Golf ball

Abstract

The invention provides a golf ball having a core formed by vulcanizing a rubber composition and a cover composed primarily of a polyurethane material. The rubber composition of the core includes 100 parts by weight of a base rubber, from 10 to 40 parts by weight of an unsaturated carboxylic acid or a metal salt thereof, a peroxyketal (a) and a monophenol-type antioxidant (b), the weight ratio (a)/(b) of the peroxyketal to the monophenol-type antioxidant being from 5 to 50. The ball has an excellent discoloration resistance and an outstanding distance and feel on shots taken with a middle iron.

1 . A golf ball comprising a core formed by vulcanizing a rubber composition and a cover composed primarily of a polyurethane material, wherein the rubber composition of the core includes 100 parts by weight of a base rubber, from 10 to 40 parts by weight of an unsaturated carboxylic acid or a metal salt thereof, a peroxyketal (a) and a monophenol-type antioxidant (b),
 wherein the core has a deflection when compressed under a final load of 130 kgf from an initial load of 10 kgf of from 2.0 to 6.0 mm, and the ball has a deflection when compressed under a final load of 130 kgf from an initial load of 10 kgf of from 2.2 to 5.0 mm, and the value obtained by subtracting (the Shore D hardness in a portion of the core 5 mm inside the core surface) from (the Shore D hardness of the surface portion of the core) is in a range of from 3 to 13.   
     
     
         2 . The golf ball of  claim 1 , wherein the peroxyketal is 1,1-bis(t-butylperoxy)cyclohexane and is included in an amount of from 1.5 to 3.0 parts by weight per 100 parts by weight of the base rubber. 
     
     
         3 . The golf ball of  claim 1 , wherein the monophenol-type antioxidant is 2,6-di-t-butyl-4-methylphenol and is included in an amount of from 0.1 to 0.2 part by weight per 100 parts by weight of the base rubber. 
     
     
         4 . The golf ball of  claim 1 , wherein the polyurethane material of the cover is a material formed by injection-molding a single resin blend composed primarily of (A) a thermoplastic polyurethane and (B) a polyisocyanate compound, in at least some portion of the polyisocyanate compound all the isocyanate groups on the molecule remain in an unreacted state. 
     
     
         5 . The golf ball of  claim 1 , wherein the ball has from 250 to 350 dimples formed on a surface thereof, which dimples are of at least five types, include from 6 to 30 small-diameter dimples with a diameter of not more than 3.0 mm, and have a dimple surface coverage (SR), defined as the sum of the surface areas on a hypothetical sphere that are circumscribed by the edges of the respective dimples as a proportion of the surface area of the hypothetical sphere, of at least 70%; and the ball, when struck, has a coefficient of lift CL at a Reynolds number of 70,000 and a spin ratio of 2,000 rpm which is at least 60% of the coefficient of lift CL at a Reynolds number of 80,000 and a spin rate of 2,000 rpm. 
     
     
         6 . The golf ball of  claim 1 , wherein the weight ratio (a)/(b) of the peroxyketal to the monophenol-type antioxidant is from 15 to 50. 
     
     
         7 . The golf ball of  claim 1 , wherein the base rubber comprises at least 60% by weight of polybutadiene.