Golf ball

Abstract

To provide a golf ball having excellent impact durability and excellent flight distance performance.SOLUTION: The present disclosure provides a golf ball comprising a constituent member, wherein at least one part of the constituent member is formed of a cured product of a rubber composition containing (a) a base rubber, (b) a co-crosslinking agent and (c) a crosslinking initiator, (a) the base rubber includes (a1) a polybutadiene synthesized by using a cobalt-based catalyst and (a2) a natural rubber, (b) the co-crosslinking agent includes an unsaturated carboxylic acid and / or a metal salt thereof, and (c) the crosslinking initiator includes an organic peroxide.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a golf ball. [Background technology]

[0002] Golf balls are typically used repeatedly. Therefore, golf balls are required to have durability against impact. As a method for improving the durability of golf balls against impact, it has been proposed to compound a specific natural rubber into the rubber composition.

[0003] For example, Patent Document 1 describes a golf ball for use at a driving range obtained from a composition containing 3 to 35 parts by weight of 10 to 60 mol % epoxidized natural rubber, 20 to 35 parts by weight of methacrylic acid, and 20 to 50 parts by weight of zinc oxide, relative to 100 parts by weight of base rubber (see Patent Document 2 (Claim 1, page 2, lower left column, line 4 to lower right column, line 2)).

[0004] Furthermore, since golf balls are required to have a high flying distance, golf balls with improved core resilience have been proposed. For example, Patent Documents 2 and 3 disclose golf balls in which the rubber base material of the rubber composition forming the constituent elements of the golf ball has 60% by weight or more of cis-1,4-bonds and a Mooney viscosity (ML 1+4 It is disclosed that polybutadiene synthesized using a Group VIII catalyst and / or a rare earth element catalyst having a modulus of reactivity (100°C) of 50 to 120 is used (see Patent Document 2 (paragraph 0010, Tables 1 and 2) and Patent Document 3 (paragraph 0010, Tables 1 and 2)). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 61-71069 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-180716 [Patent Document 3] Japanese Patent Application Laid-Open No. 2004-180720 Summary of the Invention [Problem to be solved by the invention]

[0006] By blending natural rubber into the rubber composition that constitutes a golf ball, the impact durability of the golf ball can be improved, but there is a problem in that the flight distance performance is reduced. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a golf ball that is excellent in durability against impact and also in distance performance. [Means for solving the problem]

[0007] The golf ball of the present invention, which has been able to solve the above-mentioned problems, has at least a portion of its components formed from a cured product of a rubber composition containing (a) a base rubber, (b) a co-crosslinking agent, and (c) a crosslinking initiator, wherein the (a) base rubber contains (a1) polybutadiene synthesized using a cobalt-based catalyst and (a2) natural rubber, the (b) co-crosslinking agent contains an unsaturated carboxylic acid and / or a metal salt thereof, and the (c) crosslinking initiator contains an organic peroxide.

[0008] By incorporating (a2) natural rubber as the base rubber of the rubber composition that forms the constituent parts of a golf ball, the impact durability of the golf ball can be improved. Also, while incorporating (a2) natural rubber tends to reduce the flight distance performance, by incorporating (a1) polybutadiene synthesized using a cobalt-based catalyst into the base rubber, this reduction in flight distance performance can be prevented. [Effects of the Invention]

[0009] According to the present invention, a golf ball having excellent durability against impact and excellent distance performance can be obtained. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a partially cutaway cross-sectional view showing a one-piece golf ball according to one embodiment of the present invention. [Figure 2] 1 is a partially cutaway cross-sectional view showing a multi-piece golf ball according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] The golf ball of the present invention is characterized in that at least some of its components are formed from a cured product of a rubber composition containing (a) a base rubber, (b) a co-crosslinking agent, and (c) a crosslinking initiator, wherein the (a) base rubber contains (a1) polybutadiene synthesized using a cobalt-based catalyst and (a2) natural rubber, the (b) co-crosslinking agent contains an unsaturated carboxylic acid and / or a metal salt thereof, and the (c) crosslinking initiator contains an organic peroxide.

[0012] By incorporating (a2) natural rubber as the base rubber of the rubber composition forming the constituent members of a golf ball, the impact durability of the golf ball can be improved. Furthermore, while incorporating (a2) natural rubber tends to reduce flight distance performance, incorporating (a1) polybutadiene synthesized using a cobalt-based catalyst into the base rubber can prevent this reduction in flight distance performance. Therefore, the golf ball of the present invention is a golf ball that has excellent impact durability and also excellent flight distance performance.

[0013] (a) Base rubber The (a) base rubber contains (a1) polybutadiene synthesized using a cobalt-based catalyst and (a2) natural rubber.

[0014] (a1) Polybutadiene synthesized using a cobalt-based catalyst The polybutadiene (a1) synthesized using a cobalt-based catalyst can be synthesized by polymerizing 1,3-butadiene in the presence of a cobalt-based catalyst. The polybutadiene (a1) synthesized using a cobalt-based catalyst may be used alone or in combination of two or more.

[0015] Examples of the cobalt-based catalyst include cobalt salts such as cobalt chloride, cobalt bromide, cobalt nitrate, cobalt octylate (ethylhexanoate), cobalt naphthenate, cobalt acetate, and cobalt malonate; organic base complexes or ethyl alcohol complexes such as cobalt bisacetylacetonate, cobalt trisacetylacetonate, cobalt acetoethyl ester, and pyridine complexes and picoline complexes of cobalt salts.

[0016] The method for polymerizing butadiene is not particularly limited, and examples thereof include bulk polymerization in which a monomer is polymerized using a conjugated diene compound monomer such as 1,3-butadiene as a polymerization solvent, and solution polymerization in which a monomer is polymerized in a state of being dissolved in a solvent.

[0017] The content of cis-1,4 structure in the polybutadiene synthesized using the (a1) cobalt-based catalyst is preferably 90% by mass or more, more preferably 93% by mass or more, and even more preferably 96% by mass or more, and is preferably 99% by mass or less, more preferably 98.5% by mass or less, and even more preferably 98% by mass or less. If the content of cis-1,4 structure is 90% by mass or more, the resilience of the cured product of the rubber composition is further improved, and if it is 99% by mass or less, the processability of the rubber composition is good.

[0018] The content of trans-1,4 structure in the polybutadiene synthesized using the (a1) cobalt-based catalyst is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more, and is preferably 10% by mass or less, more preferably 7% by mass or less, and even more preferably 3% by mass or less. If the content of trans-1,4 structure is 0.1% by mass or more, the processability of the rubber composition is good, and if it is 10% by mass or less, the resilience of the cured product of the rubber composition is further improved.

[0019] The content of 1,2-vinyl structures in the polybutadiene synthesized using the (a1) cobalt-based catalyst is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more, and is preferably 10% by mass or less, more preferably 7% by mass or less, and even more preferably 3% by mass or less. If the content of 1,2-vinyl structures is 0.1% by mass or more, the processability of the rubber composition is improved, and if it is 10% by mass or less, the resilience of the cured product of the rubber composition is further improved.

[0020] The Mooney viscosity (ML) of the polybutadiene synthesized using the (a1) cobalt-based catalyst 1+4 (100°C)) is preferably 20 or more, more preferably 25 or more, and even more preferably 30 or more, and is preferably 70 or less, more preferably 65 or less, and even more preferably 60 or less. The Mooney viscosity (ML 1+4 If the temperature (100°C) is within the above range, the processability of the rubber composition will be good. In this specification, Mooney viscosity (ML 1+4 (100°C)) is a value measured in accordance with JIS K6300 (2013) using an L rotor, with a preheating time of 1 minute, rotor rotation time of 4 minutes, and at 100°C.

[0021] The viscosity (25°C) of a 5% by mass toluene solution of the polybutadiene synthesized using the (a1) cobalt-based catalyst is preferably 50 cps or more, more preferably 60 cps or more, and even more preferably 70 cps or more, and is preferably 160 cps or less, more preferably 140 cps or less, and even more preferably 120 cps or less. If the viscosity (25°C) of a 5% by mass toluene solution of the polybutadiene synthesized using the (a1) cobalt-based catalyst is within the above range, the processability of the rubber composition will be good. The viscosity of the 5% by mass toluene solution (25°C) was measured at 25°C using a Cannon-Fenske viscometer No. 400 after dissolving 2.28 g of polybutadiene in 50 ml of toluene. The standard solution used was a standard solution for calibrating viscometers (JIS Z8809).

[0022] The content of (a1) polybutadiene synthesized using a cobalt-based catalyst in 100% by mass of the (a) base rubber is preferably at least 35% by mass, more preferably at least 38% by mass, and even more preferably at least 40% by mass, and is preferably at most 75% by mass, more preferably at most 73% by mass, and even more preferably at most 70% by mass. If the content is within the above range, the cured product of the rubber composition will have improved resilience and impact durability.

[0023] (a2) Natural rubber The (a2) natural rubber is produced by wounding a plant that produces natural rubber latex (milky liquid), recovering the latex, and coagulating the rubber component contained in the latex. The (a2) natural rubber may be used alone or in combination of two or more types.

[0024] Examples of the plants that produce (a2) natural rubber latex include Hevea brasiliensis and Hevea brasiliensis of the Euphorbiaceae family, Rubber tree, Hevea brasiliensis, and Hevea lagos of the Moraceae family, Gum arabicum and Tragacanth of the Fabaceae family, Curculionidae, Zanzibar vine, Huntsumia elastica, and Urceola of the Asteraceae family, Guayule and rubber dandelion, Gutta-percha, Balata and Sapodilla of the Sapotaceae family, Morning glory of the Asclepiadaceae family, and Eucommia of the Eucommiaaceae family.

[0025] The (a2) natural rubber includes CV grades in which the rubber viscosity is stabilized by adding a viscosity stabilizer or the like to the raw latex, and non-CV grades in which the rubber viscosity is not stabilized. These may be used alone or in combination of two or more. Among these, CV grades, which have particularly stable viscosity, are preferred. The natural rubber may be any of STR (standard Thai rubber), SMR (standard Malaysian rubber), and SVR (standard Vietnamese rubber).

[0026] The (a2) natural rubber is cis-1,4-polyisoprene, and either sheet rubber or block rubber can be used. Natural rubber also includes modified natural rubbers, such as epoxidized natural rubber, methacrylic acid-modified natural rubber, halogen-modified natural rubber, deproteinized natural rubber, maleic acid-modified natural rubber, sulfonic acid-modified natural rubber, and styrene-modified natural rubber. Among these, it is preferable that the natural rubber does not contain epoxidized natural rubber.

[0027] The (a2) natural rubber is preferably Technical Specified Rubbers (TSR) or Ribbed Smoked Sheet (RSS), and may contain a viscosity stabilizer.

[0028] The (a2) Mooney viscosity of natural rubber (ML 1+4 (100°C)) is preferably 30 or more, more preferably 35 or more, and even more preferably 40 or more, and is preferably 90 or less, more preferably 80 or less, and even more preferably 75 or less. The (a2) Mooney viscosity of natural rubber (ML 1+4 If the temperature (100°C) is within the above range, the processability of the rubber composition will be good.

[0029] The content of the (a2) natural rubber in 100% by mass of the (a) base rubber is preferably 15% by mass or more, more preferably 18% by mass or more, and even more preferably 20% by mass or more, and is preferably 55% by mass or less, more preferably 53% by mass or less, and even more preferably 50% by mass or less. If the content is 15% by mass or more, the impact durability of the cured product of the rubber composition will be improved, and if it is 55% by mass or less, the flight distance of the golf ball will be greater.

[0030] The mass ratio ((a1) / (a2)) of the (a1) polybutadiene synthesized using a cobalt-based catalyst to the (a2) natural rubber in the (a) base rubber is preferably 40 / 60 or greater, more preferably 50 / 50 or greater, and even more preferably 55 / 45 or greater, and is preferably 80 / 20 or less, more preferably 75 / 25 or less, and even more preferably 70 / 30 or less. If the mass ratio ((a1) / (a2)) is within the above range, the golf ball can achieve a high balance between good distance performance and durability upon impact.

[0031] (Other rubber components) The (a) base rubber may contain (a1) polybutadiene synthesized using a cobalt-based catalyst and (a2) rubber components other than natural rubber. When the (a) base rubber contains other rubber components, the total content of the (a1) polybutadiene synthesized using a cobalt-based catalyst and the (a1) natural rubber in 100% by mass of the (a) base rubber is preferably 75% by mass or more, more preferably 80% by mass or more, and even more preferably 85% by mass or more.

[0032] Examples of the other rubber component include diene rubbers such as polybutadiene rubber (BR) synthesized using a catalyst other than a cobalt-based catalyst (e.g., polybutadiene rubber synthesized using a nickel-based catalyst, polybutadiene rubber synthesized using a neodymium-based catalyst), polyisoprene rubber (IR), styrene polybutadiene rubber (SBR), chloroprene rubber (CR), butyl rubber (IIR), and acrylonitrile butadiene rubber (NBR); and non-diene rubbers such as ethylene propylene rubber (EPM), ethylene-propylene-diene rubber (EPDM), urethane rubber, silicone rubber, acrylic rubber, epichlorohydrin rubber, polysulfide rubber, fluororubber, and chlorosulfonated polyethylene rubber. These may be used alone or in combination of two or more.

[0033] ((b) Co-crosslinking agent) The (b) co-crosslinking agent has the effect of crosslinking rubber molecules by graft polymerizing with the base rubber molecular chains. The rubber composition contains an unsaturated carboxylic acid and / or a metal salt thereof as a co-crosslinking agent (b). The unsaturated carboxylic acid and / or a metal salt thereof may be used alone or in combination of two or more kinds.

[0034] Examples of the unsaturated carboxylic acid include acrylic acid, methacrylic acid, fumaric acid, maleic acid, and crotonic acid.

[0035] Examples of metals constituting the metal salt of unsaturated carboxylic acid include monovalent metal ions such as sodium, potassium, and lithium; divalent metal ions such as magnesium, calcium, zinc, barium, and cadmium; trivalent metal ions such as aluminum; and other ions such as tin and zirconium. The metal components can be used alone or as a mixture of two or more. Among these, divalent metals such as magnesium, calcium, zinc, barium, and cadmium are preferred as the metal component.

[0036] The unsaturated carboxylic acid and / or metal salt thereof is preferably an α,β-unsaturated carboxylic acid and / or metal salt thereof having 3 to 8 carbon atoms. The α,β-unsaturated carboxylic acid preferably has 3 to 8 carbon atoms, more preferably 3 to 6 carbon atoms, and even more preferably 3 or 4 carbon atoms.

[0037] The (b) co-crosslinking agent preferably contains methacrylic acid and / or a metal salt thereof. By containing methacrylic acid and / or a metal salt thereof as the (b) co-crosslinking agent, the hardness and resilience of the golf ball can be improved.

[0038] The content of the (b) co-crosslinking agent is preferably 15 parts by mass or more, more preferably 18 parts by mass or more, and even more preferably 20 parts by mass or more, per 100 parts by mass of the (a) base rubber, and is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, even more preferably 60 parts by mass or less, and particularly preferably 40 parts by mass or less. When the content of the (b) co-crosslinking agent is 15 parts by mass or more, a small amount of the (c) crosslinking initiator can be used to impart an appropriate hardness to a member formed from the rubber composition. Furthermore, when the content of the (b) co-crosslinking agent is 100 parts by mass or less, the member formed from the rubber composition does not become too hard, improving the shot feel of the golf ball.

[0039] ((c) Crosslinking initiator) The (c) crosslinking initiator is blended to crosslink the (a) base rubber component. An organic peroxide is suitable as the (c) crosslinking initiator. Specific examples of the organic peroxide include dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and di-t-butyl peroxide. These organic peroxides may be used alone or in combination of two or more. Among these, dicumyl peroxide is preferably used.

[0040] The content of the (c) crosslinking initiator is preferably 0.2 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 0.7 parts by mass or more, and is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, and even more preferably 3.0 parts by mass or less, per 100 parts by mass of the (a) base rubber. If the content of the (c) crosslinking initiator is 0.2 parts by mass or more, the crosslinked rubber molded article formed from the rubber composition will not be too soft and will have a good shot feeling, and if it is 5.0 parts by mass or less, the crosslinked rubber molded article formed from the rubber composition will have an appropriate hardness.

[0041] ((d)Organic sulfur compound) The rubber composition may further contain (d) an organic sulfur compound. When the rubber composition contains (d) an organic sulfur compound, the resilience performance of the golf ball can be further improved.

[0042] The (d) organic sulfur compound may be, for example, at least one compound selected from the group consisting of thiophenols, thionaphthols, polysulfides, thiurams, thiocarboxylic acids, dithiocarboxylic acids, sulfenamides, dithiocarbamates, thiazoles, and metal salts thereof. The (d) organic sulfur compound may be used alone or in combination of two or more. The (d) organic sulfur compound is preferably an organic sulfur compound having a thiol group (-SH) or a metal salt thereof, and more preferably a thiophenol, a thionaphthol, or a metal salt thereof.

[0043] Examples of the thiophenols include thiophenol, thiophenol substituted with a halogen group, and metal salts thereof. Examples of the thiophenol substituted with a halogen group include thiophenols substituted with a fluoro group, such as 4-fluorothiophenol, 2,5-difluorothiophenol, 2,6-difluorothiophenol, 2,4,5-trifluorothiophenol, 2,4,5,6-tetrafluorothiophenol, and pentafluorothiophenol; 2-chlorothiophenol, 4-chlorothiophenol, 2,4-dichlorothiophenol, 2,5-dichlorothiophenol, 2,6-dichlorothiophenol, 2,4,5-trichlorothiophenol, 2,4,5,6-tetrachlorothiophenol, and pentachlorothiophenol. thiophenols substituted with a chloro group such as 4-bromothiophenol, 2,5-dibromothiophenol, 2,6-dibromothiophenol, 2,4,5-tribromothiophenol, 2,4,5,6-tetrabromothiophenol, and pentabromothiophenol; thiophenols substituted with an iodo group such as 4-iodothiophenol, 2,5-diiodothiophenol, 2,6-diiodothiophenol, 2,4,5-triiodothiophenol, 2,4,5,6-tetraiodothiophenol, and pentaiodothiophenol; or metal salts thereof. Zinc salts are preferred as the metal salt.

[0044] Examples of the thionaphthols (naphthalene thiols) include 2-thionaphthol, 1-thionaphthol, 1-chloro-2-thionaphthol, 2-chloro-1-thionaphthol, 1-bromo-2-thionaphthol, 2-bromo-1-thionaphthol, 1-fluoro-2-thionaphthol, 2-fluoro-1-thionaphthol, 1-cyano-2-thionaphthol, 2-cyano-1-thionaphthol, 1-acetyl-2-thionaphthol, 2-acetyl-1-thionaphthol, and metal salts thereof, with 2-thionaphthol and 1-thionaphthol being preferred. The metal salt is preferably a divalent metal salt, more preferably a zinc salt. Specific examples of the metal salt include the zinc salt of 1-thionaphthol and the zinc salt of 2-thionaphthol.

[0045] The polysulfides are organic sulfur compounds having polysulfide bonds, such as disulfides, trisulfides, and tetrasulfides. Diphenyl polysulfides are preferred as the polysulfides.

[0046] Examples of the diphenyl polysulfides include, in addition to diphenyl disulfide, bis(4-fluorophenyl) disulfide, bis(2,5-difluorophenyl) disulfide, bis(2,6-difluorophenyl) disulfide, bis(2,4,5-trifluorophenyl) disulfide, bis(2,4,5,6-tetrafluorophenyl) disulfide, bis(pentafluorophenyl) disulfide, bis(4-chlorophenyl) disulfide, Bis(2,5-dichlorophenyl) disulfide, bis(2,6-dichlorophenyl) disulfide, bis(2,4,5-trichlorophenyl) disulfide, bis(2,4,5,6-tetrachlorophenyl) disulfide, bis(pentachlorophenyl) disulfide, bis(4-bromophenyl) disulfide, bis(2,5-dibromophenyl) disulfide, bis(2,6-dibromophenyl) disulfide, bis(2,4,5-tribromo phenyl) disulfide, bis(2,4,5,6-tetrabromophenyl) disulfide, bis(pentabromophenyl) disulfide, bis(4-iodophenyl) disulfide, bis(2,5-diiodophenyl) disulfide, bis(2,6-diiodophenyl) disulfide, bis(2,4,5-triiodophenyl) disulfide, bis(2,4,5,6-tetraiodophenyl) disulfide, bis(pentaiodophenyl) disulfide diphenyl disulfides substituted with a halogen group such as bis(4-methylphenyl) disulfide, bis(2,4,5-trimethylphenyl) disulfide, bis(pentamethylphenyl) disulfide, bis(4-t-butylphenyl) disulfide, bis(2,4,5-tri-t-butylphenyl) disulfide, bis(penta-t-butylphenyl) disulfide, and the like; and diphenyl disulfides substituted with an alkyl group such as bis(4-methylphenyl) disulfide, bis(2,4,5-tri-t-butylphenyl) disulfide, bis(penta-t-butylphenyl) disulfide.

[0047] Examples of the thiurams include thiuram monosulfides such as tetramethylthiuram monosulfide, thiuram disulfides such as tetramethylthiuram disulfide, tetraethylthiuram disulfide, and tetrabutylthiuram disulfide, and thiuram tetrasulfides such as dipentamethylenethiuram tetrasulfide. Examples of thiocarboxylic acids include naphthalene thiocarboxylic acid. Examples of dithiocarboxylic acids include naphthalene dithiocarboxylic acid. Examples of sulfenamides include N-cyclohexyl-2-benzothiazole sulfenamide, N-oxydiethylene-2-benzothiazole sulfenamide, and Nt-butyl-2-benzothiazole sulfenamide.

[0048] Examples of the thiazoles include 2-mercaptobenzothiazole and its metal salts, 2-(4-morpholinodithio)benzothiazole, etc. Examples of the metal salts of 2-mercaptobenzothiazole include the zinc salt of 2-mercaptobenzothiazole and the cyclohexylamine salt of 2-mercaptobenzothiazole.

[0049] The (d) organic sulfur compound is preferably a thiophenol and / or a metal salt thereof, a thionaphthol and / or a metal salt thereof, a diphenyl disulfide, a thiuram disulfide, or a thiazole and / or a metal salt thereof, more preferably 2,4-dichlorothiophenol, 2,6-difluorothiophenol, 2,6-dichlorothiophenol, 2,6-dibromothiophenol, 2,6-diiodothiophenol, 2,4,5-trichlorothiophenol, pentachlorothiophenol, 2-mercaptobenzothiazole, or a metal salt thereof.

[0050] The amount of the (d) sulfur compound in the rubber composition is preferably at least 0.01 part by weight, more preferably at least 0.1 part by weight, and even more preferably at least 0.2 part by weight, per 100 parts by weight of the (a) base rubber, and is preferably at most 20 parts by weight, more preferably at most 15 parts by weight, even more preferably at most 10 parts by weight, and particularly preferably at most 5 parts by weight. If the (d) sulfur compound is at least 0.01 part by weight, the resilience is further improved, and if it is at most 20 parts by weight, the hardness of the golf ball is further improved.

[0051] ((e) Metal compounds) The rubber composition may further contain (e) a metal compound. By containing the (e) metal compound, metal crosslinks can be formed in the unsaturated carboxylic acid blended as (b) a co-crosslinking agent.

[0052] The (e) metal compound is not particularly limited as long as it can neutralize the unsaturated carboxylic acid in the rubber composition. Examples of the (e) metal compound include metal hydroxides such as magnesium hydroxide, zinc hydroxide, calcium hydroxide, sodium hydroxide, lithium hydroxide, potassium hydroxide, and copper hydroxide; metal oxides (excluding titanium oxide) such as magnesium oxide, calcium oxide, zinc oxide, and copper oxide; and metal carbonates such as magnesium carbonate, zinc carbonate, sodium carbonate, lithium carbonate, and potassium carbonate. Divalent metal compounds are preferred as the (e) metal compound, and zinc compounds are more preferred. Divalent metal compounds react with unsaturated carboxylic acids to form metal crosslinks. Furthermore, the use of zinc compounds improves the hardness of golf balls. (e) metal compounds may be used alone or in combination.

[0053] The content of the (e) metal compound is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 20 parts by mass or more, per 100 parts by mass of the (b) co-crosslinking agent, and is preferably 100 parts by mass or less, more preferably 90 parts by mass or less, even more preferably 80 parts by mass or less, particularly preferably 70 parts by mass or less, and most preferably 30 parts by mass or less. If the content of the (e) metal compound is within the above range, the appropriate weight for a golf ball can be maintained.

[0054] (Other ingredients) The rubber composition may contain additives such as pigments, fillers for adjusting the weight, antioxidants, peptizers, softeners, carboxylic acids, etc., as needed. The rubber composition may also contain rubber powder obtained by pulverizing the core of a golf ball or scraps generated during the production of the core.

[0055] Examples of pigments that can be compounded into the rubber composition include white pigments, blue pigments, and purple pigments. Titanium oxide is preferably used as the white pigment. The type of titanium oxide is not particularly limited, but rutile-type titanium oxide is preferably used because of its good hiding power. The content of titanium oxide is preferably 0.5 parts by mass or more, more preferably 0.7 parts by mass or more, and even more preferably 0.9 parts by mass or more, per 100 parts by mass of (a) base rubber, and is preferably 8 parts by mass or less, more preferably 6 parts by mass or less, and even more preferably 4 parts by mass or less.

[0056] In another preferred embodiment, the rubber composition contains a white pigment and a blue pigment. The blue pigment is blended to make the white color appear more vivid, and examples of the blue pigment include ultramarine, cobalt blue, and phthalocyanine blue. Examples of the purple pigment include anthraquinone violet, dioxazine violet, and methyl violet.

[0057] The filler used in the rubber composition is blended as a weight adjuster to adjust the mass of the resulting crosslinked rubber molded product, and may be blended as needed. Examples of the filler include inorganic fillers such as calcium carbonate, barium sulfate, tungsten powder, and molybdenum powder.

[0058] The content of the antioxidant is preferably 0.1 part by weight to 1 part by weight per 100 parts by weight of the (a) base rubber, and the content of the peptizing agent is preferably 0.1 part by weight to 5 parts by weight per 100 parts by weight of the (a) base rubber.

[0059] (Preparation of Rubber Composition) The rubber composition is obtained by mixing and kneading (a) a base rubber, (b) a co-crosslinking agent, (c) a crosslinking initiator, and, if necessary, other additives, etc. The kneading method is not particularly limited, and may be carried out using a known kneading machine such as a kneading roll, a Banbury mixer, or a kneader.

[0060] (Cured product of rubber composition) The cured product of the rubber composition can be obtained by heat-molding the kneaded rubber composition in a mold. The molding temperature is preferably 120°C or higher, more preferably 150°C or higher, and preferably 250°C or lower, more preferably 200°C or lower. The molding pressure is preferably 2.9MPa or higher, more preferably 5.0MPa or higher, and preferably 25MPa or lower, more preferably 11.8MPa or lower. The molding time is preferably 10 to 60 minutes.

[0061] [Golf balls] The golf ball of the present invention has components at least partially formed from the cured product of the rubber composition. Examples of the golf ball include a one-piece golf ball in which the golf ball body is formed from the cured product of the rubber composition, and a multi-piece golf ball having a spherical core and at least one layer of cover enclosing the spherical core, at least a portion of the spherical core being formed from the cured product of the rubber composition.

[0062] (One-piece golf ball) The one-piece golf ball may be a one-piece golf ball consisting of only a golf ball body; or a one-piece golf ball consisting of a golf ball body and a coating film covering the golf ball body.

[0063] The diameter of the one-piece golf ball is preferably 40 mm to 45 mm. From the viewpoint of satisfying the United States Golf Association (USGA) standards, a diameter of 42.67 mm or more is particularly preferred. From the viewpoint of suppressing air resistance, a diameter of 44 mm or less is more preferred, and 42.80 mm or less is particularly preferred. The mass of the one-piece golf ball is preferably 40 g to 50 g. From the viewpoint of obtaining large inertia, a mass of 44 g or more is more preferred, and 45.00 g or more is particularly preferred. From the viewpoint of satisfying the USGA standards, a mass of 45.93 g or less is particularly preferred.

[0064] When the one-piece golf ball has a diameter of 40 mm to 45 mm, the compressive deformation (amount of shrinkage in the compressive direction) when an initial load of 98 N is applied and a final load of 1275 N is applied is preferably 2.0 mm or more, more preferably 2.2 mm or more, and even more preferably 2.4 mm or more, and is preferably 6.0 mm or less, more preferably 5.5 mm or less, and even more preferably 5.0 mm or less. If the compressive deformation is within the above range, the golf ball will have a better shot feel.

[0065] When the one-piece golf ball has a diameter of 40 mm to 45 mm, the coefficient of restitution (e40) is preferably 0.500 or more, more preferably 0.520 or more, and even more preferably 0.550 or more, and is preferably 0.800 or less, more preferably 0.780 or less, and even more preferably 0.750 or less. The method for measuring the coefficient of restitution (e40) will be described later.

[0066] The one-piece golf ball body preferably has a center hardness (H0) of 60.0 or more, more preferably 62.0 or more, and even more preferably 64.0 or more, in Shore C hardness, and preferably has a center hardness (H0) of 74.0 or less, more preferably 72.0 or less, and even more preferably 70.0 or less. A center hardness (H0) within the above range provides a good shot feel.

[0067] The surface hardness (Hs) of the one-piece golf ball body is preferably 75.0 or more, more preferably 76.0 or more, and even more preferably 77.7 or more, in Shore C hardness, and is preferably 85.0 or less, more preferably 84.0 or less, and even more preferably 83.0 or less. If the surface hardness (Hs) is within the above range, the shot feel is good.

[0068] The hardness difference (Hs-H0) between the center hardness (H0) and surface hardness (Hs) of the one-piece golf ball body is preferably 10.0 or more, more preferably 11.0 or more, and even more preferably 12.0 or more, in Shore C hardness, and is preferably 20.0 or less, more preferably 19.0 or less, and even more preferably 18.0 or less. If the hardness difference (Hs-H0) is within the above range, the amount of spin upon impact increases, resulting in good controllability on iron shots.

[0069] The golf ball body of the one-piece golf ball typically has depressions called dimples formed on its surface. The total number of dimples is preferably 200 to 500. If the total number of dimples is 200 or more, the effect of the dimples will be greater, while if the total number is 500 or less, the size of each dimple will be larger, resulting in a greater effect. The shape (shape in plan view) of the dimples formed is not particularly limited, and the following may be used alone or in combination: circular; polygonal such as approximately triangular, approximately rectangular, approximately pentagonal, or approximately hexagonal; or other irregular shapes.

[0070] The golf ball body of the one-piece golf ball can be produced by heat-molding the rubber composition in a mold. The molding temperature is preferably 120°C or higher, more preferably 140°C or higher, and even more preferably 160°C or higher, and preferably 200°C or lower. The molding pressure is preferably 5 MPa to 25 MPa. The molding time is preferably 10 to 60 minutes.

[0071] The one-piece golf ball may have a coating or markings formed on the surface of the golf ball body. The coating thickness is not particularly limited, but is preferably 5 μm or more, more preferably 6 μm or more, even more preferably 8 μm or more, and preferably 50 μm or less, more preferably 40 μm or less, and even more preferably 30 μm or less. A coating thickness of 5 μm or more makes the coating less susceptible to wear and wear even with continued use, while a coating thickness of 50 μm or less prevents the effect of the dimples from being reduced and improves the flight performance of the golf ball.

[0072] (Multi-piece golf ball) The multi-piece golf ball is a golf ball having a spherical core and at least one layer of cover enclosing the spherical core, and at least a portion of the spherical core is formed from a cured product of the rubber composition.

[0073] The spherical core may have either a single-layer structure or a multi-layer structure, including a single-layer core formed from a cured product of the rubber composition, a two-layer core having an inner layer and an outer layer, and the inner layer and / or the outer layer being formed from a cured product of the rubber composition, and the like.

[0074] The diameter of the spherical core is preferably 34.8 mm or more, and 42.2 mm or less, more preferably 41.8 mm or less, even more preferably 41.2 mm or less, and particularly preferably 40.8 mm or less. If the diameter of the spherical core is 34.8 mm or more, the cover will not be too thick, resulting in better durability against impact. On the other hand, if the diameter of the spherical core is 42.2 mm or less, the cover will not be too thin, resulting in better performance of the cover.

[0075] When the core has a diameter of 34.8 mm to 42.2 mm, the amount of compressive deformation (the amount the core shrinks in the compressive direction) from an initial load of 98 N to a final load of 1275 N is preferably 2.0 mm or more, more preferably 2.3 mm or more, and even more preferably 2.5 mm or more, and is preferably 5.0 mm or less, more preferably 4.5 mm or less, and even more preferably 4.3 mm or less. If the amount of compressive deformation is within the above range, the shot feel will be better.

[0076] The spherical core can be produced by mixing and kneading the rubber composition and molding it in a mold. The conditions for this process are not particularly limited, but the process is usually carried out at 130°C to 200°C, under a pressure of 5 MPa to 25 MPa, for 10 to 60 minutes.

[0077] The cover of the golf ball is formed from a cover composition containing a resin component, such as an ionomer resin, a thermoplastic polyurethane elastomer commercially available from BASF Japan Ltd. under the trade name "Elastollan (registered trademark)," a thermoplastic polyamide elastomer commercially available from Arkema K.K. under the trade name "Pebax (registered trademark)," a thermoplastic polyester elastomer commercially available from DuPont-Toray Co., Ltd. under the trade name "Hytrel (registered trademark)," or a thermoplastic styrene elastomer commercially available from Mitsubishi Chemical Corporation under the trade name "TEFABLOC."

[0078] In addition to the resin components described above, the cover composition may contain pigment components such as white pigments (e.g., titanium oxide), blue pigments, and red pigments, weight adjusters such as zinc oxide, calcium carbonate, and barium sulfate, dispersants, antioxidants, ultraviolet absorbers, light stabilizers, fluorescent materials, or fluorescent brighteners, to the extent that the performance of the cover is not impaired.

[0079] Examples of methods for molding the cover of the golf ball include a method in which a hollow shell is molded from a cover composition, the core is coated with multiple shells, and the resulting mixture is compression molded (preferably a method in which a hollow half shell is molded from a cover composition, the core is coated with two half shells, and the resulting mixture is compression molded), or a method in which the cover composition is directly injection molded onto the core.

[0080] The thickness of the cover is preferably 4.0 mm or less, more preferably 3.0 mm or less, and even more preferably 2.0 mm or less. If the cover thickness is 4.0 mm or less, the shot feel of the resulting golf ball will be better. The thickness of the cover is preferably 0.3 mm or more, more preferably 0.4 mm or more, and even more preferably 0.5 mm or more. If the cover thickness is 0.3 mm or more, the durability and abrasion resistance of the cover will be better. If the cover has multiple layers, the total thickness of the multiple cover layers preferably falls within the above range.

[0081] When molding a cover, depressions called dimples are usually formed on the surface. The total number of dimples formed on the cover is preferably 200 to 500. If the total number of dimples is 200 or more, the effect of the dimples will be greater, and if the total number is 500 or less, the size of each dimple will be larger and the effect of the dimples will be greater. The shape (shape in plan view) of the formed dimples is not particularly limited, and the following may be used alone or in combination: circular; polygonal such as approximately triangular, approximately rectangular, approximately pentagonal, or approximately hexagonal; or other irregular shapes.

[0082] The golf ball body with the molded cover is preferably removed from the mold and, if necessary, subjected to surface treatments such as deburring, cleaning, and sandblasting. A coating film or markings can also be formed as desired. The coating film thickness is not particularly limited, but is preferably 5 μm or more, more preferably 6 μm or more, even more preferably 8 μm or more, and preferably 50 μm or less, more preferably 40 μm or less, and even more preferably 30 μm or less. A coating film thickness of 5 μm or more makes the coating less susceptible to wear and tear even with continued use, while a coating film thickness of 50 μm or less prevents the effect of the dimples from being reduced and improves the flight performance of the golf ball.

[0083] The diameter of the multi-piece golf ball is preferably 40 mm to 45 mm. From the viewpoint of meeting the United States Golf Association (USGA) standards, a diameter of 42.67 mm or more is particularly preferred. From the viewpoint of reducing air resistance, a diameter of 44 mm or less is more preferred, and 42.80 mm or less is particularly preferred. The weight of the golf ball is preferably 40 g or more and 50 g or less. From the viewpoint of obtaining high inertia, a weight of 44 g or more is more preferred, and 45.00 g or more is particularly preferred. From the viewpoint of meeting the USGA standards, a weight of 45.93 g or less is particularly preferred.

[0084] An example of a golf ball of the present invention will be described with reference to Figures 1 and 2. Figure 1 is a partially cutaway cross-sectional view showing a one-piece golf ball according to one embodiment of the present invention. Figure 2 is a partially cutaway cross-sectional view showing a multi-piece golf ball according to one embodiment of the present invention.

[0085] The golf ball 1 in Figure 1 is a one-piece golf ball composed of a golf ball body 2 and a paint film 3 that covers the golf ball body 2. A large number of dimples 21 are formed on the surface of the golf ball body 2. The portions of the surface of this golf ball 1 other than the dimples 21 are lands 22. This golf ball 1 has the paint film 3 formed on the outside of the golf ball body 2.

[0086] The golf ball 1 in Figure 2 has a golf ball body made up of a spherical core 4 and a cover 5 that encases the spherical core 4. A large number of dimples 51 are formed on the surface of the cover 5. The portion of the surface of the golf ball 1 other than the dimples 51 is a land 52. The golf ball 1 has a paint film 3 formed on the outside of the cover 5. [Example]

[0087] The present invention will be described in detail below with reference to examples. However, the present invention is not limited to the following examples, and all modifications and embodiments that do not deviate from the spirit of the present invention are included within the scope of the present invention.

[0088] [Evaluation method] (1) Compression deformation (mm) The amount of deformation in the compression direction (the amount the golf ball shrinks in the compression direction) was measured when an initial load of 98 N was applied to the golf ball and a final load of 1275 N was applied. The amount of compressive deformation was measured using a Yamada compression tester "SCH." In this tester, a golf ball is placed on a metal plate, and a metal cylinder is gradually lowered toward the golf ball. The golf ball, sandwiched between the bottom of the cylinder and the plate, deforms. The cylinder's travel distance was measured from when an initial load of 98 N was applied to the golf ball until a final load of 1275 N was applied. The cylinder's travel speed until the initial load was applied was 0.83 mm / s. The cylinder's travel speed from when the initial load was applied to when the final load was applied was 1.67 mm / s.

[0089] (2) Restitution coefficient A 198.4g metal cylinder was collided with each golf ball at a speed of 40m / s, the speeds of the cylinder and golf ball were measured before and after the collision, and the coefficient of restitution of each golf ball was calculated from their respective speeds and weights. Measurements were made for 12 golf balls each, and the average value was used as the coefficient of restitution of each golf ball.

[0090] (3) Flight distance A W#1 driver (Sumitomo Rubber Industries, Ltd., "XXIO (registered trademark) 12", shaft hardness: S, loft angle: 10.5 degrees) was attached to a Golf Laboratory swing machine, and the impact point was set to the face center. The golf ball was hit at a head speed of 40 m / s, and the flight distance (distance from the launch point to the stopping point) was measured. Measurements were made for 12 golf balls, and the average value was taken as the flight distance of that golf ball.

[0091] (4) Impact durability A W#1 driver (Sumitomo Rubber Industries, Ltd., "XXIO (registered trademark) 12", shaft hardness: S, loft angle: 10.5 degrees) was attached to a Golf Laboratory swing machine, and the golf balls were repeatedly hit at a head speed of 40 m / s to measure the number of hits until cracks occurred. Measurements were made on 12 golf balls each, and the average value was taken as the number of hits for that golf ball. The durability of each golf ball was expressed as an index, with the number of hits for golf ball No. 9 set at 100.

[0092] [Manufacturing one-piece golf balls] The rubber compositions having the formulation shown in Table 1 were kneaded with kneading rolls and then hot-pressed at 170° C. for 20 minutes in upper and lower molds having hemispherical cavities to obtain golf ball bodies having a diameter of 42.7 mm.

[0093] [Table 1] Polybutadiene rubber (Co): UBE Elastomers, "BR150L" (high cis-butadiene rubber synthesized using a cobalt catalyst) (cis-1,4 structure content = 98% by mass, trans-1,4 structure content = 1% by mass, 1,2-vinyl structure content = 1% by mass, Mooney viscosity (ML 1+4 (100°C) = 43, 5 mass% toluene solution viscosity: 105 cps Polybutadiene rubber (Ni): "BR01" (high cis-butadiene rubber synthesized using a nickel-based catalyst) manufactured by JSR Corporation (cis-1,4 structure content = 95% by mass, Mooney viscosity (ML 1+4 (100℃))=45) Polybutadiene rubber (Nd): "BR730" (high cis polybutadiene rubber synthesized using a neodymium catalyst) manufactured by JSR Corporation (cis-1,4 structure content = 95% by mass, Mooney viscosity (ML 1+4 (100℃))=55) Isoprene rubber: IR2200 (Mooney viscosity (ML) 1+4 (100℃))=82) Natural rubber: SRIJAROEN RUBBER CO., LTD., "STR5L" (Mooney viscosity (ML) 1+4 (100℃))=72) Zinc oxide: "Ginrei R" manufactured by Toho Zinc Co., Ltd. Methacrylic acid: Mitsubishi Chemical Corporation Pentachlorothiophenol zinc salt: Fujifilm Wako Pure Chemical Industries, Ltd. (contains 28% to 32% by mass of zinc stearate) Stearic acid: NOF Corporation Titanium oxide: Ishihara Sangyo Kaisha, Ltd., "CR-60" Dicumyl peroxide: NOF Corporation, "Percumyl (registered trademark) D"

[0094] Golf ball No. 1 is a ball having a mass ratio ((a1) / (a2)) of the (a1) polybutadiene synthesized using a cobalt-based catalyst to the (a2) natural rubber in the (a) base rubber of less than 40 / 60. Golf ball No. 1 exhibited poor distance performance.

[0095] Golf balls Nos. 2 to 5 were made in the case where the mass ratio ((a1) / (a2)) of the (a1) polybutadiene synthesized using a cobalt-based catalyst to the (a2) natural rubber in the (a) base rubber was 40 / 60 to 80 / 20. These golf balls Nos. 2 to 5 were excellent in impact durability and distance performance.

[0096] Golf ball No. 6 is a ball having a mass ratio ((a1) / (a2)) of the (a1) polybutadiene synthesized using a cobalt-based catalyst to the (a2) natural rubber in the (a) base rubber of more than 80 / 20. Golf ball No. 6 had poor impact durability.

[0097] Golf ball No. 7 is a ball having a base rubber containing (a2) natural rubber and not containing (a1) polybutadiene synthesized using a cobalt-based catalyst. Golf ball No. 7 exhibited poor distance performance.

[0098] Golf ball No. 8 is a ball in which (a) the base rubber contains only (a1) polybutadiene synthesized using a cobalt-based catalyst. Golf ball No. 8 was inferior in impact durability.

[0099] Golf ball No. 9 is a ball having (a) a base rubber containing polybutadiene synthesized using a nickel-based catalyst, polybutadiene synthesized using a neodymium-based catalyst, and isoprene rubber. This golf ball No. 9 has poor impact durability.

[0100] The present invention (1) is a golf ball characterized in that at least a portion of the components are formed from a cured product of a rubber composition containing (a) a base rubber, (b) a co-crosslinking agent, and (c) a crosslinking initiator, wherein the (a) base rubber contains (a1) polybutadiene synthesized using a cobalt-based catalyst and (a2) natural rubber, the (b) co-crosslinking agent contains an unsaturated carboxylic acid and / or a metal salt thereof, and the (c) crosslinking initiator contains an organic peroxide.

[0101] The present invention (2) is the golf ball according to the present invention (1), wherein the mass ratio ((a1) / (a2)) of the (a1) polybutadiene synthesized using a cobalt-based catalyst to the (a2) natural rubber in the (a) base rubber is 40 / 60 to 80 / 20.

[0102] The present invention (3) is the golf ball according to the present invention (1) or (2), wherein the unsaturated carboxylic acid and / or its metal salt contained in the (b) co-crosslinking agent is methacrylic acid and / or its metal salt.

[0103] The present invention (4) is the golf ball according to any one of the present inventions (1) to (3), wherein the rubber composition further contains an organic sulfur compound.

[0104] The present invention (5) is a one-piece golf ball according to any one of the present inventions (1) to (4), in which the golf ball body is formed from a cured product of the rubber composition. [Explanation of symbols]

[0105] 1: Golf ball, 2: Golf ball body, 3: Coating, 4: Spherical core, 5: Cover

Claims

1. At least a portion of the component is formed from a cured product of a rubber composition containing (a) a base rubber, (b) a co-crosslinking agent, and (c) a crosslinking initiator, the (a) base rubber contains (a1) polybutadiene synthesized using a cobalt-based catalyst and (a2) natural rubber; the (b) co-crosslinking agent contains an unsaturated carboxylic acid and / or a metal salt thereof, A golf ball characterized in that the crosslinking initiator (c) contains an organic peroxide.

2. 2. The golf ball according to claim 1, wherein the mass ratio ((a1) / (a2)) of the polybutadiene synthesized using a cobalt-based catalyst (a1) to the natural rubber (a2) in the base rubber (a) is 40 / 60 to 80 / 20.

3. 2. The golf ball according to claim 1, wherein the unsaturated carboxylic acid and / or metal salt thereof contained in the co-crosslinking agent (b) is methacrylic acid and / or metal salt thereof.

4. 2. The golf ball according to claim 1, wherein the rubber composition further contains an organic sulfur compound.

5. 2. The golf ball according to claim 1, which is a one-piece golf ball, the golf ball body being formed from a cured product of said rubber composition.

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