Multi-piece solid golf ball

Abstract

This golf ball minimizes the loss of distance under low swing speed conditions, offers controllability in the short game, and provides excellent durability for repeated impacts. [Solution] A golf ball G comprising a core 1, an intermediate layer 2, a cover 3, and dimples D, wherein the Shore C hardness of the core surface is H100, and the Shore C hardnesses 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 formula 0 ≤ (H62.5 - H50) < (H100 - H87.5) < (H87.5 - H75) < (H75 - H62.5) ≤ 7.0, and (H100 - H50) / (H50 - H0) ≥ 2.7 A golf ball that satisfies the following conditions and has a specific dimple volume occupancy rate.

Description

Technical Field

[0001] The present invention relates to a multi-piece solid golf ball comprising a core, an intermediate layer and a cover, and having a plurality of dimples formed on the outer surface of the cover.

Background Art

[0002] In December 2023, the R&A and USGA announced a decision to implement new rules that modify the test conditions for golf balls starting from January 2028. Specifically, the test conditions used for the conformity test of golf balls based on the standard overall distance (ODS) were updated, and regarding the speed to be tested, the head speed (HS) was increased from 54 m / s to 56 m / s. That is, while increasing the launch speed, other launch conditions were also modified. This change in the ODS test most affects golfers who generate the fastest ball speeds, and for the longest hitters, a decrease of 13 - 15 yards (12 - 14 m) is expected with a club using a driver. Also, the estimated impact on average PGA Tour and DP World Tour players is a decrease of 9 - 11 yards (8 - 10 m), and for average LPGA and LET players, a decrease of 5 - 7 yards (5 - 6 m). However, at this new test speed, the decrease in carry distance for most recreational golfers is minimal and is estimated to be 1 - 5 yards.

[0003] The development of golf balls suitable for the above announcement of the new ODS rules is desired. Therefore, it is desired to develop each component member such as the core, the intermediate layer, the cover, and the dimples and to explore the optimization of the combination thereof.

[0004] Conventionally, methods for adjusting the cross-sectional hardness of the core include appropriately adjusting the compounding components of the core rubber composition, the vulcanization temperature and time. For example, the following Patent Documents 1 - 27 provide a specific cross-sectional hardness inside the core by adjusting the selection and compounding amount of co-crosslinking agents and organic peroxides regarding the compounding components of the core rubber composition, and by compounding water, organic sulfur compounds, etc., as other components.

[0005] However, the golf balls described in these patent documents still had challenges in satisfying all the requirements of professional and advanced players: full shot distance, short game control, and resistance to cracking from repeated impacts.

[0006] Regarding dimples formed on the surface of the ball, the total volume of dimples formed downwards from the plane surrounded by the edges of the dimples is specified within a predetermined range to obtain a dimple volume occupancy rate VR, which suppresses distance in the high head speed (HS) range while obtaining superior distance in the low HS range. Examples of such golf balls have been proposed, as shown in Patent Documents 28 to 36 below.

[0007] However, with the golf ball proposed above, the distance a long hitter can hit with a driver (W#1) will decrease, and the desired distance for both long hitters and average hitters when hitting with irons will also be lost. Therefore, it is desirable for both long hitters and average hitters to prevent a decrease in distance when hitting with irons as much as possible. [Prior art documents] [Patent Documents]

[0008] [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

Patent Document 28

Patent Document 29

Patent Document 30

Patent Document 31

Patent Document 32

Patent Document 33

Patent Document 34

Patent Document 35

Patent Document 36

Summary of the Invention

Problems to be Solved by the Invention

[0009] The present invention has been made in view of the above circumstances. In the future, due to changes in the test conditions for the standard total carry distance (ODS) of golf balls, there is a possibility of changing to a rule that suppresses the carry distance of long hitters. Instead of simply reducing the carry distance, the carry distance under the hitting conditions of long hitters is reduced compared to the conventional level, but the reduction in the carry distance under the hitting conditions of golfers with lower clubhead speeds is suppressed. The purpose is to provide a multi-piece solid golf ball that has controllability for short games that can be used by professionals and advanced players, and further has good repeated hitting durability.

Means for Solving the Problems

[0010] The inventors of the present invention have conducted diligent studies to achieve the above objectives and have found that, in a multi-piece solid golf ball comprising a single-layer core, an intermediate layer, and a cover, with numerous dimples formed on the outer surface of the cover, the combination of a unique core hardness distribution and unique dimples allows for a golf ball conforming to rules that restrict the distance of long hitters. Even if the distance reduced is greater when a long hitter hits with a driver, the distance reduced when a golfer with a lower head speed hits the ball can be kept to a minimum, providing the controllability of a short game usable by professionals and advanced players, and furthermore, it offers good durability against repeated impacts. This led to the present invention. Specifically, in the present invention, regarding the hardness distribution of the core, not only the overall hardness distribution shape of the core, but also the hardness distribution shape from the midpoint between the core surface and the center to the core surface has been improved. In particular, the hardness distribution has been improved so that the hardness gradient in the part close to the core surface is gentler. As a specific method, when 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, the following two equations 0 ≤ (H62.5 - H50) < (H100 - H87.5) < (H87.5 - H75) < (H75 - H62.5) ≤ 7.0, and (H100-H50) / (H50-H0)≧2.7 The goal is to satisfy the above conditions. On the other hand, regarding the dimples, the goal is to adjust their volume occupancy rate (VR) to within the range of 0.75-0.89% so that the ball trajectory is relatively low.

[0011] Therefore, the present invention provides the following multi-piece solid golf ball. 1. A multi-piece solid golf ball comprising a core, an intermediate layer, and a cover, wherein numerous dimples are formed on the outer surface of the cover, and in the hardness distribution of the core, when 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 formulas 0 ≤ (H62.5 - H50) < (H100 - H87.5) < (H87.5 - H75) < (H75 - H62.5) ≤ 7.0, and (H100-H50) / (H50-H0)≧2.7 A multi-piece solid golf ball that satisfies the above conditions and is characterized in that the volume occupancy rate (VR) of the dimples is 0.75 to 0.89%. 2. When the ratio of the lift coefficient CL1 to the drag coefficient CD1 at a Reynolds number of 218,000 and a spin rate of 2,300 rpm is A1 (CL1 / CD1), and the ratio of the lift coefficient CL2 to the drag coefficient CD2 at a Reynolds number of 158,000 and a spin rate of 3,100 rpm is A2 (CL2 / CD2), the following two equations apply: 0.530 ≤ A1 ≤ 0.600, and 0.695 ≤ A2 A multi-piece solid golf ball as described in item 1 above that satisfies the requirements. 3. The following formula, (H100-H87.5) / (H87.5-H75)≦0.90 A multi-piece solid golf ball as described in 1 or 2 above, which satisfies the requirements. 4. 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 multi-piece solid golf ball as described in 1 or 2 above, where all values ​​are positive. 5. 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 multi-piece solid 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). 6. The multi-piece solid golf ball according to item 5, wherein the hindered phenol antioxidant, which is component (e) above, has a chemical structure having at least one methyl group in the ortho position. 7. The multi-piece solid golf ball according to item 5 above, wherein the hindered phenol antioxidant component (e) has two or more substituents having a thioether structure. 8. A multi-piece solid 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. 9. A multi-piece solid golf ball as described in 1 or 2 above, wherein when the core is subjected to an initial load of 98N (10kgf) and a final load of 1,275N (130kgf), the amount of deflection is A (mm), and when the golf ball is subjected to an initial load of 98N (10kgf) and a final load of 1,275N (130kgf), the amount of deflection is B (mm), and the value of A and B is less than 1.0 mm. 10. The relationship between the surface hardness of a sphere (intermediate layer coated sphere) in which the above core is covered with the above intermediate layer and the surface hardness of a 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 multi-piece solid golf ball as described in 1 or 2 above, which satisfies the requirements.

[0012] The term "long hitter" above refers to a user whose driver (W#1) head speed is approximately 50 m / s or higher, while the term "average hitter" above refers to a user whose driver (W#1) head speed is approximately 45 m / s or lower. [Effects of the Invention]

[0013] With the golf ball of the present invention, in response to the possibility that the rules may be changed in the future to restrict the distance of long hitters by changing the test conditions for the standard total distance (ODS) of golf balls, the present invention does not simply reduce the distance, but rather reduces the distance under the hitting conditions of long hitters compared to conventional balls, while limiting the reduction in distance under the hitting conditions of golfers with lower head speeds. Furthermore, as a golf ball for professionals and advanced players, it has good controllability in the short game and excellent durability against repeated impacts. [Brief explanation of the drawing]

[0014] [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 1-5 and Comparative Examples 1-3,8. [Figure 5] This graph shows the core hardness distribution for Comparative Examples 4-7. [Modes for carrying out the invention]

[0015] The present invention will be described in more detail below. The multi-piece solid golf ball of the present invention has a core, an intermediate layer, 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, a single-layer intermediate layer 2 covering the core 1, and a single-layer cover 3 covering the intermediate layer. This cover 3, excluding the paint layer, is the outermost layer in the layer structure of the golf ball. Each of the core and intermediate layers is formed as a single layer as shown in Figure 1, and a surrounding layer may also be provided between the core and the intermediate layer. Numerous dimples D are formed on the surface of the cover (outermost layer) 3 in order to achieve the aerodynamic characteristics targeted by the present invention. 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.

[0016] 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.

[0017] The diameter of the core is not particularly limited, but is preferably 37.0 mm or more, more preferably 38.0 mm or more, and even more preferably 38.3 mm or more. The upper limit is preferably 39.7 mm or less, more preferably 39.3 mm or less, and even more preferably 39.0 mm or less. If the core diameter 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 cause the ball to travel less than the target distance. On the other hand, if the core diameter is too large, the amount of spin during a full shot may increase, which may cause the ball to travel less than the target distance, especially when hitting with irons.

[0018] 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 3.05mm 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 amount of spin will increase too much, which may result in a loss of distance, especially when hitting with irons, and 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 will be too low, which may result in a loss of distance when hitting with a driver (W#1) by long hitters, and the feel may become too soft, and the durability against cracking when repeatedly hit may be poor.

[0019] 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.

[0020] 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.

[0021] 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 ball spin during full shots, which may prevent average hitters from achieving their desired distance when using a driver (W#1) or iron. On the other hand, if the above value is too high, the club may have poor crack resistance after repeated impacts, or the feel may become too hard.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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 core's rebound will be low, which may result in excessive distance when a long hitter hits a driver (W#1) or poor crack resistance when repeatedly hitting the ball. If this value is too high, the amount of ball spin will be increased, which may result in an inability to achieve the desired distance when an average hitter hits a driver (W#1) or an iron, or the feel may become too hard.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] The hardness difference 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 will increase, and the target distance may not be achieved, especially when an average hitter hits a driver (W#1) or an iron.

[0031] 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.

[0032] 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.

[0033] 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 hitting a full shot will increase, which may result in the inability to achieve the desired distance, especially when average hitters hit with a driver (W#1) and irons.

[0034] 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 target distance may not be achieved, especially when an average hitter hits a driver (W#1) or an iron. 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.

[0035] 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 a position 62.5% of the core radius when viewed from the core center.

[0036] 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 will increase, which may result in a loss of distance, especially when average hitters hit with a driver (W#1) and irons.

[0037] 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 will increase, which may result in a loss of distance, especially when average hitters hit with a driver (W#1) and irons.

[0038] 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 will increase, and the target distance may not be achieved, especially when average hitters hit with a driver (W#1) and irons.

[0039] 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 0.99 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 will increase, and the target distance may not be achieved, especially when average hitters hit with a driver (W#1) and irons.

[0040] 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 deteriorate. On the other hand, if this value is too low, the amount of spin on the ball when taking a full shot will increase, and the target distance may not be achieved, especially when average hitters hit with a driver (W#1) and irons.

[0041] The value of (H50-H12.5) in the above formula is preferably 1.3 or higher, more preferably 1.4 or higher, and even more preferably 1.5 or higher, with an upper limit of preferably 4.0 or lower, more preferably 3.5 or lower, and even more preferably 3.0 or lower. If this value deviates from the above range, the amount of spin on the ball when taking a full shot will increase, and the target distance may not be achieved, especially when an average hitter hits a driver (W#1) or an iron.

[0042] Furthermore, the value of (H100-H50) / (H50-H0) is 2.7 or greater, preferably 2.8 or greater, more preferably 2.9 or greater, and the upper limit is preferably 15.0 or less, more preferably 10.0 or less, and even more preferably 8.0 or less. 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 will increase, and the target distance may not be achieved, especially when an average hitter hits a driver (W#1) or an iron.

[0043] 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 will increase, and the target distance may not be achieved, especially when average hitters hit a driver (W#1) or an iron.

[0044] 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.

[0045] 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

[0046] The base rubber of component (a) above is not particularly limited, but polybutadiene is particularly preferred.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] The polybutadiene described above can be synthesized using rare earth element catalysts or group VIII metal compound catalysts.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] (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.

[0056] (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.

[0057] (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.

[0058] (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.

[0059] (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.

[0060] 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).

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] (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.

[0069] (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.

[0070] 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.

[0071] The hindered phenol antioxidant, which is component (e) above, is preferably represented by the following general formula (I). [ka]

[0072] In the above formula, x is an integer of 1 or more, and preferably x is an integer of 8 or more.

[0073] (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.

[0074] (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 (e) 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.

[0075] (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.

[0076] 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.

[0077] (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]

[0078] 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.

[0079] (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.

[0080] (g) Component is sulfur or an alkylphenol disulfide polymer having the following chemical structure. [ka]

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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."

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] Next, I will explain the middle class. The material hardness of the intermediate layer is not particularly limited, but in terms of Shore C hardness, it is preferably 92 or higher, more preferably 94 or higher, and even more preferably 95 or higher, with an upper limit of preferably 100 or less, more preferably 98 or less, and even more preferably 96 or less. In terms of Shore D hardness, it is preferably 62 or higher, more preferably 64 or higher, and even more preferably 66 or higher, with an upper limit of preferably 72 or less, more preferably 70 or less, and even more preferably 68 or less.

[0093] The surface hardness of a sphere with a core covered by an intermediate layer (intermediate layer-covered sphere) is preferably 93 or higher, more preferably 95 or higher, and even more preferably 97 or higher on the Shore C hardness scale, with an upper limit of preferably 100 or less, more preferably 99 or less, and even more preferably 98 or less. On the Shore D hardness scale, it is preferably 68 or higher, more preferably 70 or higher, and even more preferably 72 or higher, with an upper limit of preferably 78 or less, more preferably 76 or less, and even more preferably 74 or less.

[0094] If the material hardness and surface hardness of these intermediate layers are too soft compared to the above range, the amount of spin may be too high or the initial ball speed may be too low when hitting a full shot, resulting in a loss of distance. On the other hand, if the material hardness and surface hardness of the intermediate layers are too hard compared to the above range, the durability against cracking during repeated impacts may be poor, or the amount of spin may be too low during the short game.

[0095] 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, it is preferable that the thickness of the intermediate layer be thicker than the cover described later. Also, 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 with a full shot may not provide a good balance of appropriate hardness and rebound, which may not be perceived as a good feel by professionals or advanced players, or the crack resistance when repeatedly hit may be poor. On the other hand, if the above values ​​are too high, the feel of the ball hitting the club may diminish, and it may not feel good to professionals or advanced players.

[0096] The value obtained by subtracting the cover thickness (described later) from the intermediate layer thickness is preferably greater than 0 mm, 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 during a full shot may increase, the actual initial velocity may decrease, and the desired distance may not be achieved. On the other hand, if this value is too small, the crack resistance when repeatedly struck may be poor.

[0097] For the intermediate layer material, it is preferable to use ionomer resin as the main material. When using ionomer resin as the main material, it is desirable to use a mixture of zinc-neutralized ionomer resin and sodium-neutralized ionomer resin as the main material. The mixing ratio of zinc-neutralized type / sodium-neutralized type (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 may become too low, resulting in a loss of distance when hitting with a driver (W#1) and irons for average hitters. Furthermore, the crack resistance during repeated impacts at room temperature may be poor, as may the crack resistance at low temperatures (below freezing).

[0098] Furthermore, the ionomer resin material preferably contains a high acid content ionomer resin with an unsaturated carboxylic acid content (also called "acid content") of 16% by mass or more.

[0099] Furthermore, the content of 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, based on 100% by mass of the resin material, with an upper limit of preferably 100% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less. If the amount of the high-acid-content ionomer resin is too low, the amount of spin on the ball during a full shot may increase, and the distance may decrease when hitting with an iron.

[0100] 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.

[0101] The average particle size of the above-mentioned granular inorganic filler is not particularly limited, but is preferably 0.01 to 100 μm, and more preferably 0.1 to 10 μm. If the average particle size of the above-mentioned granular inorganic filler is too small or too large, the dispersibility during material preparation may deteriorate. The above-mentioned average particle size refers to the particle size measured by a particle size distribution analyzer when dispersed in an aqueous solution with a suitable dispersant.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] 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 will increase too much on full shots, and the target distance may not be achieved, especially when average hitters hit with a driver (W#1) and irons. On the other hand, if the material hardness and surface hardness are too hard, scratch resistance may be poor, and the amount of spin may be insufficient in the short game.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] The combined mass of component (I) and component (II) described above 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) described above are described in detail below.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] 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.).

[0115] 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.

[0116] 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).

[0117] 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.

[0118] 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.

[0119] 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 2.8mm or less. If the amount of deflection of the golf ball is too small, i.e., if it is too hard, the amount of spin on the ball will increase too much, which may reduce the distance when an average hitter hits a driver (W#1) or an iron, or the feel may become too hard. On the other hand, if the amount of deflection is too large, i.e., if the ball is too soft, the durability against cracking when repeatedly hit will be poor, and the actual initial ball speed may decrease, which may reduce the distance when a long hitter hits a driver (W#1).

[0120] [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 hit with a driver (W#1), especially by long hitters, will be low, resulting in insufficient distance, or the feel may be perceived as poor by professionals and advanced players with high head speeds, and the crack resistance when repeatedly hit may be poor. On the other hand, if this value is too small, the feel may be perceived as poor, and the crack resistance when repeatedly hit may be poor.

[0121] 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, especially when hit by a long hitter with a driver (W#1), will be low, resulting in insufficient distance, a poor feel for professionals and advanced players with high head 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.

[0122] [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 and increasing the amount of spin on the ball during a full shot, which may prevent the target distance from being achieved, especially when average hitters hit a driver (W#1) or an iron. On the other hand, if the above value is too large, the amount of spin on the ball during a full shot will increase, which may prevent the target distance from being achieved, especially when average hitters hit a driver (W#1) or an iron.

[0123] [Hardness relationship of each layer] The intermediate layer-coated sphere preferably has a higher surface hardness than the ball. The difference in surface hardness (surface hardness of the intermediate layer-coated 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 less, more preferably 12 or less, and even more preferably 10 or less. 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 less, more preferably 14 or less, and even more preferably 12 or less. If the above values ​​are small, the amount of spin when approaching may decrease, and spin control in shot games may deteriorate. On the other hand, if the above values ​​are large, and the large value is due to the material hardness of the intermediate layer, the crack resistance due to repeated impacts may deteriorate. 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, especially when average hitters hit with a driver (W#1) and irons.

[0124] 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 may increase on a full shot, and the desired distance may not be achieved. On the other hand, if the above value is too large, the cracking resistance when repeatedly struck may decrease, and the actual initial velocity of the ball may decrease, resulting in a particularly low distance when a long hitter hits with a driver (W#1).

[0125] 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.

[0126] [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.

[0127] 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 280 or more, preferably 300 or more, more preferably 310 or more, and as an upper limit, preferably 450 or less, more preferably 400 or less, and even more preferably 350 or less. If the number of dimples deviates from the above range, the distance of the driver (W#1) hit by an average hitter may decrease.

[0128] 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.

[0129] The dimple occupancy rate of the golf ball's surface, specifically the ratio (SR value) of the total dimple area defined by the plane edges surrounded by the edges of the dimples to the ball's surface area assuming no dimples exist, is preferably 75% or more, more preferably 80% or more, and even more preferably 84% or more. The upper limit is 90% or less, more preferably 88% or less, and even more preferably 86% or less. If this SR value deviates from the above range, the distance an average hitter will hit with a driver (W#1) may decrease, and the distance a long hitter will hit with a driver (W#1) may decrease too much.

[0130] The ratio (VR value) of the total dimple volume formed below the plane surrounded by the edges of the dimples to the ball volume assuming no dimples exist is 0.75% or more, preferably 0.78% or more, more preferably 0.80% or more, with an upper limit of 0.89% or less, more preferably 0.88% or less, and more preferably 0.86% or less. If this VR value is greater than the above range, the distance of a long hitter's driver (W#1) shot may drop too much, or an average hitter's driver (W#1) shot may not achieve the desired distance. In this case, the trajectory may be lower, making it difficult to achieve carry distance and making it difficult to clear valleys and water hazards. On the other hand, if the above value is too small, the distance of a long hitter's driver (W#1) shot may not drop, and the ball may fly too far, exceeding the standard distance of the new distance rules assumed by the R&A and USGA.

[0131] The value V0, obtained by dividing the spatial volume of the dimples beneath 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 0.35 or more, more preferably 0.38 or more, and even more preferably 0.40 or more, with an upper limit of 0.80 or less, more preferably 0.70 or less, and even more preferably 0.60 or less. If this V0 value deviates from the above range, the distance of the driver (W#1) hit by long hitters and average hitters may be lower than intended.

[0132] For the golf ball of the present invention, when the ratio of the lift coefficient CL1 to the drag coefficient CD1 at a Reynolds number of 218,000 and a spin rate of 2,300 rpm is CL1 / CD1, and the ratio of the lift coefficient CL2 to the drag coefficient CD2 at a Reynolds number of 158,000 and a spin rate of 3,100 rpm is CL2 / CD2, then the following two equations apply: 0.530 ≤ A1 ≤ 0.600, and 0.695 ≤ A2 The dimples are designed as appropriate to satisfy the requirements.

[0133] In this specification, the "lift coefficient (CL1, CL2) and drag coefficient (CD1, CD2)" are measured in accordance with the ITR (Indoor Test Range) defined by the USGA (United States Golf Association). The lift coefficient and drag coefficient can be adjusted by adjusting the configuration (arrangement, diameter, depth, volume, number, shape, etc.) of the golf ball's dimples. The lift coefficient and drag coefficient do not depend on the internal configuration of the golf ball. The Reynolds number (Re) is a dimensionless number used in the field of fluid dynamics. The Reynolds number (Re) is calculated by the following equation (1). Re = ρvL / μ (1) In equation (1) above, ρ represents the fluid density, v represents the average velocity of the object relative to the fluid flow, L represents the characteristic length, and μ represents the viscosity coefficient of the fluid.

[0134] In this invention, A1 is defined as the ratio CL1 / CD1 of the lift coefficient CL1 to the drag coefficient CD1 at a Reynolds number of 218,000 and a spin rate of 2,300 rpm, and A2 is defined as the ratio CL2 / CD2 of the lift coefficient CL2 to the drag coefficient CD2 at a Reynolds number of 158,000 and a spin rate of 3,100 rpm.

[0135] To explain the conditions under which the above-mentioned lift coefficient CL1 and drag coefficient CD1 are measured—a Reynolds number of 218,000 and a spin rate of 2,300 rpm—this high-speed condition corresponds to the conditions under which a long hitter hits a golf ball with a driver (W#1). This Reynolds number corresponds to the ball speed when a golf ball is hit with a head speed (HS) of 54 m / s, and a spin rate of 2,300 rpm is a typical spin condition for a player with a head speed (HS) of 54 m / s.

[0136] To explain the conditions under which the lift coefficient CL2 and drag coefficient CD2 are measured, namely a Reynolds number of 158,000 and a spin rate of 3,100 rpm, these low-speed conditions correspond to the conditions under which an average hitter hits a golf ball with a driver (W#1) at a head speed (HS) of 40 m / s. The Reynolds number corresponds to the ball speed when a golf ball is hit at a head speed (HS) of 40 m / s, and a spin rate of 3,100 rpm is a typical spin condition for a player with a head speed (HS) of 40 m / s.

[0137] The ratio of the lift coefficient CL1 to the drag coefficient CD1, i.e., the value of CL1 / CD1=A1, is preferably 0.530 or higher, more preferably 0.535 or higher, and even more preferably 0.540 or higher. The upper limit is preferably 0.600 or lower, more preferably 0.585 or lower, and even more preferably 0.570 or lower. If this value is too high, the effect of suppressing the distance when a long hitter hits with a driver (W#1) is insufficient, and the ball may travel too far. On the other hand, if the above value is too low, the actual distance may be too low compared to the intended distance.

[0138] The ratio of the lift coefficient CL2 to the drag coefficient CD2, i.e., the value of CL2 / CD2=A2, is preferably 0.695 or higher, more preferably 0.710 or higher, and even more preferably 0.722 or higher. The upper limit is preferably 0.815 or lower, more preferably 0.810 or lower, and even more preferably 0.800 or lower. If this value is too low, when hitting with a driver (W#1) at a head speed (HS) of 40 m / s, the carry distance may not be achieved, and the target total distance may not be obtained. On the other hand, if the above value is too high, when hitting with a driver (W#1) at a head speed (HS) of 40 m / s, the trajectory may balloon, and the target distance may not be obtained.

[0139] Furthermore, the multi-piece solid 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 does not 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]

[0140] 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.

[0141] [Examples 1-5, Comparative Examples 1-8] [Core formation] After preparing the rubber compositions for each of the Examples 1-5 and Comparative Examples 1-8 shown in Table 1, a solid core for each example was produced by vulcanizing and molding at the temperature and time shown in Table 1.

[0142] [Table 1]

[0143] 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.

[0144] [Formation of the intermediate layer and cover (outermost layer)] Next, in each of Examples 1-5 and Comparative Examples 1-8, an intermediate layer is formed by injection molding using an injection mold with the intermediate layer resin material No. 1, No. 2, or No. 3 shown in Table 2 around the core surface. Then, using another injection mold, a cover is formed by injection molding using the cover (outermost layer) resin material No. 4 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.

[0145] [Table 2]

[0146] The details of the ingredients listed in Table 2 are as follows. "Hymiran 1605", "Hymiran 1557", "Hymiran 1706", "AM7318" - Ionomers manufactured by Mitsui Dow Polychemicals. "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" is a product name "Pandex" manufactured by DIC Covestropolymer, an ether-type thermoplastic polyurethane with a material hardness (Shore D) of 47.

[0147] For each example and comparative example, the following dimples (1) to (5) are used. Each 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. Figure 3 shows the arrangement (pattern) of dimples (1) to (5). Figure 3(A) is a plan view of the dimples, and Figure 3(B) is a side view thereof.

[0148] [Table 3]

[0149] 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.

[0150] Furthermore, Table 4 below shows the lift coefficient CL1, drag coefficient CD1, and ratio CL1 / CD1=A1 for a ball with the above-mentioned dimples (1) to (5) formed on its cover surface at a Reynolds number of 218,000 and a spin rate of 2,300 rpm, and the lift coefficient CL2, drag coefficient CD2, and ratio CL2 / CD2=A2 for a Reynolds number of 158,000 and a spin rate of 3,100 rpm. These lift and drag coefficients are measured in accordance with the ITR (Indoor Test Range) defined by the USGA.

[0151] [Table 4]

[0152] 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 5 and 6.

[0153] [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.

[0154] [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.

[0155] [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.

[0156] [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 5. 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 5 are Shore C hardness values.

[0157] Furthermore, graphs of the core hardness distribution for Examples 1-5 and Comparative Examples 1-8 are shown in Figures 4 and 5.

[0158] [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℃.

[0159] [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℃.

[0160] [Table 5]

[0161] [Table 6]

[0162] 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 7.

[0163] Flight evaluation (W#1, HS54m / s) A golf swing robot will be fitted with a driver club and hit the ball at a head speed (HS) of 54 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 the results will be evaluated according to the following criteria. 〔Judgment criteria〕 ○...The total distance compared to Comparative Example 1 is greater than -17.0m and less than or equal to -10.0m. △ ··· The total distance compared to Comparative Example 1 is less than -17.0. × ··· The total distance compared to Comparative Example 1 is greater than -10.0m.

[0164] 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 -5.0m or more. △ ··· The total distance compared to Comparative Example 1 is -10.0m or more and less than -5.0m. × ··· The total distance compared to Comparative Example 1 is less than -10.0m.

[0165] 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 0m or more. △ ··· The total distance compared to Comparative Example 1 is -5.0m or more and less than 0m. × ··· The total distance compared to Comparative Example 1 is less than -5.0m.

[0166] 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 5200 rpm △ ··· Spin rate over 4700 rpm, under 5200 rpm × ··· Spin rate 4700 rpm or less

[0167] Repeated impact durability The durability of the golf balls was evaluated using the ADC Ball COR Durability Tester manufactured by Automated Design Corporation, USA. This test machine launches a golf ball using air pressure and then continuously impacts it 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 ball to break was measured, and the average value of the five fastest-breaking golf balls out of 10 measured golf balls was calculated. An index was calculated using the above average value from Example 2 as a baseline of 100, and the evaluation was performed according to the following criteria. 〔Judgment criteria〕 ◎ ··· Index is 120 or higher ○ ··· Index is 95 or higher, but less than 120 △ ··· Index is 70 or higher, but less than 95 × ··· Index is less than 70

[0168] [Table 7]

[0169] As shown in the results in Table 7, the golf balls of Comparative Examples 1 to 8 are inferior to the present invention (example) in the following respects. Comparative Example 1 has a dimple volume occupancy rate (VR) less than 0.75%. As a result, when struck with a driver (W#1) under high head speed conditions of 54 m / s, the distance is too great, and it does not meet the new ODS rule. Comparative Example 2 has a dimple volume occupancy rate (VR) less than 0.75%. As a result, when struck with a driver (W#1) under high head speed conditions of 54 m / s, the distance is too great, and it does not meet the new ODS rule. In Comparative Example 3, the core hardness distribution shows that (H87.5-H75) is greater than (H75-H62.5). As a result, it exhibits inferior resistance to repeated impacts compared to the example. Comparative Example 4 has a core hardness distribution where (H100-H87.5) is greater than (H87.5-H75), and (H100-H50) / (H50-H0) is less than 2.7. As a result, compared to the example, the amount of spin during a full iron shot is greater and the distance is inferior. In Comparative Example 5, the core hardness distribution shows that (H87.5-H75) is greater than (H75-H62.5), and (H62.5-H50) is greater than (H100-H87.5). As a result, it has inferior resistance to repeated impacts compared to the example. Comparative Example 6 has a core hardness distribution where the (H87.5-H75) value is greater than 7.0, and (H87.5-H75) is greater than (H75-H62.5). As a result, it has inferior repeated impact durability compared to the example. Comparative Example 7 has a core hardness distribution where 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 has inferior resistance to repeated impacts compared to the example. Comparative Example 8 has a dimple volume occupancy rate (VR) greater than 0.89%. As a result, the distance is too low when hitting with a driver (W#1) under high head speed conditions of 54 m / s, and the distance is also low under other hitting conditions.

Claims

1. A multi-piece solid golf ball comprising a core, an intermediate layer, and a cover, wherein numerous dimples are formed on the outer surface of the cover, and in the hardness distribution of the core, when 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 formulas 0 ≤ (H62.5 - H50) < (H100 - H87.5) < (H87.5 - H75) < (H75 - H62.5) ≤ 7.0, and (H100-H50) / (H50-H0)≧2.7 A multi-piece solid golf ball that satisfies the above conditions and is characterized in that the volume occupancy rate VR of the dimples is 0.75 to 0.89%.

2. When the ratio of the lift coefficient CL1 to the drag coefficient CD1 at a Reynolds number of 218,000 and a spin rate of 2,300 rpm is CL1 / CD1, let A1 be the ratio of the lift coefficient CL2 to the drag coefficient CD2 at a Reynolds number of 158,000 and a spin rate of 3,100 rpm, let A2 be the ratio of the lift coefficient CL2 to the drag coefficient CD2, then the following two equations apply: 0.530 ≤ A1 ≤ 0.600, and 0.695 ≤ A2 A multi-piece solid golf ball according to claim 1 that satisfies the requirements.

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

4. 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 multi-piece solid golf ball according to claim 1 or 2, wherein all of the values ​​are positive.

5. 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 multi-piece solid golf ball according to claim 1 or 2, 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).

6. The multi-piece solid golf ball according to claim 5, wherein the hindered phenol antioxidant, which is component (e) above, has a chemical structure having at least one methyl group at the ortho position.

7. The multi-piece solid golf ball according to claim 5, wherein the hindered phenol antioxidant component (e) has two or more substituents having a thioether structure.

8. The multi-piece solid golf ball according to claim 1 or 2, wherein the deflection of the core from an initial load of 98 N (10 kgf) to a final load of 1,275 N (130 kgf) is 3.8 mm or less.

9. A multi-piece solid 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.

10. The relationship between the surface hardness of a sphere (intermediate layer coated sphere) in which the above core is covered with the above intermediate layer and the surface hardness of a 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 multi-piece solid golf ball according to claim 1 or 2 that satisfies the requirements.

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