JP5160056B2 - Two piece golf balls - Google Patents

Description

  The present invention relates to a two-piece golf ball having a core, a cover, and dimples.

  Flight performance is important for golf balls. Flight performance is highly dependent on the aerodynamic characteristics of the golf ball. Flight performance is also highly dependent on the resilience performance of the golf ball.

  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. Turbulent separation shifts the separation point of air from the golf ball backwards, reducing drag. Turbulent separation promotes the deviation between the upper separation point and the lower separation point of the golf ball due to backspin, and increases the lift acting on the golf ball. The reduction of drag and the improvement of lift are referred to as “dimple effect”. Excellent dimples better disturb the air flow. Excellent dimples produce a great flight distance.

  It is known to those skilled in the art that a great dimple effect can be obtained in a golf ball in which dimples are densely arranged. Several proposals regarding dimple patterns aimed at improving the dimple effect have been made.

  Japanese Patent Application Laid-Open No. 50-8630 (USP 5080367) discloses a golf ball having a large number of dimples having a uniform size. In this golf ball, the pitch is smaller than 0.065 inches in most of the dimple pairs. In this golf ball, the relationship between the pitch and the dimple diameter is not considered. In contrast to a typical dimple diameter, the 0.065 inch pitch is not small enough. In a pattern having dimples of uniform size, the diameter cannot be set large. The dimples on this golf ball are not dense enough.

  Japanese Patent Application Laid-Open No. 62-192181 (US Pat. No. 4,831,677) discloses a golf ball having large dimples and small dimples. In this golf ball, a high dimple density is achieved by arranging small dimples in a region surrounded by a plurality of large dimples. However, small dimples do not fully contribute to the dimple effect.

  Japanese Laid-Open Patent Publication No. 4-347177 (USP 5292132) discloses a golf ball in which dimples are arranged so that a rectangle having a predetermined size cannot be formed on a land. In this golf ball, a small land ratio is achieved by arranging a large number of small dimples. However, small dimples do not fully contribute to the dimple effect.

  Commercially available golf balls include a two-piece structure and a three-piece structure. The two-piece golf ball includes a core and a cover. The structure of the two-piece golf ball is simple. Two-piece golf balls can be manufactured at low cost. Various improvements have been proposed for two-piece golf balls.

  JP-A-6-319831 discloses a two-piece golf ball having a core formed from a rubber composition containing pentachlorothiophenol. The rebound performance of this golf ball is not sufficient.

  Japanese Patent Application Laid-Open No. 8-280845 discloses a two-piece golf ball having a predetermined amount of compression deformation. This golf ball includes a cover having a thickness of 1.4 mm to 2.5 mm. This cover is thick. With this golf ball, an appropriate deformation behavior cannot be obtained. The rebound performance of this golf ball is not sufficient.

  Japanese Patent Application Laid-Open No. 60-163673 discloses a two-piece golf ball having a cover having a predetermined bending rigidity value. In this golf ball, no consideration is given to matching between the structure and the dimples. The flight performance of this golf ball is not sufficient.

  Japanese Patent Application Laid-Open No. 62-57571 discloses a two-piece golf ball in which a specific polybutadiene is used for the core. In this golf ball, no consideration is given to matching between the structure and the dimples. The aerodynamic characteristics of this golf ball are not sufficient.

Japanese Patent Application Laid-Open No. 2004-180790 discloses a two-piece golf ball in which a specific polybutadiene is used for a core and has a predetermined dimple volume and dimple area. In this golf ball, no consideration is given to the dimple pattern. The aerodynamic characteristics of this golf ball are not sufficient.
Japanese Patent Laid-Open No. 50-8630 JP-A-62-192181 JP-A-4-347177 JP-A-6-319831 JP-A-8-280845 JP 60-163673 A JP-A-62-57571 JP 2004-180790 A

  A golfer's greatest concern with golf balls is flight distance. From the viewpoint of flight performance, the two-piece golf ball has room for improvement. An object of the present invention is to provide a two-piece golf ball having excellent flight performance.

  The two-piece golf ball according to the present invention includes a spherical core, a cover covering the core, and a large number of dimples formed on the surface of the cover. This cover has a thickness of less than 1.3 mm and a hardness of 59 or more. The amount of compressive deformation of this golf ball is less than 2.4 mm. When the average diameter of all the dimples is Da, the ratio (N1 / N) of the number N1 of adjacent dimple pairs whose pitch is (Da / 4) or less to the total number N of dimples is 2.70 or more. The ratio (N2 / N1) of the number N2 of the adjacent dimple pairs whose pitch is (Da / 20) or less to the number N1 is 0.50 or more.

  The core is formed by crosslinking a rubber composition. Preferably, the main component of the base rubber of the rubber composition is polybutadiene synthesized using a rare earth element-based catalyst. Preferably, the rubber composition includes a polysulfide compound containing a bromo group.

  The cover is made of a resin composition. Preferably, the base resin of the resin composition includes a thermoplastic elastomer containing an ionomer resin as a main component and having a material hardness of less than 50.

  Preferably, the ratio (N2 / N1) is 0.60 or more. Preferably, the average diameter Da is 4.00 mm or more. Preferably, the total number N of dimples is 362 or less. Preferably, the ratio of the total area of all the dimples to the surface area of the phantom sphere is 75% or more.

  Preferably, each of the northern hemisphere and the southern hemisphere on the surface of the golf ball includes a pole vicinity region, an equator vicinity region, and an adjustment region. This adjustment region is located between the pole vicinity region and the equator vicinity region. The dimple pattern in the pole vicinity region is composed of a plurality of units. These units are rotationally symmetric with respect to each other about the pole. The dimple pattern in the vicinity of the equator is composed of a plurality of units. These units are rotationally symmetric with respect to each other about the pole. The number of units in the pole vicinity region is different from the number of units in the equator vicinity region. The dimple pattern in the adjustment region cannot be divided into a plurality of units that are rotationally symmetric with respect to each other around the pole, or consists of a plurality of units that are rotationally symmetric with respect to the pole and the number of units is This is different from the number of units in the pole vicinity region and the equator vicinity region.

  It is preferable that there is no great circle that does not intersect with the dimples on the surface of the golf ball.

  The golf ball according to the present invention is excellent in resilience performance and aerodynamic characteristics. Due to the synergistic effect of resilience performance and aerodynamic characteristics, this golf ball provides a great flight distance.

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

  FIG. 1 is a schematic cross-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 that covers the core 4. A large number of dimples 8 are formed on the surface of the cover 6. A portion of the surface of the golf ball 2 other than the dimples 8 is a land 10. The golf ball 2 includes a paint layer and a mark layer outside the cover 6, but these layers are not shown.

  The golf ball 2 has a diameter of 40 mm or greater and 45 mm or less. From the viewpoint of satisfying the standards of the US Golf Association (USGA), the diameter is more preferably 42.67 mm or more. 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 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. From the viewpoint that the USGA standard is satisfied, the mass is more preferably 45.93 g or less.

  The core 4 is formed by crosslinking a rubber composition. Examples of the base rubber of the rubber composition 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 proportion of polybutadiene in the total base rubber is preferably 50% by mass or more, particularly 80% by mass or more. Polybutadiene having a cis-1,4 bond ratio of 40 mol% or more, more preferably 80 mol% or more is preferred.

  Polybutadiene synthesized using a rare earth element-based catalyst is particularly preferred. By using this polybutadiene, the excellent resilience performance of the golf ball 2 can be achieved. The rare earth element-based catalyst includes a lanthanum series rare earth element compound, an organoaluminum compound, an alumoxane, and a halogen-containing compound. Lanthanum series rare earth element compounds are preferred. The lanthanum series rare earth element compounds include halides, carboxylates, alcoholates, thioalcolates, and amides of elements having atomic numbers of 57 to 71. A neodymium catalyst (a catalyst containing a neodymium compound) is particularly preferred. The molar ratio of butadiene to the lanthanum series rare earth element compound during polymerization is preferably 1000/1 or more, and more preferably 5000/1 or more. The molar ratio is preferably 2000000/1 or less, and more preferably 1000000/1 or less.

  It is preferable that polybutadiene synthesized using a rare earth element-based catalyst is further modified with a compound having an alkoxysilyl group. The modified polybutadiene has 90 mol% or more of cis-1,4 bonds. With this modified polybutadiene, the excellent resilience performance of the golf ball 2 is achieved.

  The compound having an alkoxysilyl group includes an epoxy group-containing alkoxysilane and an isocyanate group-containing alkoxysilane compound. Specific examples of the epoxy group-containing alkoxysilane include 3-glycidyloxypropyltrimethoxysilane, 3-glycidyloxypropyltriethoxysilane, (3-glycidyloxypropyl) methyldimethoxysilane, and (3-glycidyloxypropyl) methyldiethoxy. Silane, β- (3,4-epoxycyclohexyl) trimethoxysilane, β- (3,4-epoxycyclohexyl) triethoxysilane, β- (3,4-epoxycyclohexyl) methyldimethoxysilane, β- (3,4 -Epoxycyclohexyl) ethyldimethoxysilane, 3-glycidyloxypropyltrimethoxysilane condensate and (3-glycidyloxypropyl) methyldimethoxysilane condensate. Specific examples of the isocyanate group-containing alkoxysilane compound include 3-isocyanatopropyltrimethoxysilane, 3-isocyanatopropyltriethoxysilane, (3-isocyanatopropyl) methyldimethoxysilane, and (3-isocyanatopropyl) methyl. Examples include condensates of diethoxysilane, 3-isocyanatopropyltrimethoxysilane and (3-isocyanatopropyl) methyldimethoxysilane.

In this modified polybutadiene, the ratio (Mw / Mn) of the weight average molecular weight Mw to the number average molecular weight Mn is 1.0 to 3.5, particularly 1.0 to 3.3. The modified polybutadiene has a Mooney viscosity ML _{1 + 4} (100 ° C.) of 30 to 100, in particular 50 to 90.

  The rubber composition for the core 4 includes 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. Specific examples of preferred co-crosslinking agents include zinc acrylate, magnesium acrylate, zinc methacrylate and magnesium methacrylate. Zinc acrylate and zinc methacrylate are particularly preferable because of high resilience performance.

  As a co-crosslinking agent, an α, β-unsaturated carboxylic acid having 2 to 8 carbon atoms and a metal oxide may be blended. Both react in the rubber composition to obtain a salt. This salt contributes to the crosslinking reaction. Preferred α, β-unsaturated carboxylic acids include acrylic acid and methacrylic acid. Preferred metal oxides include zinc oxide and magnesium oxide.

  The amount of the co-crosslinking agent is preferably 20 parts by mass or more and 55 parts by mass or less with respect to 100 parts by mass of the base rubber. By setting the blending amount to 20 parts by mass or more, excellent resilience performance can be achieved. In this respect, the amount is more preferably equal to or greater than 25 parts by weight, and particularly preferably equal to or greater than 30 parts by weight. By setting the blending amount to 55 parts by mass or less, an excellent feel at impact can be achieved. In this respect, the amount to be blended is more preferably equal to or less than 50 parts by weight.

  Preferably, the rubber composition of the core 4 includes an organic peroxide together with a co-crosslinking agent. The organic peroxide functions as a crosslinking initiator. Organic peroxides contribute to resilience performance. 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. A particularly versatile organic peroxide is dicumyl peroxide.

  The compounding amount of the organic peroxide is preferably 0.1 parts by mass or more and 3.0 parts by mass or less with respect to 100 parts by mass of the base rubber. By setting the blending amount to 0.1 parts by mass or more, excellent resilience performance can be achieved. In this respect, the amount is more preferably equal to or greater than 0.3 parts by weight, and particularly preferably equal to or greater than 0.5 parts by weight. By setting the blending amount to 3.0 parts by mass or less, an excellent feel at impact can be achieved. In this respect, the amount to be blended is 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 core 4 includes an organic sulfur compound. By using the organic sulfur compound, the excellent resilience performance of the golf ball 2 can be achieved. In particular, a polysulfide compound containing a bromo group is preferable. This polysulfide compound is represented by the following chemical formula.

  In the above chemical formula, R1 to R10 represent H or Br. In the above chemical formula, n is an integer of 2 or more. At least one of R1 to R5 is Br. At least one of R6 to R10 is Br. It is preferable that three or more of R1 to R5 are Br and three or more of R6 to R10 are Br. More preferably, all of R1 to R10 are Br. From the viewpoint of easy availability, disulfide compounds are preferred.

  Specific examples of disulfide compounds containing bromo groups include bis (bromophenyl) disulfide, bis (dibromophenyl) disulfide, bis (tribromophenyl) disulfide, bis (tetrabromophenyl) disulfide and bis (pentabromophenyl) disulfide. Is mentioned. Bis (pentabromophenyl) disulfide is particularly preferred.

  Other organic sulfur compounds may be used along with polysulfide compounds containing bromo groups. When a polysulfide compound containing a bromo group and another organic sulfur compound are used in combination, the ratio of the polysulfide compound containing a bromo group is preferably 50% by mass or more, and more preferably 80% by mass or more.

  From the viewpoint of the resilience performance of the golf ball 2, the compounding amount of the organic sulfur compound is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more with respect to 100 parts by mass of the base rubber, and 0.1 mass Part or more is particularly preferable. From the viewpoint of soft feel at impact, the compounding amount of the organic sulfur compound is preferably 5 parts by mass or less, more preferably 4 parts by mass or less, and particularly preferably 3 parts by mass or less with respect to 100 parts by mass of the base rubber.

  A filler may be blended in the core 4 for the purpose of adjusting specific gravity and the like. Suitable fillers include zinc oxide, barium sulfate, calcium carbonate and magnesium carbonate. 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 core 4 is achieved. A particularly preferred filler is zinc oxide. Zinc oxide functions not only as a specific gravity adjuster but also as a crosslinking aid. Various additives such as sulfur, an antioxidant, a colorant, a plasticizer, and a dispersant are blended in the core 4 in appropriate amounts as necessary. The core 4 may be blended with a crosslinked rubber powder or a synthetic resin powder.

  The surface hardness of the core 4 is preferably 50 or greater and 75 or less. Excellent resilience performance can be achieved by the core 4 having a surface hardness of 50 or more. In this respect, the surface hardness is more preferably 55 or more. An excellent feel at impact can be achieved by the core 4 having a surface hardness of 75 or less. In this respect, the surface hardness is more preferably 70 or less. The surface hardness is measured by pressing a Shore D type hardness meter against the surface of the core 4. For the measurement, an automatic rubber hardness measuring machine (trade name “P1” by Kobunshi Keiki Co., Ltd.) equipped with this hardness meter is used.

  The amount of compressive deformation of the core 4 is preferably 1.5 mm or greater and 3.0 mm or less. An excellent feel at impact can be achieved by the core 4 having a compression deformation amount of 1.5 mm or more. In this respect, the amount of compressive deformation is more preferably equal to or greater than 1.8 mm, and particularly preferably equal to or greater than 2.0 mm. As will be described later, the cover 6 of the golf ball 2 is thin. When the golf ball 2 is hit, the core 4 is greatly deformed due to the thin cover 6. Excellent resilience performance can be achieved by the core 4 having an amount of compressive deformation of 3.0 mm or less. In this respect, the amount of compressive deformation is more preferably 2.8 mm or less, and particularly preferably 2.5 mm or less.

  In the measurement of the amount of compressive deformation, first, a sphere (core 4 or golf ball 2) is placed on a metal rigid plate. Next, the 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 the amount of compressive deformation.

  From the viewpoint that the core 4 sufficiently contributes to the resilience performance, the diameter of the core 4 is preferably 40.2 mm or more, and more preferably 40.8 mm or more. From the viewpoint that the cover 6 sufficiently contributes to durability and deformation behavior, the diameter is preferably 42.4 mm or less, and more preferably 42.2 mm or less. The mass of the core 4 is preferably 35.0 g or more and 44.5 g or less. The crosslinking temperature of the core 4 is usually 140 ° C. or higher and 180 ° C. or lower. The crosslinking time of the core 4 is usually 10 minutes or longer and 60 minutes or shorter.

  The cover 6 is made of a thermoplastic resin composition. Examples of the base polymer of the resin composition include ionomer resins, styrene block-containing thermoplastic elastomers, thermoplastic polyester elastomers, thermoplastic polyamide elastomers, thermoplastic polyurethane elastomers, and thermoplastic polyolefin elastomers. In particular, an ionomer resin is preferable. The ionomer resin is highly elastic. By using the ionomer resin, the excellent resilience performance of the golf ball 2 can be achieved.

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

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

  Specific examples of the ionomer resin include Mitsui Dupont Polychemical's trade names “HIMILAN 1555”, “HIMILAN 1557”, “HIMILAN 1605”, “HIMILAN 1706”, “HIMILAN 1707”, “HIMILAN 1856” and “HIMILAN 1855”. "High Milan AM 7311", "High Milan AM 7315", "High Milan AM 7317", "Hi Milan AM 7318", "Hi Milan AM 7329" and "Hi Milan MK7320"; DuPont's trade names "Surlin 6120", "Surlin 6910", "Surlin 7930" "Surlyn 7940", "Surlin 8140", "Surlin 8150", "Surlin 8940", "Surlin 8945", "Surlin 9120", "Surlin 9150", "Surlin 9910" Surlyn 9945 "and" Surlyn AD8546 "; 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. An ionomer resin neutralized with a monovalent metal ion and an ionomer resin neutralized with a divalent metal ion may be used in combination.

  Preferably, an ionomer resin having a material hardness of 50 or more and 70 or less is used. The ionomer resin having a material hardness of 50 or more contributes to the resilience performance of the golf ball 2. From the viewpoint of resilience performance, the material hardness of the ionomer resin is more preferably 53 or more, and particularly preferably 55 or more. The ionomer resin having a material hardness of 70 or less contributes to the feel at impact of the golf ball 2. In light of feel at impact, the material hardness of the ionomer resin is more preferably 67 or less, and particularly preferably 65 or less.

  In the present invention, the hardness of the cover 6 and the material hardness of the resin are measured in accordance with the provisions of “ASTM-D 2240-68”. For the measurement, an automatic rubber hardness measuring machine (trade name “P1”, available from Kobunshi Keiki Co., Ltd.) equipped with a Shore D hardness tester is used. For the measurement, a sheet formed by hot pressing 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. For measuring the hardness of the cover 6, a sheet made of the same material as the cover 6 is used. A sheet made of this resin alone is used for measuring the material hardness of the resin.

  An ionomer resin and another resin may be used in combination. When used in combination, the ionomer resin is the main component of the base polymer from the viewpoint of resilience performance. The ratio of the ionomer resin to the total base polymer is preferably 80% by mass or more, more preferably 85% by mass or more, and particularly preferably 90% or more.

  From the viewpoint of excellent compatibility with the ionomer resin, it is preferable to use a styrene block-containing thermoplastic elastomer in combination. The styrene block-containing thermoplastic elastomer contributes to the shot feel and strength of the golf ball 2. The styrene block-containing thermoplastic elastomer includes a polystyrene block as a hard segment and a soft segment. A typical soft segment is a diene block. The styrene block-containing thermoplastic elastomer includes styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS), styrene-isoprene-butadiene-styrene block copolymer (SIBS), SBS hydrogenated, SIS hydrogenated and SIBS hydrogenated are included. Examples of the hydrogenated product of SBS include styrene-ethylene-butylene-styrene block copolymer (SEBS). As a hydrogenated product of SIS, styrene-ethylene-propylene-styrene block copolymer (SEPS) can be mentioned. Examples of the hydrogenated product of SIBS include styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS).

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

  In the present invention, the styrene block-containing thermoplastic elastomer includes an alloy of one or two or more selected from the group consisting of SBS, SIS, SIBS, SEBS, SEPS and SEEPS, and hydrogenated products thereof, and an olefin. included. The olefin component in the alloy is presumed to contribute to the improvement of compatibility with the ionomer resin. By using this alloy, the resilience performance of the golf ball 2 is improved. Preferably, an olefin having 2 to 10 carbon atoms is used. Suitable olefins include ethylene, propylene, butene and tempen. Ethylene and propylene are particularly preferred.

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

  Preferably, a styrene block-containing thermoplastic elastomer having a material hardness of less than 50 is used. This elastomer can contribute to the feel at impact even if the blending amount is small. By using this elastomer, the ionomer resin can be blended in the cover 6 at a high ratio. By using this elastomer, both the resilience performance and feel at impact of the golf ball 2 can be achieved. In this respect, the material hardness is more preferably less than 30, and particularly preferably less than 10. The material hardness is preferably 3 or more.

  In light of feel at impact, the ratio of the styrene block-containing thermoplastic elastomer to the total base polymer is preferably 1% by mass or more, more preferably 2% by mass or more, and particularly preferably 3% by mass or more. In light of resilience performance, this ratio is preferably equal to or less than 20% by weight, more preferably equal to or less than 15% by weight, and particularly preferably equal to or less than 10% by weight.

  The cover 6 has a hardness of 59 or more. With the cover 6 having a hardness of 59 or more, excellent resilience performance and a large launch angle can be achieved. This cover 6 further suppresses spin. From these viewpoints, the hardness is more preferably 61 or more, and particularly preferably 63 or more. In light of feel at impact, the hardness is preferably equal to or less than 70, and particularly preferably equal to or less than 67.

  The cover 6 has a thickness of less than 1.3 mm. This cover 6 is thin. When the golf ball 2 is hit, since the cover 6 is thin, the core 4 is greatly deformed. By restoring the deformation, the golf ball 2 is provided with excellent resilience performance. The thin cover 6 suppresses spin. A large launch angle is achieved by the thin cover 6. From these viewpoints, the thickness of the cover 6 is more preferably 1.0 mm or less, and particularly preferably 0.8 mm or less. The thickness is preferably 0.2 mm or more. The cover 6 having a thickness of 0.2 mm or more contributes to the durability of the golf ball 2. In this respect, the thickness is more preferably equal to or greater than 0.3 mm.

  The amount of compressive deformation of the golf ball 2 is less than 2.4 mm. This golf ball 2 is excellent in resilience performance. In light of resilience performance, the amount of compressive deformation is preferably 2.3 mm or less, more preferably 2.1 mm or less, and particularly preferably 2.0 mm or less. In light of feel at impact, the amount of compressive deformation is preferably equal to or greater than 1.5 mm, more preferably equal to or greater than 1.7 mm, and particularly preferably equal to or greater than 1.8 mm.

  FIG. 2 is an enlarged front view showing the golf ball 2 of FIG. In FIG. 2, the types of the dimples 8 are indicated by reference signs A to G. The planar shape of all the dimples 8 is a circle. The golf ball 2 includes a dimple A having a diameter of 4.5 mm, a dimple B having a diameter of 4.4 mm, a dimple C having a diameter of 4.3 mm, a dimple D having a diameter of 4.1 mm, A dimple E having a diameter of 4.0 mm, a dimple F having a diameter of 3.5 mm, and a dimple G having a diameter of 3.0 mm are provided. The number of dimples A is 60, the number of dimples B is 86, the number of dimples C is 56, the number of dimples D is 10, the number of dimples E is 76, and the number of dimples F is 22 and the number of dimples G is 18. The total number of dimples 8 is 328. The average diameter Da is 4.16 mm.

  FIG. 3 is an enlarged cross-sectional view showing a part of the golf ball 2 of FIG. FIG. 3 shows a cross section along a plane passing through the center (deepest part) of the dimple 8 and the center of the golf ball 2. The vertical direction in FIG. 3 is the depth direction of the dimple 8. What is indicated by a two-dot chain line 12 in FIG. 3 is a virtual sphere. The phantom sphere 12 is the surface of the golf ball 2 when it is assumed that the dimple 8 does not exist. The dimple 8 is recessed from the phantom sphere 12. The land 10 coincides with the phantom sphere 12.

  In FIG. 3, what is indicated by a double-headed arrow Di is the diameter of the dimple 8. The diameter Di is a distance between one contact point Ed and the other contact point Ed when a common tangent line T is drawn on both sides of the dimple 8. The contact point Ed is also an edge of the dimple 8. The edge Ed defines the contour of the dimple 8. The diameter Di is preferably 2.00 mm or greater and 6.00 mm or less. By setting the diameter Di to be 2.00 mm or more, a large dimple effect can be obtained. From this viewpoint, the diameter Di is more preferably 2.20 mm or more, and particularly preferably 2.40 mm or more. By setting the diameter Di to 6.00 mm or less, the original characteristic of the golf ball 2 that is substantially a sphere is not impaired. In this respect, the diameter Di is more preferably equal to or less than 5.80 mm, and particularly preferably equal to or less than 5.60 mm.

  FIG. 4 is an enlarged front view showing a part of the golf ball 2 of FIG. FIG. 4 shows dimples 8a, dimples 8b, dimples 8c, dimples 8d, and dimples 8e. The plane along the line VV in FIG. 4 passes through the center of the dimple 8a and the center of the dimple 8b.

  FIG. 5 is a cross-sectional view taken along line VV in FIG. In FIG. 5, what is indicated by the symbol Oa is the center of the dimple 8a, and what is indicated by the symbol Ob is the center of the dimple 8b. What is indicated by a symbol Ca is an intersection of a line La that passes through the center Oa and extends in the radial direction of the golf ball 2 and the phantom sphere 12. What is indicated by a symbol Cb is an intersection of a line Lb that passes through the center Ob and extends in the radial direction of the golf ball 2 and the phantom sphere 12. An arc connecting point Ca and point Cb is referred to as a “joint arc”. The joint arc exists on the surface of the phantom sphere 12. The joint arc is part of a great circle. The joint arc does not intersect with the other dimples 8. In the present invention, a dimple pair whose joint arc does not intersect with other dimples 8 is referred to as an “adjacent dimple pair”. The dimple 8a and the dimple 8b constitute an adjacent dimple pair. The edge Ed of the dimple 8a is on the joint arc (Ca-Cb). The edge Ed of the dimple 8b is also on the joint arc (Ca-Cb). The arc (Ed-Ed) is a part of the joint arc (Ca-Cb). The length of the arc (Ed-Ed) is the pitch of the adjacent dimple pair (8a-8b). When the dimple 8a and the dimple 8b are separated from each other, the pitch is positive. When the dimple 8a and the dimple 8b are in contact with each other, the pitch is zero. When the dimple 8a and the dimple 8b intersect, the pitch is zero.

  As is clear from FIG. 4, the joint arc (Ca—Cc) does not intersect with the other dimples 8. The dimple 8a and the dimple 8c constitute an adjacent dimple pair. The joint arc (Ca-Cd) does not intersect with the other dimples 8. The dimple 8a and the dimple 8d constitute an adjacent dimple pair. The joint arc (Ca-Ce) does not intersect with the other dimples 8. The dimple 8a and the dimple 8e constitute an adjacent dimple pair. The joint arc (Cb-Cc) intersects the dimple 8d. The pair of the dimple 8b and the dimple 8c is not an adjacent dimple pair.

  The golf ball 2 includes 1382 adjacent dimple pairs. 914 adjacent dimple pairs have a pitch of (Da / 4) or less. The 546 adjacent dimple pairs have a pitch of (Da / 20) or less. The pitch which is (Da / 20) or less is extremely small in comparison with the average diameter Da. In this golf ball 2, the ratio (N1 / N) of the number N1 of adjacent dimple pairs whose pitch is (Da / 4) or less to the total number N of dimples is 2.79. In this golf ball 2, the ratio (N2 / N1) of the number N2 of adjacent dimple pairs whose pitch is (Da / 20) or less to the number N1 is 0.60.

The ratio (N1 / N) is preferably 2.70 or more, and the ratio (N2 / N1) is preferably 0.50 or more. In other words, the golf ball 2 preferably satisfies the following mathematical formulas (I) and (II).
(N1 / N) ≧ 2.70 (I)
(N2 / N1) ≧ 0.50 (II)

  In the present invention, the pitch is compared with the average diameter Da in calculating the numbers N1 and N2. In a conventional golf ball in which many small dimples are arranged in order to achieve high density, (N1 / N) and (N2 / N1) are small. On the other hand, in the golf ball 2 satisfying the above formulas (I) and (II), the dimples 8 are arranged extremely densely and the number of small dimples 8 is small. In this golf ball 2, each dimple 8 can contribute to the dimple effect. This golf ball 2 is excellent in flight performance.

  In light of flight performance, the ratio (N1 / N) is more preferably equal to or greater than 2.75 and particularly preferably equal to or greater than 2.90. The ratio (N1 / N) is preferably 4.00 or less. In light of flight performance, the ratio (N2 / N1) is more preferably equal to or greater than 0.54, still more preferably equal to or greater than 0.60, and particularly preferably equal to or greater than 0.64. The ratio (N2 / N1) is 1.00 or less.

  From the standpoint that each dimple 8 exhibits a dimple effect, the average diameter Da is preferably 4.00 mm or more, more preferably 4.10 mm or more, and particularly preferably 4.15 mm or more. The average diameter Da is preferably 5.50 mm or less. By setting the average diameter Da to be equal to or less than 5.50 mm, the original characteristic of the golf ball 2 that is substantially a sphere is not impaired.

The area s of the dimple 8 is an area of a region surrounded by a contour line when the center of the golf ball 2 is viewed from infinity. In the case of the circular dimple 8, the area s is calculated by the following mathematical formula.
s = (Di / 2) ²・ π
In the golf ball 2 shown in FIG. 2, the area of the dimple A is 15.90 mm ² , the area of the dimple B is 15.20 mm ² , the area of the dimple C is 14.52 mm ² , and area was 13.20mm ^2, the area of the dimple E is 12.57mm ^2, the area of the dimple F is 9.62mm ^2, the area of the dimple G is 7.07mm ^2.

In the present invention, the ratio of the total area s of all the dimples 8 to the surface area of the phantom sphere 12 is referred to as an occupation ratio. From the viewpoint of obtaining a sufficient dimple effect, the occupation ratio is preferably 75% or more, more preferably 78% or more, and particularly preferably 81% or more. The occupation ratio is preferably 90% or less. In the golf ball 2 shown in FIG. 2, the total area of the dimples 8 is 4500.5 mm ² . Since the surface area of the phantom sphere 12 of this golf ball 2 is 5728.0 mm ² , the occupation ratio is 78.6%.

  If the diameter Di of the dimple 8 is set large, the dimples 8 may intersect each other. In the golf ball 2 having a large number of intersections, the apparent occupation ratio of the dimples 8 is large, but the effective area of the dimples 8 is small. From the viewpoint of flight performance, it is preferable that the effective area be large in comparison with the apparent occupation ratio. In other words, it is preferable that the number of intersections between the dimples 8 is small. The ratio (N3 / N1) of the number N3 of the adjacent dimple pairs intersecting to the number N1 is preferably 0.10 or less, more preferably 0.08 or less, and particularly preferably 0.06 or less. Ideally, the ratio (N3 / N1) is zero. In the golf ball 2 shown in FIG. 2, the number N3 is 12, and the ratio (N3 / N1) is 0.013.

  From the viewpoint of the dimple effect, the ratio (N4 / N) of the number N4 of the dimples 8 having a diameter of 3.50 mm or less to the total number N (N4 / N) is preferably 0.20 or less, more preferably 0.15 or less, and 0.10 or less. Particularly preferred. Ideally, the ratio (N4 / N) is zero.

  From the viewpoint that a sufficient occupation ratio can be achieved, the total number of the dimples 8 is preferably 200 or more, and particularly preferably 252 or more. From the viewpoint that the individual dimples 8 can have a sufficient diameter, the total number is preferably 362 or less, more preferably 360 or less, further 332 or less, and further 328 or less.

  It is preferable that a plurality of types of dimples 8 having different diameters are arranged. By arranging a plurality of types of dimples 8, a golf ball 2 having a large ratio (N1 / N), a large ratio (N2 / N1), a large average diameter Da, and a small ratio (N3 / N1) is achieved. Can be done. In this respect, the number of types of dimples 8 is more preferably 3 or more, and particularly preferably 4 or more. From the viewpoint of easy mold manufacture, the number of types is preferably 15 or less.

In the present invention, the “dimple volume” means a volume of a portion surrounded by a plane including the outline of the dimple 8 and the surface of the dimple 8. From the viewpoint of rising of the golf ball 2 is suppressed, the total volume of the dimples 8 is preferably 250 mm ³ or more, more preferably 260 mm ³ or more, 270 mm ³ or more is particularly preferable. In view of dropping of the golf ball 2 is suppressed, the total volume is preferably 400 mm ³ or less, more preferably 390 mm ³ or less, 380 mm ³ or less is particularly preferred.

  In light of suppression of hops of the golf ball 2, the depth of the dimple 8 is preferably 0.05 mm or more, more preferably 0.08 mm or more, and particularly preferably 0.10 mm or more. In light of suppression of dropping of the golf ball 2, the depth is preferably equal to or less than 0.60 mm, more preferably equal to or less than 0.45 mm, and particularly preferably equal to or less than 0.40 mm. The depth is a distance between the tangent line T and the deepest part of the dimple 8.

  In the present invention, the great circle that is on the phantom sphere 12 and does not intersect the dimple 8 is referred to as a “great circle zone”. When the spin axis of the back spin is orthogonal to the plane including the great circle zone, the peripheral speed of the back spin is the fastest in this great circle zone. When the spin axis of backspin is orthogonal to the plane including the great circle band, a sufficient dimple effect cannot be obtained. The great circle obstructs flight performance. The great circle further impedes aerodynamic symmetry. It is preferable that the golf ball 2 does not have a great circle band.

  In FIG. 2, two pole points P, two first latitude lines 14, two second latitude lines 16, and an equator 18 are depicted. The latitude of the pole P is 90 °, and the latitude of the equator 18 is 0 °. The latitude of the first latitude line 14 is greater than the latitude of the second latitude line 16.

  The golf ball 2 includes a northern hemisphere N above the equator 18 and a southern hemisphere S below the equator 18. Each of the northern hemisphere N and the southern hemisphere S includes a pole vicinity region 20, an equator vicinity region 22, and an adjustment region 24. The first latitude line 14 is a boundary line between the pole vicinity region 20 and the adjustment region 24. The second latitude line 16 is a boundary line between the equator vicinity region 22 and the adjustment region 24. The pole vicinity region 20 is located between the pole point P and the first latitude line 14. The equator vicinity region 22 is located between the second latitude line 16 and the equator 18. The adjustment region 24 is located between the first latitude line 14 and the second latitude line 16. In other words, the adjustment region 24 is located between the pole vicinity region 20 and the equator vicinity region 22.

  In the dimple 8 that intersects the first latitude line 14 or the second latitude line 16, the region to which the dimple 8 belongs is determined based on the center position. The dimple 8 that intersects the first latitude line 14 and whose center is located in the pole vicinity region 20 belongs to the pole vicinity region 20. The dimple 8 that intersects the first latitude line 14 and whose center is located in the adjustment region 24 belongs to the adjustment region 24. The dimple 8 that intersects the second latitude line 16 and whose center is located in the equator vicinity region 22 belongs to the equator vicinity region 22. The dimple 8 that intersects the second latitude line 16 and whose center is located in the adjustment region 24 belongs to the adjustment region 24.

  6, 7 and 8 are plan views showing the golf ball 2 of FIG. In FIG. 6, five first meridians 26 are shown together with the first latitude line 14 and the second latitude line 16. In FIG. 6, the pole vicinity region 20 is surrounded by the first latitude line 14. The pole vicinity region 20 can be partitioned into five units Up. The unit Up is a spherical triangle. The outline of the unit Up consists of a part of the first latitude line 14 and two first meridians 26. In FIG. 6, the type of the dimple 8 is indicated by the symbols A, B, D, E, and G for one unit Up.

  The dimple pattern of the five units Up is 72 ° rotationally symmetric. In other words, when the dimple pattern of a certain unit Up rotates 72 degrees in the longitude direction around the pole P, it substantially overlaps with the dimple pattern of the adjacent unit Up. Here, the “substantially overlap” state includes not only a state where one dimple 8 completely coincides with the other dimple 8, but also a state where one dimple 8 slightly deviates from the other dimple 8. Here, the “slightly shifted state” includes a state in which the center of one dimple 8 is slightly separated from the center of the other dimple 8. The distance between the center of one dimple 8 and the center of the other dimple 8 is preferably 1.0 mm or less, and more preferably 0.5 mm or less. Here, the “slightly shifted state” includes a state in which the size of one dimple 8 is slightly different from the size of the other dimple 8. The dimensional difference is preferably 0.5 mm or less, and more preferably 0.3 mm or less. The dimension means the length of the longest line segment that can be drawn on the outline of the dimple 8. In the case of the circular dimple 8, the dimension thereof matches the diameter.

  In FIG. 7, six second meridians 28 are shown together with the first latitude line 14 and the second latitude line 16. In FIG. 7, the outside of the second latitude line 16 is the equator vicinity region 22. The equator vicinity region 22 can be partitioned into six units Ue. The unit Ue is a spherical trapezoid. The outline of the unit Ue consists of a part of the second latitude line 16, two second meridians 28, and a part of the equator 18 (see FIG. 2). In FIG. 7, the types of the dimples 8 are indicated by the symbols B, C, and E for one unit Ue.

  The dimple pattern of the six units Ue is 60 ° rotationally symmetric. In other words, when the dimple pattern of a certain unit Ue rotates 60 ° in the longitude direction around the pole P, it substantially overlaps with the dimple pattern of the adjacent unit Ue. The dimple pattern in the equator vicinity region 22 can be divided into three units. In this case, the dimple pattern of each unit is 120 ° rotationally symmetric. The dimple pattern in the equator vicinity region 22 can be divided into two units. In this case, the dimple pattern of each unit is 180 ° rotationally symmetric. The dimple pattern in the equator vicinity region 22 has three rotational symmetry angles (ie, 60 °, 120 °, and 180 °). In a region having a plurality of rotational symmetry angles, the unit Ue is determined based on the smallest rotational symmetry angle (60 ° in this example).

  FIG. 8 shows a first latitude line 14 and a second latitude line 16. In FIG. 8, the adjustment region 24 is surrounded by the first latitude line 14 and the second latitude line 16. In FIG. 8, the types of the dimples 8 included in the adjustment region 24 are indicated by symbols C, E, F, and G.

  The dimple pattern in the adjustment region 24 is line symmetric with respect to the XX line in plan view. This dimple pattern has no axis of symmetry other than XX line. When the rotation is about 0 ° or more and less than 360 ° around the pole P, the dimple patterns do not overlap each other. In other words, the dimple pattern in the adjustment region 24 cannot be partitioned into a plurality of units that are rotationally symmetric with respect to each other.

  The dimple pattern of the adjustment region 24 may be divided into a plurality of units that are rotationally symmetric. In this case, the number of units in the adjustment region 24 needs to be different from the number of units Up in the pole vicinity region 20, and further needs to be different from the number of units Ue in the equator vicinity region 22.

  In this golf ball 2, the number Np of units Up in the pole vicinity region 20 is 5, and the number Ne of units Ue in the equator vicinity region 22 is 6. They are different. The dimple pattern in which the number Np and the number Ne are different is rich in change. In the golf ball 2, the air flow during flight is well disturbed. This golf ball 2 is excellent in flight performance. The combination (Np, Ne) of the number Np and the number Ne is not limited to (5, 6). Other combinations include (2,3), (2,4), (2,5), (2,6), (3,2), (3,4), (3,5), (3 , 6), (4,2), (4,3), (4,5), (4,6), (5,2), (5,3), (5,4), (6,2) ), (6, 3), (6, 4) and (6, 5).

  Although the details of the reason are unknown, according to the knowledge obtained by the present inventor, when one of the number Np and the number Ne is an odd number and the other is an even number, a large dimple effect is obtained. Furthermore, when the difference between the number Np and the number Ne is 1, a particularly large dimple effect is obtained. Combinations with this difference of 1 include (2,3), (3,2), (3,4), (4,3), (4,5), (5,4), (5,6 ) And (6, 5).

  From the viewpoint of the dimple effect, it is preferable that the pole vicinity region 20 has a sufficient area and the equator vicinity region 22 has a sufficient area. From the viewpoint of the area of the equator vicinity region 22, the latitudes of the first latitude line 14 and the second latitude line 16 are preferably 15 ° or more, and more preferably 20 ° or more. From the viewpoint of the area of the pole vicinity region 20, the latitude of the first latitude line 14 and the second latitude line 16 is preferably 45 ° or less, and more preferably 40 ° or less. The first latitude line 14 can be arbitrarily selected from an infinite number of latitude lines. The second latitude line 16 can also be arbitrarily selected from an infinite number of latitude lines. In the golf ball 2 shown in FIGS. 2 and 6 to 8, the latitude of the first latitude line 14 is 42 °, and the latitude of the second latitude line 16 is 30 °.

  From the viewpoint of contribution of the pole vicinity region 20 to the dimple effect, the ratio of the number of the dimples 8 existing in the pole vicinity region 20 to the total number of the dimples 8 is preferably 20% or more, and more preferably 25% or more. This ratio is preferably 45% or less.

  From the viewpoint of contribution of the equator vicinity region 22 to the dimple effect, the ratio of the number of the dimples 8 existing in the equator vicinity region 22 to the total number of the dimples 8 is preferably 30% or more, and more preferably 35% or more. This ratio is preferably 65% or less.

  If the pole vicinity region 20 is adjacent to the equator vicinity region 22 across the boundary line, the dimples 8 cannot be densely arranged near the boundary line due to the difference in the number of units. In this case, there is a wide land 10 in the vicinity of the boundary line. The wide land 10 inhibits the dimple effect. In the golf ball 2 according to the present invention, the adjustment region 24 exists between the pole vicinity region 20 and the equator vicinity region 22. In the adjustment region 24, since the dimples 8 can be arranged without being restricted by the number of units, the area of the land 10 can be suppressed. This adjustment area 24 achieves a high occupation rate.

  From the viewpoint of the occupation ratio, it is preferable that the adjustment region 24 has a sufficient area. From this point of view, the difference between the latitude of the first latitude line 14 and the latitude of the second latitude line 16 is preferably 4 ° or more. If the adjustment region 24 is too wide, the dimple effect due to the difference between the number Np and the number Ne is impaired. From the viewpoint of the dimple effect, the difference between the latitude of the first latitude line 14 and the latitude of the second latitude line 16 is preferably 20 ° or less, and more preferably 15 ° or less.

  From the viewpoint of the occupation ratio, the ratio of the number of dimples 8 existing in the adjustment region 24 to the total number of dimples 8 is preferably 5% or more, and more preferably 8% or more. From the viewpoint of the dimple effect due to the difference between the number Np and the number Ne, this ratio is preferably 24% or less, more preferably 22% or less, and particularly preferably 20% or less.

  In the golf ball 2 in which the pole vicinity region 20 is partitioned into units Up and the equator vicinity region 22 is partitioned into units Ue, a pattern period is generated by rotation. The greater the number Np of units Up and the number Ne of units Ue, the shorter the period. The smaller the number Np and the number Ne, the longer the period. An appropriate period enhances the dimple effect. From the viewpoint of an appropriate period, the number Np and the number Ne are preferably 4 or more and 6 or less, and particularly preferably 5 or more and 6 or less. The most preferable combinations (NP, Ne) of the number Np and the number Ne are (5, 6) and (6, 5). In the golf ball 2 shown in FIGS. 2 and 6 to 8, (Np, Ne) is (5, 6).

  From the viewpoint of aerodynamic symmetry, it is preferable that the dimple pattern of the northern hemisphere N and the dimple pattern of the southern hemisphere S are equivalent. When a pattern that is symmetrical with the dimple pattern of the northern hemisphere N with respect to the plane including the equator 18 substantially overlaps with the dimple pattern of the southern hemisphere S, the two patterns are equivalent. When a pattern that is symmetric with the dimple pattern of the northern hemisphere N with respect to the plane including the equator 18 substantially overlaps the dimple pattern of the southern hemisphere S when rotated about the pole P, the two patterns are equivalent. .

  In the present invention, the size of each part of the dimple 8 is measured in the golf ball 2 having a paint layer.

  FIG. 9 is a front view showing a golf ball 30 according to another embodiment of the present invention. In FIG. 9, the types of the dimples 32 are indicated by reference signs A to G. The planar shape of all the dimples 32 is a circle. The golf ball 30 includes a dimple A having a diameter of 4.60 mm, a dimple B having a diameter of 4.45 mm, a dimple C having a diameter of 4.30 mm, a dimple D having a diameter of 4.10 mm, A dimple E having a diameter of 3.90 mm, a dimple F having a diameter of 3.40 mm, and a dimple G having a diameter of 3.00 mm are provided. The number of dimples A is 80, the number of dimples B is 60, the number of dimples C is 62, the number of dimples D is 58, the number of dimples E is 38, and the number of dimples F is 18 and the number of dimples G is 14. The total number of dimples 32 is 330.

  The golf ball 30 includes 1476 adjacent dimple pairs. The 964 adjacent dimple pairs have a pitch of (Da / 4) or less. 614 adjacent dimple pairs have a pitch of (Da / 20) or less. The ratio (N1 / N) of the number N1 of adjacent dimple pairs whose pitch is (Da / 4) or less to the total number N of dimples is 2.92. The ratio (N2 / N1) of the number N2 of adjacent dimple pairs whose pitch is (Da / 20) or less to the number N1 is 0.64. In the golf ball 30, the dimples 32 are arranged extremely densely and the number of small dimples 32 is small. In this golf ball 30, each dimple 32 can contribute to the dimple effect. This golf ball 30 is excellent in flight performance.

  The golf ball 30 has an average diameter Da of 4.21 mm and an occupation ratio of 81.1%. This golf ball 30 includes seven types of dimples 32. In this golf ball 30, the number N3 of adjacent dimple pairs intersecting is 58, and the ratio (N3 / N1) is 0.060. In this golf ball 30, the ratio (N4 / N) of the number N4 of dimples 32 having a diameter of 3.50 mm or less to the total number N is 0.10. In this golf ball 30, the ratio (N1 / N) is large, the ratio (N2 / N1) is large, the average diameter Da is large, the ratio (N3 / N1) is small, and the ratio (N4 / N) is small. This golf ball 30 is excellent in flight performance.

  As shown in FIG. 9, the golf ball 30 includes an equator 33, a northern hemisphere N, and a southern hemisphere S. The equator 33 is a great circle zone. Each of the northern hemisphere N and the southern hemisphere S includes a pole vicinity region 34, an equator vicinity region 36, and an adjustment region 38.

  10, 11 and 12 are plan views showing the golf ball 30 of FIG. In FIG. 10, the pole vicinity region 34 is surrounded by the first latitude line 40. The pole vicinity region 34 can be partitioned into five units Up. The unit Up is a spherical triangle. The outline of the unit Up consists of a part of the first latitude line 40 and two first meridians 42. In FIG. 10, the type of the dimple 32 is indicated by reference signs A, B, C, E, and G for one unit Up. The dimple pattern of the five units Up is 72 ° rotationally symmetric.

  In FIG. 11, the outer side of the second latitude line 44 is the equator vicinity region 36. The equator vicinity region 36 can be divided into six units Ue. The unit Ue is a spherical trapezoid. The outline of the unit Ue includes a part of the second latitude line 44, two second meridians 46, and a part of the equator 33 (see FIG. 9). In FIG. 11, the types of the dimples 32 are indicated by symbols B, C, D, E, and G for one unit Ue. The dimple pattern of the six units Ue is 60 ° rotationally symmetric.

  In FIG. 12, the adjustment region 38 is surrounded by the first latitude line 40 and the second latitude line 44. In FIG. 12, the types of the dimples 32 included in the adjustment region 38 are indicated by reference signs A, B, C, D, E, and F. The dimple pattern in the adjustment region 38 is line symmetric with respect to the YY line in plan view. This dimple pattern has no axis of symmetry other than the Y-Y line. When the rotation is about 0 ° or more and less than 360 ° around the pole P, the dimple patterns do not overlap each other. In other words, the dimple pattern in the adjustment region 38 cannot be partitioned into a plurality of units that are rotationally symmetric with respect to each other.

  In the golf ball 30 shown in FIGS. 9 to 12, the latitude of the first latitude line 40 is 35 °, and the latitude of the second latitude line 44 is 21 °.

  In this golf ball 30, the number Np of units Up in the pole vicinity region 34 is 5, and the number Ne of units Ue in the equator vicinity region 36 is 6. This dimple pattern is varied. In the golf ball 30, the adjustment region 38 contributes to a large occupation ratio. This golf ball 30 is excellent in flight performance.

  FIG. 13 is a front view showing a golf ball 48 according to still another embodiment of the present invention, and FIG. 14 is a plan view thereof. As shown in FIG. 13, the golf ball 48 includes an equator 50, a northern hemisphere N, and a southern hemisphere S. As shown in FIG. 14, each of the northern hemisphere N and the southern hemisphere S can be divided into five units U. Unit U is a spherical triangle. The outline of the unit U consists of two meridians 52 and a part of the equator 50 (see FIG. 13). In FIG. 14, the type of the dimple 54 is indicated by the symbol A for one unit U. The diameter of the dimple A is 4.318 mm. The total number N of the dimples 54 is 332. The dimple pattern of the five units U is 72 ° rotationally symmetric.

  The golf ball 48 includes 1450 adjacent dimple pairs. The 990 adjacent dimple pairs have a pitch of (Da / 4) or less. The 540 adjacent dimple pairs have a pitch of (Da / 20) or less. The ratio (N1 / N) of the number N1 of adjacent dimple pairs whose pitch is (Da / 4) or less to the total number N of dimples is 2.98. The ratio (N2 / N1) of the number N2 of the adjacent dimple pairs whose pitch is (Da / 20) or less to the number N1 is 0.55. In the golf ball 48, the dimples 54 are arranged very densely, and the number of small dimples 54 is small. In the golf ball 48, each dimple 54 can contribute to the dimple effect. This golf ball 48 is excellent in flight performance.

  The golf ball 48 has an average diameter Da of 4.318 mm and an occupation ratio of 84.9%. In this golf ball 48, the ratio (N4 / N) of the number N4 of the dimples 54 having a diameter of 3.50 mm or less to the total number N is zero. In this golf ball 48, the ratio (N1 / N) is large, the ratio (N2 / N1) is large, the average diameter Da is large, and the ratio (N4 / N) is small.

  In this golf ball 48, the number N3 of adjacent dimple pairs that intersect is 260, and the ratio (N3 / N1) is 0.263. This ratio (N3 / N1) is large. In the golf ball 48, the effective area is small in comparison with the apparent occupation ratio. A small effective area is disadvantageous in terms of the dimple effect. As is clear from FIG. 13, the equator 50 does not intersect the dimple 54. The equator 54 is a great circle zone. The golf ball 48 has one great circle band. The existence of the great circle is disadvantageous from the viewpoint of the dimple effect.

  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 polybutadiene (trade name “BR-730” of JSR Corporation) synthesized using a rare earth element-based catalyst, 37 parts by weight of zinc acrylate, 10 parts by weight of zinc oxide, an appropriate amount of barium sulfate, 0.3 parts by mass of bis (pentabromophenyl) disulfide and 0.5 parts by mass of dicumyl peroxide (Nippon Yushi Co., Ltd.) were kneaded to obtain a rubber composition. This rubber composition was put into a mold composed of an upper mold and a lower mold each having a hemispherical cavity and heated at 170 ° C. for 20 minutes to obtain a core having a diameter of 40.9 mm. On the other hand, 55 parts by mass of an ionomer resin (previously referred to as “HIMILAN 1605”), 40 parts by mass of another ionomer resin (described above “HIMILAN 1706”), 5 parts by mass of a styrene block-containing thermoplastic elastomer (previously described “Lavalon T3339C”). )) And 3 parts by mass of titanium dioxide were kneaded to obtain a resin composition. A half shell was obtained from this resin composition by compression molding. The core was covered with two half shells. The half shell and the core 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 Tc was 0.9 mm. A large number of dimples having a reversed pimple shape were formed on the cover. A paint layer was formed around the cover to obtain a golf ball of Example 1. This golf ball had a diameter of 42.7 mm and a mass of 45.4 g. This golf ball has a type I dimple pattern shown in Table 3 below.

[Examples 2 to 4 and Comparative Examples 1 to 2]
Golf balls of Examples 2 to 4 and Comparative Examples 1 to 2 were obtained in the same manner as Example 1 except that the final mold was changed and the dimple patterns shown in Tables 4 and 5 below were formed. . Details of the dimple specifications are shown in Table 3 below.

[Examples 5 to 8 and Comparative Examples 3 to 7]
Golf balls of Examples 5 to 8 and Comparative Examples 3 to 7 were obtained in the same manner as in Example 1 except that the core and cover types were as shown in Tables 4 to 7 below. Details of the core and cover composition are shown in Tables 1 and 2 below.

[Measurement of coefficient of restitution]
An aluminum hollow cylinder having a mass of 200 g was caused to collide with the golf ball at a speed of 45 m / s. The velocity of the hollow cylinder before and after the collision and the velocity of the golf ball after the collision were measured, and the coefficient of restitution of the golf ball was obtained. The average value of the data obtained by 12 measurements is shown in Tables 4 to 7 below as indices.

[Measurement of flight distance]
A driver with a metal head was attached to a golf laboratory swing machine. A golf ball was hit under the condition that the head speed was 45 m / sec, and the distance from the launch point to the rest point was measured. Average values of 10 measurements are shown in Tables 4 to 7 below.

[Evaluation of feel at impact]
A senior golfer hit a golf ball with a driver. This golfer was given a hit feeling based on the following criteria.
A: Good with small impact B: Normal C: Bad with large impact This result is shown in Tables 4 to 7 below.

  As shown in Tables 4 to 7, the golf balls of the examples are excellent in flight performance. From this evaluation result, the superiority of the present invention is clear.

  The golf ball according to the present invention is suitable for golf course practice and driving range practice.

FIG. 1 is a schematic cross-sectional view showing 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 an enlarged cross-sectional view showing a part of the golf ball of FIG. FIG. 4 is an enlarged front view showing a part of the golf ball of FIG. FIG. 5 is a cross-sectional view taken along line VV in FIG. FIG. 6 is a plan view showing the golf ball of FIG. FIG. 7 is a plan view showing the golf ball of FIG. FIG. 8 is a plan view showing the golf ball of FIG. FIG. 9 is a front view showing a golf ball according to another embodiment of the present invention. FIG. 10 is a plan view showing the golf ball of FIG. FIG. 11 is a plan view showing the golf ball of FIG. 12 is a plan view showing the golf ball of FIG. FIG. 13 is a front view showing a golf ball according to still another embodiment of the present invention. FIG. 14 is a plan view showing the golf ball of FIG. FIG. 15 is a plan view showing a golf ball according to Comparative Example 1. FIG. FIG. 16 is a plan view showing a golf ball according to Comparative Example 2. FIG.

Explanation of symbols

2, 30, 48 ... Golf ball 4 ... Core 6 ... Cover 8, 32, 54 ... Dimple 10 ... Land 12 ... Virtual sphere 14, 40 ... First latitude line 16 44, second latitude line 18, 33, 50 ... equator 20, 34 ... pole vicinity region 22, 36 ... equator vicinity region 24, 38 ... adjustment region 26, 42 ... first First meridian 28, 46 ... Second meridian 30 ... Virtual sphere AG ... Dimple N ... Northern hemisphere P ... Pole S ... Southern hemisphere U, Up, Us ... Unit

Claims (11)

A spherical core, a cover covering the core, and a large number of dimples formed on the surface of the cover are provided. When the average diameter of all the dimples is Da, the pitch is (Da / 4). A two-piece golf ball in which a ratio (N3 / N1) of the number N3 of adjacent dimple pairs at which two dimples intersect each other to the number N1 of adjacent dimple pairs is 0.10 or less,
This cover has a thickness of less than 1.3 mm and a hardness of 59 or more,
The amount of compressive deformation is less than 2.4 mm,
The ratio of the number N1 to the total number N of dimples (N1 / N) is 2.70 or more,
A two-piece golf ball, wherein a ratio (N2 / N1) of the number N2 of adjacent dimple pairs having a pitch of (Da / 20) or less to a number N1 is 0.50 or more.   2. The golf according to claim 1, wherein the core is formed by crosslinking a rubber composition, and the main component of the base rubber of the rubber composition is polybutadiene synthesized using a rare earth element-based catalyst. ball.   The golf ball according to claim 1, wherein the core is formed by crosslinking a rubber composition, and the rubber composition includes a polysulfide compound containing a bromo group.   4. The cover according to claim 1, wherein the cover is made of a resin composition, and a base resin of the resin composition contains a thermoplastic elastomer containing an ionomer resin as a main component and having a material hardness of less than 50. Golf ball.   The golf ball according to claim 1, wherein the ratio (N2 / N1) is 0.60 or more. The average diameter Da is 4.00 mm or more,
The total number N of dimples is 362 or less,
The golf ball according to claim 1, wherein a ratio of a total area of all the dimples to a surface area of the phantom sphere is 75% or more. Each of the northern hemisphere and the southern hemisphere on the surface includes a pole vicinity region, an equator vicinity region, and an adjustment region located between the pole vicinity region and the equator vicinity region,
The dimple pattern in the pole vicinity region consists of a plurality of units that are rotationally symmetric with respect to the pole point,
The dimple pattern in the region near the equator consists of a plurality of units that are rotationally symmetric with respect to each other around the pole,
The number of units in the pole vicinity region is different from the number of units in the equator vicinity region,
The golf ball according to claim 1, wherein the dimple pattern in the adjustment region cannot be divided into a plurality of units that are rotationally symmetric with respect to a pole.   The golf ball according to claim 1, wherein a great circle that does not intersect the dimple does not exist on the surface thereof.   The golf ball according to claim 1, wherein all the dimples have a circular planar shape.   The golf ball according to claim 1, wherein an average diameter Da of the dimples is 4.00 mm or more and 5.50 mm or less.   The golf ball according to claim 1, wherein the total number of dimples is 200 or more and 362 or less.

Images