Golf ball

Abstract

To provide a golf ball that has improved controllability in an iron shot.SOLUTION: A golf ball 2 includes a spherical core 4, a middle layer 6, and an outermost layer cover 8 provided with a plurality of dimples 10. The spherical core 4 is formed of a rubber composition containing polybutadiene rubber and a predetermined amount of butyl rubber. Slab hardness of a middle layer composition forming the middle layer 6 is greater than the slab hardness of a cover composition forming the outermost layer cover 8, and lower part total volume of the plurality of dimples 10 is more than or equal to 365 mm3. In the outermost layer cover 8, occupancy occupied by a total area of the plurality of dimples 10 is 75% or more in a surface area of a virtual ball when it is assumed that the plurality of dimples does not exist.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Iron shots are shots to carry the ball to the green or a desired location, and the important thing is not the distance it travels, but the control it has to be able to hit the ball the desired distance. The distance a golf ball travels is the sum of the distance it travels from when it is hit until it lands on the ground (the carry) and the distance it travels from when it lands until it stops (the run). Therefore, in order to control the distance a golf ball travels, it is necessary to control both the run and the carry.

[0003] Here, the face of the 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. The higher the backspin speed, the smaller the run. In other words, by using a golf ball with a high backspin speed, the player can easily stop the golf ball at the target point. Therefore, a golf ball with excellent spin performance has high controllability.

[0004] Conventionally, golf balls with improved controllability have been proposed. For example, Patent Document 1 discloses a golf ball having a diameter in the range of about 0.015 to about 0.900 inches and a specific gravity in the range of about 1.18 to about 5.00 g / cc (SG inner ), and (ii) an inner core having a thickness ranging from about 0.100 to about 0.600 inches and a specific gravity ranging from about 0.080 to about 1.20 g / cc (SG intermediate ), and (iii) an intermediate core layer having a thickness in the range of about 0.010 to about 0.200 inches and a specific gravity of about 1.18 to about 5.00 g / cc (SG outer) and an outer core layer in the range of SG inner SG intermediate Bigger and SG intermediate SG outer A golf ball having a smaller, multi-layer core and a cover having at least one layer has been disclosed (see Patent Document 1 (claim 1, paragraph 0030)). Furthermore, Patent Documents 2 and 3 disclose golf balls in which butyl rubber is used as the material constituting the core (see Patent Document 2 (Claim 2) and Patent Document 3 (Claim 4)). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2013-39361 A [Patent Document 2] Japanese Patent Publication No. 63-54181 [Patent Document 3] Japanese Patent Application Publication No. 60-92780 Summary of the Invention [Problem to be solved by the invention]

[0006] The run (rolling distance) of an iron shot can be controlled by improving the spin performance of the golf ball and increasing the amount of backspin. However, as the amount of backspin increases, the ball will fly up and the highest point of the ball will become higher, making the golf ball more susceptible to the effects of wind. However, it is difficult for average golfers to read the wind, making it difficult to control the flight distance of an iron shot. The present invention has been made in consideration of the above circumstances, and has an object to provide a golf ball which provides improved controllability on iron shots. [Means for solving the problem]

[0007] The golf ball of the present invention, which has been able to solve the above problems, has a spherical core, an intermediate layer covering the spherical core, and an outermost cover layer located outside the intermediate layer and having a plurality of dimples formed thereon, the spherical core being formed from a rubber composition containing a base rubber, a co-crosslinking agent, and a crosslinking initiator, the base rubber containing polybutadiene rubber and butyl rubber, the butyl rubber content in 100% by mass of the base rubber being 10% by mass to 60% by mass, the intermediate layer composition forming the intermediate layer having a slab hardness greater than a slab hardness of a cover composition forming the outermost cover, and a total volume below the plurality of dimples being 365 mm 3 The outermost cover is characterized in that the total area of ​​the plurality of dimples occupies 75% or more of the surface area of ​​a virtual sphere if the plurality of dimples did not exist.

[0008] The golf ball of the present invention uses a predetermined amount of butyl rubber in the base rubber forming the spherical core, controls the hardness difference between the intermediate layer and the cover, and controls the total lower volume and surface coverage of the dimples in the outermost cover layer, thereby increasing the spin rate on iron shots and lowering the peak height during flight. As a result, the golf ball of the present invention has a reduced rolling distance on iron shots and excellent controllability. Effect of the Invention

[0009] The golf ball of the present invention is excellent in controllability upon iron shots. [Brief description of the drawings]

[0010] [Figure 1] 1 is a partially cutaway cross-sectional view showing a golf ball according to an embodiment of the present invention. [Diagram 2] FIG. 2 is an enlarged cross-sectional view of a dimple formed on the outermost cover layer. [Diagram 3] FIG. 2 is a front view of dimple patterns Nos. I to VI formed on the outermost cover layer. [Figure 4]FIG. 2 is a plan view of dimple patterns Nos. I to VI formed on the outermost cover layer. [Diagram 5] FIG. 7 is a front view of dimple pattern No. VII formed on the outermost cover layer. [Figure 6] FIG. 7 is a plan view of dimple pattern No. VII formed on the outermost cover layer. [Figure 7] FIG. 8 is a front view of dimple pattern No. VIII formed on the outermost cover layer. [Figure 8] FIG. 8 is a plan view of dimple pattern No. VIII formed on the outermost cover layer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The golf ball of the present invention has a spherical core, a mid layer encasing the spherical core, and an outermost cover located outside the mid layer and having a plurality of dimples formed thereon.

[0012] 1 has a spherical core 4, an intermediate layer 6 that encases the core 4, and an outermost cover layer 8 that is positioned 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 outermost cover layer 8, but these layers are omitted from the illustration.

[0013] (Spherical core) The spherical core is formed from a rubber composition containing a base rubber, a co-crosslinking agent, and a crosslinking initiator.

[0014] The base rubber contains polybutadiene rubber and butyl rubber.

[0015] The polybutadiene rubber is preferably a high-cis polybutadiene having cis-1,4-bonds in an amount of 40% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more, and further preferably 95% by mass or more.

[0016] The high-cis polybutadiene preferably has a 1,2-vinyl bond content of 2.0% by mass or less, more preferably 1.7% by mass or less, and further preferably 1.5% by mass or less.

[0017] The high-cis polybutadiene is preferably one synthesized using a rare earth element catalyst. In particular, the use of a neodymium-based catalyst using a neodymium compound, which is a lanthanum series rare earth element compound, is preferred because it can produce a polybutadiene rubber having a high content of 1,4-cis bonds and a low content of 1,2-vinyl bonds with excellent polymerization activity.

[0018] The Mooney viscosity (ML 1+4 (100°C)) is preferably 30 or more, more preferably 32 or more, even more preferably 35 or more, and is preferably 140 or less, more preferably 120 or less, even more preferably 100 or less, and most preferably 55 or less. The Mooney viscosity (ML 1+4 (100°C) is a value measured in accordance with JIS K6300 using an L rotor with a preheating time of 1 minute, rotor rotation time of 4 minutes, and at 100°C.

[0019] The molecular weight distribution Mw / Mn (Mw: weight average molecular weight, Mn: number average molecular weight) of the high cis polybutadiene is preferably 2.0 or more, more preferably 2.2 or more, even more preferably 2.4 or more, and most preferably 2.6 or more, and is preferably 6.0 or less, more preferably 5.0 or less, even more preferably 4.0 or less, and most preferably 3.0 or less. The molecular weight distribution is measured by gel permeation chromatography (manufactured by Tosoh Corporation, "HLC-8120GPC") using a differential refractometer as a detector under the conditions of column: GMHHXL (manufactured by Tosoh Corporation), column temperature: 40°C, and mobile phase: tetrahydrofuran, and is calculated as a standard polystyrene equivalent value.

[0020] The content of polybutadiene rubber in the base rubber is preferably 30% by mass or more, more preferably 35% by mass or more, and even more preferably 40% by mass or more, and is preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less.

[0021] The butyl rubber is a copolymer of isobutylene and isoprene. The degree of unsaturation of the butyl rubber is preferably 0.6 mol % or more, more preferably 0.8 mol % or more, and even more preferably 1.0 mol % or more, and is preferably 3.5 mol % or less, more preferably 3.3 mol % or less, and even more preferably 3.1 mol % or less.

[0022] The Mooney viscosity (ML 1+8 (125°C)) is preferably 28 or more, more preferably 30 or more, and even more preferably 32 or more, and is preferably 60 or less, more preferably 58 or less, and even more preferably 56 or less. Note that the Mooney viscosity (ML 1+8 (125°C) is the value measured using an L rotor with a preheating time of 1 minute, rotor rotation time of 8 minutes, and at 125°C.

[0023] The content of the butyl rubber in the base rubber is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more, and is preferably 60% by mass or less, more preferably 55% by mass or less, and even more preferably 50% by mass or less. If the content of the butyl rubber is within the above range, it affects the deformation inside the spherical core upon impact, the spin amount upon iron shots increases, and the initial velocity of the ball decreases.

[0024] The mass ratio of polybutadiene rubber to butyl rubber (polybutadiene rubber / butyl rubber) in the base rubber is preferably 40 / 60 or more, more preferably 45 / 55 or more, and even more preferably 50 / 50 or more, and is preferably 90 / 10 or less, more preferably 85 / 15 or less, and even more preferably 80 / 20 or less.

[0025] The base rubber may contain only polybutadiene rubber and butyl rubber, or may contain other rubbers. Examples of the other rubbers include natural rubber, polyisoprene rubber, styrene-butadiene rubber, and ethylene-propylene-diene rubber. When the base rubber contains the other rubbers, the total content of the polybutadiene rubber and the butyl rubber in the base rubber is preferably 75% by mass or more, more preferably 80% by mass or more, and even more preferably 85% by mass or more.

[0026] The co-crosslinking agent has the effect of crosslinking rubber molecules by graft polymerization with the base rubber molecular chain. The co-crosslinking agent may be used alone or in combination of two or more. The co-crosslinking agent is preferably an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and / or a metal salt thereof. Examples of the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms include acrylic acid, methacrylic acid, fumaric acid, maleic acid, and crotonic acid.

[0027] Examples of the metal constituting the metal salt of the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms 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; and other ions such as tin and zirconium. The metal components can be used alone or in combination of two or more. Among these, divalent metals such as magnesium, calcium, zinc, barium, and cadmium are preferred as the metal components. This is because the use of a divalent metal salt of an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms facilitates the formation of metal crosslinks between rubber molecules. In particular, zinc acrylate is preferred as the divalent metal salt because it increases the resilience of the resulting golf ball. The α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and / or its metal salt may be used alone or in combination of two or more.

[0028] The content of the co-crosslinking agent may be appropriately adjusted depending on the desired hardness of the spherical core. The content of the co-crosslinking agent is preferably 15 parts by mass or more, more preferably 20 parts by mass or more, and even more preferably 25 parts by mass or more, and is preferably 50 parts by mass or less, more preferably 45 parts by mass or less, and even more preferably 35 parts by mass or less, based on 100 parts by mass of the base rubber.

[0029] The crosslinking initiator is blended to crosslink the base rubber component. As the crosslinking initiator, an organic peroxide is suitable. Specific examples of the organic peroxide 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. These organic peroxides may be used alone or in combination of two or more. Among these, dicumyl peroxide is preferably used.

[0030] The content of the crosslinking initiator may be appropriately adjusted depending on the desired hardness of the spherical core. The content of the crosslinking initiator is preferably 0.2 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 0.7 parts by mass or more, and is preferably 5.0 parts by mass or less, more preferably 2.5 parts by mass or less, and even more preferably 2.0 parts by mass or less, based on 100 parts by mass of the base rubber.

[0031] When the rubber composition contains only an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms as a co-crosslinking agent, it is preferable that the rubber composition further contains a metal compound. By neutralizing the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms in the rubber composition with a metal compound, substantially the same effect as when a metal salt of an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms is used as a co-crosslinking agent can be obtained. In addition, when an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and its metal salt are used in combination as a co-crosslinking agent, a metal compound may be used.

[0032] The metal compound is not particularly limited as long as it can neutralize the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms in the rubber composition. Examples of the metal compound include metal hydroxides such as magnesium hydroxide, zinc hydroxide, calcium hydroxide, sodium hydroxide, lithium hydroxide, potassium hydroxide, and copper hydroxide; metal oxides such as magnesium oxide, calcium oxide, zinc oxide, and copper oxide; and metal carbonates such as magnesium carbonate, zinc carbonate, calcium carbonate, sodium carbonate, lithium carbonate, and potassium carbonate. The metal compound is preferably a divalent metal compound, and more preferably a zinc compound. This is because the divalent metal compound reacts with the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms to form a metal bridge. These metal compounds may be used alone or in combination of two or more kinds.

[0033] The rubber composition may further contain an organic sulfur compound. The organic sulfur compound improves the resilience of the spherical core. The organic sulfur compound is not particularly limited as long as it is an organic compound having a sulfur atom in the molecule, and examples thereof include organic compounds having a thiol group (-SH) or a polysulfide bond (-SS-, -SSS-, or -SSSS-) having 2 to 4 sulfur groups, or metal salts thereof (-SM, -SMS-, etc., where M is a metal atom). The organic sulfur compounds can be used alone or in combination of two or more kinds.

[0034] Examples of the organic sulfur compounds include thiophenols, thionaphthols, polysulfides, thiurams, thiocarboxylic acids, dithiocarboxylic acids, sulfenamides, dithiocarbamates, thiazoles, etc. As the organic sulfur compounds, diphenyl disulfides (e.g., diphenyl disulfide, bis(pentabromophenyl) disulfide), thiophenols, and thionaphthols (e.g., 2-thionaphthol) can be suitably used.

[0035] The content of the organic sulfur compound may be appropriately adjusted depending on the desired resilience performance of the spherical core. The content of the organic sulfur compound is, for example, preferably at least 0.05 parts by mass, more preferably at least 0.1 parts by mass, and preferably at most 5.0 parts by mass, more preferably at most 3.0 parts by mass, per 100 parts by mass of the base rubber.

[0036] The rubber composition may further contain a carboxylic acid and / or a metal salt thereof. The carboxylic acid and / or a metal salt thereof is preferably a carboxylic acid having 1 to 30 carbon atoms and / or a salt thereof. The carboxylic acid may be either an aliphatic carboxylic acid (saturated fatty acid, unsaturated fatty acid) or an aromatic carboxylic acid (benzoic acid, etc.). The amount of the carboxylic acid and / or a metal salt thereof is preferably 1 part by mass or more and 40 parts by mass or less per 100 parts by mass of the base rubber.

[0037] The rubber composition may contain additives such as a filler for adjusting the weight, an antioxidant, a peptizer, and a softener, as required.

[0038] The filler used in the rubber composition is mainly used as a weight adjusting agent for adjusting the weight of the final golf ball product, and may be added as needed. Examples of the filler include inorganic fillers such as barium sulfate, calcium carbonate, magnesium oxide, tungsten powder, and molybdenum powder.

[0039] The rubber composition is obtained by kneading the base rubber, the co-crosslinking agent, the crosslinking initiator, and other components that are mixed as necessary. The kneading method is not particularly limited, and may be performed using a known kneading machine such as a kneading roll, a Banbury mixer, or a kneader.

[0040] The spherical core can be molded, for example, by hot pressing the rubber composition for the core. The hot press molding conditions for the rubber composition for the core may be appropriately set depending on the rubber composition, but it is usually preferable to heat the rubber composition at 130°C to 200°C for 10 to 60 minutes, or to heat the rubber composition at 130°C to 150°C for 20 to 40 minutes, and then heat the rubber composition at 160°C to 180°C for 5 to 15 minutes in two stages.

[0041] The diameter of the spherical core is preferably 34.8 mm or more, more preferably 36.8 mm or more, even more preferably 38.0 mm or more, and is preferably 42.2 mm or less, more preferably 41.8 mm or less, even more preferably 41.2 mm or less, and most preferably 40.8 mm or less.

[0042] When the diameter of the spherical core is 34.8 mm to 42.2 mm, the amount of compressive deformation (the amount of shrinkage of the spherical core in the compressive direction) from when an initial load of 98 N is applied to when a final load of 1275 N is applied is preferably 2.0 mm or more, more preferably 2.5 mm or more, even more preferably 3.0 mm or more, and is preferably 5.0 mm or less, more preferably 4.5 mm or less, even more preferably 4.0 mm or less. If the amount of compressive deformation is within the above range, the hitting feeling is better.

[0043] The spherical core has a central hardness (H0), a hardness at a point 2.5 mm away from the center of the spherical core in the radial direction (H 2.5 ), and the hardness (H 5.0 ), and the hardness (H 7.5 ), and the hardness (H 10 ), and the hardness (H 12.5 ), and the hardness (H 15 ) but H0 <H 2.5 <H 5.0 <H 7.5 <H 10 <H 12.5 <H15 and the central hardness (H0) and the hardness at a point 10 mm away from the center of the spherical core in the radial direction (H 10 ) and hardness difference (H 10 -H0) is preferably equal to or greater than 10 in Shore C hardness. When the hardness distribution of the spherical core satisfies the above relationship, the spherical core deforms smoothly upon impact and the shear force upon iron shots is efficiently converted into spin, resulting in good controllability.

[0044] The spherical core has a center hardness (H0) and a hardness (H 10 ) and hardness difference (H 10 -H0) is preferably 10 or more, more preferably 12 or more, and even more preferably 14 or more, in Shore C hardness, and is preferably 25 or less, more preferably 23 or less, and even more preferably 21 or less.

[0045] The hardness (H 5.0 ) and the hardness (H 12.5 ) and hardness difference (H 12.5 -H 5.0 ) is preferably 5 or more, more preferably 6 or more, and even more preferably 7 or more in Shore C hardness. 12.5 -H 5.0 If the difference in hardness (H) is 5 or more on the Shore C scale, the ball will have a low spin rate on driver shots, resulting in good flight distance performance. 12.5 -H 5.0 ) is preferably 18 or less, more preferably 17 or less, and further preferably 16 or less in Shore C hardness.

[0046] The spherical core has a center hardness (H0) of preferably 48 or more, more preferably 49 or more, and even more preferably 50 or more, in Shore C hardness, and is preferably 60 or less, more preferably 59 or less, and even more preferably 58 or less.

[0047] The hardness (H 5.0 ) is preferably 56 or more, more preferably 58 or more, and even more preferably 60 or more, in Shore C hardness, and is preferably 72 or less, more preferably 70 or less, and even more preferably 68 or less.

[0048] The hardness (H 10 ) is preferably 62 or more, more preferably 64 or more, and even more preferably 66 or more, in Shore C hardness, and is preferably 78 or less, more preferably 76 or less, and even more preferably 74 or less.

[0049] The hardness (H 12.5 ) is preferably 66 or more, more preferably 68 or more, and even more preferably 70 or more, in Shore C hardness, and is preferably 80 or less, more preferably 79 or less, and even more preferably 78 or less.

[0050] The hardness (H 15 ) is preferably 70 or more, more preferably 72 or more, and even more preferably 74 or more, in Shore C hardness, and is preferably 85 or less, more preferably 83 or less, and even more preferably 81 or less.

[0051] The spherical core has a surface hardness (Hs) of preferably 70 or more, more preferably 72 or more, and even more preferably 74 or more, in Shore C hardness, and preferably 85 or less, more preferably 83 or less, and even more preferably 81 or less.

[0052] (Middle class) The golf ball of the present invention has an intermediate layer that encases the spherical core.

[0053] The intermediate layer composition constituting the intermediate layer preferably has a slab hardness (Hm) of 50 or more, more preferably 53 or more, and even more preferably 55 or more, in Shore D hardness. If the slab hardness (Hm) is 50 or more, the distance performance during driver shots is good. Furthermore, the slab hardness (Hm) is preferably 74 or less, more preferably 72 or less, and even more preferably 70 or less, in Shore D hardness. If the slab hardness (Hm) is 74 or less, a good hitting feeling is obtained during impact. When a plurality of intermediate layers are provided, the material hardness Hm is the material hardness of the intermediate layer composition constituting the outermost intermediate layer.

[0054] The thickness (Tm) of the intermediate layer is preferably 0.8 mm or more, more preferably 0.9 mm or more, and even more preferably 1.0 mm or more, and is preferably 3.0 mm or less, more preferably 2.6 mm or less, and even more preferably 2.2 mm or less. When there are multiple intermediate layers, the total thickness of all the intermediate layers is defined as the thickness Tm of the intermediate layers.

[0055] (Outermost cover) The golf ball of the present invention has an outermost cover layer located outside the intermediate layer.

[0056] The cover composition constituting the outermost cover layer preferably has a slab hardness (Hc) of 40 or less, more preferably 38 or less, and even more preferably 36 or less, in Shore D hardness. If the slab hardness (Hc) is 40 or less, the shot feeling during approach shots is good. Furthermore, the slab hardness (Hc) is preferably 20 or more, more preferably 22 or more, and even more preferably 24 or more, in Shore D hardness. If the slab hardness (Hc) is 20 or more, the spin rate during driver shots is not too high, and the flight distance performance is good.

[0057] The intermediate layer composition forming the intermediate layer preferably has a slab hardness (Hm) greater than the slab hardness (Hc) of the cover composition forming the outermost cover layer. If the slab hardness (Hm) is greater than the slab hardness (Hc), the controllability of the golf ball can be improved and the amount of spin on driver shots can be reduced.

[0058] The hardness difference (Hm-Hc) between the slab hardness (Hm) and the slab hardness (Hc), in Shore D hardness, is preferably more than 0, more preferably 5 or more, more preferably 10 or more, and is preferably 50 or less, more preferably 48 or less, and even more preferably 46 or less.

[0059] The thickness (Tc) of the outermost cover layer is preferably 0.4 mm or more, more preferably 0.5 mm or more, and even more preferably 0.6 mm or more; and is preferably 1.0 mm or less, more preferably 0.9 mm or less, and even more preferably 0.8 mm or less.

[0060] (Cover composition, intermediate layer composition) The outermost cover layer and the intermediate layer are preferably formed from a resin composition containing a base resin.

[0061] Examples of base resins used in the resin compositions forming the outermost cover layer and the intermediate layer include ionomer resins, urethane resins (thermoplastic polyurethane elastomers, thermosetting polyurethane elastomers), thermoplastic styrene elastomers, thermoplastic polyamide elastomers, and thermoplastic polyester elastomers.

[0062] Examples of the ionomer resin include a binary ionomer resin in which at least a portion of the carboxyl groups in a binary copolymer of an olefin and an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms are neutralized with a metal ion; a ternary ionomer resin in which at least a portion of the carboxyl groups in a ternary copolymer of an olefin, an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms, and an α,β-unsaturated carboxylic acid ester are neutralized with a metal ion; and a mixture thereof.

[0063] Examples of the binary ionomer resin include Himilan (registered trademark) 1555 (Na), 1557 (Zn), 1605 (Na), 1706 (Zn), 1707 (Na), AM7311 (Mg), AM7329 (Zn), and AM7337 (manufactured by Mitsui Dow Polychemicals); Surlyn (registered trademark) 8945 (Na), 9945 (Zn), 8140 (Na), 8150 (Na), 9120 (Zn), 9150 (Zn), 6910 (Mg), 6120 (Mg), 7930 (Li), 7940 (Li), and AD8546 (Li) (manufactured by DuPont); and Iotek (registered trademark) 8000 (Na), 8030 (Na), 7010 (Zn), and 7030 (Zn) (manufactured by ExxonMobil Chemicals).

[0064] Examples of the ternary ionomer resin include Himilan AM7327(Zn), 1855(Zn), 1856(Na), and AM7331(Na) (manufactured by Mitsui Dow Polychemicals); Surlyn 6320(Mg), 8120(Na), 8320(Na), 9320(Zn), 9320W(Zn), HPF1000(Mg), and HPF2000(Mg) (manufactured by DuPont); and Iotec 7510(Zn), 7520(Zn) (manufactured by ExxonMobil Chemicals). Note that Na, Zn, Li, Mg, and the like written in parentheses after the trade name of the ionomer resin indicate the metal species of these neutralizing metal ions.

[0065] The urethane resin has a urethane bond in its molecule. The urethane bond can be formed by a reaction between a polyol and a polyisocyanate. The polyol, which is a raw material for the urethane bond, has a plurality of hydroxyl groups, and a low molecular weight polyol and a high molecular weight polyol can be used.

[0066] Specific examples of the thermoplastic polyurethane elastomer include Elastollan (registered trademark) NY80A, NY84A, NY88A, NY95A, ET885, and ET890 (manufactured by BASF Japan Ltd.).

[0067] As the thermoplastic styrene-based elastomer, a thermoplastic elastomer containing a styrene block can be preferably used. The styrene block-containing thermoplastic elastomer has a polystyrene block as a hard segment and a soft segment.

[0068] 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).

[0069] Examples of the thermoplastic styrene-based elastomer include TEFABLOC (registered trademark) T3221C, T3339C, SJ4400N, SJ5400N, SJ6400N, SJ7400N, SJ8400N, SJ9400N, and SR04 (manufactured by Mitsubishi Chemical Corporation).

[0070] The resin composition (cover composition) forming the outermost cover layer preferably contains a urethane resin and / or an ionomer resin as a base resin, and more preferably contains a urethane resin. When the outermost cover layer contains a urethane resin as a base resin, the spin performance of the golf ball is further improved, and the spin amount in approach shots in particular is further improved.

[0071] When the cover composition contains a urethane resin as a base resin, the content of the urethane resin in the base resin is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more. The cover composition may contain only a urethane resin (preferably a thermoplastic urethane elastomer) as a base resin. When the cover composition contains an ionomer resin as a base resin, the content of the ionomer resin in the base resin is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more. When the ionomer resin is contained, it is also preferable to use a thermoplastic styrene elastomer in combination.

[0072] The resin composition forming the intermediate layer (intermediate layer composition) preferably contains an ionomer resin as a base resin. When the intermediate layer composition contains an ionomer resin, the resilience performance of the golf ball is improved, and the resilience performance in driver shots is particularly excellent. The content of the ionomer resin in the base resin of the intermediate layer composition is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more. When the ionomer resin is contained, it is also preferable to use a thermoplastic styrene elastomer in combination.

[0073] The resin composition forming the outermost cover layer and the intermediate layer may contain, in addition to the base resin described above, pigment components such as white pigments (e.g., titanium oxide), blue pigments, and red pigments, weight adjusters such as zinc oxide, calcium carbonate, and barium sulfate, dispersants, antioxidants, ultraviolet absorbers, light stabilizers, fluorescent materials, or fluorescent brighteners.

[0074] The content of the white pigment (e.g., titanium oxide) is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and preferably 10 parts by mass or less, more preferably 8 parts by mass or less, based on 100 parts by mass of the base resin. By making the content of the white pigment 0.5 parts by mass or more, it is possible to impart hiding power to the intermediate layer and the outermost cover layer. In addition, if the content of the white pigment is 10 parts by mass or less, the durability of the obtained intermediate layer and the outermost cover layer is good.

[0075] The method for forming the intermediate layer is not particularly limited, but examples include a method in which the intermediate layer composition is first molded into a hemispherical half shell, two of which are used to encase a spherical core and then pressure molded, or a method in which the intermediate layer composition is directly injection molded onto the spherical core to encase the sphere.

[0076] Methods for molding the cover include, for example, a method in which a hollow shell is molded from the cover composition, and a sphere (a sphere with a spherical core or an intermediate layer) is coated with the multiple shells and compression molded (preferably, a method in which a hollow half shell is molded from the cover composition, and the sphere is coated with two half shells and compression molded), or a method in which the cover composition is directly injection molded onto the sphere.

[0077] The golf ball body with the molded cover is removed from the mold, and is preferably subjected to surface treatment such as deburring, cleaning, and sandblasting, as necessary.

[0078] If desired, a coating film or mark can be formed. The thickness of the coating film is not particularly limited, but is preferably 5 μm or more, more preferably 6 μm or more, even more preferably 7 μm or more, preferably 50 μm or less, more preferably 40 μm or less, and even more preferably 30 μm or less. If the thickness is 5 μm or more, the coating film is less likely to wear away even with continuous use, and if the thickness is 50 μm or less, the effect of the dimples can be fully obtained. Note that the coating film is very thin, so it does not impair the effect of the present invention.

[0079] (dimple) The golf ball of the present invention has an outermost cover layer on which a plurality of dimples are formed. The dimples are recesses formed in the outermost cover layer. The dimples formed in the outermost cover layer of the golf ball of the present invention will be described below with reference to the drawings.

[0080] 1, a large number of dimples 10 are provided on the surface of the outermost cover of the golf ball 2. The outline of each dimple 10 is a circle.

[0081] FIG. 2 shows a cross section of the golf ball 2 along a plane passing through the center of the dimple 10 and the center of the golf ball 2. The up-down direction in FIG. 2 is the depth direction of the dimple 10. A phantom sphere is indicated by a two-dot chain line 14 in FIG. 2. The surface of the phantom sphere 14 is the surface of the golf ball 2 when it is assumed that the dimple 10 does not exist. The diameter of the phantom sphere 14 is the same as the diameter of the golf ball 2. The dimple 10 is recessed from the surface of the phantom sphere 14. The land 12 coincides with the surface of the phantom sphere 14. In this embodiment, the cross-sectional shape of the dimple 10 is substantially a circular arc. The radius of curvature of this circular arc is indicated by the symbol CR in FIG. 2.

[0082] 2 indicates the diameter of the dimple 10. This diameter Dm is the distance between one tangent point Ed and the other tangent point Ed when a tangent line Tg common to both sides of the dimple 10 is drawn. The tangent point Ed is also the edge of the dimple 10. The edge Ed defines the contour of the dimple 10.

[0083] In the present invention, the "volume of the lower part of the dimple" is the volume of the lower part of the dimple surrounded by a plane connecting the intersection points Ed-Ed on the dimple surface and the surface of the dimple 10. The "total volume Vi of the lower part of the dimple" is the sum of the volumes of the lower parts of all the dimples.

[0084] The golf ball has a lower total volume Vi of the plurality of dimples of 365 mm 3More than 385mm, preferably 385mm 3 More preferably, 400 mm 3 The total lower volume Vi is 365 mm 3 If the total lower volume Vi is 500 mm or more, the maximum height of the iron shot can be suppressed. 3 It is preferable that the length is less than 480 mm. 3 More preferably, it is 460 mm or less. 3 It is more preferable that the total lower volume Vi is 500 mm or less. 3 If the ball has a diameter not larger than this, sufficient lift is obtained upon driver shots, resulting in good flight distance performance.

[0085] The diameter Dm of the dimple 10 is preferably 2.0 mm or more, more preferably 2.5 mm or more, and even more preferably 2.8 mm or more, and is preferably 6.0 mm or less, more preferably 5.5 mm or less, and even more preferably 5.0 mm or less. If the diameter Dm is 2.0 mm or more, the dimples are more likely to contribute to turbulence, and if it is 6.0 mm or less, the essence of a golf ball being substantially spherical can be maintained.

[0086] The plurality of dimples may be formed with a single diameter, or may be a combination of dimples with a plurality of different diameters. For example, the golf ball 2 shown in Figures 3 and 4 has five types of dimples: dimple A with a diameter of 4.400 mm, dimple B with a diameter of 4.285 mm, dimple C with a diameter of 4.150 mm, dimple D with a diameter of 3.875 mm, and dimple E with a diameter of 3.000 mm.

[0087] 2, what is indicated by a double-headed arrow Dp1 is the first depth of the dimple 10. This first depth Dp1 is the distance between the deepest part of the dimple 10 and the surface of the phantom sphere 14. The first depth Dp1 is preferably 0.15 mm or more, more preferably 0.17 mm or more, and even more preferably 0.20 mm or more, and is preferably 0.45 mm or less, more preferably 0.43 mm or less, and even more preferably 0.40 mm or less. If the first depth Dp1 is 0.15 mm or more, the lift provided by the dimples can be sufficiently generated, and if it is 0.45 mm or less, the essence of a golf ball being substantially spherical can be maintained.

[0088] 2, what is indicated by the double-headed arrow Dp2 is the second depth of the dimple 10. This second depth Dp2 is the distance between the deepest part of the dimple 10 and the tangent line Tg. The second depth Dp2 is preferably 0.08 mm or more, more preferably 0.10 mm or more, and even more preferably 0.12 mm or more, and is preferably 0.30 mm or less, more preferably 0.28 mm or less, and even more preferably 0.26 mm or less. If the second depth Dp2 is 0.08 mm or more, the dimples are likely to contribute to turbulence, and if it is 0.30 mm or less, the lift force obtained by the dimples is not too large, resulting in good distance performance on driver shots.

[0089] The area A of the dimple 10 is the area of ​​the region surrounded by the outline of the dimple 10 when viewing the center of the golf ball 2 from infinity. In the case of a circular dimple 10, the area A is calculated by the following formula. A = π × (Dm / 2) 2

[0090] For example, in the golf ball 2 shown in FIG. 3 and FIG. 4, the area of ​​the dimple A is 15.21 mm 2 and the area of ​​dimple B is 14.42 mm 2 and the area of ​​dimple C is 13.53 mm 2 and the area of ​​dimple D is 11.79 mm 2 and the area of ​​dimple E is 7.07 mm 2 It is.

[0091] In the outermost cover layer, the ratio of the total area of ​​the dimples to the surface area of ​​a hypothetical sphere if the dimples did not exist (total area of ​​dimples / surface area of ​​hypothetical sphere) is referred to as the occupation ratio So. The occupation ratio So is preferably 75% or more, more preferably 78% or more, and even more preferably 81% or more, and is preferably 95% or less, more preferably 92% or less, and even more preferably 90% or less. If the occupation ratio So is within the above range, the dimples can perform to their full potential.

[0092] The number of dimples may be adjusted as appropriate depending on the diameter and occupation rate of the dimples. Taking into consideration the occupation rate and the effect of each individual dimple, the total number of dimples 10 is preferably 250 or more, more preferably 280 or more, and even more preferably 300 or more, and is preferably 450 or less, more preferably 410 or less, and even more preferably 390 or less.

[0093] (Golf ball structure) The golf ball of the present invention has a spherical core, an intermediate layer covering the spherical core, and an outermost cover covering the intermediate layer. The structure of the golf ball includes a three-piece golf ball consisting of an intermediate layer covering the spherical core and an outermost cover covering the intermediate layer, and a multi-piece golf ball (four-piece golf ball, five-piece golf ball, etc.) consisting of a single-layer spherical core, two or more intermediate layers covering the spherical core, and an outermost cover covering the intermediate layer.

[0094] The diameter of the golf ball of the present invention is preferably 40 mm to 45 mm. From the viewpoint of satisfying the standards of the United States Golf Association (USGA), the diameter is particularly preferably 42.67 mm or more. From the viewpoint of suppressing air resistance, the diameter is more preferably 44 mm or less, and particularly preferably 42.80 mm or less. In addition, the mass of the golf ball of the present invention is preferably 40 g to 50 g. From the viewpoint of obtaining large inertia, the mass is more preferably 44 g or more, and particularly preferably 45.00 g or more. From the viewpoint of satisfying the standards of the USGA, the mass is particularly preferably 45.93 g or less.

[0095] When the golf ball has a diameter of 40 mm to 45 mm, the amount of compressive deformation (amount of shrinkage in the compressive direction) when a final load of 1275 N is applied from an initial load of 98 N is preferably 2.0 mm or more, more preferably 2.1 mm or more, and even more preferably 2.2 mm or more, and is preferably 3.0 mm or less, more preferably 2.9 mm or less, and even more preferably 2.8 mm or less. If the amount of compressive deformation is within the above range, the golf ball provides a good shot feeling.

[0096] The surface hardness of the golf ball, in Shore D hardness, is preferably at least 45, more preferably at least 48, and even more preferably at least 50, and is preferably at most 65, more preferably at most 63, and even more preferably at most 61. If the surface hardness of the golf ball is within the above range, it will have excellent impact resistance and will be less susceptible to surface scratches. EXAMPLES

[0097] The present invention will be described in detail below with reference to examples. However, the present invention is not limited to the following examples, and all modifications and embodiments that do not deviate from the spirit of the present invention are included within the scope of the present invention.

[0098] [Evaluation method] (1) Compressive deformation amount (mm) A Yamada compression tester "SCH" was used to measure the amount of compressive deformation. In this tester, a golf ball or spherical core is placed on a metal hard plate. A metal cylinder is gradually lowered toward the golf ball or spherical core. The golf ball or spherical core is deformed when sandwiched between the bottom of the cylinder and the hard plate. The distance traveled by the cylinder from when an initial load of 98N is applied to the golf ball or spherical core until a final load of 1275N is applied is measured. The amount of compressive deformation (mm) is this distance traveled. 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.

[0099] (2) Core hardness (Shore C hardness) The hardness measured on the surface of the core was taken as the core surface hardness. The core was cut into a hemisphere, and the hardness was measured at the center of the cut surface and at a specified distance in the radial direction from the center. Each hardness was calculated by measuring the hardness at four points and averaging these values. The hardness was measured using an automatic hardness tester (Digitest II, manufactured by H. Burleith Co., Ltd.). The detector used was "Shore C."

[0100] (3) Slab hardness (Shore D hardness) A sheet with a thickness of about 2 mm was prepared by injection molding using the resin composition and stored at 23° C. for two weeks. The hardness was measured using an automatic hardness tester (Digitest II, manufactured by H. Burleith Co.) in a state where three or more sheets were stacked so as not to be affected by the measurement substrate, etc. The detector used was "Shore D."

[0101] (4) Golf ball surface hardness The hardness of the land portion of the surface of the golf ball was measured and taken as the ball surface hardness. Hardness was measured at four points and calculated by averaging these values. Hardness was measured using an automatic hardness tester (Digitest II, manufactured by H. Burleith Co., Ltd.). The detector used was "Shore D".

[0102] (5) No. 8 iron test (I#8 shot) An 8-iron (Sumitomo Rubber Industries, "SRIXON ZX7", shaft hardness: S, loft angle: 36°) was attached to a Golf Laboratory swing machine. The impact point was set to the face center. The golf ball was hit under the condition of a head speed of 39 m / sec, and the ball speed, spin rate, and peak height immediately after impact were measured. Measurements were performed 12 times for each golf ball, and the average value was used as the measured value for that golf ball. The ball speed and spin rate were measured by taking continuous photographs of the golf ball immediately after it was hit. The peak height was measured using a trajectory measuring device (TrackMan, "TRACKMAN4").

[0103] [Manufacturing of golf balls] (1) Preparation of spherical cores The raw materials were kneaded with a kneading roll so as to obtain the composition shown in Table 1, thereby obtaining a core composition. The core composition shown in Table 1 was hot-pressed in upper and lower molds having hemispherical cavities to obtain a spherical core. An appropriate amount of barium sulfate was added so that the mass of the resulting golf ball would be 45.3 g.

[0104] [Table 1]

[0105] The materials used in Table 1 are as follows: Polybutadiene rubber: JSR Corporation, "BR-730" (high cis polybutadiene rubber, cis-1,4-bond content 95% by mass, 1,2-vinyl bond content 1.3% by mass, Mooney viscosity (ML 1+4 (100℃))55, molecular weight distribution (Mw / Mn)3) Butyl rubber: "Butyl 268" (unsaturation level 1.5 mol%, Mooney viscosity (ML 1+8 (125℃)51) Zinc acrylate: Nisshoku Techno Fine Chemical Co., Ltd., "ZN-DA90S" Zinc oxide: "Ginrei R" manufactured by Toho Zinc Co., Ltd. Barium sulfate: Sakai Chemical Industry Co., Ltd., "Barium Sulfate BD" Benzoic acid: Tokyo Chemical Industry Co., Ltd. (purity 98% or more) Bis(pentabromophenyl) disulfide: Kawaguchi Chemical Industry Co., Ltd. Diphenyl disulfide: Sumitomo Seika Chemicals Dicumyl peroxide: NOF Corporation, "Percumyl (registered trademark) D"

[0106] (2) Preparation of Resin Compositions (Composition for Intermediate Layer, Composition for Cover) The raw materials were extruded using a twin-screw kneading extruder so as to obtain the composition shown in Table 2, to prepare a pellet-shaped resin composition.

[0107] [Table 2] Surlyn® 8150: Sodium ion neutralized ethylene-methacrylic acid copolymer ionomer resin manufactured by DuPont Himilan (registered trademark) 1605: Sodium ion-neutralized ethylene-methacrylic acid copolymer ionomer resin manufactured by Mitsui Dow Polychemicals Himilan (registered trademark) AM7329: Sodium ion neutralized ethylene-methacrylic acid copolymer ionomer resin manufactured by Mitsui Dow Polychemicals Himilan (registered trademark) 1555: Sodium ion-neutralized ethylene-methacrylic acid copolymer ionomer resin manufactured by Mitsui Dow Polychemicals Himilan (registered trademark) 1557: Manufactured by Mitsui Dow Polychemicals, zinc ion neutralized ethylene-methacrylic acid copolymer ionomer resin Tefablock (registered trademark) T3221C: Thermoplastic styrene-based elastomer manufactured by Mitsubishi Chemical Corporation Elastollan (registered trademark) NY80A: BASF Japan, thermoplastic polyurethane elastomer Elastollan (registered trademark) NY84A: BASF Japan, thermoplastic polyurethane elastomer Elastollan (registered trademark) NY88A: BASF Japan, thermoplastic polyurethane elastomer Elastollan (registered trademark) NY95A: BASF Japan, thermoplastic polyurethane elastomer Tinuvin (registered trademark) 770: BASF Japan, hindered amine light stabilizer Titanium dioxide: Ishihara Sangyo Kaisha, A-220

[0108] (3) Formation of the mid-layer and cover The resin composition (composition for intermediate layer) was injection molded onto a spherical core to obtain an intermediate layer-coated sphere. The obtained intermediate layer-coated sphere was placed into a final mold having a large number of dimples on the cavity surface. A half shell was obtained from the resin composition (composition for cover) by compression molding. Two half shells were coated onto the intermediate layer-coated sphere placed in the final mold to obtain a golf ball in which a large number of dimples were formed on the outermost cover, the shapes of which were the inverse of the dimples on the cavity surface. The specifications of the dimples formed on the outermost cover are shown in Tables 3 and 4. The evaluation results of the obtained golf balls are shown in Tables 5 and 6.

[0109] [Table 3]

[0110] [Table 4]

[0111] [Table 5]

[0112] [Table 6]

[0113] Golf balls Nos. 1 to 11 each have a spherical core formed from a rubber composition containing a predetermined amount of polybutadiene rubber and butyl rubber, a slab hardness of the intermediate layer composition is greater than a slab hardness of the cover composition, and a total volume of the lower portions of the plurality of dimples is 365 mm 3 or more, and the surface coverage of the plurality of dimples is 75% or more. These golf balls Nos. 1 to 11 have high spin performance on iron shots, and the peak height is suppressed, improving controllability.

[0114] Golf balls Nos. 12 to 14 have spherical cores formed from a rubber composition that does not contain butyl rubber. Golf balls Nos. 15, 17 and 18 are cases in which the slab hardness of the intermediate layer composition is lower than the slab hardness of the cover composition. Golf balls No. 16, 19 to 21 have a total lower volume of multiple dimples of 365 mm 3 This is the case when it is less than . These golf balls Nos. 12 to 21 have low spin performance in iron shots and / or the highest point height cannot be controlled, and controllability is not improved.

[0115] (Embodiments of the present invention) The present invention (1) is a golf ball having a spherical core, an intermediate layer covering the spherical core, and an outermost cover layer located outside the intermediate layer and having a plurality of dimples, wherein the spherical core is formed from a rubber composition containing a base rubber, a co-crosslinking agent, and a crosslinking initiator, the base rubber contains polybutadiene rubber and butyl rubber, and a content of the butyl rubber in 100% by mass of the base rubber is 10% by mass to 60% by mass, the slab hardness of the intermediate layer composition forming the intermediate layer is greater than a slab hardness of a cover composition forming the outermost cover, and a total volume below the plurality of dimples is 365 mm 3 The above is a golf ball characterized in that the outermost cover layer has a surface coverage of 75% or more, which is the total area of ​​the plurality of dimples, of the surface area of ​​a phantom sphere if the plurality of dimples did not exist.

[0116] In the present invention (2), the total volume of the lower portions of the plurality of dimples is 400 mm 3 The above is the golf ball according to present invention (1).

[0117] The present invention (3) is characterized in that the central hardness (H0) of the spherical core and the hardness (H 2.5 ), and the hardness (H 5.0), and the hardness (H 7.5 ), and the hardness (H 10 ), and the hardness (H 12.5 ), and the hardness (H 15 ) but H0 <H 2.5 <H 5.0 <H 7.5 <H 10 <H 12.5 <H 15 The relationship between the center hardness (H0) and the hardness at a point 10 mm away from the center of the spherical core in the radial direction (H 10 ) and hardness difference (H 10 -H0) is a Shore C hardness of 10 or more.

[0118] The present invention (4) is a method for measuring the hardness (H 5.0 ) and the hardness (H 12.5 ) and hardness difference (H 12.5 -H 5.0 ) has a Shore C hardness of 5 or more.

[0119] The present invention (5) is the golf ball according to any one of the present inventions (1) to (4), wherein the spherical core has a center hardness (H0) of 60 or less in Shore C hardness.

[0120] The present invention (6) is the golf ball according to any one of the present inventions (1) to (5), wherein the intermediate layer composition forming the intermediate layer is a resin composition containing an ionomer resin as a base resin, and the cover composition forming the outermost cover layer is a resin composition containing a urethane resin as a base resin.

[0121] The present invention (7) is the golf ball according to any one of the present inventions (1) to (6), wherein the cover composition forming the outermost cover layer has a slab hardness of 40 or less in Shore D hardness.

[0122] The present invention (8) is the golf ball according to any one of the present inventions (1) to (7), wherein the intermediate layer composition forming the intermediate layer has a slab hardness of 50 or more in Shore D hardness. [Explanation of symbols]

[0123] 2: Golf ball, 4: Spherical core, 6: Intermediate layer, 8: Outermost cover, 10: Dimples, 12: Land, 14: Virtual sphere

Claims

1. A golf ball having a spherical core, a mid layer encasing the spherical core, and an outermost cover layer located outside the mid layer and having a plurality of dimples thereon, the spherical core is formed from a rubber composition containing a base rubber, a co-crosslinking agent, and a crosslinking initiator, the base rubber contains polybutadiene rubber and butyl rubber, and the content of the butyl rubber in 100% by mass of the base rubber is 10% by mass to 60% by mass; the slab hardness of the intermediate layer composition forming the intermediate layer is greater than the slab hardness of the cover composition forming the outermost cover layer, The total lower volume of the plurality of dimples is 365 mm 3 That's all. a total area of ​​the plurality of dimples in the outermost cover layer occupies 75% or more of the surface area of ​​a virtual sphere if the plurality of dimples did not exist;

2. The total lower volume of the plurality of dimples is 400 mm 3 2. The golf ball according to claim 1,

3. The central hardness (H0) of the spherical core, and the hardness (H 2.5 ), hardness at a radial distance of 5.0 mm from the center of the spherical core (H 5.0 ), hardness at a radial distance of 7.5 mm from the center of the spherical core (H 7.5 ), hardness at a radial distance of 10 mm from the center of the spherical core (H 10 ), hardness at a radial distance of 12.5 mm from the center of the spherical core (H 12.5 ), hardness at a radial distance of 15 mm from the center of the spherical core (H 15 ) is H0 < H 2.5 <H 5.0 <H 7.5 <H 10 <H 12.5 <H 15 Satisfying the relationship, The central hardness (H0) and the hardness (H 10 ) and the hardness difference (H 10 2. The golf ball according to claim 1, wherein the Shore C hardness (-H0) is 10 or greater.

4. The hardness (H 5.0 ) and the hardness (H 12.5 ) and the hardness difference (H 12.5 -H 5.0 2. The golf ball according to claim 1, wherein said hardness is 5 or more in Shore C hardness.

5. 2. The golf ball according to claim 1, wherein the spherical core has a center hardness (H0) of 60 or less in Shore C hardness.

6. the intermediate layer composition forming the intermediate layer is a resin composition containing an ionomer resin as a base resin, 2. The golf ball according to claim 1, wherein the cover composition forming the outermost cover layer is a resin composition containing a urethane resin as a base resin.

7. 2. The golf ball according to claim 1, wherein the cover composition forming the outermost cover layer has a slab hardness of 40 or less in Shore D hardness.

8. 2. The golf ball according to claim 1, wherein the intermediate layer composition forming the intermediate layer has a slab hardness of 50 or more in Shore D hardness.

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