Multi-piece solid golf ball

Abstract

Providing golf balls that deliver high spin performance. [Solution] In a golf ball comprising a core 1, an intermediate layer 2, and a cover 3, when the Shore C hardness of the core surface, the 87.5% outside the core radius from the core center, the 75% outside, the 62.5% outside, the 50% outside, the 37.5% outside, the 25% outside, the 12.5% ​​outside, and the core center are H100, H87.5, H75, H62.5, H50, H37.5, H25, H12.5, and H0, respectively, the following formula (H87.5-H50) / (H50-H12.5)≧3.5 Core deflection (CT) > (H100 - H50) / (H50 - H0) (Hardness of the intermediate layer material - Hardness of the cover material) > (Surface hardness of the intermediate layer-covered sphere - H62.5) (However, the hardness values ​​mentioned above are Shore C values.) A golf ball G characterized by satisfying the following conditions.

Description

Technical Field

[0001] The present invention relates to a golf ball having a three-layer structure or more including a core, a cover, and at least one intermediate layer sandwiched therebetween, and is a golf ball at an advanced level even among amateurs.

Background Art

[0002] Golf players called advanced players among amateurs have a high level of shot accuracy. Since it is difficult to achieve long flight distances with power, there is a demand for a ball that can achieve a longer flight distance when hitting a full shot. However, generally, golf balls for golfers with low club head speeds tend to have less spin performance at approach than balls for professionals.

[0003] In addition, focusing on the hardness distribution of the core, several techniques for providing a high-performance golf ball by designing the internal hardness distribution of the core in various modes have been proposed. Examples of such technical documents include, for example, the golf balls of Patent Documents 1 to 12 below. However, in these proposed golf balls, there are still problems in achieving both excellent flight distance performance when hitting with a driver (W#1) or an iron full shot by a user who is an advanced player but whose club head speed is not as fast as that of a professional, and high spin performance at approach. In particular, there is a demand for a golf ball that can achieve both excellent flight distance and higher spin performance at approach than before for advanced players with not-so-fast club head speeds.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

[0005] This invention has been made in view of the above circumstances, and aims to provide a golf ball that enables advanced amateur golfers, whose head speed is not as fast as that of professionals, to achieve excellent distance performance when hitting with a driver (W#1) or when taking full iron shots, and furthermore, to achieve high spin performance when taking approach shots, thereby providing a golf ball that combines excellent distance and high spin performance. [Means for solving the problem]

[0006] The inventors, after diligent research to achieve the above objective, have determined the hardness distribution of the core in a multi-piece solid golf ball comprising a core, an intermediate layer, and a cover, focusing on the hardness at each position: hardness of the core surface (H100), hardness at 87.5% outside the core radius from the core center (H87.5), hardness at 75% outside the core radius from the core center (H75), hardness at 62.5% outside the core radius from the core center (H62.5), hardness at 50% outside the core radius from the core center (H50), hardness at 37.5% outside the core radius from the core center (H37.5), hardness at 25% outside the core radius from the core center (H25), hardness at 12.5% ​​outside the core radius from the core center (H12.5), and hardness at the core center (H0), using the following formula (H87.5-H50) / (H50-H12.5)≧3.5 In addition to satisfying the above conditions, when the deflection CT (mm) is applied to the core from an initial load of 98N (10kgf) to a final load of 1,275N (130kgf), the following formula CT>(H100-H50) / (H50-H0) The following formula satisfies the conditions and describes the relationship between the positional hardness (H62.5) 62.5% outside the core radius from the core center, the material hardness of the intermediate layer and cover, and the surface hardness of the covered sphere with the intermediate layer covering the core: (Hardness of intermediate layer material - Hardness of cover material) > (Surface hardness of intermediate layer-covered sphere - H62.5) (However, the material hardness and surface hardness values ​​mentioned above are Shore C values.) When we manufactured a multi-piece solid golf ball to satisfy the requirements, we discovered that it offered superior distance when taken by amateur golfers whose head speed is not as fast as that of professionals, i.e., golfers with a driver (W#1) head speed of around 40 m / s, and that its spin performance during approach shots was at a level equal to or better than that of professional-grade balls. This led to the creation of the present invention.

[0007] Therefore, the present invention provides the following multi-piece solid golf ball. 1. A multi-piece solid golf ball comprising a core, an intermediate layer, and a cover, wherein, in the hardness distribution of the core, 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, then the following formula (H87.5-H50) / (H50-H12.5)≧3.5 In addition to satisfying the above conditions, when the deflection CT (mm) is applied to the core from an initial load of 98N (10kgf) to a final load of 1,275N (130kgf), the following formula CT>(H100-H50) / (H50-H0) The following equation satisfies the conditions, and the relationship between the Shore C hardness (H62.5) at a position 62.5% outside the core radius from the core center, the material hardness of the intermediate layer and cover, and the surface hardness of the covered sphere with the intermediate layer covering the core is given by the following formula. (Hardness of intermediate layer material - Hardness of cover material) > (Surface hardness of intermediate layer-covered sphere - H62.5) (However, the material hardness and surface hardness values ​​mentioned above are Shore C values.) A multi-piece solid golf ball characterized by satisfying the following conditions. 2. The multi-piece solid golf ball described in item 1 above, wherein the value of (intermediate layer material hardness - cover material hardness) is 34 or higher. 3. A multi-piece solid golf ball as described in 1 or 2 above, wherein the value of the above (surface hardness of the intermediate layer coated sphere - H62.5) is 30 or more and 36 or less. 4. The following formula, Shore C hardness of the core center ≤ Shore C hardness of the cover material A multi-piece solid golf ball as described in 1 or 2 above, which satisfies the requirements. 5. The multi-piece solid golf ball according to claim 1 or 2, wherein the Shore C hardness of the cover material is 50 or less. 6. In the core hardness distribution, the following formula H0 < H12.5 < H25 < H37.5 < H50 < H62.5 < H75 < H87.5 < H100 is satisfied, and the multi-piece solid golf ball according to claim 1 or 2. 7. In the core hardness distribution, the following formula (Shore C hardness of the core surface - Shore C hardness of the core center) ≥ 24 is satisfied, and the multi-piece solid golf ball according to claim 1 or 2. 8. The cover is formed by injection molding a single resin composition mainly composed of (I) thermoplastic polyurethane and (II) polyisocyanate compound, and in the resin composition, there is a polyisocyanate compound in which all isocyanate groups in one molecule remain in an unreacted state at least in part, and the multi-piece solid golf ball according to claim 1 or 2.

[0008] In the present specification, a user who is not as fast as a professional in head speed but is an advanced amateur means a user whose head speed at the time of hitting a driver (W#1) is around 40 m / s, more specifically, about 35 to 43 m / s or more.

Advantages of the Invention

[0009] The golf ball of the present invention is excellent in flight distance when an advanced amateur-level golfer who is not as fast as a professional hits a full shot with a driver (W#1), and moreover, the spin performance at the time of approach has a level equal to or higher than that of a ball for professionals.

Brief Description of the Drawings

[0011] The present invention will be described in more detail below. The multi-piece solid golf ball of the present invention has a core, an intermediate layer, and a cover, an example of which is shown in Figure 1. The golf ball G shown in Figure 1 has a single-layer core 1, a single-layer intermediate layer 2 covering the core 1, and a single-layer cover 3 covering the intermediate layer. This cover 3, excluding the paint layer, is the outermost layer in the layer structure of the golf ball. Each of the core and intermediate layers is formed as a single layer as shown in Figure 1, and a surrounding layer may also be provided between the core and the intermediate layer. In addition, a large number of dimples D are usually formed on the surface of the cover (outermost layer) 3 for the purpose of providing aerodynamic properties. In addition, although not specifically shown in the figures, a paint layer is usually formed on the surface of the cover 3. The above layers will be described in detail below.

[0012] The above core can be formed in a single layer or multiple layers, but a single layer is preferred. In the case of a multi-layered rubber core, delamination may occur at the interface when repeatedly struck, causing the core to crack prematurely.

[0013] The diameter of the core is not particularly limited, but is preferably 36.7 mm or larger, more preferably 37.2 mm or larger, and even more preferably 37.6 mm or larger. The upper limit is preferably 40.1 mm or smaller, more preferably 39.0 mm or smaller, and even more preferably 38.2 mm or smaller. If the core diameter is too small, the initial velocity of the ball will be low, or the overall hardness of the ball will be too hard, meaning the amount of deflection will be small, the amount of spin during a full shot will increase, and the target distance may not be achieved. On the other hand, if the core diameter is too large, the amount of spin during a full shot will increase, making it difficult to achieve the target distance, or the durability against cracking when repeatedly struck may be poor.

[0014] Next, the hardness distribution of the core described above will be explained. Note that the hardness of the core described below refers to Shore C hardness. This Shore C hardness is the hardness value measured using a Shore C hardness tester compliant with the ASTM D2240 standard.

[0015] 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 as H87.5, the Shore C hardness at a position 75% outside the core radius from the core center as H75, the Shore C hardness at a position 62.5% outside the core radius from the core center as H62.5, the Shore C hardness at a position 50% outside the core radius from the core center as H50, the Shore C hardness at a position 37.5% outside the core radius from the core center as H37.5, the Shore C hardness at a position 25% outside the core radius from the core center as H25, the Shore C hardness at a position 12.5% ​​outside the core radius from the core center as H12.5, and the Shore C hardness at the core center as H0.

[0016] The surface hardness (H100) of the core described above is not particularly limited, but is preferably 76 or higher, more preferably 78 or higher, and even more preferably 80 or higher. Similarly, the upper limit is not particularly limited, but is preferably 91 or lower, more preferably 89 or lower, and even more preferably 87 or lower. If this value is too low, the core's rebound properties will be too low, resulting in excessive spin on the ball during full shots and potentially preventing the desired distance from being achieved. On the other hand, if the above value is too high, the resistance to cracking after repeated impacts may be poor, or the feel may become too hard.

[0017] The positional hardness (H87.5) at 87.5% outside the radius from the center of the core is not particularly limited, but is preferably 68 or higher, more preferably 70 or higher, and even more preferably 72 or higher. There is also no particular upper limit, but is preferably 83 or lower, more preferably 81 or lower, and even more preferably 79 or lower. Deviating from these hardness values ​​may lead to unfavorable results similar to those described for the surface hardness (H100) of the core.

[0018] The positional hardness (H75) at 75% outside the radius from the center of the core is not particularly limited, but is preferably 66 or higher, more preferably 68 or higher, and even more preferably 70 or higher. There is also no particular upper limit, but is preferably 76 or lower, more preferably 74 or lower, and even more preferably 72 or lower. Deviating from these hardness levels may lead to unfavorable results similar to those described for the surface hardness (H100) of the core.

[0019] The positional hardness (H62.5) located 62.5% outside the radius from the center of the core is not particularly limited, but is preferably 59 or higher, more preferably 61 or higher, and even more preferably 63 or higher. There is also no particular upper limit, but is preferably 69 or lower, more preferably 67 or lower, and even more preferably 65 or lower. Deviating from these hardness values ​​may lead to unfavorable consequences similar to those described for the surface hardness (H100) of the core.

[0020] The hardness (H50) at a position 50% outside the radius from the center of the core is not particularly limited, but is preferably 56 or higher, more preferably 58 or higher, and even more preferably 60 or higher. There is also no particular upper limit, but is preferably 68 or lower, more preferably 66 or lower, and even more preferably 64 or lower. If this value is too low, the rebound of the core will be low, which may result in not being able to achieve the desired distance or poor crack resistance when repeatedly struck. If this value is too high, the amount of spin on the ball will be high, which may result in not being able to achieve the desired distance or the feel of the ball may become too hard.

[0021] The positional hardness (H37.5) at 37.5% outside the radius from the center of the core is not particularly limited, but is preferably 55 or higher, more preferably 57 or higher, and even more preferably 59 or higher. There is also no particular upper limit, but is preferably 67 or lower, more preferably 65 or lower, and even more preferably 63 or lower. Deviating from these hardness values ​​may lead to unfavorable results similar to those described for the positional hardness (H50) at 50% outside the radius from the center of the core.

[0022] The positional hardness (H25) at 25% radius out from the center of the core is not particularly limited, but is preferably 54 or higher, more preferably 56 or higher, and even more preferably 58 or higher. There is also no particular upper limit, but is preferably 66 or lower, more preferably 64 or lower, and even more preferably 62 or lower. Deviating from these hardness values ​​may lead to unfavorable results similar to those described for the positional hardness (H50) at 50% radius out from the center of the core.

[0023] The positional hardness (H12.5) at 12.5% ​​outside the radius from the center of the core is not particularly limited, but is preferably 53 or higher, more preferably 55 or higher, and even more preferably 57 or higher. There is also no particular upper limit, but is preferably 64 or lower, more preferably 62 or lower, and even more preferably 60 or lower. If these hardness values ​​are deviated from, it may lead to unfavorable results similar to those described for the positional hardness (H50) at 50% outside the radius from the center of the core.

[0024] The central hardness (H0) of the core described above is not particularly limited, but is preferably 51 or higher, more preferably 53 or higher, and even more preferably 55 or higher. There is also no particular upper limit to the central hardness, which is preferably 61 or lower, more preferably 59 or lower, and even more preferably 57 or lower. If the hardness deviates from these values, it may lead to unfavorable consequences similar to those described for the positional hardness (H50) 50% outside the radius from the center of the core.

[0025] The hardness difference (H100-H0) between the core surface and the core center is preferably 24 or higher, more preferably 25 or higher, and even more preferably 27 or higher, with an upper limit of preferably 35 or lower, more preferably 32 or lower, and even more preferably 30 or lower. If this value is too low, the ball will spin too much and the desired distance may not be achieved. On the other hand, if this value is too high, the core's rebound properties will be low, which may result in the desired distance not being achieved or poor crack resistance when repeatedly struck.

[0026] In the core hardness distribution described above, in order to increase the amount of spin when hitting a full shot and achieve the desired distance, a hardness distribution in which the hardness gradually increases from the center of the core towards the surface is required, that is, as shown in the following equation. H0 <H12.5<H25<H37.5<H50<H62.5<H75<H87.5<H100 It is preferable that the following conditions be met.

[0027] In this invention, the following formula (H87.5-H50) / (H50-H12.5)≧3.5 The following conditions must be met. The value of (H87.5-H50) / (H50-H12.5) above is preferably 3.7 or higher, more preferably 3.9 or higher, and the upper limit is usually 20.0 or lower, preferably 8.0 or lower, and more preferably 4.4 or lower. If this value is too low, the spin will increase when using a driver (W#1) at a head speed of around 40 m / s and when using full iron shots, and the desired distance may not be achieved. On the other hand, if this value is too high, the rebound effect will be too low, and the desired distance may not be achieved, or the durability against cracking when repeatedly struck may be poor.

[0028] Furthermore, the ratio of the hardness difference from the core center to the surface to the hardness difference from the core center to the intermediate position, i.e., the value of (H100-H50) / (H50-H0), is preferably 3.0 or higher, more preferably 3.4 or higher, and even more preferably 3.8 or higher. The upper limit is usually 20.0 or lower, preferably 8.0 or lower, and more preferably 5.0 or lower. If this value is too low, the spin will increase when using a driver (W#1) at head speeds around 40 m / s and when using full iron shots, which may prevent you from achieving the desired distance. On the other hand, if this value is too high, the rebound effect may be too low, which may prevent you from achieving the desired distance, or the durability against cracking when repeatedly struck may be poor.

[0029] In the above core hardness distribution, when the hardness difference (H100-H87.5) is A, the hardness difference (H87.5-H75) is B, the hardness difference (H75-H62.5) is C, the hardness difference (H62.5-H50) is D, the hardness difference (H50-H37.5) is E, the hardness difference (H37.5-H25) is F, the hardness difference (H25-H12.5) is G, and the hardness difference (H12.5-H0) is H, it is preferable that the relationship between (E+F+G+H) and (C+D) satisfies the formula (E+F+G+H)<(C+D). This formula means that, in the core hardness distribution, the hardness increase from the midpoint between the core center and the core surface (H50) to H75 is greater than the hardness increase from the core center (H0) to the midpoint between the core center and the core surface (H50). Figure 2 shows the core hardness distribution graph of Example 1, which illustrates the above characteristics. The difference between (C+D)-(E+F+G+H) is usually greater than 0, preferably 1.0 or more, and more preferably 2.0 or more, and the upper limit is usually 14.0 or less, preferably 10.0 or less, and more preferably 6.0 or less. If this value is too small, the spin will increase when hitting with a driver (W#1) at head speeds around 40 m / s and when hitting full shots with irons, and the desired distance may not be achieved. On the other hand, if this value is too large, the crack resistance when repeatedly struck will be poor, or the actual initial velocity when hitting a full shot will be low, and the desired distance may not be achieved.

[0030] Furthermore, the relationship between (E+F+G+H) and (A+B) preferably satisfies the formula (E+F+G+H) < (A+B). This formula means that in the core hardness distribution, the hardness increase from H75 to the core surface H100 is greater than the hardness increase from the core center H0 to the midpoint between the core center and the core surface H50. Figure 2 shows the core hardness distribution graph of Example 1, which illustrates the above characteristics. The difference between (A+B)-(E+F+G+H) is usually greater than 0, preferably 2.0 or more, more preferably 4.0 or more, and the upper limit is usually 16.0 or less, preferably 13.0 or less, more preferably 10.0 or less. If this value is too small, the spin may increase during shots with a driver (W#1) at head speeds around 40 m / s and during full iron shots, making it difficult to achieve the desired distance. On the other hand, if this value is too high, the durability against cracking after repeated impacts will be poor, or the actual initial ball speed when hitting a full shot will be low, which may prevent you from achieving the desired distance.

[0031] The amount of deflection (mm) of the core when an initial load of 98N (10kgf) is applied to a final load of 1,275N (130kgf) is not particularly limited, but is preferably 3.8mm or more, more preferably 4.0mm or more, and even more preferably 4.3mm or more, with an upper limit of preferably 5.3mm or less, more preferably 5.0mm or less, and even more preferably 4.8mm or less. If the amount of deflection of the core is too small, i.e., the core is too hard, the spin will increase when hitting shots with a driver (W#1) at a head speed of around 40m / s and when hitting full shots with irons, which may result in not being able to achieve the desired distance or the feel becoming too hard. On the other hand, if the amount of deflection of the core is too large, i.e., the core is too soft, the rebound performance will be too low, which may result in not being able to achieve the desired distance or the feel becoming too soft or the durability against cracking when repeatedly struck will be poor.

[0032] In this invention, when the deflection CT (mm) is applied to the core from an initial load of 98N (10kgf) to a final load of 1,275N (130kgf), the following formula is used: CT>(H100-H50) / (H50-H0) The following conditions must be met. The above formula means that the value of the core deflection (CT) is greater than the ratio of the inclination inside to outside the core hardness gradient H50, which is the midpoint between the core center and the core surface. The value of CT-(H100-H50) / (H50-H0) is usually 0 or greater, preferably 0.2 or greater, and more preferably 0.4 or greater, and the upper limit is usually 1.2 or less, preferably 1.0 or less, and more preferably 0.8 or less. If the above value is too large, and it is due to the amount of core deflection (CT), the rebound of the core may become too low, resulting in a loss of the desired distance, a soft feel, or poor crack resistance when repeatedly struck. Also, if it is due to the internal hardness distribution of the core, the spin may increase when taking a full shot, resulting in a loss of the desired distance. On the other hand, if the above value is too small, and it is due to the amount of core deflection (CT), it may result in excessive spin on full shots, making it difficult to achieve the desired distance, or the feel may become too hard. Also, if it is due to the internal hardness distribution of the core, the core's rebound may become too low, making it difficult to achieve the desired distance, or the resistance to cracking after repeated impacts may be poor.

[0033] As a core material having the hardness distribution described above, it is preferable to use rubber as the main material. If the core is not formed from rubber, the rebound may be low and the ball may not fly far. Specifically, a rubber composition for the core can be prepared by mainly using a base rubber and blending it with a co-crosslinking agent, organic peroxide, inert filler, water, sulfur, etc.

[0034] The core components mentioned above include, in particular, the following components (A) to (D). (A) Base rubber (B) Organic peroxide (C) Water or metal monocarboxylate salt (D) Sulfur It is preferable that the rubber composition be formed from a rubber composition containing [the specified substance].

[0035] (A) It is preferable to use polybutadiene as the base rubber. Commercially available polybutadiene products can be used, for example, BR01, BR51, BR730 (manufactured by JSR Corporation), etc. The proportion of polybutadiene in the base rubber is preferably 60% by mass or more, and more preferably 80% by mass or more. Other rubber components may be blended into the base rubber in addition to the above polybutadiene, as long as they do not impair the effects of the present invention. Examples of rubber components other than the above polybutadiene include other polybutadienes, other diene rubbers, for example, styrene-butadiene rubber, natural rubber, isoprene rubber, ethylene-propylene-diene rubber, etc.

[0036] (B) Organic peroxides are used as crosslinking initiators. Specifically, commercially available organic peroxides can be used, and for example, Parkmill D (manufactured by Nippon Oil & Fats Co., Ltd.), Perhexa C-40, Perhexa 3M (manufactured by Nippon Oil & Fats Co., Ltd.), Luperco 231XL (manufactured by Atochem Co., Ltd.), etc. can be suitably used. These may be used individually or in combination of two or more. The amount of organic peroxide to be blended is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.5 parts by mass or more, per 100 parts by mass of the base rubber, with an upper limit of preferably 5 parts by mass or less, more preferably 4 parts by mass or less, even more preferably 3 parts by mass or less, and most preferably 2.5 parts by mass or less. If the blending amount is too high or too low, it may not be possible to obtain a suitable feel, durability and rebound properties.

[0037] (C) There are no particular restrictions on the water used; distilled water or tap water may be used, but it is preferable to use distilled water that does not contain impurities. The amount of water to be added is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, with an upper limit of preferably 2 parts by mass or less, and more preferably 1 part by mass or less, per 100 parts by mass of the base rubber.

[0038] By directly incorporating water or a water-containing material as component (C) into the core material, the decomposition of organic peroxides in the core compound can be promoted. It is also known that the decomposition efficiency of organic peroxides in core rubber compositions changes with temperature, with the decomposition efficiency increasing as the temperature rises above a certain point. If the temperature is too high, the amount of decomposed radicals becomes too large, leading to recombination and inactivation of the radicals. As a result, the number of radicals that effectively work for crosslinking decreases. Here, when decomposition heat is generated as organic peroxides decompose during core vulcanization, the temperature near the core surface remains at approximately the same level as the vulcanization mold, but the temperature near the core center becomes considerably higher than the mold temperature because the decomposition heat of organic peroxides that decomposed from the outside accumulates. When water or a water-containing material is directly incorporated into the core, water promotes the decomposition of organic peroxides, thus altering the radical reactions described above in the core center and on the core surface. In other words, near the core center, the decomposition of organic peroxides is further promoted, and the inactivation of radicals is further accelerated, resulting in a further reduction in the amount of effective radicals. This makes it possible to obtain cores with significantly different crosslinking densities between the core center and the core surface, as well as cores with different dynamic viscoelastic properties at the core center.

[0039] Alternatively, a monocarboxylate metal salt can be used instead of water. Monocarboxylate metal salts are presumed to have a carboxylic acid coordinate bond to the metal salt and are distinguished from dicarboxylate metal salts such as zinc diacrylate, which is represented by the chemical formula [CH2=CHCOO]2Zn. Monocarboxylate metal salts introduce water into the rubber composition through a dehydration condensation reaction, thus providing the same effect as water. Furthermore, since monocarboxylate metal salts can be incorporated into the rubber composition as a powder, the work process can be simplified, and it is easy to uniformly disperse them in the rubber composition. It should be noted that a monosalt is necessary for the above reaction to be carried out effectively. The amount of monocarboxylate metal salt to be incorporated is preferably 1 part by mass or more, and more preferably 3 parts by mass or more, per 100 parts by mass of base rubber. As an upper limit, the amount of monocarboxylate metal salt to be incorporated is preferably 60 parts by mass or less, and more preferably 50 parts by mass or less. If the amount of monocarboxylate metal salt is too small, it may be difficult to obtain an appropriate crosslinking density, and the low-spin effect of the golf ball may not be sufficiently obtained. Furthermore, if the amount of compound is too high, the core may become too hard, making it difficult to maintain a proper feel when hitting the ball.

[0040] The carboxylic acid mentioned above can be acrylic acid, methacrylic acid, maleic acid, fumaric acid, stearic acid, etc. Suitable substitution metals include Na, K, Li, Zn, Cu, Mg, Ca, Co, Ni, Pb, etc., but Zn is preferably used. Specific examples include zinc monoacrylate and zinc monomethacrylate, with zinc monoacrylate being particularly preferred.

[0041] (D) By using sulfur, the difference in hardness between the inside and outside of the core can be increased. (D)Specific examples of sulfur include the product names "Sunmix S-80N" (Sanshin Chemical Industry Co., Ltd.) and "Sulfax-5" (manufactured by Tsurumi Chemical Industry Co., Ltd.). The amount of sulfur added can be greater than 0 per 100 parts by mass of the base rubber, preferably 0.005 parts by mass or more, and more preferably 0.01 parts by mass or more. Furthermore, there is no particular upper limit to this amount, but it is preferably 0.1 parts by mass or less, more preferably 0.05 parts by mass or less, and even more preferably 0.03 parts by mass or less. Note that if the amount of sulfur added is too high, the rebound properties may decrease significantly, and the durability of repeated impacts may decrease.

[0042] Regarding the content ratio of components (D) and (C) above, the mass ratio of (D) / (C) is preferably 0.005 or more, more preferably 0.008 or more, and even more preferably 0.010 or more. The upper limit is preferably 0.200 or less, more preferably 0.100 or less, and even more preferably 0.060 or less. If the above range is exceeded, it may be difficult to achieve the target core hardness distribution, and it may become impossible to achieve both the advantageous flight distance due to low spin on the ball during full shots and good durability for repeated impacts. Note that component (D) above refers to the mass (substance) of the sulfur component contained in the product, not the mass of the sulfur product itself.

[0043] Other rubber compounding components besides the above components (A) to (D) include co-crosslinking agents, inert fillers, antioxidants, and organic sulfur compounds.

[0044] The cocrosslinking agent is an α,β-unsaturated carboxylic acid and / or its metal salt. Specific examples of unsaturated carboxylic acids include acrylic acid, methacrylic acid, maleic acid, and fumaric acid, with acrylic acid and methacrylic acid being particularly preferred. The metal salt of the unsaturated carboxylic acid is not particularly limited, but examples include those obtained by neutralizing the above-mentioned unsaturated carboxylic acid with a desired metal ion. Specifically, examples include zinc salts and magnesium salts of methacrylic acid, acrylic acid, etc., with zinc acrylate being particularly preferred.

[0045] The above-mentioned unsaturated carboxylic acid and / or its metal salt are usually blended in an amount of 5 parts by mass or more, preferably 9 parts by mass or more, more preferably 13 parts by mass or more, with an upper limit of 60 parts by mass or less, preferably 50 parts by mass or less, and more preferably 40 parts by mass or less, per 100 parts by mass of the base rubber. If the blending amount is too high, it may become too hard and the feel of hitting the ball may become unbearable, and if the blending amount is too low, the rebound may decrease.

[0046] Suitable fillers include, for example, zinc oxide, barium sulfate, and calcium carbonate. These may be used individually or in combination of two or more. The amount of filler added is preferably 1 part by mass or more, more preferably 3 parts by mass or more, per 100 parts by mass of the base rubber. The upper limit of the amount added is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 30 parts by mass or less, per 100 parts by mass of the base rubber. If the amount added is too much or too little, it may not be possible to obtain the appropriate mass and suitable rebound properties.

[0047] As an anti-aging agent, commercially available products such as Nocrack NS-6, NS-30, NS-200, and MB (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) can be used. These may be used individually or in combination of two or more.

[0048] There are no particular restrictions on the amount of antioxidant added, but it is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, with an upper limit of preferably 1.0 part by mass or less, more preferably 0.7 parts by mass or less, and even more preferably 0.5 parts by mass or less, per 100 parts by mass of base rubber. If the amount added is too much or too little, it may not be possible to obtain an appropriate core hardness gradient, and the desired rebound properties, durability, and low spin effect during full shots may not be obtained.

[0049] Organic sulfur compounds can be incorporated to control the core's rebound properties. Specifically, it is recommended to incorporate thiophenols, thionaphthols, halogenated thiophenols, or their metal salts as organic sulfur compounds. More specifically, examples include zinc salts of pentachlorothiophenol, pentafluorothiophenol, pentabromothiophenol, parachlorothiophenol, pentachlorothiophenol, diphenyl polysulfide, dibenzyl polysulfide, dibenzoyl polysulfide, dibenzothiazoyl polysulfide, and dithiobenzoyl polysulfide, which have 2 to 4 sulfur atoms. In particular, zinc salts of pentachlorothiophenol and diphenyl disulfide can be preferably used.

[0050] The organic sulfur compound is typically blended in an amount of 0.1 parts by mass or more, preferably 0.2 parts by mass or more, and more preferably 0.3 parts by mass or more, per 100 parts by mass of the base rubber. The upper limit of the amount of organic sulfur compound is typically 5 parts by mass or less, preferably 4 parts by mass or less, more preferably 3 parts by mass or less, and even more preferably 2 parts by mass or less. If the amount is too high, the core may become too soft, or the desired core hardness distribution may not be achieved. On the other hand, if the amount is too low, the core's rebound may be too low, and the desired flight distance may not be obtained.

[0051] The above-mentioned core can be manufactured by vulcanizing and curing a rubber composition containing the above-mentioned components. For example, it can be manufactured by kneading using a kneader such as a Banbury mixer or roll, compression molding or injection molding using a core mold, and then curing the molded body by appropriately heating it at a temperature of 100 to 200°C, preferably 140 to 180°C, for 10 to 40 minutes, which is sufficient for the organic peroxide and co-crosslinking agent to act.

[0052] Next, I will explain the middle class. The material hardness of the intermediate layer is not particularly limited, but in terms of Shore C hardness, it is preferably 90 or higher, more preferably 92 or higher, and even more preferably 93 or higher, with an upper limit of preferably 100 or less, more preferably 98 or less, and even more preferably 96 or less. In terms of Shore D hardness, it is preferably 64 or higher, more preferably 66 or higher, and even more preferably 67 or higher, with an upper limit of preferably 75 or less, more preferably 72 or less, and even more preferably 70 or less.

[0053] The surface hardness of a sphere with a core covered by an intermediate layer (intermediate layer-covered sphere) is preferably 95 or higher, more preferably 96 or higher, and even more preferably 97 or higher on the Shore C hardness scale, with an upper limit of preferably 100 or less, more preferably 99 or less, and even more preferably 98 or less. On the Shore D hardness scale, it is preferably 68 or higher, more preferably 69 or higher, and even more preferably 70 or higher, with an upper limit of preferably 78 or less, more preferably 75 or less, and even more preferably 72 or less.

[0054] If the material hardness and surface hardness of these intermediate layers are too soft compared to the above range, excessive spin may be generated or the initial ball speed may be reduced, resulting in a loss of the desired distance when using a driver (W#1) at head speeds around 40 m / s or when hitting full shots with irons. On the other hand, if the material hardness and surface hardness of the intermediate layers are too hard compared to the above range, the durability against cracking during repeated impacts may be reduced, or the feel of putting or short approach shots may become too hard.

[0055] The thickness of the intermediate layer is preferably 1.00 mm or more, more preferably 1.25 mm or more, and even more preferably 1.45 mm or more. On the other hand, the upper limit of the intermediate layer thickness is preferably 1.80 mm or less, more preferably 1.65 mm or less, and even more preferably 1.55 mm or less. If the thickness of the intermediate layer deviates from the above range, the low-spin effect may be insufficient for shots with a driver (W#1) at a head speed of around 40 m / s, resulting in the inability to achieve the desired distance. On the other hand, if the thickness of the intermediate layer is too thin, the crack resistance when repeatedly struck and the durability at low temperatures may be poor.

[0056] For the intermediate layer material, it is preferable to use ionomer resin as the main material. When using ionomer resin as the main material, it is desirable to use a mixture of zinc-neutralized ionomer resin and sodium-neutralized ionomer resin as the main material. The mixing ratio of zinc-neutralized type / sodium-neutralized type (mass ratio) is 5 / 95 to 95 / 5, preferably 10 / 90 to 90 / 10, and more preferably 15 / 85 to 85 / 15. If Zn-neutralized ionomer and Na-neutralized ionomer are not included in this ratio, the rebound may become too low, resulting in a loss of distance when hitting with a driver (W#1) and irons for average hitters. Furthermore, the crack resistance during repeated impacts at room temperature may be poor, as may the crack resistance at low temperatures (below freezing).

[0057] Inorganic granular fillers can be incorporated into the intermediate layer material. These inorganic granular fillers are components added to adjust the specific gravity and act as reinforcing agents. While not particularly limited, zinc oxide, barium sulfate, titanium dioxide, etc., can be used as appropriate. Furthermore, barium sulfate is preferred, and precipitated barium sulfate is even more preferred, due to its significant effect in improving crack resistance during repeated impacts.

[0058] The average particle size of the above-mentioned granular inorganic filler is not particularly limited, but is preferably 0.01 to 100 μm, and more preferably 0.1 to 10 μm. If the average particle size of the above-mentioned granular inorganic filler is too small or too large, the dispersibility during material preparation may deteriorate. The above-mentioned average particle size refers to the particle size measured by a particle size distribution analyzer when dispersed in an aqueous solution with a suitable dispersant.

[0059] The amount of inorganic granular filler added is usually more than 0 parts by mass per 100 parts by mass of the base resin of the intermediate layer material, preferably 10 parts by mass or more, more preferably 15 parts by mass or more, with an upper limit of usually 50 parts by mass or less, preferably 40 parts by mass or less, and more preferably 30 parts by mass or less. If the amount added is too little, the resistance to cracking due to repeated impact may be poor. On the other hand, if the amount added is too much, the rebound of the ball may be reduced, or the amount of spin during a full shot may increase, resulting in a loss of the intended distance.

[0060] The specific gravity of the intermediate layer material is not particularly limited, but is preferably 1.05 or higher, more preferably 1.07 or higher, and even more preferably 1.09 or higher. The upper limit is preferably 1.25 or lower, more preferably 1.20 or lower, and even more preferably 1.15 or lower. If the specific gravity of the intermediate layer is too low, the crack resistance due to repeated impacts may be poor. On the other hand, if the specific gravity of the intermediate layer is too high, the amount of inorganic granular filler to be blended into the resin material tends to increase, which can result in a lower rebound of the ball and a loss of the desired flight distance.

[0061] The intermediate layer material can be appropriately blended with any additives depending on the application. For example, various additives such as pigments, dispersants, antioxidants, UV absorbers, and light stabilizers can be added. When these additives are blended, the amount blended is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and preferably 10 parts by mass or less, and more preferably 4 parts by mass or less, per 100 parts by mass of the base resin.

[0062] For the intermediate layer material, it is preferable to polish the surface of the intermediate layer in order to improve adhesion with the polyurethane, which is suitably used in the cover material described later. Furthermore, it is preferable to apply a primer (adhesive) to the surface of the intermediate layer after the polishing treatment, or to add an adhesion-enhancing agent to the material.

[0063] For a sphere with a core covered by an intermediate layer (intermediate layer covered sphere), the amount of deflection (mm) when an initial load of 98N (10kgf) is applied to a final load of 1,275N (130kgf) is preferably 2.8mm or more, more preferably 2.9mm or more, and more preferably 3.0mm or more. The upper limit is preferably 4.0mm or less, more preferably 3.8mm or less, and even more preferably 3.6mm or less. If the amount of deflection of this intermediate layer covered sphere is too small, i.e., too hard, it may result in excessive spin during driver (W#1) shots at head speeds around 40m / s and full iron shots, preventing the desired distance from being achieved, or the feel may become too hard. On the other hand, if the above amount of deflection is too large, i.e., if the sphere is too soft, the rebound performance as a ball may become too low, preventing the desired distance from being achieved, or the feel may become too soft, or the durability against cracking when repeatedly struck may be poor.

[0064] Next, I will explain the cover. The hardness of the cover material, expressed as Shore C hardness, is preferably 50 or higher, more preferably 54 or higher, and even more preferably 57 or higher, with an upper limit of preferably 64 or lower, more preferably 61 or lower, and even more preferably 59 or lower. In terms of Shore D hardness, it is preferably 30 or higher, more preferably 35 or higher, and even more preferably 38 or higher, with an upper limit of preferably 44 or lower, more preferably 42 or lower, and even more preferably 40 or lower.

[0065] The surface hardness of the sphere, i.e., the ball, in which the cover is applied to the intermediate layer-coated sphere, is preferably 73 or higher, more preferably 78 or higher, and even more preferably 81 or higher, as expressed in Shore C hardness, with an upper limit of preferably 88 or lower, more preferably 86 or lower, and even more preferably 84 or lower. In Shore D hardness, it is preferably 50 or higher, more preferably 53 or higher, and even more preferably 56 or higher, with an upper limit of preferably 62 or lower, more preferably 60 or lower, and even more preferably 58 or lower.

[0066] If the material hardness and surface hardness of these covers are too soft compared to the above range, excessive spin may occur during driver (W#1) shots at head speeds around 40 m / s and during full iron shots, resulting in reduced distance. On the other hand, if the material hardness and surface hardness of the covers are too hard compared to the above range, sufficient spin may not be applied during approach shots, and scratch resistance may be reduced.

[0067] The thickness of the cover is preferably 0.3 mm or more, more preferably 0.4 mm or more, and even more preferably 0.6 mm or more. On the other hand, the upper limit of the cover thickness is preferably 1.0 mm or less, more preferably 0.9 mm or less, and even more preferably 0.8 mm or less. If the cover is too thick, the ball's rebound may be reduced or the spin may increase when using a driver (W#1) at a head speed of around 40 m / s and when using full iron shots, resulting in a loss of the desired distance. On the other hand, if the cover is too thin, scratch resistance may be reduced, and sufficient spin may not be applied during approach shots, resulting in a lack of control.

[0068] As the material for the cover mentioned above, various thermoplastic resins used for golf ball covers can be used, but from the standpoint of spin control and mass production, it is preferable to use a resin composition mainly composed of polyurethane resin or ionomer resin. Among these, it is preferable to use a resin material mainly composed of thermoplastic polyurethane due to its excellent scratch resistance and mass production capabilities.

[0069] Specifically, suitable resin materials mainly composed of thermoplastic polyurethane include (I) thermoplastic polyurethane and (II) resin formulations mainly composed of polyisocyanate compounds.

[0070] Regarding the thermoplastic polyurethane described in (I) above, the structure of the thermoplastic polyurethane includes a soft segment made of a high-molecular-weight polyol (polymeric glycol), which is a long-chain polyol, and a hard segment made of a chain extender and a polyisocyanate compound. Here, any long-chain polyol that has been conventionally used in thermoplastic polyurethane technology can be used as a raw material, and there are no particular restrictions, but examples include polyester polyols, polyether polyols, polycarbonate polyols, polyester polycarbonate polyols, polyolefin polyols, conjugated diene polymer polyols, castor oil polyols, silicone polyols, and vinyl polymer polyols. One type of these long-chain polyol may be used, or two or more types may be used in combination. Among these, polyether polyols are preferred because they can synthesize thermoplastic polyurethanes with a high rebound modulus and excellent low-temperature properties.

[0071] Examples of the polyether polyols mentioned above include poly(ethylene glycol), poly(propylene glycol), poly(tetramethylene glycol), and poly(methyltetramethylene glycol), which are obtained by ring-opening polymerization of cyclic ethers. One type of polyether polyol may be used, or two or more types may be used in combination. Among these, poly(tetramethylene glycol) and / or poly(methyltetramethylene glycol) are preferred.

[0072] The number-average molecular weight of these long-chain polyols is preferably in the range of 1,500 to 5,000. By using long-chain polyols having such a number-average molecular weight, it is possible to reliably obtain golf balls made of thermoplastic polyurethane compositions that have excellent properties such as the rebound and productivity described above. The number-average molecular weight of the long-chain polyols is more preferably in the range of 1,700 to 4,000, and even more preferably in the range of 1,900 to 3,000.

[0073] The number-average molecular weight of the long-chain polyols mentioned above is calculated based on the hydroxyl value measured in accordance with JIS K-1557.

[0074] As the chain extender, those used in conventional thermoplastic polyurethane technologies can be suitably used, and for example, it is preferable to use a low molecular weight compound with a molecular weight of 400 or less that has two or more active hydrogen atoms in the molecule that can react with an isocyanate group. Examples of chain extenders include, but are not limited to, 1,4-butylene glycol, 1,2-ethylene glycol, 1,3-butanediol, 1,6-hexanediol, and 2,2-dimethyl-1,3-propanediol. Among these, aliphatic diols having 2 to 12 carbon atoms are preferred as chain extenders, and 1,4-butylene glycol is more preferred.

[0075] As the polyisocyanate compound, those used in conventional thermoplastic polyurethane technology can be suitably used, and there are no particular restrictions. Specifically, one or more selected from the group consisting of 4,4'-diphenylmethane diisocyanate, 2,4-(or)2,6-toluene diisocyanate, p-phenylenediisocyanate, xylylene diisocyanate, naphthylene 1,5-diisocyanate, tetramethylxylylene diisocyanate, hydrogenated xylylene diisocyanate, dicyclohexylmethane diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, norbornene diisocyanate, trimethylhexamethylene diisocyanate, and dimer acid diisocyanate can be used. However, depending on the isocyanate species, it may be difficult to control the crosslinking reaction during injection molding. In the present invention, from the viewpoint of balancing stability during production with the physical properties that are exhibited, 4,4'-diphenylmethanediisocyanate, which is an aromatic diisocyanate, is most preferred.

[0076] The most preferred thermoplastic polyurethane of component (I) above is a thermoplastic polyurethane synthesized using a polyether polyol as the long-chain polyol, an aliphatic diol as the chain extender, and an aromatic diisocyanate as the polyisocyanate compound, wherein the polyether polyol is polytetramethylene glycol with a number average molecular weight of 1,900 or more, the chain extender is 1,4-butylene glycol, and the aromatic diisocyanate is 4,4'-diphenylmethane diisocyanate, but is not limited to these.

[0077] Furthermore, the ratio of active hydrogen atoms to isocyanate groups in the polyurethane formation reaction described above can be adjusted within a preferred range to obtain a golf ball made of a thermoplastic polyurethane composition with superior properties such as rebound, spin performance, abrasion resistance, and productivity. Specifically, when producing thermoplastic polyurethane by reacting the long-chain polyol, polyisocyanate compound, and chain extender described above, it is preferable to use each component in a ratio such that the isocyanate groups contained in the polyisocyanate compound amount to 0.95 to 1.05 moles for every 1 mole of active hydrogen atoms contained in the long-chain polyol and chain extender.

[0078] The method for producing the thermoplastic polyurethane of component (I) above is not particularly limited, and it may be produced using a long-chain polyol, a chain extender, and a polyisocyanate compound, utilizing known urethane formation reactions, by either a prepolymer method or a one-shot method. Among these, melt polymerization in the substantially absence of solvent is preferred, and it is particularly preferred to produce it by continuous melt polymerization using a multi-screw extruder.

[0079] Commercially available thermoplastic polyurethanes can be used as the specific component (I), such as Pandex T8295, T8290, T8260, and T8295 (all manufactured by DIC Covestropolymer).

[0080] Next, in a single resin formulation consisting of component (I) and component (II), it is necessary that at least a portion of the polyisocyanate compound used as component (II) remains in a state in which all isocyanate groups in one molecule are unreacted. That is, it is sufficient for a single resin formulation to contain a polyisocyanate compound in which all isocyanate groups in one molecule are completely free, and such a polyisocyanate compound and a polyisocyanate compound in which some of the molecules are free may coexist.

[0081] There are no particular restrictions on the polyisocyanate compound, but various isocyanates can be used. Specifically, one or more selected from the group consisting of 4,4'-diphenylmethane diisocyanate, 2,4-(or)2,6-toluene diisocyanate, p-phenylenediisocyanate, xylylene diisocyanate, naphthylene 1,5-diisocyanate, tetramethylxylenediisocyanate, hydrogenated xylylene diisocyanate, dicyclohexylmethane diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, norbornene diisocyanate, trimethylhexamethylene diisocyanate, and dimer acid diisocyanate can be used. Among the above group of isocyanates, 4,4'-diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, and isophorone diisocyanate are preferred from the viewpoint of balancing the influence on moldability due to viscosity increase associated with the reaction of component (A) with thermoplastic polyurethane, and the physical properties of the resulting golf ball cover material.

[0082] Although not an essential component, a thermoplastic elastomer other than the thermoplastic polyurethane can be added as component (III) to components (I) and (II) above. By adding this component (III) to the resin compound, it is possible to further improve the fluidity, resilience, scratch resistance, and other physical properties required for a golf ball cover material.

[0083] As component (III) above, thermoplastic elastomers other than the thermoplastic polyurethanes mentioned above can be specifically selected from polyester elastomers, polyamide elastomers, ionomer resins, styrene block elastomers, hydrogenated styrene-butadiene rubber, styrene-ethylene-butylene-ethylene block copolymer or modified thereof, ethylene-ethylene-butylene-ethylene block copolymer or modified thereof, styrene-ethylene-butylene-styrene block copolymer or modified thereof, ABS resin, polyacetal, polyethylene, and nylon resin, and one or more of these can be used. In particular, polyester elastomers, polyamide elastomers, and polyacetal are preferred because they improve resilience and abrasion resistance while maintaining good productivity.

[0084] There are no particular restrictions on the composition ratio of components (I), (II), and (III) above, but in order to fully exert the effects of the present invention, it is preferable that the mass ratio of (I):(II):(III) = 100:2 to 50:0 to 50, and more preferably (I):(II):(III) = 100:2 to 30:8 to 50 (mass ratio).

[0085] There are no particular restrictions on the method for preparing the resin compound by mixing the above components (I) to (III), but it is preferable to select conditions such that at least some of the polyisocyanate compounds contain polyisocyanate compounds in which all isocyanate groups remain unreacted. Specifically, it is desirable to take measures such as mixing the above components under an inert gas such as nitrogen gas or under a vacuum. Furthermore, since this resin compound will be injection molded around a core placed in a mold thereafter, it is preferable to form it into pellets with a length of 1 to 10 mm and a diameter of 0.5 to 5 mm in order to handle it smoothly and easily. Unreacted isocyanate groups remain in these resin pellets, and during injection molding onto the core or during subsequent post-processing such as annealing, the unreacted isocyanate groups react with components (A) and (III) to form crosslinked products.

[0086] Furthermore, the above resin formulation may contain various additives other than the components that make up the thermoplastic polyurethane, as needed. For example, pigments, dispersants, antioxidants, light stabilizers, UV absorbers, mold release agents, etc., can be added as appropriate.

[0087] The specific gravity of the cover is not particularly limited, but is preferably 1.00 or higher, more preferably 1.03 or higher, and even more preferably 1.06 or higher. The upper limit is preferably 1.20 or lower, more preferably 1.17 or lower, and even more preferably 1.14 or lower. If the specific gravity of the cover is lower than the above range, the proportion of low-specific-gravity materials such as ionomers blended into the main urethane cover material will increase, which may result in poor scratch resistance. On the other hand, if the specific gravity of the cover is too high, the amount of filler added will increase, which may result in the ball's rebound being too low during driver (W#1) shots at head speeds around 40 m / s and full iron shots, making it difficult to achieve the desired distance.

[0088] The manufacturing method for a golf ball formed by laminating the core, intermediate layer, and cover (outermost layer) described above can be carried out by conventional methods such as known injection molding. For example, an intermediate layer material can be injected around the core using an injection molding die to obtain each coated sphere, and then the material for the outermost cover can be injection molded to obtain a golf ball. Alternatively, a golf ball can be manufactured by wrapping each coated sphere with two pre-formed hemispherical half-cups and then heat-pressure molding them.

[0089] The amount of deflection (mm) of a golf ball when subjected to an initial load of 98N (10kgf) to a final load of 1,275N (130kgf) is preferably 2.8mm or more, more preferably 2.9mm or more, and more preferably 3.0mm or more. The upper limit is preferably 3.8mm or less, more preferably 3.6mm or less, and even more preferably 3.4mm or less. If the amount of deflection of the golf ball is too small, i.e., too hard, it may result in excessive spin during driver (W#1) shots at head speeds around 40m / s and full iron shots, reducing the desired distance, or the feel may become too hard. On the other hand, if the amount of deflection is too large, i.e., the sphere is too soft, the rebound of the ball may become too low, resulting in shorter distances, a feel may become too soft, or the durability against cracking after repeated impacts may be poor.

[0090] [Hardness relationship of each layer] The relationship between the surface hardness of the core, the intermediate layer coated sphere, and the ball is given by the following formula. Ball surface hardness <Surface hardness of the sphere coated with the intermediate layer> Core surface hardness (However, the above surface hardness is expressed in Shore C hardness.) It is preferable that the following conditions be met. That is, from the viewpoint of achieving both superior distance performance through low spin in full shots and superior control during the short game, it is preferable that the surface hardness of the intermediate layer covering sphere be higher than the surface hardness of the core and also higher than the surface hardness of the ball.

[0091] The difference between the material hardness of the intermediate layer and the material hardness of the cover, i.e., the value of (material hardness of intermediate layer - material hardness of cover), is preferably 34 or higher, more preferably 35 or higher, and even more preferably 36 or higher on the Shore C hardness scale, with an upper limit of preferably 50 or lower, more preferably 45 or lower, and even more preferably 40 or lower. If this value is too small, and if it is due to the material hardness of the intermediate layer, it may result in excessive spin during driver (W#1) shots with a head speed (HS) of around 40 m / s and full iron shots, making it difficult to achieve the desired distance. If it is due to the material hardness of the cover, it may result in too little spin during approach shots. On the other hand, if this value is too large, and if it is due to the material hardness of the intermediate layer, it may result in poor crack resistance after repeated impacts and too little spin during approach shots. If it is due to the material hardness of the cover, it may result in excessive spin during driver (W#1) shots with a head speed (HS) of around 40 m / s and full iron shots, making it difficult to achieve the desired distance.

[0092] Furthermore, regarding the relationship between the Shore C hardness (H62.5) at a position 62.5% outside the core radius from the core center and the surface hardness of the intermediate layer covering sphere, the value of (surface hardness of intermediate layer covering sphere - H62.5) is preferably 30 or higher, more preferably 31 or higher, and even more preferably 32 or higher in Shore C hardness, with an upper limit of preferably 36 or lower, more preferably 35 or lower, and even more preferably 34 or lower. If this value is too low, and it is due to the surface hardness of the intermediate layer, it may result in excessive spin during driver (W#1) shots with a head speed (HS) of around 40 m / s and full iron shots, making it difficult to achieve the desired distance. Also, if it is due to the hardness of H62.5, it may result in poor crack resistance when repeatedly struck or an overly hard feel. On the other hand, if this value is too high, and it is due to the surface hardness of the intermediate layer, it may result in poor crack resistance when repeatedly struck or an overly hard feel. Furthermore, if this is due to the hardness of H62.5, the actual ball speed may be lower when hitting driver (W#1) shots with a head speed (HS) of around 40 m / s and when hitting full iron shots, resulting in a loss of desired distance and a feel that is too soft.

[0093] The relationship between the hardness of the core at a predetermined position (H62.5), the material hardness of the intermediate layer, the material hardness of the cover, and the surface hardness of the covered sphere with the intermediate layer covering the core is given by the following formula. (Hardness of intermediate layer material - Hardness of cover material) > (Surface hardness of intermediate layer-covered sphere - H62.5) (However, the material hardness and surface hardness values ​​mentioned above are Shore C values.) It is preferable that the following conditions be met. This parameter indicates that the hardness difference between the intermediate layer material and the cover material is greater than the hardness difference between the intermediate layer surface hardness and H62.5. The above value of (intermediate layer material hardness - cover material hardness) - (surface hardness of intermediate layer coated sphere - H62.5) is preferably 1 or more, more preferably 2 or more, and even more preferably 3 or more in Shore C hardness, with an upper limit of preferably 6 or less, more preferably 5 or less, and even more preferably 4 or less. If this value falls outside the above range, the amount of spin when taking a full shot may increase, and the desired distance may not be achieved. Also, if this value is too small, the amount of spin when taking an approach shot may decrease. On the other hand, if this value is too large, the crack resistance when repeatedly struck may decrease.

[0094] The relationship between the Shore C hardness of the core center and the Shore C hardness of the cover material is given by the following formula: (Shore C hardness of the core) ≤ (Shore C hardness of the cover material) It is preferable that the following conditions be met. The above value of (Shore C hardness of cover material) - (Shore C hardness of core center) is preferably 0 or greater, more preferably 1 or greater, and even more preferably 2 or greater, with an upper limit of preferably 5 or less, more preferably 4 or less, and even more preferably 3 or less. If this value is too small, the spin will increase when using a driver (W#1) with a head speed (HS) of around 40 m / s and when using full iron shots, and the desired distance may not be achieved. On the other hand, if this value is too large, the amount of spin when approaching the ball will decrease, making it difficult to control in the short game, and the actual initial ball speed when using a driver (W#1) with a head speed (HS) of around 40 m / s will decrease, and the desired distance may not be achieved.

[0095] The relationship between the Shore C hardness H50 at a position 50% outside the core radius from the core center and the Shore C hardness of the cover material is given by the following formula: (Shore C hardness of cover material) ≤ H50 It is preferable that the following conditions be met. The above H50-(Shore C hardness of the cover material) value is preferably 0 or higher, more preferably 1 or higher, and even more preferably 2 or higher, with an upper limit of preferably 7 or lower, more preferably 6 or lower, and even more preferably 5 or lower. If this value is too low, the amount of spin when approaching will be low, resulting in poor control in the short game, or the initial ball speed when hitting with a driver (W#1) at a head speed (HS) of around 40 m / s will be low, and the target distance may not be achieved. On the other hand, if this value is too high, the amount of spin when hitting with a driver (W#1) at a head speed (HS) of around 40 m / s will be high, resulting in the target distance not being achieved, or the feel of the shot when taking a full shot may feel hard.

[0096] [Relationship between the amount of deflection between the core and the ball] When the deflection amount of the core from an initial load of 98N (10kgf) to a final load of 1,275N (130kgf) is denoted as A (mm), and the deflection amount of the golf ball from an initial load of 98N (10kgf) to a final load of 1,275N (130kgf) is denoted as B (mm), the value of AB is preferably 1.00mm or more, more preferably 1.10mm or more, and even more preferably 1.20mm or more, with an upper limit of preferably 1.80mm or less, more preferably 1.60mm or less, and even more preferably 1.40mm or less. If this value is too small, the spin will increase during driver (W#1) shots with a head speed (HS) of around 40m / s and during full iron shots, which may prevent the desired distance from being achieved. On the other hand, if this value is too high, the actual initial ball speed when hitting with a driver (W#1) at a head speed (HS) of around 40 m / s will be low, which may result in not achieving the desired distance, or the durability against cracking when repeatedly hitting the ball may be poor.

[0097] [Specific gravity of each layer] The difference in specific gravity between the core, intermediate layer, and cover is generally recommended to be within ±0.15, preferably within ±0.10, and more preferably within ±0.05. That is, the values ​​of (core specific gravity) - (intermediate layer material specific gravity), (cover specific gravity) - (intermediate layer material specific gravity), and (core specific gravity) - (cover material specific gravity) are generally -0.15 or higher, preferably -0.10 or higher, and more preferably -0.05 or higher, with an upper limit of generally 0.15 or lower, preferably 0.10 or lower, and more preferably 0.05 or lower. If the difference in specific gravity between each layer is too large, the intermediate layer material and / or cover material may not be molded perfectly concentrically with the layers located inside them, resulting in eccentricity. When the ball is struck with a putter, this can cause a large lateral deviation.

[0098] [Relationship between the thickness of the middle layer and the cover] The difference between the thickness of the intermediate layer and the thickness of the cover, i.e., (intermediate layer thickness) - (cover thickness), is usually -0.1 mm or more, preferably 0.3 mm or more, and more preferably 0.5 mm or more. The upper limit is usually 1.0 mm or less, preferably 0.8 mm or less, and more preferably 0.7 mm or less. If this value deviates from the above range, the spin may increase on full shots, or the initial ball speed may decrease, resulting in a loss of the desired distance. On the other hand, if this value is too small, the durability against cracking when repeatedly struck may be reduced.

[0099] Numerous dimples can be formed on the outer surface of the cover. There are no particular restrictions on the number of dimples arranged on the cover surface, but preferably there are 250 or more, preferably 300 or more, more preferably 320 or more, and as an upper limit, preferably 380 or less, more preferably 350 or less, and even more preferably 340 or less. If the number of dimples exceeds the above range, the ball's trajectory may become lower and the distance may decrease. On the other hand, if the number of dimples is too low, the ball's trajectory may become higher and the distance may not increase.

[0100] The dimple shape can be one or more types, such as circular, various polygons, dewdrop shapes, or elliptical shapes, and can be used as appropriate. For example, when using a circular dimple, the diameter can be approximately 2.5 mm to 6.5 mm, and the depth can be 0.08 mm to 0.30 mm.

[0101] The dimple occupancy rate of the golf ball's spherical surface, specifically the ratio (SR value) of the total dimple area defined by the surface edges of the planes surrounded by the edges of the dimples to the ball's spherical surface assuming no dimples exist, is preferably between 70% and 90% to allow for sufficient aerodynamic performance. Furthermore, the value V0, obtained by dividing the spatial volume of the dimples below the plane surrounded by the edges of each dimple by the volume of a cylinder with the plane as its base and the maximum depth of the dimples as its height, is preferably between 0.35 and 0.80 to optimize the ball's trajectory. Moreover, the VR value, which is the ratio of the total dimple volume formed below the plane surrounded by the edges of the dimples to the ball's spherical surface assuming no dimples exist, is preferably between 0.6% and 1.0%. If the values ​​deviate from the above ranges, the trajectory may not yield a good distance, and the ball may not achieve a sufficiently satisfactory distance.

[0102] Furthermore, the golf ball of the present invention can be used in competition and comply with the rules of golf. The outer diameter of the ball is such that it cannot pass through a ring with an inner diameter of 42.672 mm, and the mass can preferably be formed to 45.0 to 45.93 g. [Examples]

[0103] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0104] [Examples 1-3, Comparative Examples 1-5] [Core formation] After preparing the rubber compositions for each of Examples 1 and 3 and Comparative Examples 1 to 5 shown in Table 1, solid cores for each example were produced by vulcanizing and molding them at the temperatures and times shown in Table 1.

[0105] For Example 2, a core is prepared based on the formulation shown in Table 1, in the same manner as described above.

[0106] [Table 1]

[0107] The details of each component listed in Table 1 are as follows: • Polybutadiene A: Manufactured by ENEOS Material, product name "BR 01" • Polybutadiene B: Manufactured by ENEOS Material, product name "BR T700" • Zinc acrylate A: "ZN-DA85S" (manufactured by Nippon Shokubai Co., Ltd.) • Zinc acrylate B: "ZN-DA85SR" (manufactured by Nippon Shokubai Co., Ltd.) • Zinc stearate: Product name "Zinc Stearate GP" (manufactured by NOF Corporation) • Organic peroxide: Dicumyl peroxide, trade name "Perkmyl D" (manufactured by NOF Corporation) • Sulfur: Product name "Sunmix S-80N" (manufactured by Sanshin Chemical Industry Co., Ltd.), a sulfur masterbatch containing 80% by mass of rubber-grade powdered sulfur. • Water: Purified water (manufactured by Masaki Pharmaceutical Co., Ltd.) • Anti-aging agent A: 2,2-methylenebis(4-methyl-6-butylphenol), trade name "Nocrac NS-6" (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) • Anti-aging agent B: 2-mercaptobenzimidazole, trade name "Nocrac MB" (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) • Zinc oxide: Product name "Triple Zinc Oxide" (manufactured by Sakai Chemical Industry Co., Ltd.) • Pentachlorothiophenol zinc salt: Manufactured by Fujifilm & Wako Pure Chemical Industries, Ltd.

[0108] [Formation of the intermediate layer and cover (outermost layer)] Next, in each of Examples 1, 3 and Comparative Examples 1 to 5, an intermediate layer was formed by injection molding using an injection mold with the intermediate layer resin materials No. 1 to No. 3 shown in Table 2 around the core surface. Then, using a different injection mold, a cover was formed by injection molding using the cover (outermost layer) resin materials No. 4 to No. 6 shown in Table 2 around the intermediate layer-covered sphere. At this time, predetermined dimples (dimples common to all examples) described below were formed on the cover surface.

[0109] In Example 2, similar to the above, an intermediate layer is formed around the core surface by injection molding with the intermediate layer resin material No. 1 shown in Table 2. Then, a cover is formed around the intermediate layer-covered sphere by injection molding with the cover (outermost layer) resin material No. 4 shown in Table 2. Dimples similar to those described above (dimples common to all examples) are formed on the cover surface.

[0110] [Table 2]

[0111] The details of the ingredients listed in Table 2 are as follows. "Hymiran 1605", "Hymiran 1557", "Hymiran 1706", "AM7318" - Ionomers manufactured by Mitsui Dow Polychemicals. "Barium sulfate" - Product name "Precipitated Barium Sulfate 300" manufactured by Sakai Chemical Industry Co., Ltd. "Magnesium stearate" - a product manufactured by NOF Corporation, "Magnesium Stearate G". "Polyethylene wax," manufactured by Sanyo Chemical Industries, Ltd., product name "Sunwax 161P" Trimethylolpropane (TMP), manufactured by Tokyo Chemical Industry Co., Ltd. "Thermoplastic polyurethane (1)" Product name "Pandex" manufactured by DIC Covestropolymer, ether type "Thermoplastic polyurethane (2)" Product name "Pandex" manufactured by DIC Covestropolymer, ether type "Thermoplastic polyurethane (3)" Product name "Pandex" manufactured by DIC Covestropolymer, ether type "Thermoplastic elastomer (1)" Polyester elastomer manufactured by Toray Celanese Co., Ltd., product name "Hytrel 2401" "Thermoplastic elastomer (2)" Polyester elastomer manufactured by Toray Celanese Co., Ltd., product name "Hytrel 4001" "Additives" Blue pigment, titanium dioxide, wax, and other additives

[0112] For each example and comparative example, the following dimples common to all examples are used. These dimples consist of eight types of circular dimples, No. 1 to No. 8, with different diameters and depths, and their details are shown in Table 3 below. The arrangement (pattern) of these dimples is shown in Figure 3. Figure 3(A) is a plan view of the dimples, and Figure 3(B) is a side view thereof.

[0113] [Table 3]

[0114] Definition of a dimple Edge: The highest point in the cross-section passing through the center of the dimple. Diameter: The diameter of the plane surrounded by the rim of the dimple. Depth: Maximum depth of the dimple from the plane surrounded by the edges of the dimple. SR: The ratio of the total dimple area, defined by the plane enclosed by the edges of the dimples, to the ball's surface area assuming no dimples exist. Dimple volume: The volume of the dimple beneath the plane surrounded by the edges of the dimple. Cylinder volume ratio: The ratio of the volume of a dimple to the volume of a cylinder with the same diameter and depth as the dimple. VR: The ratio of the total dimple volume formed downwards from the plane surrounded by the edges of the dimples to the ball volume assuming no dimples exist.

[0115] For each golf ball obtained, various physical properties such as the internal hardness at each position of the core, the outer diameter of the core and each coated sphere, the thickness and material hardness of each layer, and the deflection and surface hardness of each coated sphere were evaluated using the method described below and are shown in Tables 4 and 5.

[0116] [Outer diameter of each sphere in the core and intermediate layer covering spheres] The spheres to be measured are temperature-controlled in a constant temperature chamber adjusted to 23.9±1℃ for at least 3 hours, and then measured in a room at 23.9±2℃. Five arbitrary points on the surface are measured, and the average value is taken as the measurement value for each sphere. The average value for all 10 measured spheres is then calculated.

[0117] [Ball diameter] The balls to be measured are temperature-controlled in a constant temperature chamber adjusted to 23.9±1℃ for more than 3 hours, and then measured in a room at 23.9±2℃. 15 measurements are taken at arbitrary non-dimpled areas, and the average value is taken as the measurement value for one ball. The average value for 10 balls is then calculated.

[0118] [Amount of deflection of the core, intermediate layer covering sphere, and ball] The core, intermediate layer coated sphere, or target coated sphere of the ball is placed on a hard plate, and the amount of deflection is measured from an initial load of 98N (10kgf) to a final load of 1275N (130kgf). The above deflection amounts are measured after temperature adjustment to 23.9°C. The pressure rate of the head used to compress the ball is set to 10mm / s.

[0119] [Core hardness distribution] The core surface is spherical, and the hardness is measured using the Shore C hardness scale according to ASTM D2240 by setting the needle of the hardness tester nearly perpendicular to the spherical surface. For the center and designated positions of the core, the core is cut into a hemispherical shape to create a flat cross-section, and the hardness is measured by pressing the needle of the hardness tester perpendicularly against the center and the designated positions shown in Table 4. The hardness of the center and each position is shown as a Shore C hardness value. For hardness measurement, an automatic rubber hardness tester "P2" manufactured by Polymer Instruments Co., Ltd., equipped with a Shore C hardness tester, is used. The maximum value is read. All measurements are performed in an environment of 23±2℃. The values ​​in Table 4 are Shore C hardness values.

[0120] Furthermore, graphs of the core hardness distribution for Examples 1-3 and Comparative Examples 1-5 are shown in Figure 4.

[0121] [Material hardness of the intermediate layer and cover] Each layer of resin material is molded into a 2mm thick sheet and left for two weeks. Afterward, Shore D and Shore C hardness are measured according to the ASTM D2240 standard. A P2 automatic rubber hardness tester manufactured by Polymer Instruments Co., Ltd. is used for hardness measurement. The Shore D and Shore C hardness attachments are fitted, and the respective hardnesses are measured. The maximum value is read. All measurements are performed under conditions of 23±2℃.

[0122] [Surface hardness of each sphere in the intermediate-coated sphere and ball] The hardness of each sphere is measured by pressing the needle perpendicularly against its surface. Note that the surface hardness of the ball (cover) is measured on the land portion of the ball surface where no dimples are formed. Shore D and Shore C hardness are measured according to the ASTM D2240 standard. An automatic rubber hardness tester "P2" manufactured by Polymer Instruments Co., Ltd. is used for hardness measurement. The Shore D and Shore C hardness attachments are fitted, and the respective hardnesses are measured. The maximum value is read. All measurements are performed in an environment of 23±2℃.

[0123] [Table 4]

[0124] [Table 5]

[0125] The flight distance (W#1)(I#6) and spin rate during approach shots for each golf ball were evaluated using the following method. The results are shown in Table 6.

[0126] Flight evaluation (W#1, HS40m / s) A golf hitting robot will be fitted with a driver club and hit the ball at a head speed (HS) of 40 m / s. The spin rate and total distance will be measured. The club used will be a Bridgestone Sports "J015 Driver (2016 model)" (loft angle 9.5°), and the results will be evaluated according to the following criteria. 〔Judgment criteria〕 ○ ··· The total distance is 199.0m or more. × ··· The total distance is less than 199.0m.

[0127] Flight evaluation (I#6, HS38m / s) A golf swing robot will be fitted with a 6-iron (I#6) and hit at a head speed (HS) of 38 m / s to measure spin rate and total distance. The club used will be the "JGR Forged I#6 (2016 model)" manufactured by Bridgestone Sports, and will be evaluated according to the following criteria. 〔Judgment criteria〕 ○ ··· The total distance is 158.0m or more. × ··· The total distance is less than 158.0m.

[0128] Flight evaluation (I#6, HS35m / s) A golf swing robot will be fitted with a 6-iron (I#6) and hit at a head speed (HS) of 35 m / s to measure spin rate and total distance. The club used will be the "JGR Forged I#6 (2016 model)" manufactured by Bridgestone Sports, and will be evaluated according to the following criteria. 〔Judgment criteria〕 ○ ··· The total distance is 145.0m or more. × ··· The total distance is less than 145.0m.

[0129] Evaluation of spin rate during approach shots (SW, HS20m / s) The spin rate will be determined by the amount of spin produced when a golf swing robot is hit with a sand wedge at a head speed (HS) of 20 m / s. The spin rate will be similarly measured using an initial condition measurement device immediately after impact. The sand wedge used will be a Bridgestone Sports "TourStage TW-03 (loft angle 57°) 2002 model". 〔Judgment criteria〕 ○ ··· Spin rate of 6350 rpm or more × ··· Spin rate less than 6350 rpm

[0130] Evaluation of spin rate during approach shots (SW, HS15m / s) The spin rate will be determined by the amount of spin produced when a golf swing robot is hit with a sand wedge at a head speed (HS) of 15 m / s. The spin rate will be similarly measured using an initial condition measurement device immediately after impact. The sand wedge used will be a Bridgestone Sports "TourStage TW-03 (loft angle 57°) 2002 model". 〔Judgment criteria〕 ○ ··· Spin rate of 4900 rpm or more × ··· Spin rate less than 4900 rpm

[0131] [Table 6]

[0132] As shown in the results in Table 6, the golf balls of Comparative Examples 1 to 5 are inferior to the present invention (example) in the following respects. In Comparative Example 1, the value of (Shore C hardness of the intermediate layer material - Shore C hardness of the cover material) is not greater than the value of (Shore C hardness of the intermediate layer surface - H62.5). As a result, the amount of spin during approach is low. In Comparative Example 2, the value of (Shore C hardness of the intermediate layer material - Shore C hardness of the cover material) is not greater than the value of (Shore C hardness of the intermediate layer surface - H62.5). As a result, the distance when hitting with a 6-iron (I#6) at a head speed (HS) of 35 m / s is lower compared to the example, and the amount of spin when approaching is also lower. Comparative Example 3 has a core hardness distribution where the (H87.5-H50) / (H50-H12.5) value is less than 3.5, and the core deflection under loads of 10kgf to 130kgf is less than the (H100-H50) / (H50-H0) value. As a result, the distance achieved when hitting with a driver (W#1), a head speed (HS) of 40m / s, and a 6-iron (I#6) is insufficient. Comparative Example 4 has a core hardness distribution where the (H87.5-H50) / (H50-H12.5) value is less than 3.5, and the core deflection under loads of 10kgf to 130kgf is less than the (H100-H50) / (H50-H0) value. As a result, the distance achieved when hitting with a driver (W#1), a head speed (HS) of 40m / s, and a 6-iron (I#6) is insufficient. Comparative Example 5 has a core hardness distribution where the value of (H87.5-H50) / (H50-H12.5) is less than 3.5, and the deflection of the core under loads of 10kgf to 130kgf is less than the value of (H100-H50) / (H50-H0). As a result, the distance achieved when hitting with a 6-iron (I#6) is insufficient.

Claims

1. A multi-piece solid golf ball comprising a core, an intermediate layer, and a cover, wherein, in the hardness distribution of the core, 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 (H87.5-H50) / (H50-H12.5)≧3.5 When the above conditions are met and the deflection amount CT (mm) is applied to the core from an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf), the following formula is used: CT>(H100-H50) / (H50-H0) The following equation satisfies the following conditions, and the relationship between the Shore C hardness (H62.5) at a position 62.5% outside the core radius from the core center, the material hardness of the intermediate layer and cover, and the surface hardness of the covered sphere with the intermediate layer covering the core is given by the following formula (Hardness of the intermediate layer material - Hardness of the cover material) > (Surface hardness of the intermediate layer-coated sphere - H62.5) (However, the material hardness and surface hardness values ​​mentioned above are Shore C values.) A multi-piece solid golf ball characterized by satisfying the following conditions.

2. The multi-piece solid golf ball according to claim 1, wherein the above value (hardness of intermediate layer material - hardness of cover material) is 34 or more.

3. The multi-piece solid golf ball according to claim 1 or 2, wherein the value of the above (surface hardness of the intermediate layer-coated sphere - H62.5) is 30 or more and 36 or less.

4. The following formula, Shore C hardness of the core center ≤ Shore C hardness of the cover material A multi-piece solid golf ball according to claim 1 or 2 that satisfies the requirements.

5. The multi-piece solid golf ball according to claim 1 or 2, wherein the Shore C hardness of the cover material is 50 or less.

6. In the above core hardness distribution, the following formula applies: H0<H12.5<H25<H37.5<H50<H62.5<H75<H87.5<H100 A multi-piece solid golf ball according to claim 1 or 2 that satisfies the requirements.

7. In the above core hardness distribution, the following formula applies: (Shore C hardness of core surface - Shore C hardness of core center) ≥ 24 A multi-piece solid golf ball according to claim 1 or 2 that satisfies the requirements.

8. The multi-piece solid golf ball according to claim 1 or 2, wherein the cover is formed by injection molding a single resin compound mainly composed of (I) thermoplastic polyurethane and (II) a polyisocyanate compound, and at least a portion of the resin compound contains a polyisocyanate compound in which all isocyanate groups in one molecule remain in an unreacted state.

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