Golf ball

Abstract

The invention provides a golf ball having a core and a cover of at least one layer. The cover includes an outermost layer and at least one intermediate layer interposed between the outermost layer and the core. The core has a cross-sectional hardness which, letting R (mm) be the radius of the core, A be the JIS-C hardness at the center of the core, B be the JIS-C hardness at a position R/3 mm from the core center, C be the JIS-C hardness at a position R/1.8 mm from the core center, D be the JIS-C hardness at a position R/1.5 mm from the core center, and E be the JIS-C hardness at the surface of the core, satisfies formulas (1) B−A<D−B, (2) C−A≦8, and (3) E−B≧15. The intermediate layer and the outermost layer have a hardness relationship therebetween which satisfies the formula “material hardness of intermediate layer<material hardness of outermost layer.”

1 . A golf ball comprising a core and a cover of at least one layer, wherein the cover comprises an outermost layer and at least one intermediate layer interposed between the outermost layer and the core; the core has a cross-sectional hardness which, letting R (mm) be a radius of the core, A be a JIS-C hardness at a center of the core, B be a JIS-C hardness at a position R/3 mm from the core center, C be a JIS-C hardness at a position R/1.8 mm from the core center, D be a JIS-C hardness at a position R/1.5 mm from the core center, and E be a JIS-C hardness at a surface of the core, satisfies formulas (1) to (3) below:
     B−A<D−B   (1)
       C−A≦ 8  (2)
       E−B≧ 15; and  (3)
   
       the intermediate layer and the outermost layer have a hardness relationship therebetween which satisfies the following formula:
   material hardness of intermediate layer<material hardness of outermost layer. 
 
     
     
         2 . The golf ball of  claim 1 , wherein at least one intermediate layer is formed of a material obtained by blending:
 an ionomer resin component comprising (a) an olefin-unsaturated carboxylic acid random copolymer and/or a metal ion neutralization product of an olefin-unsaturated carboxylic acid random copolymer mixed with (b) an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester random terpolymer and/or a metal ion neutralization product of an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester random terpolymer in a weight ratio between 100:0 and 0:100, and   (e) a non-ionomeric thermoplastic elastomer in a weight ratio of from 100:0 to 50:50.   
     
     
         3 . The golf ball of  claim 1 , wherein at least one intermediate layer is formed of a material obtained by blending as essential ingredients:
 100 parts by weight of a resin component composed of, in admixture,
 a base resin of (a) an olefin-unsaturated carboxylic acid random copolymer and/or a metal ion neutralization product of an olefin-unsaturated carboxylic acid random copolymer mixed with (b) an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester random terpolymer and/or a metal ion neutralization product of an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester random terpolymer in a weight ratio between 100:0 and 0:100, and 
 (e) a non-ionomeric thermoplastic elastomer in a weight ratio between 100:0 and 50:50; 
   (c) from 5 to 120 parts by weight of a fatty acid and/or fatty acid derivative having a molecular weight of from 228 to 1500; and   (d) from 0.1 to 17 parts by weight of a basic inorganic metal compound capable of neutralizing un-neutralized acid groups in the base resin and component (c).   
     
     
         4 . The golf ball of  claim 1 , wherein the ball has a deflection, when compressed under a final load of 5,880 N (600 kgf) from an initial load state of 98 N (10 kgf), of from 10 to 13 mm. 
     
     
         5 . The golf ball of  claim 1 , wherein the core is formed of a rubber composition which includes an organic peroxide having a one-minute half-life temperature of from about 165° C. to about 185° C. and sulfur. 
     
     
         6 . The golf ball of  claim 1 , wherein the ball has, at a surface of a sphere composed of the core encased by the intermediate layer, a JIS-C hardness of not more than 90. 
     
     
         7 . The golf ball of  claim 1 , wherein the outermost layer of the cover includes a base resin comprising an ionomer having a material hardness (Shore D) of from 50 to 70. 
     
     
         8 . The golf ball of  claim 1 , wherein the core has a diameter of from 32 to 41 mm. 
     
     
         9 . The golf ball of  claim 1 , wherein the core is composed of a single layer.