Multi-piece solid golf balls

Abstract

To provide a golf ball which achieves a satisfactory carry in time of a full shot not only with a driver (W#1) but also with an iron, is superior in a short game, and also has a good feel at impact and excellent scuff resistance.SOLUTION: A multi-piece solid golf ball has a core, an envelope layer, an intermediate layer and a cover. The core consists of a single layer or plural layers, formed primarily of a base rubber. The core has a diameter of at least 30 mm.The envelope layer consists of two layers of an inner layer and an outer layer. The intermediate layer and the cover each consist of a single layer, formed of a resin material. The surface hardness of the core and respective layer-encased spheres satisfies the formula: core surface hardness<surface hardness of inner envelope layer-encased sphere<surface hardness of outer envelope layer-encased sphere<surface hardness of intermediate layer-encased sphere>ball surface hardness. The Shore C hardness value obtained by subtracting the center hardness from the core surface hardness is 16 or more. The respective layers have thicknesses which satisfy the following relations: cover thickness<intermediate layer thickness; and outer envelope layer thickness<inner envelope layer thickness.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a multi-piece solid golf ball having five or more layers including a core, an inner envelope layer, an outer envelope layer, a mid layer, and a cover. [Background technology]

[0002] Various golf balls have been developed for professional and advanced golfers. Among these, multi-piece solid golf balls, which feature optimized hardness relationships among the layers covering the core, have become popular in order to achieve both superior distance performance in the high head speed range and controllability on iron shots and approach shots. Furthermore, because not only distance performance but also the feel upon impact and the amount of spin of the ball after impact with the club significantly affect ball control, optimizing the thickness and hardness of each layer of the golf ball is also an important theme. Furthermore, golf balls are required to withstand repeated impacts and to reduce the occurrence of burrs on the ball surface (improved abrasion resistance), which are observed when the ball is repeatedly hit with various clubs. Therefore, protecting the ball from external factors as much as possible is also an important theme in ball development.

[0003] Examples of such technical documents include the following Patent Documents 1 to 14. These patent documents relate to golf balls with a multi-layer structure of four or more layers, and focus on the surface hardness of each layer (core, envelope layer, intermediate layer, and cover (outermost layer)), the relationship between the ball diameter and the core diameter, and the hardness distribution of the core. Furthermore, some of the above patent documents propose a golf ball with a five-layer ball structure, i.e., four layers enclosing the core (inner envelope layer, outer envelope layer, intermediate layer, and cover (outermost layer)), with specific relationships between their hardness and thickness.

[0004] However, the proposed golf balls still have room for improvement in terms of optimizing the core hardness distribution and the thickness relationship between each layer. That is, the proposed golf balls do not provide a satisfactory distance for amateur golfers who do not have a high head speed, particularly when using a utility club or iron for full shots. Furthermore, some of the proposed golf balls, even when attempting to achieve superior distance performance on iron shots, are unable to provide sufficiently high spin performance on approaches, resulting in poor gameplay or a poor feel on full shots. Therefore, there is a need for the proposal and development of a golf ball for amateur golfers that provides improved distance on full shots with a utility club or iron, a soft and satisfactory feel on all full shots, and is also effective in short game play. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-149131 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-095358 [Patent Document 3] Japanese Patent Application Laid-Open No. 2009-095364 [Patent Document 4] Japanese Patent Application Laid-Open No. 2009-095365 [Patent Document 5] Japanese Patent Application Laid-Open No. 2009-095369 [Patent Document 6] Japanese Patent Application Laid-Open No. 2016-101254 [Patent Document 7] Japanese Patent Application Laid-Open No. 2016-101256 [Patent Document 8] US Patent Application Publication No. 2009 / 0170634 [Patent Document 9] US Patent Application Publication No. 2012 / 0129630 [Patent Document 10] US Patent Application Publication No. 2013 / 0012338 [Patent Document 11] US Patent Application Publication No. 2015 / 0251058 [Patent Document 12] US Patent Application Publication No. 2015 / 0314169 [Patent Document 13] US Patent Application Publication No. 2016 / 0317873 [Patent Document 14] US Patent Application Publication No. 2017 / 0340925 [Patent Document 15] US Patent Application Publication No. 2017 / 0361171 [Patent Document 16] US Patent Application Publication No. 2018 / 0015332 [Patent Document 17] US Patent Application Publication No. 2018 / 0008867 [Patent Document 18] US Patent Application Publication No. 2018 / 0078826 [Patent Document 19] US Patent Application Publication No. 2019 / 0344127 [Patent Document 20] US Patent Application Publication No. 2020 / 0086177 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in consideration of the above circumstances, and aims to provide a multi-piece solid golf ball that provides sufficient distance on full shots with not only a driver (W#1) but also long and middle irons, makes it easy to impart spin to the ball on approach shots, is advantageous in short games, provides a good feel on impact, and has excellent abrasion resistance. [Means for solving the problem]

[0007] As a result of intensive research by the inventors to achieve the above object, the inventors have found that a golf ball having a core, an envelope layer, an intermediate layer, and a cover has a core formed of a single layer or multiple layers, mainly made of a base rubber, the core has an overall diameter of 30 mm or more, the envelope layer is formed of two layers, an inner layer and an outer layer, the intermediate layer and the cover are both formed of a single layer made of a resin material, and the hardness relationship between the core and the surface hardness of the covered sphere of each layer is expressed by the following formula: Core surface hardness < Inner envelope layer coated ball surface hardness < Outer envelope layer coated ball surface hardness < Middle layer coated ball surface hardness > Ball surface hardness (However, the hardness of each layer mentioned above means the Shore C hardness value.) The present inventors have fabricated a multi-piece solid golf ball in which the core has a surface hardness minus a center hardness of 16 or more on the Shore C scale, and the thicknesses of the surrounding layer, intermediate layer, and cover have the following relationships: cover thickness < intermediate layer thickness, and outer surrounding layer thickness < inner surrounding layer thickness. This has led to the discovery that a multi-piece solid golf ball can be manufactured in which low spin is achieved on shots with a driver (W#1) and various irons, a high initial velocity is ensured, and good distance is achieved, and the amount of spin on approach shots in the short game is optimized to improve controllability and provide good abrasion resistance.

[0008] Accordingly, the present invention provides the following multi-piece solid golf ball. 1. A multi-piece solid golf ball comprising a core, an envelope layer, an intermediate layer, and a cover, wherein the core is formed of a single layer or multiple layers, primarily made of a base rubber, the core has an overall diameter of 30 mm or more, the envelope layer is formed of two layers, an inner layer and an outer layer, and the intermediate layer and cover are both single layers formed of a resin material, and the surface hardness of the core, the surface hardness of a sphere obtained by covering the core with the inner envelope layer (inner envelope layer-covered sphere), the surface hardness of a sphere obtained by covering the inner envelope layer-covered sphere with the outer envelope layer (outer envelope layer-covered sphere), and the surface hardness of a sphere obtained by covering the outer envelope layer-covered sphere with the intermediate layer (intermediate layer-covered sphere), and the surface hardness of the ball, are all determined by the following formula: Core surface hardness < Inner envelope layer coated ball surface hardness < Outer envelope layer coated ball surface hardness < Middle layer coated ball surface hardness > Ball surface hardness (However, the hardness of each layer mentioned above means the Shore C hardness value.) the value obtained by subtracting the center hardness from the surface hardness of the core is 16 or more in Shore C hardness, and the center hardness of the core is 60 or more in Shore C hardness, The surface hardness of the outer envelope layer-coated sphere is 52 or more and 65 or less in Shore D hardness, The thickness of each layer of the envelope layer, intermediate layer and cover must be in accordance with the following two formulas: Cover thickness < intermediate layer thickness, and outer envelope layer thickness < inner envelope layer thickness A multi-piece solid golf ball characterized by satisfying the relationship: 2. The relationship between the core's center hardness (Cc), the core's surface hardness (Cs), and the hardness at the midpoint between the core's surface and center (Cm) is: (Cs-Cm) / (Cm-Cc)≧1.5 2. The multi-piece solid golf ball according to 1 above, wherein 3. Core volume (mm 3 ) × Shore C hardness (Cm) at the midpoint between the core surface and the core center is Core vh, and the volume of the inner surrounding layer (mm 3 ) × the surface hardness (Shore C) of the inner envelope layer coated sphere is IE vh, and the volume of the outer envelope layer (mm 3 3. A multi-piece solid golf ball according to 1 or 2 above, satisfying the condition 0.4≦(OE vh + IE vh) / Core vh ≦1.1, where OE vh is the surface hardness (Shore C) of the outer envelope layer-covered sphere. 4. When the lift coefficient measured under the conditions of a Reynolds number of 80,000 and a spin rate of 2,000 rpm is 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 CL2, CL1 and CL2 are expressed by the following formula: 0.900 ≦ CL2 / CL1 4. The multi-piece solid golf ball according to any one of 1 to 3 above, which satisfies the above conditions. 5. 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 can be calculated by the following formula: 1.250 ≦ CL4 / CL3 ≦ 1.300 5. The multi-piece solid golf ball according to any one of 1 to 4 above, which satisfies the above conditions. 6. A multi-piece solid golf ball according to any one of 1 to 5 above, wherein the number of dimples arranged on the cover surface is 323 to 380. [Effects of the Invention]

[0009] The multi-piece solid golf ball of the present invention provides sufficient distance on full shots with not only a driver (W#1) but also various irons, makes it easy to impart spin to the ball on approach shots, is advantageous in short games, provides a good feel on impact, and is highly abrasion-resistant, making it a highly useful multi-layer golf ball for professionals and advanced players. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic cross-sectional view of a multi-piece solid golf ball (five-layer structure) of the present invention. [Figure 2] FIG. 2 is a plan view showing the dimple pattern common to each example and each comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention will be described in more detail below. As shown in FIG. 1, the multi-piece solid golf ball of the present invention is a golf ball G having five or more layers, including a core 1, a two-layer envelope layer 2 (inner envelope layer 2a and outer envelope layer 2b) enclosing the core, a mid layer 3 enclosing the mid layer, and a cover 4 enclosing the mid layer. Numerous dimples D are typically formed on the surface of the cover 4. Although not specifically shown, a paint layer is typically formed on the surface of the cover 4. The cover 4 is the outermost layer of the golf ball's layer structure, excluding the paint layer. The core 1 is not limited to a single layer, but can be formed of two or more layers.

[0012] The core diameter is 30.0 mm or greater. This diameter is preferably 31.4 mm or greater, and more preferably 32.0 mm or greater. The upper limit of this diameter is preferably 35.0 mm or less, more preferably 34.2 mm or less, and even more preferably 33.5 mm or less. If the core diameter is too large, the amount of spin on full shots with a driver (W#1) or iron may increase, making it difficult to achieve the desired distance. On the other hand, if the core diameter is too small, the initial velocity of the ball may decrease, resulting in a loss of distance.

[0013] The deflection (mm) of the core when subjected to 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 at least 3.0 mm, more preferably at least 3.2 mm, and even more preferably at least 3.5 mm, with the upper limit being preferably no more than 5.5 mm, more preferably no more than 5.3 mm, and even more preferably no more than 5.0 mm. If the core deflection is too small, i.e., if the core is too hard, the ball may have too much spin, resulting in a loss of flight distance, or the feel on impact may be too hard. On the other hand, if the core deflection is too large, i.e., if the core is too soft, the ball may have too little resilience, resulting in a loss of flight distance, a too soft feel, or poor durability to cracking upon repeated impact.

[0014] The core is composed of a single layer or multiple layers of a vulcanized molded product of a rubber composition mainly composed of rubber, and preferably a single layer. If the core material is not rubber, the resilience may be reduced and the ball may not fly. Furthermore, if the core is made of multiple layers, the core may crack early from the interface when repeatedly hit. The rubber composition of the core is usually composed mainly of a base rubber, to which a co-crosslinking agent, a crosslinking initiator, an inert filler, an organic sulfur compound, etc. are compounded to obtain the rubber composition.

[0015] Polybutadiene is preferably used as the base rubber. Commercially available polybutadiene products can be used, such as BR01, BR51, and BR730 (manufactured by JSR Corporation). The proportion of polybutadiene in the base rubber is preferably 60% by mass or more, and more preferably 80% by mass or more. Rubber components other than the polybutadiene may be blended into the base rubber within a range that does not impair the effects of the present invention. Examples of rubber components other than polybutadiene include polybutadienes other than the polybutadienes mentioned above, and other diene rubbers, such as styrene-butadiene rubber, natural rubber, isoprene rubber, and ethylene-propylene-diene rubber.

[0016] The co-crosslinking agent is an α,β-unsaturated carboxylic acid and / or a metal salt thereof. Specific examples of unsaturated carboxylic acids include acrylic acid, methacrylic acid, maleic acid, and fumaric acid, with acrylic acid and methacrylic acid being particularly preferred. Metal salts of unsaturated carboxylic acids are not particularly limited, but examples include those obtained by neutralizing the above-mentioned unsaturated carboxylic acids with desired metal ions. Specific examples include zinc salts and magnesium salts of methacrylic acid, acrylic acid, and the like, with zinc acrylate being particularly preferred.

[0017] The unsaturated carboxylic acid and / or metal salt thereof is blended in an amount of typically 15 parts by weight or more, preferably 20 parts by weight or more, and more preferably 25 parts by weight or more, per 100 parts by weight of the base rubber, with the upper limit typically being 50 parts by weight or less, preferably 45 parts by weight or less, and more preferably 40 parts by weight or less. If the blended amount is too high, the ball may become too hard, resulting in an unbearable feel at impact, while if the blended amount is too low, the resilience may decrease.

[0018] An organic peroxide is preferably used as the crosslinking initiator. Specifically, commercially available organic peroxides can be used, such as Percumyl D (manufactured by Nippon Oil & Fats Co., Ltd.), Perhexa C-40, Perhexa 3M (manufactured by Nippon Oil & Fats Co., Ltd.), and Luperco 231XL (manufactured by Atochem). These may be used alone or in combination of two or more. The amount of organic peroxide added is preferably 0.1 parts by weight or more, more preferably 0.3 parts by weight or more, and even more preferably 0.5 parts by weight or more, per 100 parts by weight of the base rubber. The upper limit is preferably 5 parts by weight or less, more preferably 4 parts by weight or less, even more preferably 3 parts by weight or less, and most preferably 2.5 parts by weight or less. If the amount added is too high or too low, it may be difficult to achieve a favorable feel, durability, and resilience.

[0019] Suitable fillers include, for example, zinc oxide, barium sulfate, and calcium carbonate. These may be used alone or in combination. The amount of filler added is preferably at least 4 parts by weight, more preferably at least 5 parts by weight, and even more preferably at least 7 parts by weight per 100 parts by weight of the base rubber. The upper limit of the amount added is preferably no more than 100 parts by weight, more preferably no more than 75 parts by weight, and even more preferably no more than 50 parts by weight per 100 parts by weight of the base rubber. If the amount added is too high or too low, it may be difficult to achieve the appropriate weight and appropriate resilience.

[0020] As the antioxidant, for example, commercially available products such as Nocrac NS-6, Nocrac NS-30, Nocrac 200, Nocrac MB (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) can be used. These may be used alone or in combination of two or more.

[0021] The amount of antioxidant blended is not particularly limited, but is preferably at least 0.05 part by weight, more preferably at least 0.1 part by weight, and preferably not more than 1.0 part by weight, more preferably not more than 0.7 part by weight, and even more preferably not more than 0.5 part by weight, per 100 parts by weight of base rubber. If the blended amount is too high or too low, the appropriate core hardness gradient may not be obtained, and favorable resilience, durability, and spin reduction effect on full shots may not be achieved.

[0022] Furthermore, the rubber composition can be blended with an organic sulfur compound to impart excellent resilience. Specifically, it is recommended to blend thiophenol, thionaphthol, halogenated thiophenol, or a metal salt thereof. More specifically, zinc salts of pentachlorothiophenol, pentafluorothiophenol, pentabromothiophenol, parachlorothiophenol, pentachlorothiophenol, and the like, and diphenyl polysulfide, dibenzyl polysulfide, dibenzoyl polysulfide, dibenzothiazoyl polysulfide, dithiobenzoyl polysulfide, and the like having 2 to 4 sulfur atoms can be mentioned. In particular, the zinc salt of pentachlorothiophenol and diphenyl disulfide can be preferably used.

[0023] The organic sulfur compound is blended in an amount of at least 0.05 part by weight, preferably at least 0.07 part by weight, and more preferably at least 0.1 part by weight, per 100 parts by weight of the base rubber, with an upper limit of 5 parts by weight, preferably at most 4 parts by weight, more preferably at most 3 parts by weight, and most preferably at most 2 parts by weight. If the blended amount is too high, the hardness will be too low, and if the blended amount is too low, no improvement in resilience can be expected.

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

[0025] Next, the hardness distribution of the core will be described. Note that the hardness of the core described below refers to Shore C hardness. This Shore C hardness is a hardness value measured using a Shore C hardness tester conforming to the ASTM D2240 standard.

[0026] The center hardness (Cc) of the core is preferably 54 or more, more preferably 57 or more, and even more preferably 60 or more, with the upper limit being preferably 69 or less, more preferably 67 or less, and even more preferably 65 or less. If this value is too high, the feel on impact may be too hard, or the spin rate on full shots may increase, preventing the desired flight distance from being achieved. On the other hand, if this value is too low, the resilience may be reduced, resulting in a loss of flight distance, or the durability to cracking when hit repeatedly may be reduced.

[0027] The surface hardness (Cs) of the core is preferably at least 70, more preferably at least 74, and even more preferably at least 77, with the upper limit being preferably not more than 90, more preferably not more than 87, and even more preferably not more than 85. Any deviation from these hardness limits may result in the same adverse effects as those described for the center hardness (Cc) of the core.

[0028] The hardness (Cm) at the midpoint between the core surface and center is preferably at least 58, more preferably at least 61, and even more preferably at least 64, with the upper limit being preferably not more than 75, more preferably not more than 74, and even more preferably not more than 72. Any deviation from these hardness limits may result in the same adverse effects as those described above for the center hardness (Cc) of the core.

[0029] The difference between the surface hardness (Cs) and center hardness (Cc) of the core is 16 or more, preferably 17 or more, more preferably 18 or more, with the upper limit being preferably 25 or less, more preferably 22 or less, and even more preferably 21 or less. If this value is too small, the spin rate on full driver shots will be high, and the desired distance may not be achieved. If the hardness difference is greater than the above range, the club's durability to cracking after repeated impacts may be poor, or the initial velocity on actual shots may be low, preventing the desired distance from being achieved. If the hardness difference is smaller than the above range due to an increase in the core's deflection hardness, the initial velocity on full driver shots may be low, preventing the desired distance from being achieved.

[0030] Regarding the internal hardness of the core, the value of (Cs - Cm) / (Cm - Cc) is preferably 1.5 or more, more preferably 1.7 or more, and even more preferably 1.9 or more, with the upper limit being preferably 10.0 or less, more preferably 8.0 or less, and even more preferably 5.0 or less. If this value is too large, the durability to cracking when repeatedly hit may be poor, or the initial velocity may be low, making it difficult to achieve the desired distance. On the other hand, if this value is too small, the spin rate on full shots may be high, making it difficult to achieve the desired distance.

[0031] Core volume (mm 3 ) × the hardness (Shore C) at the midpoint between the core surface and center, where Core vh is the value of Core vh. The value of Core vh is preferably 800 or more, more preferably 900 or more, and even more preferably 1000 or more, with the upper limit being preferably 1540 or less, more preferably 14805 or less, and even more preferably 1430 or less. If the value of Core vh is too small, the initial velocity of the ball may be low, resulting in a loss of distance. On the other hand, if the value of Core vh is too large, the spin rate on full iron shots may increase, preventing the desired distance from being achieved.

[0032] Next, the envelope layer will be described. In the present invention, the envelope layer is formed into two layers, an inner layer and an outer layer, which will be hereinafter referred to as the inner envelope layer and the outer envelope layer, respectively.

[0033] The material hardness of the inner envelope layer is not particularly limited, but is preferably 67 or more, more preferably 70 or more, and even more preferably 72 or more in Shore C hardness, with the upper limit being preferably 90 or less, more preferably 89 or less, and even more preferably 88 or less.The Shore D hardness is preferably 43 or more, more preferably 45 or more, and even more preferably 47 or more, with the upper limit being preferably 60 or less, more preferably 56 or less, and even more preferably 54 or less.

[0034] The surface hardness of a sphere in which a core is coated with an inner envelope layer (inner envelope layer-coated sphere) is preferably 75 or more, more preferably 78 or more, and even more preferably 80 or more, in Shore C hardness, with an upper limit of preferably 94 or less, more preferably 92 or less, and even more preferably 90 or less.The surface hardness of a sphere in which a core is coated with an inner envelope layer is preferably 49 or more, more preferably 51 or more, and even more preferably 53 or more, with an upper limit of preferably 66 or less, more preferably 62 or less, and even more preferably 60 or less.

[0035] If the material hardness and surface hardness of the inner envelope layer are too soft, the ball may spin too much on a full shot, resulting in a low initial velocity and a short distance, whereas if the material hardness and surface hardness are too hard, the ball may feel hard on impact, may have poor crack resistance when hit repeatedly, or may spin too much on a full shot, resulting in a short distance.

[0036] It is preferable that the surface hardness of the inner envelope layer-covered sphere be higher than the surface hardness of the core, otherwise the spin rate on a full shot may increase, making it difficult to achieve the desired flight distance.

[0037] The thickness of the inner envelope layer is preferably 0.8 mm or more, more preferably 1.0 mm or more, and even more preferably 1.2 mm or more. The upper limit of the thickness of the inner envelope layer is preferably 1.8 mm or less, more preferably 1.7 mm or less, and even more preferably 1.6 mm or less. If the thickness of the inner envelope layer deviates from the above range, the spin-reducing effect on full shots may be insufficient, resulting in a loss of distance. Furthermore, if the thickness of the inner envelope layer is too thin, crack resistance during repeated impacts and durability at low temperatures may be impaired.

[0038] Volume of the inner envelope layer (mm 3 If IE vh is the product of the hardness of the inner envelope layer and the surface hardness (Shore C) of the inner envelope layer and the surface hardness of the golf ball, then IE vh is preferably at least 380, more preferably at least 410, and even more preferably at least 440, with the upper limit being preferably at most 520, more preferably at most 500, and even more preferably at most 480. If IE vh is outside the above range, the low spin effect on full shots may be insufficient, resulting in a short flight distance.

[0039] The value of (OE vh + IE vh) / Core vh is preferably 0.4 or more, more preferably 0.5 or more, and even more preferably 0.6 or more, with the upper limit being preferably 1.1 or less, more preferably 1.0 or less, and even more preferably 0.9 or less. If this value is too small, the initial velocity on actual impact may be low and the flight distance may be reduced. On the other hand, if this value is too large, the initial velocity may be low or the spin rate may increase on full shots, making it impossible to achieve the desired flight distance.

[0040] On the other hand, the material hardness of the outer envelope layer is preferably 75 or more, more preferably 78 or more, and even more preferably 80 or more, in Shore C hardness, with the upper limit being preferably 95 or less, more preferably 92 or less, and even more preferably 90 or less.The Shore D hardness is preferably 46 or more, more preferably 48 or more, and even more preferably 50 or more, with the upper limit being preferably 63 or less, more preferably 59 or less, and even more preferably 57 or less.

[0041] The surface hardness of a sphere in which a core is coated with an outer envelope layer (outer envelope layer-coated sphere) is preferably 83 or more, more preferably 86 or more, and even more preferably 88 or more on the Shore C scale, with an upper limit of preferably 95 or less, more preferably 93 or less, and even more preferably 92 or less. The Shore D hardness is preferably 52 or more, more preferably 54 or more, and even more preferably 56 or more, with an upper limit of preferably 69 or less, more preferably 65 or less, and even more preferably 63 or less.

[0042] If the material hardness and surface hardness of the outer envelope layer are too soft, the ball may spin too much on a full shot, resulting in a low initial velocity and a short distance, whereas if the material hardness and surface hardness are too hard, the ball may feel hard on impact, may have poor crack resistance when hit repeatedly, or may spin too much on a full shot, resulting in a short distance.

[0043] The thickness of the outer envelope layer is preferably 0.7 mm or more, more preferably 0.9 mm or more, and even more preferably 1.1 mm or more. The upper limit of the thickness of the outer envelope layer is preferably 1.7 mm or less, more preferably 1.6 mm or less, and even more preferably 1.5 mm or less. If the thickness of the outer envelope layer is outside the above range, the low spin effect on full shots may be insufficient, resulting in a short flight distance. Furthermore, if the thickness of the outer envelope layer is too thin, crack resistance during repeated impacts and durability at low temperatures may be poor.

[0044] In order to reduce spin and increase distance on full shots, the thickness of the outer envelope layer is preferably smaller than that of the inner envelope layer. The difference between the thickness of the inner envelope layer and the thickness of the outer envelope layer is usually greater than 0 mm, preferably 0.1 mm or more, and more preferably 0.2 mm or more, with the upper limit usually being 0.5 mm or less, preferably 0.4 mm or less, and more preferably 0.3 mm or less. If this value deviates from the above range, the spin rate on full shots may increase, resulting in a loss of distance.

[0045] Volume of the outer envelope layer (mm 3 If OE vh is defined as the product of the hardness (Shore C) of the outer envelope layer and the surface hardness (Shore C) of the outer envelope layer-coated ball, then the OE vh value is preferably at least 380, more preferably at least 410, and even more preferably at least 440, with the upper limit being preferably at most 600, more preferably at least 540, and even more preferably at most 480. If the OE vh value is outside the above range, the low spin effect on full shots may be insufficient, resulting in a loss of distance.

[0046] The total thickness of the envelope layer is preferably 2.0 mm or more, more preferably 2.2 mm or more, and even more preferably 2.4 mm or more, with the upper limit being preferably 4.0 mm or less, more preferably 3.5 mm or less, and even more preferably 3.0 mm or less. If the total thickness of the envelope layer is too thick, the initial velocity may be low, and the overall flight distance may be reduced. If the thickness of the envelope layer is too thin, the low spin effect may be insufficient, and the flight distance may be reduced on full shots with an iron.

[0047] The materials for the inner envelope layer and the outer envelope layer are not particularly limited, but known resins can be used. Particularly preferred examples of the materials include the following components (A) to (D): (a-1) an olefin-unsaturated carboxylic acid binary random copolymer and / or a metal ion-neutralized product of an olefin-unsaturated carboxylic acid binary random copolymer; (a-2) a metal ion-neutralized product of an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester ternary random copolymer and / or an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester ternary random copolymer; (A) a base resin blended in a mass ratio of 100:0 to 0:100; (B) a non-ionomer thermoplastic elastomer in a mass ratio of 100:0 to 0:100, (C) 5 to 120 parts by mass of a fatty acid and / or a derivative thereof having a molecular weight of 228 to 1500; (D) 0.1 to 17 parts by mass of a basic inorganic metal compound capable of neutralizing unneutralized acid groups in the components (A) and (C) An example of the resin composition is a resin composition containing the above as essential components.

[0048] As for the components (A) to (D), for example, the resin materials (A) to (D) for the intermediate layer described in JP-A No. 2010-253268 can be suitably used.

[0049] The resin materials forming the inner and outer envelope layers may be the same or different. As described below, in the present invention, the surface hardness of the outer envelope layer-coated sphere is harder than that of the inner envelope layer-coated sphere. Therefore, to set the resin material of the outer envelope layer harder than that of the inner envelope layer, the resin material of the outer envelope layer can be made different from that of the inner envelope layer by, for example, mixing an appropriate amount of the resin materials of components (A) to (D) with a relatively hard ionomer resin.

[0050] The materials for the inner envelope layer and the outer envelope layer may each contain a non-ionomeric thermoplastic elastomer, preferably in an amount of 0 to 50 parts by mass per 100 parts by mass of the total amount of the base resin.

[0051] Examples of the non-ionomeric thermoplastic elastomer include polyolefin elastomers (including polyolefins and metallocene polyolefins), polystyrene elastomers, diene polymers, polyacrylate polymers, polyamide elastomers, polyurethane elastomers, polyester elastomers, and polyacetals.

[0052] Any additives can be added to the resin material as appropriate 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 added, the amount of the additives added is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, per 100 parts by mass of the total of the base resin, and preferably 10 parts by mass or less, more preferably 4 parts by mass or less.

[0053] Next, the intermediate layer will be described. The material hardness of the intermediate layer is not particularly limited, but is preferably 58 or more, more preferably 60 or more, and even more preferably 63 or more in Shore D hardness, with the upper limit being preferably 70 or less, more preferably 68 or less, and even more preferably 65 or less.The Shore C hardness is preferably 87 or more, more preferably 89 or more, and even more preferably 93 or more, with the upper limit being preferably 100 or less, more preferably 98 or less, and even more preferably 96 or less.

[0054] Furthermore, the surface hardness of a sphere (intermediate layer-coated sphere) obtained by coating the outer envelope layer-coated sphere with an intermediate layer, in Shore D hardness, is preferably 64 or more, more preferably 66 or more, and even more preferably 69 or more, with an upper limit of preferably 76 or less, more preferably 74 or less, and even more preferably 71 or less. The Shore C hardness is preferably 90 or more, more preferably 93 or more, and even more preferably 96 or more, with an upper limit of preferably 100 or less, more preferably 99 or less, and even more preferably 98 or less.

[0055] If the material hardness and surface hardness of the intermediate layer are too soft, the ball may spin too much on a full shot, or the initial velocity may be low, resulting in a loss of distance. On the other hand, if the material hardness and surface hardness are too hard, the ball may have poor durability against cracking during repeated shots, or the feel on impact may be too hard when hitting with a putt or on a short approach shot.

[0056] Furthermore, the surface hardness of the intermediate layer-covered sphere is set to be higher than the surface hardness of the ball and the surface hardness of the outer envelope layer-covered sphere, otherwise the spin rate on full shots may increase, resulting in a loss of distance and poor control during short games.

[0057] The thickness of the intermediate layer is preferably 0.7 mm or more, more preferably 0.8 mm or more, and even more preferably 1.0 mm or more, while the upper limit of the thickness of the intermediate layer is preferably 1.8 mm or less, more preferably 1.4 mm or less, and even more preferably 1.2 mm or less.

[0058] The thickness of the intermediate layer is preferably thicker than the cover (outermost layer) described below. The value obtained by subtracting the thickness of the cover from the thickness of the intermediate layer is preferably 0.04 mm or more, more preferably 0.08 mm or more, with the upper limit being preferably 1.5 mm or less, more preferably 1.0 mm or less, and even more preferably 0.6 mm or less. If the cover is thicker than the intermediate layer, full shots may result in increased spin or a lower initial velocity, resulting in a loss of distance. On the other hand, if the above value is too large, it may be difficult to apply spin in short games or the cover may be more likely to break when topping with a wedge.

[0059] As for the material of the intermediate layer, it is preferable to use various thermoplastic resins used as golf ball materials, in particular, highly neutralized resin materials or ionomer resins containing components (a) to (c) described in the material of the envelope layer.

[0060] Specific examples of ionomer resin materials include high-acid ionomers containing an acid content of 16% by mass or more, sodium-neutralized ionomer resins, and zinc-neutralized ionomer resins, and these can be used alone or in combination of two or more.

[0061] A particularly preferred embodiment is one in which a zinc-neutralized ionomer resin and a sodium-neutralized ionomer resin are mixed and used as the main material. The blending ratio, zinc-neutralized / sodium-neutralized (mass ratio), is 25 / 75 to 75 / 25, preferably 35 / 65 to 65 / 35, and more preferably 45 / 55 to 55 / 45. If the zinc-neutralized ionomer and sodium-neutralized ionomer are not included within this ratio, the resilience may be too low to achieve the desired distance, and crack resistance may be poor during repeated impacts at room temperature, and crack resistance may also be poor at low temperatures (below freezing).

[0062] Any additives can be added to the intermediate layer material 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 added, the amount of the additives added 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, more preferably 4 parts by mass or less, per 100 parts by mass of the base resin.

[0063] It is preferable to polish the surface of the intermediate layer material to improve adhesion with the polyurethane that is preferably used in the cover material described below. After the polishing process, it is also preferable to apply a primer (adhesive) to the surface of the intermediate layer or to add an adhesion enhancer to the material.

[0064] 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 the specific gravity is outside this range, the ball's overall resilience will decrease, resulting in a shorter flight distance and reduced durability against cracking due to repeated impacts.

[0065] Next, the cover (outermost layer) will be described. The cover material hardness is not particularly limited, but is preferably 35 or greater, more preferably 40 or greater, and even more preferably 45 or greater in Shore D hardness, with an upper limit of preferably 60 or less, more preferably 55 or less, and even more preferably 50 or less. The cover material hardness is preferably 57 or greater, more preferably 63 or greater, and even more preferably 70 or greater in Shore C hardness, with an upper limit of preferably 89 or less, more preferably 83 or less, and even more preferably 76 or less.

[0066] The surface hardness of a ball (covered ball) obtained by covering a mid layer-covered ball with a cover is preferably 50 or more, more preferably 53 or more, and even more preferably 56 or more, in Shore D hardness, with an upper limit of preferably 70 or less, more preferably 67 or less, and even more preferably 64 or less.The surface hardness of a Shore C hardness is preferably 75 or more, more preferably 80 or more, and even more preferably 85 or more, with an upper limit of preferably 95 or less, more preferably 92 or less, and even more preferably 90 or less.

[0067] If the cover material hardness and ball surface hardness are too soft, full iron shots may result in excessive spin and reduced distance, while if the material hardness and surface hardness are too hard, approach shots may not generate enough spin and the abrasion resistance may be poor.

[0068] The cover thickness is preferably 0.3 mm or more, more preferably 0.45 mm or more, and even more preferably 0.6 mm or more. The upper limit of the cover thickness is preferably 1.2 mm or less, more preferably 1.15 mm or less, and even more preferably 1.0 mm or less. It is also preferable that the cover thickness be thinner than the intermediate layer. If the cover thickness is outside the above range or is thicker than the intermediate layer, the repulsion on full shots with an iron may be insufficient or the spin may be too high, resulting in a loss of distance. On the other hand, if the cover thickness is too thin, the scuff resistance may be poor, or the spin on approaches may be insufficient, resulting in a lack of controllability.

[0069] The cover may be made from any of the thermoplastic or thermosetting resins typically used in golf ball cover materials, but a urethane resin is preferred from the viewpoints of controllability and abrasion resistance. From the viewpoint of mass production of golf ball products, it is particularly preferred to use a material primarily made of thermoplastic polyurethane, and more preferably, the cover may be made from a resin blend primarily composed of (I) a thermoplastic polyurethane and (II) a polyisocyanate compound.

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

[0071] Regarding the above-mentioned (I) thermoplastic polyurethane, the structure of the thermoplastic polyurethane includes a soft segment composed of a long-chain polyol (polymeric glycol) and a hard segment composed of a chain extender and a polyisocyanate compound. The long-chain polyol used as the raw material can be any of those conventionally used in thermoplastic polyurethane-related technologies, and is not particularly limited. Examples of such long-chain polyols 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. These long-chain polyols may be used alone or in combination. Among these, polyether polyols are preferred because they can synthesize thermoplastic polyurethanes with high rebound resilience and excellent low-temperature properties.

[0072] The chain extender may be any of those used in conventional thermoplastic polyurethane technologies, and is preferably a low-molecular-weight compound having two or more active hydrogen atoms in the molecule that can react with isocyanate groups and a molecular weight of 400 or less. Examples of the chain extender include, but are not limited to, 1,4-butylene glycol, 1,2-ethylene glycol, 1,3-butanediol, 1,6-hexanediol, and 2,2-dimethyl-1,3-propanediol. Of these, aliphatic diols having 2 to 12 carbon atoms are preferred, and 1,4-butylene glycol is more preferred.

[0073] The polyisocyanate compound may be any of those used in conventional thermoplastic polyurethane technologies, and is not particularly limited. Specifically, one or more compounds 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, tetramethylxylene diisocyanate, hydrogenated xylylene diisocyanate, dicyclohexylmethane diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, norbornene diisocyanate, trimethylhexamethylene diisocyanate, and dimer acid diisocyanate may be used. However, some isocyanate species may make it difficult to control the crosslinking reaction during injection molding. In the present invention, from the viewpoint of the balance between stability during production and the physical properties that are exhibited, 4,4'-diphenylmethane diisocyanate, which is an aromatic diisocyanate, is most preferred.

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

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

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

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

[0078] The multi-piece solid golf ball formed by laminating the above-mentioned core, inner envelope layer, outer envelope layer, intermediate layer, and cover (outermost layer) can be manufactured by conventional methods such as known injection molding. For example, the materials for the inner envelope layer, outer envelope layer, and intermediate layer are sequentially injected into respective injection molds around the core to obtain each covered sphere, and finally, the material for the cover (outermost layer) is injection molded to obtain a multi-piece golf ball. Alternatively, each covered layer can be formed by encasing the covered sphere in two half-cups previously molded into a spherical half-shell and molding the covered sphere under heat and pressure.

[0079] The deflection (mm) of the ball when subjected to 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 at least 1.8 mm, more preferably at least 2.0 mm, and even more preferably at least 2.2 mm, with the upper limit being preferably at most 3.0 mm, more preferably at most 2.7 mm, and even more preferably at most 2.5 mm. If the core deflection is too small, i.e., if the core is too hard, the ball may have too much spin, resulting in a loss of flight distance, or the feel on impact may be too hard. On the other hand, if the core deflection is too large, i.e., if the core is too soft, the ball may have too little resilience, resulting in a loss of flight distance, a too soft feel, or poor durability to cracking upon repeated impact.

[0080] [ Hardness relationship of each layer 〕 In the present invention, the surface hardness of the core, the surface hardness of a sphere obtained by covering the core with an inner envelope layer (inner envelope layer-coated sphere), the surface hardness of a sphere obtained by covering the inner envelope layer-coated sphere with an outer envelope layer (outer envelope layer-coated sphere), and the surface hardness of a sphere obtained by covering the outer envelope layer-coated sphere with an intermediate layer (intermediate layer-coated sphere), and the surface hardness of the ball are calculated based on the following formula: Core surface hardness < Inner envelope layer coated ball surface hardness < Outer envelope layer coated ball surface hardness < Middle layer coated ball surface hardness > Ball surface hardness (However, the hardness of each layer mentioned above means the Shore C hardness value.) By satisfying the above hardness relationship, sufficient distance can be obtained on full shots with a driver (W#1) or iron, and it is easy to apply spin to the ball on approach shots, making the club excellent for short games.

[0081] The surface hardness of the inner envelope layer-covered sphere minus the core surface hardness is preferably greater than 0, more preferably at least 2, and even more preferably at least 4, in Shore C hardness, with the upper limit preferably at most 20, more preferably at most 16, and even more preferably at most 13. If this value is too small, the initial velocity of the ball may be low, resulting in a loss of distance. If this value is too large, the ball may be less durable to cracking when hit repeatedly.

[0082] The surface hardness of the outer envelope layer-covered sphere minus the core center hardness is at least 23, preferably at least 25, and more preferably at least 27, on the Shore C scale. The upper limit is preferably at most 40, more preferably at most 35, and even more preferably at most 32. If this value is too small, the spin rate increases on full shots, resulting in a loss of distance. If this value is too large, the initial velocity decreases, resulting in a loss of distance and a decrease in durability to cracking due to repeated impacts.

[0083] The surface hardness of the outer envelope layer-covered sphere minus the core surface hardness is at least 5, preferably at least 6, and more preferably at least 7, on the Shore C scale. The upper limit is preferably at most 28, more preferably at most 23, and even more preferably at most 20. If this value is too small, the spin rate increases on full shots, resulting in a loss of distance. If this value is too large, the initial velocity may decrease, resulting in a loss of distance and a decrease in durability against cracking due to repeated impacts.

[0084] The surface hardness of the outer envelope layer-coated sphere minus the surface hardness of the inner envelope layer-coated sphere is preferably greater than 0, more preferably at least 2, and even more preferably at least 3, in Shore C hardness, with the upper limit preferably not greater than 16, more preferably not greater than 14, and even more preferably not greater than 12. If this value is too small, the amount of spin increases on full shots, which can reduce the distance achieved. If this value is too large, the initial velocity on impact can decrease, which can reduce the distance achieved.

[0085] The surface hardness of the intermediate layer-coated ball minus the surface hardness of the outer envelope layer-coated ball is preferably greater than 0, more preferably greater than 2, and even more preferably greater than 4, in Shore C hardness, with the upper limit preferably being 18 or less, more preferably 15 or less, and even more preferably 12 or less. If this value is too small, the spin rate may increase on full shots, resulting in a loss of distance. If this value is too large, the initial velocity may decrease, resulting in a loss of distance.

[0086] The surface hardness of the intermediate layer-covered ball minus the center hardness of the core is preferably 30 or more, more preferably 32 or more, and even more preferably 34 or more, in Shore C hardness, with the upper limit being preferably 45 or less, more preferably 43 or less, and even more preferably 40 or less. If this value is too small, the spin rate on full shots may increase, resulting in a loss of distance. If this value is too large, the initial velocity may decrease, resulting in a loss of distance and a decrease in durability against cracking due to repeated impacts.

[0087] The surface hardness of the intermediate layer-covered sphere minus the surface hardness of the ball is preferably greater than 0, more preferably greater than 2, and even more preferably greater than 4, in Shore C hardness, with an upper limit of preferably 20 or less, more preferably 17 or less, and even more preferably 14 or less. If this value is too small, i.e., if the ball surface is harder than the intermediate layer surface, the ball will not spin as well in short games (this is particularly the case when the cover is hard), and full shots will spin too much, resulting in a loss of distance (this is particularly the case when the intermediate layer is soft). On the other hand, if this value is too large, full shots will spin too much, resulting in a loss of distance (this is particularly the case when the cover is too soft), and the ball will be less durable against cracking when hit repeatedly (this is particularly the case when the intermediate layer is too hard).

[0088] [ Relationship between layers other than hardness 〕 The value obtained by dividing the total thickness of the envelope layer by the combined thickness of the cover and intermediate layer ((total envelope layer thickness) / (intermediate layer thickness + cover thickness)) is preferably 0.8 or greater, more preferably 0.9 or greater, and even more preferably 1.0 or greater, with the upper limit being preferably 1.6 or less, more preferably 1.4 or less, and even more preferably 1.2 or less. If this value is too large, the initial velocity may be low, resulting in a loss of distance and poor durability to cracking due to repeated impacts. On the other hand, if this value is too small, the low spin effect may be insufficient, resulting in a loss of distance.

[0089] The core outer diameter / ball outer diameter ratio is preferably 0.702 or greater, more preferably 0.735 or greater, and even more preferably 0.749 or greater, with the upper limit being preferably 0.821 or less, more preferably 0.802 or less, and even more preferably 0.785 or less. If this ratio is too small, the initial velocity of the ball may be low, resulting in a loss of distance. On the other hand, if this ratio is too large, the spin rate may increase on full iron shots, preventing the desired distance from being achieved.

[0090] If the deflection of the core and ball from an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf) is defined as S (mm) and B (mm), respectively, the value of BS is not particularly limited, but is preferably 0.8 mm or more, more preferably 0.9 mm or more, and even more preferably 1.0 mm or more, with the upper limit being preferably 3.3 mm or less, more preferably 2.7 mm or less, and even more preferably 2.2 mm or less. If this value is too small, the spin rate may increase on full shots, resulting in a loss of distance. On the other hand, if this value is too large, the initial velocity may decrease, resulting in a loss of distance, or the durability to cracking may be reduced when hit repeatedly.

[0091] A large number of dimples can be formed on the outer surface of the cover, which is the outermost layer. There are no particular restrictions on the number of dimples to be arranged on the cover surface, but the number is preferably 323 or more, more preferably 326 or more, and more preferably 330 or more, with the upper limit being preferably 380 or less, more preferably 360 or less, and even more preferably 350 or less. If the number of dimples exceeds the above range, the ball's trajectory may be lowered, resulting in a shorter flight distance. Conversely, if the number of dimples is too few, the ball's trajectory may be higher, resulting in a shorter flight distance.

[0092] The dimples may be of one or a combination of two or more shapes, such as circular, polygonal, dewdrop, or elliptical. For example, if circular dimples are used, the diameter may be approximately 2.5 mm to 6.5 mm, and the depth may be 0.08 mm to 0.30 mm.

[0093] The dimple coverage (SR value), which is the ratio of the total dimple area defined by the planes surrounded by the dimple edges to the ball's area assuming no dimples, is preferably 70% to 90% in order to fully demonstrate aerodynamic characteristics. Furthermore, V0, the value obtained by dividing the spatial volume of each dimple below the plane surrounded by the dimple edges by the volume of a cylinder whose base is the plane and whose height is the maximum depth of the dimple from the bottom, is preferably 0.35 to 0.80 in order to optimize the ball's trajectory. Furthermore, the VR value, which is the ratio of the total dimple volume below the planes surrounded by the dimple edges to the ball's area assuming no dimples, is preferably 0.6% to 1.0%. Any deviation from the above-mentioned ranges may result in a poor trajectory and an insufficient flight distance.

[0094] In the golf ball of the present invention, when the lift coefficient measured under conditions of a Reynolds number of 80,000 and a spin rate of 2,000 rpm is CL1, the lift coefficient measured under conditions of a Reynolds number of 70,000 and a spin rate of 1,900 rpm is CL2, the lift coefficient measured under conditions of a Reynolds number of 200,000 and a spin rate of 2,500 rpm is CL3, and the lift coefficient measured under conditions of a Reynolds number of 120,000 and a spin rate of 2,250 rpm is CL4, it is desirable to optimize CL2 / CL1 and CL4 / CL3.

[0095] In this specification, "lift coefficients (CL1, CL2, CL3, CL4)" are measured in accordance with the ITR (Indoor Test Range) established by the USGA (United States Golf Association). The lift coefficient can be adjusted by adjusting the configuration of the dimples on the golf ball (arrangement, diameter, depth, volume, number, shape, etc.). The lift coefficient is independent of the internal configuration of the golf ball. The Reynolds number (Re) is a dimensionless number used in the field of fluid dynamics. The Reynolds number (Re) is calculated using the following formula (I): Re = ρvL / μ (I) In the above formula (I), ρ represents the density of the fluid, v represents the average velocity of the object relative to the fluid flow, L represents the characteristic length, and μ represents the viscosity coefficient of the fluid.

[0096] The conditions for measuring the lift coefficient CL1, a Reynolds number of 80,000 and a spin rate of 2,000 rpm, generally correspond to the state when the lift coefficient begins to decrease (and thus the golf ball begins to fall) after the golf ball has reached its highest point since being hit. The conditions for measuring the lift coefficient CL2, a Reynolds number of 70,000 and a spin rate of 1,900 rpm, generally correspond to the state when the golf ball reaches its highest point since being hit and is about to fall to the ground. These conditions are particularly true when the golf ball is launched at high speed (e.g., initial velocity of 66 m / s, spin rate of 2,600 rpm, launch angle of 11°). These high-speed conditions correspond to the conditions used by an average amateur golfer using a driver.

[0097] The value of CL2 / CL1 is preferably 0.900 or greater, more preferably 0.970 or greater, and even more preferably 0.990 or greater. By satisfying the above range, it is possible to suppress a decrease in lift force during the flight of the golf ball, which in turn facilitates an increase in flight distance (and therefore an increase in carry) and run during flight. This results in an improvement in flight distance (total). If CL2 / CL1 is too low, the golf ball is likely to drop precipitously, making it difficult to achieve a sufficient increase in carry and run. From the perspective of improving flight distance, a higher CL2 / CL1 is preferable. However, if it is too high, the carry will increase but the run will decrease, resulting in a risk of the total flight distance falling short of the optimum value. Therefore, the upper limit of CL2 / CL1 is 1.100 or less, preferably 1.018 or less, more preferably 0.999 or less, and even more preferably 0.995 or less.

[0098] The conditions for measuring the lift coefficient CL3, i.e., a Reynolds number of 200,000 and a spin rate of 2,500 rpm, generally correspond to the state of a golf ball immediately after it is launched at high speed (e.g., initial speed of 72 m / s, spin rate of 2,500 rpm, launch angle of 10°).The conditions for measuring the lift coefficient CL4, i.e., a Reynolds number of 120,000 and a spin rate of 2,250 rpm, generally correspond to the state of a golf ball rising after it is launched at high speed (e.g., initial speed of 72 m / s, spin rate of 2,500 rpm, launch angle of 10°), approximately two seconds have passed.

[0099] The CL4 / CL3 value is preferably 1.250 or greater, more preferably 1.252 or greater, and even more preferably 1.255 or greater, with the upper limit being preferably 1.300 or less, more preferably 1.295 or less, and even more preferably 1.290 or less. By setting the CL4 / CL3 value within the above range, when the golf ball is hit under high-speed conditions (for example, when hit with a W#1), excessive lift of the golf ball can be suppressed (and thus lift can be suppressed), improving wind resistance and carry. Furthermore, run can be improved. Consequently, the total distance can be improved.

[0100] From the viewpoint of improving flight distance, the lift coefficient CL1 is preferably 0.230 or more. Furthermore, the lift coefficient CL1 is preferably 0.240 or less. From the same viewpoint, the lift coefficient CL2 is preferably 0.230 or more. Furthermore, the lift coefficient CL2 is preferably 0.240 or less. From the same viewpoint, the lift coefficient CL3 is preferably 0.145 or more. Furthermore, the lift coefficient CL3 is preferably 0.155 or less. From the same viewpoint, the lift coefficient CL4 is preferably 0.185 or more. Furthermore, the lift coefficient CL4 is preferably 0.195 or less.

[0101] A paint film layer (coating layer) can be formed on the surface of the cover. This paint film layer can be applied using various paints, and as the paint, a paint composition containing a urethane paint composed of a polyol and a polyisocyanate as the main component is preferably used, since the paint must be able to withstand the harsh conditions of use of the golf ball.

[0102] Examples of the polyol component include acrylic polyols, polyester polyols, etc. These polyols include modified polyols, and other polyols may be added to further improve workability.

[0103] As the polyol component, it is preferable to use two types of polyester polyols in combination. In this case, if the two types of polyester polyols are component (a) and component (b), the polyester polyol of component (a) can be a polyester polyol having a cyclic structure introduced into the resin skeleton, such as a polyester polyol obtained by polycondensation of a polyol having an alicyclic structure such as cyclohexanedimethanol with a polybasic acid, or a polyol having an alicyclic structure with a diol or triol with a polybasic acid. On the other hand, the polyester polyol of component (b) can be a polyester polyol having a multi-branched structure, such as a polyester polyol having a branched structure such as "NIPPOLAN 800" manufactured by Tosoh Corporation.

[0104] On the other hand, the polyisocyanate is not particularly limited and may be a commonly used aromatic, aliphatic, alicyclic, or other polyisocyanate, 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. These may be used alone or in combination.

[0105] Various organic solvents can be mixed into the coating 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 spirits.

[0106] The thickness of the coating layer made of the above coating composition is not particularly limited, but is usually 5 to 40 μm, preferably 10 to 20 μm. The coating layer thickness here refers to the average thickness of the coating measured at three locations: the center of the dimple and two locations between the center of the dimple and the edge of the dimple.

[0107] In the present invention, the elastic work recovery rate of the coating layer made of the above-mentioned coating composition must be 60% or more, and preferably 80% or more. If the elastic work recovery rate of this coating layer is within the above range, the coating layer will have high elasticity, therefore a high self-repair function and excellent abrasion resistance. Furthermore, the various performance properties of golf balls coated with the above-mentioned coating composition can be improved. The above-mentioned elastic work recovery rate can be measured as follows.

[0108] The elastic work recovery is a parameter of the nanoindentation method, which evaluates the physical properties of a coating layer. Conventional methods can only measure the size of the deformation mark (plastic deformation mark) corresponding to the maximum load. However, the nanoindentation method automatically and continuously measures the relationship between the indentation load and the indentation depth. This allows for highly accurate evaluation of the physical properties of a coating layer without the individual variability that occurs when visually measuring deformation marks with an optical microscope. Because the coating layer on a golf ball's surface is significantly affected by impacts from drivers and various clubs, and the coating layer's influence on the physical properties of a golf ball is significant, measuring the coating layer with the ultramicrohardness test method, which can be performed with higher precision than conventional methods, is a highly effective evaluation method.

[0109] The hardness of the coating layer is preferably 40 or more, more preferably 60 or more, with an upper limit of preferably 95 or less, more preferably 85 or less, in Shore M hardness. This Shore M hardness conforms to ASTM D2240. The hardness of the coating layer is preferably 40 or more, more preferably 50 or more, with an upper limit of preferably 80 or less, more preferably 70 or less, in Shore C hardness. This Shore C hardness conforms to ASTM D2240. If the coating layer has a hardness that is too high above the above range, the coating may become brittle upon repeated impacts, potentially failing to protect the cover layer. If the coating layer has a hardness that is too low below the above range, the ball surface may be easily scratched when struck by a hard object, which is undesirable.

[0110] When using the above coating composition, the coating composition of the present invention can be prepared at the time of coating a golf ball manufactured by a known method, applied to the surface using a conventional coating process, and then dried to form a coating layer on the surface of the ball. In this case, the coating method can be suitably spray coating, electrostatic coating, dipping, or the like, and is not particularly limited.

[0111] The multi-piece solid golf ball of the present invention can be made to conform to the Rules of Golf for competitive use, and can be formed to have an outer diameter of 42.80 mm or less so as not to pass through a ring with an inner diameter of 42.672 mm, and a mass of preferably 45.0 to 45.93 g. [Example]

[0112] EXAMPLES The present invention will be specifically explained below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0113] Of the following Examples 1 to 4 and Comparative Examples 1 to 18, Comparative Examples 7 to 14 are predicted data that can be inferred from the measured values ​​of the other Examples and Comparative Examples, and are not examples that have been actually experimented (implemented). However, these Comparative Examples 7 to 14 are listed in the same category as the other Examples and Comparative Examples.

[0114] [Examples 1 to 4, Comparative Examples 1 to 18] Core formation The rubber compositions of the examples and comparative examples shown in Tables 1 and 2 were prepared and then vulcanized and molded at 155° C. for 15 minutes to prepare solid cores.

[0115] [Table 1]

[0116] [Table 2]

[0117] The details of each component listed in Tables 1 and 2 are as follows: Polybutadiene (I): JSR Corporation, product name "BR730" Polybutadiene (II): JSR Corporation, product name "BR51" Zinc acrylate: "ZN-DA85S" (Nippon Shokubai Co., Ltd.) Organic peroxide: a mixture of 1,1-di(t-butylperoxy)cyclohexane and silica, trade name "Perhexa C-40" (manufactured by NOF Corporation) Zinc stearate: "Zinc Stearate G" (NOF Corporation) Antioxidant: 2,2-methylenebis(4-methyl-6-butylphenol), product name "Nocrac NS-6" (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) Zinc oxide: Product name "Triple Zinc Oxide" (manufactured by Sakai Chemical Industry Co., Ltd.) Pentachlorothiophenol zinc salt: Wako Pure Chemical Industries, Ltd.

[0118] Enveloping layer (inner / outer) Next, for each Example and Comparative Example, an inner envelope layer was formed around the core by injection molding using the inner envelope layer material shown in Table 3, and then an outer envelope layer was formed around the core by injection molding using the outer envelope layer material shown in the same table. For Comparative Examples 15 to 17, a single envelope layer (details are given in the "outer envelope layer" column in the table) was formed around the core by injection molding using the material of No. 2 formulation in Table 3. Note that for Comparative Example 18, no envelope layer was formed.

[0119] Formation of the intermediate layer and cover (outermost layer) Next, for all Examples and Comparative Examples, an intermediate layer was formed around the envelope layer-coated sphere obtained above by injection molding using the intermediate layer material shown in Table 3. Next, a cover (outermost layer) was formed around the intermediate layer-coated sphere of each Example by injection molding using the cover material shown in the same Table. At this time, a predetermined number of dimples common to all Examples and Comparative Examples were formed on the surface of the cover.

[0120] [Table 3]

[0121] The trade names of the main materials listed in the table are as follows: "HPF1000" The Dow Chemical Company's HPF (trademark) 1000 "Himilan" is an ionomer manufactured by Mitsui Dow Polychemicals "AM7315" and "AM7318" are ionomers manufactured by Mitsui Dow Polychemicals "Dynaron 6100P" hydrogenated polymer manufactured by JSR Corporation "Behenic acid" manufactured by NOF Corporation "NAA222-S beads designation" "Calcium hydroxide" manufactured by Shiraishi Kogyo Co., Ltd. "CLS-B designated" "Trimethylolpropane" (TMP) manufactured by Tokyo Chemical Industry Co., Ltd. "Polytail H" is a product name of Mitsubishi Chemical Corporation, a polyhydroxy hydrocarbon polymer "TPU" is a trade name "Pandex" manufactured by DIC Covestro Polymer, an ether-type thermoplastic polyurethane (material hardness: Shore D "48").

[0122] Dimples D use eight types of circular dimples, the details of which are shown in Table 4 below, and their arrangement is as shown in Figure 2. Figure 2(A) shows a plan view of a golf ball with dimples D formed on its surface, and Figure 2(B) shows its side view.

[0123] [Table 4]

[0124] Dimple definition Edge: The highest point on the cross section passing through the center of the dimple Diameter: The diameter of the plane enclosed by the dimple edge Depth: The maximum depth of the dimple from the plane bounded by the dimple edge SR: The ratio of the total dimple area, defined as the plane surrounded by the edges of the dimples, to the area of ​​the ball as if no dimples existed. Dimple volume: The volume of the dimple below the plane surrounded by the dimple edge Cylinder volume ratio: The ratio of the dimple volume to the volume of a cylinder with the same diameter and depth as the dimple. VR: The total volume of the dimples formed below the plane surrounded by the edges of the dimples is the volume of the ball as if no dimples existed.

[0125] The lift coefficient CL1 measured under conditions of a Reynolds number of 80,000 and a spin rate of 2,000 rpm for a ball having the above dimples D formed on the cover surface, CL2 measured under conditions of a Reynolds number of 70,000 and a spin rate of 1,900 rpm, CL3 measured under conditions of a Reynolds number of 200,000 and a spin rate of 2,500 rpm, CL4 measured under conditions of a Reynolds number of 120,000 and a spin rate of 2,250 rpm, and the values ​​of CL2 / CL1 and CL4 / CL3 are shown in Table 5 below. These lift coefficients were measured in accordance with the ITR (Indoor Test Range) established by the USGA.

[0126] [Table 5]

[0127] Formation of coating layer Next, the coating composition "C" shown in Table 6 below was used as the coating composition common to all Examples and Comparative Examples, and the coating was applied to the surface of a large number of covers (outermost layers) using an air spray gun to produce golf balls with a coating layer 15 μm thick.

[0128] [Table 6]

[0129] [Synthesis example of polyester polyol (A)] A reaction apparatus equipped with a reflux condenser, a dropping funnel, a gas inlet tube, and a thermometer was charged with 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, and the mixture was heated to 200-240°C with stirring and heated (reacted) for 5 hours. After that, a "polyester polyol (A)" with an acid value of 4, a hydroxyl value of 170, and a weight average molecular weight (Mw) of 28,000 was obtained. Next, the polyester polyol (A) synthesized above was dissolved in butyl acetate to prepare a varnish having a nonvolatile content of 70% by mass.

[0130] The coating composition in Table 6 was prepared by mixing 23 parts by mass of the polyester polyol solution with 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 to form the base. This mixture had a non-volatile content of 38.0% by mass.

[0131] Elastic work recovery rate The elastic work recovery rate of the paint is measured using a 50 μm thick coating sheet. The measuring device used is the Elionix ultra-micro hardness tester "ENT-2100," and the measurement conditions are as follows: Indenter: Berkovich indenter (material: diamond, angle α: 65.03°) Load F: 0.2mN Loading time: 10 seconds ·Holding time: 1 second ·Unloading time: 10 seconds Indentation work due to return deformation of the coating film W elast (Nm) and mechanical pushing work W total Based on this, the elastic work recovery rate is calculated using the following formula: Elastic work recovery rate = W elast / W total × 100(%)

[0132] Shore C hardness and Shore M hardness The Shore C hardness and Shore M hardness in Table 6 above were measured by preparing 2 mm thick sheets, stacking three of them as test pieces, and using a Shore C hardness tester and a Shore M hardness tester in accordance with ASTM D2240 standard.

[0133] For each of the resulting golf balls, various physical properties such as the internal hardness at each position of the core, the outer diameter of the core and each coated sphere, the thickness and material hardness of each layer, and the surface hardness of each coated sphere were evaluated using the methods described below, and the results are shown in Tables 7 to 10.

[0134] The outer diameter of each sphere: core, (inner and outer) envelope layer coated sphere, and intermediate layer coated sphere Measurements were taken at five randomly selected points on the surface at a temperature of 23.9±1°C, and the average value was used as the measurement value for each sphere. The average value for 10 measurements was then calculated.

[0135] Ball diameter Measurements were taken at 15 randomly selected non-dimpled locations at a temperature of 23.9±1°C, and the average value was used as the measurement value for one ball. The average value for 10 balls was calculated.

[0136] Deflection of the core, the sphere with the inner envelope layer, the sphere with the outer envelope layer, the sphere with the intermediate layer, and the ball Each of the target spherical objects (spheres), including the core, the sphere coated with the inner envelope layer, the sphere coated with the outer envelope layer, the sphere coated with the intermediate layer, and the ball, was placed on a hard board, and the amount of deflection was measured from an initial load of 98 N (10 kgf) to a final load of 1275 N (130 kgf). Note that the above deflection was measured after adjusting the temperature to 23.9°C.

[0137] Core hardness distribution The core surface is spherical, and the needle of the hardness tester was set almost perpendicular to the spherical surface, and the core surface hardness was measured in Shore C hardness in accordance with ASTM D2240. To measure the hardness, an automatic rubber hardness tester "P2" manufactured by Kobunshi Keiki Co., Ltd., equipped with a Shore C hardness tester, was used. The hardness value was read as the maximum value. All measurements were made in an environment of 23±2°C. The core center hardness Cc and the hardness at the midpoint between the core center and surface C mThe hardness was measured by cutting the core into a hemisphere, flattening the cross section, and pressing the needle of a hardness tester perpendicularly to the measurement area. It is expressed as a Shore C hardness value.

[0138] (Inner / outer) Material hardness of the envelope layer, mid layer, and cover (Shore C hardness, Shore D hardness) The resin material for each layer was molded into a 2 mm thick sheet and left to stand at a temperature of 23 ± 2°C for two weeks. Three sheets were stacked together during measurement. The Shore C hardness and Shore D hardness were measured using a Shore C hardness tester and a Shore D hardness tester, respectively, in accordance with the ASTM D2240 standard. To measure the hardness, an automatic rubber hardness tester "P2" manufactured by Kobunshi Keiki Co., Ltd., equipped with a Shore C or Shore D hardness tester, was used. The hardness value was read as the maximum value.

[0139] (Inner and outer) Surface hardness (Shore C hardness, Shore D hardness) of the envelope layer coated sphere, the intermediate layer coated sphere, and the ball Measurements were taken by pressing a needle perpendicularly against the surface of each sphere. The surface hardness of the ball (cover) was measured on the land area on the ball surface where no dimples were formed. Hardness was measured using an automatic rubber hardness tester "P2" manufactured by Kobunshi Keiki Co., Ltd., equipped with a Shore C or Shore D hardness tester. The hardness value was read as the maximum value.

[0140] [Table 7]

[0141] [Table 8]

[0142] [Table 9]

[0143] [Table 10]

[0144] The distance performance (W#1), distance performance (I#6) and spin rate on approach of each golf ball were evaluated by the following methods. The results are shown in Tables 11 and 12.

[0145] Distance performance (W#1) (1) A driver (W#1) was attached to the golf hitting robot, and the distance was measured when hitting the ball at a head speed of 47 m / s, and the results were judged according to the following criteria. The club used was a "TOUR B XD-5" (loft 9.5°) manufactured by Bridgestone Sports Co., Ltd. The spin rate was also measured immediately after hitting the ball using an initial condition measuring device. <Judgment criteria> Total distance over 233.0m Total distance less than 233.0m ×

[0146] (2) The flight distance was measured when hitting with the same driver as above at a head speed of 42 m / s, and was judged according to the following criteria. <Judgment criteria> Total distance: 208.0m or more Total distance less than 208.0m ×

[0147] Distance performance (I#6) A middle iron (I#6) was attached to the golf hitting robot, and the distance was measured when hitting the ball at a head speed of 43 m / s, and the results were judged according to the following criteria. The club used was the "TOUR B X-CB" manufactured by Bridgestone Sports Co., Ltd. The spin rate was also measured using an initial condition measuring device on the ball immediately after hitting. <Judgment criteria> Total distance: 164.0m or more Total distance less than 164.0m ×

[0148] Evaluating spin rate during approach A sand wedge (SW) was attached to a golf hitting robot and hit at a head speed of 16 m / s, and the amount of spin was measured. The amount of spin was also measured immediately after hitting using an initial condition measuring device. The sand wedge (SW) used was the "TOUR B XW-1" manufactured by Bridgestone Sports Co., Ltd. <Judgment criteria> Spin rate of 5300 rpm or more... Spin rate less than 5300 rpm ×

[0149] [Table 11]

[0150] [Table 12]

[0151] As shown in the results in the above table, the golf balls of Comparative Examples 1 to 18 are inferior to the products of the present invention (Examples) in the following respects. In Comparative Example 1, the core diameter is smaller than 30 mm, resulting in a low initial velocity of the ball, and as a result, the flight distance is poor on both driver (W#1) and full shots with an iron. In Comparative Example 2, the core diameter is smaller than 30 mm, resulting in a low initial velocity of the ball, and as a result, the flight distance is poor on both driver (W#1) and full shots with an iron. In Comparative Example 3, the core diameter was smaller than 30 mm, resulting in a low initial ball velocity, and the value obtained by subtracting the center hardness from the core surface hardness was less than 16 in Shore C hardness, resulting in poor flight distances on both driver (W#1) and full iron shots. In Comparative Example 4, the core diameter is smaller than 30 mm, resulting in a low initial velocity of the ball, and as a result, the flight distance is poor on both driver (W#1) and full shots with an iron. In Comparative Example 5, the core diameter is smaller than 30 mm, resulting in a low initial velocity of the ball, and as a result, the flight distance is poor on both driver (W#1) and full shots with an iron. In Comparative Example 6, the core diameter was smaller than 30 mm, resulting in a low initial ball velocity, and the value obtained by subtracting the center hardness from the core surface hardness was less than 16 in Shore C hardness, resulting in poor flight distances on both driver (W#1) and full iron shots. In Comparative Example 7, the relationship (thickness of the outer envelope layer)≧(thickness of the inner envelope layer) is established, resulting in an increased spin rate on the ball and a short flight distance on both driver (W#1) and iron full shots. In Comparative Example 8, the relationship is (thickness of the outer envelope layer)≧(thickness of the inner envelope layer), and as a result, the initial velocity of the ball when actually hit is low, and the flight distance when used with a driver (W#1) is short. Comparative Example 9 has a relationship of (cover thickness)≧(intermediate layer thickness), which results in a high spin rate and a low initial velocity of the ball, resulting in a short distance when used with a driver (W#1). In Comparative Example 10, the value obtained by subtracting the center hardness from the surface hardness of the core was less than 16 in Shore C hardness, resulting in a low initial velocity when the ball was hit and a short flight distance when used with a driver (W#1). In Comparative Example 11, the relationship is (surface hardness of ball)≧(surface hardness of intermediate layer-covered sphere), and as a result, the amount of spin on approaches in short games is insufficient. In Comparative Example 12, the relationship was (surface hardness of the intermediate layer coated ball)≦(surface hardness of the outer envelope layer coated ball), resulting in a high spin rate on full shots and poor distance when hit with a driver (W#1) or iron. In Comparative Example 13, the relationship was (surface hardness of outer envelope layer coated ball)≦(surface hardness of inner envelope layer coated ball), resulting in a large spin rate on full shots with an iron, resulting in a short flight distance. In Comparative Example 14, the relationship was (surface hardness of inner envelope layer-covered sphere)≦(surface hardness of core), resulting in a large amount of spin on full shots and a short flight distance when hit with an iron. Comparative Example 15 is a four-piece club (four-layer structure), and as a result, the initial velocity at actual impact is low and the flight distance when used with a driver (W#1) is short. Comparative Example 16 is a four-piece (four-layer structure), and as a result, the initial velocity at actual impact is low and the flight distance when used with a driver (W#1) is short. Comparative Example 17 is a four-piece club (four-layer structure), and as a result, the initial velocity at actual impact is low and the flight distance when used with a driver (W#1) is short. Comparative Example 18 is a three-piece (three-layer structure), and as a result, the initial velocity at actual impact is low and the flight distance when used with a driver (W#1) is short.

Claims

1. A multi-piece solid golf ball having a core, an envelope layer, an intermediate layer, and a cover, wherein the core is formed of a single layer or multiple layers, primarily made of a base rubber, the core has an overall diameter of 30 mm or more, the envelope layer is formed of two layers, an inner layer and an outer layer, and the intermediate layer and the cover are each formed of a single layer made of a resin material, and the surface hardness of the core, the surface hardness of a sphere obtained by covering the core with the inner envelope layer (inner envelope layer-covered sphere), the surface hardness of a sphere obtained by covering the inner envelope layer-covered sphere with the outer envelope layer (outer envelope layer-covered sphere), and the surface hardness of a sphere obtained by covering the outer envelope layer-covered sphere with the intermediate layer (intermediate layer-covered sphere), and the surface hardness of the ball are all determined by the following formula: Core surface hardness < inner envelope layer coated ball surface hardness < outer envelope layer coated ball surface hardness < middle layer coated ball surface hardness > Ball surface hardness (However, the hardness of each layer mentioned above means the Shore C hardness value.) the value obtained by subtracting the center hardness from the surface hardness of the core is 16 or greater in Shore C hardness, the center hardness of the core is 60 or greater in Shore C hardness, the surface hardness of the outer envelope layer-covered sphere is 52 or greater and 65 or less in Shore D hardness, and the thicknesses of the envelope layer, intermediate layer, and cover satisfy the following two formulas: Cover thickness < intermediate layer thickness, and outer envelope layer thickness < inner envelope layer thickness A multi-piece solid golf ball characterized by satisfying the relationship:

2. The relationship between the center hardness (Cc), the surface hardness (Cs), and the hardness (Cm) at the midpoint between the surface and the center of the core is: (Cs-Cm) / (Cm-Cc)≧1.5 2. The multi-piece solid golf ball of claim 1, wherein

3. Core volume (mm 3 ) × Shore C hardness (Cm) at the midpoint between the core surface and the core center is Core vh, and the volume of the inner envelope layer (mm 3 ) × the surface hardness (Shore C) of the inner envelope layer coated sphere is IE vh, and the volume of the outer envelope layer (mm 3 3. The multi-piece solid golf ball according to claim 1, wherein the condition 0.4≦(OE vh + IE vh) / Core vh ≦1.1 is satisfied, where OE vh is the surface hardness (Shore C) of the outer envelope layer-covered sphere.

4. 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 can be expressed by the following formula: 0.900≦CL2 / CL1 4. The multi-piece solid golf ball according to claim 1, wherein the above formula (1) is satisfied.

5. 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 can be expressed by the following formula: 1.250≦CL4 / CL3≦1.300 5. The multi-piece solid golf ball according to claim 1, wherein the above formula (1) is satisfied.

6. 6. The multi-piece solid golf ball according to claim 1, wherein the number of dimples arranged on the surface of the cover is 323 to 380.

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