An object of the present invention is to provide a golf ball showing an increased spin rate on approach shots under a wet condition while maintaining a spin rate on approach shots under a dry condition. The present invention provides a golf ball comprising a golf ball body and a paint film formed on a surface of the golf ball body, wherein the paint film has a multi-layered construction composed of two or more layers, and a difference (M in −M out ) between a 10% elastic modulus (M in ) of an innermost layer of the paint film and a 10% elastic modulus (M out ) of an outermost layer of the paint film is 25 kgf/cm 2 or more.
1. A golf ball comprising a golf ball body and a paint film formed on a surface of the golf ball body, wherein
the paint film has a multi-layered construction composed of two or more layers, and a difference (M in −M out ) between a 10% elastic modulus (M in ) of an innermost layer of the paint film and a 10% elastic modulus (M out ) of an outermost layer of the paint film is 25 kgf/cm 2 or more and 400 kgf/cm 2 or less, and
the 10% elastic modulus (M in ) of the innermost layer of the paint film is 100 kgf/cm 2 or more.
2. The golf ball according to claim 1 , wherein the 10% elastic modulus (M in ) of the innermost layer of the paint film ranges from 100 kgf/cm 2 to 450 kgf/cm 2 .
3. The golf ball according to claim 1 , wherein the 10% elastic modulus (M out ) of the outermost layer of the paint film is less than 100 kgf/cm 2 .
4. The golf ball according to claim 1 , wherein the innermost layer of the paint film has a thickness (T in ) ranging from 5 μm to 30 μm, and the outermost layer of the paint film has a thickness (T out ) ranging from 5 μm to 30 μm.
5. The golf ball according to claim 1 , wherein a base resin constituting the paint film includes a polyurethane.
6. The golf ball according to claim 5 , wherein a polyol composition constituting the polyurethane contains a urethane polyol, wherein the urethane polyol includes a polyether diol having a number average molecular weight in a range from 600 to 3000 as a constituent component.
7. The golf ball according to claim 6 , wherein the urethane polyol has a weight average molecular weight ranging from 5000 to 20000.
8. The golf ball according to claim 6 , wherein the urethane polyol has a hydroxyl value ranging from 10 mgKOH/g to 200 mgKOH/g.
9. The golf ball according to claim 6 , wherein the urethane polyol further includes a triol as a constituent component.
10. The golf ball according to claim 9 , wherein a mass ratio (triol/polyether diol) of the triol to the polyether diol ranges from 0.2 to 6.0.
11. The golf ball according to claim 6 , wherein a polyisocyanate composition constituting the polyurethane contains at least one selected from the group consisting of a biuret-modified product of hexamethylene diisocyanate, an isocyanurate of hexamethylene diisocyanate, and an isocyanurate of isophorone diisocyanate.
12. The golf ball according to claim 11 , wherein the biuret-modified product of hexamethylene diisocyanate and the isocyanurate of hexamethylene diisocyanate are used in combination, and a mass ratio (biuret-modified product/isocyanurate) of the biuret-modified product of hexamethylene diisocyanate to the isocyanurate of hexamethylene diisocyanate ranges from 20/40 to 40/20.
13. The golf ball according to claim 5 , wherein a polyol composition constituting the polyurethane contains a polyrotaxane, wherein the polyrotaxane has a cyclodextrin, a linear molecule piercing through the cyclic structure of the cyclodextrin, and blocking groups located at both terminals of the linear molecule to prevent disassociation of the cyclodextrin, and at least a part of hydroxyl groups of the cyclodextrin is modified with a caprolactone chain via —O—C 3 H 6 —O— group.
14. The golf ball according to claim 13 , wherein the polyol composition further contains a polycaprolactone polyol, and a mass ratio (polycaprolactone polyol/polyrotaxane) of the polycaprolactone polyol to the polyrotaxane ranges from 5/95 to 90/10.
15. The golf ball according to claim 13 , wherein the polyol composition further contains a hydroxyl group modified vinyl chloride-vinyl acetate copolymer, and an amount of the hydroxyl group modified vinyl chloride-vinyl acetate copolymer in a polyol component of the polyol composition ranges from 4 mass % to 50 mass %.
16. The golf ball according to claim 13 , wherein the polyol composition further contains a modified silicone.
17. The golf ball according to claim 13 , wherein a polyisocyanate composition constituting the polyurethane contains an isocyanurate of hexamethylene diisocyanate.
18. The golf ball according to claim 1 , wherein the golf ball body comprises a core and a cover covering the core, and the cover has a slab hardness of 60 or less in Shore D hardness.
19. The golf ball according to claim 1 , wherein the golf ball body comprises a core and a cover covering the core, and the cover has a 10% elastic modulus of less than 120 kgf/cm 2 .
20. The golf ball according to claim 1 , wherein the golf ball has a coefficient of friction ranging from 0.35 to 0.60 calculated using a contact force tester.