Golf ball

Abstract

To provide a golf ball compatibly achieving flight performance and durability for repetitive hitting at a high level as the golf ball for professionals and the experienced.SOLUTION: A golf ball is formed by interposing at least one intermediate layer 2 between a single-layer core 1 and a cover 3. A surface hardness relation of a spherical body (an intermediate-layer cover spherical body) formed by covering the core 1 by the intermediate layer 2 and a ball satisfies the following expression: (surface hardness of intermediate-layer cover spherical body)>(surface hardness of ball), the diameter of the core 1 is 35.5 to 39.5 mm, and in core hardness distribution, when Shore C hardness of the core surface is H100 and Shore C hardness at a position k% outside the core radius from the core center is Kh, the golf ball satisfies the following expressions: (H75-H50)>(H25-H0)>(H100-H87.5)>(H50-H25); 23.0≥(H87.5-H0)≥17.0; and absolute value of (H87.5-H0) / (H50-H0)≥3.0.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a golf ball for professionals and advanced players having a three-layer structure or more including a core, a cover, and at least one intermediate layer sandwiched therebetween.

Background Art

[0002] As golf balls for professionals and advanced players, multi-piece solid golf balls such as three-piece solid golf balls are often used. A multi-piece solid golf ball usually has a structure in which a core made of a rubber composition is coated with a plurality of layers of covers made of various resin materials. The core occupies most of the volume of the golf ball and has a great influence on various ball physical properties such as resilience, feel, and durability. Recently, various techniques have been proposed to achieve a unique core hardness gradient by appropriately adjusting the cross-sectional hardness of the core and improve the flight distance by optimizing the spin characteristics during full shots with a driver or iron. In addition, as golf balls for advanced players and professionals, polyurethane covers are often used as the outermost cover. Therefore, it is also important to improve the cracking durability when repeatedly hitting a golf ball having a soft urethane cover.

[0003] Regarding the method of adjusting the cross-sectional hardness of the core, examples include appropriately adjusting the compounding components of the rubber composition of the core, the vulcanization temperature, and the time. For example, the following Patent Documents 1 to 25 provide a unique internal cross-sectional hardness of the core by adjusting the selection and blending amount of the types of co-crosslinking agents and organic peroxides for the compounding components of the rubber composition of the core, and blending other components such as water and aromatic organic sulfur compounds.

[0004] However, the golf balls described in these patent documents do not achieve both a flight distance and repeated impact durability in a higher dimension in the high club head speed region, and further improvement in flight performance and improvement in impact durability are required.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2011-120898 [Patent Document 2] Japanese Unexamined Patent Application Publication No. 2013-230361 [Patent Document 3] Japanese Unexamined Patent Application Publication No. 2013-230362 [Patent Document 4] Japanese Unexamined Patent Application Publication No. 2013-230363 [Patent Document 5] Japanese Unexamined Patent Application Publication No. 2015-077405 [Patent Document 6] Japanese Unexamined Patent Application Publication No. 2013-230365 [Patent Document 7] Japanese Unexamined Patent Application Publication No. 2016-112308 [Patent Document 8] Japanese Unexamined Patent Application Publication No. 2016-116627 [Patent Document 9] Japanese Unexamined Patent Application Publication No. 2016-179052 [Patent Document 10] Japanese Unexamined Patent Application Publication No. 2017-000183 [Patent Document 11] Japanese Unexamined Patent Application Publication No. 2017-000470 [Patent Document 12] Japanese Unexamined Patent Application Publication No. 2017-077355 [Patent Document 13] Japanese Unexamined Patent Application Publication No. 2017-079905 [Patent Document 14] Japanese Unexamined Patent Application Publication No. 2019-198465 [Patent Document 15] Japanese Unexamined Patent Application Publication No. 2019-213606 [Patent Document 16] Japanese Unexamined Patent Application Publication No. 2021-062026 [Patent Document 17] Japanese Unexamined Patent Application Publication No. 2021-062036 [Patent Document 18] Japanese Unexamined Patent Application Publication No. 2011-217857 [Patent Document 19] Japanese Unexamined Patent Application Publication No. 2012-019820

Patent Document 20

Patent Document 21

Patent Document 22

Patent Document 23

Patent Document 24

Patent Document 25

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present invention has been made in view of the above circumstances, and an object thereof is to provide a golf ball for professionals and advanced players, which achieves high levels of flight performance and repeated impact durability simultaneously.

Means for Solving the Problems

[0007] As a result of intensive studies to achieve the above object, the inventors of the present invention found that for a golf ball having at least one intermediate layer interposed between a single-layer core and a cover, the relationship between the surface hardness of the sphere (intermediate layer-coated sphere) obtained by coating the core with the intermediate layer and the ball satisfies the relationship (surface hardness of the intermediate layer-coated sphere) > (surface hardness of the ball). The diameter of the core is designed to be 35.5 to 39.5 mm. In the core hardness distribution, when the Shore C hardness of the core surface is H100 and the Shore C hardness at a position k% outside the core radius from the core center is Hk, the following formula (H75 - H50) > (H25 - H0) > (H100 - H87.5) > (H50 - H25) 23.0 ≥ (H87.5 - H0) ≥ 17.0 The absolute value of (H87.5 - H0) / (H50 - H0) ≥ 3.0 By configuring the golf ball to satisfy the above, it has been found that professionals and advanced players can achieve sufficient carry distance when hitting with a driver (W#1) or long iron in the high head speed (HS) range, improve the repetitive impact durability of the golf ball, and further obtain high controllability during approach shots in the short game. This led to the completion of the present invention.

[0008] That is, the golf ball of the present invention is a golf ball for professionals and advanced players, which has a relatively soft cover that can achieve high-level spin control in the short game, a hard intermediate layer that suppresses excessive spin in full shots, and a core having a special hardness distribution that balances carry and crack durability due to repetitive impacts in the high head speed range. In the golf ball of the present invention, a synergistic effect of low spin and high initial ball speed in actual hitting ensures excellent carry distance, and this effect is mainly due to the core being made with a specific hardness distribution. Also, the golf ball of the present invention having the hardness distribution structure of this core has high repetitive impact durability.

[0009] In the golf ball of the present invention, the high head speed range means the target range for professional and advanced golfers with a head speed (HS) of approximately 46 to 57 m / s. is.

[0010] Therefore, the present invention provides the following golf ball. 1. In a golf ball having at least one intermediate layer interposed between a single-layer core and a cover, the surface hardness relationship between the spherical body (intermediate layer-coated spherical body) in which the core is coated with the intermediate layer and the ball is represented by the following formula (Surface hardness of the intermediate layer-coated spherical body) > (Surface hardness of the ball) Satisfying the following, the diameter of the core is 35.5 to 39.5 mm, and in the core hardness distribution, when the Shore C hardness of the core surface is H100, the Shore C hardness at a position 87.5% outside the core radius from the core center is H87.5, the Shore C hardness at a position 75% outside the core radius from the core center is H75, the Shore C hardness at a position 62.5% outside the core radius from the core center is H62.5, the Shore C hardness at a position 50% outside the core radius from the core center is H50, the Shore C hardness at a position 37.5% outside the core radius from the core center is H37.5, the Shore C hardness at a position 25% outside the core radius from the core center is H25, the Shore C hardness at a position 12.5% outside the core radius from the core center is H12.5, and the Shore C hardness at the core center is H0, the following formula (H75 - H50) > (H25 - H0) > (H100 - H87.5) > (H50 - H25) 23.0 ≥ (H87.5 - H0) ≥ 17.0 The absolute value of (H87.5 - H0) / (H50 - H0) ≥ 3.0 A golf ball characterized by satisfying the above. 2. The following formula, 0 ≤ (H100 - H87.5) ≤ 3.0 The golf ball according to Item 1 above, satisfying the above. 3. The following formula, 4.0 ≤ (H75 - H50) ≤ 9.0 The golf ball according to Item 1 or 2 above, satisfying the above. 4. The following formula, -1.0 ≤ (H50 - H25) ≤ 1.0 The golf ball according to any one of Items 1 to 3 above, satisfying the above. 5. The following formula, 3.0 ≤ (H25 - H0) ≤ 6.0 The golf ball according to any one of Items 1 to 4 above, satisfying the above. 6. When a compressive deformation amount from an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf) is applied to the above core, it is 2.5 to 3.5 mm, and when a compressive deformation amount from an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf) is applied to the ball, it is 2.1 to 2.8 mm. The golf ball according to any one of Items 1 to 5 above. 7. When the lift coefficient measured under the conditions of a Reynolds number of 80,000 and a spin rate of 2,000 rpm is defined as CL1, and the lift coefficient measured under the conditions of a Reynolds number of 70,000 and a spin rate of 1,900 rpm is defined as CL2, when CL1 and CL2 satisfy the following formula 0.900 ≤ CL2 / CL1 the golf ball according to any one of the above 1 to 6. 8. When the lift coefficient measured under the conditions of a Reynolds number of 200,000 and a spin rate of 2,500 rpm is defined as CL3, and the lift coefficient measured under the conditions of a Reynolds number of 120,000 and a spin rate of 2,250 rpm is defined as CL4, when CL3 and CL4 satisfy the following formula 1.250 ≤ CL4 / CL3 ≤ 1.300 the golf ball according to any one of the above 1 to 7. 9. The golf ball according to any one of the above 1 to 8, wherein the core is a heat-molded product of a rubber composition containing the following components (A) to (D): (A) Base rubber (B) Organic peroxide (C) Water and / or metal salt of molcarboxylic acid (D) Sulfur 10. The golf ball according to 9 above, wherein the mass ratio of the component (C) to the component (D) is (D) / (C) = 0.02 to 0.20.

Advantages of the Invention

[0011] According to the golf ball of the present invention, as a golf ball for professionals and advanced players, it is possible to secure an excellent flight distance due to the synergistic effect of low spin in the high head speed region and high initial hitting speed, and it has good controllability in short games and high repetitive hitting durability.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0013] Hereinafter, the present invention will be described in more detail. The multi-piece solid golf ball of the present invention has a single-layer core, an intermediate layer, and a cover. For example, an example thereof is shown in FIG. 1. The golf ball G shown in FIG. 1 has a single-layer core 1, a single-layer intermediate layer 2 covering the core 1, and a single-layer cover 3 covering the intermediate layer. This cover 3 is located in the outermost layer in the layer structure of the golf ball except for the paint layer. The intermediate layer can be formed of a plurality of layers in addition to the single layer as shown in FIG. 1. Note that a large number of dimples D are usually formed on the surface of the cover (outermost layer) 3 in order to improve aerodynamic characteristics. Further, although not particularly shown, a paint layer is usually formed on the surface of the cover 3. Hereinafter, each of the above layers will be described in detail.

[0014] 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. therewith.

[0015] The core used in the present invention is a heat-molded product of a rubber composition containing the following components (A) to (D). (A) Base rubber (B) Organic peroxide (C) Water and / or metal salt of molcarboxylic acid (D) Sulfur It is preferably a heat-molded product of a rubber composition containing these.

[0016] (A) As the base rubber, it is preferable to use polybutadiene. As the type of polybutadiene, commercially available products can be used, for example, BR01, BR51, BR730, T0700 (manufactured by JSR Corporation), etc. can be mentioned. Also, the proportion of polybutadiene in the base rubber is preferably 60% by mass or more, more preferably 80% by mass or more. In addition to the above polybutadiene, other rubber components can be blended in the base rubber within the range that does not impair the effects of the present invention. Examples of the rubber components other than the above polybutadiene include polybutadiene other than the above polybutadiene, and other diene rubbers, such as styrene-butadiene rubber, natural rubber, isoprene rubber, ethylene-propylene-diene rubber, etc.

[0017] (B) As the organic peroxide, it is preferable to use an organic peroxide with a relatively high thermal decomposition temperature. Specifically, an organic peroxide with a high 1-minute half-life temperature of about 165°C to 185°C is used. For example, dialkyl peroxides can be mentioned. Examples of dialkyl peroxides include dicumyl peroxide ("Perkyl D" manufactured by NOF Corporation), 2,5-dimethyl-2,5-di(t-butylperoxy)hexane ("Perhexa 25B" manufactured by NOF Corporation), di(2-t-butylperoxyisopropyl)benzene ("Perbutyl P" manufactured by NOF Corporation), etc. Among them, dicumyl peroxide can be preferably used. These can be used alone or in combination of two or more. The half-life is one of the indices representing the degree of the decomposition rate of the organic peroxide, and is indicated by the time required for the original organic peroxide to decompose until the amount of its active oxygen becomes 1 / 2. The vulcanization temperature in the core rubber composition is usually within the range of 120 to 190°C. Within this range, an organic peroxide with a high 1-minute half-life temperature of about 165°C to 185°C decomposes relatively slowly. According to the rubber composition used in the present invention, by adjusting the amount of free radicals generated with the passage of vulcanization time, a core, which is a rubber crosslinked product having a specific internal hardness shape described later, can be obtained.

[0018] (C) There are no particular restrictions on the water, and it may be distilled water or tap water. In particular, it is preferably adopted to use distilled water containing no impurities. The compounding amount of water is preferably 0.1 part by mass or more, more preferably 0.2 part by mass or more, based on 100 parts by mass of the base rubber. The upper limit is preferably 2 parts by mass or less, more preferably 1 part by mass or less.

[0019] By directly compounding water or a water-containing material as the component (C) into the core material, the decomposition of the organic peroxide during core compounding can be promoted. Also, 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. If the temperature is too high, the amount of decomposed radicals becomes too large, and the radicals recombine or become inactivated with each other. As a result, the radicals effectively working for crosslinking decrease. Here, when decomposition heat 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 decomposition heat of the organic peroxide decomposed from the outside accumulates, so it becomes much higher than the mold temperature. When water or a water-containing material is directly compounded into 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 promoted, so that the amount of effective radicals further decreases. Therefore, a core can be obtained in which the crosslink density between the core center and the core surface is significantly different, and a core with different dynamic viscoelastic properties at the core center can be obtained.

[0020] Also, instead of the above water, a metal monocarboxylate can be adopted. The metal monocarboxylate is presumed to have a carboxylic acid coordinated to the metal salt, and in the chemical formula, [CH 2 =CHCOO] 2It is distinguished from dicarboxylic acid metal salts such as zinc diacrylate represented by Zn. Since the monocarboxylic acid metal salt brings water into the rubber composition by undergoing a dehydration condensation reaction, the same effects as the above water can be obtained. In addition, since the monocarboxylic acid metal salt can be compounded into the rubber composition as a powder, the working process can be simplified and it is easy to disperse it uniformly in the rubber composition. Note that in order to effectively carry out the above reaction, it is necessary to be a monosalt. The compounding amount of the monocarboxylic acid metal salt is preferably 1 part by mass or more, more preferably 3 parts by mass or more, based on 100 parts by mass of the base rubber. As an upper limit, the compounding amount of the monocarboxylic acid metal salt is preferably 60 parts by mass or less, more preferably 50 parts by mass or less. If the compounding amount of the above monocarboxylic acid metal salt is too small, it becomes difficult to obtain an appropriate crosslinking density, and it may not be possible to sufficiently obtain the low spin effect of the golf ball. Also, when the compounding amount is too large, the core becomes too hard, and it may become difficult to maintain an appropriate hitting feeling.

[0021] As the above carboxylic acid, acrylic acid, methacrylic acid, maleic acid, fumaric acid, stearic acid, etc. can be used. Examples of the substituted metal include Na, K, Li, Zn, Cu, Mg, Ca, Co, Ni, Pb, etc., and Zn is preferably used. Specific examples include zinc monoacrylate, zinc monomethacrylate, etc., and it is particularly preferable to use zinc monoacrylate.

[0022] (D) Specifically, examples of sulfur include the product named "Sunmix S-80N" (manufactured by Sanshin Chemical Industry Co., Ltd.), "Sulfax-5" (manufactured by Tsurumi Chemical Industry Co., Ltd.), etc. The compounding amount of sulfur can be more than 0, preferably 0.005 parts by mass or more, more preferably 0.01 parts by mass or more, based on 100 parts by mass of the above base rubber. Also, although the upper limit of the compounding amount is not particularly limited, it can preferably be 0.1 parts by mass or less, more preferably 0.05 parts by mass or less, and even more preferably 0.03 parts by mass or less. By adding sulfur, the hardness difference of the core can be increased. However, if the compounding amount of sulfur is too large, the resilience may be significantly reduced, or the repeated impact durability may decrease.

[0023] Regarding the compounding ratio of the above components (C) and (D), the mass ratio of (D) / (C) is preferably 0.02 or more, more preferably 0.03 or more, and even more preferably 0.04 or more, and the upper limit value is preferably 0.20 or less, more preferably 0.16 or less, and even more preferably 0.12 or less. If it deviates from the above numerical range, it becomes difficult to achieve the desired hardness distribution of the core, and it may not be possible to achieve both an excellent flight distance and good repeated impact durability when hitting with a driver (W#1) at high head speed. Note that the above component (D) means the mass of the sulfur component contained in the product, not the mass of the sulfur product itself.

[0024] In the above rubber composition, in addition to the above components (A) to (D), a (E) co-crosslinking agent and a (F) inert filler can be compounded, and an antioxidant or an organic sulfur compound can be compounded as required. These components will be described in detail below.

[0025] (E) 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 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.

[0026] The above unsaturated carboxylic acid and / or its metal salt is usually formulated 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, 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 blending amount is too large, it may become too hard and have a difficult-to-endure hitting feeling, and if the blending amount is too small, the resilience may decrease.

[0027] (F) As the inert filler, 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 blending amount of the inert filler is preferably 1 part by mass or more, more preferably 5 parts by mass or more, and preferably 50 parts by mass or less, more preferably 40 parts by mass or less, still more preferably 36 parts by mass or less, based on 100 parts by mass of the base rubber. If the blending amount is too large or too small, it may not be possible to obtain an appropriate mass and a suitable resilience.

[0028] Furthermore, an antioxidant can be blended as needed. For example, commercially available products include Nocrack MB, 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.

[0029] The compounding amount of the anti-aging agent is preferably 0 parts by mass or more, more preferably 0.05 parts by mass or more, particularly preferably 0.1 parts by mass or more, and 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 parts by mass or less, based on 100 parts by mass of the above base rubber. If the compounding amount is too large or too small, suitable resilience and durability may not be obtained.

[0030] In addition, an organic sulfur compound can be compounded into the above core in order to impart good resilience. 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 with 2 to 4 sulfur atoms, dibenzyl polysulfide, dibenzoyl polysulfide, dibenzothiazoyl polysulfide, dithiobenzoyl polysulfide, etc. are 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, further preferably 0.1 parts by mass or more, and preferably 5 parts by mass or less, more preferably 3 parts by mass or less, further preferably 2.5 parts by mass or less, based on 100 parts by mass of the above base rubber. If the compounding amount is too large, the improvement effect on resilience (particularly, the impact by W#1) cannot be expected further, and the core may become too soft or the hitting feeling may become poor. On the other hand, if the compounding amount is too small, the improvement effect on resilience cannot be expected.

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

[0032] In the present invention, the above core is formed in a single layer. In the case of a multi-layer rubber core, peeling may occur from the interface when repeatedly struck, and the durability may deteriorate.

[0033] The diameter of the core is 35.5 to 39.5 mm, preferably 37.5 mm or more, more preferably 38.3 mm or more, and the upper limit is preferably 39.2 mm or less, more preferably 38.8 mm or less. If the diameter of the core is too small, the initial hitting speed when fully shot may be low and the flying distance may not be achieved, or the hitting feeling may deteriorate. On the other hand, if the diameter of the core is too large, the crack durability when repeatedly struck may be low.

[0034] The amount of deflection (mm) of the core 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 the upper limit value is preferably 3.5 mm or less, more preferably 3.4 mm or less, still more preferably 3.3 mm or less. If the amount of deflection of the above core is too small, that is, if the core is too hard, the spin may increase too much and the aimed flying distance may not be achieved, or the hitting feeling may become too hard. On the other hand, if the amount of deflection of the above core is too large, that is, if the core is too soft, the initial hitting speed may be low and the aimed flying distance may not be achieved, or the hitting feeling may become too soft, or the crack durability when repeatedly struck may deteriorate.

[0035] Next, the hardness distribution of the above core will be described. The hardness of the core described below means Shore C hardness. This Shore C hardness is a hardness value measured with a Shore C hardness tester conforming to ASTM D2240 standard.

[0036] In the following description of the core hardness distribution, the Shore C hardness of the core surface is defined as H100, the Shore C hardness at a position 87.5% outside the core radius from the core center is defined as H87.5, the Shore C hardness at a position 75% outside the core radius from the core center is defined as H75, the Shore C hardness at a position 62.5% outside the core radius from the core center is defined as H62.5, the Shore C hardness at a position 50% outside the core radius from the core center is defined as H50, the Shore C hardness at a position 37.5% outside the core radius from the core center is defined as H37.5, the Shore C hardness at a position 25% outside the core radius from the core center is defined as H25, the Shore C hardness at a position 12.5% outside the core radius from the core center is defined as H12.5, and the Shore C hardness at the core center is defined as H0, respectively.

[0037] The surface hardness (H100) of the above core is not particularly limited, but it can be preferably 83 or more, more preferably 85 or more, and still more preferably 87 or more. Also, the upper limit is not particularly limited, but it can be preferably 94 or less, more preferably 92 or less, and still more preferably 90 or less. If this value is too small, the resilience will be low, the jumping performance will be poor, and the crack durability when repeatedly struck may be poor. On the other hand, if the above value is too large, the hitting feeling will be hard, or the spin may increase in a full shot and the desired flying distance may not be obtained.

[0038] The hardness (H87.5) at a position 87.5% outside the radius from the center of the above core is not particularly limited, but it can be preferably 82 or more, more preferably 84 or more, and still more preferably 86 or more. Also, the upper limit is not particularly limited and can be preferably 92 or less, more preferably 90 or less, and still more preferably 88 or less. If these hardness values deviate, there is a risk of causing the same adverse results as described for the surface hardness (H100) of the above core.

[0039] The hardness (H75) at a position 75% outside the radius from the center of the above core is not particularly limited, but it can preferably be 71 or more, more preferably 73 or more, and still more preferably 75 or more. Also, the upper limit thereof is not particularly limited, and it can preferably be 83 or less, more preferably 81 or less, and still more preferably 79 or less. If these hardness values deviate, there is a risk of causing the same adverse results as those described for the surface hardness (H100) of the above core.

[0040] The hardness (H62.5) at a position 62.5% outside the radius from the center of the above core is not particularly limited, but it can preferably be 65 or more, more preferably 67 or more, and still more preferably 69 or more. Also, the upper limit thereof is not particularly limited, and it can preferably be 76 or less, more preferably 74 or less, and still more preferably 72 or less. If these hardness values deviate, there is a risk of causing the same adverse results as those described for the surface hardness (H100) of the above core.

[0041] The hardness (H50) at a position 50% outside the radius from the center of the above core is not particularly limited, but it can preferably be 65 or more, more preferably 67 or more, and still more preferably 69 or more. Also, the upper limit thereof is not particularly limited, and it can preferably be 76 or less, more preferably 74 or less, and still more preferably 72 or less. If these hardness values deviate, there is a risk of causing the same adverse results as those described for the surface hardness (H100) of the above core.

[0042] The hardness (H37.5) at a position 37.5% outside the radius from the center of the above core is not particularly limited, but it can preferably be 65 or more, more preferably 67 or more, and still more preferably 70 or more. Also, the upper limit thereof is not particularly limited, and it can preferably be 76 or less, more preferably 74 or less, and still more preferably 73 or less. If these hardness values deviate, there is a risk of causing the same adverse results as those described for the surface hardness (H100) of the above core.

[0043] The hardness (H25) at a position 25% outside the radius from the center of the above core is not particularly limited, but it can preferably be 66 or more, more preferably 68 or more, still more preferably 70 or more. Also, the upper limit thereof is not particularly limited, and it can preferably be 76 or less, more preferably 74 or less, still more preferably 72 or less. If these hardness values deviate, there is a risk of causing the same adverse results as those described for the surface hardness (H100) of the above core.

[0044] The hardness (H12.5) at a position 12.5% outside the radius from the center of the above core is not particularly limited, but it can preferably be 64 or more, more preferably 66 or more, still more preferably 68 or more. Also, the upper limit thereof is not particularly limited, and it can preferably be 74 or less, more preferably 72 or less, still more preferably 70 or less. If these hardness values deviate, there is a risk of causing the same adverse results as those described for the surface hardness (H100) of the above core.

[0045] The center hardness (H0) of the above core is not particularly limited, but it can preferably be 62 or more, more preferably 64 or more, still more preferably 66 or more. Also, the upper limit thereof is not particularly limited, and it can preferably be 72 or less, more preferably 70 or less, 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 surface hardness (H100) of the above core.

[0046] The core used in the present invention needs to satisfy the following formula. (H75 - H50) > (H25 - H0) > (H100 - H87.5) > (H50 - H25) If this relationship is not satisfied, the spin will increase in a full shot, the initial velocity of actual hitting will decrease, and the target flying distance will not be achieved, or the crack durability due to repeated hitting will deteriorate.

[0047] Regarding the value of (H75 - H50) in the above formula, it is preferably 4.0 or more, more preferably 4.3 or more, still more preferably 4.5 or more, and as the upper limit value, it is preferably 9.0 or less, more preferably 8.5 or less, still more preferably 8.0 or less. If this value is too large, the crack durability upon repeated impact may deteriorate. On the other hand, if this value is too small, the spin when a full shot is made may increase and the flying distance may not be achieved.

[0048] Regarding the value of (H25 - H0) in the above formula, it is preferably 3.0 or more, more preferably 3.2 or more, still more preferably 3.4 or more, and as the upper limit value, it is preferably 6.0 or less, more preferably 5.0 or less, still more preferably 4.5 or less. Deviating from this range may result in an increase in spin when a full shot is made and the flying distance not being achieved, or the crack durability upon repeated impact may deteriorate.

[0049] Regarding the value of (H100 - H87.5) in the above formula, it is preferably 0 or more, more preferably 0.3 or more, still more preferably 0.5 or more, and as the upper limit value, it is preferably 3.0 or less, more preferably 2.5 or less, still more preferably 2.0 or less. If this value is too large, the crack durability upon repeated impact may deteriorate. On the other hand, if this value is too small, the spin when a full shot is made may increase and the flying distance may not be achieved.

[0050] Regarding the value of (H50 - H25) in the above formula, it is preferably -1.0 or more, more preferably -0.6 or more, still more preferably -0.2 or more, and as the upper limit value, it is preferably 1.0 or less, more preferably 0.6 or less, still more preferably 0.2 or less. Deviating from this range may result in an increase in spin when a full shot is made and the flying distance not being achieved.

[0051] Regarding the value of (H75 - H50) - (H25 - H0) in the above formula, it is preferably greater than 0, more preferably 0.3 or more, still more preferably 0.6 or more. As the upper limit value, it is preferably 7.0 or less, more preferably 5.0 or less, still more preferably 3.1 or less. If it deviates from these ranges, it may not be possible to satisfy both the low spin at full shot at high head speed and the crack durability by good repeated impacts.

[0052] Regarding the value of (H25 - H0) - (H100 - H87.5) in the above formula, it is preferably greater than 0, more preferably 1.0 or more, still more preferably 1.8 or more. As the upper limit value, it is preferably 8.0 or less, more preferably 6.0 or less, still more preferably 4.1 or less. If it deviates from these ranges, there is a risk of causing the same adverse results as those described for the value of (H75 - H50) - (H25 - H0) above.

[0053] Regarding the value of (H100 - H87.5) - (H50 - H25) in the above formula, it is preferably greater than 0, more preferably 0.3 or more, still more preferably 0.6 or more. As the upper limit value, it is preferably 6.0 or less, more preferably 4.0 or less, still more preferably 1.8 or less. If it deviates from these ranges, there is a risk of causing the same adverse results as those described for the value of (H75 - H50) - (H25 - H0) above.

[0054] Also, the core used in the present invention needs to satisfy the following formula. 23.0 ≥ (H87.5 - H0) ≥ 17.0 That is, regarding the value of (H87.5 - H0) in the above formula, it is 17.0 or more, preferably 18.0 or more, more preferably 19.0 or more. The upper limit value is 23.0 or less, preferably 22.0 or less, more preferably 21.0 or less. If this value is too large, the crack durability during repeated impacts may deteriorate. On the other hand, if this value is too small, the spin when full shot may increase and the flying distance may not occur.

[0055] Furthermore, the core used in the present invention needs to satisfy the following formula. The absolute value of (H87.5 - H0) / (H50 - H0) ≥ 3.0 That is, the absolute value of (H87.5 - H0) / (H50 - H0) is 3.0 or more, preferably 3.5 or more, more preferably 4.0 or more, and as the upper limit value, it is preferably 8.0 or less, more preferably 7.0 or less, and still more preferably 6.0 or less. If this value is too large, the crack durability when repeatedly struck may deteriorate, or the initial actual shooting speed when full-shot may be low and the expected flying distance may not be achieved. On the other hand, if this value is too small, the spin when full-shot may increase and the expected flying distance may not be achieved.

[0056] In addition, it is preferable that the hardness distribution of the core used in the present invention satisfies the following requirements.

[0057] Regarding the hardness difference between the surface and the center of the core, that is, the value of (H100 - H0), it is preferably 18.0 or more, more preferably 19.0 or more, and still more preferably 20.0 or more, and as the upper limit value, it is preferably 30.0 or less, more preferably 26.0 or less, and still more preferably 23.0 or less. If this value is too large, the crack durability when repeatedly struck may deteriorate. On the other hand, if this value is too small, the spin when full-shot may increase and the flying distance may not be achieved.

[0058] Next, the intermediate layer will be described. The intermediate layer is formed as a single layer or multiple layers. As will be described later, it is preferable to form each layer with a resin material.

[0059] 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. Also, 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, the spin amount at full shot may increase too much and the flying distance may not be achieved, or the initial velocity of the ball may be low and the flying distance may not be achieved at full shot. On the other hand, if the above material hardness and surface hardness are too hard, the crack durability due to repeated impacts may deteriorate or the hitting feeling may deteriorate.

[0060] 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. Also, 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.

[0061] The thickness of the intermediate layer is preferably 0.90 mm or more, more preferably 1.10 mm or more, still more preferably 1.15 mm or more. On the other hand, as the upper limit value of the thickness of the intermediate layer, it is preferably 1.50 mm or less, more preferably 1.35 mm or less, still more preferably 1.25 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 flying distance may not be achieved. On the other hand, if the intermediate layer is too thick, the actual hitting initial velocity may be low, the aimed flying distance may not be achieved, or the hitting feeling may deteriorate.

[0062] Regarding the material of the intermediate layer, various thermoplastic resins used as golf ball materials, particularly resin materials mainly composed of ionomer resins, can be adopted.

[0063] As the ionomer resin material, it is preferable to contain an ionomer with a high acid content. For example, among commercially available ionomer resins, a high acid content ionomer resin with an acid content of 16% by mass or more is blended with a normal ionomer resin and used. By this blending, it is possible to ensure the target flight distance by achieving both low spin and high resilience during a full shot with a driver (W#1).

[0064] 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. As the upper limit value, it is preferably 22% by mass or less, more preferably 21% by mass or less, and even more preferably 20% by mass or less. If this value is too small, the spin may increase during a full shot with a driver (W#1), utility, or iron, and the target flight distance may not be obtained. Conversely, if the above value is too large, the hitting feeling may become too hard, or the crack durability during repeated hitting may deteriorate.

[0065] Also, the high acid content ionomer resin is preferably 20% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more with respect to 100% by mass of the resin material. The upper limit value is 100% by mass or less, preferably 90% by mass or less, and more preferably 85% by mass or less. If the blending amount of the above high acid content ionomer resin is too small, the spin amount during a full shot may increase and the flight distance may not be achieved. On the other hand, if the blending amount of the above high acid content ionomer resin is too large, the repeated hitting durability may deteriorate.

[0066] For the intermediate layer material, any additives can be appropriately blended according to the application. For example, various additives such as pigments, dispersants, antioxidants, 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.

[0067] 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 that is preferably used in 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.

[0068] The specific gravity of the intermediate layer material is usually less than 1.1, preferably 0.90 to 1.05, and more preferably 0.93 to 0.99. If it deviates from this range, the rebound of the whole ball may decrease and the flying distance may not be achieved, or the crack durability due to repeated impacts may deteriorate.

[0069] 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) obtained by covering the intermediate layer-coated sphere 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 range, there may be an increase in spin in a full shot and no flying distance may be achieved under any hitting conditions. On the other hand, if the above material hardness and surface hardness are too hard, the desired amount of spin may not be obtained during approach, or the scratch resistance may deteriorate.

[0070] 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, and even more preferably 70 or more. As the upper limit value, it is preferably 89 or less, more preferably 83 or less, and even 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, and even more preferably 85 or more. As the upper limit value, it is preferably 95 or less, more preferably 92 or less, and even more preferably 90 or less.

[0071] The thickness of the cover is preferably 0.3 mm or more, more preferably 0.45 mm or more, and even 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, and even more preferably 1.0 mm or less. If the cover is too thick, there may be insufficient rebound or excessive spin during a full shot with an iron, resulting in an inability to achieve the desired flight 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.

[0072] The total thickness of the thickness of the cover and the intermediate layer described above is preferably 1.4 mm or more, more preferably 1.7 mm or more, and even more preferably 2.0 mm or more. On the other hand, as the upper limit value of this total thickness, it is preferably 2.8 mm or less, more preferably 2.5 mm or less, and even more preferably 2.3 mm or less. If this total thickness is too thin, the crack durability due to repeated impacts may deteriorate. On the other hand, if this total thickness is too thick, the amount of spin during a full shot will increase, and there may be a case where not only golfers with a high head speed but also golfers with a low head speed cannot achieve the flight distance.

[0073] As the material of the cover, various thermoplastic resins used for the cover material of golf balls can be used. However, from the viewpoints of spin controllability and scratch resistance in short games, it is preferable to use a resin material mainly composed of thermoplastic polyurethane. That is, it is preferably formed of a resin composition mainly composed of (I) thermoplastic polyurethane and (II) a polyisocyanate compound.

[0074] It is recommended that the total mass of the above components (I) and (II) together be 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.

[0075] Regarding the above (I) thermoplastic polyurethane, its structure 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 used as a raw material, any of those conventionally used in technologies 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.

[0076] 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. As the chain extender, 1,4-butylene glycol, 1,2-ethylene glycol, 1,3-butanediol, 1,6-hexanediol, 2,2-dimethyl-1,3-propanediol, etc. can be mentioned, but it is not limited thereto. Among these, as the chain extender, aliphatic diols having 2 to 12 carbon atoms are preferable, and 1,4-butylene glycol is more preferable.

[0077] 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, 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 the balance between the stability during production and the physical properties exhibited, 4,4'-diphenylmethane diisocyanate, which is an aromatic diisocyanate, is most preferable.

[0078] 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.) and the like can be mentioned.

[0079] Although not an essential component, a thermoplastic elastomer other than the above-mentioned thermoplastic polyurethane can be blended as another component (III) with the above components (I) and (II). By blending this component (III) into the 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.

[0080] Although there are no particular restrictions on the composition ratio of the above components (I), (II), and (III), in order to sufficiently 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).

[0081] Furthermore, various additives other than the components constituting the above-mentioned thermoplastic polyurethane can be blended into the above resin composition as needed. For example, pigments, dispersants, antioxidants, light stabilizers, ultraviolet absorbers, mold release agents, etc. can be appropriately blended.

[0082] Regarding the manufacturing method of a golf ball formed by laminating the above-mentioned 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, an intermediate layer material can be injected with an injection molding die around the core to obtain each coated sphere, and then a golf ball can be obtained by injecting the material of the cover, which is the outermost layer. Also, as each coating layer, a golf ball can be produced by wrapping the coated sphere with two pre-formed semi-spherical half-cups and performing heat and pressure molding.

[0083] For the golf ball, the deflection amount (mm) from an initial load of 98 N (10 kgf) to when a final load of 1,275 N (130 kgf) is applied is preferably 2.1 mm or more, more preferably 2.2 mm or more, still more preferably 2.4 mm or more, and as an upper limit value, preferably 2.8 mm or less, more preferably 2.7 mm or less, still more preferably 2.6 mm or less. If the deflection amount of the golf ball is too small, that is, if it is too hard, the spin may increase too much and the ball may not fly, or the hitting feel may become too hard. On the other hand, if the above-mentioned deflection amount is too large, that is, if the spherical body is too soft, the crack durability when repeatedly hit may deteriorate, or the actual hitting initial velocity may be low and the flying distance may not be achieved with a driver (W#1) hit.

[0084] 〔 Hardness relationship of each layer 〕 The intermediate layer-coated spherical body has a higher surface hardness than the core, and the difference in these surface hardnesses is, in Shore C hardness, preferably 1 or more, more preferably 4 or more, still more preferably 8 or more, and as an upper limit value, preferably 20 or less, more preferably 15 or less, still more preferably 12 or less. If the above value is too small, the spin in a full shot may increase and the flying distance may not be achieved. On the other hand, if the above value is too large, the crack durability when repeatedly hit may deteriorate.

[0085] The intermediate layer-coated sphere has a higher surface hardness than the ball, and the difference in these surface hardnesses is, in terms of Shore C hardness, preferably 1 or more, more preferably 5 or more, still more preferably 9 or more, and the upper limit value is 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, the spin may increase during a full shot and the desired flight 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 impacts may deteriorate, or the hitting feeling may become too hard. When the large value is due to the material hardness of the cover, the spin may increase during a full shot and the desired flight distance may not be achieved.

[0086] Deflection amount relationship between core and ball From the deflection amount E (mm) of the core until a load is applied 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 deflection amount B (mm) of the ball until a load is applied from an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf) is preferably 0.3 mm or more, more preferably 0.5 mm or more, still more preferably 0.6 mm or more, and as the upper limit value, preferably 1.2 mm or less, more preferably 1.0 mm or less, still more preferably 0.8 mm or less. If this value is too small, the spin during a full shot may increase and the flight distance may not be achieved. On the other hand, if the above value is too large, the crack durability during repeated impacts may deteriorate, or there may be too much run during an iron shot.

[0087] ​​The ratio of the amount of deflection between the ball and the core, that is, the value of B / E, is preferably 0.70 or more, more preferably 0.73 or more, still more preferably 0.78 or more. As the upper limit value, it is preferably 0.84 or less, more preferably 0.82 or less, still more preferably 0.80 or less. If this value is too small, the crack durability when repeatedly struck 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 when hitting a full shot increases, and the target flight distance may not be achieved even for a golfer with a slow head speed.

[0088] A large number of dimples can be formed on the outer surface of the cover. There are no particular restrictions on the dimples arranged on the cover surface, but preferably there are 323 or more, preferably 326 or more, more preferably 330 or more, and as the upper limit, preferably 380 or less, more preferably 360 or less, still more preferably 350 or less. If the number of dimples is more than the above range, the trajectory of the ball may become lower and the flight distance may decrease. Conversely, if the number of dimples is less, the trajectory of the ball may become higher and the flight distance may not increase.

[0089] Regarding the shape of the dimples, one type or a combination of two or more types such as circular, various polygons, dew drop shapes, and other elliptical shapes 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.

[0090] Regarding the dimple occupancy rate of the dimples on the spherical surface of the golf ball, specifically, the total dimple area defined by the plane edge surrounded by the edges of the dimples, that is, the ratio (SR value) occupied by the total dimple area in the spherical surface area of the ball assuming no dimples, it is desirable that it is 70% or more and 90% or less from the viewpoint of sufficiently exhibiting aerodynamic characteristics. Also, the space volume of the dimples under the plane surrounded by the edges of each dimple is divided by the cylindrical volume with the said plane as the bottom surface and the maximum depth of the dimple from this bottom surface as the height, and the value V 0It is preferably in the range of 0.35 or more and 0.80 or less from the viewpoint of optimizing the trajectory of the ball. Further, the VR value of the total dimple volume formed downward from the plane surrounded by the edges of the dimples in the ball volume assuming no dimples is preferably 0.6% or more and 1.0% or less. If the ranges of the above-described numerical values deviate, a trajectory that cannot obtain a good flight distance may result, and a sufficiently satisfactory flight distance may not be achieved.

[0091] In the golf ball of the present invention, when the lift coefficient measured under the conditions of a Reynolds number of 80,000 and a spin rate of 2000 rpm is CL1, the lift coefficient measured under the conditions of a Reynolds number of 70,000 and a spin rate of 1900 rpm is CL2, the lift coefficient measured under the conditions of a Reynolds number of 200,000 and a spin rate of 2500 rpm is CL3, and the lift coefficient measured under the conditions of a Reynolds number of 120,000 and a spin rate of 2250 rpm is CL4, it is desirable to optimize CL2 / CL1 and CL4 / CL3.

[0092] In this specification, the "lift coefficient (CL1, CL2, CL3, CL4)" is measured in accordance with the ITR (Indoor Test Range) defined by the USGA (United States Golf Association). The lift coefficient can be adjusted by adjusting the configuration (arrangement, diameter, depth, volume, number, shape, etc.) of the dimples of the golf ball. The lift coefficient does 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 formula (I). Re = ρvL / μ (I) In the above formula (I), ρ represents the density of the fluid, v represents the relative average velocity of the object with respect to the flow of the fluid, L represents the characteristic length, and μ represents the viscosity coefficient of the fluid.

[0093] The Reynolds number of 80,000 and the spin rate of 2,000 rpm, which are the conditions under which the lift coefficient CL1 is measured, generally roughly correspond to the state at the timing when the decrease in the lift coefficient (and thus the fall of the golf ball) begins after the golf ball is hit and reaches its highest point. Also, the Reynolds number of 70,000 and the spin rate of 1,900 rpm, which are the conditions under which the lift coefficient CL2 is measured, generally roughly correspond to the state immediately before hitting the ground after the golf ball is hit and reaches its highest point. These things are particularly true when the golf ball is hit under high-speed conditions (for example, initial velocity 66 m / s, spin rate 2,600 rpm, launch angle 11°). This high-speed condition corresponds to the conditions under which an average amateur hits with a driver.

[0094] The value of CL2 / CL1 is preferably 0.900 or more, more preferably 0.970 or more, and still more preferably 0.990 or more. By satisfying the above range, it is possible to suppress the decrease in lift during the fall of the golf ball, and as a result, it is easy to cause an increase in the flight distance (and thus an increase in carry) and an increase in roll during the fall. Therefore, the total flight distance can be improved. If CL2 / CL1 is too low, the golf ball is likely to fall rapidly, making it difficult to sufficiently increase the carry and roll. Also, from the perspective of improving the flight distance, the higher CL2 / CL1 is, the better, but if it is too high, although the carry increases, the roll decreases, and as a result, the total flight distance may not reach the optimum value. Therefore, the upper limit value of CL2 / CL1 is 1.100 or less, preferably 1.018 or less.

[0095] The Reynolds number of 200,000 and the spin rate of 2,500 rpm, under which the lift coefficient CL3 is measured, generally roughly correspond to the state immediately after a golf ball is hit under high-speed conditions (for example, an initial velocity of 72 m / s, a spin rate of 2,500 rpm, and a launch angle of 10°). The Reynolds number of 120,000 and the spin rate of 2,250 rpm, under which the lift coefficient CL4 is measured, generally roughly correspond to the state at the timing when about 2 seconds have elapsed while rising after a golf ball is hit under high-speed conditions (for example, an initial velocity of 72 m / s, a spin rate of 2,500 rpm, and a launch angle of 10°).

[0096] The value of CL4 / CL3 is preferably 1.250 or more, more preferably 1.252 or more, still more preferably 1.255 or more, and the upper limit value is preferably 1.300 or less, more preferably 1.295 or less, still more preferably 1.290 or less. By setting it within the above range, when a golf ball is hit under high-speed conditions (for example, at the time of a W#1 hit), it is possible to suppress an excessive increase in the rising amount of the golf ball (and thus suppress blow-up), improve the resistance to wind, and improve carry. Also, run can be improved. Therefore, the flight distance (total) can be improved.

[0097] From the viewpoint of improving flight distance, the lift coefficient CL1 is preferably 0.230 or more. Also, the lift coefficient CL1 is preferably 0.240 or less. From the same viewpoint, the lift coefficient CL2 is preferably 0.230 or more. Also, the lift coefficient CL2 is preferably 0.240 or less. From the same viewpoint, the lift coefficient CL3 is preferably 0.145 or more. Also, the lift coefficient CL3 is preferably 0.155 or less. From the same viewpoint, the lift coefficient CL4 is preferably 0.185 or more. Also, the lift coefficient CL4 is preferably 0.195 or less.

[0098] A coating film layer is formed on the cover surface. This coating film layer can be coated using various paints, and as the paint, it is preferable to use a paint composition mainly composed of a urethane paint composed of a polyol and a polyisocyanate because it needs to withstand the severe use conditions of a golf ball.

[0099] Examples of the polyol component include acrylic polyols and polyester polyols. These polyols include modified polyols, and other polyols can be added to further improve workability.

[0100] Examples of acrylic polyols include homopolymers or copolymers of monomers having a functional group that reacts with isocyanate. Examples of such monomers include (meth)acrylate alkyl esters, specifically methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, etc. These can be used alone or in combination of two or more.

[0101] In addition, examples of modified acrylic polyols include polyester-modified acrylic polyols, etc. Examples of other polyols include polyether polyols such as polyoxyethylene glycol (PEG), polyoxypropylene glycol (PPG), and polyoxytetramethylene glycol (PTMG), condensation polyester polyols such as polyethylene adipate (PEA), polybutylene adipate (PBA), and polyhexamethylene adipate (PH2A), lactone polyester polyols such as poly-ε-caprolactone (PCL), polycarbonate polyols such as polyhexamethylene carbonate, etc. These can be used alone or in combination of two or more. Also, the ratio of these polyols to the total amount of acrylic polyols is preferably 50% by mass or less, more preferably 40% by mass or less.

[0102] The polyester polyol is obtained by polycondensation of a polyol and a polybasic acid. Examples of the polyol include diols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, hexylene glycol, dimethylolheptane, polyethylene glycol, polypropylene glycol, etc., triols, tetraols, and polyols having an alicyclic structure. Examples of the polybasic acid include aliphatic dicarboxylic acids such as succinic acid, adipic acid, sebacic acid, azelaic acid, dimer acid, aliphatic unsaturated dicarboxylic acids such as fumaric acid, maleic acid, itaconic acid, citraconic acid, aromatic polyvalent carboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, pyromellitic acid, dicarboxylic acids having an alicyclic structure such as tetrahydrophthalic acid, hexahydrophthalic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, endomethylenetetrahydrophthalic acid, and tris-2-carboxyethyl isocyanurate.

[0103] 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 having a cyclic structure 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 a polyester polyol obtained by polycondensation of a polyol having an alicyclic structure, diols or triols, and a polybasic acid can be mentioned. On the other hand, as the polyester polyol of component (B), a polyester polyol having a multi-branched structure can be adopted. For example, a polyester polyol having a branched structure such as "NIPPOLAN 800" manufactured by Tosoh Corporation can be mentioned.

[0104] The weight average molecular weight (Mw) of the whole main agent composed of the above two types of polyester polyols is preferably 13,000 to 23,000, more preferably 15,000 to 22,000. Also, the number average molecular weight (Mn) of the whole main agent composed of the above two types of polyester polyols is preferably 1,100 to 2,000, more preferably 1,300 to 1,850. If these average molecular weights (Mw and Mn) deviate from the above ranges, the abrasion resistance of the coating film layer may decrease. The weight average molecular weight (Mw) and the number average molecular weight (Mn) are measured values (polystyrene conversion values) by gel permeation chromatography (hereinafter abbreviated as GPC) measurement using a differential refractive index detector.

[0105] There is no particular limitation on the blending amounts of the above two types of polyester polyols (A) and (B) components. However, it is preferable that the blending amount of component (A) is 20 to 30% by mass based on the total amount of the main agent, and the blending amount of component (B) is 2 to 18% by mass based on the total amount of the main agent.

[0106] On the other hand, there is no particular limitation 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.

[0107] Examples of the modified product of hexamethylene diisocyanate include polyester-modified products and urethane-modified products of hexamethylene diisocyanate. Examples of the derivative of hexamethylene diisocyanate include nurate (isocyanurate) products, burette products, and adduct products of hexamethylene diisocyanate.

[0108] Regarding the molar ratio (NCO group / OH group) of the hydroxyl group (OH group) possessed by the polyol and the isocyanate group (NCO group) possessed by the polyisocyanate, it is necessary to be in the range of 0.5 to 1.5, preferably 0.8 to 1.2, and more preferably 1.0 to 1.2. When it is less than 0.5, unreacted hydroxyl groups remain, and there is a risk that the performance and water resistance of the coating film layer will deteriorate. On the other hand, when it exceeds 1.5, the isocyanate group becomes excessive, and as a result, urea groups (which are brittle) are generated by the reaction with moisture, and thus the performance of the coating film layer may decrease.

[0109] As the curing catalyst (organometallic compound), amine-based catalysts and organometallic-based catalysts can be used. As this organometallic compound, metal soaps such as aluminum, nickel, zinc, tin, etc., which have been conventionally blended as curing agents for two-component curing type urethane paints, can be preferably used.

[0110] Various organic solvents can be mixed into the paint composition 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.

[0111] To the coating composition, known coating compounding components may be added as necessary. Specifically, appropriate amounts of a thickener, an ultraviolet absorber, a fluorescent brightening agent, a slipping agent, a pigment, etc. can be blended.

[0112] There is no particular limitation on the thickness of the coating film 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 film layer means the thickness of the coating film formed on the ball surface other than the dimples (that is, also referred to as the land portion or the bank portion), not the coating film layer formed in the dimples.

[0113] In the present invention, it is necessary that the elastic work recovery rate of the coating film layer composed of the above coating composition is 60% or more, preferably 70% or more, more preferably 80% or more. If the elastic work recovery rate of this coating film layer is within the above range, since the coating film layer has a high elastic force, the self-repairing 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 method for measuring the above elastic work recovery rate is as follows.

[0114] The elastic work recovery rate is an ultra-micro hardness test method that controls the indentation load on the order of micronewtons (μN) and tracks the indenter depth during indentation with nanometer (nm) accuracy, and is one parameter of the nanoindentation method for evaluating the physical properties of the coating film layer. In the conventional method, only the size of the deformation mark (plastic deformation mark) corresponding to the maximum load could be measured, but in the nanoindentation method, by automatically and continuously measuring, the relationship between the indentation load and the indentation depth can be obtained. Therefore, it is considered that there is no individual difference as in the case of visually measuring the deformation mark with an optical microscope in the conventional manner, and the physical properties of the coating film layer can be evaluated with high accuracy. Since the coating film layer on the ball surface is greatly affected by the strikes of a driver and various clubs, and the influence of the coating film layer on the physical properties of the golf ball is not small, measuring the coating film layer by the ultra-micro hardness test method and performing it with higher accuracy than before is a very effective evaluation method.

[0115] In addition, the hardness of the paint layer, Shore M hardness, is preferably 40 or more, more preferably 60 or more, and as the 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 paint layer, Shore C hardness, is preferably 40 or more, and as the upper limit, preferably 80 or less. Note that this Shore C hardness conforms to ASTM D2240. If the hardness of the paint layer is too high 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 hardness of the paint layer is too low compared to the above hardness range, the surface of the ball may be easily damaged or dirt may easily adhere when hitting a hard object, which is not preferable.

[0116] 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 a normal painting process is adopted to apply it to the surface, and a coating film 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

[0117] Hereinafter, examples and comparative examples will be shown to specifically explain the present invention, but the present invention is not limited to the following examples.

[0118] 〔Examples 1 to 3, Comparative Examples 1 to 8〕 Formation of core After preparing the rubber compositions of Examples 1 to 3 and Comparative Examples 1 to 6 shown in Table 1, a solid core was produced by vulcanization molding at the temperature and time shown in Table 1. For Comparative Example 7 and Comparative Example 8, in the same manner as above, a solid core was produced according to the rubber composition and vulcanization conditions described in Table 1.

[0119]

Table 1

[0120] The details of each component listed in Table 1 are as follows. · Polybutadiene A: Manufactured by JSR Corporation, product name "BR01" · Polybutadiene B: Manufactured by JSR Corporation, product name "T0700" · Polybutadiene C: Manufactured by JSR Corporation, product name "BR730" · Isoprene rubber: Manufactured by Nippon Zeon Co., Ltd., product name "Nipol IR2200" · Zinc acrylate: "ZN-DA85S" (manufactured by Nippon Shokubai Co., Ltd.) · Zinc stearate: Product name "Zinc Stearate G" (manufactured by NOF Corporation) · Organic peroxide (1): Dicumyl peroxide, product name "Perkyl D" (manufactured by NOF Corporation), half-life temperature of 175.2 °C in 1 minute · Organic peroxide (2): Mixture of 1,1-di(t-butylperoxy)cyclohexane and silica, product name "Perhexa C-40" (manufactured by NOF Corporation) · Sulfur (1): Product name "Sunmix S-80N" (Sanshin Chemical Industry Co., Ltd.), sulfur masterbatch containing 80% by mass of powdered sulfur for rubber · Sulfur (2): Product name "Sulfax-5" (manufactured by Tsurumi Chemical Industry Co., Ltd.), sulfur content 95% by mass · Water: Pure water (manufactured by Shoei Yakuhin Kogyo Co., Ltd.) · Antioxidant A: 2,2-methylenebis(4-methyl-6-butylphenol), product name "No Crack NS-6" (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) · Antioxidant B: 2-mercaptobenzimidazole, product name "No Crack MB" (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) · Zinc oxide: Product name "Three Kinds of Zinc Oxide" (manufactured by Sakai Chemical Industry Co., Ltd.) · Zinc pentachlorothiophenolate: Manufactured by Wako Pure Chemical Industries, Ltd.

[0121] Formation of intermediate layer and cover (outermost layer) Next, for Examples 1 to 3 and Comparative Examples 1 to 6, an intermediate layer was formed by an injection molding method using Intermediate Layer Material No. 1 with the formulation shown in Table 2 around the core obtained above to produce an intermediate layer-coated sphere. Next, a cover (outermost layer) was formed by an injection molding method using Cover Material No. 2 with the formulation shown in the same table around the intermediate layer-coated sphere obtained above to produce a golf ball. At this time, Dimple Type-A described below was formed on the cover surface. For Comparative Example 7 and Comparative Example 8, in the same manner as above, a golf ball was produced by an injection molding method using Intermediate Layer Material No. 1 and Cover Material No. 2 with the formulations shown in Table 2. Also, the following Dimple Type-A was formed on the cover surfaces of Comparative Example 7 and Comparative Example 8.

[0122]

Table 2

[0123] The trade names of the main materials described in the table are as follows. "Himilan 1706", an ionomer manufactured by Mitsui Dow Chemical Co., Ltd. "AM7318", an ionomer manufactured by Mitsui Dow Chemical Co., Ltd. "Trimethylolpropane" (TMP), manufactured by Tokyo Chemical Industry Co., Ltd. "TPU", trade name "Pandex", an ether-type thermoplastic polyurethane manufactured by DIC Covestro Polymer GmbH

[0124] Dimple Type-A uses eight types of circular dimples. Details thereof are shown in Table 3 below, and the arrangement pattern is as shown in Fig. 2. Fig. 2(A) shows a plan view of the dimples, and Fig. 2(B) shows a side view thereof.

[0125]

Table 3

[0126] Definition of dimple Edge: The highest point in the cross-section passing through the dimple center 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 surface 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 to the ball volume assuming no dimples

[0127] Also, the lift coefficient CL1 measured under the conditions of Reynolds number 80000 and spin rate 2000 rpm of the ball forming the above dimple Type-A on the cover surface, the lift coefficient CL2 measured under the conditions of Reynolds number 70000 and spin rate 1900 rpm, the lift coefficient CL3 measured under the conditions of Reynolds number 200000 and spin rate 2500 rpm, the lift coefficient CL4 measured under the conditions of Reynolds number 120000 and spin rate 2250 rpm, and the values of CL2 / CL1 and CL4 / CL3 are shown in Table 4 below. These lift coefficients are measured in accordance with the ITR (Indoor Test Range) defined by the USGA.

[0128]

Table 4

[0129] Formation of paint layer (coating layer) Next, for Examples 1 to 3 and Comparative Examples 1 to 6, as a paint composition common to all examples and comparative examples, the paint composition shown in Table 5 below was used, and the above paint was applied to the surface of a large number of formed covers (outermost layer) by an air spray gun to produce a golf ball with a paint layer having a thickness of 15 μm. Similarly, for Comparative Example 7 and Comparative Example 8, in the same manner as above, the above paint was applied to produce a golf ball having a paint layer with a thickness of 15 μm.

[0130]

Table 5

[0131] [Synthesis Example of Polyester Polyol (A)] Into a reactor equipped with a reflux condenser, a dropping funnel, a gas inlet tube, and a 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 to 240 °C with stirring and heated (reacted) for 5 hours. Thereafter, "Polyester Polyol (A)" having an acid value of 4, a hydroxyl value of 170, and a weight average molecular weight (Mw) of 28,000 was obtained. Next, the above-synthesized polyester polyol (A) was dissolved in butyl acetate to prepare a varnish having a non-volatile content of 70% by mass.

[0132] The paint composition in Table 5 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.

[0133] Elastic work recovery rate For the measurement of the elastic work recovery rate of the paint, a paint sheet with a thickness of 50 μm was used for the measurement. The measuring device used was the ultra-micro hardness tester "ENT-2100" manufactured by Elionix Inc., and the measurement conditions were 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 amount of indentation work 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 (%)

[0134] Shore C hardness and Shore M hardness The Shore C hardness and Shore M hardness in Table 5 above are measured using a Shore C hardness tester and a Shore M hardness tester conforming to ASTM D2240 standard with a 2 mm thick sheet made and stacked in three layers as a test piece.

[0135] For each obtained golf ball, 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 Table 6.

[0136] Outer diameter of each sphere of core and intermediate layer coated sphere The sphere to be measured is temperature-adjusted in a constant temperature bath adjusted to 23.9 ± 1 °C for 3 hours or more, and then 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 spheres is obtained.

[0137] Diameter of ball The ball to be measured is temperature-adjusted in a constant temperature bath adjusted to 23.9 ± 1 °C for 3 hours or more, and then measured in a room at 23.9 ± 2 °C. Fifteen locations without any dimples are measured, and the average value is taken as the measured value of each ball, and the average value of 10 measured balls is obtained.

[0138] Deflection amount of core and ball Place the core or the target coated sphere of the ball on a hard plate, 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). The above amount of deflection is the measured value after temperature adjustment to 23.9 °C. Also, the pressurization speed of the head compressing the ball is set to 10 mm / s.

[0139] Core hardness distribution The surface of the core is spherical. The hardness meter needle is set to be approximately perpendicular to the spherical surface, and the surface hardness is measured using the Shore C hardness in accordance with ASTM D2240. For the center of the core and the predetermined positions, the core is cut into a hemispherical shape to make the cross-section flat, and the hardness meter needle is vertically pressed against the center part and the predetermined positions shown in Table 6 for measurement. The hardness of the center and each position is indicated by the value of the Shore C hardness. For the hardness measurement, an automatic rubber hardness meter "P2" manufactured by Polymer Instruments Co., Ltd. equipped with a Shore C type hardness meter is used. The maximum value of the hardness value is read. All measurements are made in an environment of 23 ± 2°C. Note that the numerical values in Table 6 are the values of the Shore C hardness.

[0140] In addition, graphs of the core hardness distributions of Examples 1 to 5 and Comparative Examples 1 to 8 are shown in FIGS. 3, 4, and 5.

[0141] Material hardness of intermediate layer and cover The resin material of each layer is formed into a sheet shape with a thickness of 2 mm and left for two weeks. Then, the Shore D hardness and the Shore C hardness are measured in accordance with the ASTM D2240 standard. For the hardness measurement, an automatic rubber hardness meter "P2" manufactured by Polymer Instruments Co., Ltd. is used. The attachments for the Shore D hardness and the Shore C hardness are attached to measure their respective hardnesses. The maximum value of the hardness value is read. All measurements are made in an environment of 23 ± 2°C.

[0142] Surface hardness of each sphere of intermediate layer coated sphere and ball The needle is pressed vertically against the surface of each sphere for measurement. Note that the surface hardness of the ball (cover) is the measured value at the land part where no dimples are formed on the ball surface. The Shore D hardness and the Shore C hardness are measured in accordance with the ASTM D2240 standard. For the hardness measurement, an automatic rubber hardness meter "P2" manufactured by Polymer Instruments Co., Ltd. is used. The attachments for the Shore D hardness and the Shore C hardness are attached to measure their respective hardnesses. The maximum value of the hardness value is read. All measurements are made in an environment of 23 ± 2°C.

[0143]

Table 6

[0144] The flight (W#1) (I#6), spin amount at approach, and repeated impact durability of each golf ball are evaluated by the following method. The results are shown in Table 7.

[0145] Jump evaluation (W#1) A driver (W#1) was attached to a golf impact robot, and the spin amount and flight distance (total) when hitting at a head speed (HS) of 53 m / s were measured respectively. The club used was the "TourB XD-5 Driver" (loft angle 8.5°) manufactured by Bridgestone Sports Co., Ltd. The spin amount was also measured for the ball immediately after hitting using an initial condition measuring device. Also, a driver (W#1) was attached to a golf impact robot, and the spin amount and flight distance (total) when hitting at a head speed (HS) of 48 m / s were measured respectively. The club used was the "JGR (2016 model) Driver" (loft angle 9.5°) manufactured by Bridgestone Sports Co., Ltd. The total flight distance of the above two conditions was calculated, and the flight performance was evaluated according to the following criteria. 〔Judgment Criteria〕 ○ ··· Total flight distance (total of two conditions of W#1) 498.0 m or more △ ··· Total flight distance (total of two conditions of W#1) 497.0 m or more and less than 498.0 m × ··· Total flight distance (total of two conditions of W#1) less than 497.0 m

[0146] Jump performance (I#6) A middle iron (I#6) was attached to a golf impact robot, and the flight distance when hitting at a head speed of 43.5 m / s was measured and judged according to the following criteria. The club used was the "JGR Forged (2016 model)" manufactured by Bridgestone Sports Co., Ltd. Also, the spin amount was measured for the ball immediately after hitting using an initial condition measuring device. 〈Judgment Criteria〉 ○ ··· Total flight distance 178.0 m or more △ ··· Total flight distance is 177.0 m or more and less than 178.0 m × ··· Total flight distance is less than 177.0 m

[0147] Evaluation of spin amount at approach It is judged by the amount of spin when a sand wedge is attached to a golf hitting robot and it is hit at a head speed (HS) of 15 m / s. The amount of spin was measured by an initial condition measuring device for the ball immediately after hitting in the same manner. As the sand wedge, "TourStage TW-03 (loft angle 57°) 2002 model" manufactured by Bridgestone Sports Co., Ltd. was used. 〔Judgment criteria〕 〇 ··· Spin amount is 4000 rpm or more × ··· Spin amount is less than 4000 rpm

[0148] Repeated impact durability A test was conducted to see the number of times a ball was repeatedly collided with a steel plate until it cracked at a launch speed of 43 m / s. N = 30 balls were repeatedly hit, and it was evaluated by the minimum value of the number of hits when the ball began to crack. The number of cracks in Example 2 was set to 100 as an index. 〈Judgment criteria〉 〇 ··· Index is 90 or more × ··· Index is less than 90

[0149]

Table 7

[0150] As shown in the results of Table 7, the golf balls of Comparative Examples 1 to 8 are inferior to the product of the present invention (Example) in the following points. In Comparative Example 1, the hardness distribution of the core is (H25 - H0) < (H100 - H87.5). As a result, the amount of spin when hitting with a driver (W#1) and a middle iron (I#6) increased, and no flight distance was obtained. In Comparative Example 2, the hardness distribution of the core was such that (H25 - H0) < (H100 - H87.5) and (H87.5 - H0) < 17. As a result, the amount of spin when hitting with the driver (W#1) increased, and no flying distance was achieved. In Comparative Example 3, (H87.5 - H0) < 17. As a result, the amount of spin when hitting with the driver (W#1) increased, and no flying distance was achieved. In Comparative Example 4, the hardness distribution of the core was such that (H25 - H0) < (H100 - H87.5) and (H87.5 - H0) < 17. As a result, the amount of spin when hitting with the driver (W#1) increased, and no flying distance was achieved. In Comparative Example 5, the hardness distribution of the core was such that (H25 - H0) < (H100 - H87.5) and (H87.5 - H0) < 17. As a result, the amount of spin when hitting with the driver (W#1) increased, and no flying distance was achieved. In Comparative Example 6, the hardness distribution of the core was such that (H25 - H0) < (H100 - H87.5) and (H87.5 - H0) < 17. As a result, the amount of spin when hitting with the driver (W#1) and the middle iron (I#6) increased, and no flying distance was achieved. In Comparative Example 7, the hardness distribution of the core was such that (H75 - H50) < (H25 - H0), (H87.5 - H0) > 23.0, and the absolute value of (H87.5 - H0) / (H50 - H0) < 3.0. When full shot was made, the actual hitting initial velocity was low, the flying distance was poor, and the repeated hitting durability was not good. In Comparative Example 8, the hardness distribution of the core was such that (H75 - H50) < (H25 - H0), (H87.5 - H0) < 17, and the absolute value of (H87.5 - H0) / (H50 - H0) < 3.0. Since the balance between the amount of spin and the actual hitting initial velocity when hitting with the driver (W#1) was not good, no flying distance was achieved.

Claims

1. In a golf ball having at least one intermediate layer interposed between a single-layer core and a cover, the surface hardness relationship between the sphere (intermediate layer-coated sphere) obtained by coating the core with the intermediate layer and the ball satisfies the following formula (Surface hardness of the intermediate layer-coated sphere) > (Surface hardness of the ball) and the diameter of the core is 35.5 to 39.5 mm. In the core hardness distribution, when the Shore C hardness of the core surface is H100, the Shore C hardness at a position 87.5% outside the core radius from the core center is H87.5, the Shore C hardness at a position 75% outside the core radius from the core center is H75, the Shore C hardness at a position 62.5% outside the core radius from the core center is H62.5, the Shore C hardness at a position 50% outside the core radius from the core center is H50, the Shore C hardness at a position 37.5% outside the core radius from the core center is H37.5, the Shore C hardness at a position 25% outside the core radius from the core center is H25, the Shore C hardness at a position 12.5% outside the core radius from the core center is H12.5, and the Shore C hardness at the core center is H0, the following formula (H75 - H50) > (H25 - H0) > (H100 - H87.5) > (H50 - H25) 23.0 ≥ (H87.5 - H0) ≥ 17.0 The absolute value of (H87.5 - H0) / (H50 - H0) ≥ 3.0 A golf ball characterized by satisfying the above.

2. The following formula, 0 ≤ (H100 - H87.5) ≤ 3.0 The golf ball according to Claim 1, which satisfies the above.

3. The following formula, 4.0 ≤ (H75 - H50) ≤ 9.0 The golf ball according to Claim 1 or 2, which satisfies the above.

4. The following formula, -1.0 ≤ (H50 - H25) ≤ 1.0 The golf ball according to any one of Claims 1 to 3, which satisfies the above.

5. The following formula, 3.0 ≤ (H25 - H0) ≤ 6.0 The golf ball according to any one of Claims 1 to 4, which satisfies the above.

6. The golf ball according to any one of Claims 1 to 5, wherein the compression deformation amount from an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf) on the above core is 2.5 to 3.5 mm, and the compression deformation amount from an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf) on the ball is 2.1 to 2.8 mm.

7. When the lift coefficient measured under the conditions of a Reynolds number of 80,000 and a spin rate of 2,000 rpm is defined as CL1, and the lift coefficient measured under the conditions of a Reynolds number of 70,000 and a spin rate of 1,900 rpm is defined as CL2, CL1 and CL2 satisfy the following formula 0.900 ≤ CL2 / CL1 The golf ball according to any one of claims 1 to 6 that satisfies the above condition.

8. When the lift coefficient measured under the conditions of a Reynolds number of 200,000 and a spin rate of 2,500 rpm is defined as CL3, and the lift coefficient measured under the conditions of a Reynolds number of 120,000 and a spin rate of 2,250 rpm is defined as CL4, CL3 and CL4 satisfy the following formula 1.250 ≤ CL4 / CL3 ≤ 1.300 The golf ball according to any one of claims 1 to 7 that satisfies the above condition.

9. The above core is a heat-molded product of a rubber composition containing the following components (A) to (D): (A) Base rubber (B) Organic peroxide (C) Water and / or metal salt of molcarboxylic acid (D) Sulfur The golf ball according to any one of claims 1 to 8, which is a heat-molded product of a rubber composition containing the above components.

10. The golf ball according to claim 9, wherein the mass ratio of the above component (C) to component (D) is (D) / (C) = 0.02 to 0.20.

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