Multi-piece solid golf ball
In a multi-piece solid golf ball having a core formed of a rubber composition, an intermediate layer formed of a polyurethane material and a cover, the ball satisfies the following condition: surface hardness of ball≤surface hardness of intermediate layer-encased sphere. When the ball is struck with a driver at a head speed of 40 m/s, the sum of the time t 1 required from contact initiation between the driver and ball for deformation of the ball to reach a maximum value and the time t 2 required from the state of maximum ball deformation for the ball and driver clubface to separate is at least 685 microseconds, and the ratio t 2 /t 1 is at least 1.35, and the core has a specific hardness profile. This ball has an excellent flight performance when hit by low or moderate head-speed golfers, is receptive to spin on approach shots and has a good, soft feel at impact.
1. A multi-piece solid golf ball comprising a core, an intermediate layer and a cover, wherein the core is formed of a rubber composition, the cover is formed primarily of a polyurethane material, the ball has a surface hardness and the sphere obtained by encasing the core with the intermediate layer (intermediate layer-encased sphere) has a surface hardness which together satisfy the following condition
surface hardness (Shore C hardness) of ball≤surface hardness (Shore C hardness) of intermediate layer-encased sphere,
and in an impact test carried out by striking the ball with a driver at a head speed of 40 m/s, the sum t 1 +t 2 of the time t 1 required from contact initiation between the driver and the ball for deformation of the ball to reach a maximum value and the time t 2 required from the state of maximum ball deformation for the ball and driver clubface to separate is at least 685 microseconds, and the ratio t 2 /t 1 is at least 1.35, and wherein the core has a hardness profile in which, letting Cc be the Shore C hardness at the core center, Cs be the Shore C hardness at a surface of the core, C M be the Shore C hardness at a midpoint M between the center and surface of the core, C M+2.5 , C M+5.0 and C M+7.5 be the respective Shore C hardnesses at positions 2.5 mm, 5.0 mm and 7.5 mm from the midpoint M toward the core surface side and C M−2.5 , C M−5.0 and C M−7.5 be the respective Shore C hardnesses at positions 2.5 mm, 5.0 mm and 7.5 mm from the midpoint M toward the core center side, the following surface areas A to F:
surface area A: ½×2.5×( C M−5.0 −C M−7.5 )
surface area B: ½×2.5×( C M−2.5 −C M−5.0 )
surface area C: ½×2.5×( C M −C M−2.5 )
surface area D: ½×2.5×( C M+2.5 −C M )
surface area E: ½×2.5×( C M+5 −C M+2.5 )
surface area F: ½×2.5×( C M+7.5 −C M+5 )
satisfy the condition
(surface area D +surface area E +surface area F )−(surface area A +surface area B +surface area C )>0.
2. The golf ball of claim 1 , wherein the ball has a deflection of at least 3.5 mm when compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf).
3. The golf ball of claim 1 , wherein the core has a center hardness Cc and a surface hardness Cs such that the difference therebetween (Cs−Cc) on the Shore C hardness scale is at least 20.
4. The golf ball of claim 1 , wherein surface areas A to F in the core hardness profile satisfy the condition
(surface area D +surface area E )−(surface area A +surface area B +surface area C )≥0.
5. The golf ball of claim 1 , wherein surface areas A to F in the core hardness profile satisfy the condition
0<[(surface area D +surface area E +surface area F )−(surface area A +surface area B +surface area C )]/( Cs−Cc )≤0.60.
6. The golf ball of claim 1 , wherein the cover has a surface on which a coating layer is formed, which coating layer has a Shore C hardness of from 40 to 80.
7. The golf ball of claim 6 , wherein the value obtained by subtracting the Shore C hardness of the coating layer from a Shore C material hardness of the cover is at least −20 and not more than +30.
8. The golf ball of claim 1 wherein, letting A be the deflection of the core in millimeters when compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) and B be the deflection of the ball in millimeters when compressed under a final load of 130 kgf from an initial load of 10 kgf, the ratio B/A is at least 0.60 and not more than 0.81.