Golf ball

Abstract

A golf ball 2 includes a core 4 , a mid layer 6 , a reinforcing layer 8 , and a cover 10 . When distances (%) from the central point of the core 4 to nine points and JIS-C hardnesses at the nine points, which are obtained by dividing a region from the central point of the core 4 to the surface of the core 4 at intervals of 12.5% of the radius of the core 4 , are plotted in a graph, R 2 of a linear approximation curve obtained by a least-square method is equal to or greater than 0.95. The difference (H(100)−H(0)) between a JIS-C hardness H(100) at the surface of the core 4 and a JIS-C hardness H(0) at the central point of the core 4 is equal to or greater than 15.

1 . A golf ball comprising a spherical core, a mid layer positioned outside the core and having one or more layers, and a cover positioned outside the mid layer, wherein
 when distances (%) from a central point of the core to nine points and JIS-C hardnesses at the nine points, which are obtained by dividing a region from the central point of the core to a surface of the core at intervals of 12.5% of a radius of the core, are plotted in a graph, R 2  of a linear approximation curve obtained by a least-square method is equal to or greater than 0.95,   a difference (H(100)−H(0)) between a JIS-C hardness H(100) at the surface of the core and a JIS-C hardness H(0) at the central point of the core is equal to or greater than 15,   a total thickness of the mid layer is equal to or less than 1.6 mm,   a thickness of the cover is equal to or less than 1.2 mm,   the cover is formed from a resin composition, and   a principal component of a base resin of the resin composition is a polyurethane.   
     
     
         2 . The golf ball according to  claim 1 , wherein
 the core is obtained by a rubber composition being crosslinked,   the rubber composition includes:
 (a) a base rubber; 
 (b) a co-crosslinking agent; 
 (c) a crosslinking initiator; and 
 (d) a carboxylic acid and/or a salt thereof, 
   the co-crosslinking agent (b) is:
 (b1) an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms; and/or 
 (b2) a metal salt of an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms, and 
   when the rubber composition includes the α,β-unsaturated carboxylic acid (b1), the rubber composition further includes a metal compound (e).   
     
     
         3 . The golf ball according to  claim 2 , wherein the rubber composition includes 100 parts by weight of the base rubber (a) and 5 parts by weight or greater but 40 parts by weight or less of the carboxylic acid and/or the salt thereof (d). 
     
     
         4 . The golf ball according to  claim 2 , wherein the carboxylic acid and/or the salt thereof (d) is a fatty acid and/or a fatty acid salt. 
     
     
         5 . The golf ball according to  claim 4 , wherein the carboxylic acid and/or the salt thereof (d) is a saturated fatty acid and/or a saturated fatty acid salt. 
     
     
         6 . The golf ball according to  claim 2 , wherein a carbon number of a carboxylic acid component of the carboxylic acid and/or the salt thereof (d) is equal to or greater than 4 but equal to or less than 30. 
     
     
         7 . The golf ball according to  claim 2 , wherein the rubber composition includes the metal salt (b2) of the α,β-unsaturated carboxylic acid. 
     
     
         8 . The golf ball according to  claim 2 , wherein the rubber composition further includes an organic sulfur compound (f). 
     
     
         9 . The golf ball according to  claim 8 , wherein the organic sulfur compound (f) is a thiophenol, a diphenyl disulfide, a thionaphthol, or a thiuram disulfide, or a metal salt thereof. 
     
     
         10 . The golf ball according to  claim 8 , wherein the rubber composition includes 0.05 parts by weight or greater but 5 parts by weight or less of the organic sulfur compound (f) per 100 parts by weight of the base rubber (a). 
     
     
         11 . The golf ball according to  claim 2 , wherein the rubber composition includes 100 parts by weight of the base rubber (a) and 15 parts by weight or greater but 50 parts by weight or less of the co-crosslinking agent (b). 
     
     
         12 . The golf ball according to  claim 1 , wherein
 a JIS-C hardness of the mid layer is equal to or greater than 90, and   a JIS-C hardness of the cover is equal to or less than 65.   
     
     
         13 . The golf ball according to  claim 1 , wherein
 the mid layer is formed from a resin composition, and   a principal component of a base resin of the resin composition is an ionomer resin.   
     
     
         14 . The golf ball according to  claim 1 , wherein a hardness of the mid layer is greater than a surface hardness of the core. 
     
     
         15 . The golf ball according to  claim 1 , wherein a hardness of the cover is less than a central hardness of the core. 
     
     
         16 . The golf ball according to  claim 1 , wherein the hardness H(0) is equal to or greater than 40.0 but equal to or less than 70.0. 
     
     
         17 . The golf ball according to  claim 1 , wherein the hardness H(100) is equal to or greater than 78.0 but equal to or less than 95.0. 
     
     
         18 . The golf ball according to  claim 1 , wherein a difference (Hm−H(100)) between a JIS-C hardness Hm of the mid layer and the hardness H(100) is equal to or greater than 2. 
     
     
         19 . The golf ball according to  claim 1 , wherein a difference (Hm−Hc) between a JIS-C hardness Hm of the mid layer and a JIS-C hardness Hc of the cover is equal to or greater than 18 but equal to or less than 70. 
     
     
         20 . The golf ball according to  claim 1 , wherein a difference (H(0)−Hc) between the hardness H(0) and a JIS-C hardness Hc of the cover is equal to or greater than 3.