RUBBER COMPOSITION FOR GOLF BALL, AND GOLF BALL
A rubber composition for golf balls includes (a) a base rubber, (b) a co-crosslinking agent which is an α,β-unsaturated carboxylic acid and/or a metal salt thereof, (c) a crosslinking initiator, (d) an alcohol and (e-1) an organosulfur, and the amount of component (d) is from 0.1 to 10 parts by weight per 100 parts by weight of the base rubber (a) and the organosulfur of component (e-1) is alkylphenoldisulfide polymers represented by the specific chemical formula. When the rubber composition is used in a golf ball having a core and a cover of one or more layers encasing the core, by setting the hardness difference in the core interior hardness profile to a large value while maintaining a desired core hardness, low spin properties can be manifested on golf ball shots, enabling the flight performance of the ball to be improved.
1 . A rubber composition for golf balls, comprising:
(a) a base rubber,
(b) a co-crosslinking agent which is an α,β-unsaturated carboxylic acid or a metal salt thereof or both,
(c) a crosslinking initiator,
(d) an alcohol,
(e-1) an organosulfur,
wherein the amount of component (d) is from 0.1 to 10 parts by weight per 100 parts by weight of the base rubber (a) and the organosulfur of component (e-1) is alkylphenoldisulfide polymers represented by the following chemical formula:
wherein R is an alkyl group and n is degree of polymerization in a range of 2 to 20.
2 . The rubber composition of claim 1 , wherein the alkyl group of R in the chemical formula is an lower alkyl group of 1 to 6 carbon atoms selected from the group consisting of methyl, ethyl, n-propyl, iso-propyl, n-butyl, tert-butyl, n-amyl (pentyl), iso-amyl (pentyl), tert-amyl (pentyl), sec-isoamyl, neopentyl, n-hexyl, iso-hexyl, tert-hexyl groups.
3 . The rubber composition of claim 1 , wherein the organosulfur of component (e-1) is amylphenoldisulfide polymers.
4 . The rubber composition of claim 1 , wherein the amount of component (e-1) is from 0.05 to 5.0 parts by weight per 100 parts by weight of the base rubber (a).
5 . The rubber composition of claim 1 , wherein component (d) is a lower alcohol having a molecular weight of less than 500.
6 . The rubber composition of claim 5 , wherein component (d) is a lower alcohol having a molecular weight of less than 200.
7 . The rubber composition of claim 1 , wherein the amount of component (d) is from 0.5 to 5 parts by weight per 100 parts by weight of the base rubber (a).
8 . The rubber composition of claim 1 , wherein component (d) is a monohydric, dihydric or trihydric alcohol.
9 . The rubber composition of claim 3 , wherein component (d) is butanol, glycerol, ethylene glycol or propylene glycol.
10 . The rubber composition of claim 1 , further comprising (e) an organosulfur compound which is different from the organosulfur of component (e-1).
11 . The rubber composition of claim 1 , wherein the vulcanized form of the rubber composition is a golf ball core.
12 . The rubber composition of claim 11 , wherein the vulcanized rubber composition has a surface and a center with a hardness difference therebetween of at least 20 on the JIS-C hardness scale.
13 . A golf ball comprising a core and a cover of one or more layers encasing the core, wherein the core is formed of the rubber composition of claim 1 .
14 . The golf ball of claim 13 , wherein the core has a hardness profile in which a surface and a center of the core have a hardness difference therebetween of at least 20 on the JIS-C hardness scale.
15 . The golf ball of claim 13 , wherein the core has a center hardness of from 50 to 65 on the JIS-C hardness scale.
16 . The golf ball of claim 13 , wherein the core has a surface hardness of from 72 to 95 on the JIS-C hardness scale.
17 . The golf ball of claim 13 , wherein the core has an amount of deflection of from 2.0 to 5.0 mm when compressed under a find load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf).