved, or the hitting feeling may deteriorate. On the other hand, if the above value is too large, the initial velocity may decrease, and especially under the hitting conditions of a driver (W#1), the flying distance may not be achieved, or there may be too much run during an iron shot.

[0079] The above ratio (t2 / t1) is preferably 1.00 or more, more preferably 1.05 or more, still more preferably 1.10 or more, and the upper limit value is preferably 1.28 or less, more preferably 1.25 or less, still more preferably 1.22 or less. If the value of this ratio is too small, especially in an iron full shot, the spin may become too much and the flying distance may not be achieved, or the hitting feeling may deteriorate. If the above value is too large, the initial velocity may decrease, and especially under the hitting conditions of a driver (W#1), the flying distance may not be achieved, or there may be too much run during an iron shot.

[0080] Also, regarding the total time of the above (t1) and (t2), it is preferably 550 μsec or more, more preferably 580 μsec or more, still more preferably 600 μsec or more, and the upper limit value is preferably 660 μsec or less, more preferably 645 μsec or less, still more preferably 630 μsec or less. If this value is too small, especially in an iron full shot, the spin may become too much and the flying distance may not be achieved, or the hitting feeling may deteriorate. On the other hand, if the above value is too large, the initial velocity may decrease, and especially under the hitting conditions of a driver (W#1), the flying distance may not be achieved, or there may be too much run during an iron shot.

[0081] In the present invention, the ball diameter is 42.8 mm or more, preferably 42.85 mm or more, and more preferably 42.9 mm or more. On the other hand, the upper limit value of the ball diameter is usually 44.0 mm or less, preferably 43.7 mm or less, and more preferably 43.5 mm or less. If this diameter is too small, the difference in flight distance when a person with a high head speed and a person without a high head speed hit with a driver (W#1) will become excessively large. On the other hand, if the ball diameter is too large, the flight distance of a person with a low head speed when hitting with a driver (W#1) will decrease, and the difficulty of golf will increase, tending to be disadvantageous in competition.

[0082] In the present invention, the ball mass is 44.9 g or less, preferably 44.7 g or less, and more preferably 44.5 g or less. On the other hand, the lower limit value of the ball mass is usually 43.0 g or more, preferably 43.2 g or more, and more preferably 43.4 g or more. If this ball mass is too large, the difference in flight distance when a person with a high head speed and a person without a high head speed hit with a driver (W#1) will become excessively large. On the other hand, if the ball mass is too small, the flight distance of a person with a low head speed when hitting with a driver (W#1) will decrease, and the difficulty of golf will increase, tending to be disadvantageous in competition.

[0083] For the golf ball, the amount of deflection (mm) from an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf) is not particularly limited, but is preferably 2.0 mm or more, more preferably 2.2 mm or more, still more preferably 2.4 mm or more. As the upper limit, it is preferably 3.2 mm or less, more preferably 3.0 mm or less, still more preferably 2.8 mm or less. If the amount of deflection of the golf ball is too small, i.e., too hard, even for a player with a low head speed, the spin may increase too much and the carry distance may not be achieved during a full shot, or the feel may become too hard. On the other hand, if the above amount of deflection is too large, i.e., the above sphere is too soft, the crack durability during repeated hitting may deteriorate, or the actual initial velocity may be low and the carry distance may not be achieved especially with a driver (W#1) for a player with a low head speed.

[0084] Regarding the specific gravity of the golf ball, it is preferably 1.02 or more, more preferably 1.03 or more, still more preferably 1.04 or more. As the upper limit, it is preferably 1.10 or less, more preferably 1.08 or less, still more preferably 1.07 or less. If the ball specific gravity is too large, the difference in carry distance when a person with a high head speed and a person without a high head speed hit with a driver (W#1) will become excessively large. On the other hand, if the ball specific gravity is too small, the carry distance when a person with a low head speed hits with a driver (W#1) will decrease, and the difficulty of golf will increase, tending to be disadvantageous in competition.

[0085] A large number of dimples can be formed on the outer surface of the cover. Regarding the dimples arranged on the cover surface, there is no particular limitation, but it is preferably 250 or more, preferably 300 or more, more preferably 320 or more. As the upper limit, it can preferably have 380 or less, more preferably 350 or less, still more preferably 340 or less. If the number of dimples exceeds the above range, the ball trajectory may become low and the carry distance may decrease. Conversely, if the number of dimples decreases, the ball trajectory may become high and the carry distance may not increase.

[0086] Regarding the shape of the dimples, one or a combination of two or more types such as circular, various polygons, teardrop shape, and other ellipses can be appropriately used. For example, when using circular dimples, the diameter can be about 2.5 mm or more and 6.5 mm or less, and the depth can be 0.08 mm or more and 0.30 mm or less.

[0087] Regarding the dimple occupancy rate of the golf ball's spherical surface, specifically, the ratio (SR value) of the total dimple area defined by the plane edges surrounded by the edges of the dimples to the spherical surface area of the ball assuming no dimples is desirably 70% or more and 90% or less from the perspective of fully exhibiting aerodynamic characteristics. Also, the value (cylindrical volume ratio) V0 obtained by dividing the spatial volume of the dimples under the plane surrounded by the edges of each dimple by the cylindrical volume with the plane as the base and the maximum depth of the dimples from this base as the height is preferably 0.35 or more and 0.80 or less from the perspective of optimizing the ball's trajectory. Furthermore, the VR value of the total dimple volume formed downward from the plane surrounded by the edges of the dimples to the ball volume of the ball assuming no dimples is preferably 0.6% or more and 1.0% or less. Deviating from the ranges of the above numerical values may result in a trajectory where a good flight distance cannot be obtained, and it may not be possible to achieve a sufficiently satisfactory flight distance.

[0088] A paint layer (coating layer) can be formed on the cover surface. This paint layer can be painted using various paints. As the paint, it is preferable to use a paint composition mainly composed of a urethane paint composed of polyol and polyisocyanate because it needs to withstand the harsh usage conditions of the golf ball.

[0089] Examples of the above polyol component include acrylic polyol and polyester polyol. These polyols include modified polyols, and other polyols can be added to further improve workability.

[0090] As the polyol component, it is preferable to use two types of polyester polyols in combination. In this case, when the two types of polyester polyols are used as component (a) and component (b), as the polyester polyol of component (a), a polyester polyol in which a cyclic structure is introduced into the resin skeleton can be adopted. For example, polycondensation of a polyol having an alicyclic structure such as cyclohexanedimethanol and a polybasic acid, or polycondensation of a polyol having an alicyclic structure, diols or triols, and a polybasic acid can be mentioned. polyester polyols obtained by On the other hand, as the polyester polyol of component (b), a polyester polyol having a multi-branched structure can be adopted. For example, polyester polyols having a branched structure such as "NIPPOLAN 800" manufactured by Tosoh Corporation can be mentioned.

[0091] On the other hand, there are no particular restrictions on the polyisocyanate, and it is a generally used polyisocyanate such as aromatic, aliphatic, alicyclic, etc. Specifically, tolylene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, lysine diisocyanate, isophorone diisocyanate, 1,4-cyclohexylene diisocyanate, naphthalene diisocyanate, trimethylhexamethylene diisocyanate, dicyclohexylmethane diisocyanate, 1-isocyanato-3,3,5-trimethyl-4-isocyanatomethylcyclohexane, etc. can be mentioned. These can be used alone or in combination.

[0092] In the coating composition, various organic solvents can be mixed depending on the coating conditions. Examples of such organic solvents include aromatic solvents such as toluene, xylene, and ethylbenzene; ester solvents such as ethyl acetate, butyl acetate, propylene glycol methyl ether acetate, and propylene glycol methyl ether propionate; ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; ether solvents such as diethylene glycol dimethyl ether, diethylene glycol diethyl ether, and dipropylene glycol dimethyl ether; alicyclic hydrocarbon solvents such as cyclohexane, methylcyclohexane, and ethylcyclohexane; and petroleum hydrocarbon solvents such as mineral spirit, etc. can be used.

[0093] There is no particular limitation on the thickness of the coating layer composed of the above coating composition, but it is usually 5 to 40 μm, preferably 10 to 20 μm. Here, the thickness of the coating layer means the average thickness of the coating measured at three locations, namely, the center of the dimple and two locations between the center of the dimple and the edge of the dimple.

[0094] In the present invention, it is necessary that the elastic work recovery rate of the coating layer composed of the above coating composition is 60% or more, preferably 80% or more. If the elastic work recovery rate of this coating layer is within the above range, since the coating layer has a high elastic force, the self-healing function is high and the wear resistance is extremely excellent. In addition, various performances of the golf ball coated with the above coating composition can be improved. The measurement method of the above elastic work recovery rate is as follows.

[0095] The elastic work recovery rate is a microhardness test method that controls the pressing load on the order of micronewtons (μN) and tracks the indenter depth during pressing with nanometer (nm) accuracy. It is one of the parameters of the nanoindentation method for evaluating the physical properties of the paint layer. In the conventional method, only the size of the deformation mark (plastic deformation mark) corresponding to the maximum load could be measured, but with the nanoindentation method, the relationship between the pressing load and the pressing depth can be obtained by automatic and continuous measurement. Therefore, it is considered that there are no individual differences as in the case of visually measuring the deformation mark with an optical microscope in the conventional way, and the physical properties of the paint layer can be evaluated with high accuracy. Since the paint layer on the ball surface is greatly affected by the impact of drivers and various clubs, and the influence of the paint layer on the physical properties of the golf ball is not small, measuring the paint layer by the microhardness test method and performing it with higher accuracy than before is a very effective evaluation method.

[0096] Also, the hardness of the above paint layer, the Shore M hardness, is preferably 40 or more, more preferably 60 or more, and as an upper limit, preferably 95 or less, more preferably 85 or less. Note that this Shore M hardness conforms to ASTM D2240. Also, the hardness of the above paint layer, the Shore C hardness, is preferably 40 or more, and as an upper limit, preferably 80 or less. Note that this Shore C hardness conforms to ASTM D2240. If the paint layer is too hard compared to the above hardness range, the paint may become brittle when repeatedly struck, and there is a risk that the cover layer cannot be protected. If the paint layer is too soft compared to the above hardness range, it is not preferable because the ball surface is likely to be damaged when hitting a hard object.

[0097] When using the above paint composition, for a golf ball manufactured by a known method, the paint composition of the present invention is adjusted during painting, and the normal painting process is adopted to apply it to the surface, and a paint layer can be formed on the ball surface through a drying process. In this case, as the painting method, a spray painting method, an electrostatic painting method, a dipping method, etc. can be preferably adopted, and there is no particular limitation.

Examples

[0098] Hereinafter, examples and comparative examples will be shown to specifically describe the present invention. However, the present invention is not limited to the following examples.

[0099] 〔Examples 1 to 4, Comparative Examples 1 to 7〕 Formation of the core After preparing the rubber compositions of each example and comparative example shown in Table 1, a solid core is produced by vulcanization molding at the temperature and for the time shown in the same table.

[0100]

Table 1

[0101] The details of each component described in Table 1 are as follows. · Polybutadiene A: Manufactured by JSR Corporation, trade name "BR01" · Polybutadiene B: Manufactured by JSR Corporation, trade name "BR730" · Zinc acrylate: "ZN-DA85S" (manufactured by Nippon Shokubai Co., Ltd.) · Organic peroxide: Dicumyl peroxide, trade name "Perk Mill D" (manufactured by NOF Corporation) · Water: Pure water (manufactured by Shoei Chemical Industry Co., Ltd.) · Antioxidant: 2,2-Methylenebis(4-methyl-6-butylphenol), trade name "No Crack NS-6" (manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.) · Zinc oxide: Trade name "Three Kinds of Zinc Oxide" (manufactured by Sakai Chemical Industry Co., Ltd.) · Zinc pentachlorothiophenolate: Manufactured by Wako Pure Chemical Industries, Ltd.

[0102] Formation of the intermediate layer and the cover (outermost layer) Next, for each example and comparative example, an intermediate layer is formed by injection molding using the intermediate layer material of the formulation shown in Table 2 around the core obtained above to produce an intermediate layer-coated sphere. Next, a cover (outermost layer) is formed by injection molding using the cover material of the formulation shown in the same table around the intermediate layer-coated sphere obtained above to produce a golf ball. At this time, a predetermined number of dimples described below are formed on the cover surface.

[0103]

Table 2

[0104] The product names of the materials described in the table are as follows. "Hymilan", an ionomer manufactured by Mitsui Dow Chemical Co., Ltd. "AM7318", an ionomer manufactured by Mitsui Dow Chemical Co., Ltd. "Surlyn", an ionomer manufactured by THE DOW CHEMICAL COMPANY "Nuclel 9-1", an ethylene-methacrylic acid copolymer manufactured by Dupont "Trimethylolpropane" (TMP), manufactured by Tokyo Chemical Industry Co., Ltd. "TPU", the product name "Pandex", an ether-type thermoplastic polyurethane, manufactured by DIC Covestro Polymer GmbH

[0105] The dimples in each example and comparative example have an arrangement pattern as shown in Fig. 6. Fig. 6(A) shows a plan view of the dimples, and Fig. 6(B) shows a side view thereof. The following dimple patterns A to E were used in each example. Each dimple pattern includes eight types of circular dimples numbered 1 to 8 with different diameters and depths. The details are shown in Table 3 below.

[0106]

Table 3

[0107] Definition of dimples Edge: The highest point in the cross-section passing through the center of the dimple Diameter: The diameter of the plane surrounded by the edge of the dimple Depth: The maximum depth of the dimple from the plane surrounded by the edge of the dimple SR: The ratio of the total dimple area defined by the plane surrounded by the edge of the dimple to the spherical area of the ball assuming no dimples Dimple volume: The dimple volume under the plane surrounded by the edge of the dimple Cylindrical volume ratio: The ratio of the dimple volume to the volume of a cylinder with the same diameter and depth as the dimple VR: The total dimple volume formed downward from the plane surrounded by the edge of the dimple, relative to the volume of a golf ball assuming no dimples

[0108] Formation of the paint layer (coating layer) Next, for each example and comparative example, as a paint composition common to all examples and comparative examples, the paint composition shown in Table 4 below was used, and the above paint was applied to the surface of a large number of formed covers (outermost layer) using an air spray gun to produce a golf ball having a paint layer with a thickness of 15 μm.

[0109] [Table 4]

[0110] [Synthesis Example of Polyester Polyol (A)] Into a reaction apparatus equipped with a reflux condenser, dropping funnel, gas inlet tube, and thermometer, 140 parts by mass of trimethylolpropane, 95 parts by mass of ethylene glycol, 157 parts by mass of adipic acid, and 58 parts by mass of 1,4-cyclohexanedimethanol were charged, and the temperature was raised to 200 - 240 °C with stirring and heated (reacted) for 5 hours. Thereafter, "Polyester Polyol (A)" with an acid value of 4, a hydroxyl value of 170, and a weight average molecular weight (Mw) of 28,000 was obtained. Next, the synthesized polyester polyol (A) was dissolved in butyl acetate to prepare a varnish with a non-volatile content of 70% by mass.

[0111] The paint composition in Table 4 was prepared by mixing 15 parts by mass of "Polyester Polyol (B)" (saturated aliphatic polyester polyol "NIPPOLAN 800" manufactured by Tosoh Corporation, weight average molecular weight (Mw) 1,000, solid content 100%) and an organic solvent with 23 parts by mass of the above polyester polyol solution as the main component. This mixture had a non-volatile content of 38.0% by mass.

[0112] Elastic work recovery rate For the measurement of the elastic work recovery rate of the paint, it is measured using a paint sheet with a thickness of 50 μm. The measuring device used is the ultra-micro hardness tester "ENT-2100" manufactured by Elionix, and the measurement conditions are as follows. · Indenter: Berkovich indenter (material: diamond, angle α: 65.03°) · Load F: 0.2 mN · Loading time: 10 seconds · Holding time: 1 second · Unloading time: 10 seconds Based on the indentation work amount Welast (Nm) due to the return deformation of the paint and the mechanical indentation work amount Wtotal (Nm), the elastic work recovery rate is calculated by the following formula. Elastic work recovery rate = Welast / Wtotal × 100 (%)

[0113] Shore C hardness and Shore M hardness The Shore C hardness and Shore M hardness in Table 4 above are measured using a Shore C hardness tester and a Shore M hardness tester that comply with ASTM D2240 standard, respectively, by creating a sheet with a thickness of 2 mm and stacking 3 sheets as test pieces.

[0114] For each of the obtained golf balls, various physical properties such as the internal hardness at each position of the core, the outer diameters of the core and each coated sphere, the thickness and material hardness of each layer, and the surface hardness of each coated sphere are evaluated by the following method and shown in Tables 5 and 6.

[0115] Outer diameter of each spherical body of the core and the intermediate layer-coated spherical body After the sphere to be measured is temperature-adjusted in a constant temperature bath adjusted to 23.9 ± 1°C for 3 hours or more, it is measured in a room at 23.9 ± 2°C. Five arbitrary surface locations are measured, and the average value is taken as the measured value of each sphere, and the average value of 10 measured numbers is obtained.

[0116] Diameter of the ball After the temperature of the ball to be measured is adjusted by a thermostatic bath adjusted to 23.9 ± 1°C for 3 hours or more, the measurement is carried out in a room at 23.9 ± 2°C. Measure 15 locations on a portion without any arbitrary dimples, and use the average value as the measured value of one ball. Then, obtain the average value of 10 balls to be measured.

[0117] Deflection amount of the core and the ball After the temperature of the ball to be measured is adjusted by a thermostatic bath adjusted to 23.9 ± 1°C for 3 hours or more, the measurement is carried out in a room at 23.9 ± 2°C. Place the core or the target coated sphere of the ball on a hard board, and measure the amount of deflection from the state of applying an initial load of 98 N (10 kgf) to the state of applying a final load of 1275 N (130 kgf). Also, the pressurization speed of the head that compresses the ball shall be 10 mm / s.

[0118] Core hardness distribution Although the surface of the core is spherical, set the needle of the hardness tester to be almost perpendicular to the spherical surface, and measure the surface hardness in Shore C hardness according to ASTM D2240. For the center and predetermined positions of the core, cut the core into a hemispherical shape to make the cross-section flat, and vertically press the needle of the hardness tester against the center part and the predetermined positions shown in Table 5 for measurement. The hardness at the center and each position is shown as the value of Shore C hardness. For the measurement of hardness, an automatic rubber hardness tester "P2" manufactured by Polymer Instruments Co., Ltd. equipped with a Shore C type hardness tester is used. Read the maximum value as the hardness value. All measurements are made in an environment at 23 ± 2°C. Note that the values in Table 5 are Shore C hardness values. Also, in the hardness distribution of the core, the Shore C hardness Cc at the center of the core, the Shore C hardness C m at the midpoint M between the center and the surface of the core, the Shore C hardness Cm-2, Cm-4, Cm-6, Cm-8 at positions 2 mm, 4 mm, 6 mm, 8 mm inward from the midpoint M, the Shore C hardness Cm+2, Cm+4, Cm+6 at positions 2 mm, 4 mm, 6 mm outward from the center M, and the Shore C hardness Cs on the surface of the core are for the following areas A to F, X · Area X: 1 / 2 × 2 × (Cm-6 - Cm-8) · 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 obtain the values of the following nine mathematical expressions. (1) Area: A + B + C (2) Area: X + A + B + C (3) Area: D + E (4) Area: D + E + F (5) (Area: D + E + F) - (Area: A + B + C) (6) (Area: D + E + F) - (Area: X + A + B + C) (7) (Area: D + E) - (Area: A + B + C) (8) (Area: D + E) - (Area: X + A + B + C) (9) [(Area: D + E + F) - (Area: A + B + C)] / (Cs - Cc)

[0119] As an explanation of the areas A to F and X of the core hardness distribution, a schematic diagram showing the areas A to F and X using the core hardness distribution data of Examples 1 and 2 is shown in FIG. 2. In addition, graphs of the core hardness distributions of Examples 1 to 4 and Comparative Examples 1 to 7 are shown in FIGS. 3 to 5.

[0120] Material hardness of the intermediate layer and the cover The resin material of each layer is formed into a sheet with a thickness of 2 mm and left for 2 weeks. Then, the Shore D hardness and Shore C hardness are measured in accordance with the ASTM D2240 standard. For the hardness measurement, an automatic rubber hardness tester "P2" manufactured by Kobunshi Keiki Co., Ltd. is used. Attach the attachments for Shore D hardness and Shore C hardness and measure each hardness. Read the maximum value as the hardness value. All measurements are made in an environment of 23 ± 2°C.

[0121] Surface hardness of each spherical body of the intermediate layer-coated spherical body and the ball Press a needle perpendicularly against the surface of each sphere for measurement. Note that the surface hardness of the ball (cover) is the measured value at the land portion where no dimples are formed on the ball surface. The Shore D hardness and Shore C hardness are measured in accordance with ASTM D2240 standard. An automatic rubber hardness tester "P2" manufactured by Kobunshi Kikai Co., Ltd. is used for the hardness measurement. Attach the attachments for Shore D hardness and Shore C hardness and measure each hardness. Read the maximum value as the hardness value. All measurements are made in an environment of 23 ± 2°C.

[0122] Deformation time of the ball Attach a driver (W#1) with a metal head, "TourB XD-5" (loft angle 9.5°) manufactured by Bridgestone Sports Co., Ltd., to the golf hitting robot and hit the golf ball under the condition of a head speed (HS) of 40 m / s. For the golf ball during hitting, use a high-speed video camera (FASTCAM SA-Z manufactured by Photron) to take pictures, analyze the taken pictures, and determine two times (in μsec): the time (t1) required from the start of contact between the driver and the golf ball until the deformation amount of the golf ball becomes the largest, and the time (t2) required from the state where the deformation amount of the golf ball becomes the largest until the golf ball and the club face of the driver are separated. Note that using the picture taken from directly side of the hitting, the point when the diameter of the golf ball in the flight direction from the contact surface between the club face and the golf ball becomes the smallest is taken as the point when the deformation amount of the golf ball is the largest.

[0123] Initial ball speed Use a COR type initial velocity meter manufactured by Hye Precision Products, which is the same type as those of R&A and USGA, to measure with the following content. First, adjust the temperature of the ball in an environment of 23.9 ± 0.6°C for 3 hours or more and then conduct the test. Fire the ball by air pressure at an incident velocity of 143.8 ft / s (43.83 m / s) and make it collide with a barrier set so that the surface normal is inclined at an angle of 5 degrees from the incident angle of the ball, measure the coefficient of restitution e, and calculate the initial velocity from the following formula. 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).〕

[0124]

Table 5

[0125]

Table 6

[0126] The jump (W#1)(I#6), spin amount at approach, and damage susceptibility of each golf ball are evaluated by the following method. The results are shown in Table 7.

[0127] Flight evaluation (W#1) Attach a driver (W#1) to a golf hitting robot, measure the total flight distances R and Q when hitting at a head speed (HS) of 55 m / s and a head speed (HS) of 42 m / s respectively, obtain the difference (R - Q) between these total flight distances, and make a determination according to the following criteria. The club used is the "TourB XD-5 Driver" (loft angle 9.5°) manufactured by Bridgestone Sports Co., Ltd. 〔Judgment Criteria (1)〕 The total flight distance Q at HS 42 m / s is 202.0 m or more ··· ○ The total flight distance Q at HS 42 m / s is less than 202.0 m ··· × 〔Judgment Criteria (2)〕 The difference (R - Q) in total flight distance is 89.0 m or less ··· ○ The difference (R - Q) in total flight distance is 89.1 m or more ··· ×

[0128] Flight evaluation (I#6) Attach a 6-iron (I#6) to a golf hitting robot, measure the carry and total when hitting at a head speed (HS) of 42 m / s, calculate the run from these distances, and determine based on the following criteria. The club used is the "TourB X-CB I#6" manufactured by Bridgestone Sports Co., Ltd. 〔Judgment Criteria〕 Run (Total - Carry) is 10.4 m or less... ○ Run (Total - Carry) is 10.5 m or more... ×

[0129] Evaluation of the spin amount during approach Judge by the amount of spin when attaching a sand wedge to a golf hitting robot and hitting at a head speed (HS) of 16 m / s. The amount of spin was measured for the ball immediately after hitting in the same way using an initial condition measuring device. The sand wedge used is the "TourB XW-1 SW" manufactured by Bridgestone Sports Co., Ltd. 〔Judgment Criteria〕 Amount of spin is 4000 rpm or more... ○ Amount of spin is less than 4000 rpm... ×

[0130] Damageability Attach a PS wedge with a corner groove to a golf hitting robot, hit at a head speed (HS) of 40 m / s, and evaluate based on the following criteria. 〔Judgment Criteria〕 Difficulty of getting damaged is equal to or higher than that of Example 1... ○ Damage is more prominent than in Example 1... ×

[0131]

Table 7

[0132] As shown in the results of Table 7, the golf balls of Comparative Examples 1 to 7 are inferior to the product of the present invention (Example) in the following points. Comparative Example 1 has a ball diameter smaller than 42.8 mm and a ball mass heavier than 44.9 g. As a result, the total difference (R-Q) between the head speeds (HS) of 55 m / s and 42 m / s becomes large. Comparative Example 2 has a ball mass heavier than 44.9 g. As a result, the total difference (R-Q) between the head speeds (HS) of 55 m / s and 42 m / s becomes large. Comparative Example 3 has a ball mass heavier than 44.9 g. As a result, the total difference (R-Q) between the head speeds (HS) of 55 m / s and 42 m / s becomes large. Comparative Example 4 has a ball diameter smaller than 42.8 mm. As a result, the total difference (R-Q) between the head speeds (HS) of 55 m / s and 42 m / s becomes large. Comparative Example 5 has a total of the ball deformation times t1 and t2 (t1 + t2) greater than 660 μsec. As a result, the number of runs during the strike with the iron (I#6) increases. Comparative Example 6 has a ball diameter smaller than 42.8 mm, a ball mass heavier than 44.9 g, and a total of the ball deformation times t1 and t2 (t1 + t2) greater than 660 μsec. As a result, the number of runs during the strike with the iron (I#6) increases. Comparative Example 7 has a cover formed mainly of ionomer resin instead of polyurethane resin. As a result, the ball surface is likely to be damaged.

Claims

1. A golf ball comprising a core and a cover, wherein the cover is formed mainly of polyurethane, the ball diameter is 42.8 mm or more, the ball mass is 44.9 g or less, and in a hitting test in which the golf ball is hit with a driver under the condition of a head speed of 40 m / s, the time (t1) required from the start of contact between the driver and the golf ball until the deformation amount of the golf ball becomes the largest, and the time (t2) required from the state where the deformation amount of the golf ball becomes the largest until the golf ball and the driver are separated, the sum (t1 + t2) is 660 μsec or less, and an intermediate layer made of a resin material is formed between the core and the cover, and the surface hardness of the spherical body (intermediate layer-coated spherical body) obtained by coating the core with the intermediate layer is 70 or more in Shore D hardness. A golf ball characterized by the above.

2. The golf ball according to claim 1, wherein the specific gravity of the ball is 1.02 to 1.

10.

3. The golf ball according to claim 1 or 2, wherein the specific gravity relationship between the core and the cover is core specific gravity ≤ cover specific gravity.

4. The golf ball according to any one of claims 1 to 3, wherein the ratio (t2 / t1) of the time (t1) to the time (t2) is 1.28 or less.

5. The golf ball according to claim 1 or 2, wherein the deflection amount (mm) until a final load of 1,275 N (130 kgf) is applied to the ball from an initial load of 98 N (10 kgf) is 3.2 mm or less.

6. The diameter of the core is 37.0 mm or more, and in the hardness distribution of the core, when the Shore C hardness at the center of the core is Cc, the Shore C hardness at the midpoint M between the center and the surface of the core is Cm, and the Shore C hardness at positions 2 mm, 4 mm, 6 mm, 8 mm inward from the midpoint M is Cm-2, Cm-4, Cm-6, Cm-8 respectively, and the Shore C hardness at positions 2 mm, 4 mm, 6 mm outward from the center M is Cm+2, Cm+4, Cm+6 respectively, and the Shore C hardness at the surface of the core is Cs, the following areas A to F ・Area X: 1 / 2 × 2 × (Cm-6 - Cm-8) ・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 20.0 ≥ (Area D + Area E + Area F) - (Area A + Area B + Area C) > 0 The golf ball according to any one of claims 1 to 5, which satisfies the above condition.

7. Regarding the areas A to F and X of the core hardness distribution, the following formula 20.0 ≥ (Area D + Area E + Area F) - (Area X + Area A + Area B + Area C) > 0 The golf ball according to claim 6, which satisfies the above condition.

8. Regarding the areas A to E of the core hardness distribution, the following formula 14.0 ≥ (Area D + Area E) - (Area A + Area B + Area C) ≥ 1 The golf ball according to claim 6, which satisfies the above condition.

9. Regarding the areas A to E and X of the core hardness distribution, the following formula 14.0 ≥ (Area D + Area E) - (Area X + Area A + Area B + Area C) > 0 The golf ball according to claim 6, which satisfies the above condition.

10. Regarding the areas A to F of the core hardness distribution, the core center hardness Cc, and the core surface hardness Cs, the following formula 0 < [(Area: D + E + F) - (Area: A + B + C)] / (Cs - Cc) ≤ 1.00 The golf ball according to claim 6, which satisfies the above condition.

11. The golf ball according to claim 6, wherein the value of the core surface hardness (Cs) - the core center hardness (Cc) is 20 or more.

12. From the deflection amount E (mm) of the ball from the initial load of 98 N (10 kgf) to the final load of 1,275 N (130 kgf), the value E - B (mm) obtained by subtracting the deflection amount B (mm) of the ball from the initial load of 98 N (10 kgf) to the final load of 1,275 N (130 kgf) is 0.3 to 1.2 mm. The golf ball according to any one of claims 1 to 11.

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