Golf ball

Abstract

To provide a golf ball that rolls only a short distance on fairway wood shots and has excellent controllability of a flight distance.SOLUTION: The golf ball comprises a spherical core, one or more intermediate layers positioned outside 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 rubber component, a co-crosslinking agent, and a crosslinking initiator. The rubber component contains a natural rubber. A total lower volume Vi (mm3) of the plurality of dimples is less than 365 mm3, and an occupation ratio of the dimples is 75% or more.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] Conventionally, as a spherical core of a golf ball, spherical cores made of various rubber materials have been proposed. For example, Patent Document 1 describes a golf ball for a practice range obtained by vulcanizing a composition containing 3 to 35 parts by weight of a low-rebound 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 with respect to 100 parts by weight of a base rubber (see Patent Document 1 (Claim 1, lines 11 to 17 in the upper left column on page 3)).

[0003] Further, Patent Document 2 describes a golf ball for a practice 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 with respect to 100 parts by weight of a base rubber (see Patent Document 2 (Claim 1, lines 4 in the lower left column on page 2 to line 2 in the lower right column)).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In golf score-making, not only the flying distance of the driver shot but also the stability of the flying distance of the golf ball after the second shot and subsequent shots are important. When the distance to the green is long, a fairway wood is used. In the shot with a fairway wood, it is particularly important to stop the golf ball at the aimed flying distance. However, in the shot with a fairway wood, there is a problem that since the initial ball speed is high and the spin amount is small, the golf ball rolls a large distance after landing, making it difficult to stop the golf ball at the aimed flying distance.

[0006] The present invention has been made in view of the above circumstances, and an object thereof is to provide a golf ball having a small rolling distance of the golf ball in a shot with a fairway wood and excellent controllability of the flying distance.

Means for Solving the Problems

[0007] The golf ball of the present invention that has solved the above problems includes a spherical core, one or more intermediate layers located outside the spherical core, and an outermost layer cover provided with a plurality of dimples arranged outside the intermediate layer, and is a golf ball having the spherical core formed from a rubber composition containing a rubber component, a co-crosslinking agent, and a crosslinking initiator, the rubber component containing natural rubber, the total volume Vi (mm 3 ) of the lower parts of the plurality of dimples is less than 365 mm 3 , and is characterized in that the occupancy rate of the dimples defined by the following formula is 75% or more. Occupancy rate of dimples (%) = 100 × total area of all dimples / surface area of a virtual sphere assuming that there are no dimples on the surface of the golf ball

[0008] ​Due to the above configuration, the golf ball of the present invention has increased lift and increased hang time. The increased hang time of the shot results in a higher height at the highest point of the hit ball and a sharper drop angle. The sharper drop angle of the golf ball can suppress the rolling distance of the golf ball after landing. Further, since the rubber component forming the spherical core contains natural rubber, the speed of the golf ball at the time of landing decreases, and the rolling distance can be shortened.

Advantages of the Invention

[0009] According to the present invention, it is possible to provide a golf ball with a small rolling distance of the golf ball in a shot with a fairway wood and excellent controllability of the flying distance.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Modes for Carrying Out the Invention

[0011] The golf ball of the present invention has a spherical core, one or more intermediate layers located outside the spherical core, and an outermost layer cover provided with a plurality of dimples disposed outside the intermediate layer, and is a golf ball characterized in that the spherical core is formed from a rubber composition containing a rubber component, a co-crosslinking agent, and a crosslinking initiator, the rubber component contains natural rubber, the total volume Vi (mm 3 ) of the lower parts of a plurality of dimples is less than 365 mm 3 , and the occupancy rate of the dimples defined by the following formula is 75% or more. Occupancy rate of dimples (%) = 100 × total area of all dimples / surface area of a virtual sphere assuming no dimples exist on the golf ball surface

[0012] (Structure of golf ball) The golf ball of the present invention has a spherical core, one or more intermediate layers disposed outside the spherical core, and an outermost layer cover provided with a plurality of dimples disposed outside the one or more intermediate layers.

[0013] Examples of the golf ball of the present invention include, for example, a three-piece golf ball composed of a spherical core, a single intermediate layer disposed so as to cover the spherical core, and a single outermost layer cover covering the intermediate layer; a multi-piece golf ball (including a three-piece golf ball) having a spherical core, one or more intermediate layers disposed so as to cover the spherical core, and an outermost layer cover disposed so as to cover the intermediate layer. The present invention can be preferably applied to any of the above-structured golf balls.

[0014] The structure of the spherical core may be either a single-layer structure or a multi-layer structure, but a single-layer structure is preferred. The intermediate layer may be one or more layers, and may be a single layer or two or more layers. The intermediate layer may be referred to as an outer core or an inner cover depending on the structure of the golf ball.

[0015] Figure 1 is a partially cut-away cross-sectional view showing a golf ball according to an embodiment of the present invention. The golf ball 2 shown in FIG. 1 has a spherical core 4, an intermediate layer 6 covering the core 4, and an outermost layer cover 8 located outside the intermediate layer 6. This 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 the land 12. This golf ball 2 is provided with a paint layer and a mark layer outside the outermost layer cover 8, but the illustration of these layers is omitted.

[0016] (Spherical core) First, the spherical core of the golf ball of the present invention will be described. The diameter of the spherical core is preferably 34.8 mm or more, more preferably 36.8 mm or more, still more preferably 38.0 mm or more, preferably 42.2 mm or less, more preferably 41.8 mm or less, still more preferably 41.2 mm or less, and most preferably 40.8 mm or less. If the diameter of the spherical core is 34.8 mm or more, the thickness of the cover will not become too thick, and the hitting feeling will be better. On the other hand, if the diameter of the spherical core is 42.2 mm or less, the cover will not become too thin, and the function of the cover will be more exerted.

[0017] The spherical core has the center hardness (H0) of the spherical core, the hardness (H 2.5 ) at a point 2.5 mm from the center of the spherical core in the radial direction, the hardness (H 5 ) at a point 5 mm from the center of the spherical core in the radial direction, the hardness (H 7.5 ) at a point 7.5 mm from the center of the spherical core in the radial direction, the hardness (H 10 ) at a point 10 mm from the center of the spherical core in the radial direction, the hardness (H 12.5 ) at a point 12.5 mm from the center of the spherical core in the radial direction, the hardness (H 15 ) at a point 15 mm from the center of the spherical core in the radial direction, and the surface hardness (Hs), such that H0 < H 2.5 < H 5 < H 7.5 < H 10 < H 12.5 < H 15It preferably satisfies the relationship of <Hs>, and the core hardness (H0) of the spherical core is 60 or less in Shore C hardness.

[0018] 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 during an approach shot becomes good. When the hitting feeling during an approach shot is good, it is easy to feel the reaction in the hand during impact, it is easy to adjust the hitting force, and the controllability of the flight distance in the approach shot is improved.

[0019] 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 preferably 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. If the hardness differences (H 2.5 - H0), (H 12.5 - H 10 ), and (H 15 - H 12.5 ) are within the above ranges, the deformation amount of the spherical core during an approach shot becomes large, the initial ball speed immediately after impact can be suppressed lower, and the controllability of the flight distance in the approach shot is further improved.

[0020] 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.

[0021] The hardness (H 10 at a point 10.0 mm from the center of the spherical core in the radial direction) and the hardness (H at a point 12.5 mm in the radial direction from the center of the spherical core 12.5 ) and the hardness difference (H 12.5 -H 10 ) is Shore C hardness, preferably 3.0 or more, more preferably 3.4 or more, still more preferably 3.8 or more, and preferably 11.0 or less, more preferably 10.0 or less, still more preferably 9.0 or less.

[0022] The hardness (H at a point 12.5 mm in the radial direction from the center of the spherical core 12.5 ) and the hardness (H at a point 15 mm in the radial direction from the center of the spherical core 15 ) and the hardness difference (H 15 -H 12.5 ) is Shore C hardness, preferably 3.0 or more, more preferably 3.4 or more, still more preferably 3.8 or more, and preferably 10.0 or less, more preferably 9.0 or less, still more preferably 8.0 or less.

[0023] The spherical core preferably satisfies the relationship that the hardness (H 5 ), the hardness (H 7.5 ) and the hardness (H 10 ) are Shore C hardness, H 7.5 -H 5 < 3.0, and H 10 -H 7.5 < 3.0. If the hardness difference (H 7.5 -H 5 ) and the hardness difference (H 10 -H 7.5 ) are within the above ranges, the deformation energy due to the impact of the approach shot is likely to be transmitted to the inside of the spherical core, and it is easy to exhibit the characteristics of the spherical core.

[0024] The hardness (H at a point 5 mm in the radial direction from the center of the spherical core 5 ) and the hardness (H at a point 7.5 mm in the radial direction from the center of the spherical core 7.5 ) and the hardness difference (H 7.5 -H 5) is Shore C hardness, preferably 0.2 or more, more preferably 0.3 or more, still more preferably 0.4 or more, and preferably less than 3.0, more preferably 2.8 or less, still more preferably 2.6 or less.

[0025] The hardness (H 7.5 ) at a point 7.5 mm in the radial direction from the center of the spherical core and the hardness (H 10 ) at a point 10 mm in the radial direction from the center of the spherical core, the hardness difference (H 10 -H 7.5 ) is Shore C hardness, preferably 0.1 or more, more preferably 0.2 or more, still more preferably 0.3 or more, and preferably less than 3.0, more preferably 2.9 or less, still more preferably 2.8 or less.

[0026] The hardness difference (Hs - H0) between the center hardness (H0) of the spherical core and the surface hardness (Hs) of the spherical core is Shore C hardness, preferably 20 or more, more preferably 22 or more, still more preferably 24 or more. If the hardness difference (Hs - H0) is 20 or more, the hitting feeling in a driver shot becomes good. The hardness difference (Hs - H0) is preferably 40 or less, more preferably 37 or less, still more preferably 35 or less.

[0027] The center hardness (H0) of the spherical core is Shore C hardness, preferably 42 or more, more preferably 44 or more, still more preferably 46 or more, and preferably 60 or less, more preferably 57 or less, still more preferably 55 or less.

[0028] The surface hardness (Hs) of the spherical core is Shore C hardness, preferably 70 or more, more preferably 72 or more, still more preferably 74 or more, and preferably 90 or less, more preferably 87 or less, still more preferably 85 or less.

[0029] The diameter of the spherical core is preferably 34.8 mm or more, more preferably 36.8 mm or more, still more preferably 38.0 mm or more, preferably 42.2 mm or less, more preferably 41.8 mm or less, still more preferably 41.2 mm or less, and most preferably 40.8 mm or less.

[0030] When the spherical core has a diameter of 34.8 mm to 42.2 mm, the compression deformation amount (the amount by which the spherical core shrinks in the compression direction) from the state of applying an initial load of 98 N to the state of applying a final load of 1275 N is preferably 2.0 mm or more, more preferably 2.5 mm or more, still more preferably 3.0 mm or more, preferably 5.0 mm or less, more preferably 4.5 mm or less, still more preferably 4.0 mm or less. If the compression deformation amount is within the above range, the hitting feeling will be better.

[0031] (Intermediate layer) The golf ball of the present invention has one or more intermediate layers disposed outside the spherical core. The intermediate layer may be a single layer or two or more layers. Depending on the structure of the golf ball, the intermediate layer may be referred to as an outer core or an inner cover.

[0032] The material hardness Hm of the intermediate layer is Shore D hardness, preferably 50 or more, more preferably 55 or more, still more preferably 60 or more, preferably 75 or less, more preferably 73 or less, still more preferably 71 or less. If the material hardness Hm is 50 or more, the flight distance will be good due to low spin in driver shots, and if it is 75 or less, the hitting feeling of driver shots will be good. The material hardness Hm of the intermediate layer is the slab hardness of the intermediate layer composition forming the intermediate layer. When there are multiple intermediate layers, the material hardness Hm is the slab hardness of the intermediate layer composition forming the outermost intermediate layer.

[0033] The thickness Tm of the intermediate layer is preferably 0.8 mm or more, more preferably 0.9 mm or more, still more preferably 1.0 mm or more, and preferably 3.0 mm or less, more preferably 2.6 mm or less, still more preferably 2.2 mm or less. If the thickness Tm is 0.8 mm or more, the durability is good, and if it is 3.0 mm or less, a good hitting feeling can be obtained at the time of driver shot. When there are a plurality of intermediate layers, the total thickness of all the intermediate layers is defined as the thickness Tm of the intermediate layer.

[0034] (Outermost layer cover) The golf ball of the present invention has an outermost layer cover disposed outside the intermediate layer. A plurality of dimples are provided on the surface of the outermost layer cover. The dimple is a recess provided in the outermost layer cover.

[0035] As shown in FIGS. 2 and 3, a large number of dimples 10 are provided on the surface of the outermost layer cover of the golf ball 2. The contour of each dimple 10 is a circle.

[0036] FIG. 4 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 vertical direction in FIG. 4 is the depth direction of the dimple 10. What is indicated by the two-dot chain line 14 in FIG. 4 is a virtual sphere. The surface of the virtual sphere 14 is the surface of the golf ball 2 when it is assumed that the dimples 10 do not exist. The diameter of the virtual sphere 14 is the same as the diameter of the golf ball 2. The dimple 10 is recessed from the surface of the virtual sphere 14. The land 12 coincides with the surface of the virtual sphere 14. In the present embodiment, the cross-sectional shape of the dimple 10 is substantially an arc. The radius of curvature of this arc is indicated by the symbol CR in FIG. 4.

[0037] What is indicated by the arrow Dm in FIG. 4 is the diameter of the dimple 10. This diameter Dm is the longest distance between one contact point Ed and the other contact point Ed when a common tangent line Tg is drawn on both sides of the dimple 10. The contact point Ed is also the edge of the dimple 10. The edge Ed defines the contour of the dimple 10.

[0038] In the present invention, the "lower volume of the dimple" refers to the volume of the lower part of the dimple surrounded by the plane in contact with the golf ball at the edge Ed of the dimple and the surface of the dimple 10. The "total lower volume Vi of the dimple" is the sum of the lower volumes of all the dimples.

[0039] In the golf ball of the present invention, it is preferable that the total lower volume Vi of the plurality of dimples is less than 365 mm 3 more preferably less than 350 mm 3 even more preferably less than 335 mm 3 If the total lower volume Vi is less than 365 mm 3 the lift force acting during the shot becomes larger and the trajectory becomes higher. The total lower volume Vi is preferably 220 mm 3 or more, more preferably 230 mm 3 or more, even more preferably 240 mm 3 or more. If the total lower volume Vi is 220 mm 3 or more, the trajectory will not blow up too much.

[0040] The diameter Dm of the dimple 10 is preferably 2.0 mm or more, more preferably 2.5 mm or more, even more preferably 2.8 mm or more, and preferably 6.0 mm or less, more preferably 5.5 mm or less, even more preferably 5.0 mm or less. If the diameter Dm is 2.0 mm or more, it is easy to contribute to the turbulent flow caused by the dimple, and if it is 6.0 mm or less, the essence of the golf ball which is substantially a sphere can be maintained.

[0041] The plurality of dimples may be formed by forming a plurality of dimples having a single diameter, or a combination of dimples of a plurality of types of diameters may be used. The golf ball 2 shown in FIGS. 2 and 3 includes five types of dimples: dimple A having a diameter of 4.400 mm, dimple B having a diameter of 4.285 mm, dimple C having a diameter of 4.150 mm, dimple D having a diameter of 3.875 mm, and dimple E having a diameter of 3.000 mm.

[0042] In FIG. 4, what is indicated by the double 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 virtual sphere 14. The first depth Dp1 is preferably 0.15 mm or more, more preferably 0.17 mm or more, still more preferably 0.20 mm or more, and preferably 0.45 mm or less, more preferably 0.43 mm or less, still more preferably 0.40 mm or less. If the first depth Dp1 is 0.15 mm or more, sufficient lift force obtained by the dimple can be generated, and if it is 0.45 mm or less, the essence of the golf ball which is substantially a sphere can be maintained.

[0043] In FIG. 4, what is indicated by the double 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, still more preferably 0.12 mm or more, and preferably 0.30 mm or less, more preferably 0.28 mm or less, still more preferably 0.26 mm or less. If the second depth Dp2 is 0.08 mm or more, it is easy to contribute to the turbulent flow caused by the dimple, and if it is 0.30 mm or less, the lift force obtained by the dimple is not too large, and the flight distance performance becomes good at the time of a driver shot.

[0044] The area A of the dimple 10 is the area of the region surrounded by the contour of the dimple 10 when viewing the center of the golf ball 2 from infinity. In the case of the circular dimple 10, the area A is calculated by the following mathematical formula. A = π × (Dm / 2) 2

[0045] In the golf ball 2 shown in FIGS. 2 and 3, the area of the dimple A is 15.21 mm 2 and the area of the dimple B is 14.42 mm 2 and the area of the dimple C is 13.53 mm 2 and the area of the dimple D is 11.79 mm 2 and the area of the dimple E is 7.07 mm 2 respectively.

[0046] For the golf ball of the present invention, the occupancy rate of the dimples is preferably 75% or more, more preferably 78% or more, still more preferably 81% or more, preferably 95% or less, more preferably 92% or less, and still more preferably 90% or less. If the occupancy rate is within the above range, the effect of turbulent flow caused by the dimples becomes greater. As a result, the maximum height of the golf ball at the shot with the fairway wood becomes higher and the falling angle becomes an acute angle. By making the falling angle of the golf ball an acute angle, the rolling distance of the golf ball after landing can be suppressed. The occupancy rate of the dimples is defined by the following formula. Occupancy rate of dimples (%) = 100 × total area of all dimples / surface area of a virtual sphere assuming no dimples exist on the golf ball surface

[0047] The number of the dimples may be appropriately adjusted according to the diameter and occupancy rate of the dimples. In consideration of the occupancy rate and the action of each dimple, the total number of the dimples 10 is preferably 250 or more, more preferably 280 or more, still more preferably 300 or more, preferably 450 or less, more preferably 410 or less, and still more preferably 390 or less.

[0048] The material hardness Hc of the outermost cover is preferably 20 or more, more preferably 22 or more, still more preferably 24 or more, and preferably 40 or less, more preferably 38 or less, still more preferably 36 or less in Shore D hardness. If the material hardness Hc is 20 or more, the amount of spin during driver shot does not become too much and the flight distance performance becomes good. If it is 40 or less, the spin performance during approach shot becomes even better. The material hardness Hc of the outermost cover is the slab hardness of the cover composition forming the outermost cover.

[0049] The thickness Tc of the outermost cover is preferably 0.4 mm or more, more preferably 0.5 mm or more, still more preferably 0.6 mm or more, and preferably 1.0 mm or less, more preferably 0.9 mm or less, still more preferably 0.8 mm or less. If the thickness Tc is 0.4 mm or more, the spin performance during approach shot becomes even better. If it is 1.0 mm or less, the amount of spin during driver shot does not become too much and the flight distance performance becomes good.

[0050] The material hardness Hm of the intermediate layer is preferably greater than the material hardness Hc of the cover. The hardness difference (Hm - Hc) between the material hardness Hm of the intermediate layer and the material hardness Hc of the cover is preferably 20 or more, more preferably 22 or more, still more preferably 24 or more, and preferably 40 or less, more preferably 39 or less, still more preferably 38 or less in Shore D hardness. If the hardness difference (Hm - Hc) is within the above range, the hitting feeling during driver shot becomes good.

[0051] The diameter of the golf ball of the present invention is preferably from 40 mm to 45 mm. From the viewpoint of meeting 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. Further, the mass of the golf ball of the present invention is preferably from 40 g to 50 g. From the viewpoint of obtaining a large inertia, the mass is more preferably 44 g or more, and particularly preferably 45.00 g or more. From the viewpoint of meeting the USGA standards, the mass is particularly preferably 45.93 g or less.

[0052] When the golf ball of the present invention has a diameter of 40 mm to 45 mm, the compression deformation amount (the amount by which the golf ball shrinks in the compression direction) when the final load of 1275 N is applied from the state where the initial load of 98 N is applied is preferably 2.0 mm or more, more preferably 2.2 mm or more, still more preferably 2.4 mm or more, and preferably 3.5 mm or less, more preferably 3.3 mm or less, still more preferably 3.1 mm or less, and particularly preferably 3.0 mm or less. A golf ball having a compression deformation amount of 2.0 mm or more is not too hard and has a good hitting feeling in a driver shot. On the other hand, by setting the compression deformation amount to 3.5 mm or less, the durability is improved.

[0053] Hereinafter, the materials constituting the golf ball of the present invention will be described.

[0054] (Spherical core) The spherical core of the golf ball of the present invention is preferably formed from a rubber composition containing (a) a rubber component, (b) a co-crosslinking agent, and (c) a crosslinking initiator (hereinafter sometimes referred to as "rubber composition for core").

[0055] The rubber component contains natural rubber (NR). By containing natural rubber in the rubber component that forms the spherical core, the golf ball speed at landing can be reduced, and the rolling distance can be shortened. The natural rubber is produced by damaging a plant that produces latex (emulsion) of natural rubber to recover the latex, and coagulating the rubber component contained in the latex. The natural rubber may be used alone or in combination of two or more kinds.

[0056] Examples of the plant that produces the latex of the natural rubber include, for example, Para rubber tree, Ceylon rubber tree of the Euphorbiaceae family, Indian rubber tree, Panama rubber tree, Lagos rubber tree of the Moraceae family, Acacia rubber tree, Tragacanth rubber tree of the Leguminosae family, Japanese staghorn sumac, Zanzibar gutta, Funtumia elastica, Urceola, Guayule rubber tree, Rubber dandelion of the Asteraceae family, Gutta percha tree of the Euphorbiaceae family, Balata rubber tree, Sapodilla, Morning glory of the Convolvulaceae family, Euonymus of the Celastraceae family, etc.

[0057] Examples of the natural rubber include a CV grade in which a constant viscosity agent or the like is added to the raw latex to stabilize the rubber viscosity, and a non-CV grade in which the rubber viscosity is not stabilized. These may be used alone or in combination of two or more kinds. Among these, a CV grade having a particularly stable viscosity is preferable. The natural rubber may be either SMR (Standard Malaysian Rubber) or SVR (Standard Vietnamese Rubber).

[0058] The natural rubber is cis-1,4-polyisoprene, and either sheet rubber or block rubber can be used. The natural rubber also includes modified natural rubbers obtained by modifying natural rubber, 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, styrene-modified natural rubber, etc. Among these, it is preferable that the natural rubber does not contain epoxidized natural rubber.

[0059] As the natural rubber, Technical Specified Rubbers (TSR) and Ribbed Smoked Sheet (RSS) are preferred. Further, the natural rubber may be compounded with a viscosity stabilizer.

[0060] The Mooney viscosity (ML 1+4 (100 °C)) of the natural rubber is preferably 30 or more, more preferably 35 or more, still more preferably 40 or more, and preferably 80 or less, more preferably 75 or less, still more preferably 70 or less. In this specification, the Mooney viscosity (ML 1+4 (100 °C)) is a value measured under the conditions of using an L rotor, a preheating time of 1 minute, a rotor rotation time of 4 minutes, and 100 °C in accordance with JIS K6300 (2013).

[0061] The rubber component may contain only natural rubber or may contain natural rubber and synthetic rubber. When the rubber component contains natural rubber and synthetic rubber, the content of natural rubber in 100% by mass of the rubber component is preferably 20% by mass or more, more preferably 30% by mass or more, still more preferably 40% by mass or more, and particularly preferably 70% by mass or more. When the content is 20% by mass or more, the hitting feeling at the time of iron shot becomes good.

[0062] Examples of the synthetic rubber include diene rubbers such as polybutadiene rubber (BR), polyisoprene rubber (IR), styrene-butadiene rubber (SBR), chloroprene rubber (CR), butyl rubber (IIR), acrylonitrile-butadiene rubber (NBR); 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, chlorosulfonated polyethylene rubber, etc. These may be used alone or in combination of two or more.

[0063] The synthetic rubber component preferably contains a diene rubber, and more preferably contains a polybutadiene rubber. In particular, it is more preferable to contain a high-cis polybutadiene having a cis-1,4 bond content 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 synthetic rubber is preferably 50% by mass or more, more preferably 70% by mass or more, still more preferably 90% by mass or more, and it is also preferable to contain only high-cis polybutadiene rubber as the synthetic rubber.

[0064] 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 still more preferably 1.5% by mass or less.

[0065] The high-cis polybutadiene is preferably synthesized with a rare earth element-based catalyst. In particular, the use of a neodymium-based catalyst using a neodymium compound, which is a lanthanum series rare earth element compound, is preferable because a polybutadiene rubber with a high content of 1,4-cis bonds and a low content of 1,2-vinyl bonds can be obtained with excellent polymerization activity.

[0066] 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, still more preferably 2.4 or more, and preferably 6.0 or less, more preferably 5.0 or less, and still more preferably 4.0 or less. When the molecular weight distribution (Mw / Mn) of the high-cis polybutadiene is within the above range, the workability is improved. The molecular weight distribution is measured by gel permeation chromatography (manufactured by Tosoh Corporation, "HLC-8120GPC") using a differential refractometer as a detector, column: GMHHXL (manufactured by Tosoh Corporation), column temperature: 40 °C, mobile phase: tetrahydrofuran, and is a value calculated as a standard polystyrene conversion value.

[0067] The Mooney viscosity (ML 1+4(100 °C)) is preferably 30 or more, more preferably 32 or more, still more preferably 35 or more, and preferably 140 or less, more preferably 120 or less, still more preferably 100 or less.

[0068] The rubber composition for the core used in the present invention contains (b) a co-crosslinking agent. (b) The co-crosslinking agent has an action of crosslinking rubber molecules by graft polymerization to the base rubber molecular chain. The co-crosslinking agent may be used alone or in combination of two or more. As the co-crosslinking agent, α,β-unsaturated carboxylic acids having 3 to 8 carbon atoms and / or their metal salts are preferable. Examples of the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms include acrylic acid, methacrylic acid, fumaric acid, maleic acid, crotonic acid, etc.

[0069] 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 component can also be used alone or as a mixture of two or more. Among these, as the metal component, divalent metals such as magnesium, calcium, zinc, barium, and cadmium are preferable. This is because when a divalent metal salt of an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms is used, metal crosslinking is likely to occur between rubber molecules. In particular, as the divalent metal salt, zinc acrylate is preferable because the resilience of the obtained golf ball becomes high. Note that 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.

[0070] (b) The content of the co-crosslinking agent may be appropriately adjusted according to the desired hardness of the spherical core. The content of the co-crosslinking agent is preferably 20 parts by mass or more, more preferably 23 parts by mass or more, still more preferably 25 parts by mass or more, preferably 60 parts by mass or less, more preferably 55 parts by mass or less, and still more preferably 50 parts by mass or less, based on 100 parts by mass of the base rubber.

[0071] (c) The crosslinking initiator is compounded to crosslink the (a) rubber component. As the (c) crosslinking initiator, organic peroxides are preferred. Specifically, examples of the organic peroxides include organic peroxides such as 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.

[0072] (c) The content of the crosslinking initiator is preferably 0.2 parts by mass or more, more preferably 0.4 parts by mass or more, still more preferably 0.6 parts by mass or more, preferably 5.0 parts by mass or less, more preferably 2.5 parts by mass or less, and still more preferably 1.0 parts by mass or less, based on 100 parts by mass of the (a) rubber component. When the content of the (c) crosslinking initiator is within the above range, the hardness of the formed core becomes appropriate and the durability of the golf ball is improved.

[0073] The rubber composition preferably further contains (d) a metal compound. As the (d) metal compound, for example, it can be used to neutralize the (b) co-crosslinking agent in the rubber composition or to adjust the mass of the rubber composition.

[0074] Examples of the (d) 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 preferred (d) metal compound is a divalent metal compound, and more preferably a zinc compound. This is because the divalent metal compound reacts with an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms to form a metal crosslink. Further, by using a zinc compound, a golf ball with good durability can be obtained. These (d) metal compounds may be used alone or in combination of two or more.

[0075] The rubber composition may further contain an (e) organic sulfur compound. The (e) organic sulfur compound is not particularly limited as long as it is an organic compound having a sulfur atom in the molecule. Examples thereof include organic compounds having a thiol group (-SH) or a polysulfide bond (-S-S-, -S-S-S-, or -S-S-S-S-) with 2 to 4 sulfur atoms, or metal salts thereof (-SM, -S-M-S-, etc., where M is a metal atom). Examples of the (e) organic sulfur compound include compounds belonging to thiophenols, thionaphthols, polysulfides, thiurams, thiocarboxylic acids, dithiocarboxylic acids, sulfenamides, dithiocarbamate salts, or thiazoles.

[0076] Examples of the thiophenols include thiophenol; thiophenols substituted with a fluoro group such as 4-fluorothiophenol, 2,4-difluorothiophenol, 2,5-difluorothiophenol, 2,6-difluorothiophenol, 2,4,5-trifluorothiophenol, 2,4,5,6-tetrafluorothiophenol, and pentafluorothiophenol; thiophenols substituted with a chloro group such as 2-chlorothiophenol, 4-chlorothiophenol, 2,4-dichlorothiophenol, 2,5-dichlorothiophenol, 2,6-dichlorothiophenol, 2,4,5-trichlorothiophenol, 2,4,5,6-tetrachlorothiophenol, and pentachlorothiophenol; thiophenols substituted with a bromo group such as 4-bromothiophenol, 2,4-dibromothiophenol, 2,5-dibromothiophenol, 2,6-dibromothiophenol, 2,4,5-tribromothiophenol, 2,4,5,6-tetrabromothiophenol, and pentabromothiophenol; thiophenols substituted with an iodo group such as 4-iodothiophenol, 2,4-diiodothiophenol, 2,5-diiodothiophenol, 2,6-diiodothiophenol, 2,4,5-triiodothiophenol, 2,4,5,6-tetraiodothiophenol, and pentaiodothiophenol; or metal salts thereof.

[0077] Examples of the thionaphthols (naphthalenethiols) include 2-thionaphthol, 1-thionaphthol, 1-chloro-2-thionaphthol, 2-chloro-1-thionaphthol, 1-bromo-2-thionaphthol, 2-bromo-1-thionaphthol, 1-fluoro-2-thionaphthol, 2-fluoro-1-thionaphthol, 1-cyano-2-thionaphthol, 2-cyano-1-thionaphthol, 1-acetyl-2-thionaphthol, 2-acetyl-1-thionaphthol, or metal salts thereof.

[0078] Polysulfides are organic sulfur compounds having a polysulfide bond, and examples thereof include disulfides, trisulfides, and tetrasulfides. As the polysulfides, diphenyl polysulfides are preferable.

[0079] Examples of diphenyl polysulfides include, in addition to diphenyl disulfide; bis(4-fluorophenyl) disulfide, bis(2,5-difluorophenyl) disulfide, bis(2,6-difluorophenyl) disulfide, bis(2,4,5-trifluorophenyl) disulfide, bis(2,4,5,6-tetrafluorophenyl) disulfide, bis(pentafluorophenyl) disulfide, bis(4-chlorophenyl) disulfide, bis(2,5-dichlorophenyl) disulfide, bis(2,6-dichlorophenyl) disulfide, bis(2,4,5-trichlorophenyl) disulfide, bis(2,4,5,6-tetrachlorophenyl) disulfide, bis(pentachlorophenyl) disulfide, bis(4-bromophenyl) disulfide, bis(2,5-dibromophenyl) disulfide, bis(2,6-dibromophenyl) disulfide, bis(2,4,5-tribromophenyl) disulfide, bis(2,4,5,6-tetrabromophenyl) disulfide, bis(pentabromophenyl) disulfide, bis(4-iodophenyl) disulfide, bis(2,5-diiodophenyl) disulfide, bis(2,6-diiodophenyl) disulfide, bis(2,4,5-triiodophenyl) disulfide, bis(2,4,5,6-tetraiodophenyl) disulfide, bis(pentaiodophenyl) disulfide and other diphenyl disulfides substituted with halogen groups; bis(4-methylphenyl) disulfide, bis(2,4,5-trimethylphenyl) disulfide, bis(pentamethylphenyl) disulfide, bis(4-t-butylphenyl) disulfide, bis(2,4,5-tri-t-butylphenyl) disulfide, bis(penta-t-butylphenyl) disulfide and other diphenyl disulfides substituted with alkyl groups; and the like.

[0080] Examples of thiurams include thiuram monosulfides such as tetramethylthiuram monosulfide, thiuram disulfides such as tetramethylthiuram disulfide, tetraethylthiuram disulfide, and tetrabutylthiuram disulfide, and thiuram tetrasulfides such as dipentamethylenethiuram tetrasulfide. Examples of thiocarboxylic acids include naphthalenethiocarboxylic acid. Examples of dithiocarboxylic acids include naphthalenedithiocarboxylic acid. Examples of sulfenamides include N-cyclohexyl-2-benzothiazolesulfenamide, N-oxydiethylene-2-benzothiazolesulfenamide, and N-t-butyl-2-benzothiazolesulfenamide.

[0081] The organic sulfur compound (e) can be used alone or in admixture of two or more.

[0082] The content of the organic sulfur compound (e) is preferably 0.05 part by mass or more, more preferably 0.1 part by mass or more, still more preferably 0.2 part by mass or more, and preferably 5.0 parts by mass or less, more preferably 3.0 parts by mass or less, still more preferably 2.0 parts by mass or less, based on 100 parts by mass of the rubber component (a). When the content of the organic sulfur compound (e) is within the above range, the processability is good and the rubber composition becomes homogeneous.

[0083] The rubber composition may further contain (f) a carboxylic acid and / or its metal salt. As the (f) carboxylic acid and / or its metal salt, a carboxylic acid having 1 to 30 carbon atoms and / or its salt is preferred. As the carboxylic acid, either aliphatic carboxylic acid (saturated fatty acid, unsaturated fatty acid) or aromatic carboxylic acid (such as benzoic acid) can be used. The blending amount of the (f) carboxylic acid and / or its metal salt is preferably 1 part by mass or more and 40 parts by mass or less based on 100 parts by mass of the rubber component.

[0084] The rubber composition may contain additives such as fillers, antioxidants, peptizers, plasticizers, etc. for mass adjustment and the like, if necessary.

[0085] The filler used in the rubber composition is mainly compounded as a mass adjuster for adjusting the mass of the golf ball obtained as the final product, and may be compounded as necessary. Examples of the filler include inorganic fillers such as zinc oxide, barium sulfate, calcium carbonate, magnesium oxide, tungsten powder, and molybdenum powder. The content of the filler is preferably 0.5 part by mass or more, more preferably 1 part by mass or more, still more preferably 2 part by mass or more, based on 100 parts by mass of the rubber component, and preferably 30 parts by mass or less, more preferably 25 parts by mass or less, still more preferably 20 parts by mass or less. If the content of the filler is 0.5 part by mass or more, mass adjustment becomes easy, and if it is 30 parts by mass or less, the weight fraction of the rubber component tends to increase and the durability tends to improve.

[0086] The content of the antioxidant is preferably 0.1 part by mass or more and 1 part by mass or less with respect to 100 parts by mass of the rubber component (a). Also, the content of the peptizer is preferably 0.1 part by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the rubber component (a).

[0087] (Composition for intermediate layer, composition for cover) The intermediate layer of the golf ball of the present invention is preferably formed from a composition for intermediate layer containing a resin component. The outermost cover of the golf ball of the present invention is preferably formed from a composition for cover containing a resin component.

[0088] Examples of the resin component used in the resin composition for forming the outermost cover and the intermediate layer include ionomer resin, polyurethane (thermoplastic polyurethane elastomer, thermosetting polyurethane elastomer), thermoplastic styrene elastomer, thermoplastic polyamide elastomer, thermoplastic polyester elastomer, and the like.

[0089] Examples of the ionomer resin include a binary ionomer resin obtained by neutralizing at least a part of carboxyl groups in a binary copolymer of an olefin and an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms with metal ions, a ternary ionomer resin obtained by neutralizing at least a part of 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 with metal ions, or a mixture thereof.

[0090] Examples of the binary ionomer resin include Himilan (registered trademark) 1555 (Na), 1557 (Zn), 1605 (Na), 1706 (Zn), 1707 (Na), AM7311 (Mg), AM7329 (Zn), AM7337 (manufactured by Mitsui Dow Polychemical Co., Ltd.); Surlyn (registered trademark) 8945 (Na), 9945 (Zn), 8140 (Na), 8150 (Na), 9120 (Zn), 9150 (Zn), 6910 (Mg), 6120 (Mg), 7930 (Li), 7940 (Li), AD8546 (Li) (manufactured by DuPont); Iotek (registered trademark) 8000 (Na), 8030 (Na), 7010 (Zn), 7030 (Zn) (manufactured by ExxonMobil Chemical Company), etc.

[0091] Examples of the ternary ionomer resin include Himilan AM7327 (Zn), 1855 (Zn), 1856 (Na), AM7331 (Na) (manufactured by Mitsui Dow Polychemical Co., Ltd.); Surlyn 6320 (Mg), 8120 (Na), 8320 (Na), 9320 (Zn), 9320W (Zn), HPF1000 (Mg), HPF2000 (Mg) (manufactured by DuPont); Iotek 7510 (Zn), 7520 (Zn) (manufactured by ExxonMobil Chemical Company), etc. Note that Na, Zn, Li, Mg, etc. described in parentheses after the trade names of the ionomer resins indicate the metal species of these neutralizing metal ions.

[0092] The thermoplastic polyurethane elastomer has a urethane bond in the molecule. This urethane bond can be formed by the reaction of 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.

[0093] Specific examples of the thermoplastic polyurethane elastomer include Elastollan (registered trademark) NY80A, NY84A, NY88A, NY95A, ET885, ET890 (manufactured by BASF Japan Ltd.).

[0094] As the thermoplastic styrene-based elastomer, a thermoplastic elastomer containing a styrene block can be preferably used. The styrene block-containing thermoplastic elastomer includes a polystyrene block as a hard segment and a soft segment.

[0095] 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 product of SBS, hydrogenated product of SIS, and hydrogenated product of SIBS. Examples of the hydrogenated product of SBS include styrene-ethylene-butylene-styrene block copolymer (SEBS). Examples of the hydrogenated product of SIS include styrene-ethylene-propylene-styrene block copolymer (SEPS). Examples of the hydrogenated product of SIBS include styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS).

[0096] Specific examples of the thermoplastic styrene-based elastomer include Tefabloc (registered trademark) T3221C, T3339C, SJ4400N, SJ5400N, SJ6400N, SJ7400N, SJ8400N, SJ9400N, SR04 (manufactured by Mitsubishi Chemical Corporation).

[0097] The cover composition constituting the cover preferably contains polyurethane and / or ionomer resin as a resin component, and particularly preferably contains polyurethane. When the cover contains polyurethane as a resin component, the bite of the outermost cover into the club face during an approach shot becomes large, and the amount of spin tends to increase.

[0098] When the cover composition contains polyurethane as a resin component, the content of polyurethane in the resin component is preferably 50% by mass or more, more preferably 60% by mass or more, and still more preferably 70% by mass or more. The cover composition may contain only polyurethane (preferably a thermoplastic polyurethane elastomer) as a resin component.

[0099] When the cover composition contains ionomer resin as a resin component, the content of ionomer resin in the resin component is preferably 50% by mass or more, more preferably 60% by mass or more, and still more preferably 70% by mass or more. When containing ionomer resin, it is also preferable to use a thermoplastic styrene elastomer in combination.

[0100] The intermediate layer composition preferably contains ionomer resin as a resin component. When the intermediate layer composition contains ionomer resin as a resin component, the deformation during a driver shot becomes smooth and the hitting feeling becomes good. When containing ionomer resin, it is also preferable to use a thermoplastic styrene elastomer in combination. The content of 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 still more preferably 70% by mass or more.

[0101] In addition to the resin components described above, the cover composition and the intermediate layer composition may contain pigment components such as white pigments (for example, titanium oxide), blue pigments, and red pigments, weight adjusters such as zinc oxide, calcium carbonate, and barium sulfate, dispersants, anti-aging agents, ultraviolet absorbers, light stabilizers, fluorescent materials, or fluorescent brighteners.

[0102] The content of the white pigment (for example, titanium oxide) is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, relative to 100 parts by mass of the base resin constituting the outermost layer cover, preferably 10 parts by mass or less, and more preferably 8 parts by mass or less. By setting the content of the white pigment to 0.5 parts by mass or more, concealability can be imparted to the cover. Also, if the content of the white pigment is 10 parts by mass or less, the durability of the resulting cover will be good.

[0103] (Method for manufacturing a golf ball) The spherical core of the golf ball of the present invention is formed from the above-described rubber composition for the core. The rubber composition for the core can be obtained by kneading (a) a rubber component, (b) a co-crosslinking agent, (c) a crosslinking initiator, and other components to be blended as necessary. The kneading method is not particularly limited, and for example, it may be carried out using a known kneader such as a kneading roll, a Banbury mixer, or a kneader.

[0104] The spherical core can be molded, for example, by hot pressing the rubber composition for the core. The hot pressing molding conditions of the rubber composition for the core may be appropriately set according to the rubber composition, but usually, it is preferable to heat at 130°C to 200°C for 10 minutes to 60 minutes, or to heat at 130°C to 150°C for 20 minutes to 40 minutes and then heat at 160°C to 180°C for 5 minutes to 15 minutes in two stages.

[0105] The method for forming the intermediate layer of the golf ball of the present invention is not particularly limited, and examples thereof include a method of previously molding the composition for the intermediate layer into a hemispherical shell-shaped half shell, using two of them to wrap the spherical core, and performing pressure molding, or a method of injection molding the composition for the intermediate layer directly onto the spherical core.

[0106] As a method for molding the outermost layer cover of the golf ball of the present invention, for example, a method of molding a hollow shell-shaped shell from a cover composition, covering a sphere with an intermediate layer formed with a plurality of shells and compression molding (preferably, a method of molding a hollow shell-shaped half shell from a cover composition, covering a sphere with two half shells and compression molding), or a method of directly injection molding a cover composition onto a sphere with an intermediate layer formed thereon can be mentioned.

[0107] The golf ball body with the cover molded thereon is preferably taken out from the mold and, if necessary, surface treatment such as deburring, washing, and sandblasting is performed.

[0108] Also, if desired, a coating film or a mark can be formed. The film thickness of the coating film is not particularly limited, but is preferably 5 μm or more, more preferably 6 μm or more, further preferably 7 μm or more, preferably 50 μm or less, more preferably 40 μm or less, and further preferably 30 μm or less. If the film thickness is 5 μm or more, the coating film is less likely to wear and disappear even with continuous use, and if the film thickness is 50 μm or less, the effect of the dimples can be sufficiently obtained. In addition, since the coating film is very thin, the effects of the present invention are not impaired.

Examples

[0109] Hereinafter, the present invention will be described in detail by way of examples. However, the present invention is not limited by the following examples, and any changes and embodiments within the scope not departing from the gist of the present invention are all included in the scope of the present invention.

[0110] [Evaluation Method] (1) Compression deformation amount (mm) For the measurement of the compression deformation amount, the YAMADA type compression tester "SCH" was used. In this tester, a golf ball or a core is placed on a rigid steel plate made of metal. A metal cylinder gradually descends toward this golf ball or core. The golf ball or core sandwiched between the bottom surface of this cylinder and the steel plate deforms. The moving distance of the cylinder from the state where an initial load of 98 N is applied to the golf ball or core to the state where a final load of 1275 N is applied was measured. The compression deformation amount (mm) is this moving distance. The moving speed of the cylinder until the initial load is applied is 0.83 mm / s. The moving speed of the cylinder from when the initial load is applied until the final load is applied is 1.67 mm / s.

[0111] (2) Hardness of the material (slab) (Shore D hardness) Using the composition for the intermediate layer or the composition for the cover, a sheet with a thickness of about 2 mm was produced by injection molding and stored at 23°C for 2 weeks. The hardness of this sheet was measured using an automatic hardness tester (manufactured by H. Barless Co., Ltd., Digi Test II) with three or more sheets stacked so as not to be affected by a measurement substrate or the like. The detector used was "Shore D".

[0112] (3) Core hardness distribution (Shore C hardness) Using an automatic hardness tester (manufactured by H. Barless Co., Ltd., Digi Test II) and with the detector using "Shore C", the Shore C hardness measured on the surface portion of the spherical core was taken as the spherical core surface hardness. Also, the spherical core was cut hemispherically along a plane passing through the center of the spherical core, and the hardness was measured at the center of the cut surface and at a predetermined distance in the radial direction from the center. Each hardness was calculated by measuring the hardness at four points and averaging them.

[0113] (4) Golf ball surface hardness The hardness measured on the land portion in the surface portion of the golf ball was taken as the ball surface hardness. The hardness was measured at four points and calculated by averaging them. The hardness was measured using an automatic hardness tester (manufactured by H. Barless Co., Ltd., Digi Test II). The detector used was "Shore D".

[0114] (5) Fairway Wood Test A fairway wood (Sumitomo Rubber Industries, Ltd., "XXIO (registered trademark) 12", size: #3, shaft hardness: R, loft angle: 15°) was attached to the swing machine of Golf Laboratory Co., Ltd. The impact point was set at the center of the face. A golf ball was struck at a head speed of 38 m / sec, and the ball speed, spin speed, and roll distance (distance from the landing point to the stopping point) immediately after the strike were measured. The measurements were taken 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 speed were measured by taking consecutive photographs of the golf ball immediately after being struck.

[0115] [Manufacture of Golf Balls] (1) Preparation of Core Composition Each raw material was kneaded by a kneading roll to obtain a core composition with the formulation shown in Table 1.

[0116]

Table 1

[0117] The materials used in Table 1 are as follows. Polybutadiene rubber: manufactured by 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 °C)) 55, molecular weight distribution (Mw / Mn) 3) Natural rubber: manufactured by Dau Tieng Rubber Corporation, "CV60" (Mooney viscosity (ML 1+4 (100 °C)) = 60) Zinc diacrylate: manufactured by Nisshoku Techno Fine Chemical Co., Ltd., "ZN-DA90S" Zinc oxide: manufactured by Toho Zinc Co., Ltd., "Ginrei R" Barium sulfate: manufactured by Sakai Chemical Co., Ltd., "Barium Sulfate BD" Benzoic acid: manufactured by Tokyo Chemical Industry Co., Ltd. (purity 98% or more) Bis(pentabromophenyl) disulfide: manufactured by Kawaguchi Chemical Industry Co., Ltd. Diphenyl disulfide: manufactured by Sumitomo Seika Chemicals Co., Ltd. Dicumyl peroxide: manufactured by NOF Corporation, "Perkyl (registered trademark) D"

[0118] (2) Preparation of the intermediate layer composition and the cover composition The raw materials were extruded using a twin-screw kneading extruder to prepare pellet-shaped intermediate layer compositions and cover compositions with the formulations shown in Table 2.

[0119]

Table 2

[0120] (4) Production of spherical core The core composition shown in Table 1 was heated and pressed in an upper and lower mold having a hemispherical cavity to obtain a spherical core. Barium sulfate was added in an appropriate amount so that the mass of the resulting golf ball was 45.3 g.

[0121] (5) Formation of intermediate layer and cover The intermediate layer composition was injection-molded onto the spherical core to obtain a sphere coated with the intermediate layer. The obtained sphere coated with the intermediate layer was put into a final mold having a large number of pimples on the cavity surface. A half shell was obtained from the cover composition by a compression molding method. Two half shells were coated on the sphere coated with the intermediate layer put into the final mold to obtain a golf ball in which a large number of dimples having a shape in which the shape of the pimples on the cavity surface was inverted were formed on the outermost layer cover. The specifications of the dimples formed on the outermost layer cover are shown in Tables 3 to 4 and FIGS. 2 to 3, 5 to 8. The results of evaluating the obtained golf balls are shown in Tables 5 to 6.

[0122]

Table 3

[0123]

Table 4

[0124]

Table 5

[0125]

Table 6

[0126] From the results in Tables 5 to 6, a golf ball having a spherical core, one or more intermediate layers located outside the spherical core, and an outermost layer cover provided with a plurality of dimples disposed outside the intermediate layer, wherein the spherical core is formed from a rubber composition containing a rubber component, a co-crosslinking agent, and a crosslinking initiator, the rubber component contains natural rubber, and the total volume Vi (mm 3 ) of the lower parts of the plurality of dimples is less than 365 mm 3 . It can be understood that the golf ball of the present invention, in which the occupancy rate of the dimples defined by the following formula is 75% or more, has a small rolling distance of the golf ball in a fairway wood shot and excellent controllability of the flying distance. Occupancy rate of dimples (%) = 100 × total area of all dimples / surface area of a virtual sphere assuming that no dimples exist on the golf ball surface

Industrial Applicability

[0127] The golf ball of the present invention has a small rolling distance of the golf ball in a fairway wood shot and excellent controllability of the flying distance.

[0128] A preferred embodiment (1) of the present invention is a golf ball having a spherical core, one or more intermediate layers located outside the spherical core, and an outermost layer cover provided with a plurality of dimples disposed outside the intermediate layer, wherein the spherical core is formed from a rubber composition containing a rubber component, a co-crosslinking agent, and a crosslinking initiator, the rubber component contains natural rubber, the total volume Vi (mm 3 ) of the lower parts of the plurality of dimples is less than 365 mm 3 , and the occupancy rate of the dimples defined by the following formula is 75% or more. Occupancy rate of dimples (%) = 100 × total area of all dimples / surface area of a virtual sphere assuming that no dimples exist on the golf ball surface

[0129] A preferred embodiment (2) of the present invention is that the core hardness (H0) of the spherical core, the hardness (H 2.5 ) at a point 2.5 mm radially from the center of the spherical core, the hardness (H 5 ) at a point 5 mm radially from the center of the spherical core, the hardness (H 7.5 ) at a point 7.5 mm radially from the center of the spherical core, the hardness (H 10 ) at a point 10 mm radially from the center of the spherical core, the hardness (H 12.5 ) at a point 12.5 mm radially from the center of the spherical core, the hardness (H 15 ) at a point 15 mm radially from the center of the spherical core, and the surface hardness (Hs) satisfy H0 < H 2.5 < H 5 < H 7.5 < H 10 < H 12.5 < H 15 < Hs, and the core hardness (H0) of the spherical core is a golf ball of the above embodiment (1) which is 60 or less in Shore C hardness.

[0130] A preferred embodiment (3) of the present invention is that the core hardness (H0), the hardness (H 2.5 ), the hardness (H 10 ), the hardness (H 12.5 ), and the hardness (H 15 ) are in Shore C hardness, 3 ≤ H 2.5 - H0, 3 ≤ H 12.5 - H 10 , and, 3 ≤ H 15 - H 12.5 and satisfy the relationship of the golf ball of the above embodiment (2).

[0131] A preferred embodiment (4) of the present invention is that the hardness (H 5 ), the hardness (H 7.5 ), and the hardness (H 10 ) are in Shore C hardness, H 7.5 - H 5 < 3, H 10 - H 7.5The golf ball of the above aspect (2) or (3) that satisfies the relationship of <3

[0132] A preferred aspect (5) of the present invention is (H S -H 0 ) is a golf ball of any one of aspects (2) to (4) that is 20 or more.

[0133] A preferred aspect (6) of the present invention is that the lower total volume Vi (mm 3 ) is a golf ball of any one of aspects (1) to (5) that is 350 mm 3 or less.

[0134] A preferred aspect (7) of the present invention is that the content of natural rubber in the rubber component is a golf ball of any one of aspects (1) to (6) that is 20% by mass or more and 100% by mass or less.

[0135] A preferred aspect (8) of the present invention is that the material hardness Hm of the intermediate layer is greater than the material hardness Hc of the outermost cover, and is a golf ball of any one of aspects (1) to (7).

[0136] A preferred aspect (9) of the present invention is that the intermediate layer has a slab hardness of 50 or more in Shore D hardness and is formed from a composition for an intermediate layer containing an ionomer resin, and is a golf ball of any one of aspects (1) to (8).

[0137] A preferred aspect (10) of the present invention is that the cover has a slab hardness of 40 or less in Shore D hardness and is formed from a composition for a cover containing polyurethane, and is a golf ball of any one of aspects (1) to (9).

Claims

Claim 1 A golf ball having a spherical core, one or more intermediate layers located outside the spherical core, and an outermost layer cover provided with a plurality of dimples disposed outside the intermediate layer, wherein the spherical core is formed from a rubber composition containing a rubber component, a co-crosslinking agent, and a crosslinking initiator, the rubber component contains natural rubber, and the golf ball is characterized in that the occupancy rate of the dimples defined by the following formula is 75% or more. The total bottom volume Vi (mm ３ ) of a plurality of dimples is less than 365 mm ３ and Occupancy rate of dimples (%) = 100 × total area of all dimples / surface area of a virtual sphere assuming no dimples on the golf ball surface Claim 2 Claim 3 The core center hardness (H0), the hardness (H ２．５ at a point 2.5 mm from the center of the spherical core in the radial direction), the hardness (H ５ at a point 5 mm from the center of the spherical core in the radial direction), the hardness (H ７．５ at a point 7.5 mm from the center of the spherical core in the radial direction), the hardness (H １０ at a point 10 mm from the center of the spherical core in the radial direction), the hardness (H １２．５ at a point 12.5 mm from the center of the spherical core in the radial direction), the hardness (H １５ at a point 15 mm from the center of the spherical core in the radial direction), and the surface hardness (Hs) satisfy H0 < H ２．５ < H ５ < H ７．５ < H １０ < H １２．５ < H １５ < Hs, and the core center hardness (H0) of the spherical core is 60 or less in Shore C hardness. The golf ball according to claim 1. Claim 4 The center hardness (H0), hardness (H ２．５ ), hardness (H １０ ), hardness (H １２．５ ), and hardness (H １５ ) are in Shore C hardness, 3 ≤ H ２．５ -H0, 3 ≤ H １２．５ -H １０ and 3 ≤ H １５ -H １２．５ The golf ball according to claim 2, which satisfies the relationship of Claim 5 The hardness (H ５ ), hardness (H ７．５ ), and hardness (H １０ ) are Shore C hardness, H ７．５ -H ５ < 3、 H １０ -H ７．５ The golf ball according to claim 2, which satisfies the relationship of < 3. Claim 6 (H Ｓ -H ０ ) is 20 or more, the golf ball according to claim 2. Claim 7 The lower total volume Vi (mm ３ ) is 350 mm ３ The golf ball according to claim 1, which is 350 mm or less. The golf ball according to claim 1, wherein the content of natural rubber in the rubber component is 20% by mass or more and 100% by mass or less. Claim 8 The golf ball according to claim 1, wherein the material hardness Hm of the intermediate layer is greater than the material hardness Hc of the outermost layer cover. Claim 9 The golf ball according to claim 1, wherein the intermediate layer has a slab hardness of 50 or more in Shore D hardness and is formed from a composition for intermediate layer containing an ionomer resin. Claim 10 The golf ball according to claim 1, wherein the cover has a slab hardness of 40 or less in Shore D hardness and is formed from a composition for cover containing polyurethane. ​

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