Multi-piece solid golf balls

Abstract

To provide a golf ball which achieves a good travel distance on full shots with a driver, utility and iron, has a good spin in a short game, has a soft feel at impact on all shots, and is useful to amateur golfers.SOLUTION: In a golf ball having a core 1, an envelope layer 2, an intermediate layer and a cover, a difference between the center hardness and a surface hardness of the core is set in a specific range, the intermediate layer is formed of a resin material that includes a high-acid ionomer, and the hardness relation (the Shore C hardness) among the hardness of the core center, a surface hardness of an envelope layer-encased sphere and a surface hardness of an intermediate layer-encased sphere satisfies the following two formulas: the surface hardness of the envelope layer-encased sphere<the surface hardness of the intermediate layer-encased sphere; and the surface hardness of the intermediate layer-encased sphere-the hardness of the core center (the Shore C hardness)≥40. The deflection (mm) is at least 2.7 mm when a prescribed load is applied on the ball.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Conventionally, many efforts have been made to design balls with a multi-layer structure, and many balls have been developed that satisfy not only professional golfers but also advanced and intermediate amateur golfers. For example, functional multi-piece solid golf balls in which the surface hardness of each layer of the core, surrounding layer, intermediate layer, and cover (outermost layer) is optimized are becoming widespread. In addition, several techniques have been proposed to provide high-performance golf balls for professionals and intermediate and advanced players by focusing on the core hardness distribution, which occupies most of the volume of the ball, and designing various modes of core internal hardness.

[0003] Examples of such technical documents include the following Patent Documents 1 to 14. These golf balls relate to golf balls with a multi-layer structure of four or more layers, and are patent documents that focus on the surface hardness of each layer of the core, surrounding layer, intermediate layer, and cover (outermost layer), the relationship between the ball diameter and the core diameter, and the hardness distribution of the core.

[0004] However, the proposed golf balls still have room for improvement in terms of optimizing the hardness distribution of the core and the thickness relationship with each layer. That is, the proposed golf balls do not provide a satisfactory flight distance for amateur users who do not have a high head speed, particularly for full shots with a utility or iron. In addition, some of the proposed golf balls cannot provide a sufficiently high spin performance when approaching in order to obtain superior flight distance performance even in iron shots, and are not highly playable or do not provide a good feel on full shots. Therefore, there is a demand for proposals and developments of golf balls for amateur golfers that improve the flight on full shots with a utility or iron, provide a soft and good feel on all full shots, and are highly playable in short games. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2006-326301 A [Patent Document 2] JP 2007-319667 A [Patent Document 3] JP 2007-330789 A [Patent Document 4] JP 2008-068077 A [Patent Document 5] JP 2008-149131 A [Patent Document 6] JP 2009-034507 A [Patent Document 7] JP 2009-095358 A [Patent Document 8] JP 2009-095364 A [Patent Document 9] JP 2009-095365 A [Patent Document 10] JP 2009-095369 A [Patent Document 11] JP 2012-071163 A [Patent Document 12] JP 2016-101254 A [Patent Document 13] JP 2016-101256 A [Patent Document 14] JP 2016-116627 A 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 has as its object to provide a golf ball for amateur golfers which provides advantageous distance on full shots with all clubs, including drivers (W#1), utilities and irons, has excellent spin performance on approaches making it ideal for short games, and further provides a soft and good feel on all shots. [Means for solving the problem]

[0007] The present inventors have conducted intensive research to achieve the above object, and have found that a golf ball having a core, an envelope layer, an intermediate layer, and a cover is formed softly by using a urethane resin material as the cover material, the envelope layer is softer than the intermediate layer, and the intermediate layer resin material contains an ionomer with a high acid content, and the hardness difference between the center and the surface of the core is optimized, and the deflection amount of the entire ball under a given load is optimized, so that the spin amount during a full shot can be reduced compared to conventional golf balls, good flight distances can be obtained with all clubs, including drivers (W#1), utilities, and irons, good spin can be applied in short games, a soft hitting feel can be imparted, and durability against repeated impacts is also good. For amateur golfers with low head speed, it has been found that a golf ball can be finished that is advantageous in terms of flight distance during full shots with drivers (W#1), utilities, and irons, and that can maintain a high level of spin performance during approaches, making it advantageous in terms of game play, and has been completed.

[0008] Accordingly, the present invention provides a multi-piece solid golf ball as follows: 1. A multi-piece solid golf ball comprising a core, an envelope layer, an intermediate layer, and a cover, the core being formed in a single layer from a rubber composition, the envelope layer being formed in one or more layers from a resin material, and the intermediate layer and the cover being each formed in a single layer from a resin material, wherein the difference between the surface hardness and center hardness of the core is 20 or more in Shore C hardness, the resin material of the intermediate layer contains an ionomer having a high acid content, and the hardness relationship (surface hardness means Shore C hardness) between the center hardness of the core, the surface hardness of a sphere obtained by covering the core with the envelope layer (enveloping layer-covered sphere), and the surface hardness of a sphere obtained by covering the envelope layer-covered sphere with an intermediate layer (intermediate layer-covered sphere) is expressed by the following formulas (1) and (2): Surface hardness of sphere coated with surrounding layer < Surface hardness of sphere coated with intermediate layer (1) Surface hardness of the intermediate layer-coated sphere - Center hardness of the core (Shore C hardness) ≧ 40 (2) The ball is deflected 2.7 mm or more when the ball is loaded from an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf). When the lift coefficient measured under the conditions of the Reynolds number of 200,000 and the spin rate of 2,500 rpm is defined as CL3, and the lift coefficient measured under the conditions of the Reynolds number of 120,000 and the spin rate of 2,250 rpm is defined as CL4, CL3 and CL4 are expressed by the following formula: 1.250 ≦ CL4 / CL3 ≦ 1.300 Fulfill A multi-piece solid golf ball. 2. 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 1. A golf ball as described above that satisfies the above requirements. 3 The diameter of the core is 35.1 to 41.3 mm, and in the hardness distribution of the core, the Shore C hardness at the center of the core is Cc, the Shore C hardness at the midpoint M between the center and the surface of the core is Cm, the Shore C hardnesses at positions 2 mm, 4 mm, and 6 mm inward from the midpoint M are Cm-2, Cm-4, and Cm-6, respectively, the Shore C hardnesses at positions 2 mm, 4 mm, and 6 mm outward from the center M are Cm+2, Cm+4, and Cm+6, respectively, and the Shore C hardness of the surface of the core is Cs. The following areas A to F are then determined. ·Area A: 1 / 2×2×(Cm-4-Cm-6) ·Area B: 1 / 2×2×(Cm-2-Cm-4) ·Area C: 1 / 2×2×(Cm-Cm-2) ·Area D: 1 / 2×2×(Cm+2-Cm) ·Area E: 1 / 2×2×(Cm+4-Cm+2) ·Area F: 1 / 2×2×(Cm+6-Cm+4) For the above, the value of (Area E + Area F) - (Area A + Area B) is 2.0 or more. 1 or 2 The golf ball described herein. 4 The thickness relationship of each layer is given by the following formula (3): Cover thickness < Intermediate layer thickness < Enveloping layer thickness (3) Satisfy the above 1~ 32. A multi-piece solid golf ball according to claim 1 . 5 Regarding the surface hardness of the core or each coated sphere, Core surface hardness < Surface hardness of the surrounding layer covered sphere < Surface hardness of the intermediate layer covered sphere > Ball surface hardness (1') Satisfy the above 1~ 4 2. A multi-piece solid golf ball according to claim 1 . 6 The material hardness of the intermediate layer is 64 or more in Shore D hardness. 5 2. A multi-piece solid golf ball according to claim 1 . 7 In the above formula (2), the upper limit of the value of (surface hardness of the intermediate layer-coated sphere) - (center hardness of the core) is 53 or less in Shore C hardness. 6 2. A multi-piece solid golf ball according to claim 1 . 8 The above 1 to 3 in which the surrounding layer is a single layer 7 2. A multi-piece solid golf ball according to claim 1 . 9 The areas A to F of the core hardness distribution are calculated by the following formula: (Area D+Area E)-(Area B+Area C)≧2.0 Satisfy the above 3 2. A multi-piece solid golf ball as described above. Effect of the Invention

[0009] The multi-piece solid golf ball of the present invention provides good distances for driver (W#1), utility and iron full shots, good spin in short games, soft feel on impact on all shots, and excellent durability against repeated impacts. It is a multi-layer golf ball that is particularly useful as a golf ball for amateur golfers. [Brief description of the drawings]

[0010] [Figure 1]1 is a schematic cross-sectional view of a multi-piece solid golf ball according to one embodiment of the present invention. [Diagram 2] FIG. 11 is a schematic diagram illustrating areas A to F of the core hardness distribution, using core hardness distribution data of Example 2. [Diagram 3] 2 is a graph showing the core hardness distributions of Examples 1 to 5 and Comparative Examples 3 and 8. [Figure 4] 2 is a graph showing the hardness distribution of cores of Comparative Examples 1, 2 and 4 to 7. [Diagram 5] FIG. 11 is a plan view showing the form (pattern) of dimples common to Examples other than Example 5 and Comparative Examples. [Figure 6] FIG. 13 is a plan view showing the form (pattern) of dimples in Example 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present invention will now be described in further detail. The multi-piece solid golf ball of the present invention has a core, an envelope layer, an intermediate layer, and a cover, and an example thereof is shown in FIG. 1. The golf ball G shown in FIG. 1 has a core 1, an envelope layer 2 covering the core 1, an intermediate layer 3 covering the envelope layer, and a cover 4 covering the intermediate layer 3. The cover 4 is located at the outermost layer in the layer structure of the golf ball, excluding the paint layer. In the present invention, the intermediate layer and the cover (outermost layer) are formed as a single layer, but the envelope layer may be formed as a single layer or as two or more layers. In addition, a large number of dimples D are usually formed on the surface of the cover (outermost layer) 4 to improve aerodynamic characteristics. In addition, although not shown in the figure, a paint layer 5 is usually formed on the surface of the cover 4. Each of the above layers will be described in detail below.

[0012] The core is mainly made of rubber. Specifically, a rubber composition can be prepared by blending a base rubber with a co-crosslinking agent, an organic peroxide, an inert filler, an organic sulfur compound, etc. The base rubber is preferably polybutadiene.

[0013] As the type of polybutadiene, commercially available 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. In addition to the polybutadiene, other rubber components can 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 the 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.

[0014] Examples of the co-crosslinking agent include unsaturated carboxylic acids and metal salts of unsaturated carboxylic acids. Specific examples of the 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 include, for example, 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 and acrylic acid, with zinc acrylate being particularly preferred.

[0015] The unsaturated carboxylic acid and / or metal salt thereof is blended in an amount of usually at least 5 parts by weight, preferably at least 9 parts by weight, and more preferably at least 13 parts by weight, with the upper limit usually not exceeding 60 parts by weight, preferably not exceeding 50 parts by weight, and more preferably not exceeding 40 parts by weight, per 100 parts by weight of the base rubber. If the blended amount is too high, the ball may become too hard, resulting in an unbearable feel on impact, whereas if the blended amount is too low, the resilience may decrease.

[0016] As the organic peroxide, commercially available products can be used, and for example, Percumyl D (manufactured by Nippon Oil & Fats Co., Ltd.), Perhexa C-40, Perhexa 3M (manufactured by Nippon Oil & Fats Co., Ltd.), Luperco 231XL (manufactured by Atochem Co., Ltd.), etc. can be suitably used. These may be used alone or in combination of two or more. The amount of organic peroxide to be blended is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.5 parts by mass or more, and is preferably 5 parts by mass or less, more preferably 4 parts by mass or less, even more preferably 3 parts by mass or less, and most preferably 2.5 parts by mass or less, per 100 parts by mass of the base rubber. If the amount is too large or too small, it may not be possible to obtain a suitable hitting feel, durability, and resilience.

[0017] Other examples of compounding agents that can be compounded with the base rubber include inert fillers, and examples of such compounds that can be suitably used include zinc oxide, barium sulfate, and calcium carbonate. These may be used alone or in combination of two or more. The amount of inert filler compounded is preferably 1 part by weight or more, more preferably 5 parts by weight or more, and preferably 50 parts by weight or less, more preferably 40 parts by weight or less, and even more preferably 36 parts by weight or less, per 100 parts by weight of the base rubber. If the amount compounded is too large or too small, it may not be possible to obtain the appropriate mass and suitable resilience.

[0018] Furthermore, an anti-aging agent can be added as necessary, and examples of commercially available products include Nocrac NS-6 and Nocrac NS-30 (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.), Yoshinox 425 (manufactured by Yoshitomi Pharmaceutical Co., Ltd.), etc. These may be used alone or in combination of two or more kinds.

[0019] The amount of the antioxidant blended per 100 parts by mass of the base rubber is preferably at least 0 part by mass, more preferably at least 0.05 parts by mass, and particularly preferably at least 0.1 parts by mass, with the upper limit being preferably no more than 3 parts by mass, more preferably no more than 2 parts by mass, particularly preferably no more than 1 part by mass, and most preferably no more than 0.5 parts by mass. If the blended amount is too high or too low, suitable resilience and durability may not be obtained.

[0020] In addition, the core may contain an organic sulfur compound to provide good resilience. The organic sulfur compound is not particularly limited as long as it can improve the resilience of the golf ball, and examples thereof include thiophenols, thionaphthols, halogenated thiophenols, and metal salts thereof. More specifically, pentachlorothiophenol, pentafluorothiophenol, pentabromothiophenol, parachlorothiophenol, zinc salt of pentachlorothiophenol, zinc salt of pentafluorothiophenol, zinc salt of pentabromothiophenol, zinc salt of parachlorothiophenol, diphenyl polysulfide with 2 to 4 sulfur, dibenzyl polysulfide, dibenzoyl polysulfide, dibenzothiazoyl polysulfide, dithiobenzoyl polysulfide, and the like are included, and the zinc salt of pentachlorothiophenol is particularly preferably used. The amount of the organic sulfur compound is preferably 0 parts by weight or more, more preferably 0.05 parts by weight or more, and even more preferably 0.1 parts by weight or more, with the upper limit being preferably 5 parts by weight or less, more preferably 3 parts by weight or less, and even more preferably 2.5 parts by weight or less, per 100 parts by weight of the base rubber. If the amount is too large, the effect of improving resilience (especially when hitting with W#1) cannot be expected any more, the core may become too soft, or the feeling of hitting may become poor. On the other hand, if the amount is too small, the effect of improving resilience cannot be expected.

[0021] More specifically, by directly blending water (materials containing water) into the core material, the decomposition of organic peroxide during core blending can be promoted. It is also known that the decomposition efficiency of organic peroxide in the rubber composition for the core changes depending on the temperature, and the higher the temperature, the higher the decomposition efficiency. If the temperature is too high, the amount of decomposed radicals becomes too large, and the radicals recombine with each other or become inactivated. As a result, the radicals that work effectively for crosslinking decrease. Here, when the organic peroxide decomposes during core vulcanization and generates decomposition heat, the temperature near the core surface remains almost the same as that of the vulcanization mold, but the temperature near the core center becomes much higher than the mold temperature because the decomposition heat of the organic peroxide decomposed from the outside accumulates. When water (materials containing water) is directly blended into the core, water acts to promote the decomposition of the organic peroxide, so that the above-mentioned radical reaction can be changed between the core center and the core surface. In other words, the decomposition of the organic peroxide is further promoted near the center of the core, and the inactivation of radicals is further promoted, further reducing the amount of available radicals, making it possible to obtain a core having a significantly different crosslink density between the core center and the core surface, and also a core having different dynamic viscoelastic properties in the center of the core.

[0022] The water to be mixed in the core material is not particularly limited, and may be distilled water or tap water, but it is particularly preferable to use distilled water that does not contain impurities. The amount of water mixed is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and the upper limit is preferably 5 parts by mass or less, more preferably 4 parts by mass or less, per 100 parts by mass of the base rubber.

[0023] The core can be produced by vulcanizing and curing a rubber composition containing the above-mentioned components. For example, the rubber composition is kneaded using a kneading machine such as a Banbury mixer or a roll, compression molded or injection molded using a core mold, and the molded body is appropriately heated at a temperature sufficient for the organic peroxide and co-crosslinking agent to act, that is, 100 to 200°C, preferably 140 to 180°C, for 10 to 40 minutes, to cure the molded body.

[0024] The core may be formed in a single layer.

[0025] The diameter of the core is usually 35.1 to 41.3 mm, preferably 35.4 mm or more, more preferably 35.8 mm or more, and the upper limit is preferably 39.2 mm or less, more preferably 38.3 mm or less. If the diameter of the core is too small, the initial velocity of the ball may be low, the deflection hardness of the entire ball may be high, and the spin rate may increase during a full shot, making it impossible to obtain the desired flight distance. On the other hand, if the diameter of the core is too large, the spin rate may increase during a full shot, making it impossible to obtain the desired flight distance, and the durability against cracking may be poor when repeatedly hit.

[0026] The deflection (mm) of the core when it is loaded with an initial load of 98N (10kgf) to a final load of 1,275N (130kgf) is not particularly limited, but is preferably 3.6mm or more, more preferably 3.8mm or more, and even more preferably 4.0mm or more, with the upper limit being preferably 6.0mm or less, more preferably 5.7mm or less, and even more preferably 5.4mm or less. If the deflection of the core is too small, i.e., if the core is too hard, the ball may have too much spin and may not fly, or the hitting feel may be too hard. On the other hand, if the deflection of the core is too large, i.e., if the core is too soft, the resilience of the ball may be too low, and the ball may not fly, or the hitting feel may be too soft, or the cracking durability during repeated impact may be poor.

[0027] 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.

[0028] The center hardness (Cc) of the core is not particularly limited, but is preferably 45 or more, more preferably 47 or more, and even more preferably 48 or more. The upper limit is also not particularly limited, but is preferably 61 or less, more preferably 59 or less, and even more preferably 57 or less. If this value is too large, the spin may increase, making it impossible to obtain the desired flight distance, or the hitting feel may be too hard. On the other hand, if the value is too small, the resilience may decrease, making it impossible to obtain the desired flight distance, or the durability against cracking when repeatedly hit may be poor.

[0029] The hardness (Cm-6) at a position 6 mm inward from the midpoint M between the center and the surface of the core (hereinafter also referred to as "midpoint M") is not particularly limited, but is preferably 45 or more, more preferably 47 or more, and even more preferably 49 or more, and there is no particular upper limit either, but is preferably 61 or less, more preferably 59 or less, and even more preferably 57 or less. Any deviation from these hardnesses may result in the same adverse effects as those described for the center hardness (Cc) of the core.

[0030] From the middle position M of the core toward the center of the core, the inner side (hereinafter simply referred to as the "inner side") The position hardness (Cm-4) of the core is not particularly limited, but is preferably 48 or more, more preferably 50 or more, and even more preferably 52 or more, and there is no particular upper limit, but is preferably 62 or less, more preferably 60 or less, and even more preferably 58 or less. 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.

[0031] The hardness (Cm-2) at a position 2 mm inward from the middle position M of the core is not particularly limited, but is preferably at least 50, more preferably at least 52, and even more preferably at least 54, and there is no upper limit either, but is preferably at most 64, more preferably at most 62, and even more preferably at most 60. Any deviation from these hardness limits may result in the same adverse effects as those described for the center hardness (Cc) of the core.

[0032] The cross-sectional hardness (Cm) of the core at the middle position M is not particularly limited, but is preferably at least 54, more preferably at least 56, and even more preferably at least 58. There is also no particular upper limit, but it is preferably at most 68, more preferably at most 66, and even more preferably at most 64. Any deviation from these hardness limits may result in the same adverse effects as those described for the center hardness (Cc) of the core.

[0033] The hardness (Cm+2) at a position 2 mm from the center position M of the core toward the outside of the core surface (hereinafter simply referred to as "outside") is not particularly limited, but is preferably 57 or more, more preferably 60 or more, and even more preferably 62 or more, and the upper limit is also not particularly limited, but is preferably 74 or less, more preferably 71 or less, and even more preferably 69 or less. If this value is too large, the durability to cracking when repeatedly hit may be poor, or the hitting feel may be too hard. On the other hand, if the value is too small, the resilience may be too low, or the spin may be too high during a full shot, making it difficult to obtain the desired flight distance.

[0034] The hardness (Cm+4) at a position 4 mm outward from the central position M of the core is not particularly limited, but is preferably 62 or more, more preferably 64 or more, and even more preferably 66 or more, and there is no upper limit either, but is preferably 77 or less, more preferably 76 or less, and even more preferably 74 or less. Any deviation from these hardness limits may result in the same adverse effects as those described for the hardness (Cm+2) at a position 2 mm away from the central position M of the core.

[0035] The hardness (Cm+6) at a position 6 mm outward from the middle position M of the core is not particularly limited, but is preferably 63 or more, more preferably 65 or more, and even more preferably 67 or more, and there is no upper limit either, but is preferably 81 or less, more preferably 79 or less, and even more preferably 77 or less. Any deviation from these hardness limits may result in the same adverse effects as those described for the hardness (Cm+2) at a position 2 mm away from the middle position M of the core.

[0036] The surface hardness (Cs) of the core is not particularly limited, but is preferably 69 or more, more preferably 71 or more, and even more preferably 73 or more. The upper limit is also not particularly limited, but is preferably 87 or less, more preferably 85 or less, and even more preferably 83 or less. If this value is too large, the durability against cracking when repeatedly hit may be poor, or the hitting feel may be too hard. On the other hand, if the value is too small, the resilience may be too low, or the spin rate may be too high during a full shot, making it impossible to obtain the desired flight distance.

[0037] In order to increase the hardness difference between the inside and outside of the core, the hardness difference between the center and the surface of the core is optimized. That is, the value of the core surface hardness (Cs)-core center C hardness (Cc) is preferably 20 or more in Shore C hardness, more preferably 22 or more, and even more preferably 24 or more. The upper limit is not particularly limited, but it can be preferably 35 or less, more preferably 30 or less, and even more preferably 28 or less. If the hardness difference is too small, the spin rate increases when a full shot is made, and the target flight distance may not be obtained. On the other hand, if the hardness difference is too large, the crack durability may deteriorate when repeatedly hitting, or the actual initial velocity may decrease, and the target flight distance may not be obtained. The center hardness (Cc) means the hardness measured at the center of the cross section obtained by cutting the core in half (through the center), and the surface hardness (Cs) means the hardness measured at the surface (spherical surface) of the core.

[0038] In addition, in the above core hardness distribution, the following areas A to F ·Area A: 1 / 2×2×(Cm-4-Cm-6) ·Area B: 1 / 2×2×(Cm-2-Cm-4) ·Area C: 1 / 2×2×(Cm-Cm-2) ·Area D: 1 / 2×2×(Cm+2-Cm) ·Area E: 1 / 2×2×(Cm+4-Cm+2) ·Area F: 1 / 2×2×(Cm+6-Cm+4) For the above, the value of (area E+area F)-(area A+area B) is preferably 2.0 or more, more preferably 4.0 or more, and even more preferably 6.0 or more, and the upper limit is preferably 20.0 or less, more preferably 16.0 or less, and even more preferably 12.0 or less. If this value is too large, the durability against cracking may deteriorate when repeatedly struck. On the other hand, if the above value is too small, the spin rate increases when a full shot is made, and the target flight distance may not be obtained. Note that FIG. 2 shows a schematic diagram illustrating areas A to F using the core hardness distribution data of Example 2. In this way, areas A to F are the areas of each triangle with the difference between each specific distance as the base and the difference between the hardness at each position as the height.

[0039] Regarding the above areas B to E, the value of (area D + area E) - (area B + area C) is not particularly limited, but is preferably 2.0 or more, more preferably 4.0 or more, and even more preferably 6.0 or more, and the upper limit is preferably 20.0 or less, more preferably 16.0 or less, and even more preferably 12.0 or less. If this value is too large, the durability against cracking when repeatedly hit may deteriorate. On the other hand, if the above value is too small, the spin rate increases when a full shot is made, and the target flight distance may not be obtained.

[0040] The above core hardness distribution areas A to F are subject to the following conditions: Area A<Area C<(Area E+Area F) It is preferable that the following condition is satisfied, and more preferable that the following condition is satisfied: Area A<Area B<Area C<(Area E+Area F) More preferably, Area A<Area B<Area C<Area D<(Area E+Area F) If this relationship is not satisfied, the spin will be too much when making a full shot with a utility or iron, and the desired flight distance may not be achieved.

[0041] The material hardness of the envelope layer is not particularly limited, but is preferably 47 or more, more preferably 49 or more, and even more preferably 51 or more in Shore D hardness, with the upper limit being preferably 62 or less, more preferably 60 or less, and even more preferably 57 or less. The surface hardness of a sphere in which the core is covered with the envelope layer (enveloping layer covered sphere) is preferably 53 or more, more preferably 55 or more, and even more preferably 57 or more in Shore D hardness, with the upper limit being preferably 68 or less, more preferably 66 or less, and even more preferably 63 or less. If the material hardness and surface hardness of the envelope layer are too softer than the above range, the spin may be too strong during 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 hitting feeling may be hard, the cracking durability may be poor when repeatedly hitting, or the spin may increase during a full shot with a utility or iron, resulting in a loss of distance.

[0042] The surface hardness of the envelope layer-covered sphere is set to be lower than that of the intermediate layer-covered sphere. If the envelope layer-covered sphere has a higher surface hardness than the intermediate layer-covered sphere, the spin rate increases on full shots, which can result in a loss of distance and a poor feel on impact.

[0043] The material hardness of the surrounding layer, expressed in Shore C hardness, is preferably 72 or more, more preferably 75 or more, and even more preferably 78 or more, with an upper limit of preferably 92 or less, more preferably 90 or less, and even more preferably 88 or less. The surface hardness of the surrounding layer-covered sphere, expressed in Shore C hardness, is preferably 80 or more, more preferably 83 or more, and even more preferably 86 or more, with an upper limit of preferably 97 or less, more preferably 95 or less, and even more preferably 93 or less.

[0044] The thickness of the envelope layer is preferably 0.8 mm or more, more preferably 0.9 mm or more, and even more preferably 1.0 mm or more. On the other hand, the upper limit of the thickness of the envelope layer is preferably 2.0 mm or less, more preferably 1.7 mm or less, and even more preferably 1.4 mm or less. If the envelope layer is too thin, the low spin effect may be insufficient when a full shot is made with a utility or iron, and the target flight distance may not be obtained. On the other hand, if the envelope layer is too thick, the initial velocity of the entire ball may be low, and the actual initial velocity may be too low, and the target flight distance may not be obtained. In addition, it is preferable that the envelope layer is formed thicker than the intermediate layer described later, or that both layers have the same thickness.

[0045] The material for the envelope layer is not particularly limited, but various thermoplastic resin materials can be suitably used. Particularly preferred examples of the material 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) an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester ternary random copolymer and / or a metal ion neutralized product of 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 50:50, (C) 5 to 120 parts by mass of a fatty acid and / or a derivative thereof having a molecular weight of 228 to 1500, and (D) 0.1 to 17 parts by mass of a basic inorganic metal compound capable of neutralizing unneutralized acid groups in the above components (A) and (C). An example of the resin composition is a resin composition containing the above as essential components.

[0046] As for the above components (A) to (D), for example, the resin materials (A) to (D) for the intermediate layer described in JP-A-2010-253268 can be suitably used.

[0047] Examples of the non-ionomeric thermoplastic elastomer include polyolefin-based elastomers (including polyolefins and metallocene polyolefins), polystyrene-based elastomers, diene-based polymers, polyacrylate-based polymers, polyamide-based elastomers, polyurethane-based elastomers, polyester-based elastomers, polyacetals, and in particular thermoplastic polyether ester elastomers such as thermoplastic polyether ester elastomers.

[0048] The above resin materials can be appropriately mixed with any additives depending on the application, such as pigments, dispersants, antioxidants, ultraviolet absorbers, and light stabilizers.

[0049] Next, the intermediate layer will be described. The material hardness of the intermediate layer is not particularly limited, but is preferably 64 or more, more preferably 65 or more, and even more preferably 66 or more in Shore D hardness, with the upper limit being preferably 75 or less, more preferably 70 or less, and even more preferably 68 or less. The surface hardness of the sphere (intermediate layer-coated sphere) obtained by coating the outer envelope layer-coated sphere with the intermediate layer is preferably 68 or more, more preferably 69 or more, and even more preferably 70 or more in Shore D hardness, with the upper limit being preferably 81 or less, more preferably 76 or less, and even more preferably 74 or less. If the material hardness and surface hardness of these intermediate layers are too softer than the above ranges, the spin may be too strong during 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 durability against cracking due to repeated impacts may be poor, or the hitting feeling during a putter or short approach may be too hard.

[0050] The material hardness of the intermediate layer, expressed in Shore C hardness, is preferably 90 or more, more preferably 92 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. The surface hardness of the intermediate layer-covered sphere, expressed in Shore C hardness, is preferably 95 or more, more preferably 96 or more, and even more preferably 97 or more, with the upper limit being preferably 100 or less, more preferably 99 or less, and even more preferably 98 or less.

[0051] The surface hardness of the intermediate layer-covered sphere is made greater than the surface hardness of the ball. If the surface hardness of the ball is greater than that of the intermediate layer-covered sphere, the ball may be less durable against cracking due to repeated impacts and the controllability during short games may be impaired.

[0052] 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. On the other hand, 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. It is preferable that the thickness of the intermediate layer is thicker than the cover (outermost layer) described later. If the thickness of the intermediate layer is out of the above range or is thinner than the cover, the low spin effect during full shots with a driver (W#1), utility or iron may be insufficient, resulting in a loss of distance. In addition, if the intermediate layer is thinner than the above range, the crack resistance during repeated impacts and the durability at low temperatures may be deteriorated.

[0053] 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 the components (A) to (D) described in the material of the surrounding layer.

[0054] Specific examples of the ionomer resin material include sodium-neutralized ionomer resins and zinc-neutralized ionomer resins, and these may be used alone or in combination of two or more.

[0055] Particularly preferred is an embodiment in which a zinc-neutralized ionomer resin and a sodium-neutralized ionomer resin are mixed and used as the main material. The blending ratio of zinc-neutralized / sodium-neutralized (mass ratio) is 5 / 95 to 95 / 5, preferably 10 / 90 to 90 / 10, and more preferably 15 / 85 to 85 / 15. If the Zn-neutralized ionomer and the Na-neutralized ionomer are not included within this ratio, the resilience may be too low to obtain the desired flight, or the crack resistance may be poor when repeatedly struck at room temperature, or the crack resistance may be poor at low temperatures (below zero).

[0056] The resin material of the intermediate layer may contain a high acid content ionomer. For example, a commercially available ionomer resin with a high acid content of 16% by mass or more may be blended with a normal ionomer resin. This blend provides good distance with low spin on full shots with a driver (W#1), utility or iron.

[0057] The content of unsaturated carboxylic acid (acid content) contained in the high acid content ionomer resin is usually 16% by mass or more, preferably 17% by mass or more, more preferably 18% by mass or more, and the upper limit is preferably 22% by mass or less, more preferably 21% by mass or less, and even more preferably 20% by mass or less. If this value is too small, the spin increases during full shots with a driver (W#1), utility or iron, and the desired flight distance may not be obtained. On the other hand, if the above value is too large, the hitting feeling may become too hard, or the cracking durability during repeated hitting may be deteriorated.

[0058] The high acid content ionomer resin is preferably 20% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more, with the upper limit being 100% by mass or less, preferably 90% by mass or less, and more preferably 85% by mass or less, based on 100% by mass of the resin material. If the amount of the high acid content ionomer resin is too small, the spin rate at the time of full shot increases, and the flight distance may not be achieved. On the other hand, if the amount of the high acid content ionomer resin is too large, the durability against repeated impacts may deteriorate.

[0059] Any additives can be appropriately blended into the intermediate layer material depending on the application. For example, various additives such as pigments, dispersants, anti-aging agents, UV absorbers, and light stabilizers can be added. When these additives are blended, the blending amount is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and the upper limit is preferably 10 parts by mass or less, more preferably 4 parts by mass or less, relative to 100 parts by mass of the base resin.

[0060] 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. Furthermore, after the polishing process, it is preferable to apply a primer (adhesive) to the intermediate layer surface or to add an adhesion enhancer to the material.

[0061] The specific gravity of the intermediate layer material is usually less than 1.1, preferably 0.90 to 1.05, and more preferably 0.93 to 0.99. If it is outside this range, the resilience of the entire ball will decrease, resulting in a shorter flight distance and reduced durability against cracking due to repeated impacts.

[0062] Next, the cover (outermost layer) will be described. The material hardness of the cover is not particularly limited, but is preferably 30 or more, more preferably 35 or more, and even more preferably 40 or more in Shore D hardness, with the upper limit being preferably 53 or less, more preferably 50 or less, and even more preferably 47 or less. The surface hardness (ball surface hardness) of the sphere in which the intermediate layer-covered sphere is covered with the cover is preferably 50 or more, more preferably 53 or more, and even more preferably 56 or more in Shore D hardness, with the upper limit being preferably 70 or less, more preferably 65 or less, and even more preferably 60 or less. If the material hardness of the cover and the surface hardness of the ball are too softer than the above ranges, the amount of spin increases during full shots with a driver (W#1), utility, or iron, and the desired flight distance may not be achieved. If the material hardness and surface hardness are too hard, the desired amount of spin may not be applied during approach, or durability against repeated impact may be deteriorated.

[0063] The material hardness of the cover, expressed in Shore C hardness, is preferably at least 50, more preferably at least 57, and even more preferably at least 63, with an upper limit of preferably 80 or less, more preferably 74 or less, and even more preferably 70 or less. The surface hardness of the ball, expressed in Shore C hardness, is preferably at least 73, more preferably at least 78, and even more preferably 83 or more, with an upper limit of preferably 95 or less, more preferably 92 or less, and even more preferably 90 or less.

[0064] The thickness of the cover is preferably 0.3 mm or more, more preferably 0.45 mm or more, and even more preferably 0.6 mm or more. On the other hand, the upper limit of the cover thickness is preferably 1.2 mm or less, more preferably 0.9 mm or less, and even more preferably 0.8 mm or less. If the cover is too thick, the repulsion may be insufficient or the spin may be too much during a full shot with a driver (W#1), utility, or iron, and the desired flight distance may not be achieved. On the other hand, if the cover is too thin, the abrasion resistance may be poor, or the spin may not be sufficient during an approach, resulting in insufficient controllability.

[0065] The cover may be made of any of the various thermoplastic resins used in golf ball cover materials, but from the viewpoints of controllability and abrasion resistance, a urethane resin is preferably used. In particular, from the viewpoint of mass production of ball products, it is preferable to use a material mainly made of thermoplastic polyurethane, and more preferably, the cover may be made of a resin blend mainly made of (I) thermoplastic polyurethane and (II) a polyisocyanate compound.

[0066] The total weight of the above components (I) and (II) is preferably 60% or more, and more preferably 70% or more, based on the total weight of the resin composition of the cover. The above components (I) and (II) are described in detail below.

[0067] Regarding the above (I) thermoplastic polyurethane, the structure of the thermoplastic polyurethane includes a soft segment made of a polymer polyol (polymeric glycol) which is a long-chain polyol, and a hard segment made of a chain extender and a polyisocyanate compound. Here, as the long-chain polyol used as the raw material, any one that has been used in the technology related to thermoplastic polyurethanes can be used, and there is no particular limitation. For example, polyester polyol, polyether polyol, polycarbonate polyol, polyester polycarbonate polyol, polyolefin polyol, conjugated diene polymer polyol, castor oil polyol, silicone polyol, vinyl polymer polyol, etc. can be mentioned. These long-chain polyols may be used alone or in combination of two or more kinds. Among these, polyether polyol is preferred in that it can synthesize a thermoplastic polyurethane with a high resilience modulus and excellent low-temperature properties.

[0068] As the chain extender, those used in conventional techniques related to thermoplastic polyurethanes can be suitably used, and for example, a low molecular weight compound having two or more active hydrogen atoms in the molecule that can react with an isocyanate group and a molecular weight of 400 or less is preferable. 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, 2,2-dimethyl-1,3-propanediol, etc. Among these, as the chain extender, an aliphatic diol having 2 to 12 carbon atoms is preferable, and 1,4-butylene glycol is more preferable.

[0069] The polyisocyanate compound may be suitably used in the conventional technology related to thermoplastic polyurethane, and is not particularly limited. Specifically, one or more selected from the group consisting of 4,4'-diphenylmethane diisocyanate, 2,4-(or) 2,6-toluene diisocyanate, p-phenylene diisocyanate, xylylene diisocyanate, naphthylene 1,5-diisocyanate, tetramethyl xylene 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 be 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 exhibited, 4,4'-diphenylmethane diisocyanate, which is an aromatic diisocyanate, is most preferred.

[0070] Specific examples of thermoplastic polyurethanes that can be used as the component (I) include commercially available products such as Pandex T8295, T8290, and T8260 (all manufactured by DIC Covestro Polymers).

[0071] Although not a required component, a thermoplastic elastomer other than the thermoplastic polyurethane can be blended as component (III) to the above components (I) and (II). By blending component (III) with the resin blend, it is possible to further improve the flowability of the resin blend and to enhance various physical properties required for a golf ball cover material, such as resilience and abrasion resistance.

[0072] 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 is preferably (I):(II):(III)=100:2-50:0-50, and more preferably (I):(II):(III)=100:2-30:8-50 (mass ratio).

[0073] Furthermore, various additives other than the components constituting the thermoplastic polyurethane may be blended into the above-mentioned resin blend as necessary. For example, pigments, dispersants, antioxidants, light resistance stabilizers, ultraviolet absorbers, release agents, etc. may be appropriately blended.

[0074] The multi-piece solid golf ball formed by laminating the above-mentioned core, surrounding layer, intermediate layer, and cover (outermost layer) can be manufactured by a conventional method such as a known injection molding method. For example, the materials for the surrounding layer and intermediate layer are sequentially injected around the core using respective injection molds to obtain each covered sphere, and finally, the material for the cover, which is the outermost layer, is injection molded to obtain a multi-piece golf ball. Alternatively, the golf ball can be manufactured by encasing the covered sphere in two half cups that have been molded into a half-shell shape in advance and molding them under heat and pressure as each covered layer.

[0075] The deflection (mm) of the golf ball when subjected to an initial load of 98N (10kgf) to a final load of 1,275N (130kgf) must be 2.7mm or more, preferably 2.9mm or more, more preferably 3.0mm or more, with the upper limit being preferably 3.8mm or less, more preferably 3.6mm or less, and even more preferably 3.4mm or less. If the deflection of the golf ball is too small, i.e., too hard, the ball may have too much spin and not fly well, or the feel on impact may be too hard. On the other hand, if the deflection is too large, i.e., the ball is too soft, the resilience of the ball may be too low, so the ball may not fly well, the feel on impact may be too soft, or the durability to cracking during repeated impact may be poor.

[0076] [ Hardness of each layer 〕 In the present invention, in order to achieve both advantageous distance performance and excellent short game characteristics when making full shots with a driver (W#1), utility or iron, the surface hardness of the core, the surface hardness of a ball obtained by covering the core with an envelope layer (enveloping layer-covered ball), the surface hardness of a ball obtained by covering the envelope layer-covered ball with an intermediate layer (intermediate layer-covered ball), and the surface hardness of a ball obtained by covering the intermediate layer-covered ball with a cover (the surface hardness means Shore C hardness) satisfy the following formula (1): Surface hardness of sphere coated with surrounding layer < Surface hardness of sphere coated with intermediate layer (1) and preferably satisfies the following formula (1'), and more preferably satisfies the following formula (1''). Surface hardness of the envelope layer coated sphere <Surface hardness of the middle layer coated sphere> Ball surface hardness (1') Core surface hardness<Surface hardness of the envelope layer coated sphere<Surface hardness of the middle layer coated sphere>Ball surface hardness> (1'')

[0077] The intermediate layer-coated sphere has a higher surface hardness than the surrounding layer-coated sphere, and the difference in surface hardness between them is preferably 1 or more, more preferably 3 or more, and even more preferably 5 or more, in Shore C hardness, with the upper limit being preferably 25 or less, more preferably 17 or less, and even more preferably 14 or less. If the above value is outside the above range, the spin will be too much when a full shot is made with a driver (W#1), utility or iron, and the desired distance may not be achieved.

[0078] The intermediate layer-covered sphere has a higher surface hardness than the ball, and the difference between the surface hardnesses is preferably 2 or more, more preferably 4 or more, and even more preferably 6 or more in Shore C hardness, with the upper limit being preferably 25 or less, more preferably 17 or less, and even more preferably 14 or less. If the above value is too small, controllability in the short game may deteriorate. If the above value is too large, the spin rate in full shots may increase, making it difficult to achieve the desired flight distance.

[0079] The envelope layer-covered sphere has a surface hardness greater than that of the core, and the difference in surface hardness between them is preferably at least 1, more preferably at least 4, and even more preferably at least 8, in Shore C hardness, with the upper limit being preferably no more than 25, more preferably no more than 20, and even more preferably no more than 15. If the above value is outside the above range, the spin rate will increase upon full shot, and the desired flight distance may not be achieved.

[0080] Regarding the relationship between the surface hardness of the envelope layer-covered sphere and the intermediate layer-covered sphere and the center hardness of the core, it is preferable that the surface hardness of the former is higher than the surface hardness of the latter.

[0081] The value of (surface hardness of the envelope-coated sphere)-(center hardness of the core) is preferably 28 or more, more preferably 32 or more, and even more preferably 35 or more in Shore C hardness, and the upper limit is preferably 45 or less, more preferably 42 or less, and even more preferably 40 or less. If the above value is too large, the durability against cracking when repeatedly hit may be poor, or the initial velocity of actual hit may be low, making it impossible to obtain the desired flight distance. On the other hand, if the above value is too small, the spin rate at the time of full shot may be high, making it impossible to obtain the desired flight distance.

[0082] The present invention relates to a compound represented by the following formula (2): Surface hardness of the intermediate layer-coated sphere - Center hardness of the core (Shore C hardness) ≧ 40 (2) That is, the value obtained by subtracting the center hardness of the core from the surface hardness of the intermediate layer-covered sphere is 40 or more, preferably 41 or more, more preferably 42 or more, and the upper limit is preferably 53 or less, more preferably 50 or less, and even more preferably 47 or less. If the above value is too large, the durability to cracking when repeatedly hit may be poor, or the initial velocity of actual hit may be low, making it impossible to obtain the desired flight distance. On the other hand, if the above value is too small, the spin rate may be high when a full shot is made with a driver (W#1), utility, or iron, making it impossible to obtain the desired flight distance.

[0083] [ Layer thickness relationships 〕 In addition, in the present invention, from the viewpoint of obtaining superior distance performance not only on full shots with a driver (W#1) but also with an iron, the thickness of the surrounding layer, the thickness of the intermediate layer and the thickness of the cover satisfy the following formula (3). Cover thickness < Intermediate layer thickness < Enveloping layer thickness (3)

[0084] [ Relationship between core diameter and ball diameter 〕 In the present invention, from the viewpoint of obtaining superior distance performance not only with a driver (W#1) but also with an iron, the value of the core diameter / ball diameter is 0.820 or more, preferably 0.830 or more, more preferably 0.840 or more, and the upper limit is preferably 0.970 or less, more preferably 0.920 or less, and even more preferably 0.900 or less. If the above value is too small, the initial velocity of the ball may be low, the deflection hardness of the entire ball may be high, and the spin rate may increase during a full shot, making it impossible to obtain the desired distance. If the above value is too large, the spin rate may increase during a full shot, making it impossible to obtain the desired distance, and the durability against cracking may be deteriorated when repeatedly hit.

[0085] A large number of dimples may be formed on the outer surface of the cover. There are no particular limitations on the number of dimples arranged on the cover surface, but the number is preferably 250 or more, more preferably 300 or more, more preferably 320 or more, and the upper limit is preferably 380 or less, more preferably 350 or less, and even more preferably 340 or less. If the number of dimples is greater than the above range, the trajectory of the ball may become lower, resulting in a shorter flight distance. Conversely, if the number of dimples is smaller, the trajectory of the ball may become higher, resulting in a shorter flight distance.

[0086] The shape of the dimples may be one or a combination of two or more of the following shapes: circular, various polygonal, dewdrop, elliptical, etc. For example, when using circular dimples, the diameter may be about 2.5 mm to 6.5 mm, and the depth may be 0.08 mm to 0.30 mm.

[0087] The dimple occupancy rate of the golf ball's spherical surface, specifically, the ratio of the total dimple area defined by the edge of the plane surrounded by the dimples to the ball's area assuming that no dimples exist (SR value), is preferably 70% to 90% in order to fully demonstrate aerodynamic characteristics. In addition, the value V0 obtained by dividing the spatial volume of the dimples below the plane surrounded by the dimples' edges by the volume of a cylinder whose base is the plane and whose height is the maximum depth of the dimples from the bottom is preferably 0.35 to 0.80 in order to optimize the trajectory of the ball. Furthermore, the VR value, which is the total volume of the dimples formed below the plane surrounded by the dimples' edges to the ball's volume assuming that no dimples exist, is preferably 0.6% to 1.0%. If the above-mentioned numerical ranges are deviated from, the ball may not achieve a satisfactory flight distance due to a poor flight trajectory.

[0088] 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.

[0089] In this specification, "lift coefficients (CL1, CL2, CL3, CL4)" are measured in accordance with the ITR (Indoor Test Range) defined by the USGA (United States Golf Association). The lift coefficient can be adjusted by adjusting the configuration (arrangement, diameter, depth, volume, number, shape, etc.) of the dimples on the golf ball. 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 by the following formula (I). Re = ρvL / μ (I) In the above equation (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.

[0090] The conditions for measuring the lift coefficient CL1, ie, a Reynolds number of 80,000 and a spin rate of 2,000 rpm, generally correspond to the state when the lift coefficient starts to decrease (and thus the golf ball starts to fall) after the golf ball has reached its highest point since being hit. The conditions for measuring the lift coefficient CL2, ie, a Reynolds number of 70,000 and a spin rate of 1,900 rpm, generally correspond to the state when the golf ball has reached its highest point since being hit and is about to fall to the ground. These conditions are particularly true when the golf ball is hit under high-speed conditions (e.g., initial speed of 66 m / s, spin rate of 2,600 rpm, and launch angle of 11°). These high-speed conditions correspond to the conditions when an average amateur hits a ball with a driver.

[0091] The value of CL2 / CL1 is preferably 0.900 or more, more preferably 0.970 or more, and even more preferably 0.990 or more. By satisfying the above range, it is possible to suppress the decrease in lift force during the fall of the golf ball, and thus it is possible to easily increase the flight distance (and therefore the carry) and run during the fall. Thus, the flight distance (total) can be improved. If CL2 / CL1 is too low, the golf ball is likely to fall suddenly, and it becomes difficult to sufficiently increase the carry and run. From the viewpoint of improving the flight distance, the higher CL2 / CL1 is, the more preferable it is. However, if it is too high, the carry will be increased but the run will be reduced, and as a result, there is a risk that the total flight distance will not be greater than the optimum value, so 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.

[0092] The conditions for measuring the lift coefficient CL3, ie, a Reynolds number of 200000 and a spin rate of 2500 rpm, generally roughly correspond to the state immediately after a golf ball is launched under high speed conditions (e.g., initial speed of 72 m / s, spin rate of 2500 rpm, launch angle of 10°). The conditions for measuring the lift coefficient CL4, ie, a Reynolds number of 120000 and a spin rate of 2250 rpm, generally roughly correspond to the state at the timing when the golf ball rises and about 2 seconds have passed after being launched under high speed conditions (e.g., initial speed of 72 m / s, spin rate of 2500 rpm, launch angle of 10°).

[0093] The value of CL4 / CL3 is preferably 1.250 or more, more preferably 1.252 or more, and even more preferably 1.255 or more, and the upper limit is preferably 1.300 or less, more preferably 1.295 or less, and even more preferably 1.290 or less. By setting the value in the above range, when the golf ball is hit under high speed conditions (for example, when hitting with W#1), the golf ball can be prevented from rising too much (and thus prevented from flying up), and the resistance to wind can be improved, leading to an improved carry. In addition, the run can be improved. Thus, the flight distance (total) can be improved.

[0094] From the viewpoint of improving the flight distance, the lift coefficient CL1 is preferably 0.230 or more. Also, the lift coefficient CL1 is preferably 0.240 or less. From the same viewpoint, the lift coefficient CL2 is preferably 0.230 or more. Also, the lift coefficient CL2 is preferably 0.240 or less. From the same viewpoint, the lift coefficient CL3 is preferably 0.145 or more. Also, the lift coefficient CL3 is preferably 0.155 or less. From the same viewpoint, the lift coefficient CL4 is preferably 0.185 or more. Also, the lift coefficient CL4 is preferably 0.195 or less.

[0095] A paint layer (coating layer) can be formed on the surface of the cover. This paint layer can be applied using various paints, and as the paint, it is preferable to use a paint composition containing, as a main component, a urethane paint made of polyol and polyisocyanate, because the paint must be able to withstand the harsh conditions of use of the golf ball.

[0096] Examples of the polyol component include acrylic polyols, polyester polyols, etc. These polyols include modified polyols, and other polyols may be added to improve workability.

[0097] As the polyol component, it is preferable to use two kinds of polyester polyols in combination. In this case, if the two kinds of polyester polyols are (a) and (b), the polyester polyol of the (a) component can be a polyester polyol having a cyclic structure introduced into the resin skeleton, for example, a polyester polyol obtained by polycondensation of a polyol having an alicyclic structure such as cyclohexane dimethanol and a polybasic acid, or a polyol having an alicyclic structure and a diol or triol and a polybasic acid. On the other hand, the polyester polyol of the (b) component can be a polyester polyol having a multi-branched structure, for example, a polyester polyol having a branched structure such as "NIPPOLAN 800" manufactured by Tosoh Corporation.

[0098] 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.

[0099] 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.

[0100] 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 by adopting a normal coating process, and then dried to form a coating layer on the ball surface. In this case, the coating method that can be suitably adopted is a spray coating method, an electrostatic coating method, a dipping method, etc., and is not particularly limited.

[0101] The thickness of the coating layer made of the coating composition is not particularly limited, but is usually 5 to 40 μm, preferably 10 to 20 μm. The thickness of the coating layer referred to here means 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.

[0102] In the present invention, the elastic work recovery rate of the paint layer made of the above-mentioned paint composition must be 60% or more, and is preferably 80% or more. If the elastic work recovery rate of this paint layer is within the above range, the paint layer has high elasticity, so that the self-repair function is high and the abrasion resistance is very excellent. In addition, the performance of the golf ball coated with the above-mentioned paint composition can be improved. The method for measuring the above-mentioned elastic work recovery rate is as follows.

[0103] The elastic work recovery is a parameter of the nanoindentation method, which is an ultra-microhardness test method that controls the indentation load on the order of micronewtons (μN) and tracks the indenter depth at the time of indentation with nanometer (nm) accuracy, and evaluates the physical properties of the paint layer. Conventional methods could only measure the size of the deformation mark (plastic deformation mark) corresponding to the maximum load, but the nanoindentation method can obtain the relationship between the indentation load and the indentation depth by measuring automatically and continuously. Therefore, it is considered that the physical properties of the paint layer can be evaluated with high accuracy without the individual differences that occur when visually measuring the deformation mark with an optical microscope as in the conventional method. The paint layer on the surface of the ball is greatly affected by the impact of various clubs such as drivers, utilities, and irons, and the influence of the paint layer on the physical properties of the golf ball is not small, so measuring the paint layer with the ultra-microhardness test method and performing it with higher accuracy than before is a very effective evaluation method.

[0104] The hardness of the paint layer is preferably 40 or more, more preferably 60 or more, and the upper limit is preferably 95 or less, more preferably 85 or less, in Shore M hardness. The Shore M hardness is in accordance with ASTM D2240. The hardness of the paint layer is preferably 40 or more, and the upper limit is preferably 80 or less, in Shore C hardness. The Shore C hardness is in accordance with ASTM D2240. If the paint layer has a hardness higher than the above range, the paint may become brittle when repeatedly struck, and the cover layer may not be protected. If the paint layer has a hardness lower than the above range, the ball surface may be easily scratched when struck against a hard object, which is undesirable.

[0105] Regarding the hardness relationship between the paint layer and the cover, the value obtained by subtracting the material hardness of the paint layer from the material hardness of the cover is preferably -20 or more in Shore C hardness, more preferably -15 or more, and even more preferably -10 or more, with the upper limit being preferably 25 or less, more preferably 20 or less, and even more preferably 15 or less. Outside the above range, the coating may be more likely to peel off when hit. EXAMPLES

[0106] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0107] [Examples 1 to 5, Comparative Examples 1 to 8] Core formation The rubber compositions of Examples 1 to 3 and Comparative Examples 4 and 5 shown in Table 1 were prepared, and then vulcanized and molded under vulcanization conditions of 152° C. and 19 minutes to prepare solid cores. Similarly, solid cores of Examples 4 and 5 and Comparative Examples 1 to 3 and 8 were prepared using the rubber compositions and vulcanization conditions shown in Table 1.

[0108] [Table 1]

[0109] The details of each component listed in Table 1 are as follows. Polybutadiene A: JSR Corporation, product name "BR51" Polybutadiene B: JSR Corporation, product name "BR730" Zinc acrylate: "ZN-DA85S" (manufactured by Nippon Shokubai Co., Ltd.) Organic peroxide (1): Dicumyl peroxide, trade name "Percumyl D" (manufactured by NOF Corp.) Organic peroxide (2): Mixture of 1,1-di(t-butylperoxy)cyclohexane and silica, trade name "Perhexa C-40" (manufactured by NOF Corp.) Water: Pure water (Seiki Pharmaceutical Co., Ltd.) Anti-aging agent: 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.

[0110] Formation of the envelope layer, intermediate layer and cover (outermost layer) Next, for Examples 1 to 3 and Comparative Examples 4 and 5, the surrounding layer and intermediate layer materials having the compositions shown in Table 2 were used to form the surrounding layer and intermediate layer in sequence by injection molding around the core obtained above, to obtain each covered sphere. For Comparative Examples 4 and 5, there was no surrounding layer, and the intermediate layer was directly coated around the core in the same manner as above, to obtain each covered sphere. Next, a cover (outermost layer) was formed around the intermediate layer-covered sphere obtained above by injection molding using the cover material having the composition shown in the same table, to produce a multi-piece solid golf ball. At this time, the following dimple A, which is common to the Examples and Comparative Examples other than Example 5, was formed on the cover surface.

[0111] Similarly, for Examples 4 and 5 and Comparative Examples 1 to 3, 6 to 8, an envelope layer and an intermediate layer are formed in the same manner as above to obtain each covered sphere. Next, a cover (outermost layer) is formed around the intermediate layer-covered sphere by injection molding using the cover material having the composition shown in the table to produce a multi-piece solid golf ball. The following dimples B, which are common to Examples and Comparative Examples other than Example 5, are formed on the cover surface. The following dimples B are also formed on the cover surface of Example 5.

[0112] [Table 2]

[0113] The trade names of the main materials listed in the table are as follows: "HPF1000" HPF(trademark) 1000 manufactured by The Dow Chemical Company "Himilan" is an ionomer manufactured by Mitsui Dow Polychemicals. "AM7318" "AM7329" Ionomers manufactured by Mitsui Dow Polychemicals "Trimethylolpropane" (TMP) manufactured by Tokyo Chemical Industry Co., Ltd. "TPU" is a trade name of DIC Covestro Polymer, "Pandex", an ether type thermoplastic polyurethane.

[0114] Dimple A uses six types of circular dimples, the details of which are shown in Table 3 below, and the arrangement is as shown in Figure 5. Figure 5(A) shows a plan view of the dimples, and Figure 5(B) shows a side view of the dimples.

[0115] [Table 3]

[0116] Dimples B use eight types of circular dimples, the details of which are shown in Table 4 below, and their arrangement is as shown in Figure 6. Figure 6(A) shows a plan view of the dimples, and Figure 6(B) shows a side view of the dimples.

[0117] [Table 4]

[0118] Definition of Dimples Edge: The highest point on the cross section passing through the center of the dimple Diameter: The diameter of the plane enclosed by the edge of the dimple Depth: The maximum depth of the dimple from the plane bounded by the dimple edge SR: The ratio of the total dimple area, defined by the plane enclosed by the edges of the dimples, to the area of ​​the ball as if the dimples did not exist. Dimple volume: The volume of the dimple below the plane surrounded by the edge of the dimple 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 the dimples did not exist.

[0119] The following table shows 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 A and B formed on the cover surface, the lift coefficient CL2 measured under conditions of a Reynolds number of 70,000 and a spin rate of 1,900 rpm, the lift coefficient CL3 measured under conditions of a Reynolds number of 200,000 and a spin rate of 2,500 rpm, the lift coefficient 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. These lift coefficients are measured in accordance with the ITR (Indoor Test Range) defined by the USGA.

[0120] [Table 5]

[0121] Formation of paint layer (coating layer) Next, for Examples 1 to 3 and Comparative Examples 4 and 5, the coating composition shown in Table 6 below was used as a coating composition common to all of the Examples and Comparative Examples. The coating composition 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 having a thickness of 15 μm. Similarly, for Examples 4 and 5 and Comparative Examples 1 to 3, and 6 to 8, the above paint was applied to prepare golf balls having a paint layer with a thickness of 15 μm.

[0122] [Table 6]

[0123] [Synthesis example of polyester polyol (A)] In a reaction apparatus equipped with a reflux condenser, a dropping funnel, a gas inlet tube, and a thermometer, 140 parts by mass of trimethylolpropane, 95 parts by mass of ethylene glycol, 157 parts by mass of adipic acid, and 58 parts by mass of 1,4-cyclohexanedimethanol were charged, and the 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 non-volatile content of 70% by mass.

[0124] The coating composition in Table 6 was prepared by mixing 23 parts by mass of the polyester polyol solution, 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.

[0125] Elastic work recovery rate The elastic work recovery rate of the paint is measured using a 50μm thick paint sheet. The measurement device used is the ultra-micro hardness tester "ENT-2100" manufactured by Elionix, and the measurement conditions are as follows: Indenter: Berkovich indenter (material: diamond, angle α: 65.03°) Load F: 0.2mN Loading time: 10 seconds ·Holding time: 1 second ·Unloading time: 10 seconds The elastic work recovery rate is calculated by the following formula based on the indentation work Welast (Nm) due to the return deformation of the paint and the mechanical indentation work Wtotal (Nm). Elastic work recovery rate = Welast / Wtotal × 100(%)

[0126] Shore C hardness and Shore M hardness The Shore C hardness and Shore M hardness in Table 6 above are measured by preparing sheets of 2 mm thickness, stacking three sheets as test pieces, and using a Shore C hardness tester and a Shore M hardness tester conforming to the ASTM D2240 standard.

[0127] 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. The results are shown in Tables 7 and 8.

[0128] The outer diameter of each of the core, the surrounding layer-coated sphere, and the intermediate layer-coated sphere Measure five randomly selected points on the surface at a temperature of 23.9±1°C, and take the average of the measurements for each sphere. Then calculate the average value for 10 spheres.

[0129] Ball diameter At a temperature of 23.9±1°C, measurements are taken at 15 randomly selected non-dimpled areas, and the average of these measurements is taken as the measurement for one ball. The average of the 10 balls measured is then calculated.

[0130] Deflection of the core and ball The core or the covered sphere of the ball is placed on a hard plate, and the amount of deflection is measured when an initial load of 98N (10kgf) is applied and a final load of 1275N (130kgf) is applied. Note that the above deflection amount is a measurement value after adjusting the temperature to 23.9°C. The pressure speed of the head compressing the ball is 10mm / s.

[0131] Core hardness distribution The surface of the core is spherical, and the needle of the hardness tester is set almost perpendicular to the spherical surface, and the surface hardness is measured in Shore C hardness according to ASTM D2240. For the center and specified positions of the core, the core is cut into a hemisphere to make the cross section flat, and the needle of the hardness tester is pressed perpendicularly against the center part and the specified positions shown in Table 5 to measure the hardness, and the hardness at the center and each position is shown in Shore C hardness values. To measure the hardness, an automatic rubber hardness tester "P2" made by Kobunshi Keiki Co., Ltd., equipped with a Shore C type hardness tester, is used. The hardness value is the maximum value. All measurements are performed in an environment of 23±2°C. The values ​​in Table 7 are Shore C hardness values. In addition, the hardness distribution of the core is expressed as the Shore C hardness Cc at the center of the core, the Shore C hardness C at the midpoint M between the center of the core and the surface, m The Shore C hardness at the positions 2mm, 4mm, and 6mm inward from the midpoint M is Cm-2, Cm-4, and Cm-6, the Shore C hardness at the positions 2mm, 4mm, and 6mm outward from the center M is Cm+2, Cm+4, and Cm+6, and the Shore C hardness of the core surface is Cs for the following areas A to F. ·Area A: 1 / 2×2×(Cm-4-Cm-6) ·Area B: 1 / 2×2×(Cm-2-Cm-4) ·Area C: 1 / 2×2×(Cm-Cm-2) ·Area D: 1 / 2×2×(Cm+2-Cm) ·Area E: 1 / 2×2×(Cm+4-Cm+2) ·Area F: 1 / 2×2×(Cm+6-Cm+4) The values ​​of the following two formulas were obtained. (1)(Area:E+F)-(Area:A+B) (2)(Area:D+E)-(Area:B+C)

[0132] To illustrate the areas A to F of the core hardness distribution, a schematic diagram showing the areas A to F using the core hardness distribution data of Example 2 is shown in FIG. Graphs of the core hardness distributions of Examples 1 to 5 and Comparative Examples 1 to 8 are shown in FIGS.

[0133] Material hardness of the envelope layer, intermediate layer and cover (Shore D hardness and Shore C hardness) The resin material for each layer is formed into a 2 mm thick sheet and left to stand for 2 weeks. The Shore D hardness and Shore C hardness are then measured in accordance with the ASTM D2240 standard. The hardness is measured using an automatic rubber hardness tester "P2" manufactured by Kobunshi Keiki Co., Ltd. Attachments for Shore D hardness and Shore C hardness are attached and the respective hardness is measured. The maximum hardness value is read. All measurements are performed in an environment of 23±2°C.

[0134] Surface hardness (Shore D hardness and Shore C hardness) of the envelope layer coated sphere, the intermediate layer coated sphere and the ball Measurements are taken by pressing a needle perpendicularly against the surface of each sphere. The surface hardness of the ball (cover) is measured on the land areas on the ball surface where no dimples are formed. Shore D hardness and Shore C hardness are measured in accordance with the ASTM D2240 standard. Hardness is measured using an automatic rubber hardness tester "P2" manufactured by Kobunshi Keiki Co., Ltd. Attachments for Shore D hardness and Shore C hardness are attached and each hardness is measured. The maximum hardness value is read. All measurements are taken in an environment of 23±2°C.

[0135] [Table 7]

[0136] [Table 8]

[0137] The flight distance of each golf ball (driver (W#1), utility, iron (I#6), iron (I#8)), spin rate at approach, hitting feeling and durability against repeated hitting were evaluated by the following methods. The results are shown in Table 9.

[0138] Distance rating [Driver (W#1)] A utility club was attached to the golf hitting robot and the flying distance was measured when the ball was hit at a head speed of 45 m / s. The club used was the Bridgestone Sports JGR (2016 model) with a loft angle of 9.5°. The amount of spin was also measured using an initial condition measuring device immediately after the ball was hit. <Judgment criteria> Total distance: 241.0m or more... ◎ Total distance: 237.5m or more, but less than 241.0m Total distance less than 237.5m ×

[0139] Flying rating (utility) A utility club was attached to the golf hitting robot and the flying distance was measured when the ball was hit at a head speed of 38 m / s. The club used was the Bridgestone Sports JGR H2 (2016 model). The amount of spin was also measured using an initial condition measuring device immediately after the ball was hit. <Judgment criteria> Total distance: 165.0m or more Total distance less than 165.0m ×

[0140] Flight rating (I#6) A No. 6 iron (I#6) was attached to the golf hitting robot, and the distance traveled when the ball was hit at a head speed of 35 m / s was measured and judged according to the following criteria. The club used was the Bridgestone Sports JGR Forged (2016 model) I#6. The amount of spin was also measured using an initial condition measuring device on the ball immediately after it was hit. <Judgment criteria> Total distance: 154.0m or more Total distance less than 154.0m ×

[0141] Flight rating (I#8) The golf hitting robot was fitted with an 8-iron (I#8) and hit with a head speed of 35m / s, the distance was measured and judged according to the following criteria. The club used was the Bridgestone Sports JGR Forged (2016 model) I#8. The amount of spin was also measured with an initial condition measuring device on the ball immediately after it was hit. <Judgment criteria> Total distance: 137.0m or more Total distance less than 137.0m ×

[0142] Evaluating the amount of spin when approaching The amount of spin was determined by hitting the ball with a golf hitting robot equipped with a sand wedge at a head speed of 15 m / s. The amount of spin was also measured immediately after hitting the ball using an initial condition measuring device. The sand wedge used was the Bridgestone Sports TourStage TW-03 (loft 57°) 2002 model. <Judgment criteria> Spin rate of 4500 rpm or more... Spin rate less than 4500 rpm ×

[0143] Hitting Feel An amateur golfer with a driver (W#1) head speed of 30 to 40 m / s hits the ball and evaluates the feel of the ball according to the following criteria. <Judgment criteria> More than 10 out of 20 people rated it as soft and with a good feel... Fewer than 9 out of 20 people rated it as soft and with a good feel.

[0144] Repeated impact durability A driver (W#1) was attached to a golf hitting robot, and N=8 balls were hit repeatedly at a head speed of 45 m / s, and the average number of hits until all the balls started to crack was used for evaluation. The number of cracks in Example 2 was assigned an index of 100. <Judgment criteria> Index 90 or higher... ○ Index less than 90 ×

[0145] [Table 9]

[0146] As shown in the results in Table 9, the golf balls of Comparative Examples 1 to 8 are inferior to the products of the present invention (Examples) in the following points. In Comparative Example 1, the surface hardness of the intermediate layer-covered ball minus the center hardness of the core was less than 40 in Shore C hardness, and the ball deflection was less than 2.7 mm. As a result, the flight distance was poor when hitting with a utility club and an I#6 club. In addition, the hitting feel was hard. In Comparative Example 2, the surface hardness of the intermediate layer-covered ball minus the center hardness of the core was less than 40 in Shore C hardness, resulting in poor flight distance when hitting with utility and I#6. In Comparative Example 3, the resin materials of the intermediate layer and surrounding layer do not contain an ionomer with a high acid content, and as a result, the flight distance is inferior when hit with a driver (W#1), utility, and I#8. Comparative Example 4 is a golf ball having a three-piece (3P) structure without an envelope layer, and as a result, durability against repeated hits is poor, and the flight distance during utility hits is poor. Comparative Example 5 is a golf ball having a three-piece (3P) structure without an envelope layer, and as a result, it is inferior in durability against repeated impacts and also inferior in distance when hit with a driver (W#1) or an iron. In Comparative Example 6, the core had a surface hardness minus center hardness of less than 20 in JIS-C hardness, resulting in poor flight distance when hit with a driver (W#1), utility or iron. In Comparative Example 7, the core had a surface hardness minus center hardness of less than 20 in JIS-C hardness, resulting in poor flight distance when hit with a driver (W#1), utility or iron. In Comparative Example 8, the surface hardness of the envelope layer coated sphere was greater than the surface hardness of the intermediate layer coated sphere, and the surface hardness of the intermediate layer coated sphere minus the core center hardness was less than 40 in Shore C hardness. As a result, the flight distance was poor when hit with a driver (W#1), utility, and I#6.

Claims

1. A multi-piece solid golf ball comprising a core, an envelope layer, an intermediate layer, and a cover, the core being formed in one layer from a rubber composition, the envelope layer being formed in one or more layers from a resin material, and the intermediate layer and the cover being each formed in one layer from a resin material, wherein the difference between the surface hardness and center hardness of the core is 20 or more in Shore C hardness, the resin material of the intermediate layer contains an ionomer having a high acid content, and the hardness relationship (surface hardness means Shore C hardness) between the center hardness of the core, the surface hardness of a sphere obtained by covering the core with the envelope layer (enveloping layer-covered sphere), and the surface hardness of a sphere obtained by covering the envelope layer-covered sphere with an intermediate layer (intermediate layer-covered sphere) satisfies the following formulas (1) and (2): Surface hardness of the envelope layer-coated sphere < Surface hardness of the intermediate layer-coated sphere ... (1) Surface hardness of intermediate layer-coated sphere−Center hardness of core (Shore C hardness)≧40 (2) and the ball has a deflection (mm) of 2.7 mm or more when an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf) is applied, and 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. If CL3 and CL4 are satisfied by the following formula: 1.250≦CL4 / CL3≦1.300 A multi-piece solid golf ball comprising:

2. 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 are expressed by the following formula: 0.900≦CL2 / CL1 2. The golf ball of claim 1, which satisfies the above.

3. The diameter of the core is 35.1 to 41.3 mm, and the hardness distribution of the core is expressed as follows: Cc is the Shore C hardness at the center of the core, Cm is the Shore C hardness at the midpoint M between the center and the surface of the core, Cm-2, Cm-4, Cm-6 are the Shore C hardnesses at positions 2 mm, 4 mm, and 6 mm inward from the midpoint M, respectively, Cm+2, Cm+4, Cm+6 are the Shore C hardnesses at positions 2 mm, 4 mm, and 6 mm outward from the center M, respectively, and Cs is the Shore C hardness of the surface of the core. The following areas A to F are then defined: ・Area A: 1 / 2 x 2 x (Cm-4-Cm-6) ・Area B: 1 / 2×2×(Cm-2-Cm-4) ・Area C: 1 / 2×2×(Cm-Cm-2) ・Area D: 1 / 2 x 2 x (Cm+2-Cm) ・Area E: 1 / 2×2×(Cm+4-Cm+2) ・Area F: 1 / 2 x 2 x (Cm+6-Cm+4) 3. The golf ball according to claim 1, wherein the value of (area E+area F)-(area A+area B) is 2.0 or greater.

4. The thickness relationship of each layer is expressed by the following formula (3). Cover thickness < intermediate layer thickness < surrounding layer thickness (3) 4. The multi-piece solid golf ball according to claim 1, which satisfies the above requirements.

5. Regarding the surface hardness of the core or each coated sphere, Core surface hardness < Enveloping layer covered sphere surface hardness < Intermediate layer covered sphere surface hardness > Ball surface hardness ... (1') 5. The multi-piece solid golf ball according to claim 1, which satisfies the above condition.

6. 6. The multi-piece solid golf ball according to claim 1, wherein the intermediate layer has a material hardness of 64 or more in Shore D hardness.

7. 7. The multi-piece solid golf ball according to claim 1, wherein in the above formula (2), the upper limit of the value of (surface hardness of the intermediate layer covered sphere) - (center hardness of the core) is 53 or less in Shore C hardness.

8. 8. The multi-piece solid golf ball of claim 1, wherein the surrounding layer is a single layer.

9. The areas A to F of the core hardness distribution are calculated by the following formula: (Area D + Area E) - (Area B + Area C) ≧2.0 4. The multi-piece solid golf ball according to claim 3, which satisfies the above.

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