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 inner cover layer has a thickness of from 0.8 to 3.0 mm and a material hardness (Shore D) of from 50 to 80, the outer cover layer has a material hardness (Shore D) of from 35 to 60, and the material hardness (Shore D) of the inner cover layer is higher than the material hardness (Shore D) of the outer cover layer. 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 the inner cover layer has a thickness of from 0.8 to 3.0 mm and a material hardness (Shore D) of from 50 to 80, the outer cover layer has a material hardness (Shore D) of from 35 to 60, and the material hardness (Shore D) of the inner cover layer is higher than the material hardness (Shore D) of the outer cover layer; 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 outer cover layer has a thickness of from 0.5 to 3.0 mm. 
     
     
         5 . 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 at least 5 but not more than 45.