Golf ball

Abstract

To provide a golf ball 2 excellent in flight performance and ball hitting feeling.SOLUTION: A golf ball 2 includes a core 4, a mid-layer 6, and a cover 8. The hardness Hm of the mid-layer 6 is greater than the hardness Hc of the cover 8. In a graph on which distances and Shore C hardnesses at the central point of the core 4, six points between the central point and the surface of the core 4, and the point on the surface are plotted, a slope A1 of a straight line connecting the central point and a first point is equal to or greater than 1.00. The maximum value Amax of the absolute values of the following slopes A2 to A7 is 0.90 or less. A2: a slope of a straight line connecting the first point and a second point. A3: a slope of a straight line connecting the second point and a third point. A4: a slope of a straight line connecting the third point and a fourth point. A5: a slope of a straight line connecting the fourth point and a fifth point. A6: a slope of a straight line connecting the fifth point and a sixth point. A7: a slope of a straight line connecting the sixth point and the point on the surface.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This specification discloses a golf ball having a core, an intermediate layer, and a cover.

Background Art

[0002] The concerns of golf players regarding golf balls are flight performance. Golf players mainly value the carry distance in driver shots. For golf players, the feel of hitting the golf ball is also important. Golf players value the feel of hitting the golf ball when it is struck with a short iron and a putter. Improvements regarding flight performance and feel of hitting are disclosed in U.S. Patent No. 7,344,455.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When struck with a golf club, the golf ball begins to fly with an initial velocity, launch angle, and spin. A golf ball with a high initial velocity is advantageous in terms of flight performance. The initial velocity correlates with the coefficient of restitution of the golf ball. A golf ball with a high coefficient of restitution has excellent flight performance.

[0005] To achieve a large carry distance, appropriate airtime and appropriate ballistic height are required. Appropriate launch angle and appropriate spin speed can achieve appropriate airtime and appropriate ballistic height. A golf ball with a high dependence of airtime and ballistic height on the launch angle has appropriate lift and drag acting on the flying golf ball. A golf ball with a high dependence of airtime and ballistic height on the launch angle has better flight performance than a golf ball with a high dependence of airtime and ballistic height on the spin speed.

[0006] The coefficient of restitution, launch angle, and initial spin depend on the hardness distribution of the golf ball. Conventional hardness distributions that can contribute to a large coefficient of restitution can result in excessive spin. The flight performance of conventional golf balls is not sufficient.

[0007] The feel at impact can also depend on the hardness distribution. Conventional hardness distributions that can contribute to a large coefficient of restitution cannot achieve excellent feel at impact. With conventional golf balls, the balance between flight performance and feel at impact is not sufficient.

[0008] It is an object of the present applicant to provide a golf ball having excellent flight performance in driver shots and excellent feel at impact in putting.

Means for Solving the Problems

[0009] The golf ball disclosed in this specification has a core with a diameter of 35 mm or more, an intermediate layer located outside the core, and a cover located outside the intermediate layer. The Shore D hardness Hm of the intermediate layer is greater than the Shore D hardness Hc of the cover. In the core, in a graph in which the distances (mm) and Shore C hardness of the center point, a first point having a distance of 2.5 mm from this center, a second point having a distance of 5.0 mm from this center, a third point having a distance of 7.5 mm from this center, a fourth point having a distance of 10.0 mm from this center, a fifth point having a distance of 12.5 mm from this center, a sixth point having a distance of 15.0 mm from this center, and a point on the surface are plotted, the slope A1 of the straight line connecting the center point and the first point is 1.00 or more. The maximum value Amax of the absolute values of the following slopes A2 to A7 is 0.90 or less. A2: The slope of the straight line connecting the first point and the second point A3: The slope of the straight line connecting the second point and the third point A4: The slope of the straight line connecting the third point and the fourth point A5: The slope of the straight line connecting the fourth point and the fifth point A6: The slope of the straight line connecting the fifth point and the sixth point A7: The slope of the straight line connecting the sixth point and the point on the surface

Advantages of the Invention

[0010] The golf ball disclosed in this specification is excellent in flight performance in driver shots and hitting feeling in putting.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0012] Hereinafter, preferred embodiments will be described in detail with reference to the drawings as appropriate.

[0013] [Golf Ball] The golf ball 2 shown in FIG. 1 has a spherical core 4, an intermediate layer 6 located outside the core 4, and a cover 8 located outside the intermediate layer 6. This golf ball 2 has a plurality of dimples 10 on its surface. The portion of the surface of the golf ball 2 other than the dimples 10 is the land 12. This golf ball 2 is provided with a paint layer and a mark layer outside the cover 8, but the illustration of these layers is omitted.

[0014] The diameter of this golf ball 2 is preferably 40 mm or more and 45 mm or less. From the viewpoint of meeting the standards of the United States Golf Association (USGA), the diameter is particularly preferably 42.67 mm or more. From the viewpoint of suppressing air resistance, the diameter is more preferably 44 mm or less, and particularly preferably 42.80 mm or less.

[0015] The mass of this golf ball 2 is preferably 40 g or more and 50 g or less. From the viewpoint of obtaining a large inertia, the mass is more preferably 44 g or more, and particularly preferably 45.00 g or more. From the viewpoint of satisfying the USGA standard, the mass is particularly preferably 45.93 g or less.

[0016] [Core] The core 4 is formed by crosslinking a rubber composition. This rubber composition (a) Base rubber (b) Co-crosslinking agent (c) Crosslinking initiator And (d) Radical scavenger contains.

[0017] [Base rubber] Preferred base rubbers include polybutadiene, polyisoprene, styrene-butadiene copolymer, ethylene-propylene-diene copolymer, and natural rubber. From the viewpoint of the resilience performance of the golf ball 2, polybutadiene is preferred. When polybutadiene is used in combination with other rubbers, it is preferably the main component. Specifically, the ratio of polybutadiene to all base rubbers is preferably 50% by mass or more, more preferably 70% by mass or more, and particularly preferably 80% by mass or more. Polybutadiene having a cis-1,4 bond ratio of 80% or more is particularly preferred. Polybutadiene may contain 1,2-vinyl bonds. From the viewpoint of the resilience performance of the golf ball 2, the content of 1,2-vinyl bonds in polybutadiene is preferably 2.0% by mass or less, more preferably 1.7% by mass or less, and particularly preferably 1.5% by mass or less.

[0018] [Co-crosslinking agent] Preferred co-crosslinking agents include α,β-unsaturated carboxylic acids and metal salts thereof. These co-crosslinking agents can crosslink rubber molecules by graft polymerization. The α,β-unsaturated carboxylic acid and the metal salt of the α,β-unsaturated carboxylic acid may be used in combination. In the α,β-unsaturated carboxylic acid and its metal salt, the number of carbon atoms is preferably 2 or more and 8 or less. Preferred α,β-unsaturated carboxylic acids include acrylic acid, methacrylic acid, fumaric acid, maleic acid, and crotonic acid.

[0019] Examples of metal ions for the metal salt of α,β-unsaturated carboxylic acid include ions of monovalent metals such as sodium, potassium, and lithium; ions of divalent metals such as magnesium, calcium, zinc, barium, and cadmium; ions of trivalent metals such as aluminum; tin ions and zirconium ions. Two or more kinds of metal ions may be used in combination. From the viewpoint of easy crosslinking of rubber molecules, divalent metal ions are preferred. Specific examples of preferred co-crosslinking agents include zinc acrylate, magnesium acrylate, zinc methacrylate, and magnesium methacrylate. Zinc acrylate is particularly preferred. Two or more co-crosslinking agents may be used in combination.

[0020] The amount of the co-crosslinking agent is preferably 20 parts by mass or more and 55 parts by mass or less with respect to 100 parts by mass of the base rubber. In the core where the amount of the co-crosslinking agent is within this range, an appropriate hardness can be achieved. From the viewpoint of hardness, this amount is more preferably 23 parts by mass or more, and particularly preferably 26 parts by mass or more. From the same viewpoint, this amount is more preferably 50 parts by mass or less, and particularly preferably 45 parts by mass or less.

[0021] [Crosslinking initiator] Preferred crosslinking initiators are organic peroxides. The organic peroxides contribute to the durability and resilience performance of the golf ball 2. Suitable organic peroxides include dicumyl peroxide, 1,1-di(t-butylperoxy)cyclohexane, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and di-t-butyl peroxide. Particularly versatile organic peroxide is dicumyl peroxide. Two or more crosslinking initiators may be used in combination.

[0022] The amount of the crosslinking initiator is preferably 0.2 parts by mass or more and 5.0 parts by mass or less with respect to 100 parts by mass of the base rubber. In the core where the amount of the crosslinking initiator is within this range, appropriate hardness can be achieved. This golf ball is excellent in durability. From this viewpoint, the amount is more preferably 0.5 parts by mass or more, and particularly preferably 0.7 parts by mass or more. From the same viewpoint, the amount is more preferably 2.5 parts by mass or less, and particularly preferably 2.0 parts by mass or less.

[0023] [Radical scavenger] The radical scavenger can stop the radical chain reaction in the rubber composition. The radical scavenger can achieve appropriate hardness of the core 4 and suppress excessive crosslinking density. Preferred radical scavengers include hindered phenol-based compounds (d1) and hindered amine-based compounds (d2). The rubber composition may contain both hindered phenol-based compounds (d1) and hindered amine-based compounds (d2).

[0024] [Hindered phenol-based compound] Hindered phenol compounds have a hydroxyphenyl structure. The hydroxyphenyl structure contains a hydroxy group and a bulky functional group. This functional group is preferably adjacent to the hydroxy group. Examples of the bulky functional group include a t-butyl group and a long-chain alkyl group. In this long-chain alkyl group, a part of the carbon may be substituted with sulfur. Preferred hindered phenol compounds have a tert-butylhydroxyphenyl structure. Particularly preferred hindered phenol compounds have a di-tert-butylhydroxyphenyl structure.

[0025] Examples of the tert-butylhydroxyphenyl structure include 3-tert-butyl-4-hydroxyphenyl and 3,5-di-tert-butyl-4-hydroxyphenyl. Hindered phenol compounds having a 3,5-di-tert-butyl-4-hydroxyphenyl structure are particularly preferred.

[0026] Examples of hindered phenol compounds having one hydroxyphenyl structure include dibutylhydroxytoluene (BHT), 4,6-bis(octylthiomethyl)-o-cresol, 4,6-bis((dodecylthio)methyl)-o-cresol, 2,4-dimethyl-6-(1-methylpentadecyl)phenol (for example, Irganox (registered trademark) 1141 manufactured by BASF Japan), and octadecyl 3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate (for example, Adeka Stab (registered trademark) AO-50 manufactured by Adeka).

[0027] As hindered phenolic compounds having two hydroxyphenyl structures, 2,2'-methylenebis(4-ethyl-6-tert-butylphenol) (for example, Yoshinox (registered trademark) 425 manufactured by Mitsubishi Chemical Corporation), 2,2'-methylenebis(4-methyl-6-tert-butylphenol) (for example, Sandant (registered trademark) 2246 manufactured by Sanshin Chemical Industry Co., Ltd.), 4,4'-butylidenebis(3-methyl-6-tert-butylphenol) (for example, Yoshinox BB manufactured by Mitsubishi Chemical Corporation), 4,4'-thiobis(3-methyl-6-tert-butylphenol) (for example, Nocrack (registered trademark) 300 manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.), 4,4-methylenebis(2,6-di-tert-butylphenol), 2,6-di-tert-butyl-4-((2-((3,5-di-tert-butyl-4-hydroxyphenyl)sulfanyl)propan-2-yl)sulfanyl)phenol (probucol), and 3,9-bis(2-(3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy)-1,1-dimethylethyl)-2,4,8,10-tetraoxaspiro(5.5)undecane (for example, AdekaStab AO-80 manufactured by Adeka Corporation) are exemplified.

[0028] As hindered phenolic compounds having three hydroxyphenyl structures, 1,3,5-tris-(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3-5-triazine-2,4,6(1H,3H,5H-)-trione (for example, AdekaStab AO-20 manufactured by Adeka Corporation), and 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene (for example, AdekaStab AO330 manufactured by Adeka Corporation) are exemplified.

[0029] As hindered phenolic compounds having four hydroxyphenyl structures, pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) (for example, AdekaStab AO-60 manufactured by Adeka Corporation) is exemplified.

[0030] As another hindered phenolic compound, 2-tert-butyl-6-(3-tert-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate (for example, Sumilizer GM manufactured by Sumitomo Chemical Co., Ltd.) is exemplified.

[0031] Preferred hindered phenolic compounds are 4,4'-butylidenebis(3-methyl-6-tert-butylphenol), 2,6-di-tert-butyl-4-((2-((3,5-di-tert-butyl-4-hydroxyphenyl)sulfanyl)propan-2-yl)sulfanyl)phenol, and 2-tert-butyl-6-(3-tert-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate. Particularly preferred hindered phenolic compound is 4,4'-butylidenebis(3-methyl-6-tert-butylphenol).

[0032] Two or more hindered phenolic compounds may be used in combination in the rubber composition.

[0033] [Hindered amine compound] Preferred hindered amine compounds have a 2,2,6,6-tetramethyl-4-piperidyl group represented by the following chemical formula (1).

[0034] [Chemical formula]

[0035] In this chemical formula (1), R 11 represents a hydrogen atom, a hydroxy group, an alkyl group, a hydroxyalkyl group, an alkoxy group, a hydroxyalkoxy group, or an oxy radical, and * represents a bond. The number of carbon atoms in this alkyl group, hydroxyalkyl group, alkoxy group, and hydroxyalkoxy group is 1 or more and 30 or less.

[0036] The compounds represented by the chemical formula (1) include the compounds represented by the following chemical formula (2) and chemical formula (3).

[0037]

Chem.

[0038] In this chemical formula (2), R 12 represents a hydrogen atom, a hydroxy group, an alkyl group, a hydroxyalkyl group or an oxy radical, and * represents a bond. The number of carbon atoms in this alkyl group and hydroxyalkyl group is from 1 to 30. The hindered amine compound containing the structure represented by chemical formula (2) is referred to as an N-alkyl type hindered amine compound or an NH type hindered amine compound.

[0039]

Chem.

[0040] In this chemical formula (3), R 12 represents an alkyl group or a hydroxyalkyl group, and * represents a bond. The number of carbon atoms in this alkyl group and hydroxyalkyl group is from 1 to 30. The hindered amine compound containing the structure represented by chemical formula (3) is referred to as an N-alkoxy type hindered amine compound.

[0041] Specific examples of the hindered amine compound include compounds represented by the following chemical formulas (4)-(6).

[0042]

Chem.

[0043] In this chemical formula (4), R 13 represents an alkylene group, R 14 and R 15Each represents a hydrogen atom, a hydroxy group, an alkyl group, a hydroxyalkyl group, an alkoxy group, a hydroxyalkoxy group, or an oxy radical. The number of carbon atoms in this alkylene group, alkyl group, hydroxyalkyl group, alkoxy group, and hydroxyalkoxy group is 1 or more and 30 or less.

[0044]

Chemical formula

[0045] In this chemical formula (5), R 16 represents a hydrogen atom, a hydroxy group, an alkyl group, a hydroxyalkyl group, an alkoxy group, a hydroxyalkoxy group, or an oxy radical, and R 17 represents an alkyl group or an alkenyl group. The number of carbon atoms in this alkyl group, hydroxyalkyl group, alkoxy group, and hydroxyalkoxy group is 1 or more and 30 or less. The number of carbon atoms in the alkenyl group is 2 or more and 30 or less.

[0046]

Chemical formula

[0047] In this chemical formula (6), R 18 and R 19 each represent a hydrogen atom, a hydroxy group, an alkyl group, a hydroxyalkyl group, an alkoxy group, a hydroxyalkoxy group, or an oxy radical. The number of carbon atoms in this alkyl group, hydroxyalkyl group, alkoxy group, and hydroxyalkoxy group is 1 or more and 30 or less.

[0048] Specific examples of the hindered amine compound include the following products of Adeka Corporation. (1) Adeka Stab LA-52 Tetrakis(1,2,2,6,6-pentamethyl-4-piperidyl) butane-1,2,3,4-tetracarboxylate (2) Adeka Stab LA-57 Tetrakis(2,2,6,6-tetramethyl-4-piperidyl) butane-1,2,3,4-tetracarboxylate (3) AdekaStab LA-63P (4) AdekaStab LA-68 (5) AdekaStab LA-72 Bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, (6) AdekaStab LA-77Y Bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate (7) AdekaStab LA-81 Bis(1-undecanoxy-2,2,6,6-tetramethylpiperidin-4-yl) carbonate

[0049] As other specific examples of the hindered amine compound, the following products of BASF Japan can be mentioned. (1) Chimassorb 2020FDL 1,6-Hexanediamine, N,N’―bis(2,2,6,6-tetramethyl-4-piperidinyl)-polymer with 2,4,6-trichloro-1,3,5-triazine, reaction products with N-butyl-1-butanamine and N-butyl-2,2,6,6-tetramethyl-4-piperidinamine (2) Chimassorb 944FDL Poly((6-((1,1,3,3-tetramethylbutyl)amino)-1,3,5-triazine-2,4-diyl)((2,2,6,6-tetramethyl-4-piperidinyl)imino)-1,6-hexanediyl((2,2,6,6-tetramethyl-4-piperidinyl)imino))) (3) Tinuvin 622SF Butanedioic acid, dimethylester, polymer with 4-hydroxy-2,2,6,6-tetramethyl-1-piperidine ethanol (4) Tinuvin PA144 Bis(1,2,2,6,6-pentamethyl-4-piperidinyl)-2-butyl-2-(4-hydroxy-3,5-di-tert.- butylbenzyl)propanedioate

[0050] Two or more hindered amine compounds may be used in combination in the rubber composition.

[0051] The amount of the radical scavenger is preferably 0.5 parts by mass or more and 4.0 parts by mass or less with respect to 100 parts by mass of the base rubber. In the core where the amount of the radical scavenger is within this range, an appropriate crosslink density can be achieved. This golf ball is excellent in durability. From this viewpoint, this amount is more preferably 0.6 parts by mass or more, and particularly preferably 0.7 parts by mass or more. From the same viewpoint, this amount is more preferably 2.0 parts by mass or less, and particularly preferably 1.8 parts by mass or less.

[0052] [Organic sulfur compound] Preferably, the rubber composition of core 4 contains an organic sulfur compound. The organic sulfur compound contributes to the repulsion performance of golf ball 2. The organic sulfur compounds include thiols, polysulfides, thiurams, thiocarboxylic acids, dithiocarboxylic acids, sulfenamides, dithiocarbamate salts and thiazoles. The thiols include thiophenols and thionaphthols.

[0053] As thiophenols, thiophenol; fluorine group-substituted thiophenols such as 4-fluorothiophenol, 2,4-difluorothiophenol, 2,5-difluorothiophenol, 2,6-difluorothiophenol, 2,4,5-trifluorothiophenol, 2,4,5,6-tetrafluorothiophenol, and pentafluorothiophenol; chlorine 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; bromine group-substituted thiophenols such as 4-bromothiophenol, 2,4-dibromothiophenol, 2,5-dibromothiophenol, 2,6-dibromothiophenol, 2,4,5-tribromothiophenol, 2,4,5,6-tetrabromothiophenol, and pentabromothiophenol; iodine group-substituted thiophenols such as 4-iodothiophenol, 2,4-diiodothiophenol, 2,5-diiodothiophenol, 2,6-diiodothiophenol, 2,4,5-triiodothiophenol, 2,4,5,6-tetraiodothiophenol, and pentaiodothiophenol; and their metal salts are exemplified. Preferred metal salts are zinc salts.

[0054] As thionaphthols, 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, and 2-acetyl-1-thionaphthol and their metal salts are exemplified. Divalent metal salts are preferred. Preferred metal salts are zinc salts. Particularly preferred thionaphthols are 2-thionaphthol, 1-thionaphthol, zinc salt of 1-thionaphthol, and zinc salt of 2-thionaphthol.

[0055] Polysulfides are organic sulfur compounds having a polysulfide bond. Polysulfides include disulfides, trisulfides and tetrasulfides. Preferred polysulfides are diphenyl polysulfides.

[0056] Examples of diphenyl polysulfides include diphenyl disulfide; 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, 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, 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 and bis(pentaiodophenyl) disulfide, which are diphenyl disulfides substituted with halogen groups; and 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, which are diphenyl disulfides substituted with alkyl groups.

[0057] Examples of thiurams 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.

[0058] Examples of thiocarboxylic acids include naphthalenethiocarboxylic acid.

[0059] Examples of dithiocarboxylic acids include naphthalenedithiocarboxylic acid.

[0060] Examples of sulfenamides include N-cyclohexyl-2-benzothiazolesulfenamide, N-oxydiethylene-2-benzothiazolesulfenamide, and N-t-butyl-2-benzothiazolesulfenamide.

[0061] Preferred organic sulfur compounds are thiophenols, metal salts of thiophenols, thionaphthols, metal salts of thionaphthols, diphenyldisulfides, and thiuram disulfides. Specific examples of preferred organic sulfur compounds include 2,4-dichlorothiophenol, 2,6-difluorothiophenol, 2,6-dichlorothiophenol, 2,6-dibromothiophenol, 2,6-diiodothiophenol, 2,4,5-trichlorothiophenol, pentachlorothiophenol, 1-thionaphthol, 2-thionaphthol, diphenyldisulfide, bis(2,6-difluorophenyl)disulfide, bis(2,6-dichlorophenyl)disulfide, bis(2,6-dibromophenyl)disulfide, bis(2,6-diiodophenyl)disulfide, and bis(pentabromophenyl)disulfide, and zinc salts thereof.

[0062] Two or more organic sulfur compounds may be used in combination in the rubber composition.

[0063] The amount of the organic sulfur compound is preferably 0.05 parts by mass or more and 5.0 parts by mass or less with respect to 100 parts by mass of the base rubber. A rubber composition in which the amount of the organic sulfur compound is within this range is excellent in processability. A homogeneous core can be obtained from this rubber composition. From this viewpoint, this amount is more preferably 0.2 parts by mass or more, and particularly preferably 0.3 parts by mass or more. From the same viewpoint, this amount is more preferably 3.0 parts by mass or less, and particularly preferably 2.0 parts by mass or less.

[0064] [Additive] The rubber composition of the core 4 may contain a filler for the purpose of adjusting specific gravity or the like. Preferred fillers include zinc oxide, barium sulfate, calcium carbonate, and magnesium carbonate. The amount of the filler is appropriately determined so that the intended specific gravity of the core 4 is achieved.

[0065] The rubber composition of the core 4 may contain appropriate amounts of various additives such as sulfur, carboxylic acid, carboxylate, antioxidant, colorant, plasticizer, and dispersant. This rubber composition may contain crosslinked rubber powder or synthetic resin powder.

[0066] [Properties of Core] The diameter of the core 4 is preferably 35.0 mm or more and 40.5 mm or less. The golf ball 2 having the core 4 with a diameter of 35.0 mm or more is excellent in repulsion performance. From this viewpoint, the diameter is more preferably 36.0 mm or more, and particularly preferably 36.5 mm or more. The golf ball 2 having the core 4 with a diameter of 40.5 mm or less is excellent in durability. From this viewpoint, the diameter is more preferably 40.0 mm or less, and particularly preferably 39.5 mm or less.

[0067] The compression deformation amount Dc of the core 4 is preferably 3.0 mm or more and 5.0 mm or less. The golf ball 2 having the core 4 with a compression deformation amount Dc of 3.0 mm or more is excellent in hitting feeling in a driver shot. From this viewpoint, the compression deformation amount Dc is more preferably 3.5 mm or more, and particularly preferably 3.8 mm or more. The golf ball 2 having the core 4 with a compression deformation amount Dc of 5.0 mm or less is excellent in repulsion performance. From this viewpoint, the compression deformation amount Dc is more preferably 4.7 mm or less, and particularly preferably 4.5 mm or less.

[0068] The compression deformation amount Dc is measured by the YAMADA type compression tester "SCH". In this tester, the core 4 is placed on a metal steel plate. A metal cylinder gradually descends toward this core 4. The core 4 sandwiched between the bottom surface of this cylinder and the steel plate deforms. The moving distance of the cylinder from the state where an initial load of 98 N is applied to the core 4 to the state where a final load of 1274 N is applied is measured. The moving speed of the cylinder until the initial load is applied is 0.83 mm / s. The moving speed of the cylinder from when the initial load is applied until the final load is applied is 1.67 mm / s.

[0069] [Hardness distribution of the core] Figure 2 is a graph showing the hardness distribution of the core 4. In this graph, the horizontal axis is the distance from the center point of the core 4, and the vertical axis is the hardness (Shore C). The following points are plotted on this graph. Center point Po First point P1 where the distance from the center is 2.5 mm Second point P2 where the distance from the center is 5.0 mm Third point P3 where the distance from the center is 7.5 mm Fourth point P4 where the distance from the center is 10.0 mm Fifth point P5 where the distance from the center is 12.5 mm Sixth point P6 where the distance from the center is 15.0 mm Point Ps on the surface

[0070] In this specification, the following hardnesses are measured. Ho: Hardness of the center point Po H(2.5): Hardness of the first point P1 H(5.0): Hardness of the second point P2 H(7.5): Hardness of the third point P3 H(10.0): Hardness of the fourth point P4 H(12.5): Hardness of the fifth point P5 H(15.0): Hardness of the sixth point P6 Hs: Hardness of the point Ps on the surface

[0071] The hardness Ho at the center point Po and the hardnesses from the first point P1 to the sixth point P6 are measured by a Shore C durometer attached to an automatic durometer (trade name "Digitest II" by H. Barleys). This durometer is pressed against the cross-section of the hemisphere obtained by cutting the golf ball 2. The measurement is made in an environment of 23°C.

[0072] The hardness Hs at the point Ps on the surface is measured by a Shore C durometer attached to the aforementioned trade name "Digitest II". This durometer is pressed against the surface of the core 4. The measurement is made in an environment of 23°C.

[0073] In this embodiment, the hardnesses are as follows. Ho: 58 H(2.5): 62 H(5.0): 64 H(7.5): 66 H(10.0): 68 H(12.5): 67 H(15.0): 65 Hs: 67

[0074] The hardness Ho is preferably 56 or more and 68 or less, more preferably 57 or more and 67 or less, and particularly preferably 58 or more and 66 or less. The hardness H(2.5) is preferably 60 or more and 70 or less, more preferably 61 or more and 69 or less, and particularly preferably 62 or more and 68 or less. The hardness H(5.0) is preferably 62 or more and 72 or less, more preferably 63 or more and 71 or less, and particularly preferably 64 or more and 70 or less. The hardness H(7.5) is preferably 63 or more and 73 or less, more preferably 64 or more and 72 or less, and particularly preferably 65 or more and 71 or less. The hardness H(10.0) is preferably 64 or more and 74 or less, more preferably 65 or more and 73 or less, and particularly preferably 66 or more and 72 or less. The hardness H(12.5) is preferably 63 or more and 76 or less, more preferably 64 or more and 75 or less, and particularly preferably 65 or more and 74 or less. The hardness H(15.0) is preferably 61 or more and 77 or less, more preferably 62 or more and 76 or less, and particularly preferably 63 or more and 75 or less. The hardness Hs is preferably 63 or more and 81 or less, more preferably 64 or more and 80 or less, and particularly preferably 65 or more and 79 or less.

[0075] In Figure 2, straight lines S1 - S7 are shown. S1: A straight line connecting the center point Po and the first point P1 S2: A straight line connecting the first point P1 and the second point P2 S3: A straight line connecting the second point P2 and the third point P3 S4: A straight line connecting the third point P3 and the fourth point P4 S5: A straight line connecting the fourth point P4 and the fifth point P5 S6: A straight line connecting the fifth point P5 and the sixth point P6 S7: A straight line connecting the sixth point P6 and the point Ps on the surface

[0076] The straight lines S1 - S7 respectively have slopes A1 - A7. The calculation formulas for the slopes A1 - A7 are as follows. The slope A1 of the straight line S1 (H(2.5) - Ho) / 2.5 = 1.60 The slope A2 of the straight line S2 (H(5.0) - H(2.5)) / 2.5 = 0.80 The slope A3 of the straight line S3 (H(7.5) - H(5.0)) / 2.5 = 0.80 The slope A4 of the straight line S4 (H(10.0) - H(7.5)) / 2.5 = 0.80 The slope A5 of the straight line S5 (H(12.5) - H(10.0)) / 2.5 = -0.40 The slope A6 of the straight line S6 (H(15.0) - H(12.5)) / 2.5 = -0.80 The slope A7 of the straight line S7 (Hs - H(15.0)) / 4.3 = 0.47

[0077] In this core 4, the slope A1 is greater than 1.00. In other words, in the vicinity of the center point, the hardness of the core 4 changes significantly. This core 4 contributes to the hitting feeling of the golf ball 2. Furthermore, this core 4 can suppress the initial spin speed. Therefore, this core 4 contributes to the flight performance of the golf ball 2. From these viewpoints, the slope A1 is more preferably 1.10 or more, and particularly preferably 1.20 or more. From the viewpoint of the durability of the golf ball 2, the slope A1 is preferably 4.00 or less, more preferably 3.00 or less, and particularly preferably 2.50 or less.

[0078] In this embodiment, the minimum value of the slopes A2 - A7 is -0.80. Furthermore, the maximum value of the slopes A2 - A7 is 0.80. All of the slopes A2 - A7 are between -0.90 and 0.90. The maximum value Amax of the absolute values of the slopes from A2 to A7 is 0.90 or less. In other words, from the first point to the surface, the hardness does not change rapidly. When the golf ball 2 is struck by a golf club, in this core 4, the energy loss is small. This core 4 can contribute to the repulsion performance of the golf ball 2. This golf ball 2 has excellent flight performance. From this viewpoint, this maximum value Amax is more preferably 0.85 or less, and particularly preferably 0.80 or less.

[0079] As is clear from FIG. 2, the surface hardness Hs is greater than the center point hardness Ho. This core 4 has an excellent hitting feeling in a driver shot. From this viewpoint, the difference (Hs - Ho) is preferably 5 or more, more preferably 6 or more, and particularly preferably 7 or more. From the viewpoint of the repulsion performance of the golf ball 2, the difference (Hs - Ho) is preferably less than 15, more preferably 14 or less, and particularly preferably 13 or less.

[0080] [Intermediate layer] The intermediate layer 6 is located outside the core 4. In this embodiment, the intermediate layer 6 is in contact with the core 4. The intermediate layer 6 is formed from a resin composition. In this embodiment, the intermediate layer 6 is formed from a thermoplastic resin composition. Examples of the base polymer of this resin composition include ionomer resin, polyamide resin, thermoplastic polyester elastomer, thermoplastic polyurethane elastomer, thermoplastic polyolefin elastomer, and thermoplastic polystyrene elastomer. In particular, ionomer resin and polyamide resin are preferred. The ionomer resin has high elasticity. The golf ball 2 having the intermediate layer 6 containing the ionomer resin is excellent in resilience performance. The intermediate layer 6 containing the polyamide resin has high rigidity. With this intermediate layer 6, an appropriate hardness distribution of the ball composed of the core 4 and the intermediate layer 6 is achieved.

[0081] Preferred ionomer resins include binary ionomer resins and ternary ionomer resins. This binary ionomer resin is a binary copolymer of an α-olefin and an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms, and at least a part of the carboxyl groups of this copolymer is neutralized with metal ions. A preferred binary ionomer resin contains 80% by mass or more and 90% by mass or less of an α-olefin and 10% by mass or more and 20% by mass or less of an α,β-unsaturated carboxylic acid. This binary ionomer resin has excellent rebound performance. The ternary ionomer resin is a terpolymer of an α-olefin, an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms, and an α,β-unsaturated carboxylic acid ester having 2 to 22 carbon atoms, and at least a part of the carboxyl groups of this copolymer is neutralized with metal ions. A preferred ternary ionomer resin contains 70% by mass or more and 85% by mass or less of an α-olefin, 5% by mass or more and 30% by mass or less of an α,β-unsaturated carboxylic acid, and 1% by mass or more and 25% by mass or less of an α,β-unsaturated carboxylic acid ester. This ternary ionomer resin has excellent rebound performance. In the binary ionomer resin and the ternary ionomer resin, preferred α-olefins are ethylene and propylene, and preferred α,β-unsaturated carboxylic acids are acrylic acid and methacrylic acid. Preferred copolymers are binary copolymers of ethylene and acrylic acid, and binary copolymers of ethylene and methacrylic acid.

[0082] Examples of the metal ions for neutralizing the carboxyl groups contained in the binary ionomer resin and the ternary ionomer resin include sodium ion, potassium ion, lithium ion, zinc ion, calcium ion, magnesium ion, aluminum ion, and neodymium ion. The neutralization may be carried out with two or more kinds of metal ions. Metal ions particularly suitable from the viewpoints of the rebound performance and durability of the golf ball 2 are sodium ion, zinc ion, lithium ion, and magnesium ion.

[0083] Specific examples of the ionomer resin include the products of Mitsui Dow Chemical Co., Ltd. under the trade names "Hymilan 1555", "Hymilan 1557", "Hymilan 1605", "Hymilan 1702", "Hymilan 1706", "Hymilan 1707", "Hymilan 1855", "Hymilan 1856", "Hymilan 8150", "Hymilan AM7311", "Hymilan AM7315", "Hymilan AM7317", "Hymilan AM7327", "Hymilan AM7329", and "Hymilan AM7337"; the products of DuPont under the trade names "Surlyn 6120", "Surlyn 6910", "Surlyn 7930", "Surlyn 7940", "Surlyn 8140", "Surlyn 8150", "Surlyn 8940", "Surlyn 8945", "Surlyn 9120", "Surlyn 9150", "Surlyn 9320", "Surlyn 9910", "Surlyn 9945", "Surlyn AD8546", "HPF1000", and "HPF2000"; and the products of ExxonMobil Chemical Co., Ltd. under the trade names "Iotek 7010", "Iotek 7030", "Iotek 7510", "Iotek 7520", "Iotek 8000", and "Iotek 8030". Two or more ionomer resins may be used in combination.

[0084] The polyamide resin has a plurality of amide bonds (-NH-CO-) in the main chain. Preferred polyamide resins include aliphatic polyamides, aromatic polyamides, and amide copolymers. Examples of aliphatic polyamides include polyamide 6, polyamide 11, polyamide 12, polyamide 66, polyamide 610, polyamide 6T, polyamide 6I, polyamide 9T, polyamide M5T, and polyamide 612. Examples of aromatic polyamides include poly-p-phenylene terephthalamide and poly-m-phenylene isophthalamide. Examples of amide copolymers include polyether block amide copolymers, polyester amide copolymers, polyether ester amide copolymers, and polyamide imide copolymers. Aliphatic polyamides are preferred, and polyamide 6, polyamide 11, and polyamide 12 are particularly preferred.

[0085] Preferably, in the base resin of the intermediate layer 6, the amount of the ionomer resin is preferably 10% by mass or more and 70% by mass or less, and the amount of the polyamide resin is preferably 30% by mass or more and 90% by mass or less. The amount of the ionomer resin is more preferably 15% by mass or more, and particularly preferably 20% by mass or more. The amount of the ionomer resin is more preferably 65% by mass or less, and particularly preferably 60% by mass or less. The amount of the polyamide resin is more preferably 35% by mass or more, and particularly preferably 40% by mass or more. The amount of the polyamide resin is more preferably 85% by mass or less, and particularly preferably 80% by mass or less.

[0086] The resin composition of the intermediate layer 6 may contain an appropriate amount of a colorant, a filler, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent agent, a fluorescent brightening agent, etc. A typical filler is barium sulfate. When the hue of the golf ball 2 is white, a typical colorant is titanium dioxide.

[0087] The thickness Tm of the intermediate layer 6 is preferably 0.5 mm or more and 2.0 mm or less. The golf ball 2 having a thickness Tm of 0.5 mm or more has excellent repulsion performance. From this viewpoint, the thickness Tm is more preferably 0.7 mm or more, and particularly preferably 0.8 mm or more. The golf ball 2 having a thickness Tm of 2.0 mm or less has excellent hitting feeling in a driver shot. From this viewpoint, the thickness Tm is more preferably 1.5 mm or less, and particularly preferably 1.3 mm or less. The thickness Tm is measured directly below the land 12.

[0088] The hardness Hm of the intermediate layer 6 is preferably 50 or more and 90 or less. The golf ball 2 having a hardness Hm of 50 or more has excellent repulsion performance. From this viewpoint, the hardness Hm is more preferably 60 or more, and particularly preferably 63 or more. The golf ball 2 having a hardness Hm of 90 or less has excellent hitting feeling in a driver shot. From this viewpoint, the hardness Hm is more preferably 80 or less, and particularly preferably 72 or less.

[0089] The hardness Hm of the intermediate layer 6 is measured in accordance with the provisions of "ASTM-D 2240-68". The hardness Hm is measured by a Shore D type hardness meter attached to an automatic hardness tester (trade name "Digital Test II" by H. Barleys). For the measurement, a sheet made of the same material as that of the intermediate layer 6, which is formed by a hot press and has a thickness of about 2 mm, is used. Prior to the measurement, the sheet is stored at a temperature of 23°C for two weeks. At the time of measurement, three sheets are stacked together.

[0090] [Cover] The cover 8 is located outside the intermediate layer 6. In the present embodiment, the cover 8 is in contact with the intermediate layer 6. The golf ball 2 may have an adhesive layer between the intermediate layer 6 and the cover 8. Through this adhesive layer, the cover 8 can be firmly joined to the intermediate layer 6. The cover 8 is formed from a resin composition. In the present embodiment, the cover 8 is formed from a thermoplastic resin composition. Examples of the base polymer of this resin composition include ionomer resin, thermoplastic polystyrene elastomer, thermoplastic polyester elastomer, thermoplastic polyamide elastomer, thermoplastic polyurethane elastomer, and thermoplastic polyolefin elastomer. In particular, ionomer resin is preferred. The ionomer resin has high elasticity. The golf ball 2 having the cover 8 containing the ionomer resin has excellent repulsion performance. This golf ball 2 has excellent flight performance in a driver shot. The ionomer resin described above with respect to the intermediate layer 6 can be used for the cover 8.

[0091] The ionomer resin and other resins may be used in combination. When used in combination, from the viewpoint of repulsion performance, the ionomer resin is the main component of the base resin. The amount of the ionomer resin in the base resin of the cover 8 is preferably 60% by mass or more, more preferably 70% by mass or more, and particularly preferably 75% by mass or more.

[0092] A preferred resin that can be used in combination with the ionomer resin is a styrene block-containing thermoplastic elastomer. The styrene block-containing thermoplastic elastomer can contribute to the low hardness of the cover 8.

[0093] The styrene block-containing thermoplastic elastomer includes a polystyrene block as a hard segment and a soft segment. A typical soft segment is a diene block. Examples of the diene block compound include butadiene, isoprene, 1,3-pentadiene, and 2,3-dimethyl-1,3-butadiene. Butadiene and isoprene are preferred. Two or more compounds may be used in combination.

[0094] The styrene block-containing thermoplastic elastomer includes styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS), styrene-isoprene-butadiene-styrene block copolymer (SIBS), a hydrogenated product of SBS, a hydrogenated product of SIS, and a hydrogenated product of SIBS. Examples of the hydrogenated product of SBS include styrene-ethylene-butylene-styrene block copolymer (SEBS). Examples of the hydrogenated product of SIS include styrene-ethylene-propylene-styrene block copolymer (SEPS). Examples of the hydrogenated product of SIBS include styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS).

[0095] In the present invention, the styrene block-containing thermoplastic elastomer includes an alloy of one or more selected from the group consisting of SBS, SIS, SIBS, SEBS, SEPS, and SEEPS and an olefin. The olefin component in this alloy is presumed to contribute to improving the compatibility with other base polymers. This alloy may contribute to the resilience performance of the golf ball 2. Olefins having 2 or more and 10 or less carbon atoms are preferred. Examples of suitable olefins include ethylene, propylene, butene, and pentene. Ethylene and propylene are particularly preferred.

[0096] Specific examples of the polymer alloy include the products named "Tefabloc T3221C", "Tefabloc T3339C", "Tefabloc SJ4400N", "Tefabloc SJ5400N", "Tefabloc SJ6400N", "Tefabloc SJ7400N", "Tefabloc SJ8400N", "Tefabloc SJ9400N", and "Tefabloc SR04" by Mitsubishi Chemical Corporation. Other specific examples of the styrene block-containing thermoplastic elastomer include the product named "Epofrend A1010" by Daicel Chemical Industries, Ltd. and the product named "Septon HG-252" by Kuraray Co., Ltd.

[0097] The resin composition of the cover 8 may contain an appropriate amount of a colorant, a filler, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent agent, a fluorescent brightening agent, etc. A typical filler is barium sulfate. When the hue of the golf ball 2 is white, a typical colorant is titanium dioxide.

[0098] The thickness Tc of the cover 8 is preferably 0.50 mm or more and 2.00 m or less. The golf ball 2 with a thickness Tc of 0.50 mm or more is excellent in durability. From this viewpoint, the thickness Tc is more preferably 0.70 mm or more, and particularly preferably 0.90 mm or more. The golf ball 2 with a thickness Tc of 2.00 mm or less is excellent in resilience performance. From this viewpoint, the thickness Tc is more preferably 1.50 mm or less, and particularly preferably 1.20 mm or less. The thickness Tc is measured directly below the land 12.

[0099] The hardness Hc of the cover 8 is 45 or less and 80 or less. The golf ball 2 with a hardness Hc of 45 or more is excellent in resilience performance. From this viewpoint, the hardness Hc is more preferably 55 or more, and particularly preferably 58 or more. The golf ball 2 with a hardness Hc of 80 or less is excellent in durability. From this viewpoint, the hardness Hc is more preferably 70 or less, and particularly preferably 67 or less. The hardness Hc of the cover 8 is measured by the same method as the method for measuring the hardness Hm of the intermediate layer 6.

[0100] Preferably, the hardness Hm of the intermediate layer 6 is greater than the hardness Hc of the cover 8. In this golf ball 2, the flight performance in a driver shot and the hitting feeling in putting can be made compatible. The difference (Hm - Hc) is preferably 2 or more, more preferably 3 or more, and particularly preferably 4 or more. The difference (Hm - Hc) is preferably 10 or less, more preferably 8 or less, and particularly preferably 6 or less.

[0101] [Physical properties of golf ball] The compression deformation amount Db of the golf ball 2 is preferably 2.5 mm or more and 4.0 mm or less. The golf ball 2 with a compression deformation amount Db of 2.5 mm or more is excellent in the hitting feeling in a driver shot. From this viewpoint, the compression deformation amount Db is more preferably 2.7 mm or more, and particularly preferably 2.8 mm or more. The golf ball 2 with a compression deformation amount Db of 4.0 mm or less is excellent in the resilience performance. From this viewpoint, the compression deformation amount Db is more preferably 3.5 mm or less, and particularly preferably 3.2 mm or less.

[0102] The compression deformation amount Db is measured by the aforementioned YAMADA type compression tester "SCH". In this tester, the golf ball 2 is placed on a metal steel plate. A metal cylinder gradually descends toward this golf ball 2. The golf ball 2 sandwiched between the bottom surface of this cylinder and the steel plate deforms. The moving distance of the cylinder from the state where an initial load of 98 N is applied to the golf ball 2 to the state where a final load of 1274 N is applied is measured. The moving speed of the cylinder until the initial load is applied is 0.83 mm / s. The moving speed of the cylinder from when the initial load is applied to when the final load is applied is 1.67 mm / s.

Example

[0103] [Example 1] 100 parts by mass of high cis - polybutadiene (trade name "BR - 730" by JSR), 27.2 parts by mass of zinc acrylate (trade name "ZN - DA90S" by Nisshoku Techno Fine Chemical Co., Ltd.), 5 parts by mass of zinc oxide (INDOLYSAGHT), 17.6 parts by mass of barium sulfate (product number "BD" by Sakai Chemical Industry Co., Ltd.), 1.2 parts by mass of dicumyl peroxide (trade name "Perkyl D" by NOF Corporation), 1.0 part by mass of 4,4’ - butylidenebis(3 - methyl - 6 - tert - butylphenol) (Tokyo Chemical Industry Co., Ltd.) as a radical scavenger, and 0.35 part by mass of zinc pentachlorothiophenolate (product number "PCTP - Zn" by Fujifilm Wako Pure Chemical Corporation) as an organic sulfur compound were kneaded to obtain a rubber composition C. This rubber composition C was put into a mold consisting of an upper mold and a lower mold both having a hemispherical cavity and heated to obtain a core with a diameter of 38.6 mm. The cross - linking temperature was 170°C. The cross - linking time was 20 minutes. The hardness distribution of this core is shown in Table 1 below.

[0104] 40 parts by mass of an ionomer resin (the aforementioned "Hy-Milan AM7337"), 20 parts by mass of another ionomer resin (the aforementioned "Hy-Milan 1555"), 40 parts by mass of polyamide 6 (Toray Industries, Inc.), 6 parts by mass of barium sulfate, and 4 parts by mass of titanium dioxide were kneaded with a twin - screw kneading extruder to obtain a resin composition f. The core was put into a mold consisting of an upper mold and a lower mold each having a hemispherical cavity. The molten resin composition f was injected around the core with an injection molding machine to form an intermediate layer. The thickness of this intermediate layer was 1.00 mm.

[0105] 40 parts by mass of an ionomer resin (the aforementioned "Hy-Milan AM7329"), 50 parts by mass of another ionomer resin (the aforementioned "Hy-Milan AM7337"), 5 parts by mass of yet another ionomer resin (the aforementioned "Hy-Milan 1555"), 5 parts by mass of a styrene block-containing thermoplastic elastomer (the aforementioned "Tefablock T3221"), 6 parts by mass of barium sulfate, and 4 parts by mass of titanium dioxide were kneaded using a twin-screw kneading extruder to obtain a resin composition c. A sphere composed of a core and an intermediate layer was placed into a mold consisting of an upper mold and a lower mold, each having a hemispherical cavity. The molten resin composition c was injection-coated around this sphere using an injection molding machine to form a cover. The thickness of this cover was 1.05 mm.

[0106] A clear paint based on a two-component curable polyurethane was applied around this cover to obtain a golf ball of Example 1 having a diameter of about 42.7 mm and a mass of about 45.5 g.

[0107] [Examples 2-9 and Comparative Examples 1-8] Golf balls of Examples 2-9 and Comparative Examples 1-8 were obtained in the same manner as in Example 1, except that the specifications of the core, intermediate layer, and cover were as shown in Tables 6-8 below. The specifications of the core are shown in Tables 1-3 below. The compositions of the intermediate layer and cover are shown in Tables 4 and 5 below.

[0108]

Table 1

[0109]

Table 2

[0110] Terpene resin: Trade name "Sylvares TP2019" by KRATON

[0111]

Table 3

[0112]

Table 4

[0113]

Table 5

[0114] [Flight Performance] A driver (W#1, trade name "XXIO" of Sumitomo Rubber Industries, shaft hardness: R) was attached to the swing machine of Golf Laboratory Co., Ltd. A golf ball was struck with this driver under the condition that the head speed was 40 m / sec, and the distance from the launch point to the stationary point was measured. At the time of the test, it was almost windless. The average value of the flight distances obtained from 12 measurements was calculated. Furthermore, this average value was rated based on the following criteria. A: 220.0 yards or more B: 219.5 yards or more and less than 220.0 yards C: 219.0 yards or more and less than 219.5 yards D: Less than 219.0 yards These results are shown in Tables 6 - 8 below.

[0115] [Feeling of Impact] Ten golf players were made to putt, and the feeling of impact was heard. Based on the number of golfers who answered that "the feeling of impact is good", the golf ball was rated according to the following criteria. A: 8 or more people B: 5 or more and 7 or less people C: 4 or less people These results are shown in Tables 6 - 8 below.

[0116] [Overall Evaluation] Based on the flight performance and the feeling of impact, the golf ball was rated according to the following criteria. A: Both the flight performance and the feeling of impact are "A". B: Both the flight performance and the feeling of impact are "A" or "B". C: One of the flight performance and hitting feeling is "A" or "B", and the other is "C" or "D". D: Both the flight performance and hitting feeling are "C" or "D". This result is shown in Table 6 - 8 below.

[0117]

Table 6

[0118]

Table 7

[0119]

Table 8

[0120] As shown in Table 6 - 8, the golf balls of each example are excellent in overall performance. From this evaluation result, the superiority of the present invention is clear.

[0121] [Disclosed Items] Each of the following items discloses a preferred embodiment.

[0122] [Item 1] It includes a core with a diameter of 35 mm or more, an intermediate layer located outside the core, and a cover located outside the intermediate layer, the Shore D hardness Hm of the intermediate layer is greater than the Shore D hardness Hc of the cover, in the core, for the center point, the first point with a distance of 2.5 mm from this center, the second point with a distance of 5.0 mm from this center, the third point with a distance of 7.5 mm from this center, the fourth point with a distance of 10.0 mm from this center, the fifth point with a distance of 12.5 mm from this center, the sixth point with a distance of 15.0 mm from this center, and the points on the surface, in the graph where these distances (mm) and Shore C hardness are plotted, The slope A1 of the straight line connecting the center point and the first point is 1.00 or more, A golf ball, wherein the maximum value Amax of the absolute values of the following slopes A2 to A7 is 0.90 or less. A2: The slope of the straight line connecting the first point and the second point A3: The slope of the straight line connecting the second point and the third point A4: The slope of the straight line connecting the third point and the fourth point A5: The slope of the straight line connecting the fourth point and the fifth point A6: The slope of the straight line connecting the fifth point and the sixth point A7: The slope of the straight line connecting the sixth point and the point on the surface

[0123] [Item 2] The Shore C hardness Hs of the surface of the core is greater than the hardness Ho of the center point of the core, and the difference (Hs - Ho) between the hardness Hs and the hardness Ho is less than 15. The golf ball according to Item 1.

[0124] [Item 3] The difference (Hm - Hc) between the hardness Hm and the hardness Hc is 10 or less. The golf ball according to Item 1 or 2.

[0125] [Item 4] The hardness Hm is 65 or more, and the hardness Hc is 60 or more. The golf ball according to any one of Items 1 to 3.

[0126] [Item 5] The core is formed by cross - linking a rubber composition, and the rubber composition (a) Base rubber (b) Co - crosslinking agent (c) Cross - linking initiator and (d) Radical scavenger The golf ball according to any one of Items 1 to 4, which contains

[0127] [Item 6] The golf ball according to item 5, wherein the radical scavenger (d) is a hindered phenol compound (d1) and / or a hindered amine compound (d2).

[0128] [Item 7] The golf ball according to item 6, wherein the radical scavenger (d) is one or more selected from the group consisting of 4,4'-butylidenebis(3-methyl-6-tert-butylphenol), 2,6-di-tert-butyl-4-((2-((3,5-di-tert-butyl-4-hydroxyphenyl)sulfanyl)propan-2-yl)sulfanyl)phenol, and 2-tert-butyl-6-(3-tert-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate.

[0129] [Item 8] The golf ball according to any one of items 5 to 7, wherein the rubber composition contains 100 parts by mass of the base rubber (a) and 0.5 part by mass or more and 4.0 parts by mass or less of the radical scavenger (d).

[0130] [Item 9] The rubber composition is (e) an organic sulfur compound further contains The golf ball according to any one of items 5 to 8, wherein the organic sulfur compound is one or more selected from the group consisting of thiols, polysulfides, thiurams, thiocarboxylic acids, dithiocarboxylic acids, sulfenamides, dithiocarbamates, and thiazoles. [Industrial Applicability]

[0131] The golf ball described above is suitable for play on a golf course, practice at a driving range, etc. [Explanation of Symbols]

[0132] 2 ··· Golf ball 4 ··· Core 6 ··· Intermediate layer 8 ··· Cover 10 ··· Dimple 12 ··· Land

Claims

1. The golf ball has a core having a diameter of 35 mm or more, a mid layer located outside the core, and a cover located outside the mid layer, the mid layer has a Shore D hardness Hm greater than a Shore D hardness Hc of the cover, In the above core, a center point, a first point that is 2.5 mm away from the center, a second point that is 5.0 mm away from the center, a third point that is 7.5 mm away from the center, a fourth point that is 10.0 mm away from the center, a fifth point that is 12.5 mm away from the center, a sixth point that is 15.0 mm away from the center, and a point on the surface are plotted against their distances (mm) and Shore C hardness. A slope A1 of a straight line connecting the center point and the first point is 1.00 or more, A golf ball, wherein a maximum value Amax of absolute values ​​of the following slopes A2 to A7 is 0.90 or less. A2: The slope of the line connecting the first point and the second point A3: The slope of the line connecting the second point and the third point A4: The slope of the line connecting the third point and the fourth point A5: The slope of the line connecting the fourth point and the fifth point A6: The slope of the line connecting the fifth point and the sixth point A7: The slope of the line connecting the sixth point and the point on the surface

2. the Shore C hardness Hs of the surface of the core is greater than the hardness Ho of the center point of the core, 2. The golf ball according to claim 1, wherein the difference between the hardness Hs and the hardness Ho (Hs-Ho) is less than 15.

3. 3. The golf ball according to claim 1, wherein the difference between the hardness Hm and the hardness Hc (Hm-Hc) is 10 or less.

4. 3. The golf ball according to claim 1, wherein the hardness Hm is 65 or greater and the hardness Hc is 60 or greater.

5. the core is formed by crosslinking a rubber composition, The rubber composition is (a) Base rubber (b) Co-crosslinking agent (c) Crosslinking Initiator and (d) Radical Scavenger The golf ball of claim 1 , comprising:

6. 6. The golf ball according to claim 5, wherein the radical scavenger (d) is a hindered phenol-based compound (d1) and / or a hindered amine-based compound (d2).

7. 7. The golf ball according to claim 6, wherein the radical scavenger (d) is one or more selected from the group consisting of 4,4'-butylidenebis(3-methyl-6-tert-butylphenol), 2,6-di-tert-butyl-4-((2-((3,5-di-tert-butyl-4-hydroxyphenyl)sulfanyl)propan-2-yl)sulfanyl)phenol, and 2-tert-butyl-6-(3-tert-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate.

8. 6. The golf ball according to claim 5, wherein the rubber composition comprises 100 parts by weight of the base rubber (a) and 0.5 parts by weight or greater and 4.0 parts by weight or less of the radical scavenger (d).

9. The rubber composition is (e) Organic sulfur compound Further comprising 6. The golf ball according to claim 5, wherein the organic sulfur compound is one or more selected from the group consisting of thiols, polysulfides, thiurams, thiocarboxylic acids, dithiocarboxylic acids, sulfenamides, dithiocarbamates, and thiazoles.

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