Multi-piece solid golf balls

Abstract

To provide a golf ball that achieves a satisfactory distance on full shots with an iron, is superior in the short game, and has a good feel at impact and a good durability.SOLUTION: The golf ball comprises a core, an envelope layer, an intermediate layer, and a cover, wherein the core is formed of a rubber composition as one or more layer; the envelope layer is formed of a resin material as one or more layer; the intermediate layer is formed of a resin material as one layer; the cover is formed of a resin material as one layer having a thickness of not more than 1.0 mm; the Shore C hardness at a surface of the core, the Shore C hardness at a surface of the sphere obtained by encasing the core with the envelope layer (envelope layer-encased sphere), the Shore C hardness at a surface of the sphere obtained by encasing the envelope layer-encased sphere with the intermediate layer (intermediate layer-encased sphere) and the Shore C hardness at a surface of the ball together satisfy the conditions (Shore C hardness at surface of envelope layer-encased sphere)>Shore C hardness at surface of core) and (Shore C hardness at surface of intermediate layer-encased sphere)>(Shore C hardness at surface of ball); the golf ball also specifying the relationship between the amount of deflection when a predetermined load is applied to the core and ball, and further specifying the internal hardness distribution of the core.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, a single or multiple surrounding layers, an intermediate layer, and a cover. [Background technology]

[0002] Many efforts have been made to design balls with multi-layer structures, 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, i.e., the core, surrounding layer, intermediate layer, and cover (outermost layer), is optimized, have become widespread. In addition, several technologies have been proposed that focus on the core hardness distribution, which accounts for the majority of the ball's volume, and design various modes of core internal hardness to provide high-performance golf balls for professionals and intermediate to advanced players.

[0003] Examples of such technical documents include the following Patent Documents 1 to 17. 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, envelope layer, intermediate layer, and cover (outermost layer), the thickness of each layer, and the core hardness distribution.

[0004] However, the proposed golf balls still have room for improvement in terms of optimizing the core hardness distribution and the thickness relationship between each layer. That is, even if the proposed golf balls can maintain good distance when hit with a driver (W#1), many of them are insufficient in terms of distance when hit with an iron. Furthermore, some of the proposed golf balls are unable to provide sufficiently high spin performance on approaches, even if they are intended to achieve superior distance performance not only when hit with a driver but also when hit with an iron, resulting in golf balls that are not highly enjoyable to play with or that do not provide a good feel on full shots.

[0005] Furthermore, for a certain segment of amateur users, the playability of the golf game may be improved if the distance performance when hitting with an iron is better than the distance when hitting with a driver. Therefore, for this segment of users, there is a demand for the proposal and development of golf balls that have a significantly improved distance performance when hitting with an iron, and that are excellent for short games while also having good other characteristics such as feel and durability. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 9-248351 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-326301 [Patent Document 3] Japanese Patent Application Laid-Open No. 2007-319667 [Patent Document 4] Japanese Patent Application Laid-Open No. 2012-071163 [Patent Document 5] Japanese Patent Application Laid-Open No. 2007-330789 [Patent Document 6] Japanese Patent Application Laid-Open No. 2008-068077 [Patent Document 7] Japanese Patent Application Laid-Open No. 2009-034507 [Patent Document 8] Japanese Patent Application Laid-Open No. 2009-095364 [Patent Document 9] Japanese Patent Application Laid-Open No. 2016-101254 [Patent Document 10] Japanese Patent Application Laid-Open No. 2016-116627 [Patent Document 11] Japanese Patent Application Laid-Open No. 2009-095358 [Patent Document 12] Japanese Patent Application Laid-Open No. 2016-101256 [Patent Document 13] Japanese Patent Application Laid-Open No. 2008-149131 [Patent Document 14] Japanese Patent Application Laid-Open No. 2009-095365 [Patent Document 15] Japanese Patent Application Laid-Open No. 2009-095369 [Patent Document 16] Japanese Patent Publication No. 2020-089633 [Patent Document 17] Patent Publication No. 2021-037157 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in consideration of the above circumstances, and has as its object to provide a multi-piece solid golf ball that ensures increased distance when hit with an iron, has good controllability in the short game, provides a soft hitting feel, and is durable against cracking due to repeated hits. [Means for solving the problem]

[0008] As a result of extensive research into achieving the above-mentioned object, the inventors of the present invention found that the problem of the present invention can be solved by forming a golf ball having a core, an envelope layer, an intermediate layer, and a cover in which the cover is relatively soft and the intermediate layer is relatively hard, and forming the envelope layer adjacent to the inside of the intermediate layer as a single layer or multiple layers that are softer than the intermediate layer and harder than the surface of the core. That is, the core is formed of a rubber composition in one or more layers, the envelope layer is formed of a resin material in one or more layers, the intermediate layer is formed of a resin material in one layer, and the cover is formed of a resin material in a single layer having a thickness of 1.0 mm or less. The hardness relationships among the core, the envelope layer-covered sphere, the intermediate layer-covered sphere, and the ball are specified to satisfy the conditions (envelopment layer-covered sphere) > (core) and (intermediate layer-covered sphere) > (ball) and, where C and B (mm) are the deflections of the core and ball when a predetermined load is applied, respectively, B ≥ 2.8 and 1.6 ≤ C / B ≤ 2.3. Furthermore, the internal hardness of the core satisfies 1.0≦(Cs-C75) / (C50-Cc)≦2.3, where Cc is the Shore C hardness at the center of the core, Cs is the Shore C hardness at the surface of the core, C75 is the Shore C hardness at a position 75% of the core radius from the center of the core toward the surface, and C50 is the Shore C hardness at a position 50% of the core radius from the center of the core toward the surface. The volume V of the core (cm 3 ) × C50 is defined as Core vh. When a golf ball was designed to satisfy the condition 630≦Core vh ≦1000, it was found that a good flight distance was achieved with a low spin effect on full iron shots, a very soft and good feel was achieved, and both resistance to cracking due to repeated hits and controllability around the green were good, leading to the invention of the present invention.

[0009] In other words, the golf ball of the present invention is a spin-type golf ball with three or more cover layers, specialized for distance on full iron shots, and satisfies the needs of users who want spin in short games and control around the green. The golf ball of the present invention also provides a soft, good feel on all shots. It is usually difficult to hit a golf ball well with a driver (W#1), and whether the ball flies well or not depends on the situation. In contrast, the golf ball of the present invention is a golf ball that reliably provides distance, at least when hit with an iron, specialized for distance on full iron shots, and is targeted at such users.

[0010] Accordingly, the present invention provides the following multi-piece solid golf ball. 1. A multi-piece solid golf ball having a core, an envelope layer, an intermediate layer, and a cover, wherein the core is formed of a rubber composition in one or more layers, the envelope layer is formed of a resin material in one or more layers, the intermediate layer is formed of a resin material in one layer, and the cover is formed of a resin material in a single layer with a thickness of 1.0 mm or less, and the Shore C hardness of the surface of the core, the Shore C hardness of the surface of a sphere obtained by covering the core with the envelope layer (enveloping layer-covered sphere), and the Shore C hardness of the surface of a sphere obtained by covering the envelope layer-covered sphere with the intermediate layer (intermediate layer-covered sphere) are The Shore C hardness of the ball's surface must satisfy the following conditions: (Shore C hardness of the surface of the envelope layer covered sphere) > (Shore C hardness of the surface of the core), and (Shore C hardness of the surface of the intermediate layer covered sphere) > (Shore C hardness of the surface of the ball). Furthermore, when the core is subjected to an initial load of 98 N (10 kgf) and a final load of 1,275 N (130 kgf), C (mm) is the deflection of the core, and when the ball is subjected to an initial load of 98 N (10 kgf) and a final load of 1,275 N (130 kgf), B (mm) is the deflection of the ball, and B is the deflection of the ball. Furthermore, the core has a volume V (cm ) of 1.6≦C / B≦2.3. Furthermore, the core has an internal hardness that satisfies the following relationship: 1.0≦(Cs-C75) / (C50-Cc)≦2.3, where Cc is the Shore C hardness at the center of the core, Cs is the Shore C hardness at the surface of the core, C75 is the Shore C hardness at 75% of the core radius from the center to the surface, and C50 is the Shore C hardness at 50% of the core radius from the center to the surface. 3 ) × C50 is Core vh, the condition 630≦ Core vh ≦1000 is met. The relationship between the core diameter and the ball diameter satisfies the condition: 0.65≦(core diameter) / (ball diameter)≦0.80 A multi-piece solid golf ball. 2. A multi-piece solid golf ball according to item 1 above, wherein the internal hardness of the core satisfies 3.0≦(Cs−C50) / (C25−Cc)≦20.0, where C25 is the Shore C hardness at a position 25% of the core radius from the center of the core toward the surface. 3. A multi-piece solid golf ball according to 1 or 2 above, wherein the core has an internal hardness that satisfies the formula (Cs-C50) / (C50-Cc)≧1.1. 4. A multi-piece solid golf ball according to any one of 1 to 3 above, wherein the relationship between the Shore C hardness of the surface of the envelope layer-coated sphere and the Shore C hardness of the surface of the intermediate layer-coated sphere satisfies the condition (surface Shore C hardness of the intermediate layer-coated sphere) > (surface Shore C hardness of the envelope layer-coated sphere). 5. A multi-piece solid golf ball according to any one of 1 to 4 above, wherein the thickness relationship of each layer satisfies the condition: (cover thickness)<(intermediate layer thickness)≦(total thickness of the surrounding layers). 6. A multi-piece solid golf ball according to any one of 1 to 5 above, wherein the ratio of the thickness of each layer satisfies the condition: (total thickness of the surrounding layers) / (cover thickness+intermediate layer thickness)≧1.0. 7. A multi-piece solid golf ball according to any one of the above items 1 to 6, wherein the envelope layer comprises an inner envelope layer and an outer envelope layer, and is formed into at least two layers. 8. The relationship between the Shore C hardness of each layer's surface hardness is as follows: 8. A multi-piece solid golf ball according to claim 7, which satisfies the condition: (Shore C hardness of the ball surface) < (Shore C hardness of the intermediate layer surface) > (Shore C hardness of the outer envelope layer surface) ≥ (Shore C hardness of the inner envelope layer surface) > (Shore C hardness of the core surface). [Effects of the Invention]

[0011] The multi-piece solid golf ball of the present invention achieves good distance with low spin when hit with an iron, provides a very soft and pleasant feel, and is both durable against cracking due to repeated hits and provides good control around the green, making it particularly useful for golfers who place importance on distance when hitting with an iron. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic cross-sectional view of a multi-piece solid golf ball (five-layer structure) of the present invention. [Figure 2] FIG. 2 is a plan view showing the dimple pattern common to each example and each comparative example. [Figure 3]1 is a graph showing hardness distributions of the cores of Examples 1 to 4. [Figure 4] 1 is a graph showing hardness distributions of the cores of Comparative Examples 1 to 5 and 7. [Figure 5] 1 is a graph showing hardness distributions of the cores of Comparative Examples 6 and 8. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described in more detail below. As shown in FIG. 1, the multi-piece solid golf ball of the present invention is a golf ball G having four or more layers, including a core 1, an envelope layer 2 enclosing the core, an intermediate layer 3 enclosing the envelope layer, and a cover 4 enclosing the intermediate layer. In FIG. 1, the envelope layer 2 is formed of two layers, an inner envelope layer 2a and an outer envelope layer 2b. Numerous dimples D are typically formed on the surface of the cover 4. Furthermore, although not specifically shown, a paint layer is typically formed on the surface of the cover 4. The cover 4 is the outermost layer in the layer structure of the golf ball, excluding the paint layer. The core 1 and envelope layer 2 are not limited to being a single layer and can each be formed of two or more layers, while the intermediate layer 3 and cover 4 are each formed of a single layer.

[0014] The core diameter is preferably 24.7 mm or more, more preferably 25.7 mm or more, and even more preferably 26.7 mm or more. The upper limit of this diameter is preferably 34.7 mm or less, more preferably 33.3 mm or less, and even more preferably 31.7 mm or less.

[0015] The core diameter / ball diameter ratio is preferably 0.65 or greater, more preferably 0.67 or greater, and even more preferably 0.70 or greater, with the upper limit being preferably 0.80 or less, more preferably 0.76 or less, and even more preferably 0.73 or less. If this ratio is too small, the initial velocity of the ball may be low, the overall deflection hardness of the ball may be high, and the spin rate on full shots may increase, preventing the desired distance from being achieved. If this ratio is too large, the spin rate on full shots with an iron may increase, preventing the desired distance from being achieved, and the durability to cracking during repeated shots may be poor.

[0016] The deflection (mm) of the core when subjected to an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf) is not particularly limited, but is preferably at least 5.0 mm, more preferably at least 5.5 mm, and even more preferably at least 6.0 mm, with the upper limit being preferably no more than 9.0 mm, more preferably no more than 8.5 mm, and even more preferably no more than 8.0 mm. If the deflection of the core is too small, i.e., if the core is too hard, the ball may have too much spin, resulting in a loss of flight distance, or the feel on impact may be too hard. On the other hand, if the deflection of the core is too large, i.e., if the core is too soft, the ball may have too little resilience, resulting in a loss of flight distance, a too soft feel, or poor durability to cracking upon repeated impact.

[0017] The core is obtained by vulcanizing a rubber composition mainly made of a rubber material, which is usually composed of a base rubber as the main component, and is compounded with a co-crosslinking agent, a crosslinking initiator, an inert filler, an organic sulfur compound, etc. to obtain the rubber composition.

[0018] Polybutadiene is preferably used as the base rubber. Commercially available polybutadiene products can be used, such as BR01, BR51, and BR730 (manufactured by JSR Corporation). The proportion of polybutadiene in the base rubber is preferably 60% by mass or more, and more preferably 80% by mass or more. Rubber components other than the polybutadiene may be blended into the base rubber within a range that does not impair the effects of the present invention. Examples of rubber components other than polybutadiene include polybutadienes other than the polybutadienes mentioned above, and other diene rubbers, such as styrene-butadiene rubber, natural rubber, isoprene rubber, and ethylene-propylene-diene rubber.

[0019] The co-crosslinking agent is an α,β-unsaturated carboxylic acid and / or a metal salt thereof. Specific examples of unsaturated carboxylic acids include acrylic acid, methacrylic acid, maleic acid, and fumaric acid, with acrylic acid and methacrylic acid being particularly preferred. Metal salts of unsaturated carboxylic acids are not particularly limited, but examples include those obtained by neutralizing the above-mentioned unsaturated carboxylic acids with desired metal ions. Specific examples include zinc salts and magnesium salts of methacrylic acid, acrylic acid, and the like, with zinc acrylate being particularly preferred.

[0020] The unsaturated carboxylic acid and / or metal salt thereof is blended in an amount of typically 5 parts by weight or more, preferably 9 parts by weight or more, and more preferably 13 parts by weight or more, per 100 parts by weight of the base rubber, with the upper limit typically being 60 parts by weight or less, preferably 50 parts by weight or less, and more preferably 40 parts by weight or less. If the blended amount is too high, the ball may become too hard, resulting in an unbearable feel at impact, while if the blended amount is too low, the resilience may decrease.

[0021] An organic peroxide is preferably used as the crosslinking initiator. Specifically, commercially available organic peroxides can be used, such as Percumyl D (manufactured by Nippon Oil & Fats Co., Ltd.), Perhexa C-40, Perhexa 3M (manufactured by Nippon Oil & Fats Co., Ltd.), and Luperco 231XL (manufactured by Atochem). These may be used alone or in combination of two or more. The amount of organic peroxide added is preferably 0.1 parts by weight or more, more preferably 0.3 parts by weight or more, and even more preferably 0.5 parts by weight or more, per 100 parts by weight of the base rubber. The upper limit is preferably 5 parts by weight or less, more preferably 4 parts by weight or less, even more preferably 3 parts by weight or less, and most preferably 2.5 parts by weight or less. If the amount added is too high or too low, it may be difficult to achieve a favorable feel, durability, and resilience.

[0022] Suitable fillers include, for example, zinc oxide, barium sulfate, and calcium carbonate. These may be used alone or in combination. The amount of filler is preferably at least 1 part by weight, and more preferably at least 3 parts by weight, per 100 parts by weight of the base rubber. The upper limit of the amount is preferably no more than 200 parts by weight, more preferably no more than 150 parts by weight, and even more preferably no more than 100 parts by weight, per 100 parts by weight of the base rubber. If the amount is too high or too low, it may be difficult to obtain the appropriate mass and appropriate resilience.

[0023] As the antioxidant, for example, commercially available products such as Nocrac NS-6, Nocrac NS-30, Nocrac 200, Nocrac MB (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) can be used. These may be used alone or in combination of two or more.

[0024] The amount of antioxidant blended is not particularly limited, but is preferably at least 0.05 part by weight, more preferably at least 0.1 part by weight, and preferably not more than 1.0 part by weight, more preferably not more than 0.7 part by weight, and even more preferably not more than 0.5 part by weight, per 100 parts by weight of base rubber. If the blended amount is too high or too low, the appropriate core hardness gradient may not be obtained, and favorable resilience, durability, and spin reduction effect on full shots may not be achieved.

[0025] Furthermore, the rubber composition can be blended with an organic sulfur compound to impart excellent resilience. Specifically, it is recommended to blend thiophenol, thionaphthol, halogenated thiophenol, or a metal salt thereof. More specifically, zinc salts of pentachlorothiophenol, pentafluorothiophenol, pentabromothiophenol, parachlorothiophenol, pentachlorothiophenol, and the like, and diphenyl polysulfide, dibenzyl polysulfide, dibenzoyl polysulfide, dibenzothiazoyl polysulfide, dithiobenzoyl polysulfide, and the like having 2 to 4 sulfur atoms can be mentioned. In particular, the zinc salt of pentachlorothiophenol and diphenyl disulfide can be preferably used.

[0026] The organic sulfur compound is blended in an amount of at least 0.05 part by weight, preferably at least 0.07 part by weight, and more preferably at least 0.1 part by weight, per 100 parts by weight of the base rubber, with an upper limit of 5 parts by weight, preferably at most 4 parts by weight, more preferably at most 3 parts by weight, and most preferably at most 2 parts by weight. If the blended amount is too high, the hardness will be too low, and if the blended amount is too low, no improvement in resilience can be expected.

[0027] The core can be produced by vulcanizing and curing a rubber composition containing the above components. For example, the core can be produced by kneading the rubber composition using a kneader such as a Banbury mixer or a roll, compression molding or injection molding using a core mold, and curing the molded product by appropriately heating the molded product at a temperature sufficient for the organic peroxide and co-crosslinking agent to act, 100 to 200°C, preferably 140 to 180°C, for 10 to 40 minutes.

[0028] The core may be formed not only as a single layer, but also as two layers, an inner core layer and an outer core layer. When the core is formed as two layers, an inner core layer and an outer core layer, the above-mentioned rubber materials can be used as the main material for both the inner and outer core layers. The rubber material of the outer core layer that covers the inner core layer may be the same as or different from the material of the inner core layer. Specific details are the same as those described above for the components of the rubber material of the core.

[0029] 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.

[0030] The center hardness (Cc) of the core is preferably 33 or more, more preferably 38 or more, and even more preferably 43 or more, with the upper limit being preferably 62 or less, more preferably 59 or less, and even more preferably 54 or less. If this value is too high, the feel on impact may be too hard, or the spin rate on full shots may increase, preventing the desired flight distance from being achieved. On the other hand, if this value is too low, the resilience may be reduced, resulting in a loss of flight distance, or the durability to cracking when hit repeatedly may be reduced.

[0031] The Shore C hardness (C25) measured from the center of the core toward the surface at 25% of the core radius is preferably at least 35, more preferably at least 40, and even more preferably at least 45, with the upper limit being preferably at most 64, more preferably at most 61, and even more preferably at most 56. 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.

[0032] The Shore C hardness (C50) at a position 50% of the core radius from the center toward the core surface is preferably 37 or greater, more preferably 42 or greater, and even more preferably 47 or greater, with the upper limit being preferably 66 or less, more preferably 63 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 core center hardness (Cc). The Shore C hardness (C50) corresponds to the hardness (Cm) at the midpoint between the core surface and the core center.

[0033] The Shore C hardness (C75) at a position 75% of the core radius from the center toward the surface is preferably at least 40, more preferably at least 45, and even more preferably at least 49, with the upper limit being preferably at most 69, more preferably at most 65, and even more preferably at most 61. 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.

[0034] The surface hardness (Cs) of the core is preferably at least 45, more preferably at least 50, and even more preferably at least 55, with the upper limit being preferably not more than 74, more preferably not more than 70, and even more preferably not more than 66. Any deviation from these hardness limits may result in the same adverse effects as those described for the center hardness (Cc) of the core.

[0035] The difference between the surface hardness (Cs) and center hardness (Cc) of the core is preferably 5 or more, more preferably 7 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. If this value is too small, the spin rate on full shots with a driver may increase, making it difficult to achieve the desired distance. If this value is too large, the durability to cracking when repeatedly hit may decrease, or the initial velocity may decrease, making it difficult to achieve the desired distance.

[0036] Regarding the internal hardness of the core, the value of (Cs-C75) / (C50-Cc) must be 1.0 or greater, preferably 1.2 or greater, more preferably 1.3 or greater, with the upper limit being 2.3 or less, preferably 2.0 or less, more preferably 1.8 or less. If this value is too large, the durability to cracking during repeated impacts may be poor, or the initial velocity may be low, making it difficult to achieve the desired distance. On the other hand, if this value is too small, the spin rate on full shots may be high, making it difficult to achieve the desired distance.

[0037] Furthermore, the value of (Cs-C50) / (C25-Cc) is preferably 3.0 or more, more preferably 3.3 or more, and even more preferably 3.6 or more, with the upper limit being preferably 20.0 or less, more preferably 13.0 or less, and even more preferably 7.0 or less. If this value is too large, the durability to cracking when repeatedly hit may be poor, or the initial velocity may be low, making it impossible to achieve the desired flight distance. On the other hand, if the value is too small, the amount of spin may be high when a full shot is made, making it impossible to achieve the desired flight distance.

[0038] Furthermore, the value of (Cs-C50) / (C50-Cc) is preferably 1.1 or more, more preferably 1.3 or more, and even more preferably 1.6 or more. The upper limit is not particularly limited, but is preferably 8.0 or less, more preferably 4.0 or less. If this value is too large, the durability to cracking when repeatedly hit may be poor, or the initial velocity of the actual shot may be low, making it impossible to achieve the desired flight distance. On the other hand, if the above value is too small, the amount of spin when hitting a full shot may be too high, making it impossible to achieve the desired flight distance.

[0039] In addition, for the core used in the present invention, the core volume V (cm 3) × C50 is taken as Core vh, Core vh must be 630 or greater, preferably 650 or greater, and more preferably 680 or greater, with the upper limit being 1000 or less, preferably 950 or less, and more preferably 900 or less. If this value is too large, the amount of spin on a full shot may be too great, making it impossible to achieve the desired distance. On the other hand, if this value is too small, the initial velocity on actual impact may be low, making it impossible to achieve the desired distance.

[0040] Next, the envelope layer will be described. In the present invention, the envelope layer can be formed as a single layer or as two or more layers. When the envelope layer is formed as two or more layers, the innermost layer is called the inner envelope layer, and the outermost layer is called the outer envelope layer. When the envelope layer is formed as a multi-layer, the material hardness and surface hardness of the envelope layer described below refer to the material hardness and surface hardness of the outer envelope layer.

[0041] The material hardness of the envelope layer is not particularly limited, but is preferably 67 or more, more preferably 70 or more, and even more preferably 72 or more in Shore C hardness, with the upper limit being preferably 90 or less, more preferably 89 or less, and even more preferably 88 or less.The Shore D hardness is preferably 43 or more, more preferably 45 or more, and even more preferably 47 or more, with the upper limit being preferably 60 or less, more preferably 56 or less, and even more preferably 54 or less.

[0042] The surface hardness of the sphere having a core coated with an envelope layer is preferably 75 or more, more preferably 78 or more, and even more preferably 80 or more, in Shore C hardness, with an upper limit of preferably 95 or less, more preferably 93 or less, and even more preferably 92 or less.The surface hardness of the sphere is preferably 49 or more, more preferably 51 or more, and even more preferably 53 or more, with an upper limit of preferably 66 or less, more preferably 62 or less, and even more preferably 60 or less, in Shore D hardness.

[0043] If the material hardness and surface hardness of the envelope layer are too soft, the ball may spin too much on a full shot, resulting in a low initial velocity and a short distance. On the other hand, if the material hardness and surface hardness of the envelope layer are too hard, the ball may feel hard on impact, may be less durable against cracking when hit repeatedly, or may have an increased spin rate on a full shot, resulting in a short distance.

[0044] When the envelope layer is made up of multiple layers, it is preferable that the surface hardness of the outer envelope layer be higher than that of the inner envelope layer. When one or more layers are interposed between the inner envelope layer and the outer envelope layer, it is preferable that the surface hardness of each layer be gradually increased from the inner envelope layer to the outer envelope layer. If this is not the case, the spin rate on full shots may increase, resulting in a loss of distance. Furthermore, a multi-layer envelope layer design may result in an advantageous flight distance due to the low spin effect on full shots compared to a single-layer envelope layer.

[0045] The thickness of the envelope layer is preferably 2.0 mm or more, more preferably 2.7 mm or more, and even more preferably 3.5 mm or more. Meanwhile, the upper limit of the envelope layer thickness is preferably 7.0 mm or less, more preferably 6.5 mm or less, and even more preferably 6.0 mm or less. Here, the envelope layer thickness refers to the total thickness of the envelope layer when the envelope layer is made up of multiple layers. If the envelope layer is too thin, the low spin effect on full shots with an iron may be insufficient, making it impossible to achieve the desired flight distance. If the envelope layer is too thick, the initial velocity of the entire ball may be low, the initial velocity at actual impact may be too low, and the desired flight distance may not be achieved.

[0046] Furthermore, the thickness of the envelope layer, in relation to the thickness of the intermediate layer and the cover described below, preferably satisfies the condition (cover thickness)<(intermediate layer thickness)≦(total envelope layer thickness). Furthermore, with regard to the ratio of the thicknesses of the individual layers, the value of (total envelope layer thickness) / (cover thickness + intermediate layer thickness) is preferably 1.0 or greater, more preferably 1.5 or greater, and even more preferably 1.8 or greater, with the upper limit being preferably 3.5 or less, more preferably 3.0 or less, and even more preferably 2.6 or less. If this value is too large, the initial velocity may be low, resulting in a loss of distance and poor durability to cracking due to repeated impacts. If this value is too small, the low spin effect may be insufficient, resulting in a loss of distance.

[0047] The material for the envelope layer is not particularly limited, but known resins can be used. Particularly preferred examples of the material include the following components (a) to (c): (a) an olefin-unsaturated carboxylic acid binary random copolymer and / or a metal ion-neutralized product of an olefin-unsaturated carboxylic acid binary random copolymer; (b) a base resin prepared by blending 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 in a mass ratio of 100:0 to 0:100; (c) A resin composition in which a non-ionomeric thermoplastic elastomer and a non-ionomeric thermoplastic elastomer are blended in a mass ratio of 100:0 to 50:50 can be exemplified.

[0048] For the components (a) to (c), for example, the resin materials for the intermediate layer described in JP-A-2010-253268 can be suitably used.

[0049] Any additives can be added to the resin material as appropriate depending on the application. For example, various additives such as pigments, dispersants, antioxidants, UV absorbers, and light stabilizers can be added. When these additives are added, the amount of the additives added is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, per 100 parts by mass of the total of the base resin, and preferably 10 parts by mass or less, more preferably 4 parts by mass or less.

[0050] Next, the intermediate layer will be described. The material hardness of the intermediate layer is not particularly limited, but is preferably 58 or more, more preferably 60 or more, and even more preferably 63 or more in Shore D hardness, with the upper limit being preferably 70 or less, more preferably 68 or less, and even more preferably 65 or less.The Shore C hardness is preferably 87 or more, more preferably 89 or more, and even more preferably 93 or more, with the upper limit being preferably 100 or less, more preferably 98 or less, and even more preferably 96 or less.

[0051] Furthermore, the surface hardness of a sphere (intermediate layer-coated sphere) obtained by coating the above-mentioned envelope layer-coated sphere with an intermediate layer, in Shore D hardness, is preferably 64 or more, more preferably 66 or more, and even more preferably 69 or more, with an upper limit of preferably 76 or less, more preferably 74 or less, and even more preferably 71 or less.The Shore C hardness is preferably 90 or more, more preferably 93 or more, and even more preferably 96 or more, with an upper limit of preferably 100 or less, more preferably 99 or less, and even more preferably 98 or less.

[0052] If the material hardness and surface hardness of the intermediate layer are too soft, the ball may spin too much on a full shot, or the initial velocity may be low, resulting in a loss of distance. On the other hand, if the material hardness and surface hardness of the intermediate layer are too hard, the ball may have poor durability against cracking during repeated shots, or the feel on impact may be too hard when hitting with a putt or on a short approach shot.

[0053] The surface hardness of the intermediate layer-coated sphere is related to the surface hardness of the ball as follows: (Surface hardness of ball with intermediate layer) > (Surface hardness of ball) If the above conditions are not met, the amount of spin on full shots will increase, resulting in less distance, and controllability during short games will be impaired.

[0054] 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. 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 be thicker than the cover (outermost layer) described below. If the thickness of the intermediate layer is outside the above range or is thinner than the cover, the low spin effect upon driver (W#1) shots may be insufficient, resulting in a loss of distance. Furthermore, if the intermediate layer is too thin, crack resistance upon repeated shots and durability at low temperatures may be impaired.

[0055] As for the material of the intermediate layer, it is preferable to use various thermoplastic resins used as golf ball materials, in particular, highly neutralized resin materials or ionomer resins containing components (a) to (c) described in the material of the envelope layer.

[0056] 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.

[0057] A particularly preferred embodiment is one in which a zinc-neutralized ionomer resin and a sodium-neutralized ionomer resin are mixed and used as the main material. The blending ratio, zinc-neutralized / sodium-neutralized (mass ratio), is 25 / 75 to 75 / 25, preferably 35 / 65 to 65 / 35, and more preferably 45 / 55 to 55 / 45. If the zinc-neutralized ionomer and sodium-neutralized ionomer are not included within this ratio, the resilience may be too low to achieve the desired distance, and crack resistance may be poor during repeated impacts at room temperature, and crack resistance may also be poor at low temperatures (below freezing).

[0058] In addition, as the resin material for the intermediate layer, a commercially available ionomer resin with a high acid content of 16% by mass or more can be blended with a regular ionomer resin. This blend provides high resilience and low spin, resulting in good distance when hit with a driver (W#1).

[0059] 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, and more preferably 18% by mass or more, with the upper limit being 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, spin increases on full shots, which may prevent the desired flight distance from being achieved. Conversely, if this value is too large, the feel at impact may be too hard, or durability to cracking during repeated impacts may be poor.

[0060] The amount of the high-acid content ionomer resin is preferably 10% by mass or more, more preferably 30% by mass or more, and even more preferably 60% by mass or more, 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 may increase when hitting with a driver (W#1), resulting in a loss of distance.

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

[0062] It is preferable to polish the surface of the intermediate layer material to improve adhesion with the polyurethane that is preferably used in the cover material described below. After the polishing process, it is also preferable to apply a primer (adhesive) to the surface of the intermediate layer or to add an adhesion enhancer to the material.

[0063] The specific gravity of the intermediate layer material is usually less than 1.1, preferably 0.90 to 1.05, and more preferably 0.93 to 0.99. If the specific gravity is outside this range, the ball's overall resilience will decrease, resulting in a shorter flight distance and reduced durability against cracking due to repeated impacts.

[0064] Next, the cover (outermost layer) will be described. The cover material hardness is not particularly limited, but is preferably 35 or greater, more preferably 40 or greater, and even more preferably 45 or greater in Shore D hardness, with an upper limit of preferably 60 or less, more preferably 55 or less, and even more preferably 50 or less. The cover material hardness is preferably 57 or greater, more preferably 63 or greater, and even more preferably 70 or greater in Shore C hardness, with an upper limit of preferably 89 or less, more preferably 83 or less, and even more preferably 76 or less.

[0065] The surface hardness of a ball (covered ball) obtained by covering a mid layer-covered ball with a cover is preferably 50 or more, more preferably 53 or more, and even more preferably 56 or more, in Shore D hardness, with an upper limit of preferably 70 or less, more preferably 67 or less, and even more preferably 64 or less.The surface hardness of a Shore C hardness is preferably 75 or more, more preferably 80 or more, and even more preferably 85 or more, with an upper limit of preferably 95 or less, more preferably 92 or less, and even more preferably 90 or less.

[0066] If the cover material hardness and ball surface hardness are too soft, the spin rate on full iron shots may increase, resulting in a loss of distance.On the other hand, if the cover material hardness and ball surface hardness are too hard, the spin rate on approaches may decrease and abrasion resistance may be reduced.

[0067] The cover thickness is preferably 0.3 mm or more, more preferably 0.45 mm or more, and even more preferably 0.6 mm or more. The upper limit of the cover thickness is 1.0 mm or less, preferably 0.9 mm or less, and even more preferably 0.85 mm or less. If the cover is too thick, full iron shots may result in insufficient repulsion or excessive spin, resulting in a loss of distance. On the other hand, if the cover is too thin, the abrasion resistance may be poor, and spin may not be applied on approaches, resulting in a lack of controllability.

[0068] The cover may be made from any of the thermoplastic or thermosetting resins typically used in golf ball cover materials, but a urethane resin is preferred from the viewpoints of controllability and abrasion resistance. From the viewpoint of mass production of golf ball products, it is particularly preferred to use a material primarily made of thermoplastic polyurethane, and more preferably, the cover may be made from a resin blend primarily composed of (I) a thermoplastic polyurethane and (II) a polyisocyanate compound.

[0069] The total mass of the components (I) and (II) is preferably 60% or more, and more preferably 70% or more, of the total mass of the resin composition of the cover. Components (I) and (II) are described in detail below.

[0070] Regarding the above-mentioned (I) thermoplastic polyurethane, the structure of the thermoplastic polyurethane includes a soft segment composed of a long-chain polyol (polymeric glycol) and a hard segment composed of a chain extender and a polyisocyanate compound. The long-chain polyol used as the raw material can be any of those conventionally used in thermoplastic polyurethane-related technologies, and is not particularly limited. Examples of such long-chain polyols include polyester polyols, polyether polyols, polycarbonate polyols, polyester polycarbonate polyols, polyolefin polyols, conjugated diene polymer polyols, castor oil polyols, silicone polyols, and vinyl polymer polyols. These long-chain polyols may be used alone or in combination. Among these, polyether polyols are preferred because they can synthesize thermoplastic polyurethanes with high rebound resilience and excellent low-temperature properties.

[0071] The chain extender may be any of those used in conventional thermoplastic polyurethane technologies, and is preferably a low-molecular-weight compound having two or more active hydrogen atoms in the molecule that can react with isocyanate groups and a molecular weight of 400 or less. Examples of the chain extender include, but are not limited to, 1,4-butylene glycol, 1,2-ethylene glycol, 1,3-butanediol, 1,6-hexanediol, and 2,2-dimethyl-1,3-propanediol. Of these, aliphatic diols having 2 to 12 carbon atoms are preferred, and 1,4-butylene glycol is more preferred.

[0072] The polyisocyanate compound may be any of those used in conventional thermoplastic polyurethane technologies, and is not particularly limited. Specifically, one or more compounds selected from the group consisting of 4,4'-diphenylmethane diisocyanate, 2,4-(or) 2,6-toluene diisocyanate, p-phenylene diisocyanate, xylylene diisocyanate, naphthylene 1,5-diisocyanate, tetramethylxylene diisocyanate, hydrogenated xylylene diisocyanate, dicyclohexylmethane diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, norbornene diisocyanate, trimethylhexamethylene diisocyanate, and dimer acid diisocyanate may be used. However, some isocyanate species may make it difficult to control the crosslinking reaction during injection molding. In the present invention, from the viewpoint of the balance between stability during production and the physical properties that are exhibited, 4,4'-diphenylmethane diisocyanate, which is an aromatic diisocyanate, is most preferred.

[0073] Specific examples of thermoplastic polyurethanes that can be used as component (I) include commercially available products such as Pandex T8295, T8290, and T8260 (all manufactured by DIC Covestro Polymers).

[0074] Although not a required component, a thermoplastic elastomer other than the thermoplastic polyurethane may be blended as component (III) in addition to components (I) and (II). By blending component (III) in the resin blend, it is possible to further improve the flowability of the resin blend and enhance the various physical properties required of a golf ball cover material, such as resilience and abrasion resistance.

[0075] There are no particular limitations on the composition ratio of the above components (I), (II), and (III). However, in order to fully and effectively exert the effects of the present invention, the mass ratio of (I):(II):(III) is preferably 100:2-50:0-50, and more preferably (I):(II):(III) is 100:2-30:8-50 (mass ratio).

[0076] Furthermore, various additives other than the components constituting the thermoplastic polyurethane may be blended into the resin blend as needed. For example, pigments, dispersants, antioxidants, light resistance stabilizers, ultraviolet absorbers, mold release agents, etc. may be blended as appropriate.

[0077] The multi-piece solid golf ball formed by laminating the above-mentioned core, envelope, intermediate layer, and cover (outermost layer) can be manufactured by conventional methods such as known injection molding. For example, the envelope and intermediate layer materials are sequentially injected into respective injection molds around the core to obtain each covered sphere, and finally, the cover material, which is the outermost layer, is injection molded to obtain a multi-piece golf ball. Alternatively, each covered layer can be formed by encasing the covered sphere in two half-cups previously molded into a spherical half-shell and molding the covered sphere under heat and pressure.

[0078] The golf ball must have a deflection (mm) of 2.8 mm or more when subjected to an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf), preferably 3.1 mm or more, and more preferably 3.4 mm or more. The upper limit of the deflection is preferably 4.5 mm or less, more preferably 4.2 mm or less, and even more preferably 4.0 mm or less. If the golf ball's deflection is too small, i.e., too hard, the spin rate may increase too much, resulting in a loss of flight distance, 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, resulting in a loss of flight distance, the feel may be too soft, or the durability to cracking upon repeated impact may be poor.

[0079] If the deflection of the core when subjected to an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf) is C (mm), and the deflection of the ball when subjected to an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf) is B (mm), the value of C / B must be 1.6 or greater, preferably 1.7 or greater. The upper limit must be 2.3 or less, preferably 2.1 or less. If this value is too high, the initial velocity on impact may be low, resulting in a loss of distance or poor durability to cracking due to repeated impacts. On the other hand, if this value is too low, the ball's spin reduction effect may be insufficient, resulting in a loss of distance.

[0080] The CB value is preferably 2.5 mm or more, more preferably 2.6 mm or more, and even more preferably 2.7 mm or more, with the upper limit being preferably 5.0 mm or less, more preferably 4.6 mm or less, and even more preferably 4.3 mm or less. If this value is too large, the initial velocity on actual impact may be low, resulting in a loss of distance or poor durability to cracking due to repeated impacts. If this value is too small, the low spin effect may be insufficient, resulting in a loss of distance.

[0081] [ Hardness of each layer 〕 In the present invention, the Shore C hardness of the surface of the core, the Shore C hardness of the surface of a sphere obtained by covering the core with an envelope layer (envelopment layer-coated sphere), the Shore C hardness of the surface of a sphere obtained by covering the envelope layer-coated sphere with an intermediate layer (intermediate layer-coated sphere), and the Shore C hardness of the surface of the ball are: (Shore C hardness of the surface of the envelope-coated sphere) > (Shore C hardness of the surface of the core), and (Shore C hardness of the surface of the ball coated with the intermediate layer) > (Shore C hardness of the surface of the ball) The following conditions must be met.

[0082] The surface hardness of the envelope-coated sphere minus the surface hardness of the core is greater than 0, preferably at least 8, more preferably at least 15, in Shore C hardness, with the upper limit being preferably not more than 50, more preferably not more than 43, and even more preferably not more than 36. If this value falls outside the above range, the amount of spin on a full shot will increase, and the desired distance may not be achieved.

[0083] The value obtained by subtracting the ball surface hardness from the surface hardness of the intermediate layer-covered sphere is greater than 0, preferably 3 or greater, more preferably 5 or greater, in Shore C hardness, with the upper limit preferably being 30 or less, more preferably 22 or less, and even more preferably 15 or less. If this value is too small, controllability in short games may be impaired. On the other hand, if this value is too large, the amount of spin on full shots may increase, making it difficult to achieve the desired distance.

[0084] Furthermore, the surface hardness of the envelope-coated sphere minus the center hardness of the core is preferably 29 or more, more preferably 32 or more, and even more preferably 35 or more, on the Shore C hardness scale. The upper limit is preferably 55 or less, more preferably 50 or less, and even more preferably 45 or less. If this value is too high, the durability to cracking after repeated impacts may be poor, or the initial velocity may be low, preventing the desired distance from being achieved. On the other hand, if this value is too low, the spin rate on full shots may be high, preventing the desired distance from being achieved.

[0085] The surface hardness of the intermediate layer-coated ball minus the surface hardness of the envelope layer-coated ball is preferably greater than 0, more preferably at least 4, and even more preferably at least 8, in Shore C hardness, with the upper limit being preferably no greater than 28, more preferably no greater than 22, and even more preferably no greater than 16. If this value falls outside the above range, the amount of spin on a full shot will increase, and the desired distance may not be achieved.

[0086] The surface hardness of the intermediate layer-covered sphere minus the center hardness of the core is preferably 33 or more, more preferably 38 or more, and even more preferably 43 or more, on the Shore C hardness scale. The upper limit is preferably 65 or less, more preferably 60 or less, and even more preferably 55 or less. If this value is too high, the durability to cracking after repeated impacts may be poor, and the initial velocity may be low, preventing the desired distance from being achieved. On the other hand, if this value is too low, the spin rate on full shots may be high, preventing the desired distance from being achieved.

[0087] [Relationship between volume and hardness of core and surrounding layer] Core volume (cm 3 ) × Shore C hardness (Cm) at the midpoint between the core surface and the core center is Core vh, and the volume of the inner envelope layer (cm 3 ) × the surface hardness (Shore C) of the inner envelope layer coated sphere is IE vh, and the volume of the outer envelope layer (cm 3 When OE vh is the sum of the surface hardness (Shore C) of the outer envelope layer and the surface hardness (OE vh + IE vh) of the coated ball, the value of (OE vh + IE vh) / Core vh is preferably 1.0 or greater, more preferably 1.2 or greater, and even more preferably 1.4 or greater, with the upper limit being preferably 2.3 or less, more preferably 2.1 or less, and even more preferably 1.9 or less. If this value is too large, the initial velocity at actual impact may be low, resulting in a loss of distance and poor durability to cracking due to repeated impacts. On the other hand, if this value is too small, the low spin effect may be insufficient, resulting in a loss of distance.

[0088] A large number of dimples can be formed on the outer surface of the cover, which is the outermost layer. There are no particular restrictions on the number of dimples arranged on the cover surface, but the number is preferably 250 or more, more preferably 300 or more, and more preferably 320 or more, with the upper limit being preferably 380 or less, more preferably 350 or less, and even more preferably 340 or less. If the number of dimples exceeds the above range, the ball's trajectory may be lowered, resulting in a shorter flight distance. Conversely, if the number of dimples is too low, the ball's trajectory may be higher, resulting in a shorter flight distance.

[0089] The dimples may be of one or a combination of two or more shapes, such as circular, polygonal, dewdrop, or elliptical. For example, if circular dimples are used, the diameter may be approximately 2.5 mm to 6.5 mm, and the depth may be 0.08 mm to 0.30 mm.

[0090] The dimple coverage (SR value), which is the ratio of the total dimple area defined by the planes surrounded by the dimple edges to the ball's area assuming no dimples, is preferably 70% to 90% in order to fully demonstrate aerodynamic characteristics. Furthermore, V0, the value obtained by dividing the spatial volume of each dimple below the plane surrounded by the dimple edges by the volume of a cylinder whose base is the plane and whose height is the maximum depth of the dimple from the bottom, is preferably 0.35 to 0.80 in order to optimize the ball's trajectory. Furthermore, the VR value, which is the ratio of the total dimple volume below the planes surrounded by the dimple edges to the ball's area assuming no dimples, is preferably 0.6% to 1.0%. Any deviation from the above-mentioned ranges may result in a poor trajectory and an insufficient flight distance.

[0091] A paint film layer (coating layer) can be formed on the surface of the cover. This paint film layer can be applied using various paints, and as the paint, a paint composition containing a urethane paint composed of a polyol and a polyisocyanate as the main component is preferably used, since the paint must be able to withstand the harsh conditions of use of the golf ball.

[0092] Examples of the polyol component include acrylic polyols, polyester polyols, etc. These polyols include modified polyols, and other polyols may be added to further improve workability.

[0093] As the polyol component, it is preferable to use two types of polyester polyols in combination. In this case, if the two types of polyester polyols are component (a) and component (b), the polyester polyol of component (a) can be a polyester polyol having a cyclic structure introduced into the resin skeleton, such as a polyester polyol obtained by polycondensation of a polyol having an alicyclic structure such as cyclohexanedimethanol with a polybasic acid, or a polyol having an alicyclic structure with a diol or triol with a polybasic acid. On the other hand, the polyester polyol of component (b) can be a polyester polyol having a multi-branched structure, such as a polyester polyol having a branched structure such as "NIPPOLAN 800" manufactured by Tosoh Corporation.

[0094] On the other hand, the polyisocyanate is not particularly limited and may be a commonly used aromatic, aliphatic, alicyclic, or other polyisocyanate, such as 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.

[0095] 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.

[0096] The thickness of the coating layer made of the above coating composition is not particularly limited, but is usually 5 to 40 μm, preferably 10 to 20 μm. The coating layer thickness here refers to the average thickness of the coating measured at three locations: the center of the dimple and two locations between the center of the dimple and the edge of the dimple.

[0097] In the present invention, the elastic work recovery rate of the coating layer made of the above-mentioned coating composition must be 60% or more, and preferably 80% or more. If the elastic work recovery rate of this coating layer is within the above range, the coating layer will have high elasticity, therefore a high self-repair function and excellent abrasion resistance. Furthermore, the various performance properties of golf balls coated with the above-mentioned coating composition can be improved. The above-mentioned elastic work recovery rate can be measured as follows.

[0098] The elastic work recovery is a parameter of the nanoindentation method, which evaluates the physical properties of a coating layer. Conventional methods can only measure the size of the deformation mark (plastic deformation mark) corresponding to the maximum load. However, the nanoindentation method automatically and continuously measures the relationship between the indentation load and the indentation depth. This allows for highly accurate evaluation of the physical properties of a coating layer without the individual variability that occurs when visually measuring deformation marks with an optical microscope. Because the coating layer on a golf ball's surface is significantly affected by impacts from drivers and various clubs, and the coating layer's influence on the physical properties of a golf ball is significant, measuring the coating layer with the ultramicrohardness test method, which can be performed with higher precision than conventional methods, is a highly effective evaluation method.

[0099] The hardness of the coating layer is preferably 40 or more, more preferably 60 or more, in Shore M hardness, with an upper limit of preferably 95 or less, more preferably 85 or less. This Shore M hardness conforms to ASTM D2240. The hardness of the coating layer is preferably 40 or more, more preferably 50 or more, in Shore C hardness. The upper limit is preferably 80 or less, more preferably 70 or less. This Shore C hardness conforms to ASTM D2240. If the coating layer has a hardness that is too high above the above range, the coating may become brittle upon repeated impacts, potentially making it unable to protect the cover layer. If the coating layer has a hardness that is too low below the above range, the ball surface may be easily scratched when hit against a hard object, which is undesirable.

[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 using a conventional coating process, and then dried to form a coating layer on the surface of the ball. In this case, the coating method can be suitably spray coating, electrostatic coating, dipping, or the like, and is not particularly limited.

[0101] The multi-piece solid golf ball of the present invention can be made to conform to the Rules of Golf for competitive use, with an outer diameter that does not pass through a ring with an inner diameter of 42.672 mm, and a mass preferably ranging from 45.0 to 45.93 g.

[0102] Furthermore, the initial velocity of a golf ball based on the R&A Golf Rules is typically 76.8 m / s, preferably 77.0 m / s or higher, more preferably 77.1 m / s or higher, with the upper limit being 77.724 m / s or lower. If this initial velocity exceeds 77.724 m / s, it is not within the scope of the official rules. On the other hand, if the initial velocity is too low, the ball may not achieve the desired distance on a full shot. [Example]

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

[0104] [Examples 1 to 4, Comparative Examples 1 to 8] Core formation The rubber compositions of the examples and comparative examples shown in Table 1 were prepared, and then vulcanized and molded under the vulcanization conditions of each example shown in Table 1 to produce solid cores.

[0105] However, for Examples 1 and 2 and Comparative Examples 7 and 8, the cores were prepared based on the formulations in Table 1 in the same manner as above.

[0106] [Table 1]

[0107] The details of each component listed in Table 1 are as follows: Polybutadiene: JSR Corporation, product name "BR730" Zinc acrylate: "ZN-DA85S" (Nippon Shokubai Co., Ltd.) Organic peroxide: a mixture of 1,1-di(t-butylperoxy)cyclohexane and silica, trade name "Perhexa C-40" (manufactured by NOF Corporation) Zinc stearate: Product name "Zinc Stearate G" (NOF Corporation) Antioxidant: 2,2-methylenebis(4-methyl-6-butylphenol), product name "Nocrac NS-6" (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) Zinc oxide: Product name "Triple Zinc Oxide" (manufactured by Sakai Chemical Industry Co., Ltd.) Pentachlorothiophenol zinc salt: Wako Pure Chemical Industries, Ltd.

[0108] Enveloping layer (inner / outer) Next, for each Example and Comparative Example except Comparative Examples 4 to 6, an inner envelope layer was formed around the core by injection molding using an inner envelope layer material with the No. 1 formulation shown in Table 2, and then an outer envelope layer was formed by injection molding using an outer envelope layer material with the No. 1, No. 2, or No. 3 formulation shown in the same table. For Comparative Examples 4 to 6, a single envelope layer (details are given in the "outer envelope layer" column in the table) was formed around the core by injection molding using the material with the No. 1 or No. 3 formulation shown in Table 2.

[0109] However, in Examples 1 and 2 and Comparative Examples 7 and 8, the envelope layer is prepared based on the formulation in Table 2 in the same manner as above.

[0110] Formation of the intermediate layer and cover (outermost layer) Next, for all Examples and Comparative Examples, an intermediate layer was formed around the envelope layer-coated sphere obtained above by injection molding using an intermediate layer material having a composition No. 4 or No. 5 of the composition shown in Table 2. Next, a cover (outermost layer) was formed around the intermediate layer-coated sphere of each Example by injection molding using a cover material having a composition No. 6 or No. 7 of the composition shown in Table 2. At this time, a predetermined number of dimples common to all Examples and Comparative Examples were formed on the surface of the cover.

[0111] However, for Examples 1 and 2 and Comparative Examples 7 and 8, the intermediate layer and cover were prepared based on the formulations in Table 2 in the same manner as above.

[0112] [Table 2]

[0113] The trade names of the main materials listed in the table are as follows: "HPF1000" and "HPF2000" are trademarks of The Dow Chemical Company. "Himilan 1605", "Himilan 1557", "Himilan 1706" are ionomers manufactured by Mitsui Dow Polychemicals "Surlyn 8120" ionomer manufactured by The Dow Chemical Company "Dynaron 6100P" hydrogenated polymer manufactured by JSR Corporation "Behenic acid" NOF Corporation's "NAA222-S" (bead specification) "Calcium hydroxide" "CLS-B" manufactured by Shiraishi Kogyo Co., Ltd. "Trimethylolpropane" manufactured by Tokyo Chemical Industry Co., Ltd. "TPU (1)" "TPU (2)" are trade names of DIC Covestro Polymers, Pandex, ether-type thermoplastic polyurethanes.

[0114] The dimples common to all examples and comparative examples were eight types of circular dimples, the details of which are shown in Table 3 below, and the arrangement of the dimples is as shown in Figure 2. Figure 2(A) shows a plan view of the dimples, and Figure 2(B) shows a side view thereof.

[0115] [Table 3]

[0116] Dimple definition Edge: The highest point on the cross section passing through the center of the dimple Diameter: The diameter of the plane enclosed by the dimple edge Depth: The maximum depth of the dimple from the plane bounded by the dimple edge SR: The ratio of the total dimple area, defined as the plane surrounded by the edges of the dimples, to the area of ​​the ball as if no dimples existed. Dimple volume: The volume of the dimple below the plane surrounded by the dimple edge Cylinder volume ratio: The ratio of the dimple volume to the volume of a cylinder with the same diameter and depth as the dimple. VR: The total volume of the dimples formed below the plane surrounded by the edges of the dimples is the volume of the ball as if no dimples existed.

[0117] Formation of paint layer (coating layer) Next, the coating composition shown in Table 4 below was used as the coating composition common to all Examples and Comparative Examples, and the coating was applied to the surface of a large number of covers (outermost layers) using an air spray gun to produce golf balls with a coating layer 15 μm thick. However, for Examples 1 and 2 and Comparative Examples 7 and 8, the above paint was applied in the same manner as above to prepare golf balls on which a paint layer having a thickness of 15 μm was formed.

[0118] [Table 4]

[0119] [Synthesis example of polyester polyol (A)] A reaction apparatus equipped with a reflux condenser, a dropping funnel, a gas inlet tube, and a thermometer was charged with 140 parts by mass of trimethylolpropane, 95 parts by mass of ethylene glycol, 157 parts by mass of adipic acid, and 58 parts by mass of 1,4-cyclohexanedimethanol, and the mixture was heated to 200-240°C with stirring and heated (reacted) for 5 hours. After that, a "polyester polyol (A)" with an acid value of 4, a hydroxyl value of 170, and a weight average molecular weight (Mw) of 28,000 was obtained. Next, the polyester polyol (A) synthesized above was dissolved in butyl acetate to prepare a varnish having a nonvolatile content of 70% by mass.

[0120] The coating composition "C" in Table 4 was prepared by mixing 23 parts by mass of the polyester polyol solution described above with 15 parts by mass of "polyester polyol (B)" (saturated aliphatic polyester polyol "NIPPOLAN 800" manufactured by Tosoh Corporation, weight average molecular weight (Mw) 1,000, solid content 100%) and an organic solvent to form the base component. This mixture had a non-volatile content of 38.0% by mass.

[0121] Elastic work recovery rate The elastic work recovery rate of the paint is measured using a 50 μm thick coating sheet. The measuring device used is the Elionix ultra-micro hardness tester "ENT-2100," and the measurement conditions are as follows: Indenter: Berkovich indenter (material: diamond, angle α: 65.03°) Load F: 0.2mN Loading time: 10 seconds ·Holding time: 1 second ·Unloading time: 10 seconds Indentation work due to return deformation of the coating film W elast (Nm) and mechanical pushing work W total Based on this, the elastic work recovery rate is calculated using the following formula: Elastic work recovery rate = W elast / W total × 100(%)

[0122] Shore C hardness and Shore M hardness The Shore C hardness and Shore M hardness in Table 3 above were measured by preparing 2 mm thick sheets, stacking three of them as test pieces, and using a Shore C hardness tester and a Shore M hardness tester in accordance with ASTM D2240 standard.

[0123] The physical properties of each of the resulting golf balls, such as the internal hardness 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 5 and 6.

[0124] The outer diameter of each sphere: core, (inner and outer) envelope layer coated sphere, and intermediate layer coated sphere Measurements were taken at five randomly selected points on the surface at a temperature of 23.9±1°C, and the average value was used as the measurement value for each sphere. The average value for 10 measurements was then calculated.

[0125] Ball diameter Measurements were taken at 15 randomly selected non-dimpled locations at a temperature of 23.9±1°C, and the average value was used as the measurement value for one ball. The average value for 10 balls was calculated.

[0126] Deflection of the core, each layer of the covered sphere, and the ball The core, each layer of covered sphere, or the target covered sphere of the ball is placed on a hard plate and the amount of deflection is measured when an initial load of 98 N (10 kgf) is applied and a final load of 1275 N (130 kgf) is applied. Note that the above deflection is measured after adjusting the temperature to 23.9°C. The head compresses the core, each layer of covered sphere, or the ball at a pressure speed of 10 mm / s.

[0127] Core hardness distribution The core surface is spherical, and the needle of the hardness tester was set nearly perpendicular to the spherical surface, and the core surface hardness was measured in Shore C hardness according to ASTM D2240. Hardness was measured using an automatic rubber hardness tester "P2" manufactured by Kobunshi Keiki Co., Ltd., equipped with a Shore C hardness tester. The maximum hardness value was read. All measurements were performed in an environment of 23±2°C. The cross-sectional hardness at predetermined positions on each core (Cc, Cs, C75, C50, C25, C25) was measured by cutting the core into a hemisphere, flattening the cross section, and pressing the needle of the hardness tester perpendicular to the measurement area. The values ​​are expressed as Shore C hardness.

[0128] The hardness distribution of the cores of each example and comparative example is shown in the graphs of FIG. 3 (Examples 1 to 4), FIG. 4 (Comparative Examples 1 to 5 and 7), and FIG. 5 (Comparative Examples 6 and 8).

[0129] (Inner / outer) Material hardness of the envelope layer, mid layer, and cover (Shore C hardness, Shore D hardness) The resin material for each layer was molded into a 2 mm thick sheet and left to stand at a temperature of 23 ± 2°C for two weeks. Three sheets were stacked together during measurement. The Shore C hardness and Shore D hardness were measured using a Shore C hardness tester and a Shore D hardness tester, respectively, in accordance with the ASTM D2240 standard. To measure hardness, an automatic rubber hardness tester "P2" manufactured by Kobunshi Keiki Co., Ltd., equipped with a Shore C or Shore D hardness tester, was used. The hardness value was read as the maximum value.

[0130] (Inner and outer) Surface hardness (Shore C hardness, Shore D hardness) of the envelope layer coated sphere, the intermediate layer coated sphere, and the ball Measurements were taken by pressing a needle perpendicularly against the surface of each sphere. The surface hardness of the ball (cover) was measured on the land area on the ball surface where no dimples were formed. Shore C hardness and Shore D hardness were measured using a Shore C hardness tester and a Shore D hardness tester, respectively, in accordance with the ASTM D2240 standard. Hardness was measured using an automatic rubber hardness tester "P2" manufactured by Kobunshi Keiki Co., Ltd., equipped with a Shore C or Shore D hardness tester. The hardness value was read as the maximum value.

[0131] initial ball speed Measurements were taken using an R&A-approved device, the same type as the USGA's drum-rotating initial velocity meter. The balls were conditioned for at least three hours in an environment of 23.9±1°C, then tested in a room at room temperature of 23.9±2°C. A 250-pound (113.4 kg) head (striking mass) was used to strike the balls at a velocity of 143.8 ft / s (43.83 m / s). A dozen balls were hit four times, each with a distance of 6.28 ft (1.91 m), and the time it took for the balls to travel this distance was measured to calculate the initial velocity (m / s). This cycle took approximately 15 minutes.

[0132] [Table 5]

[0133] [Table 6]

[0134] The distance performance (I#6), spin rate on approach, feel on impact, and durability against repeated impact of each golf ball were evaluated by the following methods. The results are shown in Table 7.

[0135] Distance performance (I#6) An iron (I#6) was attached to the golf hitting robot, and the distance was measured when hitting the ball at a head speed of 44 m / s, and judged according to the following criteria. The club used was the "TourB X-CB" (I#6) manufactured by Bridgestone Sports Co., Ltd. The spin rate was also measured using an initial condition measuring device on the ball immediately after hitting. <Judgment criteria> Total distance: 179.0m or more Total distance less than 179.0m ×

[0136] Evaluating spin rate during approach A sand wedge (SW) was attached to a golf hitting robot and hit at a head speed (HS) of 20 m / s, and the amount of spin was measured. The amount of spin was also measured immediately after hitting using an initial condition measurement device. The sand wedge (SW) used was the "TourB XW-1" (SW) manufactured by Bridgestone Sports. <Judgment criteria> Spin rate of 5900 rpm or more... Spin rate less than 5900 rpm ×

[0137] Hitting feel Amateur golfers with handicaps between 15 and 25 are using irons (I#6 The feel of the club when hitting a full shot is evaluated according to the following criteria. <Judgment criteria> More than 15 out of 20 people rated it as very soft and had a good feel. The number of people who rated the club as soft and with a good feel was between 10 and 14 out of 20. Fewer than 9 out of 20 people rated it as soft and with a good feel... ×

[0138] Resistance to cracking due to repeated impacts A driver (W#1) was attached to a golf hitting robot, and the robot repeatedly hit 10 balls at a head speed of 45 m / s, and the results were judged according to the following criteria. <Judgment criteria> The number of hits for each of the ten balls was counted until the ball began to crack, and the three balls with the fewest number of hits were selected. The average number of hits for the three balls was used to evaluate the "number of cracks" for each example. The number of cracks for Example 3 was assigned an index of 100. Index 90 or higher... 〇 Index less than 90 ×

[0139] [Table 7]

[0140] As shown in the results in Table 7, the golf balls of Comparative Examples 1 to 8 are inferior to the products of the present invention (Examples) in the following respects. In Comparative Example 1, the core volume V (cm 3 ) × C50 is smaller than 630, and the value of (Cs-C75) / (C50-Cc) is larger than 2.3. As a result, the crack resistance against repeated impacts is poor. In Comparative Example 2, the core volume V (cm 3 ) × C50, Core vh is less than 630, and the value of (Cs - C75) / (C50 - Cc) is greater than 2.3, meaning that the value of (amount of core deflection) / (amount of ball deflection) is greater than 2.3. As a result, the durability against cracking due to repeated impacts is poor, the iron's flight distance is inferior, and the feel at impact is not very good. In Comparative Example 3, the core volume V (cm 3 ) × C50, Core vh is smaller than 630, resulting in a poor feel. In Comparative Example 4, the ball deflection was less than 2.8 mm, and the value of (ball deflection) / (core deflection) was less than 1.6. Furthermore, the core volume V (cm 3The value of Core vh, which is the value of (Cs-C75) / (C50-Cc), is greater than 1000, and the value of (Cs-C75) / (C50-Cc) is less than 1.0. As a result, the iron's flight distance is short and the feel at impact is poor. In Comparative Example 5, the ball deflection was less than 2.8 mm, and the value of (ball deflection) / (core deflection) was less than 1.6. Furthermore, the core volume V (cm 3 The value of Core vh, which is the value of (Cs-C75) / (C50-Cc), is greater than 1000, and the value of (Cs-C75) / (C50-Cc) is less than 1.0. As a result, the iron's flight distance is short and the feel at impact is poor. In Comparative Example 6, the ball deflection was less than 2.8 mm, and the value of (ball deflection) / (core deflection) was less than 1.6. Furthermore, the core volume V (cm 3 The value of Core vh, which is the value of (Cs-C75) / (C50-Cc), is greater than 1000, and the value of (Cs-C75) / (C50-Cc) is less than 1.0. As a result, the iron's flight distance is short and the feel at impact is poor. In Comparative Example 7, the ball surface hardness is greater than the intermediate layer surface hardness, and as a result, the amount of spin increases when hit with an iron, resulting in a shorter flight distance and a smaller amount of spin on approaches. In Comparative Example 8, the thickness of the cover (outermost layer) was greater than 1.0 mm, resulting in an increased amount of spin when hit with an iron, a lower initial velocity on actual hit, and a shorter flight distance.

Claims

1. A multi-piece solid golf ball having a core, an envelope layer, an intermediate layer, and a cover, wherein the core is formed of a rubber composition in one or more layers, the envelope layer is formed of a resin material in one or more layers, the intermediate layer is formed of a resin material in one layer, and the cover is formed of a resin material in a single layer with a thickness of 1.0 mm or less, and the Shore C hardness of the surface of the core, the Shore C hardness of the surface of a sphere obtained by covering the core with the envelope layer (enveloping layer-covered sphere), and the Shore C hardness of the surface of a sphere obtained by covering the envelope layer-covered sphere with the intermediate layer (intermediate layer-covered sphere) are and the Shore C hardness of the surface of the ball satisfy the conditions of (Shore C hardness of the surface of the envelope layer-covered sphere) > (Shore C hardness of the surface of the core) and (Shore C hardness of the surface of the intermediate layer-covered sphere) > (Shore C hardness of the surface of the ball), and where C (mm) is the amount of deflection of the core when an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf) is applied, and B (mm) is the amount of deflection of the ball when an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf) is applied, B ≥ 2.8 Furthermore, the core has a volume V (cm ) of 1.6≦C / B≦2.

3. Furthermore, the core has an internal hardness that satisfies the following relationship: 1.0≦(Cs−C75) / (C50−Cc)≦2.3, where Cc is the Shore C hardness at the center of the core, Cs is the Shore C hardness at the surface of the core, C75 is the Shore C hardness at a position 75% of the core radius from the center of the core toward the surface, and C50 is the Shore C hardness at a position 50% of the core radius from the center of the core toward the surface. 3 ) × C50 is defined as Core vh, the condition of 630≦ Core vh ≦1000 is satisfied, and the relationship between the core diameter and the ball diameter is the condition of 0.65≦(core diameter) / (ball diameter)≦0.

80.

2. 2. The multi-piece solid golf ball of claim 1, wherein the core has an internal hardness that satisfies the following relationship: 3.0≦(Cs−C50) / (C25−Cc)≦20.0, where C25 is the Shore C hardness at a position 25% of the core radius from the center of the core toward the surface.

3. 3. The multi-piece solid golf ball according to claim 1, wherein the core has an internal hardness that satisfies the relationship (Cs-C50) / (C50-Cc)≧1.

1.

4. 4. The multi-piece solid golf ball according to claim 1, wherein the relationship between the Shore C hardness of the surface of the envelope layer-coated sphere and the Shore C hardness of the surface of the intermediate layer-coated sphere satisfies the condition: (surface Shore C hardness of the intermediate layer-coated sphere) > (surface Shore C hardness of the envelope layer-coated sphere).

5. 5. The multi-piece solid golf ball of claim 1, wherein the thicknesses of the layers satisfy the condition: (cover thickness)<(intermediate layer thickness)≦(total thickness of the surrounding layers).

6. 6. The multi-piece solid golf ball of claim 1, wherein the ratio of thickness of each layer satisfies the condition: (total thickness of the surrounding layers) / (cover thickness+intermediate layer thickness)≧1.

0.

7. 7. The multi-piece solid golf ball according to claim 1, wherein the envelope layer comprises at least two layers, an inner envelope layer and an outer envelope layer.

8. The relationship between the Shore C hardness of the surface hardness of each layer is expressed by the following formula:

8. The multi-piece solid golf ball of claim 7, which satisfies the condition: (Shore C hardness of the ball surface) < (Shore C hardness of the intermediate layer-coated sphere surface) > (Shore C hardness of the outer envelope layer-coated sphere surface) ≥ (Shore C hardness of the inner envelope layer-coated sphere surface) > (Shore C hardness of the core surface).

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