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. The value obtained by subtracting a material hardness (Shore D) of the outer cover layer from a material hardness (Shore D) of the inner cover layer is greater than −5 and less than +5. The dimples number at least 250 and 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. 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. This multi-piece solid golf ball is able to substantially reduce the distance traveled by the ball when struck at a high HS, while at the same time holding down the reduction in distance when struck at a low HS.

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 a value obtained by subtracting a material hardness (Shore D) of the outer cover layer from a material hardness (Shore D) of the inner cover layer is greater than −5 and less than +5; 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. 
     
     
         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) is at least about 0.005 but not more than about 1. 
     
     
         3 . The multi-piece solid golf ball of  claim 2 , wherein dimples Da 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 (Shore D) of the inner cover layer is from 45 to 65. 
     
     
         5 . The multi-piece solid golf ball of  claim 1 , wherein the material hardness (Shore D) of the outer cover layer is from 45 to 65. 
     
     
         6 . The multi-piece solid golf ball of  claim 1 , wherein the value obtained by subtracting the material hardness (Shore D) of the outer cover layer from the material hardness (Shore D) of the inner cover layer is within ±4.