JP5499082B2 - Golf ball - Google Patents

Description

  The present invention relates to a golf ball. More specifically, the present invention relates to a golf ball having a solid core and a cover having three or more layers.

  A golfer's greatest demand for a golf ball is flight performance. Golfers place particular importance on flight performance on shots with drivers and long irons. The flight performance correlates with the resilience performance of the golf ball. When a golf ball excellent in resilience performance is hit, it flies at a high speed and a large flight distance is achieved. Golf balls having a core with excellent resilience performance are described in Japanese Patent Application Laid-Open Nos. 61-37178, 2008-212681, 2008-523852, and 2009-119256.

  The core described in JP-A-61-37178 is obtained from a rubber composition containing a co-crosslinking agent and a crosslinking aid. This publication describes palmitic acid, stearic acid and myristic acid as crosslinking aids.

  The core described in JP2008-212681 is obtained from a rubber composition containing an organic peroxide, an α, β-unsaturated carboxylic acid metal salt and a fatty acid copper salt.

  The core described in JP-T-2008-523952 is obtained from a rubber composition containing a metal salt of an unsaturated monocarboxylic acid, a free radical initiator, and a non-conjugated diene monomer.

  The core described in JP-A-2009-119256 has a vinyl content of 2% or less, a cis 1,4-bond content of 80% or more, an active end, and the active end is an alkoxysilane compound. It is obtained from a rubber composition containing a modified polybutadiene.

  In order to achieve a large flight distance, an appropriate ballistic height is required. The ballistic height depends on the spin speed and launch angle. A golf ball that achieves a high trajectory with a high spin rate has insufficient flight distance. A golf ball that achieves a high trajectory with a large launch angle can provide a large flight distance. By adopting the outer-hard / inner-soft structure in the golf ball, a small spin speed and a large launch angle can be achieved. Devices relating to the hardness distribution of the core are described in JP-A-6-154357, JP-A-2008-194471, and JP-A-2008-194473.

  In the core described in JP-A-6-154357, the JIS-C hardness H1 at the center is 58 to 73, and the JIS-C hardness H2 in the region where the distance from the center is 5 mm to 10 mm is 65 to 75. The JIS-C hardness H3 at a point where the distance from the center is 15 mm is 74 or more and 82 or less, and the JIS-C hardness H4 of the surface is 76 or more and 84 or less. The hardness H2 is greater than the hardness H1, the hardness H3 is greater than the hardness H2, and the hardness H4 is equal to or greater than the hardness H3.

  In the core described in Japanese Patent Application Laid-Open No. 2008-194471, the Shore D hardness degree at the center is 30 or more and 48 or less, and the Shore D hardness at a point where the distance from the center is 4 mm is 34 or more and 52 or less. The Shore D hardness at a point where the distance is 8 mm is 40 to 58, the Shore D hardness at a point where the distance from the center is 12 mm is 43 to 61, and the distance from the surface is 2 mm to 3 mm. The Shore D hardness of a certain region is 36 or more and 54 or less, and the Shore D hardness of the surface is 41 or more and 59 or less.

  In the core described in Japanese Patent Application Laid-Open No. 2008-194473, the Shore D hardness at the center is 25 or more and 45 or less, and the Shore D hardness in the region where the distance from the center is 5 mm or more and 10 mm or less is 39 or more and 58 or less The Shore D hardness at a point where the distance from the center is 15 mm is 36 or more and 55 or less, and the Shore D hardness of the surface is 55 or more and 75 or less.

  Japanese Patent Application Laid-Open No. 2010-253268 describes a golf ball including a core, an envelope layer, an intermediate layer, and a cover. In this core, the hardness gradually increases from the center toward the surface. The difference between the surface JIS-C hardness and the center JIS-C hardness is 15 or more. The cover has a hardness greater than that of the intermediate layer, and the intermediate layer has a hardness greater than that of the envelope layer.

JP-A-61-37178 JP 2008-212681 A Japanese translation of PCT publication No. 2008-523952 JP 2009-119256 A JP-A-6-154357 JP 2008-194471 A JP 2008-194473 A JP 2010-253268 A

  Middle irons are often used for short hole tee shots and middle hole second shots. The golfer wants a great flight distance even in the middle iron shot. An object of the present invention is to provide a golf ball that exhibits excellent flight performance in a shot with a middle iron.

The golf ball according to the present invention includes a core, an inner cover positioned outside the core, a mid cover positioned outside the inner cover, and an outer cover positioned outside the mid cover. The distance (%) from the center point and JIS-C hardness of nine points obtained by dividing the core from the center point to the surface at an interval of 12.5% of the radius of the core were plotted in a graph. Sometimes R ² of the linear approximation curve obtained by the method of least squares is 0.95 or more. The JIS-C hardness Hi of the inner cover is larger than the JIS-C hardness Hs of the surface of the core. The outer cover has a JIS-C hardness Ho greater than the hardness Hi.

  Preferably, the difference (Hi−Hs) between the hardness Hi and the hardness Hs is 1 or more. Preferably, the difference (Ho−Hi) between the hardness Ho and the hardness Hi is 5 or more and 30 or less.

  Preferably, the difference (Hs−H (0)) between the hardness Hs and the JIS-C hardness H (0) of the center point of the core is 15 or more.

  Preferably, the thickness Ti of the inner cover is 1.2 mm or less, the thickness Tm of the mid cover is 1.2 mm or less, and the thickness To of the outer cover is 1.2 mm or less. Preferably, the sum (Ti + Tm + To) of the thickness Ti of the inner cover, the thickness Tm of the mid cover, and the thickness To of the outer cover (Ti + Tm + To) is 2.5 mm or less.

Preferably, the hardness Ho is greater than the JIS-C hardness Hm of the mid cover . Preferably, the difference between the hardness Ho and the hardness Hm (Ho−Hm) is 2 or more.

The core can be formed by crosslinking the rubber composition. Preferably, the rubber composition is
(A) base rubber,
(B) a co-crosslinking agent,
(C) a crosslinking initiator,
And (d) an acid and / or salt. The co-crosslinking agent (b)
(B1) an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and / or (b2) a metal salt of an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms. .

  Preferably, the amount of acid and / or salt (d) is 0.5 parts by mass or more and 40 parts by mass or less with respect to 100 parts by mass of the base rubber (a).

Preferred acids and / or salts (d) are
(D1) Carboxylic acid and / or a salt thereof. Preferred carboxylic acids and / or salts thereof (d1) are fatty acids and / or salts thereof. Preferably, the carboxylic acid component of the carboxylic acid and / or its salt (d1) has 1 to 30 carbon atoms. Preferred carboxylic acids and / or salts (d1) thereof are zinc salts of carboxylic acids. Preferred zinc salts of carboxylic acids include zinc octoate, zinc laurate, zinc myristate and zinc stearate.

  Preferably, the rubber composition contains 15 parts by weight or more and 50 parts by weight or less of the co-crosslinking agent (b) with respect to 100 parts by weight of the base rubber (a). Preferably, the rubber composition includes 0.2 to 5.0 parts by mass of a crosslinking initiator (c) with respect to 100 parts by mass of the base rubber (a).

Preferably, the rubber composition is
(E) An organic sulfur compound is further included. Preferred organic sulfur compounds (e) include thiophenols, diphenyl disulfides, thionaphthols and thiuram disulfides, and metal salts thereof. Preferably, a rubber composition contains 0.05 mass part or more and 5 mass parts or less of organic sulfur compounds (e) with respect to 100 mass parts base rubber (a).

When the rubber composition contains an α, β-unsaturated carboxylic acid (b1), the rubber composition
(F) It is preferable that a metal compound is further included.

  In the golf ball according to the present invention, the hardness distribution of the core and the inner cover is appropriate. In this golf ball, there is little energy loss when hit with a middle iron. The spin speed when this golf ball is hit with a middle iron is small. A large flight distance is achieved with a low spin speed.

FIG. 1 is a partially cutaway sectional view showing a golf ball according to an embodiment of the present invention. FIG. 2 is a line graph showing the hardness distribution of the core of the golf ball of FIG.

  Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

  The golf ball 2 shown in FIG. 1 includes a spherical core 4 and a cover 6 that covers the core 4. The cover 6 includes an inner cover 8, a mid cover 10 positioned outside the inner cover 8, and an outer cover 12 positioned outside the mid cover 10. The cover may have 4 or more layers. A large number of dimples 14 are formed on the surface of the outer cover 12. A portion of the surface of the golf ball 2 other than the dimples 14 is a land 16. The golf ball 2 includes a paint layer and a mark layer on the outside of the outer cover 12, but these layers are not shown.

  The golf ball 2 has a diameter of 40 mm to 45 mm. The diameter is preferably 42.67 mm or more from the viewpoint that the American Golf Association (USGA) standard is satisfied. In light of suppression of air resistance, the diameter is preferably equal to or less than 44 mm, and more preferably equal to or less than 42.80 mm. The golf ball 2 has a mass of 40 g or more and 50 g or less. From the viewpoint of obtaining a large inertia, the mass is preferably 44 g or more, and more preferably 45.00 g or more. From the viewpoint that the USGA standard is satisfied, the mass is preferably equal to or less than 45.93 g.

FIG. 2 is a line graph showing the hardness distribution of the core 4 of the golf ball 2 of FIG. The horizontal axis of this graph represents the ratio (%) of the distance from the center point of the core 4 to the radius of the core 4. The vertical axis of this graph is JIS-C hardness. Nine measurement points obtained by dividing the core 4 from the center point to the surface at an interval of 12.5% of the radius of the core 4 are plotted in this graph. The ratio of the distance from the center point of the core 4 to the radius of the core 4 at these measurement points is as follows.
First point 0.0% (center point)
Second point 12.5%
Third point 25.0%
Fourth point 37.5%
5th point 50.0%
6th point 62.5%
Seventh point 75.0%
8th 87.5%
Ninth point 100.0% (surface)
The hardness from the first point to the eighth point is measured by pressing a JIS-C type hardness meter against the cut surface of the hemisphere obtained by cutting the core 4. By pressing a JIS-C type hardness meter against the surface of the spherical core 4, the hardness Hs of the ninth point is measured. For the measurement, an automatic rubber hardness measuring machine (trade name “P1” by Kobunshi Keiki Co., Ltd.) equipped with this hardness meter is used. In the present invention, the JIS-C hardness of the measurement point whose distance from the center point of the core 4 is x (%) is represented by H (x). The hardness of the center point of the core 4 is expressed as H (0).

  FIG. 2 also shows a linear approximation curve obtained by the method of least squares based on the distance and hardness of nine measurement points. As is apparent from FIG. 2, the broken line does not greatly deviate from the linear approximation curve. In other words, the polygonal line has a shape close to a linear approximation curve. In the core 4, the hardness increases linearly from the center toward the surface. When this core 4 is hit with a middle iron, there is little energy loss. This core 4 is excellent in resilience performance. When the golf ball 2 is hit with a middle iron, the flight distance is large.

In this core 4, R ² of the linear approximation curve obtained by the least square method is 0.95 or more. R ² is an index representing the linearity of the broken line. The core 4 whose R ² is 0.95 or more has a shape of a broken line of hardness distribution close to a straight line. The core 4 having R ² of 0.95 or more is excellent in resilience performance. R ² is more preferably 0.96 or more, and particularly preferably 0.97 or more. R ² is calculated by squaring the correlation coefficient R. The correlation coefficient R is obtained by dividing the covariance between the distance (%) from the center and the hardness (JIS-C) by the standard deviation of the distance (%) from the center and the standard deviation of the hardness (JIS-C). Is calculated by

The core 4 is obtained by crosslinking the rubber composition. This rubber composition
(A) base rubber,
(B) a co-crosslinking agent,
(C) contains a crosslinking initiator and (d) an acid and / or salt.

  When the core 4 is heated and molded, the base rubber (a) is crosslinked by the co-crosslinking agent (b). The reaction heat of this cross-linking reaction accumulates near the center of the core 4. Therefore, when the core 4 is heated and molded, the temperature at the center is high. The temperature gradually decreases from the center toward the surface. In the rubber composition, it is presumed that the acid reacts with the metal salt of the co-crosslinking agent (b) and binds to the cation. In the rubber composition, it is presumed that the salt reacts with the metal salt of the co-crosslinking agent (b) to exchange cations. This bond and exchange breaks the metal bridge. This cutting is likely to occur in the central portion of the core 4 where the temperature is high, and is unlikely to occur near the surface. As a result, the crosslink density of the core 4 increases from the center toward the surface. In the core 4, an outer-hard / inner-soft structure can be achieved. The spin speed when the golf ball 2 including the core 4 is hit with a middle iron is small. With this golf ball 2, excellent flight performance is achieved in a shot with a middle iron.

  Examples of the base rubber (a) of the core 4 include polybutadiene, polyisoprene, styrene-butadiene copolymer, ethylene-propylene-diene copolymer, and natural rubber. From the viewpoint of resilience performance, polybutadiene is preferred. When polybutadiene and other rubber are used in combination, it is preferable that polybutadiene is a main component. Specifically, the ratio of the amount of polybutadiene to the total amount of the base rubber is preferably 50% by mass or more, and more preferably 80% by mass or more. The ratio of cis-1,4 bonds in the polybutadiene is preferably 40% by mass or more, and more preferably 80% by mass or more.

  Polybutadiene having a 1,2-vinyl bond ratio of 2.0% by mass or less is preferred. This polybutadiene can contribute to the resilience performance of the core 4. In this respect, the 1,2-vinyl bond ratio is preferably equal to or less than 1.7% by mass, and particularly preferably equal to or less than 1.5% by mass.

  From the viewpoint of obtaining a polybutadiene having a small ratio of 1,2-vinyl bonds and excellent polymerization activity, it is preferable to use a rare earth element-based catalyst for the synthesis of polybutadiene. In particular, polybutadiene synthesized with a catalyst containing neodymium which is a lanthanum series rare earth element compound is preferable.

The Mooney viscosity (ML _{1 + 4} (100 ° C.)) of polybutadiene is preferably 30 or more, more preferably 32 or more, and particularly preferably 35 or more. The Mooney viscosity (ML _{1 + 4} (100 ° C.)) is preferably 140 or less, more preferably 120 or less, still more preferably 100 or less, and particularly preferably 80 or less. Mooney viscosity (ML _{1 + 4} (100 ° C.)) is measured in accordance with the provisions of “JIS K6300”. The measurement conditions are as follows.
Rotor: L rotor Preheating time: 1 minute Rotor rotation time: 4 minutes Temperature: 100 ° C

  From the viewpoint of workability, the molecular weight distribution (Mw / Mn) of polybutadiene is preferably 2.0 or more, more preferably 2.2 or more, further preferably 2.4 or more, and particularly preferably 2.6 or more. In light of resilience performance, the molecular weight distribution (Mw / Mn) is preferably 6.0 or less, more preferably 5.0 or less, still more preferably 4.0 or less, and particularly preferably 3.4 or less. The molecular weight distribution (Mw / Mn) is calculated by dividing the weight average molecular weight Mw by the number average molecular weight Mn.

The molecular weight distribution is measured by gel permeation chromatography (“HLC-8120GPC” manufactured by Tosoh Corporation). The measurement conditions are as follows.
Detector: differential refractometer Column: GMHHXL (manufactured by Tosoh Corporation)
Column temperature: 40 ° C
Mobile phase: Tetrahydrofuran molecular weight distribution is calculated as a standard polystyrene equivalent value.

A preferred co-crosslinking agent (b) is:
(B1) an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and (b2) a metal salt of an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms.

  The rubber composition may contain only the α, β-unsaturated carboxylic acid (b1) or only the metal salt (b2) of the α, β-unsaturated carboxylic acid as the co-crosslinking agent (b). The rubber composition may contain both α, β-unsaturated carboxylic acid (b1) and α, β-unsaturated carboxylic acid metal salt (b2) as the co-crosslinking agent (b).

  The metal salt (b2) of α, β-unsaturated carboxylic acid crosslinks the rubber molecule by graft polymerization to the molecular chain of the base rubber. When the rubber composition contains an α, β-unsaturated carboxylic acid (b1), the rubber composition preferably further contains a metal compound (f). This metal compound (f) reacts with the α, β-unsaturated carboxylic acid (b1) in the rubber composition. The salt obtained by this reaction is graft-polymerized to the molecular chain of the base rubber.

  Examples of the metal compound (f) include metal hydroxides such as magnesium hydroxide, zinc hydroxide, calcium hydroxide, sodium hydroxide, lithium hydroxide, potassium hydroxide and copper hydroxide; magnesium oxide, calcium oxide, Metal oxides such as zinc oxide and copper oxide; and metal carbonates such as magnesium carbonate, zinc carbonate, calcium carbonate, sodium carbonate, lithium carbonate and potassium carbonate. A compound containing a divalent metal is preferred. A compound containing a divalent metal reacts with the co-crosslinking agent (b) to form a metal bridge. A particularly preferred metal compound (f) is a zinc compound. Two or more metal compounds may be used in combination.

  Examples of the α, β-unsaturated carboxylic acid include acrylic acid, methacrylic acid, fumaric acid, maleic acid and crotonic acid. The metal component in the metal salt (b2) of α, β-unsaturated carboxylic acid includes sodium ion, potassium ion, lithium ion, magnesium ion, calcium ion, zinc ion, barium ion, cadmium ion, aluminum ion, tin ion and Zirconium ions are exemplified. The metal salt (b2) of α, β-unsaturated carboxylic acid may contain two or more kinds of ions. From the viewpoint that metal crosslinking between rubber molecules is likely to occur, divalent metal ions such as magnesium ion, calcium ion, zinc ion, barium ion and cadmium ion are preferable. A particularly preferred metal salt (b2) of α, β-unsaturated carboxylic acid is zinc acrylate.

  In light of the resilience performance of the golf ball 2, the amount of the co-crosslinking agent (b) is preferably 15 parts by mass or more and particularly preferably 20 parts by mass or more with respect to 100 parts by mass of the base rubber. In light of feel at impact, this amount is preferably equal to or less than 50 parts by weight, more preferably equal to or less than 45 parts by weight, and particularly preferably equal to or less than 40 parts by weight.

  A preferred crosslinking initiator (c) is an organic peroxide. The organic peroxide contributes to the resilience performance of the golf ball 2. Suitable organic peroxides include dicumyl peroxide, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di (t- Butyl peroxy) hexane and di-t-butyl peroxide. From the viewpoint of versatility, dicumyl peroxide is preferable.

  In light of the resilience performance of the golf ball 2, the amount of the crosslinking initiator (c) is preferably 0.2 parts by mass or more and particularly preferably 0.5 parts by mass or more with respect to 100 parts by mass of the base rubber. In light of feel at impact and durability of the golf ball 2, this amount is preferably equal to or less than 5.0 parts by weight, and particularly preferably equal to or less than 2.5 parts by weight.

  The acid and / or salt (d) does not include the co-crosslinking agent (b). It is presumed that the acid and / or the salt (d) cuts the metal bridge formed by the co-crosslinking agent (b) at the center of the core 4 when the core 4 is heated and formed. Acids and / or salts (d) include oxo acids such as carboxylic acids, sulfonic acids and phosphoric acids and salts thereof; and hydrogen acids such as hydrochloric acid and hydrofluoric acid and salts thereof. Oxo acids and their salts are preferred. Carboxylic acid and / or its salt (d1) is more preferred. Carboxylate is particularly preferred.

  The carbon number of the carboxylic acid component in the carboxylic acid and / or its salt (d1) is preferably 1 or more, 30 or less, more preferably 3 or more and 30 or less, and even more preferably 5 or more and 28 or less. Examples of the carboxylic acid include aliphatic carboxylic acids (fatty acids) and aromatic carboxylic acids. Fatty acids and their salts are preferred.

  The rubber composition may contain a saturated fatty acid or a salt thereof, and may contain an unsaturated fatty acid or a salt thereof. Saturated fatty acids and salts thereof are preferred.

  As fatty acids, butyric acid (C4), valeric acid (C5), caproic acid (C6), enanthic acid (C7), caprylic acid (C8), pelargonic acid (C9), capric acid (C10), lauric acid (C12), Myristic acid (C14), myristic acid (C14), pentadecylic acid (C15), palmitic acid (C16), palmitoleic acid (C16), margaric acid (C17), stearic acid (C18), elaidic acid (C18), baxene Acid (C18), oleic acid (C18), linoleic acid (C18), linolenic acid (C18), 12-hydroxystearic acid (C18), arachidic acid (C20), gadoleic acid (C20), arachidonic acid (C20), Eicosenoic acid (C20), behenic acid (C22), erucic acid (C22), lignoceric acid (C24), ne Bon acid (C24), cerotic acid (C26), montanic acid (C28) and melissic acid (C30) can be mentioned. Two or more fatty acid salts may be used in combination. Caprylic acid (octanoic acid), lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid and behenic acid are preferred.

  The aromatic carboxylic acid has an aromatic ring and a carboxyl group. As aromatic carboxylic acid, benzoic acid, phthalic acid, isophthalic acid, terephthalic acid, hemimellitic acid (benzene-1,2,3-tricarboxylic acid), trimellitic acid (benzene-1,2,4-tricarboxylic acid), Trimesic acid (benzene-1,3,5-tricarboxylic acid), merophanic acid (benzene-1,2,3,4-tetracarboxylic acid), planitic acid (benzene-1,2,3,5-tetracarboxylic acid) , Pyromellitic acid (benzene-1,2,4,5-tetracarboxylic acid), meritic acid (benzenehexacarboxylic acid), diphenic acid (biphenyl-2,2'-dicarboxylic acid), toluic acid (methylbenzoic acid) , Xylic acid, prenylic acid (2,3,4-trimethylbenzoic acid), γ-isoduric acid (2,3,5-trimethylbenzoic acid), duric acid 2,4,5-trimethylbenzoic acid), β-isoduric acid (2,4,6-trimethylbenzoic acid), α-isoduric acid (3,4,5-trimethylbenzoic acid), cumic acid (4-isopropylbenzoic acid) Acid), ubitoic acid (5-methylisophthalic acid), α-toluic acid (phenylacetic acid), hydroatropic acid (2-phenylpropanoic acid) and hydrocinnamic acid (3-phenylpropanoic acid).

  The rubber composition may contain an aromatic carboxylic acid or a salt thereof substituted with a hydroxyl group, an alkoxy group or an oxo group. As this carboxylic acid, salicylic acid (2-hydroxybenzoic acid), anisic acid (methoxybenzoic acid), cresotic acid (hydroxy (methyl) benzoic acid), o-homosalicylic acid (2-hydroxy-3-methylbenzoic acid), m -Homosalicylic acid (2-hydroxy-4-methylbenzoic acid), p-homosalicylic acid (2-hydroxy-5-methylbenzoic acid), o-pyrocatechuic acid (2,3-dihydroxybenzoic acid), β-resorcylic acid ( 2,4-dihydroxybenzoic acid), γ-resorcylic acid (2,6-dihydroxybenzoic acid), protocatechuic acid (3,4-dihydroxybenzoic acid), α-resorcylic acid (3,5-dihydroxybenzoic acid), vanillin Acid (4-hydroxy-3-methoxybenzoic acid), isovanillic acid (3-hydroxy-4-methoxybenzoic acid), Tormic acid (3,4-dimethoxybenzoic acid), o-veratormic acid (2,3-dimethoxybenzoic acid), orthoric acid (2,4-dihydroxy-6-methylbenzoic acid), m-hemipic acid (4,5 -Dimethoxyphthalic acid), gallic acid (3,4,5-trihydroxybenzoic acid), syringic acid (4-hydroxy-3,5-dimethoxybenzoic acid), asaronic acid (2,4,5-trimethoxybenzoic acid) , Mandelic acid (hydroxy (phenyl) acetic acid), vanylmandelic acid (hydroxy (4-hydroxy-3-methoxyphenyl) acetic acid), homoanisic acid ((4-methoxyphenyl) acetic acid), homogentisic acid ((2,5-dihydroxyphenyl) ) Acetic acid), homoprotocatechuic acid ((3,4-dihydroxyphenyl) acetic acid), homovanillic acid ((4-hydroxy-3) Methoxyphenyl) acetic acid), homoisovanillic acid ((3-hydroxy-4-methoxyphenyl) acetic acid), homoveratrumic acid ((3,4-dimethoxyphenyl) acetic acid), o-homoveratric acid ((2,3-dimethoxyphenyl) ) Acetic acid), homophthalic acid (2- (carboxymethyl) benzoic acid), homoisophthalic acid (3- (carboxymethyl) benzoic acid), homoterephthalic acid (4- (carboxymethyl) benzoic acid), phthalonic acid (2- (Carboxycarbonyl) benzoic acid), isophthalonic acid (3- (carboxycarbonyl) benzoic acid), terephthalonic acid (4- (carboxycarbonyl) benzoic acid), benzylic acid (hydroxydiphenylacetic acid), atrolactic acid (2-hydroxy- 2-phenylpropanoic acid), tropic acid (3-hydroxy-2-phen Nylpropanoic acid), mellilotic acid (3- (2-hydroxyphenyl) propanoic acid), furoleto acid (3- (4-hydroxyphenyl) propanoic acid), hydrocaffeic acid (3- (3,4-dihydroxyphenyl) propanoic acid ), Hydroferulic acid (3- (4-hydroxy-3-methoxyphenyl) propanoic acid), hydroisoferulic acid (3- (3-hydroxy-4-methoxyphenyl) propanoic acid), p-coumaric acid (3- (4-hydroxyphenyl) acrylic acid), umberic acid (3- (2,4-dihydroxyphenyl) acrylic acid), caffeic acid (3- (3,4-dihydroxyphenyl) acrylic acid), ferulic acid (3- ( 4-hydroxy-3-methoxyphenyl) acrylic acid), isoferulic acid (3- (3-hydroxy-4-methoxyphenyl) Acrylic acid) and sinapinic acid (3- (4-hydroxy-3,5-dimethoxyphenyl) acrylic acid) may be exemplified.

  The cation component of the carboxylate is a metal ion or an organic cation. As metal ions, sodium ion, potassium ion, lithium ion, silver ion, magnesium ion, calcium ion, zinc ion, barium ion, cadmium ion, copper ion, cobalt ion, nickel ion, manganese ion, aluminum ion, iron ion, tin Examples include ions, zirconium ions, and titanium ions. Two or more ions may be used in combination.

  The organic cation has a carbon chain. An organic ammonium ion is mentioned as an organic cation. As organic ammonium ions, primary ammonium ions such as stearyl ammonium ion, hexyl ammonium ion, octyl ammonium ion and 2-ethylhexyl ammonium ion; secondary ammonium ions such as dodecyl (lauryl) ammonium ion and octadecyl (stearyl) ammonium ion A tertiary ammonium ion such as trioctylammonium ion; and a quaternary ammonium ion such as dioctyldimethylammonium ion and distearyldimethylammonium ion. Two or more organic cations may be used in combination.

  Preferred carboxylates include octanoic acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid or behenic acid potassium salt, magnesium salt, aluminum salt, zinc salt, iron salt, copper salt, nickel salt or cobalt salt Is exemplified. A zinc salt of a carboxylic acid is particularly preferred. Specific examples of preferred carboxylates include zinc octoate, zinc laurate, zinc myristate and zinc stearate.

  From the viewpoint of linearity of the hardness distribution of the core 4, the amount of the acid and / or salt (d) is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more with respect to 100 parts by mass of the base rubber. Preferably, 2.0 parts by mass or more is particularly preferable. In light of resilience performance, this amount is preferably less than 40 parts by weight, more preferably 30 parts by weight or less, and particularly preferably 20 parts by weight or less.

  The mass ratio of the co-crosslinking agent (b) to the acid and / or salt (d) in the rubber composition is preferably 3/7 or more and 9/1 or less, particularly preferably 4/6 or less and 8/2 or less. With the rubber composition having a mass ratio within the above range, the core 4 whose hardness increases linearly from the center point toward the surface can be obtained.

  As the co-crosslinking agent (b), zinc acrylate is preferably used. For the purpose of improving dispersibility in rubber, there is zinc acrylate whose surface is coated with stearic acid or zinc stearate. In the present invention, when the rubber composition contains the zinc acrylate, the acid and / or the salt (d) does not contain the coating agent.

  Preferably, the rubber composition further includes an organic sulfur compound (e). The organic sulfur compound (e) can contribute to control of the linearity of the hardness distribution of the core 4 and the degree of the outer-hard / inner-soft structure. Examples of the organic sulfur compound (e) include organic compounds having a thiol group or a polysulfide bond having 2 to 4 sulfur atoms. The metal salt of this organic compound is also included in the organic sulfur compound (e). As the organic sulfur compound (e), aliphatic compounds such as aliphatic thiols, aliphatic thiocarboxylic acids, aliphatic dithiocarboxylic acids and aliphatic polysulfides; heterocyclic compounds; alicyclic thiols, alicyclic thiocarboxylic acids, fats Illustrative are alicyclic compounds such as cyclic dithiocarboxylic acids and alicyclic polysulfides; and aromatic compounds. Specific examples of the organic sulfur compound (e) include thiophenols, thionaphthols, polysulfides, thiocarboxylic acids, dithiocarboxylic acids, sulfenamides, thiurams, dithiocarbamates and thiazoles. Preferred organic sulfur compounds are thiophenols, diphenyl disulfides, thionaphthols and thiuram disulfides and their metal salts.

  Specific examples of the organic sulfur compound (e) are represented by the following chemical formulas (1) to (4).

  In the chemical formula (1), R1 to R5 each represent H or a substituent.

  In the chemical formula (2), R1 to R10 each represent H or a substituent.

  In the chemical formula (3), R1 to R5 each represent H or a substituent, and M1 represents a monovalent metal atom.

  In the chemical formula (4), R1 to R10 each represent H or a substituent, and M2 represents a divalent metal atom.

In the above formulas (1) to (4), the substituent is a halogen group (F, Cl, Br, I), an alkyl group, a carboxyl group (—COOH), an ester of a carboxyl group (—COOR), a formyl group (— CHO), acyl group (—COR), halogenated carbonyl group (—COX), sulfo group (—SO ₃ H), ester of sulfo group (—SO ₃ R), halogenated sulfonyl group (—SO ₂ X), Selected from the group consisting of a sulfino group (—SO ₂ H), an alkylsulfinyl group (—SOR), a carbamoyl group (—CONH ₂ ), a halogenated alkyl group, a cyano group (—CN) and an alkoxy group (—OR). At least one kind.

  Examples of the organic sulfur compound represented by the chemical formula (1) include thiophenol; 4-fluorothiophenol, 2,5-difluorothiophenol, 2,4,5-trifluorothiophenol, 2,4,5. , 6-tetrafluorothiophenol, pentafluorothiophenol, 2-chlorothiophenol, 4-chlorothiophenol, 2,4-dichlorothiophenol, 2,5-dichlorothiophenol, 2,4,5-trichlorothiophenol 2,4,5,6-tetrachlorothiophenol, pentachlorothiophenol, 4-bromothiophenol, 2,5-dibromothiophenol, 2,4,5-tribromothiophenol, 2,4,5, 6-tetrabromothiophenol, pentabromothiophenol, 4-iodothiopheno , Thiophenols substituted with halogen groups such as 2,5-diiodothiophenol, 2,4,5-triiodothiophenol, 2,4,5,6-tetraiodothiophenol and pentaiodothiophenol 4-methylthiophenol, 2,4,5-trimethylthiophenol, pentamethylthiophenol, 4-t-butylthiophenol, 2,4,5-tri-t-butylthiophenol and penta-t-butylthiophenol; Thiophenols substituted with such alkyl groups; thiophenols substituted with carboxyl groups such as 4-carboxythiophenol, 2,4,6-tricarboxythiophenol and pentacarboxythiophenol; 4-methoxycarbonyl Thiophenol, 2,4,6-trimethoxycarbo Thiophenols substituted with alkoxycarbonyl groups such as ruthiophenol and pentamethoxycarbonylthiophenol; substituted with formyl groups such as 4-formylthiophenol, 2,4,6-triformylthiophenol and pentaformylthiophenol Thiophenols substituted with acyl groups such as 4-acetylthiophenol, 2,4,6-triacetylthiophenol and pentaacetylthiophenol; 4-chlorocarbonylthiophenol, 2,4 Thiophenols substituted with halogenated carbonyl groups such as 1,6-tri (chlorocarbonyl) thiophenol and penta (chlorocarbonyl) thiophenol; 4-sulfothiophenol, 2,4,6-trisulfothiophenol and Bae Thiophenols substituted with a sulfo group such as intersulfothiophenol; substituted with alkoxysulfonyl groups such as 4-methoxysulfonylthiophenol, 2,4,6-trimethoxysulfonylthiophenol and pentamethoxysulfonylthiophenol Thiophenols; thiophenols substituted with halogenated sulfonyl groups such as 4-chlorosulfonylthiophenol, 2,4,6-tri (chlorosulfonyl) thiophenol and penta (chlorosulfonyl) thiophenol; 4- Thiophenols substituted with sulfino groups such as sulfinothiophenol, 2,4,6-trisulfinothiophenol and pentasulfinothiophenol; 4-methylsulfinylthiophenol, 2,4,6-tri (methyls) Thiophenols substituted with alkylsulfinyl groups such as finyl) thiophenol and penta (methylsulfinyl) thiophenol; such as 4-carbamoylthiophenol, 2,4,6-tricarbamoylthiophenol and pentacarbamoylthiophenol Thiophenols substituted with carbamoyl groups; thiophenols substituted with halogenated alkyl groups such as 4-trichloromethylthiophenol, 2,4,6-tri (trichloromethyl) thiophenol and penta (trichloromethyl) thiophenol Thiophenols substituted with cyano groups such as 4-cyanothiophenol, 2,4,6-tricyanothiophenol and pentacyanothiophenol; and 4-methoxythiophenol, 2,4,6- Thiophenols substituted with an alkoxy group such as trimethoxy thiophenol and penta-methoxy thiophenol and the like. These thiophenols are substituted with one type of substituent.

As another example of the organic sulfur compound represented by the chemical formula (1), a compound substituted with at least one kind of the above substituent and another substituent can be given. Examples of other substituents include a nitro group (—NO ₂ ), an amino group (—NH ₂ ), a hydroxyl group (—OH), and a phenylthio group (—SPh). Specific examples of this compound include 4-chloro-2-nitrothiophenol, 4-chloro-2-aminothiophenol, 4-chloro-2-hydroxythiophenol, 4-chloro-2-phenylthiothiophenol, 4 -Methyl-2-nitrothiophenol, 4-methyl-2-aminothiophenol, 4-methyl-2-hydroxythiophenol, 4-methyl-2-phenylthiothiophenol, 4-carboxy-2-nitrothiophenol, 4-carboxy-2-aminothiophenol, 4-carboxy-2-hydroxythiophenol, 4-carboxy-2-phenylthiothiophenol, 4-methoxycarbonyl-2-nitrothiophenol, 4-methoxycarbonyl-2-amino Thiophenol, 4-methoxycarbonyl-2-hydroxy Thiophenol, 4-methoxycarbonyl-2-phenylthiothiophenol, 4-formyl-2-nitrothiophenol, 4-formyl-2-aminothiophenol, 4-formyl-2-hydroxythiophenol, 4-formyl-2 -Phenylthiothiophenol, 4-acetyl-2-nitrothiophenol, 4-acetyl-2-aminothiophenol, 4-acetyl-2-hydroxythiophenol, 4-acetyl-2-phenylthiothiophenol, 4-chloro Carbonyl-2-nitrothiophenol, 4-chlorocarbonyl-2-aminothiophenol, 4-chlorocarbonyl-2-hydroxythiophenol, 4-chlorocarbonyl-2-phenylthiothiophenol, 4-sulfo-2-nitrothio Phenol, 4-sulfo- -Aminothiophenol, 4-sulfo-2-hydroxythiophenol, 4-sulfo-2-phenylthiothiophenol, 4-methoxysulfonyl-2-nitrothiophenol, 4-methoxysulfonyl-2-aminothiophenol, 4- Methoxysulfonyl-2-hydroxythiophenol, 4-methoxysulfonyl-2-phenylthiothiophenol, 4-chlorosulfonyl-2-nitrothiophenol, 4-chlorosulfonyl-2-aminothiophenol, 4-chlorosulfonyl-2- Hydroxythiophenol, 4-chlorosulfonyl-2-phenylthiothiophenol, 4-sulfino-2-nitrothiophenol, 4-sulfino-2-aminothiophenol, 4-sulfino-2-hydroxythiophenol, 4-sulfino 2-phenylthiothiophenol, 4-methylsulfinyl-2-nitrothiophenol, 4-methyl-2-aminosulfinylthiophenol, 4-methylsulfinyl-2-hydroxythiophenol, 4-methylsulfinyl-2-phenylthio Thiophenol, 4-carbamoyl-2-nitrothiophenol, 4-carbamoyl-2-aminothiophenol, 4-carbamoyl-2-hydroxythiophenol, 4-carbamoyl-2-phenylthiothiophenol, 4-trichloromethyl-2 -Nitrothiophenol, 4-trichloromethyl-2-aminothiophenol, 4-trichloromethyl-2-hydroxythiophenol, 4-trichloromethyl-2-phenylthiothiophenol, 4-cyano-2-nitrothiopheno 4-cyano-2-aminothiophenol, 4-cyano-2-hydroxythiophenol, 4-cyano-2-phenylthiothiophenol, 4-methoxy-2-nitrothiophenol, 4-methoxy-2-aminothio Examples include phenol, 4-methoxy-2-hydroxythiophenol and 4-methoxy-2-phenylthiothiophenol.

  Still another example of the organic sulfur compound represented by the chemical formula (1) includes a compound substituted with two or more kinds of substituents. Specific examples of this compound include 4-acetyl-2-chlorothiophenol, 4-acetyl-2-methylthiophenol, 4-acetyl-2-carboxythiophenol, 4-acetyl-2-methoxycarbonylthiophenol, 4-acetyl 2-formylthiophenol, 4-acetyl-2-chlorocarbonylthiophenol, 4-acetyl-2-sulfothiophenol, 4-acetyl-2-methoxysulfonylthiophenol, 4-acetyl-2-chlorosulfonylthiophenol, 4-acetyl-2-sulfinothiophenol, 4-acetyl-2-methylsulfinylthiophenol, 4-acetyl-2-carbamoylthiophenol, 4-acetyl-2-trichloromethylthiophenol, 4-acetyl-2-cyanothio Phenol Beauty 4-acetyl-2-methoxy-thiophenol and the like.

  Examples of the organic sulfur compound represented by the chemical formula (2) include diphenyl disulfide; bis (4-fluorophenyl) disulfide, bis (2,5-difluorophenyl) disulfide, bis (2,4,5-trifluoro). Phenyl) disulfide, bis (2,4,5,6-tetrafluorophenyl) disulfide, bis (pentafluorophenyl) disulfide, bis (4-chlorophenyl) disulfide, bis (2,5-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 , Screws (2, 4, -Tribromophenyl) disulfide, bis (2,4,5,6-tetrabromophenyl) disulfide, bis (pentabromophenyl) disulfide, bis (4-iodophenyl) disulfide, bis (2,5-diiodophenyl) Diphenyl disulfides substituted with halogen groups such as disulfide, bis (2,4,5-triiodophenyl) disulfide, bis (2,4,5,6-tetraiodophenyl) disulfide and bis (pentaiodophenyl) disulfide 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 Diphenyl disulfides substituted with alkyl groups such as bis (penta-t-butylphenyl) disulfide; bis (4-carboxyphenyl) disulfide, bis (2,4,6-tricarboxyphenyl) disulfide and bis (penta Diphenyl disulfides substituted with carboxyl groups such as carboxyphenyl) disulfide; bis (4-methoxycarbonylphenyl) disulfide, bis (2,4,6-trimethoxycarbonylphenyl) disulfide and bis (pentamethoxycarbonylphenyl) disulfide Diphenyl disulfides substituted with alkoxycarbonyl groups such as: bis (4-formylphenyl) disulfide, bis (2,4,6-triformylphenyl) disulfide and bis (pentaformyl) Diphenyl disulfides substituted with formyl groups such as phenyl) disulfide; acyls such as bis (4-acetylphenyl) disulfide, bis (2,4,6-triacetylphenyl) disulfide and bis (pentaacetylphenyl) disulfide Group substituted diphenyl disulfides; halogens such as bis (4-chlorocarbonylphenyl) disulfide, bis (2,4,6-tri (chlorocarbonyl) phenyl) disulfide and bis (penta (chlorocarbonyl) phenyl) disulfide Diphenyl disulfides substituted with a carbonyl group; substituted with sulfo groups such as bis (4-sulfophenyl) disulfide, bis (2,4,6-trisulfophenyl) disulfide and bis (pentasulfophenyl) disulfide Diphenyl disulfides; diphenyls substituted with alkoxysulfonyl groups such as bis (4-methoxysulfonylphenyl) disulfide, bis (2,4,6-trimethoxysulfonylphenyl) disulfide and bis (pentamethoxysulfonylphenyl) disulfide Disulfides; substituted with sulfonyl halides such as bis (4-chlorosulfonylphenyl) disulfide, bis (2,4,6-tri (chlorosulfonyl) phenyl) disulfide and bis (penta (chlorosulfonyl) phenyl) disulfide Diphenyl disulfides; such as bis (4-sulfinophenyl) disulfide, bis (2,4,6-trisulfinophenyl) disulfide and bis (pentasulfinophenyl) disulfide Diphenyl disulfides substituted with a rufino group; such as bis (4-methylsulfinylphenyl) disulfide, bis (2,4,6-tri (methylsulfinyl) phenyl) disulfide and bis (penta (methylsulfinyl) phenyl) disulfide Diphenyl disulfides substituted with alkylsulfinyl groups; substituted with carbamoyl groups such as bis (4-carbamoylphenyl) disulfide, bis (2,4,6-tricarbamoylphenyl) disulfide and bis (pentacarbamoylphenyl) disulfide Diphenyl disulfides; bis (4-trichloromethylphenyl) disulfide, bis (2,4,6-tri (trichloromethyl) phenyl) disulfide and bis (penta (trichloromethyl) phenyl) Diphenyl disulfides substituted with halogenated alkyl groups such as disulfides; cyano such as bis (4-cyanophenyl) disulfide, bis (2,4,6-tricyanophenyl) disulfide and bis (pentacyanophenyl) disulfide Substituted diphenyl disulfides; and diphenyl substituted with alkoxy groups such as bis (4-methoxyphenyl) disulfide, bis (2,4,6-trimethoxyphenyl) disulfide and bis (pentamethoxyphenyl) disulfide Disulfides are exemplified. These diphenyl disulfides are substituted with one type of substituent.

As another example of the organic sulfur compound represented by the chemical formula (2), a compound substituted with at least one kind of the substituent and another substituent can be given. Examples of other substituents include a nitro group (—NO ₂ ), an amino group (—NH ₂ ), a hydroxyl group (—OH), and a phenylthio group (—SPh). Specific examples of this compound include bis (4-chloro-2-nitrophenyl) disulfide, bis (4-chloro-2-aminophenyl) disulfide, bis (4-chloro-2-hydroxyphenyl) disulfide, bis (4 -Chloro-2-phenylthiophenyl) disulfide, bis (4-methyl-2-nitrophenyl) disulfide, bis (4-methyl-2-aminophenyl) disulfide, bis (4-methyl-2-hydroxyphenyl) disulfide, Bis (4-methyl-2-phenylthiophenyl) disulfide, bis (4-carboxy-2-nitrophenyl) disulfide, bis (4-carboxy-2-aminophenyl) disulfide, bis (4-carboxy-2-hydroxyphenyl) ) Disulfide, bis (4-carboxy-2-fe) Ruthiophenyl) disulfide, bis (4-methoxycarbonyl-2-nitrophenyl) disulfide, bis (4-methoxycarbonyl-2-aminophenyl) disulfide, bis (4-methoxycarbonyl-2-hydroxyphenyl) disulfide, bis (4 -Methoxycarbonyl-2-phenylthiophenyl) disulfide, bis (4-formyl-2-nitrophenyl) disulfide, bis (4-formyl-2-aminophenyl) disulfide, bis (4-formyl-2-hydroxyphenyl) disulfide Bis (4-formyl-2-phenylthiophenyl) disulfide, bis (4-acetyl-2-nitrophenyl) disulfide, bis (4-acetyl-2-aminophenyl) disulfide, bis (4-acetyl-2-hydroxy) Enyl) disulfide, bis (4-acetyl-2-phenylthiophenyl) disulfide, bis (4-chlorocarbonyl-2-nitrophenyl) disulfide, bis (4-chlorocarbonyl-2-aminophenyl) disulfide, bis (4- Chlorocarbonyl-2-hydroxyphenyl) disulfide, bis (4-chlorocarbonyl-2-phenylthiophenyl) disulfide, bis (4-sulfo-2-nitrophenyl) disulfide, bis (4-sulfo-2-aminophenyl) disulfide Bis (4-sulfo-2-hydroxyphenyl) disulfide, bis (4-sulfo-2-phenylthiophenyl) disulfide, bis (4-methoxysulfonyl-2-nitrophenyl) disulfide, bis (4-methoxysulfonyl-2) -Aminofe Nyl) disulfide, bis (4-methoxysulfonyl-2-hydroxyphenyl) disulfide, bis (4-methoxysulfonyl-2-phenylthiophenyl) disulfide, bis (4-chlorosulfonyl-2-nitrophenyl) disulfide, bis (4 -Chlorosulfonyl-2-aminophenyl) disulfide, bis (4-chlorosulfonyl-2-hydroxyphenyl) disulfide, bis (4-chlorosulfonyl-2-phenylthiophenyl) disulfide, bis (4-sulfino-2-nitrophenyl) ) Disulfide, bis (4-sulfino-2-aminophenyl) disulfide, bis (4-sulfino-2-hydroxyphenyl) disulfide, bis (4-sulfino-2-phenylthiophenyl) disulfide, bis (4-methyl) Rufinyl-2-nitrophenyl) disulfide, bis (4-methylsulfinyl-2-aminophenyl) disulfide, bis (4-methylsulfinyl-2-hydroxyphenyl) disulfide, bis (4-methylsulfinyl-2-phenylthiophenyl) Disulfide, bis (4-carbamoyl-2-nitrophenyl) disulfide, bis (4-carbamoyl-2-aminophenyl) disulfide, bis (4-carbamoyl-2-hydroxyphenyl) disulfide, bis (4-carbamoyl-2-phenyl) Thiophenyl) disulfide, bis (4-trichloromethyl-2-nitrophenyl) disulfide, bis (4-trichloromethyl-2-aminophenyl) disulfide, bis (4-trichloromethyl-2-hydroxyphenyl) Disulfide, bis (4-trichloromethyl-2-phenylthiophenyl) disulfide, bis (4-cyano-2-nitrophenyl) disulfide, bis (4-cyano-2-aminophenyl) disulfide, bis (4-cyano-2) -Hydroxyphenyl) disulfide, bis (4-cyano-2-phenylthiophenyl) disulfide, bis (4-methoxy-2-nitrophenyl) disulfide, bis (4-methoxy-2-aminophenyl) disulfide, bis (4- Methoxy-2-hydroxyphenyl) disulfide and bis (4-methoxy-2-phenylthiophenyl) disulfide.

  Still another example of the organic sulfur compound represented by the chemical formula (2) includes a compound substituted with two or more kinds of substituents. Specific examples of this compound include bis (4-acetyl-2-chlorophenyl) disulfide, bis (4-acetyl-2-methylphenyl) disulfide, bis (4-acetyl-2-carboxyphenyl) disulfide, and bis (4-acetyl). -2-methoxycarbonylphenyl) disulfide, bis (4-acetyl-2-formylphenyl) disulfide, bis (4-acetyl-2-chlorocarbonylphenyl) disulfide, bis (4-acetyl-2-sulfophenyl) disulfide, bis (4-acetyl-2-methoxysulfonylphenyl) disulfide, bis (4-acetyl-2-chlorosulfonylphenyl) disulfide, bis (4-acetyl-2-sulfinophenyl) disulfide, bis (4-acetyl-2-methyl) Sulfinylfe Di) disulfide, bis (4-acetyl-2-carbamoylphenyl) disulfide, bis (4-acetyl-2-trichloromethylphenyl) disulfide, bis (4-acetyl-2-cyanophenyl) disulfide and bis (4-acetyl-) 2-methoxyphenyl) disulfide.

  Examples of the organic sulfur compound represented by the chemical formula (3) include thiophenol sodium salt; 4-fluorothiophenol sodium salt, 2,5-difluorothiophenol sodium salt, 2,4,5-trifluorothiophenol. Sodium salt, 2,4,5,6-tetrafluorothiophenol sodium salt, pentafluorothiophenol sodium salt, 4-chlorothiophenol sodium salt, 2,5-dichlorothiophenol sodium salt, 2,4,5-trichloro Thiophenol sodium salt, 2,4,5,6-tetrachlorothiophenol sodium salt, pentachlorothiophenol sodium salt, 4-bromothiophenol sodium salt, 2,5-dibromothiophenol sodium salt, 2,4,5 -Tribromothiophene Sodium salt, 2,4,5,6-tetrabromothiophenol sodium salt, pentabromothiophenol sodium salt, 4-iodothiophenol sodium salt, 2,5-diiodothiophenol sodium salt, 2,4,5- Thiophenol sodium salts substituted with halogen groups such as triiodothiophenol sodium salt, 2,4,5,6-tetraiodothiophenol sodium salt and pentaiodothiophenol sodium salt; 4-methylthiophenol sodium salt, 2 , 4,5-trimethylthiophenol sodium salt, pentamethylthiophenol sodium salt, 4-t-butylthiophenol sodium salt, 2,4,5-tri-t-butylthiophenol sodium salt and penta (t-butyl) thio Phenol nato Thiophenol sodium salts substituted with alkyl groups such as um salt; substituted with carboxyl groups such as 4-carboxythiophenol sodium salt, 2,4,6-tricarboxythiophenol sodium salt and pentacarboxythiophenol sodium salt Thiophenol sodium salts; sodium thiophenol substituted with alkoxycarbonyl groups such as 4-methoxycarbonylthiophenol sodium salt, 2,4,6-trimethoxycarbonylthiophenol sodium salt and pentamethoxycarbonylthiophenol sodium salt Salts; substituted with formyl groups such as 4-formylthiophenol sodium salt, 2,4,6-triformylthiophenol sodium salt and pentaformylthiophenol sodium salt Thiophenol sodium salts; thiophenol sodium salts substituted with acyl groups such as 4-acetylthiophenol sodium salt, 2,4,6-triacetylthiophenol sodium salt and pentaacetylthiophenol sodium salt; Thiophenol sodium salts substituted with halogenated carbonyl groups such as chlorocarbonylthiophenol sodium salt, 2,4,6-tri (chlorocarbonyl) thiophenol sodium salt and penta (chlorocarbonyl) thiophenol sodium salt; Thiophenol sodium salts substituted with a sulfo group such as sulfothiophenol sodium salt, 2,4,6-trisulfothiophenol sodium salt and pentasulfothiophenol sodium salt; Thiophenol sodium salts substituted with alkoxysulfonyl groups such as sodium nylthiophenol, sodium salt of 2,4,6-trimethoxysulfonylthiophenol and sodium salt of pentamethoxysulfonylthiophenol; sodium salt of 4-chlorosulfonylthiophenol 1,4,6-tri (chlorosulfonyl) thiophenol sodium salt and thiophenol sodium salts substituted with a sulfonyl halide group such as penta (chlorosulfonyl) thiophenol sodium salt; 4-sulfinothiophenol sodium salt Thiophenol sodium salts substituted with sulfino groups such as 2,4,6-trisulfinothiophenol sodium salt and pentasulfinothiophenol sodium salt; Thiophenol sodium salts substituted with alkylsulfinyl groups such as sulfinylthiophenol sodium salt, 2,4,6-tri (methylsulfinyl) thiophenol sodium salt and penta (methylsulfinyl) thiophenol sodium salt; 4-carbamoyl Thiophenol sodium salts substituted with carbamoyl groups such as thiophenol sodium salt, 2,4,6-tricarbamoylthiophenol sodium salt and pentacarbamoyl thiophenol sodium salt; 4-trichloromethylthiophenol sodium salt, 2,4,4 Thiophenols substituted with alkyl halide groups such as 6-tri (trichloromethyl) thiophenol sodium salt and penta (trichloromethyl) thiophenol sodium salt Sodium salts; thiophenol sodium salts substituted with cyano groups such as 4-cyanothiophenol sodium salt, 2,4,6-tricyanothiophenol sodium salt and pentacyanothiophenol sodium salt; and 4-methoxythiophenol sodium Illustrative are thiophenol sodium salts substituted with alkoxy groups such as salts, 2,4,6-trimethoxythiophenol sodium salt and pentamethoxythiophenol sodium salt. These thiophenol sodium salts are substituted with one kind of substituent.

As another example of the organic sulfur compound represented by the chemical formula (3), a compound substituted with at least one kind of the above substituent and another substituent can be given. Examples of other substituents include a nitro group (—NO ₂ ), an amino group (—NH ₂ ), a hydroxyl group (—OH), and a phenylthio group (—SPh). Specific examples of this compound include 4-chloro-2-nitrothiophenol sodium salt, 4-chloro-2-aminothiophenol sodium salt, 4-chloro-2-hydroxythiophenol sodium salt, 4-chloro-2- Phenylthiothiophenol sodium salt, 4-methyl-2-nitrothiophenol sodium salt, 4-methyl-2-aminothiophenol sodium salt, 4-methyl-2-hydroxythiophenol sodium salt, 4-methyl-2-phenyl Thiothiophenol sodium salt, 4-carboxy-2-nitrothiophenol sodium salt, 4-carboxy-2-aminothiophenol sodium salt, 4-carboxy-2-hydroxythiophenol sodium salt, 4-carboxy-2-phenylthio Thiophenol natri Salt, 4-methoxycarbonyl-2-nitrothiophenol sodium salt, 4-methoxycarbonyl-2-aminothiophenol sodium salt, 4-methoxycarbonyl-2-hydroxythiophenol sodium salt, 4-methoxycarbonyl-2-phenyl Thiothiophenol sodium salt, 4-formyl-2-nitrothiophenol sodium salt, 4-formyl-2-aminothiophenol sodium salt, 4-formyl-2-hydroxythiophenol sodium salt, 4-formyl-2-phenylthio Thiophenol sodium salt, 4-acetyl-2-nitrothiophenol sodium salt, 4-acetyl-2-aminothiophenol sodium salt, 4-acetyl-2-hydroxythiophenol sodium salt, 4-acetyl-2-phenol Ruthiothiophenol sodium salt, 4-chlorocarbonyl-2-nitrothiophenol sodium salt, 4-chlorocarbonyl-2-aminothiophenol sodium salt, 4-chlorocarbonyl-2-hydroxythiophenol sodium salt, 4-chlorocarbonyl- 2-phenylthiothiophenol sodium salt, 4-sulfo-2-nitrothiophenol sodium salt, 4-sulfo-2-aminothiophenol sodium salt, 4-sulfo-2-hydroxythiophenol sodium salt, 4-sulfo-2 -Phenylthiothiophenol sodium salt, 4-methoxysulfonyl-2-nitrothiophenol sodium salt, 4-methoxysulfonyl-2-aminothiophenol sodium salt, 4-methoxysulfonyl-2-hydroxythiopheno Sodium salt, 4-methoxysulfonyl-2-phenylthiothiophenol sodium salt, 4-chlorosulfonyl-2-nitrothiophenol sodium salt, 4-chlorosulfonyl-2-aminothiophenol sodium salt, 4-chlorosulfonyl-2- Hydroxythiophenol sodium salt, 4-chlorosulfonyl-2-phenylthiothiophenol sodium salt, 4-sulfino-2-nitrothiophenol sodium salt, 4-sulfino-2-aminothiophenol sodium salt, 4-sulfino-2- Hydroxythiophenol sodium salt, 4-sulfino-2-phenylthiothiophenol sodium salt, 4-methylsulfinyl-2-nitrothiophenol sodium salt, 4-methylsulfinyl-2-aminothiophene Sodium salt, 4-methylsulfinyl-2-hydroxythiophenol sodium salt, 4-methylsulfinyl-2-phenylthiothiophenol sodium salt, 4-carbamoyl-2-nitrothiophenol sodium salt, 4-carbamoyl-2-aminothio Phenol sodium salt, 4-carbamoyl-2-hydroxythiophenol sodium salt, 4-carbamoyl-2-phenylthiothiophenol sodium salt, 4-trichloromethyl-2-nitrothiophenol sodium salt, 4-trichloromethyl-2-amino Thiophenol sodium salt, 4-trichloromethyl-2-hydroxythiophenol sodium salt, 4-trichloromethyl-2-phenylthiothiophenol sodium salt, 4-cyano-2-nitrothiooff Nord sodium salt, 4-cyano-2-aminothiophenol sodium salt, 4-cyano-2-hydroxythiophenol sodium salt, 4-cyano-2-phenylthiothiophenol sodium salt, 4-methoxy-2-nitrothiophenol Examples include sodium salt, 4-methoxy-2-aminothiophenol sodium salt, 4-methoxy-2-hydroxythiophenol sodium salt and 4-methoxy-2-phenylthiothiophenol sodium salt.

  Still another example of the organic sulfur compound represented by the chemical formula (3) includes a compound substituted with two or more substituents. Specific examples of this compound include 4-acetyl-2-chlorothiophenol sodium salt, 4-acetyl-2-methylthiophenol sodium salt, 4-acetyl-2-carboxythiophenol sodium salt, 4-acetyl-2-methoxycarbonyl Thiophenol sodium salt, 4-acetyl-2-formylthiophenol sodium salt, 4-acetyl-2-chlorocarbonylthiophenol sodium salt, 4-acetyl-2-sulfothiophenol sodium salt, 4-acetyl-2-methoxysulfonyl Thiophenol sodium salt, 4-acetyl-2-chlorosulfonylthiophenol sodium salt, 4-acetyl-2-sulfinothiophenol sodium salt, 4-acetyl-2-methylsulfinylthiophenol sodium salt, 4 Acetyl-2-carbamoylthiophenol phenol sodium salt, 4-acetyl-2-trichloromethyl-thiophenol sodium salt, 4-acetyl-2-cyano thiophenol sodium salt and 4-acetyl-2-methoxy thiophenol sodium salt. In the chemical formula (3), examples of the monovalent metal represented by M1 include sodium, lithium, potassium, copper (I), and silver (I).

  As the organic sulfur compound represented by the chemical formula (4), thiophenol zinc salt; 4-fluorothiophenol zinc salt, 2,5-difluorothiophenol zinc salt, 2,4,5-trifluorothiophenol zinc salt, 2,4,5,6-tetrafluorothiophenol zinc salt, pentafluorothiophenol zinc salt, 4-chlorothiophenol zinc salt, 2,5-dichlorothiophenol zinc salt, 2,4,5-trichlorothiophenol zinc Salt, 2,4,5,6-tetrachlorothiophenol zinc salt, pentachlorothiophenol zinc salt, 4-bromothiophenol zinc salt, 2,5-dibromothiophenol zinc salt, 2,4,5-tribromo Thiophenol zinc salt, 2,4,5,6-tetrabromothiophenol zinc salt, pentabromothiophenol Lead salt, 4-iodothiophenol zinc salt, 2,5-diiodothiophenol zinc salt, 2,4,5-triiodothiophenol zinc salt, 2,4,5,6-tetraiodothiophenol zinc salt and Thiophenol zinc salts substituted with halogen groups such as pentaiodothiophenol zinc salt; 4-methylthiophenol zinc salt, 2,4,5-trimethylthiophenol zinc salt, pentamethylthiophenol zinc salt, 4-t-butyl Thiophenol zinc salts substituted with alkyl groups such as thiophenol zinc salt, 2,4,5-tri-t-butylthiophenol zinc salt and penta-t-butylthiophenol zinc salt; 4-carboxythiophenol zinc Salt, 2,4,6-tricarboxythiophenol zinc salt and pentacarboxythiophenol Thiophenol zinc salts substituted with carboxyl groups such as lead salts; alkoxy such as 4-methoxycarbonylthiophenol zinc salts, 2,4,6-trimethoxycarbonylthiophenol zinc salts and pentamethoxycarbonylthiophenol zinc salts Thiophenol zinc salts substituted with a carbonyl group; thiophenol zinc substituted with a formyl group such as 4-formylthiophenol zinc salt, 2,4,6-triformylthiophenol zinc salt and pentaformylthiophenol zinc salt Salts; 4-acetylthiophenol zinc salts, thiophenol zinc salts substituted with acyl groups such as 2,4,6-triacetylthiophenol zinc salts and pentaacetylthiophenol zinc salts; 4-chlorocarbonylthiophenol zinc Salt, 2,4,6- Thiophenol zinc salts substituted with a carbonyl halide group such as tri (chlorocarbonyl) thiophenol zinc salt and penta (chlorocarbonyl) thiophenol zinc salt; 4-sulfothiophenol zinc salt, 2,4,6-tri Thiophenol zinc salts substituted with sulfo groups such as sulfothiophenol zinc salt and pentasulfothiophenol zinc salt; 4-methoxysulfonylthiophenol zinc salt, 2,4,6-trimethoxysulfonylthiophenol zinc salt and penta Thiophenol zinc salts substituted with alkoxysulfonyl groups such as methoxysulfonylthiophenol zinc salt; 4-chlorosulfonylthiophenol zinc salt, 2,4,6-tri (chlorosulfonyl) thiophenol zinc salt and penta (chlorosulfonyl) Thio Thiophenol zinc salts substituted with a sulfonyl halide group such as enol zinc salt; such as 4-sulfinothiophenol zinc salt, 2,4,6-trisulfinothiophenol zinc salt and pentasulfinothiophenol zinc salt Thiophenol zinc salts substituted with sulfino groups; alkylsulfinyls such as 4-methylsulfinylthiophenol zinc salt, 2,4,6-tri (methylsulfinyl) thiophenol zinc salt and penta (methylsulfinyl) thiophenol zinc salt Group substituted thiophenol zinc salts; 4-carbamoylthiophenol zinc salts, thiophenol zinc salts substituted with carbamoyl groups such as 2,4,6-tricarbamoylthiophenol zinc salts and pentacarbamoylthiophenol zinc salts ; -Thiophenol zinc salts substituted with halogenated alkyl groups such as trichloromethylthiophenol zinc salt, 2,4,6-tri (trichloromethyl) thiophenol zinc salt and penta (trichloromethyl) thiophenol zinc salt; Thiophenol zinc salts substituted with a cyano group such as cyanothiophenol zinc salt, 2,4,6-tricyanothiophenol zinc salt and pentacyanothiophenol zinc salt; and 4-methoxythiophenol zinc salt, 2,4 Examples thereof include thiophenol zinc salts substituted with an alkoxy group such as 1,6-trimethoxythiophenol zinc salt and pentamethoxythiophenol zinc salt. These thiophenol zinc salts are substituted with one type of substituent.

As another example of the organic sulfur compound represented by the chemical formula (4), a compound substituted with at least one kind of the above substituent and another substituent can be given. Examples of other substituents include a nitro group (—NO ₂ ), an amino group (—NH ₂ ), a hydroxyl group (—OH), and a phenylthio group (—SPh). Specific examples of this compound include 4-chloro-2-nitrothiophenol zinc salt, 4-chloro-2-aminothiophenol zinc salt, 4-chloro-2-hydroxythiophenol zinc salt, 4-chloro-2- Phenylthiothiophenol zinc salt, 4-methyl-2-nitrothiophenol zinc salt, 4-methyl-2-aminothiophenol zinc salt, 4-methyl-2-hydroxythiophenol zinc salt, 4-methyl-2-phenyl Thiothiophenol zinc salt, 4-carboxy-2-nitrothiophenol zinc salt, 4-carboxy-2-aminothiophenol zinc salt, 4-carboxy-2-hydroxythiophenol zinc salt, 4-carboxy-2-phenylthio Thiophenol zinc salt, 4-methoxycarbonyl-2-nitrothiophenol zinc salt, 4-meth Sicarbonyl-2-aminothiophenol zinc salt, 4-methoxycarbonyl-2-hydroxythiophenol zinc salt, 4-methoxycarbonyl-2-phenylthiothiophenol zinc salt, 4-formyl-2-nitrothiophenol zinc salt, 4-formyl-2-aminothiophenol zinc salt, 4-formyl-2-hydroxythiophenol zinc salt, 4-formyl-2-phenylthiothiophenol zinc salt, 4-acetyl-2-nitrothiophenol zinc salt, 4 -Acetyl-2-aminothiophenol zinc salt, 4-acetyl-2-hydroxythiophenol zinc salt, 4-acetyl-2-phenylthiothiophenol zinc salt, 4-chlorocarbonyl-2-nitrothiophenol zinc salt, 4 -Chlorocarbonyl-2-aminothiophenol zinc salt, -Chlorocarbonyl-2-hydroxythiophenol zinc salt, 4-chlorocarbonyl-2-phenylthiothiophenol zinc salt, 4-sulfo-2-nitrothiophenol zinc salt, 4-sulfo-2-aminothiophenol zinc salt, 4-sulfo-2-hydroxythiophenol zinc salt, 4-sulfo-2-phenylthiothiophenol zinc salt, 4-methoxysulfonyl-2-nitrothiophenol zinc salt, 4-methoxysulfonyl-2-aminothiophenol zinc salt 4-methoxysulfonyl-2-hydroxythiophenol zinc salt, 4-methoxysulfonyl-2-phenylthiothiophenol zinc salt, 4-chlorosulfonyl-2-nitrothiophenol zinc salt, 4-chlorosulfonyl-2-aminothio Phenol zinc salt, 4-chlorosulfonyl- 2-hydroxythiophenol zinc salt, 4-chlorosulfonyl-2-phenylthiothiophenol zinc salt, 4-sulfino-2-nitrothiophenol zinc salt, 4-sulfino-2-aminothiophenol zinc salt, 4-sulfino- 2-hydroxythiophenol zinc salt, 4-sulfino-2-phenylthiothiophenol zinc salt, 4-methylsulfinyl-2-nitrothiophenol zinc salt, 4-methylsulfinyl-2-aminothiophenol zinc salt, 4-methyl Sulfinyl-2-hydroxythiophenol zinc salt, 4-methylsulfinyl-2-phenylthiothiophenol zinc salt, 4-carbamoyl-2-nitrothiophenol zinc salt, 4-carbamoyl-2-aminothiophenol zinc salt, 4- Carbamoyl-2-hydroxythi Phenol zinc salt, 4-carbamoyl-2-phenylthiothiophenol zinc salt, 4-trichloromethyl-2-nitrothiophenol zinc salt, 4-trichloromethyl-2-aminothiophenol zinc salt, 4-trichloromethyl-2- Hydroxythiophenol zinc salt, 4-trichloromethyl-2-phenylthiothiophenol zinc salt, 4-cyano-2-nitrothiophenol zinc salt, 4-cyano-2-aminothiophenol zinc salt, 4-cyano-2- Hydroxythiophenol zinc salt, 4-cyano-2-phenylthiothiophenol zinc salt, 4-methoxy-2-nitrothiophenol zinc salt, 4-methoxy-2-aminothiophenol zinc salt, 4-methoxy-2-hydroxy Thiophenol zinc salt and 4-methoxy-2-phenylthiothio Phenol zinc salts.

  Still another example of the organic sulfur compound represented by the chemical formula (4) includes a compound substituted with two or more kinds of substituents. Specific examples of this compound include 4-acetyl-2-chlorothiophenol zinc salt, 4-acetyl-2-methylthiophenol zinc salt, 4-acetyl-2-carboxythiophenol zinc salt, 4-acetyl-2-methoxycarbonyl Thiophenol zinc salt, 4-acetyl-2-formylthiophenol zinc salt, 4-acetyl-2-chlorocarbonylthiophenol zinc salt, 4-acetyl-2-sulfothiophenol zinc salt, 4-acetyl-2-methoxysulfonyl Thiophenol zinc salt, 4-acetyl-2-chlorosulfonylthiophenol zinc salt, 4-acetyl-2-sulfinothiophenol zinc salt, 4-acetyl-2-methylsulfinylthiophenol zinc salt, 4-acetyl-2- Carbamoylthiophenol zinc salt, 4-acetyl-2 Trichloromethylthiophenol zinc salt, 4-acetyl-2-cyano thiophenol zinc salt and 4-acetyl-2-methoxy thiophenol zinc salt. Examples of the divalent metal represented by M2 in the chemical formula (4) include zinc, magnesium, calcium, strontium, barium, titanium (II), manganese (II), iron (II), cobalt (II), nickel ( Illustrative are II), zirconium (II) and tin (II).

  As naphthalenethiols, 2-naphthalenethiol, 1-naphthalenethiol, 2-chloro-1-naphthalenethiol, 2-bromo-1-naphthalenethiol, 2-fluoro-1-naphthalenethiol, 2-cyano-1-naphthalenethiol 2-acetyl-1-naphthalenethiol, 1-chloro-2-naphthalenethiol, 1-bromo-2-naphthalenethiol, 1-fluoro-2-naphthalenethiol, 1-cyano-2-naphthalenethiol and 1-acetyl- Examples include 2-naphthalenethiol and metal salts thereof. 1-naphthalenethiol and 2-naphthalenethiol and zinc salts thereof are preferred.

  Examples of the sulfenamide-based organic sulfur compound include N-cyclohexyl-2-benzothiazole sulfenamide, N-oxydiethylene-2-benzothiazole sulfenamide, and Nt-butyl-2-benzothiazole sulfenamide. Illustrated. Examples of the thiuram-based organic sulfur compound include tetramethylthiuram monosulfide, tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide, and dipentamethylenethiuram tetrasulfide. Dithiocarbamates include zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate, zinc dibutyldithiocarbamate, zinc ethylphenyldithiocarbamate, sodium dimethyldithiocarbamate, sodium diethyldithiocarbamate, copper (II) dimethyldithiocarbamate, iron dimethyldithiocarbamate (III ), Selenium diethyldithiocarbamate and tellurium diethyldithiocarbamate. Examples of thiazole-based organic sulfur compounds include 2-mercaptobenzothiazole (MBT); dibenzothiazyl disulfide (MBTS); sodium salt, zinc salt, copper salt or cyclohexylamine salt of 2-mercaptobenzothiazole; 2- (2,4- Illustrative are dinitrophenyl) mercaptobenzothiazole; and 2- (2,6-diethyl-4-morpholinothio) benzothiazole.

  In light of resilience performance, the content of the organic sulfur compound (e) is preferably equal to or greater than 0.05 parts by weight and particularly preferably equal to or greater than 0.1 parts by weight with respect to 100 parts by weight of the base rubber. In light of resilience performance, this amount is preferably equal to or less than 5.0 parts by weight, and particularly preferably equal to or less than 2.0 parts by weight.

  A filler may be blended in the core 4 for the purpose of adjusting specific gravity and the like. Suitable 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. A particularly preferred filler is zinc oxide. Zinc oxide functions not only as a specific gravity adjusting role but also as a crosslinking aid.

  An anti-aging agent, a colorant, a plasticizer, a dispersant, sulfur, a vulcanization accelerator, and the like are added to the rubber composition of the core 4 as necessary. Crosslinked rubber powder or synthetic resin powder may be dispersed in the rubber composition.

  In the core 4, the difference (Hs−H (0)) between the surface hardness Hs and the center hardness H (0) is preferably 15 or more. This difference is great. In other words, the core 4 has an outer-hard / inner-soft structure. When the core 4 is hit with a middle iron, the recoil (twisting back) is large, so that spin is suppressed. The core 4 contributes to the flight performance of the golf ball 2. From the viewpoint of flight performance, the difference (Hs−H (0)) is more preferably 20 or more, and particularly preferably 25 or more. From the viewpoint that the core 4 can be easily molded, the difference (Hs−H (0)) is preferably 50 or less.

  The hardness H (0) of the center point of the core 4 is preferably 40.0 or more and 70.0 or less. The golf ball 2 having a hardness H (0) of 40.0 or more is excellent in resilience performance. In this respect, the hardness H (0) is more preferably 45.0 or greater and particularly preferably 50.0 or greater. In the core 4 having a hardness H (0) of 70.0 or less, an outer-hard / inner-soft structure can be achieved. In the golf ball 2 having the core 4, spin can be suppressed. In this respect, the hardness H (0) is more preferably equal to or less than 68.0, and particularly preferably equal to or less than 66.0.

  The hardness Hs of the surface of the core 4 is preferably 76.0 or more and 95.0 or less. In the core 4 having the hardness Hs of 76.0 or more, an outer-hard / inner-soft structure can be achieved. In the golf ball 2 having the core 4, spin can be suppressed. In this respect, the hardness Hs is more preferably equal to or greater than 78.0, and particularly preferably equal to or greater than 80.0. The golf ball 2 having a hardness Hs of 95.0 or less is excellent in durability. In this respect, the hardness Hs is more preferably equal to or less than 93.0, and particularly preferably equal to or less than 90.0.

  The diameter of the core 4 is preferably 36.0 mm or greater and 41.0 mm or less. The excellent resilience performance of the golf ball 2 can be achieved by the core 4 having a diameter of 36.0 mm or more. In this respect, the diameter is more preferably 36.5 mm or greater, and particularly preferably 37.0 mm or greater. In the golf ball 2 having the core 4 having a diameter of 41.0 mm or less, the inner cover 8, the mid cover 10, and the outer cover 12 can have a sufficient thickness. The golf ball 2 having a large thickness of the inner cover 8, the mid cover 10, and the outer cover 12 is excellent in durability. In this respect, the diameter is more preferably 40.0 mm or less, and particularly preferably 39.0 mm or less. The core may comprise two or more layers. The core may be hollow. The core may include a rib on its surface.

  In light of feel at impact, the amount of compressive deformation (comp′n) of the core 4 is preferably equal to or greater than 3.0 mm, and particularly preferably equal to or greater than 3.3 mm. In light of resilience performance, the amount of compressive deformation is preferably 4.6 mm or less, and particularly preferably 4.3 mm or less.

  A resin composition is suitably used for the inner cover 8. Examples of the base polymer of the resin composition include ionomer resins, styrene block-containing thermoplastic elastomers, thermoplastic polyester elastomers, thermoplastic polyamide elastomers, and thermoplastic polyolefin elastomers.

  A particularly preferred base polymer is an ionomer resin. The golf ball 2 having the inner cover 8 containing an ionomer resin is excellent in resilience performance. The inner cover 8 may be used in combination with an ionomer resin and another resin. When used in combination, the main component of the base polymer is preferably an ionomer resin. Specifically, the ratio of the ionomer resin to the total amount of the base polymer is preferably 50% by mass or more, more preferably 60% by mass or more, and particularly preferably 70% by mass or more.

  A preferable ionomer resin includes a binary copolymer of an α-olefin and an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms. A preferable binary copolymer contains 80% by mass or more and 90% by mass or less α-olefin and 10% by mass or more and 20% by mass or less α, β-unsaturated carboxylic acid. This binary copolymer is excellent in resilience performance. Other preferable ionomer resins include ternary α-olefin, α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and α, β-unsaturated carboxylic acid ester having 2 to 22 carbon atoms. A copolymer is mentioned. Preferred terpolymers are 70% to 85% by weight α-olefin, 5% to 30% by weight α, β-unsaturated carboxylic acid, and 1% to 25% by weight. α, β-unsaturated carboxylic acid ester. This ternary copolymer is excellent in resilience performance. In the binary copolymer and ternary copolymer, preferred α-olefins are ethylene and propylene, and preferred α, β-unsaturated carboxylic acids are acrylic acid and methacrylic acid. A particularly preferred ionomer resin is a copolymer of ethylene and acrylic acid or methacrylic acid.

  In the binary copolymer and ternary copolymer, some of the carboxyl groups are neutralized with metal ions. Examples of the metal ions for neutralization include sodium ions, potassium ions, lithium ions, zinc ions, calcium ions, magnesium ions, aluminum ions, and neodymium ions. Neutralization may be performed with two or more metal ions. Particularly suitable metal ions from the viewpoint of resilience performance and durability of the golf ball 2 are sodium ion, zinc ion, lithium ion and magnesium ion.

  Specific examples of the ionomer resin include Mitsui Dupont Polychemical's trade names “HIMILAN 1555”, “HIMILAN 1557”, “HIMILAN 1605”, “HIMILAN 1706”, “HIMILAN 1707”, “HIMILAN 1856” and “HIMILAN 1855”. "High Milan AM7311", "High Milan AM7315", "High Milan AM7317", "High Milan AM7318", "High Milan AM7329", "High Milan AM7337", "High Milan MK7320" and "High Milan MK7329"; DuPont's trade name "Surlin 6120" , "Surlin 6910", "Surlin 7930", "Surlin 7940", "Surlin 8140", "Surlin 8150", "Surlin 8940", "Surlin 8945", "Surlin 120 ”,“ Surlin 9150 ”,“ Surlin 9910 ”,“ Surlin 9945 ”,“ Surlin AD8546 ”,“ HPF1000 ”and“ HPF2000 ”; , “IOTEK7520”, “IOTEK8000”, and “IOTEK8030”.

  Two or more ionomer resins may be used in combination with the inner cover 8. An ionomer resin neutralized with a monovalent metal ion and an ionomer resin neutralized with a divalent metal ion may be used in combination.

  A preferred resin that can be used in combination with an ionomer resin is a styrene block-containing thermoplastic elastomer. The styrene block-containing thermoplastic elastomer is excellent in compatibility with the ionomer resin. A resin composition containing a styrene block-containing thermoplastic elastomer is excellent in fluidity.

  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.

  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), SBS hydrogenated, SIS hydrogenated and SIBS hydrogenated are included. Examples of the hydrogenated product of SBS include styrene-ethylene-butylene-styrene block copolymer (SEBS). As a hydrogenated product of SIS, styrene-ethylene-propylene-styrene block copolymer (SEPS) can be mentioned. Examples of the hydrogenated product of SIBS include styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS).

  In light of the resilience performance of the golf ball 2, the content of the styrene component in the styrene block-containing thermoplastic elastomer is preferably 10% by mass or more, more preferably 12% by mass or more, and particularly preferably 15% by mass or more. In light of the feel at impact of the golf ball 2, the content is preferably equal to or less than 50% by mass, more preferably equal to or less than 47% by mass, and particularly preferably equal to or less than 45% by mass.

  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 the alloy is presumed to contribute to the improvement of compatibility with the ionomer resin. By using this alloy, the resilience performance of the golf ball 2 is improved. Preferably, an olefin having 2 to 10 carbon atoms is used. Suitable olefins include ethylene, propylene, butene and pentene. Ethylene and propylene are particularly preferred.

  Specific examples of polymer alloys include Mitsubishi Chemical's trade names “Lavalon T3221C”, “Lavalon T3339C”, “Lavalon SJ4400N”, “Lavalon SJ5400N”, “Lavalon SJ6400N”, “Lavalon SJ7400N”, “Lavalon SJ8400N”, “ And “Lavalon SJ9400N” and “Lavalon SR04”. Other specific examples of the styrene block-containing thermoplastic elastomer include Daicel Chemical Industries' trade name “Epofriend A1010” and Kuraray's trade name “Septon HG-252”.

  If necessary, the resin composition of the inner cover 8 may include a colorant such as titanium dioxide and a fluorescent pigment, a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, and a fluorescent agent. In addition, an appropriate amount of fluorescent brightening agent or the like is blended. The inner cover 8 may include a powder made of a high specific gravity metal.

  According to the knowledge obtained by the present inventor, the inner cover 8 greatly affects the deformation behavior of the golf ball 2 when hit with a middle iron. The golf ball 2 having a high hardness Hi of the inner cover 8 is excellent in flight performance when hit with a middle iron. The inner cover 8 whose hardness Hi is not excessive can contribute to the feel at impact of the golf ball 2.

  From the viewpoint of flight performance, the hardness Hi of the inner cover 8 is preferably 75 or more, more preferably 80 or more, and particularly preferably 83 or more. In light of the feel at impact of the golf ball 2, the hardness Hi is preferably equal to or less than 95, and particularly preferably equal to or less than 90. The hardness Hi is measured by a JIS-C hardness meter attached to an automatic rubber hardness measuring device (trade name “P1” of Kobunshi Keiki Co., Ltd.). For the measurement, a slab having a thickness of about 2 mm formed by hot pressing is used. A slab stored for 2 weeks at a temperature of 23 ° C. is used for the measurement. At the time of measurement, three slabs are overlaid. A slab made of the same resin composition as the resin composition of the inner cover 8 is used.

  The hardness Hi of the inner cover 8 is larger than the surface hardness Hs of the core 4 from the viewpoint that an outer-hard / inner-soft structure is achieved in the sphere composed of the core 4 and the inner cover 8 and the spin of the golf ball 2 is suppressed. It is preferable. From the viewpoint of spin suppression, the difference between the hardness Hi and the hardness Hs (Hi−Hs) is preferably 1 or more, and particularly preferably 2 or more. The difference (Hi-Hs) is preferably 10 or less. In a sphere having a difference (Hi-Hs) of 10 or less, the hardness increases linearly from the center point toward the surface. In a sphere whose hardness increases linearly, there is little energy loss when hit with a middle iron.

  The thickness of the inner cover 8 is preferably 0.2 mm or greater and 1.2 mm or less. The inner cover 8 having a thickness of 0.2 mm or more can be easily molded. In this respect, the thickness is more preferably equal to or greater than 0.4 mm, and particularly preferably equal to or greater than 0.6 mm. The golf ball 2 including the inner cover 8 having a thickness of 1.2 mm or less has excellent resilience performance. In this respect, the thickness is more preferably equal to or less than 1.0 mm, and particularly preferably equal to or less than 0.9 mm.

  For the formation of the inner cover 8, a known method such as an injection molding method or a compression molding method may be employed.

  A resin composition is suitably used for the mid cover 10. A preferred base polymer of this resin composition is an ionomer resin. The golf ball 2 having the mid cover 10 containing an ionomer resin is excellent in resilience performance. The ionomer resin described above with respect to the inner cover 8 can be used for the mid cover 10.

  An ionomer resin and another resin may be used in combination. When used in combination, the ionomer resin is the main component of the base polymer from the viewpoint of resilience performance. The ratio of the amount of the ionomer resin to the total amount of the base polymer is preferably 50% by mass or more, more preferably 60% by mass or more, and particularly preferably 70% by mass or more.

  Another 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 described above with respect to the inner cover 8 can be used for the mid cover 10.

  The mid cover 10 is provided with a colorant such as titanium dioxide and fluorescent pigment, a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent agent, and a fluorescent whitening as necessary. An appropriate amount of agent or the like is blended.

  The JIS-C hardness Hm of the mid cover 10 is preferably 75 or greater and 96 or less. The golf ball 2 having the mid cover 10 having a hardness Hm of 75 or more has excellent flight performance in a shot with a middle iron. In this respect, the hardness Hm is more preferably equal to or greater than 80, and particularly preferably equal to or greater than 85. The golf ball 2 having the mid cover 10 having a hardness Hm of 96 or less is excellent in feel at impact. In this respect, the hardness Hm is more preferably equal to or less than 90, and particularly preferably equal to or less than 88. The hardness Hm is measured by the same method as the method for measuring the hardness Hi.

  The hardness Hm of the mid cover 10 may be larger or smaller than the hardness Hi of the inner cover 8.

  In the golf ball 2 having the hardness Hm larger than the hardness Hi, an outer-hard / inner-soft structure of a sphere composed of the core 4, the inner cover 8, and the mid cover 10 can be achieved. The spin speed when the golf ball 2 is hit with a middle iron is small. This golf ball 2 is excellent in flight performance in a shot with a middle iron. From the viewpoint of flight performance, the difference (Hm−Hi) between the hardness Hm and the hardness Hi is preferably 2 or more. The difference (Hm-Hi) is preferably 20 or less.

  In the golf ball 2 having a hardness Hm smaller than the hardness Hi, the mid cover 10 absorbs an impact when hit. This golf ball 2 is excellent in feel at impact. From the viewpoint of feel at impact, the difference between the hardness Hi and the hardness Hm (Hi−Hm) is preferably 2 or more. The difference (Hi-Hm) is preferably 20 or less.

  The thickness of the mid cover 10 is preferably 0.2 mm or greater and 1.2 mm or less. The mid cover 10 having a thickness of 0.2 mm or more can be easily molded. In this respect, the thickness is more preferably equal to or greater than 0.4 mm, and particularly preferably equal to or greater than 0.6 mm. The golf ball 2 including the mid cover 10 having a thickness of 1.2 mm or less has excellent resilience performance. In this respect, the thickness is more preferably equal to or less than 1.0 mm, and particularly preferably equal to or less than 0.9 mm.

  For the formation of the mid cover 10, a known method such as an injection molding method or a compression molding method may be employed.

  A resin composition is preferably used for the outer cover 12. A preferred base polymer of this resin composition is an ionomer resin. The golf ball 2 having the outer cover 12 containing an ionomer resin is excellent in resilience performance. The ionomer resin described above with respect to the inner cover 8 can be used for the outer cover 12.

  An ionomer resin and another resin may be used in combination. When used in combination, the ionomer resin is the main component of the base polymer from the viewpoint of resilience performance. The ratio of the amount of the ionomer resin to the total amount of the base polymer is preferably 50% by mass or more, more preferably 60% by mass or more, and particularly preferably 70% by mass or more.

  A preferred resin that can be used in combination with an ionomer resin is an ethylene- (meth) acrylic acid copolymer. This copolymer is obtained by a copolymerization reaction of a monomer composition containing ethylene and (meth) acrylic acid. In this copolymer, some of the carboxyl groups are neutralized with metal ions. This copolymer contains 3% by weight or more and 25% by weight or less (meth) acrylic acid component. An ethylene- (meth) acrylic acid copolymer having a polar functional group is particularly preferred. Specific examples of the ethylene- (meth) acrylic acid copolymer include “Nucrel”, a trade name of Mitsui DuPont Polychemical Co., Ltd.

  Another 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 described above with respect to the inner cover 8 can be used for the outer cover 12.

  The outer cover 12 may be provided with a colorant such as titanium dioxide and fluorescent pigment, a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent agent, and a fluorescent whitening as necessary. An appropriate amount of agent or the like is blended.

  The JIS-C hardness Ho of the outer cover 12 is preferably 83 or more and 98 or less. The golf ball 2 having the outer cover 12 having a hardness Ho of 83 or more is excellent in resilience performance. This golf ball 2 is excellent in flight performance. In this respect, the hardness Ho is more preferably 86 or greater, and particularly preferably 89 or greater. The golf ball 2 having the outer cover 12 having a hardness Ho of 98 or less is excellent in feel at impact. In this respect, the hardness Ho is more preferably 96 or less, and particularly preferably 94 or less. The hardness Ho is measured by the same method as the method for measuring the hardness Hi.

  It is preferable that the hardness Ho of the outer cover 12 is larger than the hardness Hi of the inner cover 8. In the golf ball 2 having the hardness Ho larger than the hardness Hi, spin can be suppressed. This golf ball 2 is excellent in flight performance in a shot with a middle iron.

  From the viewpoint of flight performance, the difference between the hardness Ho and the hardness Hi (Ho−Hi) is preferably 5 or more, more preferably 6 or more, and particularly preferably 7 or more. The difference (Ho−Hi) is preferably 30 or less.

  It is preferable that the hardness Ho of the outer cover 12 is larger than the hardness Hm of the mid cover 10. In the golf ball 2 having the hardness Ho larger than the hardness Hm, an outer-hard / inner-soft structure can be achieved. The spin speed when the golf ball 2 is hit with a middle iron is small. This golf ball 2 is excellent in flight performance in a shot with a middle iron. From the viewpoint of flight performance, the difference between the hardness Ho and the hardness Hm (Ho−Hm) is preferably 2 or more. The difference (Ho−Hm) is preferably 20 or less.

  The thickness of the outer cover 12 is preferably 0.2 mm or greater and 1.2 mm or less. The outer cover 12 having a thickness of 0.2 mm or more can be easily molded. In this respect, the thickness is more preferably equal to or greater than 0.4 mm, and particularly preferably equal to or greater than 0.6 mm. The golf ball 2 including the outer cover 12 having a thickness of 1.2 mm or less has excellent resilience performance. In this respect, the thickness is more preferably equal to or less than 1.0 mm, and particularly preferably equal to or less than 0.9 mm.

  For forming the outer cover 12, a known method such as an injection molding method or a compression molding method may be employed. When the outer cover 12 is molded, the dimples 14 are formed by pimples formed on the cavity surface of the mold.

  The total thickness of the cover 6 is preferably 2.5 mm or less. The golf ball 2 having a total thickness of 2.5 mm or less is excellent in feel at impact. In this respect, the total thickness is particularly preferably equal to or less than 2.4 mm. In light of durability of the golf ball 2, the total thickness is preferably equal to or greater than 0.3 mm, more preferably equal to or greater than 0.5 mm, and particularly preferably equal to or greater than 0.8 mm.

  In light of feel at impact, the golf ball 2 has a compression deformation amount (comp′n) of preferably 2.8 mm or greater, more preferably 2.9 mm or greater, and particularly preferably 3.0 mm or greater. In light of resilience performance, the amount of compressive deformation Db is preferably equal to or less than 3.6 mm, more preferably equal to or less than 3.5 mm, and particularly preferably equal to or less than 3.4 mm.

  A YAMADA compression tester is used to measure the amount of compression deformation (comp'n). In this tester, spheres such as the core 4 and the golf ball 2 are placed on a metal rigid plate. A metal cylinder gradually descends toward the sphere. The sphere sandwiched between the bottom surface of the cylinder and the rigid plate is deformed. The moving distance of the cylinder from the state where the initial load of 98 N is applied to the sphere to the state where the final load of 1274 N is applied is measured.

  Hereinafter, the effects of the present invention will be clarified by examples. However, the present invention should not be construed in a limited manner based on the description of the examples.

[Example 1]
100 parts by mass of high-cis polybutadiene (trade name “BR-730” from JSR), 27 parts by weight of zinc acrylate (trade name “Sunseller SR” from Sanshin Chemical Industry Co., Ltd.), 5 parts by weight of zinc oxide, appropriate amount Barium sulfate, 0.2 parts by mass of 2-naphthalenethiol, 10 parts by mass of zinc stearate and 0.75 parts by mass of dicumyl peroxide were kneaded to obtain a rubber composition. This rubber composition was put into a mold composed of an upper mold and a lower mold each having a hemispherical cavity and heated at 170 ° C. for 25 minutes to obtain a core having a diameter of 37.9 mm. The amount of barium sulfate was adjusted so that the mass of the golf ball was 45.4 g.

  24 parts by weight of ionomer resin (previously referred to as “Himiran AM7337”), 50 parts by weight of other ionomer resins (previously referred to as “Himiran AM7329”), and 26 parts by weight of a styrene block-containing thermoplastic elastomer (previously described “Lavalon T3221C”) And 6 mass parts titanium dioxide was knead | mixed with the biaxial kneading extruder, and the resin composition was obtained. The core was put into the mold. The resin composition was injected around the core by an injection molding method to mold an inner cover. The inner cover had a thickness of 0.8 mm.

  40 parts by weight of ionomer resin (previously referred to as “Himiran AM7337”), 40 parts by weight of other ionomer resins (previously referred to as “Himiran AM7329”), and 20 parts by weight of a styrene block-containing thermoplastic elastomer (previously referred to as “Lavalon T3221C”) And 6 mass parts titanium dioxide was knead | mixed with the biaxial kneading extruder, and the resin composition was obtained. A sphere consisting of a core and an inner cover was put into the mold. The resin composition was injected around the sphere by an injection molding method to form a mid cover. The thickness of this mid cover was 0.8 mm.

  5 parts by weight of ionomer resin (previously referred to as “Himiran AM7337”), 10 parts by weight of other ionomer resins (previously referred to as “Himiran 1555”), 55 parts by weight of further ionomer resins (previously referred to as “Himiran AM7329”), 30 parts by mass of ethylene- (meth) acrylic acid copolymer (trade name “Nucleel N1050H” of Mitsui DuPont Polychemical Co., Ltd., 3 parts by mass of titanium dioxide, and 0.2 parts by mass of UV absorber (Ciba Japan) The product name “Tinubin 770”) was kneaded with a twin-screw kneading extruder to obtain a resin composition, and a sphere composed of a core, an inner cover, and a mid cover was placed on a final mold having many pimples on the cavity surface. The resin composition was injected around the sphere by injection molding to form an outer cover. The thickness of the outer cover was 0.8 mm, and the outer cover was formed with dimples having a shape reversed from the shape of pimples, and a clear paint based on a two-component curable polyurethane around the outer cover. The golf ball of Example 1 having a diameter of 42.7 mm was obtained.

[Example 2-14 and Comparative Example 1-9]
The golf balls of Example 2-14 and Comparative Example 1-9 were manufactured in the same manner as in Example 1 except that the specifications of the core, inner cover, mid cover and outer cover were as shown in Table 10-14 below. Obtained. Details of the composition of the core are shown in Table 1-2 below. Details of the composition of the inner cover, mid cover and outer cover are shown in Table 3-4 below. The hardness distribution of the core is shown in Tables 5-9 below. The golf ball according to Comparative Example 7 does not have a mid cover.

[Blow by Middle Iron (I # 5)]
A No. 5 iron (Dunlop Sports brand name “XXIO”, shaft hardness: R, loft angle: 24 °) was attached to a swing machine manufactured by Golf Laboratory. A golf ball was hit under the condition that the head speed was 34 m / sec. The spin speed immediately after hitting was measured. In addition, the distance from the launch point to the stationary point was measured. Average values of data obtained by 12 measurements are shown in Table 7-11 below.

Details of the compounds described in Tables 1 and 2 are as follows.
BR730: High cis polybutadiene (cis-1,4-bond content: 96 mass%, 1,2-vinyl bond content: 1.3 mass%, Mooney viscosity (ML _{1 + 4} (100 ° C.)) from JSR Corporation
): 55, molecular weight distribution (Mw / Mn): 3)
Sunseller SR: Sanshin Chemical Co., Ltd. zinc acrylate (10 wt% stearic acid coating product)
Zinc oxide: Toho Zinc Co., Ltd. trade name “Ginbao R”
Barium sulfate: The trade name “Barium sulfate BD” by Sakai Chemical
2-Naphthalenethiol: Tokyo Kasei Kogyo Co., Ltd. Zinc Octanoate: Mitsuwa Chemicals Co., Ltd. Zinc Laurate: Mitsuwa Chemicals Co., Ltd. Zinc Myristate: NOF Corporation Zinc stearate: Wako Pure Chemical Industries, Ltd. Company name "Park Mill D"

  As shown in Tables 10-14, the golf ball according to the example is excellent in the flight performance in the middle iron. From this evaluation result, the superiority of the present invention is clear.

  The golf ball according to the present invention can be used for golf play and practice in a driving range.

2 ... Golf ball 4 ... Core 6 ... Cover 8 ... Inner cover 10 ... Mid cover 12 ... Outer cover 14 ... Dimple 16 ... Land

Claims (17)

A core, an inner cover located outside the core, a mid cover located outside the inner cover, and an outer cover located outside the mid cover;
The core is
(A) base rubber,
(B) (b1) an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and / or (b2) an α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms. A co-crosslinking agent comprising a metal salt,
(C) a crosslinking initiator,
And
(D) Carboxylic acid and / or salt thereof (excluding α, β-unsaturated carboxylic acid having 3 to 8 carbon atoms and metal salt thereof)
Is obtained by crosslinking a rubber composition containing
The distance from the center point (9 points) obtained by dividing the core from the center point to the surface by the carboxylic acid and / or salt (d) at an interval of 12.5% of the radius of the core ( %) And JIS-C hardness are plotted on the graph, the R ² value of the linear approximation curve obtained by the least square method is 0.95 or more ,
The difference (Hs-H (0)) between the JIS-C hardness Hs of the surface of the core and the JIS-C hardness H (0) of the center point of the core is 15 or more,
JIS-C hardness Hi of the inner cover is larger than the hardness Hs,
A golf ball having a JIS-C hardness Ho of the outer cover larger than the hardness Hi.   The golf ball according to claim 1, wherein a difference (Hi−Hs) between the hardness Hi and the hardness Hs is 1 or more.   The golf ball according to claim 1, wherein a difference (Ho−Hi) between the hardness Ho and the hardness Hi is 5 or more and 30 or less. The thickness Ti of the inner cover is at 1.2mm or less, the thickness Tm of the mid cover is at 1.2mm or less, to any one of claims 1 to 3 in the thickness To of the outer cover is 1.2mm or less The golf ball described. The thickness of the inner cover Ti, golf ball according to any one of claims 1 to 4, the sum of the thickness Tm and the thickness To of the outer cover of said mid cover (Ti + Tm + To) is 2.5mm or less. The hardness Ho is greater than the JIS-C hardness Hm of the mid cover, golf ball according to any one of claims 1 to 5 the difference between the hardness Ho and the hardness Hm (Ho-Hm) is 2 or more . The amount of the carboxylic acid and / or salts thereof (d) are, according to claim 1 or less 40 parts by mass or more 0.5 part by weight 6 with respect to 100 parts by weight of the base rubber (a) Golf ball. The golf ball according to claim 1 , wherein the carboxylic acid and / or a salt thereof ( d ) is a fatty acid and / or a salt thereof. The golf ball according to claim 1 , wherein the carboxylic acid component of the carboxylic acid and / or salt thereof ( d ) has 1 to 30 carbon atoms. The golf ball according to claim 1 , wherein the carboxylic acid and / or a salt thereof ( d ) is a zinc salt of a carboxylic acid. The golf ball according to claim 10 , wherein the zinc salt of carboxylic acid is one or more selected from the group consisting of zinc octoate, zinc laurate, zinc myristate, and zinc stearate. The golf ball according to claim 1 , wherein the rubber composition contains 15 to 50 parts by mass of the co-crosslinking agent (b) with respect to 100 parts by mass of the base rubber (a). . The rubber composition according to any one of claims 1 to 12 , wherein the rubber composition contains 0.2 to 5.0 parts by mass of the crosslinking initiator (c) with respect to 100 parts by mass of the base rubber (a). The golf ball described. The rubber composition is
The golf ball according to claim 1 , further comprising (e) an organic sulfur compound. The golf ball according to claim 14 , wherein the organic sulfur compound (e) is a thiophenol, diphenyl disulfide, thionaphthol, thiuram disulfide, or a metal salt thereof. The golf ball according to claim 14 or 15 , wherein the rubber composition contains 0.05 to 5 parts by mass of the organic sulfur compound (e) with respect to 100 parts by mass of the base rubber (a). The rubber composition contains the α, β-unsaturated carboxylic acid (b1),
Furthermore, this rubber composition
(F) The golf ball according to any one of claims 1 to 16 , comprising a metal compound.

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