GOLF BALL

Description

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to Japanese patent application JP 2024-174700, filed on Oct. 4, 2024, the entire contents of which is incorporated herein by reference in its entirety.

BACKGROUND

Technical Field

The present specification discloses a golf ball including a core, a mid layer, and a cover.

Background Art

A general golf ball includes a core, a mid layer, and a cover. Japanese Laid-Open Patent Publication No. 2023-4542 discloses a golf ball in which a mid layer has a hardness higher than that of a cover.

Average golf players frequently use wood-type golf clubs on the fairway. When a golf ball that includes a soft core is hit with a fairway wood, the spin rate is low. This core can contribute to flight performance. When putting this golf ball, a golf player is less likely to feel the response. The soft core impairs the stability in a rolling distance upon putting.

It is an intention of the applicant to provide a golf ball having excellent flight performance upon a shot with a fairway wood and appropriate feel at impact upon putting.

SUMMARY

A golf ball disclosed in the present specification includes a core, a mid layer positioned outside the core, and a cover positioned outside the mid layer. A Shore C hardness Ms at a surface of a sphere consisting of the core and the mid layer is equal to or greater than a Shore C hardness Cs at a surface of the core. The hardness Cs is equal to or greater than a Shore C hardness Bs at a surface of the golf ball. A value V1 calculated by the following mathematical formula is 9.15 or more and 10.85 or less.

V ⁢ 1 = ( Cc / Cd ) * Cs ,

where Cc represents an amount of compressive deformation (mm) of the core measured under conditions where an initial load is 98 N and a final load is 1274 N, and Cd represents a diameter (mm) of the core.

The golf ball disclosed in the present specification has excellent flight performance upon a shot with a fairway wood and excellent feel at impact upon putting.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE is a partially cutaway cross-sectional view showing a golf ball according to one embodiment.

DETAILED DESCRIPTION

Hereinafter, preferred embodiments will be described in detail with appropriate reference to the drawing.

A golf ball 2 shown in the FIGURE 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 plurality 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.

[Core]

The core 4 is formed by crosslinking a rubber composition. The rubber composition contains a base rubber, a co-crosslinking agent, a crosslinking initiator, an organic sulfur compound, etc.

[Base Rubber]

Examples of preferable base rubbers include polybutadienes, polyisoprenes, styrene-butadiene copolymers, ethylene-propylene-diene copolymers, and natural rubbers. From the viewpoint of resilience performance of the golf ball 2, polybutadienes are preferable. When a polybutadiene and another rubber are used in combination, it is preferred if the polybutadiene is a principal component. Specifically, the proportion of the polybutadiene to the entire base rubber is preferably 50% by mass or more, more preferably 70% by mass or more, and particularly preferably 80% by mass or more. A polybutadiene in which the proportion of cis-1,4 bonds is 80% or more is particularly preferable. A polybutadiene can contain 1,2-vinyl bonds. From the viewpoint of the resilience performance of the golf ball 2, the content of 1,2-vinyl bonds in the polybutadiene is preferably 2.0% by mass or less, more preferably 1.7% by mass or less, and particularly preferably 1.5% by mass or less.

[Co-Crosslinking Agent]

Examples of preferable co-crosslinking agents include α,β-unsaturated carboxylic acids and metal salts thereof. These co-crosslinking agents can crosslink rubber molecules by graft polymerization. An α,β-unsaturated carboxylic acid and an α,β-unsaturated carboxylic acid metal salt may be used in combination. The number of carbon atoms in each of α,β-unsaturated carboxylic acids and metal salts thereof is preferably 2 or more and 8 or less. Examples of preferable α,β-unsaturated carboxylic acids include acrylic acid, methacrylic acid, fumaric acid, maleic acid, and crotonic acid.

Examples of metal ions for α,β-unsaturated carboxylic acid metal salts include: monovalent metal ions such as those of sodium, potassium, and lithium; divalent metal ions such as those of magnesium, calcium, zinc, barium, and cadmium; trivalent metal ions such as that of aluminum; tin ion; and zirconium ion. Two or more types of metal ions may be used in combination. From the viewpoint of easily crosslinking rubber molecules, divalent metal ions are preferable. Specific examples of preferable co-crosslinking agents include zinc acrylate, magnesium acrylate, zinc methacrylate, and magnesium methacrylate. Zinc acrylate is particularly preferable. Two or more co-crosslinking agents may be used in combination.

The amount of the co-crosslinking agent per 100 parts by mass of the base rubber is preferably 10 parts by mass or more and 40 parts by mass or less. With the core 4 in which the amount of the co-crosslinking agent is in this range, an appropriate surface hardness and amount of compressive deformation (described in detail later) can be achieved. From this viewpoint, this amount is more preferably 15 parts by mass or more and particularly preferably 20 parts by mass or more. From the same viewpoint, this amount is more preferably 35 parts by mass or less and particularly preferably 30 parts by mass or less.

[Crosslinking Initiator]

A preferable crosslinking initiator is an organic peroxide. The organic peroxide contributes to the durability and the resilience performance of the golf ball 2. Examples of suitable organic peroxides include dicumyl peroxide, 1,1-di(t-butylperoxy)cyclohexane, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(t-butylperoxy) hexane, and di-t-butyl peroxide. An organic peroxide with particularly high versatility is dicumyl peroxide. Two or more crosslinking initiators may be used in combination.

The amount of the crosslinking initiator per 100 parts by mass of the base rubber is preferably 0.2 parts by mass or more and 5.0 parts by mass or less. With the core 4 in which the amount of the crosslinking initiator is in this range, an appropriate surface hardness and amount of compressive deformation (described in detail later) can be achieved. From this viewpoint, this amount is more preferably 0.4 parts by mass or more and particularly preferably 0.7 parts by mass or more. From the same viewpoint, this amount is more preferably 3.0 parts by mass or less and particularly preferably 2.0 parts by mass or less.

[Organic Sulfur Compound]

The organic sulfur compound contributes to the resilience performance of the golf ball 2. Examples of the organic sulfur compound include thiols, polysulfides, thiurams, thiocarboxylic acids, dithiocarboxylic acids, sulfenamides, dithiocarbamates, and thiazoles. Thiols include thiophenols and thionaphthols.

Preferable organic sulfur compounds are thiophenols, metal salts of thiophenols, thionaphthols, metal salts of thionaphthols, diphenyldisulfides, and thiuram disulfides. Specific examples of preferable organic sulfur compounds include 2,4-dichlorothiophenol, 2,6-difluorothiophenol, 2,6-dichlorothiophenol, 2,6-dibromothiophenol, 2,6-diiodothiophenol, 2,4,5-trichlorothiophenol, pentachlorothiophenol, 1-thionaphthol, 2-thionaphthol, diphenyldisulfide, bis(2,6-difluorophenyl)disulfide, bis(2,6-dichlorophenyl)disulfide, bis(2,6-dibromophenyl)disulfide, bis(2,6-diiodophenyl)disulfide, bis(pentabromophenyl)disulfide, and zinc salts thereof.

Two or more organic sulfur compounds may be used in combination in the rubber composition.

The amount of the organic sulfur compound per 100 parts by mass of the base rubber is preferably 0.1 parts by mass or more and 5.0 parts by mass or less. A rubber composition in which the amount of the organic sulfur compound is in this range has excellent processability. A uniform core 4 can be obtained from this rubber composition. From this viewpoint, this amount is more preferably 0.2 parts by mass or more and particularly preferably 0.3 parts by mass or more. From the same viewpoint, this amount is more preferably 3.0 parts by mass or less and particularly preferably 2.0 parts by mass or less. The golf ball 2 may include a core 4 that contains no organic sulfur compound.

[Carboxylic Acid]

The rubber composition of the core 4 may contain a carboxylic acid or a carboxylate. The carboxylic acid and the carboxylate can contribute to making the hardness distribution of the core 4 appropriate. An example of preferable carboxylic acids is benzoic acid. Examples of preferable carboxylates include zinc octoate and zinc stearate. A particularly preferable compound is benzoic acid.

The total amount of the carboxylic acid and the carboxylate per 100 parts by mass of the base rubber is preferably 1.0 part by mass or more and 7.0 parts by mass or less. The hardness distribution of the core 4 in which this total amount is in this range is appropriate. From this viewpoint, this amount is more preferably 1.5 parts by mass or more and particularly preferably 2.0 parts by mass or more. From the same viewpoint, this amount is more preferably 5.0 parts by mass or less and particularly preferably 4.0 parts by mass or less.

[Additives]

The rubber composition of the core 4 may contain a filler for the purpose of specific gravity adjustment and the like. Examples of suitable fillers include zinc oxide, barium sulfate, calcium carbonate, and magnesium carbonate. The amount of the filler is determined as appropriate so that the intended specific gravity of the core 4 is achieved.

The rubber composition of the core 4 may contain additives, such as a radical scavenger, sulfur, an anti-aging agent, a coloring agent, a plasticizer, and a dispersant, in an adequate amount. The rubber composition may contain crosslinked rubber powder or synthetic resin powder.

[Diameter of Core]

The core 4 preferably has a diameter Cd of 35.0 mm or more and 42.0 mm or less. The golf ball 2 that includes the core 4 having a diameter Cd of 35.0 mm or more has excellent resilience performance. From this viewpoint, the diameter Cd is more preferably 36.0 mm or more and particularly preferably 36.5 mm or more. The golf ball 2 that includes the core 4 having a diameter Cd of 42.0 mm or less has excellent durability. From this viewpoint, the diameter Cd is more preferably 41.5 mm or less and particularly preferably 41.0 mm or less.

[Surface Hardness of Core]

A hardness Cs at the surface of the core 4 is preferably 74 or more and 92 or less. The golf ball 2 that includes the core 4 having a hardness Cs of 74 or more contributes to the response upon putting. The golf ball 2 that includes this core 4 has excellent stability in the rolling distance of the golf ball 2 upon putting. From this viewpoint, the hardness Cs is more preferably 76 or more and particularly preferably 78 or more. The golf ball 2 that includes the core 4 having a hardness Cs of 92 or less contributes to soft feel at impact upon putting. From this viewpoint, the hardness Cs is more preferably 90 or less and particularly preferably 88 or less.

The hardness Cs 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.

[Amount of Compressive Deformation of Core]

The core 4 preferably has an amount of compressive deformation Cc of 3.60 mm or more and 6.00 mm or less. The golf ball 2 that includes the core 4 having an amount of compressive deformation Cc of 3.60 mm or more contributes to soft feel at impact upon putting. This core 4 suppresses spin upon a shot with a fairway wood. The golf ball 2 that includes this core 4 has excellent flight performance upon a shot with a fairway wood. From these viewpoints, the amount of compressive deformation Cc is more preferably 3.80 mm or more and particularly preferably 4.00 mm or more. The core 4 having an amount of compressive deformation Cc of 6.00 mm or less contributes to the response upon putting. The golf ball 2 that includes this core 4 has excellent distance stability upon putting. From this viewpoint, the amount of compressive deformation Cc is more preferably 5.50 mm or less and particularly preferably 5.00 mm or less.

The amount of compressive deformation Cc is measured with a YAMADA type compression tester “SCH”. In the tester, a sphere (the core 4, the golf ball 2, etc.) is placed on a rigid plate made of metal. Next, a cylinder made of metal gradually descends toward the sphere. The sphere squeezed between the bottom face of the cylinder and the hard plate becomes deformed. A movement distance of the cylinder, starting from the state in which an initial load of 98 N is applied to the sphere 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.

[Value V1]

A value V1 calculated for the core 4 by the following mathematical formula is 9.15 or more and 10.85 or less.

V ⁢ 1 = ( Cc / Cd ) * Cs

• • Cc: amount of compressive deformation of the core 4 measured under conditions where an initial load is 98 N and a final load is 1274 N (mm)
  • Cd: diameter of the core 4 (mm)
  • Cs: hardness (Shore C) at the surface of the core 4

The loft angle of a fairway wood is greater than the loft angle of a driver. Therefore, excessive spin may occur upon a shot with a fairway wood. The core 4 having a value V1 of 9.15 or more and 10.85 or less can suppress spin upon a shot with a fairway wood. The golf ball 2 that includes this core 4 has excellent flight performance upon a shot with a fairway wood. From this viewpoint, the value V1 is more preferably 9.25 or more and particularly preferably 9.30 or more. From the same viewpoint, the value V1 is more preferably 10.70 or less and particularly preferably 10.60 or less.

[Mid Layer]

The mid layer 6 is positioned outside the core 4. In the present embodiment, the mid layer 6 is in contact with the core 4. The mid layer 6 is formed from a resin composition. In the present embodiment, the mid layer 6 is formed from a thermoplastic resin composition.

[Base Resin]

Examples of the base resin of the resin composition of the mid layer 6 include ionomer resins, polyamide resins, thermoplastic polyester elastomers, thermoplastic polyurethane elastomers, thermoplastic polyolefin elastomers, and thermoplastic polystyrene elastomers. Ionomer resins are particularly preferable. Ionomer resins are highly elastic. The golf ball 2 that includes the mid layer 6 containing an ionomer resin has excellent resilience performance. In the case where an ionomer resin and another resin are used in combination, the principal component of the base resin is the ionomer resin. The ratio of the amount of the ionomer resin to the total amount of the base resin is preferably 60% by mass or more, more preferably 70% by mass or more, and particularly preferably 80% by mass or more. This ratio may be 100% by mass.

Examples of preferable ionomer resins include a binary ionomer resin and a ternary ionomer resin. The binary ionomer resin is a binary copolymer that is formed with an α-olefin and an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms. At least some of the carboxyl groups of this binary copolymer are neutralized with metal ions. A preferable binary ionomer resin contains 80% by mass or more and 90% by mass or less of an α-olefin, and 10% by mass or more and 20% by mass or less of an α,β-unsaturated carboxylic acid. This binary ionomer resin has excellent resilience performance. The ternary ionomer resin is a ternary copolymer that is formed with an α-olefin, an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms, and an α,β-unsaturated carboxylic acid ester having 2 to 22 carbon atoms. At least some of the carboxyl groups of this ternary copolymer are neutralized with metal ions. A preferable ternary ionomer resin contains 70% by mass or more and 85% by mass or less of an α-olefin, 5% by mass or more and 30% by mass or less of an α,β-unsaturated carboxylic acid, and 1% by mass or more and 25% by mass or less of an α,β-unsaturated carboxylic acid ester. This ternary ionomer resin has excellent resilience performance. For the binary ionomer resin and the ternary ionomer resin, preferable α-olefins are ethylene and propylene, while preferable α,β-unsaturated carboxylic acids are acrylic acid and methacrylic acid. Preferable copolymers are a binary copolymer formed with ethylene and acrylic acid and a binary copolymer formed with ethylene and methacrylic acid.

Examples of metal ions for use in neutralization of the carboxyl groups in the ionomer resin include sodium ions, potassium ions, lithium ions, zinc ions, calcium ions, magnesium ions, aluminum ions, and neodymium ions. The neutralization may be carried out with two or more types of metal ions. Particularly suitable metal ions from the viewpoint of resilience performance and durability of the golf ball 2 are sodium ions, zinc ions, lithium ions, and magnesium ions.

Specific examples of ionomer resins include trade names “HIMILAN 1555”, “HIMILAN 1557”, “HIMILAN 1605”, “HIMILAN 1702”, “HIMILAN 1706”, “HIMILAN 1707”, “HIMILAN 1855”, “HIMILAN 1856”, “HIMILAN 8150”, “HIMILAN AM7311”, “HIMILAN AM7315”, “HIMILAN AM7317”, “HIMILAN AM7327”, “HIMILAN AM7329”, and “HIMILAN AM7337”, manufactured by DOW-MITSUI POLYCHEMICALS CO., LTD.; trade names “SURLYN 6120”, “SURLYN 6910”, “SURLYN 7930”, “SURLYN 7940”, “SURLYN 8140”, “SURLYN 8150”, “SURLYN 8940”, “SURLYN 8945”, “SURLYN 9120”, “SURLYN 9150”, “SURLYN 9320”, “SURLYN 9910”, “SURLYN 9945”, “SURLYN AD8546”, “HPF1000”, and “HPF2000”, manufactured by E.I. du Pont de Nemours and Company; and trade names “IOTEK 7010”, “IOTEK 7030”, “IOTEK 7510”, “IOTEK 7520”, “IOTEK 8000”, and “IOTEK 8030”, manufactured by ExxonMobil Chemical Company. Two or more ionomer resins may be used in combination.

Examples of a preferable resin that can be used in combination with an ionomer resin include

• • (1) an unneutralized resin that is a binary copolymer of an olefin and an α,β-unsaturated carboxylic acid, and
  • (2) an unneutralized resin that is a ternary copolymer of an olefin, an α,β-unsaturated carboxylic acid, and an α,β-unsaturated carboxylic acid ester.

The binary copolymer (1) and the ternary copolymer (2) contribute to the fluidity of the melted resin composition. The mid layer 6 containing the binary copolymer (1) or the ternary copolymer (2) has excellent moldability.

The ratio of the total amount of the unneutralized resin (1) that is a binary copolymer and the unneutralized resin (2) that is a ternary copolymer to the total amount of the base resin is preferably 40% by mass or less. The mid layer 6 in which this ratio is 40% by mass or less has excellent resilience performance. From this viewpoint, this ratio is more preferably 30% by mass or less and particularly preferably 20% by mass or less. This ratio may be 0% by mass.

Specific examples of the unneutralized binary copolymer (1) include: trade names “NUCREL N1050H”, “NUCREL N2050H”, “NUCREL N1110H”, and “NUCREL N0200H” manufactured by DOW-MITSUI POLYCHEMICALS CO., LTD.; and trade name “PRIMACOR 5980I” manufactured by the Dow Chemical Company. Specific examples of the unneutralized ternary copolymer (2) include: trade names “NUCREL AN4318” and “NUCREL AN4319” manufactured by DOW-MITSUI POLYCHEMICALS CO., LTD.; and trade names “PRIMACOR AT310” and “PRIMACOR AT320” manufactured by the Dow Chemical Company.

[Additives]

The resin composition of the mid layer 6 may contain a coloring agent, a filler, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent material, a fluorescent brightener, etc., in an adequate amount. A typical filler is barium sulfate. In the case where the hue of the golf ball 2 is white, a typical coloring agent is titanium dioxide.

[Thickness]

The mid layer 6 preferably has a thickness Mt of 0.4 mm or more and 2.2 mm or less. The mid layer 6 having a thickness Mt of 0.4 mm or more can contribute to the response upon putting. The golf ball 2 that includes this mid layer 6 has excellent distance stability upon putting. From this viewpoint, the thickness Mt is more preferably 0.5 mm or more and particularly preferably 0.6 mm or more. The mid layer 6 having a thickness Mt of 2.2 mm or less can contribute to soft feel at impact upon putting. From this viewpoint, the thickness Mt is more preferably 2.1 mm or less and particularly preferably 2.0 mm or less. The thickness Mt is measured at a position immediately below the land 12.

[Melt Flow Rate]

The resin composition of the mid layer 6 preferably has a melt flow rate Mm of 2.0 g/10 min or more. The mid layer 6 having an appropriate thickness Mt can be easily molded from this resin composition. From this viewpoint, the melt flow rate Mm is more preferably 2.5 g/10 min or more and particularly preferably 3.0 g/10 min or more. The melt flow rate Mm is preferably 10.0 g/10 min or less, more preferably 9.0 g/10 min or less, and particularly preferably 8.0 g/10 min or less.

The melt flow rate Mm is measured according to the standards of “JIS K 7210-1: 2014”. The measurement conditions are as follows.

• • Reference: mass (method A)
  • Temperature: 190° C.
  • Load: 2.16 Kg
  • Die: standard
    “Flowtester CFT-100C” manufactured by SHIMADZU CORPORATION is exemplified as a device suitable for the measurement.

[Hardness]

A hardness Ms at the surface of a sphere 14 consisting of the core 4 and the mid layer 6 is preferably 85 or more. In the golf ball 2 in which the hardness Ms is 85 or more, the mid layer 6 can contribute to distance stability upon putting. From this viewpoint, the hardness Ms is more preferably 87 or more and particularly preferably 89 or more. The hardness Ms may be 100.

The hardness Ms at the surface of the sphere 14 consisting of the core 4 and the mid layer 6 is measured with a Shore C type hardness scale mounted to the above-described trade name “Digi Test II”. The hardness scale is pressed against the surface of the sphere 14 (the surface of the mid layer 6). The measurement is conducted in an environment of 23° C.

[Amount of Compressive Deformation]

The sphere 14 consisting of the core 4 and the mid layer 6 preferably has an amount of compressive deformation Mc of 3.00 mm or more and 5.00 mm or less. The sphere 14 having an amount of compressive deformation Mc of 3.00 mm or more contributes to soft feel at impact upon putting. Furthermore, the sphere 14 suppresses spin upon a shot with a fairway wood. The golf ball 2 that includes this sphere 14 has excellent flight performance upon a shot with a fairway wood. From these viewpoints, the amount of compressive deformation Mc is more preferably 3.15 mm or more and particularly preferably 3.30 mm or more. The sphere 14 having an amount of compressive deformation Mc of 5.00 mm or less contributes to the response upon putting. The golf ball 2 that includes this sphere 14 has excellent distance stability upon putting. From this viewpoint, the amount of compressive deformation Mc is more preferably 4.70 mm or less and particularly preferably 4.40 mm or less. The amount of compressive deformation Mc is measured by the same method as for the amount of compressive deformation Cc of the core 4.

[Cover]

The cover 8 is positioned outside the mid layer 6. In the present embodiment, the cover 8 is in contact with the mid layer 6. The golf ball 2 may have an adhesive layer between the mid layer 6 and the cover 8. The cover 8 can be firmly joined to the mid layer 6 via this adhesive layer. The cover 8 is formed from a resin composition. In the present embodiment, the cover 8 is formed from a thermoplastic resin composition.

[Base Resin]

Examples of the base resin of the resin composition of the cover 8 include ionomer resins, thermoplastic polystyrene elastomers, thermoplastic polyester elastomers, thermoplastic polyamide elastomers, thermoplastic polyurethane elastomers, and thermoplastic polyolefin elastomers. Ionomer resins are particularly preferable. Ionomer resins are highly elastic. The golf ball 2 that includes the cover 8 containing an ionomer resin has excellent resilience performance. The golf ball 2 has excellent flight performance upon a shot with a driver. The ionomer resins described above for the mid layer 6 can also be applied to the cover 8.

An ionomer resin and another resin may be used in combination. In this case, from the viewpoint of resilience performance, the ionomer resin is contained as the principal component of the base resin. The ratio of the amount of the ionomer resin to the total amount of the base resin is preferably 60% by mass or more, more preferably 70% by mass or more, and particularly preferably 75% by mass or more. This ratio may be 100% by mass.

Examples of a preferable resin that can be used in combination with an ionomer resin include

• • (1) an unneutralized resin that is a binary copolymer of an olefin and an α,β-unsaturated carboxylic acid, and
  • (2) an unneutralized resin that is a ternary copolymer of an olefin, an α,β-unsaturated carboxylic acid, and an α,β-unsaturated carboxylic acid ester, both resins being as described above for the mid layer 6.

The binary copolymer (1) and the ternary copolymer (2) contribute to the fluidity of the melted resin composition. The cover 8 containing the binary copolymer (1) or the ternary copolymer (2) has excellent moldability.

The principal component of the base resin of the resin composition of the cover 8 may be a polyurethane. The resin composition of the cover 8 may include a thermoplastic polyurethane or may include a thermosetting polyurethane. From the viewpoint of productivity of the golf ball 2, the thermoplastic polyurethane is preferable. The thermoplastic polyurethane includes a polyurethane component as a hard segment, and a polyester component or a polyether component as a soft segment. The thermoplastic polyurethane is flexible. The cover 8 in which the polyurethane is used has excellent scuff resistance. The thermoplastic polyurethane has a urethane bond within the molecule. The urethane bond can be formed by reacting a polyol with a polyisocyanate.

The polyol, as a material for the urethane bond, has a plurality of hydroxyl groups. Low-molecular-weight polyols and high-molecular-weight polyols can be used. Examples of low-molecular-weight polyols include diols, triols, tetraols, and hexaols. Examples of high-molecular-weight polyols include polyether polyols, condensed polyester polyols, lactone polyester polyols, polycarbonate polyols, and acrylic polyols. Two or more polyols may be used in combination.

Examples of polyisocyanates, as a material for the urethane bond, include aromatic diisocyanates, alicyclic diisocyanates, and aliphatic diisocyanates. Two or more diisocyanates may be used in combination.

Specific examples of the thermoplastic polyurethane include trade names “Elastollan NY80A”, “Elastollan NY82A”, “Elastollan NY83A”, “Elastollan NY84A”, “Elastollan NY85A”, “Elastollan NY88A”, “Elastollan NY90A”, “Elastollan NY95A”, “Elastollan NY97A”, “Elastollan NY585”, and “Elastollan KP016N”, manufactured by BASF Japan Ltd.; and trade names “RESAMINE P4585LS” and “RESAMINE PS62490”, manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.

[Additives]

The resin composition of the cover 8 may contain a coloring agent, a filler, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent material, a fluorescent brightener, etc., in an adequate amount. A typical filler is barium sulfate. In the case where the hue of the golf ball 2 is white, a typical coloring agent is titanium dioxide.

[Thickness]

The cover 8 preferably has a thickness of 0.50 mm or more and 2.00 mm or less. The golf ball 2 in which this thickness is 0.50 mm or more has excellent moldability. From this viewpoint, this thickness is more preferably 0.70 mm or more and particularly preferably 0.80 mm or more. The golf ball 2 in which this thickness is 2.00 mm or less has excellent resilience performance. From this viewpoint, this thickness is more preferably 1.50 mm or less and particularly preferably 1.20 mm or less. This thickness is measured at a position immediately below the land 12.

[Golf Ball]

[Hardness]

A hardness Bs at the surface of the golf ball 2 is preferably 60 or more and 90 or less. The golf ball 2 having a hardness Bs of 60 or more has excellent distance stability upon putting. From this viewpoint, the hardness Bs is more preferably 65 or more and particularly preferably 68 or more. The golf ball 2 having a hardness Bs of 90 or less has excellent soft feel at impact upon putting. From this viewpoint, the hardness Bs is more preferably 87 or less and particularly preferably 85 or less.

The hardness Bs at the surface of the golf ball 2 is measured with a Shore C type hardness scale mounted to the above-described trade name “Digi Test II”. The hardness scale is pressed against the surface of the golf ball 2. The measurement is conducted in an environment of 23° C.

[Amount of Compressive Deformation]

The golf ball 2 preferably has an amount of compressive deformation Bc of 3.00 mm or more and 4.30 mm or less. The golf ball 2 having an amount of compressive deformation Bc of 3.00 mm or more has excellent soft feel at impact upon putting. From this viewpoint, the amount of compressive deformation Bc is more preferably 3.20 mm or more and particularly preferably 3.30 mm or more. The golf ball 2 having an amount of compressive deformation Bc of 4.30 mm or less has excellent distance stability upon putting. From this viewpoint, the amount of compressive deformation Bc is more preferably 4.00 mm or less and particularly preferably 3.80 mm or less. The amount of compressive deformation Bc is measured by the same method as for the amount of compressive deformation Cc of the core 4.

[Diameter]

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.

[Mass]

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.

[Characteristics of Golf Ball]

The golf ball 2 satisfies the following mathematical formula.

Ms ≥ Cs ≥ Bs

In the golf ball 2, the Shore C hardness Ms at the surface of the sphere 14 consisting of the core 4 and the mid layer 6 is equal to or greater than the Shore C hardness Cs at the surface of the core 4. In the golf ball 2, the hardness Cs is equal to or greater than the Shore C hardness Bs at the surface of the golf ball 2. In the golf ball 2, the core 4 suppresses spin upon a shot with a fairway wood, the mid layer 6 contributes to distance stability upon putting, and the cover 8 contributes to soft feel at impact upon putting.

From the viewpoint of spin suppression, distance stability, and feel at impact, the difference (Ms−Cs) is preferably 4 or more, more preferably 7 or more, and particularly preferably 9 or more. From the viewpoint of the moldability of the mid layer 6, the difference (Ms−Cs) is preferably 20 or less, more preferably 18 or less, and particularly preferably 16 or less.

From the viewpoint of spin suppression, distance stability, and feel at impact, the difference (Cs−Bs) is preferably 1 or more, more preferably 2 or more, and particularly preferably 3 or more. From the viewpoint of feel at impact, the difference (Cs−Bs) is preferably 15 or less, more preferably 14 or less, and particularly preferably 13 or less.

A value V2 calculated by the following mathematical formula is preferably 253 or more and 355 or less.

V ⁢ 2 = Cs + ( Ms * Mt ) + Bs

• • Cs: hardness (Shore C) at the surface of the core 4
  • Ms: hardness (Shore C) at the surface of the sphere 14 consisting of the core 4 and the mid layer 6
  • Mt: thickness of the mid layer 6 (mm)
  • Bs: hardness (Shore C) at the surface of the golf ball 2
    The golf ball 2 for which the value V2 is in the above range has excellent flight performance upon a shot with a fairway wood and excellent distance stability and feel at impact upon putting. From these viewpoints, the value V2 is more preferably 254 or more and particularly preferably 255 or more. From the same viewpoint, the value V2 is more preferably 325 or less and particularly preferably 315 or less.

A value V3 calculated by the following mathematical formula is preferably 0.60 or more and 1.40 or less.

V ⁢ 3 = Cc / ( Mm * Mt )

• • Cc: amount of compressive deformation of the core 4 (mm)
  • Mm: melt flow rate of the mid layer 6 (g/10 min)
  • Mt: thickness of the mid layer 6 (mm)
    The golf ball 2 for which the value V3 is in the above range has excellent flight performance upon a shot with a fairway wood and excellent moldability of the mid layer 6. From these viewpoints, the value V3 is more preferably 0.75 or more and particularly preferably 0.85 or more. From the same viewpoints, the value V3 is more preferably 1.35 or less and particularly preferably 1.20 or less.

EXAMPLES

Example 1

A rubber composition C was obtained by kneading 100 parts by mass of a high-cis polybutadiene (trade name “BR-730”, manufactured by JSR Corporation), an appropriate amount of zinc acrylate (trade name “ZN-DA90S”, manufactured by NISSHOKU TECHNO FINE CHEMICAL CO., LTD.), 10 parts by mass of zinc oxide (product of INDO LYSAGHT), an appropriate amount of barium sulfate (product number “BD” of SAKAI CHEMICAL INDUSTRY CO., LTD.), 0.9 parts by mass of dicumyl peroxide (trade name “PERCUMYL D”, manufactured by NOF CORPORATION), 0.9 parts by mass of a pentachlorothiophenol zinc salt (product number “PCTP-Zn”, manufactured by FUJIFILM Wako Pure Chemical Corporation), and 3.5 parts by mass of benzoic acid (product of Tokyo Chemical Industry Co., Ltd.). This rubber composition C was placed into a mold including upper and lower mold halves each having a hemispherical cavity, and heated to obtain a core with a diameter of 38.7 mm. The crosslinking temperature was 160° C. The crosslinking time was 20 minutes.

A resin composition M1 was obtained by kneading 45.0 parts by mass of an ionomer resin (aforementioned “HIMILAN AM7329”), 45.0 parts by mass of another ionomer resin (aforementioned “HIMILAN 1605”), 10 parts by mass of a copolymer (aforementioned “NUCREL N1050H”), 6 parts by mass of barium sulfate, 4 parts by mass of titanium dioxide, and 0.2 parts by mass of an ultraviolet absorber (trade name “JF-90”, manufactured by Johoku Chemical Co., Ltd.) with a twin-screw kneading extruder. The core was placed into a mold including upper and lower mold halves each having a hemispherical cavity. The melted resin composition M1 was injected so as to cover the core in an injection molding machine to form a mid layer. The thickness of the mid layer was 1.00 mm.

A resin composition C1 was obtained by kneading 35 parts by mass of an ionomer resin (aforementioned “HIMILAN 1855”), 40 parts by mass of another ionomer resin (aforementioned “HIMILAN AM7327”), 25 parts by mass of a copolymer (aforementioned “NUCREL N1050H”), 4 parts by mass of titanium dioxide, and 0.2 parts by mass of an ultraviolet absorber (aforementioned “JF-90”) with a twin-screw kneading extruder. The sphere consisting of the core and the mid layer was placed into a mold including upper and lower mold halves each having a hemispherical cavity. The melted resin composition C1 was injected so as to cover the sphere in an injection molding machine to form a cover. The thickness of the cover was 1.00 mm.

A clear paint including a two-component curing type polyurethane as a base material was applied to this cover to obtain a golf ball of Example 1 having a diameter of about 42.7 mm and a mass of about 45.5 g.

Examples 2 to 15 and Comparative Examples 1 to 3

Golf balls of Examples 2 to 15 and Comparative Examples 1 to 3 were obtained in the same manner as Example 1, except that the specifications of the core, the mid layer, and the cover were set as shown in Tables 4 to 7 below. The composition of the core is shown in Table 1 below. The composition of the mid layer is shown in Table 2 below. The composition of the cover is shown in Table 3 below.

TABLE 1
Composition of core [parts by mass]

	A	B	C	D	E

BR-730	100	100	100	100	100
Zinc oxide	5	10	10	10	10
Zinc acrylate	22	24	28.5	33.5	26
Barium sulfate	Appropriate	Appropriate	Appropriate	Appropriate	Appropriate
	amount	amount	amount	amount	amount
Dicumyl peroxide	0.7	0.9	0.9	0.9	0.9
Pentachlorothiophenol	0.3	0.6	0.9	0.9	0.9
zinc salt
Benzoic acid	—	2.5	3.5	3.5	3.5

TABLE 2
Composition of mid layer [parts by mass]

	M1	M2	M3	M4

	HIMILAN	45.0	—	—	—
	AM7329
	HIMILAN 1605	45.0	38.0	36.0	34.0
	HIMILAN 1706	—	28.5	27.0	25.5
	HIMILAN 1707	—	28.5	27.0	25.5
	NUCREL N1050H	10	5	10	15
	Barium sulfate	6	6	6	6
	Titanium dioxide	4	4	4	4
	JF-90	0.2	0.2	0.2	0.2
	Mm [g/10 min]	4.3	3.2	4.5	5.8

TABLE 3
Composition of cover [parts by mass]

	C1	C2	C3

	HIMILAN 1855	35	—	—
	HIMILAN AM7327	40	80	—
	HIMILAN 1557	—	5	—
	NUCREL N1050H	25	15	—
	Elastollan NY88A	—	—	50
	Elastollan NY90A	—	—	50
	Titanium dioxide	4	4	4
	JF-90	0.2	0.2	0.2

[Flight Performance]

A fairway wood (W #3, trade name “XXIO 13”, manufactured by Sumitomo Rubber Industries, Ltd., shaft hardness: R) was attached to a swing machine manufactured by Golf Laboratories, Inc. A golf ball was hit with this driver under a condition of a head speed of 35 m/see, and the distance from the launch point to the stop point was measured. During the test, the weather was almost windless. The average value of flight distances obtained by 12 measurements was calculated. Furthermore, the average value was rated based on the following criteria.

• • A: 185.0 yards or more
  • B: 183.5 yards or more but less than 185.0 yards
  • C: 182.0 yards or more but less than 183.5 yards
  • D: 180.5 yards or more but less than 182.0 yards
  • E: less than 180.5 yards
    These results are shown in Tables 4 to 7 below.

[Feel at Impact]

Twenty golf players putted golf balls and were asked about feel at impact (response, stability in rolling distance). The golf balls were rated according to the following criteria based on the number of golf players who answered “the feel at impact was good”.

• • A: 16 or more
  • B: 10 or more but 15 or less
  • C: 3 or more but 9 or less
  • D: 2 or less
    The results are shown in Tables 4 to 7 below.

[Moldability]

Each golf ball was divided into two hemispheres. The uniformity of the thickness of the mid layer on the cut surface of the hemisphere was rated.

• • A: excellent
  • B: good
  • C: poor
  • D: extremely poor
    The results are shown in Tables 4 to 7 below.

[Overall Evaluation]

Combined performance of the golf balls was rated according to the following criteria.

• • A: Flight distance evaluation, evaluation of feel at impact, and moldability evaluation are “A”.
  • B: Flight distance evaluation is not “C”, “D”, or “E”, evaluation of feel at impact and moldability evaluation are neither “C” nor “D”, and flight distance evaluation, evaluation of feel at impact, or moldability evaluation is “B”.
  • C: Flight distance evaluation is neither “D” nor “E”, evaluation of feel at impact and moldability evaluation are not “D”, and flight distance evaluation, evaluation of feel at impact, or moldability evaluation is “C”.
  • D: Flight distance evaluation is not “E”, and flight distance evaluation, evaluation of feel at impact, or moldability evaluation is “D”.
  • E: Flight distance evaluation is “E”.
    The results are shown in Tables 4 to 7 below.

TABLE 4
Evaluation results

	Comparative	Comparative
	Example	Example	Example	Example	Example
	1	2	2	3	1

Core Composition	A	B	B	B	C
Diameter Cd [mm]	38.7	38.7	38.7	38.7	38.7
Amount of compressive deformation Cc	4.40	4.40	4.40	4.40	4.70
[mm]
Surface hardness Cs [Shore C]	78	82	82	82	85
Mid layer Composition	M1	M1	M1	M1	M1
Thickness Mt [mm]	1.0	1.0	1.0	1.0	1.0
Surface hardness Ms [Shore C]	98	98	98	98	98
Melt flow rate Mm [g/10 min]	4.3	4.3	4.3	4.3	4.3
Amount of compressive deformation Mc	3.75	3.65	3.65	3.65	3.90
[mm]
Cover Composition	C2	C1	C2	C3	C1
Thickness [mm]	1.0	1.0	1.0	1.0	1.0
Ball surface hardness Bs [Shore C]	79	84	79	72	84
Amount of compressive deformation Bc of	3.50	3.30	3.40	3.50	3.55
ball [mm]
Ms − Cs	20	16	16	16	13
Cs − Bs	−1	−2	3	10	1
Cc/Cd*Cs	8.87	9.32	9.32	9.32	10.32
Cs + Ms*Mt + Bs	255	264	259	252	267
Cc/(Mm*Mt)	1.02	1.02	1.02	1.02	1.09
Flight distance	E	E	C	D	A
Feel at impact	C	A	B	C	A
Moldability	A	A	A	A	A
Overall evaluation	E	E	C	D	A

TABLE 5
Evaluation results

					Comparative
	Example	Example	Example	Example	Example
	4	5	6	7	3

Core Composition	C	C	C	C	C
Diameter Cd [mm]	38.7	38.7	38.7	37.7	36.7
Amount of compressive deformation Cc	4.70	4.70	4.70	4.70	4.70
[mm]
Surface hardness Cs [Shore C]	85	85	85	85	85
Mid layer Composition	M1	M1	M2	M2	M2
Thickness Mt [mm]	1.0	1.0	1.0	1.5	2.0
Surface hardness Ms [Shore C]	98	98	94	95	96
Melt flow rate Mm [g/10 min]	4.3	4.3	4.5	4.5	4.5
Amount of compressive deformation Mc	3.90	3.90	3.95	3.75	3.65
[mm]
Cover Composition	C2	C3	C2	C2	C2
Thickness [mm]	1.0	1.0	1.0	1.0	1.0
Ball surface hardness Bs [Shore C]	79	72	79	79	79
Amount of compressive deformation Bc of	3.65	3.75	3.70	3.50	3.40
ball [mm]
Ms − Cs	13	13	9	10	11
Cs − Bs	6	13	6	6	6
Cc/Cd*Cs	10.32	10.32	10.32	10.60	10.89
Cs + Ms*Mt + Bs	262	255	258	307	356
Cc/(Mm*Mt)	1.09	1.09	1.04	0.70	0.52
Flight distance	A	C	A	B	E
Feel at impact	B	C	C	B	D
Moldability	A	A	A	C	D
Overall evaluation	B	C	C	C	E

TABLE 6
Evaluation results

	Example	Example	Example	Example
	8	9	10	11

Core Composition	C	C	C	C
Diameter Cd [mm]	38.7	37.7	38.7	37.7
Amount of compressive deformation Cc	4.70	4.70	4.70	4.70
[mm]
Surface hardness Cs [Shore C]	85	85	85	85
Mid layer Composition	M3	M3	M4	M4
Thickness Mt [mm]	1.0	1.5	1.0	1.5
Surface hardness Ms [Shore C]	94	95	94	95
Melt flow rate Mm [g/10 min]	5.8	5.8	3.2	3.2
Amount of compressive deformation Mc	3.95	3.75	3.95	3.75
[mm]
Cover Composition	C2	C2	C2	C2
Thickness [mm]	1.0	1.0	1.0	1.0
Ball surface hardness Bs [Shore C]	79	79	79	79
Amount of compressive deformation Bc of	3.70	3.50	3.70	3.50
ball [mm]
Ms − Cs	9	10	9	10
Cs − Bs	6	6	6	6
Cc/Cd*Cs	10.32	10.60	10.32	10.60
Cs + Ms*Mt + Bs	258	307	258	307
Cc/(Mm*Mt)	0.81	0.54	1.47	0.98
Flight distance	A	B	A	B
Feel at impact	C	B	C	B
Moldability	B	D	D	A
Overall evaluation	C	D	D	B

TABLE 7
Evaluation results

	Example	Example	Example	Example
	12	13	14	15

Core Composition	D	E	D	E
Diameter Cd [mm]	39.0	37.0	39.0	37.0
Amount of compressive deformation Cc	4.10	5.00	4.10	5.00
[mm]
Surface hardness Cs [Shore C]	88	79	88	79
Mid layer Composition	M1	M4	M1	M1
Thickness Mt [mm]	0.85	1.85	1.00	1.00
Surface hardness Ms [Shore C]	97	96	98	98
Melt flow rate Mm [g/10 min]	4.3	3.2	4.3	4.3
Amount of compressive deformation Mc	3.35	4.15	3.30	4.35
[mm]
Cover Composition	C1	C2	C1	C2
Thickness [mm]	1.0	1.0	0.85	1.85
Ball surface hardness Bs [Shore C]	84	79	85	77
Amount of compressive deformation Bc of	3.00	3.90	2.95	4.10
ball [mm]
Ms − Cs	9	17	10	19
Cs − Bs	4	0	3	2
Cc/Cd*Cs	9.25	10.68	9.25	10.68
Cs + Ms*Mt + Bs	254	336	271	254
Cc/(Mm*Mt)	1.12	0.84	0.95	1.16
Flight distance	C	C	B	D
Feel at impact	C	B	B	C
Moldability	A	B	A	A
Overall evaluation	C	C	B	D

As shown in Tables 4 to 7, the golf ball of each Example has excellent various performances. From the evaluation results, advantages of the present disclosure are clear.

[Disclosure Items]

Each of the following items is a disclosure of a preferred embodiment.

[Item 1]

A golf ball including a core, a mid layer positioned outside the core, and a cover positioned outside the mid layer, wherein

• • a Shore C hardness Ms at a surface of a sphere consisting of the core and the mid layer is equal to or greater than a Shore C hardness Cs at a surface of the core,
  • the hardness Cs is equal to or greater than a Shore C hardness Bs at a surface of the golf ball, and
  • a value V1 calculated by the following mathematical formula is 9.15 or more and 10.85 or less,

V ⁢ 1 = ( Cc / Cd ) * Cs ,

where Cc represents an amount of compressive deformation (mm) of the core measured under conditions where an initial load is 98 N and a final load is 1274 N, and Cd represents a diameter (mm) of the core.

[Item 2]

The golf ball according to Item 1, wherein a value V2 calculated by the following mathematical formula is 253 or more and 355 or less,

V ⁢ 2 = Cs + ( Ms * Mt ) + Bs

where Mt represents a thickness (mm) of the mid layer.

[Item 3]

The golf ball according to Item 1, wherein a value V3 calculated by the following mathematical formula is 0.60 or more and 1.40 or less,

V ⁢ 3 = Cc / ( Mn * Mt )

where Mm represents a melt flow rate (g/10 min) of the mid layer, and Mt represents a thickness (mm) of the mid layer.

[Item 4]

The golf ball according to any one of Items 1 to 3, wherein a material of the mid layer is a resin composition containing an ionomer resin as a principal component.

[Item 5]

The golf ball according to any one of Items 1 to 3, wherein a material of the cover is a resin composition containing an ionomer resin as a principal component.

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