Golf ball

Abstract

To provide a golf ball providing a golf player with excellent flight performance and ball hitting feel in a driver shot and excellent controllability and ball hitting feel in an approach hit.SOLUTION: A golf ball 2 includes a core 4, an inner cover 6 and an outer cover 8. The golf ball 2 satisfies the following mathematical expressions (1), (2) and (3): (1) 5≤(Hi*Ti-Dc*Rc)≤40, (2) 5≤(Hi*Ti-Ho*To)≤40, and (3) -20≤(Ho*To-Dc*Rc)≤20, where Dc is an amount (mm) of compression deformation of the core 4, Rc is the radius (mm) of the core 4, Hi is Shore C hardness of the inner cover 6, Ti is the thickness (mm) of the inner cover 6, Ho is Shore C hardness of the outer cover 8, and To is the thickness (mm) of the outer cover 8.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a golf ball. More specifically, the present invention relates to a golf ball having a core, an inner cover, and an outer cover.

Background Art

[0002] A typical golf ball has a core, an inner cover, and an outer cover. The core is formed by crosslinking a rubber composition. The inner cover is formed from a resin composition. The outer cover is formed from another resin composition.

[0003] The face of a golf club has a loft angle. When a golf ball is struck with this golf club, the golf ball is launched with a launch angle corresponding to the loft angle. The golf ball further generates backspin due to the loft angle. The golf ball flies with backspin.

[0004] Improvements in the structure and materials of golf balls for the purpose of improving flight performance and the like have been variously proposed. An example of an improvement is disclosed in Japanese Patent Application Laid-Open No. 2021-74198.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] For a golf player with average skills, the head speed in a driver shot is generally low. For this player, a golf ball that deforms sufficiently even when struck with a golf club with a low head speed is suitable. The golf ball struck by this player flies with a low speed. The dependence of the flight distance of a golf ball struck at a low head speed on the flight speed is not large. The dependence of the flight distance of a golf ball struck at a low head speed on the spin speed is large. For a player with average skills, a golf ball that is difficult to spin is advantageous in terms of the flight distance in a driver shot.

[0007] Golf players also value the control performance of golf balls. This control performance correlates with the spin performance. When the speed of the backspin is high, the run is small. By using a golf ball that generates a high-speed backspin, the player can stop this golf ball at the target point. When the speed of the side spin is high, the golf ball is likely to curve. By using a golf ball with a high-speed side spin, the player can intentionally curve this golf ball. Players particularly value the control performance in approach shots.

[0008] A golf ball with a soft cover has excellent control performance in approach shots. However, this cover inhibits the resilience performance of the golf ball. In this golf ball, by adopting a thin cover, the adverse effect on the resilience performance due to the cover can be suppressed. Furthermore, in this golf ball, a high-hardness core or intermediate layer compensates for the adverse effect on the resilience performance due to the cover. However, the feel of hitting this golf ball is hard.

[0009] An object of the present invention is to provide a golf ball excellent in flight performance and feel at impact in a driver shot, and control performance and feel at impact in an approach shot.

Means for Solving the Problems

[0010] The golf ball according to the present invention has a core, an inner cover located outside the core, and an outer cover located outside the inner cover. This golf ball satisfies the following mathematical formulas (1), (2), and (3). 5 ≦ (Hi*Ti - Dc*Rc) ≦ 40 (1) 5 ≦ (Hi*Ti - Ho*To) ≦ 40 (2) -20 ≦ (Ho*To - Dc*Rc) ≦ 20 (3) Dc: Compression deformation amount of the core (mm) Rc: Radius of the core (mm) Hi: Shore C hardness of the inner cover Ti: Thickness of the inner cover (mm) Ho: Shore C hardness of the outer cover To: Thickness of the outer cover (mm)

Advantages of the Invention

[0011] In the driver shot of the golf ball according to the present invention, the hardness distribution of the spherical body including the core and the inner cover contributes to a large launch angle and a small spin speed. In the driver shot of the golf ball according to the present invention, the outer cover contributes to a soft hitting feeling. This golf ball is excellent in flight performance and hitting feeling in driver shots.

[0012] In the approach shot of this golf ball, the outer cover contributes to a large spin speed. In the approach shot of this golf ball, the outer cover contributes to a soft hitting feeling. This golf ball is excellent in control performance and hitting feeling in approach shots.

Brief Description of the Drawings

[0013]

Figure 1

Modes for Carrying Out the Invention

[0014] Hereinafter, the present invention will be described in detail based on preferred embodiments while referring to the drawings as appropriate.

[0015] The golf ball 2 shown in FIG. 1 has a spherical core 4, an inner cover 6 located outside the core 4, and an outer cover 8 located outside the inner cover 6. This golf ball 2 has a plurality of dimples 10 on its surface. The portion of the surface of the golf ball 2 other than the dimples 10 is the land 12. This golf ball 2 is provided with a paint layer and a mark layer outside the outer cover 8, but the illustration of these layers is omitted.

[0016] The diameter of this golf ball 2 is preferably 40 mm or more and 45 mm or less. From the viewpoint of satisfying the standards of the United States Golf Association (USGA), the diameter is particularly preferably 42.67 mm or more. From the viewpoint of suppressing air resistance, the diameter is more preferably 44 mm or less, and particularly preferably 42.80 mm or less.

[0017] The mass of this golf ball 2 is preferably 40 g or more and 50 g or less. From the viewpoint of obtaining a large inertia, the mass is more preferably 44 g or more, and particularly preferably 45.00 g or more. From the viewpoint of satisfying the USGA standards, the mass is particularly preferably 45.93 g or less.

[0018] The core 4 is formed by crosslinking a rubber composition. Preferred base rubbers include polybutadiene, polyisoprene, styrene-butadiene copolymer, ethylene-propylene-diene copolymer, and natural rubber. From the viewpoint of the rebound performance of the golf ball 2, polybutadiene is preferred. When polybutadiene is used in combination with other rubbers, it is preferably the main component. Specifically, the ratio of polybutadiene to all base rubbers is preferably 50% by mass or more, more preferably 70% by mass or more, and particularly preferably 80% by mass or more. Polybutadiene having a cis-1,4 bond ratio of 80% or more is particularly preferred.

[0019] The rubber composition of the core 4 preferably contains a co-crosslinking agent. From the viewpoints of the durability and resilience performance of the golf ball 2, preferred co-crosslinking agents are monovalent or divalent metal salts of α,β-unsaturated carboxylic acids having 2 to 8 carbon atoms. Examples of preferred co-crosslinking agents include zinc acrylate, magnesium acrylate, zinc methacrylate, and magnesium methacrylate. Zinc acrylate and zinc methacrylate are particularly preferred.

[0020] The rubber composition may contain an α,β-unsaturated carboxylic acid having 2 to 8 carbon atoms and a metal oxide. Both react in the rubber composition to obtain a salt. This salt functions as a co-crosslinking agent. Examples of preferred α,β-unsaturated carboxylic acids include acrylic acid and methacrylic acid. Examples of preferred metal oxides include zinc oxide and magnesium oxide.

[0021] The amount of the co-crosslinking agent is preferably 10 parts by mass or more and 45 parts by mass or less with respect to 100 parts by mass of the base rubber. The golf ball 2 in which this amount is 10 parts by mass or more is excellent in resilience performance. From this viewpoint, this amount is more preferably 15 parts by mass or more, and particularly preferably 20 parts by mass or more. The golf ball 2 in which this amount is 45 parts by mass or less is excellent in hitting feeling. From this viewpoint, this amount is more preferably 40 parts by mass or less, and particularly preferably 35 parts by mass or less.

[0022] Preferably, the rubber composition of the core 4 contains an organic peroxide. The organic peroxide functions as a crosslinking initiator. The organic peroxide contributes to the durability and resilience performance of the golf ball 2. Examples of suitable organic peroxides include dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and di-t-butyl peroxide. An organic peroxide with particularly high versatility is dicumyl peroxide.

[0023] The amount of the organic peroxide is preferably 0.1 part by mass or more and 3.0 parts by mass or less with respect to 100 parts by mass of the base rubber. The golf ball 2 in which this amount is 0.1 part by mass or more is excellent in resilience performance. From this viewpoint, this amount is more preferably 0.3 part by mass or more, and particularly preferably 0.5 part by mass or more. The golf ball 2 in which this amount is 3.0 parts by mass or less is excellent in hitting feeling. From this viewpoint, this amount is more preferably 2.5 parts by mass or less, and particularly preferably 2.0 parts by mass or less.

[0024] Preferably, the rubber composition of the core 4 contains an organic sulfur compound. The organic sulfur compound contributes to the resilience performance of the golf ball 2. The organic sulfur compound includes naphthalenethiol-based compounds, benzenethiol-based compounds, and disulfide-based compounds.

[0025] Examples of the naphthalenethiol-based compounds include 1-naphthalenethiol, 2-naphthalenethiol, 4-chloro-1-naphthalenethiol, 4-bromo-1-naphthalenethiol, 1-chloro-2-naphthalenethiol, 1-bromo-2-naphthalenethiol, 1-fluoro-2-naphthalenethiol, 1-cyano-2-naphthalenethiol, and 1-acetyl-2-naphthalenethiol, and metal salts thereof. A preferable metal salt is a zinc salt.

[0026] Examples of the benzenethiol-based compounds include benzenethiol, 4-chlorobenzenethiol, 3-chlorobenzenethiol, 4-bromobenzenethiol, 3-bromobenzenethiol, 4-fluorobenzenethiol, 4-iodobenzenethiol, 2,5-dichlorobenzenethiol, 3,5-dichlorobenzenethiol, 2,6-dichlorobenzenethiol, 2,5-dibromobenzenethiol, 3,5-dibromobenzenethiol, 2-chloro-5-bromobenzenethiol, 2,4,6-trichlorobenzenethiol, 2,3,4,5,6-pentachlorobenzenethiol, 2,3,4,5,6-pentafluorobenzenethiol, 4-cyanobenzenethiol, 2-cyanobenzenethiol, 4-nitrobenzenethiol, and 2-nitrobenzenethiol, and metal salts thereof. A preferable metal salt is a zinc salt.

[0027] Examples of the disulfide compound include diphenyl disulfide, bis(4-chlorophenyl) disulfide, bis(3-chlorophenyl) disulfide, bis(4-bromophenyl) disulfide, bis(3-bromophenyl) disulfide, bis(4-fluorophenyl) disulfide, bis(4-iodophenyl) disulfide, bis(4-cyanophenyl) disulfide, bis(2,5-dichlorophenyl) disulfide, bis(3,5-dichlorophenyl) disulfide, bis(2,6-dichlorophenyl) disulfide, bis(2,5-dibromophenyl) disulfide, bis(3,5-dibromophenyl) disulfide, bis(2-chloro-5-bromophenyl) disulfide, bis(2-cyano-5-bromophenyl) disulfide, bis(2,4,6-trichlorophenyl) disulfide, bis(2-cyano-4-chloro-6-bromophenyl) disulfide, bis(2,3,5,6-tetrachlorophenyl) disulfide, bis(2,3,4,5,6-pentachlorophenyl) disulfide, and bis(2,3,4,5,6-pentabromophenyl) disulfide.

[0028] The amount of the organic sulfur compound is preferably 0.1 part by mass or more and 1.5 parts by mass or less with respect to 100 parts by mass of the base rubber. The golf ball 2 in which this amount is 0.1 part by mass or more is excellent in resilience performance. From this viewpoint, this amount is more preferably 0.2 part by mass or more, and particularly preferably 0.3 part by mass or more. The golf ball 2 in which this amount is 1.5 parts by mass or less is excellent in hitting feeling. From this viewpoint, this amount is more preferably 1.3 parts by mass or less, and particularly preferably 1.1 parts by mass or less. Two or more organic sulfur compounds may be used in combination.

[0029] Preferably, the rubber composition of the core 4 contains a carboxylic acid or a carboxylate. The carboxylic acid and the carboxylate can contribute to the optimization of the hardness distribution of the core 4. An appropriate hardness distribution can suppress the spin speed in a driver shot. Preferred carboxylic acids include benzoic acid. Preferred carboxylates include zinc octanoate and zinc stearate. The amount of the carboxylic acid and the carboxylate is preferably 0.5 parts by mass or more, more preferably 0.8 parts by mass or more, and particularly preferably 1.0 parts by mass or more with respect to 100 parts by mass of the base rubber. This amount is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and particularly preferably 10 parts by mass or less.

[0030] The rubber composition of the core 4 may contain a filler for the purpose of adjusting the specific gravity or 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.

[0031] The rubber composition of the core 4 may contain appropriate amounts of various additives such as sulfur, an anti-aging agent, a coloring agent, a plasticizer, and a dispersant. This rubber composition may contain crosslinked rubber powder or synthetic resin powder.

[0032] The diameter of the core 4 is preferably 35.0 mm or more and 40.5 mm or less. In other words, the radius Rc of the core 4 is preferably 17.5 mm or more and 20.25 mm or less. The golf ball 2 having the core 4 with a diameter of 35.0 mm or more is excellent in repulsion performance. From this viewpoint, the diameter is more preferably 36.0 mm or more, and particularly preferably 36.5 mm or more. The golf ball 2 having the core 4 with a diameter of 40.5 mm or less is excellent in durability. From this viewpoint, the diameter is more preferably 40.0 mm or less, and particularly preferably 39.5 mm or less.

[0033] The compression deformation amount Dc of the core 4 is preferably 3.1 mm or more and 5.6 mm or less. The golf ball 2 having the core 4 with the compression deformation amount Dc of 3.1 mm or more has excellent hitting feeling. From this viewpoint, the compression deformation amount Dc is more preferably 3.3 mm or more, and particularly preferably 3.5 mm or more. The golf ball 2 having the core 4 with the compression deformation amount Dc of 5.6 mm or less has excellent resilience performance. From this viewpoint, the compression deformation amount Dc is more preferably 5.4 mm or less, and particularly preferably 5.2 mm or less.

[0034] For measuring the compression deformation amount Dc, the YAMADA type compression tester "SCH" is used. In this tester, the core 4 is placed on a metal-made steel plate. A metal-made cylinder gradually descends toward this core 4. The core 4 sandwiched between the bottom surface of this cylinder and the steel plate deforms. The moving distance of the cylinder from the state where an initial load of 98 N is applied to the core 4 to the state where a final load of 1274 N is applied is measured. The moving speed of the cylinder until the initial load is applied is 0.83 mm / s. The moving speed of the cylinder from when the initial load is applied to when the final load is applied is 1.67 mm / s.

[0035] The inner cover 6 is located outside the core 4. In the present embodiment, the inner cover 6 is in contact with the core 4. The inner cover 6 is formed from a resin composition. In the present embodiment, the inner cover 6 is formed from a thermoplastic resin composition. Examples of the base polymer of this resin composition include ionomer resin, thermoplastic polyester elastomer, thermoplastic polyamide elastomer, thermoplastic polyurethane elastomer, thermoplastic polyolefin elastomer, and thermoplastic polystyrene elastomer. In particular, ionomer resin is preferable. The ionomer resin has high elasticity. The golf ball 2 having the inner cover 6 containing the ionomer resin has excellent resilience performance. This golf ball 2 has excellent flight performance in driver shots.

[0036] The ionomer resin and other resins may be used in combination. When used in combination, from the viewpoint of the repulsion performance, the ionomer resin is used as the main component of the base polymer. The ratio of the ionomer resin to the total base polymer is preferably 50% by mass or more.

[0037] Preferred ionomer resins include binary copolymers of an α-olefin and an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms. Preferred binary copolymers contain 80% by mass or more and 90% by mass or less of an α-olefin and 10% by mass or more and 20% by mass or less of an α,β-unsaturated carboxylic acid. This binary copolymer is excellent in repulsion performance. Preferred other ionomer resins include terpolymers of an α-olefin, an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms, and an α,β-unsaturated carboxylic acid ester having 2 to 22 carbon atoms. Preferred terpolymers contain 70% by mass or more and 85% by mass or less of an α-olefin, 5% by mass or more and 30% by mass or less of an α,β-unsaturated carboxylic acid, and 1% by mass or more and 25% by mass or less of an α,β-unsaturated carboxylic acid ester. This terpolymer is excellent in repulsion performance. In the binary copolymer and the terpolymer, preferred α-olefins are ethylene and propylene, and preferred α,β-unsaturated carboxylic acids are acrylic acid and methacrylic acid. Particularly preferred ionomer resins are copolymers of ethylene and acrylic acid. Particularly preferred other ionomer resins are copolymers of ethylene and methacrylic acid.

[0038] In the binary copolymer and the terpolymer, a part of the carboxyl groups is 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. The neutralization may be carried out with two or more kinds of metal ions. Particularly preferred metal ions from the viewpoints of the repulsion performance and durability of the golf ball 2 are sodium ions, zinc ions, lithium ions, and magnesium ions.

[0039] Specific examples of ionomer resins include the trade names "Hymilan 1555", "Hymilan 1557", "Hymilan 1605", "Hymilan 1706", "Hymilan 1707", "Hymilan 1855", "Hymilan 1856", "Hymilan 8150", "Hymilan AM7311", "Hymilan AM7315", "Hymilan AM7317", "Hymilan AM7329", and "Hymilan AM7337" of Mitsui Dow Polychemical Co., Ltd.; the trade names "Surlyn 6120", "Surlyn 6910", "Surlyn 7930", "Surlyn 7940", "Surlyn 8140", "Surlyn 8150", "Surlyn 8940", "Surlyn 8945", "Surlyn 9120", "Surlyn 9150", "Surlyn 9910", "Surlyn 9945", "Surlyn AD8546", "HPF1000", and "HPF2000" of DuPont; and the trade names "Iotek 7010", "Iotek 7030", "Iotek 7510", "Iotek 7520", "Iotek 8000", and "Iotek 8030" of ExxonMobil Chemical Company. Two or more ionomer resins may be used in combination.

[0040] A preferred resin that can be used in combination with the ionomer resin is a styrene block-containing thermoplastic elastomer. The styrene block-containing thermoplastic elastomer comprises 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.

[0041] Styrene block-containing thermoplastic elastomers include styrene-butadiene-styrene block copolymers (SBS), styrene-isoprene-styrene block copolymers (SIS), styrene-isoprene-butadiene-styrene block copolymers (SIBS), hydrogenated products of SBS, hydrogenated products of SIS, and hydrogenated products of SIBS. Examples of the hydrogenated product of SBS include styrene-ethylene-butylene-styrene block copolymers (SEBS). Examples of the hydrogenated product of SIS include styrene-ethylene-propylene-styrene block copolymers (SEPS). Examples of the hydrogenated product of SIBS include styrene-ethylene-ethylene-propylene-styrene block copolymers (SEEPS).

[0042] From the perspective of the resilience performance of the golf ball 2, the content of the styrene component in the styrene block-containing thermoplastic elastomer is preferably 1% by mass or more, more preferably 3% by mass or more, and particularly preferably 5% by mass or more. From the perspective of the hitting feeling of the golf ball 2, this content is preferably 50% by mass or less, more preferably 47% by mass or less, and particularly preferably 45% by mass or less.

[0043] In the present invention, the styrene block-containing thermoplastic elastomer includes an alloy of one or more selected from the group consisting of SBS, SIS, SIBS, SEBS, SEPS, and SEEPS and an olefin. The olefin component in this alloy is presumed to contribute to improving the compatibility with other base polymers. This alloy can contribute to the resilience performance of the golf ball 2. Olefins having 2 or more and 10 or less carbon atoms are preferred. Preferred olefins include ethylene, propylene, butene, and pentene. Ethylene and propylene are particularly preferred.

[0044] Specific examples of the polymer alloy include the product names "Tefabloc T3221C", "Tefabloc T3339C", "Tefabloc SJ4400N", "Tefabloc SJ5400N", "Tefabloc SJ6400N", "Tefabloc SJ7400N", "Tefabloc SJ8400N", "Tefabloc SJ9400N", and "Tefabloc SR04" of Mitsubishi Chemical Corporation. Other specific examples of the styrene block-containing thermoplastic elastomer include the product name "Epofrend A1010" of Daicel Chemical Industries, Ltd. and the product name "Septon HG-252" of Kuraray Co., Ltd.

[0045] The resin composition of the inner cover 6 may contain an appropriate amount of a colorant, a filler, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent agent, a fluorescent brightening agent, etc. When the hue of the golf ball 2 is white, a typical colorant is titanium dioxide.

[0046] The thickness Ti of the inner cover 6 is preferably 0.5 mm or more and 2.0 mm or less. The golf ball 2 with a thickness Ti of 0.5 mm or more is excellent in durability. From this viewpoint, the thickness Ti is more preferably 0.70 mm or more, and particularly preferably 0.9 mm or more. The golf ball 2 with a thickness Ti of 2.00 mm or less is excellent in hitting feeling. From this viewpoint, the thickness Ti is more preferably 1.8 mm or less, and particularly preferably 1.6 mm or less. The thickness Ti is measured directly below the land 12.

[0047] The hardness Hi of the inner cover 6 is preferably 60 or more and 100 or less. The golf ball 2 with a hardness Hi of 60 or more is excellent in resilience performance. From this viewpoint, the hardness Hi is more preferably 70 or more, and particularly preferably 75 or more. The golf ball 2 with a hardness Hi of 100 or less is excellent in hitting feeling. From this viewpoint, the hardness Hi is more preferably 98 or less, and particularly preferably 96 or less.

[0048] The hardness Hi of the inner cover 6 is measured in accordance with the provisions of "ASTM-D 2240-68". The hardness Hi is measured by a Shore C-type hardness meter attached to an automatic hardness meter (trade name "Digital Test II" by H. Barleys). For the measurement, a sheet made of the same material as the material of the inner cover 6, which is formed by a hot press and has a thickness of about 2 mm, is used. Prior to the measurement, the sheet is stored at a temperature of 23°C for two weeks. At the time of measurement, three sheets are stacked together.

[0049] The outer cover 8 is located outside the inner cover 6. In the present embodiment, the outer cover 8 is in contact with the inner cover 6. The golf ball 2 may have an adhesive layer between the inner cover 6 and the outer cover 8. Through this adhesive layer, the outer cover 8 can be firmly joined to the inner cover 6. The outer cover 8 is formed from a resin composition. In the present embodiment, the outer cover 8 is formed from a thermoplastic resin composition. Examples of the base polymer of this resin composition include ionomer resin, thermoplastic polyester elastomer, thermoplastic polyamide elastomer, thermoplastic polyurethane elastomer, thermoplastic polyolefin elastomer, and thermoplastic polystyrene elastomer. In particular, ionomer resin is preferred. The ionomer resin has high elasticity. The golf ball 2 having the outer cover 8 containing ionomer resin has excellent repulsion performance. This golf ball 2 has excellent flight performance in a driver shot. The ionomer resin described above with respect to the inner cover 6 can be used for the outer cover 8.

[0050] The ionomer resin and other resins may be used in combination. When used in combination, from the viewpoint of repulsion performance, the ionomer resin is the main component of the base polymer. The ratio of the ionomer resin to all the base polymers is preferably 50% by mass or more, more preferably 60% by mass or more, and particularly preferably 65% by mass or more.

[0051] A preferred resin that can be used in combination with the ionomer resin is a styrene block-containing thermoplastic elastomer. The styrene block-containing thermoplastic elastomer can contribute to the hitting feeling of the golf ball 2. From the viewpoint of the hitting feeling, the ratio of the styrene block-containing thermoplastic elastomer to the total base polymer is preferably 10% by mass or more, more preferably 20% by mass or more, and particularly preferably 25% by mass or more. The styrene block-containing thermoplastic elastomer described above with respect to the inner cover 6 can be used for the outer cover 8.

[0052] Another resin suitable for the outer cover 8 is a polyurethane elastomer. The resin composition of the outer cover 8 may contain a thermoplastic polyurethane or a thermosetting polyurethane. From the viewpoint of the productivity of the golf ball 2, a thermoplastic polyurethane is preferred. The thermoplastic polyurethane contains a polyurethane component as a hard segment and a polyester component or a polyether component as a soft segment. The thermoplastic polyurethane is soft. The outer cover 8 using this polyurethane is excellent in control performance and abrasion resistance.

[0053] The thermoplastic polyurethane has a urethane bond in the molecule. This urethane bond can be formed by the reaction of a polyol and a polyisocyanate. The polyol, which is a raw material of the urethane bond, has a plurality of hydroxyl groups. A low molecular weight polyol and a high molecular weight polyol can be used.

[0054] Examples of low molecular weight polyols include diols, triols, tetraols, and hexols. Specific examples of diols include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, dipropylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 2,3-dimethyl-2,3-butanediol, neopentyl glycol, pentanediol, hexanediol, heptanediol, octanediol, and 1,6-cyclohexanedimethanol. Aniline-based diols or bisphenol A-based diols may also be used. Specific examples of triols include glycerin, trimethylolpropane, and hexanetriol. Specific examples of tetraols include pentaerythritol and sorbitol.

[0055] Examples of high molecular weight polyols include polyether polyols such as polyoxyethylene glycol (PEG), polyoxypropylene glycol (PPG), and polytetramethylene ether glycol (PTMG); condensation polyester polyols such as 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. From the viewpoint of the hitting feeling of the golf ball 2, the number average molecular weight of the high molecular weight polyol is preferably 400 or more, more preferably 1000 or more. The number average molecular weight is preferably 10000 or less.

[0056] Examples of the polyisocyanate that is a raw material for the urethane bond include aromatic diisocyanates, alicyclic diisocyanates, and aliphatic diisocyanates. Two or more diisocyanates may be used in combination.

[0057] Examples of aromatic diisocyanates include 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate (MDI), 1,5-naphthylene diisocyanate (NDI), 3,3'-bitolylene-4,4'-diisocyanate (TODI), xylylene diisocyanate (XDI), tetramethylxylylene diisocyanate (TMXDI), and paraphenylene diisocyanate (PPDI). An example of an aliphatic diisocyanate is hexamethylene diisocyanate (HDI). Examples of alicyclic diisocyanates include 4,4'-dicyclohexylmethane diisocyanate (H 12 MDI), 1,3-bis(isocyanatomethyl)cyclohexane (H6XDI), isophorone diisocyanate (IPDI), and trans-1,4-cyclohexane diisocyanate (CHDI). 4,4'-Dicyclohexylmethane diisocyanate is preferred.

[0058] Specific examples of thermoplastic polyurethanes include "Elastollan NY80A", "Elastollan NY82A", "Elastollan NY83A", "Elastollan NY84A", "Elastollan NY85A", "Elastollan NY88A", "Elastollan NY90A", "Elastollan NY95A", "Elastollan NY97A", "Elastollan NY585", and "Elastollan KP016N" of BASF Japan Ltd.; and "Resamin P4585LS" and "Resamin PS62490" of Dainichi Kasei Kogyo Co., Ltd.

[0059] The resin composition of the outer cover 8 may contain an appropriate amount of a colorant, filler, dispersant, antioxidant, ultraviolet absorber, light stabilizer, fluorescent agent, fluorescent brightening agent, etc. When the hue of the golf ball 2 is white, a typical colorant is titanium dioxide.

[0060] The thickness To of the outer cover 8 is preferably 0.5 mm or more and 2.0 mm or less. The golf ball 2 with a thickness To of 0.50 mm or more is excellent in durability. From this viewpoint, the thickness To is more preferably 0.7 mm or more, and particularly preferably 0.9 mm or more. The golf ball 2 with a thickness To of 2.0 mm or less is excellent in hitting feeling. From this viewpoint, the thickness To is more preferably 1.8 mm or less, and particularly preferably 1.6 mm or less. The thickness To is measured directly below the land 12.

[0061] The hardness Ho of the outer cover 8 is preferably 40 or more and 96 or less. The golf ball 2 with a hardness Ho of 40 or more is excellent in resilience performance. From this viewpoint, the hardness Ho is more preferably 50 or more, and particularly preferably 55 or more. The golf ball 2 with a hardness Ho of 96 or less is excellent in hitting feeling. From this viewpoint, the hardness Ho is more preferably 90 or less, and particularly preferably 85 or less.

[0062] The hardness Ho of the outer cover 8 is measured by the same method as the method for measuring the hardness Hi of the inner cover 6.

[0063] The total (Ti + To) of the thickness Ti of the inner cover 6 and the thickness To of the outer cover 8 is preferably 1.6 mm or more and 3.4 mm or less. The golf ball 2 with this total (Ti + To) of 1.6 mm or more is excellent in durability. From this viewpoint, the total (Ti + To) is more preferably 1.9 mm or more, and particularly preferably 2.0 mm or more. The golf ball 2 with this total (Ti + To) of 3.4 mm or less is excellent in hitting feeling. From this viewpoint, the total (Ti + To) is more preferably 3.1 mm or less, and particularly preferably 3.0 mm or less.

[0064] The compression deformation amount Db of the golf ball 2 is preferably 2.75 mm or more. The golf ball 2 with a compression deformation amount Db of 2.75 mm or more is excellent in hitting feeling. The golf ball 2 with a compression deformation amount Db of 2.75 mm or more is particularly excellent in hitting feeling in a driver shot. From this viewpoint, the compression deformation amount Db is more preferably 2.80 mm or more, and particularly preferably 2.85 mm or more. From the viewpoint of resilience performance, the compression deformation amount Db is preferably 4.0 mm or less.

[0065] For the measurement of the compression deformation amount Db, the aforementioned YAMADA type compression tester "SCH" is used. In this tester, the golf ball 2 is placed on a metal rigid plate. A metal cylinder gradually descends toward this golf ball 2. The golf ball 2 sandwiched between the bottom surface of this cylinder and the rigid plate deforms. The moving distance of the cylinder from the state where an initial load of 98 N is applied to the golf ball 2 to the state where a final load of 1274 N is applied is measured. The moving speed of the cylinder until the initial load is applied is 0.83 mm / s. The moving speed of the cylinder from when the initial load is applied to when the final load is applied is 1.67 mm / s.

[0066] The deformation amount of the golf ball 2 in the approach shot is small. For the hitting feeling in the approach shot, the outer cover 8 mainly contributes. In the present embodiment, the hardness Ho of the outer cover 8 is smaller than the hardness Hi of the inner cover 6. A golf ball 2 with a small hardness Ho is excellent in the hitting feeling in the approach shot.

[0067] From the viewpoint of achieving both the flight performance in the driver shot and the hitting feeling in the approach shot, the difference (Hi - Ho) between the hardness Hi and the hardness Ho is preferably 5 or more, more preferably 10 or more, and particularly preferably 13 or more. The difference (Hi - Ho) is preferably 40 or less.

[0068] The product Dc * Rc of the compression deformation amount Dc and the radius Rc in the core 4 is an index correlated with the contribution degree of the core 4 to the rigidity of the golf ball 2. The product Hi * Ti of the hardness Hi and the thickness Ti in the inner cover 6 is an index correlated with the contribution degree of the inner cover 6 to the rigidity of the golf ball 2. The product Ho * To of the hardness Ho and the thickness To in the outer cover 8 is an index correlated with the contribution degree of the outer cover 8 to the rigidity of the golf ball 2.

[0069] The difference (Hi*Ti - Dc*Rc) between the product Hi*Ti in the inner cover 6 and the product Dc*Rc in the core 4 is 5 or more and 40 or less. In other words, this golf ball 2 satisfies the following mathematical formula (1). 5 ≦ (Hi*Ti - Dc*Rc) ≦ 40 (1)

[0070] The difference (Hi*Ti - Ho*To) between the product Hi*Ti in the inner cover 6 and the product Ho*To in the outer cover 8 is 5 or more and 40 or less. In other words, this golf ball 2 satisfies the following mathematical formula (2). 5 ≦ (Hi*Ti - Ho*To) ≦ 40 (2)

[0071] The difference (Ho*To - Dc*Rc) between the product Ho*To in the outer cover 8 and the product Dc*Rc in the core 4 is -20 or more and 20 or less. In other words, this golf ball 2 satisfies the following mathematical formula (3). -20 ≦ (Ho*To - Dc*Rc) ≦ 20 (3)

[0072] In the golf ball 2 that satisfies the above mathematical formulas (1), (2), and (3), the core 4 has low rigidity, the inner cover 6 has high rigidity, and the outer cover 8 has low rigidity. In this golf ball 2, the high-rigidity part (inner cover 6) is sandwiched between two low-rigidity parts (core 4 and outer cover 8).

[0073] In the driver shot of this golf ball 2, the amount of deflection of the core 4 is large, the amount of deflection of the inner cover 6 is small, and the amount of deflection of the outer cover 8 is large. In the driver shot, the core 4 and the inner cover 6 contribute to a large launch angle and a small spin rate. Therefore, in this golf ball 2, a large carry distance can be achieved in the driver shot. Further, in the driver shot, the outer cover 8 achieves a soft feel at impact. This golf ball 2 is excellent in flight performance and feel at impact in the driver shot.

[0074] In an approach shot, the kinetic energy transmitted from the golf club to the golf ball 2 is small. In an approach shot, mainly the outer cover 8 flexes. Since this outer cover 8 has low rigidity, the amount of flex of the outer cover 8 in an approach shot is large. In an approach shot, the outer cover 8 achieves a large spin speed. This outer cover 8 contributes to the control performance in an approach shot. Further, in an approach shot, the outer cover 8 achieves a soft hitting feeling. This golf ball 2 is excellent in control performance and hitting feeling in an approach shot.

[0075] The golf ball 2 that satisfies the above formulas (1), (2), and (3) (a) Flight performance in a driver shot (b) Hitting feeling in a driver shot (c) Control performance in an approach shot and (d) Hitting feeling in an approach shot are all excellent. This golf ball 2 is excellent in overall performance.

[0076] From the viewpoint of overall performance, the difference (Hi*Ti - Dc*Rc) is more preferably 8 or more, and particularly preferably 10 or more. From the viewpoint of overall performance, the difference (Hi*Ti - Dc*Rc) is more preferably 35 or less, and particularly preferably 32 or less.

[0077] From the viewpoint of overall performance, the difference (Hi*Ti - Ho*To) is more preferably 8 or more, and particularly preferably 10 or more. From the viewpoint of overall performance, the difference (Hi*Ti - Ho*To) is more preferably 35 or less, and particularly preferably 32 or less.

[0078] From the viewpoint of overall performance, the difference (Ho*To - Dc*Rc) is more preferably -15 or more, and particularly preferably -12 or more. From the viewpoint of overall performance, the difference (Ho*To - Dc*Rc) is more preferably 15 or less, and particularly preferably 12 or less.

Example

[0079] Hereinafter, the effects of the present invention will be clarified by examples, but the present invention should not be construed in a limited manner based on the description of these examples.

[0080] [Example 1] 100 parts by mass of high cis-polybutadiene (trade name "BR-730" of JSR), an appropriate amount of zinc acrylate, 5 parts by mass of zinc oxide, an appropriate amount of barium sulfate, 2.0 parts by mass of benzoic acid, 0.5 part by mass of diphenyl disulfide and 0.9 part by mass of dicumyl peroxide were kneaded to obtain a rubber composition. This rubber composition was put into a mold composed of an upper mold and a lower mold each having a hemispherical cavity and heated to obtain a core having a diameter of 38.5 mm. The amount of zinc acrylate was adjusted so that a predetermined compression deformation amount Dc was achieved. The amount of barium sulfate was adjusted so that a predetermined mass was achieved. The crosslinking temperature was 160°C. The crosslinking time was 20 minutes.

[0081] 50 parts by mass of an ionomer resin (the aforementioned "Hy-Milan AM7329"), 50 parts by mass of another ionomer resin (the aforementioned "Hy-Milan 1605"), 4 parts by mass of titanium dioxide and 0.2 part by mass of a light stabilizer (trade name "JF-90" of Johoku Chemical Industry Co., Ltd.) were kneaded with a twin-screw kneading extruder to obtain a resin composition C7. The core was put into a mold composed of an upper mold and a lower mold each having a hemispherical cavity. The resin composition C7 was coated around the core by an injection molding method to form an inner cover. The thickness of this inner cover was 1.05 mm.

[0082] 38.5 parts by mass of an ionomer resin (the aforementioned "Hymilan AM7337"), 38.5 parts by mass of an ionomer resin (the aforementioned "Hymilan AM7329"), 23 parts by mass of a styrene block-containing thermoplastic elastomer (the aforementioned "Tefabloc T3221C"), 4 parts by mass of titanium dioxide, and 0.2 parts by mass of a light stabilizer (the aforementioned "JF-90") were kneaded with a twin-screw kneading extruder to obtain a resin composition C4. A sphere composed of a core and an inner cover was put into a mold consisting of an upper mold and a lower mold each having a hemispherical cavity. The resin composition C4 was coated around the sphere by an injection molding method to form an outer cover. The thickness of this outer cover was 1.05 mm.

[0083] A clear paint based on a two-component curable polyurethane was applied around this outer cover to obtain a golf ball of Example 1 having a diameter of about 42.7 mm and a mass of about 45.6 g.

[0084] [Examples 2-8 and Comparative Examples 1-7] Golf balls of Examples 2-8 and Comparative Examples 1-7 were obtained in the same manner as in Example 1 except that the specifications of the core, inner cover, and outer cover were as shown in Table 2-4 below. Details of the compositions of the inner cover and outer cover are shown in Table 1 below.

[0085] [Flight Performance W#1] A driver (W#1) was attached to the swing machine of Golf Laboratory. The head of this driver has a body with an opening and a face that closes this opening. The face has a main part and an edge part. This edge part is joined to the main part by welding. The size of the edge part in the front-rear direction is 6 mm or less. This head further has a welding bead located at the boundary between the main part and the edge part. The thickness of the head at the face-side end of this welding bead is larger than the thickness of the head at the head-side end of this welding bead. With this driver, a golf ball was struck under the condition that the head speed was 40 m / sec, and the flight distance was measured. The flight distance is the distance from the launch point to the stationary point. During the test, there was almost no wind. The average value of the data obtained from 12 measurements was calculated. This average value was rated based on the following criteria. A: 200.0 m or more B: 198.5 m or more and less than 200.0 m C: 197.0 m or more and less than 198.5 m D: Less than 197.0 m This result is shown in Table 2-4 below.

[0086] [Feeling of hitting the ball W#1] Twenty golf players were made to hit a golf ball with the aforementioned driver. These players were asked about the feeling of hitting the ball. The number of players who answered that the feeling of hitting the ball was soft was ranked based on the following criteria. A: 16 people or more B: 10 people or more and 15 people or less C: 3 people or more and 9 people or less D: 2 people or less This result is shown in Table 2-4 below.

[0087] [Flight performance Wedge] A wedge (product name: "558RTX2.0 Tour Satin Wedge" by Cleveland, shaft hardness: S, loft angle: 52°) was attached to the swing machine of Golf Laboratory. Using this wedge, a golf ball was struck under the condition that the clubhead speed was 16 m / sec, and the spin speed was measured. The average value of the data obtained from 12 measurements was calculated. This average value was rated based on the following criteria. A: 4300 rpm or more B: 4150 rpm or more and less than 4300 rpm C: 4000 rpm or more and less than 4150 rpm D: Less than 4000 rpm This result is shown in Table 2-4 below.

[0088] [Feeling of hitting the ball - Wedge] Twenty golf players were made to hit a golf ball with the aforementioned wedge. These players were asked about the feeling of hitting the ball. The number of players who answered that the feeling of hitting the ball was soft was ranked based on the following criteria. A: 16 people or more B: 10 people or more and 15 people or less C: 3 people or more and 9 people or less D: 2 people or less This result is shown in Table 2-4 below.

[0089] [Overall evaluation] Based on the evaluations of the four aforementioned items, the overall performance was rated. Overall performance A: The number of evaluations of "A" is 4. Overall performance B: It does not reach overall performance A. Each evaluation is "A" or "B". Overall performance C: It does not reach overall performance B. The number of evaluations of "D" is zero. Overall performance D: It does not reach overall performance C.

[0090]

Table 1

[0091]

Table 2

[0092]

Table 3

[0093]

Table 4

[0094] Annotations in Table 2-4 Io: The base material of the composition is an ionomer resin. Ur: The base material of the composition is a urethane resin.

[0095] As shown in Table 2-4, the golf balls of each example are excellent in overall performance. From this evaluation result, the superiority of the present invention is clear.

[0096] [Disclosed Items] The following items are the disclosure of the preferred embodiments.

[0097] [Item 1] A golf ball comprising a core, an inner cover located outside the core, and an outer cover located outside the inner cover, and satisfying the following mathematical formulas (1), (2), and (3). 5 ≦ (Hi*Ti - Dc*Rc) ≦ 40 (1) 5 ≦ (Hi*Ti - Ho*To) ≦ 40 (2) -20 ≦ (Ho*To - Dc*Rc) ≦ 20 (3) Dc: Compression deformation amount of the core (mm) Rc: Radius of the core (mm) Hi: Shore C hardness of the inner cover Ti: Thickness of the inner cover (mm) Ho: Shore C hardness of the outer cover To: Thickness of the outer cover (mm)

[0098] [Item 2] The golf ball according to Item 1, wherein the hardness Ho is smaller than the hardness Hi.

[0099] [Item 3] The golf ball according to Item 2, wherein the difference (Hi - Ho) between the hardness Hi and the hardness Ho is 5 or more.

[0100] [Item 4] The golf ball according to any one of Items 1 to 3, wherein the compression deformation amount Db thereof is 2.75 mm or more.

[0101] [Item 5] The golf ball according to any one of Items 1 to 4, wherein the inner cover is formed from a resin composition, and the base material of this resin composition is an ionomer resin.

[0102] [Item 6] The golf ball according to any one of Items 1 to 5, wherein the outer cover is formed from a resin composition, and the base material of this resin composition is an ionomer resin.

Industrial Applicability

[0103] The golf ball according to the present invention is suitable for play on a golf course, practice at a driving range, etc.

Explanation of Signs

[0104] 2 ··· Golf ball 4 ··· Core 6 ··· Inner cover 8 ··· Outer cover 10 ··· Dimple 12 ··· Land

Claims

1. A golf ball comprising a core having a single-layer structure, an inner cover positioned outside the core, and an outer cover positioned outside the inner cover, satisfying the following formulas (1), (2), and (3). 5 ≤ (Hi * Ti - Dc * Rc) ≤ 40 (1) 5 ≤ (Hi * Ti - Ho * To) ≤ 40 (2) -20 ≤ (Ho * To - Dc * Rc) ≤ 20 (3) Dc: Compression deformation amount of the core (mm) Rc: Radius of the core (mm) Hi: Shore C hardness of the inner cover Ti: Thickness of the inner cover (mm) Ho: Shore C hardness of the outer cover To: Thickness of the outer cover (mm) 2. The golf ball according to claim 1, wherein the hardness Ho is smaller than the hardness Hi.

3. The golf ball according to claim 2, wherein the difference (Hi - Ho) between the hardness Hi and the hardness Ho is 5 or more.

4. The golf ball according to any one of claims 1 to 3, wherein the compression deformation amount Db is 2.75 mm or more.

5. The golf ball according to any one of claims 1 to 4, wherein the inner cover is formed from a resin composition, and the base material of the resin composition is an ionomer resin.

6. The golf ball according to any one of claims 1 to 5, wherein the outer cover is formed from a resin composition, and the base material of the resin composition is an ionomer resin.

Images