Rubber composition for golf ball
A rubber composition for golf balls includes (a) a base rubber, relative amounts of (b) a co-crosslinking agent which is an α,β-unsaturated carboxylic acid and/or a metal salt thereof and of (c) an organic peroxide that together satisfy a specific condition, and (d) a specific amount of a moisture-providing agent, the latter being a substance which includes on the structure thereof a water constituent other than free water and eliminates moisture under heating or a substance which thermally decomposes under heating, releasing a water constituent. When the hardness difference in the internal hardness profile of a golf ball core made of the composition is large, the ball exhibits a low spin rate on shots, improving the flight performance of the ball, and the durability of the ball to cracking is enhanced.
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) an organic peroxide,
(d) a moisture-providing agent, and
(e) an alkylphenol disulfide polymer,
wherein the moisture-providing agent is a substance which includes on a structure thereof a water constituent other than free water and eliminates moisture under heating or a substance which thermally decomposes under heating, releasing a water constituent, and components (b) and (c) are included in relative amounts such that E, defined by the formula
E=molar amount of component (b)/molar amount of active oxygens in component (c), has a value of 71 or more.
2 . The rubber composition of claim 1 , wherein component (d) is included in an amount of from 0.1 to 15 parts by weight per 100 parts by weight of component (a).
3 . The rubber composition of claim 1 , wherein the base rubber serving as component (a) is a polybutadiene synthesized using a rare earth catalyst.
4 . The rubber composition of claim 1 , further comprising:
(f) a hindered phenol or a benzimidazole of the general formula below, a metal salt of the benzimidazole or both the benzimidazole and a metal salt thereof
(wherein R is a hydrogen atom or a hydrocarbon group of 1 to 20 carbon atoms, and m is an integer from 1 to 4, with the proviso that when m is 2 or more, the occurrences of R may be the same or may mutually differ).
5 . The golf ball of claim 1 , wherein the amount of component (b) is from 45 to 60 parts by weight per 100 parts by weight of the base rubber (a).
6 . The golf ball of claim 1 , wherein the amount of component (c) is from 0.05 to 0.75 part by weight per 100 parts by weight of the base rubber (a).
7 . The golf ball of claim 1 , wherein the component (d) is hydrotalcite or aluminum hydroxide.
8 . The golf ball of claim 4 ,
wherein the component (f) is a benzimidazole of the general formula, a metal salt of the benzimidazole or both the benzimidazole and a metal salt thereof.
9 . 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) an organic peroxide, and
(d) a moisture-providing agent,
wherein the moisture-providing agent is a substance which includes on a structure thereof a water constituent other than free water and eliminates moisture under heating or a substance which thermally decomposes under heating, releasing a water constituent, and components (b) and (c) are included in relative amounts such that E, defined by the formula
E=molar amount of component (b)/molar amount of active oxygens in component (c), has a value of 71 or more,
further comprising a benzimidazole of the general formula below, a metal salt of the benzimidazole or both the benzimidazole and a metal salt thereof
(wherein R is a hydrogen atom or a hydrocarbon group of 1 to 20 carbon atoms, and m is an integer from 1 to 4, with the proviso that when m is 2 or more, the occurrences of R may be the same or may mutually differ).
10 . The rubber composition of claim 9 , wherein component (d) is included in an amount of from 0.1 to 15 parts by weight per 100 parts by weight of component (a).
11 . The rubber composition of claim 9 , wherein the base rubber serving as component (a) is a polybutadiene synthesized using a rare earth catalyst.
12 . The rubber composition of claim 9 , further comprising:
(e) sulfur or an organosulfur compound.
13 . The rubber composition of claim 12 , wherein component (e) is an organosulfur compound selected from the group consisting of thiols and alkylphenol disulfide polymers.
14 . The golf ball of claim 9 , wherein the amount of component (b) is from 45 to 60 parts by weight per 100 parts by weight of the base rubber (a).
15 . The golf ball of claim 9 , wherein the amount of component (c) is from 0.05 to 0.75 part by weight per 100 parts by weight of the base rubber (a).
16 . The golf ball of claim 9 , wherein the component (d) is hydrotalcite or aluminum hydroxide.