JP2023174167A - Golf ball - Google Patents

Abstract

To provide a golf ball which is excellent in a carry by a driver shot and is good in a spin amount by a middle iron shot.SOLUTION: A golf ball has a spherical core and a cover. Provided that a radius of the spherical core is equally divided into eight segments and points between the segments have a shore C hardness, labelled from the center as C0 (center), C1, C2, C3, C4, C5, C6, C7, and C8 (surface), a hardness difference (C1-C0), a hardness difference (C2-C1), a hardness difference (C3-C2), and a hardness difference (C4-C3) are more than 0 and equal to or less than 6.0; a hardness difference (C5-C4) is 5.0 or more; a hardness difference (C6-C5), a hardness difference (C7-C6), and a hardness difference (C8-C7) is more than 0 and equal to or less than 3.5; and difference [{(C2-C0)/2}-{(C8-C6)/2}] is 0 or more.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to golf balls, and more particularly to the hardness distribution of a spherical core.

Golf balls are required to have excellent flight distance performance on driver shots. One way to improve the flight distance of driver shots is to appropriately select the hardness distribution of the spherical core. Specifically, it is known that by increasing the difference in hardness between the surface hardness and center hardness of the spherical core, the amount of spin on driver shots can be reduced and flight distance can be improved.

For example, Patent Document 1 discloses a golf ball that includes a core, an intermediate layer, and a cover, the core being formed mainly of base rubber, the diameter of which is set within a specific range, and the intermediate layer and the cover. Each layer is formed of a resin material, and with respect to the internal hardness of the core, the positional hardness at the core center and every 2 mm interval from the core center to 16 mm, and the core surface hardness are designed so that these hardness differences are within a predetermined range, A golf ball is described in which the ball surface hardness is set lower than the surface hardness of the intermediate layer-covered sphere (Patent Document 1).

Further, Patent Document 2 discloses that in a multi-piece solid golf ball in which an intermediate layer is interposed between a core and a cover, the surface hardness of the core, the intermediate layer-coated sphere, and the ball satisfy a predetermined relationship, and the thickness of the intermediate layer is The thickness of the core and the thickness of the cover satisfy a predetermined relationship, and in the core hardness distribution, the core surface hardness (Cs), the core center C hardness (Cc), the hardness at a position 5 mm from the core center (C5), and the core surface hardness. A golf ball is described in which the hardness (Cm) at a central intermediate position satisfies a predetermined relationship (Patent Document 2).

JP2021-062036A Japanese Patent Application Publication No. 2016-112308

By the way, there are requests from professional golfers and advanced golfers not only to improve the flight distance of driver shots, but also to increase the amount of spin on middle iron shots. However, when the amount of spin on driver shots is reduced by controlling the hardness difference between the surface hardness and center hardness of the spherical core, the amount of spin on middle iron shots also tends to decrease.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a golf ball that has excellent flight distance on driver shots and a good spin rate on middle iron shots.

The golf ball of the present invention that can solve the above problems is a golf ball having a spherical core and a cover that covers the spherical core, wherein a straight line from the center of the spherical core toward the surface is divided into eight equal parts. Then, the hardness at the center of the spherical core (C0), the hardness at 12.5% from the center (C1), the hardness at 25.0% from the center (C2), and the hardness at 37.5% from the center (C3). ), Hardness at 50.0% from the center (C4), Hardness at 62.5% from the center (C5), Hardness at 75.0% from the center (C6), Hardness at 87.5% from the center (C7) and surface hardness (C8) are Shore C hardness and are characterized by satisfying formulas (1) to (9).
0<(C1-C0)≦6.0...(1)
0<(C2-C1)≦6.0...(2)
0<(C3-C2)≦6.0...(3)
0<(C4-C3)≦6.0...(4)
5.0≦(C5-C4)...(5)
0<(C6-C5)≦3.5...(6)
0<(C7-C6)≦3.5...(7)
0<(C8-C7)≦3.5...(8)
0≦[{(C2-C0)/2}-{(C8-C6)/2}] ...(9)

On a driver shot, the entire spherical core deforms significantly. Therefore, by setting the lower limits of equations (1) to (4) and (6) to (8) to more than 0, and setting the lower limit of equation (5) to 5.0, the hardness distribution of the entire spherical core can be adjusted to The inner soft structure provides recoil effect during driver shots, reducing the amount of spin. In addition, by setting the upper limit values of equations (1) to (4) to 6.0 and the upper limit values of equations (6) to (8) to 3.5, the deformation balance of the entire spherical core during driver shots is improved. This improves repulsion performance. Furthermore, by satisfying formula (9), the hardness gradient near the center of the spherical core becomes larger than the hardness gradient near the surface, and the entire spherical core deforms in a well-balanced manner upon a driver shot, further improving repulsion performance. Therefore, the flight distance performance of driver shots is improved.

In a middle iron shot, the amount of deformation of the spherical core is smaller than in a driver shot, and the hardness near the surface of the spherical core is important. Therefore, by setting the upper limit of equations (6) to (8) to 3.5, the amount of deformation near the surface of the spherical core during middle iron shots can be suppressed, and the amount of spin can be improved. Furthermore, by satisfying formula (5), the amount of deformation at the 50% to 62.5% point from the center of the spherical core during a middle iron shot becomes large, and the amount of deformation near the center becomes even smaller. This reduces the recoil effect and further improves the amount of spin on middle iron shots. Furthermore, by satisfying formula (9), the hardness gradient near the surface of the spherical core is smaller than the hardness gradient near the center, reducing energy loss during middle iron shots and further improving spin rate.

According to the present invention, a golf ball can be obtained that has excellent flight distance on driver shots and a good spin rate on middle iron shots.

1 is a partially cutaway sectional view showing a golf ball according to an embodiment of the present invention. A graph showing the hardness distribution of a spherical core. A graph showing the hardness distribution of a spherical core. A graph showing the hardness distribution of a spherical core. A graph showing the hardness distribution of a spherical core. A graph showing the hardness distribution of a spherical core. A graph showing the hardness distribution of a spherical core. A graph showing the hardness distribution of a spherical core. A graph showing the hardness distribution of a spherical core. A graph showing the hardness distribution of a spherical core.

The golf ball of the present invention has a spherical core and a cover that covers the spherical core, and when the length of a straight line from the center of the spherical core toward the surface in the radial direction is divided into eight equal parts, the length of the spherical core is Center hardness (hardness at 0% point) (C0), hardness at 12.5% point from the center (C1), hardness at 25.0% point from the center (C2), hardness at 37.5% point from the center (C3) ), Hardness at 50.0% from the center (C4), Hardness at 62.5% from the center (C5), Hardness at 75.0% from the center (C6), Hardness at 87.5% from the center (C7) and surface hardness (hardness at 100% point from the center) (C8) are Shore C hardness and are characterized by satisfying formulas (1) to (9).
0<(C1-C0)≦6.0...(1)
0<(C2-C1)≦6.0...(2)
0<(C3-C2)≦6.0...(3)
0<(C4-C3)≦6.0...(4)
5.0≦(C5-C4)...(5)
0<(C6-C5)≦3.5...(6)
0<(C7-C6)≦3.5...(7)
0<(C8-C7)≦3.5...(8)
0≦[{(C2-C0)/2}-{(C8-C6)/2}] ...(9)

The above equations (1) to (4) define the hardness distribution near the center of the spherical core. If there is a location near the center where the hardness gradient is too large, the amount of deformation at that location will be large during driver shots. As a result, the overall deformation balance of the golf ball is disrupted, and the repulsion performance is reduced, resulting in a reduction in flight distance. Therefore, by satisfying formulas (1) to (4), repulsion performance is good and driver flight distance is improved. Further, by providing a hardness gradient near the center of the spherical core, it is possible to increase the amount of recoil on driver shots. Therefore, the amount of spin on driver shots can be reduced, further improving flight distance.

The hardness difference (C1-C0) between the center hardness (C0) of the spherical core and the hardness at a 12.5% point from the center (C1) is more than 0, preferably 0.5 or more, more preferably 0.5 or more in terms of Shore C hardness. is 1.0 or more and 6.0 or less, preferably 5.5 or less, more preferably 5.0 or less.

The hardness difference (C2-C1) between the hardness at 12.5% from the center of the spherical core (C1) and the hardness at 25.0% from the center (C2) is Shore C hardness, preferably greater than 0. It is 0.5 or more, more preferably 1.0 or more, and 6.0 or less, preferably 5.5 or less, and more preferably 5.0 or less.

The hardness difference (C3-C2) between the hardness at 25.0% from the center of the spherical core (C2) and the hardness at 37.5% from the center (C3) is Shore C hardness, preferably greater than 0. It is 0.5 or more, more preferably 1.0 or more, and 6.0 or less, preferably 5.5 or less, and more preferably 5.0 or less.

The hardness difference (C4-C3) between the hardness at 37.5% from the center of the spherical core (C3) and the hardness at 50.0% from the center (C4) is Shore C hardness, preferably greater than 0. It is 0.5 or more, more preferably 1.0 or more, and 6.0 or less, preferably 5.5 or less, and more preferably 5.0 or less.

The above formula (5) defines the hardness difference (C5-C4) between the hardness at a 50.0% point from the center of the spherical core (C4) and the hardness at a 62.5% point from the center (C5). The hardness difference (C5-C4) is Shore C hardness of 5.0 or more, preferably 5.5 or more, more preferably 6.0 or more, and preferably 12.0 or less, more preferably 11.0. It is preferably 10.0 or less. If the hardness difference (C5-C4) is 5.0 or more, it is possible to increase the initial velocity on driver shots while improving the amount of spin on middle iron shots.

The above equations (6) to (8) define the hardness distribution near the surface of the spherical core. If there is a part near the surface where the hardness gradient is too large, the amount of deformation at that part will be large on a driver shot, and the golf ball as a whole will not be deformed and the repulsion performance will deteriorate. Furthermore, if there is a portion where the hardness gradient is too large near the surface, deformation near the surface becomes large in middle iron shots, resulting in large energy loss and a decrease in spin rate. Therefore, by satisfying equations (6) to (8), it is possible to both improve the flight distance of driver shots and the spin rate of middle iron shots.

The hardness difference (C6-C5) between the hardness at a 62.5% point from the center of the spherical core (C5) and the hardness at a 75.0% point from the center (C6) is Shore C hardness, preferably greater than 0. It is 0.5 or more, more preferably 1.0 or more, and 3.5 or less, preferably 3.0 or less, and more preferably 2.5 or less.

The hardness difference (C7-C6) between the hardness at 75.0% point from the center of the spherical core (C6) and the hardness at 82.5% point from the center (C7) is Shore C hardness, preferably more than 0. It is 0.5 or more, more preferably 1.0 or more, and 3.5 or less, preferably 3.0 or less, and more preferably 2.5 or less.

The hardness difference (C8-C7) between the hardness (C7) at a point 82.5% from the center of the spherical core and the surface hardness (C8) is more than 0, preferably 0.5 or more, more preferably 0.5 or more in terms of Shore C hardness. is 1.0 or more and 3.5 or less, preferably 3.0 or less, more preferably 2.5 or less.

The above formula (9) is calculated by calculating the hardness difference (C2-C0) between the center hardness (C0) of the spherical core and the hardness (C2) at 25.0% from the center, and the hardness at 75.0% from the center of the spherical core. The difference between the hardness (C6) and the hardness difference (C8-C6) between the surface hardness (C8) is defined. By satisfying formula (9), the entire spherical core deforms in a well-balanced manner upon a driver shot, further improving repulsion performance. In addition, energy loss during middle iron shots is reduced, and the amount of spin is further improved. The difference [{(C2-C0)/2}-{(C8-C6)/2}] is 0 or more, preferably 0.5 or more, more preferably 1.0 or more in Shore C hardness, It is preferably 4.0 or less, more preferably 3.5 or less, even more preferably 3.0 or less.

The spherical core preferably has hardnesses (C0), (C2), (C5), and (C7) of Shore C hardness and satisfies formula (10). By satisfying formula (10), the entire spherical core deforms in a well-balanced manner upon a driver shot, further improving repulsion performance. In addition, energy loss during middle iron shots is reduced, and the amount of spin is further improved.
0≦[{(C2-C0)/2}-{(C7-C5)/2}] ...(10)

The difference [{(C2-C0)/2}-{(C7-C5)/2}] is 0 or more, preferably 0.5 or more, more preferably 1.0 or more in Shore C hardness, It is preferably 4.0 or less, more preferably 3.5 or less, even more preferably 3.0 or less.

It is preferable that the hardness (C0), (C2), (C4), and (C5) of the spherical core be Shore C hardness and satisfy Expression (11). By satisfying formula (11), the amount of spin on middle iron shots is further improved and the amount of spin on driver shots is further reduced.
0≦[(C5-C4)-{(C2-C0)/2}] ...(11)

The difference [(C5-C4)-{(C2-C0)/2}] is 0 or more, preferably 0.5 or more, more preferably 1.0 or more, and 6.0 or less in Shore C hardness. is preferable, more preferably 5.5 or less, still more preferably 5.0 or less.

The hardness difference (C2-C0) between the center hardness (C0) of the spherical core and the hardness at a 25.0% point from the center (C2) is preferably 5.5 or more, more preferably 6.5 in terms of Shore C hardness. It is 0 or more, more preferably 6.5 or more, preferably 12.0 or less, more preferably 11.0 or less, still more preferably 10.0 or less. If the hardness difference (C2-C0) is within the above range, the amount of deformation near the center of the spherical core will be large, the recoil effect during driver shots will be even greater, and the amount of spin can be further reduced.

The hardness difference (C4-C0) between the center hardness (C0) of the spherical core and the hardness at a 50.0% point from the center (C4) is preferably more than 0, more preferably 3.0 or more in terms of Shore C hardness. , more preferably 6.0 or more, preferably 24.0 or less, more preferably 22.0 or less, still more preferably 20.0 or less.

The hardness difference (C8-C5) between the hardness (C5) at a 62.5% point from the center of the spherical core and the surface hardness (C8) is preferably 0 or more, and more preferably 1.0 or more in terms of Shore C hardness. , more preferably 2.0 or more, preferably 10.5 or less, more preferably 10.0 or less, still more preferably 9.5 or less.

The hardness difference (C8-C0) between the center hardness (C0) and surface hardness (C8) of the spherical core is preferably 18.0 or more, more preferably 19.0 or more, and even more preferably 20 .0 or more, preferably 32.0 or less, more preferably 30.0 or less, still more preferably 28.0 or less. If the hardness difference (C8-C0) is within the above range, the degree of outer hardness and inner softness of the hardness distribution of the entire spherical core will be large, and the recoil effect will be large, so the amount of spin on driver shots will be further reduced, Flying distance improves.

It is preferable that the hardness (C0), (C4), (C5) and (C8) of the spherical core be Shore C hardness and satisfy the following relationship. By satisfying the following relationship, the amount of spin on middle iron shots is further improved and the amount of spin on driver shots is further reduced.
(C4-C0)>(C5-C4)>(C8-C5)

In the spherical core, the difference between the hardness difference (C5-C4) and the hardness difference (C4-C3) {(C5-C4)-(C4-C3)} is preferably 1.0 or more in Shore C hardness, It is more preferably 1.5 or more, still more preferably 2.0 or more, preferably 10.0 or less, more preferably 9.0 or less, still more preferably 8.0 or less. If the difference {(C5-C4)-(C4-C3)} is within the above range, the amount of spin on middle iron shots is further improved and the amount of spin on driver shots is further reduced.

In the spherical core, the difference between the hardness difference (C5-C4) and the hardness difference (C6-C5) {(C5-C4)-(C6-C5)} is preferably 1.0 or more in Shore C hardness, It is more preferably 1.5 or more, still more preferably 2.0 or more, preferably 10.0 or less, more preferably 9.0 or less, still more preferably 8.0 or less. If the difference {(C5-C4)-(C6-C5)} is within the above range, the amount of spin on middle iron shots will be further improved and the amount of spin on driver shots will be further reduced.

In the spherical core, the ratio between the hardness difference (C2-C0) and the hardness difference (C5-C4) {(C2-C0)/(C5-C4)} is preferably 0.5 or more in Shore C hardness, It is more preferably 0.6 or more, still more preferably 0.7 or more, preferably 3.5 or less, more preferably 3.3 or less, still more preferably 3.0 or less. When the ratio {(C2-C0)/(C5-C4)} is within the above range, the amount of spin on middle iron shots is further improved and the amount of spin on driver shots is further reduced.

In the spherical core, the ratio between the hardness difference (C2-C0) and the hardness difference (C4-C2) {(C2-C0)/(C4-C2)} is preferably 1.0 or more in Shore C hardness, More preferably 1.2 or more, still more preferably 1.4 or more, preferably 6.5 or less, more preferably 6.0 or less, even more preferably 5.5 or less. When the ratio {(C2-C0)/(C4-C2)} is within the above range, the amount of spin on middle iron shots is further improved and the amount of spin on driver shots is further reduced.

It is preferable that the hardness (C0), (C2), (C4), and (C8) of the spherical core be Shore C hardness and satisfy Expression (12). By satisfying formula (12), the amount of spin on middle iron shots is further improved, and the amount of spin on driver shots is further reduced.
{(C8-C4)/(C2-C0)}≦3.0...(12)

The ratio {(C8-C4)/(C2-C0)} is preferably 0 or more, more preferably 0.5 or more, even more preferably 1.0 or more, and preferably 3.0 or less, more preferably It is 2.5 or less, more preferably 2.0 or less.

The spherical core has a Shore C hardness, a hardness difference (C1-C0) between hardness (C1) and hardness (C0), a hardness difference (C2-C1) between hardness (C2) and hardness (C1), and hardness ( Hardness difference (C3-C2) between hardness (C3) and hardness (C2), hardness difference (C4-C3) between hardness (C4) and hardness (C3), hardness difference (C4-C3) between hardness (C5) and hardness (C4) C5-C4), hardness difference (C6-C5) between hardness (C6) and hardness (C5), hardness difference (C7-C6) between hardness (C7) and hardness (C6), and hardness (C8) and When the largest value of the hardness difference (C8-C7) from the hardness (C7) is Cbmax and the smallest value is Cbmin, the ratio (Cbmax/Cbmin) is preferably 4.0 or more. Since the entire spherical core has parts with a large hardness difference and parts with a small difference in hardness, there are parts where the golf ball flexes when hit and parts where the movement of the golf ball is suppressed, so that the deformed parts can be converted into repulsion without waste. Note that it is preferable that the hardness difference (C5-C4) is Cbmax.

The center hardness (C0) of the spherical core is Shore C hardness, preferably 50.0 or more, more preferably 52.0 or more, even more preferably 54.0 or more, and preferably 70.0 or less, more preferably is 68.0 or less, more preferably 66.0 or less. If the center hardness (C0) is 50.0 or more, the ball will not collapse too much when it is deformed, and will exhibit repulsion performance, and if it is 70.0 or less, the ball will be deformed to the inside, providing a good feeling.

The surface hardness (C8) of the spherical core is Shore C hardness, preferably 70.0 or more, more preferably 72.0 or more, even more preferably 74.0 or more, and preferably 90.0 or less, more preferably is 88.0 or less, more preferably 86.0 or less. If the surface hardness (C8) is 70.0 or more, the ball will not be crushed too much and exhibits resilience performance, and if the surface hardness (C8) is 90.0 or less, the ball will have good durability.

The hardness (C4) at a 50.0% point from the center of the spherical core is Shore C hardness, preferably 60.0 or more, more preferably 62.0 or more, still more preferably 64.0 or more, and 80. It is preferably 0 or less, more preferably 78.0 or less, even more preferably 76.0 or less. If the hardness (C4) is 60.0 or more, the ball will not be crushed too much and will exhibit repulsion performance, and if it is 80.0 or less, recoil will be promoted and the driver will have low spin.

The diameter of the spherical core is preferably 34.8 mm or more, more preferably 36.3 mm or more, even more preferably 37.8 mm or more, and preferably 42.2 mm or less, more preferably 41.8 mm or less, even more preferably It is 41.2 mm or less, most preferably 40.8 mm or less. If the diameter of the spherical core is 34.8 mm or more, the resilience will be better. On the other hand, if the diameter of the spherical core is 42.2 mm or less, the function of the cover will be better exhibited.

When the spherical core has a diameter of 34.8 mm to 42.2 mm, the amount of compressive deformation (the amount by which the core shrinks in the compression direction) from the initial load of 98 N to the final load of 1275 N is 2.0 mm. The above is preferable, more preferably 2.3 mm or more, still more preferably 2.5 mm or more, and preferably 5.0 mm or less, more preferably 4.5 mm or less, still more preferably 4.3 mm or less. If the amount of compressive deformation is 2.0 mm or more, the shot feel will be better, and if it is 5.0 mm or less, the rebound will be better.

The structure of the spherical core may be either a single layer structure or a multilayer structure of two or more layers, but a single layer structure is preferable. A spherical core with a single-layer structure eliminates energy loss during impact at the interface of a multi-layer structure, and improves repulsion.

[Rubber composition]
The spherical core contains (a) a base rubber, (b) an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and/or a metal salt thereof as a co-crosslinking agent, and (c) a crosslinking initiator. It is preferable that the core be formed from a rubber composition containing the core rubber composition. The spherical core can be obtained by molding a core rubber composition in a mold. Molding conditions are not particularly limited, but the molding is usually carried out at 130° C. to 200° C., under a pressure of 2.9 MPa to 11.8 MPa, and for 10 minutes to 60 minutes.

The spherical core contains (a) a base rubber, (b) an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and/or a metal salt thereof as a co-crosslinking agent, (c) a crosslinking initiator, and ( d) It is preferable that the core is formed from a rubber composition containing a monophenol compound having a substituent only at the p-position. By using a rubber composition containing specific raw materials, the hardness distribution of the resulting spherical core can be easily controlled.

(a) Base Rubber (a) As the base rubber, natural rubber and/or synthetic rubber can be used. (a) As the base rubber, for example, polybutadiene rubber, natural rubber, polyisoprene rubber, styrene-butadiene rubber, ethylene-propylene-diene rubber (EPDM), etc. can be used. These may be used alone or in combination of two or more. Among these, high-cis polybutadiene having 40% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more of cis-1,4-bonds that are advantageous for repulsion. is suitable.

From the viewpoint of obtaining a core with higher resilience, the content of high-cis polybutadiene in the base rubber is preferably 60% by mass or more, more preferably 80% by mass or more, and 90% by mass or more. It is more preferable that It is also preferable that the base rubber (a) consists only of high-cis polybutadiene.

The content of 1,2-vinyl bonds in the high-cis polybutadiene is preferably 2.0% by mass or less, more preferably 1.7% by mass or less, still more preferably 1.5% by mass or less. If the content of 1,2-vinyl bonds is 2.0% by mass or less, the repulsion properties will be further improved.

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

The Mooney viscosity (ML ₁₊₄ (100°C)) of the high-cis polybutadiene is preferably 30 or more, more preferably 32 or more, even more preferably 35 or more, and preferably 140 or less, more preferably It is 120 or less, more preferably 100 or less, and most preferably 55 or less. In addition, the Mooney viscosity (ML ₁₊₄ (100°C)) as used in the present invention refers to the condition of using an L rotor, preheating time for 1 minute, rotor rotation time for 4 minutes, and 100°C according to JIS K6300. This is the value measured below.

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. It is 4 or more, most preferably 2.6 or more, preferably 6.0 or less, more preferably 5.0 or less, still more preferably 4.0 or less, most preferably 3.0 or less. If the molecular weight distribution (Mw/Mn) of the high-cis polybutadiene is within the above range, the core molding workability will be good, and the resulting spherical core will have good resilience. The molecular weight distribution was determined 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. : The value was measured under the conditions of tetrahydrofuran and calculated as a standard polystyrene equivalent value.

(b) Co-crosslinking agent (b) The α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and/or its metal salt is blended into the rubber composition as a co-crosslinking agent, and is used as a base material. It has the effect of crosslinking rubber molecules by graft polymerizing to rubber molecular chains.

Examples of the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms include acrylic acid, methacrylic acid, fumaric acid, maleic acid, and crotonic acid.

Examples of metals constituting the metal salt of α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms include monovalent metal ions such as sodium, potassium, and lithium; magnesium, calcium, zinc, barium, cadmium, etc. Divalent metal ions such as aluminum; trivalent metal ions such as aluminum; and other ions such as tin and zirconium. The metal components may be used alone or as a mixture of two or more. Among these, divalent metals such as magnesium, calcium, zinc, barium, and cadmium are preferred as the metal component. This is because by using a divalent metal salt of an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms, metal crosslinks are likely to occur between rubber molecules. Particularly, as the divalent metal salt, zinc acrylate is preferred because it increases the resilience of the resulting golf ball. 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.

(b) The content of the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and/or its metal salt is preferably 15 parts by mass or more based on 100 parts by mass of (a) the base rubber. , more preferably 20 parts by mass or more, further preferably 25 parts by mass or more, preferably 50 parts by mass or less, more preferably 45 parts by mass or less, and even more preferably 35 parts by mass or less. When the content of the component (b) is 15 parts by mass or more, the amount of the crosslinking initiator (c) required to make the core formed from the core rubber composition appropriate hardness is reduced, and the amount of crosslinking initiator obtained is reduced. This improves the repulsion of the golf ball. Further, if the content of component (b) is 50 parts by mass or less, the resulting golf ball will have a good shot feel.

(c) Crosslinking initiator (c) The crosslinking initiator is blended to crosslink the base rubber component (a). (c) As the crosslinking initiator, organic peroxides are suitable. Specifically, the organic peroxides include dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, and 2,5-dimethyl-2,5-dimethyl cyclohexane. Examples include organic peroxides such as (t-butylperoxy)hexane and di-t-butylperoxide. These organic peroxides may be used alone or in combination of two or more. Among these, dicumyl peroxide is preferably used.

(c) The content of the crosslinking initiator is preferably 0.2 parts by mass or more, more preferably 0.5 parts by mass or more, and 0.7 parts by mass or more with respect to 100 parts by mass of the base rubber (a). is more preferably 5.0 parts by mass or less, more preferably 2.5 parts by mass or less, even more preferably 2.0 parts by mass or less. When the content of component (c) is 0.2 parts by mass or more, the core formed from the core rubber composition does not become too soft and the resilience of the resulting golf ball improves, and the content is 5.0 parts by mass. If it is below, the resulting golf ball will have good resilience and durability.

(d) Monophenol compound having a substituent only at the p-position (d) A monophenol compound having a substituent only at the p-position is a compound having a substituent only at the p-position of the monophenol. The monophenol compound having a substituent only at the p-position is a compound in which a substituent is directly bonded to the p-position to one hydroxy group of the phenol, and the monophenol compound has a substituent directly bonded to the p-position of the hydroxy group, and the monophenol compound has a substituent at the o-position and m-position of the hydroxy group. It has no group. Examples of the substituent at the p-position include an alkoxy group, a halogen group, a hydrocarbon group, a nitro group, a cyano group, an amino group, a hydroxy group, and an alkoxy group is preferred.

The monophenol compound having a substituent only at the p-position (d) is preferably one represented by the following general formula (1).

［一般式（１）において、Ｒは、アルコキシ基、ハロゲン基、炭化水素基、ニトロ基、シアノ基、アミノ基、またはヒドロキシ基を表す。］

[In general formula (1), R represents an alkoxy group, a halogen group, a hydrocarbon group, a nitro group, a cyano group, an amino group, or a hydroxy group. ]

Examples of the alkoxy group include a group in which an alkyl group having one or more carbon atoms is bonded to an oxygen atom. The number of carbon atoms in the alkoxy group is not particularly limited as long as it is 1 or more, but it is preferably from 1 to 20, more preferably from 1 to 10, even more preferably from 1 to 8. The structure of the alkyl portion of the alkoxy group may be linear, branched, or cyclic. Specific examples of the alkyl moiety of the alkoxy group include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, n-pentyl group, isopentyl group. group, sec-pentyl group, tert-pentyl group, neopentyl group, n-hexyl group, isohexyl group, sec-hexyl group, tert-hexyl group, n-heptyl group, isoheptyl group, sec-heptyl group, tert-heptyl group , linear or branched alkyl groups such as n-octyl group, isooctyl group, sec-octyl group, and tert-octyl group, and cyclic groups such as cyclobutyl group, cyclopentyl group, cyclohexyl group, cycloheptyl group, and cyclooctyl group. Mention may be made of alkyl groups. Specific examples of the alkoxy group include methoxy group, ethoxy group, propoxy group (including n- and iso-structures), butoxy group (including n-, iso-, sec-, tert-, and cyclo-structures), Pentyloxy group (including n-, iso-, sec-, tert-, cyclo- structure), hexyloxy group (including n-, iso-, sec-, tert-, cyclo- structure), heptyloxy group ( examples thereof include n-, iso-, sec-, tert-, and cyclo-structures), octyloxy groups (including n-, iso-, sec-, tert-, and cyclo-structures), and the like. Note that the alkoxy group may have a substituent (for example, a halogen group, a hydroxy group, an amino group, a nitro group, a cyano group, etc.).

Examples of the halogen group include a fluoro group, a chloro group, a bromo group, and an iodo group.

Examples of the hydrocarbon group include an alkyl group, an alkenyl group, an alkynyl group, an aralkyl group, and an aryl group.

The number of carbon atoms in the alkyl group is not particularly limited as long as it is 1 or more, but it is preferably 1 to 20, more preferably 1 to 10, and even more preferably 1 to 8. The structure of the alkyl group may be linear, branched, or cyclic, and specific examples thereof include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec. -butyl group, tert-butyl group, n-pentyl group, isopentyl group, sec-pentyl group, tert-pentyl group, neopentyl group, n-hexyl group, isohexyl group, sec-hexyl group, tert-hexyl group, n- Straight chain or branched alkyl groups such as heptyl group, isoheptyl group, sec-heptyl group, tert-heptyl group, n-octyl group, isooctyl group, sec-octyl group, tert-octyl group, cyclobutyl group, cyclopentyl group, Examples include cyclic alkyl groups such as cyclohexyl group, cycloheptyl group, and cyclooctyl group. Note that the alkyl group may have a substituent (for example, a halogen group, a hydroxy group, an amino group, a nitro group, a cyano group, etc.).

The number of carbon atoms in the alkenyl group is not particularly limited as long as it is 2 or more, but it is preferably from 2 to 20, more preferably from 2 to 10, even more preferably from 2 to 8. Specific examples of the alkenyl group include vinyl group, allyl group, propenyl group, isopropenyl group, butenyl group, isobutenyl group, hexenyl group, and the like. Note that the alkenyl group may have a substituent (for example, an alkyl group, a halogen group, a hydroxy group, an amino group, a nitro group, a cyano group, etc.).

The number of carbon atoms in the alkynyl group is not particularly limited as long as it is 2 or more, but it is preferably 2 to 20, more preferably 2 to 10, and even more preferably 2 to 8. Specific examples of the alkynyl group include ethynyl group, 1-propynyl group, 2-propynyl group (propargyl group), and butynyl group. Note that the alkynyl group may have a substituent (for example, an alkyl group, a halogen group, a hydroxy group, an amino group, a nitro group, a cyano group, etc.).

The number of carbon atoms in the aralkyl group is not particularly limited as long as it is 7 or more, but it is preferably from 7 to 20, more preferably from 7 to 10, even more preferably from 7 to 8. Specific examples of the aralkyl group include benzyl group, phenylethyl group, phenylbutyl group, and α-cumyl group. Note that the aralkyl group may have a substituent (for example, an alkyl group, a halogen group, an amino group, a nitro group, a cyano group, etc.).

The number of carbon atoms in the aryl group is not particularly limited as long as it is 6 or more, but it is preferably 6 to 20, more preferably 6 to 15, and even more preferably 6 to 10. Specific examples of the aryl group include phenyl group, naphthyl group, and the like. Note that the aryl group may have a substituent (for example, an alkyl group, a halogen group, an amino group, a nitro group, a cyano group, etc.).

In general formula (1), the substituent represented by R is preferably an alkoxy group, more preferably an alkoxy group having 1 to 8 carbon atoms, and particularly preferably a methoxy group, an ethoxy group, a propoxy group, or a butoxy group.

The monophenol compound (d) having a substituent only at the p-position may be used alone or in combination of two or more types.

The blending amount of the monophenol compound having a substituent only at the p-position (d) is preferably 0.05 parts by mass or more, more preferably 0.07 parts by mass or more, based on 100 parts by mass of the base rubber (a). It is preferably 0.10 parts by mass or more, more preferably 2.0 parts by mass or less, more preferably 1.8 parts by mass or less, and even more preferably 1.6 parts by mass or less. If the blending amount of the monophenol compound having a substituent only at the p-position (d) is 0.05 parts by mass or more, the effect of adding the monophenol compound having a substituent only at the p-position (d) will be greater. , 2.0 parts by mass or less, flight distance on driver shots is further improved.

The mass ratio of component (b) and component (d) (component (b)/component (d)) is preferably 25 or more, more preferably 30 or more, even more preferably 35 or more, even more preferably 100 or more, and 200 or more. Above is especially preferable, 500 or less is preferable, 450 or less is more preferable, and 400 or less is still more preferable. If the mass ratio (component (b)/component (d)) is within the range, the shot feel will be good and the flight distance on driver shots will be further improved.

The mass ratio of component (c) and component (d) (component (c)/component (d)) is preferably 1.0 or more, more preferably 1.5 or more, even more preferably 2.0 or more, and 150 It is preferably below, more preferably 130 or less, even more preferably 110 or less, even more preferably 50 or less, and particularly preferably 20 or less. If the mass ratio (component (c)/component (d)) is within the range, the shot feel will be good and the flight distance on driver shots will be further improved.

(e) Organic sulfur compound The core rubber composition preferably further contains (e) an organic sulfur compound. (e) By containing an organic sulfur compound, the repulsion of the obtained core becomes higher.

The organic sulfur compounds (e) include thiols (thiophenols, thionaphthols), polysulfides, thiazoles, thiurams, thiocarboxylic acids, dithiocarboxylic acids, sulfenamides, and dithiocarbamates. At least one compound selected from the group.

Examples of thiols include thiophenols and thionaphthols. Examples of the thiophenols include thiophenol; 4-fluorothiophenol, 2,4-difluorothiophenol, 2,5-difluorothiophenol, 2,6-difluorothiophenol, and 2,4,5-trifluorothiophenol. Thiophenols substituted with fluoro groups such as thiophenol, 2,4,5,6-tetrafluorothiophenol, and pentafluorothiophenol; 2-chlorothiophenol, 4-chlorothiophenol, 2,4-dichlorothiophenol With chloro groups such as phenol, 2,5-dichlorothiophenol, 2,6-dichlorothiophenol, 2,4,5-trichlorothiophenol, 2,4,5,6-tetrachlorothiophenol, and pentachlorothiophenol. Substituted thiophenols; 4-bromothiophenol, 2,4-dibromothiophenol, 2,5-dibromothiophenol, 2,6-dibromothiophenol, 2,4,5-tribromothiophenol, 2, Thiophenols substituted with a bromo group such as 4,5,6-tetrabromothiophenol and pentabromothiophenol; 4-iodothiophenol, 2,4-diiodothiophenol, 2,5-diiodothiophenol , 2,6-diiodothiophenol, 2,4,5-triiodothiophenol, 2,4,5,6-tetraiodothiophenol, pentaiodothiophenol and other thiophenols substituted with an iodo group; Alternatively, metal salts thereof may be mentioned. The metal salt is preferably a divalent metal salt, more preferably a zinc salt.

The thionaphthols (naphthalenethiols) include 2-thionaphthol, 1-thionaphthol, 1-chloro-2-thionaphthol, 2-chloro-1-thionaphthol, 1-bromo-2-thionaphthol, 2-thionaphthol, -Bromo-1-thionaphthol, 1-fluoro-2-thionaphthol, 2-fluoro-1-thionaphthol, 1-cyano-2-thionaphthol, 2-cyano-1-thionaphthol, 1-acetyl-2- Examples include thionaphthol, 2-acetyl-1-thionaphthol, and metal salts thereof. The metal salt is preferably a divalent metal salt, more preferably a zinc salt.

Polysulfides are organic sulfur compounds having polysulfide bonds, and include, for example, disulfides, trisulfides, and tetrasulfides. As the polysulfides, diphenyl polysulfides are preferred.

Examples of diphenyl polysulfides include 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-tetrabromo phenyl) disulfide, bis(pentabromophenyl) disulfide, bis(4-iodophenyl) disulfide, bis(2,5-diiodophenyl) disulfide, bis(2,6-diiodophenyl) disulfide, bis(2,4 Diphenyl disulfides substituted with halogen groups such as ,5-triiodophenyl) disulfide, bis(2,4,5,6-tetraiodophenyl) disulfide, and bis(pentaiodophenyl) disulfide; 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) Diphenyl disulfides substituted with an alkyl group such as disulfide and bis(penta-t-butylphenyl) disulfide; and the like.

Examples of thiazoles include 2-mercaptobenzothiazole, di-2-benzothiazolyl disulfide, 2-(N,N-diethylthiocarbamoylthio)benzothiazole, 2-(4'-morpholinodithio)benzothiazole, 4- Methyl-2-mercaptobenzothiazole, di-(4-methyl-2-benzothiazolyl) disulfide, 5-chloro-2-mercaptobenzothiazole, 2-mercapto-6-nitrobenzothiazole, 2-mercapto-naphtho[1,2 -d]thiazole, 2-mercapto-5-methoxybenzothiazole, 6-amino-2-mercaptobenzothiazole, or metal salts thereof.

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. can be mentioned. Examples of thiocarboxylic acids include naphthalenethiocarboxylic acid. Examples of dithiocarboxylic acids include naphthalenedithiocarboxylic acid. Examples of sulfenamides include N-cyclohexyl-2-benzothiazole sulfenamide, N-oxydiethylene-2-benzothiazole sulfenamide, and Nt-butyl-2-benzothiazole sulfenamide. Can be mentioned.

The organic sulfur compounds (e) include thiophenols substituted with halogen groups, metal salts of thiophenols substituted with halogen groups, diphenyl disulfides substituted with halogen groups, thiazoles, and thiazoles. Preferably, it is at least one compound selected from the group consisting of metal salts.

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

The content of the organic sulfur compound (e) is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and even more preferably 0.2 parts by mass, based on 100 parts by mass of the base rubber (a). It is preferably at least 5.0 parts by mass, more preferably at most 3.0 parts by mass, even more preferably at most 2.0 parts by mass. If the content of component (e) is within the above range, the resulting golf ball will have better resilience.

The mass ratio of component (e) and component (d) (component (e)/component (d)) is preferably 1.0 or more, more preferably 1.5 or more, even more preferably 2.0 or more, and 100 or more. It is preferably at most 90, more preferably at most 80, even more preferably at most 40, particularly preferably at most 20. If the mass ratio (component (e)/component (d)) is within the range, the recoil effect will be greater on driver shots, and the flight distance on driver shots will be further improved.

(f) Metal compound When the core rubber composition contains only an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms as a co-crosslinking agent, it may further contain (f) a metal compound. preferable. By neutralizing the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms with a metal compound in the core rubber composition, the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms can be used as a co-crosslinking agent. This is because substantially the same effect as when using a metal salt of a saturated carboxylic acid can be obtained. Note that when an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and a metal salt thereof are used together as a co-crosslinking agent, (f) a metal compound may be used as an optional component.

The metal compound (f) is not particularly limited as long as it can neutralize the (b) α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms in the core rubber composition. . Examples of the metal compound (f) include metal hydroxides such as magnesium hydroxide, zinc hydroxide, calcium hydroxide, sodium hydroxide, lithium hydroxide, potassium hydroxide, and copper hydroxide; magnesium oxide, calcium oxide, etc. metal oxides such as , 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 metal compound (f) are divalent metal compounds, more preferably zinc compounds. 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 high resilience can be obtained.

The metal compound (f) may be used alone or in combination of two or more. Further, the content of the metal compound (f) may be adjusted as appropriate depending on the desired degree of neutralization of the (b) α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms.

(g) Carboxylic acid and/or its salt The core rubber composition may contain (g) carboxylic acid and/or its salt. By containing the above-mentioned (g) carboxylic acid and/or its salt, the degree of external hardness and internal softness of the obtained spherical core can be increased. Examples of the carboxylic acid and/or its salt (g) include aliphatic carboxylic acids, aliphatic carboxylates, aromatic carboxylic acids, and aromatic carboxylates. The carboxylic acid and/or salt (g) may be used alone or as a mixture of two or more.

The number of carbon atoms in the carboxylic acid is preferably 1 or more, preferably 30 or less, more preferably 18 or less, still more preferably 13 or less. Note that (g) carboxylic acid and/or its salt does not include (b) α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and/or its metal salt used as a co-crosslinking agent. shall be taken as a thing.

The carboxylic acids and/or their salts include saturated aliphatic acids such as caprylic acid (octanoic acid), pelargonic acid (nonanoic acid), capric acid (decanoic acid), lauric acid, myristic acid, palmitic acid, stearic acid, and behenic acid. Carboxylic acids; unsaturated aliphatic carboxylic acids such as palmitoleic acid, oleic acid, linoleic acid or arachidonic acid; or benzoic acid, butylbenzoic acid, anisic acid (methoxybenzoic acid), dimethoxybenzoic acid, trimethoxybenzoic acid, dimethylamino acid Aromatic carboxylic acids such as benzoic acid, chlorobenzoic acid, dichlorobenzoic acid, trichlorobenzoic acid, acetoxybenzoic acid, biphenylcarboxylic acid, naphthalenecarboxylic acid, anthracenecarboxylic acid, furoic acid or thenoyl acid; or Preferred are potassium salts, magnesium salts, calcium salts, aluminum salts, zinc salts, iron salts, copper salts, nickel salts, and cobalt salts. Among these, aromatic carboxylic acids and/or salts thereof are preferred, and carboxylic acids having a benzene ring and/or salts thereof are more preferred.

The content of the (g) carboxylic acid and/or its salt is, for example, preferably 0.5 parts by mass or more, more preferably 1.0 parts by mass or more, based on 100 parts by mass of the (a) base rubber. More preferably, the amount is 1.5 parts by mass or more and 40 parts by mass or less, more preferably 35 parts by mass or less, and even more preferably 30 parts by mass or less. If the content of the component (g) is 0.5 parts by mass or more, the degree of external hardness and internal softness of the spherical core increases, and if it is 40 parts by mass or less, the decrease in core hardness is suppressed and the resilience is good. becomes.

The core rubber composition may contain additives such as pigments, fillers for weight adjustment, peptizers, softeners, etc., as necessary.

The filler used in the core rubber composition is mainly blended as a weight adjuster for adjusting the weight of the golf ball obtained as a final product, and may be blended as necessary. Examples of the filler include inorganic fillers such as zinc oxide, barium sulfate, calcium carbonate, magnesium oxide, tungsten powder, and molybdenum powder. Particularly preferred as the filler is zinc oxide. It is believed that zinc oxide functions as a vulcanization aid and increases the hardness of the entire core. The content of the filler is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and preferably 30 parts by mass or less, and 25 parts by mass, based on 100 parts by mass of the base rubber (a). The amount is more preferably 20 parts by mass or less, and even more preferably 20 parts by mass or less. If the content of the filler is 30 parts by mass or less, the resilience will be good.

The content of the peptizer is preferably 0.1 parts by mass or more and 5 parts by mass or less based on 100 parts by mass of the base rubber (a).

The core rubber composition can be prepared by mixing and kneading each raw material. The kneading method is not particularly limited, and may be carried out using, for example, a known kneader such as a kneading roll, a Banbury mixer, or a kneader.

[Cover, middle layer]
The golf ball has a cover that covers a spherical core. The cover is a layer that constitutes the outermost layer of the golf ball body excluding the coating film.

The material hardness of the cover composition constituting the cover is preferably set appropriately depending on the desired performance of the golf ball. For example, in the case of a distance golf ball that emphasizes flight distance, the material hardness of the cover composition is preferably 50 or more in Shore D hardness, more preferably 55 or more, even more preferably 60 or more, and preferably 80 or less. It is more preferably 70 or less, and even more preferably 68 or less. By setting the material hardness of the cover composition to 50 or more, a golf ball with a high launch angle and low spin can be obtained on driver shots and iron shots, and the flight distance can be further improved. Furthermore, by setting the material hardness of the cover composition to 80 or less, a golf ball with excellent durability can be obtained. In the case of a spin-type golf ball where controllability is important, the material hardness of the cover composition is preferably less than 50, more preferably 48 or less, further preferably 45 or less, and preferably 20 or more in terms of Shore D hardness. , 25 or more is more preferable, and 30 or more is even more preferable. If the material hardness of the cover composition is less than 50 in terms of Shore D hardness, the spin rate on approach shots will be high, and a golf ball that will easily stop on the green will be obtained. Further, by setting the material hardness to 20 or more, the scratch resistance is improved. Note that the material hardness of the cover is slab hardness measured by molding the cover composition forming the cover into a sheet shape.

The thickness of the cover is preferably 4.0 mm or less, more preferably 3.0 mm or less, still more preferably 2.0 mm or less. If the thickness of the cover is 4.0 mm or less, the resulting golf ball will have better resilience and shot feel. The thickness of the cover is preferably 0.3 mm or more, more preferably 0.4 mm or more, and even more preferably 0.5 mm or more. If the thickness of the cover is 0.3 mm or more, the impact durability and abrasion resistance of the cover will be improved.

The golf ball may have an intermediate layer between the spherical core and the cover. The intermediate layer may be a single layer or two or more layers, but is preferably a single layer.

The material hardness of the intermediate layer composition constituting the intermediate layer is preferably 55 or more in Shore D hardness, more preferably 57 or more, even more preferably 59 or more, and preferably 74 or less, more preferably 72 or less, More preferably, it is 70 or less. If the material hardness of the intermediate layer is 55 or more, the amount of spin on driver shots will be further reduced and the flight distance will be further improved, and if the material hardness is 74 or less, the durability will be good. When there are two or more intermediate layers, it is preferable that the material hardness of the composition constituting the outermost intermediate layer is within the above range. Note that the material hardness of the intermediate layer is slab hardness measured by molding the intermediate layer composition forming the intermediate layer into a sheet shape. In the case of having a plurality of intermediate layers, the material hardness of each layer may be the same or different, but it is preferable that the hardness of all the intermediate layers is within the above range.

The thickness of the intermediate layer is preferably 0.8 mm or more, more preferably 0.9 mm or more, even more preferably 1.0 mm or more, and preferably 4.0 mm or less, more preferably 3.0 mm or less, even more preferably is 2.0 mm or less. If the thickness of the intermediate layer is 0.8 mm or more, impact durability will be good, and if it is 4.0 mm or less, good feeling will be obtained. When there are two or more intermediate layers, the thickness of the outermost intermediate layer is preferably within the above range.

It is preferable that the thickness (mm) and material hardness (Shore D) of the intermediate layer and the thickness (mm) and material hardness (Shore D) of the cover satisfy equation (21). By satisfying Equation (21), the spin performance on approach shots improves, and the recoil effect on driver shots becomes larger, further reducing the amount of spin.
{(Intermediate layer thickness x material hardness)/(cover thickness x material hardness)}≧4.0...(21)

The above ((intermediate layer thickness x material hardness)/(cover thickness x material hardness)) is preferably 4.0 or more, more preferably 4.5 or more, and still more preferably 5.0 or more, It is preferably 10.0 or less, more preferably 9.0 or less, still more preferably 8.0 or less.

The cover and the intermediate layer are preferably formed from a cover composition and an intermediate layer composition containing a resin component. Examples of the resin component include an ionomer resin, a thermoplastic polyurethane elastomer commercially available from BASF Japan Ltd. under the trade name "Elastolan (registered trademark)", and a commercially available product name "Pebax (registered trademark)" from Arkema Corporation. Thermoplastic polyamide elastomer is commercially available under the trade name "Hytrel (registered trademark)" from DuPont-Toray Co., Ltd., thermoplastic polyester elastomer is commercially available under the trade name "TEFABLOCK" from Mitsubishi Chemical Corporation. Examples include commercially available thermoplastic styrene elastomers.

Examples of the ionomer resin include a binary copolymer of an olefin and an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms, in which at least a portion of the carboxyl groups are neutralized with metal ions; and a terpolymer of α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and α,β-unsaturated carboxylic acid ester, with at least a portion of the carboxyl groups neutralized with metal ions, or , and mixtures thereof. The olefin is preferably an olefin having 2 to 8 carbon atoms, such as ethylene, propylene, butene, pentene, hexene, heptene, octene, etc., with ethylene being particularly preferred. Examples of the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms include acrylic acid, methacrylic acid, fumaric acid, maleic acid, and crotonic acid, with acrylic acid and methacrylic acid being particularly preferred. Further, as the α,β-unsaturated carboxylic acid ester, for example, methyl, ethyl, propyl, n-butyl, isobutyl esters of acrylic acid, methacrylic acid, fumaric acid, maleic acid, etc. are used, and in particular, acrylic acid ester Or methacrylic acid ester is preferable. Among these, the ionomer resins include metal ion neutralized products of ethylene-(meth)acrylic acid binary copolymers and ethylene-(meth)acrylic acid-(meth)acrylic acid ester ternary copolymers. Metal ion neutralized products are preferred.

The cover composition preferably contains a thermoplastic polyurethane elastomer or an ionomer resin as a resin component. When using an ionomer resin, it is also preferable to use a thermoplastic styrene elastomer together. The content of polyurethane or ionomer resin in the resin component of the cover composition is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more.

The intermediate layer composition preferably contains an ionomer resin as a resin component. When using an ionomer resin, it is also preferable to use a thermoplastic styrene elastomer together. The content of the ionomer resin in the resin component of the intermediate layer composition is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more.

The cover composition and the intermediate layer composition contain, in addition to the above-mentioned resin components, pigment components such as white pigments (e.g., titanium oxide), blue pigments, and red pigments, zinc oxide, calcium carbonate, barium sulfate, and the like. It may contain a regulator, a dispersant, an anti-aging agent, an ultraviolet absorber, a light stabilizer, a fluorescent material or a fluorescent brightener.

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, and 10 parts by mass based on 100 parts by mass of the resin component constituting the cover. It is preferably at most 8 parts by mass, more preferably at most 8 parts by mass. By setting the content of the white pigment to 0.5 parts by mass or more, concealing properties can be imparted to the cover. Moreover, if the content of the white pigment is 10 parts by mass or less, the durability of the obtained cover will be good.

The method for forming the intermediate layer is not particularly limited, but for example, a method in which the composition for the intermediate layer is previously formed into a hemispherical half shell, two half shells are used to wrap a spherical core, and then pressure molded. Alternatively, the intermediate layer composition may be directly injection molded onto a spherical core to envelop the spherical core.

The method for molding the cover includes, for example, a method in which a hollow shell is molded from the cover composition, a sphere (a sphere in which a spherical core or an intermediate layer is formed) is covered with a plurality of shells, and then compression molded. (Preferably, a hollow half shell is molded from the cover composition, and the sphere is covered with two half shells and compression molded.) Alternatively, the cover composition is directly injection molded onto the sphere. Here are some methods.

When forming a cover, depressions called dimples are usually formed on the surface. The total number of dimples formed on the cover is preferably 200 to 500. If the total number of dimples is 200 to 500, the size of each dimple can be increased, and the effect of the dimples will be greater. The shape of the dimples formed (plan view shape) is not particularly limited, and may be a circle; a polygon such as a substantially triangular, substantially quadrilateral, pentagonal, or hexagonal; or other irregular shape; Alternatively, two or more types may be used in combination.

The golf ball body with the cover molded thereon is preferably taken out from the mold and subjected to surface treatments such as deburring, cleaning, and sandblasting, if necessary.

Moreover, a coating film or a mark can be formed if desired. The thickness of the coating film is not particularly limited, but is preferably 5 μm or more, more preferably 6 μm or more, even more preferably 7 μm or more, preferably 50 μm or less, more preferably 40 μm or less, and even more preferably 30 μm or less. If the film thickness is 5 μm or more, the coating film will be less likely to wear out even if it is used continuously, and if the film thickness is 50 μm or less, the dimple effect will be sufficiently obtained and the flight performance of the golf ball will be improved.

[Golf ball]
The golf ball of the present invention includes, for example, a two-piece golf ball comprising a spherical core and a single-layer cover covering the spherical core; a spherical core and a single-layer intermediate layer covering the spherical core; Examples include a three-piece golf ball having a single-layer cover; a multi-piece golf ball having a spherical core, two or more intermediate layers covering the spherical core, and a single-layer cover covering the intermediate layer; It will be done. The present invention can be suitably applied to golf balls having any of the above structures.

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

When the golf ball has a diameter of 40 mm to 45 mm, the amount of compressive deformation (the amount of shrinkage in the compression direction) when a final load of 1275 N is applied from an initial load of 98 N is preferably 2.0 mm or more, It is more preferably 2.1 mm or more, still more preferably 2.2 mm or more, and preferably 3.0 mm or less, more preferably 2.9 mm or less, and still more preferably 2.8 mm or less. A golf ball having a compressive deformation amount of 2.0 mm or more has a good shot feel. On the other hand, by setting the amount of compressive deformation to 3.0 mm or less, the resilience becomes high.

When the golf ball has an intermediate layer, it is preferable that the surface hardness of the spherical core (C8), the intermediate layer surface hardness, and the ball surface hardness are Shore C hardness and satisfy formula (20). .
Core surface hardness<intermediate layer surface hardness>ball surface hardness...(20)

FIG. 1 shows an example of the golf ball of the present invention. FIG. 1 is a partially cutaway sectional view showing a golf ball 1 according to an embodiment of the present invention. The golf ball 1 includes a core 2, an intermediate layer 3 covering the core 2, and a cover 4 covering the intermediate layer 3. A large number of dimples 41 are formed on the surface of this cover 4. The portion of the surface of this golf ball other than the dimples 41 is a land 42. This golf ball 1 includes a paint layer and a mark layer on the outside of the cover 4, but illustration of these layers is omitted.

Hereinafter, the present invention will be explained in detail with reference to Examples. However, the present invention is not limited to the following Examples, and any changes or embodiments of the present invention may be made without departing from the spirit of the present invention. Included within the range.

[Evaluation method]
(1) Amount of compressive deformation (mm)
The amount of deformation in the compression direction (the amount by which the spherical core or golf ball shrinks in the compression direction) was measured from when an initial load of 98 N was applied to the spherical core or golf ball to when a final load of 1275 N was applied.

(2) Core hardness (Shore C hardness)
The hardness measured at the surface of the core was defined as the core surface hardness. Further, the core was cut into hemispherical shapes, and the hardness was measured at the center of the cut surface and at a predetermined distance from the center in the radial direction. Note that the center of the core was 0% and the surface was 100%. Further, the core hardness was calculated by measuring the hardness at four points at a predetermined distance from the center of the core cross section and averaging these values. The hardness was measured using an automatic hardness meter (manufactured by H. Burleys, Digitest II). “ShoreC” was used as a detector.

(3) Golf ball surface hardness, intermediate layer surface hardness The hardness measured at the land portion on the surface of the golf ball was defined as the ball surface hardness. Further, the hardness measured at the surface of the intermediate layer-covered sphere in which the intermediate layer was formed on the surface of the spherical core was defined as the intermediate layer surface hardness. The hardness was measured using an automatic hardness meter (manufactured by H. Burleys, Digitest II). “ShoreC” was used as a detector.

(4) Material hardness (Shore D hardness)
A sheet with a thickness of about 2 mm was produced by injection molding using the composition for the intermediate layer and the composition for the cover, and was stored at 23° C. for 2 weeks. The hardness was measured using an automatic hardness meter (Digitest II, manufactured by H. Burleys) with three or more of these sheets stacked one on top of the other so as not to be affected by the measurement substrate or the like. A "Shore D" detector was used.

(5) Driver Shot Test A driver (Sumitomo Rubber Industries, Ltd., "SRIXON ZX7", shaft hardness: S, loft angle: 10.5°) was attached to a golf laboratory swing machine. The point of impact was set at the center of the face. A golf ball was hit at a head speed of 50 m/sec, and the ball speed, spin speed, and flight distance (distance from the starting point to the falling point) immediately after hitting were measured. The measurement was performed 12 times for each golf ball, and the average value was taken as the measured value for that golf ball. Note that the initial speed, spin speed, and flight distance of each golf ball in Tables 5 and 6 are for golf ball No. It is shown as the difference from 6.

(6) Middle iron test An iron (Sumitomo Rubber Industries, Ltd., "SRIXON ZX7", count: #7, loft angle: 32°) was attached to a golf laboratory swing machine. The point of impact was set at the center of the face. A golf ball was hit at a head speed of 39 m/sec, and the spin speed immediately after the hit was measured. The measurement was performed 12 times for each golf ball, and the average value was taken as the measured value for that golf ball. Note that the spin speed of each golf ball in Tables 5 and 6 is golf ball No. It is shown as the difference from 6.

[Production of golf ball]
(1) Preparation of rubber composition Each raw material was kneaded using a kneading roll so as to have the formulation shown in Table 1 to obtain a rubber composition.

The materials used in Table 1 are as follows.
BR730: Manufactured by JSR, 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)
ZN-DA90S: Manufactured by Nippon Techno Fine Chemical Co., Ltd., zinc acrylate (contains 10% zinc stearate)
Zinc oxide: “Ginrei R” manufactured by Toho Zinc Co., Ltd.
Barium sulfate: "Barium sulfate BD" manufactured by Sakai Chemical Co., Ltd.
Benzoic acid: Emerald Kalama Chemical Co., Ltd. 4-methoxyphenol: Tokyo Chemical Industry Co., Ltd. PBDS: Kawaguchi Chemical Co., Ltd. Bis(pentabromophenyl) disulfide DPDS: Sumitomo Seika Co., Ltd., diphenyl disulfide Dicumyl peroxide: Tokyo Chemical Industry Co., Ltd. Company-made

(2) Preparation of Composition for Intermediate Layer Raw materials were extruded using a twin-screw kneading extruder so as to have the formulation shown in Table 2, to prepare a pellet-shaped composition for intermediate layer.

サーリン（登録商標）８１５０：デュポン社製、ナトリウムイオン中和エチレン－メタクリル酸共重合体アイオノマー樹脂
ハイミラン（登録商標）ＡＭ７３２９：三井・デュポン・ポリケミカル社製、ナトリウムイオン中和エチレン－メタクリル酸共重合体アイオノマー樹脂
二酸化チタン：石原産業社製、Ａ－２２０

Surlyn (registered trademark) 8150: Manufactured by DuPont, sodium ion neutralized ethylene-methacrylic acid copolymer ionomer resin Himilan (registered trademark) AM7329: Manufactured by Mitsui DuPont Polychemicals, sodium ion neutralized ethylene-methacrylic acid copolymer Combined ionomer resin Titanium dioxide: manufactured by Ishihara Sangyo Co., Ltd., A-220

(3) Preparation of cover composition Raw materials were extruded using a twin-screw kneading extruder to obtain the formulation shown in Table 3 to prepare a pellet-shaped cover composition.

エラストラン（登録商標）ＮＹ８４Ａ：ＢＡＳＦジャパン社製、熱可塑性ポリウレタンエラストマー
チヌビン（登録商標）７７０：ＢＡＳＦジャパン社製、ヒンダードアミン系光安定剤
二酸化チタン：石原産業社製、Ａ－２２０

Elastran (registered trademark) NY84A: manufactured by BASF Japan, thermoplastic polyurethane elastomer Tinuvin (registered trademark) 770: manufactured by BASF Japan, hindered amine light stabilizer Titanium dioxide: manufactured by Ishihara Sangyo Co., Ltd., A-220

(4) Preparation of core Golf ball No. 1-6, 9
A spherical core was obtained by hot pressing the rubber composition shown in Table 4 in upper and lower molds having hemispherical cavities. Note that an appropriate amount of barium sulfate was added so that the mass of the golf ball obtained was 45.6 g.

Golf ball no. 7, 8
An inner layer core was obtained by hot pressing the rubber composition (inner layer formulation) shown in Table 4 in upper and lower molds having hemispherical cavities. Next, a half shell was molded using the rubber composition (outer layer formulation) shown in Table 4. The inner layer core was covered with these two half shells. A spherical core was obtained by hot pressing this inner layer core and half shell in upper and lower molds having hemispherical cavities.

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

Golf ball no. 1 to 4, the hardness distribution of the spherical core is such that the hardness difference (C1-C0), hardness difference (C2-C1), hardness difference (C3-C2), and hardness difference (C4-C3) is more than 0 and 6.0 or less. and the hardness difference (C5-C4) is 5.0 or more, the hardness difference (C6-C5), the hardness difference (C7-C6), and the hardness difference (C8-C7) are more than 0 and 3.5 or less. , the difference [{(C2-C0)/2}-{(C8-C6)/2}] is 0 or more. Golf ball no. No. 6 is a case in which the hardness distribution of the spherical core is outer hard and inner soft, and the hardness gradient is approximately linear from the center to the surface (hardness difference (C5-C4) is less than 5.0). Golf ball no. 1 to 4 are golf ball No. Compared to 6, the flight distance on driver shots is improved, and the spin speed on middle iron shots is also improved.

The present invention (1) provides a golf ball having a spherical core and a cover that covers the spherical core, wherein when a straight line from the center of the spherical core to the surface is divided into eight equal parts, the center hardness of the spherical core is (C0), hardness at 12.5% from the center (C1), hardness at 25.0% from the center (C2), hardness at 37.5% from the center (C3), hardness at 50.0% from the center hardness (C4), hardness at 62.5% from the center (C5), hardness at 75.0% from the center (C6), hardness at 87.5% from the center (C7), and surface hardness (C8) The golf ball has a Shore C hardness and satisfies the following relationship.
0<(C1-C0)≦6.0,
0<(C2-C1)≦6.0,
0<(C3-C2)≦6.0,
0<(C4-C3)≦6.0,
5.0≦(C5-C4),
0<(C6-C5)≦3.5,
0<(C7-C6)≦3.5,
0<(C8-C7)≦3.5,
0≦[{(C2-C0)/2}-{(C8-C6)/2}]

The present invention (2) provides the golf according to the present invention (1), wherein the spherical core has hardnesses (C0), (C2), (C5), and (C7) that are Shore C hardness and satisfy the following relationship. It's a ball.
0≦[{(C2-C0)/2}-{(C7-C5)/2}]

The present invention (3) is the present invention (1) or (2), wherein the spherical core has hardness (C0), (C2), (C4), and (C5) that are Shore C hardness and satisfy the following relationship. This is the golf ball described in .
0≦[(C5-C4)-{(C2-C0)/2}]

In the present invention (4), the spherical core has a Shore C hardness, a hardness difference (C1-C0) between hardness (C1) and hardness (C0), and a hardness difference (C1-C0) between hardness (C2) and hardness (C1). C2-C1), hardness difference (C3-C2) between hardness (C3) and hardness (C2), hardness difference (C4-C3) between hardness (C4) and hardness (C3), hardness (C5) and hardness ( hardness difference (C5-C4) between hardness (C4), hardness difference (C6-C5) between hardness (C6) and hardness (C5), hardness difference (C7-C6) between hardness (C7) and hardness (C6), And, when the largest value of the hardness difference (C8-C7) between hardness (C8) and hardness (C7) is Cbmax and the smallest value is Cbmin, the ratio (Cbmax/Cbmin) is 4.0 or more. The golf ball according to any one of the inventions (1) to (3).

The present invention (5) is the spherical core according to any one of the present inventions (1) to (4), wherein the hardness (C0) and (C8) are Shore C hardness and satisfy the following relationship. It's a golf ball.
18.0≦(C8-C0)

The present invention (6) has an intermediate layer between the spherical core and the cover, and the surface hardness (C0) of the spherical core, the intermediate layer surface hardness, and the ball surface hardness are Shore C hardness. , the golf ball according to any one of the present invention (1) to (5), which satisfies the following relationship.
Core surface hardness <middle layer surface hardness> Ball surface hardness

The present invention (7) has an intermediate layer between the spherical core and the cover, and the thickness (mm) and material hardness (Shore D) of the intermediate layer, the thickness (mm) of the cover and the material The golf ball according to any one of the present invention (1) to (6), wherein the hardness (Shore D) satisfies the following relationship.
{(Intermediate layer thickness x material hardness)/(cover thickness x material hardness)}≧4.0

The present invention (8) provides that the golf ball according to any of the present inventions (1) to (7) has a compressive deformation amount of 2.8 mm or less when a final load of 1275 N is applied from an initial load of 98 N. The golf ball according to item (1).

In the present invention (9), the spherical core comprises (a) a base rubber, (b) an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and/or a metal salt thereof as a co-crosslinking agent, (c ) A crosslinking initiator, and (d) a core rubber composition containing a monophenol compound having a substituent only at the p-position. It's a golf ball.

The present invention (10) provides that the core rubber composition contains (d) 0.05 parts by mass to 100 parts by mass of (d) a monophenol compound having a substituent only at the p-position, based on 100 parts by mass of the base rubber. The golf ball according to the present invention (9) contains 2.0 parts by mass.

The present invention (11) provides the golf ball according to the present invention (9) or (10), wherein the monophenol compound (d) having a substituent only at the p-position is represented by the general formula (1). It is.

［一般式（１）において、Ｒは、アルコキシ基、ハロゲン基、炭化水素基、ニトロ基、シアノ基、アミノ基、またはヒドロキシ基を表す。］

[In general formula (1), R represents an alkoxy group, a halogen group, a hydrocarbon group, a nitro group, a cyano group, an amino group, or a hydroxy group. ]

The present invention (12) is characterized in that the core rubber composition further comprises (g) an aromatic carboxylic acid and/or a salt thereof. It's a ball.

1: Golf ball, 2: Spherical core, 3: Intermediate layer, 4: Cover, 41: Dimple, 42: Land

Claims (12)

A golf ball having a spherical core and a cover covering the spherical core,
When a straight line from the center of the spherical core to the surface is divided into eight equal parts, the center hardness of the spherical core (C0), the hardness at 12.5% from the center (C1), and the hardness at 25.0% from the center ( C2), hardness at 37.5% from the center (C3), hardness at 50.0% from the center (C4), hardness at 62.5% from the center (C5), hardness at 75.0% from the center A golf ball characterized in that the hardness (C6), the hardness at an 87.5% point from the center (C7), and the surface hardness (C8) are Shore C hardness and satisfy the following relationship.
0<(C1-C0)≦6.0,
0<(C2-C1)≦6.0,
0<(C3-C2)≦6.0,
0<(C4-C3)≦6.0,
5.0≦(C5-C4),
0<(C6-C5)≦3.5,
0<(C7-C6)≦3.5,
0<(C8-C7)≦3.5,
0≦[{(C2-C0)/2}-{(C8-C6)/2}] The golf ball according to claim 1, wherein the spherical core has hardnesses (C0), (C2), (C5), and (C7) that are Shore C hardness and satisfy the following relationship.
0≦[{(C2-C0)/2}-{(C7-C5)/2}] 3. The golf ball according to claim 1, wherein the spherical core has hardness (C0), (C2), (C4), and (C5) that are Shore C hardness and satisfy the following relationship.
0≦[(C5-C4)-{(C2-C0)/2}] The spherical core has a Shore C hardness, a hardness difference (C1-C0) between hardness (C1) and hardness (C0), a hardness difference (C2-C1) between hardness (C2) and hardness (C1), and hardness ( Hardness difference (C3-C2) between hardness (C3) and hardness (C2), hardness difference (C4-C3) between hardness (C4) and hardness (C3), hardness difference (C4-C3) between hardness (C5) and hardness (C4) C5-C4), hardness difference (C6-C5) between hardness (C6) and hardness (C5), hardness difference (C7-C6) between hardness (C7) and hardness (C6), and hardness (C8) and The golf according to claim 1, wherein the ratio (Cbmax/Cbmin) is 4.0 or more, where Cbmax is the largest value and Cbmin is the smallest value among the hardness differences (C8-C7) with respect to hardness (C7). ball. The golf ball according to claim 1, wherein hardness (C0) and hardness (C8) of the spherical core are Shore C hardness and satisfy the following relationship.
18.0≦(C8-C0) An intermediate layer is provided between the spherical core and the cover, and the surface hardness of the spherical core (C8), the intermediate layer surface hardness, and the ball surface hardness are Shore C hardness and satisfy the following relationship. The golf ball according to claim 1.
Core surface hardness <middle layer surface hardness> Ball surface hardness An intermediate layer is provided between the spherical core and the cover, and the thickness (mm) and material hardness (Shore D) of the intermediate layer are the same as the thickness (mm) and material hardness (Shore D) of the cover. The golf ball according to claim 1, which satisfies the following relationship.
(Intermediate layer thickness x material hardness) / (cover thickness x material hardness) ≧ 4.0 2. The golf ball according to claim 1, wherein the golf ball has a compressive deformation amount of 2.8 mm or less when a final load of 1275 N is applied from an initial load of 98 N. The spherical core contains (a) a base rubber, (b) an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and/or a metal salt thereof as a co-crosslinking agent, (c) a crosslinking initiator, and ( 2. The golf ball according to claim 1, wherein the golf ball is formed from a core rubber composition containing d) a monophenol compound having a substituent only at the p-position. The core rubber composition contains (d) 0.05 parts by mass to 2.0 parts by mass of a monophenol compound having a substituent only at the p-position, based on (a) 100 parts by mass of the base rubber. The golf ball according to claim 9. The golf ball according to claim 9 or 10, wherein the monophenol compound (d) having a substituent only at the p-position is represented by general formula (1).

[In general formula (1), R represents an alkoxy group, a halogen group, a hydrocarbon group, a nitro group, a cyano group, an amino group, or a hydroxy group. ] The golf ball according to claim 9, wherein the core rubber composition further contains (g) an aromatic carboxylic acid and/or a salt thereof.

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