Multi-piece solid golf ball

Abstract

The invention provides a multi-piece solid golf ball having a solid core encased by a cover of one, two or more layers, the solid core including a spherical first layer, a second layer encasing the first layer and a third layer encasing the second layer. The first layer has a diameter of from 3 to 24 mm, and the third layer is formed of a rubber composition composed primarily of polybutadiene rubber. The ball has specific relationships between the cross-sectional hardness at the core center on a cut face when the solid core has been cut in half and the respective hardnesses of the first layer 1 mm inside an interface between the first layer and the second layer, the second layer 1 mm outside the interface between the first layer and the second layer, the second layer 1 mm inside an interface between the second layer and the third layer, the third layer 1 mm outside the interface between the second layer and the third layer, and the surface of the third layer. Such a golf ball has both a reduced spin rate and a good initial velocity on shots, particularly when struck in a high head-speed range, and thus is able to achieve an increased distance, in addition to which it is also capable of having a good feel on impact.

1 . A multi-piece solid golf ball comprising a solid core encased by a cover of one, two or more layers, the solid core comprising a spherical first layer, a second layer encasing the first layer and a third layer encasing the second layer, wherein the first layer has a diameter of from 3 to 24 mm; the third layer is formed of a rubber composition composed primarily of polybutadiene rubber; and, letting (a) represent the cross-sectional hardness at a center of the core on a cut face when the solid core has been cut in half, (b) represent the cross-sectional hardness, expressed as the JIS-C hardness, of the first layer 1 mm inside an interface between the first layer and the second layer, (c) represent the cross-sectional hardness, expressed as the JIS-C hardness, of the second layer 1 mm outside the interface between the first layer and the second layer, (d) represent the cross-sectional hardness, expressed as the JIS-C hardness, of the second layer 1 mm inside an interface between the second layer and the third layer, (e) represent the cross-sectional hardness, expressed as the JIS-C hardness, of the third layer 1 mm outside the interface between the second layer and the third layer, and (f) represent the surface hardness, expressed as the JIS-C hardness, of the third layer:
 the value (b)−(c) is in a range of from 0 to 40, the value (e)−(d) is in a range of from 0 to 40, and the value (a)+(b)+(c)+(d)+(e)+(f) is in a range of from 380 to 460.   
     
     
         2 . The multi-piece solid golf ball of  claim 1 , wherein the value (f)−(a) in the solid core is in a range of from −10 to 20. 
     
     
         3 . The multi-piece solid golf ball of  claim 1 , wherein the first layer is formed of a rubber composition composed primarily of polybutadiene rubber. 
     
     
         4 . The multi-piece solid golf ball of  claim 1 , wherein the cross-sectional hardness (a) of the solid core, expressed as the JIS-C hardness, is in a range of from 60 to 95. 
     
     
         5 . The multi-piece solid golf ball of  claim 1 , wherein the second layer is formed of a rubber composition composed primarily of polybutadiene rubber. 
     
     
         6 . The multi-piece solid golf ball of  claim 1 , wherein a sphere composed of the first layer encased by the second layer (second layer-covered sphere) has a diameter of from 20 to 33 mm. 
     
     
         7 . The multi-piece solid golf ball of  claim 1 , wherein the diameter ratio between the first layer and the second layer-covered sphere (first layer diameter/second layer-covered sphere diameter) is from 0.20 to 0.50. 
     
     
         8 . The multi-piece solid golf ball of  claim 1 , wherein the volume ratio between the second layer and the solid core (second layer volume/solid core volume) is from 0.10 to 0.50. 
     
     
         9 . The multi-piece solid golf ball of  claim 1 , wherein the ratio between the deflection of the second layer-covered sphere when compressed under a final load of 1,275 N (130 kgf) from an initial load state of 98 N (10 kgf) to the deflection of the solid core when compressed under a final load of 1,275 N (130 kgf) from an initial load state of 98 N (10 kgf) (second layer-covered sphere deflection/solid core deflection) is from 1.50 to 1.80. 
     
     
         10 . The multi-piece solid golf ball of  claim 1 , wherein the ratio between the deflection of the solid core when compressed under a final load of 1,275 N (130 kgf) from an initial load state of 98 N (10 kgf) to the deflection of the ball when compressed under a final load of 1,275 N (130 kgf) from an initial load state of 98 N (10 kgf) (solid core deflection/ball deflection) is from 1.20 to 1.40. 
     
     
         11 . The multi-piece solid golf ball of  claim 1 , wherein the ratio between the deflection of the ball when compressed under a final load of 5,880 N (600 kgf) from an initial load state of 98 N (10 kgf) and the deflection of the ball when compressed under a final load of 1,275 N (130 kgf) from an initial load state of 98 N (10 kgf) (600 kgf deflection/130 kgf deflection) is from 3.50 to 3.80.