Golf ball 2 has a spherical center 10 , a mid layer 12 covering this center 10 , a reinforcing layer 6 covering this mid layer 12 , and a cover 8 covering this reinforcing layer 6 . Base polymer of the mid layer 12 is an ionomer resin. Base polymer of the cover 8 is a thermoplastic polyurethane elastomer. The cover 8 has a thickness Tc of equal to or less than 1.2 mm, and particularly equal to or less than 0.8 mm. The difference (Ho−Hc) between the central hardness Ho of the center 10 and the hardness Hc of the cover 8 is 1 or greater and 30 or less. The cover 8 has a hardness Hc of 15 or greater and 40 or less. The product (Tc·Hc) of the thickness Tc (mm) of the cover 8 and the hardness Hc of the cover 8 is equal to or less than 25.
1. A golf ball which comprises a spherical core, and a cover positioned outside of the core,
said core having a spherical center, and a mid layer positioned outside of the center,
said cover having a thickness Tc of equal to or less than 1.2 mm, and said cover having a hardness Hc being less than the central hardness Ho of the center,
wherein the difference (Ho−Hc) between the Shore D central hardness Ho of the center and the Shore D hardness Hc of the cover is 4.0 or greater,
wherein the center is obtained through crosslinking of a rubber composition,
wherein the mid layer comprises a resin composition and the principal component of the base polymer in the resin composition of the mid layer is an ionomer resin, and
wherein the cover comprises a resin composition and the principal component of the base polymer in the resin composition of the cover is a thermoplastic polyurethane elastomer.
2. The golf ball according to claim 1 wherein the difference (Ho−Hc) between the Shore D central hardness Ho of the center and the Shore D hardness Hc of the cover is 4 or greater and 30 or less.
3. The golf ball according to claim 1 wherein the cover has a thickness Te of equal to or less than 0.8 mm.
4. The golf ball according to claim 1 wherein the cover has a hardness Hc of 15 or greater and 40 or less, and the product (Tc·Hc) of the thickness Tc (mm) of the cover and the hardness Hc of the cover is equal to or less than 25.
5. The golf ball according to claim 1 wherein the ratio (D2/D3) of the amount of compressive deformation D2 of the core to the amount of compressive deformation D3 of the golf ball is 0.98 or greater and 1.10 or less.
6. The golf ball according to claim 5 wherein the amount of compressive deformation D3 thereof is 2.0 mm or greater and 3.0 mm or less.
7. The golf ball according to claim 1 wherein the hardness Hm of the mid layer is greater than the hardness Hc of the cover, the difference (Hm−Hc) is 20 or greater and 45 or less, and the sum (Tm+Tc) derived by adding the thickness Tm of the mid layer to the thickness Te of the cover is equal to or less than 2.5 mm.
8. The golf ball according to claim 1 wherein the surface hardness Hs 2 of the core is greater than the central hardness Ho of the center, and the difference (Hs 2 −Ho) is equal to or greater than 15.
9. The golf ball according to claim 1 wherein the central Shore D hardness Ho of the center is 20 or greater and 60 or less, and wherein the cover has a Shore D hardness Hc of 15 or greater and 40 or less.
10. The golf ball according to claim 1 wherein the central Shore D hardness Ho of the center is 27 or greater and 53 or less, and wherein the cover has a Shore D hardness Hc of 20 or greater and 38 or less.
11. The golf ball according to claim 1 wherein the central Shore D hardness Ho of the center is 32 or greater and 48 or less, and wherein the cover has a Shore D hardness Hc of 26 or greater and 36 or less.
12. The golf ball according to claim 1 wherein the difference (Ho−Hc) between the central hardness Ho of the center and the hardness Hc of the cover is 3 or greater and 25 or less.
13. The golf ball according to claim 9 wherein the difference (Ho−Hc) between the central hardness Ho of the center and the hardness Hc of the cover is 3 or greater and 25 or less.
14. The golf ball according to claim 1 wherein the cover has a thickness To of equal to or less than 0.5 mm.
15. The golf ball according to claim 9 wherein the cover has a thickness Tc of equal to or less than 0.5 mm.
16. The golf ball according to claim 1 wherein the Shore D hardness Hm of the mid layer is 55 or greater and 72 or less.
17. The golf ball according to claim 9 wherein the Shore D hardness Hm of the mid layer is 55 or greater and 72 or less.
18. The golf ball according to claim 13 wherein the Shore D hardness Hm of the mid layer is 55 or greater and 72 or less.
19. The golf ball according to claim 1 wherein the center comprises one or more crosslinked rubber compositions obtained from a base rubber composition selected from the group consisting of polybutadienes, polyisoprene, styrene-butadiene copolymers, ethylene-proplylene-diene copolymers and natural rubbers.