Golf ball
The invention provides a golf ball having 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 containing (A) a base rubber, (B) an organic peroxide, and (C) water and/or a metal monocarboxylate, and has a hysteresis loss of 50% or less when compressed at a load cell speed of 500 mm/min and under a constant load of 5,000 N.
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/or a metal monocarboxylate,
and has a hysteresis loss of 50% or less when compressed at a load cell speed of 500 mm/min and under a constant load of 5,000 N.
2. The golf ball of claim 1 , wherein the core has a JIS-C hardness difference obtained by subtracting a hardness at the center of the core from a hardness at a surface of the core which is at least 20.
3. The golf ball of claim 1 , wherein the core has a hardness at an interior thereof such that a value obtained by subtracting a JIS-C hardness H 5.0 at a position 5.0 mm outward from a center of the core and towards a periphery of the core from a JIS-C hardness H 15.0 at a position 15.0 mm outward from the core center and toward the core periphery is a positive value.
4. The golf ball of claim 1 , wherein the core has a diameter of not more than 42.0 mm and a deflection when compressed under a final load of 1,275 N (130 kgf) from an initial load state of 98 N (10 kgf) of from 2.0 to 6.0 mm.
5. The golf ball of claim 1 , wherein the rubber composition before vulcanization has a moisture content of at least 1,000 ppm.
6. 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.
7. The golf ball of claim 1 , wherein the core after vulcanization has a higher moisture content at a center of the core than at a surface of the core.
8. The golf ball of claim 1 , wherein a product P×E of a 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 a deflection E (mm) of the core when compressed under a final load of 1,275N (130 kgf) from an initial load state of 98N (10 kgf) is at least 28×102 mol/m 3 *mm.
9. The golf ball of claim 1 , wherein, when a loss tangent of a center of the core is measured at a temperature of −12° C. and a frequency of 15 Hz, letting tan δ 1 be a loss tangent at a dynamic strain of 1% and tan δ 10 be a 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.
10. The golf ball of claim 1 , wherein each layer of the cover has a thickness in a range from 0.5 to 2.5 mm.
11. The golf ball of claim 1 , wherein at least one layer of the cover is formed of a resin composition containing at least one of (I) and (II) below:
(I) an ionic or nonionic olefin-unsaturated carboxylic acid copolymer,
(II) an ionic or nonionic olefin-unsaturated carboxylic acid-carboxylic acid ester copolymer.
12. The golf ball of claim 11 , wherein copolymers (I) and (II) have a base monomer that is ethylenic.
13. The golf ball of claim 11 , wherein the carboxylic acid in ionic copolymers (I) and (II) is at least 30 mol % neutralized.