golf ball

Abstract

To provide a golf ball 2 with excellent flight performance, feel, scratch resistance, and moldability. [Solution] The golf ball 2 has a core 4, an intermediate layer 6, and a cover 8. The slope A1 of the line connecting the center point of the core 4 and point P1, which is 2.5 mm away from the center point, and the slope A2 of the line connecting point P1 and point P2, which is 5.0 mm away from the center point, are 1.00 or greater. The slope A5 of the line connecting point P4, which is 10.0 mm away from the center point, and point P5, which is 12.5 mm away from the center point, and the slope A6 of the line connecting point P5 and point P6, which is 15.0 mm away from the center point, are 1.50 or greater. The material of the cover 8 is a resin composition mainly composed of ionomer resin. In this resin composition, the ratio P(I) of ionomer resin to the total amount of base resin is 60% by mass or greater.

Description

Technical Field

[0007]

[0001] This specification discloses a golf ball having a core, an intermediate layer, and a cover.

Background Art

[0002] A general golf ball has a core, an intermediate layer, and a cover. Japanese Unexamined Patent Application Publication No. 2023-160402 discloses a golf ball having a cover whose main component is an ionomer resin. The ionomer resin can contribute to the repulsion performance of the cover.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] What golf players are concerned about regarding a golf ball is its flight performance. Golf players mainly value the flying distance in a driver shot. For golf players, the feel of hitting the ball is also important. Golf players value the feel of hitting the ball in putting.

[0005] Among ionomer resins, those with low hardness can contribute to the feel of hitting a golf ball. However, a cover made of this type of ionomer resin is inferior in scratch resistance. Furthermore, the contribution of this type of ionomer resin to the repulsion performance is insufficient.

[0006] Even if the cover contains a low-hardness ionomer resin, if the thickness of this cover is sufficiently small, this cover will not significantly inhibit the repulsion of the golf ball. However, forming a thin cover is accompanied by difficulties.

[0007] The applicant's intention is to provide a golf ball with excellent flight performance, feel upon impact, scratch resistance, and moldability. [Means for solving the problem]

[0008] The golf ball disclosed herein has a core, an intermediate layer located outside the core, and a cover located outside the intermediate layer. In a graph plotting the distances (mm) between the center point, point P1 at a distance of 2.5 mm from the center point, point P2 at a distance of 5.0 mm from the center point, point P4 at a distance of 10.0 mm from the center point, point P5 at a distance of 12.5 mm from the center point, and point P6 at a distance of 15.0 mm from the center point, and the Shore C hardness, The slope A1 of the line connecting the above center point and point P1 is 1.00 or greater. The slope A2 of the line connecting point P1 and point P2 is 1.00 or greater. The slope A5 of the line connecting point P4 and point P5 is 1.50 or greater. The slope A6 of the line connecting point P5 and point P6 is 1.50 or greater.

[0009] The difference between the Shore C hardness Hs of the core surface and the Shore C hardness Ho of the center point (Hs-Ho) is 30 or more. The material of the intermediate layer is a resin composition mainly composed of ionomer resin. The material of the cover is a resin composition mainly composed of ionomer resin. In the resin composition of the cover, the ratio P(I) of ionomer resin to the total amount of base resin is 60% by mass or more. In the resin composition of the cover, the ratio P(Na) of sodium ion neutralized ionomer resin to the total amount of base resin is 5% by mass or less. The product of the melt flow rate Mc (g / 10min) and thickness Tc (mm) of the cover (Mc*Tc) is 10.0 or more. The bending stiffness Fc of the cover is 75 MPa or less. [Effects of the Invention]

[0010] The golf balls disclosed herein offer superior flight performance in driver shots, feel in putting, scratch resistance, and moldability. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a partially cutaway cross-sectional view showing a golf ball according to one embodiment. [Figure 2] Figure 2 is a graph showing the hardness distribution of the golf ball core shown in Figure 1. [Modes for carrying out the invention]

[0012] Preferred embodiments will be described in detail below, with reference to drawings as appropriate.

[0013] The golf ball 2 shown in Figure 1 has a spherical core 4, an intermediate layer 6 located outside the core 4, and a cover 8 located outside the intermediate layer 6. The golf ball 2 has a plurality of dimples 10 on its surface. The parts of the golf ball 2 surface other than the dimples 10 are lands 12. The golf ball 2 has a paint layer and a marking layer on the outside of the cover 8, but these layers are not shown in the illustration.

[0014] [Core 4] Core 4 is formed by crosslinking a rubber composition. This rubber composition includes a base rubber, a co-crosslinking agent, a crosslinking initiator, a sulfur compound, and the like.

[0015] [Base rubber] Examples of preferred base rubbers include polybutadiene, polyisoprene, styrene-butadiene copolymer, ethylene-propylene-diene copolymer, and natural rubber. From the viewpoint of the rebound performance of the golf ball 2, polybutadiene is preferred. When polybutadiene is used in combination with other rubbers, it is preferable that polybutadiene is the main component. Specifically, the ratio of polybutadiene to the total base rubber is preferably 50% by mass or more, more preferably 70% by mass or more, and particularly preferably 80% by mass or more. Polybutadiene with a cis-1,4 bond ratio of 80% or more is particularly preferred. Polybutadiene may contain 1,2-vinyl bonds. From the viewpoint of the rebound performance of the golf ball 2, the content of 1,2-vinyl bonds in 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.

[0016] [Co-crosslinking agent] Preferred cocrosslinking agents include α,β-unsaturated carboxylic acids and their metal salts. These cocrosslinking agents can crosslink rubber molecules by graft polymerization. α,β-unsaturated carboxylic acids and α,β-unsaturated carboxylic acid metal salts may be used in combination. In α,β-unsaturated carboxylic acids and their metal salts, the number of carbon atoms is preferably between 2 and 8. Examples of preferred α,β-unsaturated carboxylic acids include acrylic acid, methacrylic acid, fumaric acid, maleic acid, and crotonic acid.

[0017] Examples of metal ions for α,β-unsaturated carboxylate metal salts include monovalent metal ions such as sodium, potassium, and lithium; divalent metal ions such as magnesium, calcium, zinc, barium, and cadmium; trivalent metal ions such as aluminum; tin ions and zirconium ions. Two or more metal ions may be used in combination. Divalent metal ions are preferred from the viewpoint of easily crosslinking rubber molecules. Specific examples of preferred co-crosslinking agents include zinc acrylate, magnesium acrylate, zinc methacrylate, and magnesium methacrylate. Zinc acrylate is particularly preferred. Two or more co-crosslinking agents may be used in combination.

[0018] The amount of the co-crosslinking agent is preferably 10 parts by mass or more and 40 parts by mass or less with respect to 100 parts by mass of the base rubber. In the core 4 where the amount of the co-crosslinking agent is within this range, an appropriate hardness can be achieved. From the viewpoint of hardness, 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.

[0019] [Crosslinking initiator] The preferred crosslinking initiator is an organic peroxide. 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-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.

[0020] The amount of the crosslinking initiator is preferably 0.2 parts by mass or more and 5.0 parts by mass or less with respect to 100 parts by mass of the base rubber. In the core 4 where the amount of the crosslinking initiator is within this range, an appropriate hardness can be achieved. The golf ball 2 is excellent in durability. From this viewpoint, this amount is more preferably 0.5 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.

[0021] [Organic sulfur compound] The organic sulfur compound contributes to the resilience performance of the golf ball 2. The organic sulfur compounds include thiols, polysulfides, thiurams, thiocarboxylic acids, dithiocarboxylic acids, sulfenamides, dithiocarbamate salts, and thiazoles. The thiols include thiophenols and thionaphthols.

[0022] Preferred organosulfur compounds include thiophenols, metal salts of thiophenols, thionaphthols, metal salts of thionaphthols, diphenyl disulfides, and thiuram disulfides. Specific examples of preferred organosulfur 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, diphenyl disulfide, bis(2,6-difluorophenyl) disulfide, bis(2,6-dichlorophenyl) disulfide, bis(2,6-dibromophenyl) disulfide, bis(2,6-diiodophenyl) disulfide, and bis(pentabromophenyl) disulfide, as well as their zinc salts.

[0023] The rubber composition may contain two or more organosulfur compounds in combination.

[0024] The amount of the organic sulfur compound is preferably 0.1 parts by mass or more and 5.0 parts by mass or less per 100 parts by mass of the base rubber. Rubber compositions in which the amount of the organic sulfur compound is within this range have excellent processability. A homogeneous 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 a similar 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 have a core 4 that does not contain the organic sulfur compound.

[0025] [Carboxylic acid] The rubber composition of Core 4 may contain a carboxylic acid or a carboxylate salt. The carboxylic acid and carboxylate salt can contribute to optimizing the hardness distribution of Core 4. A preferred carboxylic acid is benzoic acid. Preferred carboxylate salts include zinc octanoate and zinc stearate. A particularly preferred compound is benzoic acid.

[0026] The total amount of carboxylic acid and carboxylate salt is preferably 1.0 part by mass or more and 7.0 parts by mass or less per 100 parts by mass of the base rubber. The hardness distribution of core 4 when this total amount is within this range is appropriate. From this viewpoint, this amount is more preferably 2.0 parts by mass or more, and particularly preferably 2.5 parts by mass or more. From a similar viewpoint, this amount is more preferably 5.0 parts by mass or less, and particularly preferably 4.0 parts by mass or less.

[0027] [Additives] The rubber composition of core 4 may contain fillers for purposes such as adjusting specific gravity. Examples of suitable fillers include zinc oxide, barium sulfate, calcium carbonate, and magnesium carbonate. The amount of filler is determined appropriately to achieve the intended specific gravity of core 4.

[0028] The core 4 rubber composition may contain appropriate amounts of additives such as radical scavengers, sulfur, antioxidants, colorants, plasticizers, and dispersants. This rubber composition may also contain crosslinked rubber powder or synthetic resin powder.

[0029] [Core diameter] The diameter of the core 4 is preferably 35.0 mm or more and 40.5 mm or less. A golf ball 2 having a core 4 with a diameter of 35.0 mm or more has excellent rebound performance. From this viewpoint, a diameter of 36.0 mm or more is more preferable, and 36.5 mm or more is particularly preferable. A golf ball 2 having a core 4 with a diameter of 40.5 mm or less has excellent durability. From this viewpoint, a diameter of 40.0 mm or less is more preferable, and 39.5 mm or less is particularly preferable.

[0030] [Core compression deformation amount] The compressive deformation amount C1 of the core 4 is preferably 4.3 mm or more and 7.0 mm or less. A golf ball 2 having a core 4 with a compressive deformation amount C1 of 4.3 mm or more has excellent feel when hitting the ball during putting. From this viewpoint, a compressive deformation amount C1 of 4.4 mm or more is more preferable, and 4.5 mm or more is particularly preferable. A golf ball 2 having a core 4 with a compressive deformation amount C1 of 7.0 mm or less has excellent flight performance during driver shots. From this viewpoint, a compressive deformation amount C1 of 6.0 mm or less is more preferable, and 5.5 mm or less is particularly preferable.

[0031] The compression deformation C1 is measured using the YAMADA compression tester "SCH". In this tester, core 4 is placed on a rigid metal plate. A metal cylinder is gradually lowered towards core 4. Core 4, sandwiched between the bottom surface of the cylinder and the rigid plate, deforms. The distance the cylinder travels from the initial load of 98N to the final load of 1274N is measured. The cylinder's movement speed before the initial load is applied is 0.83 mm / s. The cylinder's movement speed from the initial load to the final load is 1.67 mm / s.

[0032] [Core hardness distribution] Figure 2 is a graph showing the hardness distribution of Core 4. In this graph, the horizontal axis represents the distance from the center point of Core 4, and the vertical axis represents hardness (Shore C). The following points are plotted on this graph: Center point Po The first point P1 is 2.5 mm from the center. The second point P2 is 5.0 mm from the center. The third point P3 is 7.5 mm from the center. The fourth point P4 is 10.0 mm from the center. The fifth point P5 is 12.5 mm from the center. The sixth point P6 is 15.0 mm from the center. Point Ps on the surface

[0033] In this specification, the following hardness is measured: Ho: Hardness at the center point Po H(2.5): Hardness at the first point P1 H(5.0): Hardness at the second point P2 H(7.5): Hardness at the third point P3 H(10.0): Hardness at the fourth point P4 H(12.5): Hardness of point P5 H(15.0): Hardness of point P6 Hs: Hardness of point Ps on the surface

[0034] The hardness of the center point Po and points P1 through P6 is measured using a Shore C hardness tester attached to an automated hardness tester (H. Barleys' product name "DigiTest II"). This hardness tester is pressed against the hemispherical cross-section obtained by cutting the golf ball 2. The measurement is performed in an environment of 23°C.

[0035] The hardness Hs of point Ps on the surface is measured using a Shore C hardness tester attached to the aforementioned product name "DigiTest II". This hardness tester is pressed against the surface of core 4. The measurement is performed in an environment of 23°C.

[0036] In this embodiment, the hardness is as follows: Ho:46 H(2.5):50 H(5.0):55 H(7.5):57 H(10.0):58 H(12.5):63 H(15.0):76 Hs:82

[0037] Figure 2 shows the line S1-S7. S1: A straight line connecting the center point Po and the first point P1. S2: A straight line connecting the first point P1 and the second point P2. S3: A straight line connecting the second point P2 and the third point P3. S4: A straight line connecting the third point P3 and the fourth point P4. S5: A straight line connecting the fourth point P4 and the fifth point P5. S6: A straight line connecting the fifth point P5 and the sixth point P6. S7: A straight line connecting the sixth point P6 and the point Ps on the surface.

[0038] Lines S1-S7 each have slopes A1-A7. The formulas for calculating slopes A1-A7 are as follows: The slope A1 of line S1 is (H(2.5) - Ho) / 2.5 = 1.92 The slope A2 of line S2 is (H(5.0) - H(2.5)) / 2.5 = 1.64 The slope A3 of line S3 is (H(7.5) - H(5.0)) / 2.5 = 1.00 The slope A4 of line S4 is (H(10.0) - H(7.5)) / 2.5 = 0.40 The slope A5 of line S5 is (H(12.5) - H(10.0)) / 2.5 = 2.00 The slope A6 of line S6 is (H(15.0) - H(12.5)) / 2.5 = 5.12 The slope A7 of line S7 is (Hs - H(15.0)) / 4.3 = 1.42

[0039] In this core 4, the inclination A1 is 1.00 or greater, the inclination A2 is 1.00 or greater, the inclination A5 is 1.50 or greater, and the inclination A6 is 1.50 or greater. Core 4 with this hardness distribution suppresses the initial spin speed in driver shots. Golf ball 2 with this core 4 has excellent flight performance. Furthermore, this core 4 contributes to a soft feel when putting.

[0040] From the viewpoint of flight performance and feel, the inclination A1 is more preferably 1.30 or higher, and particularly preferably 1.50 or higher. From the same viewpoint, the inclination A2 is more preferably 1.30 or higher, and particularly preferably 1.50 or higher. From the same viewpoint, the inclination A5 is more preferably 1.70 or higher, and particularly preferably 1.80 or higher. From the same viewpoint, the inclination A6 is more preferably 2.50 or higher, and particularly preferably 3.00 or higher. From the viewpoint of the durability of the golf ball 2, the inclination of each of the straight lines S1-S7 is preferably 10.00 or lower.

[0041] In this embodiment, the inclination A3 is smaller than the inclination A2, and the inclination A4 is smaller than the inclination A3. In this core 4, the rate of increase in hardness between the second point P2 and the fourth point P4 is small. When the golf ball 2 is struck with a driver, the energy loss is small in this core 4. This core 4 can contribute to the rebound performance of the golf ball 2. This golf ball 2 has excellent flight performance. From this viewpoint, the difference between inclination A2 and inclination A3 (A2-A3) is preferably 0.10 or more, more preferably 0.20 or more, and particularly preferably 0.25 or more. From a similar viewpoint, the difference between inclination A3 and inclination A4 (A3-A4) is preferably 0.10 or more, more preferably 0.20 or more, and particularly preferably 0.25 or more.

[0042] As is clear from Figure 2, the surface hardness Hs is greater than the hardness Ho at the center point. Core 4 with a large difference (Hs-Ho) suppresses the initial spin speed during driver shots. Golf ball 2 having this core 4 has excellent flight performance. Furthermore, this core 4 contributes to a soft feel when putting. From these viewpoints, a difference (Hs-Ho) of 30 or more is preferable, 32 or more is more preferable, and 34 or more is particularly preferable. From the viewpoint of the rebound performance of golf ball 2, a difference (Hs-Ho) of 40 or less is preferable, 39 or less is more preferable, and 38 or less is particularly preferable.

[0043] The hardness distribution shown in Figure 2 can be achieved by adding a relatively large amount of carboxylic acid or carboxylate salt to the rubber composition of core 4. The hardness distribution shown in Figure 2 can also be achieved by adjusting the crosslinking temperature and crosslinking time of core 4. For example, a preferred hardness distribution of core 4 can be achieved by crosslinking under conditions where the crosslinking temperature is 160°C and the crosslinking time is between 10 and 20 minutes.

[0044] [Middle class] The intermediate layer 6 is located on the outside of the core 4. In this embodiment, the intermediate layer 6 is in contact with the core 4. The intermediate layer 6 is molded from a resin composition. In this embodiment, the intermediate layer 6 is molded from a thermoplastic resin composition.

[0045] [Base resin] Examples of base resins for the resin composition of the intermediate layer 6 include ionomer resin, polyamide resin, thermoplastic polyester elastomer, thermoplastic polyurethane elastomer, thermoplastic polyolefin elastomer, and thermoplastic polystyrene elastomer. Ionomer resin is particularly preferred. Ionomer resin is highly elastic. A golf ball 2 having an intermediate layer 6 containing ionomer resin has excellent rebound performance. Furthermore, this intermediate layer 6 achieves an appropriate hardness distribution for the ball consisting of the core 4 and the intermediate layer 6. When ionomer resin is used in combination with other resins, the main component of the base resin is the ionomer resin.

[0046] Preferred ionomer resins include binary ionomer resins and ternary ionomer resins. The binary ionomer resin is a binary copolymer of α-olefin and α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms. At least a portion of the carboxyl groups of this binary copolymer are neutralized with metal ions. The preferred binary ionomer resin contains 80% to 90% by mass of α-olefin and 10% to 20% by mass of α,β-unsaturated carboxylic acid. This binary ionomer resin exhibits excellent rebound properties. The ternary ionomer resin is a ternary copolymer of α-olefin, α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and α,β-unsaturated carboxylic acid ester having 2 to 22 carbon atoms. At least a portion of the carboxyl groups of this ternary copolymer are neutralized with metal ions. A preferred ternary ionomer resin contains 70% to 85% by mass of α-olefin, 5% to 30% by mass of α,β-unsaturated carboxylic acid, and 1% to 25% by mass of α,β-unsaturated carboxylic acid ester. This ternary ionomer resin exhibits excellent rebound properties. In binary and ternary ionomer resins, preferred α-olefins are ethylene and propylene, and preferred α,β-unsaturated carboxylic acids are acrylic acid and methacrylic acid. Preferred copolymers are binary copolymers of ethylene and acrylic acid, and binary copolymers of ethylene and methacrylic acid.

[0047] Examples of metal ions used for neutralizing carboxyl groups in ionomer resins include sodium ions, potassium ions, lithium ions, zinc ions, calcium ions, magnesium ions, aluminum ions, and neodymium ions. Neutralization may be performed with two or more metal ions. Sodium ions, zinc ions, lithium ions, and magnesium ions are particularly suitable from the viewpoint of the rebound performance and durability of the golf ball 2.

[0048] Specific examples of ionomer resins include Mitsui Dow Polychemicals' product names "Hymilan 1555", "Hymilan 1557", "Hymilan 1605", "Hymilan 1702", "Hymilan 1706", "Hymilan 1707", "Hymilan 1855", "Hymilan 1856", "Hymilan 8150", "Hymilan AM7311", "Hymilan AM7315", "Hymilan AM7317", "Hymilan AM7327", "Hymilan AM7329", and "Hymilan AM7337"; and DuPont's product names "Sarlyn 6120" and "Sarlyn 6910". Examples include "Sarlyn 7930", "Sarlyn 7940", "Sarlyn 8140", "Sarlyn 8150", "Sarlyn 8940", "Sarlyn 8945", "Sarlyn 9120", "Sarlyn 9150", "Sarlyn 9320", "Sarlyn 9910", "Sarlyn 9945", "Sarlyn AD8546", "HPF1000", and "HPF2000"; as well as ExxonMobil Chemicals' trade names "IOTEK7010", "IOTEK7030", "IOTEK7510", "IOTEK7520", "IOTEK8000", and "IOTEK8030". Two or more ionomer resins may be used in combination.

[0049] The ratio of ionomer resin to base resin in the intermediate layer 6 is preferably 60% by mass, more preferably 70% by mass or more, and particularly preferably 80% by mass or more. This ratio may also be 100% by mass.

[0050] [Additives] The resin composition of the intermediate layer 6 may contain appropriate amounts of colorants, fillers, dispersants, antioxidants, UV absorbers, light stabilizers, fluorescent agents, fluorescent whitening agents, etc. A typical filler is barium sulfate. When the hue of golf ball 2 is white, a typical colorant is titanium dioxide.

[0051] [thickness] The thickness Tm of the intermediate layer 6 is preferably 0.5 mm or more and 2.0 mm or less. Golf balls 2 with a thickness Tm of 0.5 mm or more have excellent rebound performance. From this viewpoint, a thickness Tm of 0.7 mm or more is more preferable, and 0.8 mm or more is particularly preferable. Golf balls 2 with a thickness Tm of 2.0 mm or less have excellent feel when hitting a driver shot. From this viewpoint, a thickness Tm of 1.5 mm or less is more preferable, and 1.3 mm or less is particularly preferable. The thickness Tm is measured directly below the land 12.

[0052] [hardness] The hardness Hm of the intermediate layer 6 is preferably between 50 and 90. Golf balls 2 with a hardness Hm of 50 or higher have excellent rebound performance. From this viewpoint, a hardness Hm of 60 or higher is more preferable, and 65 or higher is particularly preferable. Golf balls 2 with a hardness Hm of 90 or lower have excellent feel when struck. From this viewpoint, a hardness Hm of 80 or lower is more preferable, and 75 or lower is particularly preferable.

[0053] The hardness Hm of the intermediate layer 6 is measured in accordance with the specifications of "ASTM-D 2240-68". The hardness Hm is measured using a Shore D hardness tester attached to an automated hardness tester (product name "DigiTest II" by H. Barleys). For the measurement, a sheet approximately 2 mm thick, made of the same material as the intermediate layer 6 and formed by hot pressing, is used. Prior to the measurement, the sheet is stored at a temperature of 23°C for two weeks. At the time of measurement, three sheets are stacked on top of each other.

[0054] [Melt Flow Rate] The melt flow rate Mm of the resin composition for the intermediate layer 6 is preferably 3.0 g / 10 min or higher. The intermediate layer 6 can be easily molded from this resin composition. From this viewpoint, the melt flow rate Mm is more preferably 4.0 g / 10 min or higher, and particularly preferably 4.5 g / 10 min or higher.

[0055] [Bending stiffness] The bending stiffness Fm of the intermediate layer 6 is preferably 300 MPa or higher. A golf ball 2 with a bending stiffness Fm of 300 MPa or higher has excellent rebound performance. From this viewpoint, a bending stiffness Fm of 310 MPa or higher is more preferable, and 315 MPa or higher is particularly preferable. From the viewpoint of the feel of the golf ball 2 when struck, a bending stiffness Fm of 400 MPa or lower is preferable, 380 MPa or lower is more preferable, and 350 MPa or lower is particularly preferable.

[0056] [cover] The cover 8 is located outside the intermediate layer 6. In this embodiment, the cover 8 is in contact with the intermediate layer 6. The golf ball 2 may have an adhesive layer between the intermediate layer 6 and the cover 8. Through this adhesive layer, the cover 8 can be firmly bonded to the intermediate layer 6. The cover 8 is molded from a resin composition. In this embodiment, the cover 8 is molded from a thermoplastic resin composition.

[0057] [Base resin] Examples of base resins for the resin composition of the cover 8 include ionomer resin, thermoplastic polystyrene elastomer, thermoplastic polyester elastomer, thermoplastic polyamide elastomer, thermoplastic polyurethane elastomer, and thermoplastic polyolefin elastomer. Ionomer resin is particularly preferred. Ionomer resin is highly elastic. A golf ball 2 having a cover 8 containing ionomer resin has excellent rebound performance. This golf ball 2 has excellent flight performance in driver shots.

[0058] Ionomer resin may be used in combination with other resins. When used in combination, the ionomer resin is used as the main component of the base resin from the viewpoint of rebound performance. The ratio P(I) of ionomer resin to the total amount of 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 P(I) may also be 100% by mass.

[0059] The ionomer resin described above for the intermediate layer 6 can also be applied to the cover 8. In particular, zinc ion neutralized ionomer resin is preferred. In a cover 8 containing zinc ion neutralized ionomer resin, both low hardness and scratch resistance can be achieved. From this viewpoint, the ratio P(Zn) of zinc ion neutralized ionomer resin to the total amount of base resin is preferably 60% by mass or more, more preferably 80% by mass or more, and particularly preferably 85% by mass or more. This ratio P(Zn) may also be 100% by mass.

[0060] From a similar viewpoint, the ratio P(Zn / I) of zinc ion-neutralized ionomer resin to the total amount of ionomer resin is preferably 90% by mass or more, more preferably 95% by mass or more, and particularly preferably 98% by mass or more. This ratio P(Zn / I) may also be 100% by mass.

[0061] It is preferable that the resin composition of cover 8 includes a zinc ion neutralized ionomer resin and a zinc ion neutralized ionomer resin whose components are different from those of the zinc ion neutralized ionomer resin. A cover 8 with appropriate physical properties can be obtained from a resin composition in which two or more zinc ion neutralized ionomer resins are blended.

[0062] From the viewpoint of scratch resistance, it is preferable that the amount of sodium ion neutralized ionomer resin in the resin composition of cover 8 be small. The ratio P(Na) of sodium ion neutralized ionomer resin to the total amount of base resin is preferably 5% by mass or less. The ideal ratio P(Na) is 0% by mass.

[0063] Preferred resins that can be used in combination with ionomer resins include (1) A binary copolymer of an olefin and an α,β-unsaturated carboxylic acid, which is an unneutralized resin, and (2) A ternary copolymer of an olefin, an α,β-unsaturated carboxylic acid, and an α,β-unsaturated carboxylic acid ester, which is not neutralized. Examples include the following. These binary copolymers (1) and ternary copolymers (2) contribute to the fluidity of the molten resin composition. Covers 8 containing these binary copolymers (1) or ternary copolymers (2) have excellent moldability.

[0064] The ratio P(n) of the total amount of unneutralized binary copolymer resin (1) and unneutralized ternary copolymer resin (2) to the total amount of base resin is preferably 10% by mass or more and 40% by mass or less. Covers 8 with a ratio P(n) of 10% by mass or more have excellent moldability. From this viewpoint, this ratio P(n) is more preferably 13% by mass or more, and particularly preferably 15% by mass or more. Covers 8 with a ratio P(n) of 40% by mass or less have excellent rebound performance. From this viewpoint, this ratio P(n) is more preferably 30% by mass or less, and particularly preferably 25% by mass or less.

[0065] Specific examples of unneutralized binary copolymers (1) include Mitsui Dow Polychemicals' trade names "Nucrel N1050H", "Nucrel N2050H", "Nucrel N1110H", and "Nucrel N0200H", as well as Dow Chemical's trade name "Primacol 5980I". Specific examples of unneutralized ternary copolymers include Mitsui Dow Polychemicals' trade names "Nucrel AN4318" and "Nucrel AN4319", as well as Dow Chemical's trade names "Primacol AT310" and "Primacol AT320".

[0066] The resin composition of cover 8 may include a styrene block-containing thermoplastic elastomer along with the ionomer resin. The styrene block-containing thermoplastic elastomer may contribute to the low hardness of cover 8.

[0067] A styrene block-containing thermoplastic elastomer comprises a polystyrene block as a hard segment and a soft segment. A typical soft segment is a diene block. Examples of diene block compounds 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.

[0068] Styrene block-containing thermoplastic elastomers include 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. Examples of hydrogenated SBS include styrene-ethylene-butylene-styrene block copolymer (SEBS). Examples of hydrogenated SIS include styrene-ethylene-propylene-styrene block copolymer (SEPS). Examples of hydrogenated SIBS include styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS).

[0069] 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, and an olefin. The olefin component in this alloy is presumed to contribute to improved compatibility with other base resins. This alloy may contribute to the rebound performance of the golf ball 2. Olefins with 2 to 10 carbon atoms are preferred. Examples of suitable olefins include ethylene, propylene, butene, and pentene. Ethylene and propylene are particularly preferred.

[0070] Specific examples of polymer alloys include Mitsubishi Chemical's product names "Tefablock T3221C," "Tefablock T3339C," "Tefablock SJ4400N," "Tefablock SJ5400N," "Tefablock SJ6400N," "Tefablock SJ7400N," "Tefablock SJ8400N," "Tefablock SJ9400N," and "Tefablock SR04." Other specific examples of styrene block-containing thermoplastic elastomers include Daicel Chemical Industries' product name "Epofriend A1010" and Kuraray's product name "Septon HG-252."

[0071] [Additives] The resin composition of cover 8 may contain appropriate amounts of colorants, fillers, dispersants, antioxidants, UV absorbers, light stabilizers, fluorescent agents, fluorescent whitening agents, etc. A typical filler is barium sulfate. If the hue of golf ball 2 is white, a typical colorant is titanium dioxide.

[0072] [thickness] The thickness Tc of the cover 8 is preferably 0.50 mm or more and 2.00 mm or less. Golf balls 2 with a thickness Tc of 0.50 mm or more have excellent moldability and durability. From this viewpoint, a thickness Tc of 0.70 mm or more is more preferable, and 0.90 mm or more is particularly preferable. Golf balls 2 with a thickness Tc of 2.00 mm or less have excellent rebound performance. From this viewpoint, a thickness Tc of 1.50 mm or less is more preferable, and 1.20 mm or less is particularly preferable. The thickness Tc is measured directly below the land 12.

[0073] [hardness] The hardness Hc of the cover 8 is preferably between 40 and 50. Golf balls 2 with a hardness Hc of 40 or higher have excellent rebound performance. From this viewpoint, a hardness Hc of 42 or higher is more preferable, and 43 or higher is particularly preferable. Golf balls 2 with a hardness Hc of 50 or lower have excellent feel when putting. From this viewpoint, a hardness Hc of 48 or lower is more preferable, and 47 or lower is particularly preferable. The hardness Hc of the cover 8 is measured by the same method as the hardness Hm of the intermediate layer 6.

[0074] [Melt Flow Rate] The melt flow rate Mc of the resin composition for cover 8 is preferably 8.0 g / 10 min or higher. Cover 8 can be easily molded from this resin composition. From this viewpoint, the melt flow rate Mc is more preferably 9.0 g / 10 min or higher, and particularly preferably 10.0 g / 10 min or higher.

[0075] The melt flow rate Mm and melt flow rate Mc are measured in accordance with the provisions of "JIS K 7210-1:2014". The measurement conditions are as follows: Standard: Mass (Method A) Temperature: 190℃ Load: 2.16 kg Die: Standard As an example of a suitable device for measurement, Shimadzu Corporation's "Flow Tester CFT-100C" is cited.

[0076] The product of the melt flow rate Mc (g / 10min) and thickness Tc (mm) of the cover 8 (Mc*Tc) is preferably 10.0 or greater. A cover 8 with this product of 10.0 or greater can be easily molded. From this viewpoint, this product is more preferably 10.2 or greater, and particularly preferably 10.4 or greater.

[0077] [Bending stiffness] The bending stiffness Fc of the cover 8 is preferably 75 MPa or less. A golf ball 2 with a bending stiffness Fc of 75 MPa or less has excellent feel when putting. From this viewpoint, a bending stiffness Fc of 70 MPa or less is more preferable, and 65 MPa or less is particularly preferable. From the viewpoint of the rebound performance of the golf ball 2, a bending stiffness Fc of 40 MPa or more is preferable.

[0078] The bending stiffness Fm and bending stiffness Fc are measured in accordance with the provisions of "JIS K 7106". A test piece with a thickness of 2 mm, a width of 20 mm, and a length of 100 mm is used for measurement. Prior to measurement, the test piece is kept for 14 days in an environment with a temperature of 23 ± 2 °C and a relative humidity of 50 ± 5%. The measurement conditions are as follows: Temperature: 23±2℃ Relative humidity: 50±5% Support point distance: 50mm Bending speed: 60° / min Bending angles: 3°, 6°, 9°, and 12° A suitable testing device for measurement is the Olsen-type stiffness tester manufactured by Toyo Seiki Seisakusho. The measurement results are plotted on a graph where the load scale is on the vertical axis and the bending angle is on the horizontal axis. The slope of the linear approximation curve of this plot is determined, and this slope is multiplied by 8.7078 and then divided by the cube of the thickness (cm) of the test specimen to calculate the bending stiffness.

[0079] [Golf balls] The diameter of golf ball 2 is preferably between 40 mm and 45 mm. From the viewpoint of meeting the standards of the United States Golf Association (USGA), a diameter of 42.67 mm or more is particularly preferred. From the viewpoint of reducing air resistance, a diameter of 44 mm or less is more preferred, and 42.80 mm or less is particularly preferred.

[0080] The mass of golf ball 2 is preferably between 40g and 50g. From the viewpoint of obtaining high inertia, a mass of 44g or more is more preferable, and 45.00g or more is particularly preferable. From the viewpoint of satisfying USGA standards, a mass of 45.93g or less is particularly preferable.

[0081] The compression deformation amount C2 of the golf ball 2 is preferably 3.0 mm or more. A golf ball 2 with a compression deformation amount C2 of 3.0 mm or more has excellent feel when hitting the ball during putting. From this viewpoint, a compression deformation amount C2 of 3.2 mm or more is more preferable, and 3.3 mm or more is particularly preferable. From the viewpoint of rebound performance, a compression deformation amount C2 of 4.5 mm or less is preferable, 4.2 mm or less is more preferable, and 4.0 mm or less is particularly preferable.

[0082] The amount of compression deformation C2 is measured using the aforementioned YAMADA compression tester "SCH". In this tester, a golf ball 2 is placed on a rigid metal plate. A metal cylinder is gradually lowered toward the golf ball 2. The golf ball 2, trapped between the bottom of the cylinder and the rigid plate, deforms. The distance the cylinder travels from the initial load of 98N on the golf ball 2 to the final load of 1274N is measured. The cylinder's movement speed before the initial load is applied is 0.83 mm / s. The cylinder's movement speed from the initial load to the final load is 1.67 mm / s. [Examples]

[0083] [Example 1] Rubber composition G was obtained by kneading 100 parts by mass of high-cis polybutadiene (JSR's product name "BR-730"), 28.5 parts by mass of zinc acrylate (Nisshoku Techno Fine Chemical's product name "ZN-DA90S"), 10 parts by mass of zinc oxide (INDOLYSAGHT), 10.7 parts by mass of barium sulfate (Sakai Chemical's product name "BD"), 1.0 part by mass of dicumyl peroxide (NOF Corporation's product name "Perkmyl D"), 3.5 parts by mass of benzoic acid (Tokyo Chemical Industries), and 1.2 parts by mass of pentachlorothiophenol zinc salt (Fujifilm Wako Pure Chemical Industries' product name "PCTP-Zn"). This rubber composition G was placed in a mold consisting of an upper mold and a lower mold, both equipped with hemispherical cavities, and heated to obtain a core with a diameter of 38.6 mm. The crosslinking temperature was 160°C. The crosslinking time was 20 minutes. The hardness distribution of this core is shown in Table 1 below.

[0084] Resin composition 1 was obtained by kneading 20 parts by mass of ionomer resin (the aforementioned "Hymiran AM7329"), 80 parts by mass of another ionomer resin (the aforementioned "Hymiran AM7337"), 6 parts by mass of barium sulfate, and 4 parts by mass of titanium dioxide in a twin-screw compounding extruder. A core was placed in a mold consisting of an upper mold and a lower mold, each equipped with a hemispherical cavity. Molten resin composition 1 was injected around the core using an injection molding machine to form an intermediate layer. The thickness of this intermediate layer was 1.00 mm.

[0085] 80 parts by mass of ionomer resin (the aforementioned "Hymiran AM7327"), 10 parts by mass of another ionomer resin (the aforementioned "Hymiran 1557"), 10 parts by mass of copolymer (the aforementioned "Nucrel N1050H"), and 4 parts by mass of titanium dioxide were kneaded in a twin-screw extruder to obtain resin composition E. 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 equipped with a hemispherical cavity. Molten resin composition E was injected around the sphere using an injection molding machine to form a cover. The thickness of this cover was 1.05 mm.

[0086] A clear coating based on two-component curing polyurethane was applied around this cover to obtain the golf ball of Example 1, which had a diameter of approximately 42.7 mm and a mass of approximately 45.5 g.

[0087] [Examples 2-10 and Comparative Examples 1-10] Golf balls for Example 2-10 and Comparative Example 1-10 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 Table 6-9 below. The specifications of the core are shown in Tables 1 and 2 below. The composition of the intermediate layer is shown in Table 3 below. The composition of the cover is shown in Tables 4 and 5 below.

[0088] [Table 1]

[0089] [Table 2]

[0090] [Table 3]

[0091] [Table 4]

[0092] [Table 5]

[0093] The neutralized metal ions of the ionomer resins shown in Tables 4 and 5 are as follows: Hymilan 1855: Zinc Ion Hymilan AM7327: Zinc Ion Hymiran 1555: Sodium Ion Hymiran 1557: Zinc Ion

[0094] [Scratch resistance] A sand wedge (Sumitomo Rubber Industries' product name "XXIO 13 (2023 model)", shaft stiffness: R) was mounted on Golf Laboratory's swing machine. A golf ball was struck with this sand wedge at a head speed of 36 m / sec. The scratch resistance was assessed by visually inspecting the cover's appearance. The results are shown in Table 6-9 below.

[0095] [Moldability] The injection pressure of the injection molding machine during cover molding was set to 10% lower to obtain golf balls. The appearance of the covers was visually inspected to determine the presence or absence of voids. The results are shown in Table 6-9 below.

[0096] [Flight performance] A driver (W#1, Sumitomo Rubber Industries' product name "XXIO PRIME 12 (2023 model)", shaft stiffness: R) was mounted on Golf Laboratory's swing machine. A golf ball was struck with this driver at a head speed of 30 m / sec, and the distance from the launch point to the resting point was measured. The test was conducted under nearly no wind conditions. The average distance obtained from 12 measurements was calculated. Furthermore, this average value was ranked based on the following criteria. A: 155.0 yards or more B: 154.5 yards or more, less than 155.0 yards C: 154.0 yards or more, less than 154.5 yards D: Less than 154.0 yards These results are shown in Table 6-9 below.

[0097] [Ball feel] Ten golfers were asked to putt and their feedback on the feel of the ball was collected. Based on the number of golfers who answered "good feel," the golf balls were ranked according to the following criteria. A:8 or more people B: More than 6 people and less than 7 people C: More than 4 people and less than 5 people D: 3 or less people These results are shown in Table 6-9 below.

[0098] [comprehensive evaluation] The overall performance of the golf balls was rated according to the following criteria. A: Scratch resistance and moldability are "Good," and distance and feel are rated "A." B: Scratch resistance and moldability are "Good," and the distance evaluation and feel evaluation are not "C" and "D," but either the distance evaluation or the feel evaluation is "B." C: Scratch resistance and moldability are "Good," and the distance evaluation and feel evaluation are not "D," but either the distance evaluation or the feel evaluation is "C." D: Either the scratch resistance or moldability is "Bad," or the distance evaluation or feel evaluation is "D." These results are shown in Table 6-9 below.

[0099] [Table 6]

[0100] [Table 7]

[0101] [Table 8]

[0102] [Table 9]

[0103] As shown in Table 6-9, the golf balls of each embodiment exhibit excellent performance in various aspects. The superiority of the present invention is evident from these evaluation results.

[0104] [Disclosure items] Each of the following items discloses a preferred embodiment.

[0105] [Item 1] It comprises a core, an intermediate layer located outside the core, and a cover located outside the intermediate layer. In the graph plotting the Shore C hardness of the following points in the core described above: the center point, point P1 located 2.5 mm from the center point, point P2 located 5.0 mm from the center point, point P4 located 10.0 mm from the center point, point P5 located 12.5 mm from the center point, and point P6 located 15.0 mm from the center point, The slope A1 of the line connecting the above center point and point P1 is 1.00 or greater. The slope A2 of the line connecting point P1 and point P2 is 1.00 or greater. The slope A5 of the line connecting point P4 and point P5 is 1.50 or greater. The slope A6 of the line connecting point P5 and point P6 is 1.50 or greater. The difference (Hs-Ho) between the Shore C hardness Hs of the surface of the core and the Shore C hardness Ho of the center point is 30 or more. The material of the above intermediate layer is a resin composition mainly composed of ionomer resin. The material of the above cover is a resin composition mainly composed of ionomer resin. In the resin composition of the above cover, the ratio P(I) of ionomer resin to the total amount of base resin is 60% by mass or more. In the resin composition of the above cover, the ratio P(Na) of sodium ion neutralized ionomer resin to the total amount of the base resin is 5% by mass or less. The product of the melt flow rate Mc (g / 10min) and thickness Tc (mm) of the above cover (Mc*Tc) is 10.0 or greater. A golf ball in which the bending rigidity Fc of the cover described above is 75 MPa or less.

[0106] [Item 2] The base resin of the resin composition of the above cover contains a zinc ion neutralized ionomer resin. The golf ball described in item 1, wherein the ratio P(Zn) of the zinc ion neutralized ionomer resin to the total amount of the base resin is 60% by mass or more.

[0107] [Item 3] The base resin of the resin composition of the above cover contains a zinc ion neutralized ionomer resin. The golf ball according to item 1, wherein the ratio P(Zn / I) of the zinc ion neutralized ionomer resin to the total amount of the ionomer resin in the resin composition is 90% by mass or more.

[0108] [Item 4] The golf ball according to item 2 or 3, wherein the base resin of the resin composition of the cover comprises a zinc monoion neutralized ionomer resin and a zinc diionion neutralized ionomer resin.

[0109] [Item 5] The base resin of the resin composition of the above cover is (1) A binary copolymer of an olefin and an α,β-unsaturated carboxylic acid, which is an unneutralized resin, or (2) A ternary copolymer of an olefin, an α,β-unsaturated carboxylic acid, and an α,β-unsaturated carboxylic acid ester, which is not neutralized. It includes, A golf ball according to any one of items 1 to 4, wherein the ratio P(n) of the total amount of the binary copolymer resin (1) and the ternary copolymer resin (2) to the total amount of the base resin is 10% by mass or more and 40% by mass or less.

[0110] [Item 6] A golf ball as described in any of items 1 to 5, wherein the melt flow rate Mc is 8.0 g / 10 min.

[0111] [Item 7] A golf ball described in any of items 1 to 6, with a Shore D hardness of 40 or more and 50 or less on the cover.

[0112] [Item 8] A golf ball as described in any of items 1 to 7, wherein the bending stiffness Fm of the above-mentioned intermediate layer is 300 MPa or more.

[0113] [Item 9] A golf ball as described in any of items 1 to 8, wherein the compressive deformation amount C1 of the core measured under the conditions of an initial load of 98N and a final load of 1274N is 4.3 mm or more, and the compressive deformation amount C2 of the golf ball measured under the same conditions is 3.3 mm or more. [Industrial applicability]

[0114] The golf balls described above are suitable for playing on the golf course, practicing at the driving range, etc. [Explanation of Symbols]

[0115] 2. Golf balls 4 cores 6. Middle Class 8. Cover 10... Dimples 12...land

Claims

1. It comprises a core, an intermediate layer located outside the core, and a cover located outside the intermediate layer. In the graph plotting the Shore C hardness of the following points in the core described above: the center point, point P1 at a distance of 2.5 mm from the center point, point P2 at a distance of 5.0 mm from the center point, point P4 at a distance of 10.0 mm from the center point, point P5 at a distance of 12.5 mm from the center point, and point P6 at a distance of 15.0 mm from the center point, The slope A1 of the line connecting the above center point and point P1 is 1.00 or greater. The slope A2 of the line connecting point P1 and point P2 is 1.00 or greater. The slope A5 of the line connecting point P4 and point P5 is 1.50 or greater. The slope A6 of the line connecting point P5 and point P6 is 1.50 or greater. The difference between the Shore C hardness Hs of the surface of the core and the Shore C hardness Ho of the center point (Hs - Ho) is 30 or more. The material of the above intermediate layer is a resin composition mainly composed of ionomer resin. The material of the above cover is a resin composition mainly composed of ionomer resin. In the resin composition of the above cover, the ratio P(I) of ionomer resin to the total amount of base resin is 60% by mass or more. In the resin composition of the above cover, the ratio P(Na) of sodium ion neutralized ionomer resin to the total amount of the base resin is 5% by mass or less. The product of the melt flow rate Mc (g / 10min) and thickness Tc (mm) of the above cover (Mc * Tc) is 10.0 or greater. A golf ball in which the bending rigidity Fc of the cover described above is 75 MPa or less.

2. The base resin of the resin composition of the above cover contains a zinc ion neutralized ionomer resin. The golf ball according to claim 1, wherein the ratio P(Zn) of the zinc ion neutralized ionomer resin to the total amount of the base resin is 60% by mass or more.

3. The base resin of the resin composition of the above cover contains a zinc ion neutralized ionomer resin. The golf ball according to claim 1, wherein the ratio P(Zn / I) of the zinc ion neutralized ionomer resin to the total amount of the ionomer resin in the resin composition is 90% by mass or more.

4. The golf ball according to claim 2 or 3, wherein the base resin of the resin composition of the cover comprises a zinc monoion neutralized ionomer resin and a zinc diionion neutralized ionomer resin.

5. The base resin of the resin composition of the above cover is (1) A binary copolymer of an olefin and an α,β-unsaturated carboxylic acid, which is an unneutralized resin. or (2) A ternary copolymer of an olefin, an α,β-unsaturated carboxylic acid, and an α,β-unsaturated carboxylic acid ester, which is not neutralized. It includes, The golf ball according to claim 1 or 2, wherein the ratio P(n) of the total amount of the binary copolymer resin (1) and the ternary copolymer resin (2) to the total amount of the base resin is 10% by mass or more and 40% by mass or less.

6. The golf ball according to claim 1 or 2, wherein the melt flow rate Mc is 8.0 g / 10 min.

7. The golf ball according to claim 1 or 2, wherein the Shore D hardness of the cover is 40 or more and 50 or less.

8. The golf ball according to claim 1 or 2, wherein the bending rigidity Fm of the intermediate layer is 300 MPa or more.

9. The golf ball according to claim 1 or 2, wherein the compressive deformation amount C1 of the core measured under the conditions of an initial load of 98 N and a final load of 1274 N is 4.3 mm or more, and the compressive deformation amount C2 of the golf ball measured under the same conditions is 3.3 mm or more.

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