Golf balls

Abstract

To provide a golf ball excellent both in a carry performance and in a sense of hitting.SOLUTION: A golf ball 2 includes a core 4, an intermediate layer 6, and a cover 8. The golf ball 2 satisfies formula (1) and formula (2). Formula (1): C1>(124.8-Hs) / 11.5 and formula (2): C2-C1≥(-1 / 6*C1+(68-H2) / 20+(5-Hd) / 100)*T2 C1: compressive deformation amount (mm) of the core 4 C2: compressive deformation amount (mm) of a sphere consisting of the core 4 and the intermediate layer 6 Hd: Hs-Ho Ho: center hardness of the core 4 (Shore C) Hs: surface hardness of the core 4 (Shore C) H2: hardness of the intermediate layer 6 (Shore D) T2: thickness (mm) of the intermediate layer 6. The compressive deformation amount C3 of the golf ball 2 is 2.80 mm or more.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a golf ball, more particularly to a golf ball having a core, a mid layer and a cover. [Background technology]

[0002] A typical golf ball has a core, an intermediate layer, and a cover. The core is formed by crosslinking a rubber composition. The core may have two or more layers. The intermediate layer is formed from a resin composition. The cover is formed from another resin composition.

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

[0004] The biggest concern for golf players regarding golf balls is flight performance. Players attach importance to the flight distance on driver shots. Players with average skill also attach importance to the flight distance on shots with middle irons. A golf ball that provides a long flight distance on shots with middle irons can contribute to a good score. To achieve a long flight distance, a suitable flight height is necessary. The flight height depends on the launch angle and the spin rate.

[0005] Another concern for golf players and others regarding golf balls is the feel at impact. Generally, players prefer a soft feel at impact. Players of average skill place a high priority on feel when putting.

[0006] Various improvements have been proposed in the structure and materials of golf balls to improve various performances. One example of such an improvement is disclosed in JP 2018-93998 A. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP2018-93998A Summary of the Invention [Problem to be solved by the invention]

[0008] SUMMARY OF THE PRESENT ART Golf players have increasingly more demanding needs for golf balls. An object of the present invention is to provide a golf ball that is excellent in both flight performance when shot with a middle iron and shot feel when putting. [Means for solving the problem]

[0009] The golf ball according to the present invention has a core, a mid layer located outside the core, and a cover located outside the mid layer. The golf ball satisfies the following formulas (1) and (2). The amount of compressive deformation C3 of the golf ball is 2.80 mm or more. C1 > (124.8 - Hs) / 11.5 (1) C2 - C1 ≥ (-1 / 6 * C1 + (68 - H2) / 20 + (5 - Hd) / 100) * T2 (2) C1: Compressive deformation of the core (mm) C2: Amount of compression deformation of the sphere consisting of the core and the intermediate layer (mm) Hd: Hs-Ho Ho: Center hardness of the core (Shore C) Hs: Surface hardness of the core (Shore C) H2: Hardness of the middle layer (Shore D) T2: Thickness of the middle layer (mm)

[0010] Preferably, the golf ball further satisfies the following formula (3). (C2 - C1) / (C3 - C2) ≧1.60 (3) C3: Amount of compression deformation of the golf ball (mm)

[0011] Preferably, the difference Hd between the surface hardness Hs (Shore C) and the center hardness Ho (Shore C) is 15 or greater and 40 or less. Preferably, the sum (T2+T3) of the thickness T2 (mm) of the intermediate layer and the thickness T3 (mm) of the cover is 1.0 mm or greater and 4.5 mm or less. Preferably, the hardness H2 (Shore D) of the intermediate layer is 45 or greater.

[0012] The cover is made of a resin composition, and the base material of the resin composition is preferably an ionomer resin.

[0013] The material of the intermediate layer may be a resin composition. Preferably, the base material of the resin composition is an ionomer resin.

[0014] Preferably, the difference (H3-H2) between the hardness H3 of the cover and the hardness H2 of the intermediate layer is equal to or less than -11. Effect of the Invention

[0015] When the golf ball according to the present invention is hit with a middle iron, it is launched with a small spin rate. The trajectory height of this golf ball is appropriate. When this golf ball is shot with a middle iron, a long flight distance can be obtained. When this golf ball is hit with a putter, the impact is small. When putting, the golf player can obtain a soft shot feeling. This golf ball is excellent in both flight performance and shot feeling. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a partially cutaway cross-sectional view showing a golf ball according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, the present invention will be described in detail based on preferred embodiments with reference to the drawings as appropriate.

[0018] 1 has a spherical core 4, an intermediate layer 6 located on the outside of the core 4, and a cover 8 located on the outside of the intermediate layer 6. The golf ball 2 has a plurality of dimples 10 on its surface. The portion of the surface of the golf ball 2 other than the dimples 10 is land 12. The golf ball 2 has a paint layer and a mark layer on the outside of the cover 8, but these layers are omitted from the illustration.

[0019] The diameter of the golf ball 2 is preferably 40 mm or greater and 45 mm or less. From the viewpoint of satisfying the standards of the United States Golf Association (USGA), the diameter is particularly preferably 42.67 mm or greater. From the viewpoint of suppressing air resistance, the diameter is more preferably 44 mm or less, and particularly preferably 42.80 mm or less.

[0020] The mass of the golf ball 2 is preferably 40 g or greater and 50 g or less. From the viewpoint of obtaining a large inertia, the mass is more preferably 44 g or greater, and particularly preferably 45.00 g or greater. From the viewpoint of satisfying the USGA standard, the mass is particularly preferably 45.93 g or less.

[0021] The core 4 is formed by crosslinking a rubber composition. Examples of preferred base rubbers include polybutadiene, polyisoprene, styrene-butadiene copolymer, ethylene-propylene-diene copolymer, and natural rubber. From the viewpoint of the resilience performance of the golf ball 2, polybutadiene is preferred. When polybutadiene is used in combination with other rubber, it is preferred that polybutadiene be the main component. Specifically, the ratio of polybutadiene to the total base rubber is preferably 50% by mass or more, and particularly preferably 80% by mass or more. Polybutadiene having a ratio of cis-1,4 bonds of 80% or more is particularly preferred.

[0022] The rubber composition of the core 4 preferably contains a co-crosslinking agent. From the viewpoint of durability and resilience performance of the golf ball 2, a preferred co-crosslinking agent is a monovalent or divalent metal salt of an α,β-unsaturated carboxylic acid having 2 to 8 carbon atoms. Preferred co-crosslinking agents include zinc acrylate, magnesium acrylate, zinc methacrylate, and magnesium methacrylate. Zinc acrylate and zinc methacrylate are particularly preferred.

[0023] The rubber composition may contain an α,β-unsaturated carboxylic acid having 2 to 8 carbon atoms and a metal oxide. The two react in the rubber composition to obtain a salt. The salt functions as a co-crosslinking agent. Preferred α,β-unsaturated carboxylic acids include acrylic acid and methacrylic acid. Preferred metal oxides include zinc oxide and magnesium oxide.

[0024] The amount of the co-crosslinking agent is preferably 10 parts by mass or more and 45 parts by mass or less per 100 parts by mass of the base rubber. Golf ball 2 having this amount of 10 parts by mass or more has excellent resilience performance. From this viewpoint, this amount is more preferably 15 parts by mass or more, and particularly preferably 20 parts by mass or more. Golf ball 2 having this amount of 45 parts by mass or less has excellent shot feeling. From this viewpoint, this amount is more preferably 40 parts by mass or less, and particularly preferably 35 parts by mass or less.

[0025] Preferably, the rubber composition of the core 4 contains an organic peroxide. The organic peroxide functions as a crosslinking initiator. The organic peroxide contributes to the durability and resilience performance of the golf ball 2. Examples of suitable organic peroxides include dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and di-t-butyl peroxide. A particularly versatile organic peroxide is dicumyl peroxide.

[0026] The amount of organic peroxide is preferably 0.1 parts by weight or more and 3.0 parts by weight or less per 100 parts by weight of the base rubber. Golf ball 2 having this amount of 0.1 parts by weight or more has excellent resilience performance. From this viewpoint, this amount is more preferably 0.3 parts by weight or more, and particularly preferably 0.5 parts by weight or more. Golf ball 2 having this amount of 3.0 parts by weight or less has excellent shot feeling. From this viewpoint, this amount is more preferably 2.5 parts by weight or less, and particularly preferably 2.0 parts by weight or less.

[0027] Preferably, the rubber composition of the core 4 contains an organic sulfur compound. The organic sulfur compound contributes to the flight distance on a driver shot. The organic sulfur compound includes a naphthalene thiol-based compound, a benzene thiol-based compound, and a disulfide-based compound.

[0028] Examples of naphthalene-based compounds include 1-naphthalene-thiol, 2-naphthalene-thiol, 4-chloro-1-naphthalene-thiol, 4-bromo-1-naphthalene-thiol, 1-chloro-2-naphthalene-thiol, 1-bromo-2-naphthalene-thiol, 1-fluoro-2-naphthalene-thiol, 1-cyano-2-naphthalene-thiol, and 1-acetyl-2-naphthalene-thiol, as well as metal salts thereof. A preferred metal salt is zinc salt.

[0029] Examples of benzenethiol compounds include benzenethiol, 4-chlorobenzenethiol, 3-chlorobenzenethiol, 4-bromobenzenethiol, 3-bromobenzenethiol, 4-fluorobenzenethiol, 4-iodobenzenethiol, 2,5-dichlorobenzenethiol, 3,5-dichlorobenzenethiol, 2,6-dichlorobenzenethiol, 2,5-dibromobenzenethiol, 3,5-dibromobenzenethiol, 2-chloro-5-bromobenzenethiol, 2,4,6-trichlorobenzenethiol, 2,3,4,5,6-pentachlorobenzenethiol, 2,3,4,5,6-pentafluorobenzenethiol, 4-cyanobenzenethiol, 2-cyanobenzenethiol, 4-nitrobenzenethiol and 2-nitrobenzenethiol, as well as their metal salts.Preferred metal salt is zinc salt.

[0030] Disulfide compounds include diphenyl disulfide, bis(4-chlorophenyl) disulfide, bis(3-chlorophenyl) disulfide, bis(4-bromophenyl) disulfide, bis(3-bromophenyl) disulfide, bis(4-fluorophenyl) disulfide, bis(4-iodophenyl) disulfide, bis(4-cyanophenyl) disulfide, bis(2,5-dichlorophenyl) disulfide, bis(3,5-dichlorophenyl) disulfide, bis(2,6-dichlorophenyl) disulfide, and bis(2,5-dibutyl). Examples of such disulfides include bis(3,5-dibromophenyl) disulfide, bis(2-chloro-5-bromophenyl) disulfide, bis(2-cyano-5-bromophenyl) disulfide, bis(2,4,6-trichlorophenyl) disulfide, bis(2-cyano-4-chloro-6-bromophenyl) disulfide, bis(2,3,5,6-tetrachlorophenyl) disulfide, bis(2,3,4,5,6-pentachlorophenyl) disulfide and bis(2,3,4,5,6-pentabromophenyl) disulfide.

[0031] The amount of the organic sulfur compound is preferably 0.1 parts by weight or more and 1.5 parts by weight or less per 100 parts by weight of the base rubber. When this amount is 0.1 parts by weight or more, the golf ball 2 has excellent resilience performance. From this viewpoint, this amount is more preferably 0.2 parts by weight or more, and particularly preferably 0.3 parts by weight or more. When this amount is 1.5 parts by weight or less, the golf ball 2 has excellent shot feeling. From this viewpoint, this amount is more preferably 1.3 parts by weight or less, and particularly preferably 1.1 parts by weight or less. Two or more organic sulfur compounds may be used in combination.

[0032] Preferably, the rubber composition of the core 4 contains a carboxylic acid or a carboxylate. The carboxylic acid and the carboxylate can contribute to optimizing the hardness distribution of the core 4. The appropriate hardness distribution can suppress the spin rate in a shot with a middle iron. A preferred carboxylic acid is benzoic acid. A preferred carboxylate is zinc octanoate and zinc stearate. The amount of the carboxylic acid and the carboxylate is preferably 0.5 parts by weight or more, more preferably 0.8 parts by weight or more, and particularly preferably 1.0 parts by weight or more, per 100 parts by weight of the base rubber. This amount is preferably 20 parts by weight or less, more preferably 15 parts by weight or less, and particularly preferably 10 parts by weight or less.

[0033] The rubber composition of the core 4 may contain a filler for the purpose of adjusting the specific gravity, etc. Examples of suitable fillers include zinc oxide, barium sulfate, calcium carbonate, and magnesium carbonate. The amount of the filler is appropriately determined so that the intended specific gravity of the core 4 is achieved.

[0034] The rubber composition of the core 4 may contain appropriate amounts of various additives such as sulfur, antioxidants, colorants, plasticizers, dispersants, etc. This rubber composition may contain crosslinked rubber powder or synthetic resin powder.

[0035] The diameter of the core 4 is preferably 35.0 mm or greater and 40.5 mm or less. A golf ball 2 having a core 4 with a diameter of 35.0 mm or greater has excellent resilience performance. From this viewpoint, the diameter is more preferably 36.0 mm or greater, and particularly preferably 36.5 mm or greater. A golf ball 2 having a core 4 with a diameter of 40.5 mm or less has excellent durability. From this viewpoint, the diameter is more preferably 40.0 mm or less, and particularly preferably 39.5 mm or less.

[0036] The hardness Ho of the center of the core 4 is preferably 35 or greater and 80 or less. A golf ball 2 having a hardness Ho of 35 or greater has excellent resilience performance. From this viewpoint, the hardness Ho is more preferably 40 or greater, and particularly preferably 45 or greater. A golf ball 2 having a hardness Ho of 80 or less has an excellent shot feeling. From this viewpoint, the hardness Ho is more preferably 70 or less, and particularly preferably 65 or less.

[0037] The hardness Ho is measured by a Shore C hardness tester attached to an automatic hardness tester (H. Burleith Co., Ltd., product name "Digitest II"). The hardness tester is pressed against the center of a cross section of a hemisphere obtained by cutting the golf ball 2. The measurement is performed in an environment of 23°C.

[0038] The surface hardness Hs of the core 4 is preferably 65 or greater and 95 or less. A golf ball 2 having a hardness Hs of 65 or greater has excellent resilience performance. From this viewpoint, the hardness Hs is more preferably 67 or greater, and particularly preferably 69 or greater. A golf ball 2 having a hardness Hs of 95 or less has an excellent shot feeling. From this viewpoint, the hardness Hs is more preferably 93 or less, and particularly preferably 91 or less.

[0039] The hardness Hs is measured by a Shore C hardness tester attached to an automatic hardness tester ("Digitest II" product name, manufactured by H. Burleith Co., Ltd.). The hardness tester is pressed against the surface of the core 4. The measurement is performed in an environment of 23°C.

[0040] In the core 4, the difference Hd (=Hs-Ho) between the surface hardness Hs and the center hardness Ho is preferably 15 or greater and 40 or less. A golf ball 2 having a core 4 with a difference Hd of 15 or greater has suppressed spin upon shots with a middle iron. This golf ball 2 has a long flight distance when hit with a middle iron. From this viewpoint, the difference Hd is more preferably 18 or greater, and particularly preferably 20 or greater. A core 4 with a difference Hd of 40 or less has excellent durability. From this viewpoint, the difference Hd is more preferably 37 or less, and particularly preferably 35 or less.

[0041] The amount of deformation C1 of the core 4 is preferably 3.2 mm or more and 5.2 mm or less. A golf ball 2 having a core 4 with a deformation amount C1 of 3.2 mm or more has an excellent shot feeling. From this viewpoint, the amount of deformation C1 is more preferably 3.4 mm or more, and particularly preferably 3.6 mm or more. When a golf ball 2 having a core 4 with a deformation amount C1 of 5.2 mm or less is hit with a middle iron, it can be launched with a high initial velocity. From this viewpoint, the amount of deformation C1 is more preferably 5.0 mm or less, and particularly preferably 4.8 mm or less.

[0042] A Yamada compression tester "SCH" is used to measure the amount of compressive deformation C1. In this tester, the core 4 is placed on a metal hard plate. A metal cylinder is gradually lowered towards the core 4. The core 4, which is sandwiched between the bottom of the cylinder and the hard plate, is deformed. The distance traveled by the cylinder from when an initial load of 98N is applied to the core 4 until a final load of 1274N is applied is measured. The speed of travel of the cylinder until the initial load is applied is 0.83mm / s. The speed of travel of the cylinder from when the initial load is applied to when the final load is applied is 1.67mm / s.

[0043] Compression molding is suitable for the core 4. In the compression molding, a rubber composition is put into a mold having a cavity. The rubber composition is pressurized and heated in the cavity. Pressurization causes the rubber composition to flow in the cavity. Heating causes the rubber to undergo a crosslinking reaction. As described above, from the viewpoint of spin suppression, the difference Hd between the surface hardness Hs and the center hardness Ho in the core 4 is preferably 15 or more. In other words, from the viewpoint of flight performance, a large hardness difference Hd is preferable. In the compression molding, the rubber composition is pressurized at a relatively low pressure and heated at a relatively high temperature, so that a large hardness difference Hd can be achieved. The compression molding may be achieved in multiple stages.

[0044] The intermediate layer 6 is located outside the core 4. The intermediate layer 6 is formed from a thermoplastic resin composition. Examples of base polymers of this resin composition include ionomer resins, thermoplastic polyester elastomers, thermoplastic polyamide elastomers, thermoplastic polyurethane elastomers, thermoplastic polyolefin elastomers, and thermoplastic polystyrene elastomers. In particular, ionomer resins are preferred. Ionomer resins have high elasticity. A golf ball 2 having an intermediate layer 6 containing an ionomer resin has excellent resilience performance. This golf ball 2 has excellent flight performance on driver shots.

[0045] The ionomer resin may be used in combination with other resins. In that case, the ionomer resin is the main component of the base polymer from the viewpoint of resilience performance. The ratio of the ionomer resin to the total base polymer is preferably 50% by mass or more.

[0046] A preferred ionomer resin is a binary copolymer of an α-olefin and an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms. A preferred binary copolymer contains 80% to 90% by mass of an α-olefin and 10% to 20% by mass of an α,β-unsaturated carboxylic acid. This binary copolymer has excellent resilience performance. Another preferred ionomer resin is a ternary copolymer of an α-olefin, an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms, and an α,β-unsaturated carboxylic acid ester having 2 to 22 carbon atoms. A preferred ternary copolymer contains 70% to 85% by mass of an α-olefin, 5% to 30% by mass of an α,β-unsaturated carboxylic acid, and 1% to 25% by mass of an α,β-unsaturated carboxylic acid ester. This ternary copolymer has excellent resilience performance. In the copolymers and terpolymers, the preferred α-olefins are ethylene and propylene, and the preferred α,β-unsaturated carboxylic acids are acrylic acid and methacrylic acid. Particularly preferred ionomer resins are copolymers of ethylene and acrylic acid. Another particularly preferred ionomer resin is a copolymer of ethylene and methacrylic acid.

[0047] In the binary copolymer and ternary copolymer, a portion of the carboxyl groups is neutralized with a metal ion. Examples of metal ions for neutralization include sodium ions, potassium ions, lithium ions, zinc ions, calcium ions, magnesium ions, aluminum ions, and neodymium ions. Neutralization may be performed with two or more types of metal ions. Particularly preferred metal ions from the viewpoint of the resilience performance and durability of the golf ball 2 are sodium ions, zinc ions, lithium ions, and magnesium ions.

[0048] Specific examples of ionomer resins include trade names "Himilan 1555", "Himilan 1557", "Himilan 1605", "Himilan 1706", "Himilan 1707", "Himilan 1855", "Himilan 1856", "Himilan 8150", "Himilan AM7311", "Himilan AM7315", "Himilan AM7317", "Himilan AM7329" and "Himilan AM7337" from Dow Mitsui Polychemicals; and trade names "Surlyn 6120", "Surlyn 6910" and "Surlyn 6920" from DuPont. 7930", "Surlyn 7940", "Surlyn 8140", "Surlyn 8150", "Surlyn 8940", "Surlyn 8945", "Surlyn 9120", "Surlyn 9150", "Surlyn 9910", "Surlyn 9945", "Surlyn AD8546", "HPF1000" and "HPF2000"; and ExxonMobil Chemical Company trade names "IOTEK7010", "IOTEK7030", "IOTEK7510", "IOTEK7520", "IOTEK8000" and "IOTEK8030". Two or more ionomer resins may be used in combination.

[0049] The resin composition of the mid layer 6 may contain appropriate amounts of colorants, fillers, dispersants, antioxidants, UV absorbers, light stabilizers, fluorescent agents, fluorescent brighteners, etc. When the color of the golf ball 2 is white, a typical colorant is titanium dioxide.

[0050] The thickness T2 of the mid layer 6 is preferably 0.50 mm or greater and 2.50 mm or less. A golf ball 2 having a thickness T2 of 0.50 mm or greater has excellent resilience performance. From this viewpoint, the thickness T2 is more preferably 0.70 mm or greater, and particularly preferably 0.90 mm or greater. A golf ball 2 having a thickness T2 of 2.50 mm or less has excellent shot feeling. From this viewpoint, the thickness T2 is more preferably 2.30 mm or less, and particularly preferably 2.10 mm or less. The thickness T2 is measured directly below the land 12.

[0051] The hardness H2 of the mid layer 6 is preferably 45 or greater and 75 or less. A golf ball 2 having a hardness H2 of 45 or greater has excellent resilience performance. In this respect, the hardness H2 is more preferably 53 or greater, and particularly preferably 60 or greater. A golf ball 2 having a hardness H2 of 75 or less has excellent shot feeling. In this respect, the hardness H2 is more preferably 72 or less, and particularly preferably 70 or less.

[0052] The hardness H2 of the intermediate layer 6 is measured in accordance with the standard "ASTM-D 2240-68". The hardness H2 is measured using a Shore D hardness tester attached to an automatic hardness tester (H. Burleith Co., Ltd., trade name "Digitest II"). For the measurement, a sheet having a thickness of about 2 mm and made of the same material as the material of the intermediate layer 6, which is formed by a hot press, is used. Prior to the measurement, the sheet is stored at a temperature of 23°C for two weeks. When measuring, three sheets are stacked.

[0053] The amount of deformation C2 of the sphere consisting of the core 4 and the intermediate layer 6 is preferably 2.6 mm or more and 4.5 mm or less. A golf ball 2 having a sphere with a deformation amount C2 of 2.6 mm or more provides an excellent shot feeling. From this viewpoint, the amount of deformation C2 is more preferably 2.8 mm or more, and particularly preferably 2.9 mm or more. When a golf ball 2 having a sphere with a deformation amount C2 of 4.5 mm or less is hit with a middle iron, it can be launched with a high initial velocity. From this viewpoint, the amount of deformation C2 is more preferably 4.2 mm or less, and particularly preferably 4.0 mm or less.

[0054] The aforementioned YAMADA compression tester "SCH" is used to measure the amount of compressive deformation C2. In this tester, a sphere is placed on a metal hard plate. A metal cylinder is gradually lowered towards the sphere. The sphere, sandwiched between the bottom of the cylinder and the hard plate, deforms. The distance traveled by the cylinder from when an initial load of 98N is applied to the sphere to when a final load of 1274N is applied is measured. The speed at which the cylinder moves until the initial load is applied is 0.83mm / s. The speed at which the cylinder moves from when the initial load is applied to when the final load is applied is 1.67mm / s.

[0055] The difference (C2-C1) between the amount of compressive deformation C2 of the sphere and the amount of compressive deformation C1 of the core 4 is preferably -1.2 or greater and -0.2 or less. When a golf ball 2 having a difference (C2-C1) within this range is hit with a middle iron, it can be launched with a great initial velocity. From this viewpoint, the difference (C2-C1) is more preferably -1.1 or greater, and particularly preferably -1.0 or greater. The difference (C2-C1) is more preferably -0.3 or less, and particularly preferably -0.4 or less.

[0056] The cover 8 is located outside the mid layer 6. The cover 8 is molded from a thermoplastic resin composition. Examples of base polymers of this resin composition include ionomer resins, thermoplastic polyester elastomers, thermoplastic polyamide elastomers, thermoplastic polyurethane elastomers, thermoplastic polyolefin elastomers, and thermoplastic polystyrene elastomers. In particular, ionomer resins are preferred. Ionomer resins have high elasticity. A golf ball 2 having a cover 8 containing an ionomer resin has excellent resilience performance. This golf ball 2 has excellent flight performance in driver shots. The ionomer resins described above for the mid layer 6 can be used for the cover 8.

[0057] The ionomer resin may be used in combination with other resins. In this case, the ionomer resin is the main component of the base polymer from the viewpoint of resilience performance. The ratio of the ionomer resin to the total base polymer is preferably 50% by mass or more, more preferably 70% by mass or more, and particularly preferably 80% by mass or more.

[0058] A preferred resin that can be used in combination with the ionomer resin is an ethylene-(meth)acrylic acid copolymer. This copolymer is obtained by copolymerization of a monomer composition containing ethylene and (meth)acrylic acid. In this copolymer, a part of the carboxyl groups is neutralized with a metal ion. This copolymer contains 3% by mass or more and 25% by mass or less of a (meth)acrylic acid component. An ethylene-(meth)acrylic acid copolymer having a polar functional group is particularly preferred. A specific example of an ethylene-(meth)acrylic acid copolymer is the trade name "Nucrel" of Dow Mitsui Polychemicals.

[0059] The resin composition of the cover 8 may contain a styrene block-containing thermoplastic elastomer. The styrene block-containing thermoplastic elastomer has a polystyrene block as a hard segment and a soft segment. A typical soft segment is a diene block. Examples of the diene block compound include butadiene, isoprene, 1,3-pentadiene, and 2,3-dimethyl-1,3-butadiene. Butadiene and isoprene are preferred. Two or more compounds may be used in combination.

[0060] The styrene block-containing thermoplastic elastomer includes styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS), styrene-isoprene-butadiene-styrene block copolymer (SIBS), hydrogenated SBS, hydrogenated SIS, and hydrogenated SIBS. Hydrogenated SBS includes styrene-ethylene-butylene-styrene block copolymer (SEBS). Hydrogenated SIS includes styrene-ethylene-propylene-styrene block copolymer (SEPS). Hydrogenated SIBS includes styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS).

[0061] The content of the styrene component in the styrene block-containing thermoplastic elastomer is preferably 1% by mass or more, more preferably 3% by mass or more, and particularly preferably 5% by mass or more, from the standpoint of the resilience performance of the golf ball 22. From the standpoint of the shot feeling of the golf ball 22, this content is preferably 50% by mass or less, more preferably 47% by mass or less, and particularly preferably 45% by mass or less.

[0062] In the present invention, the styrene block-containing thermoplastic elastomer includes an alloy of one or more selected from the group consisting of SBS, SIS, SIBS, SEBS, SEPS, and SEEPS with an olefin. The olefin component in this alloy is presumed to contribute to improving compatibility with other base polymers. This alloy can contribute to the resilience performance of the golf ball 22. An olefin having a carbon number of 2 or more and 10 or less is preferred. Examples of suitable olefins include ethylene, propylene, butene, and pentene. Ethylene and propylene are particularly preferred.

[0063] Specific examples of polymer alloys include trade names "TEFABLOC T3221C", "TEFABLOC T3339C", "TEFABLOC SJ4400N", "TEFABLOC SJ5400N", "TEFABLOC SJ6400N", "TEFABLOC SJ7400N", "TEFABLOC SJ8400N", "TEFABLOC SJ9400N" and "TEFABLOC SR04" manufactured by Mitsubishi Chemical Corporation. Other specific examples of styrene block-containing thermoplastic elastomers include trade names "Epofriend A1010" manufactured by Daicel Chemical Industries, Ltd. and trade name "Septon HG-252" manufactured by Kuraray Co., Ltd.

[0064] The resin composition of the cover 8 may contain appropriate amounts of colorants, fillers, dispersants, antioxidants, UV absorbers, light stabilizers, fluorescent agents, fluorescent brighteners, etc. When the color of the golf ball 2 is white, a typical colorant is titanium dioxide.

[0065] The thickness T3 of the cover 8 is preferably 0.50 mm or greater and 2.50 mm or less. In a golf ball 2 having a thickness T3 of 0.50 mm or greater, the cover 8 can contribute to the shot feeling. From this viewpoint, the thickness T3 is more preferably 0.70 mm or greater, and particularly preferably 0.90 mm or greater. In a golf ball 2 having a thickness T3 of 2.50 mm or less, the cover 8 does not impair the resilience performance. From this viewpoint, the thickness T3 is more preferably 2.30 mm or less, and particularly preferably 2.10 mm or less. The thickness T3 is measured directly below the land 12.

[0066] The hardness H3 of the cover 8 is preferably 30 or greater and 60 or less. A golf ball 2 having a hardness H3 of 30 or greater has excellent resilience performance. From this viewpoint, the hardness H3 is more preferably 33 or greater, and particularly preferably 35 or greater. A golf ball 2 having a hardness H3 of 60 or less will experience a small impact when hit with a putter. This golf ball 2 has an excellent shot feeling. From this viewpoint, the hardness H3 is more preferably 57 or less, and particularly preferably 55 or less.

[0067] The hardness H3 of the cover 8 is measured in accordance with the standard "ASTM-D 2240-68". The hardness H3 is measured using a Shore D hardness tester attached to an automatic hardness tester (H. Burleith's product name "Digitest II"). For the measurement, a sheet of the same material as the material of the cover 8, formed by a hot press, and having a thickness of about 2 mm is used. Prior to the measurement, the sheet is stored at a temperature of 23°C for two weeks. When measuring, three sheets are stacked.

[0068] The amount of compressive deformation C3 of the golf ball 2 is preferably 2.8 mm or more and 4.2 mm or less. A golf ball 2 having a compressive deformation amount C3 of 2.8 mm or more provides an excellent shot feeling during putting. From this viewpoint, the amount of compressive deformation C3 is more preferably 2.9 mm or more, and particularly preferably 3.0 mm or more. When a golf ball 2 having a compressive deformation amount C3 of 4.2 mm or less is hit with a middle iron, it can be launched with a high initial velocity. From this viewpoint, the amount of compressive deformation C3 is more preferably 4.1 mm or less, and particularly preferably 4.0 mm or less.

[0069] The aforementioned YAMADA compression tester "SCH" is used to measure the amount of compressive deformation C3. In this tester, the golf ball 2 is placed on a metal hard plate. A metal cylinder gradually descends towards the golf ball 2. The golf ball 2, sandwiched between the bottom of the cylinder and the hard plate, deforms. The distance traveled by the cylinder from a state in which an initial load of 98N is applied to the golf ball 2 to a state in which a final load of 1274N is applied, is measured. The speed at which the cylinder moves until the initial load is applied is 0.83mm / s. The speed at which the cylinder moves from the application of the initial load to the application of the final load is 1.67mm / s.

[0070] The sum (T2+T3) of the thickness T2 (mm) of the intermediate layer 6 and the thickness T3 (mm) of the cover 8 is preferably 1.0 mm or more and 4.5 mm or less. A golf ball 2 having a sum (T2+T3) within this range is excellent in both flight performance in shots with a middle iron and shot feel in putting. From this viewpoint, the sum (T2+T3) is more preferably 1.5 mm or more, and particularly preferably 2.0 mm or more. The sum (T2+T3) is more preferably 4.0 mm or less, and particularly preferably 3.5 mm or less.

[0071] The difference (H3-H2) between the hardness H3 of the cover 8 and the hardness H2 of the intermediate layer 6 is preferably -11 or less. A golf ball 2 having the difference (H3-H2) of -11 or less is excellent in both flight performance in shots with a middle iron and shot feel in putting. From this viewpoint, the difference (H3-H2) is more preferably -13 or less, and particularly preferably -15 or less. The difference (H3-H2) is preferably -30 or greater.

[0072] The difference (C3-C2) between the compressive deformation amount C3 of the golf ball 2 and the compressive deformation amount C2 of a sphere consisting of the core 4 and the mid layer 6 is preferably -0.60 or greater and -0.10 or less. When a golf ball 2 having a difference (C3-C2) within this range is hit with a middle iron, it can be hit with a great initial velocity. From this viewpoint, the difference (C3-C2) is more preferably -0.55 or greater, and particularly preferably -0.50 or greater. The difference (C3-C2) is more preferably -0.15 or less, and particularly preferably -0.20 or less.

[0073] In the present invention, the value Vx is calculated by the following formula: Vx = (124.8- Hs) / 11.5 The amount of compressive deformation C1 of the core 4 is greater than this value Vx. In other words, the golf ball 2 satisfies the following formula (1). C1 > (124.8 - Hs) / 11.5 (1) In a golf ball 2 that satisfies the above mathematical formula (1), the difference Hd between the surface hardness Hs and the center hardness Ho of the core 4 is large. When this golf ball 2 is hit with a middle iron, the spin rate is low. This golf ball 2 has excellent flight performance in shots with a middle iron. When this golf ball 2 is hit with a putter, the impact is small. This golf ball 2 has an excellent shot feel when putting. This golf ball 2 achieves both flight performance and shot feel.

[0074] In light of the flight performance and the shot feeling, the difference (C1-Vx) between the amount of compressive deformation C1 and the value Vx is preferably equal to or greater than 0.05, more preferably equal to or greater than 0.08, and particularly preferably equal to or greater than 0.10. The difference (C1-Vx) is preferably equal to or less than 1.00.

[0075] In the present invention, the value Vy is calculated by the following formula: Vy = (-1 / 6 * C1 + (68 - H2) / 20 + (5 - Hd) / 100) * T2 The difference (C2-C1) is equal to or greater than this value Vy. In other words, the golf ball 2 satisfies the following formula (2). C2 - C1 ≥ (-1 / 6 * C1 + (68 - H2) / 20 + (5 - Hd) / 100) * T2 (2) The spin rate of this golf ball 2 is small when it is hit with a middle iron, and this golf ball 2 is excellent in flight performance when hit with a middle iron.

[0076] In respect of flight performance, the difference ((C2-C1)-Vy) between the difference (C2-C1) and the value Vy is preferably equal to or greater than 0.02, more preferably equal to or greater than 0.03, and particularly preferably equal to or greater than 0.04. The difference ((C2-C1)-Vy) is preferably equal to or less than 0.3.

[0077] In the present invention, the value Vz is calculated by the following formula: Vz = (C2 - C1) / (C3 - C2) This value Vz is equal to or greater than 1.60. In other words, the golf ball 2 satisfies the following formula (3). (C2 - C1) / (C3 - C2) ≧1.60 (3) The spin rate of this golf ball 2 is low when it is hit with a middle iron. This golf ball 2 has excellent flight performance when shot with a middle iron. This golf ball 2 has a small impact when it is hit with a putter. This golf ball 2 has an excellent shot feeling when putting. This golf ball 2 achieves both flight performance and shot feeling. In respect of flight performance and shot feeling, the value Vz is more preferably 1.70 or greater, and particularly preferably 1.80 or greater. The value Vz is preferably 4.50 or less. EXAMPLES

[0078] The effects of the present invention will be clarified by the following examples, but the present invention should not be construed as being limited based on the description of these examples.

[0079] [Example 1] 100 parts by mass of high cis polybutadiene (JSR Corporation's product name "BR-730"), 27 parts by mass of zinc acrylate, 10 parts by mass of zinc oxide, 12.5 parts by mass of barium sulfate, 0.9 parts by mass of dicumyl peroxide, 0.9 parts by mass of pentachlorothiophenol zinc salt, and 2.0 parts by mass of benzoic acid were kneaded to obtain a rubber composition 1B. This rubber composition 1B was placed in a mold consisting of an upper mold and a lower mold, each of which had a hemispherical cavity. This rubber composition 1B was pressurized and heated under the following conditions to obtain a core with a diameter of 38.6 mm. First stage Temperature: 120℃ Pressure: 35kgf / cm 2 Time: 5 minutes Second Stage Temperature: 150℃ Pressure: 35kgf / cm 2 Time: 20 minutes

[0080] 50 parts by mass of an ionomer resin (the above-mentioned "Himilan AM7329"), 25 parts by mass of another ionomer resin (the above-mentioned "Himilan 1605"), 25 parts by mass of yet another ionomer resin (the above-mentioned "Surlyn 8150"), 7.5 parts by mass of barium sulfate, and 4 parts by mass of titanium dioxide were kneaded in a twin-screw kneading extruder to obtain a resin composition 2A. A core was placed in a mold consisting of an upper mold and a lower mold, each of which had a hemispherical cavity. The resin composition 2A was coated around the core by injection molding to form an intermediate layer. The thickness of this intermediate layer was 1.00 mm.

[0081] 80 parts by mass of ionomer resin (the above-mentioned "Himilan 1855"), 20 parts by mass of ethylene-(meth)acrylic acid copolymer (Mitsui Dow Polychemicals' trade name "Nucrel N1050H"), 3 parts by mass of titanium dioxide, and 0.2 parts by mass of light stabilizer (Johoku Chemical Industry's trade name "JF-90") were kneaded in a twin-screw kneading extruder to obtain resin composition 3A. A sphere consisting of a core and an intermediate layer was placed in a mold consisting of an upper mold and a lower mold, each of which had a hemispherical cavity. Resin composition 3A was coated around the sphere by injection molding to form a cover. The thickness of this cover was 1.05 mm.

[0082] A clear paint based on a two-component curing polyurethane was applied around the cover to obtain a golf ball of Example 1 having a diameter of about 42.7 mm and a mass of about 45.6 g.

[0083] [Examples 2-20 and Comparative Examples 1-8] Golf balls of Examples 2-20 and Comparative Examples 1-8 were obtained in the same manner as in Example 1, except that the specifications of the core, intermediate layer, and cover were as shown in Tables 5-14 below. Details of the composition of the core are shown in Tables 1 and 2 below. Details of the composition of the intermediate layer are shown in Table 3 below. Details of the composition of the cover are shown in Table 4 below.

[0084] [Flight test on I#7] An iron-type golf club (Sumitomo Rubber Industries, Ltd., product name "XXIO 11", shaft hardness: R, #7) was attached to a swing machine manufactured by Golf Laboratory. A golf ball was hit under the condition of a head speed of 33 m / sec, and the spin rate and flight distance were measured. The flight distance is the distance from the launch point to the rest point. There was almost no wind during the test. The average value of the data obtained from 12 measurements was calculated. The difference between this average value and the average value of Example 5 is shown in Tables 10-14 below.

[0085] [Flight performance evaluation] The above flight distance differences were ranked based on the following criteria. A: Over 1.2 yards B: More than 0.4 yards and less than 1.2 yards C: -0.4 yards or more and 0.4 yards or less D: -1.2 yards or less - less than 0.4 yards E: Less than -1.2 yards The results are shown in Tables 10-14 below.

[0086] [Evaluation of hitting feeling] Twenty golf players were asked to hit golf balls with a putter. These players were asked about the shot feeling. The number of players who answered that the shot feeling was good was ranked based on the following criteria. A: 18 or more people B: More than 14 people and less than 17 people C: 10 to 13 people D: More than 6 people and less than 9 people E: 5 people or less The results are shown in Tables 10-14 below.

[0087] [comprehensive evaluation] The overall evaluation of the flight performance (first evaluation) and the hitting feel (second evaluation) was ranked based on the following criteria. A: First grade is "A"-"C", second grade is "A"-"C". B: One of the first and second evaluations is "A"-"C" and the other is "D". C: First grade is "D" and second grade is "D". D: One or both of the first and second evaluations are "E". The results are shown in Tables 10-14 below.

[0088] [Table 1]

[0089] [Table 2]

[0090] [Table 3]

[0091] [Table 4]

[0092] [Table 5]

[0093] [Table 6]

[0094] [Table 7]

[0095] [Table 8]

[0096] [Table 9]

[0097] [Table 10]

[0098] [Table 11]

[0099] [Table 12]

[0100] [Table 13]

[0101] [Table 14]

[0102] As shown in Tables 10 to 14, the golf balls of the examples are excellent in flight performance and shot feeling. From these evaluation results, the superiority of the present invention is clear. [Industrial Applicability]

[0103] The golf ball according to the present invention is suitable for playing on a golf course, practicing at a driving range, and the like. [Explanation of symbols]

[0104] 2. Golf ball 4. Core 6. Middle tier 8. Cover 10 Dimples 12···Rand

Claims

1. The golf ball has a core, a mid layer located outside the core, and a cover located outside the mid layer, Satisfying the following formulas (1) and (2), The compressive deformation amount C3 is 2.80 mm or more, C1 > (124.8 - Hs) / 11.5 (1) C2 - C1 ≧ (-1 / 6 * C1 + (68 - H2) / 20 + (5 - Hd) / 100) * T2 (2) C1: Compressive deformation of the core (mm) C2: Amount of compression deformation of the sphere consisting of the core and the intermediate layer (mm) Hd: Hs-Ho Ho: Center hardness of the core (Shore C) Hs: Core surface hardness (Shore C) H2: Hardness of the middle layer (Shore D) T2: Thickness of the middle layer (mm) A golf ball, wherein the difference between the value (C2-C1) and the value ((-1 / 6*C1+(68-H2) / 20+(5-Hd) / 100)*T2) is 0.13 or more.

2. 2. The golf ball according to claim 1, further satisfying the following formula (3): (C2 - C1) / (C3 - C2) ≧ 1.60 (3) C3: Amount of compression deformation of the golf ball (mm)

3. 3. The golf ball according to claim 1, wherein a difference Hd between the surface hardness Hs (Shore C) and the center hardness Ho (Shore C) is 22.5 or greater and 40 or less.

4. 4. The golf ball according to claim 1, wherein the sum (T2+T3) of the thickness T2 (mm) of the intermediate layer and the thickness T3 (mm) of the cover is 1.0 mm or greater and 4.5 mm or less.

5. 5. The golf ball according to claim 1, wherein the intermediate layer has a hardness H2 (Shore D) of 45 or greater.

6. 6. The golf ball according to claim 1, wherein the cover is made of a resin composition, and the base material of the resin composition is an ionomer resin.

7. 7. The golf ball according to claim 6, wherein the intermediate layer is made of a resin composition, and the base material of the resin composition is an ionomer resin.

8. 8. The golf ball according to claim 7, wherein the difference (H3-H2) between the hardness H3 of the cover and the hardness H2 of the intermediate layer is -11 or less.

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