Multi-piece solid golf ball

Abstract

A multi-piece solid golf ball has a core, at least one intermediate layer encasing the core, and a cover of at least one layer encasing the intermediate layer. The core is formed of a base rubber, and the intermediate layer and cover are each formed of a resin material. The intermediate layer has a thickness (a) and the cover has a thickness (b) such that the ratio a/b is from 0.7 to 1.9, and the core has a diameter (c) such that the ratio c/a with the intermediate layer thickness (a) is from 23 to 38. The intermediate layer has a material hardness (Shore D) of from 42 to 76, and the cover has a material hardness (Shore D) of from 41 to 69. The ball satisfies the following relationship: cover material hardness<intermediate layer material hardness>core surface hardness, and wherein a Shore D hardness at the core surface minus a Shore D hardness at the core center is not more than 17 units. This golf ball has an improved flight performance and a good, solid feel on impact.

1 . A multi-piece solid golf ball comprising a core, at least one intermediate layer encasing the core, and a cover of at least one layer encasing the intermediate layer, wherein the core is formed of a base rubber, the intermediate layer and cover are each formed of a resin material, the intermediate layer has a thickness (a) and the cover has a thickness (b) such that the ratio a/b is from 0.7 to 1.9, the core has a diameter (c) such that the ratio c/a with the intermediate layer thickness (a) is from 23 to 38, the intermediate layer has a material hardness (Shore D) of from 42 to 76, the cover has a material hardness (Shore D) of from 41 to 69, and the ball satisfies the following relationship:
 cover material hardness<intermediate layer material hardness>core surface hardness, and wherein a Shore D hardness at the core surface minus a Shore D hardness at the core center is not more than 17 units.   
     
     
         2 . The multi-piece solid golf ball of  claim 1  wherein, letting the ball deflection (mm) when compressed under a final load of 490 N (50 kgf) from an initial load state of 98 N (10 kgf) be A and letting the ball deflection (mm) when compressed under a final load of 5,880 N (600 kgf) from an initial load state of 98 N (10 kgf) be B, the value of B/A×100 is from 830 to 930. 
     
     
         3 . The multi-piece solid golf ball of  claim 1 , wherein the ball deflection B is from 7.0 to 10.0 mm, and the core deflection when compressed under a final load of 1,275 N (130 kgf) from an initial load state of 98 N (10 kgf) is from 2.1 to 4.1 mm. 
     
     
         4 . The multi-piece solid golf ball of  claim 1 , wherein the resin material of the cover is formed by injection molding a single resin blend composed primarily of (A) a thermoplastic polyurethane and (B) a polyisocyanate compound, which resin blend includes a polyisocyanate compound in at least some portion of which all the isocyanate groups on the molecule remain in an unreacted state. 
     
     
         5 . The multi-piece solid golf ball of  claim 1 , wherein a plurality of dimples are formed on a surface of the ball, the total number of dimples is from 250 to 350, the dimples have a surface coverage (SR) of at least 75%, and the ball, when hit, has a coefficient of lift CL at a Reynolds number of 70,000 and a spin rate of 2,000 rpm which is at least 60% of the coefficient of lift CL at a Reynolds number of 80,000 and a spin rate of 2,000 rpm. 
     
     
         6 . The multi-piece solid golf ball of  claim 5  which uses at least five types of dimples of differing diameter and/or depth, and which includes from 6 to 30 small dimples having a diameter of 3.0 mm or less.