An object of the present invention is to provide a golf ball striking a good balance between flight distance on driver shots and spin rate on approach shots, and excellent in stain resistance and shot feeling. The present invention provides a golf ball comprising a paint film, wherein a base resin of the paint film contains a polyurethane obtained by a reaction between a polyisocyanate composition and a polyol composition containing a urethane polyol having a polyether diol with a number average molecular weight in a range from 800 to 3,000 as a constituent component, and the following requirements are satisfied: Mp≦200× X −75 Mp≦100 Minm−Moum>40 Moum−Mc<5 Tinm≧Toum>Tc>Tp (Tinm×Minm)/(Toum×Moum)>2.0 (Toum×Moum)/(Tc×Mc)<3.0 (Tc×Mc)/(Tp×Mp)>10.0 [where Mp, Minm, Moum, and Mc represent a 10% elastic modulus (kgf/cm 2 ) of the paint film, inner intermediate layer, outer intermediate layer and cover, respectively; Tp, Tinm, Toum, and Tc represent a thicknesses (mm) of the paint film, inner intermediate layer, outer intermediate layer and cover, respectively; and X represents a molar ratio (NCO/OH) of a NCO group in the polyisocyanate composition to a OH group in the polyol composition.].
1. A golf ball comprising: a golf ball body including a spherical core, an inner intermediate layer covering the spherical core, an outer intermediate layer covering the inner intermediate layer, and a cover covering the outer intermediate layer; and a paint film formed on a surface of the golf ball body,
wherein a base resin constituting the paint film contains a polyurethane obtained by a reaction between a polyol composition and a polyisocyanate composition,
the polyol composition contains a urethane polyol having a polyether diol with a number average molecular weight in a range from 800 to 3,000 as a constituent component, and
following requirements are satisfied:
Mp≦200× X− 75
Mp≦100
Minm−Moum>40
Moum−Mc <5
Tinm≧Toum>Tc>Tp
(Tinm−Minm)/(Toum−Moum)>2.0
(Toum−Moum)/(Tc−Mc)<3.0
(Tc−Mc)/(Tp−Mp)>10.0
wherein
Mp represents a 10% elastic modulus (kgf/cm 2 ) of the paint film,
Minm represents a 10% elastic modulus (kgf/cm 2 ) of the inner intermediate layer,
Moum represents a 10% elastic modulus (kgf/cm 2 ) of the outer intermediate layer, and
Mc represents a 10% elastic modulus (kgf/cm 2 ) of the cover;
Tp represents a thickness (mm) of the paint film,
Tinm represents a thickness (mm) of the inner intermediate layer,
Toum represents a thickness (mm) of the outer intermediate layer, and
Tc represents a thickness (mm) of the cover; and
X represents a molar ratio (NCO/OH) of isocyanate groups (NCO groups) of the polyisocyanate composition to hydroxyl groups (OH groups) of the polyol composition.
2. The golf ball according to claim 1 , wherein an absolute value (|Mp−Mc |) of a difference between the 10% elastic modulus Mp of the paint film and the 10% elastic modulus Mc of the cover is 65 kgf/cm 2 or less.
3. The golf ball according to claim 1 , wherein a proportion occupied by a volume Vc of the cover in the golf ball body is less than 10 vol. %.
4. The golf ball according to claim 1 , wherein the 10% elastic modulus Mc of the cover is 100 kgf/cm 2 or less.
5. The golf ball according to claim 1 , wherein the 10% elastic modulus Minm of the inner intermediate layer is 120 kgf/cm 2 or more.
6. The golf ball according to claim 1 , wherein a difference (Hs—Ho) between a surface hardness Hs and a center hardness Ho of the spherical core is 20 or more in Shore C hardness.
7. The golf ball according to claim 1 , wherein the spherical core includes at least one layer foamed from a rubber composition containing a fatty acid and/or a metal salt thereof, and wherein the fatty acid and/or the metal salt thereof excludes α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms or a metal salt thereof used as a co-crosslinking agent.
8. The golf ball according to claim 1 , wherein the spherical core is a dual-layered core composed of an inner core and an outer core covering the inner core.
9. The golf ball according to claim 1 , wherein the spherical core has a diameter in a range from 37.0 mm to 40.5 mm.
10. The golf ball according to claim 1 , wherein the urethane polyol has a weight average molecular weight in a range from 5000 to 20,000.
11. The golf ball according to claim 1 , wherein the polyisocyanate composition contains a biuret product and an isocyanurate product of hexamethylene diisocyanate, and a mass ratio (biuret product/isocyanurate product) of the biuret-modified product to the isocyanurate-modified product ranges from 20/40 to 40/20.
12. The golf ball according to claim 1 , wherein the thickness Tinm of the inner intermediate layer ranges from 0.7 mm to 1.6 mm.
13. The golf ball according to claim 1 , wherein the thickness Toum of the outer intermediate layer ranges from 0.5 mm to 1.2 mm.
14. The golf ball according to claim 1 , wherein the thickness Tc of the cover ranges from 0.1 mm to 0.6 mm.
15. The golf ball according to claim 1 , wherein a slab hardness of the inner intermediate layer ranges from 62 to 75 in Shore D hardness.
16. The golf ball according to claim 1 , wherein a slab hardness of the outer intermediate layer ranges from 42 to 63 in Shore D hardness.
17. The golf ball according to claim 1 , wherein a slab hardness of the cover ranges from 40 to 65 in Shore D hardness.
18. The golf ball according to claim 1 , wherein a proportion occupied by a volume Vinm of the inner intermediate layer in the golf ball body is 18.0 vol % or less.
19. The golf ball according to claim 1 , wherein a proportion occupied by a volume Voum of the outer intermediate layer in the golf ball body is 15.0 vol % or less.
20. The golf ball according to claim 1 , wherein the 10% elastic modulus Mourn of the outer intermediate layer is 35 kgf/cm 2 or more.
21. The golf ball according to claim 1 , wherein Mourn−Mc<0.
22. The golf ball according to claim 1 , wherein
(Tinm×Minm)/(Toum×Moum)≦8.0.
23. The golf ball according to claim 1 , wherein in a reaction between the polyol composition and the polyisocyanate composition, a molar ratio (NCO groups/OH groups) of isocyanate groups (NCO groups) of the polyisocyanate composition to hydroxyl groups (OH groups) of the polyol composition is more than 0.5 and 0.85 or less.