Golf ball 2 has a center 4 , a mid layer 6 , a reinforcing layer 8 and a cover 10. Base polymer of the mid layer 6 includes an ionomer resin as a principal component. A melting point of the resin composition is equal to or greater than 95° C. The mid layer 6 has a thickness of 0.5 mm or greater and 2.5 mm or less. The cover 10 includes a thermoplastic resin. The cover 10 has a nominal thickness Tc of 0.1 mm or greater and 0.9 mm or less. The mid layer 6 has recessed parts which correspond to dimples 12. In the golf ball 2 , the resin composition of the mid layer 6 does not flow out from a seam when forming the cover 10.
1. A method of the production of a golf ball which comprises:
a first step in which a spherical center is formed;
a second step in which a mid layer material including a thermoplastic resin and having a melting point of equal to or greater than 95° C. is prepared;
a third step in which said center is covered by said mid layer material to form a mid layer;
a fourth step in which a material for a cover comprising a thermoplastic resin is prepared;
a fifth step in which a half shell is formed by said cover material;
a sixth step in which a core comprising said center and said mid layer is covered by two half shells and placed into a mold having numerous pimples; and
a seventh step in which said core and said half shells are compressed and heated in the mold, said pimples form dimples on the surface of the cover, and said pimples simultaneously form recessed parts on the mid layer which correspond to all the dimples, and a cover is formed having a thickness Td immediately below the deepest site of each dimple being greater than a difference between a nominal thickness Tc and a depth of each dimple (Tc−Dp).
2. The method of the production according to claim 1 wherein the mid layer material which is prepared in said second step, includes an ionomer resin.
3. The method of the production according to claim 1 wherein a melted mid layer material is injected around the center which is held in a mold.
4. The method of the production according to claim 1 wherein said third step comprises a step in which the center is covered by two half shells comprising the mid layer material, and a step in which the center and the half shells are compressed and heated in the mold.
5. The method of the production according to claim 2 wherein the mid layer material which is prepared in said second step, includes an ionomer resin having a melting point of equal to or greater than 102° C.
6. The method of the production according to claim 1 wherein the nominal thickness Tc is 0.1 mm or greater and 0.9 mm or less.
7. The method of the production according to claim 1 wherein the nominal thickness Tc is 0.1 mm or greater and 0.5 mm or less.