| abstract |
A golf ball 2 includes a core 4 , a first mid layer 6 , a second mid layer 8 , and a cover 12 . The core 4 includes a center 18 and an envelope layer 20 . The center 18 is formed by crosslinking a first rubber composition, and the envelope layer 20 is formed by crosslinking a second rubber composition. The first rubber composition or the second rubber composition includes a base rubber, a co-crosslinking agent, a crosslinking initiator, and an acid and/or a salt. The co-crosslinking agent is:n (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.n nA hardness Hm2 of the second mid layer 8 is greater than a hardness Hm1 of the first mid layer 6 . The hardness Hm2 is greater than a hardness Hc of the cover 12. |