Multi-piece solid golf ball

Abstract

The invention provides a multi-piece solid golf ball having a solid core, an inner cover layer and an outer cover layer, which outer cover layer has a plurality of dimples on a surface thereof. In the golf ball, the hardness relationship between the inner cover layer and the outer cover layer, the ratio of deflection between the solid core and a sphere composed of the solid core encased by the inner cover layer, and the dimple conditions are all optimized. This multi-piece solid golf ball is able to substantially reduce the distance traveled by the ball when struck at a high head speed, while at the same time holding down the decrease in distance when struck at a low head speed.

1 . A multi-piece solid golf ball comprising a solid core, an inner cover layer and an outer cover layer, which outer cover layer has a plurality of dimples on a surface thereof, wherein the value obtained by subtracting a material hardness of the outer cover layer from a material hardness of the inner cover layer, in terms of Shore D hardness, is greater than −5 and less than +5; the ratio of deflection by a sphere composed of the solid core encased by the inner cover layer (inner cover layer-encased sphere) when compressed under a final load of 1,275 N (130 kgf) from an initial load state of 98 N (10 kgf) to deflection by 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), which ratio is represented as (inner cover layer-encased sphere deflection)/(solid core deflection), is from 0.85 to 0.98; the dimples number at least 250 but not more than 500, have a surface coverage (SR) of at least 70% and a volume ratio (VR) of at least 1.0%, are of at least three types of mutually differing dimple diameter (DM) and/or dimple depth (DP), and have an average depth of at least about 0.18 mm and a diameter-to-depth ratio (DM/DP) of not more than about 23; and the ball has a coefficient of lift CL at a Reynolds number of 70,000 and a spin rate of 2,000 rpm which is maintained at 60% or more of the coefficient of lift CL at a Reynolds number of 80,000 and a spin rate of 2,000 rpm. 
     
     
         2 . The multi-piece solid golf ball of  claim 1  wherein, letting Da represent a dimple having a diameter of at least 3.7 mm and Db represent a dimple having a diameter of less than 3.7 mm, the ratio (total number of Db)/(total number of Da) has a value of at least about 0.005 but not more than about 1. 
     
     
         3 . The multi-piece solid golf ball of  claim 2 , wherein the dimples Da having a diameter of at least 3.7 mm account for at least about 75% of the total dimple volume. 
     
     
         4 . The multi-piece solid golf ball of  claim 1 , wherein the material hardness of the inner cover layer, in terms of Shore D hardness, is from 45 to 65. 
     
     
         5 . The multi-piece solid golf ball of  claim 1 , wherein the material hardness of the outer cover layer, in terms of Shore D hardness, is from 45 to 65. 
     
     
         6 . The multi-piece solid golf ball of  claim 1 , wherein the value obtained by subtracting the material hardness of the outer cover layer from the material hardness of the inner cover layer, in terms of Shore D hardness, is within ±4. 
     
     
         7 . The multi-piece solid golf ball of  claim 1 , wherein the number of dimple types of mutually differing diameter DM and/or depth DP is from 3 to 14. 
     
     
         8 . The multi-piece solid golf ball of  claim 1 , wherein the value obtained by adding a core surface hardness to a core center hardness (core center hardness+core surface hardness) and the value obtained by adding the outer cover layer material hardness to the inner cover layer material hardness (inner cover layer material hardness+outer cover layer material hardness) satisfy the relationship:
   core center hardness+core surface hardness<inner cover layer material hardness+outer cover layer material hardness.   
     
     
         9 . The multi-piece solid golf ball of  claim 1 , wherein the value obtained by subtracting the inner cover layer material hardness from a core surface hardness, in terms of Shore D hardness, is greater than −10 and less than +10. 
     
     
         10 . The multi-piece solid golf ball of  claim 1 , wherein the value obtained by subtracting the inner cover layer material hardness from a core surface hardness, in terms of Shore D hardness, is within ±5. 
     
     
         11 . The multi-piece solid golf ball of  claim 1 , wherein the value obtained by subtracting the outer cover layer material hardness from a core surface hardness, in terms of Shore D hardness, is greater than −10 and less than +10. 
     
     
         12 . The multi-piece solid golf ball of  claim 1 , wherein the value obtained by subtracting the outer cover layer material hardness from a core surface hardness, in terms of Shore D hardness, is within ±5. 
     
     
         13 . The multi-piece solid golf ball of  claim 1 , wherein the value obtained by subtracting a core center hardness from a core surface hardness (core surface hardness−core center hardness) and a value obtained by subtracting the outer cover layer material hardness from the inner cover layer material hardness (inner cover layer material hardness−outer cover layer material hardness) satisfy the relationship:
   core surface hardness−core center hardness>inner cover layer material hardness−outer cover layer material hardness.
 
 
     
     
         14 . The multi-piece solid golf ball of  claim 1 , wherein the solid core is a single layer. 
     
     
         15 . The multi-piece solid golf ball of  claim 1 , wherein the ratio of deflection by the sphere composed of the solid core encased by the inner cover layer (inner cover layer-encased sphere) when compressed under a final load of 1,275 N (130 kgf) from an initial load state of 98 N (10 kgf) to deflection by 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), which ratio is represented as (inner cover layer-encased sphere deflection)/(solid core deflection), is from 0.88 to 0.94. 
     
     
         16 . The multi-piece solid golf ball of  claim 1 , wherein the ratio of deflection by the sphere composed of the solid core encased by the inner cover layer (inner cover layer-encased sphere) when compressed under a final load of 1,275 N (130 kgf) from an initial load state of 98 N (10 kgf) to deflection by the ball when compressed under a final load of 1,275 N (130 kgf) from an initial load state of 98 N (10 kgf), which ratio is represented as (inner cover layer-encased sphere deflection/ball deflection), is from 0.74 to 0.80. 
     
     
         17 . The multi-piece solid golf ball of  claim 1  wherein dimples Da of a diameter of at least 3.7 mm have an average diameter of at least 3.7 mm but not more than 6 mm and dimples of a diameter of less than 3.7 mm have an average diameter of at least 1 mm m but less than 3.7 mm. 
     
     
         18 . The multi-piece solid golf ball of  claim 1 , wherein dimples Da of a diameter of at least 3.7 mm have an average depth of from 0.05 to 0.5 mm, and dimples Db of a diameter of less than 3.7 mm have an average depth of from 0.05 to 0.3 mm. 
     
     
         19 . The multi-piece solid golf ball of  claim 1 , wherein dimples Da of a diameter of at least 3.7 mm have an average volume of from 0.8 to 3.0 mm 3 , and dimples Db of a diameter of less than 3.7 mm have an average volume of from 0.2 to 1.5 mm 3 . 
     
     
         20 . The multi-piece solid golf ball of  claim 1 , wherein dimples Da of a diameter of at least 3.7 mm have an average diameter to average depth ratio Dm/Dp of from 7 to 25. 
     
     
         21 . The multi-piece solid golf ball of  claim 1 , wherein dimples Db of a diameter of less than 3.7 mm have an average diameter to average depth ratio Dm/Dp of from 10 to 30. 
     
     
         22 . The multi-piece solid golf ball of  claim 1 , wherein the cover is formed of a material comprising:
 (A) a thermoplastic polyurethane material, and   (B) an isocyanate mixture obtained by dispersing (B-1) an isocyanate compound having as functional groups at least two isocyanate groups per molecule in (B-2) a thermoplastic resin (B-2) that is substantially non-reactive with isocyanate.   
     
     
         23 . The multi-piece solid golf ball of  claim 1 , wherein the cover is formed of a material comprising:
 (D) a thermoplastic polyurethane, and   (E) a polyisocyanate compound.