golf ball

Abstract

The goal is to provide golf balls for professionals and advanced players that offer a high level of balance between distance performance and durability against repeated impacts. [Solution] A golf ball comprising a single-layer core and cover, wherein in the hardness distribution of the core, the Shore C hardness of the core surface is H100, the Shore C hardness at positions 87.5%, 75%, 62.5%, 50%, 37.5%, 25%, and 12.5% ​​outside the core radius from the core center are H87.5, H75, H62.5, H50, H37.5, H25, and H12.5 respectively, and the Shore C hardness at the core center is H0, then the following two equations 0 ≤ (H62.5 - H50) < (H100 - H87.5) < (H87.5 - H75) < (H75 - H62.5) ≤ 7.0, and (H87.5-H50) / (H50-H12.5)≧3.0 A golf ball characterized by satisfying the following conditions.

Description

Technical Field

[0001] The present invention relates to a golf ball having a single-layer core and a cover, and is directed to a golf ball for professionals and advanced players.

Background Art

[0002] As golf balls for professionals and advanced players, solid golf balls such as two-piece solid golf balls and three-piece solid golf balls are often used. A solid golf ball usually has a structure in which a core made of a rubber composition is coated with a single-layer or multiple-layer cover made of various resin materials. The core occupies most of the volume of the golf ball and has a great influence on various ball physical properties such as resilience, feel, and durability. Recently, various techniques have been proposed to achieve a specific core hardness gradient by appropriately adjusting the cross-sectional hardness of the core, and to improve the flying distance by optimizing the spin characteristics during a full shot with a driver or an iron. In addition, as a golf ball for advanced players and professionals, a polyurethane cover is often used as the outermost cover. It is also important to improve the cracking durability when repeatedly hitting a golf ball having such a structure.

[0003] Regarding the method of adjusting the cross-sectional hardness of the core, examples include appropriately adjusting the blending components of the rubber composition of the core, the vulcanization temperature, and the time. For example, in the following Patent Documents 1 to 27, regarding the blending components of the rubber composition of the core, the selection and blending amount of co-crosslinking agents and organic peroxides are adjusted, and as other components, water, organic sulfur compounds, etc. are blended to provide a specific internal cross-sectional hardness of the core.

[0004] However, the golf balls described in these patent documents still have problems in satisfying all of the full shot flight, short game controllability, and cracking durability by repeated hitting that satisfy professionals and advanced players.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2011-120898 [Patent Document 2] Japanese Patent Publication No. 2013-230361 [Patent Document 3] Japanese Patent Publication No. 2013-230362 [Patent Document 4] Japanese Patent Publication No. 2013-230363 [Patent Document 5] Japanese Patent Publication No. 2015-077405 [Patent Document 6] Japanese Patent Publication No. 2013-230365 [Patent Document 7] Japanese Patent Publication No. 2016-112308 [Patent Document 8] Japanese Patent Publication No. 2016-116627 [Patent Document 9] Japanese Patent Publication No. 2016-179052 [Patent Document 10] Japanese Patent Publication No. 2017-000183 [Patent Document 11] Japanese Patent Publication No. 2017-000470 [Patent Document 12] Japanese Patent Publication No. 2017-077355 [Patent Document 13] Japanese Patent Publication No. 2017-079905 [Patent Document 14] Japanese Patent Publication No. 2019-198465 [Patent Document 15] Japanese Patent Publication No. 2019-213606 [Patent Document 16] Japanese Patent Publication No. 2021-062026 [Patent Document 17] Japanese Patent Publication No. 2021-062036 [Patent Document 18] Japanese Patent Publication No. 2011-217857 [Patent Document 19] Japanese Patent Publication No. 2012-019820 [Patent Document 20] Japanese Patent Publication No. 2012-010726 [Patent Document 21] U.S. Patent Application Publication No. 2013 / 0157781 [Patent Document 22] Japanese Patent Publication No. 2015-006314 [Patent Document 23] Japanese Patent Publication No. 2013-009814 [Patent Document 24] Japanese Patent Publication No. 2013-031640 [Patent Document 25] Japanese Patent Publication No. 2013-248298 [Patent Document 26] Japanese Patent Publication No. 2023-175347 [Patent Document 27] Japanese Patent Publication No. 2023-031970 [Overview of the project] [Problems that the invention aims to solve]

[0006] This invention has been made in view of the above circumstances, and aims to provide a golf ball for professional and advanced golfers that achieves a high level of both distance performance and durability against repeated impacts. [Means for solving the problem]

[0007] The inventors, after diligent research to achieve the above objective, have found that for a golf ball comprising a single-layer core and cover, when the hardness distribution of the core is as follows, with the Shore C hardness of the core surface being H100, the Shore C hardness at a position 87.5% outside the core radius from the core center being H87.5, the Shore C hardness at a position 75% outside the core radius from the core center being H75, the Shore C hardness at a position 62.5% outside the core radius from the core center being H62.5, the Shore C hardness at a position 50% outside the core radius from the core center being H50, the Shore C hardness at a position 37.5% outside the core radius from the core center being H37.5, the Shore C hardness at a position 25% outside the core radius from the core center being H25, the Shore C hardness at a position 12.5% ​​outside the core radius from the core center being H12.5, and the Shore C hardness at the core center being H0, the following two equations 0 ≦ (H62.5 - H50) < (H100 - H87.5) < (H87.5 - H75) < (H75 - H62.5) ≦ 7.0, and (H87.5 - H50) / (H50 - H12.5) ≧ 3.0 By configuring the golf ball so as to satisfy the above conditions, it has been found that professional and advanced players can achieve low spin of the ball in a full shot, the carry distance when hitting with a driver (W#1) and an iron is sufficiently extended, and it has excellent repeated hitting durability. Furthermore, high spin controllability during an approach shot in a short game can also be obtained, leading to the completion of the present invention.

[0008] That is, in the golf ball of the present invention, paying particular attention to the hardness distribution of the core, by improving the hardness distribution of the core, by achieving low spin in a full shot, when hitting with a driver (W#1) in a high head speed region, it has excellent carry distance, and also has good carry distance when hitting with an iron. Regarding the core hardness distribution in the present invention, the core hardness distribution is defined by parameters obtained based on nine measurement points obtained by equally dividing the core radius from the center to the surface of the core cross-section into eight parts. Also, not only the hardness distribution shape of the entire core, but also the hardness distribution shape from the midpoint between the surface and the center of the core to the core surface is improved. Specifically, by setting the hardness gradient in the surface direction to gradually become gentler from the position of 62.5% of the core radius from the core center, excellent repeated hitting durability is achieved. In addition, the golf ball of the present invention also imparts spin performance in a short game that can satisfy professional and advanced players.

[0009] Therefore, the present invention provides the following golf ball. 1. A golf ball comprising a single-layer core and cover, wherein the hardness distribution of the core is as follows: the Shore C hardness of the core surface is H100, the Shore C hardness at a position 87.5% outside the core radius from the core center is H87.5, the Shore C hardness at a position 75% outside the core radius from the core center is H75, the Shore C hardness at a position 62.5% outside the core radius from the core center is H62.5, the Shore C hardness at a position 50% outside the core radius from the core center is H50, the Shore C hardness at a position 37.5% outside the core radius from the core center is H37.5, the Shore C hardness at a position 25% outside the core radius from the core center is H25, the Shore C hardness at a position 12.5% ​​outside the core radius from the core center is H12.5, and the Shore C hardness at the core center is H0. Then, the following two equations apply: 0 ≤ (H62.5 - H50) < (H100 - H87.5) < (H87.5 - H75) < (H75 - H62.5) ≤ 7.0, and (H87.5-H50) / (H50-H12.5)≧3.0 A golf ball characterized by satisfying the following conditions. 2. The following formula, (H100-H87.5) / (H87.5-H75)≦0.90 The golf balls described above that meet the requirements. 3. The following formula, 50≦(H87.5-H75) / (H75-H62.5)≦0.99 A golf ball as described in item 1 or 2 above that satisfies the requirements. 4. The following formula, 1.0 ≤ (H100 - H87.5) ≤ 6.0 A golf ball as described in item 1 above that satisfies the requirements. 5. The following formula, 2.0 ≤ (H87.5 - H75) ≤ 6.5 A golf ball as described in item 1 or 2 above that satisfies the requirements. 6. The following formula, 4.0 ≤ (H75 - H62.5) ≤ 7.0 A golf ball as described in item 1 or 2 above that satisfies the requirements. 7. The following formula, 0 ≤ (H62.5 - H50) ≤ 3.0 A golf ball as described in item 1 or 2 above that satisfies the requirements. 8. The following formula, 0 ≤ (H50 - H25) ≤ 3.0 A golf ball as described in item 1 or 2 above that satisfies the requirements. 9. The values ​​of the following eight expressions, H100-H87.5 H87.5-H75, H75-H62.5, H62.5-H50 H50-H37.5 H37.5-H25 H25-H12.5 H12.5-H0 A golf ball as described in item 1 or 2 above, where all values ​​are positive. 10. The above core consists of each of the following components (a) to (e): (a) Base rubber, (b) As a cocrosslinking agent, α,β-unsaturated carboxylic acids and / or metal salts thereof (c) organic peroxide; (d) Water or a water-providing agent, (e) Hindered phenol antioxidants having substituents with a thioether structure A golf ball according to claim 1 or 2 above, comprising a rubber composition containing, wherein the moisture-providing agent is a substance that contains water components other than free water in its structure and releases water by heating, or a substance that releases water components by thermal decomposition by heating, and the amount of component (e) is 0.2 parts by mass or more per 100 parts by mass of component (a). 11. The golf ball according to 10, wherein the hindered phenol antioxidant, which is component (e) above, has a chemical structure having at least one methyl group in the ortho position. 12. The golf ball according to 10 above, wherein the hindered phenol antioxidant component (e) has two or more substituents having a thioether structure. 13. A golf ball as described in 1 or 2 above, wherein the deflection of the core from an initial load of 98N (10kgf) to a final load of 1,275N (130kgf) is 3.8mm or less. 14. When the amount of deflection of the above-mentioned core from an initial load of 98N (10kgf) to a final load of 1,275N (130kgf) is applied is A (mm), and when the amount of deflection of the above-mentioned golf ball from an initial load of 98N (10kgf) to a final load of 1,275N (130kgf) is applied is B (mm), the golf ball described in 1 or 2 above is characterized in that the value of AB is less than 1.0 mm. 15. A golf ball consisting of three or more pieces, with a resin intermediate layer interposed between the core and the cover, wherein the relationship between the surface hardness of the sphere (intermediate layer-coated sphere) with the core covered by the intermediate layer and the surface hardness of the ball is given by the following formula: (Shore D hardness of the surface of the intermediate layer-coated sphere) - (Shore D hardness of the surface of the ball) ≥ 3 A golf ball as described in item 1 or 2 above that satisfies the requirements. [Effects of the Invention]

[0010] According to the golf ball of the present invention, as a golf ball for professionals and advanced players, it can achieve low spin during full shots to ensure superior distance, while also providing good control in the short game and high durability against repeated impacts. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic cross-sectional view of a golf ball, which is one embodiment of the present invention. [Figure 2] This graph shows the core hardness distribution data for Example 1. [Figure 3] This is a plan view showing the dimple pattern common to both the examples and comparative examples. [Figure 4] This graph shows the core hardness distribution for Examples 1-3 and Comparative Examples 1-3. [Figure 5] This graph shows the core hardness distribution for Comparative Examples 4-9. [Modes for carrying out the invention]

[0012] The present invention will be described in more detail below. The golf ball of the present invention has a single-layer core and a cover, an example of which is shown in Figure 1. The golf ball G shown in Figure 1 has a single-layer core 1 and a single-layer cover 3, and further has a single-layer intermediate layer 2 between them. The cover 3, excluding the paint layer, is located in the outermost layer of the golf ball's layer structure. The core is formed as a single layer as shown in Figure 1, and the cover is also formed as a single layer as shown in Figure 1. Furthermore, a surrounding layer made of a single or multiple layers of resin may be included between the intermediate layer and the core. The surface of the cover (outermost layer) 3 usually has many dimples D formed on it to improve aerodynamic properties. In addition, although not specifically shown, a paint layer is usually formed on the surface of the cover 3. The above layers will be described in detail below.

[0013] The core described above is formed in a single layer. In the case of a multi-layered rubber core, repeated impacts can cause delamination at the interface, resulting in poor durability.

[0014] There are no particular restrictions on the diameter of the core, but it is preferably 37.0 mm or larger, more preferably 38.0 mm or larger, and even more preferably 38.3 mm or larger. The upper limit is preferably 39.7 mm or smaller, more preferably 39.3 mm or smaller, and even more preferably 39.0 mm or smaller. If the diameter of the core is too small, the overall hardness of the ball will be too hard, meaning that the amount of deflection will be small, which may increase the amount of spin during a full shot and prevent you from achieving the desired distance. On the other hand, if the diameter of the core is too large, it may increase the amount of spin during a full shot and prevent you from achieving the desired distance.

[0015] The amount of deflection (mm) of the core when an initial load of 98N (10kgf) is applied to a final load of 1,275N (130kgf) is not particularly limited, but is preferably 2.7mm or more, more preferably 2.9mm or more, and even more preferably 3.1mm or more, with an upper limit of preferably 3.8mm or less, more preferably 3.7mm or less, and even more preferably 3.65mm or less. If the amount of deflection of the core is too small, i.e., the core is too hard, the spin may increase too much, resulting in a loss of distance, or the feel may become too hard. On the other hand, if the amount of deflection of the core is too large, i.e., the core is too soft, the rebound may be too low, resulting in a loss of distance, or the feel may become too soft, or the durability against cracking when repeatedly struck may be poor.

[0016] Next, the hardness distribution of the core described above will be explained. Note that the hardness of the core described below refers to Shore C hardness. This Shore C hardness is the hardness value measured using a Shore C hardness tester compliant with the ASTM D2240 standard.

[0017] In the following description of the core hardness distribution, the Shore C hardness of the core surface is defined as H100, the Shore C hardness at a position 87.5% outside the core radius from the core center as H87.5, the Shore C hardness at a position 75% outside the core radius from the core center as H75, the Shore C hardness at a position 62.5% outside the core radius from the core center as H62.5, the Shore C hardness at a position 50% outside the core radius from the core center as H50, the Shore C hardness at a position 37.5% outside the core radius from the core center as H37.5, the Shore C hardness at a position 25% outside the core radius from the core center as H25, the Shore C hardness at a position 12.5% ​​outside the core radius from the core center as H12.5, and the Shore C hardness at the core center as H0.

[0018] The surface hardness (H100) of the core described above is not particularly limited, but is preferably 79 or higher, more preferably 81 or higher, and even more preferably 83 or higher. Similarly, the upper limit is not particularly limited, but is preferably 92 or lower, more preferably 90 or lower, and even more preferably 88 or lower. If this value is too low, the core's rebound properties will be too low, resulting in excessive spin on the ball during full shots and potentially failing to achieve the desired distance. On the other hand, if the above value is too high, the resistance to cracking after repeated impacts may be poor, or the feel may become too hard.

[0019] The positional hardness (H87.5) located 87.5% outside the radius from the center of the core is not particularly limited, but is preferably 76 or higher, more preferably 78 or higher, and even more preferably 80 or higher. There is also no particular upper limit, but is preferably 88 or lower, more preferably 86 or lower, and even more preferably 84 or lower. Deviating from these hardness values ​​may lead to unfavorable consequences similar to those described for the surface hardness (H100) of the core.

[0020] The positional hardness (H75) at 75% outside the radius from the center of the core is not particularly limited, but is preferably 71 or higher, more preferably 73 or higher, and even more preferably 75 or higher. There is also no particular upper limit, but is preferably 83 or lower, more preferably 81 or lower, and even more preferably 79 or lower. Deviating from these hardness values ​​may lead to unfavorable results similar to those described for the surface hardness (H100) of the core.

[0021] The positional hardness (H62.5) located 62.5% outside the radius from the center of the core is not particularly limited, but is preferably 64 or higher, more preferably 66 or higher, and even more preferably 68 or higher. There is also no particular upper limit, but is preferably 77 or lower, more preferably 75 or lower, and even more preferably 73 or lower. Deviating from these hardness values ​​may lead to unfavorable results similar to those described for the surface hardness (H100) of the core.

[0022] The positional hardness (H50) at 50% outside the radius from the center of the core is not particularly limited, but is preferably 64 or higher, more preferably 66 or higher, and even more preferably 68 or higher. There is also no particular upper limit, but is preferably 77 or lower, more preferably 75 or lower, and even more preferably 73 or lower. Deviating from these hardness levels may lead to unfavorable results similar to those described for the surface hardness (H100) of the core.

[0023] The hardness (H37.5) at a position 37.5% outside the radius from the center of the core is not particularly limited, but is preferably 64 or higher, more preferably 66 or higher, and even more preferably 68 or higher. There is also no particular upper limit, but is preferably 77 or lower, more preferably 75 or lower, and even more preferably 73 or lower. If this value is too low, the rebound of the core will be low, making it difficult to achieve the desired distance, and the durability against cracking when repeatedly struck may be poor. If this value is too high, the amount of spin on the ball will be high, making it difficult to achieve the desired distance, and the feel of the ball may become too hard.

[0024] The positional hardness (H25) at 25% radius outside the center of the core is not particularly limited, but is preferably 63 or higher, more preferably 65 or higher, and even more preferably 67 or higher. There is also no particular upper limit, but is preferably 76 or lower, more preferably 74 or lower, and even more preferably 72 or lower. Deviating from these hardness values ​​may lead to unfavorable results similar to those described for the positional hardness (H37.5) at 37.5% radius outside the center of the core.

[0025] The positional hardness (H12.5) at 12.5% ​​outside the radius from the center of the core is not particularly limited, but is preferably 62 or higher, more preferably 64 or higher, and even more preferably 66 or higher. There is also no particular upper limit, but is preferably 75 or lower, more preferably 73 or lower, and even more preferably 71 or lower. If these hardness values ​​are exceeded, it may lead to unfavorable results similar to those described for the positional hardness (H37.5) at 37.5% outside the radius from the center of the core.

[0026] The central hardness (H0) of the core described above is not particularly limited, but is preferably 59 or higher, more preferably 61 or higher, and even more preferably 63 or higher. There is also no particular upper limit to the central hardness, which is preferably 72 or lower, more preferably 71 or lower, and even more preferably 70 or lower. If these hardness values ​​are deviated from, it may lead to unfavorable results similar to those described for the positional hardness (H37.5) 37.5% outside the radius from the center of the core.

[0027] The difference in hardness between H75 and H62.5 (H75-H62.5) is preferably such that it satisfies the following formula. (H75-H62.5)≦7.0 ···(i) The value of (H75-H62.5) in the above formula is preferably 4.0 or higher, more preferably 4.5 or higher, and even more preferably 5.0 or higher, with an upper limit of preferably 7.0 or lower, more preferably 6.8 or lower, and even more preferably 6.5 or lower. If this value is too high, the cracking resistance when repeatedly struck may be poor. On the other hand, if this value is too low, the amount of spin on the ball when taking a full shot may increase, resulting in a loss of distance.

[0028] Furthermore, it is preferable that the following equation is satisfied. (H87.5-H75)<(H75-H62.5) (ii) If the above formula is not met, the crack resistance when repeatedly struck may be reduced.

[0029] Furthermore, it is preferable that the following equation is satisfied. (H100-H87.5)<(H87.5-H75)...(iii) If the above formula is not met, the crack resistance when repeatedly struck may be reduced.

[0030] Furthermore, it is preferable that the following equation is satisfied. (H62.5-H50)<(H100-H87.5) (iv) If the above formula is not met, the amount of spin on the ball when taking a full shot may increase, and you may not be able to achieve your target distance.

[0031] Furthermore, it is preferable that the following equation is satisfied. (H62.5-H50)≧0 ···(v) If the above formula is not satisfied, the amount of spin on the ball when taking a full shot will increase, and the desired distance may not be achieved. The value of (H62.5-H50) in the above formula is preferably 0 or more, more preferably 0.1 or more, and even more preferably 0.2 or more, with an upper limit of preferably 3.0 or less, more preferably 2.0 or less, and even more preferably 1.0 or less.

[0032] Combining the above (i) to (v) into a single equation results in the following: 0≦(H62.5-H50)<(H100-H87.5)<(H87.5-H75)<(H75-H62.5)≦7.0 In other words, the above equation means that the hardness gradient in the direction of the surface gradually becomes gentler from the 62.5% position of the core radius from the core center.

[0033] The value of (H100-H87.5) in the above formula is preferably 1.0 or higher, more preferably 2.0 or higher, and even more preferably 3.0 or higher, with an upper limit of preferably 6.0 or lower, more preferably 5.0 or lower, and even more preferably 4.0 or lower. If this value is too high, the cracking resistance when repeatedly struck may be poor. On the other hand, if this value is too low, the amount of spin on the ball when taking a full shot may increase, resulting in a loss of distance.

[0034] The value of (H87.5-H75) in the above formula is preferably 2.0 or higher, more preferably 3.5 or higher, and even more preferably 5.0 or higher, with an upper limit of preferably 6.5 or lower, more preferably 6.3 or lower, and even more preferably 6.2 or lower. If this value is too high, the cracking resistance when repeatedly struck may be poor. On the other hand, if this value is too low, the amount of spin on the ball when taking a full shot may increase, resulting in a loss of distance.

[0035] The value of (H100-H87.5) / (H87.5-H75) is preferably 0.35 or higher, more preferably 0.45 or higher, and even more preferably 0.55 or higher, with an upper limit of preferably 0.90 or lower, more preferably 0.80 or lower, and even more preferably 0.70 or lower. In other words, the hardness gradient from H87.5 to H100 is gentler than the hardness gradient from H75 to H87.5. If this value is too high, the crack resistance when repeatedly struck may be poor. On the other hand, if this value is too low, the amount of spin on the ball when taking a full shot may increase, and the desired distance may not be achieved.

[0036] The value of (H87.5-H75) / (H75-H62.5) is preferably 0.50 or higher, more preferably 0.60 or higher, and even more preferably 0.70 or higher, with an upper limit of preferably 0.999 or lower, more preferably 0.95 or lower, and even more preferably 0.90 or lower. In other words, the hardness gradient from H75 to H87.5 is gentler than the hardness gradient from H62.5 to H75. If this value is too high, the crack resistance when repeatedly struck may be poor. On the other hand, if this value is too low, the amount of spin on the ball when taking a full shot may increase, and the desired distance may not be achieved.

[0037] Furthermore, the value of (H87.5-H50) / (H50-H12.5) is preferably 3.0 or higher, more preferably 3.4 or higher, and even more preferably 3.8 or higher, with an upper limit of preferably 15.0 or lower, more preferably 10.0 or lower, and even more preferably 8.0 or lower. If this value is too high, the cracking resistance when repeatedly struck may be poor. On the other hand, if this value is too low, the amount of spin on the ball when taking a full shot may increase, and the desired distance may not be achieved.

[0038] Furthermore, the value of (H100-H50) / (H50-H0) is preferably 2.0 or higher, more preferably 2.5 or higher, and even more preferably 2.8 or higher, with an upper limit of preferably 15.0 or lower, more preferably 10.0 or lower, and even more preferably 8.0 or lower. If this value is too high, the crack resistance when repeatedly struck may be poor. On the other hand, if this value is too low, the amount of spin on the ball when taking a full shot may increase, and the desired distance may not be achieved.

[0039] Furthermore, it is preferable that all of the hardness differences between the nine points obtained by dividing the core radius on the surface from the center of the core cross-section into eight equal parts, namely (H100-H87.5), (H87.5-H75), (H75-H62.5), (H62.5-H50), (H50-H37.5), (H37.5-H25), (H25-H12.5), and (H12.5-H0), are positive values. In other words, the hardness increases continuously from the center of the core toward the surface without any decrease. For example, Figure 2 shows the core hardness distribution data for Example 1. As shown in this graph, the hardness gradient is upward sloping to the right with no dips. If all of these values ​​are not positive, the amount of spin on the ball when taking a full shot may increase, and the desired distance may not be achieved.

[0040] As a core material having the hardness distribution described above, it is preferable to use rubber as the main material. If the core is not formed from rubber, the rebound may be low and the ball may not fly far. Specifically, a rubber composition for the core can be prepared by mainly using a base rubber and blending it with a co-crosslinking agent, organic peroxide, inert filler, organic sulfur compound, etc.

[0041] Furthermore, it is preferable that the above rubber material contains each of the following components (a) to (e). (a) Base rubber, (b) As a cocrosslinking agent, α,β-unsaturated carboxylic acids and / or metal salts thereof (c) organic peroxide; (d) Water or water-providing agent (e) Hindered phenol antioxidants having substituents with a thioether structure

[0042] The base rubber of component (a) above is not particularly limited, but polybutadiene is particularly preferred.

[0043] The polybutadiene described above preferably has 60% or more, preferably 80% or more, more preferably 90% or more, and most preferably 95% or more, cis-1,4-bonds in its polymer chain. If the proportion of cis-1,4-bonds in the polybutadiene molecule is too low, the repulsive properties may decrease.

[0044] Furthermore, the 1,2-vinyl bond content in the polybutadiene is typically 2% or less, preferably 1.7% or less, and more preferably 1.5% or less in the polymer chain. If the 1,2-vinyl bond content is too high, the resilience may decrease.

[0045] The above polybutadiene has a (ML1+4(100℃)) ratio of preferably 20 or more, more preferably 30 or more, with an upper limit of preferably 120 or less, more preferably 100 or less, and even more preferably 80 or less.

[0046] The Mooney viscosity mentioned above is an industrial viscosity index (JIS K 6300) measured with a Mooney viscometer, a type of rotational plasticity meter, and its unit symbol is ML1+4 (100°C). M represents Mooney viscosity, L represents the large rotor (L-type), 1+4 indicates a preheating time of 1 minute, a rotor rotation time of 4 minutes, and that the measurement was taken under conditions of 100°C.

[0047] The above-mentioned polybutadiene can be synthesized using rare earth element catalysts or group VIII metal compound catalysts.

[0048] Furthermore, the base rubber may contain polybutadiene rubber synthesized with a catalyst different from the lanthanum series rare earth element compounds mentioned above. In addition, styrene-butadiene rubber (SBR), natural rubber, polyisoprene rubber, ethylene propylene diene rubber (EPDM), etc., may be blended, either individually or in combination of two or more.

[0049] The proportion of the above-mentioned polybutadiene in the total rubber is preferably 60% by mass or more, more preferably 70% by mass or more, and most preferably 90% by mass or more. Alternatively, 100% by mass of the base rubber, i.e., the entire base rubber, may be the above-mentioned polybutadiene.

[0050] Next, component (b) is a co-crosslinking agent, which is an α,β-unsaturated carboxylic acid and / or its metal salt. The number of carbon atoms in this unsaturated carboxylic acid is preferably 3 to 8, and specific examples include acrylic acid, methacrylic acid, maleic acid, and fumaric acid. Specific examples of the metal in the above unsaturated carboxylic acid include zinc, sodium, magnesium, calcium, and aluminum, with zinc being particularly preferred. Therefore, zinc acrylate is the most preferred co-crosslinking agent.

[0051] (b) The amount of component (b) blended is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, and even more preferably 20 parts by mass or more, per 100 parts by mass of the base rubber of component (a), with an upper limit of preferably 65 parts by mass or less, more preferably 60 parts by mass or less, and even more preferably 55 parts by mass or less. If the blending amount is less than the above range, it will become too soft and have poor rebound properties, and if it is more than the above range, it will become too hard and have a poor feel when hitting the ball, as well as be brittle and have poor durability.

[0052] (b) The co-crosslinking agent of component (b) preferably has an average particle size of 3 to 30 μm, more preferably 5 to 25 μm, and even more preferably 8 to 15 μm. If the average particle size of the co-crosslinking agent is less than 3 μm, it tends to aggregate in the rubber composition, increasing the reactivity between the acrylic acids and decreasing the reactivity between the base rubbers, which may result in insufficient rebound performance of the golf ball. If the average particle size of the co-crosslinking agent exceeds 30 μm, the co-crosslinking agent particles become too large, leading to greater variation in the properties of the resulting golf ball.

[0053] (c) Component is an organic peroxide, and it is particularly preferable to use an organic peroxide having a 1-minute half-life temperature of 110 to 185°C. Examples of such organic peroxides include dicumyl peroxide (NOF Corporation's "Permil D"), 2,5-dimethyl-2,5-di(t-butylperoxy)hexane (NOF Corporation's "Perhexa 25B"), di(2-t-butylperoxyisopropyl)benzene (NOF Corporation's "Perbutyl P"), and dicumyl peroxide can be suitably used. Other commercially available products include "Perhexa C-40", "Niper BW", "Perloyl L" (all manufactured by NOF Corporation), or Luperco 231XL (manufactured by Atochem). These may be used individually or in combination of two or more.

[0054] (c) The amount of component blended is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, per 100 parts by mass of base rubber, with an upper limit of preferably 5 parts by mass or less, more preferably 4 parts by mass or less, and even more preferably 3 parts by mass or less.

[0055] (d) Component is water or a water-providing agent. There are no particular restrictions on the water in component (d); it may be distilled water or tap water, but it is preferable to use distilled water that is free of impurities.

[0056] Furthermore, if component (d) is a water-donating agent, this water-donating agent is defined as a substance that contains water components other than free water in its structure and releases water upon heating, or a substance that releases water components through thermal decomposition upon heating. Common types of water include free water, adsorbed water, intercalated water, zeolite water, and bound water. Clay minerals are said to contain adsorbed water, intercalated water, and free water, and clay minerals containing such intercalated water can be used as component (d).

[0057] Examples of the clay minerals mentioned above include layered double hydroxides such as hydrotalcite. Layered double hydroxides (LDHs) are minerals with a multilayered structure, and chemically bonded water (interlayer water) exists between the layers. For example, in the case of Mg-Al LDHs, the interlayer water is almost completely removed in the range of 180-300°C. In the case of Zn-Al LDHs, the interlayer water is removed at a lower temperature of 170-200°C.

[0058] Furthermore, as component (d), substances containing bound water are exemplified. Specifically, these are substances that have water (coordinating water) that acts as ligands to form complex ions, and examples include hydrates of inorganic compounds. As the above inorganic compounds, for example, one or more selected from calcium sulfate 0.5 hydrate, calcium sulfate dihydrate, aluminum sulfate 14-18 hydrate, magnesium sulfate heptahydrate, beryllium sulfate tetrahydrate, zirconium sulfate tetrahydrate, manganese sulfate pentahydrate, iron sulfate heptahydrate, cobalt sulfate heptahydrate, nickel sulfate hexahydrate, cupric sulfate pentahydrate, zinc sulfate heptahydrate, cadmium sulfate octahydrate, indium sulfate nonahydrate, zinc sulfate dihydrate, etc., can be used in combination.

[0059] Furthermore, as component (d), examples include substances that release water components through thermal decomposition by heating. For example, substances that exist as hydroxide ions in the substance but escape as water (H2O) when heated include aluminum hydroxide and magnesium hydroxide.

[0060] Regarding the moisture-providing agent, it is preferable that the moisture dissociation rate by mass is 60% or more when the rubber composition is heated to the vulcanization temperature, or when the inside of the core reaches its maximum temperature due to the heat of self-reaction during vulcanization. Furthermore, from the viewpoint of improving the efficiency of moisture supply, it is preferable to use a moisture-providing agent with a high moisture content by mass.

[0061] Specifically, for example, the water content in the molecular formula of the water-providing agent is preferably 6% or more by mass, and more preferably 15% or more. A higher water content in the molecular formula of the water-providing agent is preferable, and there is no particular upper limit, but from the viewpoint of ease of availability, for example, it can be 90% or less by mass.

[0062] As a moisture-releasing agent, it is preferable that it can release as much moisture as possible when the rubber composition is vulcanized. However, vulcanization conditions such as vulcanization temperature and vulcanization time may vary depending on the base rubber and components contained in the rubber composition, such as organic peroxides. For this reason, it is preferable to select a moisture-releasing agent that can release an appropriate amount of moisture at the vulcanization conditions, such as vulcanization temperature, in accordance with the vulcanization conditions of the rubber composition to which the moisture-releasing agent is added.

[0063] Furthermore, since it is preferable that the water-supplying agent has a low water dissociation rate when kneading the rubber composition, it is preferable that the water dissociation rate when heated to 90°C, i.e., the cumulative water dissociation rate when heated to 90°C, be 60% or less by mass.

[0064] (d) The amount of component is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.5 parts by mass or more, per 100 parts by mass of base rubber, with an upper limit of preferably 15 parts by mass or less, more preferably 10 parts by mass or less, even more preferably 5 parts by mass or less, and even more preferably 3 parts by mass or less. If the amount of component is too high, the hardness will soften and the desired feel, durability, and rebound properties cannot be obtained, and if the amount is too low, the desired core hardness distribution cannot be obtained, and it may not be possible to sufficiently achieve low spin on the ball when hitting it.

[0065] (e) Component is a hindered phenol antioxidant having substituents with a thioether structure. This hindered phenol antioxidant preferably has a chemical structure having at least one methyl group in the ortho position. Furthermore, in the hindered phenol antioxidant, it is preferable that there are two or more substituents with thioether structures.

[0066] By incorporating component (e) above into the rubber composition, the normal impact resistance performance can be improved, and even if foreign matter is mixed into the rubber material, the decrease in impact resistance can be maintained at a certain level or higher.

[0067] The hindered phenol antioxidant, which is component (e) above, is preferably represented by the following general formula (I). [ka]

[0068] In the above formula, x is an integer of 1 or more, and preferably x is an integer of 8 or more.

[0069] (e) Specifically, the following can be used as ingredients: product names "Antage HP500" and "Antage HP400" (both manufactured by Kawaguchi Chemical Industry Co., Ltd.), and product name "Irganox 1520L" manufactured by BASF.

[0070] (e) The amount of component is 0.2 parts by mass or more, preferably 0.3 parts by mass or more, and more preferably 0.5 parts by mass or more, per 100 parts by mass of the base rubber. The upper limit is preferably 3.0 parts by mass or less, more preferably 2.0 parts by mass or less, and even more preferably 1.5 parts by mass or less. If the amount of component is too high, the hardness will soften and the desired feel, durability, and rebound properties will not be obtained, and if the amount is too low, the desired effect of impact durability will not be obtained.

[0071] (e) The addition of component (a) may be added to component (a) during the manufacture of the rubber composition, or it may be added in advance during the manufacture of component (a), or these addition methods may be used in combination.

[0072] In addition to the components (a) to (e) described above, various additives such as components (f), (g), and (h) described below, as well as fillers and processing aids, may be incorporated, as long as they do not interfere with the effects of the present invention.

[0073] (f) The component is benzimidazole and / or its metal salt, represented by the following general formula (II), and is used as an anti-aging agent. [ka]

[0074] In formula (II) above, R is a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms, and m is an integer from 1 to 4. When m is 2 or greater, these may be the same or different from each other. Examples of benzimidazoles having formula (II) above include 2-mercaptobenzimidazole, 2-mercaptomethylbenzimidazole, and their metal salts, with zinc salt being preferred as the metal salt.

[0075] (f) The amount of benzimidazole and / or its metal salt represented by the above specific formula in component (f) is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, per 100 parts by mass of the base rubber, with an upper limit of preferably 5 parts by mass or less, more preferably 3 parts by mass or less. If the amount of component (f) is too small, the crosslinking reaction near the core surface will not be efficiently promoted, the crosslinking density will not be sufficiently large, a hard layer will not be sufficiently formed, the hardness difference between the core surface and the core center will not be sufficiently large, and sufficient impact resistance may not be obtained. On the other hand, the effect obtained by arbitrarily increasing the amount of component (f) will not change beyond the above-mentioned preferred amount.

[0076] (g) Component is sulfur or an alkylphenol disulfide polymer having the following chemical structure. [ka]

[0077] In the above formula (III), R represents an alkyl group, and n represents a degree of polymerization in the range of 2 to 20. The alkyl group of R is preferably a lower alkyl group having 1 to 6 carbon atoms, and specifically, can be selected from the group consisting of methyl group, ethyl group, n-propyl group, iso-propyl group, n-butyl group, tert-butyl group, n-amyl group (pentyl group), iso-amyl group (pentyl group), tert-amyl group (pentyl group), sec-isoamyl group, neopentyl group, n-hexyl group, iso-hexyl group, and tert-hexyl group. More preferably, the organic sulfur compound of component (g-1) is an amylphenol disulfide polymer, and specifically, commercially available products such as "Sanceler AP" (manufactured by Sanshin Chemical Industry Co., Ltd.) and "Vultac 5" (manufactured by Arkema Japan Co., Ltd.) can be used.

[0078] There are no particular restrictions on the amount of component (g), which is an alkylphenol disulfide polymer, but it is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and most preferably 0.3 parts by mass or more, per 100 parts by mass of the above rubber component. The upper limit is preferably 5.0 parts by mass or less, more preferably 3.0 parts by mass or less, and most preferably 2.0 parts by mass or less. If the amount is too high, the crosslinking reaction by organic peroxides is inhibited by the effect of sulfur, and the overall hardness of the molded product tends to soften significantly.

[0079] On the other hand, if component (g) is sulfur, commercially available sulfur can be used. For example, Tsurumi Chemical Industries' "Sulfax 5," Sanshin Chemical Industries' "Sunmix S-80N" and "Sunmix IS-60N," and Akrochem's "AKROFORM S-80 / EPR / P" can be used.

[0080] There are no particular restrictions on the amount of sulfur added, but it is preferably 0.01 parts by mass or more, more preferably 0.03 parts by mass or more, and most preferably 0.05 parts by mass or more, per 100 parts by mass of the above rubber component. The upper limit is preferably 5.0 parts by mass or less, more preferably 2.0 parts by mass or less, and most preferably 1.0 part by mass or less. If the amount added is too high, the crosslinking reaction by organic peroxides is inhibited by the effect of sulfur, and the overall hardness of the molded product tends to soften significantly. On the other hand, if the amount added is too low, it may not be possible to make a large difference in hardness between the surface and the center in the hardness of the core.

[0081] Furthermore, with regard to sulfur, it is desirable to use it in the form of a masterbatch to improve the dispersibility of trace amounts of sulfur. Examples of such sulfur masterbatches include the aforementioned product names "Sunmix S-80N," "Sunmix IS-60N," and "AKROFORM S-80 / EPR / P."

[0082] Suitable fillers include, for example, zinc oxide, barium sulfate, and calcium carbonate. These may be used individually or in combination of two or more. The amount of filler added is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, per 100 parts by mass of the base rubber. The upper limit of this addition is preferably 100 parts by mass or less, more preferably 60 parts by mass or less, and even more preferably 40 parts by mass or less, per 100 parts by mass of the base rubber. If the amount added is too much or too little, it may not be possible to obtain the appropriate mass and suitable rebound properties.

[0083] Component (h) is an organosulfur compound different from component (g). There are no particular restrictions on this organosulfur compound, but examples include thiophenols, thionaphthols, diphenyl polysulfides, halogenated thiophenols, or their metal salts. Specifically, examples include zinc salts of pentachlorothiophenol, pentafluorothiophenol, pentabromothiophenol, parachlorothiophenol, etc., diphenyl polysulfides with 2 to 4 sulfur atoms, dibenzyl polysulfides, dibenzoyl polysulfides, dibenzothiazoyl polysulfides, dithiobenzoyl polysulfides, 2-thionaphthol, etc. These may be used individually or in combination of two or more. Among these, zinc salts of pentachlorothiophenol and / or diphenyl disulfides can be preferably used.

[0084] The amount of the above-mentioned organic sulfur compound 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 or more, per 100 parts by mass of the base rubber, with an upper limit of preferably 3 parts by mass or less, more preferably 2 parts by mass or less, and even more preferably 1 part by mass or less. If the amount of organic sulfur compound is too high, the hardness of the heat-molded product of the rubber composition may become too soft, while if it is too low, improvement in rebound properties may not be expected.

[0085] As processing aids, higher fatty acids and their metal salts can be suitably used. Examples of higher fatty acids include stearic acid, palmitic acid, oleic acid, linoleic acid, linolenic acid, and myristic acid, with stearic acid being particularly preferred. Examples of metal salts of higher fatty acids include lithium salts, sodium salts, potassium salts, copper salts, magnesium salts, calcium salts, strontium salts, barium salts, tin salts, cobalt salts, nickel salts, zinc salts, and aluminum salts, with zinc stearate being particularly preferred. The amount of processing aid added can be preferably 1 part by mass or more, more preferably 3 parts by mass or more, and even more preferably 5 parts by mass or more, per 100 parts by mass of the base rubber. Furthermore, the upper limit of this amount can be preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 10 parts by mass or less, per 100 parts by mass of the base rubber. If the amount is too high, sufficient hardness and resilience cannot be obtained, and if it is too low, the added chemicals may not be sufficiently dispersed, and the expected physical properties may not be obtained. Regarding the method of adding the processing aid, there are several methods, but they are not limited to the above. These include adding it to the mixer at the same time as other chemicals, pre-mixing it with other chemicals such as component (b) above and then adding it, coating it on the surface of other chemicals such as component (b) above and then adding it, or preparing a masterbatch in advance together with component (a) above and then adding it.

[0086] Furthermore, the above rubber composition may contain an anti-aging agent different from component (e). Specifically, examples of hindered phenol-based anti-aging agents include 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-ethylphenol, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 1,3,5-tris(3',5'-di-t-butyl-4-hydroxybenzyl)isocyanuric acid, 2,2'-methylenebis(4-methyl-6-tert-butylphenol), and 4,4',4''-(1-methylpropanyl-3-ylidene)tris(6-tert-butyl-m-cresol). Commercially available examples include Nocrack 200, M-17, NS-6 (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.), IRGANOX 1010 (manufactured by BASF), and Adekastab. AO-20, AO-30 (manufactured by ADEKA), etc., can be used. These may be used individually or in combination of two or more. There are no particular restrictions on the amount of this anti-aging agent, but it is preferably 1.0 part by mass or less, more preferably 0.7 parts by mass or less, and even more preferably 0.5 parts by mass or less, per 100 parts by mass of the base rubber. If the amount is too high, the durability improvement effect of component (e) may not be obtained.

[0087] A core, which is a vulcanized molded product, can be manufactured by vulcanizing and curing the above rubber composition. For example, the composition can be kneaded using a kneader such as a Banbury mixer or roll, then compression molded or injection molded using a core mold, and the molded body can be cured by appropriately heating it at a temperature of approximately 100 to 200°C for 10 to 40 minutes, which is sufficient for the organic peroxide and co-crosslinking agent to act, thereby manufacturing a core, which is a vulcanized molded product.

[0088] Next, I will explain the cover. The hardness of the cover material is not particularly limited, but is preferably 35 or higher on the Shore D scale, more preferably 40 or higher, and even more preferably 43 or higher, with an upper limit of preferably 53 or less, more preferably 50 or less, and even more preferably 47 or less. The surface hardness of the sphere (ball surface hardness) is preferably 54 or higher on the Shore D scale, more preferably 56 or higher, and even more preferably 58 or higher, with an upper limit of preferably 64 or less, more preferably 62 or less, and even more preferably 60 or less. If the hardness of the cover material and the ball surface hardness are too soft compared to the above ranges, the amount of spin on a full shot may increase too much, resulting in a loss of distance. On the other hand, if the material hardness and surface hardness are too hard, scratch resistance may be poor, or the amount of spin in the short game may be insufficient.

[0089] The material hardness of the cover is preferably 57 or higher, more preferably 63 or higher, and even more preferably 67 or higher, expressed as a Shore C hardness scale, with an upper limit of preferably 80 or lower, more preferably 76 or lower, and even more preferably 72 or lower. The surface hardness of the ball is preferably 77 or higher, more preferably 80 or higher, and even more preferably 85 or higher, expressed as a Shore C hardness scale, with an upper limit of preferably 93 or lower, more preferably 91 or lower, and even more preferably 89 or lower.

[0090] The thickness of the cover is preferably 0.3 mm or more, more preferably 0.45 mm or more, and even more preferably 0.6 mm or more. On the other hand, the upper limit of the cover thickness is preferably 1.2 mm or less, more preferably 1.15 mm or less, and even more preferably 1.0 mm or less. If the cover is too thick, there may be insufficient rebound or excessive spin during full shots with an iron, resulting in a loss of desired distance. On the other hand, if the cover is too thin, scratch resistance may be poor, or sufficient spin may not be applied during approach shots, resulting in a lack of control.

[0091] As the material for the above cover, various thermoplastic resins used for golf ball covers can be used. However, in order to obtain excellent spin performance that can satisfy professionals and advanced players, a soft material is necessary. Furthermore, in order to achieve both excellent scratch resistance and rebound properties, it is preferable to use a resin material mainly composed of thermoplastic polyurethane. Specifically, it is preferable to form it with a resin compound mainly composed of (I) thermoplastic polyurethane and (II) a polyisocyanate compound.

[0092] The total mass of component (I) and component (II) combined is recommended to be 60% or more, and more preferably 70% or more, of the total amount of the resin composition of the cover. Component (I) and component (II) are described in detail below.

[0093] Regarding the thermoplastic polyurethane described in (I) above, the structure of the thermoplastic polyurethane includes a soft segment made of a high-molecular-weight polyol (polymeric glycol), which is a long-chain polyol, and a hard segment made of a chain extender and a polyisocyanate compound. Here, any long-chain polyol that has been conventionally used in thermoplastic polyurethane technology can be used as a raw material, and there are no particular restrictions, but examples include polyester polyols, polyether polyols, polycarbonate polyols, polyester polycarbonate polyols, polyolefin polyols, conjugated diene polymer polyols, castor oil polyols, silicone polyols, and vinyl polymer polyols. One type of these long-chain polyol may be used, or two or more types may be used in combination. Among these, polyether polyols are preferred because they can synthesize thermoplastic polyurethanes with a high rebound modulus and excellent low-temperature properties.

[0094] As the chain extender, those used in conventional thermoplastic polyurethane technologies can be suitably used, and for example, it is preferable to use a low molecular weight compound with a molecular weight of 400 or less that has two or more active hydrogen atoms in the molecule that can react with an isocyanate group. Examples of chain extenders include, but are not limited to, 1,4-butylene glycol, 1,2-ethylene glycol, 1,3-butanediol, 1,6-hexanediol, and 2,2-dimethyl-1,3-propanediol. Among these, aliphatic diols having 2 to 12 carbon atoms are preferred as chain extenders, and 1,4-butylene glycol is more preferred.

[0095] As the polyisocyanate compound, those used in conventional thermoplastic polyurethane technology can be suitably used, and there are no particular restrictions. Specifically, one or more selected from the group consisting of 4,4'-diphenylmethane diisocyanate, 2,4-(or)2,6-toluene diisocyanate, p-phenylenediisocyanate, xylylene diisocyanate, naphthylene 1,5-diisocyanate, tetramethylxylylene diisocyanate, hydrogenated xylylene diisocyanate, dicyclohexylmethane diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, norbornene diisocyanate, trimethylhexamethylene diisocyanate, and dimer acid diisocyanate can be used. However, depending on the isocyanate species, it may be difficult to control the crosslinking reaction during injection molding. In the present invention, from the viewpoint of balancing stability during production with the physical properties that are exhibited, 4,4'-diphenylmethanediisocyanate, an aromatic diisocyanate, is most preferred.

[0096] The specific thermoplastic polyurethane component (I) can be a commercially available product, such as Pandex T8295, T8290, and T8260 (all manufactured by DIC Covestropolymer Co., Ltd.).

[0097] Although not an essential component, a thermoplastic elastomer other than the thermoplastic polyurethane can be added to components (I) and (II) above as component (III). By adding this component (III) to the resin compound, it is possible to further improve the fluidity, resilience, abrasion resistance, and other physical properties required for a golf ball cover material.

[0098] There are no particular restrictions on the composition ratio of components (I), (II), and (III) above, but in order to fully exert the effects of the present invention, it is preferable that the mass ratio of (I):(II):(III) = 100:2 to 50:0 to 50, and more preferably (I):(II):(III) = 100:2 to 30:8 to 50 (mass ratio).

[0099] Furthermore, the above resin formulation may contain various additives other than the components that make up the thermoplastic polyurethane, as needed. For example, pigments, dispersants, antioxidants, light stabilizers, UV absorbers, mold release agents, etc., can be added as appropriate.

[0100] An intermediate layer can be interposed between the core and the cover. This intermediate layer is preferably formed from a resin material, as will be described later.

[0101] The material hardness of the intermediate layer is not particularly limited, but in terms of Shore D hardness, it is preferably 62 or more, more preferably 64 or more, still more preferably 66 or more, and as the upper limit value, it is preferably 72 or less, more preferably 70 or less, still more preferably 68 or less. Further, the surface hardness of the sphere (intermediate layer-coated sphere) in which the core is coated with the intermediate layer is, in terms of Shore D hardness, preferably 68 or more, more preferably 70 or more, still more preferably 72 or more, and as the upper limit value, it is preferably 78 or less, more preferably 76 or less, still more preferably 74 or less. If the material hardness and surface hardness of these intermediate layers are too soft compared to the above ranges, the spin amount at full shot may increase too much and the flying distance may not be achieved, or the initial velocity of the ball may be low and the flying distance may not be achieved at full shot. On the other hand, if the above material hardness and surface hardness are too hard, the crack durability due to repeated impacts may deteriorate, or the spin amount in the short game may decrease too much.

[0102] In addition, when the material hardness of the intermediate layer is expressed in terms of Shore C hardness, it is preferably 92 or more, more preferably 94 or more, still more preferably 95 or more, and as the upper limit value, it is preferably 100 or less, more preferably 98 or less, still more preferably 96 or less. Further, the surface hardness of the intermediate layer-coated sphere, when expressed in terms of Shore C hardness, is preferably 93 or more, more preferably 95 or more, still more preferably 97 or more, and as the upper limit value, it is preferably 100 or less, more preferably 99 or less, still more preferably 98 or less.

[0103] The thickness of the intermediate layer is preferably 1.00 mm or more, more preferably 1.10 mm or more, and even more preferably 1.15 mm or more. On the other hand, the upper limit of the thickness of the intermediate layer is preferably 1.45 mm or less, more preferably 1.35 mm or less, and even more preferably 1.25 mm or less. Furthermore, the value of intermediate layer thickness (mm) / ball diameter (mm) is preferably 0.023 or more, more preferably 0.026 or more, and even more preferably 0.027 or more, with an upper limit of preferably 0.034 or less, more preferably 0.032 or less, and even more preferably 0.029 or less. If the above value is too small, the feel of hitting the ball with a full shot may not be able to balance appropriate hardness and rebound, which may not be perceived as a good feel by professionals and advanced players, or the crack resistance when repeatedly hitting the ball may be poor. On the other hand, if the above value is too large, the rebound may be diminished, which may not be perceived as a good feel by professionals and advanced players.

[0104] The value obtained by subtracting the cover thickness from the thickness of the intermediate layer is preferably greater than 0, more preferably 0.20 mm or more, and even more preferably 0.32 mm or more. The upper limit is preferably 0.62 mm or less, more preferably 0.58 mm or less, and even more preferably 0.55 mm or less. If this value deviates from the above range, the amount of spin on the ball may increase or the initial ball speed may decrease during a full shot, and the desired distance may not be achieved. On the other hand, if this value is too small, the durability against cracking when repeatedly struck may be poor.

[0105] For the intermediate layer material, various thermoplastic resins used as golf ball materials, particularly resin materials mainly composed of ionomer resin, can be used.

[0106] The ionomer resin material preferably contains an ionomer with a high acid content. For example, a commercially available ionomer resin with an acid content of 16% by mass or more is blended with a regular ionomer resin. This blend allows for both low spin and high rebound during full shots with a driver (W#1), thereby ensuring the desired distance.

[0107] The content of unsaturated carboxylic acids (acid content) in high-acid-content ionomer resins is usually 16% by mass or more, preferably 17% by mass or more, more preferably 18% by mass or more, with an upper limit of preferably 22% by mass or less, more preferably 21% by mass or less, and even more preferably 20% by mass or less. If this value is too low, spin may increase during full shots with drivers (W#1), utilities, and irons, and the desired distance may not be achieved. Conversely, if the above value is too high, the feel may become too hard, or the durability against cracking during repeated impacts may be poor.

[0108] Furthermore, the high acid content ionomer resin is preferably 20% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more, relative to 100% by mass of the resin material. The upper limit is 100% by mass or less, preferably 90% by mass or less, and more preferably 85% by mass or less. If the amount of the high acid content ionomer resin is too low, the amount of spin during a full shot may increase, resulting in a loss of distance. On the other hand, if the amount of the high acid content ionomer resin is too high, the durability of repeated impacts may deteriorate.

[0109] Furthermore, when using ionomer resin as the base resin, it is desirable to use a mixture of zinc-neutralized ionomer resin and sodium-neutralized ionomer resin as the base resin. The mixing ratio of zinc-neutralized type to sodium-neutralized type (by mass ratio) is 5 / 95 to 95 / 5, preferably 10 / 90 to 90 / 10, and more preferably 15 / 85 to 85 / 15. If Zn-neutralized ionomer and Na-neutralized ionomer are not included in this ratio, the rebound properties may become too low, resulting in an undesirable flight, or the crack resistance during repeated impacts at room temperature may deteriorate, and crack resistance at even lower temperatures (below freezing) may also deteriorate.

[0110] Inorganic granular fillers can be incorporated into the intermediate layer material. These inorganic granular fillers are components added to adjust the specific gravity and act as reinforcing agents. While not particularly limited, zinc oxide, barium sulfate, titanium dioxide, etc., can be used as appropriate. Furthermore, barium sulfate is preferred, and precipitated barium sulfate is even more preferred, due to its significant effect in improving crack resistance during repeated impacts.

[0111] The average particle size of the above-mentioned granular inorganic filler is not particularly limited, but is between 0.01 and 10. It is preferable to set it to 0 μm, and more preferably to 0.1 to 10 μm. If the average particle size of the granular inorganic filler is too small or too large, dispersion during material preparation will be affected. The properties may deteriorate. Note that the above average particle size is determined by separating the particles in an aqueous solution with an appropriate dispersant. This refers to the particle size measured by a particle size distribution analyzer after the particles have been dispersed.

[0112] The amount of inorganic granular filler added is usually more than 0 parts by mass per 100 parts by mass of the base resin of the intermediate layer material, preferably 10 parts by mass or more, more preferably 15 parts by mass or more, with an upper limit of usually 50 parts by mass or less, preferably 40 parts by mass or less, and more preferably 30 parts by mass or less. If the amount added is too little, the resistance to cracking due to repeated impact may be poor. On the other hand, if the amount added is too much, the rebound of the ball may be reduced, or the amount of spin during a full shot may increase, resulting in a loss of the intended distance.

[0113] The intermediate layer material can be appropriately blended with any additives depending on the application. For example, various additives such as pigments, dispersants, antioxidants, UV absorbers, and light stabilizers can be added. When these additives are blended, the amount blended is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and preferably 10 parts by mass or less, and more preferably 4 parts by mass or less, per 100 parts by mass of the base resin.

[0114] For the intermediate layer material, it is preferable to polish the surface of the intermediate layer in order to improve adhesion with the polyurethane, which is suitably used in the cover material described later. Furthermore, it is preferable to apply a primer (adhesive) to the surface of the intermediate layer after the polishing treatment, or to add an adhesion-enhancing agent to the material.

[0115] The specific gravity of the intermediate layer material is not particularly limited, but is preferably 0.94 or higher, more preferably 1.06 or higher, and even more preferably 1.08 or higher. The upper limit is preferably 1.25 or lower, more preferably 1.20 or lower, and even more preferably 1.15 or lower. If the specific gravity of the intermediate layer is too low, the resistance to cracking due to repeated impacts may be poor. On the other hand, if the specific gravity of the intermediate layer is too high, the rebound of the ball may be reduced, or the amount of spin during a full shot may increase, resulting in a loss of the intended distance.

[0116] The manufacturing method for a golf ball formed by laminating the core, intermediate layer, and cover (outermost layer) described above can be carried out by conventional methods such as known injection molding. For example, an intermediate layer material can be injected around the core using an injection molding die to obtain each coated sphere, and then the material for the outermost cover can be injection molded to obtain a golf ball. Alternatively, a golf ball can be manufactured by wrapping each coated sphere with two pre-formed hemispherical half-cups and then heat-pressure molding them.

[0117] The amount of deflection (mm) of a golf ball when subjected to an initial load of 98N (10kgf) to a final load of 1,275N (130kgf) is preferably 2.0mm or more, more preferably 2.2mm or more, and more preferably 2.4mm or more. The upper limit is preferably 3.1mm or less, more preferably 2.9mm or less, and even more preferably 2.7mm or less. If the amount of deflection of the golf ball is too small, i.e., too hard, the amount of spin on the ball may increase too much, resulting in a shorter flight distance or a hard feel. On the other hand, if the amount of deflection is too large, i.e., the sphere is too soft, the durability against cracking when repeatedly struck may decrease, and the actual initial ball speed may decrease, resulting in a shorter flight distance when hitting with a driver (W#1).

[0118] [Relationship between the amount of deflection between the core and the ball] When the deflection amount of the core from an initial load of 98N (10kgf) to a final load of 1,275N (130kgf) is applied, let A (mm) be the deflection amount of the golf ball from an initial load of 98N (10kgf) to a final load of 1,275N (130kgf) be applied, then the value of AB is preferably 0.55mm or more, more preferably 0.60mm or more, and even more preferably 0.65mm or more, with an upper limit of preferably less than 1.0mm, more preferably 0.95mm or less, and even more preferably 0.90mm or less. If this value is too large, the actual initial ball speed when struck with a driver (W#1) will be low, making it difficult to achieve the desired distance, and it may feel bad to professionals and advanced players with high head speeds, and the cracking resistance when repeatedly struck may be poor. On the other hand, if this value is too small, it may feel bad, and the cracking resistance when repeatedly struck may be poor.

[0119] The ratio of the deflection between the core and the ball, i.e., the A / B value, is preferably 1.15 or higher, more preferably 1.20 or higher, and even more preferably 1.25 or higher, with an upper limit of preferably 1.40 or lower, more preferably 1.35 or lower, and even more preferably 1.32 or lower. If this value is too high, the actual initial ball speed when struck with a driver (W#1) will be low, resulting in a loss of the desired distance, a poor feel for professionals and advanced players with high swing speeds, and poor durability against cracking after repeated impacts. On the other hand, if this value is too low, the feel may be poor, and the durability against cracking after repeated impacts may also be poor.

[0120] [Core diameter and ball diameter] The relationship between the core diameter and the ball diameter, i.e., the value of (core diameter) / (ball diameter), is preferably 0.867 or higher, more preferably 0.890 or higher, and even more preferably 0.897 or higher. On the other hand, the upper limit is preferably 0.930 or lower, more preferably 0.920 or lower, and even more preferably 0.913 or lower. If this value is too small, the amount of deflection of the entire ball will decrease, making the ball harder, which may increase the amount of spin on the ball during a full shot and prevent you from achieving the desired distance. On the other hand, if the above value is too large, the amount of spin on the ball during a full shot may increase and prevent you from achieving the desired distance.

[0121] [Hardness relationship of each layer] The intermediate layer covering sphere preferably has a higher surface hardness than the ball. The difference in surface hardness (surface hardness of the intermediate layer covering sphere - surface hardness of the ball) is preferably 1 or higher, more preferably 3 or higher, and even more preferably 5 or higher in Shore C hardness, with an upper limit of preferably 15 or lower, more preferably 12 or lower, and even more preferably 10 or lower. Expressed in Shore D hardness, it is preferably 1 or higher, more preferably 3 or higher, and even more preferably 5 or higher, with an upper limit of preferably 16 or lower, more preferably 14 or lower, and even more preferably 12 or lower. If the above value is small, the amount of spin when approaching may decrease, which may result in poor spin control in shot games. On the other hand, if the above value is large, and the large value is due to the material hardness of the intermediate layer, the durability against cracking due to repeated impacts may decrease. If the large value is due to the material hardness of the cover, the amount of spin may increase on full shots, and the target distance may not be achieved.

[0122] The intermediate layer coating sphere preferably has a higher surface hardness than the core. The difference in surface hardness (surface hardness of the intermediate layer coating sphere - surface hardness of the core) is preferably 1 or higher, more preferably 6 or higher, and even more preferably 10 or higher on the Shore C hardness scale, with an upper limit of preferably 25 or lower, more preferably 20 or lower, and even more preferably 15 or lower. If the above value is too small, the amount of spin on a full shot may increase, making it difficult to achieve the desired distance. On the other hand, if the above value is too large, the durability against cracking when repeatedly struck may decrease, or the actual initial velocity of the ball may decrease, making it difficult to achieve the desired distance.

[0123] The value obtained by subtracting the core's center hardness from the surface hardness of the intermediate layer-coated sphere is preferably 23 or higher, more preferably 25 or higher, and even more preferably 28 or higher on the Shore C hardness scale. The upper limit is preferably 47 or lower, more preferably 42 or lower, and even more preferably 35 or lower. If the above value is too low, the amount of spin may increase with a full shot, and the target distance may not be achieved. On the other hand, if the above value is too high, the crack resistance when repeatedly struck may decrease, or the actual initial ball speed may decrease when struck with a driver (W#1), and the target distance may not be achieved.

[0124] [Specific gravity of each layer] The difference in specific gravity between the core, intermediate layer, and cover is generally recommended to be within ±0.15, preferably within ±0.10, and more preferably within ±0.05. That is, the values ​​of (core specific gravity) - (intermediate layer material specific gravity), (cover specific gravity) - (intermediate layer material specific gravity), and (core specific gravity) - (cover material specific gravity) are generally -0.15 or higher, preferably -0.10 or higher, and more preferably -0.05 or higher, with an upper limit of generally 0.15 or lower, preferably 0.10 or lower, and more preferably 0.05 or lower. If the difference in specific gravity between each layer is too large, the intermediate layer material and / or cover material may not be molded perfectly concentrically with the layers located inside them, resulting in eccentricity. When the ball is struck with a putter, this can cause a large lateral deviation.

[0125] Numerous dimples can be formed on the outer surface of the cover. There are no particular restrictions on the number of dimples arranged on the cover surface, but preferably there are 250 or more, preferably 300 or more, more preferably 320 or more, and as an upper limit, preferably 380 or less, more preferably 350 or less, and even more preferably 340 or less. If the number of dimples exceeds the above range, the ball's trajectory may become lower and the distance may decrease. Conversely, if the number of dimples is too low, the ball's trajectory may become higher and the distance may not increase.

[0126] The dimple shape can be one or more types, such as circular, various polygons, dewdrop shapes, or elliptical shapes, and can be used as appropriate. For example, when using a circular dimple, the diameter can be approximately 2.5 mm to 6.5 mm, and the depth can be 0.08 mm to 0.30 mm.

[0127] The dimple occupancy rate of the golf ball's spherical surface, specifically the ratio (SR value) of the total dimple area defined by the surface edges of the planes surrounded by the edges of the dimples to the ball's spherical surface assuming no dimples exist, is preferably between 70% and 90% to allow for sufficient aerodynamic performance. Furthermore, the value V0, obtained by dividing the spatial volume of the dimples below the plane surrounded by the edges of each dimple by the volume of a cylinder with the plane as its base and the maximum depth of the dimples from this base as its height, is preferably between 0.35 and 0.80 to optimize the ball's trajectory. Moreover, the VR value, which is the ratio of the total dimple volume formed below the plane surrounded by the edges of the dimples to the ball's spherical surface assuming no dimples exist, is preferably between 0.6% and 0.8%. If the values ​​deviate from the above ranges, the trajectory may not yield a good distance, and the ball may not achieve a sufficiently satisfactory distance.

[0128] Furthermore, the golf ball of the present invention can be used in competition and comply with the rules of golf. The outer diameter of the ball is such that it cannot pass through a ring with an inner diameter of 42.672 mm, and the mass can preferably be formed to 45.0 to 45.93 g. [Examples]

[0129] The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0130] [Examples 1-3, Comparative Examples 1-9] [Core formation] After preparing the rubber compositions of Examples 1 and 2 and Comparative Examples 1 to 4 shown in Table 1, solid cores were produced by vulcanization molding at the temperatures and times shown in Table 1. For Example 3 and Comparative Examples 5-9, solid cores were prepared using the rubber compositions and vulcanization conditions described in Table 1, in the same manner as described above.

[0131] [Table 1]

[0132] The details of each component listed in Table 1 are as follows: • Polybutadiene A: Manufactured by ENEOS Material, product name "BR 01" • Polybutadiene B: Manufactured by ENEOS Material, product name "BR T700" • Zinc acrylate A: "ZN-DA85S" (manufactured by Nippon Shokubai Co., Ltd.) • Zinc acrylate B: "ZN-DA85SR" (manufactured by Nippon Shokubai Co., Ltd.) • Zinc stearate: Product name "Zinc Stearate GP" (manufactured by NOF Corporation) • Organic peroxide A: Dicumyl peroxide, trade name "Perkmyl D" (manufactured by NOF Corporation) • Organic peroxide B: A mixture of 1,1-di(t-butylperoxy)cyclohexane and silica, trade name "Perhexa C-40" (manufactured by NOF Corporation) • Sulfur: Product name "Sunmix S-80N" (manufactured by Sanshin Chemical Industry Co., Ltd.), a sulfur masterbatch containing 80% by mass of rubber-grade powdered sulfur. • Water: Purified water (manufactured by Masaki Pharmaceutical Co., Ltd.) • Anti-aging agent A: 2,2-methylenebis(4-methyl-6-butylphenol), trade name "Nocrac NS-6" (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) • Anti-aging agent B: 2-mercaptobenzimidazole, trade name "Nocrac MB" (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) • Anti-aging agent C: Product name "Antage HP500" (manufactured by Kawaguchi Chemical Industry Co., Ltd.) • Zinc oxide: Product name "Triple Zinc Oxide" (manufactured by Sakai Chemical Industry Co., Ltd.) • Pentachlorothiophenol zinc salt: Manufactured by Fujifilm & Wako Pure Chemical Industries, Ltd.

[0133] [Formation of the intermediate layer and cover (outermost layer)] Next, in Examples 1 and 2 and Comparative Examples 1 to 4, an intermediate layer was formed by injection molding using an injection mold with the intermediate layer resin material No. 1 or No. 2 shown in Table 2 around the core surface. Then, using a different injection mold, a cover was formed by injection molding using the cover (outermost layer) resin material No. 5 or No. 6 shown in Table 2 around the intermediate layer-covered sphere. At this time, a predetermined number of dimples described below were formed on the cover surface.

[0134] In Example 3 and Comparative Examples 5-9, an intermediate layer is formed by injection molding using an injection mold with the intermediate layer resin material No. 1, No. 3, or No. 4 shown in Table 2 around the core surface. Then, using a different injection mold, a cover is formed by injection molding using the cover (outermost layer) resin material No. 5 shown in Table 2 around the intermediate layer-covered sphere. At this time, a predetermined number of dimples described below are formed on the cover surface.

[0135] [Table 2]

[0136] The details of the ingredients listed in Table 2 are as follows. "Hymiran 1605", "Hymiran 1557", "Hymiran 1706", "AM7329" - Ionomers manufactured by Mitsui Dow Polychemicals. "S9320" Ionomer manufactured by THE DOW CHEMICAL COMPANY "Barium sulfate" - Product name "Precipitated Barium Sulfate 300" manufactured by Sakai Chemical Industry Co., Ltd. Trimethylolpropane (TMP), manufactured by Tokyo Chemical Industry Co., Ltd. "Polyethylene wax," manufactured by Sanyo Chemical Industries, Ltd., product name "Sunwax 161P" "TPU(1)" is a product name "Pandex" manufactured by DIC Covestropolymer, an ether-type thermoplastic polyurethane, with a material hardness (Shore D) of "47". "TPU(2)" is a product name "Pandex" manufactured by DIC Covestropolymer, an ether-type thermoplastic polyurethane, with a material hardness (Shore D) of "43".

[0137] The dimples in each example and comparative example used the following common dimple configuration. This dimple configuration includes eight types of circular dimples, No. 1 to No. 8, with different diameters and depths. Details are shown in Table 3 below. The arrangement (pattern) of these dimples is shown in Figure 3. Figure 3(A) is a plan view of the dimples, and Figure 3(B) is a side view thereof.

[0138] [Table 3]

[0139] Definition of a dimple Edge: The highest point in the cross-section passing through the center of the dimple. Diameter: The diameter of the plane surrounded by the rim of the dimple. Depth: Maximum depth of the dimple from the plane surrounded by the edges of the dimple. SR: The ratio of the total dimple area, defined by the plane enclosed by the edges of the dimples, to the ball's surface area assuming no dimples exist. Dimple volume: The volume of the dimple beneath the plane surrounded by the edges of the dimple. Cylinder volume ratio: The ratio of the volume of a dimple to the volume of a cylinder with the same diameter and depth as the dimple. VR: The ratio of the total dimple volume formed downwards from the plane surrounded by the edges of the dimples to the ball volume assuming no dimples exist.

[0140] For each golf ball obtained, various physical properties such as the internal hardness at each position of the core, the outer diameter of the core and each coated sphere, the thickness and material hardness of each layer, and the deflection and surface hardness of each coated sphere were evaluated using the method described below and are shown in Tables 4 and 5.

[0141] [Outer diameter of each sphere in the core and intermediate layer covering spheres] The spheres to be measured are temperature-controlled in a constant temperature chamber adjusted to 23.9±1℃ for at least 3 hours, and then measured in a room at 23.9±2℃. Five arbitrary points on the surface are measured, and the average value is taken as the measurement value for each sphere. The average value for all 10 measured spheres is then calculated.

[0142] [Ball diameter] The balls to be measured are temperature-controlled in a constant temperature chamber adjusted to 23.9±1℃ for more than 3 hours, and then measured in a room at 23.9±2℃. 15 measurements are taken at arbitrary non-dimpled areas, and the average value is taken as the measurement value for one ball. The average value for 10 balls is then calculated.

[0143] [Amount of deflection of the core, intermediate layer covering sphere, and ball] The core, intermediate layer coated sphere, or target coated sphere of the ball is placed on a hard plate, and the amount of deflection is measured from an initial load of 98N (10kgf) to a final load of 1275N (130kgf). The above deflection amounts are measured after temperature adjustment to 23.9°C. The pressure rate of the head used to compress the ball is set to 10mm / s.

[0144] [Core hardness distribution] The core surface is spherical, and the hardness is measured using the Shore C hardness scale according to ASTM D2240 by setting the needle of the hardness tester nearly perpendicular to the spherical surface. For the center and designated positions of the core, the core is cut into a hemispherical shape to create a flat cross-section, and the hardness is measured by pressing the needle of the hardness tester perpendicularly against the center and the designated positions shown in Table 4. The hardness of the center and each position is shown as a Shore C hardness value. For hardness measurement, an automatic rubber hardness tester "P2" manufactured by Polymer Instruments Co., Ltd., equipped with a Shore C hardness tester, is used. The maximum value is read. All measurements are performed in an environment of 23±2℃. The values ​​in Table 6 are Shore C hardness values.

[0145] Furthermore, graphs of the core hardness distribution for Examples 1-4 and Comparative Examples 1-9 are shown in Figures 4 and 5.

[0146] [Material hardness of the intermediate layer and cover] Each layer of resin material is molded into a 2mm thick sheet and left for two weeks. Afterward, Shore D and Shore C hardness are measured according to the ASTM D2240 standard. A P2 automatic rubber hardness tester manufactured by Polymer Instruments Co., Ltd. is used for hardness measurement. The Shore D and Shore C hardness attachments are fitted, and the respective hardnesses are measured. The maximum value is read. All measurements are performed under conditions of 23±2℃.

[0147] [Surface hardness of each sphere in the intermediate-coated sphere and ball] The hardness of each sphere is measured by pressing the needle perpendicularly against its surface. Note that the surface hardness of the ball (cover) is measured on the land portion of the ball surface where no dimples are formed. Shore D and Shore C hardness are measured according to the ASTM D2240 standard. An automatic rubber hardness tester "P2" manufactured by Polymer Instruments Co., Ltd. is used for hardness measurement. The Shore D and Shore C hardness attachments are fitted, and the respective hardnesses are measured. The maximum value is read. All measurements are performed in an environment of 23±2℃.

[0148] [Table 4]

[0149] [Table 5]

[0150] The flight distance (W#1)(I#6), spin rate during approach shots, and durability for repeated impacts of each golf ball were evaluated using the following method. The results are shown in Table 6.

[0151] Flight evaluation (W#1, HS50m / s) A golf hitting robot will be fitted with a driver club and hit the ball at a head speed (HS) of 50 m / s. The spin rate and total distance will be measured. The club used will be a Bridgestone Sports "TourB XD-5 Driver (2017 model)" (loft angle 8.5°), and will be evaluated according to the following criteria. 〔Judgment criteria〕 ◎...The total distance compared to Comparative Example 1 is more than +2.0m. ○ ··· The total distance compared to Comparative Example 1 is between -1.0m and +2.0m. △ ··· The total distance compared to Comparative Example 1 is -2.0m or more and less than -1.0m. × ··· The total distance compared to Comparative Example 1 is less than -2.0m.

[0152] Flight evaluation (W#1, HS45m / s) A golf swing robot will be fitted with a driver club and struck at a head speed (HS) of 45 m / s to measure spin rate and total distance. The club used will be a Bridgestone Sports "J015 Driver (2016 model)" (loft angle 9.5°), and will be evaluated according to the following criteria. 〔Judgment criteria〕 ◎...The total distance compared to Comparative Example 1 is more than +2.0m. ○ ··· The total distance compared to Comparative Example 1 is between -1.0m and +2.0m. △ ··· The total distance compared to Comparative Example 1 is -2.0m or more and less than -1.0m. × ··· The total distance compared to Comparative Example 1 is less than -2.0m.

[0153] Flight evaluation (I#6, HS42m / s) A golf hitting robot will be fitted with a 6-iron (I#6) and hit at a head speed (HS) of 42 m / s to measure spin rate and total distance. The club used will be the "JGR Forged I#6 (2016 model)" manufactured by Bridgestone Sports, and will be evaluated according to the following criteria. 〔Judgment criteria〕 ◎...The total distance compared to Comparative Example 1 is more than +2.0m. ○ ··· The total distance compared to Comparative Example 1 is between -1.0m and +2.0m. △ ··· The total distance compared to Comparative Example 1 is -2.0m or more and less than -1.0m. × ··· The total distance compared to Comparative Example 1 is less than -2.0m.

[0154] Evaluating spin rate during approach shots The spin rate will be determined by the amount of spin produced when a golf swing robot is hit with a sand wedge at a head speed (HS) of 15 m / s. The spin rate will be similarly measured using an initial condition measurement device immediately after impact. The sand wedge used will be a Bridgestone Sports "TourStage TW-03 (loft angle 57°) 2002 model". 〔Judgment criteria〕 ◎ ··· Spin rate exceeding 5500 rpm ○ ··· Spin rate over 5200 rpm, 5500 rpm or less △ ··· Spin rate over 4900 rpm, under 5200 rpm × ··· Spin rate 4900 rpm or less

[0155] Repeated impact durability The durability of the golf balls will be evaluated using the ADC Ball COR Durability Tester manufactured by Automated Design Corporation, USA. This test machine launches golf balls using air pressure and then continuously impacts them against two parallel metal plates. The incident velocity on the metal plates was set to 43 m / s. The number of launches required for the golf balls to break will be measured, and the average value of the measurements for 10 golf balls will be calculated. The following criteria will be used for evaluation. 〔Judgment criteria〕 ◎ ··· Number of shots fired exceeds 300 ○ ··· Number of shots fired: more than 200, less than 300 △ ··· Number of shots fired: more than 120, less than 200 × ··· Number of shots fired: 120 or less

[0156] [Table 6]

[0157] As shown in the results in Table 6, the golf balls of Comparative Examples 1 to 9 are inferior to the present invention (example) in the following respects. In Comparative Example 1, the core hardness distribution showed that (H87.5-H75) was greater than (H75-H62.5), and (H100-H87.5) was greater than (H87.5-H75). As a result, it was inferior to the Example in terms of flight during full shots or durability against repeated impacts. In Comparative Example 2, the core hardness distribution showed that (H87.5-H75) was greater than (H75-H62.5), resulting in inferior flight during full shots or durability against repeated impacts compared to the Example. In Comparative Example 3, the core hardness distribution showed that (H87.5-H75) was greater than (H75-H62.5), and (H100-H87.5) was greater than (H87.5-H75). As a result, it was inferior to the Example in terms of flight during full shots or durability against repeated impacts. In Comparative Example 4, the core hardness distribution showed that (H87.5-H75) was greater than (H75-H62.5), resulting in inferior flight during full shots or durability against repeated impacts compared to the example. Comparative Example 5 has a core hardness distribution where (H100-H87.5) is greater than (H87.5-H75), and (H87.5-H50) / (H50-H12.5) is less than 3.0. As a result, it is inferior to the example in terms of flight performance during a full shot. Comparative Example 6 has a core hardness distribution where (H100-H87.5) is greater than (H87.5-H75), and (H87.5-H50) / (H50-H12.5) is less than 3.0. As a result, it is inferior to the example in terms of flight during full shots and durability against repeated impacts. In Comparative Example 7, the core hardness distribution showed that (H87.5-H75) was greater than (H75-H62.5), and (H62.5-H50) was greater than (H100-H87.5). As a result, it was inferior to the Example in terms of flight during full shots or durability against repeated impacts. In Comparative Example 8, the core hardness distribution shows that the value of (H87.5-H75) is greater than 7.0, and (H87.5-H75) is greater than (H75-H62.5). As a result, it exhibits inferior repeated impact durability compared to the example. In Comparative Example 9, the core hardness distribution shows that the value of (H87.5-H75) is greater than 7.0, and (H87.5-H75) is greater than (H75-H62.5). As a result, it exhibits inferior repeated impact durability compared to the example.

Claims

1. A golf ball comprising a single-layer core and cover, wherein, in the hardness distribution of the core, the Shore C hardness of the core surface is H100, the Shore C hardness at a position 87.5% outside the core radius from the core center is H87.5, the Shore C hardness at a position 75% outside the core radius from the core center is H75, the Shore C hardness at a position 62.5% outside the core radius from the core center is H62.5, the Shore C hardness at a position 50% outside the core radius from the core center is H50, the Shore C hardness at a position 37.5% outside the core radius from the core center is H37.5, the Shore C hardness at a position 25% outside the core radius from the core center is H25, the Shore C hardness at a position 12.5% ​​outside the core radius from the core center is H12.5, and the Shore C hardness at the core center is H0, then the following two equations 0 ≤ (H62.5 - H50) < (H100 - H87.5) < (H87.5 - H75) < (H75 - H62.5) ≤ 7.0, and (H87.5-H50) / (H50-H12.5)≧3.0 A golf ball characterized by satisfying the following conditions.

2. The following formula, (H100-H87.5) / (H87.5-H75)≦0.90 A golf ball according to claim 1 that satisfies the requirements.

3. The following formula, 50≦(H87.5-H75) / (H75-H62.5)≦0.99 A golf ball according to claim 1 or 2 that satisfies the requirements.

4. The following formula, 1.0≦(H100-H87.5)≦6.0 A golf ball according to claim 1 that satisfies the requirements.

5. The following formula, 2.0≦(H87.5-H75)≦6.5 A golf ball according to claim 1 or 2 that satisfies the requirements.

6. The following formula, 4.0≦(H75-H62.5)≦7.0 A golf ball according to claim 1 or 2 that satisfies the requirements.

7. The following formula, 0≦(H62.5-H50)≦3.0 A golf ball according to claim 1 or 2 that satisfies the requirements.

8. The following formula, 0≦(H50-H25)≦3.0 A golf ball according to claim 1 or 2 that satisfies the requirements.

9. The values ​​of the following eight formulas, H100-H87.5, H87.5-H75, H75-H62.5, H62.5-H50, H50-H37.5 H37.5-H25 H25-H12.5 H12.5-H0 A golf ball according to claim 1 or 2, wherein all of the values ​​are positive.

10. The above core consists of the following components (a) to (e): (a) Base rubber, (b) As a cocrosslinking agent, α,β-unsaturated carboxylic acids and / or their metal salts, (c) organic peroxide; (d) Water or a water-providing agent, (e) Hindered phenol antioxidants having substituents with a thioether structure A golf ball according to claim 1 or 2, wherein the above-mentioned water-providing agent is a substance that contains water components other than free water in its structure and releases water by heating, or a substance that releases water components by thermal decomposition by heating, and the amount of component (e) is 0.2 parts by mass or more per 100 parts by mass of component (a), formed from a rubber composition.

11. The golf ball according to claim 10, wherein the hindered phenol antioxidant, which is component (e) above, has a chemical structure having at least one methyl group in the ortho position.

12. The golf ball according to claim 10, wherein the hindered phenol antioxidant component (e) has two or more substituents having a thioether structure.

13. The golf ball according to claim 1 or 2, wherein the amount of deflection when the core is loaded with an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf) is 3.8 mm or less.

14. The golf ball according to claim 1 or 2, wherein when the core is subjected to an initial load of 98 N (10 kgf) and a final load of 1,275 N (130 kgf), the amount of deflection is A (mm), and when the golf ball is subjected to an initial load of 98 N (10 kgf) and a final load of 1,275 N (130 kgf), the amount of deflection is B (mm), and the golf ball is subjected to an initial load of 98 N (10 kgf) and a final load of 1,275 N (130 kgf), the value of A - B is less than 1.0 mm.

15. A golf ball consisting of three or more pieces, with a resin intermediate layer interposed between the core and the cover, wherein the relationship between the surface hardness of the sphere (intermediate layer-coated sphere) covered with the core and the surface hardness of the ball is given by the following formula: (Shore D hardness of the surface of the intermediate layer-coated sphere) - (Shore D hardness of the surface of the ball) ≥ 3 A golf ball according to claim 1 or 2 that satisfies the requirements.

Images