Golf ball

Abstract

The invention provides a golf ball endowed with an improved distance and durability. The ball has a core and a cover, the core being formed of a rubber composition containing a base rubber, a co-crosslinking agent, a crosslinking initiator and a metal oxide. The co-crosslinking agent is methacrylic acid. The core has a hardness profile in which, letting (A) be the JIS-C hardness at the core surface, (B) be the JIS-C hardness at a position 2 mm in from the surface toward the center of the core, (C) be the JIS-C hardness at a position 5 mm in from the surface toward the center of the core, (D) be the JIS-C hardness at a position 10 mm in from the surface toward the center of the core, (E) be the JIS-C hardness at a position 15 mm in from the surface toward the center of the core, and (F) be the JIS-C hardness at the center of the core, (A) to (F) have specific hardnesses.

1 . A golf ball comprising a core and a cover, wherein the core is formed of a rubber composition comprising a base rubber, a co-crosslinking agent, a crosslinking initiator and a metal oxide, the co-crosslinking agent being methacrylic acid; wherein the core has a hardness profile in which, letting (A) be the JIS-C hardness at a surface of the core, (B) be the JIS-C hardness at a position 2 mm in from the surface toward a center of the core, (C) be the JIS-C hardness at a position 5 mm in from the surface toward the center of the core, (D) be the JIS-C hardness at a position 10 mm in from the surface toward the center of the core, (E) be the JIS-C hardness at a position 15 mm in from the surface toward the center of the core, and (F) be the JIS-C hardness at the center of the core: (A) is from 75 to 95, (B) is from 70 to 90, (C) is from 68 to 88, (D) is from 65 to 80, (E) is from 58 to 73, (F) is from 50 to 65, the hardness relationship (A)>(B)≧(C)>(D)>(E)>(F) is satisfied, the value (A)-(F) is at least 20, the core is formed in such a way that (A) has the highest hardness value among (A) to (F), and the value (A)-(C) is from 3 to 15; and wherein the core has a specific gravity of from 1.05 to 1.2. 
     
     
         2 . The golf ball of  claim 1 , wherein the crosslinking initiator is included in an amount of from 1.2 to 5 parts by weight per 100 parts by weight of the base rubber. 
     
     
         3 . The golf ball of  claim 1 , wherein the rubber composition further includes a fatty acid metal salt. 
     
     
         4 . The golf ball of  claim 3 , wherein the fatty acid metal salt is zinc stearate. 
     
     
         5 . The golf ball of  claim 3 , wherein the fatty acid metal salt is included in an amount of from 0.1 to 5 parts by weight per 100 parts by weight of the base rubber. 
     
     
         6 . The golf ball of  claim 1 , wherein the cover is formed of a resin material which has a breaking strength of from 20 to 80 MPa and an elongation of from 150 to 600%. 
     
     
         7 . The golf ball of  claim 1 , wherein the metal oxide in the rubber composition is zinc oxide. 
     
     
         8 . The golf ball of  claim 1 , wherein the core has a deflection (CH), when compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf), of from 2.0 to 7.0 mm.