Golf ball

Abstract

A golf ball 2 includes a spherical core 4 , an inner mid layer 6 positioned outside the core 4 , an outer mid layer 8 positioned outside the inner mid layer 6 , a reinforcing layer 10 positioned outside the outer mid layer 8 , and a cover 12 positioned outside the reinforcing layer 10 . When distances (%) from a central point of the core 4 to nine points and JIS-C hardnesses at the nine points, which nine points are obtained by dividing a region from the central point of the core 4 to a surface of the core 4 at intervals of 12.5% of a 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.

1 . A golf ball comprising a spherical core, an inner mid layer positioned outside the core, an outer mid layer positioned outside the inner mid layer, and a cover positioned outside the outer mid layer, wherein
 when distances (%) from a central point of the core to nine points and JIS-C hardnesses at the nine points, which nine points 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 Shore D hardness Hmo of the outer mid layer is greater than a Shore D hardness Hmi of the inner mid layer, and   a Shore D hardness Hc of the cover is less than the hardness Hmo.   
     
     
         2 . The golf ball according to  claim 1 , wherein a difference (Hmo−Hc) between the hardness Hmo and the hardness Hc is equal to or greater than 20 but equal to or less than 40. 
     
     
         3 . The golf ball according to  claim 1 , wherein the hardness Hc is less than the hardness Hmi. 
     
     
         4 . The golf ball according to  claim 3 , wherein a difference (Hmi−Hc) between the hardness Hmi and the hardness Hc is equal to or greater than 10 but equal to or less than 30. 
     
     
         5 . The golf ball according to  claim 1 , wherein the hardness H(100) is greater than a JIS-C hardness of the cover. 
     
     
         6 . The golf ball according to  claim 5 , wherein a difference between the hardness H(100) and the JIS-C hardness of the cover is equal to or greater than 10. 
     
     
         7 . The golf ball according to  claim 1 , wherein a difference (Hmo−Hmi) between the hardness Hmo and the hardness Hmi is equal to or greater than 5. 
     
     
         8 . The golf ball according to  claim 1 , wherein
 a JIS-C hardness of the inner mid layer is greater than the hardness H(100), and   a difference between the JIS-C hardness of the inner mid layer and the hardness H(100) is equal to or greater than 2.   
     
     
         9 . 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 (e) a metal compound.   
     
     
         10 . The golf ball according to  claim 9 , 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). 
     
     
         11 . The golf ball according to  claim 9 , wherein the rubber composition includes the metal salt (b2) of the α,β-unsaturated carboxylic acid. 
     
     
         12 . The golf ball according to  claim 9 , 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). 
     
     
         13 . The golf ball according to  claim 9 , wherein the carboxylic acid and/or the salt thereof (d) is a fatty acid and/or a fatty acid salt. 
     
     
         14 . The golf ball according to  claim 9 , wherein the carboxylic acid and/or the salt thereof (d) is a zinc salt of a carboxylic acid. 
     
     
         15 . The golf ball according to  claim 14 , wherein the zinc salt is zinc octoate, zinc laurate, zinc myristate, or zinc stearate. 
     
     
         16 . The golf ball according to  claim 9 , 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. 
     
     
         17 . The golf ball according to  claim 9 , wherein the rubber composition further includes (f) an organic sulfur compound. 
     
     
         18 . The golf ball according to  claim 17 , wherein the organic sulfur compound (f) is at least one member selected from the group consisting of thiophenols, diphenyl disulfides, thionaphthols and thiuram disulfides, and metal salts thereof. 
     
     
         19 . The golf ball according to  claim 17 , wherein the rubber composition includes 100 parts by weight of the base rubber (a) and 0.05 parts by weight or greater but 5 parts by weight or less of the organic sulfur compound (f). 
     
     
         20 . A golf ball comprising a spherical core, an inner mid layer positioned outside the core, an outer mid layer positioned outside the inner mid layer, and a cover positioned outside the outer mid layer, wherein
 when distances (%) from a central point of the core to nine points and JIS-C hardnesses at the nine points, which nine points 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,   the core is obtained by a rubber composition being crosslinked,   the inner mid layer is formed from a resin composition of which a principal component of a base resin is an ionomer resin,   the outer mid layer is formed from a resin composition of which a principal component of a base resin is an ionomer resin,   the cover is formed from a resin composition of which a principal component of a base resin is a polyurethane, and   a Shore D hardness Hmo of the outer mid layer is greater than a Shore D hardness Hmi of the inner mid layer.