Golf ball

Abstract

To provide a golf ball that ensures both an improved durability and an extended flight distance, in which cracks or breakage of a core can be prevented while making the hardness of the core surface greater so as to obtain the greater difference in hardness between the core surface and the core center. The golf ball of the present invention includes a core and a cover that surrounds the core, in which the core includes a base rubber and an unsaturated carboxylic acid or its salt as a co-crosslinking agent, the core has a surface hardness of 80 or more in terms of JIS-C hardness, and the unsaturated carboxylic acid or its salt contained in a region ranging from a surface of the core toward its center by less than 2 mm has an average particle diameter of less than 90 μm.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]This Application claims priority from Japanese Patent Application No. 2016-256210 filed Dec. 28, 2016, which is incorporated herein by reference in its entirety.BACKGROUND OF THE INVENTION[0002]The present invention relates to a golf ball, and more particularly, relates to a golf ball that ensures both improved durability and extended flight distance.[0003]The core of a golf ball is manufactured by molding a rubber composition, in which an unsaturated carboxylic acid or its salt as a co-crosslinking agent is contained in a base rubber such as butadiene rubber, under heat and pressure. In this rubber composition, the unsaturated carboxylic acid or its salt is contained in a large amount with respect to the base rubber. However, the unsaturated carboxylic acid or its salt is more likely to adhere to the surface of the inner wall of a kneading machine during kneading, thereby hindering kneading operation. Furthermore, since the unsaturated ca...

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Benefits of technology

[0008]It is therefore an object of the present invention to provide a golf ball that ensures both an improved durability and an increased flight distance, in which cracks or breakage of a core can be prevented while making the hardness of the core surface greater so as to obtain the larger difference in hardness between the core surface and the core center.

[0014]The fact that cracks or breakage occur on the core surface has been found from studies on the reasons that golf balls having a core with a core surface hardness of 80 or more in terms of JIS-C hardness exhibit poor durability. This is supposedly because if the core surface of the golf ball is too hard, cracks occur due to being unable to resist deformation at the time of impact, thereby leading to breakage. Furthermore, as a result of further studies on the above reason by the present inventors, it has been found that since an unsaturated carboxylic acid or its salt as a co-crosslinking agent remains dispersedly in a base rubber, if the core surface is too hard, cracks occur only when the co-crosslinking agent having larger particles is contained in the core surface. In other words, according to the present invention, even if the core surface is hard and has a hardness of 80 or more in terms of JIS-C hardness, cracks can be avoided by excluding the unsaturated carboxylic acid or its salt having an average particle diameter of 90 μm or more from the region ranging from the core surface toward the core center by less than 2 mm, thereby enabling the provision of a golf ball with both improved durability and extended flight distance.

[0015]The above problem can be solved by using the unsaturated carboxylic acid or its salt having a smaller average particle diameter as the co-crosslinking agent added to the base rubber. However, since not only does it take time to form the unsaturated carboxylic acid or its salt having a smaller average particle diameter, but it also requires complicated manufacturing steps, the problem of increased manufacturing cost further arises due to longer time for manufacturing the core and in turn, manufacturing a golf ball. Therefore, the core of the present invention may comprise a multi-layer structure having at least a center core located in the center of the core and an outer core surrounding the center core and having a thickness of 2 mm or more. By making the average particle diameter of the unsaturated carboxylic acid or its salt contained in the center core 90 μm or more, the amount of usage of the unsaturated carboxylic acid or its salt having a smaller average particle diameter can be reduced and its manufacturing time can be shortened, thereby reducing the manufacturing cost.

Problems solved by technology

However, a golf ball, which adopts a core having a harder core surface to obtain the greater difference in hardness between the core surface and core center, has such problems in durability that cracks occur in the core and the core breaks at the time of impact of the golf ball.

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