Golf ball

Abstract

To provide a golf ball that rolls in a lowered distance on fairway wood shots.SOLUTION: A golf ball comprises a spherical core, an intermediate layer covering the spherical core, and an outermost cover positioned outside the intermediate layer and provided with a plurality of dimples. 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 natural rubber, and in a surface area of a virtual sphere assumed to have no dimples on the outermost cover, an occupation ratio of a total area of the plurality of dimples is 45% or more and less than 75%.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 layer, and dimples.

[0002] Conventionally, spherical cores made from various rubber materials have been proposed as the spherical core of a golf ball. For example, Patent Document 1 describes a golf ball for driving ranges obtained by vulcanizing a composition containing 100 parts by weight of base rubber, 3 to 35 parts by weight of low-resilience rubber, 20 to 30 parts by weight of methacrylic acid, and 20 to 50 parts by weight of a metal compound capable of forming a metal salt with methacrylic acid (see Patent Document 1 (Claim 1, page 3, upper left column, lines 11 to 17)).

[0003] Patent Document 2 describes a golf ball for use at a driving range obtained from a composition containing 3 to 35 parts by weight of 10 to 60 mol % epoxidized natural rubber, 20 to 35 parts by weight of methacrylic acid, and 20 to 50 parts by weight of zinc oxide, per 100 parts by weight of base rubber (see Patent Document 2 (Claim 1, page 2, lower left column, line 4 to lower right column, line 2)). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 60-92780 [Patent Document 2] Japanese Patent Application Publication No. 61-71069 Summary of the Invention [Problem to be solved by the invention]

[0005] In a golf round, fairway woods are used for relatively long shots from the second shot onwards. Shots with fairway woods tend to have a long rolling distance due to the long flight distance. Therefore, depending on the slope of the landing point, the rolling distance after landing can be too long, making it difficult to stop the ball at the intended position. In particular, for average golfers, it is difficult to take into account the rolling distance of fairway wood shots, making it difficult to control the flight distance of fairway wood shots.

[0006] The present invention has been made in view of the above circumstances, and has as its object to provide a golf ball that reduces the rolling distance when shot with a fairway wood. [Means for solving the problem]

[0007] The golf ball of the present invention, which has solved the above-mentioned problems, is a golf ball having a spherical core, an intermediate layer that encases the spherical core, and an outermost cover layer that is located outside the intermediate layer and has a plurality of dimples formed thereon, wherein the spherical core is formed from a rubber composition that contains a base rubber, a co-crosslinking agent, and a crosslinking initiator, the base rubber contains natural rubber, and the outermost cover layer is characterized in that the total area of ​​the plurality of dimples occupies 45% or more and less than 75% of the surface area of ​​a hypothetical sphere that would be formed if the plurality of dimples were not present.

[0008] The spherical core is formed from a rubber composition containing natural rubber, which reduces the ball speed when shot with a fairway wood, thereby reducing the rolling distance. Furthermore, by reducing the dimple coverage, the lift of the ball is increased. This results in a sharper descent angle when the golf ball lands, further reducing the rolling distance after landing. [Effects of the Invention]

[0009] The golf ball of the present invention has a sharper landing angle and a reduced ball speed when shot with a fairway wood, thereby reducing the rolling distance, making it easier for even average golfers to control the distance of fairway wood shots. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a partially cutaway cross-sectional view showing a golf ball according to one embodiment of the present invention. [Figure 2] FIG. 2 is an enlarged cross-sectional view of a dimple formed on the outermost cover layer. [Figure 3] FIG. 2 is a front view of dimple pattern No. I formed on the outermost cover layer. [Figure 4] FIG. 2 is a plan view of dimple pattern No. I formed on the outermost cover layer. [Figure 5] FIG. 1 is a front view of dimple pattern No. II formed on the outermost cover layer. [Figure 6] FIG. 2 is a plan view of dimple pattern No. II formed on the outermost cover layer. [Figure 7] FIG. 1 is a front view of dimple pattern No. III formed on the outermost cover layer. [Figure 8] FIG. 1 is a plan view of dimple pattern No. III formed on the outermost cover layer. [Figure 9] FIG. 1 is a front view of dimple pattern No. IV formed on the outermost cover layer. [Figure 10] FIG. 1 is a plan view of dimple pattern No. IV formed on the outermost cover layer. [Figure 11] FIG. 1 is a front view of dimple pattern No. V formed on the outermost cover layer. [Figure 12] FIG. 1 is a plan view of dimple pattern No. V formed on the outermost cover layer. DETAILED DESCRIPTION OF THE INVENTION

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

[0012] The golf ball 2 shown in Figure 1 has a spherical core 4, a mid layer 6 that encases the core 4, and an outermost cover layer 8 that is positioned on the outside of the mid 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 not shown in the figure.

[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 natural rubber (NR), which reduces the initial velocity of the ball on fairway shots and reduces the ball's speed upon landing, thereby shortening the rolling distance. Natural rubber is produced by nicking a plant that produces natural rubber latex (a milky liquid), recovering the latex, and coagulating the rubber component contained in the latex. One type of natural rubber may be used alone, or two or more types may be used in combination.

[0015] Examples of plants that produce natural rubber latex include Hevea brasiliensis and Hevea brasiliensis of the Euphorbiaceae family, Rubber tree, Hevea brasiliensis, and Hevea lagos of the Moraceae family, Gum arabicum and Tragacanth of the Fabaceae family, Curculionidae, Zanzibar vine, Huntsumia elastica, and Urceola of the Asteraceae family, Guayule and the rubber dandelion, Gutta-percha, Balata and Sapodilla of the Sapotaceae family, Morning glory of the Asclepiadaceae family, and Eucommia of the Eucommiaaceae family.

[0016] The natural rubber may be a CV grade, in which the rubber viscosity is stabilized by adding a viscosity stabilizer or the like to the raw latex, or a non-CV grade, in which the rubber viscosity is not stabilized. These may be used alone or in combination of two or more. Of these, the CV grade, which has a particularly stable viscosity, is preferred. The natural rubber may be either SMR (standard Malaysian rubber) or SVR (standard Vietnamese rubber).

[0017] The natural rubber is cis-1,4-polyisoprene, and either sheet rubber or block rubber can be used. Natural rubber also includes modified natural rubbers, such as epoxidized natural rubber, methacrylic acid-modified natural rubber, halogen-modified natural rubber, deproteinized natural rubber, maleic acid-modified natural rubber, sulfonic acid-modified natural rubber, and styrene-modified natural rubber. Among these, it is preferable that the natural rubber does not contain epoxidized natural rubber.

[0018] The natural rubber is preferably Technical Specified Rubbers (TSR) or Ribbed Smoked Sheet (RSS). The natural rubber may also contain a viscosity stabilizer.

[0019] The Mooney viscosity (ML 1+4 (100°C)) is preferably 30 or more, more preferably 35 or more, and even more preferably 40 or more, and is preferably 80 or less, more preferably 75 or less, and even more preferably 70 or less. In this specification, the Mooney viscosity (ML 1+4 (100°C)) is a value measured in accordance with JIS K6300 (2013) using an L rotor, with a preheating time of 1 minute, rotor rotation time of 4 minutes, and at 100°C.

[0020] The base rubber may contain only natural rubber, or may contain natural rubber and synthetic rubber. When the base rubber contains natural rubber and synthetic rubber, the content of natural rubber in 100% by mass of the base rubber is preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, and particularly preferably 70% by mass or more. A content of 20% by mass or more further reduces the initial velocity of the ball upon shot.

[0021] Examples of the synthetic rubber include diene rubbers such as polybutadiene rubber (BR), polyisoprene rubber (IR), styrene polybutadiene rubber (SBR), chloroprene rubber (CR), butyl rubber (IIR), and acrylonitrile butadiene rubber (NBR); and non-diene rubbers such as ethylene propylene rubber (EPM), ethylene-propylene-diene rubber (EPDM), urethane rubber, silicone rubber, acrylic rubber, epichlorohydrin rubber, polysulfide rubber, fluororubber, and chlorosulfonated polyethylene rubber. These may be used alone or in combination of two or more.

[0022] The base rubber may contain a diene rubber as a synthetic rubber. In this case, the content of the diene rubber in 100% by mass of the base rubber is preferably at least 5% by mass, more preferably at least 10% by mass, and even more preferably at least 15% by mass, and is preferably at most 80% by mass, more preferably at most 70% by mass, and even more preferably at most 60% by mass.

[0023] The base rubber preferably contains polybutadiene rubber as the diene rubber. In particular, it is more preferable that it contains high-cis polybutadiene having cis-1,4-bonds in an amount of 40% by mass or more, preferably 80% by mass or more, and more preferably 90% by mass or more. The content of high-cis polybutadiene in the diene rubber is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more. It is also preferable that the diene rubber contains only high-cis polybutadiene rubber.

[0024] 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 even more preferably 1.5% by mass or less.

[0025] The high-cis polybutadiene is preferably synthesized using a rare earth element catalyst, and 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 polybutadiene rubber having a high content of 1,4-cis bonds and a low content of 1,2-vinyl bonds with excellent polymerization activity.

[0026] The high-cis polybutadiene preferably has a molecular weight distribution Mw / Mn (Mw: weight-average molecular weight, Mn: number-average molecular weight) of 2.0 or more, more preferably 2.2 or more, even more preferably 2.4 or more, and preferably 6.0 or less, more preferably 5.0 or less, and even more preferably 4.0 or less. When the molecular weight distribution (Mw / Mn) of the high-cis polybutadiene is within the above range, workability is improved. The molecular weight distribution was measured by gel permeation chromatography (manufactured by Tosoh Corporation, "HLC-8120GPC") using a differential refractometer as a detector, a column: GMHHXL (manufactured by Tosoh Corporation), a column temperature: 40°C, and a mobile phase: tetrahydrofuran, and calculated as a value converted into a standard polystyrene.

[0027] The Mooney viscosity (ML 1+4 (100°C)) is preferably 30 or more, more preferably 32 or more, and even more preferably 35 or more, and is preferably 140 or less, more preferably 120 or less, and even more preferably 100 or less.

[0028] The co-crosslinking agent has the effect of crosslinking rubber molecules by graft polymerizing with the base rubber molecular chains. One type of co-crosslinking agent may be used alone, or two or more types may be used in combination. 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.

[0029] Examples of metals 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 component. 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. Zinc acrylate is particularly preferred as the divalent metal salt, as it enhances 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.

[0030] The content of the co-crosslinking agent may be adjusted appropriately depending on the desired hardness of the spherical core. The content of the co-crosslinking agent is preferably at least 20 parts by mass, more preferably at least 23 parts by mass, and even more preferably at least 25 parts by mass, per 100 parts by mass of the base rubber, and is preferably at most 60 parts by mass, more preferably at most 55 parts by mass, and even more preferably at most 50 parts by mass.

[0031] The crosslinking initiator is blended to crosslink the base rubber component. An organic peroxide is suitable as the crosslinking initiator. 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.

[0032] The content of the crosslinking initiator may be adjusted appropriately depending on the desired hardness of the spherical core, and is preferably at least 0.2 parts by mass, more preferably at least 0.5 parts by mass, and even more preferably at least 0.7 parts by mass, and is preferably at most 5.0 parts by mass, more preferably at most 2.5 parts by mass, and even more preferably at most 2.0 parts by mass, per 100 parts by mass of the base rubber.

[0033] 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. Furthermore, a metal compound may also be used 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.

[0034] 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. Divalent metal compounds are preferred as the metal compound, and zinc compounds are more preferred. Divalent metal compounds react with α,β-unsaturated carboxylic acids having 3 to 8 carbon atoms to form metal crosslinks. These metal compounds may be used alone or in combination.

[0035] The rubber composition may further contain an organic sulfur compound, but it is also preferable that the rubber composition does not contain an organic sulfur compound.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 having 2 to 4 sulfur atoms (-SS-, -SSS-, or -SSSS-), 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.

[0036] Examples of the organic sulfur compounds include thiophenols, thionaphthols, polysulfides, thiurams, thiocarboxylic acids, dithiocarboxylic acids, sulfenamides, dithiocarbamates, thiazoles, etc. Suitable examples of the organic sulfur compounds include diphenyl disulfides (e.g., diphenyl disulfide, bis(pentabromophenyl)disulfide), thiophenols, and thionaphthols (e.g., 2-thionaphthol).

[0037] The content of the organic sulfur compound may be adjusted appropriately depending on the desired resilience performance of the spherical core. For example, the content of the organic sulfur compound is preferably at least 0.05 parts by weight, more preferably at least 0.1 parts by weight, and even more preferably at least 0.2 parts by weight, per 100 parts by weight of the base rubber, and is preferably at most 5.0 parts by weight, more preferably at most 3.0 parts by weight, and even more preferably at most 2.0 parts by weight.

[0038] 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 and / or a salt thereof having 1 to 30 carbon atoms. The carboxylic acid may be either an aliphatic carboxylic acid (saturated fatty acid, unsaturated fatty acid) or an aromatic carboxylic acid (benzoic acid, etc.). When the carboxylic acid and / or a metal salt thereof is compounded, 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.

[0039] The rubber composition may contain additives such as a filler for adjusting the weight, an antioxidant, a peptizer, and a softener, as required.

[0040] The filler used in the rubber composition is primarily used as a weight adjuster to adjust 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.

[0041] The rubber composition is obtained by kneading a base rubber, a co-crosslinking agent, a crosslinking initiator, and other components that are blended as needed. 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.

[0042] The spherical core can be molded, for example, by hot-pressing the core rubber composition. The hot-press molding conditions for the core rubber composition may be appropriately set depending on the rubber composition, but typically, heating is preferably performed at 130°C to 200°C for 10 to 60 minutes, or in two stages: heating at 130°C to 150°C for 20 to 40 minutes, followed by heating at 160°C to 180°C for 5 to 15 minutes.

[0043] 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.

[0044] When the diameter of the spherical core is 34.8 mm to 42.2 mm, the amount of compressive deformation (the amount the spherical core shrinks in the compressive direction) from an initial load of 98 N to a final load of 1275 N is preferably 2.0 mm or more, more preferably 2.5 mm or more, and even more preferably 3.0 mm or more, and is preferably 5.0 mm or less, more preferably 4.5 mm or less, and even more preferably 4.0 mm or less. If the amount of compressive deformation is within the above range, the shot feel will be better.

[0045] The spherical core has a center 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 ), hardness (H 5.0 ), hardness (H 7.5 ), hardness at a radial distance of 10 mm from the center of the spherical core (H 10 ), hardness (H 12.5 ), hardness at a radial distance of 15 mm from the center of the spherical core (H 15 ) and surface hardness (Hs) are H0 <H 2.5 <H 5.0 <H 7.5 <H 10 <H 12.5<H 15 Satisfies the relationship of <Hs>, and the core hardness (H0) of the spherical core is 70 or less in Shore C hardness. By satisfying the above requirements for the hardness distribution of the spherical core, the deformation of the spherical core during impact occurs smoothly, and the hitting feeling is good.

[0046] The spherical core has the core hardness (H0), the hardness (H 2.5 ), the hardness (H 10 ), the hardness (H 12.5 ), and the hardness (H 15 ) that satisfy the relationship of Shore C hardness: H 2.5 - H0 ≧ 3.0, H 12.5 - H 10 ≧ 3.0, and H 15 - H 12.5 ≧ 3.0. It is preferable that the hardness differences (H 2.5 - H0), (H 12.5 - H 10 ), and (H 15 - H 12.5 ) are within the above range. If so, the deformation amount of the spherical core during a shot becomes large, the initial ball speed immediately after hitting can be suppressed lower, and the controllability of the flight distance in a shot is further improved.

[0047] The hardness difference (H 2.5 - H0) between the core hardness (H0) of the spherical core and the hardness (H 2.5 ) at a point 2.5 mm from the center of the spherical core in the radial direction is preferably 3.0 or more, more preferably 3.3 or more, still more preferably 3.5 or more, and preferably 12.0 or less, more preferably 11.0 or less, still more preferably 10.0 or less in Shore C hardness.

[0048] The hardness difference (H 10 - H 12.5 ) between the hardness (H 12.5 ) at a point 10.0 mm from the center of the spherical core in the radial direction and the hardness (H 10) is preferably 3.0 or more, more preferably 3.4 or more, and even more preferably 3.8 or more in Shore C hardness, and is preferably 11.0 or less, more preferably 10.0 or less, and even more preferably 9.0 or less.

[0049] The hardness (H 12.5 ) and the hardness (H 15 ) and hardness difference (H 15 -H 12.5 ) is preferably 3.0 or more, more preferably 3.4 or more, and even more preferably 3.8 or more in Shore C hardness, and is preferably 10.0 or less, more preferably 9.0 or less, and even more preferably 8.0 or less.

[0050] The spherical core has a hardness (H 5.0 ), the hardness (H 7.5 ) and the hardness (H 10 ) is Shore C hardness, H 7.5 -H 5.0 <3.0, and H 10 -H 7.5 It is preferable to satisfy the relationship of <3.0. 7.5 -H 5.0 ) and hardness difference (H 10 -H 7.5 ) is within the above range, the deformation energy due to impact is easily transmitted to the inside of the spherical core, making it easier for the spherical core to exhibit its properties.

[0051] The hardness (H 5.0 ) and the hardness (H 7.5 ) and hardness difference (H 7.5 -H 5.0 ) is preferably 0.2 or more, more preferably 0.3 or more, and even more preferably 0.4 or more, in Shore C hardness, and is preferably less than 3.0, more preferably 2.8 or less, and even more preferably 2.6 or less.

[0052] The hardness (H 7.5 ) and the hardness (H 10 ) and hardness difference (H 10 -H 7.5 ) is preferably 0.1 or more, more preferably 0.2 or more, and even more preferably 0.3 or more in Shore C hardness, and is preferably less than 3.0, more preferably 2.9 or less, and even more preferably 2.8 or less.

[0053] The difference in hardness (Hs-H0) between the center hardness (H0) of the spherical core and the surface hardness (Hs) of the spherical core is preferably at least 20, more preferably at least 22, and even more preferably at least 24, in Shore C hardness. If the difference in hardness (Hs-H0) is at least 20, the amount of spin on driver shots is suppressed, improving the distance of driver shots. The hardness difference (Hs-H0) is preferably 40 or less, more preferably 37 or less, and even more preferably 35 or less.

[0054] The spherical core preferably has a center hardness (H0) of 70 or less in Shore C hardness, more preferably 67 or less, and even more preferably 65 or less. If the center hardness (H0) is 70 or less in Shore C hardness, the shot feel is good. The center hardness (H0) is preferably 42 or more, more preferably 44 or more, and even more preferably 46 or more, in Shore C hardness.

[0055] The spherical core preferably has a surface hardness (Hs) of 70 or more, more preferably 72 or more, and even more preferably 74 or more, in Shore C hardness, and preferably 90 or less, more preferably 87 or less, and even more preferably 85 or less.

[0056] (middle class) The golf ball of the present invention has a mid layer that encases the spherical core.

[0057] The intermediate layer composition constituting the intermediate layer preferably has a slab hardness (Hm) of 50 or more, more preferably 55 or more, and even more preferably 60 or more, in Shore D hardness. A slab hardness (Hm) of 50 or more results in low spin on driver shots, resulting in good distance performance. 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. When multiple intermediate layers are used, the material hardness Hm refers to the material hardness of the intermediate layer composition constituting the outermost intermediate layer.

[0058] 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.

[0059] (Outermost cover) The golf ball of the present invention has an outermost cover layer located outside the intermediate layer.

[0060] 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 feel on 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 on driver shots is reduced, resulting in good distance performance.

[0061] 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 spin rate on driver shots can be reduced, resulting in improved distance control.

[0062] The hardness difference (Hm-Hc) between the slab hardness (Hm) and the slab hardness (Hc) is, in Shore D hardness, preferably greater than 0, 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.

[0063] 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.

[0064] (Cover composition, intermediate layer composition) The outermost cover layer and the intermediate layer are preferably formed from a resin composition containing a base resin.

[0065] 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.

[0066] Examples of the ionomer resin include binary ionomer resins 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 metal ions; ternary ionomer resins in which at least a portion of the carboxyl groups in a terpolymer 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 metal ions; and mixtures thereof.

[0067] 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 Iotec (registered trademark) 8000 (Na), 8030 (Na), 7010 (Zn), and 7030 (Zn) (manufactured by ExxonMobil Chemical Co.).

[0068] Examples of the ternary ionomer resins 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) and 7520(Zn) (manufactured by ExxonMobil Chemical Co.). Note that the Na, Zn, Li, Mg, etc., listed in parentheses after the trade name of the ionomer resin indicates the metal species of these neutralizing metal ions.

[0069] The urethane resin has a urethane bond in its molecule. This urethane bond can be formed by the reaction of a polyol with a polyisocyanate. The polyol, which is the raw material for the urethane bond, has multiple hydroxyl groups, and both low-molecular-weight polyols and high-molecular-weight polyols can be used.

[0070] Specific examples of the thermoplastic polyurethane elastomer include Elastollan (registered trademark) NY80A, NY84A, NY88A, NY95A, ET885, and ET890 (manufactured by BASF Japan Ltd.).

[0071] The thermoplastic styrene elastomer preferably includes a thermoplastic elastomer containing a styrene block. The styrene block-containing thermoplastic elastomer includes a polystyrene block as a hard segment and a soft segment.

[0072] The styrene block-containing thermoplastic elastomers include styrene-butadiene-styrene block copolymers (SBS), styrene-isoprene-styrene block copolymers (SIS), styrene-isoprene-butadiene-styrene block copolymers (SIBS), hydrogenated SBS, hydrogenated SIS, and hydrogenated SIBS. Hydrogenated SBS includes styrene-ethylene-butylene-styrene block copolymers (SEBS). Hydrogenated SIS includes styrene-ethylene-propylene-styrene block copolymers (SEPS). Hydrogenated SIBS includes styrene-ethylene-ethylene-propylene-styrene block copolymers (SEEPS).

[0073] Examples of the thermoplastic styrene elastomer include TEFABLOC (registered trademark) T3221C, T3339C, SJ4400N, SJ5400N, SJ6400N, SJ7400N, SJ8400N, SJ9400N, and SR04 (manufactured by Mitsubishi Chemical Corporation).

[0074] 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 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 rate, particularly on approach shots, is further improved.

[0075] When the cover composition contains a urethane resin as the 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 the 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 an ionomer resin is contained, it is also preferable to use a thermoplastic styrene elastomer in combination.

[0076] The resin composition forming the intermediate layer (intermediate layer composition) preferably contains an ionomer resin as a base resin. 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 an ionomer resin is contained, it is also preferable to use a thermoplastic styrene elastomer in combination. When the intermediate layer contains an ionomer resin, the entire sphere consisting of the spherical core and the intermediate layer deforms smoothly upon driver shots, resulting in a good feel at impact.

[0077] 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.

[0078] 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 even more preferably 1.5 parts by mass or more, per 100 parts by mass of the base resin, and is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and even more preferably 6 parts by mass or less. By setting the content of the white pigment to 0.5 parts by mass or more, it is possible to impart hiding power to the intermediate layer and the outermost cover layer. Furthermore, if the content of the white pigment is 10 parts by mass or less, the durability of the resulting intermediate layer and the outermost cover layer will be good.

[0079] 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.

[0080] Examples of methods for molding the cover include a method in which a hollow shell is molded from a cover composition, and a sphere (a sphere with a spherical core or intermediate layer formed thereon) is coated with multiple shells and compression molded (preferably a method in which a hollow half shell is molded from a 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 a sphere.

[0081] 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 required.

[0082] Furthermore, 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 effects of the present invention.

[0083] (dimple) The golf ball of the present invention has an outermost cover layer on which a plurality of dimples are formed. 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.

[0084] 1, a large number of dimples 10 are provided on the surface of the outermost cover layer of the golf ball 2. The outline of each dimple 10 is a circle.

[0085] FIG. 2 shows a cross section of the golf ball 2 taken 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 corresponds to the depth direction of the dimple 10. A two-dot chain line 14 in FIG. 2 indicates a phantom sphere. The surface of the phantom sphere 14 would be the surface of the golf ball 2 if the dimple 10 were not present. 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 arc is indicated by the symbol CR in FIG. 2.

[0086] The arrow Dm in Figure 2 indicates the diameter of the dimple 10. This diameter Dm is the distance between one point of contact Ed and the other point of contact Ed when a tangent line Tg common to both sides of the dimple 10 is drawn. The point of contact Ed is also the edge of the dimple 10. The edge Ed defines the outline of the dimple 10.

[0087] In the present invention, the "volume below the dimple" refers to the volume below the dimple that is surrounded by the surface of the dimple 10 and a plane connecting the intersection points Ed-Ed on the dimple surface. The "total volume below the dimple Vi" refers to the sum of the volumes below all of the dimples.

[0088] The golf ball has a lower total volume Vi of the plurality of dimples of 220 mm 3 More than 230mm, preferably 3 More than 240mm, preferably 3 The total lower volume Vi is 220 mm 3 If the total volume of the lower part Vi is 365mm, the trajectory of the shot will not rise too high. 3 Preferably, it is less than 350 mm 3 It is more preferable that it is 335 mm or less. 3 It is more preferable that the total lower volume Vi is 365 mm or less. 3 If the ball is below this value, sufficient lift will be generated at the time of the shot, resulting in a high trajectory.

[0089] The diameter Dm of the dimples 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, while if it is 6.0 mm or less, the essence of a golf ball being substantially spherical can be maintained.

[0090] The plurality of dimples may be formed as a plurality of dimples having a single diameter, or may be a combination of dimples having 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 4.150 mm, dimple B with a diameter of 4.050 mm, dimple C with a diameter of 3.900 mm, dimple D with a diameter of 3.650 mm, and dimple E with a diameter of 2.750 mm.

[0091] 2, what is indicated by the 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 is sufficiently generated, and if it is 0.45 mm or less, the essence of a golf ball being substantially spherical can be maintained.

[0092] 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 generated by the dimples is not too great, resulting in good distance performance on shots.

[0093] 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

[0094] For example, in the golf ball 2 shown in FIGS. 3 and 4, the area of ​​dimple A is 13.53 mm 2 and the area of ​​dimple B is 12.88 mm 2 and the area of ​​dimple C is 11.95 mm 2 and the area of ​​dimple D is 10.46 mm 2 and the area of ​​dimple E is 5.94 mm 2 is.

[0095] In the outermost cover layer, the ratio of the total area of ​​the dimples to the surface area of ​​a hypothetical sphere assuming the dimples do 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 45% or more, more preferably 47% or more, and even more preferably 50% or more, and is preferably less than 75%, more preferably 74% or less, and even more preferably 72% or less. If the occupation ratio So is 45% or more, the lift provided by the dimples is not too great, resulting in good distance performance on shots. If the occupation ratio So is less than 75%, the ball's highest point can be increased on fairway wood shots.

[0096] 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.

[0097] (Golf ball structure) The golf ball of the present invention has a spherical core, an intermediate layer enclosing the spherical core, and an outermost cover layer enclosing the intermediate layer. Examples of the golf ball structure include a three-piece golf ball consisting of an intermediate layer enclosing the spherical core and an outermost cover layer enclosing 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 enclosing the spherical core, and an outermost cover layer enclosing the intermediate layer.

[0098] 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. The weight of the golf ball of the present invention is preferably 40 g to 50 g. From the viewpoint of obtaining large inertia, the weight 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 weight is particularly preferably 45.93 g or less.

[0099] When the golf ball has a diameter of 40 mm to 45 mm, the amount of compressive deformation (the amount of shrinkage in the compressive direction) when an initial load of 98 N is applied and a final load of 1275 N is applied 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 will have a good shot feel.

[0100] 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 scratches on the surface. [Example]

[0101] 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.

[0102] [Evaluation method] (1) Compression deformation (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, sandwiched between the bottom of the cylinder and the hard plate, deforms. The distance traveled by the cylinder from when an initial load of 98 N was applied to the golf ball or spherical core until a final load of 1275 N was applied, was measured. The amount of compressive deformation (mm) is the travel distance. The speed of the cylinder before the initial load was applied was 0.83 mm / s. The speed of the cylinder after the initial load was applied until the final load was applied was 1.67 mm / s.

[0103] (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 predetermined distance from the center in the radial direction. 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.). A Shore C detector was used.

[0104] (3) Slab hardness (Shore D hardness) The resin composition was injection molded into a sheet approximately 2 mm thick and stored at 23°C for two weeks. Three or more of these sheets were stacked to avoid the influence of the measurement substrate, and the hardness was measured using an automatic hardness tester (Digitest II, manufactured by H. Burleith Co.). A Shore D detector was used.

[0105] (4) Golf ball surface hardness The hardness measured at the land portion of the surface of the golf ball was 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.). The detector used was "Shore D."

[0106] (5) Fairway wood shot A fairway wood (Sumitomo Rubber Industries, Ltd., "XXIO (registered trademark) 12", club number: #5, loft angle: 18°, shaft flex: R) was attached to a Golf Laboratory swing machine. The impact point was set to the face center. The golf ball was hit at a head speed of 35 m / sec, and the ball speed, spin rate, and rolling distance (distance from the landing point to the stopping point) immediately after impact were measured. Measurements were made 12 times for each golf ball, and the average values ​​were used as the measurement values ​​for that golf ball. Ball speed and spin rate were measured by taking continuous photographs of the golf ball immediately after impact.

[0107] [Manufacturing 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 compositions shown in Table 1 were hot-pressed in upper and lower molds having hemispherical cavities to obtain spherical cores. An appropriate amount of barium sulfate was added so that the mass of the resulting golf ball would be 45.3 g.

[0108] [Table 1]

[0109] The materials used in Table 1 are as follows: Polybutadiene rubber: "BR-730" manufactured by JSR Corporation (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) Natural rubber: Dau Tieng Rubber Corporation, "CV60" (Mooney viscosity (ML) 1+4 (100℃))=60) Zinc diacrylate: 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"

[0110] (2) Preparation of Resin Compositions (Intermediate Layer Composition, Cover Composition) The raw materials were extruded using a twin-screw kneading extruder so as to have the composition shown in Table 2, to prepare a resin composition in the form of pellets.

[0111] [Table 2] Surlyn® 8150: Sodium ion-neutralized ethylene-methacrylic acid copolymer ionomer resin, manufactured by DuPont Himilan® 1605: Sodium ion-neutralized ethylene-methacrylic acid copolymer ionomer resin, manufactured by Mitsui Dow Polychemicals Himilan® 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® 1557: Zinc ion-neutralized ethylene-methacrylic acid copolymer ionomer resin, manufactured by Mitsui Dow Polychemicals TEFABLOC (registered trademark) T3221C: Thermoplastic styrene elastomer manufactured by Mitsubishi Chemical Corporation Elastollan (registered trademark) NY80A: BASF Japan, thermoplastic polyurethane elastomer Elastollan (registered trademark) NY84A: BASF Japan, thermoplastic polyurethane elastomer Tinuvin (registered trademark) 770: BASF Japan, hindered amine light stabilizer Titanium dioxide: Ishihara Sangyo Kaisha, Ltd., A-220

[0112] (3) Formation of the mid-layer and cover The resin composition (intermediate layer composition) was injection molded onto a spherical core to obtain an intermediate layer-coated sphere. The obtained intermediate layer-coated sphere was placed in a final mold with numerous pimples on the cavity surface. Half shells were obtained from the resin composition (cover composition) by compression molding. Two half shells were placed on the intermediate layer-coated sphere placed in the final mold to coat it, resulting in a golf ball with numerous dimples on the outermost cover that were the inverse of the pimples 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 Table 5.

[0113] [Table 3]

[0114] [Table 4]

[0115] [Table 5]

[0116] Golf balls Nos. 1 to 11 have spherical cores formed from a rubber composition containing natural rubber, and the surface coverage of the multiple dimples is 45% or more and less than 75%. These golf balls Nos. 1 to 11 have reduced rolling distances when shot with a fairway wood.

[0117] Golf balls Nos. 12 to 14 have spherical cores formed from a rubber composition that does not contain natural rubber. These golf balls Nos. 12 to 14 had high ball speeds and long rolling distances when shot. Golf balls No. 15 and 16 are those in which the surface occupancy rate of a plurality of dimples is less than 45% or 75% or more. In these golf balls No. 15 and 16, the maximum height during a fairway shot was low and the rolling distance was long.

[0118] (Aspect of the present invention) The present invention (1) has a spherical core, an intermediate layer covering the spherical core, and an outermost layer cover located outside the intermediate layer and provided with a plurality of dimples. 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 natural rubber. The outermost layer cover is a golf ball characterized in that the occupancy rate of the total area of the plurality of dimples in the surface area of a virtual sphere assuming that the plurality of dimples do not exist is 45% or more and less than 75%.

[0119] The present invention (2) relates to the core hardness (H0) of the spherical core, the hardness (H 2.5 ) at a point 2.5 mm in the radial direction from the center of the spherical core, the hardness (H 5.0 ) at a point 5.0 mm in the radial direction from the center of the spherical core, the hardness (H 7.5 ) at a point 7.5 mm in the radial direction from the center of the spherical core, the hardness (H 10 ) at a point 10 mm in the radial direction from the center of the spherical core, the hardness (H 12.5 ) at a point 12.5 mm in the radial direction from the center of the spherical core, the hardness (H 15 ) at a point 15 mm in the radial direction from the center of the spherical core, and the surface hardness (Hs) satisfy the relationship H0 < H 2.5 < H 5.0 < H 7.5 < H 10 < H 12.5 < H 15 < Hs, and the core hardness (H0) of the spherical core is 70 or less in Shore C hardness, which is the golf ball according to the present invention (1).

[0120] The present invention (3) relates to the core hardness (H0) of the spherical core, the hardness (H 2.5), and the hardness (H 10 ), and the hardness (H 12.5 ) and the hardness (H 15 ) is Shore C hardness, H 2.5 -H0≧3.0, H 12.5 -H 10 ≧3.0, and H 15 -H 12.5 The golf ball of the present invention (1) or (2) satisfies the relationship of ≧3.0.

[0121] The present invention (4) is a method for measuring the hardness (H 5.0 ), and the hardness (H 7.5 ) and the hardness (H 10 ) is Shore C hardness, H 7.5 -H 5.0 <3.0, and H 10 -H 7.5 The golf ball according to any one of the present inventions (1) to (3) satisfies the relationship of <3.0.

[0122] The present invention (5) is the golf ball according to any one of the present inventions (1) to (4), wherein the difference in hardness (Hs-H0) between the center hardness (H0) of the spherical core and the surface hardness (Hs) of the spherical core is 20 or more in Shore C hardness.

[0123] The present invention (6) is the golf ball according to any one of the present inventions (1) to (5), wherein the content of the natural rubber is 20% by mass to 100% by mass of 100% by mass of the base rubber.

[0124] The present invention (7) is the golf ball according to any one of the present inventions (1) to (6), wherein 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.

[0125] The present invention (8) is the golf ball according to any one of the present inventions (1) to (7), wherein the cover composition forming the outermost cover layer is a resin composition containing a urethane resin as a base resin, and the cover composition forming the outermost cover layer has a slab hardness of 40 or less in Shore D hardness.

[0126] The present invention (9) is a golf ball according to any one of the present inventions (1) to (8), wherein the intermediate layer composition forming the intermediate layer is a resin composition containing an ionomer resin as a base resin, and the intermediate layer composition forming the intermediate layer has a slab hardness of 50 or more in Shore D hardness. [Explanation of symbols]

[0127] 2: Golf ball, 4: Spherical core, 6: Mid layer, 8: Outermost cover, 10: Dimples, 12: Land

Claims

1. A golf ball having a spherical core, a mid layer enclosing the spherical core, and an outermost cover layer positioned outside the mid layer and having a plurality of dimples formed 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 natural rubber, a surface area of ​​a phantom sphere that would be assumed to have no dimples, and the total area of ​​the dimples in the outermost cover layer is 45% or more and less than 75% of the surface area of ​​the phantom sphere that would have no dimples;

2. The spherical core has a center 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 ), hardness (H 5.0 ), hardness (H 7.5 ), hardness (H 10 ), hardness (H 12.5 ), hardness (H 15 ) and surface hardness (Hs) are H0<H 2.5 <H 5.0 <H 7.5 <H 10 <H 12.5 <H 15 <Hs relationship is satisfied, 2. The golf ball according to claim 1, wherein the spherical core has a center hardness (H0) of 70 or less in Shore C hardness.

3. The spherical core has a center hardness (H0), a hardness at a point 2.5 mm radially from the center of the spherical core (H 2.5 ), hardness (H 10 ), hardness (H 12.5 ) and the hardness (H 15 ) is the Shore C hardness, H 2.5 -H0≧3.0、 H 12.5 -H 10 ≧3.0, and H 15 -H 12.5 2. The golf ball according to claim 1, which satisfies the relationship: .gtoreq.3.

0.

4. The spherical core has a hardness (H 5.0 ), hardness (H 7.5 ) and the hardness (H 10 ) is the Shore C hardness, H 7.5 -H 5.0 < 3.0, and H 10 -H 7.5 2. The golf ball according to claim 1, wherein the relationship of .lambda.<3.0 is satisfied.

5. 2. The golf ball according to claim 1, wherein the difference in hardness (Hs-H0) between the center hardness (H0) of the spherical core and the surface hardness (Hs) of the spherical core is 20 or more in Shore C hardness.

6. 2. The golf ball according to claim 1, wherein the content of the natural rubber is 20% by weight to 100% by weight based on 100% by weight of the base rubber.

7. 2. The golf ball according to claim 1, wherein 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.

8. the cover composition forming the outermost cover layer is a resin composition containing a urethane resin as a base resin, 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.

9. 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 intermediate layer composition forming the intermediate layer has a slab hardness of 50 or greater in Shore D hardness.

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