Rubber composition for golf ball, and golf ball
The present invention provides the rubber composition for a golf ball 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, and (d) an alcohol, 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 compounding ratio between component (b) and component (c) is set to at least 60 of E value that is represented by “E=the molar amount of component (b)/the molar amount of the active oxygen of component (c), and a golf ball using the rubber composition, in order to achieve the object that good durability of the golf ball to impact is maintained.
1 . 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, comprising:
(a) a base rubber,
(b) zinc diacrylate (ZDA) as a co-crosslinking agent,
(c) a crosslinking initiator, and
(d) an alcohol,
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 compounding ratio between component (b) and component (c) is set to at least 60 of E value that is represented by “E=the molar amount of component (b)/the molar amount of the active oxygen of component (c)”, the core includes grafted polymers of BR-ZDA in which ZDA nanoparticles agglomerate to become secondary particles and further the secondary particles are connected mutually such that a network structure is formed, and the core has a hardness profile in which a surface and a center of the core have a hardness difference therebetween of at least 16 on the JIS-C hardness scale.
2 . The golf ball of claim 1 , wherein the core has an amount of deflection of not more than 3.2 mm when compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf).
3 . The golf ball of claim 1 , wherein component (d) is a lower alcohol having a molecular weight of less than 200.
4 . The golf ball of claim 1 , wherein component (d) is butanol, glycerol, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, or tripropylene glycol.
5 . The golf ball of claim 1 , wherein component (d) has a value obtained by dividing the molecular weight by the number of hydroxyl groups (valence) that is 100 or less.
6 . The golf ball of claim 1 , wherein the amount of component (d) is from 0.1 to 5 parts by weight per 100 parts by weight of the base rubber (a).
7 . The golf ball of claim 1 , wherein the E value is at least 70.
8 . The golf ball of claim 1 , wherein component (a) is polybutadiene synthesized with a rare-earth catalyst.
9 . The golf ball of claim 1 , further comprising sulfur or an organosulfur compound serving as component (e).
10 . The golf ball of claim 1 , wherein the component (e) is the organosulfur compound selected among thiols and alkylphenoldisulfide polymers.
11 . The golf ball of claim 1 , wherein, further as component (f), hinderedphenol or benzoimidazole of the following general formula (1) and/or a metal salt is included
wherein in formula (1), 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 each R being the same or different when m is 2 or more.
12 . The golf ball of claim 1 , wherein the amount of component (b) is from 38.5 to 60 parts by weight per 100 parts by weight of the base rubber (a).
13 . The golf ball of claim 1 , wherein the amount of component (c) is from 0.05 to 0.80 part by weight per 100 parts by weight of the base rubber (a).
14 . The golf ball of claim 1 , wherein component (d) is glycerol.
15 . The golf ball of claim 10 , wherein the component (e) is the alkylphenoldisulfide polymers.
16 . The golf ball of claim 15 , wherein the alkylphenoldisulfide polymers are amylphenoldisulfide polymers.