JP2016010564A - Golf ball - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a golf ball 2 capable of satisfying players having slow head speeds.SOLUTION: The golf ball 2 includes a center 8, an intermediate layer 10, and a cover 6. Further the golf ball 2 has multiple dimples 12 on the surface thereof. Shore D hardness of the cover 6 is not less than 30 and not more than 50. An amount of compression deformation of the golf ball 2 is 3.0 mm-5.0 mm. The golf ball 2 satisfies the numerical expression (I): 0.80≤((L1+L2)/2)≤0.95. L1 represents a ratio of a lift coefficient CL1 measured under conditions that Reynolds number is 1.290×10and a spin rate is 2820 rpm, to a drag coefficient CD1. L2 represents a ratio of a lift coefficient CL1 measured under conditions that Reynolds number is 1.771×10and a spin rate is 2940 rpm to a drag coefficient CD2.

Description

  The present invention relates to a golf ball. In particular, the present invention relates to improving the aerodynamic characteristics of golf balls.

  The golf ball has a large number of dimples on its surface. The dimples disturb the air flow around the golf ball during flight and cause turbulent separation. This phenomenon is called “turbulence”. Due to the turbulent flow, the separation point of air from the golf ball shifts backward, and drag is reduced. The turbulent flow promotes the deviation between the upper peeling point and the lower peeling point of the golf ball due to backspin, and the lift acting on the golf ball is enhanced. Excellent dimples better disturb the air flow. Excellent dimples produce a great flight distance.

  The golf player can select the brand of the golf ball used by the golf player. In golf competitions, the brand of a golf ball used by one player may be different from that of another player. In this respect, golf is a rare ball game.

  Golf should be a competition that competes for the skill of the player. It is not preferable that the player's performance greatly differs from the brand of the golf ball. From this point of view, the US Golf Association (USGA) has established various rules regarding the characteristics of golf balls. For example, rules regarding mass, diameter, initial speed, flight distance, and symmetry are defined.

  Various golf balls that can satisfy the player while satisfying the rules have been proposed.

  Japanese Patent Application Laid-Open No. 5-103846 discloses a golf ball having dimples having an optimized diameter, depth and number.

  Japanese Patent Application Laid-Open No. 10-43342 discloses a golf ball having dimples with a proper ratio of diameter to depth.

  Japanese Patent Application Laid-Open No. 10-43343 discloses a golf ball in which the ratio of the dimple volume to the ball volume is optimized.

  Japanese Patent Application Laid-Open No. 2000-107338 discloses a golf ball whose diameter and mass are optimized.

JP-A-5-103846 Japanese Patent Laid-Open No. 10-43342 Japanese Patent Laid-Open No. 10-43343 JP 2000-107338 A

  The technological innovation of golf balls and golf clubs is remarkable. In recent tour competitions, the average flight distance of tee shots is increasing. This large flight distance facilitates the second shot. This great flight distance detracts from the public interest in the competition.

  The USGA will change the rules regarding flight distance. The head speed of professional players participating in the competition is high. The USGA will tighten restrictions on flight distance when struck at high head speeds.

  On the other hand, the flight distance when hit at a low head speed is not regulated. Amateur players want more distance. A golf ball that has a long flight distance when hit at a low head speed in spite of conforming to USGA rules is desired.

  Feeling is important for the player as well as the flight distance. Players place emphasis on striking feeling and ballistic feeling. Players prefer a soft hit feeling. Players also prefer high trajectories.

  An object of the present invention is to provide a golf ball that gives satisfaction to a player with a slow head speed.

The golf ball according to the present invention includes a core and a cover positioned outside the core. This golf ball has a large number of dimples on its surface. The cover has a Shore D hardness of 30 to 50. The amount of compressive deformation of this golf ball measured under the conditions that the initial load is 98 N and the final load is 1274 N is 3.0 mm or greater and 5.0 mm or less. This golf ball satisfies the following mathematical formula (I).
0.80 ≦ ((L1 + L2) / 2) ≦ 0.95 (I)
In this equation, L1 represents the ratio (CL1 / CD1) of the lift coefficient CL1 to the drag coefficient CD1 measured under the conditions where the Reynolds number is 1.290 × 10 ⁵ and the spin rate is 2820 rpm. In this equation, L2 represents the ratio (CL2 / CD2) of the lift coefficient CL2 to the drag coefficient CD2 measured under the conditions where the Reynolds number is 1.771 × 10 ⁵ and the spin rate is 2940 rpm.

Preferably, the total volume of the dimples is not less than 430 mm ^{3 and not} more than 580 mm ³ .

  Preferably, the cover has a thickness of 0.3 mm to 1.8 mm.

  Preferably, the ratio L1 is not less than 0.85 and not more than 0.93. Preferably, the ratio L2 is 0.76 or more and 0.92 or less.

  With the golf ball according to the present invention, a sufficient flight distance can be obtained when hit by a player with a slow head speed. This golf ball gives a favorable feeling to a player with a slow head speed.

FIG. 1 is a cross-sectional view illustrating a golf ball according to an embodiment of the present invention. FIG. 2 is an enlarged front view showing the golf ball of FIG. FIG. 3 is a plan view showing the golf ball of FIG. FIG. 4 is an enlarged cross-sectional view showing a part of the golf ball of FIG.

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

  FIG. 1 is a partially cutaway sectional view showing a golf ball 2 according to an embodiment of the present invention. The golf ball 2 includes a spherical core 4 and a cover 6 positioned outside the core 4. The core 4 includes a spherical center 8 and an intermediate layer 10 located outside the center 8. The golf ball 2 includes a paint layer and a mark layer outside the cover 6, but these layers are not shown. Further, the golf ball 2 has a large number of dimples 12 on the surface thereof. A portion of the surface of the golf ball 2 other than the dimples 12 is a land 14. The golf ball 2 may include another layer between the center 8 and the mid layer 10. The golf ball 2 may include another layer between the mid layer 10 and the cover 6.

  The golf ball 2 preferably has a diameter of 40 mm or greater and 45 mm or less. The diameter is particularly preferably equal to or greater than 42.67 mm from the viewpoint that US Golf Association (USGA) standards are satisfied. In light of suppression of air resistance, the diameter is more preferably equal to or less than 44 mm, and particularly preferably equal to or less than 42.80 mm. The golf ball 2 preferably has a mass of 40 g or more and 50 g or less. In light of attainment of great inertia, the mass is more preferably equal to or greater than 44 g, and particularly preferably equal to or greater than 45.00 g. In light of satisfying the USGA standard, the mass is particularly preferably equal to or less than 45.93 g.

  The center 8 is obtained by crosslinking the rubber composition. Examples of preferable base rubber include polybutadiene, polyisoprene, styrene-butadiene copolymer, ethylene-propylene-diene copolymer, and natural rubber. From the viewpoint of resilience performance, polybutadiene is preferred. When polybutadiene and other rubber are used in combination, it is preferable that polybutadiene is a main component. Specifically, the ratio of polybutadiene to the total base rubber is preferably 50% 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 preferable.

  The rubber composition of the center 8 preferably contains a co-crosslinking agent. A preferred co-crosslinking agent from the viewpoint of resilience performance is a monovalent or divalent metal salt of an α, β-unsaturated carboxylic acid having 2 to 8 carbon atoms. Preferred examples of the co-crosslinking agent include zinc acrylate, magnesium acrylate, zinc methacrylate, and magnesium methacrylate. From the viewpoint of resilience performance, zinc acrylate and zinc methacrylate are particularly preferred.

  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. Preferred α, β-unsaturated carboxylic acids include acrylic acid and methacrylic acid. Preferred metal oxides include zinc oxide and magnesium oxide.

  From the viewpoint of the resilience performance of the golf ball 2, the amount of the co-crosslinking agent is preferably 10 parts by mass or more and particularly preferably 15 parts by mass or more with respect to 100 parts by mass of the base rubber. From the viewpoint of soft feel at impact, this amount is preferably 50 parts by mass or less, and particularly preferably 45 parts by mass or less.

  Preferably, the rubber composition of the center 8 includes an organic peroxide together with a co-crosslinking agent. The organic peroxide functions as a crosslinking initiator. The organic peroxide contributes to the resilience performance of the golf ball 2. Suitable organic peroxides include dicumyl peroxide, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di (t-butyl). Peroxy) hexane and di-t-butyl peroxide are exemplified. A particularly versatile organic peroxide is dicumyl peroxide.

  In light of the resilience performance of the golf ball 2, the amount of the organic peroxide is preferably equal to or greater than 0.1 parts by weight, more preferably equal to or greater than 0.3 parts by weight, based on 100 parts by weight of the base rubber. Part or more is particularly preferable. From the viewpoint of soft feel at impact, this amount is preferably 3.0 parts by mass or less, more preferably 2.8 parts by mass or less, and particularly preferably 2.5 parts by mass or less.

  Preferably, the rubber composition of the center 8 includes an organic sulfur compound. Preferred organic sulfur compounds include diphenyl disulfide, bis (4-chlorophenyl) disulfide, bis (3-chlorophenyl) disulfide, bis (4-bromophenyl) disulfide, bis (3-bromophenyl) disulfide, and bis (4-fluorophenyl). Monosubstituted compounds such as disulfide, bis (4-iodophenyl) disulfide and 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 and bis (2-cyano-5-bromide) Disubstituted compounds such as phenyl) disulfide; trisubstituted compounds such as bis (2,4,6-trichlorophenyl) disulfide and bis (2-cyano-4-chloro-6-bromophenyl) disulfide; Tetra substituents such as 3,5,6-tetrachlorophenyl) disulfide; and bis (2,3,4,5,6-pentachlorophenyl) disulfide and bis (2,3,4,5,6-pentabromophenyl) ) Examples of penta-substituted compounds such as disulfides. Organic sulfur compounds contribute to resilience performance. Particularly preferred organic sulfur compounds are diphenyl disulfide and bis (pentabromophenyl) disulfide.

  In light of the resilience performance of the golf ball 2, the amount of the organic sulfur compound is preferably equal to or greater than 0.1 parts by weight and particularly preferably equal to or greater than 0.2 parts by weight with respect to 100 parts by weight of the base rubber. From the viewpoint of soft feel at impact, this amount is preferably 1.5 parts by mass or less, more preferably 1.0 part by mass or less, and particularly preferably 0.8 part by mass or less.

  The center 8 may be blended with a filler for the purpose of adjusting specific gravity and the like. Examples of suitable fillers include zinc oxide, barium sulfate, calcium carbonate, and magnesium carbonate. As a filler, a powder made of a high specific gravity metal may be blended. Specific examples of the high specific gravity metal include tungsten and molybdenum. The blending amount of the filler is appropriately determined so that the intended specific gravity of the center 8 is achieved. A particularly preferred filler is zinc oxide. Zinc oxide functions not only as a specific gravity adjusting role but also as a crosslinking aid. In the rubber composition of the center 8, various additives such as sulfur, an antioxidant, a colorant, a plasticizer, and a dispersant are blended in appropriate amounts as necessary. The center 8 may be blended with a crosslinked rubber powder or a synthetic resin powder.

  The surface hardness H1 of the center 8 is preferably 35 or more and 60 or less. Excellent resilience performance can be achieved by the center 8 having a surface hardness H1 of 35 or more. In this respect, the surface hardness H1 is more preferably equal to or greater than 40, and particularly preferably equal to or greater than 45. An excellent feel at impact can be achieved by the center 8 having a surface hardness H1 of 60 or less. In this respect, the surface hardness H1 is more preferably equal to or less than 55, and particularly preferably equal to or less than 50. A surface hardness H1 is measured by pressing a Shore D type hardness meter against the surface of the center 8 from which the intermediate layer 10 and the cover 6 have been peeled off. For the measurement, an automatic rubber hardness measuring machine (trade name “P1” by Kobunshi Keiki Co., Ltd.) equipped with this hardness meter is used.

  In light of feel at impact, the center 8 has an amount of compressive deformation CD1 of preferably 3.5 mm or greater, more preferably 4.0 mm or greater, and particularly preferably 4.5 mm or greater. In light of resilience performance, the amount of compressive deformation CD1 is preferably equal to or less than 6.5 mm, more preferably equal to or less than 6.5 mm, and particularly preferably equal to or less than 6.0 mm.

  A YAMADA compression tester is used to measure the amount of compressive deformation. In this tester, a sphere (center 8, core 4, golf ball 2, etc.) to be measured is placed on a metal rigid plate. A metal cylinder gradually descends toward the sphere. The sphere sandwiched between the bottom surface of the cylinder and the rigid plate is deformed. The moving distance of the cylinder from the state where the initial load of 98 N is applied to the sphere to the state where the 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 the initial load to the final load is 1.67 mm / s. The atmospheric temperature at the time of measurement is 23 ° C. Prior to the measurement, the sphere is held in a thermostat at 23 ° C. for 24 hours or more.

  The diameter of the center 8 is preferably 35.0 mm or greater and 40.0 mm or less. The mass of the center 8 is preferably 30 g or more and 41 g or less. The crosslinking temperature of the center 8 is 140 ° C. or higher and 180 ° C. or lower. The crosslinking time of the center 8 is 10 minutes or more and 60 minutes or less. The center may have two or more layers. The center may include a rib on the surface. The center may be hollow.

  The mid layer 10 is formed from a thermoplastic resin composition. Examples of the base polymer of the resin composition include ionomer resins, thermoplastic polyester elastomers, thermoplastic polyamide elastomers, thermoplastic polyurethane elastomers, thermoplastic polyolefin elastomers, and thermoplastic polystyrene elastomers. In particular, an ionomer resin is preferable. The ionomer resin is highly elastic. As will be described later, the cover 6 of the golf ball 2 is thin. When the golf ball 2 is hit, the mid layer 10 is greatly deformed due to the thin cover 6. Therefore, the mid layer 10 has a great influence on the resilience performance. The golf ball 2 having the mid layer 10 containing an ionomer resin is excellent in resilience performance.

  An ionomer resin and another resin may be used in combination. When used in combination, the ionomer resin is the main component of the base polymer from the viewpoint of resilience performance. The proportion of the ionomer resin in the total base polymer is preferably 50% by mass or more, more preferably 70% by mass or more, and particularly preferably 85% or more.

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

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

  As specific examples of the ionomer resin, trade names “Hi-Milan 1555”, “Hi-Milan 1557”, “Hi-Milan 1605”, “Hi-Milan 1706”, “Hi-Milan 1856”, “Hi-Milan 1856”, “Hi-Milan 1855” “Himiran AM7311”, “Himiran AM7315”, “Himiran AM7317”, “Himiran AM7329” and “Himiran AM7337”; DuPont's trade names “Surlin 6120”, “Surlin 6910”, “Surlin 7930”, “Surlin 7940”, “Surling 8140”, “Surling 8150”, “Surling 8940”, “Surling 8945”, “Surling 9120”, “Surling 9150”, “Surling 9910”, “Surling 9945”, “Surry AD8546 "," HPF1000 "and" HPF2000 "; and ExxonMobil Chemical Co. under the trade name of" IOTEK7010 "," IOTEK7030 "," IOTEK7510 "," IOTEK7520 "includes" IOTEK8000 "and" IOTEK8030 ". Two or more ionomer resins may be used in combination.

  A filler may be blended in the resin composition of the mid layer 10 for the purpose of adjusting specific gravity and the like. Examples of suitable fillers include zinc oxide, barium sulfate, calcium carbonate, and magnesium carbonate. As a filler, a powder made of a high specific gravity metal may be blended. Specific examples of the high specific gravity metal include tungsten and molybdenum. The blending amount of the filler is appropriately determined so that the intended specific gravity of the mid layer 10 is achieved. The mid layer 10 may be blended with a colorant, a crosslinked rubber powder, or a synthetic resin powder.

  The thickness of the mid layer 10 is preferably 0.5 mm or more, and more preferably 1.0 mm or more. This thickness is preferably 2.0 mm or less, and more preferably 1.8 mm or less.

  The mid layer 10 has a hardness H2 of preferably 55 or greater, more preferably 60 or greater, and particularly preferably 63 or greater. The hardness H2 is preferably 75 or less, more preferably 72 or less, and particularly preferably 70 or less.

  In the present invention, the hardness H2 of the mid layer 10 and the hardness H3 of the cover 6 are measured in accordance with the provisions of “ASTM-D 2240-68”. For the measurement, an automatic rubber hardness meter (trade name “P1”, available from Kobunshi Keiki Co., Ltd.) equipped with a Shore D hardness meter is used. For the measurement, a sheet made of the same material as that of the intermediate layer 10 (or the cover 6) and having a thickness of about 2 mm is used. Prior to measurement, the sheet is stored at a temperature of 23 ° C. for 2 weeks. At the time of measurement, three sheets are overlaid.

  The diameter of the core 4 (that is, the center 8 and the intermediate layer 10) is preferably 41.0 mm or greater and 42.0 mm or less. The mass of the core 4 is preferably 42.0 g or more and 44.0 g or less. The amount of compressive deformation CD2 of the core 4 is preferably 3.0 mm or greater and 5.0 mm or less.

  The cover 6 is formed from a resin composition. Examples of the base resin of this resin composition include polyurethane, polyamide elastomer, styrene block-containing thermal elastomer, polyester elastomer, polyolefin elastomer, and ionomer resin.

  A preferred base polymer is polyurethane. The resin composition may contain a thermoplastic polyurethane or a thermosetting polyurethane. From the viewpoint of productivity, thermoplastic polyurethane is preferred. The thermoplastic polyurethane includes a polyurethane component as a hard segment and a polyester component or a polyether component as a soft segment. Thermoplastic polyurethane is soft. The cover 6 using this polyurethane is excellent in scratch resistance. When the thermoplastic polyurethane and other resin are used in combination in the cover 6, the ratio of the thermoplastic polyurethane to the total base resin is preferably 50% by mass or more, more preferably 60% by mass or more, and particularly preferably 70% by mass or more. .

  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. Low molecular weight polyols and high molecular weight polyols can be used.

  Examples of the low molecular weight polyol include diol, triol, tetraol and hexaol. Specific examples of the diol 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-cyclohexanedimethylol. An aniline diol or bisphenol A diol may be used. Specific examples of triols include glycerin, trimethylolpropane, and hexanetriol. Specific examples of tetraol include pentaerythritol and sorbitol.

  As high molecular weight polyols, polyether polyols such as polyoxyethylene glycol (PEG), polyoxypropylene glycol (PPG) and polytetramethylene ether glycol (PTMG); polyethylene adipate (PEA), polybutylene adipate (PBA) ) And polyhexamethylene adipate (PHMA); lactone polyester polyols such as poly-ε-caprolactone (PCL); polycarbonate polyols such as polyhexamethylene carbonate; and acrylic polyols. Two or more polyols may be used in combination. In light of the feel at impact of the golf ball 2, the number average molecular weight of the high molecular weight polyol is preferably 400 or more, and more preferably 1000 or more. The number average molecular weight is preferably 10,000 or less.

  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.

As aromatic diisocyanates, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4′-diphenylmethane diisocyanate (MDI), 1,5-naphthylene diisocyanate (NDI), 3,3′-vitrylene-4, Examples are 4'-diisocyanate (TODI), xylylene diisocyanate (XDI), tetramethylxylylene diisocyanate (TMXDI) and paraphenylene diisocyanate (PPDI). As the aliphatic diisocyanate, hexamethylene diisocyanate (HDI) is exemplified. As the alicyclic diisocyanate, 4,4′-dicyclohexylmethane diisocyanate (H ₁₂ MDI), 1,3-bis (isocyanatomethyl) cyclohexane (H ₆ XDI), isophorone diisocyanate (IPDI) and trans-1,4-cyclohexane Diisocyanate (CHDI) is exemplified. 4,4′-dicyclohexylmethane diisocyanate is preferred.

  Specific examples of thermoplastic polyurethanes include BASF Japan's trade names “Elastolan XNY80A”, “Elastolan XNY82A”, “Elastolan XNY85A”, “Elastolan XNY90A”, “Elastolan XNY97A”, “Elastolan XNY585” and “Elastollan XKP016N”; trade names “Rezamin P4585LS” and “Rezamin PS62490” of Dainichi Seika Kogyo Co., Ltd.

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

  The cover 6 has a hardness H3 of preferably 30 or greater and 50 or less. The golf ball 2 having a hardness H3 of 30 or more is excellent in resilience performance. When the golf ball 2 is hit by an amateur player, a great flight distance can be obtained. From this viewpoint, the hardness H3 is more preferably 31 or more, and particularly preferably 32 or more. The golf ball 2 having a hardness H3 of 50 or less is excellent in spin performance. A high trajectory of the golf ball 2 is achieved by the spin. When this golf ball 2 is hit by an amateur player, an excellent ballistic feeling can be obtained. In this respect, the hardness H3 is more preferably equal to or less than 45, and particularly preferably equal to or less than 40.

  The thickness of the cover 6 is preferably 0.3 mm or greater and 1.8 mm or less. The golf ball 2 having a thickness of 0.3 mm or more is excellent in spin performance. A high trajectory of the golf ball 2 is achieved by the spin. When this golf ball 2 is hit by an amateur player, an excellent ballistic feeling can be obtained. In this respect, the thickness is more preferably equal to or greater than 0.4 mm, and particularly preferably equal to or greater than 0.5 mm. The golf ball 2 having a thickness of 1.8 mm or less is excellent in resilience performance. When the golf ball 2 is hit by an amateur player, a great flight distance can be obtained. Furthermore, the golf ball 2 having a thickness of 1.8 mm or less is excellent in hit feeling. From these viewpoints, the thickness is more preferably 1.0 mm or less, and particularly preferably 0.8 mm or less.

  The golf ball 2 may include a reinforcing layer between the mid layer 10 and the cover 6. The reinforcing layer is firmly attached to the intermediate layer 10 and is also firmly attached to the cover 6. The reinforcing layer suppresses peeling of the cover 6 from the intermediate layer 10. The reinforcing layer is formed from a resin composition. As a preferable base polymer of the reinforcing layer, a two-component curable epoxy resin and a two-component curable urethane resin are exemplified.

  The compression deformation amount CD3 of the golf ball 2 is 3.0 mm or greater and 5.0 mm or less. The golf ball 2 having a compression deformation amount CD3 of 3.0 mm or more does not have excessive resilience performance. This golf ball 2 can be adapted to the flight distance rule set by the USGA. Further, in the golf ball 2 having the compression deformation amount CD3 of 3.0 mm or more, a soft hit feeling can be obtained. From these viewpoints, the amount of compressive deformation CD3 is more preferably 3.5 mm or more, and particularly preferably 3.8 mm or more. The golf ball 2 having a compression deformation amount CD3 of 5.0 mm or less is excellent in resilience performance. In this respect, the amount of compressive deformation CD3 is more preferably equal to or less than 4.7 mm, and particularly preferably equal to or less than 4.5 mm.

  As shown in FIGS. 2 and 3, the contour of the dimple 12 is a circle. The golf ball 2 includes a dimple A having a diameter of 4.6 mm, a dimple B having a diameter of 4.4 mm, a dimple C having a diameter of 4.2 mm, a dimple D having a diameter of 4.0 mm, A dimple E having a diameter of 3.9 mm and a dimple F having a diameter of 2.6 mm are provided. The number of types of dimples 12 is six. The golf ball 2 may have a non-circular dimple instead of the circular dimple 12 or together with the circular dimple 12.

  The number of dimples A is 42, the number of dimples B is 72, the number of dimples C is 66, the number of dimples D is 126, the number of dimples E is 12, The number of dimples F is twelve. The total number of dimples 12 is 330.

  FIG. 4 shows a cross section along a plane passing through the center of the dimple 12 and the center of the golf ball 2. The vertical direction in FIG. 4 is the depth direction of the dimple 12. In FIG. 4, a virtual sphere 16 is indicated by a two-dot chain line. The surface of the phantom sphere 16 is the surface of the golf ball 2 when it is assumed that the dimple 12 does not exist. The dimple 12 is recessed from the surface of the phantom sphere 16. The land 14 coincides with the surface of the phantom sphere 16. In the present embodiment, the cross-sectional shape of the dimple 12 is substantially an arc.

  In FIG. 4, the diameter of the dimple 12 is indicated by a double arrow Dm. The diameter Dm is the distance between one contact point Ed and the other contact point Ed when a common tangent line Tg is drawn on both sides of the dimple 12. The contact point Ed is also the edge of the dimple 12. The edge Ed defines the contour of the dimple 12. In FIG. 4, what is indicated by a double arrow Dp is the depth of the dimple 12. This depth Dp is the distance between the deepest part of the dimple 12 and the phantom sphere 16.

  The diameter Dm of each dimple 12 is preferably 2.0 mm or greater and 6.0 mm or less. The dimples 12 having a diameter Dm of 2.0 mm or more contribute to turbulence. In this respect, the diameter Dm is more preferably equal to or greater than 2.5 mm, and particularly preferably equal to or greater than 2.8 mm. The dimple 12 having a diameter Dm of 6.0 mm or less does not impair the essence of the golf ball 2 that is substantially a sphere. In this respect, the diameter Dm is more preferably equal to or less than 5.5 mm, and particularly preferably equal to or less than 5.0 mm.

  From the viewpoint that hops of the golf ball 2 are suppressed, the depth Dp of the dimple 12 is preferably 0.10 mm or more, more preferably 0.13 mm or more, and particularly preferably 0.15 mm or more. In light of suppression of dropping of the golf ball 2, the depth Dp is preferably equal to or less than 0.60 mm, more preferably equal to or less than 0.55 mm, and particularly preferably equal to or less than 0.50 mm.

The spherical area s of the dimple 12 is an area of a zone surrounded by the outline of the dimple 12 in the surface of the phantom sphere 16 of the golf ball 2. In the golf ball 2 shown in FIGS. 2 and 3, the spherical area s of the dimple A is 16.61 mm ² , the spherical area s of the dimple B is 15.20 mm ² , and the spherical area s of the dimple C is 13.3. is 85 mm ^2, the spherical area s of the dimple D is 12.56mm ^2, the spherical area s of the dimple E is 11.94 mm ^2, the spherical area s of the dimple F is 5.31mm ^2.

The ratio of the total spherical area s of all the dimples 12 to the surface area of the phantom sphere 16 is referred to as an occupation ratio. From the viewpoint of turbulence, the occupation ratio is preferably 0.780 or more, more preferably 0.800 or more, and particularly preferably 0.840 or more. The occupation ratio is preferably 0.950 or less. In the golf ball 2 shown in FIGS. 2 and 3, the total spherical area s is 4495.3 mm ² . Since the surface area of the phantom sphere 16 of this golf ball 2 is 5728.0 mm ² , the occupation ratio is 0.785.

  From the viewpoint of achieving a sufficient occupation ratio, the total number of the dimples 12 is preferably 250 or more, more preferably 280 or more, and particularly preferably 300 or more. From the viewpoint that each dimple 12 can contribute to turbulence, the total number N is preferably 450 or less, more preferably 400 or less, and particularly preferably 380 or less.

In the present invention, the “dimple volume” means the volume of the portion surrounded by the phantom sphere 16 and the surface of the dimple 12. The total volume of the dimples 12 of this golf ball 2 is preferably 580 mm ³ or less. In the golf ball 2 having a total volume of 580 mm ³ or less, a high trajectory is achieved. When this golf ball 2 is hit by an amateur player, an excellent ballistic feeling can be obtained. In this respect, the total volume is more preferably 560 mm ³ or less, 550 mm ³ or less is particularly preferred. From the standpoint that hops of the golf ball 2 are suppressed, the total volume is preferably 430 mm ³ or more.

This golf ball 2 satisfies the following formula (I).
0.80 ≦ ((L1 + L2) / 2) ≦ 0.95 (I)
In this equation, L1 represents the ratio (CL1 / CD1) of the lift coefficient CL1 to the drag coefficient CD1 measured under the conditions where the Reynolds number is 1.290 × 10 ⁵ and the spin rate is 2820 rpm. In this equation, L2 represents the ratio (CL2 / CD2) of the lift coefficient CL2 to the drag coefficient CD2 measured under the conditions where the Reynolds number is 1.771 × 10 ⁵ and the spin rate is 2940 rpm. The lift coefficient and drag coefficient are measured in accordance with ITR (Indoor Test Range) defined by USGA.

The Reynolds number is a dimensionless number used in the field of fluid dynamics. The Reynolds number (Re) can be calculated by the following mathematical formula.
Re = ρvL / μ
In this equation, ρ represents the density of the fluid, v represents the velocity of the object, L represents the characteristic length, and μ represents the viscosity coefficient of the fluid.

As described above, the Reynolds number when measuring the lift coefficient CL1 and the drag coefficient CD1 is 1.290 × 10 ⁵ . The Reynolds number corresponds to the ball speed when the golf ball 2 flying in the air is hit with a driver whose head speed is 35 m / s. The spin rate when measuring the lift coefficient CL1 and the drag coefficient CD1 is 2820 rpm. This spin rate is an average value of a golfer whose head speed is 35 m / s. In the measurement of the ratio L1, a golfer with a head speed of 35 m / s is assumed.

As described above, the Reynolds number when measuring the lift coefficient CL2 and the drag coefficient CD2 is 1.771 × 10 ⁵ . This Reynolds number corresponds to the ball speed when the golf ball 2 flying in the air is hit with a driver whose head speed is 45 m / s. The spin rate when measuring the lift coefficient CL2 and the drag coefficient CD2 is 2940 rpm. This spin rate is an average value of a golfer whose head speed is 45 m / s. In the measurement of the ratio L2, a golfer with a head speed of 45 m / s is assumed.

  The head speed of many amateur players is 35 m / s or more and 45 m / s or less. In the above formula (I), the ratio L1 corresponding to the head speed of 35 m / s and the ratio L2 corresponding to the head speed of 45 m / s are averaged. The golf ball 2 having an average value ((L1 + L2) / 2) of 0.80 or more and 0.95 or less is suitable for many amateur players.

  When the golf ball 2 whose average value ((L1 + L2) / 2) is 0.80 or more is hit by an amateur player, a high trajectory is obtained. Even though the golf ball 2 conforms to the USGA flight distance rules, the player is satisfied with the trajectory. This golf ball 2 is excellent in ballistic feeling. In this respect, the average value ((L1 + L2) / 2) is more preferably equal to or greater than 0.84, and particularly preferably equal to or greater than 0.88.

  The golf ball 2 having an average value ((L1 + L2) / 2) of 0.95 or less is unlikely to hop. In this respect, the average value ((L1 + L2) / 2) is more preferably equal to or less than 0.93, and particularly preferably equal to or less than 0.92.

By optimizing the specifications of the dimple 12, an average value ((L1 + L2) / 2) within the above range can be achieved. In particular,
(1) Optimization of the depth of the dimple 12 (2) Optimization of the area of the dimple 12 (3) Optimization of the volume of the dimple 12 (4) Optimization of the number of dimples 12 (5) Occupancy rate of the dimple 12 By means such as optimization, the ratio L1 and the ratio L2 are optimized, and an average value ((L1 + L2) / 2) within the above range can be achieved.

  The ratio L1 is preferably 0.85 or more and 0.93 or less. When the golf ball 2 having the ratio L1 of 0.85 or more is hit with a driver having a head speed of 35 m / s, a high trajectory is obtained. Even though the golf ball 2 conforms to the USGA flight distance rules, the player is satisfied with the trajectory. This golf ball 2 is excellent in ballistic feeling. In this respect, the ratio L1 is more preferably equal to or greater than 0.87, and particularly preferably equal to or greater than 0.88. The golf ball 2 having the ratio L1 of 0.93 or less is difficult to hop. In this respect, the ratio L1 is particularly preferably equal to or less than 0.92.

  The ratio L2 is preferably 0.76 or more and 0.92 or less. When the golf ball 2 having the ratio L2 of 0.76 or more is hit with a driver having a head speed of 45 m / s, a high trajectory is obtained. Even though the golf ball 2 conforms to the USGA flight distance rules, the player is satisfied with the trajectory. This golf ball 2 is excellent in ballistic feeling. In this respect, the ratio L2 is more preferably equal to or greater than 0.80, and particularly preferably equal to or greater than 0.86. The golf ball 2 having the ratio L2 of 0.92 or less is difficult to hop. In this respect, the ratio L2 is particularly preferably equal to or less than 0.91.

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

[Example 1]
100 parts by weight of high-cis polybutadiene (trade name “BR-730” from JSR) 22.5 parts by weight of zinc acrylate, 5 parts by weight of zinc oxide, appropriate amount of barium sulfate, 0.5 parts by weight of diphenyl disulfide And 0.6 mass part dicumyl peroxide was knead | mixed and the rubber composition was obtained. This rubber composition was put into a mold composed of an upper mold and a lower mold each having a hemispherical cavity, and heated at 170 ° C. for 18 minutes to obtain a center having a diameter of 38.5 m.

  50 parts by weight of ionomer resin (trade name “HIMILAN 1605” from Mitsui DuPont Polychemical), 50 parts by weight of other ionomer resin (trade name “HIMIRAN AM7329” from Mitsui DuPont Polychemical) and 4 parts by weight of titanium dioxide. Were kneaded with a twin-screw kneading extruder to obtain a resin composition. This resin composition was coated around the core by an injection molding method to form an intermediate layer. The thickness of this intermediate layer was 1.6 mm.

  A coating composition (trade name “Porin 750LE”, manufactured by Shinto Paint Co., Ltd.) using a two-pack curable epoxy resin as a base polymer was prepared. The curing agent liquid of this coating composition is composed of 40 parts by mass of modified polyamidoamine, 55 parts by mass of solvent, and 5 parts by mass of titanium dioxide. The mass ratio with respect to the curing agent liquid was 1/1, and this coating composition was applied to the surface of the intermediate layer with a spray gun and held at 23 ° C. for 6 hours to obtain a reinforcing layer. The thickness of the reinforcing layer was 10 μm.

  100 parts by mass of a thermoplastic polyurethane elastomer (BASF Japan trade name “Elastolan XNY85A”) and 4 parts by mass of titanium dioxide were kneaded with a twin screw extruder to obtain a resin composition. A half shell was obtained from this resin composition by compression molding. A sphere composed of a core, an intermediate layer and a reinforcing layer was covered with two half shells. The half shell and the sphere were both put into a final mold including an upper mold and a lower mold having a hemispherical cavity and a large number of pimples on the cavity surface, and a cover was obtained by a compression molding method. The cover thickness was 0.5 mm. A dimple having a shape obtained by inverting the shape of the pimple was formed on the cover. A clear paint based on a two-component curable polyurethane was applied around the 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. This golf ball has a dimple specification D3 shown in Table 1 below.

[Example 2-11 and Comparative Example 1-9]
Golf balls of Example 2-11 and Comparative Example 1-9 were obtained in the same manner as in Example 1 except that the specifications of the center, intermediate layer, cover and dimple were as shown in Table 5-8 below. . Details of the composition of the center are shown in Table 1 below. Details of the composition of the interlayer and cover are shown in Table 2 below. Details of the dimple specifications are shown in Tables 3 and 4 below.

[Flight test]
A driver equipped with a titanium alloy head (trade name “XXIO”, Dunlop Sports Co., Ltd., shaft hardness: R, loft angle: 11 °) equipped with a titanium alloy head was attached to a swing machine manufactured by Golf Laboratory. A golf ball was hit under the condition that the head speed was 40 m / sec, and the ball speed, launch angle, spin rate, maximum point coordinates (x, y), and carry were measured. The coordinate x is the horizontal distance from the launch point to the highest point. The coordinate y is the vertical distance from the launch point to the highest point. Carry is the distance from the launch point to the fall point. The results are shown in Tables 9-12 below.

[sensory evaluation]
Ten testers were struck by a golf ball with a driver and evaluated for ballistic feel and feel. Rating was performed according to the following criteria. The results are shown in Tables 9-12 below.
Ballistic feel: Number of testers who feel that the flight distance is large A: 8 or more B: 5 or more and 7 or less C: 2 or more and 4 or less D: 1 or less Blow feel rig: Number of testers who feel soft A : 8 or more B: 5 or more and 7 or less C: 2 or more and 4 or less D: 1 or less

  As shown in Tables 9-12, the golf balls of the examples are excellent in various performances. From this evaluation result, the superiority of the present invention is clear.

  The golf ball according to the present invention is suitable for playing on a golf course, practice in a driving range, and the like.

2 ... Golf ball 4 ... Core 6 ... Cover 8 ... Center 10 ... Intermediate layer 12 ... Dimple 14 ... Land 16 ... Virtual sphere

Claims (5)

A core and a cover located outside the core;
It has a large number of dimples on its surface,
The cover has a Shore D hardness of 30 to 50,
The amount of compressive deformation measured under conditions where the initial load is 98 N and the final load is 1274 N is 3.0 mm or more and 5.0 mm or less,
A golf ball that satisfies the following mathematical formula (I).
0.80 ≦ ((L1 + L2) / 2) ≦ 0.95 (I)
(In this equation, L1 represents the ratio (CL1 / CD1) of the lift coefficient CL1 to the drag coefficient CD1 measured under the conditions where the Reynolds number is 1.290 × 10 ⁵ and the spin rate is 2820 rpm, and L2 is the Reynolds number. Represents the ratio of the lift coefficient CL2 to the drag coefficient CD2 (CL2 / CD2) measured under the condition of 1.771 × 10 ⁵ and the spin rate of 2940 rpm.) The golf ball according to claim 1, wherein a total volume of the dimples is 430 mm ³ or more and 580 mm ³ or less.   The golf ball according to claim 1, wherein the cover has a thickness of 0.3 mm to 1.8 mm.   The golf ball according to claim 1, wherein the ratio L1 is not less than 0.85 and not more than 0.93.   The golf ball according to claim 1, wherein the ratio L2 is 0.76 or more and 0.92 or less.

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