JP2013240546A - Golf ball - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a golf ball which is excellent in high flight performance and controllability and has durability.SOLUTION: A golf ball includes a spherical core 4, an inner mid layer 6 positioned on the outer side of the core 4, an outer mid layer 8 positioned on the outer side of the inner mid layer 6, a reinforcing layer 10 positioned on the outer side of the outer mid layer 8, and a cover 12 positioned on the outer side of the reinforcing layer 10. When distances (%) from a central point of the core 4 and JIS-C hardnesses of nine points, which are obtained by dividing a region from the central point to a surface at intervals of 12.5% of a radius of the core 4, are plotted in a graph, an Rvalue of a linear approximation curve obtained by a least-square method is equal to or greater than 0.95. A Shore D hardness Hm1 of the inner mid layer 6 is greater than a Shore D hardness Hm2 of the outer mid layer 8. A Shore D hardness Hc of the cover is less than the hardness Hm1. A thickness T2 of the outer mid layer 8 is equal to or greater than 0.5 mm and is equal to or less than 1.6 mm.

Description

  The present invention relates to a golf ball. Specifically, the present invention relates to a golf ball having a solid core, an inner intermediate layer, an outer intermediate layer, and a cover.

  A golfer's greatest demand for a golf ball is high flight performance. Golfers place particular importance on high flight distance performance in shots with a driver. The high flight distance 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 center JIS-C hardness H1 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 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 the 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.

  Golfers also attach great importance to golf ball control performance. The control performance depends on the spin speed. If the backspin rate is high, the run is small. For golfers, a golf ball that is subject to backspin is likely to be stationary at a target point. When the side spin rate is high, the golf ball tends to bend. For golfers, golf balls that are susceptible to side spin tend to bend intentionally. A golf ball that is easily spun has excellent control performance. Advanced golfers place particular importance on control performance in shots with short irons.

  Golfers are also interested in the durability of golf balls. When a golf ball is hit with a driver or the like, it undergoes a large impact and deforms. When a local load is applied to a part of the ball due to deformation, the golf ball is destroyed. Golf balls that are resistant to deformation due to impact can be used continuously for a long time.

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

  As described above, when a golf ball having a large launch angle and a low spin speed is hit with a driver, a large flight distance can be obtained. However, a golf ball with a low spin rate is inferior in control performance. Golfers want to achieve both flight distance and control performance. Furthermore, there is a need for a golf ball that can be used continuously and has excellent durability to impact.

  An object of the present invention is to provide a golf ball having excellent durability with high flight distance performance on a driver shot and control performance on a short iron shot.

A golf ball according to the present invention includes a spherical core, an inner intermediate layer positioned outside the core, an outer intermediate layer positioned outside the inner intermediate layer, and a cover positioned outside the outer intermediate layer. Is provided. The distance (%) from the center point and JIS-C hardness of 9 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 are plotted in a graph. R ² of the linear approximation curve obtained by the least square method is 0.95 or more. The shore D hardness Hm1 of the inner intermediate layer is greater than the shore D hardness Hm2 of the outer intermediate layer. The cover has a Shore D hardness Hc smaller than the hardness Hm1. The thickness T2 of the outer intermediate layer is not less than 0.5 mm and not more than 1.6 mm.

  Preferably, the JIS-C hardness H (0.0) of the center point of the core is 40 or more and 70 or less. The core has a surface hardness Hs of 78 or more and 96 or less.

  Preferably, the difference (Hs-H (0.0)) between the surface hardness Hs of the core and the JIS-C hardness H (0.0) of the center point of the core is 15 or more.

  Preferably, the difference (Hm1-Hm2) between the hardness Hm1 and the hardness Hm2 is 8 or more.

  Preferably, the difference (Hm1−Hc) between the hardness Hm1 and the hardness Hc is 30 or more.

  Preferably, the sum (T1 + T2) of the thickness T1 of the inner intermediate layer and the thickness T2 of the outer intermediate layer is 1.0 mm or more and 3.0 mm or less. The cover thickness Tc is 0.8 mm or less.

Preferably, the core is obtained by crosslinking the rubber composition. This rubber composition
(A) base rubber,
(B) a co-crosslinking agent,
(C) includes a crosslinking initiator and (d) an acid and / or salt. This 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 acid and / or salt (d) is
(D1) Carboxylic acid and / or a salt thereof.

  Preferably, the carboxylic acid component of the carboxylic acid and / or its salt (d1) has 1 to 30 carbon atoms. Preferably, the carboxylic acid and / or its salt (d1) is a fatty acid and / or its salt.

  Preferred carboxylic acids and / or salts (d1) thereof are zinc salts of carboxylic acids. Preferably, one or more carboxylic acids and / or their salts (d1) are selected from the group consisting of zinc octoate, zinc laurate, zinc myristate and zinc stearate.

  Preferably, the rubber composition contains 100 parts by mass of the base rubber (a) and 1.0 part by mass or more and 40 parts by mass or less of the acid and / or salt (d).

When the rubber composition contains an α, β-unsaturated carboxylic acid (b1), preferably the rubber composition
(E) It further contains a metal compound.

  Preferably, the rubber composition contains 100 parts by mass of the base rubber (a) and 15 to 50 parts by mass of the co-crosslinking agent (b).

  Preferably, the rubber composition contains 100 parts by mass of the base rubber (a) and 0.2 parts by mass or more and 5 parts by mass or less of the crosslinking initiator (c).

  Preferably, the rubber composition contains a metal salt (b2) of an α, β-unsaturated carboxylic acid.

  The outer intermediate layer may be made of a resin composition, and the cover may be made of another resin composition. The main component of the base resin of the resin composition of the outer intermediate layer may be different from the main component of the base resin of the resin composition of the cover. Preferably, the golf ball further includes a reinforcing layer between the outer intermediate layer and the cover.

Preferably, the rubber composition is
(F) An organic sulfur compound is further included. Preferred organic sulfur compounds (f) are thiophenols, diphenyl disulfides, thionaphthols and thiuram disulfides and metal salts thereof. Preferably, the rubber composition contains 100 parts by mass of the base rubber (a) and 0.05 parts by mass or more and 5 parts by mass or less of the organic sulfur compound (f).

  In the golf ball according to the present invention, the hardness distribution is appropriate. In this golf ball, there is little energy loss when hit. This golf ball is excellent in resilience performance. When this golf ball is hit with a driver, the spin speed is small. A large flight distance is achieved by a large resilience performance and a low spin speed. When this golf ball is hit with a short iron, the spin rate is high. This golf ball is excellent in control performance. In this golf ball, the local load applied when hit is small. This golf ball is excellent in durability. Further, with this golf ball, a soft feel at impact is obtained.

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.

  A golf ball 2 shown in FIG. 1 includes a spherical core 4, an inner intermediate layer 6 positioned outside the core 4, an outer intermediate layer 8 positioned outside the inner intermediate layer 6, and the outer intermediate layer 6. A reinforcing layer 10 positioned outside the layer 8 and a cover 12 positioned outside the reinforcing layer 10 are provided. A large number of dimples 14 are formed on the surface of the 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 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.

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.

  Examples of the base rubber (a) 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 that a polybutadiene having a small ratio of 1,2-vinyl bonds and excellent polymerization activity can be obtained, a polybutadiene synthesized with a rare earth element-based catalyst is preferable. 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, 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.

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. .

  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 (e). This metal compound (e) 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 metal compounds (e) 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 (e) is a zinc compound. Two or more metal compounds may be used in combination.

  Examples of the α, β-unsaturated carboxylic acid (b1) 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, the amount is preferably 5 parts by mass or less, and particularly preferably 2.5 parts by mass or less.

  The acid component contained in the acid and / or salt (d) has reactivity with the cation component. The acid is dissociated when the core 4 is heated and molded, and reacts with the cation component of the co-crosslinking agent (b). The acid is considered to inhibit metal crosslinking by the co-crosslinking agent (b) at the center of the core 4. The acid component contained in the salt exchanges a cation component with the co-crosslinking agent (b). It is presumed that the salt 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 molded.

  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. From the viewpoint of affinity with the base rubber, preferred acid and / or salt (d) is carboxylic acid and / or salt (d1) thereof. In the present invention, the concept of acid and / or salt (d) does not include the co-crosslinking agent (b).

  From the viewpoint of reactivity with the co-crosslinking agent (b), the number of carbon atoms of the carboxylic acid and / or salt (d1) thereof is preferably 1 or more, and more preferably 5 or more. 30 or less are preferable and, as for carbon number of the carboxylic acid component in carboxylic acid and / or its salt (d1), 20 or less are especially preferable. Preferred carboxylic acids and / or salts (d1) thereof include aliphatic carboxylic acids (fatty acids) and salts thereof, and aromatic carboxylic acids and salts thereof. From the viewpoint of affinity with the base rubber, fatty acids and salts thereof are preferred.

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

  As fatty acids, butyric acid (C4), valeric acid (C5), caproic acid (C6), enanthic acid (C7), caprylic acid (octanoic acid) (C8), pelargonic acid (C9), capric acid (decanoic acid) (C10) ), Lauric acid (C12), myristic acid (C14), myristoleic acid (C14), pentadecylic acid (C15), palmitic acid (C16), palmitoleic acid (C16), margaric acid (C17), stearic acid (C18) , Elaidic acid (C18), vaccenic 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), Noserin acid (C24), nervonic acid (C24), cerotic acid (C26), montanic acid (C28) and melissic acid (C30) can be mentioned. Two or more fatty acids 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 include an aromatic carboxylic acid substituted with a hydroxyl group, an alkoxy group, or an oxo group. Specifically, 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), veratrmic 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-dimethoxyphthalate) 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-methoxy) Phenyl) acetic acid), homoisovanillic acid ((3-hydroxy-4-methoxyphenyl) acetic acid), homoveratormic acid ((3,4-dimethoxyphenyl) acetic acid), o-homoveratormic 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-phenylpropanoic acid) 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 ) And sinapinic acid (3- (4-hydroxy-3,5-dimethoxyphenyl) acrylic acid) may be exemplified.

  The cation component contained in the acid and / or salt (d) 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. Zinc ions and magnesium ions are preferred.

  An organic cation is a cation having 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.

  In view of the ease of the cation exchange reaction, fatty acid salts are particularly preferred. Fatty acids and fatty acid salts may be used in combination, or two or more fatty acid salts may be used in combination.

  Preferred carboxylic acid salts include octanoic acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid and behenic acid potassium salt, magnesium salt, aluminum salt, zinc salt, iron salt, copper salt, nickel salt and cobalt. Salts are exemplified. A zinc salt of a carboxylic acid is particularly preferred. Particularly preferred carboxylic acid salts include zinc octoate, zinc laurate, zinc myristate and zinc stearate.

  From the viewpoint of optimizing 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, preferably 1.0 part by mass or more with respect to 100 parts by mass of the base rubber. 1.5 parts by mass or more is more preferable, and 2 parts by mass or more is more preferable. In light of resilience performance, this amount is preferably equal to or less than 45 parts by weight, more preferably equal to or less than 40 parts by weight, and particularly preferably equal to or less than 30 parts by weight.

  The mass ratio between the co-crosslinking agent (b) and 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 more 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 toward the surface is 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. When this zinc acrylate is contained in the rubber composition, stearic acid or zinc stearate coated on zinc acrylate is not included in the concept of acid and / or salt (d).

  Preferably, the rubber composition further includes an organic sulfur compound (f). The organic sulfur compound (f) 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 (f) include an organic compound 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 (f). As the organic sulfur compound (f), 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 (f) include thiophenols, thionaphthols, polysulfides, thiocarboxylic acids, dithiocarboxylic acids, sulfenamides, thiurams, dithiocarbamates and thiazoles. Preferred organic sulfur compounds (e) are thiophenols, diphenyl disulfides, thionaphthols and thiuram disulfides and metal salts thereof.

  Specific examples of the organic sulfur compound (f) 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, 2,6-dichlorothiophenol, 2 , 4,5-trichlorothiophenol, 2,4,5,6-tetrachlorothiophenol, pentachlorothiophenol, 4-bromothiophenol, 2,5-dibromothiophenol, 2,4,5-tribromothio Phenol, 2,4,5,6-tetrabromothiophenol, pentabromothiol Halogen groups such as diol, 4-iodothiophenol, 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 Thiophenols substituted with alkyl groups such as t-butylthiophenol; Thio substituted with carboxyl groups such as 4-carboxythiophenol, 2,4,6-tricarboxythiophenol and pentacarboxythiophenol Phenols; 4-methoxycarbonylthiophenol Thiophenols substituted with alkoxycarbonyl groups such as 2,4,6-trimethoxycarbonylthiophenol and pentamethoxycarbonylthiophenol; 4-formylthiophenol, 2,4,6-triformylthiophenol and pentaformyl Thiophenols substituted with formyl groups such as thiophenol; Thiophenols substituted with acyl groups such as 4-acetylthiophenol, 2,4,6-triacetylthiophenol and pentaacetylthiophenol; 4 Thiophenols substituted with carbonyl halide groups such as chlorocarbonylthiophenol, 2,4,6-tri (chlorocarbonyl) thiophenol and penta (chlorocarbonyl) thiophenol; 4-sulfothiophenol, 2, 4,6 -Thiophenols substituted with sulfo groups such as trisulfothiophenol and pentasulfothiophenol; such as 4-methoxysulfonylthiophenol, 2,4,6-trimethoxysulfonylthiophenol and pentamethoxysulfonylthiophenol Thiophenols substituted with alkoxysulfonyl groups; substituted with halogenated sulfonyl groups such as 4-chlorosulfonylthiophenol, 2,4,6-tri (chlorosulfonyl) thiophenol and penta (chlorosulfonyl) thiophenol Thiophenols; thiophenols substituted with sulfino groups such as 4-sulfinothiophenol, 2,4,6-trisulfinothiophenol and pentasulfinothiophenol; 4-methylsulfinylthiopheno Thiophenols substituted with alkylsulfinyl groups such as 2,4,6-tri (methylsulfinyl) thiophenol and penta (methylsulfinyl) thiophenol; 4-carbamoylthiophenol, 2,4,6-tri Thiophenols substituted with carbamoyl groups such as carbamoylthiophenol and pentacarbamoylthiophenol; such as 4-trichloromethylthiophenol, 2,4,6-tri (trichloromethyl) thiophenol and penta (trichloromethyl) thiophenol Thiophenols substituted with various halogenated alkyl groups; thiophenols substituted with cyano groups such as 4-cyanothiophenol, 2,4,6-tricyanothiophenol and pentacyanothiophenol; and 4-meth Shi thiophenol, thiophenols substituted with an alkoxy group such as 2,4,6-methoxythiophenol 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 thionaphthols, 2-thionaphthol, 1-thionaphthol, 2-chloro-1-thionaphthol, 2-bromo-1-thionaphthol, 2-fluoro-1-thionaphthol, 2-cyano-1-thionaphthol 2-acetyl-1-thionaphthol, 1-chloro-2-thionaphthol, 1-bromo-2-thionaphthol, 1-fluoro-2-thionaphthol, 1-cyano-2-thionaphthol and 1-acetyl- Examples include 2-thionaphthol and metal salts thereof. 1-thionaphthol and 2-thionaphthol and their zinc salts 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. As the thiazole-based organic sulfur compound, 2-mercaptobenzothiazole (MBT); dibenzothiazyl disulfide (MBTS); sodium salt, zinc salt, copper salt and cyclohexylamine salt of 2-mercaptobenzothiazole; 2- (2,4- Examples include dinitrophenyl) mercaptobenzothiazole; and 2- (2,6-diethyl-4-morpholinothio) benzothiazole.

  Particularly preferred organic sulfur compounds (e) are 2-thionaphthol, bis (pentabromophenyl) disulfide, and 2,6-dichlorothiophenol from the viewpoint that an outer-hard / inner-soft structure is easily obtained.

  In light of the inner-hard inner rigid structure of the core 4, the content of the organic sulfur compound (f) is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, based on 100 parts by mass of the base rubber. 2 parts by mass or more is particularly preferable. From the viewpoint of resilience performance, this amount is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, and particularly preferably 1 part by mass or less.

  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.

  When the core 4 is heated and molded, the reaction heat of the cross-linking reaction of the base rubber is accumulated 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. The acid and / or salt (d) reacts with the metal salt of the co-crosslinking agent (b) to break the metal bridge. This reaction is promoted in the high temperature region. That is, the cutting of the metal bridge is likely to occur in the central portion of the core 4 where the temperature is high and hardly occurs in the vicinity of the surface. As a result, the crosslink density of the core 4 increases from the center toward the surface. In the core 4, the hardness increases linearly from the center toward the surface. Furthermore, when the rubber composition contains the organic sulfur compound (f) together with the acid and / or salt (d), the gradient of the hardness distribution can be controlled, and the degree of the outer-hard / inner-soft structure of the core 4 is increased. Can do.

FIG. 2 is a line graph showing the hardness distribution of the core 4 of the golf ball 2 of FIG. 1 according to the present invention. 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. The hardness of the ninth point is measured by pressing a JIS-C type hardness meter against the surface of the spherical core 4. For the measurement, an automatic rubber hardness measuring machine (trade name “P1” by Kobunshi Keiki Co., Ltd.) equipped with this hardness meter is used.

  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. In FIG. 2, the broken line does not deviate significantly from the linear approximation curve. In other words, the polygonal line has a shape close to a linear approximation curve. That is, in the core 4 according to the present invention, the hardness increases linearly from the center toward the surface. When the golf ball 2 having the core 4 is hit with a driver, there is little energy loss. This core 4 is excellent in resilience performance. When the golf ball 2 is hit with a driver, the flight distance is large. In the core 4, the hardness continuously increases from the center toward the surface. The core 4 has no discontinuities due to the multilayer structure. When the golf ball 2 including the core 4 is deformed by hitting, no local load is applied. This golf ball 2 is excellent in durability.

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. In this respect, R ² is more preferably equal to or greater than 0.97, and particularly preferably equal to or greater than 0.99. 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

  In the present invention, the JIS-C hardness of the measurement point where the ratio of the distance from the center point of the core 4 to the radius 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 (0.0). The surface hardness of the core 4 is expressed as Hs. The difference (Hs−H (0.0)) between the surface hardness Hs and the center hardness H (0.0) is 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 driver, the recoil (return torsion) 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 (0.0)) is more preferably 25 or more, and particularly preferably 30 or more. From the viewpoint that the core 4 can be easily molded, the difference (Hs−H (0.0)) is preferably 50 or less.

  The hardness H (0.0) of the center point of the core 4 is preferably 40 or greater and 70 or less. The golf ball 2 including the core 4 having a hardness H (0.0) of 40 or more is excellent in resilience performance. More preferable hardness H (0.0) is 45 or more, and particularly preferably 50 or more. In the core 4 having a hardness H (0.0) of 70 or less, an outer-hard / inner-soft structure can be achieved. In the golf ball 2 having the core 4, spin can be suppressed. More preferred hardness H (0.0) is 68 or less, and particularly preferred is 65 or less.

  The hardness Hs of the surface of the core 4 is preferably 78 or more and 96 or less. In the core 4 having the hardness Hs of 78 or more, an outer-hard / inner-soft structure can be achieved. In the golf ball 2 having the core 4, spin can be suppressed. The more preferable hardness Hs is 80 or more, and particularly preferably 82 or more. The golf ball 2 including the core 4 having a hardness Hs of 96 or less is excellent in durability. The more preferable hardness Hs is 94 or less, and particularly preferably 92 or less.

  The diameter of the core 4 is preferably 36.0 mm or more. 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. An outer-hard / inner-soft structure of the golf ball 2 can be achieved by the core 4 having a diameter of 36.0 mm or more. From this viewpoint, the diameter is more preferably 37.0 mm or more, and particularly preferably 38.0 mm or more. Furthermore, the diameter of the core 4 is preferably 40.1 mm or less. In the golf ball 2 having the core 4 having a diameter of 40.1 mm or less, the inner intermediate layer 6, the outer intermediate layer 8, and the cover 12 can have a sufficient thickness. The golf ball 2 in which the inner intermediate layer 6, the outer intermediate layer 8, and the cover 12 have a large thickness is excellent in durability. In this respect, the diameter is particularly preferably 38.8 mm or less. The core 4 may include two or more layers.

  In light of feel at impact, the amount of compressive deformation Dc of the core 4 is preferably equal to or greater than 3.0 mm, and particularly preferably equal to or greater than 3.2 mm. In light of resilience performance, the amount of compressive deformation Dc is preferably equal to or less than 3.8 mm, and particularly preferably equal to or less than 3.5 mm.

  A resin composition is suitably used for the inner intermediate layer 6. Examples of the base resin of this resin composition include ionomer resins, polystyrene, polyester, polyamide and polyolefin.

  A particularly preferable base resin is an ionomer resin. The golf ball 2 having the inner mid layer 6 containing an ionomer resin is excellent in resilience performance. The inner intermediate layer 6 may be used in combination with an ionomer resin and another resin. When used in combination, the main component of the base resin is preferably an ionomer resin. Specifically, the ratio of the ionomer resin to the total amount of the base resin is preferably 80% by mass or more, and more preferably 90% 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 MK7320" and "High Milan MK7329"; DuPont's trade names "Surlin 6120" and "Surlin 6910" , “Surlin 7930”, “Surlin 7940”, “Surlin 8140”, “Surlin 8150”, “Surlin 8940”, “Surlin 8945”, “Surlin 9120”, “Surlin 915” ", Surlyn 9910", "Surlin 9945", "Surlin AD8546", "HPF1000" and "HPF2000"; and ExxonMobil Chemical's trade names "IOTEK7010", "IOTEK7030", "IOTEK7510", "IOTEK7520", " IOTEK8000 "and" IOTEK8030 ".

  Two or more ionomer resins may be used in combination with the inner intermediate layer 6. An ionomer resin neutralized with a monovalent metal ion and an ionomer resin neutralized with a divalent metal ion may be used in combination.

  The inner mid layer 6 may be blended with a highly elastic resin. Specific examples of the highly elastic resin include polyamide.

  If necessary, the resin composition of the inner intermediate layer 6 may include a colorant such as titanium dioxide, a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent agent, and a fluorescent agent. An appropriate amount of a whitening agent or the like is blended.

  From the viewpoint that an outer-hard / inner-soft structure can be achieved in a sphere composed of the core 4 and the inner intermediate layer 6, the Shore D hardness Hm 1 of the inner intermediate layer 6 is preferably 55 or more, and more preferably 60 or more. In the golf ball 2 including the inner mid layer 6 having the hardness Hm1 in this range, the spin speed is sufficiently suppressed in the driver shot. The golf ball 2 has a large flight distance. In light of control performance of the golf ball 2, the hardness Hm1 is preferably equal to or less than 70, and particularly preferably equal to or less than 68. When the golf ball 2 is hit with a short iron, the spin speed is high.

  The Shore D hardness Hm1 of the inner intermediate layer 6 is a Shore D type attached to an automatic rubber hardness measuring device (trade name “P1” of Kobunshi Keiki Co., Ltd.) in accordance with the provisions of “ASTM-D 2240-68”. Measured with a hardness meter. 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 that of the inner intermediate layer 6 is used.

  The thickness T1 of the inner intermediate layer 6 is preferably 0.5 mm or greater and 1.6 mm or less. From the viewpoint of durability, a more preferable thickness T1 is 0.7 mm or more. From the viewpoint of resilience performance, a more preferable thickness T1 is 1.2 mm or less.

  For the outer intermediate layer 8, a resin composition is suitably used. Examples of the base resin of this resin composition include ionomer resins, polystyrene, polyester, polyamide and polyolefin.

  A particularly preferable base resin is an ionomer resin. The ionomer resin described above for the inner intermediate layer 6 can also be used for the outer intermediate layer 8. The golf ball 2 having the outer intermediate layer 8 containing an ionomer resin is excellent in resilience performance. The outer intermediate layer 8 may be used in combination with an ionomer resin and another resin. When used in combination, the main component of the base resin is preferably an ionomer resin. Specifically, the ratio of the ionomer resin to the total amount of the base resin is preferably 45% by mass or more, and more preferably 60% by mass or more.

  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 70% by weight, more preferably equal to or less than 65% by weight, and particularly preferably equal to or less than 60% by weight.

  In the present invention, the styrene block-containing thermoplastic elastomer includes a polymer alloy of one or more selected from the group consisting of SBS, SIS and SIBS, and hydrogenated products thereof, and an olefin. The olefin component in the polymer alloy is presumed to contribute to the improvement of compatibility with the ionomer resin. By using this polymer 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 outer intermediate layer 8 may include a colorant such as titanium dioxide, a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent agent, and a fluorescent agent. An appropriate amount of a whitening agent or the like is blended.

  From the viewpoint of a spin suppression effect in driver shots, the outer D layer 8 has a Shore D hardness Hm2 of preferably 25 or more, and more preferably 30 or more. The golf ball 2 has a large flight distance. In light of control performance of the golf ball 2, the hardness Hm2 is preferably 60 or less, and particularly preferably 54 or less. When the golf ball 2 is hit with a short iron, the spin speed is high. The hardness Hm2 is measured by the same method as the hardness Hm1.

  From the viewpoint of durability and feel at impact, it is preferable that the hardness Hm1 of the inner intermediate layer 6 is greater than the hardness Hm2 of the outer intermediate layer 8. When the golf ball 2 having the hardness Hm1 larger than the hardness Hm2 is hit with a driver, the impact given to the golf ball 2 by the driver is reduced. This golf ball 2 is excellent in durability. The feel at impact of the golf ball 2 is soft.

  The difference (Hm1-Hm2) between the hardness Hm2 of the outer intermediate layer 8 and the hardness Hm1 of the inner intermediate layer 6 is preferably 8 or more, and particularly preferably 14 or more. From the viewpoint of resilience performance, the difference (Hm1-Hm2) is preferably 35 or less. In the golf ball 2 including the outer intermediate layer 8 having the hardness Hm2 in this range, the spin speed when hit with a driver is low. The golf ball 2 has a large flight distance. When the golf ball 2 is hit with a short iron, the spin speed is high.

  The thickness T2 of the outer intermediate layer 8 is preferably 0.5 mm or more. In the golf ball 2 including the outer intermediate layer 8 having a thickness T2 of 0.5 mm or more, the impact due to impact is reduced, and thus the durability is excellent. In this respect, the thickness T2 is more preferably equal to or greater than 0.7 mm. The thickness T2 is preferably 1.6 mm or less. The golf ball 2 including the outer intermediate layer 8 having a thickness T2 of 1.6 mm or less includes a relatively large core 4. This golf ball 2 exhibits sufficient resilience performance. In this respect, the thickness T2 is particularly preferably equal to or less than 1.2 mm.

  The sum (T1 + T2) of the thickness T1 and the thickness T2 is preferably 1.0 mm or more. This golf ball 2 is excellent in durability since the impact due to impact is reduced. In this respect, the sum (T1 + T2) is more preferably equal to or greater than 1.3 mm. The sum (T1 + T2) is preferably 3.0 mm or less. The golf ball 2 includes a relatively large core 4. This golf ball 2 exhibits sufficient resilience performance. In this respect, the sum (T1 + T2) is more preferably equal to or less than 2.0 mm. A plurality of intermediate layers may be provided between the inner intermediate layer 6 and the outer intermediate layer 8.

  For the formation of the outer intermediate layer 8, 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 cover 12. A preferred base resin of this resin composition is a urethane resin or a urea resin. The main component of the urethane resin is polyurethane. Polyurethane is soft. When the golf ball 2 provided with the cover 12 made of a resin composition containing polyurethane is hit with a short iron, the spin rate is high. The cover 12 made of this resin composition contributes to control performance in a shot with a short iron. The polyurethane also contributes to the scratch resistance performance of the cover 12. Furthermore, polyurethane can contribute to an excellent feel at impact when hit with a putter or a short iron.

  From the viewpoint of easy molding of the cover 12, a preferred base resin is a thermoplastic polyurethane elastomer. The thermoplastic polyurethane elastomer includes a polyurethane component as a hard segment and a polyester component or a polyether component as a soft segment. Examples of the isocyanate for the polyurethane component include alicyclic diisocyanates, aromatic diisocyanates and aliphatic diisocyanates. Two or more diisocyanates may be used in combination.

Examples of alicyclic diisocyanates include 4,4′-dicyclohexylmethane diisocyanate (H ₁₂ MDI), 1,3-bis (isocyanatomethyl) cyclohexane (H ₆ XDI), isophorone diisocyanate (IPDI), and trans-1,4- Examples are cyclohexane diisocyanate (CHDI). From the viewpoint of versatility and workability, H ₁₂ MDI is preferable.

  Aromatic diisocyanates include 4,4'-diphenylmethane diisocyanate (MDI) and toluene diisocyanate (TDI). As the aliphatic diisocyanate, hexamethylene diisocyanate (HDI) is exemplified.

  In particular, alicyclic diisocyanates are preferred. Since the alicyclic diisocyanate does not have a double bond in the main chain, yellowing of the cover 12 is suppressed. Moreover, since the alicyclic diisocyanate is excellent in strength, the cover 12 is prevented from being damaged.

  Specific examples of the thermoplastic polyurethane elastomer include BASF Japan trade names “Elastolan NY80A”, “Elastolan NY82A”, “Elastolan NY84A”, “Elastolan NY85A”, “Elastolan NY88A”, “Elastolan NY90A”. "Elastolan NY97A", "Elastolan NY585", "Elastolan XKP016N", "Elastolan 1195ATR", "Elastolan ET890A" and "Elastolan ET88050"; And “Rezamin PS62490”. From the viewpoint that a small hardness of the cover 12 can be achieved, “Elastolan NY80A”, “Elastolan NY82A”, “Elastolan NY84A”, “Elastolan NY85A”, “Elastolan NY90A” and “Elastolan NY97A” are Particularly preferred.

  A thermoplastic polyurethane elastomer and other resin may be used in combination. Examples of the resin that can be used in combination include thermoplastic polyester elastomers, thermoplastic polyamide elastomers, thermoplastic polyolefin elastomers, styrene block-containing thermoplastic elastomers, and ionomer resins. When the thermoplastic polyurethane elastomer is used in combination with another resin, the thermoplastic polyurethane elastomer is the main component of the base polymer from the viewpoint of spin performance and scratch resistance. The ratio of the thermoplastic polyurethane elastomer in the total base polymer is preferably 50% by mass or more, more preferably 70% by mass or more, and particularly preferably 85% by mass or more.

  If necessary, the cover 12 includes a colorant such as titanium dioxide, a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent agent, a fluorescent whitening agent, and the like. Appropriate amount is blended.

  The cover 12 preferably has a Shore D hardness Hc of 48 or less. The golf ball 2 having the cover 12 having a hardness Hc of 48 or less is excellent in control performance. In this respect, the hardness Hc is more preferably equal to or less than 40, and particularly preferably equal to or less than 32. From the viewpoint of flight distance in driver shots, the hardness Hc is preferably 10 or more, more preferably 15 or more, and particularly preferably 20 or more. The hardness Hc is measured by the same method as that for measuring the hardness Hm1 and the hardness Hm2.

  The hardness Hc of the cover 12 is smaller than the hardness Hm1 of the inner mid layer 6. When the golf ball 2 is hit with a driver, the sphere composed of the core 4 and the inner intermediate layer 6 is greatly distorted because the head speed is high. Since this sphere has an outer-hard / inner-soft structure, the spin rate is suppressed. Since the hardness of the core 4 changes linearly, the golf ball 2 is launched at a high speed by the deformation and restoration of the core 4. A great flight distance is achieved by suppressing the spin speed and the high launch speed. When the golf ball 2 is hit with a short iron, since the head speed is low, the distortion of the sphere is small. The behavior of the golf ball 2 when hit with a short iron mainly depends on the cover 12. Since the cover 12 is soft, slip between the golf ball 2 and the club face is suppressed. By suppressing the slip, a high spin speed can be obtained. Excellent control performance is achieved due to the high spin rate. In the golf ball 2, high flight distance performance in a shot with a driver and control performance in a shot with a short iron are compatible. In this respect, the hardness Hc is more preferably smaller than the hardness Hm2 of the outer intermediate layer 8.

  When the golf ball 2 is hit, the cover 12 containing polyurethane absorbs the impact. This absorption achieves a soft feel at impact. In particular, when hit with a short iron or a putter, an excellent shot feeling is achieved by the cover 12.

  From the viewpoint of achieving both flight performance and control performance, the difference (Hm1-Hc) between the hardness Hm1 of the inner intermediate layer 6 and the hardness Hc of the cover 12 is preferably 30 or more, more preferably 33 or more, and particularly preferably 35 or more. . The difference (Hm1-Hc) is preferably 45 or less, and particularly preferably 40 or less. In the golf ball 2 in which the hardness of the inner mid layer 6 and the hardness of the cover 12 satisfy this condition, the spin speed on driver shots is suppressed. In this golf ball 2, the spin rate of back spin in approach shots is increased.

  Furthermore, from the viewpoint of achieving both flight performance and control performance, the difference (Hm2−Hc) between the hardness Hm2 of the outer intermediate layer 8 and the hardness Hc of the cover 12 is preferably 10 or more, and particularly preferably 18 or more. The difference (Hm2−Hc) is preferably 30 or less.

  Preferably, the JIS-C hardness of the cover 12 is smaller than the surface hardness Hs of the core 4. When the golf ball 2 is hit with a short iron, the soft cover 12 is sandwiched between the hard core 4 and the hard club face. By this pinching, the slip of the golf ball 2 with respect to the club face is suppressed. By suppressing the slip, a high spin speed can be obtained. Suppression suppresses variations in spin speed. From the viewpoint of slip suppression, the difference between the surface hardness Hs of the core 4 and the JIS-C hardness of the cover 12 is preferably 30 or more, and particularly preferably 40 or more.

  From the viewpoint of flight distance performance in a shot with a driver, the thickness Tc of the cover 12 is preferably 0.8 mm or less, and more preferably 0.6 mm or less. In light of durability and control performance, the thickness Tc is preferably equal to or greater than 0.3 mm, and particularly preferably equal to or greater than 0.5 mm. The golf ball 2 may include a plurality of covers.

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

  From the viewpoint of achieving both high flight distance performance and control performance, urethane resin or urea resin is preferable as the main component of the base resin of the resin composition of the cover 12, and the main component of the base resin of the resin composition of the outer intermediate layer 8 As an ionomer resin, it is preferable. That is, the main component of the base resin of the outer intermediate layer 8 is different from the main component of the base resin of the cover 12.

  From the viewpoint of durability, the golf ball 2 having the reinforcing layer 10 between the outer intermediate layer 8 and the cover 12 is preferable. The reinforcing layer 10 is located between the outer intermediate layer 8 and the cover 12. The reinforcing layer 10 is firmly attached to the outer intermediate layer 8 and is also firmly attached to the cover 12. The reinforcement layer 10 suppresses the peeling of the cover 12 from the outer intermediate layer 8. As described above, the cover 12 of the golf ball 2 is thin. When the golf ball 2 is hit with the edge of the club face, wrinkles are likely to occur. The reinforcing layer 10 suppresses wrinkles and improves the durability of the golf ball 2.

  A two-component curable thermosetting resin is preferably used for the base polymer of the reinforcing layer 10. Specific examples of the two-component curable thermosetting resin include an epoxy resin, a urethane resin, an acrylic resin, a polyester resin, and a cellulose resin. From the viewpoint of the strength and durability of the reinforcing layer 10, a two-component curable epoxy resin and a two-component curable urethane resin are preferable.

  The two-component curable epoxy resin is obtained by curing the epoxy resin with a polyamide curing agent. Examples of the epoxy resin used in the two-component curable epoxy resin include bisphenol A type epoxy resin, bisphenol F type epoxy resin, and bisphenol AD type epoxy resin. The bisphenol A type epoxy resin is obtained by a reaction between bisphenol A and an epoxy group-containing compound such as epichlorohydrin. The bisphenol F type epoxy resin is obtained by a reaction between bisphenol F and an epoxy group-containing compound. The bisphenol AD type epoxy resin is obtained by a reaction between bisphenol AD and an epoxy group-containing compound. From the viewpoint of the balance of flexibility, chemical resistance, heat resistance and toughness, bisphenol A type epoxy resin is preferable.

  The polyamide-based curing agent has a plurality of amino groups and one or more amide groups. This amino group can react with an epoxy group. Specific examples of the polyamide curing agent include a polyamide amine curing agent and a modified product thereof. The polyamidoamine curing agent is obtained by a condensation reaction between a polymerized fatty acid and a polyamine. Typical polymerized fatty acids can be obtained by synthesizing natural fatty acids containing a large amount of unsaturated fatty acids such as linoleic acid and linolenic acid by heating in the presence of a catalyst. Specific examples of unsaturated fatty acids include tall oil, soybean oil, linseed oil and fish oil. A polymerized fatty acid having a dimer content of 90% by mass or more, a trimer content of 10% by mass or less, and hydrogenated is preferable. Preferred polyamines include polyethylene diamine, polyoxyalkylene diamine and derivatives thereof.

  In mixing the epoxy resin and the polyamide curing agent, the ratio of the epoxy equivalent of the epoxy resin and the amine active hydrogen equivalent of the polyamide curing agent is preferably 1.0 / 1.4 or more and 1.0 / 1.0 or less. .

  The two-component curable urethane resin is obtained by a reaction between the main agent and the curing agent. A two-component curable urethane resin obtained by a reaction between a main component containing a polyol component and a curing agent containing a polyisocyanate or a derivative thereof, a main component containing an isocyanate group-terminated urethane prepolymer, and a curing agent having active hydrogen. A two-component curable urethane resin obtained by reaction may be used. In particular, a two-component curable urethane resin obtained by a reaction between a main component containing a polyol component and a curing agent containing polyisocyanate or a derivative thereof is preferable.

  It is preferable that urethane polyol is used as the polyol component of the main agent. The urethane polyol has a urethane bond and at least two or more hydroxyl groups. Preferably, the urethane polyol has a hydroxyl group at its terminal. The urethane polyol can be obtained by reacting the polyol and the polyisocyanate at a ratio such that the hydroxyl group of the polyol component is excessive in molar ratio with respect to the isocyanate group of the polyisocyanate.

  The polyol used for the production of the urethane polyol has a plurality of hydroxyl groups. A polyol having a weight average molecular weight of 50 or more and 2000 or less is preferable, and a polyol having a weight average molecular weight of 100 or more and 1000 or less is particularly preferable. Examples of the low molecular weight polyol include diol and triol. Specific examples of the diol include ethylene glycol, diethylene glycol, triethylene glycol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol and 1,6-hexanediol. Specific examples of the triol include trimethylolpropane and hexanetriol. High molecular weight polyols include polyether polyols such as polyoxyethylene glycol (PEG), polyoxypropylene glycol (PPG) and polyoxytetramethylene glycol (PTMG); polyethylene adipate (PEA), polybutylene adipate (PBA) ) And polyhexamethylene adipate (PHMA); lactone polyester polyols such as poly-ε-caprolactone (PCL); polycarbonate polyols such as polyhexamethylene carbonate; and acrylic polyols. Two or more polyols may be used in combination.

The polyisocyanate used for the production of the urethane polyol has a plurality of isocyanate groups. Specific examples of the polyisocyanate include 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, a mixture of 2,4-toluene diisocyanate and 2,6-toluene diisocyanate (TDI), 4,4′-diphenylmethane diisocyanate (MDI). ), 1,5-naphthylene diisocyanate (NDI), 3,3′-vitrylene-4,4′-diisocyanate (TODI), xylylene diisocyanate (XDI), tetramethylxylylene diisocyanate (TMXDI) and paraphenylene diisocyanate ( aromatic polyisocyanates such as PPDI); 4,4'-dicyclohexylmethane diisocyanate _(H 12 MDI), hydrogenated xylylene diisocyanate _(H 6 XDI) and isophorone diisocyanate ( Alicyclic polyisocyanates such as PDI); and aliphatic polyisocyanates such as hexamethylene diisocyanate (HDI) and the like. Two or more polyisocyanates may be used in combination. From the viewpoint of weather resistance, TMXDI, XDI, HDI, H ₆ XDI, IPDI and H ₁₂ MDI are preferred.

  A known catalyst can be used in the reaction of the polyol and the polyisocyanate for producing the urethane polyol. A typical catalyst is dibutyltin dilaurate.

  From the viewpoint of the strength of the reinforcing layer 10, the ratio of the urethane bond contained in the urethane polyol is preferably 0.1 mmol / g or more. From the viewpoint of followability of the reinforcing layer 10 to the cover 12, the ratio of the urethane bond contained in the urethane polyol is preferably 5 mmol / g or less. The ratio of the urethane bond can be adjusted by adjusting the molecular weight of the polyol as a raw material and adjusting the blending ratio of the polyol and the polyisocyanate.

  In light of the short time required for the reaction between the main agent and the curing agent, the weight average molecular weight of the urethane polyol is preferably 4000 or more, and particularly preferably 4500 or more. From the viewpoint of adhesion of the reinforcing layer 10, the urethane polyol has a weight average molecular weight of preferably 10,000 or less, particularly preferably 9000 or less.

  From the viewpoint of adhesiveness of the reinforcing layer 10, the hydroxyl value (mgKOH / g) of the urethane polyol is preferably 15 or more, and particularly preferably 73 or more. From the viewpoint that the time required for the reaction between the main agent and the curing agent is short, the hydroxyl value of the urethane polyol is preferably 130 or less, and particularly preferably 120 or less.

  The main agent may contain a polyol having no urethane bond together with the urethane polyol. The aforementioned polyol, which is a raw material for urethane polyol, can be used as the main agent. Polyols that are compatible with urethane polyols are preferred. From the viewpoint that the time required for the reaction between the main agent and the curing agent is short, the ratio of the urethane polyol in the main agent is preferably 50% by mass or more and particularly preferably 80% by mass or more in terms of solid content. Ideally this ratio is 100% by weight.

  The curing agent contains polyisocyanate or a derivative thereof. The aforementioned polyisocyanate, which is a raw material of urethane polyol, can be used as a curing agent.

  The reinforcing layer 10 may contain additives such as a colorant (typically titanium dioxide), a phosphoric acid stabilizer, an antioxidant, a light stabilizer, a fluorescent brightener, an ultraviolet absorber, and an antiblocking agent. . The additive may be added to the main component of the two-component curable thermosetting resin, or may be added to the curing agent.

  The reinforcing layer 10 is obtained by applying a liquid in which the main agent and the curing agent are dissolved or dispersed in a solvent to the surface of the outer intermediate layer 8. From the viewpoint of workability, application with a spray gun is preferred. After application, the solvent volatilizes and the main agent and the curing agent react to form the reinforcing layer 10. Preferred solvents include toluene, isopropyl alcohol, xylene, methyl ethyl ketone, methyl isobutyl ketone, ethylene glycol monomethyl ether, ethylbenzene, propylene glycol monomethyl ether, isobutyl alcohol and ethyl acetate.

  In light of feel at impact, the golf ball 2 has an amount of compressive deformation Db of preferably 2.1 mm or greater, more preferably 2.2 mm or greater, and particularly preferably 2.3 mm or greater. In light of resilience performance, the amount of compressive deformation Db is preferably equal to or less than 3.2 mm, more preferably equal to or less than 3.0 mm, and particularly preferably equal to or less than 2.8 mm.

  In the measurement of the amount of compressive deformation, a sphere (golf ball 2, core 4 or the like) is 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 98N is applied to the sphere to the state where the final load of 1274N 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), 38 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-thionaphthol, 0.9 parts by mass of dicumyl peroxide (trade name “PARKMILL D” from NOF Corporation) and 2 parts by mass of zinc octoate (Mitsuwa Chemical) Was kneaded to obtain a rubber composition. This rubber composition is put into a mold composed of an upper mold and a lower mold each having a hemispherical cavity, and heated at a temperature of 170 ° C. for 25 minutes to obtain a spherical core having a diameter of 38.5 mm. It was. The amount of barium sulfate was adjusted so that the mass of the golf ball was 45.6 g.

  55 parts by mass of ionomer resin (the above-mentioned “Surlin 8945”), 45 parts by mass of other ionomer resin (the above-mentioned “Himilan AM7329”) and 3 parts by mass of titanium dioxide were kneaded with a twin-screw kneading extruder to obtain a resin composition. I got a thing. The extrusion conditions were a screw diameter of 45 mm, a screw speed of 200 rpm, a screw L / D of 35, and a die temperature of 160 ° C. to 230 ° C. The core was put into the mold. The resin composition was injected around the core by an injection molding method to mold the inner intermediate layer. The inner layer had a thickness of 0.8 mm.

  27 parts by mass of ionomer resin (previously “Surline 8945”), 45 parts by mass of other ionomer resin (previously “Himiran AM7329”), 28 parts by mass of styrene block-containing thermoplastic elastomer (previously “Lavalon T3221C”) And 3 parts by mass of titanium dioxide were kneaded with a twin-screw kneading extruder under the aforementioned extrusion conditions to obtain a resin composition. A sphere composed of a core and an inner intermediate layer was introduced into the mold. The resin composition was injected around a sphere by an injection molding method to form an outer intermediate layer. The thickness of this outer intermediate layer was 0.8 mm.

  A coating composition (trade name “Porin 750LE”, manufactured by Shinto Paint Co., Ltd.) using a two-pack curable epoxy resin as a base polymer was prepared. The curing agent liquid of this coating composition is composed of 40 parts by mass of modified polyamidoamine, 55 parts by mass of solvent, and 5 parts by mass of titanium dioxide. The mass ratio with respect to the curing agent liquid is 1 / 1.This coating composition was applied to the surface of the outer intermediate layer with an air gun, and held at 23 ° C. for 12 hours to obtain a reinforcing layer. The thickness of was 10 μm.

  100 parts by mass of thermoplastic polyurethane elastomer (previously referred to as “Elastollan NY82A”), 0.2 parts by mass of hindered amine light stabilizer (trade name “Tinuvin 770” from Ciba Japan), 4 parts by mass of titanium dioxide and 0 parts by mass .04 parts by mass of ultramarine blue was kneaded with a twin-screw kneading extruder under the aforementioned extrusion conditions to obtain a resin composition. A half shell was molded from this resin composition by compression molding. A sphere composed of a core, an inner intermediate layer, an outer intermediate layer, and a reinforcing layer was covered with two half shells. Both the sphere and the half shell were put into a final mold which was composed of an upper mold and a lower mold each provided with a hemispherical cavity, and had many pimples on the cavity surface. A cover was obtained by compression molding. The thickness of this cover was 0.5 mm. A dimple having a shape obtained by inverting the shape of the pimple was formed on the cover. The surface of this cover was polished. A clear paint based on a two-component curable polyurethane was applied around the cover with an air gun and dried and cured to obtain a golf ball of Example 1 having a diameter of 42.7 mm and a mass of 45.6 g.

[Examples 2 to 17 and Comparative Examples 1 to 6]
Golf balls of Examples 2 to 17 and Comparative Examples 1 to 6 were the same as Example 1 except that the specifications of the core, inner intermediate layer, outer intermediate layer and cover were as shown in Tables 6 to 10 below. Got. Details of the composition and hardness of the core are shown in Tables 1 to 3 below. The composition and hardness of the inner and outer intermediate layers are shown in Table 4 below. The composition and hardness of the cover are shown in Table 5 below.

[Blow by driver (W # 1)]
A driver with a titanium head (trade name “XXIO” from Dunlop Sports, shaft hardness: S, loft angle: 10.0 °) equipped with a titanium head was mounted on a swing machine manufactured by Tsurtemper. A golf ball was hit under the condition that the head speed was 45 m / sec. The spin speed immediately after hitting was measured. In addition, the flight distance from the launch point to the stationary point was measured. The average values of the data obtained by 10 measurements are shown in Tables 6 to 10 below.

[Blowing by sand wedge (SW)]
A sand wedge (trade name “XXIO”, Dunlop Sports Co., Ltd., shaft hardness: R, loft angle: 56.0 °) was mounted on a swing machine manufactured by Tsurutemper. A golf ball was hit under the condition that the head speed was 21 m / sec. The backspin rate immediately after impact was measured. The average values of the data obtained by 10 measurements are shown in Tables 6 to 10 below.

[durability]
A driver equipped with a titanium head (trade name “XXIO” from Dunlop Sports, shaft hardness: S, loft angle: 10.0 °) was attached to a swing robot M / C manufactured by Tsurutemper. A golf ball stored for 12 hours at a temperature of 23 ° C. was used for the measurement. The golf ball was hit repeatedly under the condition that the head speed was 45 m / sec. The number of hits until the golf ball was destroyed was measured. The indices of the average values of the data obtained for 12 golf balls are shown in Tables 6 to 10 below. The larger the index, the better the durability of the golf ball.

[Hit feel]
A golfer was hit with a golf ball by a driver equipped with a titanium head (trade name “XXIO” of Dunlop Sports, shaft hardness: S, loft angle: 10.0 °). The feel at impact was evaluated according to the following criteria.
A: Extremely good (soft)
B: Good (soft)
C: Slightly bad (slightly hard)
D: Defect (hard)

Details of the compounds described in Tables 1 to 3 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: 55, molecular weight distribution (Mw / Mn): 3)
Sunseller SR: Sanshin Chemical Co., Ltd. zinc acrylate (10 wt% stearic acid coating product)
ZN-DA90S: Zinc acrylate (10% by mass zinc stearate coated product) manufactured by Nippon Distillation Co., Ltd.
Zinc oxide: Toho Zinc Co., Ltd. trade name “Ginbao R”
Barium sulfate: The trade name “Barium sulfate BD” by Sakai Chemical
2-thionaphthol: Tokyo Chemical Industry Co., Ltd. Bis (pentabromophenyl) disulfide: Kawaguchi Chemical Industry Co., Ltd. Dicumyl peroxide: Product name "Park Mill D" of Nippon Oil & Fats Co., Ltd.
Zinc octoate: Mitsuwa Chemicals (purity: 99% or more)
Zinc stearate: Wako Pure Chemical Industries, Ltd. (Purity: 99% or more)
Zinc myristate: NOF Corporation (purity: 90% or more)

  As shown in Tables 6 to 10, the golf balls according to the examples are excellent in various performances. 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 ... inner intermediate layer 8 ... outer intermediate layer 10 ... reinforcing layer 12 ... cover 14 ... dimple 16 ... land

Claims (21)

A spherical core, an inner intermediate layer located outside the core, an outer intermediate layer located outside the inner intermediate layer, and a cover located outside the outer intermediate layer;
The distance (%) from the center point and JIS-C hardness of 9 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 are plotted in a graph. R ^{2 of the} linear approximation curve obtained by the least square method is 0.95 or more,
The Shore D hardness Hm1 of the inner intermediate layer is larger than the Shore D hardness Hm2 of the outer intermediate layer, and the Shore D hardness Hc of the cover is smaller than the hardness Hm1,
A golf ball having a thickness T2 of the outer intermediate layer of 0.5 mm to 1.6 mm.   2. The golf ball according to claim 1, wherein the core has a JIS-C hardness H (0.0) of 40 or more and 70 or less and a surface hardness Hs of the core of 78 or more and 96 or less.   The golf according to claim 1 or 2, wherein a difference (Hs-H (0.0)) between a surface hardness Hs of the core and a JIS-C hardness H (0.0) of a center point of the core is 15 or more. ball.   The golf ball according to any one of claims 1 to 3, wherein a difference (Hm1-Hm2) between the hardness Hm1 and the hardness Hm2 is 8 or more.   The golf ball according to claim 1, wherein a difference (Hm1−Hc) between the hardness Hm1 and the hardness Hc is 30 or more.   The sum (T1 + T2) of the thickness T1 of the inner intermediate layer and the thickness T2 is 1.0 mm or more and 3.0 mm or less, and the thickness Tc of the cover is 0.8 mm or less. The golf ball described in 1. The core is obtained by crosslinking the rubber composition,
The rubber composition is
(A) base rubber,
(B) a co-crosslinking agent,
(C) contains a crosslinking initiator and (d) an acid and / or salt,
The co-crosslinking agent (b) is
(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. The golf ball according to claim 1. The acid and / or salt (d) is
(D1) The golf ball according to claim 7, which is a carboxylic acid and / or a salt thereof.   The golf ball according to claim 8, wherein the carboxylic acid component of the carboxylic acid and / or salt thereof (d1) has 1 to 30 carbon atoms.   The golf ball according to claim 8 or 9, wherein the carboxylic acid and / or salt (d1) thereof is a fatty acid and / or a salt thereof.   The golf ball according to claim 8, wherein the carboxylic acid and / or salt (d1) thereof is a zinc salt of carboxylic acid.   The carboxylic acid and / or salt (d1) thereof is one or more selected from the group consisting of zinc octoate, zinc laurate, zinc myristate and zinc stearate. The golf ball described.   The rubber composition according to any one of claims 7 to 12, wherein the rubber composition contains 100 parts by mass of the base rubber (a) and 1.0 part by mass or more and 40 parts by mass or less of the acid and / or salt (d). The golf ball described. The rubber composition contains the α, β-unsaturated carboxylic acid (b1), and the rubber composition contains
The golf ball according to claim 7, further comprising (e) a metal compound.   The golf ball according to claim 7, wherein the rubber composition includes 100 parts by mass of the base rubber (a) and 15 to 50 parts by mass of the co-crosslinking agent (b). .   The rubber composition according to any one of claims 7 to 15, wherein the rubber composition contains 100 parts by mass of the base rubber (a) and 0.2 to 5 parts by mass of the crosslinking initiator (c). Golf ball.   The golf ball according to claim 7, wherein the rubber composition contains a metal salt (b2) of the α, β-unsaturated carboxylic acid.   The outer intermediate layer is made of a resin composition, the cover is made of another resin composition, the main component of the base resin of the resin composition of the outer intermediate layer, and the main component of the base resin of the resin composition of the cover The golf ball according to claim 1, further comprising a reinforcing layer between the outer intermediate layer and the cover. The rubber composition is
The golf ball according to claim 7, further comprising (f) an organic sulfur compound.   The golf ball according to claim 19, wherein the organic sulfur compound (f) is a thiophenol, a diphenyl disulfide, a thionaphthol, a thiuram disulfide, or a metal salt thereof.   The golf ball according to claim 19 or 20, wherein the rubber composition contains 100 parts by mass of the base rubber (a) and 0.05 to 5 parts by mass of the organic sulfur compound (f).

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