Multi-piece solid golf ball

Abstract

Provided is a multi-piece solid golf ball including a core, a surrounding layer, an intermediate layer, and a cover, in which the core is formed of a rubber composition and in a hardness profile of the core, letting a Shore C hardness at a core surface be H100, the Shore C hardnesses at each of an 87.5% outer position, a 75% outer position, a 62.5% outer position, a 50% outer position, a 37.5% outer position, a 25% outer position, and a 12.5% outer position of a core radius from a core center be H87.5, H75, H62.5, H50, H37.5, H25, and H12.5, and the Shore C hardness at the core center be HO, the following two conditions are satisfied:0≤(H⁢62.5-H⁢50)<(H⁢100-H 87.5)<(H⁢87.5-H⁢75)<(H⁢75-H 62.5)≤7.,and(H 87.5-H⁢50) / (H⁢50-H 12.5)≥3..

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This non-provisional application claims priority under 35 U.S.C. § 119 (a) on Patent Application No. 2025-040408 filed in Japan on Mar. 13, 2025, the entire contents of which are hereby incorporated by reference.TECHNICAL FIELD

[0002] The present invention relates to a multi-piece solid golf ball composed of at least four layers including a core, a surrounding layer, an intermediate layer, and a cover.BACKGROUND ART

[0003] Conventionally, many attempts for designing a ball into a layer construction have been made, and many balls that satisfy not only professionals but also general amateur golfers from beginners to skilled amateur golfers have been developed. For example, functional multi-piece solid golf balls in which a material hardness and a surface hardness of each layer of a core, a surrounding layer, an intermediate layer, and a cover (outermost layer) are optimized have been widely used. Focusing on a core hardness profile that accounts for most of a volume of the ball, several techniques have been proposed to provide high-performance golf balls by designing core internal hardness in various aspects.

[0004] Examples of such technical documents include the following Patent Documents 1 to 8. These golf balls are golf balls having a layer construction of at least four layers, and by blending water and a plurality of organic peroxides into a rubber composition which is a core material, a specific core hardness gradient is realized, and a distance is improved by optimizing spin characteristics on full shots with a driver or an iron.

[0005] However, in the golf balls described in these patent documents, there remains a problem in achieving both sufficient flight with a low spin rate on full shots and durability to cracking on repeated impact at a high level.CITATION LISTPatent Document 1: JP-A 2015-173860

[0007] Patent Document 2: JP-A 2016-016117

[0008] Patent Document 3: JP-A 2016-116627

[0009] Patent Document 4: JP-A 2016-179052

[0010] Patent Document 5: JP-A 2019-198467

[0011] Patent Document 6: JP-A 2021-176378

[0012] Patent Document 7: JP-A 2021-176380

[0013] Patent Document 8: JP-A 2021-176381SUMMARY OF THE INVENTION

[0014] At The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a multi-piece solid golf ball that achieves both flight performance and durability to repeated impact on full shots with a driver (W #1) and an iron at a high level.

[0015] As a result of intensive studies to achieve the above object, the present inventor has found that, for a golf ball comprising at least four layers including a rubber core and a resin surrounding layer, intermediate layer, and a cover, the core has a hardness profile in which, letting a Shore C hardness at a core surface be H100, a Shore C hardness at a position outside by 87.5% of a core radius from a core center be H87.5, a Shore C hardness at a position outside by 75% of the core radius from the core center be H75, a Shore C hardness at a position outside by 62.5% of the core radius from the core center be H62.5, a Shore C hardness at a position outside by 50% of the core radius from the core center be H50, a Shore C hardness at a position outside by 37.5% of the core radius from the core center be H37.5, a Shore C hardness at a position outside by 25% of the core radius from the core center be H25, a Shore C hardness at a position outside by 12.5% of the core radius from the core center be H12.5, and a Shore C hardness at the core center be H0, the following two conditions are satisfied:0≤(H⁢62.5-H⁢50)<(H⁢100-H 87.5)<(H⁢87.5-H⁢75)<(H⁢75-H 62.5)≤7.,and(H 87.5-H⁢50) / (H⁢50-H 12.5)≥3..

[0016] The present inventor has found that by configuring the golf ball so as to satisfy the above conditions, a spin rate of the ball on full shots is reduced, a distance on shots with a driver (W #1) and an iron is sufficiently extended, and the golf ball has excellent durability to repeated impact, and thus has completed the present invention.

[0017] That is, in the golf ball of the present invention, focusing on the hardness profile of the core in particular, by improving the hardness profile of the core, the spin rate is reduced on full shots, whereby the golf ball has an excellent distance on shots with a driver (W #1) due to a high head speed region, and also has a good distance on shots with an iron. In the core hardness profile in the present invention, the core radius of the center to the surface of a core cross-section is divided into eight equal parts, and the core hardness profile is defined by parameters obtained based on a total of nine measurement points. By improving not only a hardness profile shape of an entire core but also a hardness profile shape from an intermediate point between the surface and the center of the core to the core surface, specifically, by setting a hardness gradient from the position of 62.5% of the core radius from the core center to a surface direction to be gradually gentle, excellent durability to repeated impact is achieved.

[0018] Accordingly, the present invention provides a multi-piece solid golf ball including

[0019] a core, a surrounding layer, an intermediate layer, and a cover, wherein the core is formed of a rubber composition, the surrounding layer, the intermediate layer, and the cover are all formed of a resin composition, and in a hardness profile of the core, letting a Shore C hardness at a core surface be H100, a Shore C hardness at a position outside by 87.5% of a core radius from a core center be H87.5, a Shore C hardness at a position outside by 75% of the core radius from the core center be H75, a Shore C hardness at a position outside by 62.5% of the core radius from the core center be H62.5, a Shore C hardness at a position outside by 50% of the core radius from the core center be H50, a Shore C hardness at a position outside by 37.5% of the core radius from the core center be H37.5, a Shore C hardness at a position outside by 25% of the core radius from the core center be H25, a Shore C hardness at a position outside by 12.5% of the core radius from the core center be H12.5, and a Shore C hardness at the core center be H0, the following two conditions are satisfied:0≤(H⁢62.5-H⁢50)<(H⁢100-H 87.5)<(H⁢87.5-H⁢75)<(H⁢75-H 62.5)≤7.,and(H 87.5-H⁢50) / (H⁢50-H 12.5)≥3..

[0020] In a preferred embodiment of the golf ball according to the invention, the following condition is satisfied:(H⁢100-H 87.5) / (H 87.5-H⁢75)≤0.9.

[0021] In another preferred embodiment of the inventive golf ball, the following six conditions are satisfied:0.5≤(H⁢87.5-H⁢75) / (H⁢75-H 62.5)<1.1.≤(H⁢100-H 87.5)≤6.2.≤(H 87.5-H⁢75)≤6.54.≤(H⁢75-H 62.5)≤7.0≤(H⁢62.5-H⁢50)≤3.0≤(H⁢50-H⁢25)≤3..

[0022] In yet another preferred embodiment, a relationship between thicknesses of the surrounding layer and the intermediate layer and a diameter of the ball satisfies the following condition:0.040≤(intermediate layer thickness+surrounding layer thickness) / (ball diameter)≤0.072.

[0023] In still another preferred embodiment, the core includes the following components (a) to (e):

[0024] (a) a base rubber,

[0025] (b) an α,β-unsaturated carboxylic acid and / or a metal salt thereof as a co-crosslinking agent,

[0026] (c) an organic peroxide,

[0027] (d) water or a moisture-providing agent, and

[0028] (e) a hindered phenol antioxidant having a substituent having a thioether structure.

[0029] Further, the core is formed of a rubber composition wherein the moisture-providing agent is a substance that contains a water component other than free water in its structure and desorbs moisture by heating, or a substance that releases a water component by thermal decomposition by heating, and a compounding amount of the component (e) is at least 0.2 parts by weight per 100 parts by weight of the component (a).

[0030] In a further preferred embodiment, the hindered phenol antioxidant as the component (e) has a chemical structure having at least one methyl group at an ortho position.

[0031] In a yet further preferred embodiment, in the hindered phenol antioxidant as the component (e), the number of substituents having a thioether structure is at least two.

[0032] In a still further preferred embodiment, letting a deflection when the core is compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) be A (mm), and a deflection when the golf ball is compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) be B (mm), the following condition is satisfied:0.9≤A-B≤1.4.

[0033] In another preferred embodiment, a relationship between surface hardnesses of each of the core, the surrounding layer, the intermediate layer, and the ball satisfies the following condition:surface hardness of core≤surface hardness of surrounding layer-encased sphere<surface hardness of intermediate layer-encased sphere>surface hardness of ball.

[0034] In yet another preferred embodiment, the cover is formed by injection-molding a single resin blend containing a thermoplastic polyurethane (I) and a polyisocyanate compound (II) as principal components, and at least a part of the resin blend contains a polyisocyanate compound in which all isocyanate groups in one molecule remain in an unreacted state.Advantageous Effects of the Invention

[0035] According to the multi-piece solid golf ball of the present invention, it is possible to realize a low spin rate on full shots and secure a superior distance, and durability to repeated impact is high.BRIEF DESCRIPTION OF THE DRAWINGS

[0036] FIG. 1 is a schematic cross-sectional view of a golf ball according to one embodiment of the present invention.

[0037] FIG. 2 is a graph showing core hardness profile data in Example 1.

[0038] FIGS. 3A and 3B are plan views illustrating a mode (pattern) of dimples common to Examples and Comparative Examples.

[0039] FIG. 4 is a graph showing core hardness profiles in Examples 1 to 3 and Comparative Example 1.

[0040] FIG. 5 is a graph showing core hardness profiles in Comparative Examples 2 to 5.

[0041] FIG. 6 is a graph showing core hardness profiles in Comparative Examples 6 to 9.DETAILED DESCRIPTION OF THE INVENTION

[0042] Hereinafter, the present invention is described in more detail.

[0043] A golf ball according to the present invention has a core, a surrounding layer, an intermediate layer, and a cover, and an example thereof is shown in FIG. 1, for example. A golf ball G shown in FIG. 1 is the golf ball G having at least four layers including a core 1, a surrounding layer 2 encasing the core, an intermediate layer 3 encasing the surrounding layer, and a cover 4 encasing the intermediate layer. A large number of dimples D are typically formed on a surface of the cover 4. Although not particularly illustrated, a coating film layer is typically formed on the surface of the cover 4 by coating. The cover 4 is positioned at an outermost layer in the layer construction of the golf ball except for the coating film layer. The core 1 or the surrounding layer 2 is not limited to a single layer and may be formed in a plurality of layers of at least two layers, but the intermediate layer 3 or the cover 4 is formed in a single layer or a plurality of layers. Hereinafter, each of the above layers is described in detail.

[0044] The core is formed in a single layer or a plurality of layers. From the viewpoint of obtaining good durability to repeated impact, the core is preferably formed in a single layer.

[0045] A diameter of the core is not particularly limited, although the diameter is preferably at least 35.1 mm, more preferably at least 35.3 mm, and still more preferably at least 35.4 mm, and the upper limit value is preferably not more than 41.3 mm, more preferably not more than 39.2 mm, and still more preferably not more than 38.3 mm. If the diameter of the core is too small, a hardness of an entire ball may become too hard, that is, a deflection may become small, a spin rate on full shots may increase, and an intended distance may not be attainable. On the other hand, if the diameter of the core is too large, the spin rate on full shots increases, so that the intended distance may not be attainable, particularly on shots with a driver (W #1) at a head speed of not more than 40 m / s and on shots with an iron, and a durability to cracking on repeated impact may worsen.

[0046] The deflection (mm) when the core is compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) is not particularly limited, although the deflection is preferably at least 2.9 mm, more preferably at least 3.1 mm, and still more preferably at least 3.3 mm, and the upper limit value is preferably not more than 4.3 mm, more preferably not more than 4.1 mm, and still more preferably not more than 3.9 mm. If the deflection of the core is too small, that is, the core is too hard, the spin rate may rise excessively, a good distance may not be achieved, and a feel at impact may be excessively hard. On the other hand, if the deflection of the core is too large, that is, if the core is too soft, a rebound may become too low and the distance may not be increased, the feel at impact may be too soft, and the durability to cracking on repeated impact may worsen.

[0047] Next, the core hardness profile is described. It is noted that the hardness of the core described below means Shore C hardness. The Shore C hardness is a hardness value measured with a Shore C durometer conforming to the ASTM D2240 standard.

[0048] In the following description of the core hardness profile, the Shore C hardness of a core surface is defined as H100, a Shore C hardness at a position outside by 87.5% of a core radius from a core center is defined as H87.5, a Shore C hardness at a position outside by 75% of the core radius from the core center is defined as H75, a Shore C hardness at a position outside by 62.5% of the core radius from the core center is defined as H62.5, a Shore C hardness at a position outside by 50% of the core radius from the core center is defined as H50, a Shore C hardness at a position outside by 37.5% of the core radius from the core center is defined as H37.5, a Shore C hardness at a position outside by 25% of the core radius from the core center is defined as H25, a Shore C hardness at a position outside by 12.5% of the core radius from the core center is defined as H12.5, and the Shore C hardness at the core center is defined as H0.

[0049] The surface hardness of the core (H100) is not particularly limited, although the surface hardness may be preferably at least 77, more preferably at least 79, and still more preferably at least 81. The upper limit is not particularly limited, although the upper limit may be preferably not more than 89, more preferably not more than 87, and still more preferably not more than 85. If this value is too small, the rebound of the core may become too low, the spin rate of the ball on full shots may increase, and in particular, the intended distance may not be attainable on shots with a driver (W #1) at a head speed of not more than 40 m / s and on shots with an iron. On the other hand, if this value is too large, the durability to cracking on repeated impact may worsen, and the feel at impact may be too hard.

[0050] The position hardness (H87.5) outside by 87.5% of the core radius from the core center is not particularly limited, although the position hardness may be preferably at least 74, more preferably at least 76, and still more preferably at least 78. The upper limit is also not particularly limited, although the upper limit may be preferably not more than 86, more preferably not more than 84, and still more preferably not more than 82. Hardnesses that deviate from these values may lead to undesirable results similar to those described above for the core surface hardness (H100).

[0051] The position hardness (H75) outside by 75% of the core radius from the core center is not particularly limited, although the position hardness may be preferably at least 69, more preferably at least 71, and still more preferably at least 73. The upper limit is also not particularly limited, although the upper limit may be preferably not more than 81, more preferably not more than 79, and still more preferably not more than 77. Hardnesses that deviate from these values may lead to undesirable results similar to those described above for the core surface hardness (H100).

[0052] The position hardness (H62.5) outside by 62.5% of the core radius from the core center is not particularly limited, although the position hardness may be preferably at least 63, more preferably at least 65, and still more preferably at least 67. The upper limit is also not particularly limited, although the upper limit may be preferably not more than 75, more preferably not more than 73, and still more preferably not more than 71. If this value is too large, the spin rate increases on full shots, and in particular, the intended distance may not be attainable on shots with a driver (W #1) at a head speed of not more than 40 m / s and on full shots with an iron, and the feel at impact may become too hard. On the other hand, if this value is too small, the rebound of the core may become low, and in particular, the intended distance may not be attainable on shots with a driver (W #1) at a head speed of at least 45 m / s, and the durability to cracking on repeated impact may worsen.

[0053] The position hardness (H50) outside by 50% of the core radius from the core center is not particularly limited, although the position hardness may be preferably at least 63, more preferably at least 65, and still more preferably at least 67. The upper limit is also not particularly limited, although the upper limit may be preferably not more than 75, more preferably not more than 73, and still more preferably not more than 71. Hardnesses that deviate from these values may lead to undesirable results similar to those described above for the position hardness (H62.5) outside by 62.5% of the core radius from the core center.

[0054] The position hardness (H37.5) outside by 37.5% of the core radius from the core center is not particularly limited, although the position hardness may be preferably at least 63, more preferably at least 65, and still more preferably at least 67. The upper limit is also not particularly limited, although the upper limit may be preferably not more than 75, more preferably not more than 73, and still more preferably not more than 71. Hardnesses that deviate from these values may lead to undesirable results similar to those described above for the position hardness (H62.5) outside by 62.5% of the core radius from the core center.

[0055] The position hardness (H25) outside by 25% of the core radius from the core center is not particularly limited, although the position hardness may be preferably at least 62, more preferably at least 64, and still more preferably at least 66. The upper limit is also not particularly limited, although the upper limit may be preferably not more than 74, more preferably not more than 72, and still more preferably not more than 70. Hardnesses that deviate from these values may lead to undesirable results similar to those described above for the position hardness (H62.5) outside by 62.5% of the core radius from the core center.

[0056] The position hardness (H12.5) outside by 12.5% of the core radius from the core center is not particularly limited, although the position hardness may be preferably at least 60, more preferably at least 62, and still more preferably at least 64. The upper limit is also not particularly limited, although the upper limit may be preferably not more than 72, more preferably not more than 70, and still more preferably not more than 68. Hardnesses that deviate from these values may lead to undesirable results similar to those described above for the position hardness (H62.5) outside by 62.5% of the core radius from the core center.

[0057] The center hardness (H0) of the core is not particularly limited, although the center hardness may be preferably at least 57, more preferably at least 59, and still more preferably at least 61. The upper limit is also not particularly limited, although the upper limit may be preferably not more than 70, more preferably not more than 68, and still more preferably not more than 66. Hardnesses that deviate from these values may lead to undesirable results similar to those described above for the position hardness (H62.5) outside by 62.5% of the core radius from the core center.

[0058] A value of a hardness difference (H75-H62.5) between H75 and H62.5 preferably satisfies the following condition.(H⁢75-H 62.5)⁢≤7.0(i)

[0059] The value of (H75-H62.5) in the above condition is preferably at least 4.0, more preferably at least 4.5, and still more preferably at least 5.0, and the upper limit value is preferably not more than 7.0, more preferably not more than 6.8, and still more preferably not more than 6.5. If this value is too large, the durability to cracking on repeated impact may worsen. On the other hand, if this value is too small, the spin rate of the ball on full shots may rise, and the intended distance may not be attainable.

[0060] In addition, the following condition is preferably satisfied.(H 87.5-H⁢75)<(H⁢75-H 62.5)(ii)

[0061] If the above condition is not satisfied, the durability to cracking on repeated impact may worsen.

[0062] In addition, the following condition is preferably satisfied.(H⁢100-H 87.5)<(H⁢87.5-H⁢75)(iii)

[0063] If the above condition is not satisfied, the durability to cracking on repeated impact may worsen.

[0064] In addition, the following condition is preferably satisfied.(H 62.5-H⁢50)<(H⁢100-H 87.5)(iv)

[0065] If the above condition is not satisfied, the spin rate of the ball on full shots may increase, and the intended distance may not be attainable.

[0066] Further, the following condition is preferably satisfied.(H 62.5-H⁢50)≥0(v)

[0067] If the above condition is not satisfied, the spin rate of the ball on full shots may increase, and the intended distance may not be attainable. The value of (H62.5−H50) in the above condition is preferably at least 0, more preferably at least 0.1, and still more preferably at least 0.2, and the upper limit value is preferably not more than 3.0, more preferably not more than 2.0, and still more preferably not more than 1.0.

[0068] The above (i) to (v) are expressed by one condition as follows.0≤(H⁢62.5-H⁢50)<(H⁢100-H 87.5)<(H⁢87.5-H⁢75)<(H⁢75-H 62.5)≤7.0

[0069] That is, the above condition means that a hardness gradient from the position of 62.5% of the core radius from the core center to a surface direction gradually becomes gentle.

[0070] The value of (H100−H87.5) in the above condition is preferably at least 1.0, more preferably at least 2.0, and still more preferably at least 3.0, and the upper limit value is preferably not more than 6.0, more preferably not more than 5.0, and still more preferably not more than 4.0. If this value is too large, the durability to cracking on repeated impact may worsen. On the other hand, if this value is too small, the spin rate of the ball on full shots increases, and the distance may not be increased.

[0071] The value of (H87.5−H75) in the above condition is preferably at least 2.0, more preferably at least 3.5, and still more preferably at least 4.0, and the upper limit value is preferably not more than 6.5, more preferably not more than 6.0, and still more preferably not more than 5.0. If this value is too large, the durability to cracking on repeated impact may worsen. On the other hand, if this value is too small, the spin rate of the ball on full shots increases, and the distance may not be increased.

[0072] A value of (H100−H87.5) / (H87.5−H75) is preferably at least 0.4, more preferably at least 0.5, and still more preferably at least 0.6, and the upper limit value is preferably not more than 0.9, more preferably not more than 0.8, and still more preferably not more than 0.7. That is, a hardness gradient from H87.5 to H100 is gentler than a hardness gradient from H75 to H87.5. If this value is too large, the durability to cracking on repeated impact may worsen. On the other hand, if this value is too small, the spin rate of the ball on full shots may rise, and the intended distance may not be attainable.

[0073] A value of (H87.5−H75) / (H75−H62.5) is preferably at least 0.5, more preferably at least 0.6, and still more preferably at least 0.7, and the upper limit value is preferably not more than 0.99, more preferably not more than 0.95, and still more preferably not more than 0.90. That is, a hardness gradient from H75 to H87.5 is gentler than a hardness gradient from H62.5 to H75. If this value is too large, the durability to cracking on repeated impact may worsen. On the other hand, if this value is too small, the spin rate of the ball on full shots may rise, and the intended distance may not be attainable.

[0074] A value of (H87.5−H50) / (H50−H12.5) is preferably at least 3.0, more preferably at least 3.4, and still more preferably at least 3.8, and the upper limit value is preferably not more than 15.0, more preferably not more than 10.0, and still more preferably not more than 8.0. If this value is too large, the durability to cracking on repeated impact may worsen. On the other hand, if this value is too small, the spin rate of the ball on full shots may rise, and the intended distance may not be attainable.

[0075] A value of (H100−H50) / (H50−H0) is preferably at least 2.0, more preferably at least 2.5, and still more preferably at least 2.8, and the upper limit value is preferably not more than 15.0, more preferably not more than 10.0, and still more preferably not more than 8.0. If this value is too large, the durability to cracking on repeated impact may worsen. On the other hand, if this value is too small, the spin rate of the ball on full shots may rise, and the intended distance may not be attainable.

[0076] A value of (H50−H25) is preferably at least 0, more preferably at least 0.1, and still more preferably at least 0.3, and the upper limit value is preferably not more than 3.0, more preferably not more than 2.0, and still more preferably not more than 1.0. If this value deviates from the above ranges, the spin rate on full shots may rise, and the intended distance may not be attainable.

[0077] A value of (H100−H0) is preferably at least 17, more preferably at least 18, and still more preferably at least 19, and the upper limit value is preferably not more than 25, more preferably not more than 23, and still more preferably not more than 21. If this value is too small, the spin rate rises on full shots, and the intended distance may not be attainable. On the other hand, if this value is too large, the durability to cracking on repeated impact may worsen, and in particular, an actual initial velocity on shots with a driver (W #1) at a head speed of at least 45 m / s may be lowered, and the intended distance may not be attainable.

[0078] It is preferable that all the values of hardness differences among a total of nine points obtained by dividing the core radius of a core cross-section from the center to the surface of the core into eight equal parts, that is, all the values of (H100−H87.5), (H87.5−H75), (H75−H62.5), (H62.5−H50), (H50−H37.5), (H37.5−H25), (H25−H12.5), and (H12.5−H0), are positive values. That is, there is no place where an increase continues from the center of the core toward the surface and decreases. For example, FIG. 2 shows core hardness profile data of Example 1. As shown in this graph, there are no places where the hardness gradient is dented upward. In a case where all of these values are not positive values, the spin rate of the ball on full shots increases, and the intended distance may not be attainable.

[0079] As a material of the core having the hardness profile described above, a rubber material is preferably used as a chief material. If the core is not formed of a rubber material, the rebound may be reduced, and a good distance of the ball may not be achieved. Specifically, the rubber material contains a base rubber as a chief material, and a co-crosslinking agent, an organic peroxide, an inert filler, an organosulfur compound, or the like may be blended with the base rubber to prepare a rubber composition for the core.

[0080] The rubber material preferably contains the following components (a) to (e).

[0081] (a) A base rubber,

[0082] (b) An α,β-unsaturated carboxylic acid and / or a metal salt thereof as a co-crosslinking agent,

[0083] (c) An organic peroxide,

[0084] (d) Water or a moisture-providing agent, and

[0085] (e) A hindered phenol antioxidant having a substituent having a thioether structure.

[0086] The base rubber of the component (a) is not particularly limited, although polybutadiene is particularly preferably used.

[0087] It is preferable that the polybutadiene has a cis-1,4 bond in a polymer chain thereof of at least 60%, preferably at least 80%, more preferably at least 90%, and most preferably at least 95%. If the amount of the cis-1,4 bond in the bond in the polybutadiene molecule is too small, the rebound may be reduced.

[0088] In addition, a content of a 1,2-vinyl bond contained in the polybutadiene is typically not more than 2%, preferably not more than 1.7%, and more preferably not more than 1.5% in the polymer chain. If the content of the 1,2-vinyl bond is too large, the rebound may be reduced.

[0089] The polybutadiene (ML1+4 (100° C.)) is preferably at least 20, and more preferably at least 30, and the upper limit is preferably not more than 120, more preferably not more than 100, and still more preferably not more than 80.

[0090] A Mooney viscosity is an index of industrial viscosity (JIS K 6300) measured by a Mooney viscometer, which is one type of rotational viscometer, and ML1+4 (100° C.) is used as a unit symbol. M represents the Mooney viscosity, L represents a large rotor (L type), 1+4 represents a preheating time of 1 minute, and a rotation time of the rotor is 4 minutes, which indicate that measurement has been performed under conditions of 100° C.

[0091] As the polybutadiene, one synthesized using a rare earth element-based catalyst or a Group VIII metal compound catalyst may be used.

[0092] In the base rubber, a polybutadiene rubber synthesized with a catalyst different from a lanthanum-series rare earth element compound may be blended. Styrene-butadiene rubber (SBR), natural rubber, polyisoprene rubber, ethylene propylene diene rubber (EPDM), and the like may be blended, and one kind thereof may be used alone, or two or more kinds thereof may be used in combination.

[0093] A proportion of the polybutadiene in the whole rubber is preferably at least 60 wt %, more preferably at least 70 wt %, and most preferably at least 90 wt %. 100 wt % of the base rubber, that is, all of the base rubber, may be the polybutadiene.

[0094] Next, the component (b) is a co-crosslinking agent, and is an α,β-unsaturated carboxylic acid and / or a metal salt thereof. A number of carbon atoms of the unsaturated carboxylic acid is preferably 3 to 8, and specific examples thereof include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, and fumaric acid. Specific examples of a metal of the unsaturated carboxylic acid include zinc, sodium, magnesium, calcium, and aluminum, and zinc is particularly preferable. Therefore, zinc acrylate is most preferable as the co-crosslinking agent.

[0095] A compounding amount of the component (b) is preferably at least 10 parts by weight, more preferably at least 15 parts by weight, and still more preferably at least 20 parts by weight per 100 parts by weight of the base rubber of the component (a), and the upper limit is preferably not more than 65 parts by weight, more preferably not more than 60 parts by weight, and still more preferably not more than 55 parts by weight. If the compounding amount is less than the above range, the golf ball becomes too soft and has poor rebound, and if the compounding amount is more than the above range, the golf ball becomes too hard and has a poor feel at impact, and is fragile and inferior in durability.

[0096] The co-crosslinking agent of the component (b) preferably has an average particle size of from 3 to 30 μm, more preferably from 5 to 25 μm, and still more preferably from 8 to 15 μm. If the average particle size of the co-crosslinking agent is less than 3 μm, the co-crosslinking agent is easily aggregated in the rubber composition, a reactivity between acrylic acids is improved, and a reactivity between the base rubbers is reduced, so that a rebound performance of the golf ball may not be sufficiently attainable. If the average particle size of the co-crosslinking agent exceeds 30 μm, the co-crosslinking agent particles become too large, and variations in characteristics of the resulting golf ball become large.

[0097] The component (c) is an organic peroxide, and as the organic peroxide, it is particularly preferable to use an organic peroxide having a one-minute half-life temperature of from 110 to 185° C. Examples of such an organic peroxide include dicumyl peroxide (“Percumyl D” manufactured by NOF Corporation), 2,5-dimethyl-2,5-di(t-butylperoxy) hexane (“PERHEXA 25B” manufactured by NOF Corporation), and di(2-t-butylperoxyisopropyl)benzene (“Perbutyl P” manufactured by NOF Corporation), and dicumyl peroxide may be suitably used. Examples of other commercially available products include “PERHEXA C-40”, “NYPER BW”, “PEROYL L” (all manufactured by NOF Corporation), and Luperco 231XL (manufactured by AtoChem Corporation). These may be used singly, or two or more may be used in combination.

[0098] A compounding amount of the component (c) is preferably at least 0.1 parts by weight, and more preferably at least 0.3 parts by weight per 100 parts by weight of the base rubber, and the upper limit value is preferably not more than 5 parts by weight, more preferably not more than 4 parts by weight, and still more preferably not more than 3 parts by weight.

[0099] The component (d) is water or a moisture-providing agent. The water as the component (d), although not particularly limited, may be distilled water or tap water, but it is particularly suitable to employ distilled water free of impurities.

[0100] If the component (d) is a moisture-providing agent, the moisture-providing agent is defined as a substance that contains a water component other than free water in its structure and desorbs moisture by heating, or a substance that releases a water component by thermal decomposition by heating. In general, examples of the type of water include free water, adsorbed water, interlayer water, zeolite water, and bound water. It is said that adsorbed water, interlayer water, and free water exist in a clay mineral, and a clay mineral containing such interlayer water may be adopted as the component (d).

[0101] Examples of the clay mineral include layered double hydroxides such as hydrotalcite. That is, the layered double hydroxide (hereinafter also referred to as “LDH”) is a mineral having a multilayer construction, and water having a chemical bond between layers (interlayer water) exists. For example, in a case of Mg—Al based LDH, the interlayer water almost completely desorbs in the range of from 180 to 300° C. In a case of a Zn—Al-based LDH, interlayer water is desorbed at a lower temperature of from 170 to 200° C.

[0102] In addition, a substance containing bound water is exemplified as the component (d). Specifically, the substance containing bound water is a substance having water (coordination water) that forms a complex ion as a ligand, and examples thereof include hydrates of inorganic compounds. As the inorganic compound, for example, one or more selected from calcium sulfate 0.5 hydrate, calcium sulfate dihydrate, aluminum sulfate 14 to 18 hydrate, magnesium sulfate heptahydrate, beryllium sulfate tetrahydrate, zirconium sulfate tetrahydrate, manganese sulfate pentahydrate, iron sulfate heptahydrate, cobalt sulfate heptahydrate, nickel sulfate hexahydrate, cupric sulfate pentahydrate, zinc sulfate heptahydrate, cadmium sulfate octahydrate, indium sulfate nonahydrate, zinc sulfate dihydrate, and the like may be used in combination.

[0103] Further, examples of the component (d) include a substance that releases a water component by thermal decomposition by heating. Examples thereof include a substance which exists as a hydroxide ion in the substance but escapes as water (H2O) when heated, and examples thereof include aluminum hydroxide and magnesium hydroxide.

[0104] Regarding the moisture-providing agent, it is preferable that a dissociation ratio of moisture is at least 60% in weight ratio if the rubber composition is heated to a temperature at which the rubber composition is vulcanized or if a temperature inside the core reaches the maximum temperature due to self-reaction heat during vulcanization. From the viewpoint of enhancing a supply efficiency of moisture, it is preferable to use a moisture-providing agent having a high moisture content by weight ratio.

[0105] Specifically, for example, a content ratio of moisture in a molecular formula of the moisture-providing agent is preferably at least 6%, and more preferably at least 15% in weight ratio. The content ratio of moisture in the molecular formula of the moisture-providing agent is preferably high, and the upper limit value is not particularly limited, although the upper limit value may be, for example, not more than 90% in terms of weight ratio from the viewpoint of availability and the like.

[0106] As the moisture-providing agent, it is preferable that moisture may be released as much as possible when the rubber composition is vulcanized. However, vulcanization conditions such as a vulcanization temperature and a vulcanization time may change depending on components contained in the rubber composition such as a base rubber and an organic peroxide. Therefore, it is preferable to select a moisture-providing agent capable of releasing a desired amount of moisture under vulcanization conditions such as the vulcanization temperature according to the vulcanization conditions of the rubber composition to which the moisture-providing agent is added.

[0107] Since the dissociation ratio of moisture of the moisture-providing agent when the rubber composition is kneaded is preferably low, for example, the dissociation ratio of moisture if the rubber composition is heated to 90° C., that is, a cumulative dissociation ratio of moisture if the rubber composition is heated to 90° C., is preferably not more than 60% in terms of weight ratio.

[0108] A compounding amount of the component (d) is preferably at least 0.1 parts by weight, more preferably at least 0.3 parts by weight, and still more preferably at least 0.5 parts by weight per 100 parts by weight of the base rubber, and the upper limit value is preferably not more than 15 parts by weight, more preferably not more than 10 parts by weight, still more preferably not more than 5 parts by weight, and most preferably not more than 3 parts by weight. If the compounding amount of the component (d) is too large, the hardness is softened, and a desired feel at impact, durability, and rebound may not be obtained. If the compounding amount is too small, a desired core hardness profile may not be obtained, and it may be impossible to sufficiently realize a low spin rate of the ball on shots.

[0109] The component (e) is a hindered phenol antioxidant having a substituent having a thioether structure. The hindered phenol antioxidant preferably has a chemical structure having at least one methyl group at an ortho position. In the hindered phenol antioxidant, the number of substituents having a thioether structure is preferably at least two.

[0110] By blending the component (e) into the rubber composition, normal striking durability performance may be improved, and even if foreign matter is mixed into the rubber material, a decrease in striking durability may be suppressed so as to be maintained at least at a certain level.

[0111] Specifically, the hindered phenol antioxidant as the component (e) preferably has the following general formula (I).

[0112] In the above formula, x is an integer of at least 1, and preferably x is an integer of at least 8.

[0113] Specifically, trade names “Antage HP-500” and “Antage HP-400” (all manufactured by Kawaguchi Chemical Industry Co., LTD.) and trade name “Irganox 1520 L” manufactured by BASF may be used as the component (e).

[0114] A compounding amount of the component (e) is at least 0.2 parts by weight, preferably at least 0.3 parts by weight, and more preferably at least 0.5 parts by weight per 100 parts by weight of the base rubber. The upper limit value is preferably not more than 3.0 parts by weight, more preferably not more than 2.0 parts by weight, and still more preferably not more than 1.5 parts by weight. If the compounding amount of the component (e) is too large, the hardness is softened, and the desired feel at impact, the durability and rebound may not be obtained, and if the compounding amount is too small, an effect of a desired striking durability may not be obtained.

[0115] The component (e) may be added to the component (a) at the time of producing the rubber composition, or may be added in advance at the time of producing the component (a), or these addition methods may be used in combination.

[0116] In addition to the components (a) to (e) described above, for example, various additives such as a component (f), a component (g), a component (h), a filler, and a processing aid described below may be blended as long as effects of the present invention are not hindered.

[0117] The component (f) is benzimidazole having the following general formula (II) and / or a metal salt thereof, and is used as an antioxidant.

[0118] R in the above formula (II) is a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms, m is an integer of 1 to 4, and if m is 2 or more, these may be the same as or different from each other. Specific examples of the benzimidazole having the above formula (II) include 2-mercaptobenzimidazole, 2-mercaptomethylbenzimidazole, and metal salts thereof, and the metal salt is preferably a zinc salt.

[0119] A compounding amount of the benzimidazole having the above specific formula and / or the metal salt thereof as the component (f) is preferably at least 0.1 parts by weight, and more preferably at least 0.3 parts by weight, and the upper limit value is preferably not more than 5 parts by weight, and more preferably not more than 3 parts by weight per 100 parts by weight of the base rubber. If the compounding amount of the component (f) is too small, a crosslinking reaction in a vicinity of the core surface is not efficiently promoted, a crosslinking density is not sufficiently increased, a hard layer having hardness is not sufficiently formed, a hardness difference between the core surface and the core center as an entire core is not sufficiently increased, and sufficient striking durability performance may not be obtained. On the other hand, even if the compounding amount of the component (f) is unnecessarily increased, an obtained effect does not change to the above suitable addition amount or more.

[0120] The component (g) is sulfur or an alkylphenol disulfide polymer having the following chemical structure.

[0121] In the above formula (III), R represents an alkyl group, and n represents a polymerization degree in a range of 2 to 20. The alkyl group of R is preferably a lower alkyl group having 1 to 6 carbon atoms, and specific examples of the alkyl group include those selected from groups of a methyl group, an ethyl group, an n-propyl group, an iso-propyl group, an n-butyl group, a tert-butyl group, an n-amyl group (pentyl group), an iso-amyl group (pentyl group), a tert-amyl group (pentyl group), a sec-isoamyl group, a neopentyl group, an n-hexyl group, an iso-hexyl group, and a tert-hexyl group. More preferably, an organosulfur compound as a component (g-1) is an amylphenol disulfide polymer, and specifically, commercially available products such as “Sanceler AP” (manufactured by Sanshin Chemical Industry Co., Ltd.) and “Vultac 5” (manufactured by Arkema K.K.) may be used.

[0122] A compounding amount of the component (g) which is an alkylphenol disulfide polymer is not particularly limited, although the compounding amount is preferably at least 0.05 parts by weight, more preferably at least 0.1 parts by weight, and most preferably at least 0.3 parts by weight per 100 parts by weight of the rubber component. The upper limit value is preferably not more than 5.0 parts by weight, more preferably not more than 3.0 parts by weight, and most preferably not more than 2.0 parts by weight. If the compounding amount is too large, the crosslinking reaction by the organic peroxide is inhibited by an influence of sulfur, and an entire hardness of a molded product tends to be greatly softened.

[0123] On the other hand, if the component (g) is sulfur, commercially available products may be used as the sulfur, and for example, “SULFAX 5” manufactured by Tsurumi Chemical Industry Co., Ltd., “SANMIX S-80 N” and “SANMIX IS-60 N” manufactured by Sanshin Chemical Industry Co., Ltd., and “AKROFORM S-80 / EPR / P” manufactured by Akrochem Corporation may be adopted.

[0124] A compounding amount of the sulfur is not particularly limited, although the compounding amount is preferably at least 0 parts by weight per 100 parts by weight of the rubber component. The upper limit value is preferably not more than 5.0 parts by weight, more preferably not more than 2.0 parts by weight, and most preferably not more than 1.0 part by weight. If the compounding amount is too large, the crosslinking reaction by the organic peroxide is inhibited by an influence of sulfur, and an entire hardness of a molded product tends to be greatly softened.

[0125] Sulfur is desirably used in the form of a masterbatch in order to enhance dispersibility of a minute amount of the sulfur. Examples of such a sulfur masterbatch may include the above-mentioned trade names “SANMIX S-80 N”, “SANMIX IS-60 N”, and “AKROFORM S-80 / EPR / P”.

[0126] As a filler, for example, zinc oxide, barium sulfate, calcium carbonate, or the like may be suitably used. These may be used singly, or two or more may be used in combination. A compounding amount of the filler may be preferably at least 1 part by weight, more preferably at least 3 parts by weight, and still more preferably at least 5 parts by weight per 100 parts by weight of the base rubber. The upper limit of the compounding amount may be preferably not more than 100 parts by weight, more preferably not more than 60 parts by weight, and still more preferably not more than 40 parts by weight per 100 parts by weight of the base rubber. If the compounding amount is too large or too small, it may not be possible to obtain an appropriate weight and a suitable rebound.

[0127] The component (h) is an organosulfur compound different from the component (g). The organosulfur compound is not particularly limited, and examples thereof include thiophenols, thionaphthols, diphenyl polysulfides, halogenated thiophenols, and metal salts thereof. Specific examples include zinc salts such as pentachlorothiophenol, pentafluorothiophenol, pentabromothiophenol, and parachlorothiophenol, diphenyl polysulfide having 2 to 4 sulfur atoms, dibenzyl polysulfide, dibenzoyl polysulfide, dibenzothiazolyl polysulfide, dithiobenzoyl polysulfide, and 2-thionaphthol. These may be used singly, or two or more kinds may be used in combination. Among them, a zinc salt of pentachlorothiophenol and / or diphenyl disulfide may be suitably used.

[0128] A compounding amount of the organosulfur compound is preferably at least 0.05 parts by weight, more preferably at least 0.1 parts by weight, and still more preferably at least 0.2 parts by weight per 100 parts by weight of the base rubber, and the upper limit is preferably not more than 3 parts by weight, more preferably not more than 2 parts by weight, and still more preferably not more than 1 part by weight. If the compounding amount of the organosulfur compound is too large, a hardness of a heat-molded product of the rubber composition may become too soft, whereas if the compounding amount is too small, the rebound may not be expected to be improved.

[0129] As the processing aid, a higher fatty acid, a metal salt thereof, or the like may be suitably used. Examples of the higher fatty acid include stearate, palmitic acid, oleic acid, linoleic acid, linolenic acid, and myristic acid, and stearate is particularly preferable. Examples of the metal salt of the higher fatty acid include a lithium salt, a sodium salt, a potassium salt, a copper salt, a magnesium salt, a calcium salt, a strontium salt, a barium salt, a tin salt, a cobalt salt, a nickel salt, a zinc salt, and an aluminum salt, and in particular, zinc stearate is suitably used. A compounding amount of the processing aid may be preferably at least 1 part by weight, more preferably at least 3 parts by weight, and still more preferably at least 5 parts by weight per 100 parts by weight of the base rubber. The upper limit of the compounding amount may be preferably not more than 20 parts by weight, more preferably not more than 15 parts by weight, and still more preferably not more than 10 parts by weight per 100 parts by weight of the base rubber. If the compounding amount is too large, sufficient hardness and rebound may not be obtained, and if the compounding amount is too small, an additive agent is not sufficiently dispersed, and expected physical properties may not be obtained. Examples of a method for adding the processing aid include, but are not particularly limited to, a method in which the processing aid is put into a mixer simultaneously with other chemicals, a method in which the processing aid is added in advance by mixing with other chemicals such as the component (b) in advance, a method in which the processing aid is added by coating a surface of other chemicals such as the component (b), and a method in which a masterbatch is prepared in advance together with the component (a) and added.

[0130] The rubber composition may contain an antioxidant different from the component (e). Specific examples of a hindered phenol antioxidant include hindered phenol antioxidants such as 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-ethylphenol, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate], 1,3,5-tris(3′,5′-di-t-butyl-4-hydroxybenzyl) isocyanuric acid, 2,2′-methylenebis(4-methyl-6-tert-butylphenol), and 4,4′,4″-(1-methylpropanyl-3-ylidene)tris(6-tert-butyl-m-cresol), and commercially available products thereof which may be adopted include Nocrac 200, Nocrac M-17, and Nocrac NS-6 (manufactured by Ouchi Shinko Chemical Industrial Co., Ltd.), IRGANOX 1010 (manufactured by BASF), ADK STAB AO-20 and ADK STAB AO-30 (manufactured by ADEKA CORPORATION), and the like. These may be used singly, or two or more may be used in combination. A compounding amount of the antioxidant is not particularly limited, although the compounding amount is preferably not more than 1.0 part by weight, more preferably not more than 0.7 parts by weight, and still more preferably not more than 0.5 parts by weight per 100 parts by weight of the base rubber. If the compounding amount is too large, an effect of improving durability by the component (e) may not be obtained.

[0131] A core that is a vulcanized molded product may be manufactured by vulcanizing and hardening the rubber composition. For example, the rubber composition is intensively mixed using a mixing apparatus such as a Banbury mixer or a roll mill, the mixture is compression molded or injection molded using a core mold, and the resulting molded body is cured by appropriately heating the molded body at a temperature sufficient for the organic peroxide or the co-crosslinking agent to act, such as at a temperature of approximately 100 to 200° C., for 10 to 40 minutes, whereby a core which is a vulcanized molded product may be manufactured.

[0132] Next, the surrounding layer is described.

[0133] The surrounding layer has a material hardness on the Shore D hardness scale which, although not particularly limited, is preferably at least 47, more preferably at least 49, and still more preferably at least 51, and the upper limit value is preferably not more than 62, more preferably not more than 60, and still more preferably not more than 57. The material hardness on the Shore C hardness scale is preferably at least 72, more preferably at least 75, and still more preferably at least 78, and the upper limit value is preferably not more than 92, more preferably not more than 90, and still more preferably not more than 88. If the material hardness of the surrounding layer is too soft, the spin rate may increase on full shots, or an initial velocity may decrease and the intended distance may not be increased. On the other hand, if the material hardness is too hard, the feel at impact may become hard, and the durability to cracking on repeated impact may worsen. Furthermore, the spin rate on full shots may increase excessively.

[0134] A surface hardness of a surrounding layer-encased sphere in which the core is encased with the surrounding layer is not particularly limited, although the surface hardness is preferably at least 53, more preferably at least 55, and still more preferably at least 57 on the Shore D hardness scale, and the upper limit value is preferably not more than 68, more preferably not more than 66, and still more preferably not more than 63. The surface hardness on the Shore C hardness scale is preferably at least 80, more preferably at least 83, and still more preferably at least 86, and the upper limit value is preferably not more than 97, more preferably not more than 95, and still more preferably not more than 94. If the surface hardness of the surrounding layer-encased sphere is too soft, the spin rate may increase on full shots, or the initial velocity may decrease and the intended distance may not be increased. On the other hand, if the surface hardness of the surrounding layer-encased sphere is too hard, the feel at impact may become hard, and the durability to cracking on repeated impact may worsen. Furthermore, the spin rate on full shots may increase excessively.

[0135] If the surrounding layer is formed in a plurality of layers, the above-mentioned material hardness means a material hardness of an outer surrounding layer, and the above-mentioned surface hardness means a surface hardness of an outer surrounding layer-encased sphere.

[0136] A thickness of the surrounding layer is preferably at least 0.8 mm, more preferably at least 1.0 mm, and still more preferably at least 1.2 mm. On the other hand, the upper limit value of the thickness of the surrounding layer is preferably not more than 2.0 mm, more preferably not more than 1.6 mm, and still more preferably not more than 1.4 mm. If the thickness deviates from the above numerical range, a spin rate-lowering effect on full shots is insufficient, and thus an intended distance may not be increased on shots with a driver (W #1) at a head speed of not more than 40 m / s and on full shots with an iron. If the thickness of the surrounding layer is too thin, the durability to cracking on repeated impact may worsen. The surrounding layer is preferably formed to be thicker than the intermediate layer to be described later because it is easy to achieve a low spin rate on full shots.

[0137] The material of the surrounding layer is made of a resin material from the viewpoint of securing excellent durability to repeated impact, and in particular, various thermoplastic resin materials may be suitably used. Examples of the resin material of the surrounding layer that may be used include an ionomer resin,

[0138] and a resin composition that is a blend of:

[0139] a base resin (A) that is a blend of the following components:

[0140] (a-1) a metal ion neutralized product of an olefin-unsaturated carboxylic acid binary random copolymer and / or an olefin-unsaturated carboxylic acid binary random copolymer, and

[0141] (a-2) a metal ion neutralized product of an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester ternary random copolymer and / or an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester ternary random copolymer

[0142] at a weight ratio of 100:0 to 0:100,

[0143] and a non-ionomer thermoplastic elastomer (B) at a weight ratio of 100:0 to 0:100.

[0144] Further, a resin composition composed of the components (A) and (B) that blends:

[0145] (C) 5 to 120 parts by weight per 100 parts by weight of the resin component of a fatty acid having a molecular weight of from 228 to 1,500 and / or a derivative thereof, and (D) 0.1 to 17 parts by weight per 100 parts by weight of the resin component of a basic inorganic metal compound capable of neutralizing unneutralized acid groups in the components (A) and (C),

[0146] is preferably adopted.

[0147] As the components (A) to (D), for example, components (A) to (D) of a resin material of an intermediate layer described in JP-A 2010-253268 may be suitably adopted. A resin material having these components is generally a material called a highly neutralized ionomer, and examples of commercially available products thereof include “HPF 1000” and “HPF 2000”, trade names of Dow Chemical Company.

[0148] Examples of the non-ionomer thermoplastic elastomer include polyolefin-based elastomers (polyolefin, metallocene polyolefin), polystyrene-based elastomers, diene-based polymers, polyacrylate-based polymers, polyamide-based elastomers, polyurethane-based elastomers, polyester-based elastomers, and polyacetals, and particularly include thermoplastic polyether ester elastomers such as thermoplastic polyether ester elastomers.

[0149] Any additive may be appropriately blended in the resin material according to the application. For example, various additives such as a pigment, a dispersant, an antioxidant, an ultraviolet absorber, and a light stabilizer can be included.

[0150] Next, the intermediate layer is described.

[0151] The intermediate layer has a material hardness on the Shore D hardness scale which, although not particularly limited, is preferably at least 64, more preferably at least 66, and still more preferably at least 67, and the upper limit value is preferably not more than 75, more preferably not more than 72, and still more preferably not more than 70. The material hardness on the Shore C hardness scale is preferably at least 90, more preferably at least 92, and still more preferably at least 93, and the upper limit value is preferably not more than 100, more preferably not more than 98, and still more preferably not more than 96. If the material hardness of the intermediate layer is too soft, the ball may be too receptive to spin on full shots, the initial velocity may be lowered, and the intended distance may not be increased on shots with a driver (W #1) and an iron. On the other hand, if the material hardness of the intermediate layer is too hard, the durability to cracking on repeated impact may worsen, and the feel at impact on shots with a putter or on short approaches may be too hard.

[0152] A surface hardness of the intermediate layer-encased sphere obtained by encasing the surrounding layer-encased sphere with the intermediate layer is not particularly limited, although the surface hardness is preferably at least 68, more preferably at least 69, and still more preferably at least 70 in Shore D hardness, and the upper limit value is preferably not more than 78, more preferably not more than 75, and still more preferably not more than 72. The surface hardness on the Shore C hardness scale is preferably at least 95, more preferably at least 96, and still more preferably at least 97, and the upper limit value is preferably not more than 100, more preferably not more than 99, and still more preferably not more than 98. If the surface hardness of the intermediate layer-encased sphere is too soft, the ball may be too receptive to spin on full shots, the initial velocity may be lowered, and the intended distance may not be increased on shots with a driver (W #1) and an iron. On the other hand, if the surface hardness of the intermediate layer-encased sphere is too hard, the durability to cracking on repeated impact may worsen, and the feel at impact on shots with a putter or on short approaches may become too hard.

[0153] The intermediate layer has a thickness which is preferably at least 0.7 mm, more preferably at least 0.8 mm, and still more preferably at least 1.0 mm. On the other hand, the intermediate layer thickness has an upper limit value that is preferably not more than 1.6 mm, more preferably not more than 1.4 mm, and still more preferably not more than 1.2 mm. If the thickness of the intermediate layer deviates from the above numerical range or becomes thinner than the thickness of the cover to be described later, the spin rate-lowering effect may become insufficient, and in particular, the intended distance may not be increased on shots with a driver (W #1) at a head speed of not more than 40 m / s and on shots with an iron. If the thickness of the intermediate layer is too thin, the durability to cracking on repeated impact may worsen.

[0154] As the material of the intermediate layer, various thermoplastic resins used as a golf ball material, and particularly a resin material chiefly composed of an ionomer resin, may be adopted.

[0155] The ionomer resin material preferably contains an ionomer having a high acid content. For example, it is preferable to blend a high-acid ionomer resin having an acid content of at least 16 wt % among commercially available ionomer resins with an ordinary ionomer resin. With this blending, it is possible to secure the intended distance by achieving both a low spin rate and high rebound on full shots with a driver (W #1).

[0156] A proportion of the high-acid ionomer resin in the resin material is preferably at least 20 wt %, more preferably at least 50 wt %, and still more preferably at least 60 wt % per 100 wt % of the resin material, and the upper limit value is not more than 100 wt %, preferably not more than 90 wt %, and more preferably not more than 85 wt %. If the compounding amount of the high-acid ionomer resin is too small, the spin rate on full shots may increase, the initial velocity may decrease, and the intended distance may not be increased on full shots. On the other hand, when the content of this high-acid ionomer resin is too high, the durability to repeated impact may worsen.

[0157] In addition, if an ionomer resin is employed as the base resin, an aspect that uses in admixture a zinc-neutralized ionomer resin and a sodium-neutralized ionomer resin as the base resin is desirable. The blending ratio in terms of zinc-neutralized ionomer resin / sodium-neutralized ionomer resin (weight ratio) is from 5 / 95 to 95 / 5, preferably from 10 / 90 to 90 / 10, and more preferably from 15 / 85 to 85 / 15. If the zinc-neutralized ionomer and the sodium-neutralized ionomer are not included in this ratio, the rebound may become too low to obtain a desired flight on full shots, the durability to cracking on repeated impact at room temperature may worsen, and the durability to cracking at a low temperature (below zero) may worsen.

[0158] In the intermediate layer material, an optional additive may be appropriately included depending on the intended use. For example, various additives such as a pigment, a dispersant, an antioxidant, an ultraviolet absorber, and a light stabilizer can be included. If these additives are included, the compounding amount thereof is preferably 0.1 parts by weight or more, and more preferably 0.5 parts by weight or more, and an upper limit thereof is preferably 10 parts by weight or less, and more preferably 4 parts by weight or less per 100 parts by weight of the base resin.

[0159] For the intermediate layer material, it is suitable to abrade the surface of the intermediate layer in order to increase the degree of adhesion to a polyurethane suitably used in a cover material described later. Further, it is preferable that a primer (adhesive agent) is applied to the surface of the intermediate layer after the abrasion treatment, or an adhesion reinforcing agent is added to the intermediate layer material.

[0160] Next, the cover is described.

[0161] The cover has a material hardness on the Shore D hardness scale which, although not particularly limited, is preferably at least 35, more preferably at least 40, and still more preferably at least 43, and the upper limit value is preferably not more than 53, more preferably not more than 50, and still more preferably not more than 47. The material hardness on the Shore C hardness scale is preferably at least 57, more preferably at least 63, and still more preferably at least 67, and the upper limit value is preferably not more than 80, more preferably not more than 76, and still more preferably not more than 72. If the material hardness of the cover is too soft, the spin rate increases on full shots, and in particular, the intended distance may not be increased on shots with a driver (W #1) at a head speed of not more than 40 m / s and on shots with an iron. On the other hand, if the material hardness of the cover is too hard, the ball may not be receptive to spin on approach shots, and a scuff resistance may worsen.

[0162] A surface hardness of an encased sphere obtained by encasing the intermediate layer-encased sphere with the cover, that is, the ball, is not particularly limited, although the surface hardness is preferably at least 50, more preferably at least 53, and still more preferably at least 56 in Shore D hardness, and the upper limit value is preferably not more than 70, more preferably not more than 65, and still more preferably not more than 60. The surface hardness on the Shore C hardness scale is preferably at least 73, more preferably at least 78, and still more preferably at least 83, and the upper limit value is preferably not more than 95, more preferably not more than 92, and still more preferably not more than 90. If the surface hardness of the ball is too soft, the spin rate increases on full shots, and in particular, the intended distance may not be increased on shots with a driver (W #1) at a head speed of not more than 40 m / s and on shots with an iron. On the other hand, if the surface hardness of the ball is too hard, the ball may not be receptive to spin on approach shots, and the scuff resistance may worsen.

[0163] The cover has a thickness of preferably at least 0.3 mm, more preferably at least 0.5 mm, and still more preferably at least 0.6 mm. On the other hand, the upper limit value in the cover thickness is preferably not more than 1.2 mm, more preferably not more than 0.9 mm, and still more preferably not more than 0.85 mm. If the cover is too thick, the rebound may be lowered or the spin rate may be increased on full shots, and the intended distance may not be increased. On the other hand, if the cover is too thin, the scuff resistance may worsen, and the ball may not be receptive to spin on approach shots and may thus lack sufficient controllability in the short game.

[0164] As a material of the cover, various thermoplastic resins used as a cover material of golf balls may be used, but from the viewpoints of spin controllability and mass productivity, it is preferable to use a resin composition containing a polyurethane resin or an ionomer resin as a chief material. Among these materials, it is preferable to use a resin material mainly composed of thermoplastic polyurethane from the viewpoints of excellent scuff resistance and mass productivity.

[0165] Specific examples of the resin material principally composed of a thermoplastic polyurethane include resin blends containing a thermoplastic polyurethane (I) and a polyisocyanate compound (II) as principal components.

[0166] Describing the thermoplastic polyurethane (I), the construction of the thermoplastic polyurethane includes a soft segment composed of a polymeric polyol (polymeric glycol), which is a long-chain polyol, and a hard segment composed of a chain extender and a polyisocyanate compound. Here, as the long-chain polyol serving as a starting material, any of those hitherto used in the art related to thermoplastic polyurethane can be used, and are not particularly limited, and examples thereof can include polyester polyol, polyether polyol, polycarbonate polyol, polyester polycarbonate polyol, polyolefin polyol, conjugated diene polymer-based polyol, castor oil-based polyol, silicone-based polyol, and vinyl polymer-based polyol. These long-chain polyols may be used singly, or two or more may be used in combination. Among them, a polyether polyol is preferable from the viewpoint that a thermoplastic polyurethane having a high rebound resilience and excellent low-temperature properties can be synthesized.

[0167] Examples of the polyether polyol include poly(ethylene glycol), poly(propylene glycol), poly (tetramethylene glycol), and poly(methyltetramethylene glycol) obtained by ring-opening polymerization of a cyclic ether. One kind of polyether polyol may be used, or two or more kinds of polyether polyol may be used in combination. Among these polyether polyols, poly (tetramethylene glycol) and / or poly (methyltetramethylene glycol) are preferred.

[0168] A numerical average molecular weight of these long-chain polyols is preferably within a range of from 1,500 to 5,000. By using a long-chain polyol having such a numerical average molecular weight, it is possible to reliably obtain a golf ball made of a thermoplastic polyurethane composition excellent in various properties such as productivity and the above-mentioned rebound. The numerical average molecular weight of the long-chain polyol is more preferably within a range of from 1,700 to 4,000, and still more preferably within a range of from 1,900 to 3,000.

[0169] The numerical average molecular weight of the long-chain polyol is a numerical average molecular weight calculated based on a hydroxyl value measured in accordance with JIS K 1557.

[0170] As the chain extender, those hitherto used in the art related to thermoplastic polyurethanes can be suitably used, and for example, a low-molecular-weight compound having on the molecule two or more active hydrogen atoms capable of reacting with an isocyanate group and having 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, or the like. Among them, the chain extender is preferably an aliphatic diol having from 2 to 12 carbon atoms, and is more preferably 1,4-butylene glycol.

[0171] As the polyisocyanate compound, those hitherto used in the art related to thermoplastic polyurethane can be suitably used, and are not particularly limited. Specifically, one or more selected from a group consisting of 4,4′-diphenylmethane diisocyanate, 2,4-toluene diisocyanate (or) 2,6-toluene diisocyanate, p-phenylene diisocyanate, xylylene diisocyanate, 1,5-naphthylene 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, it may be difficult to control a crosslinking reaction during injection molding depending on the type of isocyanate. In the present invention, 4,4′-diphenylmethane diisocyanate, which is an aromatic diisocyanate, is most preferable from the viewpoint of providing a balance between stability during production and physical properties to be manifested.

[0172] Although not particularly limited, the most preferable thermoplastic polyurethane as the component (I) is a thermoplastic polyurethane synthesized using a polyether polyol as the long-chain polyol, an aliphatic diol as the chain extender, and an aromatic diisocyanate as the polyisocyanate compound, in which the polyether polyol is polytetramethylene glycol having a numerical average molecular weight of at least 1,900, the chain extender is 1,4-butylene glycol, and the aromatic diisocyanate is 4,4′-diphenylmethane diisocyanate.

[0173] A blending ratio of active hydrogen atoms: isocyanate groups in the polyurethane forming reaction may be adjusted within a preferable range so that a golf ball composed of a thermoplastic polyurethane composition more excellent in various properties such as rebound, spin performance, scuff resistance, and productivity may be obtained. Specifically, when the above-described long-chain polyol, the polyisocyanate compound, and the chain extender are reacted to manufacture the thermoplastic polyurethane, it is preferable to use each component at such a ratio that the isocyanate group contained in the polyisocyanate compound is from 0.95 to 1.05 mol, based on 1 mol of active hydrogen atoms of the long-chain polyol and the chain extender.

[0174] A method for manufacturing the thermoplastic polyurethane as the component (I) is not particularly limited, and the thermoplastic polyurethane may be manufactured by either a prepolymer method or a one-shot method using the long-chain polyol, the chain extender, and the polyisocyanate compound by utilizing a known urethanization reaction. Among these methods, it is preferable to perform melt polymerization substantially in the absence of a solvent, and it is particularly preferable to manufacture the thermoplastic polyurethane by continuous melt polymerization using a multi-screw extruder.

[0175] As specific examples of the thermoplastic polyurethane as the component (I), commercially available products may be used such as Pandex T-8295, Pandex T-8290, Pandex T-8260, and Pandex T-8295 (all manufactured by DIC Covestro Polymer, Ltd.).

[0176] Next, in a single resin blend including the component (I) and the component (II), at least a part of the polyisocyanate compound used as the component (II) needs to be in a state in which all isocyanate groups in one molecule remain in an unreacted state. That is, a polyisocyanate compound in which all isocyanate groups in one molecule are completely free may be present in a single resin blend, and such a polyisocyanate compound and a polyisocyanate compound in which some isocyanate groups in one molecule are free may coexist.

[0177] Although not particularly limited, various isocyanates may be used in the polyisocyanate compound, and specifically, one or more selected from a group consisting of 4,4′-diphenylmethane diisocyanate, 2,4-toluene diisocyanate (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. It is preferable to employ 4,4′-diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, and isophorone diisocyanate among the above group of isocyanates from the viewpoint of a balance between an influence on moldability due to an increase in viscosity associated with a reaction of the thermoplastic polyurethane of the component (A) and physical properties of the resulting golf ball cover material.

[0178] Although not an essential component, a thermoplastic elastomer other than the thermoplastic polyurethane may be included as a component (III) with the components (I) and (II). By including the component (III) in the resin blend, a flowability of the resin blend can be further improved, and various physical properties required of the golf ball cover material can be increased, such as rebound and scuff resistance.

[0179] As the component (III), specifically, one or more selected from a polyester elastomer, a polyamide elastomer, an ionomer resin, a styrene block elastomer, a hydrogenated styrene butadiene rubber, a styrene-ethylene-butylene-ethylene block copolymer or a modified product thereof, an ethylene-ethylene-butylene-ethylene block copolymer or a modified product of an ethylene-ethylene-butylene-ethylene block copolymer, a styrene-ethylene-butylene-styrene block copolymer or a modified product of a styrene-ethylene-butylene-styrene block copolymer, an ABS resin, polyacetal, polyethylene, and a nylon resin may be used as the thermoplastic elastomer other than the thermoplastic polyurethane. In particular, it is preferable to employ a polyester elastomer, a polyamide elastomer, and a polyacetal for the reason that rebound and scuff resistance are improved while productivity is well maintained.

[0180] Although a compositional ratio of the components (I), (II), and (III) is not particularly limited, in order to sufficiently and effectively exhibit advantageous effects of the present invention, a compositional ratio (I): (II): (III) is preferably in the weight ratio range of 100:2 to 50:0 to 50, and still more preferably 100:2 to 30:8 to 50.

[0181] Although a method for mixing the above components (I) to (III) to prepare a resin blend is not particularly limited, it is preferable to select conditions under which the polyisocyanate compound in which all isocyanate groups remain in an unreacted state is present in at least a part of the polyisocyanate compound. Specifically, it is desirable to take measures such as mixing the above components with an inert gas such as nitrogen gas or in a vacuum state. This resin blend is then injection molded around a core disposed in a mold, and is preferably formed into a pellet shape having a length of 1 to 10 mm and a diameter of 0.5 to 5 mm for the reason of smoothly and easily handling the resin blend. An unreacted isocyanate group remains in the resin pellet, and the unreacted isocyanate group reacts with the component (A) and the component (III) to form a crosslinked product during injection molding in the core or by a post-treatment such as subsequent annealing.

[0182] Furthermore, various additives other than the components constituting the thermoplastic polyurethane can be included in the resin blend as necessary, and for example, a pigment, a dispersant, an antioxidant, a light stabilizer, an ultraviolet absorber, an internal mold lubricant, or the like can be appropriately included.

[0183] The manufacture of a multi-piece solid golf ball in which the above-described core, surrounding layer, intermediate layer, and cover (outermost layer) are formed as successive layers may be performed by a customary method such as a known injection molding process. For example, each material of the surrounding layer and the intermediate layer is sequentially injected around the core with each injection mold to obtain each layer-encased sphere, and finally, a cover material, which is the outermost layer, is injection molded to obtain a multi-piece golf ball. In addition, as each encasing layer, it is also possible to produce the golf ball by preparing two half-cups pre-molded into hemispherical shapes, enclosing the layer-encased sphere within the two half-cups, and molding the encased spheres under applied heat and pressure.

[0184] The deflection (mm) when the golf ball is compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) is preferably at least 2.0 mm, more preferably at least 2.2 mm, and still more preferably at least 2.3 mm, and an upper limit value is preferably not more than 3.3 mm, more preferably not more than 3.0 mm, and still more preferably not more than 2.7 mm. If the deflection of the golf ball is too small, that is, if the golf ball is too hard, the spin rate increases on full shots, and in particular, the intended distance may not be increased on shots with a driver (W #1) at a head speed (HS) of not more than 40 m / s and on full shots with an iron, and the feel at impact may become too hard. On the other hand, if the deflection is too large, that is, if the golf ball is too soft, the actual initial velocity on full shots may become low, and in particular, the intended distance may not be increased on shots with a driver (W #1) at a high head speed of at least HS 40 m / s. In addition, the feel at impact may be too soft, and the durability to cracking on repeated impact may worsen.[Relationship Between Deflection of Core and Ball]

[0185] Letting the deflection when the core is compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) be A (mm), and the deflection when the golf ball is compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) be B (mm), a value of A-B is preferably at least 0.9 mm, more preferably at least 0.95 mm, and still more preferably at least 1.0 mm, and the upper limit value is preferably not more than 1.4 mm, more preferably not more than 1.3 mm, and still more preferably not more than 1.2 mm. If this value is too large, the actual initial velocity on shots with a driver (W #1) may become low, the intended distance may not be attainable, and the durability to cracking on repeated impact may worsen. On the other hand, if this value is too small, the feel at impact on full shots may feel hard, and the durability to cracking on repeated impact may worsen.

[0186] A ratio of the deflection of the core to the deflection of the ball, that is, a value of A / B, is preferably at least 1.35, more preferably at least 1.37, and still more preferably at least 1.40, and the upper limit value is preferably not more than 1.55, more preferably not more than 1.50, and still more preferably not more than 1.45. If this value is too large, the actual initial velocity on shots with a driver (W #1) may become low, the intended distance may not be attainable, and the durability to cracking on repeated impact may worsen. On the other hand, if this value is too small, the feel at impact on full shots may feel hard, and the durability to cracking on repeated impact may worsen.[Hardness Relationships of Layers]

[0187] Expressed on the Shore C hardness scale, a value obtained by subtracting the surface hardness of the ball from the surface hardness of the intermediate layer-encased sphere is preferably at least 1, more preferably at least 5, and still more preferably at least 7, and an upper limit value is preferably not more than 15, more preferably not more than 13, and still more preferably not more than 11. If the above value is too small, the spin rate on approach shots is reduced, and controllability in the short game may worsen. On the other hand, if the above value is too large, in a case where the cause is the intermediate layer, the durability to cracking on repeated impact may worsen. In a case where the cause is the cover, the spin rate on full shots increases, and the intended distance may not be attainable.

[0188] Expressed on the Shore C hardness scale, a value obtained by subtracting the surface hardness of the surrounding layer-encased sphere from the surface hardness of the intermediate layer-encased sphere is preferably at least 1, more preferably at least 3, and still more preferably at least 4, and the upper limit value is preferably not more than 12, more preferably not more than 8, and still more preferably not more than 6. If this value falls outside of the above numerical ranges, the spin rate on full shots increases, and the intended distance may not be attainable.

[0189] Expressed on the Shore C hardness scale, a value obtained by subtracting the core surface hardness from the surface hardness of the surrounding layer-encased sphere is preferably at least 1, more preferably at least 4, and still more preferably at least 8, and the upper limit value is preferably not more than 20, more preferably not more than 17, and still more preferably not more than 14. Expressed on the Shore C hardness scale, a value obtained by subtracting the core center hardness from the surface hardness of the surrounding layer-encased sphere is preferably at least 20, more preferably at least 23, and still more preferably at least 27, and the upper limit value is preferably not more than 39, more preferably not more than 36, and still more preferably not more than 33. If the above value is too large, the durability to cracking on repeated impact may worsen, and in particular, on shots with a driver (W #1) at a head speed of at least 50 m / s, the actual initial velocity may be lowered, and the intended distance may not be attainable. On the other hand, if the above value becomes too small, the spin rate on full shots may increase, and in particular, the intended distance may not be attainable on shots with a driver (W #1) at a head speed of not more than 40 m / s and on full shots with an iron.

[0190] Expressed on the Shore C hardness scale, a value obtained by subtracting the core surface hardness from the surface hardness of the ball is preferably at least 0, more preferably at least 1, and still more preferably at least 2, and the upper limit value is preferably not more than 12, more preferably not more than 8, and still more preferably not more than 6. Expressed on the Shore C hardness scale, a value obtained by subtracting the core center hardness from the surface hardness of the ball is preferably at least 17, more preferably at least 19, and still more preferably at least 21, and the upper limit value is preferably not more than 32, more preferably not more than 28, and still more preferably not more than 26. If the value is too large, in a case where the cause is the ball surface hardness, the spin rate on approach shots may be insufficient. In addition, in the above case, in a case where the cause is the surface hardness of the core or the center hardness of the core, the durability to cracking on repeated impact may worsen. On the other hand, if the above value is too small, the spin rate on full shots may become too large, and the intended distance may not be attainable.

[0191] A hardness relationship of the entire ball preferably satisfies the following condition.

[0192] Core surface hardness≤surface hardness of surrounding layer-encased sphere<surface hardness of intermediate layer-encased sphere>ball surface hardness.

[0193] If the above condition is not satisfied, it may be difficult to achieve both a superior distance on full shots and superior controllability in the short game.[Thickness Relationships of Layers]

[0194] A value obtained by subtracting the intermediate layer thickness from the surrounding layer thickness is preferably at least 0.05 mm, more preferably at least 0.10 mm, and still more preferably at least 0.20 mm, and the upper limit value is preferably not more than 0.60 mm, more preferably not more than 0.50 mm, and still more preferably not more than 0.40 mm. If the above value deviates from the above range, the spin rate on full shots may increase, and in particular, the intended distance may not be increased on shots with a driver (W #1) at a head speed of not more than 40 m / s and on full shots with an iron.

[0195] A sum of the thickness of the surrounding layer and the thickness of the intermediate layer is preferably at least 1.8 mm, more preferably at least 2.0 mm, and still more preferably at least 2.2 mm, and the upper limit value is preferably not more than 3.6 mm, more preferably not more than 3.0 mm, and still more preferably not more than 2.5 mm. A value obtained by dividing the above (sum of surrounding layer thickness and intermediate layer thickness) by a diameter of the ball, that is, a value of (surrounding layer thickness+intermediate layer thickness) / ball diameter, is preferably at least 0.040, more preferably at least 0.047, and still more preferably at least 0.052, and the upper limit value is preferably not more than 0.072, more preferably not more than 0.065, and still more preferably not more than 0.059. If the above value deviates from the above range, the spin rate on full shots may increase, and in particular, the intended distance may not be increased on shots with a driver (W #1) at a head speed of not more than 40 m / s and on full shots with an iron. If this value is too small, the durability to cracking on repeated impact may worsen.

[0196] The thickness of the intermediate layer is preferably larger than the thickness of the cover. In this case, a value obtained by subtracting the cover thickness from the intermediate layer thickness is preferably at least 0.05 mm, more preferably at least 0.10 mm, and still more preferably at least 0.20 mm, and the upper limit value is preferably not more than 0.60 mm, more preferably not more than 0.50 mm, and still more preferably not more than 0.40 mm. If this value is too large, in a case where the cause is the cover thickness, there may be insufficient spin on approach shots. In addition, in the above case, in a case where the cause is the intermediate layer thickness, the feel at impact may feel hard. On the other hand, if the above value is too small, in a case where the cause is the cover thickness, the rebound of the ball may become low, the spin rate may become large on full shots, and the intended distance may not be attainable. In addition, in a case where the cause is the intermediate layer thickness, the durability to cracking on repeated impact may worsen.

[0197] Numerous dimples may be formed on the outside surface of the cover. The number of dimples arranged on the surface of the cover is not particularly limited, but is preferably 250 or more, preferably 300 or more, and more preferably 320 or more, and an upper limit thereof can be preferably 380 or less, more preferably 350 or less, and even more preferably 340 or less. If the number of dimples is larger than the above range, a ball trajectory may become lower, and a distance traveled by the ball may decrease. On the other hand, if the number of dimples decreases, the ball trajectory may become higher, and the distance traveled by the ball may not increase.

[0198] As for the shape of the dimples, one type or a combination of two or more types such as a circular shape, various polygonal shapes, a dewdrop shape, and other oval shapes may be appropriately used. For example, if circular dimples are used, the diameter can be about 2.5 mm or more and 6.5 mm or less, and the depth may be 0.08 mm or more and 0.30 mm or less.

[0199] A dimple coverage ratio of the dimples on the spherical surface of the golf ball, specifically, a ratio (SR value) of a sum of the individual dimple surface areas, each defined by a flat plane circumscribed by an edge of a dimple, to a ball spherical surface area on the assumption that the ball has no dimples is desirably 70% or more and 90% or less from the viewpoint of sufficiently exhibiting aerodynamic properties. In addition, a value Vo obtained by dividing the spatial volume of the dimples below the flat plane circumscribed by the edge of each dimple by a volume of a cylinder whose base is the flat plane and whose height is a maximum depth of the dimple from the base is suitably 0.35 or more and 0.80 or less from the viewpoint of optimizing the ball trajectory. Furthermore, a VR value of a sum of the volumes of the individual dimples formed below the flat plane circumscribed by the edge of a dimple to a ball spherical volume on the assumption that the ball has no dimples is preferably at least 0.6% and not more than 0.8%. If there is a deviation from the ranges of each numerical value described above, the resulting trajectory may not enable a good distance to be attained, and the ball may fail to travel a sufficiently satisfactory distance.

[0200] The golf ball of the present invention may be made to conform to the Rules of Golf for play. The inventive ball may be formed to a diameter which is such that the ball does not pass through a ring having an inner diameter of 42.672 mm and to a weight which is preferably between 45.0 and 45.93 g.EXAMPLES

[0201] Hereinafter, the present invention is specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.Examples 1 to 3 and Comparative Examples 1 to 9[Formation of Core]

[0202] Rubber compositions of each of Examples 1 to 3 and Comparative Examples 1 to 9 shown in Table 1 are prepared, and then vulcanization molding is performed at temperatures and for times shown in Table 1 to produce a solid core.TABLE 1ExampleComparative Example123123456789(a)Polybutadiene A100100100100100100100808080100100(a)Polybutadiene B202020(b)Zinc acrylate A27.2(b)Zinc acrylate B36.135.333.733.732.931.434.440.839.038.135.6—Zinc stearate2.02.02.02.0(c)Organic peroxide A1.01.01.01.01.01.00.61.01.01.01.01.0(c)Organic peroxide B0.6—Sulfur0.0250.0250.025(d)Water0.50.50.50.30.30.31.01.21.20.50.5(e′)Antioxidant A0.10.10.10.20.10.10.1(e′)Antioxidant B0.30.30.30.30.3(e)Antioxidant C0.50.50.50.50.5—Zinc oxide24.224.525.124.124.324.94.04.04.04.016.517.5—Barium sulfate24.721.418.819.4—Zinc salt of0.40.40.40.40.40.40.250.50.30.30.40.4pentachlorothiophenolVulcanization temperature (° C.)158158158150150150158155155155158158Vulcanization time (min)181818212121161415151818

[0203] The details of each component described in Table 1 are as follows.

[0204] Polybutadiene A: Trade name “BR 01” (manufactured by ENEOS Materials Corporation)

[0205] Polybutadiene B: Trade name “BR T700” (manufactured by ENEOS Materials Corporation)

[0206] Zinc acrylate A: Trade name “ZN-DA85S” (manufactured by Nippon Shokubai Co., Ltd.)

[0207] Zinc acrylate B: Trade name “ZN-DA85SR” (manufactured by Nippon Shokubai Co., Ltd.)

[0208] Zinc stearate: Trade name “Zinc stearate GP” (manufactured by NOF Corporation)

[0209] Organic peroxide A: Dicumyl peroxide, trade name “Percumyl D” (manufactured by NOF Corporation)

[0210] Organic peroxide B: A mixture of 1,1-di(t-butylperoxy)cyclohexane and silica, trade name “Perhexa C-40” (manufactured by NOF Corporation)

[0211] Sulfur: Trade name “SANMIX S-80N” (manufactured by Sanshin Chemical Industry Co., Ltd.), sulfur masterbatch containing 80 wt % of sulfur powder for rubber

[0212] Water: Pure water (manufactured by Seiki Co., Ltd.)

[0213] Antioxidant A: 2,2-methylenebis(4-methyl-6-butylphenol), trade name “Nocrac NS-6” (manufactured by Ouchi Shinko Chemical Industrial Co., Ltd.)

[0214] Antioxidant B: 2-mercaptobenzimidazole, trade name “Nocrac MB” (manufactured by Ouchi Shinko Chemical Industrial Co., Ltd.)

[0215] Antioxidant C: Trade name “Antage HP-500” (manufactured by Kawaguchi Chemical Industry Co., LTD.)

[0216] Zinc oxide: Trade name “Grade 3 Zinc Oxide” (manufactured by Sakai Chemical Industry Co., Ltd.)

[0217] Zinc salt of pentachlorothiophenol: Manufactured by FUJIFILM Wako Pure Chemical Corporation[Formation of Intermediate Layer and Cover (Outermost Layer)]

[0218] Next, a resin material No. 1 of a surrounding layer shown in Table 2 is injection-molded around a core surface of each example using an injection mold to obtain surrounding layer-encased spheres. In Comparative Examples 8 and 9, the surrounding layer is not formed. Next, using another injection mold, a resin material No. 2 of an intermediate layer shown in Table 2 is injection-molded around the surrounding layer-encased sphere to obtain an intermediate layer-encased sphere. Further, a resin material No. 3 of a cover shown in Table 2 is injection-molded around the intermediate layer-encased sphere using another injection mold to obtain a golf ball. Furthermore, at this time, a plurality of predetermined dimples described below are formed on a cover surface.TABLE 2High-acidMetalResin composition (pbw)ionomertypeNo. 1No. 2No. 3HPF 1000Not applicableMg100Himilan 1706Not applicableZn15AM7318ApplicableNa85Titanium oxide3.0Polyethylene wax1.2Trimethylolpropane1.1Thermoplastic100polyurethanePolyisocyanate compound10.6Thermoplastic elastomer14.5Additive6.5

[0219] Details of the blending components in Table 2 are as follows.

[0220] “HPF 1000” manufactured by Dow Chemical Company

[0221] “Himilan 1706” and “AM7318” ionomer resins manufactured by Dow-Mitsui Polychemicals Co., Ltd.

[0222] “Trimethylolpropane” manufactured by Tokyo Chemical Industry Co., Ltd.

[0223] Trade name “Sun Wax 161-P” polyethylene wax manufactured by Sanyo Chemical Industries, Ltd.

[0224] Ether-type thermoplastic polyurethane, trade name “Pandex” manufactured by DIC Covestro Polymer Ltd.

[0225] Thermoplastic elastomer, trade name “Hytrel 2401”, polyester elastomer manufactured by Toray Celanese Co., Ltd.

[0226] Additives such as blue pigment, titanium oxide, and wax

[0227] For the dimples of each of the Examples and Comparative Examples, the following common dimple mode is used. This dimple mode includes eight types of circular dimples of No. 1 to No. 8 having different diameters and depths. The details are listed in Table 3 below. In addition, this dimple arrangement mode (pattern) is illustrated in FIGS. 3A and 3B. FIG. 3A is a plan view of the dimples, and FIG. 3B is a side view of the dimples.TABLE 3CylinderTotalDiameterDepthVolumevolume ratiovolumeSRVRTypeQuantity(mm)(mm)(mm3)Vo(mm3)(%)(%)No. 1124.630.1221.0090.491278840.68No. 21984.500.1190.9190.486No. 3363.920.1150.6550.472No. 4122.870.0860.2450.442No. 5364.490.1260.9650.483No. 6243.920.1240.7110.473No. 763.310.1330.5500.479No. 863.210.1320.4570.430Total330[Definition of Dimple]Edge: Highest point in cross section passing through the center of the dimpleDiameter: Diameter of the flat plane circumscribed by the edge of the dimple

[0230] Depth: Maximum depth of the dimple from the flat plane circumscribed by the edge of the dimple

[0231] SR: Ratio of the sum of the individual dimple surface areas, each defined by the flat plane circumscribed by the edge of the dimple, to the ball spherical surface area on the assumption that the ball has no dimples

[0232] Dimple volume: Volume of the dimple under the flat plane circumscribed by the edge of the dimple

[0233] Total dimple volume: Sum of the dimple volumes of all dimples

[0234] Cylinder volume ratio: Ratio of the dimple volume to the volume of a cylinder having a depth with the same diameter as the dimple

[0235] VR: Ratio of the sum of volumes of the individual dimples formed below the flat plane circumscribed by the edge of the dimple to the ball spherical volume on the assumption that the ball has no dimples

[0236] For each resulting golf ball, various physical properties such as internal hardnesses at various positions of the core, outer diameters of the core and each layer-encased sphere, thicknesses and material hardnesses of each layer, and deflections and surface hardnesses of each layer-encased sphere are evaluated by the following methods, and are shown in Tables 4 and 5.[Outer Diameters of Each Sphere of Core, Surrounding Layer-Encased Sphere, and Intermediate Layer-Encased Sphere]

[0237] After being temperature-adjusted to 23.9±1° C. for at least three hours in a thermostatic bath, the sphere to be measured is measured in a room at a temperature of 23.9±2° C. Five random places on the surface are measured, and using an average value of these measurements as a measured value of each sphere, an average value for the diameter of 10 such spheres is determined.[Ball Diameter]

[0238] After being temperature-adjusted to 23.9±1° C. for at least three hours in a thermostatic bath, the ball to be measured is measured in a room at a temperature of 23.9±2° C. Fifteen random places on a portion with no dimples are measured, and using an average value of these measurements as a measured value of one ball, an average value for the diameter of 10 such balls is determined.[Deflections of Core and Ball]

[0239] A subject layer-encased sphere of the core or ball is placed on a hard plate, and the deflection when compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) is measured. The deflection is a measured value after the temperature is adjusted to 23.9° C. A pressing speed of a head that compresses the subject layer-encased sphere is set to 10 mm / s.[Core Hardness Profile]

[0240] The core surface is spherical, but an indenter of a durometer is set substantially perpendicular to the spherical core surface, and a core surface hardness expressed on the Shore C scale is measured in accordance with ASTM D2240. With respect to the core center and a predetermined position of the core, the core is cut into hemispheres to obtain a flat cross-section, the hardness is measured by perpendicularly pressing the indenter of the durometer against a center portion and the predetermined positions shown in Table 4, and the hardnesses at the center and each position are shown as Shore C hardness values. For the measurement of the hardness, a P2 Automatic Rubber Hardness Tester manufactured by Kobunshi Keiki Co., Ltd. equipped with a Shore C durometer is used. For the hardness value, a maximum value is read. All measurements are carried out in an environment of 23±2° C. The numerical values in Table 6 are Shore C hardness values.

[0241] Graphs of core hardness profiles of Examples 1 to 3 and Comparative Examples 1 to 9 are shown in FIGS. 4, 5, and 6.[Material Hardnesses of Surrounding Layer, Intermediate Layer, and Cover]

[0242] The resin material of each layer is molded into a sheet having a thickness of 2 mm and left for two weeks. Thereafter, the Shore D hardness and the Shore C hardness are measured in accordance with the ASTM D2240 standard. For the measurement of the hardness, the P2 Automatic Rubber Hardness Tester manufactured by Kobunshi Keiki Co., Ltd. is used. Shore D hardness and Shore C hardness attachments are attached to measure each hardness. For the hardness value, a maximum value is read. All measurements are carried out in an environment of 23±2° C.[Surface Hardnesses of Each Layer-Encased Sphere]

[0243] A measurement is performed by perpendicularly pressing the indenter against the surface of each sphere. It is noted that a surface hardness of a ball (cover) is a measured value at a dimple-free area (land) on the surface of the ball. The Shore D hardness and the Shore C hardness are measured in accordance with the ASTM D2240 standard. For the measurement of the hardness, the P2 Automatic Rubber Hardness Tester manufactured by Kobunshi Keiki Co., Ltd. is used. Shore D hardness and Shore C hardness attachments are attached to measure each hardness. For the hardness value, a maximum value is read. All measurements are carried out in an environment of 23±2° C.TABLE 4ExampleComparative Example123123CoreOuter diameter (mm)36.2736.2936.3236.2736.2936.32Weight (g)30.0330.0630.1330.0330.0630.13Deflection (mm)3.393.563.873.393.563.87CoreH100 (surface)84.983.781.686.384.781.8hardness profileH87.581.880.678.379.879.178.0(Shore C hardness)H7576.875.874.074.073.071.0H62.570.669.467.169.968.465.6H50 (intermediate)70.669.467.169.467.764.7H37.570.469.167.069.067.364.1H2569.768.466.168.766.963.7H12.567.666.564.568.166.563.5H0 (center)66.064.461.468.066.463.5H100 − H87.53.13.13.36.55.63.8H87.5 − H755.04.84.35.86.17.0H75 − H62.56.26.46.94.14.65.4H62.5 − H500.00.00.00.50.70.9H50 − H37.50.20.30.10.40.40.6H37.5 − H250.70.70.90.30.40.4H25 − H12.52.11.91.60.60.40.2H12.5 − H01.62.13.10.10.10.0H100 − H0 (surface − center)18.919.320.218.318.318.3H87.5 − H015.816.216.911.812.714.5H100 − H758.17.97.612.311.710.8H75 − H506.26.46.94.65.36.3H50 − H250.91.01.00.70.81.0H25 − H03.74.04.70.70.50.2(H75 − H62.5) − (H87.5 − H75)1.21.62.6−1.7−1.5−1.6(H87.5 − H75) − (H100 − H87.5)1.91.71.0−0.70.53.2(H100 − H87.5) − (H62.5 − H50)3.13.13.36.04.92.9(H87.5 − H50) / (H50 − H12.5)3.73.94.38.09.511.1(H100 − H50) / (H50 − H0)3.12.92.512.113.114.3(H100 − H87.5) / (H87.5 − H75)0.60.60.81.10.90.5(H87.5 − H75) / (H75 − H62.5)0.80.80.61.41.31.3Comparative Example456789CoreOuter diameter (mm)36.2736.3236.2736.2938.6338.63Weight (g)30.0330.1330.0330.0635.1035.09Deflection (mm)3.393.873.393.563.003.50CoreH100 (surface)80.687.393.491.887.684.2hardness profileH87.572.380.281.380.484.681.0(Shore C hardness)H7572.174.874.974.279.176.1H62.568.970.270.069.273.569.8H50 (intermediate)66.767.467.165.973.169.6H37.565.965.566.665.372.969.5H2564.963.866.465.172.768.9H12.561.862.164.563.170.166.9H0 (center)61.860.261.659.769.865.0H100 − H87.58.37.112.111.43.03.2H87.5 − H750.25.46.46.25.54.9H75 − H62.53.24.64.95.05.66.3H62.5 − H502.22.82.93.30.40.2H50 − H37.50.81.90.50.60.20.1H37.5 − H251.01.70.20.20.20.6H25 − H12.53.11.71.92.02.62.0H12.5 − H00.01.92.93.40.31.9H100 − H0 (surface − center)18.827.131.832.117.819.2H87.5 − H010.520.019.720.714.816.0H100 − H758.512.518.517.68.58.1H75 − H505.47.47.88.36.06.5H50 − H251.83.60.70.80.40.7H25 − H03.13.64.85.42.93.9(H75 − H62.5) − (H87.5 − H75)3.0−0.8−1.5−1.20.11.4(H87.5 − H75) − (H100 − H87.5)−8.1−1.7−5.7−5.22.51.7(H100 − H87.5) − (H62.5 − H50)6.14.39.28.12.63.0(H87.5 − H50) / (H50 − H12.5)1.12.45.55.23.84.2(H100 − H50) / (H50 − H0)2.82.84.84.24.43.2(H100 − H87.5) / (H87.5 − H75)41.51.31.91.80.50.7(H87.5 − H75) / (H75 − H62.5)0.11.21.31.21.00.8TABLE 5ExampleComparative Example123123Construction (piece)4P4P4P4P4P4PSurrounding layerMaterialNo. 1No. 1No. 1No. 1No. 1No. 1Thickness (mm)1.331.301.291.331.301.29Material hardness (Shore C)888888888888Material hardness (Shore D)575757575757SurroundingOuter diameter (mm)38.9338.8938.9038.9338.8938.90layer-encased sphereWeight (g)35.7435.6535.6235.7435.6535.62Surface hardness (Shore C)949494949494Surface hardness (Shore D)636363636363Intermediate layerMaterialNo. 2No. 2No. 2No. 2No. 2No. 2Thickness (mm)1.061.081.071.061.081.07Weight (g)4.975.075.044.975.075.04Material hardness (Shore C)949494949494Material hardness (Shore D)676767676767IntermediateOuter diameter (mm)41.0541.0541.0441.0541.0541.04layer-encased sphereWeight (g)40.7140.7240.6640.7140.7240.66Surface hardness (Shore C)989898989898Surface hardness (Shore D)717171717171CoverMaterialNo. 3No. 3No. 3No. 3No. 3No. 3Thickness (mm)0.830.830.830.830.830.83Material hardness (Shore C)727272727272Material hardness (Shore D)474747474747BallOuter diameter (mm)42.7042.7142.7042.7042.7142.70Weight (g)45.5345.5645.5345.5345.5645.53Deflection (mm)2.372.512.682.372.512.68Surface hardness (Shore C)878787878787Surface hardness (Shore D)606060606060Surface hardness of surrounding layer-encased sphere −9.110.312.47.79.312.2core surface hardness (Shore C)Surface hardness of surrounding layer-encased sphere −28.029.632.626.027.630.5core center hardness (Shore C)Surface hardness of intermediate layer-encased sphere −4.04.04.04.04.04.0surface hardness of surrounding layer-encased sphere (Shore C)Surface hardness of intermediate layer-encased sphere −11.011.011.011.011.011.0ball surface hardness (Shore C)Intermediate layer thickness + surrounding layer thickness (mm)2.392.382.362.392.382.36(Intermediate layer thickness + surrounding layer thickness) / 0.0560.0560.0550.0560.0560.055ball diameterSurrounding layer thickness − intermediate layer thickness (mm)0.270.220.220.270.220.22Intermediate layer thickness − cover thickness (mm)0.230.250.240.230.250.24Ball surface hardness − core surface hardness (Shore C)2.13.35.40.72.35.2Ball surface hardness − core center hardness (Shore C)21.022.625.619.020.623.5(Core deflection) − (ball deflection) (mm)1.021.051.191.021.051.19(Core deflection) / (ball deflection)1.431.421.441.431.421.44Comparative Example456789Construction (piece)4P4P4P4P3P3PSurrounding layerMaterialNo. 1No. 1No. 1No. 1——Thickness (mm)1.331.291.331.30——Material hardness (Shore C)88888888——Material hardness (Shore D)57575757——SurroundingOuter diameter (mm)38.9338.9038.9338.89——layer-encased sphereWeight (g)35.7435.6235.7435.65——Surface hardness (Shore C)94949494——Surface hardness (Shore D)63636363——Intermediate layerMaterialNo. 2No. 2No. 2No. 2No. 2No. 2Thickness (mm)1.061.071.061.081.211.21Weight (g)4.975.044.975.075.625.63Material hardness (Shore C)949494949494Material hardness (Shore D)676767676767IntermediateOuter diameter (mm)41.0541.0441.0541.0541.0441.04layer-encased sphereWeight (g)40.7140.6640.7140.7240.7240.72Surface hardness (Shore C)989898989898Surface hardness (Shore D)717171717171CoverMaterialNo. 3No. 3No. 3No. 3No. 3No. 3Thickness (mm)0.830.830.830.830.840.84Material hardness (Shore C)727272727272Material hardness (Shore D)474747474747BallOuter diameter (mm)42.7042.7042.7042.7142.7242.72Weight (g)45.5345.5345.5345.5645.5845.58Deflection (mm)2.372.682.372.512.372.68Surface hardness (Shore C)878787878787Surface hardness (Shore D)606060606060Surface hardness of surrounding layer-encased sphere −13.46.70.62.2——core surface hardness (Shore C)Surface hardness of surrounding layer-encased sphere −32.233.832.434.3——core center hardness (Shore C)Surface hardness of intermediate layer-encased sphere −4.04.04.04.0——surface hardness of surrounding layer-encased sphere (Shore C)Surface hardness of intermediate layer-encased sphere −11.11.011.011.011.011.0ball surface hardness (Shore C)Intermediate layer thickness + surrounding layer thickness (mm)2.392.362.392.381.211.21(Intermediate layer thickness + surrounding layer thickness) / 0.0560.0550.0560.0560.0280.028ball diameterSurrounding layer thickness − intermediate layer thickness (mm)0.270.220.270.22——Intermediate layer thickness − cover thickness (mm)0.230.240.230.250.360.36Ball surface hardness − core surface hardness (Shore C)6.4−0.3−6.4−4.8−0.62.8Ball surface hardness − core center hardness (Shore C)25.226.825.427.317.222.0(Core deflection) − (ball deflection) (mm)1.021.191.021.050.630.82(Core deflection) / (ball deflection)1.431.441.431.421.271.31The flight on shots (W #1) (I #6), the spin rate on approach shots, and the durability to repeated impact of each golf ball are evaluated by the following methods. The results are shown in Table 6.[Evaluation of Flight (W #1, HS 50 m / s)]A driver is mounted on a golf swing robot, and a spin rate and a distance traveled (total) by a ball when struck at a head speed (HS) of 50 m / s are measured. The club used is a B-Limited 415 Driver / loft angle 9° (2022 model) manufactured by Bridgestone Sports Co., Ltd. and is evaluated according to the following rating criteria.[Rating Criteria]Good: Total distance is at least 272.0 mFair: Total distance is at least 270.0 m and less than 272.0 m

[0248] NG: Total distance is less than 270.0 m[Evaluation of Flight (W #1, HS 45 m / s)]

[0249] A driver is mounted on the golf swing robot, and the spin rate and the distance traveled (total) by a ball when struck at a head speed (HS) of 45 m / s are measured. The club used is a J015 Driver / loft angle 9.5° (2016 model) manufactured by Bridgestone Sports Co., Ltd. and is evaluated according to the following rating criteria.[Rating Criteria]Good: Total distance is at least 234.0 m

[0251] Fair: Total distance is at least 232.0 m and less than 234.0 m

[0252] NG: Total distance is less than 232.0 m[Evaluation of Flight (W #1, HS 40 m / s)]

[0253] A driver is mounted on the golf swing robot, and the spin rate and the distance traveled (total) by a ball when struck at a head speed (HS) of 40 m / s are measured. The club used is a JGR Driver / loft angle 9.5° (2016 model) manufactured by Bridgestone Sports Co., Ltd. and is evaluated according to the following rating criteria.[Rating Criteria]Good: Total distance is at least 199.0 m

[0255] Fair: Total distance is at least 197.0 m and less than 199.0 m

[0256] NG: Total distance is less than 197.0 m[Evaluation of Flight (I #6, HS 42 m / s)]

[0257] A number six iron (I #6) is mounted on the golf swing robot, and the spin rate and the distance traveled (total) by a ball when struck at a head speed (HS) of 42 m / s are measured. The club used is a JGR Forged I #6 (2016 model) manufactured by Bridgestone Sports Co., Ltd. and is evaluated according to the following rating criteria.[Rating Criteria]Good: Total distance is at least 182.0 m

[0259] Fair: Total distance is at least 180.0 m and less than 182.0 m

[0260] NG: Total distance is less than 180.0 m[Evaluation of Flight (I #6, HS 35 m / s)]

[0261] The number six iron (I #6) is mounted on the golf swing robot and the spin rate and the distance traveled (total) by a ball when struck at a head speed (HS) of 35 m / s are measured. The club used is a JGR Forged I #6 (2016 model) manufactured by Bridgestone Sports Co., Ltd. and is evaluated according to the following rating criteria.[Rating Criteria]Good: Total distance is at least 162.5 m

[0263] Fair: Total distance is at least 160.5 m and less than 162.5 m

[0264] NG: Total distance is less than 160.5 m[Evaluation of Spin Rate on Approach Shots]

[0265] A judgment is made based on a spin rate when a sand wedge is mounted on the golf swing robot and a ball is struck at an HS of 15 m / s. Similarly, a spin rate immediately after the ball is struck is measured by a device for measuring initial conditions. The sand wedge used is a TOURSTAGE TW-03 (loft angle 57°) 2002 model manufactured by Bridgestone Sports Co., Ltd.[Rating Criteria]Good: Spin rate is at least 4,600 rpm

[0267] NG: Spin rate is less than 4,600 rpm[Durability to Repeated Impact]

[0268] A durability of the golf ball is evaluated using an ADC Ball COR Durability Tester produced by Automated Design Corporation (U.S.). This tester has a function of causing a golf ball to be fired pneumatically and then to continuously collide with two metal plates installed in parallel. An incident velocity on the metal plate is 43 m / s. The number of shots required until the golf ball cracks is measured, and an average value of the measured values of 10 golf balls is calculated. Evaluation is performed according to the following criteria using an index when the average value of the number of shots required for cracking in Example 3 is set to 100.[Rating Criteria]Good: Index of at least 100

[0270] Fair: Index of at least 80 and less than 100

[0271] NG: Index of less than 80TABLE 6ExampleComparative Example123123FlightW#1Spin rate (rpm)2,6462,5532,5792,6882,5942,620HS 50 m / sTotal (m)275.6275.4272.3274.1273.9270.8RatingGoodGoodGoodGoodGoodFairW#1Spin rate (rpm)2,7932,7842,7032,8452,8362,754HS 45 m / sTotal (m)235.6234.7234.7234.4233.5233.5RatingGoodGoodGoodGoodFairFairW#1Spin rate (rpm)3,2613,1743,0993,3223,2343,157HS 40 m / sTotal (m)199.9200.7201.3198.7199.5200.1RatingGoodGoodGoodFaiGoodGoodI#6Spin rate (rpm)5,2585,1895,0215,3545,2845,113HS 42 m / sTotal (m)182.5184.0186.1181.7183.2185.3RatingGoodGoodGoodFairGoodGoodI#6Spin rate (rpm)4,9924,8124,6265,0834,9004,711HS 35 m / sTotal (m)162.6163.5165.2161.8162.7164.4RatingGoodGoodGoodFairGoodGoodApproachSWSpin rate (rpm)4,7504,7234,6154,7814,7544,645shotsHS 15 m / sRatingGoodGoodGoodGoodGoodGoodDurabilityIndex103105100878984to repeatedRatingGoodGoodGoodFairFairFairimpactRatingFlightW#1 HS 50m / s222221(score)W#1 HS 45m / s222211W#1 HS 40m / s222122I#6 HS 42m / s222122I#6 HS 35m / s222122Spin performance on approach shots222222Durability to Repeated Impact222111Total141414101211Comparative Example456789FlightW#1Spin rate (rpm)2,8302,5472,5232,4352,6912,624HS 50 m / sTotal (m)274.9273.5273.4273.0274.1273.8RatingGoodGoodGoodGoodGoodGoodW#1Spin rate (rpm)2,9462,6252,5412,5332,8682,778HS 45 m / sTotal (m)234.1234.6234.7234.7234.1234.3RatingGoodGoodGoodGoodGoodGoodW#1Spin rate (rpm)3,4403,0652,9132,8363,3113,149HS 40 m / sTotal (m)196.3202.1204.2205.3198.7200.9RatingNGGoodGoodGoodFairGoodI#6Spin rate (rpm)5,5965,1335,0654,9755,2985,061HS 42 m / sTotal (m)179.1184.5185.3186.5182.4185.4RatingNGGoodGoodGoodGoodGoodI#6Spin rate (rpm)5,3134,8734,7234,6975,0324,666HS 35 m / sTotal (m)159.5163.4164.6164.8162.1165.0RatingNGGoodGoodGoodFairGoodApproachSWSpin rate (rpm)4,8114,6104,7724,7274,7514,616shotsHS 15 m / sRatingGoodGoodGoodGoodGoodGoodDurabilityIndex1052732288365to repeatedRatingGoodNGNGNGFairNGimpactRatingFlightW#1 HS 50 m / s222222(score)W#1 HS 45 m / s222222W#1 HS 40 m / s022212I#6 HS 42 m / s022222I#6 HS 35 m / s022212Spin performance on approach shots222222Durability to Repeated Impact200010Total81212121112*The score is counted with “Good” as 2 points, “Fair” as 1 point, and “NG” as 0 points.*The score is counted with “Good” as 2 points, “Fair” as 1 point, and “NG” as 0 points.

[0272] As shown in the results in Table 6, the golf balls of Comparative Examples 1 to 9 are inferior in the following respects to the golf balls according to the present invention (Examples).

[0273] In Comparative Example 1, in the hardness profile of the core, (H87.5−H75) is larger than (H75−H62.5), and (H100−H87.5) is larger than (H87.5−H75). For this reason, shots with a driver (W #1), at a head speed of HS 40 m / s, and with an iron (I #6) have inferior distance and inferior durability to repeated impact.

[0274] In Comparative Example 2, (H87.5−H75) is larger than (H75−H62.5) in the hardness profile of the core. For this reason, shots with a driver (W #1) and at a head speed of HS 45 m / s have inferior distance to the Examples, and inferior durability to repeated impact.

[0275] In Comparative Example 3, (H87.5−H75) is larger than (H75−H62.5) in the hardness profile of the core. For this reason, shots with driver (W #1), at a head speed of HS 50 m / s, and at a head speed of HS 45 m / s have inferior distance to the Examples, and inferior durability to repeated impact.

[0276] In Comparative Example 4, (H100−H87.5) is larger than (H87.5−H75) in the hardness profile of the core. For this reason, shots with a driver (W #1), at a head speed of HS 40 m / s, and with an iron (I #6) have inferior distance.

[0277] In Comparative Example 5, in the hardness profile of the core, (H87.5−H75) is larger than (H75−H62.5), and (H100−H87.5) is larger than (H87.5−H75). For this reason, durability to repeated impact is inferior.

[0278] In Comparative Example 6, in the hardness profile of the core, (H87.5−H75) is larger than (H75−H62.5), and (H100−H87.5) is larger than (H87.5−H75). For this reason, durability to repeated impact is inferior.

[0279] In Comparative Example 7, in the hardness profile of the core, (H87.5−H75) is larger than (H75−H62.5), and (H100−H87.5) is larger than (H87.5−H75). For this reason, durability to repeated impact is inferior.

[0280] Comparative Example 8 has a three-piece structure without a surrounding layer, and (H87.5−H75) is larger than (H75−H62.5) in the hardness profile of the core. For this reason, shots with a driver (W #1), at a head speed of HS 40 m / s, and with an iron (I #6) have inferior distance and inferior durability to repeated impact.

[0281] Comparative Example 9 is a three-piece structure without a surrounding layer. For this reason, durability to repeated impact is inferior.

[0282] Japanese Patent Application No. 2025-040408 is incorporated herein by reference. Although some preferred embodiments have been described, many modifications and variations may be made thereto in light of the above teachings. It is therefore to be understood that the invention may be practiced otherwise than as specifically described without departing from the scope of the appended claims.

Claims

1. A multi-piece solid golf ball comprising a core, a surrounding layer, an intermediate layer, and a cover, wherein the core is formed of a rubber composition, the surrounding layer, the intermediate layer, and the cover are all formed of a resin composition, and in a hardness profile of the core, letting a Shore C hardness at a core surface be H100, a Shore C hardness at a position outside by 87.5% of a core radius from a core center be H87.5, a Shore C hardness at a position outside by 75% of the core radius from the core center be H75, a Shore C hardness at a position outside by 62.5% of the core radius from the core center be H62.5, a Shore C hardness at a position outside by 50% of the core radius from the core center be H50, a Shore C hardness at a position outside by 37.5% of the core radius from the core center be H37.5, a Shore C hardness at a position outside by 25% of the core radius from the core center be H25, a Shore C hardness at a position outside by 12.5% of the core radius from the core center be H12.5, and a Shore C hardness at the core center be H0, the following two conditions are satisfied:0≤(H⁢62.5-H⁢50)<(H⁢100-H 87.5)<(H⁢87.5-H⁢75)<(H⁢75-H 62.5)≤7.,and(H 87.5-H⁢50) / (H⁢50-H 12.5)≥3..

2. The multi-piece solid golf ball of claim 1, wherein the following condition is satisfied:(H100−H87.5) / (H87.5−H75)≤0.9.

3. The multi-piece solid golf ball of claim 1, wherein all of the following six conditions are satisfied:0.5≤(H⁢87.5-H⁢75) / (H⁢75-H 62.5)<1.1.≤(H⁢100-H 87.5)≤6.2.≤(H 87.5-H⁢75)≤6.54.≤(H⁢75-H 62.5)≤7.0≤(H⁢62.5-H⁢50)≤3.0≤(H⁢50-H⁢25)≤3..

4. The multi-piece solid golf ball of claim 1, wherein a relationship between thicknesses of the surrounding layer and the intermediate layer and a diameter of the ball satisfies the following condition:0.040≤(intermediate layer thickness+surrounding layer thickness) / (ball diameter)≤0.072.

5. The multi-piece solid golf ball of claim 1, wherein the core includes the following components (a) to (e):(a) a base rubber,(b) an α,β-unsaturated carboxylic acid and / or a metal salt thereof as a co-crosslinking agent,(c) an organic peroxide,(d) water or a moisture-providing agent, and(e) a hindered phenol antioxidant having a substituent having a thioether structure,the core is formed of a rubber composition wherein the moisture-providing agent is a substance that contains a water component other than free water in its structure and desorbs moisture by heating, or a substance that releases a water component by thermal decomposition by heating, and a compounding amount of the component (e) is at least 0.2 parts by weight per 100 parts by weight of the component (a).

6. The multi-piece solid golf ball of claim 5, wherein the hindered phenol antioxidant as the component (e) has a chemical structure having at least one methyl group at an ortho position.

7. The multi-piece solid golf ball of claim 5, wherein in the hindered phenol antioxidant as the component (e), a number of substituents having a thioether structure is at least two.

8. The multi-piece solid golf ball of claim 1, wherein letting a deflection when the core is compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) be A (mm), and a deflection when the golf ball is compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) be B (mm), the following condition is satisfied:0.9≤A-B≤1.4.

9. The multi-piece solid golf ball of claim 1, wherein a relationship between surface hardnesses of each of the core, the surrounding layer, the intermediate layer, and the ball satisfies the following condition:surface hardness of core≤surface hardness of surrounding layer-encased sphere<surface hardness of intermediate layer-encased sphere>surface hardness of ball.

10. The multi-piece solid golf ball of claim 1, wherein the cover is formed by injection molding a single resin blend containing a thermoplastic polyurethane (I) and a polyisocyanate compound (II) as principal components, and the resin blend contains, in at least a part thereof, a polyisocyanate compound in which all isocyanate groups in one molecule remain in an unreacted state.

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