Golf ball
The invention provides a golf ball having a core and a cover of one layer or a plurality of layers, the core being formed of a material molded under heat from a rubber composition which includes (A) a base rubber, (B) an organic peroxide, and (C) water and/or a metal monocarboxylate. The product P×E of the difference P (mol/m 3 ) in crosslink density between the core surface and the core center, as measured based on a toluene swelling test, multiplied by the deflection E (mm) of the core when compressed under a final load of 1,275 N (130 kgf) from an initial load state of 98 N (10 kgf) is at least 28×10 2 mol/m 3 ·mm.
1. A golf ball comprising a core and a cover of one layer or a plurality of layers, wherein the core is formed of a material molded under heat from a rubber composition comprising the following components (A) to (C):
(A) a base rubber,
(B) an organic peroxide, and
(C) water;
and the product P×E of the difference P (mol/m 3 ) in crosslink density between a surface of the core and a center of the core, as measured based on a toluene swelling test, multiplied by the deflection E (mm) of the core when compressed under a final load of 1,275 N (130 kgf) from an initial load state of 98 N (10 kgf) is at least 28×10 2 mol/m 3 ·mm.
2. The golf ball of claim 1 , wherein the rubber composition before vulcanization has a moisture content of at least 1,000 ppm.
3. The golf ball of claim 1 , wherein the core after vulcanization has a higher moisture content at the core center than at the core surface.
4. The golf ball of claim 1 , wherein the difference between the crosslink density at the core surface and the crosslink density at the core center, both of which are crosslink densities measured based on a toluene swelling test, is at least 9×10 2 mol/m 3 .
5. The golf ball of claim 1 , wherein the rubber composition includes from 0.1 to 5 parts by weight of an organosulfur compound per 100 parts by weight of the base rubber.
6. The golf ball of claim 1 , wherein the core of the golf ball after molding of the cover has an initial velocity V 0 , as measured after peeling away the cover, of at least 77.0 m/s and not more than 78.5 m/s.
7. The golf ball of claim 1 which satisfies the relationship V 0 −V 60 <0.7, wherein V 0 is the initial velocity of the core in the golf ball after molding of the cover, as measured after peeling away the cover, and V 60 is the initial velocity of the core 60 days after measuring V 0 .
8. The golf ball of claim 1 wherein, when the loss tangent of the core center is measured at a temperature of −12° C. and a frequency of 15 Hz, letting tan δ 1 be the loss tangent at a dynamic strain of 1% and tan δ 10 be the loss tangent at a dynamic strain of 10%, the slope of these tan δ values, expressed as [(tan δ 10 −tan δ 1 )/(10% −1% )], is not more than 0.003.
9. The golf ball of claim 1 , wherein the JIS-C hardness difference obtained by subtracting a core center hardness from a core surface hardness is at least 20 and not more than 40.
10. A golf ball comprising a core and a cover of one layer or a plurality of layers, wherein the core is formed of a material molded under heat from a rubber composition comprising the following components (A) to (C):
(A) a base rubber,
(B) an organic peroxide, and
(C) water;
and, when the loss tangent of the core center is measured at a temperature of −12° C. and a frequency of 15 Hz, letting tan δ 1 be the loss tangent at a dynamic strain of 1% and tan δ 10 be the loss tangent at a dynamic strain of 10%, the slope of these tan δ values, expressed as [(tan δ 10 −tan δ 1 )/(10% −1% )], is not more than 0.003.
11. The golf ball of claim 10 , wherein the rubber composition before vulcanization has a moisture content of at least 1,000 ppm.
12. The golf ball of claim 10 , wherein the core after vulcanization has a higher moisture content at the core center than at the core surface.
13. The golf ball of claim 10 , wherein the core of the golf ball after molding of the cover has an initial velocity V 0 , as measured after peeling away the cover, of at least 77.0 m/s and not more than 78.5 m/s.
14. The golf ball of claim 10 , wherein the rubber composition includes from 0.1 to 5 parts by weight of an organosulfur compound per 100 parts by weight of the base rubber.
15. The golf ball of claim 10 which satisfies the relationship V 0 −V 60 <0.7, wherein V 0 is the initial velocity of the core in the golf ball after molding of the cover, as measured after peeling away the cover, and V 60 is the initial velocity of the core 60 days after measuring V 0 .
16. The golf ball of claim 10 , wherein the JIS-C hardness difference obtained by subtracting a core center hardness from a core surface hardness is at least 20 and not more than 40.