Multi-piece solid golf ball

Abstract

A multi-piece solid golf ball includes a core, a surrounding layer, an intermediate layer, and a cover, in which a large number of dimples are formed on an outside surface of the cover, a relationship of surface hardnesses of each sphere is specified, an initial velocity of the ball is set to 75.0 to 77.724 m / s, and a relationship of a ratio to a lift coefficient / drag coefficient at a Reynolds number of 218,000 and a spin rate of 2,800 rpm, a lift coefficient / drag coefficient at a Reynolds number of 184,000 and a spin rate of 2,900 rpm, and a lift coefficient / drag coefficient at a Reynolds number of 158,000 and a spin rate of 3,100 rpm is specified.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This non-provisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2024-047427 filed in Japan on Mar. 25, 2024, the entire contents of which are hereby incorporated by reference.TECHNICAL FIELD

[0002] The present invention relates to a multi-piece solid golf ball that has a good flight and rises easily on approach shots by amateur users, and seeks to make the game of golf easy, while seeking to comply with new Overall Distance Standard (ODS) rules applicable from January 2028.BACKGROUND ART

[0003] In March 2022, manufacturers of golf balls were notified by the Royal and Ancient Golf Club of St Andrews (hereinafter, R&A) and the United States Golf Association (hereinafter, USGA) that they would start research to suppress a distance by the longest hitters by changing test conditions for the Overall Distance Standard (hereinafter, ODS) of golf balls in the future. Further, the R&A and the USGA specifically announced the following in December 2023.

[0004] “Club head speeds in ODS for rule compliance will be increased from the current 54 m / s to 56 m / s. That is, an influence of 13 to 15 yards (11.9 to 13.7 m) is predicted under striking conditions of the longest hitters.”

[0005] This test change is to be implemented from January 2028, but it is said that the current test conditions may be used until Jan. 1, 2030 for recreational golf, which is non-competitive.

[0006] Therefore, under the striking conditions of the longest hitters having a high head speed, a time is approaching when the ball as described above with a suppressed distance compared to the current ball is required. On the other hand, as a golf ball for amateur users, it is desired that even a ball in which the above-described distance is suppressed has as long a distance as possible under striking conditions at a head speed of amateur users. In addition, since it is difficult for the ball to rise on approach shots by an amateur user who is non-competitive, making it easy for the ball to rise on approach shots, that is, raising a launch angle, makes it easy for the ball to be regarded as “a ball that makes approach shots easy”. Moreover, while striking the ball softly, amateur users prefer a feel at impact with a sense of bounce and a sense that the ball will fly. It is desirable to develop a ball that satisfies all these characteristics simultaneously for amateur users.

[0007] In addition, in the past, some golf balls in which an initial velocity of the ball is set lower than that of a normal game ball have been proposed. Examples of such technical documents include the following Patent Documents 1 to 5.

[0008] However, each of the proposed golf balls is a practice ball for a driving range that is simply designed so as not to have a longer distance than the game ball. Therefore, in each of the above-mentioned Patent Documents, good distance performance on shots by amateur users, and the ball rising easily and the feel at impact on approach shots are not considered at all.

[0009] Further, Patent Documents 6 to 14 listed below each disclose a golf ball in which, as for dimples formed on the ball surface, 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, that is, a dimple volume occupancy ratio VR, is specified within a predetermined range, whereby a superior distance may be obtained in the low head speed (HS) range while reducing the distance in the high HS range.

[0010] However, with respect to the proposed golf balls, the reducing of the distance in the high head speed range is too great, and a distance on full shots by amateur users may not be satisfactory. Further, in each of the above Patent Documents, the ball rising easily and the feel at impact on approach shots are not considered at all.CITATION LISTPatent Document 1: JP-A 2012-228470

[0012] Patent Document 2: JP-A 2014-069045

[0013] Patent Document 3: JP-A 2013-138857

[0014] Patent Document 4: JP-A 2013-138839

[0015] Patent Document 5: JP-A 2013-138840

[0016] Patent Document 6: JP-A 2011-218160

[0017] Patent Document 7: JP-A 2011-218161

[0018] Patent Document 8: JP-A 2011-218162

[0019] Patent Document 9: JP-A 2011-240122

[0020] Patent Document 10: JP-A 2011-240123

[0021] Patent Document 11: JP-A 2011-240124

[0022] Patent Document 12: JP-A 2011-240125

[0023] Patent Document 13: JP-A 2011-240126

[0024] Patent Document 14: JP-A 2011-240127SUMMARY OF THE INVENTION

[0025] 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 for complying with new ODS rules applicable from January 2028, in which not only suppression of a distance on shots by the longest hitters is caused to at least a specific level, but also a distance on full shots with a driver (W #1) and an iron by amateur users may be favorably maintained without decreasing, and moreover, a launch angle on approach shots by amateur users becomes high, the ball rises easily, and there is a sense of bounce and a sense that the ball will fly in the feel at impact.

[0026] As a result of intensive studies to achieve the above object, the present inventor has found that in a multi-piece solid golf ball including a core, a surrounding layer, an intermediate layer, and a cover, in which a large number of dimples are formed on an outside surface of the cover, the core is formed of a rubber material, the surrounding layer, the intermediate layer, and the cover are formed of a resin material, a relationship between a surface hardness of each sphere of the ball, a surrounding layer-encased sphere, and an intermediate layer-encased sphere satisfies the following conditions (1-a) and (1-b):(surface hardness of ball)>(surface hardness of surrounding layer-encased sphere)   (1-a)(surface hardness of ball)>(surface hardness of intermediate layer-encased sphere)   (1-b)and a relationship between the surface hardness of each sphere of the core, the surrounding layer-encased sphere, and the intermediate layer-encased sphere satisfies at least one of the following conditions (2-a) or (2-b):(surface hardness of surrounding layer-encased sphere)<(surface hardness of core)   (2-a)(surface hardness of intermediate layer-encased sphere)<(surface hardness of core)   (2-b).Further, when an initial velocity of the ball is set to a range of from 75.0 to 77.724 m / s, a ratio CL1 / CD1 of a lift coefficient CL1 at a Reynolds number of 218,000 and a spin rate of 2,800 rpm to a drag coefficient CD1 is denoted by A1, a ratio CL2 / CD2 of a lift coefficient CL2 at a Reynolds number of 184,000 and a spin rate of 2,900 rpm to a drag coefficient CD2 is denoted by A2, and a ratio CL3 / CD3 of a lift coefficient CL3 at a Reynolds number of 158,000 and a spin rate of 3,100 rpm to a drag coefficient CD3 is denoted by A3, the following two conditions are satisfied:0.59≤A⁢1≤0.655 and(A⁢2+A⁢3) / 2≥0.67and when a volume occupancy ratio VR of the dimples is from 0.75 to 0.89%, a total volume of the dimples is denoted by D (mm3), and a deflection when the ball is compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) is denoted by B (mm), the following condition is satisfied:95≤D / B≤140.The present inventor has found that by designing the multi-piece solid golf ball so as to satisfy the conditions described above, new ODS rules may be complied with, that is, a suppression of a distance on shots by the longest hitters is caused to at least a specific level, a distance on full shots with a driver (W #1) and an iron by amateur users does not decrease, and conversely, the distance on full shots with a driver (W #1) and an iron by amateur users increases. In addition, the present inventor has found that in the above-described designed multi-piece solid golf ball, a launch angle of the ball is increased on approach shots by amateur users, the ball rises easily, the ball becomes a ball that is “easy on approach shots”, and further, on full shots by amateur users, the ball has a feel at impact that has softness, a sense of bounce, and a sense that the ball will fly, and has completed the present invention.The above “longest hitters” refers to golfers whose head speed on shots with a driver (W #1) is at least 50 m / s, and the above “non-competitive amateur golfers” refers to golfers who have a head speed with a driver (W #1) of not more than 45 m / s and a handicap of approximately 30 or more.Accordingly, the present invention provides a multi-piece solid golf ball includinga core, a single-layer or multiple-layer surrounding layer, a single-layer intermediate layer, and a single-layer cover, wherein a large number of dimples are formed on an outside surface of the cover, the core is formed of a rubber material, the surrounding layer, the intermediate layer, and the cover are formed of a resin material, a relationship between a surface hardness of each sphere of the ball, a surrounding layer-encased sphere, and an intermediate layer-encased sphere satisfies the following conditions (1-a) and (1-b):(surface hardness of ball)>(surface hardness of surrounding layer-encased sphere)   (1-a)(surface hardness of ball)>(surface hardness of intermediate layer-encased sphere)   (1-b)where hardness means Shore C hardness,and a relationship between the surface hardness of each sphere of the core, the surrounding layer-encased sphere, and the intermediate layer-encased sphere satisfies at least one of the following conditions (2-a) or (2-b):(surface hardness of surrounding layer-encased sphere)<(surface hardness of core)   (2-a)(surface hardness of intermediate layer-encased sphere)<(surface hardness of core)   (2-b)where hardness means Shore C hardness.Further, when an initial velocity of the ball is from 75.0 to 77.724 m / s, a ratio CL1 / CD1 of a lift coefficient CL1 at a Reynolds number of 218,000 and a spin rate of 2,800 rpm to a drag coefficient CD1 is denoted by A1, a ratio CL2 / CD2 of a lift coefficient CL2 at a Reynolds number of 184,000 and a spin rate of 2,900 rpm to a drag coefficient CD2 is denoted by A2, and a ratio CL3 / CD3 of a lift coefficient CL3 at a Reynolds number of 158,000 and a spin rate of 3,100 rpm to a drag coefficient CD3 is denoted by A3, the following two conditions are satisfied:0.59≤A⁢1≤0.655 and(A⁢2+A⁢3) / 2≥0.67.A further characteristic of the multi-piece solid golf ball is that when a volume occupancy ratio VR of the dimples is from 0.75 to 0.89%, a total volume of the dimples is denoted by D (mm3), and a deflection when the ball is compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) is denoted by B (mm), the following condition is satisfied:95≤D / B≤140.In a preferred embodiment of the multi-piece solid golf ball according to the invention, a value of A1 is from 0.590 to 0.613, a value of A2 is from 0.635 to 0.668, and a value of A3 is from 0.695 to 0.734.In another preferred embodiment of the inventive golf ball, a value of A1 is from 0.614 to 0.655, a value of A2 is from 0.669 to 0.750, and a value of A3 is from 0.735 to 0.815.In yet another preferred embodiment, a value of (A2+A3) / 2 is from 0.670 to 0.783.

[0042] In still another preferred embodiment, the cover is formed of an ionomer resin as a chief material.

[0043] In a further preferred embodiment, the relationship between the surface hardness of each sphere satisfies the following condition:(surface hardness of ball)>(surface hardness of intermediate layer-encased sphere)>(surface hardness of surrounding layer-encased sphere)<(surface hardness of core)where hardness means Shore C hardness.

[0045] In a yet further preferred embodiment, the core has a hardness profile in which, letting the Shore C hardness at a core center be Cc, the Shore C hardness at a midpoint M between the core center and a core surface be Cm, the Shore C hardnesses at positions 2 mm, 4 mm, and 6 mm inward from the midpoint M be Cm-2, Cm-4, and Cm-6 respectively, the Shore C hardnesses at positions 2 mm, 4 mm, and 6 mm outward from the midpoint M be Cm+2, Cm+4, and Cm+6 respectively, and the Shore C hardness at the core surface be Cs, and defining surface areas A to F as follows:surface⁢ area⁢ A:1 / 2×2×(Cm-4-Cm-6)surface⁢ area⁢ B:1 / 2×2×(Cm-2-Cm-4)surface⁢ area⁢ C:1 / 2×2×(Cm-Cm-2)surface⁢ area⁢ D:1 / 2×2×(Cm+2-Cm)surface⁢ area⁢ E:1 / 2×2×(Cm+4-Cm+2)surface⁢ area⁢ F:1 / 2×2×(Cm+6-Cm+4)the following condition is satisfied:{(surface⁢ area⁢ D+surface⁢ area⁢ E)-(surface⁢ area⁢ A+surface⁢ area⁢ B)}≥4..In a still further preferred embodiment, the core has a hardness profile in which the following condition is satisfied:(Cs-Cc)≥20.In another preferred embodiment, the core has a hardness profile in which the following condition is satisfied:(Cs-Cc) / (Cm-Cc)≥4..In yet another preferred embodiment, the core has a hardness profile in which the following condition is satisfied:surface area E >surface area D>surface area C.In still another preferred embodiment, the core is formed of a rubber composition containing the following components (A) to (D):(A) a base rubber,

[0052] (B) an organic peroxide,

[0053] (C) water or a monocarboxylic acid metal salt, and

[0054] (D) sulfur

[0055] Advantageous Effects of the Invention

[0056] The multi-piece solid golf ball according to the present invention is a golf ball which is intended to comply with new ODS rules applicable from January 2028, and may increase the distance on full shots with a driver (W #1) and an iron by amateur users while reducing the distance on shots with a driver by the longest hitters. In addition, with the golf ball of the present invention, the launch angle of the ball becomes high on approach shots by amateur users, the ball rises easily, and easiness can be felt on approach shots. Furthermore, the golf ball of the present invention has a feel at impact that combines softness and a sense that the ball will fly on full shots by amateur users.BRIEF DESCRIPTION OF THE DRAWINGS

[0057] FIG. 1 is a schematic cross-sectional view of a multi-piece solid golf ball (four-layer structure) of the present invention.

[0058] FIG. 2 is a graph that uses core hardness profile data in Example 1 to describe surface areas A to F in the core hardness profile.

[0059] FIG. 3 is a graph showing core hardness profiles in Examples 1 to 4 and Comparative Examples 1 to 5.

[0060] FIG. 4 is a graph showing core hardness profiles in Comparative Examples 6 to 15.

[0061] FIGS. 5A and 5B show an arrangement mode (pattern) of dimples (1) to (5) used in Examples 1 to 4 and Comparative Examples 1 to 15, where FIG. 5A shows a plan view of the dimples, and FIG. 5B shows a side view thereof.DETAILED DESCRIPTION OF THE INVENTION

[0062] Hereinafter, the present invention is described in more detail.

[0063] A multi-piece solid 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. A golf ball G illustrated in FIG. 1 has a single-layer core 1, a single-layer surrounding layer 2 encasing the core, a single-layer intermediate layer 3 encasing the surrounding layer, and a single-layer cover 4 encasing the intermediate layer. The cover 4 is positioned at the outermost layer in the layer construction of the golf ball except for the coating layer. Each layer of the core and the surrounding layer may be formed as a single layer as illustrated in FIG. 1 or a plurality of layers. A large number of dimples D are formed on a surface of the cover (outermost layer) 4 in order to obtain aerodynamic properties as intended properties of the present invention. In addition, although not particularly illustrated, the coating layer is typically formed on the surface of the cover 4. Hereinafter, each of the above layers is described in detail.

[0064] The core is obtained by vulcanizing a rubber composition containing a rubber material as a chief material. If the core material is not a rubber composition, a rebound of the core may become low, and a desired distance may not be attainable not only on shots by the longest hitters, but also on shots with a driver (W #1) and an iron by amateur users. The rubber composition typically contains a base rubber as the chief material, and is obtained with the inclusion of a co-crosslinking agent, a co-crosslinking initiator, an inert filler, an organosulfur compound, or the like.

[0065] In particular, the core is suitably formed of a rubber composition containing the following components (A) to (D):

[0066] (A) a base rubber,

[0067] (B) an organic peroxide,

[0068] (C) water or a monocarboxylic acid metal salt, and

[0069] (D) sulfur.

[0070] The base rubber (A) may include a diene rubber. Examples of the diene rubber include polybutadiene, natural rubber, isoprene rubber, and ethylene propylene diene rubber.

[0071] As the organic peroxide (B), an organic peroxide having a relatively high thermal decomposition temperature is suitably used. Specifically, a high-temperature organic peroxide having a one-minute half-life temperature of about 165 to 185° C. is used, and examples thereof include dialkyl peroxides. Examples of the dialkyl peroxides include a dicumyl peroxide (“Percumyl D” manufactured by NOF Corporation), a 2,5-dimethyl-2,5-di(t-butylperoxy) hexane (“Perhexa 25B” manufactured by NOF Corporation), and a di(2-t-butylperoxyisopropyl) benzene (“Perbutyl P” manufactured by NOF Corporation), and a dicumyl peroxide may be suitably used. These may be used singly, or two or more may be used in combination. The half-life is one of the indices representing a degree of a decomposition rate of the organic peroxide, and is indicated by a time required for the original organic peroxide to be decomposed and its active oxygen amount to reach 1 / 2. A vulcanization temperature in the core-forming rubber composition is typically within a range of 120 to 190° C., and in that range, an organic peroxide having a one-minute half-life temperature of a high temperature, which is about 165° C. to 185° C., is thermally decomposed relatively slowly. With the rubber composition used in the present invention, by adjusting an amount of free radicals produced, which increases with the lapse of a vulcanization time, it is possible to obtain a core that is a rubber cross-linked product having a specific internal hardness shape described later.

[0072] The water (C), although not particularly limited, may be distilled water or tap water, but it is particularly suitable to employ distilled water free of impurities. The compounding amount of the water included per 100 parts by weight of the base rubber is preferably at least 0.1 part by weight, and more preferably at least 0.2 part by weight, and an upper limit thereof is preferably not more than 2 parts by weight, and more preferably not more than 1 part by weight.

[0073] By blending the water or a material containing water as the component (C) directly into the core material, a decomposition of the organic peroxide during the core formulation may be promoted. In addition, it is known that the decomposition efficiency of the organic peroxide in the core-forming rubber composition changes depending on temperature, and the decomposition efficiency increases as the temperature becomes higher than a certain temperature. If the temperature is too high, the amount of decomposed radicals becomes too large, and the radicals are recombined or deactivated. As a result, fewer radicals act effectively in crosslinking. Here, when decomposition heat is generated by the decomposition of the organic peroxide at the time of core vulcanization, a temperature near the core surface is maintained at substantially the same level as a temperature of a vulcanization mold, but the temperature around the core center is considerably higher than the mold temperature due to an accumulation of decomposition heat by the organic peroxide decomposing from the outside. If the water or a material containing water is directly included in the core, the water acts to promote the decomposition of the organic peroxide, so that the radical reactions as described above can be changed at the core center and the core surface. That is, the decomposition of the organic peroxide is further promoted near the core center, and the deactivation of radicals is further promoted, so that the amount of active radicals is further reduced, and as a result, a core may be obtained in which the crosslink densities at the core center and the core surface differ markedly, and the dynamic viscoelasticity of the core center portion is different.

[0074] In addition, a monocarboxylic acid metal salt may be employed instead of the water. In the monocarboxylic acid metal salt, it is presumed that a carboxylic acid is coordinate-bonded to the metal salt, and the monocarboxylic acid metal salt is distinguished from a dicarboxylic acid metal salt such as zinc diacrylate, which is represented by a chemical formula [CH2=CHCOO]2Zn The monocarboxylic acid metal salt brings water into the rubber composition by a dehydration condensation reaction, so that the same effect as that of the water may be obtained. In addition, since the monocarboxylic acid metal salt may be blended into the rubber composition as a powder, a working process may be simplified, and it is easy to uniformly disperse the monocarboxylic acid metal salt in the rubber composition. In order to effectively perform the above reaction, it is necessary to use a mono-salt. A compounding amount of the monocarboxylic acid metal salt is preferably at least 1 part by weight, and more preferably at least 3 parts by weight per 100 parts by weight of the base rubber. As an upper limit thereof, the compounding amount of the monocarboxylic acid metal salt is preferably not more than 60 parts by weight, and more preferably not more than 50 parts by weight per 100 parts by weight of the base rubber. If the compounding amount of the monocarboxylic acid metal salt is too small, it is difficult to obtain an appropriate crosslinking density, and it may not be possible to obtain an adequate golf ball spin rate-lowering effect. In addition, if the compounding amount is too large, the core becomes too hard, so that it may be difficult to maintain an appropriate feel at impact.

[0075] As the carboxylic acid, an acrylic acid, a methacrylic acid, a maleic acid, a fumaric acid, a stearic acid, or the like may be used. Examples of a substitute metal include Na, K, Li, Zn, Cu, Mg, Ca, Co, Ni, and Pb, and Zn is preferably used. Specific examples thereof include a zinc monoacrylate and a zinc monomethacrylate, and it is particularly preferable to use a zinc monoacrylate.

[0076] Specific examples of the sulfur (D) include trade names “SANMIX S-80N” (manufactured by Sanshin Chemical Industry Co., Ltd.) and “SULFAX-5” (manufactured by Tsurumi Chemical Industry Co., Ltd.). A compounding amount of the sulfur may exceed 0, and may be preferably at least 0.005 parts by weight, and even more preferably at least 0.01 parts by weight per 100 parts by weight of the base rubber. In addition, an upper limit of the compounding amount is not particularly limited, although the upper limit may be preferably not more than 0.1 parts by weight, more preferably not more than 0.05 parts by weight, and even more preferably not more than 0.03 parts by weight. The addition of the sulfur may increase a difference in hardness of the core. If the compounding amount of the sulfur is too large, rebound may be greatly reduced, or a durability on repeated impact may worsen.

[0077] In the rubber composition, a co-crosslinking agent, a filler, an antioxidant, an organosulfur compound, and the like may be included as components other than the components (A) to (D).

[0078] The co-crosslinking agent is an α,β-unsaturated carboxylic acid and / or a metal salt thereof. Specific examples of the unsaturated carboxylic acid include acrylic acid, methacrylic acid, maleic acid, fumaric acid, or the like, and in particular, acrylic acid and methacrylic acid are suitably used. The metal salt of the unsaturated carboxylic acid is not particularly limited, and examples thereof include those obtained by neutralizing the unsaturated carboxylic acid with a desired metal ion. Specific examples thereof include zinc salts and magnesium salts such as methacrylic acid and acrylic acid, and in particular, zinc acrylate is suitably used.

[0079] The unsaturated carboxylic acid and / or the metal salt thereof is typically included in an amount of at least 5 parts by weight, preferably at least 9 parts by weight, and even more preferably at least 13 parts by weight, and an upper limit thereof is typically not more than 60 parts by weight, preferably not more than 50 parts by weight, and even 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, the core may become too hard, giving the ball an unpleasant feel at impact, and if the compounding amount is too small, rebound may become low.

[0080] 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 4 parts by weight, more preferably at least 8 parts by weight, and even more preferably at least 11 parts by weight per 100 parts by weight of the base rubber. In addition, an upper limit of the compounding amount is preferably not more than 50 parts by weight, more preferably not more than 40 parts by weight, and even more preferably not more than 35 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.

[0081] As an antioxidant, for example, commercially available products such as Nocrac NS-6, Nocrac NS-30, Nocrac NS-200, and Nocrac MB (all manufactured by Ouchi Shinko Chemical Industrial Co., Ltd.) may be employed. These may be used singly, or two or more may be used in combination.

[0082] The compounding amount of the antioxidant is not particularly limited, but is preferably 0.05 parts by weight or more, and more preferably 0.1 parts by weight or more, and the upper limit is preferably 1.0 part by weight or less, more preferably 0.7 parts by weight or less, and even more preferably 0.5 parts by weight or less per 100 parts by weight of the base rubber. If the compounding amount is too large or too small, a suitable core hardness gradient cannot be obtained, and it may not be possible to obtain suitable rebound, durability, and a spin rate-lowering effect on full shots.

[0083] The organosulfur compound may be included in order to control the rebound of the core so that it is increased. As the organosulfur compound, specifically, it is recommended to include thiophenol, thionaphthol, halogenated thiophenol, or a metal salt thereof. More specifically, examples of the organosulfur compound include zinc salts such as pentachlorothiophenol, pentafluorothiophenol, pentabromothiophenol, p-chlorothiophenol, and pentachlorothiophenol, and any of the following having 2 to 4 sulfur atoms: diphenylpolysulfide, dibenzylpolysulfide, dibenzoylpolysulfide, dibenzothiazoylpolysulfide, and dithiobenzoylpolysulfide. In particular, diphenyldisulfide and the zinc salt of pentachlorothiophenol is preferably used.

[0084] An upper limit of a compounding amount of the organosulfur compound is preferably not more than 5 parts by weight, more preferably not more than 4 parts by weight, even more preferably not more than 3 parts by weight, and most preferably not more than 2 parts by weight per 100 parts by weight of the base rubber. If the compounding amount is too large, the core hardness becomes too soft or the rebound of the core becomes too high, and the distance on shots with a driver by the longest hitters may be too long.

[0085] The core can be manufactured by vulcanizing and curing the rubber composition containing the above components. For example, a molded body can be manufactured by intensively mixing the rubber composition using a mixing apparatus such as a Banbury mixer or a roll mill, subsequently compression molding or injection molding the mixture using a core mold, and curing the resulting molded body by appropriately heating it at a temperature sufficient for the organic peroxide or the co-crosslinking agent to act, such as at a temperature of 100 to 200° C., and preferably at a temperature of 140 to 180° C., for 10 to 40 minutes.

[0086] In the present invention, the core is formed as a single layer or a plurality of layers, although it is preferably formed as a single layer. If a rubber core is produced as a plurality of layers of rubber, layer separation at an interface may arise when the ball is repeatedly struck, possibly leading to cracking at an earlier stage.

[0087] The diameter of the core is preferably at least 32.7 mm, more preferably at least 34.3 mm, and even more preferably at least 34.9 mm. The upper limit of the diameter of the core is preferably not more than 36.5 mm, more preferably not more than 36.1 mm, and even more preferably not more than 35.7 mm. If the diameter of the core is too small, an initial velocity of the ball may become too low, or a deflection of an entire ball may become small, a spin rate of the ball on full shots may increase, and the desired distance may not be attainable on full shots by amateur users. On the other hand, if the diameter of the core is too large, the spin rate on full shots increases, and the desired distance of amateur users may not be attainable, or a durability to cracking on repeated impact may worsen.

[0088] 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 3.6 mm, more preferably at least 4.0 mm, and even more preferably at least 4.3 mm, and the upper limit thereof is preferably not more than 5.5 mm, more preferably not more than 5.2 mm, and even more preferably not more than 4.9 mm. If the deflection of the core is too small, that is, if the core is too hard, the spin rate on full shots increases too much, the distance on shots with a driver (W #1) and an iron by amateur users may not be sufficiently increased, and the feel at impact may be too hard. On the other hand, if the deflection of the core is too large, that is, if the core is too soft, an actual initial velocity becomes too low, so that the distance on shots with a driver (W #1) by the longest hitters and amateur users may be too short, the sense of bounce and the sense that the ball will fly may be lost in the feel at impact, and the durability to cracking on repeated impact may become too poor.

[0089] 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.

[0090] A core center hardness (Cc) is preferably at least 50, more preferably at least 52, and even more preferably at least 54, and the upper limit is preferably not more than 62, more preferably not more than 59, and even more preferably not more than 56. If this value is too large, the spin rate of the ball on full shots may rise, the desired distance may not be attainable on shots with a driver (W #1) and an iron by amateur users, or the feel at impact may be too hard. On the other hand, if the above value is too small, the rebound becomes low, and the desired distance on shots by amateur users may not be attainable, the sense of bounce and the sense that the ball will fly may be lost in the feel at impact, or the durability to cracking on repeated impact may worsen.

[0091] A hardness (Cm-6) at a position 6 mm inward from a point M (hereinafter, also referred to as “midpoint M”) between the core center and the core surface is not particularly limited, although the hardness may be preferably at least 51, more preferably at least 53, and even more preferably at least 55, and the upper limit is also not particularly limited, and may be preferably not more than 63, more preferably not more than 60, and even more preferably not more than 57. Hardnesses that deviate from these values may lead to undesirable results similar to those described above for the core center hardness (Cc).

[0092] A hardness (Cm-4) at a position 4 mm inward from the midpoint M between the core center and the core surface is not particularly limited, although the hardness may be preferably at least 51, more preferably at least 53, and even more preferably at least 55, and the upper limit is also not particularly limited, and may be preferably not more than 63, more preferably not more than 60, and even more preferably not more than 57. Hardnesses that deviate from these values may lead to undesirable results similar to those described above for the core center hardness (Cc).

[0093] A hardness (Cm-2) at a position 2 mm inward from the midpoint M of the core is not particularly limited, although the hardness may be preferably at least 53, more preferably at least 55, and even more preferably at least 57. The upper limit is also not particularly limited, and may be preferably not more than 64, more preferably not more than 61, and even more preferably not more than 59. Hardnesses that deviate from these values may lead to undesirable results similar to those described above for the core center hardness (Cc).

[0094] Although not particularly limited, a cross-sectional hardness (Cm) at the midpoint M of the core may be preferably at least 54, more preferably at least 56, and even more preferably at least 58. In addition, the upper limit is not particularly limited, although the upper limit may be preferably not more than 66, more preferably not more than 63, and even more preferably not more than 60. Hardnesses that deviate from these values may lead to undesirable results similar to those described above for the core center hardness (Cc).

[0095] A core surface hardness (Cs) is preferably at least 70, more preferably at least 72, and even more preferably at least 74. The upper limit is preferably not more than 82, more preferably not more than 79, and even more preferably not more than 77. If this value is too large, the durability to cracking on repeated impact may worsen, or the feel at impact may be too hard. On the other hand, if the above value is too small, the rebound may become low, or the spin rate on full shots may rise, and the desired distance on shots with a driver (W #1) and an iron by amateur users may not be attainable.

[0096] A hardness (Cm+2) at a position 2 mm outward toward the core surface (hereinafter, simply referred to as “outward”) from the midpoint M of the core is not particularly limited, although the hardness may be preferably at least 59, more preferably at least 61, and even more preferably at least 63. The upper limit is also not particularly limited, and may be preferably not more than 70, more preferably not more than 67, and even more preferably not more than 65. Hardnesses that deviate from these values may lead to undesirable results similar to those described above for the core surface hardness (Cs).

[0097] A hardness (Cm+4) at a position 4 mm outward from the midpoint M of the core is not particularly limited, although the hardness may be preferably at least 63, more preferably at least 65, and even more preferably at least 67. The upper limit is also not particularly limited, and may be preferably not more than 74, more preferably not more than 72, and even more preferably not more than 70. Hardnesses that deviate from these values may lead to undesirable results similar to those described above for the core surface hardness (Cs).

[0098] A hardness (Cm+6) at a position 6 mm outward from the midpoint M of the core is not particularly limited, although the hardness may be preferably at least 64, more preferably at least 66, and even more preferably at least 68. The upper limit is also not particularly limited, and may be preferably not more than 75, more preferably not more than 73, and even more preferably not more than 71. Hardnesses that deviate from these values may lead to undesirable results similar to those described above for the core surface hardness (Cs).

[0099] A value obtained by subtracting the core center hardness from the core surface hardness, that is, the value of Cs−Cc, is preferably at least 18, more preferably at least 20, and even more preferably at least 21, and the upper limit thereof is preferably not more than 30, more preferably not more than 27, and even more preferably not more than 24. If this value is too small, the spin rate of the ball on full shots may rise, the desired distance may not be attainable on shots with a driver (W #1) and an iron by amateur users, or the feel at impact may be too hard. On the other hand, if this value is too large, the rebound may become low, the desired distance on shots with a driver (W #1) and an iron by amateur users may not be attainable, or the durability to cracking on repeated impact may worsen.

[0100] In addition, it is preferable to optimize the value of (Cs−Cc) / (Cm−Cc) for the core hardness profile. The value of (Cs−Cc) indicates a difference in hardness between the core center and the core surface, and a value of (Cm−Cc) indicates a difference in hardness between the core center and the midpoint between the core surface and the core center, and the above expression represents the ratio of these differences in hardness. The value of (Cs-Cc) / (Cm−Cc) is preferably at least 3.0, more preferably at least 3.5, and even more preferably at least 4.0, and an upper limit thereof is preferably not more than 30.0, more preferably not more than 20.0, and even more preferably not more than 10.0. If this value is too small, the spin rate of the ball on full shots may rise, and the desired distance may not be attainable on shots with a driver (W #1) and an iron by amateur users. On the other hand, if this value is too large, the rebound becomes low, an intended distance may not be attainable on shots with a driver (W #1) and an iron by amateur users, and the durability to cracking on repeated impact may worsen.

[0101] In the core hardness profile, the surface areas A to F defined as follows:surface⁢ area⁢ A:1 / 2×2×(Cm-4-Cm-6)surface⁢ area⁢ B:1 / 2×2×(Cm-2-Cm-4)surface⁢ area⁢ C:1 / 2×2×(Cm-Cm-2)surface⁢ area⁢ D:1 / 2×2×(Cm+2-Cm)surface⁢ area⁢ E:1 / 2×2×(Cm+4-Cm+2)surface⁢ area⁢ F:1 / 2×2×(Cm+6-Cm+4)are characterized in that a value of (surface area D+surface area E)−(surface area A+surface area B) is preferably at least 4.0, more preferably at least 4.5, and even more preferably at least 5.0, and the upper limit is preferably not more than 15.0, more preferably not more than 10.0, and even more preferably not more than 8.0. If this value is too small, the spin rate of the ball on full shots may rise, and the desired distance may not be attainable on shots with a driver (W #1) and an iron by amateur users. On the other hand, if this value is too large, the rebound may become low, the desired distance on shots with a driver (W #1) and an iron by amateur users may not be attainable, or the durability to cracking on repeated impact may worsen.

[0103] A value of (surface area D+surface area E)−(surface area B+surface area C) is preferably at least 3.5, more preferably at least 4.0, and even more preferably at least 4.5, and the upper limit is preferably not more than 15.0, more preferably not more than 10.0, and even more preferably not more than 7.0. If this value is too small, the spin rate of the ball on full shots may rise, and the desired distance may not be attainable on shots with a driver (W #1) and an iron by amateur users. On the other hand, if this value is too large, the rebound may become low, the desired distance on shots with a driver (W #1) and an iron by amateur users may not be attainable, or the durability to cracking on repeated impact may worsen.

[0104] In addition, a value of {(surface area D+surface area E)−(surface area A +surface area B)}×(Cs−Cc) is preferably at least 80, more preferably at least 90, and even more preferably at least 110, and the upper limit is preferably not more than 200, more preferably not more than 180, and even more preferably not more than 160. In addition, a value of {(surface area D+surface area E)−(surface area B+surface area C)}×(Cs−Cc) is preferably at least 70, more preferably at least 80, and even more preferably at least 95, and the upper limit is preferably not more than 200, more preferably not more than 180, and even more preferably not more than 140. In addition, if these values are too small, the spin rate of the ball on full shots may rise, and the desired distance may not be attainable on shots with a driver (W #1) and an iron by amateur users. On the other hand, if these values are too large, the rebound may become low, and the desired distance may not be attainable on shots with a driver (W #1) and an iron by amateur users, or the durability to cracking on repeated impact may worsen.

[0105] A relationship of each surface area calculated from the hardness profile is preferably surface area E>surface area C >surface area A, more preferably (surface area E+surface area F)>surface area D >surface area C >surface area A, and even more preferably (surface area E+surface area F)>surface area D >(surface area B+surface area C)>area A. If these relational expressions are not satisfied, the spin rate of the ball on full shots may rise, and the desired distance may not be attainable on shots with a driver (W #1) and an iron by amateur users.

[0106] FIG. 2 shows a graph describing the surface areas A to F using the core hardness profile data of Example 1. In this way, the surface areas A to F are surface areas of each triangle whose base is a difference between each specific distance and whose height is a difference in hardness between each position at these specific distances.

[0107] Next, the surrounding layer is described.

[0108] The surrounding layer is formed of a single layer or a plurality of layers. If the surrounding layer has a plurality of layers, a total thickness corresponds to the following thickness for the thickness of the surrounding layer, and an average hardness for a material hardness (sheet hardness) of the surrounding layer is taken as the material hardness.

[0109] Regarding surface hardness if the surrounding layer has a plurality of layers, a surface hardness of a layer-encased sphere of an outermost surrounding layer of the surrounding layer corresponds to the following surface hardnesses.

[0110] The surrounding layer has a material hardness on the Shore C hardness scale which, although not particularly limited, is preferably at least 43, more preferably at least 50, and even more preferably at least 57, and the upper limit is preferably not more than 83, more preferably not more than 76, and even more preferably not more than 70. The surface hardness on the Shore D hardness scale is preferably at least 25, more preferably at least 30, and even more preferably at least 35, and the upper limit is preferably not more than 55, more preferably not more than 50, and even more preferably not more than 45.

[0111] The surface hardness of the surrounding layer-encased sphere in which the core is encased with the surrounding layer is preferably at least 51, more preferably at least 58, and even more preferably at least 65, and the upper limit thereof is preferably not more than 91, more preferably not more than 84, and even more preferably not more than 78 on the Shore C hardness scale. The surface hardness on the Shore D hardness scale is preferably at least 31, more preferably at least 36, and even more preferably at least 41, and the upper limit is preferably not more than 61, more preferably not more than 56, and even more preferably not more than 51.

[0112] If the material hardness and the surface hardness of the surrounding layer are too soft in comparison with the above ranges, the spin rate of the ball on full shots may rise, and the distance on shots with a driver (W #1) and an iron by amateur users may not be increased. In addition, the durability to cracking on repeated impact may worsen. On the other hand, if the material hardness and the surface hardness of the surrounding layer are too hard in comparison with the above ranges, the feel at impact may become too hard for a soft feeling to be felt, and the distance on shots by the longest hitters may be too long.

[0113] The surrounding layer has a thickness that is preferably at least 0.8 mm, more preferably at least 1.0 mm, and even more preferably at least 1.2 mm. On the other hand, the thickness of the surrounding layer has an upper limit that is preferably not more than 1.5 mm, more preferably not more than 1.4 mm, and even more preferably not more than 1.3 mm. If the surrounding layer is too thin, it may not be possible for a soft feeling to be felt on full shots by amateur users, or molding becomes difficult and mass productivity may deteriorate. On the other hand, if the surrounding layer is too thick, the rebound becomes low or the spin rate increases, so that it may be difficult for the distance on full shots by amateur users to increase.

[0114] The material of the surrounding layer is not particularly limited, and a known resin material may be used. Specifically, one or more of ionomer resins, and of thermoplastic elastomers selected from the group consisting of urethane-based, amide-based, ester-based, olefin-based, and styrene-based elastomers may be used. In the present invention, since high rebound is obtained in a desired hardness range, an ester-based thermoplastic elastomer, particularly a thermoplastic polyether ester elastomer, may be suitably used.

[0115] Next, the intermediate layer is described.

[0116] The intermediate layer has a material hardness on the Shore C hardness scale which, although not particularly limited, is preferably at least 71, more preferably at least 78, and even more preferably at least 84, and the upper limit is preferably not more than 95, more preferably not more than 92, and even more preferably not more than 90. The material hardness on the Shore D hardness scale is preferably at least 46, more preferably at least 50, and even more preferably at least 53, and the upper limit is preferably not more than 61, more preferably not more than 60, and even more preferably not more than 59.

[0117] The intermediate layer-encased sphere obtained by encasing the core with the surrounding layer and the intermediate layer has a surface hardness on the Shore C hardness scale which is preferably at least 80, more preferably at least 85, and even more preferably at least 90. The upper limit is preferably not more than 96, more preferably not more than 95, and even more preferably not more than 94. The surface hardness on the Shore D hardness scale is preferably at least 52, more preferably at least 56, and even more preferably at least 59, and the upper limit is preferably not more than 67, more preferably not more than 65, and even more preferably not more than 63.

[0118] If the material hardness and the surface hardness of the intermediate layer are too soft in comparison with the above ranges, the spin rate of the ball on full shots may rise, and the distance on shots with a driver (W #1) and an iron by amateur users may not be increased. In addition, the launch angle on approach shots may become low, and the ball may be felt to be difficult to handle for amateur users. On the other hand, if the material hardness and the surface hardness of the intermediate layer are too hard in comparison with the above ranges, the feel at impact may be too hard, the durability to cracking on repeated impact may worsen, or the distance on shots by the longest hitters may be too long.

[0119] The intermediate layer has a thickness that is preferably at least 0.8 mm, more preferably at least 1.0 mm, and even more preferably at least 1.2 mm. On the other hand, the intermediate layer thickness has an upper limit that is preferably not more than 1.5 mm, more preferably not more than 1.4 mm, and even more preferably not more than 1.35 mm. If the intermediate layer is too thin, the durability to cracking on repeated impact may worsen, or molding becomes difficult and mass productivity may deteriorate. On the other hand, if the intermediate layer is too thick, the feel at impact may be too hard, the rebound may become low, and it may be difficult for the distance on shots by amateur users to increase. In addition, if the intermediate layer thickness deviates from the above ranges, the spin rate on full shots may increase, and a good distance may not be attainable on shots by amateur users.

[0120] As a material of the intermediate layer, a resin material containing an ionomer resin as a chief material is used, and particularly among ionomer resins, a highly neutralized ionomer is suitably used. As the highly neutralized ionomer, a commercially available product may be used, and examples thereof include “HPF 1000”, “HPF 2000”, “HPF AD1035”, and “HPF AD1040” (all manufactured by the Dow Chemical Company). By adopting the highly neutralized ionomer, the rebound of the ball is increased while reducing the spin rate of the ball on full shots, and a good distance may be reliably obtained on full shots by amateur users. In order to adjust a desired material hardness and the like of the intermediate layer, the highly neutralized ionomer may be appropriately blended with a general ionomer.

[0121] Next, the cover is described.

[0122] The cover has a material hardness on the Shore C hardness scale which, although not particularly limited, is preferably at least 83, more preferably at least 89, and even more preferably at least 93, and the upper limit is preferably not more than 100, more preferably not more than 97, and even more preferably not more than 95. The material hardness on the Shore D hardness scale is preferably at least 55, more preferably at least 60, and even more preferably at least 63, and the upper limit is preferably not more than 75, more preferably not more than 70, and even more preferably not more than 68.

[0123] The surface hardness of the ball (whole sphere) including the core and the cover is preferably at least 90, more preferably at least 93, and even more preferably at least 95, and the upper limit thereof is preferably not more than 100, more preferably not more than 99, and even more preferably not more than 98 on the Shore C hardness scale. The surface hardness on the Shore D hardness scale is preferably at least 62, more preferably at least 67, and even more preferably at least 69, and the upper limit is preferably not more than 76, more preferably not more than 74, and even more preferably not more than 72.

[0124] If the material hardness and the surface hardness of the cover are too soft in comparison with the above ranges, the spin rate may rise on full shots, and the distance on shots with a driver (W #1) and an iron by amateur users may not be increased. In addition, the launch angle on approach shots may become low, and the ball may be felt to be difficult to handle for amateur users. On the other hand, if the material hardness and the surface hardness of the cover are too hard in comparison with the above ranges, the feel at impact may become too hard, the durability to cracking on repeated impact may worsen, and the distance on shots by the longest hitters may become too long.

[0125] The cover has a thickness of preferably at least 0.8 mm, more preferably at least 1.0 mm, and even more preferably at least 1.2 mm. On the other hand, the upper limit of the cover thickness is preferably not more than 1.5 mm, more preferably not more than 1.4 mm, and even more preferably not more than 1.35 mm. If the cover is too thin, the durability to cracking on repeated impact may worsen, or it may be difficult to mold the cover and mass productivity may deteriorate. On the other hand, if the cover is too thick, the feel at impact may be too hard, the rebound may become low, and it may be difficult for the distance on shots by amateur users to increase. In addition, if the cover thickness deviates from the above ranges, the spin rate on full shots may increase, and a good distance may not be attainable on shots by amateur users.

[0126] As a material of the cover, a resin material containing an ionomer resin as a chief material is used. If a urethane material, which is not a hard material, is used as the cover material, the launch angle on approach shots is lowered and the ball may be felt to be difficult to handle for amateur users. In addition, even if a material having the hardest grade among types of urethane materials is selected, the rebound is lower than that of an ionomer material having the same hardness, and the distance on shots by amateur users may not reach a target. In addition, when the cover is formed, from the viewpoint of mass productivity, it is preferable to adopt a method of encasing the intermediate layer-encased sphere with the cover by injection molding.

[0127] The resin material containing an ionomer resin as a chief material is used, but at that time, an aspect that uses in admixture a zinc-neutralized ionomer resin and a sodium-neutralized ionomer as chief materials 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 20 / 80 to 90 / 10, and more preferably from 25 / 75 to 75 / 25. 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, 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.

[0128] Various additives may be blended in the cover material as necessary, and for example, a pigment, a dispersant, an antioxidant, a light stabilizer, an ultraviolet absorber, an internal mold lubricant, and the like may be appropriately blended.

[0129] 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 an injection mold to obtain the surrounding layer-encased sphere and the intermediate layer-encased sphere, and finally, the cover material, which is the outermost layer, is injection molded to obtain the multi-piece golf ball. In addition, it is also possible to produce a golf ball by preparing two half-cups pre-molded into hemispherical shapes, enclosing the core and the intermediate layer-encased sphere within the two half cups, and molding the core and the intermediate layer-encased sphere under applied heat and pressure.

[0130] The golf ball has a deflection (mm) when compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) which is preferably at least 2.5 mm, more preferably at least 2.8 mm, and even more preferably at least 3.0 mm. An upper limit of the deflection is preferably not more than 3.8 mm, more preferably not more than 3.5 mm, and even more preferably not more than 3.3 mm. If the deflection of the golf ball is too small, the spin rate of the ball on full shots increases excessively, and the distance on shots with a driver (W #1) and an iron by amateur users may not be increased, or the feel at impact may be too hard. On the other hand, if the deflection is too large, the actual initial velocity becomes too low, so that the distance on shots with a driver (W #1) by the longest hitters and amateur users may be too short, the feel at impact may be too soft, or the durability to cracking on repeated impact may become too poor.

[0131] The initial velocity of the ball is preferably at least 75.0 m / s, more preferably at least 76.5 m / s, and even more preferably at least 77.0 m / s. An upper limit thereof is not more than 77.724 m / s. If this initial velocity value is too high, the official rules of R&A and USGA are not satisfied. On the other hand, if the initial velocity is too low, the actual initial velocity may become low and the desired distance may not be attainable under all striking conditions on full shots. The value of the initial velocity in this case is a numerical value measured by a device for measuring a coefficient of restitution (COR) (Golf Ball Testing Machine) of the same type as the R&A. Specifically, a device for measuring a COR manufactured by Hye Precision USA is used. As a condition, at the time of measurement, an air pressure is changed in four stages and measured, a relational expression between the incident velocity and the COR is constructed, and the initial velocity at an incident velocity of 43.83 m / s is determined from the relational expression. For a measurement environment of the device for measuring a COR, a ball temperature-controlled for at least three hours in a thermostatic bath adjusted to 23.9±1° C. is used, and measurement is performed at a room temperature of 23.9±2° C. In addition, a barrel diameter is selected such that a clearance on one side with respect to an outer diameter of the object being measured is from 0.2 to 2.0 mm.

[0132] A value obtained by dividing the initial velocity of the ball by the deflection of the ball is preferably at least 19, more preferably at least 21, and even more preferably at least 23, and the upper limit is preferably not more than 30, more preferably not more than 28, and even more preferably not more than 26. This value has a meaning of measuring a magnitude of the actual initial velocity of the ball. If this value is too large, the distance on shots by the longest hitters becomes too long, and it may be impossible to comply with new ODS rules. On the other hand, if this value is too small, the spin rate of the ball on full shots increases, or the actual initial velocity may become low, and the desired distance may not be attainable under all striking conditions.

[0133] A total thickness of the cover and the intermediate layer is preferably at least 2.0 mm, more preferably at least 2.2 mm, and even more preferably at least 2.4 mm. On the other hand, the upper limit of the total thickness is preferably not more than 3.8 mm, more preferably not more than 3.0 mm, and even more preferably not more than 2.7 mm. If the total thickness is too thin, the durability to cracking on repeated impact may worsen, it may be difficult to mold the intermediate layer and the cover, and as a result, mass productivity of balls may deteriorate. On the other hand, if the total thickness is too thick, the feel at impact may be too hard, the rebound may become low, and it may be difficult for the distance on shots by amateur users to increase. In addition, if the total thickness deviates from the above ranges, the spin rate on full shots may increase, and a good distance may not be attainable on shots by amateur users.

[0134] A total thickness of the cover, the intermediate layer, and the surrounding layer is preferably at least 3.1 mm, more preferably at least 3.3 mm, and even more preferably at least 3.5 mm. On the other hand, the upper limit of the total thickness is preferably not more than 5.0 mm, more preferably not more than 4.2 mm, and even more preferably not more than 3.9 mm. A total thickness that deviates from the above ranges may lead to undesirable results similar to those described for the total thickness of the cover and the intermediate layer.[Relationships Between Surface Hardnesses of Each Sphere]

[0135] In the present invention, a relationship between the surface hardness of each sphere of the ball, the surrounding layer-encased sphere, and the intermediate layer-encased sphere satisfies the following expressions (1-a) and (1-b):(surface⁢ hardness⁢ of⁢ ball)>(surface⁢ hardness⁢ of⁢ surrounding⁢ layer-encased⁢ sphere)(1-a)(surface⁢ hardness⁢ of⁢ ball)>(surface⁢ hardness⁢ of⁢ intermediate⁢ layer-encased⁢ sphere)(1-b)and it is necessary that a relationship between the surface hardness of each sphere of the core, the surrounding layer-encased sphere, and the intermediate layer-encased sphere satisfies at least one of the following conditions (2-a) or (2-b):(surface⁢ hardness⁢ of⁢ surrounding⁢ layer-encased⁢ sphere)<(surface⁢ hardness⁢ of⁢ core(2-a)(surface⁢ hardness⁢ of⁢ intermediate⁢ layer-encased⁢ sphere)<(surface⁢ hardness⁢ of⁢ core).(2-b)Surface hardness in the above conditions means Shore C hardness. If the surface hardness of the ball is softer than the surface hardness of the inner layers, the launch angle on approach shots by amateur users may become low, and the ball may be difficult for amateur users. In addition, the softer surface hardness among the surface hardnesses of the intermediate layer-encased sphere and the surrounding layer-encased sphere is required to be lower than the core surface hardness. If this hardness relationship is not satisfied, it may be difficult to achieve both a soft feel at impact on full shots and a feel at impact with a sense of bounce and a sense that the ball will fly.

[0138] A more preferable aspect of the above hardness relationship satisfies the following condition:

[0139] (surface hardness of ball)>(surface hardness of intermediate layer-encased sphere)>(surface hardness of surrounding layer-encased sphere). If this hardness relationship is not satisfied, it may be impossible to achieve both an easy rising of the ball and a good feel at impact on approach shots by amateur users, and good durability on repeated impact.

[0140] The most suitable hardness relationship in the present invention satisfies the following condition:(surface hardness of ball)>(surface hardness of intermediate layer-encased sphere)>(surface hardness of surrounding layer-encased sphere)<(surface hardness of core).

[0141] Expressed on the Shore C hardness scale, a value obtained by subtracting the surface hardness of the intermediate layer-encased sphere from the surface hardness of the ball is preferably larger than 0, more preferably at least 2, and even more preferably at least 4. An upper limit thereof is preferably not more than 25, more preferably not more than 15, and even more preferably not more than 10. If the above value is too small, the spin rate on full shots may rise, and the intended distance may not be attainable on full shots with a driver (W #1) and an iron by amateur users, or the launch angle on approach shots becomes lower, and approach shots may be felt to be difficult to handle for amateur users. If the above value is too large, the durability to cracking on repeated impact may worsen, the actual initial velocity may become lower, and all distances on shots with a driver (W #1) may be shorter than the desired distance.

[0142] 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 larger than 0, more preferably at least 10, and even more preferably at least 20, and an upper limit thereof is preferably not more than 40, more preferably not more than 32, and even more preferably not more than 25. If this value is too large, the durability to cracking on repeated impact may worsen, the spin rate may rise and the actual initial velocity may be lowered on full shots, and all distances on shots with a driver (W #1) may be shorter than the desired distance.

[0143] A value obtained by subtracting the surface hardness of the surrounding layer-encased sphere from the surface hardness of the core is preferably larger than 0, more preferably at least 2, and even more preferably at least 4, and the upper limit is preferably not more than 12, more preferably not more than 9, and even more preferably not more than 6. In addition, 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 8, more preferably at least 12, and even more preferably at least 15, and an upper limit thereof is preferably not more than 30, more preferably not more than 25, and even more preferably not more than 20. If these values are too large, a soft feeling on full shots may not be felt. On the other hand, if these values are too small, the spin rate on full shots may rise, and the intended distance may not be attainable on full shots with a driver (W #1) and an iron by amateur users.

[0144] 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 10, more preferably at least 13, and even more preferably at least 18, and an upper limit thereof is preferably not more than 35, more preferably not more than 30, and even more preferably not more than 25. 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 30, more preferably at least 35, and even more preferably at least 40, and an upper limit thereof is preferably not more than 55, more preferably not more than 50, and even more preferably not more than 45. If these values are too large, the durability to cracking on repeated impact may worsen, the actual initial velocity may become lower, and all distances on shots with a driver (W #1) may be shorter than the desired distance. On the other hand, if these values are too small, the spin rate of the ball on full shots may rise, and the desired distance may not be attainable on shots with a driver (W #1) and an iron by amateur users.[Relationship between Deflection of Core and Ball]

[0145] Letting each deflection (mm) when each sphere of the core and the ball is compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) be C (mm) and B (mm) respectively, a value of C-B is preferably at least 1.00 mm, more preferably at least 1.20 mm, and even more preferably at least 1.40 mm, and an upper limit thereof is preferably not more than 2.00 mm, more preferably not more than 1.80 mm, and even more preferably not more than 1.60 mm. In addition, a value of C / B is preferably at least 1.20, more preferably at least 1.30, and even more preferably at least 1.40, and the upper limit thereof is preferably not more than 1.60, more preferably not more than 1.55, and even more preferably not more than 1.50. If these values are too large, the durability to cracking on repeated impact may worsen, the actual initial velocity becomes lower, and all distances on shots with a driver (W #1) may be shorter than the desired distance. Alternatively, on full shots, a core may not be felt and the sense that the ball will fly may not be felt. On the other hand, if these values are too small, the spin rate on full shots may increase, the desired distance on shots with a driver (W #1) and an iron by amateur users may not be attainable, or a soft feel at impact may not be felt.[Core Diameter and Ball Diameter]

[0146] A relationship between the core diameter and the ball diameter, that is, a value of (core diameter) / (ball diameter) is preferably at least 0.766, more preferably at least 0.803, and even more preferably at least 0.817. On the other hand, an upper limit thereof is preferably not more than 0.855, more preferably not more than 0.845, and even more preferably not more than 0.836. If this value is too small, the initial velocity of the ball becomes low, or the deflection of the entire ball becomes small and the ball becomes hard, the spin rate of the ball on full shots increases, and the desired distance on full shots by amateur users may not be attainable. On the other hand, if the above value is too large, the spin rate of the ball on full shots increases, the desired distance on full shots by amateur users may not be attainable, and the durability to cracking on repeated impact may worsen.

[0147] Numerous dimples may be formed on the outside surface of the cover. Although not particularly limited, the number of dimples arranged on the surface of the cover is preferably at least 280, preferably at least 300, and more preferably at least 310, and the upper limit thereof can be preferably not more than 450, more preferably not more than 400, and even more preferably not more than 350. If the number of dimples deviates from the above ranges, the distance on shots with a driver (W #1) by amateur users may be decreased.

[0148] 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 can 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 can be 0.08 mm or more and 0.30 mm or less.

[0149] A dimple coverage ratio of the dimples on the spherical surface of the golf ball, specifically, a ratio (surface area coverage ratio, hereinafter, 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 preferable at least 75%, more preferably at least 80%, and even more preferably at least 84%. The upper limit is not more than 90%, more preferably not more than 88%, and even more preferably not more than 86%. If the SR value deviates from the above ranges, the distance on shots with a driver (W #1) by amateur users may be decreased.

[0150] A VR value of a sum of volumes of the individual dimples formed below the flat plane circumscribed by the edge of the dimple to a ball spherical volume on the assumption that the ball has no dimples is at least 0.75%, preferably at least 0.78%, and more preferably at least 0.80%. An upper limit thereof is not more than 0.89%, more preferably not more than 0.88%, and even more preferably not more than 0.86%. If this VR value is larger than the above ranges, the distance on shots with a driver (W #1) by the longest hitters may be too short, or the intended distance on shots with a driver (W #1) by amateur users may not be attainable. In addition, in this case, a ball trajectory may become lower, it becomes difficult to carry, and it may become difficult to go over a valley or a pond. On the other hand, if the above value is too small, the distance on shots with a driver (W #1) by the longest hitters does not decrease, and the ball may fly too much further than an upper limit distance of the new ODS rules.

[0151] A total volume of the dimples means a sum of volumes of the individual dimples formed below the flat plane circumscribed by the edge of the dimples in all the dimples formed in one ball. The total dimple volume is not particularly limited, although the total dimple volume is preferably at least 306 mm3, more preferably at least 318 mm3, and even more preferably at least 326 mm3, and the upper limit thereof is preferably not more than 363 mm3, more preferably not more than 359 mm3, and even more preferably not more than 351 mm3. If this total dimple volume is larger than the above ranges, the distance on shots with a driver (W #1) by the longest hitters may be too short, or the intended distance on shots with a driver (W #1) by amateur users may not be attainable. In addition, in this case, a ball trajectory may become lower, it becomes difficult to carry, and it may become difficult to go over a valley or a pond. On the other hand, if the above value is too small, the distance on shots with a driver (W #1) by the longest hitters does not decrease, and the ball may fly too much further than an upper limit distance of the new ODS rules.

[0152] A value V0 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 preferably at least 0.35, more preferably at least 0.38, and further preferably at least 0.40. The upper limit is not more than 0.80, more preferably not more than 0.70, and even more preferably not more than 0.60. If the V0 value deviates from the above ranges, the distance on shots with a driver (W #1) by the longest hitters and amateur users may be shorter than the intended distance.

[0153] In the golf ball of the present invention, when a ratio (CL1 / CD1) of a lift coefficient CL1 at a Reynolds number of 218000 and a spin rate of 2800 rpm to a drag coefficient CD1 is denoted by A1, a ratio (CL2 / CD2) of a lift coefficient CL2 at a Reynolds number of 184000 and a spin rate of 2900 rpm to a drag coefficient CD2 is denoted by A2, and a ratio (CL3 / CD3) of a lift coefficient CL3 at a Reynolds number of 158000 and a spin rate of 3100 rpm to a drag coefficient CD3 is denoted by A3, the dimples are designed to satisfy the following two conditions:0.59≤A⁢1≤0.6⁢55⁢and⁢(A⁢2+A⁢3) / 2≥0.6⁢7⁢0.

[0154] In the present specification, the “lift coefficients (CL1, CL2, CL3), drag coefficients (CD1, CD2, CD3)” are measured in accordance with the Indoor Test Range (ITR) defined by the USGA (United States Golf Association). The lift coefficients and the drag coefficients can be adjusted by adjusting the configuration of the dimples of the golf ball (arrangement, diameter, depth, volume, number, shape, and the like). The lift coefficients and the drag coefficients are independent of the internal configuration of the golf ball. The Reynolds number (Re) is a dimensionless number used in the field of hydrodynamics. The Reynolds number (Re) is calculated by the following equation (1).Re=ρ⁢vL / μ(1)

[0155] In Equation (1) above, p represents the density of a fluid, v represents the average velocity of an object relative to the flow of the fluid, L represents a characteristic length, and μ represents the viscosity coefficient of the fluid.

[0156] In the present invention, when a ratio CL1 / CD1 of a lift coefficient CL1 at a Reynolds number of 218000 and a spin rate of 2800 rpm to a drag coefficient CD1 is defined as A1, a ratio CL2 / CD2 of a lift coefficient CL2 at a Reynolds number of 184000 and a spin rate of 2900 rpm to a drag coefficient CD2 is defined as A2, and a ratio CL3 / CD3 of a lift coefficient CL3 at a Reynolds number of 158000 and a spin rate of 3100 rpm to a drag coefficient CD3 is defined as A3.

[0157] If a condition of the Reynolds number 218,000 and the spin rate 2,800 rpm under which the lift coefficient CL1 and the drag coefficient CD1 are measured is described, this high-speed condition corresponds to a condition provided by the longest hitters with a driver (W #1), this Reynolds number corresponds to a ball speed when the golf ball is driven out at a head speed (HS) of 54 m / s, and the spin rate 2,800 rpm is an average spin condition of a player with a head speed (HS) of 54 m / s.

[0158] If a condition of the Reynolds number 184,000 and the spin rate 2,900 rpm under which the lift coefficient CL2 and the drag coefficient CD2 are measured is described, this middle-speed condition corresponds to a condition provided by an amateur user with a driver (W #1) at a head speed (HS) of 45 m / s, this Reynolds number corresponds to the ball speed when the golf ball is driven out at a head speed (HS) of 45 m / s, and the spin rate 2,900 rpm is an average spin condition of a player with a head speed (HS) of 45 m / s.

[0159] If a condition of the Reynolds number 158,000 and the spin rate 3,100 rpm under which the lift coefficient CL3 and the drag coefficient CD3 are measured is described, this low-speed condition corresponds to a condition provided by an amateur user with a driver (W #1) at a head speed (HS) of 40 m / s, this Reynolds number corresponds to the ball speed when the golf ball is driven out at a head speed (HS) of 40 m / s, and the spin rate 3,100 rpm is an average spin condition of a player with a head speed (HS) of 40 m / s.

[0160] The ratio between the lift coefficient CL1 and the drag coefficient CD1, that is, the value of CL1 / CD1=A1 is at least 0.590, preferably at least 0.595, and more preferably at least 0.600, and an upper limit thereof is not more than 0.655, preferably not more than 0.640, and more preferably not more than 0.627. If this value is too large, the distance on shots with a driver (W #1) by the longest hitters does not decrease, and the ball may fly too much further than the upper limit distance of the new ODS rules. On the other hand, if the above value is too small, the distance may be too much shorter than the intended distance under all striking conditions.

[0161] When the value of A1 is from 0.590 to 0.613, the ratio between the lift coefficient CL2 and the drag coefficient CD2, that is, a value of CL2 / CD2=A2, is preferably at least 0.635, more preferably at least 0.645, and even more preferably at least 0.655, and an upper limit thereof is preferably not more than 0.668, more preferably not more than 0.666, and even more preferably not more than 0.664. When the value of A1 is from 0.614 to 0.655, the value of A2 is preferably at least 0.669, more preferably at least 0.671, and even more preferably at least 0.673, and an upper limit thereof is preferably not more than 0.750, more preferably not more than 0.725, and even more preferably not more than 0.700. If the above value deviates from the above ranges, under all striking conditions, the ball may blow up or the distance may not increase, there may be a trajectory in which the ball does not carry, and an intended total distance may not be attainable.

[0162] When the value of A1 is from 0.590 to 0.613, the ratio between the lift coefficient CL3 and the drag coefficient CD3, that is, a value of CL3 / CD3=A3, is preferably at least 0.695, more preferably at least 0.705, and even more preferably at least 0.715, and an upper limit thereof is preferably not more than 0.734, more preferably not more than 0.731, and even more preferably not more than 0.728. In addition, when the value of A1 is from 0.614 to 0.655, the value of A3 is preferably at least 0.735, more preferably at least 0.738, and even more preferably at least 0.741, and an upper limit thereof is preferably not more than 0.815, more preferably not more than 0.780, and even more preferably not more than 0.760. If the above value deviates from the above ranges, under all striking conditions, the ball may blow up or the distance may not increase, there may be a trajectory in which the ball does not carry, and an intended total distance may not be attainable.

[0163] The average value of the above A2 and A3, that is, the value of (A2+A3) / 2 is at least 0.670, preferably at least 0.680, and more preferably at least 0.690, and an upper limit thereof is preferably not more than 0.783, more preferably not more than 0.775, and even more preferably not more than 0.765. If this value is too low, it becomes difficult for the ball to carry on shots with a driver (W #1) by amateur users, and the intended total distance may not be attainable. On the other hand, if the above value is too high, the ball trajectory may be blown up on shots with a driver (W #1) by amateur users, and the intended distance may not be attainable.

[0164] When the total volume of the dimples is denoted by D (mm3) and the deflection when the ball is compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) is denoted by B (mm), a value of D / B is preferably not more than 140, more preferably not more than 130, and even more preferably not more than 120. On the other hand, the lower limit is preferably at least 95, more preferably at least 97, and even more preferably at least 100. This D / B means an index in which an appropriate distance suppression effect is produced on shots with a driver (W #1) by the longest hitters, and a good distance is easily obtained on shots by amateur users. If this value deviates from the above ranges, the intended distance may not be attainable on shots with a driver (W #1) by the longest hitters and amateur users.

[0165] 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

[0166] 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 4 and Comparative Examples 1 to 15[Formation of Core]

[0167] In Comparative Examples 8, 10, and 12 to 14, a rubber composition of each Example shown in Table 1 was prepared, and then vulcanization molding was performed under vulcanization conditions according to each Example shown in Table 1 to produce a solid core.

[0168] In Examples 1 to 4 and Comparative Examples 1 to 7, 9, 11, and 15, cores are produced based on the formulations in Table 1 in the same manner as described above.TABLE 1Core formulationExampleComparative Example(pbw)1234123456Polybutadiene A10010010010035100100100100100Polybutadiene BPolybutadiene CIsoprene rubberStyrene-butadiene65rubberZinc acrylate27.527.527.525.321.727.527.532.533.033.4Zinc methacrylate1.0Methacrylic acidZinc stearate2.02.02.02.02.02.02.02.02.0Organic peroxide A1.01.01.01.01.01.01.01.01.01.0Organic peroxide BSulfur0.0250.0250.0250.0250.0250.0250.0250.0250.025Water0.30.30.30.30.40.30.30.30.20.3Antioxidant0.10.10.10.10.10.10.10.10.10.1Zinc oxide31.931.931.932.728.031.931.928.328.111.8Barium sulfateZinc salt of1.01.01.01.00.71.01.00.10.1pentachlorothio-phenolVulcanization-Temp.150150150150150150150150150150conditions(° C.)Time19191919191919191919(min)Core formulationComparative Example(pbw)789101112131415Polybutadiene A1001001001001003595Polybutadiene B2020Polybutadiene C8080Isoprene rubber5Styrene-butadiene65rubberZinc acrylate26.037.037.037.037.033.533.526.9Zinc methacrylate1.01.01.01.01.0Methacrylic acid23.5Zinc stearate5.02.02.0Organic peroxide A0.61.01.01.01.01.01.01.01.2Organic peroxide B0.6Sulfur0.0250.025Water0.40.40.40.40.60.60.4Antioxidant0.10.10.10.10.10.10.10.10.2Zinc oxide14.214.814.814.814.819.319.316.523.5Barium sulfate1.0Zinc salt of1.01.01.01.01.00.60.6pentachlorothio-phenolVulcanization-Temp.160150150150150160160150163conditions(° C.)Time111919191914141921(min)

[0169] Details of the above formulations are as follows.

[0170] Polybutadiene A: Trade name “BR 01”, (manufactured by ENEOS Materials Corporation)

[0171] Polybutadiene B: Trade name “LDiene™ 645” (Firestone Polymers)

[0172] Polybutadiene C: Trade name “BUDENE® 1224 Gl” (Goodyear Tire & Rubber Company)

[0173] Isoprene rubber: Trade name “JR 2200” (manufactured by ENEOS Materials Corporation)

[0174] Styrene-butadiene rubber: Trade name “SBR 1507” (manufactured by ENEOS Materials Corporation)

[0175] Zinc acrylate: Trade name “ZN-DA85 S” (manufactured by Nippon Shokubai Co., Ltd.)

[0176] Zinc methacrylate: Trade name “ZDA-90” (manufactured by Asada Chemical Industry Co., Ltd.)

[0177] Zinc stearate: Trade name “BR-3T” (manufactured by Akrochem Corporation)

[0178] Organic peroxide A: Dicumyl peroxide, trade name “Percumyl D” (manufactured by NOF Corporation)

[0179] Organic peroxide B: A mixture of 1,1-di(t-butylperoxy)cyclohexane and silica, trade name “Perhexa C-40” (manufactured by NOF Corporation)

[0180] Sulfur: Trade name “SANMIX S-80N” (manufactured by Sanshin Chemical Industry Co., Ltd., containing sulfur powder for rubber in an amount of 80 wt %)

[0181] Water: Pure water (manufactured by Seiki Co., Ltd.)

[0182] Antioxidant: 2,2-methylenebis(4-methyl-6-butylphenol), trade name “Nocrac NS-6” (manufactured by Ouchi Shinko Chemical Industrial Co., Ltd.)

[0183] Zinc oxide: Trade name “Grade 3 Zinc Oxide” (manufactured by Sakai Chemical Industry Co., Ltd.)

[0184] Zinc salt of pentachlorothiophenol: Manufactured by FUJIFILM Wako Pure Chemical Corporation[Formation of Surrounding Layer, Intermediate Layer, and Cover (Outermost Layer)]

[0185] Next, in Comparative Examples 8, 10, and 12 to 14, the intermediate layer was formed by injection molding the resin material No. 4 or No. 5 of the intermediate layer shown in Table 2 around the core surface using an injection mold. Subsequently, the cover was formed by injection molding the resin material No. 10 of the cover (outermost layer) shown in Table 2 around the intermediate layer-encased sphere using a separate injection mold. At this time, a predetermined large number of dimples described below were formed on the surface of the cover.

[0186] In Examples 1 to 4 and Comparative Examples 1 to 3, the surrounding layer is formed by injection molding the resin material No. 1 of the surrounding layer shown in Table 2 around the core surface using an injection mold. Next, using another injection mold, injection molding is performed around the surrounding layer-encased sphere using the resin material No. 2 of the intermediate layer shown in the same table to form an intermediate layer. Subsequently, the cover is formed by injection molding the resin material No. 6 of the cover (outermost layer) shown in the same table around the intermediate layer-encased sphere using a separate injection mold. In Comparative Examples 4, 5, 9, and 11, the cover is formed by injection molding the resin material No. 2, No. 3, or No. 4 shown in Table 2 around the core surface using an injection mold to form the intermediate layer, and then injection molding the resin materials No. 7 to No. 10 ofthe cover (outermost layer) shown in the same table. In Comparative Examples 6, 7, and 15, the cover is formed around the core surface by injection molding using an injection mold and the resin material No. 8, No. 9, or No. 11 shown in Table 2. At this time, a large number of predetermined dimples described below are formed on the cover surface.TABLE 2Resin material(pbw)No. 1No. 2No. 3No. 4No. 5No. 6No. 7No. 8No. 9No. 10No. 11Hytrel ® 4047N100HPF100056100Himilan 160544505050Himilan 160137.5Himilan 15571537.5Himilan 1706153550AM732950AM732725AM73188575AN431925Titanium oxide444433Barium sulfate20Magnesium stearate1Trimethylolpropane1.11.1TPU (1)100TPU (2)100

[0187] Details of the blending components in Table 2 are as follows.

[0188] “Hytrel® 4047N” polyester elastomer manufactured by Toray Celanese Co., Ltd.

[0189] “HPF 1000” highly neutralized ionomer manufactured by The Dow Chemical Company

[0190] “Himilan 1605”, “Himilan 1601”, “Himilan 1557”, “Himilan 1706”, “AM7329”,

[0191] “AM7327”, and “AM7318” ionomer resins manufactured by Dow-Mitsui Polychemicals Co., Ltd.

[0192] “Nucrel AN4319” manufactured by Dow-Mitsui Polychemicals Co., Ltd.

[0193] Trade name “Precipitated Barium Sulfate 300” barium sulfate manufactured by Sakai Chemical Industry Co., Ltd.

[0194] Trade name “Magnesium stearate G” magnesium stearate manufactured by NOF Corporation

[0195] “Trimethylolpropane” (TMP) manufactured by Tokyo Chemical Industry Co., Ltd.

[0196] Trade name “Pandex” ether-type thermoplastic polyurethane (TPU (1)), material hardness (Shore D) 50, manufactured by DIC Covestro Polymer Ltd.

[0197] Trade name “Pandex” ether-type thermoplastic polyurethane (TPU (2)), material hardness (Shore D) 47, manufactured by DIC Covestro Polymer Ltd.

[0198] For the dimples of the Examples and Comparative Examples, the following dimples (1) to (5) were used. Each dimple mode includes eight types of circular dimples of No. 1 to No. 8 having different diameters and depths. Details thereof are listed in Table 3 below. In addition, an arrangement mode (pattern) of the dimples (1) to (5) is illustrated in FIGS. 5A and 5B. FIG. 5A is a plan view of the dimples, and FIG. 5B is a side view thereof.TABLE 3CylinderTotal volumeDiameterDepthVolumevolumeSRVRof dimplesTypeQuantity(mm)(mm)(mm3)ratio Vo(%)(%)(mm3)Dimple (1)No. 1124.630.1221.0090.491840.68278No. 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. 863.210.1320.4570.430Total330Dimple (2)No. 1124.690.1441.2200.493860.81331No. 21984.540.1401.1000.486No. 3363.960.1340.7660.467No. 4122.920.1090.3220.441No. 5364.540.1461.1410.485No. 6243.960.1440.8270.468No. 763.360.1360.5900.491No. 863.220.1270.4330.421Total330Dimple (3)No. 1124.690.1461.2360.490860.83338No. 21984.540.1431.1220.484No. 3363.960.1370.7900.470No. 4122.920.1060.3100.438No. 5364.540.1491.1620.482No. 6243.960.1470.8460.467No. 763.380.1380.6080.493No. 863.280.1320.4700.423Total330Dimple (4)No. 1124.700.1491.2520.487860.85345No. 21984.550.1461.1440.483No. 3363.970.1400.8150.472No. 4122.910.1030.2980.435No. 5364.550.1521.1830.480No. 6243.970.1500.8640.467No. 763.400.1400.6270.495No. 863.330.1380.5100.426Total330Dimple (5)No. 1124.680.1641.3910.493850.93378No. 21984.530.1611.2580.485No. 3363.950.1540.8830.468No. 4122.900.1140.3310.440No. 5364.530.1681.2940.480No. 6243.950.1650.9490.470No. 763.360.1540.6630.487No. 863.260.1520.5380.426Total330[Definition of Dimple]Edge: highest point in cross section passing through center of a dimpleDiameter: diameter of the flat plane circumscribed by the edge of a dimple

[0201] Depth: maximum depth of a dimple from the flat plane circumscribed by the edge of the dimple

[0202] SR: a ratio 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

[0203] Dimple volume: a dimple volume under a flat plane circumscribed by an edge of a dimple

[0204] Cylinder volume ratio: a ratio of the dimple volume to the cylinder volume having the same diameter as the dimple

[0205] VR: 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

[0206] The ratio CL1 / CD1=A1 of the lift coefficient CL1 at a Reynolds number of 218000 and a spin rate of 2800 rpm to the drag coefficient CD1, the ratio CL2 / CD2=A2 of the lift coefficient CL2 at a Reynolds number of 184000 and a spin rate of 2900 rpm to the drag coefficient CD2, and the ratio CL3 / CD3=A3 of the lift coefficient CL3 at a Reynolds number of 158000 and a spin rate of 3100 rpm to the drag coefficient CD3 of the balls with the above dimples (1) to (5) formed on their cover surfaces are listed in the table below. These lift coefficients and drag coefficients are measured in accordance with the Indoor Test Range (ITR) defined by USGA.TABLE 4DimpleDimpleDimpleDimpleDimple(1)(2)(3)(4)(5)CL10.1510.1470.1460.1450.143CD10.2300.2370.2380.2390.244CL1 / CD1 = A10.6570.6200.6130.6070.586CL20.1680.1620.1610.1600.156CD20.2330.2400.2410.2420.246CL2 / CD2 = A20.7210.6750.6680.6610.634CL30.1900.1820.1810.1790.173CD30.2420.2450.2460.2470.250CL3 / CD3 = A30.7850.7430.7340.7250.692

[0207] 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, surface hardnesses of each layer-encased sphere, and ball initial velocities are evaluated by the following methods, and are shown in Tables 5 to 8.[Core Hardness Profile]

[0208] 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 Tables 5 and 6, 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. Note that the numerical values in the table are Shore C hardness values.

[0209] In addition, in the core hardness profile, letting the Shore C hardness at the core center be Cc, the Shore C hardness at the midpoint M between the core center and the core surface be Cm, the respective Shore C hardnesses at positions 2 mm, 4 mm, and 6 mm inward from the midpoint M be Cm-2, Cm-4, and Cm-6, the respective Shore C hardnesses at positions 2 mm, 4 mm, and 6 mm outward from the midpoint M be Cm+2, Cm+4, and Cm+6, and the Shore C hardness at the core surface be Cs, the surface areas A to F are calculated as follows:surface⁢ area⁢ A: 1 / 2×2×(Cm-4-Cm-6)surface⁢ area⁢ B: 1 / 2×2×(Cm-2-Cm-4)surface⁢ area⁢ C: 1 / 2×2×(Cm-Cm-2)surface⁢ area⁢ D: 1 / 2×2×(Cm+2-Cm)surface⁢ area⁢ E: 1 / 2×2×(Cm+4-Cm+2)surface⁢ area⁢ F: 1 / 2×2×(Cm+6-Cm+4)and the values of the following nine expressions are determined.Surface⁢ area⁢ A+surface⁢ area⁢ B(1)Surface⁢ area⁢ B+surface⁢ area⁢ C(2)Surface⁢ area⁢ C+surface⁢ area⁢ D(3)Surface⁢ area⁢ D+surface⁢ area⁢ E(4)Surface⁢ area⁢ E+surface⁢ area⁢ F(5)(Surface⁢ area⁢ D+surface⁢ area⁢ E)-(surface⁢ area⁢ A+surface⁢ area⁢ B)(6)(Surface⁢ area⁢ D+surface⁢ area⁢ E)-(surface⁢ area⁢ B+surface⁢ area⁢ C)(7){(Surface⁢ area⁢ D+surface⁢ area⁢ E)-(surface⁢ area⁢ A+surface⁢ area⁢ B)}×(Cs-Cc)(8){(Surface⁢ area⁢ D+surface⁢ area⁢ E)-(surface⁢ area⁢ B+surface⁢ area⁢ C)}×(Cs-Cc)(9)The surface areas A to F in the core hardness profile are described in FIG. 2, which shows a graph that illustrates surface areas A to F using the core hardness profile data from Example 1.

[0212] In addition, FIGS. 3 and 4 show graphs of core hardness profiles for Examples 1 to 4 and Comparative Examples 1 to 15.[Outer Diameters of Each Sphere of Core, Surrounding Layer-Encased Sphere, and Intermediate Layer-Encased Sphere]

[0213] At a temperature adjusted to 23.9±1° C. for at least three hours or more in a thermostatic bath, five random places on the surface are measured in a room with a temperature of 23.9±2° C., 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]

[0214] At a temperature adjusted to 23.9±1° C. for at least three hours or more in a thermostatic bath, a diameter at 15 random dimple-free places is measured in a room at a temperature of 23.9±2° C., and, using an average value of these measurements as a measured value of one ball, an average value for the diameter of 10 balls is determined.[Deflection of Core and Ball]

[0215] Each subject layer-encased sphere of the core or the 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. It is noted that the deflection in each case is a measurement value measured in a room at a temperature of 23.9±2° C. after temperature adjustment to 23.9±1° C. for at least three hours or more in a thermostatic bath. As a measuring device, a high-load compression tester manufactured by MU Instruments Trading Corp. is used, and a down speed of a pressure head that compresses the core or the ball is set to 10 mm / s.[Material Hardnesses of Surrounding Layer, Intermediate Layer, and Cover (Shore C and Shore D Hardnesses)]

[0216] The resin material of each layer is molded into a sheet having a thickness of 2 mm and left at a temperature of 23±2° C. for two weeks. At the time of measurement, three such sheets are stacked together. The Shore C hardness and the Shore D hardness are each measured with a Shore C durometer and a Shore D durometer conforming to the ASTM D2240 standard. For the measurement of the hardness, the P2 Automatic Rubber Hardness Tester manufactured by Kobunshi Keiki Co., Ltd. to which a Shore C durometer or a Shore D durometer is mounted is used. For the hardness value, a maximum value is read. The measurement method is in accordance with the ASTM D2240 standard.[Surface Hardnesses of Each Sphere of Surrounding Layer-Encased Sphere, Intermediate Layer-Encased Sphere, and Ball]

[0217] 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 C hardness and the Shore D hardness are each measured with a Shore C durometer and a Shore D durometer conforming to the ASTM D2240 standard. For the measurement of the hardness, the P2 Automatic Rubber Hardness Tester manufactured by Kobunshi Keiki Co., Ltd. to which a Shore C durometer or a Shore D durometer is mounted is used. For the hardness value, a maximum value is read. The measurement method is in accordance with the ASTM D2240 standard.[Initial Velocity of Ball]

[0218] The initial velocity of each sphere is measured at a temperature of 23.9±2° C. using a device for measuring COR manufactured by Hye Precision Products of the same type as the R&A. The measurement principle is as follows.

[0219] An air pressure is changed to four stages of 35.5 psi, 36.5 psi, 39.5 psi, and 40.5 psi, and a ball is fired at four stages of incident velocity by respective air pressures, collided with a barrier, and its COR is measured. That is, a correlation equation between the incident velocity and the COR is created by changing the air pressure in four stages. Similarly, a correlation equation between the incident velocity and a contact time is created.

[0220] Then, from these correlation equations, the COR (coefficient of restitution) and the contact time (μs) at an incident velocity of 43.83 m / s are determined and substituted into the following initial velocity conversion equation to calculate an initial velocity of each sphere.IV=1⁢3⁢6.8+1⁢3⁢6.3⁢e+0.0⁢19⁢tc

[0221] Here, e is a coefficient of restitution, and tc is a contact time (μs) at a collision speed of 143.8 ft / s (43.83 m / s).

[0222] In the initial velocity measurement of the balls of all examples, a barrel diameter of 43.18 mm is selected.TABLE 5ExampleComparative Example1234123456Ball structure (piece)4P4P4P4P4P4P4P3P3P2PCoreOuter diameter (mm)35.1735.1735.1735.1735.1735.1735.1737.3037.3039.30Weight (g)27.7927.7927.7927.7927.7927.7927.7932.8032.8035.83Deflection (mm)4.544.544.544.824.544.544.543.403.303.12Cs [surface] (Shore C)76.576.576.574.566.676.576.585.586.588.3Cm + 6 (Shore C)71.071.071.068.565.871.071.075.376.177.5Cm + 4 (Shore C)69.469.469.467.164.769.469.469.570.171.1Cm + 2 (Shore C)64.164.164.163.364.664.164.164.565.166.1Cm [intermediate] (Shore C)59.859.859.858.863.059.859.863.264.065.4Cm − 2 (Shore C)58.758.758.757.959.158.758.763.063.865.2Cm − 4 (Shore C)56.556.556.555.254.956.556.562.263.164.7Cm − 6 (Shore C)56.356.356.355.053.156.356.361.862.864.6Cc [center] (Shore C)55.155.155.153.652.955.155.161.562.664.6Cs − Cc (Shore C)21.421.421.420.913.721.421.424.023.923.7(Cs − Cc) / (Cm − Cc)4.64.64.64.01.44.64.614.117.129.Surface area A0.20.20.20.21.80.20.20.40.30.1Surface area B2.22.22.22.74.22.22.20.80.70.5Surface area C1.11.11.10.93.91.11.10.20.20.2Surface area D4.34.34.34.51.64.34.31.31.10.7Surface area E5.35.35.33.80.15.35.35.05.05.0Surface area F1.61.61.61.41.11.61.65.86.06.4Surface area A + surface area B2.42.42.42.96.02.42.41.21.00.6Surface area B + surface area C3.33.33.33.68.13.33.31.00.90.7Surface area C + surface area D5.45.45.45.45.55.45.41.51.30.9Surface area D + surface area E9.69.69.68.31.79.69.66.36.15.7Surface area E + surface area F6.96.96.95.21.26.96.910.811.011.4(Surface areas: D + E) −7.27.27.25.4−4.37.27.25.15.15.1(surface areas: A + B)(Surface areas: D + E) −6.36.36.34.7−6.46.36.35.35.25.0(surface areas: B + C){(Surface areas: D + E) −154154154113−59154154122122121(surface areas: A + B)} × (Cs − Cc){(Surface areas: D + E) −13513513598−88135135127124119(surface areas: B + C)} × (Cs − Cc)TABLE 6Comparative Example789101112131415Ball structure (piece)2P3P3P3P3P3P3P3P2PCoreOuter diameter (mm)39.7038.6538.6538.6538.6538.0638.0638.6439.80Weight (g)37.7435.0935.0935.0935.0933.8333.8335.1036.99Deflection (mm)4.502.922.922.922.924.134.132.932.63Cs [surface] (Shore C)76.087.487.487.487.486.386.381.584.3Cm + 6 (Shore C)66.580.480.480.480.474.174.180.579.0Cm + 4 (Shore C)64.975.875.875.875.865.965.979.075.9Cm + 2 (Shore C)63.470.870.870.870.861.361.376.272.8Cm [intermediate] (Shore C)62.966.366.366.366.361.061.072.370.8Cm − 2 (Shore C)62.465.665.665.665.661.461.468.469.8Cm − 4 (Shore C)61.364.964.964.964.961.061.066.968.4Cm − 6 (Shore C)59.763.363.363.363.360.160.165.466.3Cc [center] (Shore C)56.262.662.662.662.657.957.962.760.7Cs − Cc (Shore C)19.824.824.824.824.828.428.418.823.6(Cs − Cc) / (Cm − Cc)3.06.76.76.76.79.29.22.02.3Surface area A1.61.61.61.61.60.90.91.52.1Surface area B1.10.70.70.70.70.40.41.51.4Surface area C0.50.70.70.70.7−0.4−0.43.91.0Surface area D0.54.54.54.54.50.30.33.92.0Surface area E1.55.05.05.05.04.64.62.83.1Surface area F1.64.64.64.64.68.28.21.53.1Surface area A + surface area B2.72.32.32.32.31.31.33.03.5Surface area B + surface area C1.61.41.41.41.40.00.05.42.4Surface area C + surface area D1.05.25.25.25.2−0.1−0.17.83.0Surface area D + surface area E2.09.59.59.59.54.94.96.75.1Surface area E + surface area F3.19.69.69.69.612.812.84.36.2(Surface areas: D + E) −−0.77.27.27.27.23.63.63.71.6(surface areas: A + B)(Surface areas: D + E) −0.48.18.18.18.14.94.91.32.7(surface areas: B + C){(Surface areas: D + E) −−141791791791791021027038(surface areas: A + B)} × (Cs − Cc){(Surface areas: D + E) −82012012012011391392464(surface areas: B + C)} × (Cs − Cc)TABLE 7ExampleComparative Example12341SurroundingMaterialNo. 1No. 1No. 1No. 1No. 1layerThickness (mm)1.241.241.241.241.24Material hardness (Shore C)6363636363Material hardness (Shore D)4040404040SurroundingOuter diameter (mm)37.6537.6537.6537.6537.65layer-Weight (g)33.6433.6433.6433.6433.64encasedSurface hardness (Shore C)7171717171sphereSurface hardness (Shore D)4646464646IntermediateMaterialNo. 2No. 2No. 2No. 2No. 2layerThickness (mm)1.311.311.311.311.31Material hardness (Shore C)9090909090Material hardness (Shore D)5959595959IntermediateOuter diameter (mm)40.2740.2740.2740.2740.27layer-Weight (g)39.639.639.639.639.6encasedSurface hardness (Shore C)9494949494sphereSurface hardness (Shore D)6363636363CoverMaterialNo. 6No. 6No. 6No. 6No. 6Thickness (mm)1.211.211.211.211.21Material hardness (Shore C)9393939393Material hardness (Shore D)6363636363DimpleType(2)(3)(4)(2)(1)Quantity330330330330330Surface area coverage ratio: SR (%)8686868684Volume occupancy ratio: VR (%)0.810.830.850.810.68Total dimple volume (mm3)331338345331278A1: CL1 / CD10.6200.6130.6070.6200.657A2: CL2 / CD20.6750.6680.6610.6750.721A3: CL3 / CD30.7430.7340.7250.7430.785Average value of A2 and A30.7090.7010.6930.7090.753BallOuter diameter (mm)42.7042.7042.7042.7042.70Weight (g)45.5045.5045.5045.5045.50Deflection (mm)3.083.083.083.323.08Initial velocity (m / s)77.277.277.277.274.0Initial velocity / deflection25.125.125.123.324.0Surface hardness (Shore C)9898989898Surface hardness (Shore D)6969696969Cover thickness + intermediate layer thickness (mm)2.532.532.532.532.53Cover thickness + intermediate layer thickness +3.773.773.773.773.77surrounding layer thickness (mm)Total dimple volume / deflection of ball (mm2)10711011210090Ball surface hardness − intermediate layer-encased44444sphere surface hardness (Shore C)Ball surface hardness − surrounding layer-encased2727272727sphere surface hardness (Shore C)Intermediate layer-encased sphere surface hardness −2323232323surrounding layer-encased sphere surface hardness(Shore C)Intermediate layer-encased sphere surface hardness −1818182027core surface hardness (Shore C)Surrounding layer-encased sphere surface hardness −−6−6−6−44core surface hardness (Shore C)Surrounding layer-encased sphere surface hardness −1616161718core center hardness (Shore C)Intermediate layer-encased sphere surface hardness −3939394041core center hardness (Shore C)Ball surface hardness − core surface hardness (Shore C)2222222431Ball surface hardness − core center hardness (Shore C)4343434445Deflection of core − deflection of ball (mm)1.461.461.461.501.46Deflection of core / deflection of ball1.471.471.471.451.47Core diameter / ball diameter0.8240.8240.8240.8240.824Comparative Example23456SurroundingMaterialNo. 1No. 1———layerThickness (mm)1.241.24———Material hardness (Shore C)6363———Material hardness (Shore D)4040———SurroundingOuter diameter (mm)37.6537.65———layer-Weight (g)33.6433.64———encasedSurface hardness (Shore C)7171———sphereSurface hardness (Shore D)4646———IntermediateMaterialNo. 2No. 2No. 2No. 3—layerThickness (mm)1.311.311.351.35—Material hardness (Shore C)90909084—Material hardness (Shore D)59595954—IntermediateOuter diameter (mm)40.2740.2740.0040.00—layer-Weight (g)39.639.638.938.9—encasedSurface hardness (Shore C)94949490—sphereSurface hardness (Shore D)63636359—CoverMaterialNo. 6No. 6No. 7No. 7No. 8Thickness (mm)1.211.211.351.351.70Material hardness (Shore C)9393939394Material hardness (Shore D)6363646465DimpleType(1)(5)(4)(2)(4)Quantity330330330330330Surface area coverage ratio: SR (%)8485868686Volume occupancy ratio: VR (%)0.680.930.850.810.85Total dimple volume (mm3)278378345331345A1: CL1 / CD10.6570.5860.6070.6200.607A2: CL2 / CD20.7210.6340.6610.6750.661A3: CL3 / CD30.7850.6920.7250.7430.725Average value of A2 and A30.7530.6630.6930.7090.693BallOuter diameter (mm)42,7042.7042.7042.7042.70Weight (g)45.5045.5045.5045.5045.50Deflection (mm)3.083.082.702.702.71Initial velocity (m / s)77.277.277.277.277.0Initial velocity / deflection25.125.128.628.628.4Surface hardness (Shore C)9898989898Surface hardness (Shore D)6969707071Cover thickness + intermediate layer thickness (mm)2.532.532.702.701.70Cover thickness + intermediate layer thickness +3.773.772.702.701.70surrounding layer thickness (mm)Total dimple volume / deflection of ball (mm2)90123128123127Ball surface hardness − intermediate layer-encased4448—sphere surface hardness (Shore C)Ball surface hardness − surrounding layer-encased2727———sphere surface hardness (Shore C)Intermediate layer-encased sphere surface hardness −2323———surrounding layer-encased sphere surface hardness(Shore C)Intermediate layer-encased sphere surface hardness −181894—core surface hardness (Shore C)Surrounding layer-encased sphere surface hardness −−6−6———core surface hardness (Shore C)Surrounding layer-encased sphere surface hardness −1616———core center hardness (Shore C)Intermediate layer-encased sphere surface hardness −39393327—core center hardness (Shore C)Ball surface hardness − core surface hardness (Shore C)2222131210Ball surface hardness − core center hardness (Shore C)4343373533Deflection of core − deflection of ball (mm)1.461.460.700.600.41Deflection of core / deflection of ball1.471.471.261.221.15Core diameter / ball diameter0.8240.8240.8740.8740.920TABLE 8Comparative Example789101112131415SurroundingMaterial—————————layerThickness (mm)—————————Material hardness (Shore C)—————————Material hardness (Shore D)—————————SurroundingOuter diameter (mm)—————————layer-Weight (g)—————————encasedSurface hardness (Shore C)—————————sphereSurface hardness (Shore D)—————————IntermediateMaterial—No. 4No. 4No. 4No. 4No. 5No. 5No. 4—layerThickness (mm)—1.171.171.171.171.471.471.21—Material hardness (Shore C)—94949494949494—Material hardness (Shore D)—67676767656567—IntermediateOuter diameter (mm)—40.9940.9940.9940.9941.0041.0041.06—layer-Weight (g)—40.6340.6340.6340.6340.6540.6540.81—encasedSurface hardness (Shore C)—97979797979797—sphereSurface hardness (Shore D)—71717171717171—CoverMaterialNo. 9No. 10No. 10No. 10No. 10No. 10No. 10No. 10No. 11Thickness (mm)1.500.850.850.850.850.840.840.811.46Material hardness (Shore C)847171717171717167Material hardness (Shore D)565050505050505047DimpleType(4)(4)(2)(1)(5)(1)(4)(1)(2)Quantity330330330330330330330330330Surface area coverage ratio: SR (%)868686848584868486Volume occupancy ratio: VR (%)0.850.850.810.680.930.680.850.680.81Total dimple volume (mm3)345345331278378278345278331A1: CL1 / CD10.6070.6070.6200.6570.5860.6570.6070.6570.620A2: CL2 / CD20.6610.6610.6750.7210.6340.7210.6610.7210.675A3: CL3 / CD30.7250.7250.7430.7850.6920.7850.7250.7850.743Average value of A2 and A30.6930.6930.7090.7530.6630.7530.6930.7530.709BallOuter diameter (mm)42.7042.6942.6942.6942.6942.6842.6942.6842.72Weight (g)45.4045.4945.5245.5545.5245.6045.5245.5145.66Deflection (mm)4.002.372.352.322.352.962.982.382.51Initial velocity (m / s)77.077.077.177.277.176.977.073.173.4Initial velocity / deflection19.332.532.633.332.826.025.830.729.2Surface hardness (Shore C)928787878786868779Surface hardness (Shore D)626161616160606153Cover thickness + intermediate layer thickness (mm)1.502.022.022.022.022.312.322.021.46Cover thickness + intermediate layer thickness +1.502.022.022.022.022.312.322.021.46surrounding layer thickness (mm)Total dimple volume / deflection of ball (mm2)8614514112016194116117132Ball surface hardness − intermediate layer-encased—−10−10−10−10−11−11−10—sphere surface hardness (Shore C)Ball surface hardness − surrounding layer-encased—————————sphere surface hardness (Shore C)Intermediate layer-encased sphere surface hardness −—————————surrounding layer-encased sphere surface hardness(Shore C)Intermediate layer-encased sphere surface hardness −—10101010111116—core surface hardness (Shore C)Surrounding layer-encased sphere surface hardness −—————————core surface hardness (Shore C)Surrounding layer-encased sphere surface hardness −—————————core center hardness (Shore C)Intermediate layer-encased sphere surface hardness −—34343434393934—core center hardness (Shore C)Ball surface hardness − core surface hardness (Shore C)160000006−5Ball surface hardness − core center hardness (Shore C)362424242428282418Deflection of core − deflection of ball (mm)0.500.550.570.600.571.171.150.550.12Deflection of core / deflection of ball1.131.231.241.261.241.401.391.231.05Core diameter / ball diameter0.9300.9050.9050.9050.9050.8920.8920.9050.932The flight (W #1 and I #6) and the controllability on approach shots of each golf ball are evaluated by the following methods. The results are shown in Table 9.[Evaluation of Flight (W #1, HS 54 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 54 m / s are measured. The club used is a TOUR B XD-5 Driver / loft angle 8.5° (2017 model) manufactured by Bridgestone Sports Co., Ltd. and is evaluated according to the following rating criteria.[Rating Criteria]Good: Total compared with Comparative Example 10 is not more than −10 m, and at least −14 m.Fair: Total compared with Comparative Example 10 is less than −14 m.NG: Total compared with Comparative Example 10 is more than −10 m.[Evaluation of Flight (W #1, HS 40 m / s)]The 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 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 compared with Comparative Example 10 is at least 0 m.Fair: Total compared with Comparative Example 10 is at least −5 m and less than 0 m.

[0231] NG: Total compared with Comparative Example 10 is less than −5 m.[Evaluation of Flight (I #6, HS 42 m / s)]

[0232] When a number six iron (I #6) is mounted on the golf swing robot and a ball is struck at an HS of 42 m / s, a spin rate and a distance traveled (total) 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 compared with Comparative Example 10 is at least 5 m.

[0234] Fair: Total compared with Comparative Example 10 is at least 0 m and less than 5 m.

[0235] NG: Total compared with Comparative Example 10 is less than 0 m.[Evaluation of Flight (I #6, HS 35 m / s)]

[0236] When a number six iron (I #6) is mounted on the golf swing robot and a ball is struck at an HS of 35 m / s, a spin rate and a distance traveled (total) 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 / Total]Good: Total compared with Comparative Example 10 is at least 3 m.

[0238] Fair: Total compared with Comparative Example 10 is at least −3 m and less than 3 m.

[0239] NG: Total compared with Comparative Example 10 is less than −3 m.[Evaluation of Launch Angle on Approach Shots]

[0240] A judgment is made based on a launch angle when a sand wedge is mounted on the golf swing robot and a ball is struck at an HS of 15 m / s. The launch angle 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: Launch angle is at least 35.0°.

[0242] NG: Launch angle is less than 35.0°.[Evaluation of Feel at Impact]

[0243] Sensory evaluation of a feel at impact is performed by an amateur golfer having a handicap of at least 25 and a head speed on shots with a driver (W #1) of 30 to 40 m / s. Evaluation is performed according to the following rating criteria.[Rating Criteria]Good: Good feel at impact with a soft feeling and a sense of bounce.

[0245] Fair: One of the soft feeling and the sense of bounce cannot be said to have a good feel at impact.

[0246] NG: Both the soft feeling and the sense of bounce do not have a good feel at impact. Alternatively, either the soft feeling or the sense of bounce is obviously not good.TABLE 9ExampleComparative Example1234123456FlightSpin rate2,5852,5852,5852,4832,7472,5852,5852,3952,3082,423W#1(rpm)HSTotal271.2270.3269.3270.3272.1279.4257.4268.7269.1268.654 m / s(m)Total (m)−10.3−11.2−12.2−11.2−9.4−2.1−24.1−12.8−12.4−12.9comparedwithComp.Ex. 10RatingGoodGoodGoodGoodGoodNGFairGoodGoodGoodFlightSpin rate2,9582,9582,9582,8483,0662,9582,9582,7402,6622,754W#1(rpm)HSTotal198.7199.2199.6198.9187.5197.5197.7201.9201.1200.040 m / s(m)Total (m)0.40.91.30.6−10.8−0.8−0.63.62.81.7comparedwithComp.Ex. 10RatingGoodGoodGoodGoodNGFairFairGoodGoodGoodFlightSpin rate5,1305,1305,1305,0085,5195,1305,1305,2295,4305,271I#6(rpm)HSTotal185.8185.5185.1186.1170.2182.6181.7185.0185.6183.242 m / s(m)Total (m)7.77.47.08.0−7.94.53.66.97.55.1comparedwithComp.Ex. 10RatingGoodGoodGoodGoodNGFairFairGoodGoodGoodFlightSpin rate5,0025,0025,0024,7625,2945,0024,9205,0995,2945,139I#6(rpm)HSTotal143.1144.2145.2143.5134.7143.4145.6145.3143.1143.935 m / s(m)Total (m)3.04.15.13.4−5.43.35.55.23.03.8comparedwithComp.Ex. 10RatingGoodGoodGoodGoodNGGoodGoodGoodGoodGoodApproachLaunch41.841.841.841.940.841.841.841.241.241.1(SW)angle (°)RatingGoodGoodGoodGoodGoodGoodGoodGoodGoodGoodEvaluation ofGoodGoodGoodGoodNGGoodGoodFairFairFairFeel at ImpactComparative Example789101112131415FlightSpin rate2,4792,8012,7942,7862,7942,5422,5452,9813,149W#1(rpm)HSTotal267.0271.5273.3281.5259.6276.1268.8269.3259.854 m / s(m)Total (m)−14.5−10.0−8.20.0−21.9−5.4−12.7−12.2−21.7comparedwithComp.Ex. 10RatingFairGoodNGNGFairNGGoodGoodFairFlightSpin rate2,6923,1773,1663,1543,1662,9122,9003,3723,629W#1(rpm)HSTotal198.1200.4199.5198.3198.6199.5200.4184.9179.040 m / s(m)Total (m)−0.22.11.20.00.31.22.1−13.4−19.3comparedwithComp.Ex. 10RatingFairGoodGoodGoodGoodGoodGoodNGNGFlightSpin rate5,1435,7805,7515,7215,7514,9485,0396,2496,354I#6(rpm)HSTotal184.3180.6181.3178.1177.2184.4186.6163.4167.142 m / s(m)Total (m)6.22.53.20.0−0.96.38.5−14.7−11.0comparedwithComp.Ex. 10RatingGoodFairFairFairNGGoodGoodNGNGFlightSpin rate4,9335,4485,4685,4875,4684,7244,8075,8816,067I#6(rpm)HSTotal144.8141.9139.8140.1142.3144.7146.0129.8131.135 m / s(m)Total (m)4.71.8−0.30.02.24.65.9−10.3−9.0comparedwithComp.Ex. 10RatingGoodFairFairFairFairGoodGoodNGNGApproachLaunch36.732.532.532.632.532.832.831.532.6(SW)angle (°)RatingGoodNGNGNGNGNGNGNGNGEvaluation ofFairNGNGNGNGFairFairNGNGFeel at Impact

[0247] As shown in the results in Table 9, the golf balls of Comparative Examples 1 to 15 are inferior in the following respects to the golf balls according to the present invention (Examples).

[0248] In Comparative Example 1, the dimple VR is smaller than 0.75%, and A1 is larger than 0.655. In addition, the initial velocity of the ball is lower than 75.0 m / s. Further, the value (hereinafter referred to as “D / B value”) obtained by dividing the total dimple volume D (mm3) by the deflection B (mm) of the ball under a load of 10 to 130 kgf is smaller than 95. As a result, the distance on shots with a driver (W #1) at a head speed (HS) of 40 m / s is inferior, and the distance on shots with a number six iron (I #6) is inferior. In addition, for the feel at impact, the sense of bounce is obviously not sufficient.

[0249] In Comparative Example 2, the dimple VR is smaller than 0.75%, and A1 is larger than 0.655. In addition, the D / B value is smaller than 95. As a result, the distance on shots with a driver (W #1) at a head speed (HS) of 54 m / s becomes long, and does not comply with the new ODS rules.

[0250] In Comparative Example 3, the dimple VR is larger than 0.89%. In addition, A1 is smaller than 0.590, and (A2+A3) / 2 is smaller than 0.670. As a result, the distance under striking conditions on shots with a driver (W #1) is inferior at head speeds (HS) of both 54 m / s and 40 m / s.

[0251] Comparative Example 4 is a golf ball having a three-piece structure without a surrounding layer, and the surface hardness of the intermediate layer-encased sphere is larger than the surface hardness of the core. As a result, regarding the feel at impact, the soft feeling is inferior to that of each Example.

[0252] Comparative Example 5 is a golf ball having a three-piece structure without a surrounding layer, and the surface hardness of the intermediate layer-encased sphere is larger than the surface hardness of the core. As a result, regarding the feel at impact, the soft feeling is inferior to that of each Example.

[0253] Comparative Example 6 is a golf ball having a two-piece structure including only a core and a cover. As a result, regarding the feel at impact, the soft feeling is inferior to that of each example.

[0254] Comparative Example 7 is a golf ball having a two-piece structure including only a core and a cover. In addition, the D / B value is smaller than 95. As a result, the distance on shots with a driver (W #1) at a head speed (HS) of 54 m / s is excessively reduced, and the distance on shots with a driver (W #1) at a head speed (HS) of 40 m / s is slightly inferior, so that the sense of bounce is not sufficient in the feel at impact.

[0255] Comparative Example 8 has a three-piece structure in which the ball surface hardness is softer than the surface hardness of the intermediate layer-encased sphere. In addition, the D / B value is larger than 140, and the surface hardness of the intermediate layer-encased sphere is harder than the core surface hardness. As a result, the distance on shots with an iron (I #6) was inferior, and the launch angle on approach shots was too low, so that the ball was difficult for an amateur. In addition, the soft feeling was inferior.

[0256] Comparative Example 9 has a three-piece structure in which the ball surface hardness is softer than the surface hardness of the intermediate layer-encased sphere. In addition, the D / B value is larger than 140, and the surface hardness of the intermediate layer-encased sphere is harder than the core surface hardness. As a result, the distance on shots with a driver (W #1) at a head speed (HS) of 54 m / s becomes long, and does not comply with the new ODS rules. In addition, the distance on shots with an iron (I #6) is inferior, and the launch angle on approach shots is too low, so that the ball is difficult for an amateur. Furthermore, the soft feeling is inferior.

[0257] Comparative Example 10 is an embodiment currently used by male professionals. The ball has a three-piece structure in which the ball surface hardness is smaller than the surface hardness of the intermediate layer-encased sphere. In addition, the dimple VR is smaller than 0.75%, and A1 is larger than 0.655. Furthermore, the surface hardness of the intermediate layer-encased sphere is harder than the core surface hardness. As a result, the distance on shots with a driver (W #1) at a head speed (HS) of 54 m / s was long, and did not comply with the new ODS rules. In addition, the distance on shots with a driver (W #1) at a head speed (HS) of 40 m / s and on shots with an iron (I #6) was inferior, and the launch angle on approach shots was too low, so that the ball was difficult for an amateur. Furthermore, the soft feeling was inferior.

[0258] Comparative Example 11 has a three-piece structure in which the ball surface hardness is softer than the surface hardness of the intermediate layer-encased sphere. Further, the dimple VR is larger than 0.89%, A1 is smaller than 0.590, and (A2+A3) / 2 is smaller than 0.670. Furthermore, the D / B value is larger than 140, and the surface hardness of the intermediate layer-encased sphere is harder than the core surface hardness. As a result, the distance on shots with a driver (W #1) at a head speed (HS) of 54 m / s is excessively reduced, and the distances on shots with a driver (W #1) at a head speed (HS) of 40 m / s and on shots with an iron (I #6) at a head speed (HS) of 42 m / s are inferior. In addition, since the launch angle on approach shots is too low, the ball became difficult for an amateur, and the soft feeling is inferior.

[0259] Comparative Example 12 has a three-piece structure in which the ball surface hardness is softer than the surface hardness of the intermediate layer-encased sphere. In addition, the dimple VR is smaller than 0.75%, and A1 is larger than 0.655. In addition, the value of D / B is smaller than 95, and the surface hardness of the intermediate layer-encased sphere is harder than the core surface hardness. As a result, the distance on shots with a driver (W #1) at a head speed (HS) of 54 m / s was excessively reduced, the launch angle on approach shots was too low, so that the ball became difficult for an amateur, and the soft feeling was not sufficient.

[0260] Comparative Example 13 has a three-piece structure in which the ball surface hardness is softer than the surface hardness of the intermediate layer-encased sphere. In addition, the surface hardness of the intermediate layer-encased sphere is harder than the core surface hardness. As a result, the launch angle on approach shots is too low, so that the ball becomes difficult for an amateur, and the soft feeling is inferior.

[0261] Comparative Example 14 has a three-piece structure in which the ball surface hardness is softer than the surface hardness of the intermediate layer-encased sphere. In addition, the dimple VR is smaller than 0.75%, and A1 is larger than 0.655. Furthermore, the initial velocity of the ball is lower than 75.0 m / s, and the surface hardness of the intermediate layer-encased sphere is harder than the core surface hardness. As a result, the distance on shots with a driver (W #1) at a head speed (HS) of 40 m / s and on shots with an iron (I #6) is inferior, and the launch angle on approach shots is too low, so that the ball is difficult for an amateur. In addition, the feel at impact is hard and the sense of bounce is not good.

[0262] Comparative Example 15 is a golf ball having a two-piece structure for a driving range, and has a ball initial velocity of less than 75.0 m / s. As a result, the actual initial velocity decreases under all the striking conditions. The distance on shots with a driver (W #1) at a head speed (HS) of 54 m / s is excessively decreased, and the distance decreases even under other striking conditions. In addition, as a game ball used in a round of golf, the launch angle on approach shots is too low, so that the ball is difficult for an amateur. In addition, the sense of bounce is not good in the feel at impact.

[0263] Japanese Patent Application No. 2024-047427 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.

Examples

examples

[0166]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.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This non-provisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2024-047427 filed in Japan on Mar. 25, 2024, the entire contents of which are hereby incorporated by reference.TECHNICAL FIELD

[0002] The present invention relates to a multi-piece solid golf ball that has a good flight and rises easily on approach shots by amateur users, and seeks to make the game of golf easy, while seeking to comply with new Overall Distance Standard (ODS) rules applicable from January 2028.BACKGROUND ART

[0003] In March 2022, manufacturers of golf balls were notified by the Royal and Ancient Golf Club of St Andrews (hereinafter, R&A) and the United States Golf Association (hereinafter, USGA) that they would start research to suppress a distance by the longest hitters by changing test conditions for the Overall Distance Standard (hereinafter, ODS) of golf balls in the future. Further, the R&A and the USGA specifically announced the following in December 2023.

[0004] “Club head speeds in ODS for rule compliance will be increased from the current 54 m / s to 56 m / s. That is, an influence of 13 to 15 yards (11.9 to 13.7 m) is predicted under striking conditions of the longest hitters.”

[0005] This test change is to be implemented from January 2028, but it is said that the current test conditions may be used until Jan. 1, 2030 for recreational golf, which is non-competitive.

[0006] Therefore, under the striking conditions of the longest hitters having a high head speed, a time is approaching when the ball as described above with a suppressed distance compared to the current ball is required. On the other hand, as a golf ball for amateur users, it is desired that even a ball in which the above-described distance is suppressed has as long a distance as possible under striking conditions at a head speed of amateur users. In addition, since it is difficult for the ball to rise on approach shots by an amateur user who is non-competitive, making it easy for the ball to rise on approach shots, that is, raising a launch angle, makes it easy for the ball to be regarded as “a ball that makes approach shots easy”. Moreover, while striking the ball softly, amateur users prefer a feel at impact with a sense of bounce and a sense that the ball will fly. It is desirable to develop a ball that satisfies all these characteristics simultaneously for amateur users.

[0007] In addition, in the past, some golf balls in which an initial velocity of the ball is set lower than that of a normal game ball have been proposed. Examples of such technical documents include the following Patent Documents 1 to 5.

[0008] However, each of the proposed golf balls is a practice ball for a driving range that is simply designed so as not to have a longer distance than the game ball. Therefore, in each of the above-mentioned Patent Documents, good distance performance on shots by amateur users, and the ball rising easily and the feel at impact on approach shots are not considered at all.

[0009] Further, Patent Documents 6 to 14 listed below each disclose a golf ball in which, as for dimples formed on the ball surface, 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, that is, a dimple volume occupancy ratio VR, is specified within a predetermined range, whereby a superior distance may be obtained in the low head speed (HS) range while reducing the distance in the high HS range.

[0010] However, with respect to the proposed golf balls, the reducing of the distance in the high head speed range is too great, and a distance on full shots by amateur users may not be satisfactory. Further, in each of the above Patent Documents, the ball rising easily and the feel at impact on approach shots are not considered at all.CITATION LISTPatent Document 1: JP-A 2012-228470

[0012] Patent Document 2: JP-A 2014-069045

[0013] Patent Document 3: JP-A 2013-138857

[0014] Patent Document 4: JP-A 2013-138839

[0015] Patent Document 5: JP-A 2013-138840

[0016] Patent Document 6: JP-A 2011-218160

[0017] Patent Document 7: JP-A 2011-218161

[0018] Patent Document 8: JP-A 2011-218162

[0019] Patent Document 9: JP-A 2011-240122

[0020] Patent Document 10: JP-A 2011-240123

[0021] Patent Document 11: JP-A 2011-240124

[0022] Patent Document 12: JP-A 2011-240125

[0023] Patent Document 13: JP-A 2011-240126

[0024] Patent Document 14: JP-A 2011-240127SUMMARY OF THE INVENTION

[0025] 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 for complying with new ODS rules applicable from January 2028, in which not only suppression of a distance on shots by the longest hitters is caused to at least a specific level, but also a distance on full shots with a driver (W #1) and an iron by amateur users may be favorably maintained without decreasing, and moreover, a launch angle on approach shots by amateur users becomes high, the ball rises easily, and there is a sense of bounce and a sense that the ball will fly in the feel at impact.

[0026] As a result of intensive studies to achieve the above object, the present inventor has found that in a multi-piece solid golf ball including a core, a surrounding layer, an intermediate layer, and a cover, in which a large number of dimples are formed on an outside surface of the cover, the core is formed of a rubber material, the surrounding layer, the intermediate layer, and the cover are formed of a resin material, a relationship between a surface hardness of each sphere of the ball, a surrounding layer-encased sphere, and an intermediate layer-encased sphere satisfies the following conditions (1-a) and (1-b):(surface hardness of ball)>(surface hardness of surrounding layer-encased sphere)   (1-a)(surface hardness of ball)>(surface hardness of intermediate layer-encased sphere)   (1-b)and a relationship between the surface hardness of each sphere of the core, the surrounding layer-encased sphere, and the intermediate layer-encased sphere satisfies at least one of the following conditions (2-a) or (2-b):(surface hardness of surrounding layer-encased sphere)<(surface hardness of core)   (2-a)(surface hardness of intermediate layer-encased sphere)<(surface hardness of core)   (2-b).Further, when an initial velocity of the ball is set to a range of from 75.0 to 77.724 m / s, a ratio CL1 / CD1 of a lift coefficient CL1 at a Reynolds number of 218,000 and a spin rate of 2,800 rpm to a drag coefficient CD1 is denoted by A1, a ratio CL2 / CD2 of a lift coefficient CL2 at a Reynolds number of 184,000 and a spin rate of 2,900 rpm to a drag coefficient CD2 is denoted by A2, and a ratio CL3 / CD3 of a lift coefficient CL3 at a Reynolds number of 158,000 and a spin rate of 3,100 rpm to a drag coefficient CD3 is denoted by A3, the following two conditions are satisfied:0.59≤A⁢1≤0.655 and(A⁢2+A⁢3) / 2≥0.67and when a volume occupancy ratio VR of the dimples is from 0.75 to 0.89%, a total volume of the dimples is denoted by D (mm3), and a deflection when the ball is compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) is denoted by B (mm), the following condition is satisfied:95≤D / B≤140.The present inventor has found that by designing the multi-piece solid golf ball so as to satisfy the conditions described above, new ODS rules may be complied with, that is, a suppression of a distance on shots by the longest hitters is caused to at least a specific level, a distance on full shots with a driver (W #1) and an iron by amateur users does not decrease, and conversely, the distance on full shots with a driver (W #1) and an iron by amateur users increases. In addition, the present inventor has found that in the above-described designed multi-piece solid golf ball, a launch angle of the ball is increased on approach shots by amateur users, the ball rises easily, the ball becomes a ball that is “easy on approach shots”, and further, on full shots by amateur users, the ball has a feel at impact that has softness, a sense of bounce, and a sense that the ball will fly, and has completed the present invention.The above “longest hitters” refers to golfers whose head speed on shots with a driver (W #1) is at least 50 m / s, and the above “non-competitive amateur golfers” refers to golfers who have a head speed with a driver (W #1) of not more than 45 m / s and a handicap of approximately 30 or more.Accordingly, the present invention provides a multi-piece solid golf ball includinga core, a single-layer or multiple-layer surrounding layer, a single-layer intermediate layer, and a single-layer cover, wherein a large number of dimples are formed on an outside surface of the cover, the core is formed of a rubber material, the surrounding layer, the intermediate layer, and the cover are formed of a resin material, a relationship between a surface hardness of each sphere of the ball, a surrounding layer-encased sphere, and an intermediate layer-encased sphere satisfies the following conditions (1-a) and (1-b):(surface hardness of ball)>(surface hardness of surrounding layer-encased sphere)   (1-a)(surface hardness of ball)>(surface hardness of intermediate layer-encased sphere)   (1-b)where hardness means Shore C hardness,and a relationship between the surface hardness of each sphere of the core, the surrounding layer-encased sphere, and the intermediate layer-encased sphere satisfies at least one of the following conditions (2-a) or (2-b):(surface hardness of surrounding layer-encased sphere)<(surface hardness of core)   (2-a)(surface hardness of intermediate layer-encased sphere)<(surface hardness of core)   (2-b)where hardness means Shore C hardness.Further, when an initial velocity of the ball is from 75.0 to 77.724 m / s, a ratio CL1 / CD1 of a lift coefficient CL1 at a Reynolds number of 218,000 and a spin rate of 2,800 rpm to a drag coefficient CD1 is denoted by A1, a ratio CL2 / CD2 of a lift coefficient CL2 at a Reynolds number of 184,000 and a spin rate of 2,900 rpm to a drag coefficient CD2 is denoted by A2, and a ratio CL3 / CD3 of a lift coefficient CL3 at a Reynolds number of 158,000 and a spin rate of 3,100 rpm to a drag coefficient CD3 is denoted by A3, the following two conditions are satisfied:0.59≤A⁢1≤0.655 and(A⁢2+A⁢3) / 2≥0.67.A further characteristic of the multi-piece solid golf ball is that when a volume occupancy ratio VR of the dimples is from 0.75 to 0.89%, a total volume of the dimples is denoted by D (mm3), and a deflection when the ball is compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) is denoted by B (mm), the following condition is satisfied:95≤D / B≤140.In a preferred embodiment of the multi-piece solid golf ball according to the invention, a value of A1 is from 0.590 to 0.613, a value of A2 is from 0.635 to 0.668, and a value of A3 is from 0.695 to 0.734.In another preferred embodiment of the inventive golf ball, a value of A1 is from 0.614 to 0.655, a value of A2 is from 0.669 to 0.750, and a value of A3 is from 0.735 to 0.815.In yet another preferred embodiment, a value of (A2+A3) / 2 is from 0.670 to 0.783.

[0042] In still another preferred embodiment, the cover is formed of an ionomer resin as a chief material.

[0043] In a further preferred embodiment, the relationship between the surface hardness of each sphere satisfies the following condition:(surface hardness of ball)>(surface hardness of intermediate layer-encased sphere)>(surface hardness of surrounding layer-encased sphere)<(surface hardness of core)where hardness means Shore C hardness.

[0045] In a yet further preferred embodiment, the core has a hardness profile in which, letting the Shore C hardness at a core center be Cc, the Shore C hardness at a midpoint M between the core center and a core surface be Cm, the Shore C hardnesses at positions 2 mm, 4 mm, and 6 mm inward from the midpoint M be Cm-2, Cm-4, and Cm-6 respectively, the Shore C hardnesses at positions 2 mm, 4 mm, and 6 mm outward from the midpoint M be Cm+2, Cm+4, and Cm+6 respectively, and the Shore C hardness at the core surface be Cs, and defining surface areas A to F as follows:surface⁢ area⁢ A:1 / 2×2×(Cm-4-Cm-6)surface⁢ area⁢ B:1 / 2×2×(Cm-2-Cm-4)surface⁢ area⁢ C:1 / 2×2×(Cm-Cm-2)surface⁢ area⁢ D:1 / 2×2×(Cm+2-Cm)surface⁢ area⁢ E:1 / 2×2×(Cm+4-Cm+2)surface⁢ area⁢ F:1 / 2×2×(Cm+6-Cm+4)the following condition is satisfied:{(surface⁢ area⁢ D+surface⁢ area⁢ E)-(surface⁢ area⁢ A+surface⁢ area⁢ B)}≥4..In a still further preferred embodiment, the core has a hardness profile in which the following condition is satisfied:(Cs-Cc)≥20.In another preferred embodiment, the core has a hardness profile in which the following condition is satisfied:(Cs-Cc) / (Cm-Cc)≥4..In yet another preferred embodiment, the core has a hardness profile in which the following condition is satisfied:surface area E >surface area D>surface area C.In still another preferred embodiment, the core is formed of a rubber composition containing the following components (A) to (D):(A) a base rubber,

[0052] (B) an organic peroxide,

[0053] (C) water or a monocarboxylic acid metal salt, and

[0054] (D) sulfur

[0055] Advantageous Effects of the Invention

[0056] The multi-piece solid golf ball according to the present invention is a golf ball which is intended to comply with new ODS rules applicable from January 2028, and may increase the distance on full shots with a driver (W #1) and an iron by amateur users while reducing the distance on shots with a driver by the longest hitters. In addition, with the golf ball of the present invention, the launch angle of the ball becomes high on approach shots by amateur users, the ball rises easily, and easiness can be felt on approach shots. Furthermore, the golf ball of the present invention has a feel at impact that combines softness and a sense that the ball will fly on full shots by amateur users.BRIEF DESCRIPTION OF THE DRAWINGS

[0057] FIG. 1 is a schematic cross-sectional view of a multi-piece solid golf ball (four-layer structure) of the present invention.

[0058] FIG. 2 is a graph that uses core hardness profile data in Example 1 to describe surface areas A to F in the core hardness profile.

[0059] FIG. 3 is a graph showing core hardness profiles in Examples 1 to 4 and Comparative Examples 1 to 5.

[0060] FIG. 4 is a graph showing core hardness profiles in Comparative Examples 6 to 15.

[0061] FIGS. 5A and 5B show an arrangement mode (pattern) of dimples (1) to (5) used in Examples 1 to 4 and Comparative Examples 1 to 15, where FIG. 5A shows a plan view of the dimples, and FIG. 5B shows a side view thereof.DETAILED DESCRIPTION OF THE INVENTION

[0062] Hereinafter, the present invention is described in more detail.

[0063] A multi-piece solid 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. A golf ball G illustrated in FIG. 1 has a single-layer core 1, a single-layer surrounding layer 2 encasing the core, a single-layer intermediate layer 3 encasing the surrounding layer, and a single-layer cover 4 encasing the intermediate layer. The cover 4 is positioned at the outermost layer in the layer construction of the golf ball except for the coating layer. Each layer of the core and the surrounding layer may be formed as a single layer as illustrated in FIG. 1 or a plurality of layers. A large number of dimples D are formed on a surface of the cover (outermost layer) 4 in order to obtain aerodynamic properties as intended properties of the present invention. In addition, although not particularly illustrated, the coating layer is typically formed on the surface of the cover 4. Hereinafter, each of the above layers is described in detail.

[0064] The core is obtained by vulcanizing a rubber composition containing a rubber material as a chief material. If the core material is not a rubber composition, a rebound of the core may become low, and a desired distance may not be attainable not only on shots by the longest hitters, but also on shots with a driver (W #1) and an iron by amateur users. The rubber composition typically contains a base rubber as the chief material, and is obtained with the inclusion of a co-crosslinking agent, a co-crosslinking initiator, an inert filler, an organosulfur compound, or the like.

[0065] In particular, the core is suitably formed of a rubber composition containing the following components (A) to (D):

[0066] (A) a base rubber,

[0067] (B) an organic peroxide,

[0068] (C) water or a monocarboxylic acid metal salt, and

[0069] (D) sulfur.

[0070] The base rubber (A) may include a diene rubber. Examples of the diene rubber include polybutadiene, natural rubber, isoprene rubber, and ethylene propylene diene rubber.

[0071] As the organic peroxide (B), an organic peroxide having a relatively high thermal decomposition temperature is suitably used. Specifically, a high-temperature organic peroxide having a one-minute half-life temperature of about 165 to 185° C. is used, and examples thereof include dialkyl peroxides. Examples of the dialkyl peroxides include a dicumyl peroxide (“Percumyl D” manufactured by NOF Corporation), a 2,5-dimethyl-2,5-di(t-butylperoxy) hexane (“Perhexa 25B” manufactured by NOF Corporation), and a di(2-t-butylperoxyisopropyl) benzene (“Perbutyl P” manufactured by NOF Corporation), and a dicumyl peroxide may be suitably used. These may be used singly, or two or more may be used in combination. The half-life is one of the indices representing a degree of a decomposition rate of the organic peroxide, and is indicated by a time required for the original organic peroxide to be decomposed and its active oxygen amount to reach 1 / 2. A vulcanization temperature in the core-forming rubber composition is typically within a range of 120 to 190° C., and in that range, an organic peroxide having a one-minute half-life temperature of a high temperature, which is about 165° C. to 185° C., is thermally decomposed relatively slowly. With the rubber composition used in the present invention, by adjusting an amount of free radicals produced, which increases with the lapse of a vulcanization time, it is possible to obtain a core that is a rubber cross-linked product having a specific internal hardness shape described later.

[0072] The water (C), although not particularly limited, may be distilled water or tap water, but it is particularly suitable to employ distilled water free of impurities. The compounding amount of the water included per 100 parts by weight of the base rubber is preferably at least 0.1 part by weight, and more preferably at least 0.2 part by weight, and an upper limit thereof is preferably not more than 2 parts by weight, and more preferably not more than 1 part by weight.

[0073] By blending the water or a material containing water as the component (C) directly into the core material, a decomposition of the organic peroxide during the core formulation may be promoted. In addition, it is known that the decomposition efficiency of the organic peroxide in the core-forming rubber composition changes depending on temperature, and the decomposition efficiency increases as the temperature becomes higher than a certain temperature. If the temperature is too high, the amount of decomposed radicals becomes too large, and the radicals are recombined or deactivated. As a result, fewer radicals act effectively in crosslinking. Here, when decomposition heat is generated by the decomposition of the organic peroxide at the time of core vulcanization, a temperature near the core surface is maintained at substantially the same level as a temperature of a vulcanization mold, but the temperature around the core center is considerably higher than the mold temperature due to an accumulation of decomposition heat by the organic peroxide decomposing from the outside. If the water or a material containing water is directly included in the core, the water acts to promote the decomposition of the organic peroxide, so that the radical reactions as described above can be changed at the core center and the core surface. That is, the decomposition of the organic peroxide is further promoted near the core center, and the deactivation of radicals is further promoted, so that the amount of active radicals is further reduced, and as a result, a core may be obtained in which the crosslink densities at the core center and the core surface differ markedly, and the dynamic viscoelasticity of the core center portion is different.

[0074] In addition, a monocarboxylic acid metal salt may be employed instead of the water. In the monocarboxylic acid metal salt, it is presumed that a carboxylic acid is coordinate-bonded to the metal salt, and the monocarboxylic acid metal salt is distinguished from a dicarboxylic acid metal salt such as zinc diacrylate, which is represented by a chemical formula [CH2=CHCOO]2Zn The monocarboxylic acid metal salt brings water into the rubber composition by a dehydration condensation reaction, so that the same effect as that of the water may be obtained. In addition, since the monocarboxylic acid metal salt may be blended into the rubber composition as a powder, a working process may be simplified, and it is easy to uniformly disperse the monocarboxylic acid metal salt in the rubber composition. In order to effectively perform the above reaction, it is necessary to use a mono-salt. A compounding amount of the monocarboxylic acid metal salt is preferably at least 1 part by weight, and more preferably at least 3 parts by weight per 100 parts by weight of the base rubber. As an upper limit thereof, the compounding amount of the monocarboxylic acid metal salt is preferably not more than 60 parts by weight, and more preferably not more than 50 parts by weight per 100 parts by weight of the base rubber. If the compounding amount of the monocarboxylic acid metal salt is too small, it is difficult to obtain an appropriate crosslinking density, and it may not be possible to obtain an adequate golf ball spin rate-lowering effect. In addition, if the compounding amount is too large, the core becomes too hard, so that it may be difficult to maintain an appropriate feel at impact.

[0075] As the carboxylic acid, an acrylic acid, a methacrylic acid, a maleic acid, a fumaric acid, a stearic acid, or the like may be used. Examples of a substitute metal include Na, K, Li, Zn, Cu, Mg, Ca, Co, Ni, and Pb, and Zn is preferably used. Specific examples thereof include a zinc monoacrylate and a zinc monomethacrylate, and it is particularly preferable to use a zinc monoacrylate.

[0076] Specific examples of the sulfur (D) include trade names “SANMIX S-80N” (manufactured by Sanshin Chemical Industry Co., Ltd.) and “SULFAX-5” (manufactured by Tsurumi Chemical Industry Co., Ltd.). A compounding amount of the sulfur may exceed 0, and may be preferably at least 0.005 parts by weight, and even more preferably at least 0.01 parts by weight per 100 parts by weight of the base rubber. In addition, an upper limit of the compounding amount is not particularly limited, although the upper limit may be preferably not more than 0.1 parts by weight, more preferably not more than 0.05 parts by weight, and even more preferably not more than 0.03 parts by weight. The addition of the sulfur may increase a difference in hardness of the core. If the compounding amount of the sulfur is too large, rebound may be greatly reduced, or a durability on repeated impact may worsen.

[0077] In the rubber composition, a co-crosslinking agent, a filler, an antioxidant, an organosulfur compound, and the like may be included as components other than the components (A) to (D).

[0078] The co-crosslinking agent is an α,β-unsaturated carboxylic acid and / or a metal salt thereof. Specific examples of the unsaturated carboxylic acid include acrylic acid, methacrylic acid, maleic acid, fumaric acid, or the like, and in particular, acrylic acid and methacrylic acid are suitably used. The metal salt of the unsaturated carboxylic acid is not particularly limited, and examples thereof include those obtained by neutralizing the unsaturated carboxylic acid with a desired metal ion. Specific examples thereof include zinc salts and magnesium salts such as methacrylic acid and acrylic acid, and in particular, zinc acrylate is suitably used.

[0079] The unsaturated carboxylic acid and / or the metal salt thereof is typically included in an amount of at least 5 parts by weight, preferably at least 9 parts by weight, and even more preferably at least 13 parts by weight, and an upper limit thereof is typically not more than 60 parts by weight, preferably not more than 50 parts by weight, and even 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, the core may become too hard, giving the ball an unpleasant feel at impact, and if the compounding amount is too small, rebound may become low.

[0080] 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 4 parts by weight, more preferably at least 8 parts by weight, and even more preferably at least 11 parts by weight per 100 parts by weight of the base rubber. In addition, an upper limit of the compounding amount is preferably not more than 50 parts by weight, more preferably not more than 40 parts by weight, and even more preferably not more than 35 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.

[0081] As an antioxidant, for example, commercially available products such as Nocrac NS-6, Nocrac NS-30, Nocrac NS-200, and Nocrac MB (all manufactured by Ouchi Shinko Chemical Industrial Co., Ltd.) may be employed. These may be used singly, or two or more may be used in combination.

[0082] The compounding amount of the antioxidant is not particularly limited, but is preferably 0.05 parts by weight or more, and more preferably 0.1 parts by weight or more, and the upper limit is preferably 1.0 part by weight or less, more preferably 0.7 parts by weight or less, and even more preferably 0.5 parts by weight or less per 100 parts by weight of the base rubber. If the compounding amount is too large or too small, a suitable core hardness gradient cannot be obtained, and it may not be possible to obtain suitable rebound, durability, and a spin rate-lowering effect on full shots.

[0083] The organosulfur compound may be included in order to control the rebound of the core so that it is increased. As the organosulfur compound, specifically, it is recommended to include thiophenol, thionaphthol, halogenated thiophenol, or a metal salt thereof. More specifically, examples of the organosulfur compound include zinc salts such as pentachlorothiophenol, pentafluorothiophenol, pentabromothiophenol, p-chlorothiophenol, and pentachlorothiophenol, and any of the following having 2 to 4 sulfur atoms: diphenylpolysulfide, dibenzylpolysulfide, dibenzoylpolysulfide, dibenzothiazoylpolysulfide, and dithiobenzoylpolysulfide. In particular, diphenyldisulfide and the zinc salt of pentachlorothiophenol is preferably used.

[0084] An upper limit of a compounding amount of the organosulfur compound is preferably not more than 5 parts by weight, more preferably not more than 4 parts by weight, even more preferably not more than 3 parts by weight, and most preferably not more than 2 parts by weight per 100 parts by weight of the base rubber. If the compounding amount is too large, the core hardness becomes too soft or the rebound of the core becomes too high, and the distance on shots with a driver by the longest hitters may be too long.

[0085] The core can be manufactured by vulcanizing and curing the rubber composition containing the above components. For example, a molded body can be manufactured by intensively mixing the rubber composition using a mixing apparatus such as a Banbury mixer or a roll mill, subsequently compression molding or injection molding the mixture using a core mold, and curing the resulting molded body by appropriately heating it at a temperature sufficient for the organic peroxide or the co-crosslinking agent to act, such as at a temperature of 100 to 200° C., and preferably at a temperature of 140 to 180° C., for 10 to 40 minutes.

[0086] In the present invention, the core is formed as a single layer or a plurality of layers, although it is preferably formed as a single layer. If a rubber core is produced as a plurality of layers of rubber, layer separation at an interface may arise when the ball is repeatedly struck, possibly leading to cracking at an earlier stage.

[0087] The diameter of the core is preferably at least 32.7 mm, more preferably at least 34.3 mm, and even more preferably at least 34.9 mm. The upper limit of the diameter of the core is preferably not more than 36.5 mm, more preferably not more than 36.1 mm, and even more preferably not more than 35.7 mm. If the diameter of the core is too small, an initial velocity of the ball may become too low, or a deflection of an entire ball may become small, a spin rate of the ball on full shots may increase, and the desired distance may not be attainable on full shots by amateur users. On the other hand, if the diameter of the core is too large, the spin rate on full shots increases, and the desired distance of amateur users may not be attainable, or a durability to cracking on repeated impact may worsen.

[0088] 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 3.6 mm, more preferably at least 4.0 mm, and even more preferably at least 4.3 mm, and the upper limit thereof is preferably not more than 5.5 mm, more preferably not more than 5.2 mm, and even more preferably not more than 4.9 mm. If the deflection of the core is too small, that is, if the core is too hard, the spin rate on full shots increases too much, the distance on shots with a driver (W #1) and an iron by amateur users may not be sufficiently increased, and the feel at impact may be too hard. On the other hand, if the deflection of the core is too large, that is, if the core is too soft, an actual initial velocity becomes too low, so that the distance on shots with a driver (W #1) by the longest hitters and amateur users may be too short, the sense of bounce and the sense that the ball will fly may be lost in the feel at impact, and the durability to cracking on repeated impact may become too poor.

[0089] 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.

[0090] A core center hardness (Cc) is preferably at least 50, more preferably at least 52, and even more preferably at least 54, and the upper limit is preferably not more than 62, more preferably not more than 59, and even more preferably not more than 56. If this value is too large, the spin rate of the ball on full shots may rise, the desired distance may not be attainable on shots with a driver (W #1) and an iron by amateur users, or the feel at impact may be too hard. On the other hand, if the above value is too small, the rebound becomes low, and the desired distance on shots by amateur users may not be attainable, the sense of bounce and the sense that the ball will fly may be lost in the feel at impact, or the durability to cracking on repeated impact may worsen.

[0091] A hardness (Cm-6) at a position 6 mm inward from a point M (hereinafter, also referred to as “midpoint M”) between the core center and the core surface is not particularly limited, although the hardness may be preferably at least 51, more preferably at least 53, and even more preferably at least 55, and the upper limit is also not particularly limited, and may be preferably not more than 63, more preferably not more than 60, and even more preferably not more than 57. Hardnesses that deviate from these values may lead to undesirable results similar to those described above for the core center hardness (Cc).

[0092] A hardness (Cm-4) at a position 4 mm inward from the midpoint M between the core center and the core surface is not particularly limited, although the hardness may be preferably at least 51, more preferably at least 53, and even more preferably at least 55, and the upper limit is also not particularly limited, and may be preferably not more than 63, more preferably not more than 60, and even more preferably not more than 57. Hardnesses that deviate from these values may lead to undesirable results similar to those described above for the core center hardness (Cc).

[0093] A hardness (Cm-2) at a position 2 mm inward from the midpoint M of the core is not particularly limited, although the hardness may be preferably at least 53, more preferably at least 55, and even more preferably at least 57. The upper limit is also not particularly limited, and may be preferably not more than 64, more preferably not more than 61, and even more preferably not more than 59. Hardnesses that deviate from these values may lead to undesirable results similar to those described above for the core center hardness (Cc).

[0094] Although not particularly limited, a cross-sectional hardness (Cm) at the midpoint M of the core may be preferably at least 54, more preferably at least 56, and even more preferably at least 58. In addition, the upper limit is not particularly limited, although the upper limit may be preferably not more than 66, more preferably not more than 63, and even more preferably not more than 60. Hardnesses that deviate from these values may lead to undesirable results similar to those described above for the core center hardness (Cc).

[0095] A core surface hardness (Cs) is preferably at least 70, more preferably at least 72, and even more preferably at least 74. The upper limit is preferably not more than 82, more preferably not more than 79, and even more preferably not more than 77. If this value is too large, the durability to cracking on repeated impact may worsen, or the feel at impact may be too hard. On the other hand, if the above value is too small, the rebound may become low, or the spin rate on full shots may rise, and the desired distance on shots with a driver (W #1) and an iron by amateur users may not be attainable.

[0096] A hardness (Cm+2) at a position 2 mm outward toward the core surface (hereinafter, simply referred to as “outward”) from the midpoint M of the core is not particularly limited, although the hardness may be preferably at least 59, more preferably at least 61, and even more preferably at least 63. The upper limit is also not particularly limited, and may be preferably not more than 70, more preferably not more than 67, and even more preferably not more than 65. Hardnesses that deviate from these values may lead to undesirable results similar to those described above for the core surface hardness (Cs).

[0097] A hardness (Cm+4) at a position 4 mm outward from the midpoint M of the core is not particularly limited, although the hardness may be preferably at least 63, more preferably at least 65, and even more preferably at least 67. The upper limit is also not particularly limited, and may be preferably not more than 74, more preferably not more than 72, and even more preferably not more than 70. Hardnesses that deviate from these values may lead to undesirable results similar to those described above for the core surface hardness (Cs).

[0098] A hardness (Cm+6) at a position 6 mm outward from the midpoint M of the core is not particularly limited, although the hardness may be preferably at least 64, more preferably at least 66, and even more preferably at least 68. The upper limit is also not particularly limited, and may be preferably not more than 75, more preferably not more than 73, and even more preferably not more than 71. Hardnesses that deviate from these values may lead to undesirable results similar to those described above for the core surface hardness (Cs).

[0099] A value obtained by subtracting the core center hardness from the core surface hardness, that is, the value of Cs−Cc, is preferably at least 18, more preferably at least 20, and even more preferably at least 21, and the upper limit thereof is preferably not more than 30, more preferably not more than 27, and even more preferably not more than 24. If this value is too small, the spin rate of the ball on full shots may rise, the desired distance may not be attainable on shots with a driver (W #1) and an iron by amateur users, or the feel at impact may be too hard. On the other hand, if this value is too large, the rebound may become low, the desired distance on shots with a driver (W #1) and an iron by amateur users may not be attainable, or the durability to cracking on repeated impact may worsen.

[0100] In addition, it is preferable to optimize the value of (Cs−Cc) / (Cm−Cc) for the core hardness profile. The value of (Cs−Cc) indicates a difference in hardness between the core center and the core surface, and a value of (Cm−Cc) indicates a difference in hardness between the core center and the midpoint between the core surface and the core center, and the above expression represents the ratio of these differences in hardness. The value of (Cs-Cc) / (Cm−Cc) is preferably at least 3.0, more preferably at least 3.5, and even more preferably at least 4.0, and an upper limit thereof is preferably not more than 30.0, more preferably not more than 20.0, and even more preferably not more than 10.0. If this value is too small, the spin rate of the ball on full shots may rise, and the desired distance may not be attainable on shots with a driver (W #1) and an iron by amateur users. On the other hand, if this value is too large, the rebound becomes low, an intended distance may not be attainable on shots with a driver (W #1) and an iron by amateur users, and the durability to cracking on repeated impact may worsen.

[0101] In the core hardness profile, the surface areas A to F defined as follows:surface⁢ area⁢ A:1 / 2×2×(Cm-4-Cm-6)surface⁢ area⁢ B:1 / 2×2×(Cm-2-Cm-4)surface⁢ area⁢ C:1 / 2×2×(Cm-Cm-2)surface⁢ area⁢ D:1 / 2×2×(Cm+2-Cm)surface⁢ area⁢ E:1 / 2×2×(Cm+4-Cm+2)surface⁢ area⁢ F:1 / 2×2×(Cm+6-Cm+4)are characterized in that a value of (surface area D+surface area E)−(surface area A+surface area B) is preferably at least 4.0, more preferably at least 4.5, and even more preferably at least 5.0, and the upper limit is preferably not more than 15.0, more preferably not more than 10.0, and even more preferably not more than 8.0. If this value is too small, the spin rate of the ball on full shots may rise, and the desired distance may not be attainable on shots with a driver (W #1) and an iron by amateur users. On the other hand, if this value is too large, the rebound may become low, the desired distance on shots with a driver (W #1) and an iron by amateur users may not be attainable, or the durability to cracking on repeated impact may worsen.

[0103] A value of (surface area D+surface area E)−(surface area B+surface area C) is preferably at least 3.5, more preferably at least 4.0, and even more preferably at least 4.5, and the upper limit is preferably not more than 15.0, more preferably not more than 10.0, and even more preferably not more than 7.0. If this value is too small, the spin rate of the ball on full shots may rise, and the desired distance may not be attainable on shots with a driver (W #1) and an iron by amateur users. On the other hand, if this value is too large, the rebound may become low, the desired distance on shots with a driver (W #1) and an iron by amateur users may not be attainable, or the durability to cracking on repeated impact may worsen.

[0104] In addition, a value of {(surface area D+surface area E)−(surface area A +surface area B)}×(Cs−Cc) is preferably at least 80, more preferably at least 90, and even more preferably at least 110, and the upper limit is preferably not more than 200, more preferably not more than 180, and even more preferably not more than 160. In addition, a value of {(surface area D+surface area E)−(surface area B+surface area C)}×(Cs−Cc) is preferably at least 70, more preferably at least 80, and even more preferably at least 95, and the upper limit is preferably not more than 200, more preferably not more than 180, and even more preferably not more than 140. In addition, if these values are too small, the spin rate of the ball on full shots may rise, and the desired distance may not be attainable on shots with a driver (W #1) and an iron by amateur users. On the other hand, if these values are too large, the rebound may become low, and the desired distance may not be attainable on shots with a driver (W #1) and an iron by amateur users, or the durability to cracking on repeated impact may worsen.

[0105] A relationship of each surface area calculated from the hardness profile is preferably surface area E>surface area C >surface area A, more preferably (surface area E+surface area F)>surface area D >surface area C >surface area A, and even more preferably (surface area E+surface area F)>surface area D >(surface area B+surface area C)>area A. If these relational expressions are not satisfied, the spin rate of the ball on full shots may rise, and the desired distance may not be attainable on shots with a driver (W #1) and an iron by amateur users.

[0106] FIG. 2 shows a graph describing the surface areas A to F using the core hardness profile data of Example 1. In this way, the surface areas A to F are surface areas of each triangle whose base is a difference between each specific distance and whose height is a difference in hardness between each position at these specific distances.

[0107] Next, the surrounding layer is described.

[0108] The surrounding layer is formed of a single layer or a plurality of layers. If the surrounding layer has a plurality of layers, a total thickness corresponds to the following thickness for the thickness of the surrounding layer, and an average hardness for a material hardness (sheet hardness) of the surrounding layer is taken as the material hardness.

[0109] Regarding surface hardness if the surrounding layer has a plurality of layers, a surface hardness of a layer-encased sphere of an outermost surrounding layer of the surrounding layer corresponds to the following surface hardnesses.

[0110] The surrounding layer has a material hardness on the Shore C hardness scale which, although not particularly limited, is preferably at least 43, more preferably at least 50, and even more preferably at least 57, and the upper limit is preferably not more than 83, more preferably not more than 76, and even more preferably not more than 70. The surface hardness on the Shore D hardness scale is preferably at least 25, more preferably at least 30, and even more preferably at least 35, and the upper limit is preferably not more than 55, more preferably not more than 50, and even more preferably not more than 45.

[0111] The surface hardness of the surrounding layer-encased sphere in which the core is encased with the surrounding layer is preferably at least 51, more preferably at least 58, and even more preferably at least 65, and the upper limit thereof is preferably not more than 91, more preferably not more than 84, and even more preferably not more than 78 on the Shore C hardness scale. The surface hardness on the Shore D hardness scale is preferably at least 31, more preferably at least 36, and even more preferably at least 41, and the upper limit is preferably not more than 61, more preferably not more than 56, and even more preferably not more than 51.

[0112] If the material hardness and the surface hardness of the surrounding layer are too soft in comparison with the above ranges, the spin rate of the ball on full shots may rise, and the distance on shots with a driver (W #1) and an iron by amateur users may not be increased. In addition, the durability to cracking on repeated impact may worsen. On the other hand, if the material hardness and the surface hardness of the surrounding layer are too hard in comparison with the above ranges, the feel at impact may become too hard for a soft feeling to be felt, and the distance on shots by the longest hitters may be too long.

[0113] The surrounding layer has a thickness that is preferably at least 0.8 mm, more preferably at least 1.0 mm, and even more preferably at least 1.2 mm. On the other hand, the thickness of the surrounding layer has an upper limit that is preferably not more than 1.5 mm, more preferably not more than 1.4 mm, and even more preferably not more than 1.3 mm. If the surrounding layer is too thin, it may not be possible for a soft feeling to be felt on full shots by amateur users, or molding becomes difficult and mass productivity may deteriorate. On the other hand, if the surrounding layer is too thick, the rebound becomes low or the spin rate increases, so that it may be difficult for the distance on full shots by amateur users to increase.

[0114] The material of the surrounding layer is not particularly limited, and a known resin material may be used. Specifically, one or more of ionomer resins, and of thermoplastic elastomers selected from the group consisting of urethane-based, amide-based, ester-based, olefin-based, and styrene-based elastomers may be used. In the present invention, since high rebound is obtained in a desired hardness range, an ester-based thermoplastic elastomer, particularly a thermoplastic polyether ester elastomer, may be suitably used.

[0115] Next, the intermediate layer is described.

[0116] The intermediate layer has a material hardness on the Shore C hardness scale which, although not particularly limited, is preferably at least 71, more preferably at least 78, and even more preferably at least 84, and the upper limit is preferably not more than 95, more preferably not more than 92, and even more preferably not more than 90. The material hardness on the Shore D hardness scale is preferably at least 46, more preferably at least 50, and even more preferably at least 53, and the upper limit is preferably not more than 61, more preferably not more than 60, and even more preferably not more than 59.

[0117] The intermediate layer-encased sphere obtained by encasing the core with the surrounding layer and the intermediate layer has a surface hardness on the Shore C hardness scale which is preferably at least 80, more preferably at least 85, and even more preferably at least 90. The upper limit is preferably not more than 96, more preferably not more than 95, and even more preferably not more than 94. The surface hardness on the Shore D hardness scale is preferably at least 52, more preferably at least 56, and even more preferably at least 59, and the upper limit is preferably not more than 67, more preferably not more than 65, and even more preferably not more than 63.

[0118] If the material hardness and the surface hardness of the intermediate layer are too soft in comparison with the above ranges, the spin rate of the ball on full shots may rise, and the distance on shots with a driver (W #1) and an iron by amateur users may not be increased. In addition, the launch angle on approach shots may become low, and the ball may be felt to be difficult to handle for amateur users. On the other hand, if the material hardness and the surface hardness of the intermediate layer are too hard in comparison with the above ranges, the feel at impact may be too hard, the durability to cracking on repeated impact may worsen, or the distance on shots by the longest hitters may be too long.

[0119] The intermediate layer has a thickness that is preferably at least 0.8 mm, more preferably at least 1.0 mm, and even more preferably at least 1.2 mm. On the other hand, the intermediate layer thickness has an upper limit that is preferably not more than 1.5 mm, more preferably not more than 1.4 mm, and even more preferably not more than 1.35 mm. If the intermediate layer is too thin, the durability to cracking on repeated impact may worsen, or molding becomes difficult and mass productivity may deteriorate. On the other hand, if the intermediate layer is too thick, the feel at impact may be too hard, the rebound may become low, and it may be difficult for the distance on shots by amateur users to increase. In addition, if the intermediate layer thickness deviates from the above ranges, the spin rate on full shots may increase, and a good distance may not be attainable on shots by amateur users.

[0120] As a material of the intermediate layer, a resin material containing an ionomer resin as a chief material is used, and particularly among ionomer resins, a highly neutralized ionomer is suitably used. As the highly neutralized ionomer, a commercially available product may be used, and examples thereof include “HPF 1000”, “HPF 2000”, “HPF AD1035”, and “HPF AD1040” (all manufactured by the Dow Chemical Company). By adopting the highly neutralized ionomer, the rebound of the ball is increased while reducing the spin rate of the ball on full shots, and a good distance may be reliably obtained on full shots by amateur users. In order to adjust a desired material hardness and the like of the intermediate layer, the highly neutralized ionomer may be appropriately blended with a general ionomer.

[0121] Next, the cover is described.

[0122] The cover has a material hardness on the Shore C hardness scale which, although not particularly limited, is preferably at least 83, more preferably at least 89, and even more preferably at least 93, and the upper limit is preferably not more than 100, more preferably not more than 97, and even more preferably not more than 95. The material hardness on the Shore D hardness scale is preferably at least 55, more preferably at least 60, and even more preferably at least 63, and the upper limit is preferably not more than 75, more preferably not more than 70, and even more preferably not more than 68.

[0123] The surface hardness of the ball (whole sphere) including the core and the cover is preferably at least 90, more preferably at least 93, and even more preferably at least 95, and the upper limit thereof is preferably not more than 100, more preferably not more than 99, and even more preferably not more than 98 on the Shore C hardness scale. The surface hardness on the Shore D hardness scale is preferably at least 62, more preferably at least 67, and even more preferably at least 69, and the upper limit is preferably not more than 76, more preferably not more than 74, and even more preferably not more than 72.

[0124] If the material hardness and the surface hardness of the cover are too soft in comparison with the above ranges, the spin rate may rise on full shots, and the distance on shots with a driver (W #1) and an iron by amateur users may not be increased. In addition, the launch angle on approach shots may become low, and the ball may be felt to be difficult to handle for amateur users. On the other hand, if the material hardness and the surface hardness of the cover are too hard in comparison with the above ranges, the feel at impact may become too hard, the durability to cracking on repeated impact may worsen, and the distance on shots by the longest hitters may become too long.

[0125] The cover has a thickness of preferably at least 0.8 mm, more preferably at least 1.0 mm, and even more preferably at least 1.2 mm. On the other hand, the upper limit of the cover thickness is preferably not more than 1.5 mm, more preferably not more than 1.4 mm, and even more preferably not more than 1.35 mm. If the cover is too thin, the durability to cracking on repeated impact may worsen, or it may be difficult to mold the cover and mass productivity may deteriorate. On the other hand, if the cover is too thick, the feel at impact may be too hard, the rebound may become low, and it may be difficult for the distance on shots by amateur users to increase. In addition, if the cover thickness deviates from the above ranges, the spin rate on full shots may increase, and a good distance may not be attainable on shots by amateur users.

[0126] As a material of the cover, a resin material containing an ionomer resin as a chief material is used. If a urethane material, which is not a hard material, is used as the cover material, the launch angle on approach shots is lowered and the ball may be felt to be difficult to handle for amateur users. In addition, even if a material having the hardest grade among types of urethane materials is selected, the rebound is lower than that of an ionomer material having the same hardness, and the distance on shots by amateur users may not reach a target. In addition, when the cover is formed, from the viewpoint of mass productivity, it is preferable to adopt a method of encasing the intermediate layer-encased sphere with the cover by injection molding.

[0127] The resin material containing an ionomer resin as a chief material is used, but at that time, an aspect that uses in admixture a zinc-neutralized ionomer resin and a sodium-neutralized ionomer as chief materials 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 20 / 80 to 90 / 10, and more preferably from 25 / 75 to 75 / 25. 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, 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.

[0128] Various additives may be blended in the cover material as necessary, and for example, a pigment, a dispersant, an antioxidant, a light stabilizer, an ultraviolet absorber, an internal mold lubricant, and the like may be appropriately blended.

[0129] 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 an injection mold to obtain the surrounding layer-encased sphere and the intermediate layer-encased sphere, and finally, the cover material, which is the outermost layer, is injection molded to obtain the multi-piece golf ball. In addition, it is also possible to produce a golf ball by preparing two half-cups pre-molded into hemispherical shapes, enclosing the core and the intermediate layer-encased sphere within the two half cups, and molding the core and the intermediate layer-encased sphere under applied heat and pressure.

[0130] The golf ball has a deflection (mm) when compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) which is preferably at least 2.5 mm, more preferably at least 2.8 mm, and even more preferably at least 3.0 mm. An upper limit of the deflection is preferably not more than 3.8 mm, more preferably not more than 3.5 mm, and even more preferably not more than 3.3 mm. If the deflection of the golf ball is too small, the spin rate of the ball on full shots increases excessively, and the distance on shots with a driver (W #1) and an iron by amateur users may not be increased, or the feel at impact may be too hard. On the other hand, if the deflection is too large, the actual initial velocity becomes too low, so that the distance on shots with a driver (W #1) by the longest hitters and amateur users may be too short, the feel at impact may be too soft, or the durability to cracking on repeated impact may become too poor.

[0131] The initial velocity of the ball is preferably at least 75.0 m / s, more preferably at least 76.5 m / s, and even more preferably at least 77.0 m / s. An upper limit thereof is not more than 77.724 m / s. If this initial velocity value is too high, the official rules of R&A and USGA are not satisfied. On the other hand, if the initial velocity is too low, the actual initial velocity may become low and the desired distance may not be attainable under all striking conditions on full shots. The value of the initial velocity in this case is a numerical value measured by a device for measuring a coefficient of restitution (COR) (Golf Ball Testing Machine) of the same type as the R&A. Specifically, a device for measuring a COR manufactured by Hye Precision USA is used. As a condition, at the time of measurement, an air pressure is changed in four stages and measured, a relational expression between the incident velocity and the COR is constructed, and the initial velocity at an incident velocity of 43.83 m / s is determined from the relational expression. For a measurement environment of the device for measuring a COR, a ball temperature-controlled for at least three hours in a thermostatic bath adjusted to 23.9±1° C. is used, and measurement is performed at a room temperature of 23.9±2° C. In addition, a barrel diameter is selected such that a clearance on one side with respect to an outer diameter of the object being measured is from 0.2 to 2.0 mm.

[0132] A value obtained by dividing the initial velocity of the ball by the deflection of the ball is preferably at least 19, more preferably at least 21, and even more preferably at least 23, and the upper limit is preferably not more than 30, more preferably not more than 28, and even more preferably not more than 26. This value has a meaning of measuring a magnitude of the actual initial velocity of the ball. If this value is too large, the distance on shots by the longest hitters becomes too long, and it may be impossible to comply with new ODS rules. On the other hand, if this value is too small, the spin rate of the ball on full shots increases, or the actual initial velocity may become low, and the desired distance may not be attainable under all striking conditions.

[0133] A total thickness of the cover and the intermediate layer is preferably at least 2.0 mm, more preferably at least 2.2 mm, and even more preferably at least 2.4 mm. On the other hand, the upper limit of the total thickness is preferably not more than 3.8 mm, more preferably not more than 3.0 mm, and even more preferably not more than 2.7 mm. If the total thickness is too thin, the durability to cracking on repeated impact may worsen, it may be difficult to mold the intermediate layer and the cover, and as a result, mass productivity of balls may deteriorate. On the other hand, if the total thickness is too thick, the feel at impact may be too hard, the rebound may become low, and it may be difficult for the distance on shots by amateur users to increase. In addition, if the total thickness deviates from the above ranges, the spin rate on full shots may increase, and a good distance may not be attainable on shots by amateur users.

[0134] A total thickness of the cover, the intermediate layer, and the surrounding layer is preferably at least 3.1 mm, more preferably at least 3.3 mm, and even more preferably at least 3.5 mm. On the other hand, the upper limit of the total thickness is preferably not more than 5.0 mm, more preferably not more than 4.2 mm, and even more preferably not more than 3.9 mm. A total thickness that deviates from the above ranges may lead to undesirable results similar to those described for the total thickness of the cover and the intermediate layer.[Relationships Between Surface Hardnesses of Each Sphere]

[0135] In the present invention, a relationship between the surface hardness of each sphere of the ball, the surrounding layer-encased sphere, and the intermediate layer-encased sphere satisfies the following expressions (1-a) and (1-b):(surface⁢ hardness⁢ of⁢ ball)>(surface⁢ hardness⁢ of⁢ surrounding⁢ layer-encased⁢ sphere)(1-a)(surface⁢ hardness⁢ of⁢ ball)>(surface⁢ hardness⁢ of⁢ intermediate⁢ layer-encased⁢ sphere)(1-b)and it is necessary that a relationship between the surface hardness of each sphere of the core, the surrounding layer-encased sphere, and the intermediate layer-encased sphere satisfies at least one of the following conditions (2-a) or (2-b):(surface⁢ hardness⁢ of⁢ surrounding⁢ layer-encased⁢ sphere)<(surface⁢ hardness⁢ of⁢ core(2-a)(surface⁢ hardness⁢ of⁢ intermediate⁢ layer-encased⁢ sphere)<(surface⁢ hardness⁢ of⁢ core).(2-b)Surface hardness in the above conditions means Shore C hardness. If the surface hardness of the ball is softer than the surface hardness of the inner layers, the launch angle on approach shots by amateur users may become low, and the ball may be difficult for amateur users. In addition, the softer surface hardness among the surface hardnesses of the intermediate layer-encased sphere and the surrounding layer-encased sphere is required to be lower than the core surface hardness. If this hardness relationship is not satisfied, it may be difficult to achieve both a soft feel at impact on full shots and a feel at impact with a sense of bounce and a sense that the ball will fly.

[0138] A more preferable aspect of the above hardness relationship satisfies the following condition:

[0139] (surface hardness of ball)>(surface hardness of intermediate layer-encased sphere)>(surface hardness of surrounding layer-encased sphere). If this hardness relationship is not satisfied, it may be impossible to achieve both an easy rising of the ball and a good feel at impact on approach shots by amateur users, and good durability on repeated impact.

[0140] The most suitable hardness relationship in the present invention satisfies the following condition:(surface hardness of ball)>(surface hardness of intermediate layer-encased sphere)>(surface hardness of surrounding layer-encased sphere)<(surface hardness of core).

[0141] Expressed on the Shore C hardness scale, a value obtained by subtracting the surface hardness of the intermediate layer-encased sphere from the surface hardness of the ball is preferably larger than 0, more preferably at least 2, and even more preferably at least 4. An upper limit thereof is preferably not more than 25, more preferably not more than 15, and even more preferably not more than 10. If the above value is too small, the spin rate on full shots may rise, and the intended distance may not be attainable on full shots with a driver (W #1) and an iron by amateur users, or the launch angle on approach shots becomes lower, and approach shots may be felt to be difficult to handle for amateur users. If the above value is too large, the durability to cracking on repeated impact may worsen, the actual initial velocity may become lower, and all distances on shots with a driver (W #1) may be shorter than the desired distance.

[0142] 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 larger than 0, more preferably at least 10, and even more preferably at least 20, and an upper limit thereof is preferably not more than 40, more preferably not more than 32, and even more preferably not more than 25. If this value is too large, the durability to cracking on repeated impact may worsen, the spin rate may rise and the actual initial velocity may be lowered on full shots, and all distances on shots with a driver (W #1) may be shorter than the desired distance.

[0143] A value obtained by subtracting the surface hardness of the surrounding layer-encased sphere from the surface hardness of the core is preferably larger than 0, more preferably at least 2, and even more preferably at least 4, and the upper limit is preferably not more than 12, more preferably not more than 9, and even more preferably not more than 6. In addition, 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 8, more preferably at least 12, and even more preferably at least 15, and an upper limit thereof is preferably not more than 30, more preferably not more than 25, and even more preferably not more than 20. If these values are too large, a soft feeling on full shots may not be felt. On the other hand, if these values are too small, the spin rate on full shots may rise, and the intended distance may not be attainable on full shots with a driver (W #1) and an iron by amateur users.

[0144] 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 10, more preferably at least 13, and even more preferably at least 18, and an upper limit thereof is preferably not more than 35, more preferably not more than 30, and even more preferably not more than 25. 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 30, more preferably at least 35, and even more preferably at least 40, and an upper limit thereof is preferably not more than 55, more preferably not more than 50, and even more preferably not more than 45. If these values are too large, the durability to cracking on repeated impact may worsen, the actual initial velocity may become lower, and all distances on shots with a driver (W #1) may be shorter than the desired distance. On the other hand, if these values are too small, the spin rate of the ball on full shots may rise, and the desired distance may not be attainable on shots with a driver (W #1) and an iron by amateur users.[Relationship between Deflection of Core and Ball]

[0145] Letting each deflection (mm) when each sphere of the core and the ball is compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) be C (mm) and B (mm) respectively, a value of C-B is preferably at least 1.00 mm, more preferably at least 1.20 mm, and even more preferably at least 1.40 mm, and an upper limit thereof is preferably not more than 2.00 mm, more preferably not more than 1.80 mm, and even more preferably not more than 1.60 mm. In addition, a value of C / B is preferably at least 1.20, more preferably at least 1.30, and even more preferably at least 1.40, and the upper limit thereof is preferably not more than 1.60, more preferably not more than 1.55, and even more preferably not more than 1.50. If these values are too large, the durability to cracking on repeated impact may worsen, the actual initial velocity becomes lower, and all distances on shots with a driver (W #1) may be shorter than the desired distance. Alternatively, on full shots, a core may not be felt and the sense that the ball will fly may not be felt. On the other hand, if these values are too small, the spin rate on full shots may increase, the desired distance on shots with a driver (W #1) and an iron by amateur users may not be attainable, or a soft feel at impact may not be felt.[Core Diameter and Ball Diameter]

[0146] A relationship between the core diameter and the ball diameter, that is, a value of (core diameter) / (ball diameter) is preferably at least 0.766, more preferably at least 0.803, and even more preferably at least 0.817. On the other hand, an upper limit thereof is preferably not more than 0.855, more preferably not more than 0.845, and even more preferably not more than 0.836. If this value is too small, the initial velocity of the ball becomes low, or the deflection of the entire ball becomes small and the ball becomes hard, the spin rate of the ball on full shots increases, and the desired distance on full shots by amateur users may not be attainable. On the other hand, if the above value is too large, the spin rate of the ball on full shots increases, the desired distance on full shots by amateur users may not be attainable, and the durability to cracking on repeated impact may worsen.

[0147] Numerous dimples may be formed on the outside surface of the cover. Although not particularly limited, the number of dimples arranged on the surface of the cover is preferably at least 280, preferably at least 300, and more preferably at least 310, and the upper limit thereof can be preferably not more than 450, more preferably not more than 400, and even more preferably not more than 350. If the number of dimples deviates from the above ranges, the distance on shots with a driver (W #1) by amateur users may be decreased.

[0148] 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 can 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 can be 0.08 mm or more and 0.30 mm or less.

[0149] A dimple coverage ratio of the dimples on the spherical surface of the golf ball, specifically, a ratio (surface area coverage ratio, hereinafter, 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 preferable at least 75%, more preferably at least 80%, and even more preferably at least 84%. The upper limit is not more than 90%, more preferably not more than 88%, and even more preferably not more than 86%. If the SR value deviates from the above ranges, the distance on shots with a driver (W #1) by amateur users may be decreased.

[0150] A VR value of a sum of volumes of the individual dimples formed below the flat plane circumscribed by the edge of the dimple to a ball spherical volume on the assumption that the ball has no dimples is at least 0.75%, preferably at least 0.78%, and more preferably at least 0.80%. An upper limit thereof is not more than 0.89%, more preferably not more than 0.88%, and even more preferably not more than 0.86%. If this VR value is larger than the above ranges, the distance on shots with a driver (W #1) by the longest hitters may be too short, or the intended distance on shots with a driver (W #1) by amateur users may not be attainable. In addition, in this case, a ball trajectory may become lower, it becomes difficult to carry, and it may become difficult to go over a valley or a pond. On the other hand, if the above value is too small, the distance on shots with a driver (W #1) by the longest hitters does not decrease, and the ball may fly too much further than an upper limit distance of the new ODS rules.

[0151] A total volume of the dimples means a sum of volumes of the individual dimples formed below the flat plane circumscribed by the edge of the dimples in all the dimples formed in one ball. The total dimple volume is not particularly limited, although the total dimple volume is preferably at least 306 mm3, more preferably at least 318 mm3, and even more preferably at least 326 mm3, and the upper limit thereof is preferably not more than 363 mm3, more preferably not more than 359 mm3, and even more preferably not more than 351 mm3. If this total dimple volume is larger than the above ranges, the distance on shots with a driver (W #1) by the longest hitters may be too short, or the intended distance on shots with a driver (W #1) by amateur users may not be attainable. In addition, in this case, a ball trajectory may become lower, it becomes difficult to carry, and it may become difficult to go over a valley or a pond. On the other hand, if the above value is too small, the distance on shots with a driver (W #1) by the longest hitters does not decrease, and the ball may fly too much further than an upper limit distance of the new ODS rules.

[0152] A value V0 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 preferably at least 0.35, more preferably at least 0.38, and further preferably at least 0.40. The upper limit is not more than 0.80, more preferably not more than 0.70, and even more preferably not more than 0.60. If the V0 value deviates from the above ranges, the distance on shots with a driver (W #1) by the longest hitters and amateur users may be shorter than the intended distance.

[0153] In the golf ball of the present invention, when a ratio (CL1 / CD1) of a lift coefficient CL1 at a Reynolds number of 218000 and a spin rate of 2800 rpm to a drag coefficient CD1 is denoted by A1, a ratio (CL2 / CD2) of a lift coefficient CL2 at a Reynolds number of 184000 and a spin rate of 2900 rpm to a drag coefficient CD2 is denoted by A2, and a ratio (CL3 / CD3) of a lift coefficient CL3 at a Reynolds number of 158000 and a spin rate of 3100 rpm to a drag coefficient CD3 is denoted by A3, the dimples are designed to satisfy the following two conditions:0.59≤A⁢1≤0.6⁢55⁢and⁢(A⁢2+A⁢3) / 2≥0.6⁢7⁢0.

[0154] In the present specification, the “lift coefficients (CL1, CL2, CL3), drag coefficients (CD1, CD2, CD3)” are measured in accordance with the Indoor Test Range (ITR) defined by the USGA (United States Golf Association). The lift coefficients and the drag coefficients can be adjusted by adjusting the configuration of the dimples of the golf ball (arrangement, diameter, depth, volume, number, shape, and the like). The lift coefficients and the drag coefficients are independent of the internal configuration of the golf ball. The Reynolds number (Re) is a dimensionless number used in the field of hydrodynamics. The Reynolds number (Re) is calculated by the following equation (1).Re=ρ⁢vL / μ(1)

[0155] In Equation (1) above, p represents the density of a fluid, v represents the average velocity of an object relative to the flow of the fluid, L represents a characteristic length, and μ represents the viscosity coefficient of the fluid.

[0156] In the present invention, when a ratio CL1 / CD1 of a lift coefficient CL1 at a Reynolds number of 218000 and a spin rate of 2800 rpm to a drag coefficient CD1 is defined as A1, a ratio CL2 / CD2 of a lift coefficient CL2 at a Reynolds number of 184000 and a spin rate of 2900 rpm to a drag coefficient CD2 is defined as A2, and a ratio CL3 / CD3 of a lift coefficient CL3 at a Reynolds number of 158000 and a spin rate of 3100 rpm to a drag coefficient CD3 is defined as A3.

[0157] If a condition of the Reynolds number 218,000 and the spin rate 2,800 rpm under which the lift coefficient CL1 and the drag coefficient CD1 are measured is described, this high-speed condition corresponds to a condition provided by the longest hitters with a driver (W #1), this Reynolds number corresponds to a ball speed when the golf ball is driven out at a head speed (HS) of 54 m / s, and the spin rate 2,800 rpm is an average spin condition of a player with a head speed (HS) of 54 m / s.

[0158] If a condition of the Reynolds number 184,000 and the spin rate 2,900 rpm under which the lift coefficient CL2 and the drag coefficient CD2 are measured is described, this middle-speed condition corresponds to a condition provided by an amateur user with a driver (W #1) at a head speed (HS) of 45 m / s, this Reynolds number corresponds to the ball speed when the golf ball is driven out at a head speed (HS) of 45 m / s, and the spin rate 2,900 rpm is an average spin condition of a player with a head speed (HS) of 45 m / s.

[0159] If a condition of the Reynolds number 158,000 and the spin rate 3,100 rpm under which the lift coefficient CL3 and the drag coefficient CD3 are measured is described, this low-speed condition corresponds to a condition provided by an amateur user with a driver (W #1) at a head speed (HS) of 40 m / s, this Reynolds number corresponds to the ball speed when the golf ball is driven out at a head speed (HS) of 40 m / s, and the spin rate 3,100 rpm is an average spin condition of a player with a head speed (HS) of 40 m / s.

[0160] The ratio between the lift coefficient CL1 and the drag coefficient CD1, that is, the value of CL1 / CD1=A1 is at least 0.590, preferably at least 0.595, and more preferably at least 0.600, and an upper limit thereof is not more than 0.655, preferably not more than 0.640, and more preferably not more than 0.627. If this value is too large, the distance on shots with a driver (W #1) by the longest hitters does not decrease, and the ball may fly too much further than the upper limit distance of the new ODS rules. On the other hand, if the above value is too small, the distance may be too much shorter than the intended distance under all striking conditions.

[0161] When the value of A1 is from 0.590 to 0.613, the ratio between the lift coefficient CL2 and the drag coefficient CD2, that is, a value of CL2 / CD2=A2, is preferably at least 0.635, more preferably at least 0.645, and even more preferably at least 0.655, and an upper limit thereof is preferably not more than 0.668, more preferably not more than 0.666, and even more preferably not more than 0.664. When the value of A1 is from 0.614 to 0.655, the value of A2 is preferably at least 0.669, more preferably at least 0.671, and even more preferably at least 0.673, and an upper limit thereof is preferably not more than 0.750, more preferably not more than 0.725, and even more preferably not more than 0.700. If the above value deviates from the above ranges, under all striking conditions, the ball may blow up or the distance may not increase, there may be a trajectory in which the ball does not carry, and an intended total distance may not be attainable.

[0162] When the value of A1 is from 0.590 to 0.613, the ratio between the lift coefficient CL3 and the drag coefficient CD3, that is, a value of CL3 / CD3=A3, is preferably at least 0.695, more preferably at least 0.705, and even more preferably at least 0.715, and an upper limit thereof is preferably not more than 0.734, more preferably not more than 0.731, and even more preferably not more than 0.728. In addition, when the value of A1 is from 0.614 to 0.655, the value of A3 is preferably at least 0.735, more preferably at least 0.738, and even more preferably at least 0.741, and an upper limit thereof is preferably not more than 0.815, more preferably not more than 0.780, and even more preferably not more than 0.760. If the above value deviates from the above ranges, under all striking conditions, the ball may blow up or the distance may not increase, there may be a trajectory in which the ball does not carry, and an intended total distance may not be attainable.

[0163] The average value of the above A2 and A3, that is, the value of (A2+A3) / 2 is at least 0.670, preferably at least 0.680, and more preferably at least 0.690, and an upper limit thereof is preferably not more than 0.783, more preferably not more than 0.775, and even more preferably not more than 0.765. If this value is too low, it becomes difficult for the ball to carry on shots with a driver (W #1) by amateur users, and the intended total distance may not be attainable. On the other hand, if the above value is too high, the ball trajectory may be blown up on shots with a driver (W #1) by amateur users, and the intended distance may not be attainable.

[0164] When the total volume of the dimples is denoted by D (mm3) and the deflection when the ball is compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) is denoted by B (mm), a value of D / B is preferably not more than 140, more preferably not more than 130, and even more preferably not more than 120. On the other hand, the lower limit is preferably at least 95, more preferably at least 97, and even more preferably at least 100. This D / B means an index in which an appropriate distance suppression effect is produced on shots with a driver (W #1) by the longest hitters, and a good distance is easily obtained on shots by amateur users. If this value deviates from the above ranges, the intended distance may not be attainable on shots with a driver (W #1) by the longest hitters and amateur users.

[0165] 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

[0166] 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 4 and Comparative Examples 1 to 15[Formation of Core]

[0167] In Comparative Examples 8, 10, and 12 to 14, a rubber composition of each Example shown in Table 1 was prepared, and then vulcanization molding was performed under vulcanization conditions according to each Example shown in Table 1 to produce a solid core.

[0168] In Examples 1 to 4 and Comparative Examples 1 to 7, 9, 11, and 15, cores are produced based on the formulations in Table 1 in the same manner as described above.TABLE 1Core formulationExampleComparative Example(pbw)1234123456Polybutadiene A10010010010035100100100100100Polybutadiene BPolybutadiene CIsoprene rubberStyrene-butadiene65rubberZinc acrylate27.527.527.525.321.727.527.532.533.033.4Zinc methacrylate1.0Methacrylic acidZinc stearate2.02.02.02.02.02.02.02.02.0Organic peroxide A1.01.01.01.01.01.01.01.01.01.0Organic peroxide BSulfur0.0250.0250.0250.0250.0250.0250.0250.0250.025Water0.30.30.30.30.40.30.30.30.20.3Antioxidant0.10.10.10.10.10.10.10.10.10.1Zinc oxide31.931.931.932.728.031.931.928.328.111.8Barium sulfateZinc salt of1.01.01.01.00.71.01.00.10.1pentachlorothio-phenolVulcanization-Temp.150150150150150150150150150150conditions(° C.)Time19191919191919191919(min)Core formulationComparative Example(pbw)789101112131415Polybutadiene A1001001001001003595Polybutadiene B2020Polybutadiene C8080Isoprene rubber5Styrene-butadiene65rubberZinc acrylate26.037.037.037.037.033.533.526.9Zinc methacrylate1.01.01.01.01.0Methacrylic acid23.5Zinc stearate5.02.02.0Organic peroxide A0.61.01.01.01.01.01.01.01.2Organic peroxide B0.6Sulfur0.0250.025Water0.40.40.40.40.60.60.4Antioxidant0.10.10.10.10.10.10.10.10.2Zinc oxide14.214.814.814.814.819.319.316.523.5Barium sulfate1.0Zinc salt of1.01.01.01.01.00.60.6pentachlorothio-phenolVulcanization-Temp.160150150150150160160150163conditions(° C.)Time111919191914141921(min)

[0169] Details of the above formulations are as follows.

[0170] Polybutadiene A: Trade name “BR 01”, (manufactured by ENEOS Materials Corporation)

[0171] Polybutadiene B: Trade name “LDiene™ 645” (Firestone Polymers)

[0172] Polybutadiene C: Trade name “BUDENE® 1224 Gl” (Goodyear Tire & Rubber Company)

[0173] Isoprene rubber: Trade name “JR 2200” (manufactured by ENEOS Materials Corporation)

[0174] Styrene-butadiene rubber: Trade name “SBR 1507” (manufactured by ENEOS Materials Corporation)

[0175] Zinc acrylate: Trade name “ZN-DA85 S” (manufactured by Nippon Shokubai Co., Ltd.)

[0176] Zinc methacrylate: Trade name “ZDA-90” (manufactured by Asada Chemical Industry Co., Ltd.)

[0177] Zinc stearate: Trade name “BR-3T” (manufactured by Akrochem Corporation)

[0178] Organic peroxide A: Dicumyl peroxide, trade name “Percumyl D” (manufactured by NOF Corporation)

[0179] Organic peroxide B: A mixture of 1,1-di(t-butylperoxy)cyclohexane and silica, trade name “Perhexa C-40” (manufactured by NOF Corporation)

[0180] Sulfur: Trade name “SANMIX S-80N” (manufactured by Sanshin Chemical Industry Co., Ltd., containing sulfur powder for rubber in an amount of 80 wt %)

[0181] Water: Pure water (manufactured by Seiki Co., Ltd.)

[0182] Antioxidant: 2,2-methylenebis(4-methyl-6-butylphenol), trade name “Nocrac NS-6” (manufactured by Ouchi Shinko Chemical Industrial Co., Ltd.)

[0183] Zinc oxide: Trade name “Grade 3 Zinc Oxide” (manufactured by Sakai Chemical Industry Co., Ltd.)

[0184] Zinc salt of pentachlorothiophenol: Manufactured by FUJIFILM Wako Pure Chemical Corporation[Formation of Surrounding Layer, Intermediate Layer, and Cover (Outermost Layer)]

[0185] Next, in Comparative Examples 8, 10, and 12 to 14, the intermediate layer was formed by injection molding the resin material No. 4 or No. 5 of the intermediate layer shown in Table 2 around the core surface using an injection mold. Subsequently, the cover was formed by injection molding the resin material No. 10 of the cover (outermost layer) shown in Table 2 around the intermediate layer-encased sphere using a separate injection mold. At this time, a predetermined large number of dimples described below were formed on the surface of the cover.

[0186] In Examples 1 to 4 and Comparative Examples 1 to 3, the surrounding layer is formed by injection molding the resin material No. 1 of the surrounding layer shown in Table 2 around the core surface using an injection mold. Next, using another injection mold, injection molding is performed around the surrounding layer-encased sphere using the resin material No. 2 of the intermediate layer shown in the same table to form an intermediate layer. Subsequently, the cover is formed by injection molding the resin material No. 6 of the cover (outermost layer) shown in the same table around the intermediate layer-encased sphere using a separate injection mold. In Comparative Examples 4, 5, 9, and 11, the cover is formed by injection molding the resin material No. 2, No. 3, or No. 4 shown in Table 2 around the core surface using an injection mold to form the intermediate layer, and then injection molding the resin materials No. 7 to No. 10 ofthe cover (outermost layer) shown in the same table. In Comparative Examples 6, 7, and 15, the cover is formed around the core surface by injection molding using an injection mold and the resin material No. 8, No. 9, or No. 11 shown in Table 2. At this time, a large number of predetermined dimples described below are formed on the cover surface.TABLE 2Resin material(pbw)No. 1No. 2No. 3No. 4No. 5No. 6No. 7No. 8No. 9No. 10No. 11Hytrel ® 4047N100HPF100056100Himilan 160544505050Himilan 160137.5Himilan 15571537.5Himilan 1706153550AM732950AM732725AM73188575AN431925Titanium oxide444433Barium sulfate20Magnesium stearate1Trimethylolpropane1.11.1TPU (1)100TPU (2)100

[0187] Details of the blending components in Table 2 are as follows.

[0188] “Hytrel® 4047N” polyester elastomer manufactured by Toray Celanese Co., Ltd.

[0189] “HPF 1000” highly neutralized ionomer manufactured by The Dow Chemical Company

[0190] “Himilan 1605”, “Himilan 1601”, “Himilan 1557”, “Himilan 1706”, “AM7329”,

[0191] “AM7327”, and “AM7318” ionomer resins manufactured by Dow-Mitsui Polychemicals Co., Ltd.

[0192] “Nucrel AN4319” manufactured by Dow-Mitsui Polychemicals Co., Ltd.

[0193] Trade name “Precipitated Barium Sulfate 300” barium sulfate manufactured by Sakai Chemical Industry Co., Ltd.

[0194] Trade name “Magnesium stearate G” magnesium stearate manufactured by NOF Corporation

[0195] “Trimethylolpropane” (TMP) manufactured by Tokyo Chemical Industry Co., Ltd.

[0196] Trade name “Pandex” ether-type thermoplastic polyurethane (TPU (1)), material hardness (Shore D) 50, manufactured by DIC Covestro Polymer Ltd.

[0197] Trade name “Pandex” ether-type thermoplastic polyurethane (TPU (2)), material hardness (Shore D) 47, manufactured by DIC Covestro Polymer Ltd.

[0198] For the dimples of the Examples and Comparative Examples, the following dimples (1) to (5) were used. Each dimple mode includes eight types of circular dimples of No. 1 to No. 8 having different diameters and depths. Details thereof are listed in Table 3 below. In addition, an arrangement mode (pattern) of the dimples (1) to (5) is illustrated in FIGS. 5A and 5B. FIG. 5A is a plan view of the dimples, and FIG. 5B is a side view thereof.TABLE 3CylinderTotal volumeDiameterDepthVolumevolumeSRVRof dimplesTypeQuantity(mm)(mm)(mm3)ratio Vo(%)(%)(mm3)Dimple (1)No. 1124.630.1221.0090.491840.68278No. 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. 863.210.1320.4570.430Total330Dimple (2)No. 1124.690.1441.2200.493860.81331No. 21984.540.1401.1000.486No. 3363.960.1340.7660.467No. 4122.920.1090.3220.441No. 5364.540.1461.1410.485No. 6243.960.1440.8270.468No. 763.360.1360.5900.491No. 863.220.1270.4330.421Total330Dimple (3)No. 1124.690.1461.2360.490860.83338No. 21984.540.1431.1220.484No. 3363.960.1370.7900.470No. 4122.920.1060.3100.438No. 5364.540.1491.1620.482No. 6243.960.1470.8460.467No. 763.380.1380.6080.493No. 863.280.1320.4700.423Total330Dimple (4)No. 1124.700.1491.2520.487860.85345No. 21984.550.1461.1440.483No. 3363.970.1400.8150.472No. 4122.910.1030.2980.435No. 5364.550.1521.1830.480No. 6243.970.1500.8640.467No. 763.400.1400.6270.495No. 863.330.1380.5100.426Total330Dimple (5)No. 1124.680.1641.3910.493850.93378No. 21984.530.1611.2580.485No. 3363.950.1540.8830.468No. 4122.900.1140.3310.440No. 5364.530.1681.2940.480No. 6243.950.1650.9490.470No. 763.360.1540.6630.487No. 863.260.1520.5380.426Total330[Definition of Dimple]Edge: highest point in cross section passing through center of a dimpleDiameter: diameter of the flat plane circumscribed by the edge of a dimple

[0201] Depth: maximum depth of a dimple from the flat plane circumscribed by the edge of the dimple

[0202] SR: a ratio 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

[0203] Dimple volume: a dimple volume under a flat plane circumscribed by an edge of a dimple

[0204] Cylinder volume ratio: a ratio of the dimple volume to the cylinder volume having the same diameter as the dimple

[0205] VR: 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

[0206] The ratio CL1 / CD1=A1 of the lift coefficient CL1 at a Reynolds number of 218000 and a spin rate of 2800 rpm to the drag coefficient CD1, the ratio CL2 / CD2=A2 of the lift coefficient CL2 at a Reynolds number of 184000 and a spin rate of 2900 rpm to the drag coefficient CD2, and the ratio CL3 / CD3=A3 of the lift coefficient CL3 at a Reynolds number of 158000 and a spin rate of 3100 rpm to the drag coefficient CD3 of the balls with the above dimples (1) to (5) formed on their cover surfaces are listed in the table below. These lift coefficients and drag coefficients are measured in accordance with the Indoor Test Range (ITR) defined by USGA.TABLE 4DimpleDimpleDimpleDimpleDimple(1)(2)(3)(4)(5)CL10.1510.1470.1460.1450.143CD10.2300.2370.2380.2390.244CL1 / CD1 = A10.6570.6200.6130.6070.586CL20.1680.1620.1610.1600.156CD20.2330.2400.2410.2420.246CL2 / CD2 = A20.7210.6750.6680.6610.634CL30.1900.1820.1810.1790.173CD30.2420.2450.2460.2470.250CL3 / CD3 = A30.7850.7430.7340.7250.692

[0207] 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, surface hardnesses of each layer-encased sphere, and ball initial velocities are evaluated by the following methods, and are shown in Tables 5 to 8.[Core Hardness Profile]

[0208] 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 Tables 5 and 6, 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. Note that the numerical values in the table are Shore C hardness values.

[0209] In addition, in the core hardness profile, letting the Shore C hardness at the core center be Cc, the Shore C hardness at the midpoint M between the core center and the core surface be Cm, the respective Shore C hardnesses at positions 2 mm, 4 mm, and 6 mm inward from the midpoint M be Cm-2, Cm-4, and Cm-6, the respective Shore C hardnesses at positions 2 mm, 4 mm, and 6 mm outward from the midpoint M be Cm+2, Cm+4, and Cm+6, and the Shore C hardness at the core surface be Cs, the surface areas A to F are calculated as follows:surface⁢ area⁢ A: 1 / 2×2×(Cm-4-Cm-6)surface⁢ area⁢ B: 1 / 2×2×(Cm-2-Cm-4)surface⁢ area⁢ C: 1 / 2×2×(Cm-Cm-2)surface⁢ area⁢ D: 1 / 2×2×(Cm+2-Cm)surface⁢ area⁢ E: 1 / 2×2×(Cm+4-Cm+2)surface⁢ area⁢ F: 1 / 2×2×(Cm+6-Cm+4)and the values of the following nine expressions are determined.Surface⁢ area⁢ A+surface⁢ area⁢ B(1)Surface⁢ area⁢ B+surface⁢ area⁢ C(2)Surface⁢ area⁢ C+surface⁢ area⁢ D(3)Surface⁢ area⁢ D+surface⁢ area⁢ E(4)Surface⁢ area⁢ E+surface⁢ area⁢ F(5)(Surface⁢ area⁢ D+surface⁢ area⁢ E)-(surface⁢ area⁢ A+surface⁢ area⁢ B)(6)(Surface⁢ area⁢ D+surface⁢ area⁢ E)-(surface⁢ area⁢ B+surface⁢ area⁢ C)(7){(Surface⁢ area⁢ D+surface⁢ area⁢ E)-(surface⁢ area⁢ A+surface⁢ area⁢ B)}×(Cs-Cc)(8){(Surface⁢ area⁢ D+surface⁢ area⁢ E)-(surface⁢ area⁢ B+surface⁢ area⁢ C)}×(Cs-Cc)(9)The surface areas A to F in the core hardness profile are described in FIG. 2, which shows a graph that illustrates surface areas A to F using the core hardness profile data from Example 1.

[0212] In addition, FIGS. 3 and 4 show graphs of core hardness profiles for Examples 1 to 4 and Comparative Examples 1 to 15.[Outer Diameters of Each Sphere of Core, Surrounding Layer-Encased Sphere, and Intermediate Layer-Encased Sphere]

[0213] At a temperature adjusted to 23.9±1° C. for at least three hours or more in a thermostatic bath, five random places on the surface are measured in a room with a temperature of 23.9±2° C., 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]

[0214] At a temperature adjusted to 23.9±1° C. for at least three hours or more in a thermostatic bath, a diameter at 15 random dimple-free places is measured in a room at a temperature of 23.9±2° C., and, using an average value of these measurements as a measured value of one ball, an average value for the diameter of 10 balls is determined.[Deflection of Core and Ball]

[0215] Each subject layer-encased sphere of the core or the 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. It is noted that the deflection in each case is a measurement value measured in a room at a temperature of 23.9±2° C. after temperature adjustment to 23.9±1° C. for at least three hours or more in a thermostatic bath. As a measuring device, a high-load compression tester manufactured by MU Instruments Trading Corp. is used, and a down speed of a pressure head that compresses the core or the ball is set to 10 mm / s.[Material Hardnesses of Surrounding Layer, Intermediate Layer, and Cover (Shore C and Shore D Hardnesses)]

[0216] The resin material of each layer is molded into a sheet having a thickness of 2 mm and left at a temperature of 23±2° C. for two weeks. At the time of measurement, three such sheets are stacked together. The Shore C hardness and the Shore D hardness are each measured with a Shore C durometer and a Shore D durometer conforming to the ASTM D2240 standard. For the measurement of the hardness, the P2 Automatic Rubber Hardness Tester manufactured by Kobunshi Keiki Co., Ltd. to which a Shore C durometer or a Shore D durometer is mounted is used. For the hardness value, a maximum value is read. The measurement method is in accordance with the ASTM D2240 standard.[Surface Hardnesses of Each Sphere of Surrounding Layer-Encased Sphere, Intermediate Layer-Encased Sphere, and Ball]

[0217] 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 C hardness and the Shore D hardness are each measured with a Shore C durometer and a Shore D durometer conforming to the ASTM D2240 standard. For the measurement of the hardness, the P2 Automatic Rubber Hardness Tester manufactured by Kobunshi Keiki Co., Ltd. to which a Shore C durometer or a Shore D durometer is mounted is used. For the hardness value, a maximum value is read. The measurement method is in accordance with the ASTM D2240 standard.[Initial Velocity of Ball]

[0218] The initial velocity of each sphere is measured at a temperature of 23.9±2° C. using a device for measuring COR manufactured by Hye Precision Products of the same type as the R&A. The measurement principle is as follows.

[0219] An air pressure is changed to four stages of 35.5 psi, 36.5 psi, 39.5 psi, and 40.5 psi, and a ball is fired at four stages of incident velocity by respective air pressures, collided with a barrier, and its COR is measured. That is, a correlation equation between the incident velocity and the COR is created by changing the air pressure in four stages. Similarly, a correlation equation between the incident velocity and a contact time is created.

[0220] Then, from these correlation equations, the COR (coefficient of restitution) and the contact time (μs) at an incident velocity of 43.83 m / s are determined and substituted into the following initial velocity conversion equation to calculate an initial velocity of each sphere.IV=1⁢3⁢6.8+1⁢3⁢6.3⁢e+0.0⁢19⁢tc

[0221] Here, e is a coefficient of restitution, and tc is a contact time (μs) at a collision speed of 143.8 ft / s (43.83 m / s).

[0222] In the initial velocity measurement of the balls of all examples, a barrel diameter of 43.18 mm is selected.TABLE 5ExampleComparative Example1234123456Ball structure (piece)4P4P4P4P4P4P4P3P3P2PCoreOuter diameter (mm)35.1735.1735.1735.1735.1735.1735.1737.3037.3039.30Weight (g)27.7927.7927.7927.7927.7927.7927.7932.8032.8035.83Deflection (mm)4.544.544.544.824.544.544.543.403.303.12Cs [surface] (Shore C)76.576.576.574.566.676.576.585.586.588.3Cm + 6 (Shore C)71.071.071.068.565.871.071.075.376.177.5Cm + 4 (Shore C)69.469.469.467.164.769.469.469.570.171.1Cm + 2 (Shore C)64.164.164.163.364.664.164.164.565.166.1Cm [intermediate] (Shore C)59.859.859.858.863.059.859.863.264.065.4Cm − 2 (Shore C)58.758.758.757.959.158.758.763.063.865.2Cm − 4 (Shore C)56.556.556.555.254.956.556.562.263.164.7Cm − 6 (Shore C)56.356.356.355.053.156.356.361.862.864.6Cc [center] (Shore C)55.155.155.153.652.955.155.161.562.664.6Cs − Cc (Shore C)21.421.421.420.913.721.421.424.023.923.7(Cs − Cc) / (Cm − Cc)4.64.64.64.01.44.64.614.117.129.Surface area A0.20.20.20.21.80.20.20.40.30.1Surface area B2.22.22.22.74.22.22.20.80.70.5Surface area C1.11.11.10.93.91.11.10.20.20.2Surface area D4.34.34.34.51.64.34.31.31.10.7Surface area E5.35.35.33.80.15.35.35.05.05.0Surface area F1.61.61.61.41.11.61.65.86.06.4Surface area A + surface area B2.42.42.42.96.02.42.41.21.00.6Surface area B + surface area C3.33.33.33.68.13.33.31.00.90.7Surface area C + surface area D5.45.45.45.45.55.45.41.51.30.9Surface area D + surface area E9.69.69.68.31.79.69.66.36.15.7Surface area E + surface area F6.96.96.95.21.26.96.910.811.011.4(Surface areas: D + E) −7.27.27.25.4−4.37.27.25.15.15.1(surface areas: A + B)(Surface areas: D + E) −6.36.36.34.7−6.46.36.35.35.25.0(surface areas: B + C){(Surface areas: D + E) −154154154113−59154154122122121(surface areas: A + B)} × (Cs − Cc){(Surface areas: D + E) −13513513598−88135135127124119(surface areas: B + C)} × (Cs − Cc)TABLE 6Comparative Example789101112131415Ball structure (piece)2P3P3P3P3P3P3P3P2PCoreOuter diameter (mm)39.7038.6538.6538.6538.6538.0638.0638.6439.80Weight (g)37.7435.0935.0935.0935.0933.8333.8335.1036.99Deflection (mm)4.502.922.922.922.924.134.132.932.63Cs [surface] (Shore C)76.087.487.487.487.486.386.381.584.3Cm + 6 (Shore C)66.580.480.480.480.474.174.180.579.0Cm + 4 (Shore C)64.975.875.875.875.865.965.979.075.9Cm + 2 (Shore C)63.470.870.870.870.861.361.376.272.8Cm [intermediate] (Shore C)62.966.366.366.366.361.061.072.370.8Cm − 2 (Shore C)62.465.665.665.665.661.461.468.469.8Cm − 4 (Shore C)61.364.964.964.964.961.061.066.968.4Cm − 6 (Shore C)59.763.363.363.363.360.160.165.466.3Cc [center] (Shore C)56.262.662.662.662.657.957.962.760.7Cs − Cc (Shore C)19.824.824.824.824.828.428.418.823.6(Cs − Cc) / (Cm − Cc)3.06.76.76.76.79.29.22.02.3Surface area A1.61.61.61.61.60.90.91.52.1Surface area B1.10.70.70.70.70.40.41.51.4Surface area C0.50.70.70.70.7−0.4−0.43.91.0Surface area D0.54.54.54.54.50.30.33.92.0Surface area E1.55.05.05.05.04.64.62.83.1Surface area F1.64.64.64.64.68.28.21.53.1Surface area A + surface area B2.72.32.32.32.31.31.33.03.5Surface area B + surface area C1.61.41.41.41.40.00.05.42.4Surface area C + surface area D1.05.25.25.25.2−0.1−0.17.83.0Surface area D + surface area E2.09.59.59.59.54.94.96.75.1Surface area E + surface area F3.19.69.69.69.612.812.84.36.2(Surface areas: D + E) −−0.77.27.27.27.23.63.63.71.6(surface areas: A + B)(Surface areas: D + E) −0.48.18.18.18.14.94.91.32.7(surface areas: B + C){(Surface areas: D + E) −−141791791791791021027038(surface areas: A + B)} × (Cs − Cc){(Surface areas: D + E) −82012012012011391392464(surface areas: B + C)} × (Cs − Cc)TABLE 7ExampleComparative Example12341SurroundingMaterialNo. 1No. 1No. 1No. 1No. 1layerThickness (mm)1.241.241.241.241.24Material hardness (Shore C)6363636363Material hardness (Shore D)4040404040SurroundingOuter diameter (mm)37.6537.6537.6537.6537.65layer-Weight (g)33.6433.6433.6433.6433.64encasedSurface hardness (Shore C)7171717171sphereSurface hardness (Shore D)4646464646IntermediateMaterialNo. 2No. 2No. 2No. 2No. 2layerThickness (mm)1.311.311.311.311.31Material hardness (Shore C)9090909090Material hardness (Shore D)5959595959IntermediateOuter diameter (mm)40.2740.2740.2740.2740.27layer-Weight (g)39.639.639.639.639.6encasedSurface hardness (Shore C)9494949494sphereSurface hardness (Shore D)6363636363CoverMaterialNo. 6No. 6No. 6No. 6No. 6Thickness (mm)1.211.211.211.211.21Material hardness (Shore C)9393939393Material hardness (Shore D)6363636363DimpleType(2)(3)(4)(2)(1)Quantity330330330330330Surface area coverage ratio: SR (%)8686868684Volume occupancy ratio: VR (%)0.810.830.850.810.68Total dimple volume (mm3)331338345331278A1: CL1 / CD10.6200.6130.6070.6200.657A2: CL2 / CD20.6750.6680.6610.6750.721A3: CL3 / CD30.7430.7340.7250.7430.785Average value of A2 and A30.7090.7010.6930.7090.753BallOuter diameter (mm)42.7042.7042.7042.7042.70Weight (g)45.5045.5045.5045.5045.50Deflection (mm)3.083.083.083.323.08Initial velocity (m / s)77.277.277.277.274.0Initial velocity / deflection25.125.125.123.324.0Surface hardness (Shore C)9898989898Surface hardness (Shore D)6969696969Cover thickness + intermediate layer thickness (mm)2.532.532.532.532.53Cover thickness + intermediate layer thickness +3.773.773.773.773.77surrounding layer thickness (mm)Total dimple volume / deflection of ball (mm2)10711011210090Ball surface hardness − intermediate layer-encased44444sphere surface hardness (Shore C)Ball surface hardness − surrounding layer-encased2727272727sphere surface hardness (Shore C)Intermediate layer-encased sphere surface hardness −2323232323surrounding layer-encased sphere surface hardness(Shore C)Intermediate layer-encased sphere surface hardness −1818182027core surface hardness (Shore C)Surrounding layer-encased sphere surface hardness −−6−6−6−44core surface hardness (Shore C)Surrounding layer-encased sphere surface hardness −1616161718core center hardness (Shore C)Intermediate layer-encased sphere surface hardness −3939394041core center hardness (Shore C)Ball surface hardness − core surface hardness (Shore C)2222222431Ball surface hardness − core center hardness (Shore C)4343434445Deflection of core − deflection of ball (mm)1.461.461.461.501.46Deflection of core / deflection of ball1.471.471.471.451.47Core diameter / ball diameter0.8240.8240.8240.8240.824Comparative Example23456SurroundingMaterialNo. 1No. 1———layerThickness (mm)1.241.24———Material hardness (Shore C)6363———Material hardness (Shore D)4040———SurroundingOuter diameter (mm)37.6537.65———layer-Weight (g)33.6433.64———encasedSurface hardness (Shore C)7171———sphereSurface hardness (Shore D)4646———IntermediateMaterialNo. 2No. 2No. 2No. 3—layerThickness (mm)1.311.311.351.35—Material hardness (Shore C)90909084—Material hardness (Shore D)59595954—IntermediateOuter diameter (mm)40.2740.2740.0040.00—layer-Weight (g)39.639.638.938.9—encasedSurface hardness (Shore C)94949490—sphereSurface hardness (Shore D)63636359—CoverMaterialNo. 6No. 6No. 7No. 7No. 8Thickness (mm)1.211.211.351.351.70Material hardness (Shore C)9393939394Material hardness (Shore D)6363646465DimpleType(1)(5)(4)(2)(4)Quantity330330330330330Surface area coverage ratio: SR (%)8485868686Volume occupancy ratio: VR (%)0.680.930.850.810.85Total dimple volume (mm3)278378345331345A1: CL1 / CD10.6570.5860.6070.6200.607A2: CL2 / CD20.7210.6340.6610.6750.661A3: CL3 / CD30.7850.6920.7250.7430.725Average value of A2 and A30.7530.6630.6930.7090.693BallOuter diameter (mm)42,7042.7042.7042.7042.70Weight (g)45.5045.5045.5045.5045.50Deflection (mm)3.083.082.702.702.71Initial velocity (m / s)77.277.277.277.277.0Initial velocity / deflection25.125.128.628.628.4Surface hardness (Shore C)9898989898Surface hardness (Shore D)6969707071Cover thickness + intermediate layer thickness (mm)2.532.532.702.701.70Cover thickness + intermediate layer thickness +3.773.772.702.701.70surrounding layer thickness (mm)Total dimple volume / deflection of ball (mm2)90123128123127Ball surface hardness − intermediate layer-encased4448—sphere surface hardness (Shore C)Ball surface hardness − surrounding layer-encased2727———sphere surface hardness (Shore C)Intermediate layer-encased sphere surface hardness −2323———surrounding layer-encased sphere surface hardness(Shore C)Intermediate layer-encased sphere surface hardness −181894—core surface hardness (Shore C)Surrounding layer-encased sphere surface hardness −−6−6———core surface hardness (Shore C)Surrounding layer-encased sphere surface hardness −1616———core center hardness (Shore C)Intermediate layer-encased sphere surface hardness −39393327—core center hardness (Shore C)Ball surface hardness − core surface hardness (Shore C)2222131210Ball surface hardness − core center hardness (Shore C)4343373533Deflection of core − deflection of ball (mm)1.461.460.700.600.41Deflection of core / deflection of ball1.471.471.261.221.15Core diameter / ball diameter0.8240.8240.8740.8740.920TABLE 8Comparative Example789101112131415SurroundingMaterial—————————layerThickness (mm)—————————Material hardness (Shore C)—————————Material hardness (Shore D)—————————SurroundingOuter diameter (mm)—————————layer-Weight (g)—————————encasedSurface hardness (Shore C)—————————sphereSurface hardness (Shore D)—————————IntermediateMaterial—No. 4No. 4No. 4No. 4No. 5No. 5No. 4—layerThickness (mm)—1.171.171.171.171.471.471.21—Material hardness (Shore C)—94949494949494—Material hardness (Shore D)—67676767656567—IntermediateOuter diameter (mm)—40.9940.9940.9940.9941.0041.0041.06—layer-Weight (g)—40.6340.6340.6340.6340.6540.6540.81—encasedSurface hardness (Shore C)—97979797979797—sphereSurface hardness (Shore D)—71717171717171—CoverMaterialNo. 9No. 10No. 10No. 10No. 10No. 10No. 10No. 10No. 11Thickness (mm)1.500.850.850.850.850.840.840.811.46Material hardness (Shore C)847171717171717167Material hardness (Shore D)565050505050505047DimpleType(4)(4)(2)(1)(5)(1)(4)(1)(2)Quantity330330330330330330330330330Surface area coverage ratio: SR (%)868686848584868486Volume occupancy ratio: VR (%)0.850.850.810.680.930.680.850.680.81Total dimple volume (mm3)345345331278378278345278331A1: CL1 / CD10.6070.6070.6200.6570.5860.6570.6070.6570.620A2: CL2 / CD20.6610.6610.6750.7210.6340.7210.6610.7210.675A3: CL3 / CD30.7250.7250.7430.7850.6920.7850.7250.7850.743Average value of A2 and A30.6930.6930.7090.7530.6630.7530.6930.7530.709BallOuter diameter (mm)42.7042.6942.6942.6942.6942.6842.6942.6842.72Weight (g)45.4045.4945.5245.5545.5245.6045.5245.5145.66Deflection (mm)4.002.372.352.322.352.962.982.382.51Initial velocity (m / s)77.077.077.177.277.176.977.073.173.4Initial velocity / deflection19.332.532.633.332.826.025.830.729.2Surface hardness (Shore C)928787878786868779Surface hardness (Shore D)626161616160606153Cover thickness + intermediate layer thickness (mm)1.502.022.022.022.022.312.322.021.46Cover thickness + intermediate layer thickness +1.502.022.022.022.022.312.322.021.46surrounding layer thickness (mm)Total dimple volume / deflection of ball (mm2)8614514112016194116117132Ball surface hardness − intermediate layer-encased—−10−10−10−10−11−11−10—sphere surface hardness (Shore C)Ball surface hardness − surrounding layer-encased—————————sphere surface hardness (Shore C)Intermediate layer-encased sphere surface hardness −—————————surrounding layer-encased sphere surface hardness(Shore C)Intermediate layer-encased sphere surface hardness −—10101010111116—core surface hardness (Shore C)Surrounding layer-encased sphere surface hardness −—————————core surface hardness (Shore C)Surrounding layer-encased sphere surface hardness −—————————core center hardness (Shore C)Intermediate layer-encased sphere surface hardness −—34343434393934—core center hardness (Shore C)Ball surface hardness − core surface hardness (Shore C)160000006−5Ball surface hardness − core center hardness (Shore C)362424242428282418Deflection of core − deflection of ball (mm)0.500.550.570.600.571.171.150.550.12Deflection of core / deflection of ball1.131.231.241.261.241.401.391.231.05Core diameter / ball diameter0.9300.9050.9050.9050.9050.8920.8920.9050.932The flight (W #1 and I #6) and the controllability on approach shots of each golf ball are evaluated by the following methods. The results are shown in Table 9.[Evaluation of Flight (W #1, HS 54 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 54 m / s are measured. The club used is a TOUR B XD-5 Driver / loft angle 8.5° (2017 model) manufactured by Bridgestone Sports Co., Ltd. and is evaluated according to the following rating criteria.[Rating Criteria]Good: Total compared with Comparative Example 10 is not more than −10 m, and at least −14 m.Fair: Total compared with Comparative Example 10 is less than −14 m.NG: Total compared with Comparative Example 10 is more than −10 m.[Evaluation of Flight (W #1, HS 40 m / s)]The 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 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 compared with Comparative Example 10 is at least 0 m.Fair: Total compared with Comparative Example 10 is at least −5 m and less than 0 m.

[0231] NG: Total compared with Comparative Example 10 is less than −5 m.[Evaluation of Flight (I #6, HS 42 m / s)]

[0232] When a number six iron (I #6) is mounted on the golf swing robot and a ball is struck at an HS of 42 m / s, a spin rate and a distance traveled (total) 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 compared with Comparative Example 10 is at least 5 m.

[0234] Fair: Total compared with Comparative Example 10 is at least 0 m and less than 5 m.

[0235] NG: Total compared with Comparative Example 10 is less than 0 m.[Evaluation of Flight (I #6, HS 35 m / s)]

[0236] When a number six iron (I #6) is mounted on the golf swing robot and a ball is struck at an HS of 35 m / s, a spin rate and a distance traveled (total) 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 / Total]Good: Total compared with Comparative Example 10 is at least 3 m.

[0238] Fair: Total compared with Comparative Example 10 is at least −3 m and less than 3 m.

[0239] NG: Total compared with Comparative Example 10 is less than −3 m.[Evaluation of Launch Angle on Approach Shots]

[0240] A judgment is made based on a launch angle when a sand wedge is mounted on the golf swing robot and a ball is struck at an HS of 15 m / s. The launch angle 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: Launch angle is at least 35.0°.

[0242] NG: Launch angle is less than 35.0°.[Evaluation of Feel at Impact]

[0243] Sensory evaluation of a feel at impact is performed by an amateur golfer having a handicap of at least 25 and a head speed on shots with a driver (W #1) of 30 to 40 m / s. Evaluation is performed according to the following rating criteria.[Rating Criteria]Good: Good feel at impact with a soft feeling and a sense of bounce.

[0245] Fair: One of the soft feeling and the sense of bounce cannot be said to have a good feel at impact.

[0246] NG: Both the soft feeling and the sense of bounce do not have a good feel at impact. Alternatively, either the soft feeling or the sense of bounce is obviously not good.TABLE 9ExampleComparative Example1234123456FlightSpin rate2,5852,5852,5852,4832,7472,5852,5852,3952,3082,423W#1(rpm)HSTotal271.2270.3269.3270.3272.1279.4257.4268.7269.1268.654 m / s(m)Total (m)−10.3−11.2−12.2−11.2−9.4−2.1−24.1−12.8−12.4−12.9comparedwithComp.Ex. 10RatingGoodGoodGoodGoodGoodNGFairGoodGoodGoodFlightSpin rate2,9582,9582,9582,8483,0662,9582,9582,7402,6622,754W#1(rpm)HSTotal198.7199.2199.6198.9187.5197.5197.7201.9201.1200.040 m / s(m)Total (m)0.40.91.30.6−10.8−0.8−0.63.62.81.7comparedwithComp.Ex. 10RatingGoodGoodGoodGoodNGFairFairGoodGoodGoodFlightSpin rate5,1305,1305,1305,0085,5195,1305,1305,2295,4305,271I#6(rpm)HSTotal185.8185.5185.1186.1170.2182.6181.7185.0185.6183.242 m / s(m)Total (m)7.77.47.08.0−7.94.53.66.97.55.1comparedwithComp.Ex. 10RatingGoodGoodGoodGoodNGFairFairGoodGoodGoodFlightSpin rate5,0025,0025,0024,7625,2945,0024,9205,0995,2945,139I#6(rpm)HSTotal143.1144.2145.2143.5134.7143.4145.6145.3143.1143.935 m / s(m)Total (m)3.04.15.13.4−5.43.35.55.23.03.8comparedwithComp.Ex. 10RatingGoodGoodGoodGoodNGGoodGoodGoodGoodGoodApproachLaunch41.841.841.841.940.841.841.841.241.241.1(SW)angle (°)RatingGoodGoodGoodGoodGoodGoodGoodGoodGoodGoodEvaluation ofGoodGoodGoodGoodNGGoodGoodFairFairFairFeel at ImpactComparative Example789101112131415FlightSpin rate2,4792,8012,7942,7862,7942,5422,5452,9813,149W#1(rpm)HSTotal267.0271.5273.3281.5259.6276.1268.8269.3259.854 m / s(m)Total (m)−14.5−10.0−8.20.0−21.9−5.4−12.7−12.2−21.7comparedwithComp.Ex. 10RatingFairGoodNGNGFairNGGoodGoodFairFlightSpin rate2,6923,1773,1663,1543,1662,9122,9003,3723,629W#1(rpm)HSTotal198.1200.4199.5198.3198.6199.5200.4184.9179.040 m / s(m)Total (m)−0.22.11.20.00.31.22.1−13.4−19.3comparedwithComp.Ex. 10RatingFairGoodGoodGoodGoodGoodGoodNGNGFlightSpin rate5,1435,7805,7515,7215,7514,9485,0396,2496,354I#6(rpm)HSTotal184.3180.6181.3178.1177.2184.4186.6163.4167.142 m / s(m)Total (m)6.22.53.20.0−0.96.38.5−14.7−11.0comparedwithComp.Ex. 10RatingGoodFairFairFairNGGoodGoodNGNGFlightSpin rate4,9335,4485,4685,4875,4684,7244,8075,8816,067I#6(rpm)HSTotal144.8141.9139.8140.1142.3144.7146.0129.8131.135 m / s(m)Total (m)4.71.8−0.30.02.24.65.9−10.3−9.0comparedwithComp.Ex. 10RatingGoodFairFairFairFairGoodGoodNGNGApproachLaunch36.732.532.532.632.532.832.831.532.6(SW)angle (°)RatingGoodNGNGNGNGNGNGNGNGEvaluation ofFairNGNGNGNGFairFairNGNGFeel at Impact

[0247] As shown in the results in Table 9, the golf balls of Comparative Examples 1 to 15 are inferior in the following respects to the golf balls according to the present invention (Examples).

[0248] In Comparative Example 1, the dimple VR is smaller than 0.75%, and A1 is larger than 0.655. In addition, the initial velocity of the ball is lower than 75.0 m / s. Further, the value (hereinafter referred to as “D / B value”) obtained by dividing the total dimple volume D (mm3) by the deflection B (mm) of the ball under a load of 10 to 130 kgf is smaller than 95. As a result, the distance on shots with a driver (W #1) at a head speed (HS) of 40 m / s is inferior, and the distance on shots with a number six iron (I #6) is inferior. In addition, for the feel at impact, the sense of bounce is obviously not sufficient.

[0249] In Comparative Example 2, the dimple VR is smaller than 0.75%, and A1 is larger than 0.655. In addition, the D / B value is smaller than 95. As a result, the distance on shots with a driver (W #1) at a head speed (HS) of 54 m / s becomes long, and does not comply with the new ODS rules.

[0250] In Comparative Example 3, the dimple VR is larger than 0.89%. In addition, A1 is smaller than 0.590, and (A2+A3) / 2 is smaller than 0.670. As a result, the distance under striking conditions on shots with a driver (W #1) is inferior at head speeds (HS) of both 54 m / s and 40 m / s.

[0251] Comparative Example 4 is a golf ball having a three-piece structure without a surrounding layer, and the surface hardness of the intermediate layer-encased sphere is larger than the surface hardness of the core. As a result, regarding the feel at impact, the soft feeling is inferior to that of each Example.

[0252] Comparative Example 5 is a golf ball having a three-piece structure without a surrounding layer, and the surface hardness of the intermediate layer-encased sphere is larger than the surface hardness of the core. As a result, regarding the feel at impact, the soft feeling is inferior to that of each Example.

[0253] Comparative Example 6 is a golf ball having a two-piece structure including only a core and a cover. As a result, regarding the feel at impact, the soft feeling is inferior to that of each example.

[0254] Comparative Example 7 is a golf ball having a two-piece structure including only a core and a cover. In addition, the D / B value is smaller than 95. As a result, the distance on shots with a driver (W #1) at a head speed (HS) of 54 m / s is excessively reduced, and the distance on shots with a driver (W #1) at a head speed (HS) of 40 m / s is slightly inferior, so that the sense of bounce is not sufficient in the feel at impact.

[0255] Comparative Example 8 has a three-piece structure in which the ball surface hardness is softer than the surface hardness of the intermediate layer-encased sphere. In addition, the D / B value is larger than 140, and the surface hardness of the intermediate layer-encased sphere is harder than the core surface hardness. As a result, the distance on shots with an iron (I #6) was inferior, and the launch angle on approach shots was too low, so that the ball was difficult for an amateur. In addition, the soft feeling was inferior.

[0256] Comparative Example 9 has a three-piece structure in which the ball surface hardness is softer than the surface hardness of the intermediate layer-encased sphere. In addition, the D / B value is larger than 140, and the surface hardness of the intermediate layer-encased sphere is harder than the core surface hardness. As a result, the distance on shots with a driver (W #1) at a head speed (HS) of 54 m / s becomes long, and does not comply with the new ODS rules. In addition, the distance on shots with an iron (I #6) is inferior, and the launch angle on approach shots is too low, so that the ball is difficult for an amateur. Furthermore, the soft feeling is inferior.

[0257] Comparative Example 10 is an embodiment currently used by male professionals. The ball has a three-piece structure in which the ball surface hardness is smaller than the surface hardness of the intermediate layer-encased sphere. In addition, the dimple VR is smaller than 0.75%, and A1 is larger than 0.655. Furthermore, the surface hardness of the intermediate layer-encased sphere is harder than the core surface hardness. As a result, the distance on shots with a driver (W #1) at a head speed (HS) of 54 m / s was long, and did not comply with the new ODS rules. In addition, the distance on shots with a driver (W #1) at a head speed (HS) of 40 m / s and on shots with an iron (I #6) was inferior, and the launch angle on approach shots was too low, so that the ball was difficult for an amateur. Furthermore, the soft feeling was inferior.

[0258] Comparative Example 11 has a three-piece structure in which the ball surface hardness is softer than the surface hardness of the intermediate layer-encased sphere. Further, the dimple VR is larger than 0.89%, A1 is smaller than 0.590, and (A2+A3) / 2 is smaller than 0.670. Furthermore, the D / B value is larger than 140, and the surface hardness of the intermediate layer-encased sphere is harder than the core surface hardness. As a result, the distance on shots with a driver (W #1) at a head speed (HS) of 54 m / s is excessively reduced, and the distances on shots with a driver (W #1) at a head speed (HS) of 40 m / s and on shots with an iron (I #6) at a head speed (HS) of 42 m / s are inferior. In addition, since the launch angle on approach shots is too low, the ball became difficult for an amateur, and the soft feeling is inferior.

[0259] Comparative Example 12 has a three-piece structure in which the ball surface hardness is softer than the surface hardness of the intermediate layer-encased sphere. In addition, the dimple VR is smaller than 0.75%, and A1 is larger than 0.655. In addition, the value of D / B is smaller than 95, and the surface hardness of the intermediate layer-encased sphere is harder than the core surface hardness. As a result, the distance on shots with a driver (W #1) at a head speed (HS) of 54 m / s was excessively reduced, the launch angle on approach shots was too low, so that the ball became difficult for an amateur, and the soft feeling was not sufficient.

[0260] Comparative Example 13 has a three-piece structure in which the ball surface hardness is softer than the surface hardness of the intermediate layer-encased sphere. In addition, the surface hardness of the intermediate layer-encased sphere is harder than the core surface hardness. As a result, the launch angle on approach shots is too low, so that the ball becomes difficult for an amateur, and the soft feeling is inferior.

[0261] Comparative Example 14 has a three-piece structure in which the ball surface hardness is softer than the surface hardness of the intermediate layer-encased sphere. In addition, the dimple VR is smaller than 0.75%, and A1 is larger than 0.655. Furthermore, the initial velocity of the ball is lower than 75.0 m / s, and the surface hardness of the intermediate layer-encased sphere is harder than the core surface hardness. As a result, the distance on shots with a driver (W #1) at a head speed (HS) of 40 m / s and on shots with an iron (I #6) is inferior, and the launch angle on approach shots is too low, so that the ball is difficult for an amateur. In addition, the feel at impact is hard and the sense of bounce is not good.

[0262] Comparative Example 15 is a golf ball having a two-piece structure for a driving range, and has a ball initial velocity of less than 75.0 m / s. As a result, the actual initial velocity decreases under all the striking conditions. The distance on shots with a driver (W #1) at a head speed (HS) of 54 m / s is excessively decreased, and the distance decreases even under other striking conditions. In addition, as a game ball used in a round of golf, the launch angle on approach shots is too low, so that the ball is difficult for an amateur. In addition, the sense of bounce is not good in the feel at impact.

[0263] Japanese Patent Application No. 2024-047427 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.

Examples

examples

[0166]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.

Claims

1. A multi-piece solid golf ball comprising a core, a single-layer or multiple-layer surrounding layer, a single-layer intermediate layer, and a single-layer cover, wherein a large number of dimples are formed on an outside surface of the cover, the core is formed of a rubber material, the surrounding layer, the intermediate layer, and the cover are formed of a resin material, a relationship between a surface hardness of each sphere of the ball, a surrounding layer-encased sphere, and an intermediate layer-encased sphere satisfies the following conditions (1-a) and (1-b):(surface⁢ hardness⁢ of⁢ ball)>(surface⁢ hardness⁢ of⁢ surrounding⁢ layer-encased⁢ sphere)(1-a)(surface⁢ hardness⁢ of⁢ ball)>(surface⁢ hardness⁢ of⁢ intermediate⁢ layer-encased⁢ sphere)(1-b)where hardness means Shore C hardness,and a relationship between the surface hardness of each sphere of the core, the surrounding layer-encased sphere, and the intermediate layer-encased sphere satisfies at least one of the following conditions (2-a) or (2-b):(surface⁢ hardness⁢ of⁢ surrounding⁢ layer-encased⁢ sphere)<(surface⁢ hardness⁢ of⁢ core(2-a)(surface⁢ hardness⁢ of⁢ intermediate⁢ layer-encased⁢ sphere)<(surface⁢ hardness⁢ of⁢ core).(2-b)where hardness means Shore C hardness,when an initial velocity of the ball is from 75.0 to 77.724 m / s, a ratio CL1 / CD1 of a lift coefficient CL1 at a Reynolds number of 218,000 and a spin rate of 2,800 rpm to a drag coefficient CD1 is denoted by A1, a ratio CL2 / CD2 of a lift coefficient CL2 at a Reynolds number of 184,000 and a spin rate of 2,900 rpm to a drag coefficient CD2 is denoted by A2, and a ratio CL3 / CD3 of a lift coefficient CL3 at a Reynolds number of 158,000 and a spin rate of 3,100 rpm to a drag coefficient CD3 is denoted by A3, the following two conditions are satisfied:0.59≤A⁢1≤0.6⁢55⁢and⁢(A⁢2+A⁢3) / 2≥0.6⁢70and when a volume occupancy ratio VR of the dimples is from 0.75 to 0.89%, a total volume of the dimples is denoted by D (mm3), and a deflection when the ball is compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) is denoted by B (mm), the following condition is satisfied:9⁢5≤D / B≤1⁢4⁢0.

2. The multi-piece solid golf ball of claim 1, wherein a value of A1 is from 0.590 to 0.613, a value of A2 is from 0.635 to 0.668, and a value of A3 is from 0.695 to 0.734.

3. The multi-piece solid golf ball of claim 1, wherein a value of A1 is from 0.614 to 0.655, a value of A2 is from 0.669 to 0.750, and a value of A3 is from 0.735 to 0.815.

4. The multi-piece solid golf ball of claim 1, wherein a value of (A2+A3) / 2 is from 0.670 to 0.783.

5. The multi-piece solid golf ball of claim 1, wherein the cover is formed of an ionomer resin as a chief material.

6. The multi-piece solid golf ball of claim 1, wherein the relationship between the surface hardness of each sphere satisfies the following condition:(surface hardness of ball)>(surface hardness of intermediate layer-encased sphere)>(surface hardness of surrounding layer-encased sphere)<(surface hardness of core)where hardness means Shore C hardness.

7. The multi-piece solid golf ball of claim 1, wherein the core has a hardness profile in which, letting the Shore C hardness at a core center be Cc, the Shore C hardness at a midpoint M between the core center and a core surface be Cm, the Shore C hardnesses at positions 2 mm, 4 mm, and 6 mm inward from the midpoint M be Cm-2, Cm-4, and Cm-6 respectively, the Shore C hardnesses at positions 2 mm, 4 mm, and 6 mm outward from the midpoint M be Cm+2, Cm+4, and Cm+6 respectively, and the Shore C hardness at the core surface be Cs, and defining surface areas A to F as follows:surface⁢ area⁢ A: 1 / 2×2×(Cm-4-Cm-6)surface⁢ area⁢ B: 1 / 2×2×(Cm-2-Cm-4)surface⁢ area⁢ C: 1 / 2×2×(Cm-Cm-2)surface⁢ area⁢ D: 1 / 2×2×(Cm+2-Cm)surface⁢ area⁢ E: 1 / 2×2×(Cm+4-Cm+2)surface⁢ area⁢ F: 1 / 2×2×(Cm+6-Cm+4)the following condition is satisfied:{(surface⁢ area⁢ D+surface⁢ area⁢ E)-(surface⁢ area⁢ A+surface⁢ area⁢ B)}≥4..

8. The multi-piece solid golf ball of claim 7, wherein the core hardness profile satisfies the following condition:(Cs-Cc)⁢≥2⁢0.

9. The multi-piece solid golf ball of claim 7, wherein the core has a hardness profile in which the following condition is satisfied:(Cs-Cc) / (Cm-Cc)⁢≥4.0.

10. The multi-piece solid golf ball of claim 7, wherein the core has a hardness profile in which the following condition is satisfied:surface area E >surface area D >surface area C.

11. The multi-piece solid golf ball of claim 1, wherein the core is formed of a rubber composition containing the following components (A) to (D):(A) a base rubber,(B) an organic peroxide,(C) water or a monocarboxylic acid metal salt, and(D) sulfur.

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