Golf ball

Abstract

To provide a golf ball that curves significantly on short iron shots and that rolls only a short distance after landing.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. The co-crosslinking agent contains methacrylic acid and / or a metal salt thereof. 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] Advanced golfers use draw shots and fade shots to avoid obstacles on the course. Draw shots and fade shots are shots that intentionally bend the golf ball to the left or right, allowing obstacles to be avoided.

[0003] In order to hit draw shots and fade shots, the golfer's shot technique is important. On the other hand, for a golf ball, it is important to make it easier to apply draw and fade by controlling spin characteristics and aerodynamic characteristics.

[0004] For example, in Patent Document 1, in a golf ball having a plurality of dimples and joining lines formed on the outer peripheral edge, a center-of-gravity display point for displaying the center of gravity of the golf ball is formed on the outer surface of the golf ball, a balance line passing through the center-of-gravity display point is formed, and a fade line for guiding a fade shot and a draw line for guiding a draw shot are formed at a constant gap on both sides with the balance line as the center. The balance line passes through the center-of-gravity display point and is formed on an arbitrary line perpendicular to the joining line. A golf ball having a hitting line for hitting fade shots and draw shots is disclosed.

[0005] Patent Document 2 discloses a golf ball having a specific relationship among the spin speed, moment of inertia, lift, and drag of the ball. The golf ball disclosed in Patent Document 2 is a golf ball having a core and a cover, and has a moment of inertia of about 0.46 oz / in 2 or greater, and at a Reynolds number of about 145000, the lift coefficient is greater than about 0.20 and the drag coefficient is less than about 0.22.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] When applying side spin to hit a draw ball, there is a problem in that the rolling distance after falling becomes long and it is difficult to stop at the targeted point. In particular, shots with short irons (8-iron to pitching wedge) are shots aimed at the green surface, and it is required that the rolling distance after landing on the green is small. An object of the present invention is to provide a ball that has a large amount of curve in a short iron shot and a small rolling distance after landing.

Means for Solving the Problems

[0008] The golf ball of the present invention that solves 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 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 co-crosslinking agent contains methacrylic acid and / or a metal salt thereof, 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. A golf ball characterized by the above. Dimple occupancy rate (%) = 100 × total area of all dimples / surface area of a virtual sphere assuming no dimples on the golf ball surface

[0009] By being configured as described above, the golf ball of the present invention can apply a large amount of side spin, and the lift force increases and the hang time increases. When the hang time of the shot increases, the turning width increases. Also, when the hang time increases, the height of the highest point of the hit ball increases and the falling angle becomes acute. When the falling angle of the golf ball becomes acute, the rolling distance of the golf ball after landing can be suppressed. 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

[0010] According to the present invention, it is possible to provide a ball having a large turning width during a draw shot or fade shot of a short iron and a small rolling distance after landing.

Brief Description of the Drawings

[0011]

Figure 1

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Figure 9

Mode for Carrying Out the Invention

[0012] The golf ball of the present invention includes a spherical core, one or more intermediate layers located outside the spherical core, and an outermost cover provided with a plurality of dimples disposed outside the intermediate layer, and is a golf ball having: 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 co-crosslinking agent contains methacrylic acid and / or a metal salt thereof, The total volume Vi (mm 3 ) of the lower parts of the plurality of dimples is less than 365 mm 3 , A golf ball 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 no dimples on the golf ball surface

[0013] (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 cover provided with a plurality of dimples disposed outside the one or more intermediate layers.

[0014] Examples of the golf ball of the present invention include, for example, a three-piece golf ball composed of a spherical core, a single-layer intermediate layer disposed so as to cover the spherical core, and a single-layer outermost layer cover that covers the intermediate layer; a multi-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 (including a three-piece golf ball). The present invention can be preferably applied to any of the golf balls having the above structures.

[0015] 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.

[0016] FIG. 1 is a partially cutaway 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 that covers 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.

[0017] (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 feel 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 effectively exerted.

[0018] The spherical core has the core 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), such that H0 < H 2.5 < H 5 < H 7.5 < H 10 < H 12.5 < H 15 < Hs, satisfying the relationship. By the hardness distribution of the spherical core satisfying the above requirements, the deformation of the spherical core during impact occurs smoothly, and the hitting feeling during iron shots is good.

[0019] The spherical core has the core hardness (H0), the hardness (H 2.5 ), the hardness (H 5 ), the hardness (H 7.5 ), the hardness (H 10 ), the hardness (H 12.5 ), the hardness (H 15 ), and the surface hardness (Hs) in Shore C hardness, such that H 2.5 - H0 < 4, H 5 - H 2.5 < 4, H 7.5 - H 5 < 4, H 10 - H 7.5 < 4, H 12.5 - H 10 < 4, H 15 - H 12.5 < 4, and it is preferable to satisfy the relationship of Hs - H 15 < 4.

[0020] The hardness difference (H 2.5 - H0), the hardness difference (H 5 - H2.5 ), hardness difference (H 7.5 -H 5 ), hardness difference (H 10 -H 7.5 ), hardness difference (H 12.5 -H 10 ), hardness difference (H 15 -H 12.5 ), and hardness difference (Hs - H 15 ) are within the above ranges, the deformation of the spherical core during iron shot occurs smoothly, and the hitting feeling becomes better.

[0021] 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 0.3 or more, more preferably 0.4 or more, still more preferably 0.5 or more in Shore C hardness, and preferably less than 4, more preferably 3.8 or less, still more preferably 3.5 or less.

[0022] The hardness difference (H 2.5 -H 5 ) between the hardness (H 5 ) at a point 2.5 mm from the center of the spherical core in the radial direction and the hardness (H 2.5 ) at a point 5.0 mm from the center of the spherical core in the radial direction is preferably 0.5 or more, more preferably 0.6 or more, still more preferably 0.7 or more in Shore C hardness, and preferably less than 4, more preferably 3.8 or less, still more preferably 3.5 or less.

[0023] The hardness difference (H 5 -H 7.5 ) between the hardness (H 7.5 ) at a point 5.0 mm from the center of the spherical core in the radial direction and the hardness (H 5 ) at a point 7.5 mm from the center of the spherical core in the radial direction is preferably 0.5 or more, more preferably 0.6 or more, still more preferably 0.7 or more in Shore C hardness, and preferably less than 4, more preferably 3.8 or less, still more preferably 3.5 or less.

[0024] 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, and the hardness difference (H 10 -H 7.5 ) are in Shore C hardness, preferably 0.5 or more, more preferably 0.6 or more, still more preferably 0.7 or more, and preferably less than 4, more preferably 3.8 or less, still more preferably 3.5 or less.

[0025] The hardness difference (H 10 ) at a point 10.0 mm in the radial direction from the center of the spherical core and the hardness (H 12.5 ) at a point 12.5 mm in the radial direction from the center of the spherical core, and the hardness difference (H 12.5 -H 10 ) are in Shore C hardness, preferably 0.5 or more, more preferably 0.6 or more, still more preferably 0.7 or more, and preferably less than 4, more preferably 3.8 or less, still more preferably 3.5 or less.

[0026] The hardness difference (H 12.5 ) at a point 12.5 mm in the radial direction from the center of the spherical core and the hardness (H 15 ) at a point 15 mm in the radial direction from the center of the spherical core, and the hardness difference (H 15 -H 12.5 ) are in 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 4, more preferably 3.8 or less, still more preferably 3.5 or less.

[0027] The hardness difference (Hs - H 15 ) between 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) of the spherical core is in Shore C hardness, preferably more than 0, more preferably 0.1 or more, still more preferably 0.2 or more, and preferably less than 4, more preferably 3.8 or less, still more preferably 3.5 or less.

[0028] The hardness difference (Hs - H0) between the core hardness (H0) of the spherical core and the surface hardness (Hs) of the spherical core is preferably 10 or less, more preferably 9.7 or less, and even more preferably 9.5 or less in Shore C hardness. If the hardness difference (Hs - H0) is 10 or less, the spin performance during the approach shot will be good. The hardness difference (Hs - H0) is preferably 2 or more, more preferably 3 or more, and even more preferably 4 or more.

[0029] The core hardness (H0) of the spherical core is preferably 55 or more, more preferably 58 or more, and even more preferably 60 or more in Shore C hardness, and preferably 77 or less, more preferably 75 or less, and even more preferably 73 or less.

[0030] The surface hardness (Hs) of the spherical core is preferably 60 or more, more preferably 63 or more, and even more preferably 65 or more in Shore C hardness, and preferably 87 or less, more preferably 85 or less, and even more preferably 83 or less.

[0031] 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, and even more preferably 3.0 mm or more, and preferably 5.0 mm or less, more preferably 4.5 mm or less, and even more preferably 4.0 mm or less. If the compression deformation amount is 2.0 mm or more, the hitting feeling of the driver shot will be better, and if it is 5.0 mm or less, the durability will be better.

[0032] (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.

[0033] 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, and 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 during 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 composition for the intermediate layer that forms the intermediate layer. When there are multiple intermediate layers, the material hardness Hm is the slab hardness of the composition for the intermediate layer that forms the outermost intermediate layer.

[0034] 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 will be good, and if it is 3.0 mm or less, a good hitting feeling can be obtained during driver shots. When there are multiple intermediate layers, the total thickness of all intermediate layers is defined as the thickness Tm of the intermediate layer.

[0035] (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 dimples are recesses provided in the outermost layer cover.

[0036] 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.

[0037] 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 dashed two-dot 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 dimple 10 does 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.

[0038] 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 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.

[0039] In the present invention, the "lower volume of the dimple" is the volume of the lower part of the dimple surrounded by the plane that contacts 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.

[0040] 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 and more preferably less than 350 mm 3 and 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, and even more preferably 240 mm 3 or more. If the total lower volume Vi is 220 mm 3This is because, if it is as described above, the trajectory will not be overly lofted.

[0041] The diameter Dm of the dimple 10 is preferably 2.0 mm or more, more preferably 2.5 mm or more, still more preferably 2.8 mm or more, and preferably 6.0 mm or less, more preferably 5.5 mm or less, still more preferably 5.0 mm or less. If the diameter Dm is 2.0 mm or more, it is easy to contribute to the turbulence caused by the dimple, and if it is 6.0 mm or less, the essence of the golf ball, which is substantially spherical, can be maintained.

[0042] For the plurality of dimples, a plurality of dimples having a single diameter may be formed, or dimples of a plurality of types of diameters may be combined. 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.

[0043] In FIG. 4, 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 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, the lift force obtained by the dimple can be sufficiently generated, and if it is 0.45 mm or less, the essence of the golf ball, which is substantially spherical, can be maintained.

[0044] In FIG. 4, 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, 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 dimples. If it is 0.30 mm or less, the lift force obtained by the dimples is not too large, and the flight distance performance is good during the driver shot.

[0045] 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 formula. A = π×(Dm / 2) 2

[0046] 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 and so on.

[0047] The occupancy rate of the dimples of the golf ball of the present invention is preferably 75% or more, more preferably 78% or more, still more preferably 81% or more, and preferably 95% or less, more preferably 92% or less, 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 hang time of the shot becomes longer and the turning width becomes larger. Also, when the hang time increases, the maximum height of the golf ball becomes higher and the falling angle becomes an acute angle. When the falling angle of the golf ball becomes an acute angle, the rolling distance of the golf ball after landing becomes smaller. The occupancy rate of the dimples is defined by the following formula. Dimple occupancy rate (%) = 100 × total area of all dimples / surface area of a virtual ball assuming no dimples on the golf ball surface

[0048] 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 effects of individual dimples, 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.

[0049] The material hardness Hc of the outermost cover is Shore D hardness, preferably 20 or more, more preferably 22 or more, still more preferably 24 or more, preferably 40 or less, more preferably 38 or less, and still more preferably 36 or less. If the material hardness Hc is 20 or more, the spin amount during driver shot does not become too much and the flight distance performance is 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.

[0050] 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, preferably 1.0 mm or less, more preferably 0.9 mm or less, and 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 spin amount during driver shot does not become too much and the flight distance performance is good.

[0051] 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, preferably 40 or less, more preferably 39 or less, and still more preferably 38 or less in Shore D hardness. This is because when the hardness difference (Hm - Hc) is within the above range, the hitting feeling during driver shots becomes good.

[0052] The diameter of the golf ball of the present invention is preferably from 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. Also, 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 satisfying the USGA standards, the mass is particularly preferably 45.93 g or less.

[0053] 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 an 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, 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 with a compression deformation amount of 2.0 mm or more does not become too hard and has a good hitting feeling in driver shots. On the other hand, by setting the compression deformation amount to 3.5 mm or less, the durability is improved.

[0054] Hereinafter, the materials constituting the golf ball of the present invention will be described.

[0055] (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").

[0056] The rubber component contains natural rubber (NR). By containing natural rubber, the speed of the golf ball at landing decreases and the rolling distance becomes shorter. 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.

[0057] Examples of plants that produce the latex of 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 Fabaceae family, Japanese staghorn sumac of the Anacardiaceae family, Zanzibar gutta, Funtumia elastica, Urceola, Guayule rubber tree of the Asteraceae family, Rubber dandelion, Gataparcha tree of the Achatocarpaceae family, Balata rubber tree, Sapodilla, Obaana asagao of the Convolvulaceae family, and Tochu of the Bignoniaceae family.

[0058] 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. Among these, a CV grade having a particularly stable viscosity is preferable. The natural rubber may be any of SMR (Standard Malaysian Rubber) and SVR (Standard Vietnamese Rubber).

[0059] The natural rubber is cis-1,4-polyisoprene, and either sheet rubber or block rubber can be used. Further, the natural rubber 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 obtained by modifying natural rubber. Among these, it is preferable that the natural rubber does not contain epoxidized natural rubber.

[0060] As the natural rubber, Technical Specified Rubbers (TSR) and Ribbed Smoked Sheet (RSS) are preferable. Further, a viscosity stabilizer may be blended in the natural rubber.

[0061] 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).

[0062] 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 10% by mass or more, more preferably 25% by mass or more, still more preferably 40% by mass or more, and preferably 100% by mass or less, more preferably 90% by mass or less, still more preferably 80% by mass or less. When the content is 10% by mass or more, the hitting feeling in a driver shot becomes good, and when it is 100% by mass or less, the rolling during a putter shot becomes good and the distance feeling is easy to match.

[0063] 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), 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. These may be used alone or in combination of two or more.

[0064] The synthetic rubber component preferably contains a diene rubber, more preferably contains polybutadiene rubber. In particular, it is more preferable to contain high-cis polybutadiene having a cis-1,4 bond of 40% by mass or more, preferably 80% by mass or more, 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.

[0065] The high-cis polybutadiene preferably has a content of 1,2-vinyl bond of 2.0% by mass or less, more preferably 1.7% by mass or less, still more preferably 1.5% by mass or less.

[0066] 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 bond and a low content of 1,2-vinyl bond can be obtained with excellent polymerization activity.

[0067] As for the high cis - polybutadiene, the molecular weight distribution Mw / Mn (Mw: weight - average molecular weight, Mn: number - average molecular weight) is preferably 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, still more preferably 4.0 or less. If 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, with the column: GMHHXL (manufactured by Tosoh Corporation), column temperature: 40 °C, and mobile phase: tetrahydrofuran, and is a value calculated as a standard polystyrene - converted value.

[0068] The Mooney viscosity (ML 1+4 (100 °C)) of the high cis - polybutadiene 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.

[0069] The rubber composition for the core used in the present invention contains (b) a co - crosslinking agent. The (b) co - crosslinking agent has the effect of cross - linking rubber molecules by graft - polymerizing to the rubber component. The (b) co - crosslinking agent of the rubber composition for the core used in the present invention contains methacrylic acid and / or its metal salt. By containing methacrylic acid and / or its metal salt as the (b) co - crosslinking agent, it is easy to have a gentle hardness gradient and the controllability during the approach shot becomes good.

[0070] Examples of the metal ions constituting the metal salt of methacrylic acid 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.

[0071] In the present invention, it is preferable to use methacrylic acid as the (b) co-crosslinking agent.

[0072] (b) The content of the co-crosslinking agent is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, still more preferably 20 parts by mass or more, preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and still more preferably 30 parts by mass or less with respect to 100 parts by mass of the (a) rubber component. When the content of the (b) co-crosslinking agent is 10 parts by mass or more, the formed core has an appropriate hardness and the durability of the golf ball is improved. On the other hand, when the content of the (b) co-crosslinking agent is 50 parts by mass or less, the formed core does not become too hard.

[0073] In addition to methacrylic acid and / or its metal salt, the (b) co-crosslinking agent may contain an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms (excluding methacrylic acid) and / or its metal salt.

[0074] Examples of the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms (excluding methacrylic acid) include acrylic acid, fumaric acid, maleic acid, crotonic acid and the like.

[0075] Examples of the metal constituting the metal salt of the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms (excluding methacrylic acid) 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 metal crosslinking is likely to occur between rubber molecules by using a divalent metal salt of an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms.

[0076] (b) When the co-crosslinking agent contains an α,β-unsaturated carboxylic acid (excluding methacrylic acid) having 3 to 8 carbon atoms and / or a metal salt thereof in addition to methacrylic acid and / or a metal salt thereof, the content of methacrylic acid and / or a metal salt thereof in the (b) co-crosslinking agent component is preferably 50% by mass or more, more preferably 60% by mass or more, still more preferably 70% by mass or more, preferably 99% by mass or less, more preferably 98% by mass or less, and still more preferably 97% by mass or less. When the content of methacrylic acid and / or a metal salt thereof is within the above range, the reactivity in the rubber becomes uniform and the quality is stable. It is also preferable that the (b) co-crosslinking agent contains only methacrylic acid and / or a metal salt thereof, and it is more preferable that it contains only methacrylic acid.

[0077] (c) The crosslinking initiator is compounded to crosslink the (a) rubber component. As the (c) crosslinking initiator, an organic peroxide is suitable. Specific examples of the organic peroxide 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.

[0078] (c) The content of the crosslinking initiator is preferably 0.2 part by mass or more, more preferably 0.4 part by mass or more, still more preferably 0.6 part 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 2.0 parts by mass or less with respect to 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 becomes good.

[0079] The rubber composition preferably further contains (d) a metal compound. The (d) metal compound can be used, for example, to neutralize the (b) co-crosslinking agent in the rubber composition or to adjust the mass of the rubber composition.

[0080] 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. Preferred as the (d) metal compound is a divalent metal compound, 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. Also, 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.

[0081] The rubber composition may further contain (e) an 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 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, dithiocarbamates, or thiazoles.

[0082] 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.

[0083] 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.

[0084] Polysulfides are organic sulfur compounds having a polysulfide bond, and examples thereof include disulfides, trisulfides, and tetrasulfides. As the polysulfides, diphenyl polysulfides are preferred.

[0085] 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.

[0086] 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.

[0087] The organic sulfur compound (e) can be used alone or in combination of two or more.

[0088] 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.

[0089] 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 compounding 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.

[0090] The rubber composition may contain additives such as fillers, anti-aging agents, peptizing agents, softening agents, etc. for mass adjustment or the like, if necessary.

[0091] 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 parts by mass or more, more preferably 1 part by mass or more, still more preferably 2 parts 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 parts 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.

[0092] The content of the anti-aging agent is preferably 0.1 parts 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 peptizing agent is preferably 0.1 parts by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the rubber component (a).

[0093] (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.

[0094] 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.

[0095] 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.

[0096] 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), and the like.

[0097] 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), and the like. 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.

[0098] 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.

[0099] Specific examples of the thermoplastic polyurethane elastomer include Elastollan (registered trademark) NY80A, NY84A, NY88A, NY95A, ET885, ET890 (manufactured by BASF Japan Ltd.).

[0100] 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.

[0101] 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).

[0102] 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).

[0103] 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.

[0104] 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.

[0105] 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.

[0106] The intermediate layer composition preferably contains ionomer resin as a resin component. 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.

[0107] In addition to the resin components described above, the cover composition and the intermediate layer composition may contain 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, anti-aging agents, ultraviolet absorbers, light stabilizers, fluorescent materials, or fluorescent brighteners.

[0108] 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, with respect 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.

[0109] (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.

[0110] The spherical core can be molded, for example, by heat-pressing the rubber composition for the core. The heat-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.

[0111] 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 intermediate layer composition 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 intermediate layer composition directly onto the spherical core.

[0112] 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.

[0113] The golf ball body with the cover molded thereon is preferably taken out of the mold and, if necessary, surface treatment such as deburring, washing, and sandblasting is performed.

[0114] Also, if desired, a coating film or a mark can be formed. The film thickness of the coating film is not particularly limited, but 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. Note that since the coating film is very thin, the effects of the present invention are not impaired.

Examples

[0115] 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 spirit of the present invention are all included in the scope of the present invention.

[0116] [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 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.

[0117] (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".

[0118] (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 part of the spherical core was taken as the spherical core surface hardness. Further, 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.

[0119] (4) Golf ball surface hardness The hardness measured at the land part on the surface part 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".

[0120] (5) Measurement of the curvature width (m) and rolling distance (m) of the iron shot An 8-iron (I#8) (Sumitomo Rubber Industries, "SRIXON (registered trademark) ZX7", shaft hardness: X, loft angle: 36°) was attached to the swing machine of Golf Laboratories. The impact point was set at a point 10 mm from the face center to the toe side. The golf ball was struck at a head speed of 39 m / sec, and the side spin speed immediately after the strike, the rolling distance (distance from the landing point to the stopping position), and the trajectory were measured. The spin speed immediately after the strike was measured by taking consecutive photographs of the golf ball immediately after being struck. The trajectory was measured using the "TRACK MAN4" manufactured by TrackMan. As shown in Figure 9, when the trajectory viewed from above was coordinated, with the line connecting the hitting position and the landing position as the Y-axis and the orthogonal coordinate as the X-axis (the right direction from the hitting direction is +), the maximum value in the X-axis direction was defined and calculated as the curvature width. Each golf ball was tested 12 times, and the average value was taken as the measured value of that golf ball.

[0121] [Manufacture of Golf Balls] (1) Preparation of the core composition Each raw material was kneaded by a kneading roll to obtain the core composition according to the formulation shown in Table 1.

[0122]

Table 1

[0123] The materials used in Table 1 are as follows. Polybutadiene rubber: manufactured by JSR, "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) Methacrylic acid: manufactured by Mitsubishi Gas Chemical Company Zinc diacrylate: manufactured by Nisshu Techno Fine Chemical Co., Ltd., "ZN-DA90S" Zinc oxide: manufactured by Toho Zinc Co., Ltd., "Ginrei R" Barium sulfate: manufactured by Sakai Chemical Industry 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 Dicumyl peroxide: manufactured by NOF Corporation, "Perkyl (registered trademark) D"

[0124] (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 composition and cover composition so as to have the formulations shown in Table 2.

[0125]

Table 2

[0126] (4) Preparation of spherical core The core composition shown in Table 1 was heat - 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.

[0127] (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 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 having a number of dimples with a shape in which the shape of the pimples on the cavity surface was reversed on the outermost cover. The specifications of the dimples formed on the outermost cover are shown in Tables 3 - 4 and Figures 2 - 3, 5 - 8. The evaluation results of the obtained golf balls are shown in Tables 5 - 6.

[0128]

Table 3

[0129]

Table 4

[0130]

Table 5

[0131]

Table 6

[0132] From the results of Table 5 to Table 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, the co-crosslinking agent contains methacrylic acid and / or a metal salt thereof, and the total volume Vi (mm 3 ) of the lower portions 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 large amount of curvature in short iron shots and a small rolling distance after landing. Occupancy rate of dimples (%) = 100 × total area of all dimples / surface area of a virtual sphere assuming no dimples on the golf ball surface

Industrial Applicability

[0133] The golf ball of the present invention has a large amount of curvature in short iron shots and a small rolling distance after landing.

[0134] 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 co-crosslinking agent contains methacrylic acid and / or a metal salt thereof, and the total volume Vi (mm 3 ) of the lower portions of the plurality of dimples is less than 365 mm3 is less than, a golf ball characterized in that the occupancy ratio of dimples defined by the following formula is 75% or more. Occupancy ratio of dimples (%) = 100 × total area of all dimples / surface area of a virtual sphere assuming no dimples exist on the golf ball surface

[0135] A preferred embodiment (2) of the present invention is that the core hardness (H0), 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 ) at a point 5 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 of H0 < H 2.5 < H 5 < H 7.5 < H 10 < H 12.5 < H 15 < Hs, which is a golf ball of embodiment (1).

[0136] A preferred embodiment (3) of the present invention is that the core hardness (H0), the hardness (H 2.5 ), the hardness (H 5 ), the hardness (H 7.5 ), the hardness (H 10 ), the hardness (H 12.5 ), the hardness (H 15 ) and the surface hardness (Hs) are in Shore C hardness, H 2.5 - H0 < 4, H 5 - H 2.5 < 4, H 7.5 - H 5 < 4, H 10 - H 7.5 < 4, H12.5 -H 10 <4, H 15 -H 12.5 <4 and, Hs-H 15 <4 is a golf ball of embodiment (2) that satisfies the relationship.

[0137] A preferred embodiment (4) of the present invention is (H S -H 0 ) is a golf ball of embodiment (2) or (3) that is 10 or less.

[0138] A preferred embodiment (5) of the present invention is that the lower total volume Vi (mm 3 ) is a golf ball of any one of embodiments (1) to (4) that is 350 mm 3 or less.

[0139] A preferred embodiment (6) of the present invention is a golf ball of any one of embodiments (1) to (5) in which the content of natural rubber in the rubber component is 10% by mass or more and 80% by mass or less.

[0140] A preferred embodiment (7) of the present invention is a golf ball of any one of embodiments (1) to (6) in which the material hardness Hm of the intermediate layer is greater than the material hardness Hc of the outermost layer cover.

[0141] A preferred embodiment (8) of the present invention is a golf ball of any one of embodiments (1) to (7) in which 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.

[0142] A preferred embodiment (9) of the present invention is a golf ball of any one of embodiments (1) to (8) in which 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.

Claims

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, the co-crosslinking agent contains methacrylic acid and / or a metal salt thereof, 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 volume Vi (mm ３ ) of the lower parts of the 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

2.

3. The core center hardness (H0), the hardness (H ２．５ ), the hardness (H ５ ), the hardness (H ７．５ ), the hardness (H １０ ), the hardness (H １２．５ ), the hardness (H １５ ), and the surface hardness (Hs) at a point where the radial distance from the center of the spherical core is 2.5 mm, 5 mm, 7.5 mm, 10 mm, 12.5 mm, and 15 mm respectively satisfy the relationship H0 < H ２．５ < H ５ < H ７．５ < H １０ < H １２．５ < H １５ < Hs. The golf ball according to claim 1.

4. The center hardness (H0), hardness (H ２．５ ), hardness (H ５ ), hardness (H ７．５ ), hardness (H １０ ), hardness (H １２．５ ), hardness (H １５ ) and surface hardness (Hs) are in Shore C hardness, H ２．５ -H0 < 4, H ５ -H ２．５ < 4、 H ７．５ -H ５ < 4、 H １０ -H ７．５ <4, H １２．５ -H １０ < 4、 H １５ -H １２．５ <4, and, Hs-H １５ The golf ball according to claim 2, satisfying the relationship of <4.

5. (H Ｓ -H ０ ) is 10 or less, the golf ball according to claim 2.

6. 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 10% by mass or more and 80% by mass or less.

7. 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.

8. 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.

9. 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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