Golf ball

Abstract

In a golf ball 2, values V1 and V2 are each −3.0 or more and 3.0 or less, a difference (V3−V4) between values V3 and V4 is 5.0 or more and 10.0 or less, a value V5 is 65.0 or more and 73.0 or less, and a value Z is −25.0 or more and less than 0.0.V⁢1=(H⁢5-H⁢0)-(H⁢15-H⁢10)V⁢2=(H⁢10-H⁢5)-(Hs-H⁢15)V⁢3=((H⁢5-H⁢0)+(H⁢15-H⁢10)) / 2V⁢4=((H⁢10-H⁢5)+(H⁢s-H⁢1⁢5)) / 2V⁢5=(H⁢5+H⁢1⁢0+H⁢1⁢5) / 3Z=-536.36*Db+146.46*Lb-238.52*Da+225.22*La+111.21Db: drag coefficient under a first conditionLb: lift coefficient under the first conditionDa: drag coefficient under a second conditionLa: lift coefficient under the second condition

Description

CROSS REFERENCE TO RELATED APPLICATION(S)The present application claims priority to Japanese patent application JP 2025-048439, filed on Mar. 24, 2025, the entire content of which is incorporated herein by reference in its entirety.BACKGROUNDTechnical FieldThe present specification discloses a golf ball including a core and a cover and further having a large number of dimples on a surface thereof.Background ArtA golf ball has a large number of dimples on a surface thereof. The dimples optimize the lift and drag generated during the flight of the golf ball. The dimples contribute to a large flight distance of the golf ball. Improved dimples are disclosed in Japanese Laid-Open Patent Publication No. 2016-7369.The technologies of golf clubs and golf balls are advancing day by day. As a result, in golf courses, a trend of excessive flight distances being achieved upon shots with drivers has been recently seen. In response to this trend, the Royal and Ancient Golf Club of St Andrews (R&A) and the United States Golf Association (USGA) have announced changes to the test conditions for the Overall Distance Standard (ODS), which is one of the rules for golf balls. Golf balls that do not achieve excessive flight distance when hit by players with high head speeds can comply with the new rules.

[0005] Players seek a pleasing trajectory from golf balls. Players also seek controllability with short irons for golf balls. Furthermore, players seek good feel at impact from golf balls.

[0006] It is an intention of the applicant to provide a golf ball that complies with the above-described new rules and has excellent trajectory pleasantness, controllability, and feel at impact.SUMMARY

[0007] A golf ball disclosed in the present specification includes a spherical core and a cover. A value V1 calculated by the following mathematical formula (1) is −3.0 or more and 3.0 or less, a value V2 calculated by the following mathematical formula (2) is −3.0 or more and 3.0 or less, a difference (V3−V4) between a value V3 calculated by the following mathematical formula (3) and a value V4 calculated by the following mathematical formula (4) is 5.0 or more and 10.0 or less, a value V5 calculated by the following mathematical formula (5) is 65.0 or more and 73.0 or less. The golf ball has a plurality of dimples on a surface thereof. A ratio X of a total area of all the dimples to a surface area of a phantom sphere of the golf ball is 70% or more. In the golf ball, a value Z calculated by the following mathematical formula (6) is −25.0 or more and less than 0.0.V⁢1=(H⁢5-H⁢0)-(H⁢15-H⁢10)(1)V⁢2=(H⁢10-H⁢5)-(Hs-H⁢15)(2)V⁢3=((H⁢5-H⁢0)+(H⁢15-H⁢10)) / 2(3)V⁢4=((H⁢10-H⁢5)+(H⁢s-H⁢1⁢5)) / 2(4)V⁢5=(H⁢5+H⁢1⁢0+H⁢1⁢5) / 3(5)Z=-536.36*Db+146.46*Lb-238.52*Da+225.22*La+111.21(6)

[0008] In the mathematical formulas (1) to (5), H0, H5, H10, and H15 respectively represent hardnesses (Shore C) of the core at points whose distances from a central point of the core are 0 mm, 5 mm, 10 mm, and 15 mm, and Hs represents a surface hardness (Shore C) of the core.

[0009] In the mathematical formula (6), Db represents a drag coefficient under a condition where a Reynolds number is 1.20*105 and a ratio (rω / V) is 0.131, Lb represents a lift coefficient under a condition where the Reynolds number is 1.20*105 and the ratio (rω / V) is 0.131, Da represents a drag coefficient under a condition where the Reynolds number is 0.83*105 and the ratio (rω / V) is 0.179, La represents a lift coefficient under a condition where the Reynolds number is 0.83*105 and the ratio (rω / V) is 0.179, and the ratio (rω / V) is calculated by dividing a product of a radius r (m) and a backspin rate ω (rad / s) of the golf ball by a speed V (m / s) of the golf ball.

[0010] The aerodynamic characteristics of this golf ball when flying under new test conditions are inferior to those of a conventional golf ball. This golf ball can comply with new rules. The golf ball further has excellent trajectory pleasantness, controllability, and feel at impact.BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 is a cross-sectional view schematically showing a golf ball according to one embodiment;

[0012] FIG. 2 is a graph showing the hardness distribution of a core of the golf ball in

[0013] FIG. 1;

[0014] FIG. 3 is a plan view showing the golf ball in FIG. 1;

[0015] FIG. 4 is a front view showing the golf ball in FIG. 3;

[0016] FIG. 5 is a partially enlarged cross-sectional view of the golf ball in FIG. 1;

[0017] FIG. 6 is a plan view showing a golf ball according to Comparative Example 5; and

[0018] FIG. 7 is a front view showing the golf ball in FIG. 6.DETAILED DESCRIPTION

[0019] Hereinafter, preferred embodiments will be described in detail with appropriate reference to the drawings.

[0020] A golf ball 2 shown in FIG. 1 includes a spherical core 4, a mid layer 6 positioned outside the core 4, and a cover 8 positioned outside the mid layer 6. The golf ball 2 has a large number of dimples 10 on the surface thereof. Of the surface of the golf ball 2, a part other than the dimples 10 is a land 12. The golf ball 2 includes a paint layer and a mark layer on the external side of the cover 8, but these layers are not shown in the drawing. The golf ball 2 may have a structure that does not include the mid layer 6.

[0021] The golf ball 2 preferably has a diameter of 40 mm or more and 45 mm or less. From the viewpoint of conformity to the rules established by the United States Golf Association (USGA), the diameter is particularly preferably 42.67 mm or more. From the viewpoint of suppression of air resistance, the diameter is more preferably 44 mm or less and particularly preferably 42.80 mm or less.

[0022] The golf ball 2 preferably has a mass of 40 g or more and 50 g or less. From the viewpoint of attainment of great inertia, the mass is more preferably 44 g or more and particularly preferably 45.00 g or more. From the viewpoint of conformity to the rules established by the USGA, the mass is particularly preferably 45.93 g or less.

[0023] The core 4 is formed by crosslinking a rubber composition. Examples of the base rubber of the rubber composition include polybutadienes, polyisoprenes, styrene-butadiene copolymers, ethylene-propylene-diene copolymers, and natural rubbers. Two or more rubbers may be used in combination. From the viewpoint of resilience performance, polybutadienes are preferable, and high-cis polybutadienes are particularly preferable. The proportion of cis bonds in the high-cis polybutadiene is preferably 60% by mass or more, more preferably 80% by mass or more, and particularly preferably 90% by mass or more.

[0024] The rubber composition of the core 4 includes a co-crosslinking agent. Examples of preferable co-crosslinking agents include an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and metal salts thereof. Examples of preferable metals in the metal salts include zinc, magnesium, calcium, aluminum, and sodium. Zinc is particularly preferred. From the viewpoint of the resilience performance of the core 4, preferable co-crosslinking agents are zinc acrylate, magnesium acrylate, zinc methacrylate, and magnesium methacrylate. The content of the co-crosslinking agent in the rubber composition is preferably 20 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the base rubber.

[0025] The rubber composition preferably includes an organic peroxide. Examples of preferable organic peroxides include dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(t-butylperoxy) hexane, and di-t-butyl peroxide. The content of the organic peroxide in the rubber composition is preferably 0.20 parts by mass or more and 3 parts by mass or less per 100 parts by mass of the base rubber.

[0026] The rubber composition of the core 4 may include a monophenol compound. A preferable monophenol compound has a substituent at the para-position and no substituent at the ortho- and meta-positions. Examples of the substituent include alkoxy groups, halogen groups, hydrocarbon groups, a nitro group, a cyano group, an amino group, and a hydroxyl group. Alkoxy groups are preferred. A preferred example of the monophenol compound is 4-methoxyphenol. The content of the monophenol compound having a substituent only at the para-position in the rubber composition is preferably 0.05 parts by mass or more and 2.0 parts by mass or less per 100 parts by mass of the base rubber.

[0027] The rubber composition of the core 4 may include an organic sulfur compound. Examples of preferable organic sulfur compounds include: diphenyl disulfides such as diphenyl disulfide and bis(pentabromophenyl)disulfide; thiophenols; and thionaphthols. The content of the organic sulfur compound in the rubber composition is preferably 0.1 parts by mass or more and 5.0 parts by mass or less per 100 parts by mass of the base rubber.

[0028] The rubber composition of the core 4 may include a carboxylic acid or may include a carboxylate. This rubber composition may include both a carboxylic acid and a carboxylate. The number of carbon atoms in the carboxylic acid (or its salt) is preferably 1 or more and 30 or less. Examples of preferable carboxylic acids include aromatic carboxylic acids such as benzoic acid, and aliphatic carboxylic acids. The total content of the carboxylic acid and the carboxylate in the rubber composition is preferably 1 part by mass or more and 40 parts by mass or less per 100 parts by mass of the base rubber.

[0029] The rubber composition of the core 4 may include additives such as a filler, sulfur, a vulcanization accelerator, an anti-aging agent, a coloring agent, a plasticizer, and a dispersant. The rubber composition may include synthetic resin powder or crosslinked rubber powder.

[0030] The core 4 can be molded by heating the rubber composition in a mold such that the rubber undergoes a crosslinking reaction. The crosslinking may be performed in two stages. Preferred conditions for the two-stage crosslinking are as follows.First-Stage CrosslinkingTemperature: 140° C. to 150° C.

[0032] Time: 8 minutes to 12 minutesSecond-Stage CrosslinkingTemperature: 150° C. to 160° C.

[0034] Time: 10 minutes to 15 minutes

[0035] The core 4 has a diameter of preferably 30.0 mm or more and particularly preferably 38.0 mm or more. The diameter of the core 4 is preferably 42.0 mm or less and particularly preferably 41.5 mm or less. The core 4 may have two or more layers. The core 4 may have a rib on the surface thereof. The core 4 may be hollow.

[0036] FIG. 2 is a graph showing the hardness distribution of the core 4. In this graph, the horizontal axis indicates a distance (mm) from the central point of the core 4, and the vertical axis indicates a hardness (Shore C) of the core 4. The details of the reference characters in FIG. 2 are as follows.

[0037] H0: the hardness of the core 4 at a point whose distance from the central point is 0 mm

[0038] H5: the hardness of the core 4 at a point whose distance from the central point is 5 mm

[0039] H10: the hardness of the core 4 at a point whose distance from the central point is 10 mm

[0040] H15: the hardness of the core 4 at a point whose distance from the central point is 15 mm

[0041] Hs: the surface hardness of the core 4

[0042] Each of the hardness H0, the hardness H5, the hardness H10, and the hardness H15 is measured with a Shore C type hardness scale mounted to an automated hardness meter (trade name “Digi Test II” manufactured by Heinrich Bareiss Prüfgerätebau GmbH). The hardness scale is pressed against the cross-section of a hemisphere obtained by cutting the golf ball 2. The measurement is conducted in an environment of 23° C.

[0043] The surface hardness Hs is measured with a Shore C type hardness scale mounted to an automated hardness meter (trade name “Digi Test II” manufactured by Heinrich Bareiss Prüfgerätebau GmbH). The hardness scale is pressed against the surface of the core 4. The measurement is conducted in an environment of 23° C.

[0044] In the core 4, a value V1 calculated by the following mathematical formula (1) is −3.0 or more and 3.0 or less, a value V2 calculated by the following mathematical formula (2) is −3.0 or more and 3.0 or less, and the difference (V3−V4) between a value V3 calculated by the following mathematical formula (3) and a value V4 calculated by the following mathematical formula (4) is 5.0 or more and 10.0 or less.V⁢1=(H⁢5-H⁢0)-(H⁢15-H⁢10)(1)V⁢2=(H⁢10-H⁢5)-(Hs-H⁢15)(2)V⁢3=((H⁢5-H⁢0)+(H⁢15-H⁢10)) / 2(3)V⁢4=((H⁢10-H⁢5)+(H⁢s-H⁢1⁢5)) / 2(4)

[0045] When the golf ball 2 in which the value V1 is −3.0 or more and 3.0 or less, the value V2 is −3.0 or more and 3.0 or less, and the difference (V3−V4) is 5.0 or more and 10.0 or less is hit with a short iron, the spin rate is high. The golf ball 2 has excellent controllability upon a shot with a short iron.

[0046] From the viewpoint of controllability, the value V1 is more preferably −2.5 or more and particularly preferably −2.0 or more. From the viewpoint of controllability, the value V1 is more preferably 2.5 or less and particularly preferably 2.0 or less. From the viewpoint of controllability, the value V2 is more preferably −2.5 or more and particularly preferably −2.0 or more. From the viewpoint of controllability, the value V2 is more preferably 2.5 or less and particularly preferably 2.0 or less. From the viewpoint of controllability, the difference (V3−V4) is more preferably 5.5 or more and particularly preferably 6.0 or more. From the viewpoint of controllability, the difference (V3−V4) is more preferably 9.5 or less and particularly preferably 9.0 or less.

[0047] The value V3 is preferably 6.0 or more. The golf ball 2 in which the value V3 is within this range has excellent feel at impact. From this viewpoint, the value V3 is more preferably 6.5 or more and particularly preferably 7.0 or more. From the viewpoint of the durability of the golf ball 2, the value V3 is preferably 11.0 or less, more preferably 10.5 or less, and particularly preferably 10.0 or less.

[0048] The value V4 is preferably 0.0 or more. The golf ball 2 in which the value V4 is within this range has excellent feel at impact. From the viewpoint of feel at impact, the value V4 is more preferably 0.5 or more and particularly preferably 1.0 or more. From the viewpoint of the durability of the golf ball 2, the value V4 is preferably 2.0 or less.

[0049] In the core 4, a value V5 calculated by the following mathematical formula (5) is 65.0 or more and 73.0 or less.V⁢5=(H⁢5+H⁢1⁢0+H⁢1⁢5) / 3(5)The golf ball 2 in which the value V5 is 65.0 or more and 73.0 or less has excellent feel at impact. From this viewpoint, the value V5 is more preferably 66.0 or more and particularly preferably 67.0 or more.From the viewpoint of the feel at impact of the golf ball 2, the difference (Hs−H0) between the hardness Hs and the hardness H0 is preferably 18.0 or more. From the viewpoint of the durability of the golf ball 2, the difference (Hs−H0) is preferably 30.0 or less, more preferably 28.0 or less, and particularly preferably 26.0 or less.

[0051] The hardness H0 is preferably 55 or more. The golf ball 2 in which the hardness H0 is within this range has excellent durability. From this viewpoint, the hardness H0 is more preferably 57 or more and particularly preferably 58 or more. From the viewpoint of feel at impact, the hardness H0 is preferably 70 or less, more preferably 68 or less, and particularly preferably 66 or less.

[0052] Typically, the mid layer 6 is formed from a resin composition. A preferable base polymer for the resin composition is an ionomer resin. Examples of preferable ionomer resins include binary copolymers formed with an α-olefin and an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms. Examples of other preferable ionomer resins include ternary copolymers formed with: an α-olefin; an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms; and an α,β-unsaturated carboxylate ester having 2 to 22 carbon atoms. For the binary copolymers and the ternary copolymers, preferable α-olefins are ethylene and propylene, and preferable α,β-unsaturated carboxylic acids are acrylic acid and methacrylic acid. In the binary copolymers and the ternary copolymers, some of the carboxyl groups are neutralized with metal ions. Examples of metal ions for neutralization include sodium ions, potassium ions, lithium ions, zinc ions, calcium ions, magnesium ions, aluminum ions, and neodymium ions.

[0053] The resin composition of the mid layer 6 may include another polymer instead of an ionomer resin. Examples of the other polymer include polystyrenes, polyamides, polyesters, polyolefins, and polyurethanes. The resin composition may include two or more polymers.

[0054] The resin composition of the mid layer 6 may include a coloring agent such as titanium dioxide, a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent material, a fluorescent brightener, etc. For the purpose of specific gravity adjustment, the resin composition may include powder of a metal with a high specific gravity such as tungsten and molybdenum.

[0055] The mid layer 6 has a thickness of preferably 0.2 mm or more, more preferably 0.3 mm or more, and particularly preferably 0.4 mm or more. The thickness of the mid layer 6 is preferably 2.5 mm or less, more preferably 2.2 mm or less, and particularly preferably 2.0 mm or less. The mid layer 6 has a specific gravity of preferably 0.90 or more and particularly preferably 0.95 or more. The specific gravity of the mid layer 6 is preferably 1.10 or less and particularly preferably 1.05 or less. The mid layer 6 may have two or more layers.

[0056] Typically, the cover 8 is formed from a resin composition. A preferable base polymer of the resin composition is a polyurethane. The base polymer may be a thermoplastic polyurethane or a thermosetting polyurethane. From the viewpoint of ease of molding the cover 8, a thermoplastic polyurethane is preferred.

[0057] The polyurethane can be obtained by the reaction of a polyol with a polyisocyanate. The polyol has two or more hydroxyl groups in its molecule. A polyol having a number-average molecular weight of 200 or more and 6000 or less is preferred. This polyol can form a soft segment in the polyurethane. The soft segment can contribute to the flexibility of the cover 8. The number-average molecular weight of the polyol is more preferably 300 or more and particularly preferably 1000 or more. The number-average molecular weight is more preferably 4000 or less and particularly preferably 3000 or less. The polyurethane may also be obtained by the reaction of two or more polyols.

[0058] Preferably, the polyurethane is obtained by the reaction of a polymer polyol with a polyisocyanate. The polymer polyol can be obtained by a polymerization reaction of a low-molecular-weight compound. The polymer polyol has a plurality of hydroxyl groups. Compounds derived from petroleum resources may be subjected to the polymerization reaction, and compounds derived from biomass resources may also be subjected to the polymerization reaction. Examples of the polymer polyol include polyether polyols, condensed polyester polyols, lactone polyester polyols, polycarbonate polyols, and acrylic polyols. Two or more polymer polyols may be used in combination.

[0059] Examples of polyether polyols include polyoxyethylene glycol (PEG), polyoxypropylene glycol (PPG), polytrimethylene ether glycol (PO3G), and polytetramethylene ether glycol (PTMG). Examples of the condensed polyester polyols include polyethylene adipate (PEA), polybutylene adipate (PBA), and polyhexamethylene adipate (PHMA). Examples of the lactone polyester polyols include poly-s-caprolactone (PCL). Examples of the polycarbonate polyols include polyhexamethylene carbonate.

[0060] A preferable polymer polyol is a polymer diol. The polymer diol has two hydroxyl groups. A linear thermoplastic polyurethane can be obtained by the reaction of the polymer diol with a polyisocyanate. The cover 8 containing this polyurethane can be easily molded.

[0061] A particularly preferable polyol is a polyether polyol. The cover 8 containing a polyurethane obtained by a reaction of a polyether polyol has excellent strength. When a polyether polyol and another polyol are used in combination, the ratio of the polyether polyol to all polyols is preferably 50% by mass or more, more preferably 55% by mass or more, and particularly preferably 60% by mass or more.

[0062] The above-described polyisocyanate has two or more isocyanate groups. The polyurethane may be obtained by the reaction of a polyol with two or more polyisocyanates. Examples of preferable polyisocyanates include aromatic polyisocyanates, alicyclic polyisocyanates, and aliphatic polyisocyanates.

[0063] Examples of aromatic polyisocyanates include 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, a mixture (TDI) of 2,4-toluene diisocyanate and 2,6-toluene diisocyanate, 4,4′-diphenylmethane diisocyanate (MDI), 1,5-naphthylene diisocyanate (NDI), 3,3′-bitolylene-4,4′-diisocyanate (TODI), xylylene diisocyanate (XDI), tetramethylxylylene diisocyanate (TMXDI), and paraphenylene diisocyanate (PPDI).

[0064] Examples of alicyclic polyisocyanates or aliphatic polyisocyanates include 4,4′-dicyclohexylmethane diisocyanate (H12MDI), hydrogenated xylylene diisocyanate (H6XDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), and norbornene diisocyanate (NBDI).

[0065] From the viewpoint of the scuff resistance of the cover 8, aromatic polyisocyanates are preferred. From the viewpoint of the weather resistance of the cover 8, non-yellowing polyisocyanates are preferred. Examples of non-yellowing polyisocyanates include TMXDI, XDI, HDI, H6XDI, IPDI, H12MDI, and NBDI. H12MDI (4,4′-dicyclohexylmethane diisocyanate) is particularly preferred. H12MDI has a rigid structure. Therefore, H12MDI can also contribute to the scuff resistance of the cover 8.

[0066] A chain extender may be used for the reaction of the polyurethane. Examples of the chain extender component include low-molecular-weight polyols and low-molecular-weight polyamines.

[0067] Examples of low-molecular-weight polyols include: diols such as ethylene glycol, diethylene glycol, triethylene glycol, propanediols, dipropylene glycol, butanediols, neopentyl glycol, pentanediol, hexanediol, heptanediol, octanediol, and 1,4-cyclohexanedimethanol; triols such as glycerin, trimethylolpropane, and hexanetriol; and tetraols or hexols such as pentaerythritol and sorbitol. Examples of propanediols include 1,2-propanediol, 1,3-propanediol, and 2-methyl-1,3-propanediol. Examples of butanediols include 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, and 2,3-dimethyl-2,3-butanediol.

[0068] The low-molecular-weight polyamines which are chain extenders each have two or more amino groups. Examples of such polyamines include: aliphatic polyamines such as ethylenediamine, propylenediamine, butylenediamine, and hexamethylenediamine; alicyclic polyamines such as isophoronediamine and piperazine; and aromatic polyamines.

[0069] An aromatic polyamine has two or more amino groups. Each amino group is directly or indirectly bonded to an aromatic ring. The amino group may be bonded to the aromatic ring via a lower alkylene group or the like. Examples of aromatic polyamines include monocyclic aromatic polyamines and polycyclic aromatic polyamines. In a monocyclic aromatic polyamine, two or more amino groups are bonded to a single aromatic ring. A polycyclic aromatic polyamine has two or more aminophenyl groups. Each aminophenyl group includes one amino group and one aromatic ring.

[0070] Examples of monocyclic aromatic polyamines in which the amino groups are directly bonded to the aromatic ring include phenylenediamine, toluenediamine, diethyltoluenediamine, and dimethylthiotoluenediamine. An example of monocyclic aromatic polyamines in which the amino groups are bonded to the aromatic ring via a lower alkylene group is xylylenediamine.

[0071] An example of polycyclic aromatic polyamines in which the aminophenyl groups are directly bonded to the aromatic ring is poly(aminobenzene). The aminophenyl groups may be bonded to the aromatic ring via a lower alkylene group or an alkylene oxide group. A preferable polycyclic aromatic polyamine is a diaminodiphenyl alkane. 4,4′-diaminodiphenylmethane and derivatives thereof are particularly preferred. In 4,4′-diaminodiphenylmethane, two aminophenyl groups are bonded to the aromatic ring via a lower alkylene group.

[0072] The molecular weight of the chain extender is preferably 400 or less, more preferably 350 or less, and particularly preferably less than 200. The molecular weight is preferably 30 or more, more preferably 40 or more, and particularly preferably 45 or more.

[0073] Instead of the polyurethane, the resin composition of the cover 8 may include another polymer. Examples of the other polymer include ionomer resins, polystyrenes, polyamides, polyesters, and polyolefins. The resin composition may include two or more polymers.

[0074] The resin composition of the cover 8 may include a coloring agent such as titanium dioxide, a filler such as barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent material, a fluorescent brightener, etc.

[0075] The cover 8 has a thickness of preferably 0.2 mm or more, more preferably 0.3 mm or more, and particularly preferably 0.4 mm or more. The thickness of the cover 8 is preferably 2.5 mm or less, more preferably 2.2 mm or less, and particularly preferably 2.0 mm or less. The cover 8 has a specific gravity of preferably 0.90 or more and particularly preferably 0.95 or more. The specific gravity of the cover 8 is preferably 1.10 or less and particularly preferably 1.05 or less. The cover 8 may have two or more layers.

[0076] The golf ball 2 may include a reinforcing layer between the mid layer 6 and the cover 8. The reinforcing layer firmly adheres to the mid layer 6 and also to the cover 8. The reinforcing layer suppresses separation of the cover 8 from the mid layer 6. The reinforcing layer is formed from a polymer composition. Examples of the base polymer of the reinforcing layer include two-component curing type epoxy resins and two-component curing type urethane resins.

[0077] As shown in FIGS. 3 and 4, the contour of each dimple 10 is circular. The golf ball 2 has: dimples 10A each having a diameter of 4.40 mm; dimples 10B each having a diameter of 4.30 mm; dimples 10C each having a diameter of 4.15 mm; dimples 10D each having a diameter of 3.90 mm; and dimples 10E each having a diameter of 3.00 mm. The number of types of the dimples 10 is five. The golf ball 2 may have dimples 10 each having a non-circular contour.

[0078] The number of the dimples 10A is 60; the number of the dimples 10B is 158; the number of the dimples 10C is 72; the number of the dimples 10D is 36; and the number of the dimples 10E is 12. The total number N of the dimples 10 is 338. A dimple pattern is formed by these dimples 10 and the land 12.

[0079] From the viewpoint of the appearance of the golf ball 2 and the flight performance of the golf ball 2 upon a shot with an iron, the total number N of the dimples 10 is preferably 250 or more and 450 or less. The total number N is more preferably 270 or more and particularly preferably 280 or more. The total number N is more preferably 410 or less and particularly preferably 380 or less.

[0080] FIG. 5 shows a cross-section of the golf ball 2 along a plane passing through the central point of the dimple 10 and the central point of the golf ball 2. In FIG. 5, the up-down direction is the depth direction of the dimple 10. In FIG. 5, an alternate long and two short dashes line 14 indicates a phantom sphere. The surface of the phantom sphere 14 is the surface of the golf ball 2 when it is postulated that no dimple 10 exists. The diameter of the phantom sphere 14 is the same as the diameter of the golf ball 2. The dimple 10 is recessed from the surface of the phantom sphere 14. The land 12 coincides with the surface of the phantom sphere 14. In the present embodiment, the cross-sectional shape of each dimple 10 is substantially an arc. The curvature radius of the arc is indicated by reference character CR in FIG. 5.

[0081] In FIG. 5, an arrow Dm indicates the diameter of the dimple 10. The diameter Dm is the distance between two tangent points Ed appearing on a tangent line Tg that is drawn tangent to the opposite ends of the dimple 10. Each tangent point Ed is also the edge of the dimple 10. The edge Ed defines the contour of the dimple 10. The diameter Dm is preferably 2.0 mm or more and 6.0 mm or less.

[0082] In FIG. 5, a double headed arrow Dp indicates the depth of the dimple 10. The depth Dp is the distance between the deepest part of the dimple 10 and the plane including the contour of the dimple 10. The depth Dp is preferably 0.05 mm or more and 0.25 mm or less.

[0083] The area S of the dimple 10 is the area of a region surrounded by the contour line of the dimple 10 when the central point of the golf ball 2 is viewed at infinity. In the case of the dimple 10 having a circular contour, the area S is calculated by the following mathematical formula.S=(D⁢m / 2)2*π

[0084] In the golf ball 2 shown in FIGS. 3 and 4, the area of each dimple 10A is 15.21 mm2, the area of each dimple 10B is 14.52 mm2, the area of each dimple 10C is 13.53 mm2, the area of each dimple 10D is 11.95 mm2, and the area of each dimple 10E is 7.07 mm2.

[0085] In the present specification, the ratio X of the sum of the areas S of all the dimples 10 to the surface area of the phantom sphere 14 is referred to as “occupation ratio”. From the viewpoint of trajectory pleasantness, the occupation ratio X is preferably 70% or more, more preferably 75% or more, and particularly preferably 80% or more. The occupation ratio X is preferably 95% or less. In the golf ball 2 shown in FIGS. 3 and 4, the total area of the dimples 10 is 4695.6 mm2. The surface area of the phantom sphere 14 of the golf ball 2 is 5728.0 mm2, and thus the occupation ratio X is 82%.

[0086] In the present specification, the “volume of the dimple” means the volume of the portion surrounded by the plane including the contour of the dimple 10 and the surface of the dimple 10. The total of the volumes of all the dimples 10 is referred to as “total volume Y”. In the golf ball 2 shown in FIGS. 3 and 4, the volume of each dimple 10A is 1.263 mm3, the volume of each dimple 10B is 1.206 mm3, the volume of each dimple 10C is 1.124 mm3, the volume of each dimple 10D is 0.993 mm3, and the volume of each dimple 10E is 0.588 mm3. Accordingly, the total volume Y of the dimples 10 is 390 mm3.

[0087] In the present embodiment, a first drag coefficient Db, a first lift coefficient Lb, a second drag coefficient Da, and a second lift coefficient La are measured. The first drag coefficient Db and the first lift coefficient Lb are measured under the following first condition. The second drag coefficient Da and the second lift coefficient La are measured under the following second condition.First ConditionReynolds number: 1.20*105

[0089] Ratio (rω / V): 0.131Second ConditionReynolds number: 0.83*105

[0091] Ratio (rω / V): 0.179The ratio (rω / V) is calculated by dividing the product of the radius r (m) and a backspin rate ω (rad / s) of the golf ball 2 by a speed V (m / s) of the golf ball 2.

[0092] The first condition generally corresponds to a condition at a point 70 yards before the peak of a trajectory upon a shot with a driver at a head speed of 50 m / s. The second condition generally corresponds to a condition at the peak of a trajectory upon a shot with driver at a head speed of 50 m / s. According to the findings obtained by the present inventor, the first drag coefficient Db, the first lift coefficient Lb, the second drag coefficient Da, and the second lift coefficient La have a significant influence on the flight distance of the golf ball 2. From this viewpoint, in the present embodiment, the drag and lift coefficients are measured under the first and second conditions.

[0093] In the present specification, a value Z is calculated by the following mathematical formula (6).Z=-536.36*Db+146.46*Lb-238.52*Da+225.22*La+111.21(6)According to the findings obtained by the present inventor, when the golf ball 2 having a value Z of less than 0.0 flies under new test conditions, the flight distance thereof is smaller than that of a conventional golf ball. This golf ball 2 can comply with these new rules. From the viewpoint of compliance with the new rules, the value Z is more preferably −0.2 or less and particularly preferably −0.5 or less. From the viewpoint of trajectory pleasantness, the value Z is preferably −25.0 or more, more preferably −20.0 or more, and particularly preferably −15.0 or more.The golf ball 2 having a small value Z can comply with the new rule even if the golf ball 2 has excellent resilience performance. The golf ball 2 having excellent resilience performance can have excellent flight performance upon a shot at a low head speed. The golf ball 2 may have both a small value Z and inferior resilience performance.

[0095] The golf ball 2 having a small value Z can comply with the new rule even if the ball diameter thereof is not excessively large. The golf ball 2 having an appropriate ball diameter has low air resistance during flight. The trajectory of this golf ball 2 is less likely to be affected by wind. The golf ball 2 may have both a small value Z and a large ball diameter.

[0096] The golf ball 2 having a small value Z can comply with the new rule even if the mass thereof is not excessively small. The golf ball 2 having an appropriate mass has high inertia. The trajectory of this golf ball 2 is less likely to be affected by wind. The golf ball 2 may have both a small value Z and a small mass.

[0097] A value Z of less than 0.0 can be achieved by adopting a small total number N for the golf ball 2. A value Z of less than 0.0 can be achieved by adopting a small occupation ratio X for the golf ball 2. A value Z of less than 0.0 can be achieved by adopting an extremely small total volume Y for the golf ball 2. A value Z of less than 0.0 can be achieved by adopting an extremely large total volume Y for the golf ball 2.

[0098] The ratio (Lb / Db) of the first lift coefficient Lb to the first drag coefficient Db is preferably 0.82 or less. When the golf ball 2 having a ratio (Lb / Db) of 0.82 or less flies under the new test condition, the trajectory thereof is low. This trajectory can achieve a short flight distance under the new test condition. From this viewpoint, the ratio (Lb / Db) is more preferably 0.81 or less and particularly preferably 0.80 or less. From the viewpoint of controllability and trajectory pleasantness, the ratio (Lb / Db) is preferably 0.65 or more, more preferably 0.67 or more, and particularly preferably 0.70 or more.

[0099] The total volume Y of the dimple 10 is preferably 330 mm3 or more. The dimples 10 having a total volume Y of 330 mm3 or more can achieve a low trajectory when the golf ball 2 flies under the condition of the new rule. From this viewpoint, the total volume Y is more preferably 360 mm3 or more and particularly preferably 390 mm3 or more. From the viewpoint of controllability and trajectory pleasantness, the total volume Y is preferably 550 mm3 or less, more preferably 520 mm3 or less, and particularly preferably 500 mm3 or less.

[0100] The golf ball 2 having a sufficiently large total volume Y can comply with the new rule even if the number N of the dimples 10 is appropriate. The golf ball 2 having a sufficiently large total volume Y can comply with the new rule even if the occupation ratio X is appropriate. The golf ball 2 having an appropriate number N and occupation ratio X has excellent appearance.

[0101] In the present specification, a value T is calculated by the following mathematical formula (7).T=-0.55*X+0.115*Y+0.3(7)The value Tis preferably 0.00 or more. The dimples 10 having a value T of 0.00 or more can achieve a low trajectory when the golf ball 2 flies under the condition of the new rule. From this viewpoint, the value T is more preferably 0.05 or more and particularly preferably 0.10 or more. From the viewpoint of controllability and trajectory pleasantness, the value Tis preferably 15.0 or less, more preferably 12.0 or less, and particularly preferably 10.0 or less.The golf ball 2 has an amount of compressive deformation CDb of preferably 2.70 mm or more. The golf ball 2 having an amount of compressive deformation CDb of 2.70 mm or more has excellent feel at impact. From this viewpoint, the amount of compressive deformation CDb is more preferably 2.75 mm or more and particularly preferably 2.80 mm or more. From the viewpoint of trajectory pleasantness, the amount of compressive deformation CDb is preferably 3.30 mm or less, more preferably 3.20 mm or less, and particularly preferably 3.10 mm or less.

[0103] The amount of compressive deformation CDb is measured with a YAMADA type compression tester. In the tester, the golf ball 2 is placed on a rigid plate made of metal. A cylinder made of metal gradually descends toward the golf ball 2. The golf ball 2 becomes deformed by being squeezed between the bottom face of the cylinder and the rigid plate. A movement distance of the cylinder, starting from the state in which an initial load of 98 Nis applied to the golf ball 2 up to the state in which a final load of 1274 N is applied thereto, is measured. A movement speed of the cylinder until the initial load is applied is 0.83 mm / s. A movement speed of the cylinder after the initial load is applied until the final load is applied is 1.67 mm / s. An amount of compressive deformation CDc of the core 4 is also measured in the same manner.EXAMPLES

[0104] Hereinafter, the advantageous effects of golf balls according to Examples will be shown, but the scope disclosed in the present specification should not be construed in a limited manner on the basis of the description of these Examples.Example 1

[0105] A rubber composition was obtained by kneading 100 parts by mass of a high-cis polybutadiene, 29 parts by mass of zinc diacrylate, 10 parts by mass of zinc oxide, an appropriate amount of barium sulfate, 0.4 parts by mass of bis(pentabromophenyl)disulfide, and 0.7 parts by mass of dicumyl peroxide. The rubber composition was placed into a mold including upper and lower mold halves each having a hemispherical cavity. The rubber composition was heated at 142° C. for 10 minutes and further heated at 155° C. for 12 minutes to obtain a core having a diameter of 39.5 mm.

[0106] A resin composition was obtained by kneading 50 parts by mass of an ionomer resin (trade name “HIMILAN AM7337”, manufactured by Du Pont-MITSUI POLYCHEMICALS Co., Ltd.), 50 parts by mass of another ionomer resin (trade name “HIMILAN AM7938”, manufactured by Du Pont-MITSUI POLYCHEMICALS Co., Ltd.), 4 parts by mass of titanium dioxide, and an appropriate amount of barium sulfate with a twin-screw kneading extruder. The core was covered with the resin composition by injection molding to form a mid layer. The thickness of the mid layer was 1.0 mm.

[0107] A composition (trade name “POLIN 750LE”, manufactured by SHINTO PAINT CO., LTD.) including a two-component curing type epoxy resin as a base polymer was prepared. The base material liquid of this composition includes 30 parts by mass of a bisphenol A type solid epoxy resin and 70 parts by mass of a solvent. The curing agent liquid of this composition includes 40 parts by mass of a modified polyamide amine, 55 parts by mass of a solvent, and 5 parts by mass of titanium dioxide. The weight ratio of the base material liquid to the curing agent liquid is 1 / 1. This composition was applied to the surface of the mid layer with a spray gun, and kept at 23° C. for 6 hours to obtain a reinforcing layer. The thickness of the reinforcing layer was 10 μm.

[0108] A first polyurethane was obtained by reacting 1.00 part by mass of a polytetramethylene ether glycol (number-average molecular weight: 1400), 3.81 parts by mass of dicyclohexylmethane diisocyanate, and 2.81 parts by mass of butanediol. A second polyurethane was obtained by reacting 1.00 part by mass of another polytetramethylene ether glycol (number-average molecular weight: 2000), 4.50 parts by mass of dicyclohexylmethane diisocyanate, and 3.50 parts by mass of butanediol. A resin composition was obtained by kneading 90 parts by mass of the first polyurethane, 10 parts by mass of the second polyurethane, and 4 parts by mass of titanium dioxide with a twin-screw kneading extruder. The material hardness of this resin composition was 82 (Shore A). Half shells were obtained from this resin composition by compression molding. The sphere consisting of the core, the mid layer, and the reinforcing layer was covered with two of these half shells. These half shells and the sphere were placed into a final mold including upper and lower mold halves each having a hemispherical cavity and having a large number of pimples on its cavity face, and a cover was obtained by compression molding. The thickness of the cover was 0.6 mm. Dimples having a shape that is the inverted shape of the pimples were formed on the cover. A clear paint including a two-component curing type polyurethane as a base material was applied to 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. The dimple pattern of the golf ball is shown in FIGS. 3 and 4. The specifications of the dimples of the golf ball are shown in Tables 4 and 5 below.Examples 2 to 9 and Comparative Examples 1 to 6

[0109] Golf balls of Examples 2 to 9 and Comparative Examples 1 to 6 were obtained in the same manner as Example 1, except that the specifications of the core, the mid layer, and the dimples were changed.TABLE 1Core specifications12345Polybutadiene100100100100100Zinc diacrylate2927262624Zinc oxide1010101010Barium sulfateAppropriateAppropriateAppropriateAppropriateAppropriateamountamountamountamountamountBenzoic acid——1.0—3.04-methoxyphenol——0.10.10.1PBDS0.40.40.40.40.4DPDS—————DCP0.70.71.21.01.2First-stage crosslinkingTemperature [° C.]142142156156160Time [min]1010181816Second-stage crosslinkingTemperature [° C.]155155———Time [min]1212———Diameter [mm]39.539.539.539.539.5Amount of compressive3.353.553.353.353.36deformation CDc [mm]H0 [Shore C]6159596254H5 [Shore C]6967676862H10 [Shore C]7169697065H15 [Shore C]7876777776Hs [Shore C]7978787877TABLE 2Core specifications67891011Polybutadiene100100100100100100Zinc diacrylate34.53230292923.5Zinc oxide5105101010Barium sulfateAppropriateAppropriateAppropriateAppropriateAppropriateAppropriateamountamountamountamountamountamountBenzoic acid—2.01.5———4-methoxyphenol——0.1———PBDS—0.40.40.40.40.4DPDS0.5—————DCP0.70.71.20.70.70.7First-stage crosslinkingTemperature [° C.]170150156140142142Time [min]141918101010Second-stage crosslinkingTemperature [° C.]———160170155Time [min]———121212Diameter [mm]39.539.539.539.539.539.5Amount of3.253.222.953.283.503.90compressivedeformation CDc [mm]H0 [Shore C]625461595856H5 [Shore C]706369686964H10 [Shore C]706972717166H15 [Shore C]747880787874Hs [Shore C]807981818176Polybutadiene: trade name “BR-730”, manufactured by JSR CorporationZinc diacrylate: trade name “ZN-DA90S”, manufactured by NISSHOKU TECHNO FINE CHEMICAL CO., LTD.

[0112] Zinc oxide: trade name “Ginrei R”, manufactured by Toho Zinc Co., Ltd.

[0113] Barium sulfate: trade name “Barium Sulfate BD”, manufactured by SAKAI CHEMICAL INDUSTRY CO., LTD.

[0114] Benzoic acid: product of Emerald Kalama Chemical, LLC

[0115] 4-methoxyphenol: product of Tokyo Chemical Industry Co., Ltd.

[0116] PBDS: bis(pentabromophenyl)disulfide (manufactured by Kawaguchi Chemical Industry Co., Ltd.)

[0117] DPDS: diphenyl disulfide (manufactured by Sumitomo Seika Chemicals Company, Limited.)

[0118] DCP: dicumyl peroxide (trade name “PERCUMYL D”, manufactured by NOF CORPORATION)TABLE 3Mid layer composition [parts by mass]ABHIMILAN AM733750—HIMILAN AM793850—U161-RV2—100Titanium dioxide44Barium sulfateAppropriateAppropriateamountamountHardness [Shore D]6972U161-RV2: polyamide (Toray Industries, Inc.)TABLE 4Dimple specificationsTotalPlanDiameterDepthCurvaturevolumeRatioviewDmDpCrVolumeAreaYXFrontTypeNumber[mm][mm][mm][mm3][mm2][mm3][%]view1A604.4000.165814.681.26315.2139082FIG. 3B1584.3000.165814.021.20614.52FIG. 4C724.1500.165813.071.12413.53D363.9000.165811.550.99311.95E123.0000.16586.870.5887.072A604.4000.172114.151.31115.2140582FIG. 3B1584.3000.172113.521.25214.52FIG. 4C724.1500.172112.601.16713.53D363.9000.172111.131.03111.95E123.0000.17216.620.6117.073A604.4000.191212.751.45715.2145082FIG. 3B1584.3000.191212.181.39214.52FIG. 4C724.1500.191211.361.29713.53D363.9000.191210.041.14611.95E123.0000.19125.980.6797.07TABLE 5Dimple specificationsTotalPlanDiameterDepthCurvaturevolumeRatioviewDmDpCrVolumeAreaYXFrontTypeNumber[mm][mm][mm][mm3][mm2][mm3][%]view4A164.5920.139518.961.15716.5634085FIG. 6B304.4920.139518.151.10715.85FIG. 7C304.3920.139517.351.05815.15D1504.2920.139516.581.01114.47E304.1920.139515.820.96413.80F664.0920.139515.070.91913.15G103.7920.139512.950.78911.29H123.3920.139510.380.6329.045A164.5920.237211.231.97116.5655085FIG. 6B304.4920.237210.751.88715.85FIG. 7C304.3920.237210.281.80415.15D1504.2920.23729.831.72314.47E304.1920.23729.381.64413.80F664.0920.23728.941.56713.15G103.7920.23727.701.34611.29H123.3920.23726.181.0799.04[Spin Performance]An 8-iron club (trade name “SRIXON ZX7 Mk II”, manufactured by Sumitomo Rubber Industries, Ltd., loft: 36°, shaft hardness: S) was attached to a swing machine manufactured by Golf Laboratories, Inc. A golf ball was hit under the condition of a head speed of 39 m / sec, and the spin rate was measured. The measurement was conducted 12 times, and the average value of the obtained data was calculated. The difference between each of the average values of the golf balls of Examples 1 to 9 and Comparative Examples 1 to 4 and 6 and the average value of the golf ball of Comparative Example 5 was calculated. The rating was conducted according to the following criteria.A: Difference is 0 rpm or more.B: Difference is −130 rpm or more and less than 0 rpm.

[0122] C: Difference is −260 rpm or more and less than-130 rpm.

[0123] D: Difference is less than-260 rpm.The results are shown in Tables 6 to 8 below.[Flight Test]

[0124] A driver (trade name “SRIXON ZX7 Mk II”, manufactured by Sumitomo Rubber Industries, Ltd., loft angle: 9.5°, shaft hardness: S) was attached to a swing machine manufactured by Golf Laboratories, Inc. A golf ball was hit under the condition of a head speed of 50.0 m / sec, and the flight distance was measured. The flight distance is the distance from the hitting spot to the spot at which the golf ball stopped. The measurement was conducted 12 times, and the average value of the obtained data was calculated. The difference between each of the average values of the golf balls of Examples 1 to 9 and Comparative Examples 1 to 4 and 6 and the average value of the golf ball of Comparative Example 5 was calculated. The rating was conducted according to the following criteria.

[0125] A: Difference is less than-5 yards.

[0126] B: Difference is −5 yards or more and less than 0 yards.

[0127] C: Difference is 0 yards or more and less than 5 yards.

[0128] D: Difference is 5 yards or more.The results are shown in Tables 6 to 8 below.[Trajectory Pleasantness (Height)]

[0129] Twenty players with powerful swings were asked to hit golf balls with a driver and evaluate the trajectory height. The number of players who answered “it is good that the trajectory is low” was counted, and the rating was conducted according to the following criteria.

[0130] A: 15 players or more

[0131] B: 10 to 14 players

[0132] C: 5 to 9 players

[0133] D: 4 players or fewerThe results are shown in Tables 6 to 8 below.[Trajectory Pleasantness (Flight Distance)]

[0134] Twenty players with powerful swings were asked to hit golf balls and evaluate the flight distance. The number of players who answered “a large flight distance is achieved” was counted, and the rating was conducted according to the following criteria.

[0135] A: 15 players or more

[0136] B: 10 to 14 players

[0137] C: 5 to 9 players

[0138] D: 4 players or fewerThe results are shown in Tables 6 to 8 below.[Feel at Impact (W #1)]

[0139] Twenty players with powerful swings were asked to hit golf balls with a driver and evaluate the feel at impact. The number of players who answered “the feel at impact is soft and the spin rate is appropriate” was counted, and the rating was conducted according to the following criteria.

[0140] A: 16 players or more

[0141] B: 12 to 15 players

[0142] C: 8 to 11 players

[0143] D: 7 players or fewerThe results are shown in Tables 6 to 8 below.[Feel at Impact (I #8)]

[0144] Twenty players with powerful swings were asked to hit golf balls with an 8-iron club and evaluate the feel at impact. The number of players who answered “the feel at impact is soft and the spin rate is appropriate” was counted, and the rating was conducted according to the following criteria.

[0145] A: 16 players or more

[0146] B: 12 to 15 players

[0147] C: 8 to 11 players

[0148] D: 7 players or fewerThe results are shown in Tables 6 to 8 below.[Overall Evaluation]

[0149] The rating was conducted according to the following criteria.

[0150] A: The rating is “A” or “B” in all evaluations.

[0151] B: The rating is “C” in at least one evaluation, and “A” or “B” in the remaining evaluations.

[0152] C: The rating is “D” in at least one evaluation.TABLE 6Evaluation resultsEx. 1Ex. 2Ex. 3Ex. 4Ex. 5Core111211V11.01.01.01.00.0V21.01.01.00.00.0V37.57.57.57.58.0V41.51.51.52.02.0V3 − V46.06.06.05.56.0V572.772.772.770.768.0Hs − H018.018.018.019.020.0Mid layerAAAAAMid layer thickness [mm]1.01.01.01.01.0Cover thickness [mm]0.60.60.60.60.6Amount of compressive2.852.852.853.013.28deformation CDb [mm]Dimples12311T0.051.786.950.050.05Db0.2390.2390.2440.2390.239Lb0.1900.1840.1780.1900.190Da0.2740.2690.2650.2740.274La0.2410.2330.2210.2410.241Lb / Db0.7920.7710.7320.7920.792Z−0.5−1.4−6.8−0.5−0.5Spin rate [rpm]000−50−130AAABBFlight distance [yard]−3.1−4.9−11.1−3.6−3.7BBABBFlight distance feelingABBAATrajectory height feelingBBABBFeel at impact W#1AAAAAFeel at impact I#8AAAAAOverall evaluationAAAAATABLE 7Evaluation resultsComp.Ex. 6Ex. 7Ex. 8Ex. 9Ex. 1Core945310V12.0−1.0−3.00.04.0V20.01.02.01.0−1.0V38.06.59.58.09.0V43.01.52.01.52.5V3 − V45.05.07.56.56.5V572.371.767.771.072.7Hs − H022.016.023.019.023.0Mid layerAAABAMid layer thickness [mm]1.01.01.01.61.0Cover thickness [mm]0.60.60.60.60.6Amount of compressive2.722.832.862.603.00deformation CDb [mm]Dimples11111T0.050.050.050.050.05Db0.2390.2390.2390.2390.239Lb0.1900.1900.1900.1900.190Da0.2740.2740.2740.2740.274La0.2410.2410.2410.2410.241Lb / Db0.7920.7920.7920.7920.792Z−0.5−0.5−0.5−0.5−0.5Spin rate [rpm]0−40−10080−220ABBACFlight distance [yard]−1.8−3.8−3.1−2.0−3.1BBBBBFlight distance feelingAAAAATrajectory height feelingBBBBBFeel at impact W#1BAABAFeel at impact I#8BAABAOverall evaluationAAAABTABLE 8Evaluation resultsComp.Comp.Comp.Comp.Comp.Ex. 2Ex. 3Ex. 4Ex. 5Ex. 6Core67811V14.00.00.01.01.0V2−6.05.02.01.01.0V36.09.08.07.57.5V43.03.52.01.51.5V3 − V43.05.56.06.06.0V571.370.073.772.772.7Hs − H018.025.020.018.018.0Mid layerAAAAAMid layer thickness [mm]1.01.01.01.01.0Cover thickness [mm]0.60.60.60.60.6Amount of compressive2.752.722.452.852.85deformation CDb [mm]Dimples11145T0.050.050.05−7.3532.00Db0.2390.2390.2390.2370.263Lb0.1900.1900.1900.1990.163Da0.2740.2740.2740.2780.276La0.2410.2410.2410.2480.198Lb / Db0.7920.7920.7920.8410.618Z−0.5−0.5−0.53.0−27.5Spin rate [rpm]150−15017500ACAAAFlight distance [yard]−4.1−1.1−1.80.0−30.1BBBCAFlight distance feelingAAAADTrajectory height feelingBBBDAFeel at impact W#1CBCAAFeel at impact I#8BBCAAOverall evaluationBBBCCAs shown in Tables 6 to 8, the flight distance of the golf ball of each Example is short. The golf ball of each Example can comply with new rules established by the R&A and the USGA. Furthermore, the golf ball of each Example has excellent controllability, trajectory pleasantness, and feel at impact. From the evaluation results, advantages of the golf ball are clear.[Disclosure Items]Each of the following items is a disclosure of a preferred embodiment.Item 1

[0155] A golf ball including a spherical core and a cover, wherein

[0156] a value V1 calculated by the following mathematical formula (1) is −3.0 or more and 3.0 or less,

[0157] a value V2 calculated by the following mathematical formula (2) is −3.0 or more and 3.0 or less,

[0158] a difference (V3−V4) between a value V3 calculated by the following mathematical formula (3) and a value V4 calculated by the following mathematical formula (4) is 5.0 or more and 10.0 or less,

[0159] a value V5 calculated by the following mathematical formula (5) is 65.0 or more and 73.0 or less,

[0160] the golf ball has a plurality of dimples on a surface thereof,

[0161] a ratio X of a total area of all the dimples to a surface area of a phantom sphere of the golf ball is 70% or more, and

[0162] a value Z calculated by the following mathematical formula (6) is −25.0 or more and less than 0.0,V⁢1=(H⁢5-H⁢0)-(H⁢15-H⁢10),(1)V⁢2=(H⁢10-H⁢5)-(Hs-H⁢15),(2)V⁢3=((H⁢5-H⁢0)+(H⁢15-H⁢10)) / 2,(3)V⁢4=((H⁢10-H⁢5)+(H⁢s-H⁢1⁢5)) / 2,(4)V⁢5=(H⁢5+H⁢1⁢0+H⁢1⁢5) / 3,(5)Z=-536.36*Db+146.46*Lb-238.52*Da+225.22*La+111.21,(6)in the mathematical formulas (1) to (5), H0, H5, H10, and H15 respectively represent hardnesses (Shore C) of the core at points whose distances from a central point of the core are 0 mm, 5 mm, 10 mm, and 15 mm, and Hs represents a surface hardness (Shore C) of the core, and

[0164] in the mathematical formula (6), Db represents a drag coefficient under a condition where a Reynolds number is 1.20*105 and a ratio (rω / V) is 0.131, Lb represents a lift coefficient under a condition where the Reynolds number is 1.20*105 and the ratio (rω / V) is 0.131, Da represents a drag coefficient under a condition where the Reynolds number is 0.83*105 and the ratio (rω / V) is 0.179, La represents a lift coefficient under a condition where the Reynolds number is 0.83*105 and the ratio (rω / V) is 0.179, and the ratio (rω / V) is calculated by dividing a product of a radius r (m) and a backspin rate ω (rad / s) of the golf ball by a speed V (m / s) of the golf ball.Item 2

[0165] The golf ball according to Item 1, wherein a ratio (Lb / Db) of the lift coefficient Lb to the drag coefficient Db is 0.82 or less.Item 3

[0166] The golf ball according to Item 1 or 2, wherein a total volume Y of all the dimples is 330 mm3 or more, and a value T calculated by the following mathematical formula (7) is 0.00 or more,T=-0.55*X+0.115*Y+0.3.(7)Item 4

[0167] The golf ball according to any one of Items 1 to 3, wherein the value V3 is 6.0 or more.Item 5

[0168] The golf ball according to any one of Items 1 to 4, wherein the value V4 is 2.0 or less.Item 6

[0169] The golf ball according to any one of Items 1 to 5, wherein a difference (Hs−H0) is 18.0 or more.Item 7

[0170] The golf ball according to any one of Items 1 to 6, wherein the hardness H0 is 55 or more.Item 8

[0171] The golf ball according to any one of Items 1 to 7, wherein an amount of compressive deformation CDb of the golf ball is 2.70 mm or more.

[0172] The above-described golf ball is suitable for, for example, playing golf on golf courses and practicing at driving ranges.

Claims

1. A golf ball comprising a spherical core and a cover, whereina value V1 calculated by the following mathematical formula (1) is −3.0 or more and 3.0 or less,a value V2 calculated by the following mathematical formula (2) is −3.0 or more and 3.0 or less,a difference (V3−V4) between a value V3 calculated by the following mathematical formula (3) and a value V4 calculated by the following mathematical formula (4) is 5.0 or more and 10.0 or less,a value V5 calculated by the following mathematical formula (5) is 65.0 or more and 73.0 or less,the golf ball has a plurality of dimples on a surface thereof,a ratio X of a total area of all the dimples to a surface area of a phantom sphere of the golf ball is 70% or more, anda value Z calculated by the following mathematical formula (6) is −25.0 or more and less than 0.0,V⁢1=(H⁢5-H⁢0)-(H⁢15-H⁢10),(1)V⁢2=(H⁢10-H⁢5)-(Hs-H⁢15),(2)V⁢3=((H⁢5-H⁢0)+(H⁢15-H⁢10)) / 2,(3)V⁢4=((H⁢10-H⁢5)+(H⁢s-H⁢1⁢5)) / 2,(4)V⁢5=(H⁢5+H⁢1⁢0+H⁢1⁢5) / 3,(5)Z=-536.36*Db+146.46*Lb-238.52*Da+225.22*La+111.21,(6)in the mathematical formulas (1) to (5), H0, H5, H10, and H15 respectively represent hardnesses (Shore C) of the core at points whose distances from a central point of the core are 0 mm, 5 mm, 10 mm, and 15 mm, and Hs represents a surface hardness (Shore C) of the core, andin the mathematical formula (6), Db represents a drag coefficient under a condition where a Reynolds number is 1.20*105 and a ratio (rω / V) is 0.131, Lb represents a lift coefficient under a condition where the Reynolds number is 1.20*105 and the ratio (rω / V) is 0.131, Da represents a drag coefficient under a condition where the Reynolds number is 0.83*105 and the ratio (rω / V) is 0.179, La represents a lift coefficient under a condition where the Reynolds number is 0.83*105 and the ratio (rω / V) is 0.179, and the ratio (rω / V) is calculated by dividing a product of a radius r (m) and a backspin rate ω (rad / s) of the golf ball by a speed V (m / s) of the golf ball.

2. The golf ball according to claim 1, wherein a ratio (Lb / Db) of the lift coefficient Lb to the drag coefficient Db is 0.82 or less.

3. The golf ball according to claim 1, wherein a total volume Y of all the dimples is 330 mm3 or more, and a value T calculated by the following mathematical formula (7) is 0.00 or more,T=-0.55*X+0.115*Y+0.3.(7)4. The golf ball according to claim 1, wherein the value V3 is 6.0 or more.

5. The golf ball according to claim 1, wherein the value V4 is 2.0 or less.

6. The golf ball according to claim 1, wherein a difference (Hs−H0) is 18.0 or more.

7. The golf ball according to claim 1, wherein the hardness H0 is 55 or more.

8. The golf ball according to claim 1, wherein an amount of compressive deformation CDb of the golf ball is 2.70 mm or more.

9. The golf ball according to claim 4, wherein the value V3 is 7.0 or more and 10.0 or less.

10. The golf ball according to claim 5, wherein the value V4 is 1.0 or more.

11. The golf ball according to claim 6, wherein the difference (Hs−H0) is 18.0 or more and 26.0 or less.

12. The golf ball according to claim 7, wherein the hardness H0 is 58 or more and 66 or less.

13. The golf ball according to claim 2, wherein the ratio (Lb / Db) is 0.70 or more and 0.80 or less.

14. The golf ball according to claim 1, wherein the value Z is −15.0 or more and −0.5 or less.

15. The golf ball according to claim 3, wherein the total volume Y is 390 mm3 or more and 500 mm3 or less.

16. The golf ball according to claim 3, wherein the value T is 0.10 or more and 10.0 or less.

17. The golf ball according to claim 1, wherein the ratio X is 80% or more and 95% or less.

18. The golf ball according to claim 1, wherein a total number N of the dimples is 280 or more and 380 or less.

19. The golf ball according to claim 8, wherein the amount of compressive deformation CDb is 2.80 mm or more and 3.10 mm or less.

20. A golf ball comprising a spherical core and a cover, whereinthe core has a diameter of 38.0 mm or more and 41.5 mm or less,a value V1 calculated by the following mathematical formula (1) is −2.0 or more and 2.0 or less,a value V2 calculated by the following mathematical formula (2) is −2.0 or more and 2.0 or less,a difference (V3−V4) between a value V3 calculated by the following mathematical formula (3) and a value V4 calculated by the following mathematical formula (4) is 5.5 or more and 9.0 or less,a value V5 calculated by the following mathematical formula (5) is 67.0 or more and 73.0 or less,a hardness H0 is 58 or more and 66 or less,a difference (Hs−H0) is 18.0 or more and 26.0 or less,the golf ball has a plurality of dimples on a surface thereof,a ratio X of a total area of all the dimples to a surface area of a phantom sphere of the golf ball is 75% or more and 95% or less,a total volume Y of all the dimples is 390 mm3 or more and 500 mm3 or less,a value T calculated by the following mathematical formula (7) is 0.00 or more and 10.0 or less,a value Z calculated by the following mathematical formula (6) is −15.0 or more and −0.5 or less, andan amount of compressive deformation CDb of the golf ball is 2.80 mm or more and 3.10 mm or less,V⁢1=(H⁢5-H⁢0)-(H⁢15-H⁢10),(1)V⁢2=(H⁢10-H⁢5)-(Hs-H⁢15),(2)V⁢3=((H⁢5-H⁢0)+(H⁢15-H⁢10)) / 2,(3)V⁢4=((H⁢10-H⁢5)+(H⁢s-H⁢1⁢5)) / 2,(4)V⁢5=(H⁢5+H⁢1⁢0+H⁢1⁢5) / 3,(5)Z=-536.36*Db+146.46*Lb-238.52*Da+225.22*La+111.21,(6)T=-0.55*X+0.115*Y+0.3,(7)in the mathematical formulas (1) to (5), H0, H5, H10, and H15 respectively represent hardnesses (Shore C) of the core at points whose distances from a central point of the core are 0 mm, 5 mm, 10 mm, and 15 mm, and Hs represents a surface hardness (Shore C) of the core, andin the mathematical formula (6), Db represents a drag coefficient under a condition where a Reynolds number is 1.20×105 and a ratio (rw / V) is 0.131, Lb represents a lift coefficient under a condition where the Reynolds number is 1.20×105 and the ratio (rw / V) is 0.131, Da represents a drag coefficient under a condition where the Reynolds number is 0.83×105 and the ratio (rw / V) is 0.179, La represents a lift coefficient under a condition where the Reynolds number is 0.83×105 and the ratio (rw / V) is 0.179, and the ratio (rw / V) is calculated by dividing a product of a radius r (m) and a backspin rate w (rad / s) of the golf ball by a speed V (m / s) of the golf ball.

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