golf ball

Abstract

To provide a golf ball that is improved in a carry by a driver shot, and is excellent in an approach shot (especially, in a condition of getting stuck in a turf), and spin performance at a middle iron shot.SOLUTION: A golf ball has: a spherical core; and a cover positioned outside the spherical core. When a center hardness of the spherical core (shore C hardness), hardnesses (shore C hardnesses) at points of 2.5 mm, 5 mm, 7.5 mm, 10 mm, 12.5 mm, and 15 mm toward the surface from the center of the spherical core, and a surface hardness (shore C hardness) of the spherical core are H0, H2.5, H5, H7.5, H10, H12.5, H15, and Hs, respectively, the following relations are satisfied: (H2.5-H0)>(H12.5-H10)>(Hs-H15); (H10-H0)≥7; and 0≤(Hs-H15)≤5.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to golf balls, and more particularly to improvements in the hardness distribution of the core. [Background technology]

[0002] Various studies have been conducted to increase the distance of driver shots. For example, there is a technology that increases the distance of driver shots by increasing the difference in hardness between the surface and the center of the core and reducing the amount of spin. In addition to the distance of driver shots, there is also a demand for good distance for mid-iron shots and good spin performance for approach shots. Examples of such technologies include Patent Documents 1 and 2.

[0003] Patent Document 1 describes a multi-piece solid golf ball comprising a core, an intermediate layer, and a cover, wherein the core is formed mainly from a base rubber material and has a diameter of 32 mm or more, and the intermediate layer and cover are each formed from a resin material, and the internal hardness of the core is as follows: Shore C hardness at the center of the core is Cc, Shore C hardness at a position 2 mm from the center of the core is C2, Shore C hardness at a position 4 mm from the center of the core is C4, Shore C hardness at a position 6 mm from the center of the core is C6, Shore C hardness at a position 8 mm from the center of the core is C8, Shore C hardness at a position 10 mm from the center of the core is C10, and the core center When the Shore C hardness at a position 12 mm from the core is C12, the Shore C hardness at a position 14 mm from the core center is C14, the Shore C hardness at a position 16 mm from the core center is C16, the Shore C hardness of the core surface is Cs, the Shore C hardness at a position 3 mm inside the core surface is Cs-3, and the hardness at a position midway between the core surface and the core center is Cm, the values ​​of C8-C6, C6-C4, C4-C2, and C2-Cc are all within 4.0, and the values ​​of C16-C14, C14-C12, C12-C10, and C10-C8 are all within 5.5, and the following formulas (1), (2) and (3) Cs-Cc≧22 ···(1) (Cs-Cm) / (C4-Cc)≧4.0 ···(2) Cs - Cs - 3 ≤ 5.0 ···(3) The following conditions must be met, and the surface hardness of the sphere (intermediate layer coated sphere) in which the above core is covered with an intermediate layer and the surface hardness of the ball must be equal to the following formula Ball surface hardness < Surface hardness of sphere with intermediate layer coating ... (4) (However, the hardness values ​​for each layer mentioned above refer to the Shore C hardness values.) A multi-piece solid golf ball is disclosed that satisfies the following conditions.

[0004] Patent Document 2 discloses a multi-piece solid golf ball in which an intermediate layer is interposed between the core and the cover, characterized in that the surface hardness of the core, the sphere covered with the intermediate layer around the core (intermediate layer covered sphere), and the ball are all Shore D hardness, satisfying the relationship ball surface hardness ≤ surface hardness of the intermediate layer covered sphere ≥ surface hardness of the core, the thickness of the intermediate layer and the thickness of the cover satisfy the relationship (thickness of intermediate layer - thickness of cover) ≥ 0, and in the core hardness distribution, in JIS-C hardness, the relationship 22 ≤ core surface hardness (Cs) - core center hardness (Cc), 5 ≥ [hardness at a position 5 mm from the core center (C5) - core center hardness (Cc)] > 0, and [core surface hardness (Cs) - core center hardness (Cc)] / [hardness at a position midway between the surface and the center of the core (Cm) - core center hardness (Cc)] ≥ 4 is satisfied. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2021-62036 [Patent Document 2] Japanese Patent Publication No. 2016-112308 [Overview of the project] [Problems that the invention aims to solve]

[0006] There is a desire among professionals and advanced players to increase the amount of spin in middle iron shots. However, reducing the amount of spin to increase the driving distance of a driver shot also decreases the amount of spin in middle iron shots. Additionally, increasing the amount of spin in approach shots in the rough is also demanded by professionals and advanced players. The present invention has been made in view of the above circumstances, and an object thereof is to provide a golf ball having an improved driving distance and excellent spin performance in approach shots (particularly in rough conditions) and middle iron shots.

Means for Solving the Problems

[0007] The golf ball of the present invention is a golf ball having a spherical core and a cover located outside the spherical core, and the core hardness (Shore C hardness) of the spherical core, the hardness (Shore C hardness) at points 2.5 mm, 5 mm, 7.5 mm, 10 mm, 12.5 mm, and 15 mm from the center to the surface of the spherical core, and the surface hardness (Shore C hardness) of the spherical core are respectively H0, H 2.5 , H5, H 7.5 , H 10 , H 12.5 , H 15 , H s When set as such, it is characterized by satisfying the following relationships. (H 2.5 [[ID=2Z5]]-H0) > (H 12.5 -H 10 ) > (H s -H 15 ) (H 10 -H0) ≥ 7 0 ≤ (H s -H 15 ) ≤ 5

Advantages of the Invention

[0008] According to the present invention, it is possible to provide a golf ball having an improved driving distance in driver shots and excellent spin performance in approach shots (particularly in rough conditions) and middle iron shots.

Brief Description of the Drawings

[0009] [Figure 1] A partially cutaway cross-sectional view showing a golf ball according to one embodiment of the present invention. [Modes for carrying out the invention]

[0010] The present invention relates to a golf ball having a spherical core and a cover located outside the spherical core, wherein the central hardness (Shore C hardness) of the spherical core, the hardness (Shore C hardness) at points 2.5 mm, 5 mm, 7.5 mm, 10 mm, 12.5 mm, and 15 mm from the center of the spherical core toward the surface, and the surface hardness (Shore C hardness) of the spherical core are H0 and H0, respectively. 2.5 H5, H 7.5 H 10 H 12.5 H 15 H s When this is the case, the following relationship is satisfied. (H 2.5 -H0)>(H 12.5 -H 10 )>(H s -H 15 ) (H 10 -H0)≧7 0≦(H s -H 15 )≦5

[0011] The golf ball of the present invention, configured as described above, increases the initial velocity during driver shots and increases the spin speed during approach shots (especially under conditions where the ball is gripping the grass) and mid-iron shots. As a result, the distance of driver shots is increased, and the spin performance of approach shots and mid-iron shots is improved.

[0012] The central hardness (Shore C hardness) of a spherical core, and the hardness (Shore C hardness) at points 2.5 mm, 5 mm, 7.5 mm, 10 mm, 12.5 mm, and 15 mm from the center of the spherical core toward the surface, are measured at the center of the cross-section and at predetermined distances from the center, after cutting the spherical core through the center of the spherical core. The surface hardness of the spherical core is the hardness measured on the surface of the spherical core.

[0013] In the present invention, the spherical core is (H 2.5 -H0)>(H 12.5 -H 10 ) satisfies the following conditions. The aforementioned difference in hardness (H 2.5 -H0) and hardness difference (H 12.5 -H 10 ) difference ((H 2.5 -H0)-(H 12.5 -H 10 )) is Shore C hardness, preferably greater than 0, more preferably 0.5 or greater, even more preferably 1 or greater, preferably 5 or less, more preferably 4.5 or less, and even more preferably 4 or less. 2.5 -H0)-(H 12.5 -H 10 If the above range is present, the ball speed of driver shots, and the ball spin speed of approach shots (especially under conditions where the ball is gripping the grass) and mid-iron shots will be higher.

[0014] In the present invention, the spherical core is (H 12.5 -H 10 )>(H s -H 15 ) satisfies the following conditions. The aforementioned difference in hardness (H 12.5 -H 10 ) and hardness difference (H s -H 15 ) difference ((H 12.5 -H 10 )-(H s -H 15The Shore C hardness is preferably greater than 0, more preferably 0.5 or greater, even more preferably 1 or greater, preferably 5 or less, more preferably 4 or less, and even more preferably 3 or less. 12.5 -H 10 )-(H s -H 15 If the above range is present, the ball speed of driver shots, and the ball spin speed of approach shots (especially under conditions where the ball is gripping the grass) and mid-iron shots will be higher.

[0015] In the present invention, the spherical core is (H 10 -H0)≧7 is satisfied. The aforementioned difference in hardness (H 10 -H0) is preferably 7 or higher on the Shore C hardness scale, more preferably 8 or higher, and even more preferably 9 or higher. Hardness difference (H 10 If the hardness difference (H0) is 7 or higher on the Shore C hardness scale, the initial velocity of the golf ball in a driver shot will be higher. 10 -H0) is not particularly limited, but is preferably 20 or less in Shore C hardness, more preferably 18 or less, and even more preferably 16 or less.

[0016] In the present invention, the spherical core is 0 ≤ (H s -H 15 ) ≤ 5 satisfies. Hardness difference (H s -H 15 The hardness (H) is preferably 5 or less on the Shore C scale, more preferably 4.5 or less, and even more preferably 4 or less. s -H 15 If the hardness of the shore C is 5 or less, the spin speed of approach shots (especially under conditions where the club is gripping the grass) and mid-iron shots will increase. Also, the hardness difference (H s -H 15 ) is not particularly limited, but is preferably 0 or higher in Shore C hardness, more preferably 0.5 or higher, and even more preferably 1 or higher.

[0017] The aforementioned difference in hardness (H 2.5 -H0) is preferably 5 or higher on the Shore C hardness scale, more preferably 5.5 or higher, and even more preferably 6 or higher. Also, the hardness difference (H 2.5 The upper limit of -H0) is not particularly limited, but it is preferably 11 or less in Shore C hardness, more preferably 10 or less, and even more preferably 9 or less. 2.5 This is because if -H0) is within the aforementioned range, the initial velocity of the golf ball in a driver shot will be faster.

[0018] The aforementioned difference in hardness (H 12.5 -H 10 The hardness (H) is preferably 2 or higher on the Shore C scale, more preferably 2.5 or higher, even more preferably 3 or higher, preferably 7 or lower, more preferably 6 or lower, and even more preferably 5 or lower. 12.5 -H 10 This is because if the value is within the aforementioned range, the spin speed with middle irons will increase.

[0019] The aforementioned difference in hardness (H 10 -H0) and hardness difference (H s -H 15 ) ratio ((H 10 -H0) / (H s -H 15 The hardness difference (H) is preferably 2 or more, more preferably 3 or more, even more preferably 4 or more, preferably 12 or less, more preferably 11 or less, and even more preferably 10 or less. 10 -H0) and hardness difference (H s -H 15 ) ratio ((H 10 -H0) / (H s -H 15 This is because, if it falls within the aforementioned range, the spin speed with a middle iron will increase.

[0020] Surface hardness of spherical core (H s) and the hardness difference (H s -H0) is in Shore C hardness and is preferably 15 or more, more preferably 16 or more, still more preferably 17 or more, preferably 25 or less, more preferably 22 or less, and still more preferably 20 or less. If the hardness difference (H s -H0) is within the above range, the spin speed in a driver shot is suppressed and the flying distance increases.

[0021] The hardness (H5) at a point 5 mm from the center of the spherical core and the hardness (H 2.5 ) at a point 2.5 mm from the center of the spherical core, the hardness difference (H5 - H 2.5 ) is in Shore C hardness and is preferably 3 or less, more preferably 2.5 or less, still more preferably 2 or less, preferably 0 or more, more preferably 0.5 or more, and still more preferably 1 or more. If the hardness difference (H5 - H 2.5 ) is within the above range, the initial velocity of the golf ball in a driver shot becomes faster.

[0022] The hardness (H 7.5 ) at a point 7.5 mm from the center of the spherical core and the hardness (H5) at a point 5 mm from the center of the spherical core, the hardness difference (H 7.5 -H5) is in Shore C hardness and is preferably 3 or less, more preferably 2.5 or less, still more preferably 2 or less, preferably 0 or more, more preferably 0.5 or more, and still more preferably 1 or more. If the hardness difference (H 7.5 -H5) is within the above range, the initial velocity of the golf ball in a driver shot becomes faster.

[0023] The hardness (H 10 ) at a point 10 mm from the center of the spherical core and the hardness (H 7.5 ) at a point 7.5 mm from the center of the spherical core, the hardness difference (H 10 -H 7.5The hardness (H) is preferably 3 or less on the Shore C scale, more preferably 2.5 or less, even more preferably 2 or less, preferably 0 or more, more preferably 0.5 or more, and even more preferably 1 or more. 10 -H 7.5 This is because, within the aforementioned range, the initial velocity of the golf ball during a driver shot will be high, and the feel of the driver shot will be soft and pleasant.

[0024] Hardness (H) at a point 15 mm from the center of the spherical core 15 ) and hardness (H) at a point 12.5 mm from the center of the spherical core 12.5 ) Hardness difference (H 15 -H 12.5 The hardness (H) is preferably 7 or less on the Shore C scale, more preferably 6 or less, even more preferably 5 or less, preferably greater than 0, more preferably 0.5 or more, and even more preferably 1 or more. 15 -H 12.5 This is because, within the aforementioned range, the spin speed on middle iron shots will be faster, resulting in a softer and better feel.

[0025] Hardness (H) at a point 2.5 mm from the center of the spherical core 2.5 ) and the hardness at 5mm (H5) and the hardness at 7.5mm (H 7.5 ) and hardness at 10mm (H 10 ) average hardness ((H 2.5 +H5+H 7.5 +H 10 ) / 4) has a Shore C hardness of preferably 70 or higher, more preferably 71 or higher, even more preferably 72 or higher, preferably 80 or lower, more preferably 79 or lower, and even more preferably 78 or lower. This is because if the average hardness is within the above range, the initial velocity of the golf ball in a driver shot will be faster and the increase in spin speed will be suppressed.

[0026] Hardness (H) at a point 15 mm from the center of the spherical core 15) and the surface hardness (H) of the spherical core s ) average hardness ((H 15 +H s ) / 2) has a Shore C hardness, preferably 75 or higher, more preferably 76 or higher, even more preferably 77 or higher, preferably 85 or lower, more preferably 84 or lower, and even more preferably 83 or lower. This is because if the average hardness is within the above range, the spin speed on middle iron shots will be faster and the durability will be better.

[0027] The surface hardness (H) of the spherical core s The surface hardness (H) is not particularly limited, but is preferably 75 or higher on the Shore C hardness scale, more preferably 76 or higher, even more preferably 77 or higher, preferably 85 or lower, more preferably 84 or lower, and even more preferably 83 or lower. s This is because if the values ​​fall within the above range, the feel of approach shots will be softer, and the durability will be better.

[0028] The central hardness (H0) of the spherical core is not particularly limited, but is preferably 60 or higher on the Shore C hardness scale, more preferably 61 or higher, even more preferably 62 or higher, preferably 72 or lower, more preferably 71 or lower, and even more preferably 70 or lower. This is because if the central hardness (H0) of the spherical core is within the above range, the initial velocity of the golf ball in a driver shot will be faster and the spin speed will be suppressed.

[0029] The spherical core of the golf ball of the present invention is preferably formed from a rubber composition (hereinafter sometimes referred to as "core rubber composition") containing (a) a base rubber, (b) an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and / or its metal salt as a co-crosslinking agent, and (c) a crosslinking initiator.

[0030] (a) As the base rubber, natural rubber and / or synthetic rubber can be used, for example, polybutadiene rubber, natural rubber, polyisoprene rubber, styrene-polybutadiene rubber, ethylene-propylene-diene rubber (EPDM), etc. These may be used alone or in combination of two or more. Among these, high-cis polybutadiene having 40% by mass or more, preferably 80% by mass or more, and more preferably 90% by mass or more, of cis-1,4-bonds which are advantageous for repulsion is particularly preferred.

[0031] The high-cis polybutadiene preferably has a 1,2-vinyl bond content of 2% by mass or less, more preferably 1.7% by mass or less, and even more preferably 1.5% by mass or less. If the 1,2-vinyl bond content is 2% by mass or less, the resilience improves.

[0032] The high-cis polybutadiene is preferably synthesized using a rare earth element catalyst, and in particular, the use of a neodymium catalyst using a neodymium compound, which is a lanthanum series rare earth element compound, is preferable because it allows for the production of polybutadiene rubber with a high content of 1,4-cis bonds and a low content of 1,2-vinyl bonds with excellent polymerization activity.

[0033] The aforementioned high-cis polybutadiene has a Mooney viscosity (ML). 1+4 The Mooney viscosity (ML) in this invention is preferably 30 or higher, more preferably 32 or higher, even more preferably 35 or higher, preferably 140 or lower, more preferably 120 or lower, even more preferably 100 or lower, and most preferably 80 or lower. 1+4 (100℃)) refers to the value measured in accordance with JIS K6300, using an L rotor, with a preheating time of 1 minute, a rotor rotation time of 4 minutes, and under conditions of 100℃.

[0034] The high-cis polybutadiene preferably has a molecular weight distribution Mw / Mn (Mw: weight-average molecular weight, Mn: number-average molecular weight) of 2.0 or higher, more preferably 2.2 or higher, even more preferably 2.4 or higher, most preferably 2.6 or higher, preferably 6.0 or lower, more preferably 5.0 or lower, even more preferably 4.0 or lower, and most preferably 3.4 or lower. If the molecular weight distribution (Mw / Mn) of the high-cis polybutadiene is 2.0 or higher, the workability is improved, and if it is 6.0 or lower, the repulsiveness is increased. The molecular weight distribution was measured using gel permeation chromatography (Tosoh Corporation, "HLC-8120GPC") with a differential refractometer as the detector, under the conditions of column: GMHHXL (Tosoh Corporation), column temperature: 40°C, mobile phase: tetrahydrofuran, and the value was calculated as a standard polystyrene equivalent.

[0035] (b) α,β-unsaturated carboxylic acids and / or metal salts thereof having 3 to 8 carbon atoms are incorporated into the rubber composition as co-crosslinking agents and have the effect of crosslinking rubber molecules by graft polymerization onto the base rubber molecular chains.

[0036] Examples of α,β-unsaturated carboxylic acids having 3 to 8 carbon atoms include acrylic acid, methacrylic acid, fumaric acid, maleic acid, and crotonic acid.

[0037] Examples of metals that constitute the metal salts of α,β-unsaturated carboxylic acids having 3 to 8 carbon atoms include monovalent metal ions such as sodium, potassium, and lithium; divalent metal ions such as magnesium, calcium, zinc, barium, and cadmium; trivalent metal ions such as aluminum; and other ions such as tin and zirconium. The aforementioned metal components can be used individually or as a mixture of two or more. Among these, divalent metals such as magnesium, calcium, zinc, barium, and cadmium are preferred as the metal components. This is because using divalent metal salts of α,β-unsaturated carboxylic acids having 3 to 8 carbon atoms makes it easier for metal crosslinks to form between rubber molecules. In particular, zinc acrylate is preferred as the divalent metal salt because it increases the rebound properties of the resulting golf ball. Note that α,β-unsaturated carboxylic acids having 3 to 8 carbon atoms and / or their metal salts may be used individually or in combination of two or more.

[0038] (b) The content of α,β-unsaturated carboxylic acids and / or their metal salts having 3 to 8 carbon atoms is preferably 15 parts by mass or more, more preferably 20 parts by mass or more, even more preferably 25 parts by mass or more, preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 30 parts by mass or less, per 100 parts by mass of the base rubber. (b) If the content of α,β-unsaturated carboxylic acids and / or their metal salts having 3 to 8 carbon atoms is 15 parts by mass or more, the formed core will have an appropriate hardness and the rebound properties of the golf ball will be improved. On the other hand, if the content of α,β-unsaturated carboxylic acids and / or their metal salts having 3 to 8 carbon atoms is 50 parts by mass or less, the formed core will not become too hard and the feel of the golf ball when struck will be good.

[0039] (c) The crosslinking initiator is added to (a) crosslink the base rubber component. (c) Organic peroxides are preferred as crosslinking initiators. Specifically, examples of organic peroxides include dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and di-t-butyl peroxide. These organic peroxides may be used individually or in combination of two or more. Among these, dicumyl peroxide is preferred.

[0040] (c) The content of the crosslinking initiator is preferably 0.2 parts by mass or more, more preferably 0.4 parts by mass or more, even more preferably 0.6 parts by mass or more, preferably 5.0 parts by mass or less, more preferably 2.5 parts by mass or less, and even more preferably 1.0 part by mass or less, per 100 parts by mass of the base rubber. (c) If the content of the crosslinking initiator is within the above range, the hardness of the formed core will be appropriate, and the rebound properties of the golf ball will be good.

[0041] When the rubber composition contains only α,β-unsaturated carboxylic acids having 3 to 8 carbon atoms as a co-crosslinking agent, it is preferable that it further contains (d) a metal compound. This is because neutralizing the α,β-unsaturated carboxylic acids having 3 to 8 carbon atoms with a metal compound in the rubber composition provides substantially the same effect as when a metal salt of the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms is used as a co-crosslinking agent. Furthermore, when using both an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and its metal salt as co-crosslinking agents, a metal compound (d) may also be used.

[0042] The (d) metal compound is not particularly limited as long as it can neutralize the (b) α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms in the rubber composition. Examples of the (d) metal compound include metal hydroxides such as magnesium hydroxide, zinc hydroxide, calcium hydroxide, sodium hydroxide, lithium hydroxide, potassium hydroxide, and copper hydroxide; metal oxides such as magnesium oxide, calcium oxide, zinc oxide, and copper oxide; and metal carbon oxides such as magnesium carbonate, zinc carbonate, calcium carbonate, sodium carbonate, lithium carbonate, and potassium carbonate. A divalent metal compound is preferred as the (d) metal compound, and a zinc compound is more preferred. This is because divalent metal compounds react with α,β-unsaturated carboxylic acids having 3 to 8 carbon atoms to form metal crosslinks. Furthermore, using a zinc compound can yield a golf ball with high rebound. These (d) metal compounds may be used individually or in combination of two or more.

[0043] The rubber composition preferably further contains (e) an organic sulfur compound. The (e) organic sulfur compound is not particularly limited as long as it is an organic compound having a sulfur atom in its molecule, and examples include organic compounds having a thiol group (-SH) or a polysulfide bond with 2 to 4 sulfur atoms (-SS-, -SSS-, or -SSSS-), or metal salts thereof (-SM, -SMS-, etc., where M is a metal atom). Examples of the (e) organic sulfur compound include thiophenols, thionaphthols, polysulfides, thiurams, thiocarboxylic acids, dithiocarboxylic acids, sulfenamides, dithiocarbamates, thiazoles, and the like.

[0044] Examples of the thiophenols include thiophenols; thiophenols substituted with fluoro groups such as 4-fluorothiophenol, 2,4-difluorothiophenol, 2,5-difluorothiophenol, 2,6-difluorothiophenol, 2,4,5-trifluorothiophenol, 2,4,5,6-tetrafluorothiophenol, and pentafluorothiophenol; and chloro-group-substituted thiophenols such as 2-chlorothiophenol, 4-chlorothiophenol, 2,4-dichlorothiophenol, 2,5-dichlorothiophenol, 2,6-dichlorothiophenol, 2,4,5-trichlorothiophenol, 2,4,5,6-tetrachlorothiophenol, and pentachlorothiophenol. Thiophenols substituted with bromo groups; thiophenols substituted with bromo groups such as 4-bromothiophenol, 2,4-dibromothiophenol, 2,5-dibromothiophenol, 2,6-dibromothiophenol, 2,4,5-tribromothiophenol, 2,4,5,6-tetrabromothiophenol, and pentabromothiophenol; thiophenols substituted with iodine groups such as 4-iodothiophenol, 2,4-diiodothiophenol, 2,5-diiodothiophenol, 2,6-diiodothiophenol, 2,4,5-triiodothiophenol, 2,4,5,6-tetraiodothiophenol, and pentaiodothiophenol; or metal salts thereof.

[0045] Examples of the aforementioned thionaphthols (naphthalenchiols) include 2-thionaphthol, 1-thionaphthol, 1-chloro-2-thionaphthol, 2-chloro-1-thionaphthol, 1-bromo-2-thionaphthol, 2-bromo-1-thionaphthol, 1-fluoro-2-thionaphthol, 2-fluoro-1-thionaphthol, 1-cyano-2-thionaphthol, 2-cyano-1-thionaphthol, 1-acetyl-2-thionaphthol, 2-acetyl-1-thionaphthol, or metal salts thereof.

[0046] Polysulfides are organosulfur compounds having polysulfide bonds, and examples include disulfides, trisulfides, and tetrasulfides. Diphenyl polysulfides are preferred as the polysulfides.

[0047] Diphenyl polysulfides include diphenyl disulfide, as well as bis(4-fluorophenyl) disulfide, bis(2,5-difluorophenyl) disulfide, bis(2,6-difluorophenyl) disulfide, bis(2,4,5-trifluorophenyl) disulfide, bis(2,4,5,6-tetrafluorophenyl) disulfide, bis(pentafluorophenyl) disulfide, bis(4-chlorophenyl) disulfide, and bis(4-chlorophenyl) disulfide. Bis(2,5-dichlorophenyl) disulfide, bis(2,6-dichlorophenyl) disulfide, bis(2,4,5-trichlorophenyl) disulfide, bis(2,4,5,6-tetrachlorophenyl) disulfide, bis(pentachlorophenyl) disulfide, bis(4-bromophenyl) disulfide, bis(2,5-dibromophenyl) disulfide, bis(2,6-dibromophenyl) disulfide, bis(2,4,5-tribromophenyl) disulfide phenyl disulfide, bis(2,4,5,6-tetrabromophenyl) disulfide, bis(pentabromophenyl) disulfide, bis(4-iodophenyl) disulfide, bis(2,5-diiodophenyl) disulfide, bis(2,6-diiodophenyl) disulfide, bis(2,4,5-triiodophenyl) disulfide, bis(2,4,5,6-tetraiodophenyl) disulfide, bis(pentaiodophenyl) disulfide Examples include diphenyl disulfides substituted with halogen groups such as; diphenyl disulfides substituted with alkyl groups such as bis(4-methylphenyl) disulfide, bis(2,4,5-trimethylphenyl) disulfide, bis(pentamethylphenyl) disulfide, bis(4-t-butylphenyl) disulfide, bis(2,4,5-tri-t-butylphenyl) disulfide, and bis(penta-t-butylphenyl) disulfide; and so on.

[0048] Examples of thiuram compounds include thiuram monosulfides such as tetramethylthiuram monosulfide, thiuram disulfides such as tetramethylthiuram disulfide, tetraethylthiuram disulfide, and tetrabutylthiuram disulfide, and thiuram tetrasulfides such as dipentamethylenethiuram tetrasulfide. Examples of thiocarboxylic acids include naphthalenthiocarboxylic acid. Examples of dithiocarboxylic acids include naphthalenedithiocarboxylic acid. Examples of sulfenamides include N-cyclohexyl-2-benzothiazole sulfenamide, N-oxydiethylene-2-benzothiazole sulfenamide, and Nt-butyl-2-benzothiazole sulfenamide.

[0049] The aforementioned (e) organosulfur compounds can be used individually or as a mixture of two or more.

[0050] The content of the (e) organic sulfur compound is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, even more preferably 0.2 parts by mass or more, preferably 5.0 parts by mass or less, more preferably 3.0 parts by mass or less, and even more preferably 2.0 parts by mass or less, per 100 parts by mass of the (a) base rubber. If the content of the (e) organic sulfur compound is within the above range, the rebound properties will be good.

[0051] The rubber composition may further contain (f) a carboxylic acid and / or its metal salt. The (f) carboxylic acid and / or its metal salt is preferably a carboxylic acid and / or its salt having 1 to 30 carbon atoms. The carboxylic acid can be either an aliphatic carboxylic acid (saturated fatty acid, unsaturated fatty acid) or an aromatic carboxylic acid (such as benzoic acid). The amount of the (f) carboxylic acid and / or its metal salt is preferably 1 part by mass or more and 40 parts by mass or less per 100 parts by mass of the base rubber.

[0052] The rubber composition may optionally contain additives such as fillers for weight adjustment, antioxidants, decongestants, and softeners.

[0053] The fillers used in the rubber composition are primarily weight adjusters used to adjust the weight of the final golf ball product, and may be added as needed. Examples of such fillers include inorganic fillers such as zinc oxide, barium sulfate, calcium carbonate, magnesium oxide, tungsten powder, and molybdenum powder. The content of the filler is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, preferably 30 parts by mass or less, more preferably 25 parts by mass or less, and even more preferably 20 parts by mass or less, per 100 parts by mass of the base rubber. This is because a filler content of 0.5 parts by mass or more makes weight adjustment easier, and a content of 30 parts by mass or less tends to increase the weight fraction of the rubber component and thus increase the rebound properties.

[0054] The content of the anti-aging agent is preferably 0.1 parts by mass or more and 1 part by mass or less per 100 parts by mass of the base rubber (a). Furthermore, the content of the deconjugating agent is preferably 0.1 parts by mass or more and 5 parts by mass or less per 100 parts by mass of the base rubber (a).

[0055] The rubber composition is obtained by kneading (a) a base rubber, (b) an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and / or its metal salt, (c) a crosslinking initiator, and other components as needed. The kneading method is not particularly limited and may be carried out using known kneaders such as kneading rolls, Banbury mixers, and kneaders.

[0056] Spherical cores can be obtained by vulcanizing (heat press molding) the kneaded rubber composition in a mold. From the viewpoint of easily satisfying the core hardness requirements mentioned above, it is preferable to perform vulcanization in two stages, and it is more preferable to perform vulcanization under the following conditions.

[0057] In the first stage, the vulcanization temperature is preferably 120°C or higher, more preferably 125°C or higher, even more preferably 130°C or higher, preferably 160°C or lower, more preferably 155°C or lower, and even more preferably 150°C or lower. The vulcanization time is preferably 5 minutes or more, more preferably 6 minutes or more, even more preferably 7 minutes or more, preferably less than 20 minutes, more preferably 18 minutes or less, and even more preferably 15 minutes or less.

[0058] In the second stage, the vulcanization temperature is preferably 130°C or higher, more preferably 135°C or higher, even more preferably 140°C or higher, preferably 170°C or lower, more preferably 165°C or lower, and even more preferably 160°C or lower. The vulcanization time is preferably 5 minutes or more, more preferably 6 minutes or more, even more preferably 7 minutes or more, preferably 20 minutes or less, more preferably 18 minutes or less, and even more preferably 15 minutes or less.

[0059] The difference between the vulcanization temperature of the second stage and the first stage (vulcanization temperature of the second stage - vulcanization temperature of the first stage) is preferably 2°C or more, more preferably 3°C or more, even more preferably 4°C or more, preferably 20°C or less, more preferably 18°C ​​or less, and even more preferably 16°C or less.

[0060] The structure of the spherical core may be either a single-layer structure or a multi-layer structure, but a single-layer structure is preferred.

[0061] The diameter of the spherical core is preferably 34.8 mm or more, more preferably 36.8 mm or more, even more preferably 38.8 mm or more, preferably 42.2 mm or less, more preferably 41.8 mm or less, even more preferably 41.2 mm or less, and most preferably 40.8 mm or less. If the diameter of the spherical core is 34.8 mm or more, the thickness of the cover will not become too thick, and the resilience will be better. On the other hand, if the diameter of the spherical core is 42.2 mm or less, the cover will not become too thin, and the function of the cover will be better performed.

[0062] For spherical cores with a diameter of 34.8 mm to 42.2 mm, the amount of compressive deformation (the amount the spherical core shrinks in the compression direction) from an initial load of 98 N to a final load of 1275 N is preferably 2.0 mm or more, more preferably 2.5 mm or more, even more preferably 3.0 mm or more, preferably 5.0 mm or less, more preferably 4.5 mm or less, and even more preferably 4.0 mm or less. If the amount of compressive deformation is 2.0 mm or more, the feel of hitting the ball will be better, and if it is 5.0 mm or less, the rebound performance will be better.

[0063] The golf ball of the present invention has a cover located on the outside of the core. Preferably, the cover is formed from a resin composition containing a resin component. Examples of the resin component include ionomer resin, thermoplastic polyurethane elastomer sold by BASF Japan Ltd. under the trade name "Elastran®", thermoplastic polyamide elastomer sold by Arkema Inc. under the trade name "Pebax®", thermoplastic polyester elastomer sold by Toray DuPont Ltd. under the trade name "Hytrel®", and thermoplastic styrene elastomer sold by Mitsubishi Chemical Corporation under the trade name "Tefablock".

[0064] Examples of the ionomer resin include a binary copolymer of an olefin and an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms, in which at least a portion of the carboxyl groups are neutralized with metal ions; a terpolymer of an olefin and an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and an α,β-unsaturated carboxylic acid ester, in which at least a portion of the carboxyl groups are neutralized with metal ions; or mixtures thereof. The olefin is preferably an olefin having 2 to 8 carbon atoms, such as ethylene, propylene, butene, pentene, hexene, heptene, octene, etc., with ethylene being particularly preferred. Examples of the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms include acrylic acid, methacrylic acid, fumaric acid, maleic acid, crotonic acid, etc., with acrylic acid or methacrylic acid being particularly preferred. Furthermore, as α,β-unsaturated carboxylic acid esters, for example, methyl, ethyl, propyl, n-butyl, and isobutyl esters of acrylic acid, methacrylic acid, fumaric acid, maleic acid, etc. can be used, with acrylic acid esters or methacrylic acid esters being particularly preferred. Among these, as the ionomer resin, metal ion neutralized products of ethylene-(meth)acrylic acid binary copolymers and metal ion neutralized products of ethylene-(meth)acrylic acid-(meth)acrylic acid ester terpolymers are preferred.

[0065] A specific example of the aforementioned ionomer resin, exemplified by its trade name, is "Himilan (registered trademark)" commercially available from Mitsui DuPont Polychemical Co., Ltd. (for example, Himilan 1555 (Na), Himilan 1557 (Zn), Himilan 1605 (Na), Himilan 1706 (Zn), Himilan 1707 (Na), Himilan AM3711 (Mg), Himilan AM7329 (Zn), etc., and as a ternary copolymer ionomer resin, Himilan 1856 (Na), Himilan 1855 (Zn), etc.)."

[0066] Furthermore, examples of ionomer resins commercially available from DuPont include "Surlyn" (registered trademark) (for example, Surlyn 8945 (Na), Surlyn 9945 (Zn), Surlyn 8140 (Na), Surlyn 8150 (Na), Surlyn 9120 (Zn), Surlyn 9150 (Zn), Surlyn 6910 (Mg), Surlyn 6120 (Mg), Surlyn 7930 (Li), Surlyn 7940 (Li), Surlyn AD8546 (Li), etc., and examples of ternary copolymer ionomer resins include Surlyn 8120 (Na), Surlyn 8320 (Na), Surlyn 9320 (Zn), Surlyn 6320 (Mg), HPF1000 (Mg), HPF2000 (Mg), etc.).

[0067] In addition, examples of ionomer resins commercially available from ExxonMobil Chemicals, Inc. include "Iotek (registered trademark) (for example, Iotek 8000 (Na), Iotek 8030 (Na), Iotek 7010 (Zn), Iotek 7030 (Zn), etc., and as ternary copolymer ionomer resins, Iotek 7510 (Zn), Iotek 7520 (Zn), etc.)."

[0068] The Na, Zn, Li, Mg, etc., listed in parentheses after the trade names of the ionomer resins indicate the metal species of the neutralized metal ions. The ionomer resins may be used alone or in mixtures of two or more types.

[0069] The resin composition preferably contains a thermoplastic polyurethane elastomer or an ionomer resin as a resin component. The content of the thermoplastic polyurethane elastomer or ionomer resin in the resin component of the resin composition is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more. The resin composition may contain only a thermoplastic polyurethane elastomer or an ionomer resin as a resin component.

[0070] In addition to the resin components described above, the resin composition may also contain pigment components such as white pigments (e.g., titanium dioxide), blue pigments, and red pigments, weight adjusters such as zinc oxide, calcium carbonate, and barium sulfate, dispersants, antioxidants, ultraviolet absorbers, light stabilizers, fluorescent materials, or fluorescent whitening agents, to the extent that they do not impair the performance of the cover.

[0071] The content of the white pigment (for example, titanium dioxide) is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, even more preferably 1.5 parts by mass, preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and even more preferably 6 parts by mass or less, per 100 parts by mass of the resin component constituting the cover. By setting the content of the white pigment to 0.5 parts by mass or more, the cover can be given opacity. Furthermore, if the content of the white pigment is 10 parts by mass or less, the durability of the resulting cover will not be impaired.

[0072] The material hardness of the cover (i.e., the slab hardness of the resin composition constituting the cover) is preferably set appropriately according to the desired performance of the golf ball. For example, in the case of distance-type golf balls that prioritize distance, the material hardness of the cover is preferably 50 or higher on the Shore D scale, more preferably 55 or higher, even more preferably 60 or higher, preferably 80 or lower, more preferably 70 or lower, and even more preferably 68 or lower. By setting the material hardness of the cover to 50 or higher, a golf ball with a high launch angle and low spin can be obtained in driver shots and iron shots, improving distance. Also, by setting the material hardness of the cover to 80 or lower, a golf ball with excellent durability can be obtained. Furthermore, in the case of spin-type golf balls that prioritize control, the material hardness of the cover is preferably less than 50 on the Shore D scale, more preferably 48 or lower, even more preferably 45 or lower, preferably 20 or higher, more preferably 23 or higher, and even more preferably 26 or higher. If the hardness of the cover material is less than 50 on the Shore D scale, the amount of spin on approach shots will increase, resulting in a golf ball that stops more easily on the green. Furthermore, setting the slab hardness to 20 or higher improves scratch resistance. In the case of multiple cover layers, the hardness of the materials constituting each layer may be the same or different.

[0073] Examples of methods for forming the cover include a method in which a hollow shell is formed from the resin composition and the core is covered with multiple shells and then compression molded (preferably, a method in which a hollow half-shell is formed from the resin composition and the core is covered with two half-shells and then compression molded), or a method in which the resin composition is directly injection molded onto the core.

[0074] When forming a cover by compression molding, the half-shell can be formed by either compression molding or injection molding, but compression molding is preferred. Conditions for compressing the resin composition to form a half-shell include, for example, a pressure of 1 MPa to 20 MPa and a molding temperature of -20°C to 70°C relative to the flow start temperature of the resin composition. By using these molding conditions, a half-shell with a uniform thickness can be formed. As a method for forming a cover using a half-shell, for example, a method of covering a core with two half-shells and then compression molding can be used. Conditions for compressing the half-shell to form a cover include, for example, a molding pressure of 0.5 MPa to 25 MPa and a molding temperature of -20°C to 70°C relative to the flow start temperature of the resin composition. By using these molding conditions, a cover with a uniform thickness can be formed.

[0075] When forming a cover by injection molding a resin composition, the resin composition may be used in the form of extruded pellets, or the cover material, such as the base resin component and pigment, may be dry-blended and directly injection-molded. For the upper and lower molds used for molding the cover, it is preferable to use molds having hemispherical cavities and pimples, where a portion of the pimples also serves as a movable hold pin. The cover can be formed by injection molding by protruding the hold pins, inserting and holding the core, injecting the resin composition, and then cooling it. For example, this can be done by injecting a resin composition heated to 200°C to 250°C into a mold clamped at a pressure of 9 MPa to 15 MPa over 0.5 to 5 seconds, cooling it for 10 to 60 seconds, and then opening the mold.

[0076] When forming the cover, indentations called dimples are usually formed on the surface. Preferably, the total number of dimples formed on the cover is between 200 and 500. If the total number of dimples is within the above range, the dimple size will be appropriate, and the effect of the dimples will be easily obtained. The shape of the formed dimples (planar view shape) is not particularly limited, and a circle; a polygon such as a roughly triangular, roughly square, roughly pentagon, roughly hexagon; or other irregular shapes may be used individually or in combination of two or more types.

[0077] The thickness of the cover is preferably 4.0 mm or less, more preferably 3.0 mm or less, and even more preferably 2.0 mm or less. If the cover thickness is 4.0 mm or less, the rebound and feel of the resulting golf ball will be better. The thickness of the cover is preferably 0.3 mm or more, more preferably 0.4 mm or more, and even more preferably 0.5 mm or more. If the cover thickness is 0.3 mm or more, the impact durability and abrasion resistance of the cover will be improved. In the case of multiple cover layers, it is preferable that the total thickness of the multiple cover layers is within the above range.

[0078] The cover may be a single layer or multiple layers. In this invention, if the cover has multiple layers, the cover layer located between the spherical core and the outermost cover layer may simply be referred to as the "intermediate layer".

[0079] The golf ball body with the cover molded onto it is preferably removed from the mold and subjected to surface treatment such as deburring, cleaning, and sandblasting as necessary. A coating or mark can also be formed as desired. The thickness of the coating is not particularly limited, but is preferably 5 μm or more, more preferably 6 μm or more, even more preferably 7 μm or more, preferably 50 μm or less, more preferably 40 μm or less, and even more preferably 30 μm or less. A thickness of 5 μm or more makes the coating less likely to wear away even with continuous use, and a thickness of 50 μm or less allows for sufficient dimple effect, improving the flight performance of the golf ball.

[0080] The diameter of the golf ball of the present invention is preferably 40 mm to 45 mm. From the viewpoint of satisfying the standards of the United States Golf Association (USGA), a diameter of 42.67 mm or more is particularly preferred. From the viewpoint of suppressing air resistance, a diameter of 44 mm or less is more preferred, and 42.80 mm or less is particularly preferred. Furthermore, the mass of the golf ball of the present invention is preferably 40 g to 50 g. From the viewpoint of obtaining a large inertia, a mass of 44 g or more is more preferred, and 45.00 g or more is particularly preferred. From the viewpoint of satisfying the standards of the USGA, a mass of 45.93 g or less is particularly preferred.

[0081] In the golf ball of the present invention, when the diameter is 40 mm to 45 mm, the amount of compression deformation (the amount the golf ball shrinks in the compression direction) when an initial load of 98 N is applied and a final load of 1275 N is applied is preferably 2.0 mm or more, more preferably 2.2 mm or more, even more preferably 2.4 mm or more, preferably 3.5 mm or less, more preferably 3.3 mm or less, even more preferably 3.1 mm or less, and particularly preferably 2.8 mm or less. A golf ball with a compression deformation of 2.0 mm or more is not too hard and has a good feel when hit. On the other hand, by making the compression deformation amount 3.5 mm or less, the rebound performance is increased.

[0082] The structure of the golf ball of the present invention is not particularly limited as long as it has a spherical core and a cover located outside the spherical core. Figure 1 is a partially cutaway cross-sectional view showing a golf ball 1 according to one embodiment of the present invention. The golf ball 1 has a spherical core 2 and a cover 3 that covers the spherical core 2. Numerous dimples 31 are formed on the surface of the cover. The portion of the surface of the golf ball 1 other than the dimples 31 is a land 32. The golf ball 1 has a paint layer and a mark layer on the outside of the cover 3, but these layers are not shown in the illustration.

[0083] Examples of golf balls of the present invention include a two-piece golf ball consisting of a spherical core and a single-layer cover disposed to cover the spherical core; and a multi-piece golf ball (including a three-piece golf ball) having a spherical core, one or more intermediate layers disposed to cover the spherical core, and a single-layer cover disposed to cover the intermediate layers. The present invention can be suitably used for golf balls of any of the above structures.

[0084] In a preferred embodiment, the golf ball of the present invention has a spherical core, one or more intermediate layers, and a cover, and the surface hardness (Shore C hardness) of the spherical core, the surface hardness (Shore C hardness) of the intermediate layers, and the surface hardness (Shore C hardness) of the ball satisfy the relationship: surface hardness of the spherical core < surface hardness of the intermediate layers > surface hardness of the ball. This relationship is satisfied because it increases the initial velocity of the golf ball in a driver shot and increases the spin speed in an approach shot. When two or more intermediate layers are provided, the surface hardness of the intermediate layers is the hardness measured on the surface of a sphere in which all two or more intermediate layers are formed on the spherical core.

[0085] The surface hardness of the intermediate layer is preferably 80 or higher on the Shore C scale, more preferably 85 or higher, even more preferably 90 or higher, preferably 100 or lower, more preferably 99 or lower, and even more preferably 98 or lower. This is because if the surface hardness of the intermediate layer is within the above range, the initial velocity of the golf ball in a driver shot will be faster. Note that the surface hardness of the intermediate layer is the surface hardness of the sphere covered with the intermediate layer.

[0086] The slab hardness of the intermediate layer is preferably 60 or higher on the Shore D scale, more preferably 62 or higher, even more preferably 64 or higher, preferably 76 or lower, more preferably 74 or lower, and even more preferably 72 or lower. This is because if the slab hardness of the intermediate layer is within the above range, the spin speed of the golf ball during a driver shot is suppressed, resulting in a softer feel.

[0087] The thickness of the intermediate layer is preferably 0.8 mm or more, more preferably 0.9 mm or more, even more preferably 1.0 mm or more, preferably 2.0 mm or less, more preferably 1.9 mm or less, and even more preferably 1.8 mm or less. This is because if the thickness of the intermediate layer is within the above range, durability will be good and the feel of the shot with a middle iron will be soft and good.

[0088] The surface hardness of the golf ball of the present invention is preferably 50 or higher on the Shore C scale, more preferably 55 or higher, even more preferably 60 or higher, preferably 80 or lower, more preferably 75 or lower, and even more preferably 70 or lower. This is because if the surface hardness of the golf ball is within the above range, the initial spin velocity on approach shots will be faster. [Examples]

[0089] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following examples, and any modifications and embodiments that do not depart from the spirit of the present invention are all included within the scope of the present invention.

[0090] [Evaluation Method] (1) Compression deformation amount (mm) The amount of deformation in the compressive direction (the amount the core or golf ball shrinks in the compressive direction) was measured from an initial load of 98N applied to the core or golf ball until a final load of 1275N was applied.

[0091] (2) Slab hardness (Shore D hardness) Using an intermediate layer composition or a cover composition, sheets with a thickness of approximately 2 mm were manufactured by injection molding and stored at 23°C for two weeks. These sheets were stacked in groups of three or more to avoid interference from the measurement substrate, and measured using a P1 automatic rubber hardness tester manufactured by Polymer Instruments Co., Ltd., equipped with a Shore D spring hardness tester as specified in ASTM-D2240.

[0092] (3) Core hardness distribution (Shore C hardness) The core surface hardness was defined as the Shore C hardness measured on the surface of the core using a Model P1 automatic rubber hardness tester manufactured by Polymer Instruments Co., Ltd., which is equipped with a spring-type Shore C hardness tester. Additionally, the core was cut into hemispherical sections, and the hardness was measured at the center of the cut surface and at predetermined distances from the center. The core hardness was calculated by measuring the hardness at four points at predetermined distances from the center of the core cross-section and averaging these values.

[0093] (4) Surface hardness of the intermediate layer and surface hardness of the ball (Shore C hardness) Using a P1 automatic rubber hardness tester manufactured by Polymer Instruments Co., Ltd., equipped with a spring-type Shore C hardness tester, the Shore C hardness was measured on the surface of an intermediate-layer coated sphere (in which an intermediate layer is formed on a spherical core) and the surface of a golf ball. These values ​​were defined as the surface hardness of the intermediate layer and the surface hardness of the ball, respectively.

[0094] (5) Ball speed, spin rate, and distance of driver shots A W#1 driver (manufactured by Sumitomo Rubber Industries, product name "SRIXON ZX7", loft angle: 10.5°) was mounted on a swing machine manufactured by Golf Laboratory. The point of impact was set to the center of the face. Golf balls were struck at a head speed of 50 m / s, and the ball speed (m / s), spin rate (rpm), and distance (distance from the launch point to the landing point (m)) of the golf ball immediately after impact were measured. Measurements were taken 12 times for each golf ball, and the average value was used as the measurement value for that golf ball. The spin rate of the golf ball immediately after impact was measured by taking a series of photographs of the golf ball after impact. The spin rate, ball speed, and distance of the driver shot are shown in Tables 4 to 6 as the difference compared to golf ball No. 6.

[0095] (6) Spin rate of mid-iron shots A swing machine manufactured by Golf Laboratory Inc. was fitted with an I#7 iron (manufactured by Sumitomo Rubber Industries, product name "SRIXON ZX7", loft angle: 32°). The point of impact was set to the center of the face. Golf balls were struck at a head speed of 39 m / s, and the spin rate (rpm) of the golf ball immediately after impact was measured. Measurements were taken 12 times for each golf ball, and the average value was used as the measurement for that golf ball. The spin rate of the golf ball immediately after impact was measured by taking a series of photographs of the golf ball after impact. The spin rate of the middle iron shot is shown in Tables 4 to 6 as the difference from golf ball No. 6.

[0096] (7) Amount of spin on approach shots (under conditions where the ball is gripping the grass) A sand wedge (Cleveland Golf, product name "RTX ZIPCORE", loft angle: 58°) was attached to a swing machine manufactured by Golf Laboratory, and two blades of wild grass (approximately 3 cm long) were attached to the golf ball to be measured. The golf ball was struck at a head speed of 16 m / s, ensuring that the wild grass was positioned between the clubface and the golf ball during impact, and the spin rate (rpm) of the golf ball immediately after impact was measured. Each golf ball was measured 12 times, and the average value was taken as the measurement for that golf ball. The spin rate of the golf ball immediately after impact was measured by taking a series of photographs of the golf ball after impact. The spin rate of approach shots is shown in Tables 4 to 6 as the difference from golf ball No. 6.

[0097] [Golf ball manufacturing] (1) Core fabrication The rubber compositions shown in Table 1 were kneaded using a kneading roll, and then molded in upper and lower molds having hemispherical cavities under the vulcanization conditions shown in Table 1 to obtain spherical cores with diameters of 38.9 mm to 39.7 mm. The amount of barium sulfate was adjusted so that the mass of the golf ball was 45.6 g.

[0098] [Table 1]

[0099] Polybutadiene: JSR Corporation, "BR730 (High-Sys Polybutadiene)" Zinc acrylate: Manufactured by Nichishoku Techno Fine Chemical Co., Ltd., "ZN-DA90S" Zinc oxide: Manufactured by Toho Zinc Co., Ltd., "Ginrei R" Barium sulfate: "Barium Sulfate BD" manufactured by Sakai Chemical Co., Ltd. Benzoic acid: Manufactured by Tokyo Chemical Industry Co., Ltd. (purity 98% or higher) Pentabromodiphenyl disulfide: Manufactured by Kawaguchi Chemical Industry Co., Ltd. Diphenyl disulfide: Manufactured by Sumitomo Seika Co., Ltd. Dicumyl peroxide: Manufactured by NOF Corporation, "Percumyl (registered trademark) D"

[0100] (2) Preparation of the intermediate layer composition and the cover composition The materials for the formulations shown in Tables 2 and 3 were mixed using a twin-screw compounding extruder to prepare pelletized intermediate layer compositions and cover compositions. The extrusion conditions were a screw diameter of 45 mm, a screw rotation speed of 200 rpm, and a screw L / D ratio of 35. The mixture was heated to 160-240°C at the position of the extruder die.

[0101] [Table 2]

[0102] Surlin® 8150: Sodium ion-neutralized ethylene-methacrylic acid copolymer ionomer resin, manufactured by DuPont. Hymiran (registered trademark) AM7329: Manufactured by Mitsui DuPont Polychemicals, zinc ion-neutralized ethylene-methacrylic acid copolymer ionomer resin. Hymiran AM1605: Manufactured by Mitsui DuPont Polychemicals, sodium ion-neutralized ethylene-methacrylic acid copolymer ionomer resin. Titanium dioxide: Manufactured by Ishihara Sangyo Co., Ltd., "A-220"

[0103] [Table 3]

[0104] Elastran (registered trademark) NY84A: Thermoplastic polyurethane elastomer manufactured by BASF Japan. Elastran (registered trademark) NY82A: Thermoplastic polyurethane elastomer manufactured by BASF Japan. Chinuvin® 770: Manufactured by BASF Japan, bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate Titanium dioxide: Manufactured by Ishihara Sangyo Co., Ltd., "A-220"

[0105] (3) Making golf balls The intermediate layer composition was injection molded onto the spherical core obtained as described above to obtain an intermediate layer coated sphere. The obtained intermediate layer coated sphere was placed into a final mold having numerous dimples on the cavity surface. Half shells were obtained from the cover composition by compression molding. Two half shells were placed on the intermediate layer coated sphere in the final mold to obtain a golf ball in which numerous dimples were formed on the cover, with the shape of the dimples being inverted from the shape of the dimples on the cavity surface. The results of the evaluation of the obtained golf balls are shown in Tables 4 to 6.

[0106] [Table 4]

[0107] [Table 5]

[0108] [Table 6]

[0109] From the results in Tables 4 to 6, a golf ball having a spherical core and a cover located outside the spherical core is provided, wherein the central hardness (Shore C hardness) of the spherical core, the hardness (Shore C hardness) at points 2.5 mm, 5 mm, 7.5 mm, 10 mm, 12.5 mm, and 15 mm from the center of the spherical core toward the surface, and the surface hardness (Shore C hardness) of the spherical core are H0 and H0, respectively. 2.5 H5, H 7.5 H 10 H 12.5 H 15 H s In this case, golf balls that satisfy the following relationship all exhibit improved distance in driver shots and superior spin performance in approach shots (especially under conditions where the ball is gripping the grass) and mid-iron shots. (H 2.5 -H0)>(H 12.5 -H 10 )>(H s -H 15 ) (H 10 -H0)≧7 0≦(H s -H 15 )≦5 [Industrial applicability]

[0110] The golf ball of the present invention offers improved distance in driver shots and superior spin performance in approach shots (especially under conditions where the ball is gripping the grass) and mid-iron shots.

[0111] A preferred embodiment of the present invention is a golf ball having a spherical core and a cover located outside the spherical core, wherein the central hardness (Shore C hardness) of the spherical core, the hardness (Shore C hardness) at points 2.5 mm, 5 mm, 7.5 mm, 10 mm, 12.5 mm, and 15 mm from the center of the spherical core toward the surface, and the surface hardness (Shore C hardness) of the spherical core are H0 and H0, respectively. 2.5 H5, H 7.5 H 10 H 12.5 H 15 H sThe golf ball is characterized by satisfying the following relationship. (H 2.5 -H0)>(H 12.5 -H 10 )>(H s -H 15 ) (H 10 -H0)≧7 0≦(H s -H 15 )≦5

[0112] A preferred embodiment of the present invention is (H 2.5 This is the golf ball according to embodiment 1 that satisfies the relationship -H0)≧5.

[0113] A preferred embodiment 3 of the present invention is 2 ≤ (H 12.5 -H 10 The golf ball is according to embodiment 1 or 2, satisfying the relationship ) ≤ 7.

[0114] A preferred embodiment of the present invention is (H 2.5 -H0)-(H 12.5 -H 10 The golf ball is one of the embodiments 1 to 3 above that satisfies the relationship )≦5.

[0115] A preferred embodiment of the present invention is (H 12.5 -H 10 )-(H s -H 15 The golf ball is one of the embodiments 1 to 4 above that satisfies the relationship ) ≤ 5.

[0116] A preferred embodiment of the present invention is (H 10 -H0) / (H s -H 15 A golf ball according to any one of the above embodiments 1 to 5 that satisfies the relationship )≧2.

[0117] A preferred embodiment of the present invention, 7, is 15 ≤ (H s This is a golf ball according to any one of the above embodiments 1 to 6 that satisfies the relationship -H0) ≤ 25.

[0118] A preferred embodiment 8 of the present invention is a golf ball according to any one of embodiments 1 to 7 that satisfies the relationship H0 ≥ 60.

[0119] A preferred embodiment 9 of the present invention is a golf ball according to any one of embodiments 1 to 8, having an intermediate layer between the spherical core and the cover, wherein the surface hardness (Shore C hardness) of the spherical core, the surface hardness (Shore C hardness) of the intermediate layer, and the surface hardness of the ball (Shore C hardness) satisfy the relationship: surface hardness of the spherical core < surface hardness of the intermediate layer > surface hardness of the ball.

[0120] A preferred embodiment 10 of the present invention is a golf ball according to any one of embodiments 1 to 9, wherein the amount of compressive deformation when a final load of 1275N is applied to the golf ball from a state in which an initial load of 98N is applied is 2.80 mm or less.

Claims

1. A golf ball having a spherical core and a cover located outside the spherical core, wherein the central hardness of the spherical core (Shore C hardness), the hardness at points 2.5 mm, 5 mm, 7.5 mm, 10 mm, 12.5 mm, and 15 mm from the center of the spherical core toward the surface (Shore C hardness), and the surface hardness of the spherical core (Shore C hardness) are all measured as H ０ H ２．５ H ５ H ７．５ H １０ H １２．５ H １５ H ｓ A golf ball characterized by satisfying the following relationship. (H ２．５ -H ０ )>(H １２．５ -H １０ )>(H ｓ -H １５ ) (H １０ -H ０ )≧7 0≦(H ｓ -H １５ )≦5 (H 2.5 - H 0 )≧5

2. A golf ball having a spherical core and a cover located outside the spherical core, characterized in that when the central hardness (Shore C hardness) of the spherical core, the hardness (Shore C hardness) at points 2.5 mm, 5 mm, 7.5 mm, 10 mm, 12.5 mm, and 15 mm from the center of the spherical core toward the surface are H0, H2.5, H5, H7.5, H10, H12.5, H15, and Hs respectively, the following relationship is satisfied. (H 2.5 - H 0 )>(H 12.5 - H 10 )>(H s -H 15 ) (H 10 −H 0 )≧7 0≦(H s −H 15 )≦5 15≦(H s −H 0 )≦25

3. A golf ball having a spherical core, a cover located outside the spherical core, and an intermediate layer between the spherical core and the cover, The surface hardness of the spherical core (Shore C hardness), the surface hardness of the intermediate layer (Shore C hardness), and the surface hardness of the ball (Shore C hardness) satisfy the relationship: surface hardness of the spherical core < surface hardness of the intermediate layer > surface hardness of the ball. A golf ball characterized in that, when the central hardness (Shore C hardness) of the spherical core, the hardness (Shore C hardness) at points 2.5 mm, 5 mm, 7.5 mm, 10 mm, 12.5 mm, and 15 mm from the center of the spherical core toward the surface are H0, H2.5, H5, H7.5, H10, H12.5, H15, and Hs respectively, the golf ball satisfies the following relationship. (H 2.5 - H 0 )>(H 12.5 - H 10 )>(H s -H 15 ) (H 10 −H 0 )≧7 0≦(H s −H 15 )≦5

4. (H ２．５ -H ０ A golf ball according to claim 2 or 3 that satisfies the relationship ) ≥ 5.

5. 2 ≤ (H １２．５ -H １０ A golf ball according to any one of claims 1 to 3 that satisfies the relationship ) ≤ 7.

6. (H ２．５ -H ０ ) - (H １２．５ -H １０ A golf ball according to any one of claims 1 to 3 that satisfies the relationship ) ≤ 5.

7. (H １２．５ -H １０ ) - (H ｓ -H １５ A golf ball according to any one of claims 1 to 3 that satisfies the relationship ) ≤ 5.

8. (H １０ -H ０ ) / (H ｓ -H １５ A golf ball according to any one of claims 1 to 3 that satisfies the relationship ) ≥ 2.

9. 15 ≤ (H ｓ -H ０ A golf ball according to claim 1 or 3 that satisfies the relationship ) ≤ 25.

10. H ０ A golf ball according to any one of claims 1 to 3 that satisfies the relationship ≥ 60.

11. A golf ball according to claim 1 or 2, having an intermediate layer between the spherical core and the cover, wherein the surface hardness of the spherical core (Shore C hardness), the surface hardness of the intermediate layer (Shore C hardness), and the surface hardness of the ball (Shore C hardness) satisfy the relationship: surface hardness of the spherical core < surface hardness of the intermediate layer > surface hardness of the ball.

12. A golf ball according to any one of claims 1 to 3, wherein the amount of compressive deformation when a final load of 1275 N is applied to the golf ball after an initial load of 98 N has been applied is 2.80 mm or less.

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