Golf ball
An object of the present invention is to provide a golf ball having good spin performance on approach shots and good shot feeling as well as excellent stain resistance by precisely controlling physical properties of a paint film actually formed on a surface of a golf ball body. 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 is such that a linear approximation curve obtained by a least square method has a slope in an absolute value ranging from 0.0001 to 0.0020 when a loss tangent tan δ thereof measured by a nanoindentation method is plotted as a vertical axis against a measuring frequency (Hz) as a horizontal axis, and that an elastic modulus thereof measured by a nanoindentation method ranges from 0.040 GPa to 0.600 GPa.
1. A golf ball comprising a golf ball body and a paint film formed on a surface of the golf ball body, wherein
a base resin constituting the paint film is a polyurethane obtained through a reaction between a polyol compound and a polyisocyanate compound,
the polyol compound contains a urethane polyol,
the urethane polyol contains a polyether diol having a number average molecular weight of 550 or more and 3000 or less as a polyol component, and
the paint film is such that a linear approximation curve obtained by a least square method has a slope in an absolute value ranging from 0.0004 to 0.0015 when a loss tangent tan δ of the paint film in a state of being formed on the surface of the golf ball body measured by the following measuring condition 1 is plotted as a vertical axis against a measuring frequency (Hz) as a horizontal axis, and that an elastic modulus of the paint film in the state of being formed on the surface of the golf ball body measured by the following measuring condition 2 ranges from 0.040 GPa to 0.600 GPa:
<Measuring condition 1>
Measuring apparatus: “TI950 Tribo Indenter” available from Hysitron, Inc.
Indenter specification: Berkovich type
Test load (maximum indenting load): 100 μN
Frequency: 1 Hz, 10 Hz, 105 Hz
Measuring environment: 23° C., RH 50%, in the atmosphere;
<Measuring condition 2>
Measuring apparatus: “TI950 Tribo Indenter” available from Hysitron, Inc.
Indenter specification: Berkovich type
Maximum indenting depth: 300 nm
Measuring environment: 23° C., RH 50%, in the atmosphere.
2. The golf ball according to claim 1 , wherein the linear approximation curve has the slope in an absolute value ranging from 0.0005 to 0.0013.
3. The golf ball according to claim 1 , wherein the loss tangent tan δ of the paint film in the state of being formed on the surface of the golf ball body at the measuring frequency of 1 Hz ranges from 0.200 to 0.700.
4. The golf ball according to claim 1 , wherein the loss tangent tan δ of the paint film in the state of being formed on the surface of the golf ball body at the measuring frequency of 10 Hz ranges from 0.150 to 0.400.
5. The golf ball according to claim 1 , wherein the loss tangent tan δ of the paint film in the state of being formed on the surface of the golf ball body at the measuring frequency of 105 Hz ranges from 0.140 to 0.300.
6. The golf ball according to claim 1 , wherein a hardness of the paint film in the state of being formed on the surface of the golf ball body measured by the above measuring condition 2 ranges from 0.001 GPa to 0.020 GPa.
7. The golf ball according to claim 1 , wherein the paint film has a thickness in a range from 5 μm to 50 μm.
8. The golf ball according to claim 1 , wherein the polyisocyanate compound contains an isocyanurate-modified product of hexamethylene diisocyanate, a biuret-modified product of hexamethylene diisocyanate and an isocyanurate-modified product of isophorone diisocyanate.
9. The golf ball according to claim 1 , wherein in a reaction between the polyol compound and the polyisocyanate compound, a molar ratio (NCO/OH) of an isocyanate group (NCO group) in the polyisocyanate compound to a hydroxyl group (OH group) in the polyol compound ranges from 0.15 to 1.20.
10. The golf ball according to claim 1 , wherein the golf ball body comprises a core and a cover covering the core.
11. The golf ball according to claim 10 , wherein the golf ball body further comprises at least one intermediate layer between the core and the cover.
12. The golf ball according to claim 11 , wherein a hardness difference (intermediate layer-cover) between the intermediate layer and the cover ranges from 10 to 60 in Shore D hardness.
13. The golf ball according to claim 11 , wherein a Shore D hardness ratio (intermediate layer/cover) of the intermediate layer to the cover ranges from 1.1 to 5.
14. The golf ball according to claim 11 , wherein the intermediate layer has a material hardness ranging from 50 to 80 in Shore D hardness.
15. The golf ball according to claim 10 , wherein a hardness difference (Hs−Ho) between a surface hardness Hs of the core and a center hardness Ho of the core ranges from 10 to 50 in Shore C hardness.
16. The golf ball according to claim 15 , wherein the surface hardness Hs of the core ranges from 60 to 100 in Shore C hardness.
17. The golf ball according to claim 15 , wherein the center hardness Ho of the core ranges from 40 to 80 in Shore C hardness.
18. The golf ball according to claim 1 , wherein the golf ball body is a two-piece construction.