Golf ball

Abstract

A golf ball 2 includes a core 4 , amid layer 6 , and a cover 10 . The core 4 includes a center 16 , a first envelope layer 18 , and a second envelope layer 20 . The first envelope layer 18 is formed by a first rubber composition being crosslinked. The second envelope layer 20 is formed by a second rubber composition being crosslinked. The first rubber composition and/or the second rubber composition include: a base rubber; a co-crosslinking agent; a crosslinking initiator; and an acid and/or a salt. The co-crosslinking agent is (1) an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms; and/or (2) a metal salt of an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms.

What is claimed is: 
     
         1 . A golf ball comprising a core, a mid layer positioned outside the core, and a cover positioned outside the mid layer, wherein
 the core comprises a center, a first envelope layer positioned outside the center, and a second envelope layer positioned outside the first envelope layer,   the first envelope layer is formed by a first rubber composition being crosslinked,   the second envelope layer is formed by a second rubber composition being crosslinked,   the first rubber composition and/or the second rubber composition include:
 (a) a base rubber; 
 (b) a co-crosslinking agent; 
 (c) a crosslinking initiator; and 
 (d) an acid and/or a salt, and 
   the co-crosslinking agent (b) is:
 (b-1) an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms; and/or 
 (b-2) a metal salt of an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms. 
   
     
     
         2 . The golf ball according to  claim 1 , wherein an amount of the acid and/or the salt (d) is equal to or greater than 0.5 parts by weight but equal to or less than 45 parts by weight, per 100 parts by weight of the base rubber (a). 
     
     
         3 . The golf ball according to  claim 1 , wherein the acid and/or the salt (d) is a carboxylic acid and/or a salt thereof (d-1). 
     
     
         4 . The golf ball according to  claim 3 , wherein a carbon number of a carboxylic acid component of the carboxylic acid and/or the salt thereof (d-1) is equal to or greater than 1 but equal to or less than 30. 
     
     
         5 . The golf ball according to  claim 3 , wherein the carboxylic acid and/or the salt thereof (d-1) is a fatty acid and/or a salt thereof. 
     
     
         6 . The golf ball according to  claim 3 , wherein the carboxylic acid and/or the salt thereof (d-1) is a zinc salt of a carboxylic acid. 
     
     
         7 . The golf ball according to  claim 6 , wherein the zinc salt of the carboxylic acid is one or more members selected from the group consisting of zinc octoate, zinc laurate, zinc myristate, and zinc stearate. 
     
     
         8 . The golf ball according to  claim 1 , wherein the first rubber composition and/or the second rubber composition further include an organic sulfur compound (e). 
     
     
         9 . The golf ball according to  claim 8 , wherein the organic sulfur compound (e) is at least one member selected from the group consisting of thiophenols, diphenyl disulfides, thionaphthols, thiuram disulfides, and metal salts thereof. 
     
     
         10 . The golf ball according to  claim 8 , wherein the organic sulfur compound (e) is one or more members selected from the group consisting of 2-thionaphthol, bis(pentabromophenyl)disulfide, and 2,6-dichlorothiophenol. 
     
     
         11 . The golf ball according to  claim 8 , wherein an amount of the organic sulfur compound (e) is equal to or greater than 0.05 parts by weight but equal to or less than 5.0 parts by weight, per 100 parts by weight of the base rubber (a). 
     
     
         12 . The golf ball according to  claim 1 , wherein an amount of the co-crosslinking agent (b) is equal to or greater than 15 parts by weight but equal to or less than 50 parts by weight, per 100 parts by weight of the base rubber (a). 
     
     
         13 . The golf ball according to  claim 1 , wherein an amount of the crosslinking initiator (c) is equal to or greater than 0.2 parts by weight but equal to or less than 5.0 parts by weight, per 100 parts by weight of the base rubber (a). 
     
     
         14 . The golf ball according to  claim 1 , wherein
 the first rubber composition and/or the second rubber composition include the α,β-unsaturated carboxylic acid (b-1), and   the first rubber composition and/or the second rubber composition further include a metal compound (f).   
     
     
         15 . The golf ball according to  claim 1 , wherein
 a JIS-C hardness H(0) at a central point of the core is equal to or greater than 40 but equal to or less than 70, and   a JIS-C hardness H(100) at a surface of the core is equal to or greater than 78 but equal to or less than 96.   
     
     
         16 . The golf ball according to  claim 15 , wherein a difference (H(100)−H(0)) between the hardness H(100) and the hardness H(0) is equal to or greater than 15. 
     
     
         17 . The golf ball according to  claim 1 , wherein a Shore D hardness Hm of the mid layer is greater than a Shore D hardness Hc of the cover. 
     
     
         18 . The golf ball according to  claim 17 , wherein a difference (Hm−Hc) between the hardness Hm and the hardness Hc is equal to or greater than 18. 
     
     
         19 . The golf ball according to  claim 1 , wherein a JIS-C hardness H(39) at a point whose ratio of a distance from a central point of the core to a radius of the core is 39% is greater than a JIS-C hardness H(36) at a point whose ratio of a distance from the central point of the core to the radius of the core is 36%. 
     
     
         20 . The golf ball according to  claim 1 , wherein a JIS-C hardness H(76) at a point whose ratio of a distance from a central point of the core to a radius of the core is 76% is greater than a JIS-C hardness H(75) at a point whose ratio of a distance from the central point of the core to the radius of the core is 75%. 
     
     
         21 . The golf ball according to  claim 1 , wherein a JIS-C hardness H(100) at a surface of the core is greater than a JIS-C hardness H(75) at a point whose ratio of a distance from a central point of the core to a radius of the core is 75%. 
     
     
         22 . The golf ball according to  claim 21 , wherein a difference (H(100)−H(75)) between the hardness H(100) and the hardness H(75) is equal to or greater than 4. 
     
     
         23 . The golf ball according to  claim 1 , wherein
 the mid layer is formed from a resin composition,   the cover is formed from a resin composition whose base resin is different from a base resin of the mid layer, and   the golf ball further comprises a reinforcing layer between the mid layer and the cover.   
     
     
         24 . The golf ball according to  claim 1 , wherein a diameter of the center is equal to or greater than 10 mm but equal to or less than 20 mm.