A golf ball containing a core, a reinforcing layer and a cover. The core is formed by a center and a mid layer. The center is formed by a center inner sphere and a center outer layer. The center inner sphere and the center outer layer are obtained through crosslinking of a rubber composition. The base polymer of the mid layer is an ionomer resin. The base polymer of the cover is a thermoplastic polyurethane elastomer. The thickness Tc of the cover is equal to or less than 1.0 mm. The hardness Hc of the cover is 20 or greater and 50 or less. The ratio (D 2 /D 3 ) of the amount of compressive deformation D 2 of the core to the amount of compressive deformation D 3 of the golf ball is 0.98 or greater and 1.10 or less.
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 center having a center inner sphere and a center outer layer positioned outside of the inner sphere, wherein a peak in a hardness curve from a center point of said inner sphere to a surface of the cover is attained in the mid layer,
said cover having a thickness Tc equal to or less than 1.0 mm,
said cover having a hardness Hc of 20 or greater and 50 or less, and
wherein a ratio (D 2 /D 3 ) of the amount of compressive deformation D 2 of said core to the amount of compressive deformation D 3 of the golf ball is 0.98 or greater and 1.10 or less.
2. The golf ball according to claim 1 wherein said center inner sphere and said center outer layer are formed by a composition including a thermosetting polymer as a base, and the mid layer and the cover are formed by a composition including a thermoplastic polymer as a base.
3. The golf ball according to claim 2 wherein a principal component of a base polymer of said mid layer is an ionomer resin, and
a principal component of a base polymer of said cover is thermoplastic polyurethane elastomer.
4. The golf ball according to claim 1 which further has a reinforcing layer having a thickness of 3 μm or greater and 50 μm or less, and being positioned between said mid layer and said cover.
5. The golf ball according to claim 1 wherein a difference (Hs 1 −Hi) between the surface hardness Hs 1 of the center and the central hardness Hi of the inner sphere is 20 or greater.
6. The golf ball according to claim 5 wherein the difference (Hs 1 −Hi) is 25 or greater.
7. The golf ball according to claim 1 wherein a difference (Hs 1 −Hsi) between the surface hardness Hs 1 of the center and the surface hardness Hsi of the inner sphere is 1 or greater.
8. The golf ball according to claim 7 wherein the difference (Hs 1 −Hsi) is 3 or greater.
9. 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 center having a center inner sphere and a center outer layer positioned outside of the center inner sphere, and
wherein a product (Tc·Hc) of a thickness Tc (mm) of the cover and a hardness Hc of the cover is equal to or less than 25,
the amount of compressive deformation is 2.20 or greater and 2.90 or less, and wherein said cover has a hardness Hc which is smaller than the central hardness Hi of the inner sphere.
10. The golf ball according to claim 9 wherein a principal component of a base polymer of said mid layer is an ionomer resin, and
a principal component of a base polymer of said cover is a thermoplastic polyurethane elastomer.
11. The golf ball according to claim 9 which further contains a reinforcing layer having a thickness of 3 μm or greater and 50 μm or less, which is positioned between said mid layer and said cover.
12. The golf ball according to claim 9 wherein a difference (Hs 1 −Hi) between the surface hardness Hs 1 of the center and the central hardness Hi of the inner sphere is 20 or greater.
13. The golf ball according to claim 12 wherein the difference (Hs 1 −Hi) is 25 or greater.
14. The golf ball according to claim 9 wherein a difference (Hs 1 −Hsi) between the surface hardness Hs 1 of the center and the surface hardness Hsi of the inner sphere is 1 or greater.
15. The golf ball according to claim 14 wherein the difference (Hs 1 −Hsi) is 3 or greater.
16. 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 center having a center inner sphere and a center outer layer positioned outside of the inner sphere,
wherein said center inner sphere and said center outer layer are formed by a composition including a thermosetting polymer as a base, and the mid layer and the cover are formed by a composition including a thermoplastic polymer as a base,
said cover having a thickness Tc equal to or less than 1.0 mm,
said cover having a hardness Hc of 20 or greater and 50 or less, and wherein a ratio (D 2 /D 3 ) of the amount of compressive deformation D 2 of said core to the amount of compressive deformation D 3 of the golf ball is 0.98 or greater and 1.10 or less.
17. The golf ball according to claim 16 wherein a principal component of a base polymer of said mid layer is an ionomer resin, and
a principal component of a base polymer of said cover is thermoplastic polyurethane elastomer.
18. The golf ball according to claim 16 which further has a reinforcing layer having a thickness of 3 μm or greater and 50 μm or less, and being positioned between said mid layer and said cover.
19. The golf ball according to claim 16 wherein a difference (Hs 1 −Hi) between the surface hardness Hs 1 of the center and the central hardness Hi of the inner sphere is 20 or greater.
20. The golf ball according to claim 19 wherein the difference (Hs 1 −Hi) is 25 or greater.
21. The golf ball according to claim 16 wherein a difference (Hs 1 −Hsi) between the surface hardness Hs 1 of the center and the surface hardness Hsi of the inner sphere is 1 or greater.
22. The golf ball according to claim 21 wherein the difference (Hs 1 −Hsi) is 3 or greater.