golf ball

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 a hardness difference (C2-C0) is 5.5 or more.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a golf ball, and particularly to the hardness distribution of a spherical core.

Background Art

[0002] A golf ball is required to have excellent flight distance performance in a driver shot. As a means for improving the flight distance of a driver shot, appropriately selecting the hardness distribution of a spherical core can be mentioned. Specifically, it is known that by increasing the hardness difference between the surface hardness and the center hardness of the spherical core, the amount of spin in a driver shot can be reduced and the flight distance can be improved.

[0003] For example, Patent Document 1 discloses a golf ball including a core, an intermediate layer, and a cover, wherein the core is formed mainly of a base rubber, its diameter is set within a specific range, each layer of the intermediate layer and the cover is formed of a resin material, and regarding the internal hardness of the core, for the core center, the position hardness at intervals of 2 mm up to 16 mm from the core center, and the core surface hardness, the hardness differences are designed to be within a predetermined range, and the ball surface hardness is set lower than the surface hardness of the intermediate layer-coated sphere (Patent Document 1).

[0004] Further, Patent Document 2 discloses a multi-piece solid golf ball having an intermediate layer interposed between a core and a cover, in which the surface hardnesses of the core, the intermediate layer-coated sphere, and the ball satisfy a predetermined relationship, the thicknesses of the intermediate layer and 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 (C5) at a position 5 mm from the core center, and the hardness (Cm) at an intermediate position between the surface and the center of the core satisfy a predetermined relationship (Patent Document 2).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] Incidentally, professional golfers and advanced players have expressed a desire not only to improve the distance of their driver shots, but also to increase the amount of spin on their mid-iron shots. However, when the amount of spin on driver shots is reduced by controlling the difference in hardness between the surface hardness and the core hardness of the spherical core, the amount of spin on mid-iron shots also tends to decrease.

[0007] This invention has been made in view of the above circumstances, and aims to provide a golf ball that excels in driver shot distance and has good spin rate on middle iron shots. [Means for solving the problem]

[0008] The golf ball of the present invention, which has solved the above problems, is a golf ball having a spherical core and a cover that covers the spherical core, characterized in that when a straight line from the center of the spherical core toward the surface is divided into 8 equal parts, the central hardness (C0), the hardness at the 12.5% ​​point from the center (C1), the hardness at the 25.0% point from the center (C2), the hardness at the 37.5% point from the center (C3), the hardness at the 50.0% point from the center (C4), the hardness at the 62.5% point from the center (C5), the hardness at the 75.0% point from the center (C6), the hardness at the 87.5% point from the center (C7), and the surface hardness (C8) of the spherical core are Shore C hardness and satisfy 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) 5.5 ≤ (C2 - C0) ... (9)

[0009] During 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 greater than 0, and the lower limit of equation (5) to 5.0, the hardness distribution of the entire spherical core becomes a rigid-outside, flexible-inside structure, resulting in a recoil effect during driver shots and reducing spin. Furthermore, by setting the lower limit of equation (9) to 5.5, the deformation near the center of the spherical core increases, further enhancing the recoil effect during driver shots and reducing spin even more. Moreover, by setting the upper limits of equations (1) to (4) to 6.0 and the upper limits of equations (6) to (8) to 3.5, the deformation balance of the entire spherical core during driver shots improves, enhancing rebound performance. Thus, the distance performance of driver shots improves.

[0010] In middle iron shots, the deformation of the spherical core is smaller compared to driver shots, making the hardness near the surface of the spherical core important. Therefore, by setting the upper limit of equations (6) to (8) to 3.5, the deformation near the surface of the spherical core during middle iron shots can be suppressed, improving spin. Furthermore, by satisfying equation (5), the deformation at the 50% to 62.5% point from the center of the spherical core during middle iron shots becomes larger, and the deformation near the center becomes even smaller. This reduces the recoil effect, further improving spin on middle iron shots. [Effects of the Invention]

[0011] According to the present invention, a golf ball can be obtained that has excellent distance for driver shots and good spin rate for middle iron shots. [Brief explanation of the drawing]

[0012] [Figure 1]A partially cut-away cross-sectional view showing a golf ball according to an embodiment of the present invention. [Figure 2] A graph showing the hardness distribution of the spherical core. [Figure 3] A graph showing the hardness distribution of the spherical core. [Figure 4] A graph showing the hardness distribution of the spherical core. [Figure 5] A graph showing the hardness distribution of the spherical core. [Figure 6] A graph showing the hardness distribution of the spherical core. [Figure 7] A graph showing the hardness distribution of the spherical core. [Figure 8] A graph showing the hardness distribution of the spherical core. [Figure 9] A graph showing the hardness distribution of the spherical core. [Figure 10] A graph showing the hardness distribution of the spherical core.

Embodiments for Carrying Out the Invention

[0013] The golf ball of the present invention has a spherical core and a cover covering the spherical core. 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 core hardness (hardness at the 0% point) (C0), the hardness at the 12.5% point from the center (C1), the hardness at the 25.0% point from the center (C2), the hardness at the 37.5% point from the center (C3), the hardness at the 50.0% point from the center (C4), the hardness at the 62.5% point from the center (C5), the hardness at the 75.0% point from the center (C6), the hardness at the 87.5% point from the center (C7), and the surface hardness (hardness at the 100% point from the center) (C8) of the spherical core are Shore C hardness and satisfy the 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) 5.5 ≤ (C2 - C0) ... (9)

[0014] Equations (1) to (4) above define the hardness distribution near the center of the spherical core. If there are areas near the center where the hardness gradient is too large, the amount of deformation at those areas will be large during a driver shot. As a result, the deformation balance of the entire golf ball is disrupted, the rebound performance decreases, and the distance decreases. Therefore, satisfying equations (1) to (4) results in good rebound performance and improved driver distance. In addition, by creating a hardness gradient near the center of the spherical core, the amount of recoil during a driver shot can be increased. As a result, the amount of spin during a driver shot can be reduced, and the distance can be further improved.

[0015] The hardness difference (C1-C0) between the central hardness (C0) of the spherical core and the hardness (C1) at 12.5% ​​from the center is greater than 0, preferably 0.5 or more, more preferably 1.0 or more, and 6.0 or less, preferably 5.5 or less, more preferably 5.0 or less, in Shore C hardness.

[0016] The difference in hardness (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 greater than 0, preferably 0.5 or more, more preferably 1.0 or more, and 6.0 or less, preferably 5.5 or less, more preferably 5.0 or less, in Shore C hardness.

[0017] The difference in hardness (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 greater than 0, preferably 0.5 or higher, more preferably 1.0 or higher, and 6.0 or lower, preferably 5.5 or lower, more preferably 5.0 or lower, in Shore C hardness.

[0018] 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 greater than 0, preferably 0.5 or higher, more preferably 1.0 or higher, and 6.0 or lower, preferably 5.5 or lower, more preferably 5.0 or lower, in Shore C hardness.

[0019] Formula (5) defines the hardness difference (C5-C4) between the hardness at 50.0% from the center of the spherical core (C4) and the hardness at 62.5% from the center (C5). The hardness difference (C5-C4) is 5.0 or higher, preferably 5.5 or higher, more preferably 6.0 or higher, preferably 12.0 or lower, more preferably 11.0 or lower, and even more preferably 10.0 or lower, in Shore C hardness. If the hardness difference (C5-C4) is 5.0 or higher, it is possible to improve the spin rate in middle iron shots while increasing the initial velocity in driver shots.

[0020] Equations (6) to (8) above define the hardness distribution near the surface of the spherical core. If there are areas near the surface where the hardness gradient is too large, the amount of deformation at those areas will be large during a driver shot, and the entire golf ball will not deform, resulting in a decrease in rebound performance. Also, if there are areas near the surface where the hardness gradient is too large, the deformation near the surface will be large during a middle iron shot, resulting in a large energy loss and a decrease in spin rate. Therefore, by satisfying equations (6) to (8), it is possible to achieve both increased distance for driver shots and improved spin rate for middle iron shots.

[0021] The hardness difference (C6-C5) between the hardness at 62.5% from the center of the spherical core (C5) and the hardness at 75.0% from the center (C6) is greater than 0, preferably 0.5 or higher, more preferably 1.0 or higher, and 3.5 or lower, preferably 3.0 or lower, more preferably 2.5 or lower, in Shore C hardness.

[0022] The hardness difference (C7-C6) between the hardness at 75.0% from the center of the spherical core (C6) and the hardness at 82.5% from the center (C7) is greater than 0, preferably 0.5 or higher, more preferably 1.0 or higher, and 3.5 or lower, preferably 3.0 or lower, more preferably 2.5 or lower, in Shore C hardness.

[0023] The hardness difference (C8-C7) between the hardness at the 82.5% point from the center of the spherical core (C7) and the surface hardness (C8) is greater than 0, preferably 0.5 or more, more preferably 1.0 or more, and 3.5 or less, preferably 3.0 or less, more preferably 2.5 or less, in Shore C hardness.

[0024] Formula (9) defines the hardness difference (C2-C0) between the central hardness (C0) of the spherical core and the hardness (C2) at 25.0% from the center. By satisfying formula (9), the amount of deformation near the center of the spherical core increases, the recoil effect during driver shots increases further, and the amount of spin can be further reduced. The hardness difference (C2-C0) is preferably 5.5 or higher on the Shore C hardness scale, more preferably 6.0 or higher, even more preferably 6.5 or higher, preferably 12.0 or lower, more preferably 11.0 or lower, and even more preferably 10.0 or lower.

[0025] The spherical core preferably has hardnesses (C0), (C2), (C4), and (C5) that are Shore C hardness and satisfy formula (10). Satisfying formula (10) improves spin on mid-iron shots and reduces spin on driver shots. 0.5≦{(C2-C0) / (C5-C4)} ···(10)

[0026] The ratio {(C2-C0) / (C5-C4)} is preferably 0.5 or higher, more preferably 0.6 or higher, even more preferably 0.7 or higher, preferably 3.5 or lower, more preferably 3.3 or lower, and even more preferably 3.0 or lower in terms of Shore C hardness.

[0027] The spherical core preferably has hardnesses (C0), (C2), and (C4) that are Shore C hardness and satisfy formula (11). Satisfying formula (11) improves spin on mid-iron shots and reduces spin on driver shots. 1.0≦{(C2-C0) / (C4-C2)} ···(11)

[0028] The ratio {(C2-C0) / (C4-C2)} is preferably 1.0 or higher, more preferably 1.2 or higher, even more preferably 1.4 or higher, preferably 6.5 or lower, more preferably 6.0 or lower, and even more preferably 5.5 or lower in terms of Shore C hardness.

[0029] The hardness difference (C4-C0) between the central hardness (C0) of the spherical core and the hardness at the 50.0% point from the center (C4) is preferably greater than 0 in Shore C hardness, more preferably 3.0 or higher, even more preferably 6.0 or higher, preferably 24.0 or lower, more preferably 22.0 or lower, and even more preferably 20.0 or lower.

[0030] The hardness difference (C2-C0) between the central hardness (C0) of the spherical core and the hardness at 25.0% from the center (C2) is preferably 5.5 or higher on the Shore C hardness scale, more preferably 6.0 or higher, even more preferably 6.5 or higher, preferably 12.0 or lower, more preferably 11.0 or lower, and even more preferably 10.0 or lower. If the hardness difference (C2-C0) is within the above range, the amount of deformation near the center of the spherical core increases, the recoil effect during driver shots increases further, and the amount of spin can be further reduced.

[0031] The hardness difference (C8-C5) between the hardness at the 62.5% point from the center of the spherical core (C5) and the surface hardness (C8) is preferably 0 or greater, more preferably 1.0 or greater, even more preferably 2.0 or greater, preferably 10.5 or less, even more preferably 10.0 or less, and even more preferably 9.5 or less in Shore C hardness.

[0032] The hardness difference (C8-C0) between the central hardness (C0) and surface hardness (C8) of the spherical core is preferably 18.0 or higher, more preferably 19.0 or higher, even more preferably 20.0 or higher, preferably 32.0 or lower, more preferably 30.0 or lower, and even more preferably 28.0 or lower, in terms of Shore C hardness. If the hardness difference (C8-C0) is within the above range, the degree of outer rigidity and inner softness in the hardness distribution of the entire spherical core increases, and the recoil effect increases, so the amount of spin in driver shots is further reduced and the distance is improved.

[0033] The spherical core has a hardness difference of {(C5-C4)-(C4-C3)} between the hardness difference (C5-C4) and the hardness difference (C4-C3), which is preferably 1.0 or higher, more preferably 1.5 or higher, even more preferably 2.0 or higher, preferably 10.0 or lower, more preferably 9.0 or lower, and even more preferably 8.0 or lower, in Shore C hardness. If the difference {(C5-C4)-(C4-C3)} 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.

[0034] The spherical core has a hardness difference of {(C5-C4)-(C6-C5)} between the hardness difference (C5-C4) and the hardness difference (C6-C5), which is preferably 1.0 or higher, more preferably 1.5 or higher, even more preferably 2.0 or higher, preferably 10.0 or lower, more preferably 9.0 or lower, and even more preferably 8.0 or lower, in Shore C hardness. 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.

[0035] The spherical core preferably has hardnesses (C0), (C4), (C5), and (C8) that are Shore C hardness, and satisfies the following relationship. Satisfying this relationship improves spin on middle iron shots and reduces spin on driver shots. (C4-C0)>(C5-C4)>(C8-C5)

[0036] The spherical core preferably has hardnesses (C0), (C2), (C4), and (C8) that are Shore C hardness and satisfy formula (12). Satisfying formula (12) improves spin on mid-iron shots and reduces spin on driver shots. {(C8-C4) / (C2-C0)}≦3.0 ···(12)

[0037] The ratio {(C8-C4) / (C2-C0)} is preferably 0 or greater, more preferably 0.5 or greater, even more preferably 1.0 or greater, preferably 3.0 or less, more preferably 2.5 or less, and even more preferably 2.0 or less.

[0038] The spherical core has a Shore C hardness, with the hardness difference between hardness (C1) and hardness (C0) being (C1-C0), the hardness difference between hardness (C2) and hardness (C1) being (C2-C1), the hardness difference between hardness (C3) and hardness (C2) being (C3-C2), the hardness difference between hardness (C4) and hardness (C3) being (C4-C3), and the hardness difference between hardness (C5) and hardness (C4) being (C5-C4). When the largest value among the hardness differences between hardness (C6) and hardness (C5) (C6-C5), the hardness difference between hardness (C7) and hardness (C6) (C7-C6), and the hardness difference between hardness (C8) and hardness (C7) (C8-C7) is Cbmax and the smallest value is Cbmin, it is preferable that the ratio (Cbmax / Cbmin) is 4.0 or greater. The entire spherical core has parts with large and small hardness differences, so that when the golf ball is struck, there are parts where the golf ball flexes and parts where the movement of the golf ball is suppressed, so that the deformed parts can be converted into rebound without waste. It is preferable that the hardness difference (C5-C4) is Cbmax.

[0039] The central hardness (C0) of the spherical core is preferably 50.0 or higher on the Shore C scale, more preferably 52.0 or higher, even more preferably 54.0 or higher, and preferably 70.0 or lower, more preferably 68.0 or lower, and even more preferably 66.0 or lower. If the central hardness (C0) is 50.0 or higher, the ball will not deform excessively when deformed, and will exhibit good rebound performance. If it is 70.0 or lower, deformation will occur even inside the ball, resulting in a good feel.

[0040] The surface hardness (C8) of the spherical core is preferably 70.0 or higher on the Shore C scale, more preferably 72.0 or higher, even more preferably 74.0 or higher, preferably 90.0 or lower, more preferably 88.0 or lower, and even more preferably 86.0 or lower. If the surface hardness (C8) is 70.0 or higher, the ball will not deform too much and will exhibit good rebound performance, and if it is 90.0 or lower, the ball will have good durability.

[0041] The hardness (C4) at the 50.0% point from the center of the spherical core is preferably 60.0 or higher on the Shore C hardness scale, more preferably 62.0 or higher, even more preferably 64.0 or higher, preferably 80.0 or lower, more preferably 78.0 or lower, and even more preferably 76.0 or lower. If the hardness (C4) is 60.0 or higher, the ball will not compress too much and will exhibit rebound performance, while if it is 80.0 or lower, it will promote recoil generation and result in low spin with the driver.

[0042] 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, preferably 42.2 mm or less, more preferably 41.8 mm or less, even more preferably 41.2 mm or less, and most preferably 40.8 mm or less. If the diameter of the spherical core is 34.8 mm or more, the rebound properties are better. On the other hand, if the diameter of the spherical core is 42.2 mm or less, the cover function is better performed.

[0043] For the spherical core with a diameter of 34.8 mm to 42.2 mm, the amount of compressive deformation (the amount the core shrinks in the compression direction) from an initial load of 98 N to a final load of 1275 N is preferably 2.0 mm or more, more preferably 2.3 mm or more, even more preferably 2.5 mm or more, preferably 5.0 mm or less, more preferably 4.5 mm or less, and even more preferably 4.3 mm or less. If the amount of compressive deformation is 2.0 mm or more, the feel of hitting the ball will be better, and if it is 5.0 mm or less, the rebound performance will be better.

[0044] The spherical core may have either a single-layer structure or a multilayer structure of two or more layers, but a single-layer structure is preferred. A single-layer spherical core eliminates energy loss during impact at the interface of the multilayer structure, resulting in improved resilience.

[0045] [Rubber composition] The spherical core is preferably formed from a core rubber composition containing (a) a base rubber, (b) an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and / or its metal salt as a co-crosslinking agent, and (c) a crosslinking initiator. The spherical core can be obtained by molding the core rubber composition in a mold. The molding conditions are not particularly limited, but are usually carried out at 130°C to 200°C and a pressure of 2.9 MPa to 11.8 MPa for 10 to 60 minutes.

[0046] The spherical core is preferably formed from a core rubber composition containing (a) a base rubber, (b) an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and / or its metal salt as a co-crosslinking agent, (c) a crosslinking initiator, and (d) a monophenol compound having substituents 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.

[0047] (a) Base rubber (a) Natural rubber and / or synthetic rubber can be used as the base rubber. (a) For example, polybutadiene rubber, natural rubber, polyisoprene rubber, styrene-butadiene rubber, ethylene-propylene-diene rubber (EPDM), etc. can be used as the base rubber. 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, and even more preferably 95% by mass or more, of cis-1,4-bonds which are advantageous for repulsion is particularly preferred.

[0048] 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 even more preferably 90% by mass or more. (a) It is also preferable that the base rubber consists only of high-cis polybutadiene.

[0049] The high-cis polybutadiene preferably has a 1,2-vinyl bond content of 2.0% by mass or less, more preferably 1.7% by mass or less, and even more preferably 1.5% by mass or less. If the 1,2-vinyl bond content is 2.0% by mass or less, the resilience is further improved.

[0050] The high-cis polybutadiene is preferably synthesized using a rare earth element catalyst, and in particular, the use of a neodymium catalyst using a neodymium compound, which is a lanthanum series rare earth element compound, is preferable because it allows for the production of polybutadiene rubber with a high content of 1,4-cis bonds and a low content of 1,2-vinyl bonds with excellent polymerization activity.

[0051] The aforementioned high-cis polybutadiene has a Mooney viscosity (ML). 1+4 The Mooney viscosity (ML) in this invention is preferably 30 or higher, more preferably 32 or higher, even more preferably 35 or higher, preferably 140 or lower, more preferably 120 or lower, even more preferably 100 or lower, and most preferably 55 or lower. 1+4 (100℃)) refers to the value measured in accordance with JIS K6300, using an L rotor, with a preheating time of 1 minute, a rotor rotation time of 4 minutes, and under conditions of 100℃.

[0052] 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 higher, more preferably 2.2 or higher, even more preferably 2.4 or higher, most preferably 2.6 or higher, preferably 6.0 or lower, more preferably 5.0 or lower, even more preferably 4.0 or lower, and most preferably 3.0 or lower. If the molecular weight distribution (Mw / Mn) of the high-cis polybutadiene is within the above range, the workability of core molding will be good, and the resulting spherical core will have good resilience. The molecular weight distribution was measured using gel permeation chromatography (Tosoh Corporation, "HLC-8120GPC") with a differential refractometer as the detector, under the conditions of column: GMHHXL (Tosoh Corporation), column temperature: 40°C, mobile phase: tetrahydrofuran, and the value was calculated as a standard polystyrene equivalent.

[0053] (b) Cocrossant (b) The α,β-unsaturated carboxylic acids having 3 to 8 carbon atoms and / or their metal salts are incorporated into the rubber composition as co-crosslinking agents and have the effect of crosslinking rubber molecules by graft polymerization onto the base rubber molecular chains.

[0054] Examples of α,β-unsaturated carboxylic acids having 3 to 8 carbon atoms include acrylic acid, methacrylic acid, fumaric acid, maleic acid, and crotonic acid.

[0055] Examples of metals that constitute the metal salts of α,β-unsaturated carboxylic acids having 3 to 8 carbon atoms include monovalent metal ions such as sodium, potassium, and lithium; divalent metal ions such as magnesium, calcium, zinc, barium, and cadmium; trivalent metal ions such as aluminum; and other ions such as tin and zirconium. The metal components can be used individually 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 components. This is because using divalent metal salts of α,β-unsaturated carboxylic acids having 3 to 8 carbon atoms makes it easier for metal crosslinks to form between rubber molecules. In particular, zinc acrylate is preferred as the divalent metal salt because it increases the rebound properties of the resulting golf ball. Note that α,β-unsaturated carboxylic acids having 3 to 8 carbon atoms and / or their metal salts may be used individually or in combination of two or more.

[0056] (b) The content of the α,β-unsaturated carboxylic acid and / or its metal salt having 3 to 8 carbon atoms is preferably 15 parts by mass or more, more preferably 20 parts by mass or more, even more 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, per 100 parts by mass of the base rubber (a). If the content of component (b) is 15 parts by mass or more, the amount of (c) crosslinking initiator required to give the core formed from the core rubber composition an appropriate hardness is reduced, and the rebound properties of the resulting golf ball are improved. Also, if the content of component (b) is 50 parts by mass or less, the resulting golf ball will have a good feel when struck.

[0057] (c) Crosslinking initiator (c) The crosslinking initiator is formulated to crosslink the base rubber component (a). (c) Organic peroxides are preferred as crosslinking initiators. Specifically, examples of organic peroxides include dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and di-t-butyl peroxide. These organic peroxides may be used individually or in combination of two or more. Among these, dicumyl peroxide is preferred.

[0058] (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, even more preferably 0.7 parts by mass or more, preferably 5.0 parts by mass or less, more preferably 2.5 parts by mass or less, and even more preferably 2.0 parts by mass or less, per 100 parts by mass of the base rubber (a). If the content of component (c) is 0.2 parts by mass or more, the core formed from the core rubber composition will not become too soft, and the rebound properties of the resulting golf ball will be improved. If the content is 5.0 parts by mass or less, the rebound properties and durability of the resulting golf ball will be good.

[0059] (d) Monophenol compounds having substituents only at the p position (d) A monophenol compound having substituents only at the p-position is a compound having substituents only at the p-position of a monophenol. The said monophenol compound having substituents only at the p-position is a compound in which a substituent is directly bonded to the p-position of one hydroxyl group of phenol, and the hydroxyl group does not have substituents at the o-position and m-position. Examples of substituents at the p-position include alkoxy groups, halogen groups, hydrocarbon groups, nitro groups, cyano groups, amino groups, and hydroxyl groups, with alkoxy groups being preferred.

[0060] As for monophenol compounds having substituents only at the (d)p position, those represented by the following general formula (1) are preferred.

[0061] [ka] [In general formula (1), R represents an alkoxy group, halogen group, hydrocarbon group, nitro group, cyano group, amino group, or hydroxyl group.]

[0062] 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 one or more, but is preferably 1 to 20, more preferably 1 to 10, and even more preferably 1 to 8. The structure of the alkyl portion of the alkoxy group may be linear, branched, or cyclic. Specific examples of the alkyl portion of the alkoxy group include linear or branched alkyl groups such as 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-heptyl group, isoheptyl group, sec-heptyl group, tert-heptyl group, n-octyl group, isooctyl group, sec-octyl group, and tert-octyl group, as well as cyclic alkyl groups such as cyclobutyl group, cyclopentyl group, cyclohexyl group, cycloheptyl group, and cyclooctyl group. Specific examples of the alkoxy group include methoxy, ethoxy, propoxy (including n- and iso- structures), butoxy (including n-, iso-, sec-, tert-, and cyclo- structures), pentyloxy (including n-, iso-, sec-, tert-, and cyclo- structures), hexyloxy (including n-, iso-, sec-, tert-, and cyclo- structures), heptyloxy (including n-, iso-, sec-, tert-, and cyclo- structures), octyloxy (including n-, iso-, sec-, tert-, and cyclo- structures), and the like. The alkoxy group may also have substituents (for example, halogen groups, hydroxyl groups, amino groups, nitro groups, cyano groups, etc.).

[0063] Examples of the halogen group include a fluoro group, a chloro group, a bromo group, and an iodo group.

[0064] Examples of the hydrocarbon group include alkyl groups, alkenyl groups, alkynyl groups, aralkyl groups, and aryl groups.

[0065] The number of carbon atoms in the alkyl group is not particularly limited as long as it is 1 or more, but 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. Specific examples include linear or branched alkyl groups such as 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-heptyl group, isoheptyl group, sec-heptyl group, tert-heptyl group, n-octyl group, isooctyl group, sec-octyl group, tert-octyl group, and cyclic alkyl groups such as cyclobutyl group, cyclopentyl group, cyclohexyl group, cycloheptyl group, and cyclooctyl group. The alkyl group may have substituents (for example, halogen groups, hydroxyl groups, amino groups, nitro groups, cyano groups, etc.).

[0066] The number of carbon atoms in the alkenyl group is not particularly limited as long as it is 2 or more, but is preferably 2 to 20, more preferably 2 to 10, and even more preferably 2 to 8. Specific examples of the alkenyl group include vinyl, allyl, propenyl, isopropenyl, butenyl, isobutenyl, and hexenyl groups. The alkenyl group may also have substituents (for example, alkyl groups, halogen groups, hydroxyl groups, amino groups, nitro groups, cyano groups, etc.).

[0067] The number of carbon atoms in the alkynyl group is not particularly limited as long as it is 2 or more, but 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, 1-propynyl, 2-propynyl (propargyl) groups, and butynyl groups. The alkynyl group may also have substituents (for example, alkyl groups, halogen groups, hydroxyl groups, amino groups, nitro groups, cyano groups, etc.).

[0068] The number of carbon atoms in the aralkyl group is not particularly limited as long as it is 7 or more, but is preferably 7 to 20, more preferably 7 to 10, and even more preferably 7 to 8. Specific examples of the aralkyl group include benzyl, phenylethyl, phenylbutyl, and α-cumyl groups. The aralkyl group may also have substituents (for example, alkyl groups, halogen groups, amino groups, nitro groups, cyano groups, etc.).

[0069] The number of carbon atoms in the aryl group is not particularly limited as long as it is 6 or more, but is preferably 6 to 20, more preferably 6 to 15, and even more preferably 6 to 10. Specific examples of the aryl group include a phenyl group and a naphthyl group. The aryl group may also have substituents (for example, alkyl groups, halogen groups, amino groups, nitro groups, cyano groups, etc.).

[0070] 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.

[0071] The monophenol compound having substituents only at the (d)p position may be used alone or in combination of two or more types.

[0072] The amount of the monophenol compound having substituents only at the (d)p position is preferably 0.05 parts by mass or more, more preferably 0.07 parts by mass or more, even more preferably 0.10 parts by mass or 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, per 100 parts by mass of the base rubber (a). If the amount of the monophenol compound having substituents only at the (d)p position is 0.05 parts by mass or more, the effect of adding the monophenol compound having substituents only at the (d)p position will be greater, and if it is 2.0 parts by mass or less, the distance of the driver shot will be further improved.

[0073] The mass ratio of component (b) to 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, particularly preferably 200 or more, preferably 500 or less, more preferably 450 or less, and even more preferably 400 or less. If the mass ratio (component (b) / component (d)) is within the above range, the feel of the ball is good and the distance of the driver shot is further improved.

[0074] The mass ratio of component (c) to component (d) (component (c) / component (d)) is preferably 1.0 or higher, more preferably 1.5 or higher, even more preferably 2.0 or higher, preferably 150 or lower, more preferably 130 or lower, even more preferably 110 or lower, even more preferably 50 or lower, and particularly preferably 20 or lower. If the mass ratio (component (c) / component (d)) is within the above range, the feel of the ball is good and the distance of the driver shot is further improved.

[0075] (e)Organic sulfur compounds The rubber composition for the core preferably further contains (e) an organic sulfur compound. The inclusion of (e) an organic sulfur compound increases the resilience of the resulting core.

[0076] The (e) organic sulfur compounds include at least one compound selected from the group consisting of thiols (thiophenols, thionaphthols), polysulfides, thiazoles, thiurams, thiocarboxylic acids, dithiocarboxylic acids, sulfenamides, and dithiocarbamates.

[0077] Examples of thiols include thiophenols and thionaphthols. Examples of thiophenols include thiophenols; thiophenols substituted with fluoro groups such as 4-fluorothiophenol, 2,4-difluorothiophenol, 2,5-difluorothiophenol, 2,6-difluorothiophenol, 2,4,5-trifluorothiophenol, 2,4,5,6-tetrafluorothiophenol, and pentafluorothiophenol; and chlorothiophenols 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 bromo groups; thiophenols substituted with bromo groups 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 iodine groups 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. Preferably, the metal salt is a divalent metal salt, more preferably a zinc salt.

[0078] Examples of the aforementioned thionaphthols (naphthalenchiols) 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. The metal salt is preferably a divalent metal salt, more preferably a zinc salt.

[0079] Polysulfides are organosulfur compounds having polysulfide bonds, and examples include disulfides, trisulfides, and tetrasulfides. Diphenyl polysulfides are preferred as the polysulfides.

[0080] Diphenyl polysulfides include diphenyl disulfide, as well as 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, and 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 phenyl 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 Examples include diphenyl disulfides substituted with halogen groups such as; diphenyl disulfides substituted with alkyl groups such as 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, and bis(penta-t-butylphenyl) disulfide; and so on.

[0081] 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.

[0082] Examples of thiuram compounds 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 naphthalenthiocarboxylic 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.

[0083] The (e) organic sulfur compound is preferably at least one compound selected from the group consisting of halogen-substituted thiophenols, halogen-substituted thiophenols, halogen-substituted diphenyl disulfides, thiazoles, and thiazoles.

[0084] The aforementioned (e) organosulfur compounds can be used individually or as a mixture of two or more.

[0085] The content of the (e) organic sulfur compound is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, even more preferably 0.2 parts by mass or more, preferably 5.0 parts by mass or less, more preferably 3.0 parts by mass or less, and even more preferably 2.0 parts by mass or less, per 100 parts by mass of the (a) base rubber. If the content of component (e) is within the above range, the rebound properties of the resulting golf ball will be better.

[0086] The mass ratio (component(e) / component(d)) of component(e) to component(d) is preferably 1.0 or higher, more preferably 1.5 or higher, even more preferably 2.0 or higher, preferably 100 or lower, more preferably 90 or lower, even more preferably 80 or lower, even more preferably 40 or lower, and particularly preferably 20 or lower. If the mass ratio (component(e) / component(d)) is within the above range, the recoil effect in driver shots will be increased, and the distance will be further improved.

[0087] (f) Metal compounds When the core rubber composition contains only α,β-unsaturated carboxylic acids having 3 to 8 carbon atoms as a co-crosslinking agent, it is preferable that it further contains (f) a metal compound. This is because neutralizing the α,β-unsaturated carboxylic acids having 3 to 8 carbon atoms with a metal compound in the core rubber composition provides substantially the same effect as when a metal salt of the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms is used as a co-crosslinking agent. When using both an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and its metal salt as co-crosslinking agents, (f) a metal compound may be used as an optional component.

[0088] The (f) metal compound 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 (f) 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 carbon oxides such as magnesium carbonate, zinc carbonate, calcium carbonate, sodium carbonate, lithium carbonate, and potassium carbonate. The (f) metal compound is preferably a divalent metal compound, and more preferably a zinc compound. This is because divalent metal compounds react with α,β-unsaturated carboxylic acids having 3 to 8 carbon atoms to form metal crosslinks. Furthermore, by using a zinc compound, a golf ball with high rebound can be obtained.

[0089] The metal compound (f) may be used alone or in combination of two or more. The content of the metal compound (f) may be adjusted as appropriate depending on the degree of neutralization of the desired (b) α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms.

[0090] (g) Carboxylic acid and / or salt thereof The core rubber composition may contain (g) carboxylic acid and / or a salt thereof. The inclusion of the (g) carboxylic acid and / or a salt thereof can increase the external rigidity and internal flexibility of the resulting spherical core. Examples of the (g) carboxylic acid and / or a salt thereof include aliphatic carboxylic acids, aliphatic carboxylate salts, aromatic carboxylic acids, and aromatic carboxylate salts. The (g) carboxylic acid and / or salt may be used alone or as a mixture of two or more.

[0091] The carbon number of the carboxylic acid is preferably 1 or more, preferably 30 or less, more preferably 18 or less, and even more preferably 13 or less. (g) The carboxylic acid and / or its salts shall not include (b) α,β-unsaturated carboxylic acids and / or their metal salts having 3 to 8 carbon atoms used as cocrosslinking agents.

[0092] The carboxylic acids and / or their salts are preferably saturated aliphatic carboxylic 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; unsaturated aliphatic carboxylic acids such as palmitoleic acid, oleic acid, linoleic acid, or arachidonic acid; or aromatic carboxylic acids such as benzoic acid, butylbenzoic acid, anisic acid (methoxybenzoic acid), dimethoxybenzoic acid, trimethoxybenzoic acid, dimethylaminobenzoic acid, chlorobenzoic acid, dichlorobenzoic acid, trichlorobenzoic acid, acetoxybenzoic acid, biphenyl carboxylic acid, naphthalene carboxylic acid, anthracene carboxylic acid, furanic acid, or thenoyl acid; or potassium salts, magnesium salts, calcium salts, aluminum salts, zinc salts, iron salts, copper salts, nickel salts, and cobalt salts of these carboxylic acids. Among these, aromatic carboxylic acids and / or their salts are preferred, and carboxylic acids having a benzene ring and / or their salts are more preferred.

[0093] The content of (g) carboxylic acid and / or its salt is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more, even more preferably 1.5 parts by mass or more, preferably 40 parts by mass or less, more preferably 35 parts by mass or less, and even more preferably 30 parts by mass or less, per 100 parts by mass of (a) base rubber. If the content of component (g) is 0.5 parts by mass or more, the external rigidity and internal softness of the spherical core will increase, and if it is 40 parts by mass or less, the decrease in core hardness will be suppressed and the rebound properties will be good.

[0094] The rubber composition for the core may optionally contain additives such as pigments, fillers for weight adjustment, decongestants, and softeners.

[0095] The fillers used in the core rubber composition are primarily weight adjusters used to adjust the weight of the final golf ball product, and may be added as needed. Examples of such fillers include inorganic fillers such as zinc oxide, barium sulfate, calcium carbonate, magnesium oxide, tungsten powder, and molybdenum powder. Zinc oxide is particularly preferred as the filler. Zinc oxide is thought to function as a vulcanization aid, thereby increasing the overall hardness of the core. The content of the filler is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, preferably 30 parts by mass or less, more preferably 25 parts by mass or less, and even more preferably 20 parts by mass or less, per 100 parts by mass of the base rubber. Good rebound properties are obtained when the filler content is 30 parts by mass or less.

[0096] The content of the decongestant is preferably 0.1 parts by mass or more and 5 parts by mass or less per 100 parts by mass of the base rubber.

[0097] The rubber composition for the core can be prepared by mixing and kneading the raw materials. The kneading method is not particularly limited and can be carried out using known kneading machines such as kneading rolls, Banbury mixers, and kneaders.

[0098] [Cover, middle layer] The golf ball has a cover that encloses a spherical core. The cover is the outermost layer of the golf ball body, excluding the coating.

[0099] The material hardness of the cover composition constituting the cover is preferably set appropriately according to the desired performance of the golf ball. For example, in the case of a distance-type golf ball that prioritizes distance, the material hardness of the cover composition is preferably 50 or higher on the Shore D scale, more preferably 55 or higher, even more preferably 60 or higher, preferably 80 or lower, more preferably 70 or lower, and even more preferably 68 or lower. By setting the material hardness of the cover composition to 50 or higher, a golf ball with a high launch angle and low spin can be obtained in driver shots and iron shots, further improving distance. Also, by setting the material hardness of the cover composition to 80 or lower, a golf ball with excellent durability can be obtained. Furthermore, in the case of a spin-type golf ball that prioritizes control, the material hardness of the cover composition is preferably less than 50 on the Shore D scale, more preferably 48 or lower, even more preferably 45 or lower, preferably 20 or higher, more preferably 25 or higher, and even more preferably 30 or higher. If the material hardness of the cover composition is less than 50 on the Shore D hardness scale, the amount of spin on approach shots will increase, resulting in a golf ball that stops more easily on the green. Furthermore, increasing the material hardness to 20 or higher improves scratch resistance. Note that the material hardness of the cover is the slab hardness measured after forming the cover composition into a sheet.

[0100] The thickness of the cover is preferably 4.0 mm or less, more preferably 3.0 mm or less, and even more preferably 2.0 mm or less. If the cover thickness is 4.0 mm or less, the rebound and feel of the resulting golf ball will be better. 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 cover thickness is 0.3 mm or more, the impact durability and wear resistance of the cover will be improved.

[0101] 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 a single layer is preferred.

[0102] The material hardness of the intermediate layer composition constituting the intermediate layer is preferably 55 or higher on the Shore D hardness scale, more preferably 57 or higher, even more preferably 59 or higher, preferably 74 or lower, more preferably 72 or lower, and even more preferably 70 or lower. If the material hardness of the intermediate layer is 55 or higher, the amount of spin in a driver shot will be further reduced and the distance will be further improved, and if it is 74 or lower, the durability will be good. If 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 the slab hardness measured by forming the intermediate layer composition into a sheet. If there are multiple intermediate layers, the material hardness of each layer may be the same or different, but it is preferable that the hardness of all intermediate layers is within the above range.

[0103] 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, preferably 4.0 mm or less, more preferably 3.0 mm or less, and even more preferably 2.0 mm or less. If the thickness of the intermediate layer is 0.8 mm or more, impact resistance will be good, and if it is 4.0 mm or less, a good feel will be achieved. If there are two or more intermediate layers, it is preferable that the thickness of the outermost intermediate layer is within the above range.

[0104] The thickness (mm) and material hardness (Shore D) of the intermediate layer and the thickness (mm) and material hardness (Shore D) of the cover preferably satisfy equation (21). Satisfying equation (21) improves spin performance in approach shots and increases the recoil effect in driver shots, further reducing the amount of spin. {(thickness of the intermediate layer × material hardness) / (thickness of the cover × material hardness)} ≥ 4.0 ···(21)

[0105] The above ((thickness of the intermediate layer × material hardness) / (thickness of the cover × material hardness)) is preferably 4.0 or higher, more preferably 4.5 or higher, even more preferably 5.0 or higher, preferably 10.0 or lower, more preferably 9.0 or lower, and even more preferably 8.0 or lower.

[0106] The cover and intermediate layer are preferably formed from a cover composition and an intermediate layer composition containing a resin component. Examples of the resin component include ionomer resin, thermoplastic polyurethane elastomer sold by BASF Japan Ltd. under the trade name "Elastran®", thermoplastic polyamide elastomer sold by Arkema Inc. under the trade name "Pebax®", thermoplastic polyester elastomer sold by Toray DuPont Ltd. under the trade name "Hytrel®", and thermoplastic styrene elastomer sold by Mitsubishi Chemical Corporation under the trade name "Tefablock".

[0107] 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; a terpolymer of an olefin and an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and an α,β-unsaturated carboxylic acid ester, in which at least a portion of the carboxyl groups are neutralized with metal ions; or 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, crotonic acid, etc., with acrylic acid or methacrylic acid being particularly preferred. Furthermore, as α,β-unsaturated carboxylic acid esters, for example, methyl, ethyl, propyl, n-butyl, and isobutyl esters of acrylic acid, methacrylic acid, fumaric acid, maleic acid, etc. can be used, with acrylic acid esters or methacrylic acid esters being particularly preferred. Among these, as the ionomer resin, metal ion neutralized products of ethylene-(meth)acrylic acid binary copolymers and metal ion neutralized products of ethylene-(meth)acrylic acid-(meth)acrylic acid ester terpolymers are preferred.

[0108] 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 in combination. 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.

[0109] The aforementioned 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 in combination. 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.

[0110] In addition to the resin components described above, the cover composition and the intermediate layer composition may also contain pigment components such as white pigments (e.g., titanium dioxide), blue pigments, and red pigments, zinc oxide, weight adjusters such as calcium carbonate and barium sulfate, dispersants, antioxidants, ultraviolet absorbers, light stabilizers, fluorescent materials, or fluorescent whitening agents.

[0111] The content of the white pigment (for example, titanium dioxide) is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, preferably 10 parts by mass or less, and more preferably 8 parts by mass or less, per 100 parts by mass of the resin component constituting the cover. By setting the content of the white pigment to 0.5 parts by mass or more, the cover can be given opacity. Furthermore, if the content of the white pigment is 10 parts by mass or less, the durability of the resulting cover will be good.

[0112] The method for forming the intermediate layer is not particularly limited, but examples include a method in which the intermediate layer composition is pre-formed into a hemispherical half-shell, two of these are used to enclose a spherical core, and then pressure-molded, or a method in which the intermediate layer composition is directly injection-molded onto the spherical core to enclose the sphere.

[0113] Examples of methods for forming the cover include a method in which a hollow shell is formed from the cover composition, and a sphere (a sphere with a spherical core or intermediate layer formed thereon) is covered with multiple shells and compressed (preferably, a method in which a hollow half-shell is formed from the cover composition, and a sphere is covered with two half-shells and compressed), or a method in which the cover composition is directly injection molded onto the sphere.

[0114] When forming the cover, indentations called dimples are usually formed on the surface. The total number of dimples formed on the cover is preferably between 200 and 500. If the total number of dimples is between 200 and 500, the size of each individual dimple can be increased, and the effect of the dimples will be greater. The shape of the formed dimples (planar shape) is not particularly limited, and may be a circle; a polygon such as a roughly triangular, roughly square, roughly pentagon, roughly hexagon; or other irregular shapes; either used alone or in combination of two or more types.

[0115] The golf ball body, with the cover molded, is preferably removed from the mold and subjected to surface treatment such as deburring, cleaning, and sandblasting as necessary.

[0116] Furthermore, a coating or mark can be formed as desired. The thickness of the coating is not particularly limited, but is preferably 5 μm or more, more preferably 6 μm or more, even more preferably 7 μm or more, preferably 50 μm or less, more preferably 40 μm or less, and even more preferably 30 μm or less. If the thickness is 5 μm or more, the coating is less likely to wear away even with continuous use, and if the thickness is 50 μm or less, the dimple effect is sufficiently obtained and the flight performance of the golf ball is improved.

[0117] [Golf balls] Examples of golf balls of the present invention include: a two-piece golf ball consisting of a spherical core and a single-layer cover covering the spherical core; a three-piece golf ball having a spherical core, a single-layer intermediate layer covering the spherical core, and a single-layer cover covering the intermediate layer; and 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. The present invention can be suitably used in any of the above-mentioned golf ball structures.

[0118] The diameter of the golf ball is preferably 40 mm to 45 mm. From the viewpoint of meeting the standards of the United States Golf Association (USGA), a diameter of 42.67 mm or more is particularly preferred. From the viewpoint of suppressing air resistance, a diameter of 44 mm or less is more preferred, and 42.80 mm or less is particularly preferred. The mass of the golf ball is preferably 40 g to 50 g. From the viewpoint of obtaining a large inertia, a mass of 44 g or more is more preferred, and 45.00 g or more is particularly preferred. From the viewpoint of meeting the standards of the USGA, a mass of 45.93 g or less is particularly preferred.

[0119] For the aforementioned golf ball with a diameter of 40 mm to 45 mm, the amount of compression deformation (amount of shrinkage in the compression direction) when an initial load of 98 N is applied and a final load of 1275 N is applied is preferably 2.0 mm or more, more preferably 2.1 mm or more, even more preferably 2.2 mm or more, preferably 3.0 mm or less, more preferably 2.9 mm or less, and even more preferably 2.8 mm or less. Golf balls with a compression deformation of 2.0 mm or more have a good feel when hit. On the other hand, by making the compression deformation amount 3.0 mm or less, the rebound performance is increased.

[0120] If the golf ball has an intermediate layer, it is preferable that the surface hardness (C8) of the spherical core, the surface hardness of the intermediate layer, and the surface hardness of the ball satisfy formula (20) in Shore C hardness. Core surface hardness <Intermediate layer surface hardness> Ball surface hardness ... (20)

[0121] Figure 1 shows an example of a golf ball according to the present invention. Figure 1 is a partially cutaway cross-sectional view showing a golf ball 1 according to one embodiment of the present invention. The golf ball 1 has a core 2, an intermediate layer 3 covering the core 2, and a cover 4 covering the intermediate layer 3. Numerous dimples 41 are formed on the surface of the cover 4. The portion of the surface of the golf ball other than the dimples 41 is a land 42. The golf ball 1 has a paint layer and a mark layer on the outside of the cover 4, but these layers are not shown in the illustration. [Examples]

[0122] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following examples, and any modifications and embodiments that do not depart from the spirit of the present invention are all included within the scope of the present invention.

[0123] [Evaluation Method] (1) Compression deformation amount (mm) The amount of deformation in the compressive direction (the amount the spherical core or golf ball shrinks in the compressive direction) was measured from an initial load of 98N on a spherical core or golf ball to a final load of 1275N.

[0124] (2) Core hardness (Shore C hardness) The hardness measured on the surface of the core was defined as the core surface hardness. Additionally, the core was cut into a hemispherical shape, and the hardness was measured at the center of the cut surface and at predetermined radial distances from the center. The core center was defined as 0%, and the surface as 100%. Core hardness was calculated by measuring the hardness at four points at predetermined distances from the center of the core cross-section and averaging these values. Hardness was measured using an automated hardness tester (H. Barleys, DigiTest II). The detector used was "ShoreC".

[0125] (3) Golf ball surface hardness, intermediate layer surface hardness The hardness of the land area on the surface of a golf ball was defined as the ball surface hardness. Additionally, the hardness of the surface of an intermediate-layer coated sphere (a spherical core with an intermediate layer formed on its surface) was defined as the intermediate layer surface hardness. Hardness was measured using an automated hardness tester (H. Barleys, DigiTest II). The detector used was "ShoreC".

[0126] (4) Material hardness (Shore D hardness) Using the intermediate layer composition and the cover composition, sheets approximately 2 mm thick were fabricated by injection molding and stored at 23°C for two weeks. Three or more of these sheets were stacked to avoid interference from the measurement substrate, and their hardness was measured using an automated hardness tester (H. Barleys, DigiTest II). A "Shore D" detector was used.

[0127] (5) Driver shot test A driver (Sumitomo Rubber Industries, "SRIXON ZX7", shaft stiffness: S, loft angle: 10.5°) was mounted on Golf Laboratory's swing machine. The point of impact was set to the center of the face. Under the condition of a head speed of 50 m / sec, golf balls were struck, and the ball speed, spin speed, and distance (distance from the launch point to the landing point) immediately after impact were measured. Measurements were taken 12 times for each golf ball, and the average value was used as the measurement value for that golf ball. Note that the initial speed, spin speed, and distance of each golf ball in Tables 5 and 6 are shown as the difference from golf ball No. 6.

[0128] (6) Middle Iron Test An iron (Sumitomo Rubber Industries, "SRIXON ZX7", club number: #7, loft angle: 32°) was mounted on Golf Laboratory's swing machine. The point of impact was set to the center of the face. Under the condition of a head speed of 39 m / sec, golf balls were struck and the spin speed immediately after impact was measured. Measurements were taken 12 times for each golf ball, and the average value was taken as the measurement value for that golf ball. Note that the spin speeds of each golf ball in Tables 5 and 6 are shown as the difference from golf ball No. 6.

[0129] [Golf ball manufacturing] (1) Preparation of rubber composition The raw materials were kneaded using a kneading roll to obtain the rubber composition shown in Table 1.

[0130] [Table 1]

[0131] The materials used in Table 1 are as follows: BR730: Manufactured by JSR Corporation, high-cis polybutadiene rubber (cis-1,4-bond content = 95% by mass, 1,2-vinyl bond content = 1.3% by mass, Mooney viscosity (ML) 1+4 (100℃)=55, molecular weight distribution (Mw / Mn)=3) ZN-DA90S: Manufactured by Nichishoku Techno Fine Chemical Co., Ltd., zinc acrylate (containing 10% zinc stearate) Zinc oxide: Manufactured by Toho Zinc Co., Ltd., "Ginrei R" Barium sulfate: "Barium Sulfate BD" manufactured by Sakai Chemical Co., Ltd. Benzoic acid: Manufactured by Emerald Kalama Chemical Co., Ltd. 4-Methoxyphenol: Manufactured by Tokyo Chemical Industry Co., Ltd. PBDS: Bis(pentabromopenyne) disulfide manufactured by Kawaguchi Chemical Industry Co., Ltd. DPDS: Diphenyl disulfide, manufactured by Sumitomo Seika Co., Ltd. Dicumyl peroxide: Manufactured by Tokyo Chemical Industry Co., Ltd.

[0132] (2) Preparation of the intermediate layer composition The raw materials were extruded using a twin-screw kneading extruder to prepare pellet-shaped intermediate layer compositions according to the formulations shown in Table 2.

[0133] [Table 2] Surlin® 8150: Sodium ion-neutralized ethylene-methacrylic acid copolymer ionomer resin, manufactured by DuPont. Hymiran (registered trademark) AM7329: Sodium ion-neutralized ethylene-methacrylic acid copolymer ionomer resin, manufactured by Mitsui DuPont Polychemicals. Titanium dioxide: Manufactured by Ishihara Sangyo Co., Ltd., A-220

[0134] (3) Preparation of the cover composition The raw materials were extruded using a twin-screw kneading extruder to prepare pelletized cover compositions according to the formulations shown in Table 3.

[0135] [Table 3] Elastran (registered trademark) NY84A: Thermoplastic polyurethane elastomer manufactured by BASF Japan. Chinuvin (registered trademark) 770: A hindered amine-based light stabilizer manufactured by BASF Japan. Titanium dioxide: Manufactured by Ishihara Sangyo Co., Ltd., A-220

[0136] (4) Core fabrication Golf balls No. 1-6, 9 A spherical core was obtained by heating and pressing the rubber composition shown in Table 4 in upper and lower molds having hemispherical cavities. Barium sulfate was added in an appropriate amount so that the mass of the resulting golf ball was 45.6 g.

[0137] Golf balls No. 7, 8 An inner core was obtained by heating and 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 core was covered with these two half-shells. A spherical core was obtained by heating and pressing both the inner core and the half-shells in upper and lower molds having hemispherical cavities.

[0138] (5) Formation of the intermediate layer and cover The intermediate layer composition was injection molded onto a spherical core to obtain an intermediate layer-coated sphere. The obtained intermediate layer-coated sphere was placed into a final mold having numerous dimples on the cavity surface. Half shells were obtained from the cover composition by compression molding. Two half shells were placed on the intermediate layer-coated sphere in the final mold to obtain a golf ball in which numerous dimples were formed on the cover, with the shape of the dimples being inverted from those on the cavity surface. The results of the evaluation of the obtained golf ball are shown in Tables 5 and 6.

[0139] [Table 4]

[0140] [Table 5]

[0141] [Table 6]

[0142] Golf balls No. 1-4 have a spherical core hardness distribution where the hardness differences (C1-C0), (C2-C1), (C3-C2), and (C4-C3) are greater than 0 and 6.0 or less, the hardness difference (C5-C4) is 5.0 or more, the hardness differences (C6-C5), (C7-C6), and (C8-C7) are greater than 0 and 3.5 or less, and the hardness difference (C2-C0) is 5.5 or more. Golf ball No. 6 has a spherical core hardness distribution that is hard on the outside and soft on the inside, and the hardness gradient is almost linear from the center to the surface (hardness difference (C5-C4) is less than 5). Compared to golf ball No. 6, golf balls No. 1-4 show improved driver shot distance and improved spin speed on middle iron shots.

[0143] The present invention (1) is a golf ball having a spherical core and a cover covering the spherical core, characterized in that when a straight line from the center of the spherical core toward the surface is divided into eight equal parts, the central hardness (C0), the hardness at 12.5% ​​from the center (C1), the hardness at 25.0% from the center (C2), the hardness at 37.5% from the center (C3), the hardness at 50.0% from the center (C4), the hardness at 62.5% from the center (C5), the hardness at 75.0% from the center (C6), the hardness at 87.5% from the center (C7), and the surface hardness (C8) of the spherical core 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, 5.5 ≤ (C2 - C0)

[0144] The present invention (2) is a golf ball according to the present invention (1), wherein the spherical core has hardnesses (C0), (C2), (C4), and (C5) that are Shore C hardness, and satisfies the following relationship. 0.5 ≤ {(C2-C0) / (C5-C4)}

[0145] The present invention (3) is a golf ball according to the present invention (1) or (2), wherein the spherical core has hardnesses (C0), (C2), and (C4) that are Shore C hardness and satisfy the following relationship. 1.0 ≤ {(C2-C0) / (C4-C2)}

[0146] The present invention (4) is that the spherical core has a Shore C hardness, with a hardness difference of (C1-C0) between hardness (C1) and hardness (C0), a hardness difference of (C2-C1) between hardness (C2) and hardness (C1), a hardness difference of (C3-C2) between hardness (C3) and hardness (C2), a hardness difference of (C4-C3) between hardness (C5) and hardness (C4) (C5-C4), and a hardness of (C6) This is a golf ball according to any one of the present invention (1) to (3), wherein when the largest value among the hardness difference between hardness (C6-C5) and hardness (C7-C6) (C7-C6) and the hardness difference between hardness (C8-C7) (C8-C7) is Cbmax and the smallest value is Cbmin, the ratio (Cbmax / Cbmin) is 4.0 or greater.

[0147] The present invention (5) is a golf ball according to any one of the present inventions (1) to (4), wherein the spherical core has hardness (C0) and (C8) on the Shore C hardness scale and satisfies the following relationship. 18.0 ≤ (C8 - C0)

[0148] The present invention (6) is a golf ball according to any one of the present inventions (1) to (5), wherein an intermediate layer is provided between the spherical core and the cover, and the surface hardness (C0) of the spherical core, the surface hardness of the intermediate layer, and the surface hardness of the ball are Shore C hardness and satisfy the following relationship. Core surface hardness <Intermediate layer surface hardness> Ball surface hardness

[0149] The present invention (7) is a golf ball according to any one of the present inventions (1) to (6), wherein 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 and the thickness (mm) and material hardness (Shore D) of the cover satisfy the following relationship. {(thickness of the intermediate layer × material hardness) / (thickness of the cover × material hardness)} ≥ 4.0

[0150] The present invention (8) is a golf ball according to any one of the present inventions (1) to (7), wherein the amount of compression deformation when a final load of 1275N is applied from a state in which an initial load of 98N is applied is 2.8 mm or less.

[0151] The present invention (9) is a golf ball according to any one of the present inventions (1) to (8), wherein the spherical core is formed from a core rubber composition containing (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 monophenol compound having substituents only at the p position.

[0152] The present invention (10) is a golf ball according to the present invention (9), wherein the core rubber composition contains (a) 100 parts by mass of base rubber and (d) 0.05 parts by mass to 2.0 parts by mass of a monophenol compound having substituents only at the p position.

[0153] The present invention (11) is a golf ball according to the present invention (9) or (10), wherein the monophenol compound having substituents only at the (d)p position is represented by general formula (1).

[0154] [ka] [In general formula (1), R represents an alkoxy group, halogen group, hydrocarbon group, nitro group, cyano group, amino group, or hydroxyl group.]

[0155] The present invention (12) is a golf ball according to any one of the present inventions (9) to (11), wherein the core rubber composition further contains (g) an aromatic carboxylic acid and / or a salt thereof. [Explanation of symbols]

[0156] 1: Golf ball, 2: Spherical core, 3: Middle layer, 4: Cover, 41: Dimples, 42: Lands

Claims

1. A golf ball having a spherical core and a cover that covers the spherical core, The aforementioned spherical core has a single-layer structure, A golf ball characterized in that, when a straight line extending from the center of the spherical core to the surface is divided into eight equal parts, the central hardness (C0), the hardness at 12.5% ​​from the center (C1), the hardness at 25.0% from the center (C2), the hardness at 37.5% from the center (C3), the hardness at 50.0% from the center (C4), the hardness at 62.5% from the center (C5), the hardness at 75.0% from the center (C6), the hardness at 87.5% from the center (C7), and the surface hardness (C8) of the spherical core are Shore C hardness and satisfy the following relationship. 0.5≦(C1-C0)≦5.5, 0.5≦(C2-C1)≦5.5, 0.5≦(C3-C2)≦5.5, 0.5≦(C4-C3)≦5.5, 5.5≦(C5-C4)≦12.0, 0<(C6-C5)≦3.0, 0<(C7-C6)≦3.0, 0<(C8-C7)≦3.0, 6.0≦(C2-C0)≦10.0 20.0≦(C8-C0)≦28.0 54.0 ≤ C0 ≤ 66.0 74.0 ≤ C8 ≤ 86.0

2. The golf ball according to claim 1, wherein the spherical core has hardnesses (C0), (C2), (C4), and (C5) on the Shore C hardness scale, satisfying the following relationship. 0.5≦{(C2-C0) / (C5-C4)}

3. The golf ball according to claim 1 or 2, wherein the spherical core has hardnesses (C0), (C2), and (C4) on the Shore C scale, satisfying the following relationship. 1.0≦{(C2-C0) / (C4-C2)}

4. The golf ball according to claim 1, wherein the spherical core has a Shore C hardness, and when the largest value among the hardness differences between hardness (C1) and hardness (C0) (C1-C0), hardness differences between hardness (C2) and hardness (C1) (C2-C1), hardness differences between hardness (C3) and hardness (C2) (C3-C2), hardness differences between hardness (C4) and hardness (C3) (C4-C3), hardness differences between hardness (C5) and hardness (C4) (C5-C4), hardness differences between hardness (C6) and hardness (C5) (C6-C5), hardness differences between hardness (C7) and hardness (C6) (C7-C6), and hardness differences between hardness (C8) and hardness (C7) (C8-C7) is Cbmax and the smallest value is Cbmin, the ratio (Cbmax / Cbmin) is 4.0 or more.

5. The golf ball according to claim 4, wherein the hardness difference (C5-C4) is Cbmax.

6. The golf ball according to claim 1, wherein an intermediate layer is provided between the spherical core and the cover, and the surface hardness (C8) of the spherical core, the surface hardness of the intermediate layer, and the surface hardness of the ball satisfy the following relationship in Shore C hardness. Core surface hardness < Intermediate layer surface hardness > Ball surface hardness

7. The golf ball according to claim 1, wherein 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 and the thickness (mm) and material hardness (Shore D) of the cover satisfy the following relationship. {(thickness of the intermediate layer × material hardness) / (thickness of the cover × material hardness)} ≥ 4.0

8. The golf ball according to claim 1, wherein the amount of compressive deformation when a final load of 1275N is applied from a state in which an initial load of 98N is applied is 2.8 mm or less.

9. The golf ball according to claim 1, wherein the spherical core is formed from a core rubber composition containing (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 cocrosslinking agent, (c) a crosslinking initiator, and (d) a monophenol compound having substituents only at the p position.

10. The golf ball according to claim 9, wherein the core rubber composition contains (a) 100 parts by mass of base rubber and (d) 0.05 parts by mass to 2.0 parts by mass of a monophenol compound having substituents only at the p position.

11. The golf ball according to claim 9 or 10, wherein the monophenol compound having substituents only at the (d)p position is represented by general formula (1). 【Chemistry 1】 [In general formula (1), R represents an alkoxy group, halogen group, hydrocarbon group, nitro group, cyano group, amino group, or hydroxyl group.]

12. The golf ball according to claim 9, wherein the core rubber composition further comprises (g) an aromatic carboxylic acid and / or a salt thereof.

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