An object of the present invention is to provide a golf ball traveling a great flight distance on driver shots. The present invention provides a golf ball comprising a spherical core and at least one cover layer covering the spherical core, wherein the spherical core is formed from a rubber composition containing (a) base rubber, (b) an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and/or a metal salt thereof as a co-crosslinking agent, (c) a crosslinking initiator, (d) a carboxylic acid having 1 to 14 carbon atoms and/or a salt thereof, and (e) a halogen-substituted thiophenol and/or a metal salt thereof as an organic sulfur compound, provided that the rubber composition further contains (f) a metal compound in the case of containing only (b) the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms as the co-crosslinking agent.
1. A golf ball having a spherical core and at least one cover layer covering the spherical core, wherein the spherical core is formed from a rubber composition containing
(a) a base rubber,
(b) an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and/or a metal salt thereof as a co-crosslinking agent,
(c) a crosslinking initiator,
(d) a carboxylic acid having 1 to 14 carbon atoms and/or a salt thereof, excluding (b) the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and/or metal salt thereof, and
(e) a halogen-substituted thiophenol and/or a metal salt thereof as an organic sulfur compound,
provided that the rubber composition further contains (f) a metal compound if only (b) the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms as the co-crosslinking agent, and
wherein the rubber composition contains (d) the carboxylic acid having 1 to 14 carbon atoms and/or the salt thereof in a content ranging from 0.5 parts to 30 parts by mass with respect to 100 parts by mass of (a) the base rubber.
2. The golf ball according to claim 1 , wherein (d) the carboxylic acid having 1 to 14 carbon atoms and/or the salt thereof is a fatty acid and/or a fatty acid salt.
3. The golf ball according to claim 1 , wherein (e) the organic sulfur compound is a thiophenol substituted with 1 to 5 chlorine atoms and/or a metal salt thereof.
4. The golf ball according to claim 1 , wherein (e) the organic sulfur compound is 2,4-dichlorothiophenol, 2,6-dichlorothiophenol, 2,4,5-trichlorothiophenol, pentachlorothiophenol or a metal salt thereof.
5. The golf ball according to claim 1 , wherein (e) the organic sulfur compound is 2,6-dichlorothiophenol, 2,4,5-trichlorothiophenol or a metal salt thereof.
6. The golf ball according to claim 1 , wherein the rubber composition contains (e) the organic sulfur compound in a content ranging from 0.05 part to 5 parts by mass with respect to 100 parts by mass of (a) the base rubber.
7. The golf ball according to claim 1 , wherein the rubber composition contains (b) the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and/or the metal salt thereof in a content ranging from 15 parts to 50 parts by mass with respect to 100 parts by mass of (a) the base rubber.
8. The golf ball according to claim 1 , wherein the spherical core has a hardness difference between a surface hardness and a center hardness of 28 or more in JIS-C hardness.
9. The golf ball according to claim 1 , wherein the spherical core has a surface hardness in a range from 76 to 100 in JIS-C hardness.
10. The golf ball according to claim 1 , wherein the spherical core has a center hardness in a range from 30 to 70 in JIS-C hardness.
11. The golf ball according to claim 1 , wherein the spherical core has a hardness distribution such that if JIS-C hardness is measured at nine points obtained by dividing the radius of the spherical core into equal parts having 12.5% intervals therebetween with the core center and core surface included as points, and theses points are plotted against distance (%) from the core center, then R 2 of a linear approximation curve obtained from the least square method is 0.85 or higher.
12. The golf ball according to claim 1 , wherein the rubber composition contains (d) the carboxylic acid having 3 to 12 carbon atoms and/or the salt thereof.
13. The golf ball according to claim 1 , wherein the rubber composition contains (d) the carboxylic acid having 3 to 8 carbon atoms and/or the salt thereof.
14. The golf ball according to claim 1 , wherein the rubber composition contains (d) the carboxylic acid having 1 to 14 carbon atoms and/or the salt thereof in a content ranging from 0.5 part to 20 parts by mass with respect to 100 parts by mass of (a) the base rubber.
15. The golf ball according to claim 1 , wherein the rubber composition contains (d) the carboxylic acid having 1 to 14 carbon atoms and/or the salt thereof in a content ranging from 0.5 part to 15 parts by mass with respect to 100 parts by mass of (a) the base rubber.
16. The golf ball according to claim 1 , wherein the rubber composition contains (d) the carboxylic acid having 1 to 14 carbon atoms and/or the salt thereof in a content ranging from 1.0 part to 15 parts by mass with respect to 100 parts by mass of (a) the base rubber.
17. The golf ball according to claim 1 , wherein the rubber composition contains (d) the carboxylic acid having 1 to 14 carbon atoms and/or the salt thereof in a content ranging from 1.0 part to 8 parts by mass with respect to 100 parts by mass of (a) the base rubber.
18. The golf ball according to claim 1 , wherein the rubber composition contains (d) the carboxylic acid having 1 to 14 carbon atoms and/or the salt thereof in a content ranging from 1.0 part to 7 parts by mass with respect to 100 parts by mass of (a) the base rubber.
19. The golf ball according to claim 1 , wherein the rubber composition contains (d) the carboxylic acid having 1 to 14 carbon atoms and/or the salt thereof in a content of 1.0 part or more and less than 6 parts by mass with respect to 100 parts by mass of (a) the base rubber.
20. The golf ball according to claim 1 , wherein
(d) the carboxylic acid and/or salt thereof has 3 to 12 carbon atoms and is a fatty acid and/or a fatty acid salt;
the rubber composition contains (b) the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and/or the metal salt thereof in a content ranging from 15 parts to 50 parts by mass with respect to 100 parts by mass of (a) the base rubber;
the rubber composition contains (e) the organic sulfur compound in a content ranging from 0.05 part to 5 parts by mass with respect to 100 parts by mass of (a) the base rubber;
the spherical core has a hardness difference between a surface hardness and a center hardness of 28 or more in JIS-C hardness; and
the spherical has a hardness distribution such that if JIS-C hardness is measured at nine points obtained by dividing the radius of the spherical core into equal parts having 12.5% intervals therebetween with the core center and core surface included as points, and these points are plotted against distance (%) from the core center, then R 2 of a linear approximation curve obtained from the least square method is 0.85 or higher.