Solid golf ball

Details Solid golf ball Solid golf ball

1999-12-16

2001-09-18

Graham, Mark S. (Department: 3711)

Games using tangible projectile

Golf

Ball

Reexamination Certificate

active

06290612

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multilayer golf ball having at least four layers and having excellent durability and a good “feel” when hit with a golf club.
2. Related Art
A number of approaches have been tried to enhance the feel and distance of solid golf balls composed of a solid core and a cover. One such approach has been to increase the number of layers in the ball. For example, JP-A 10-127819 discloses a golf ball wherein the solid core is formed to a three-layer construction of an inner layer, an intermediate layer, and an outer layer. The inner and outer layers are each made of rubber compositions, and the intermediate layer is composed of a thermoplastic elastomer, typically thermoplastic polyamide elastomer. These choices are made in order to provide improved distance and a soft feel.
Similarly intending to provide a good feel and improved distance, JP-A 10-179797 discloses a golf ball that has a four-layer construction comprising two inner and outer intermediate layers situated between a “center” serving as the core and a cover which corresponds to the ball's surface. The thickness and JIS-C hardness ranges are prescribed for each layer. Essentially, the inner intermediate layer made of ionomer resin is situated between the core and the outer intermediate layer made of rubber compositions as illustrated in the examples of this reference.
The above art attempts to enhance the feel and distance of a golf ball by increasing the number of layers and specifying the material and hardness for each layer.
However, in these prior-art golf balls, providing larger differences in hardness between the respective layers so as to further enhance performance tends to lead to stress concentration at the boundary surfaces between the layers, making the ball more prone to failure when hit. This problem is most acute in balls that use a rubber material in the intermediate layer to achieve relatively good resilience.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a multilayer golf ball composed of at least four layers which uses a rubber material in the intermediate layer to achieve good resilience and, even when the differences in hardness between the layers are increased to maximize the performance enhancing effect, exhibits excellent durability and feel.
Accordingly, the invention provides a solid golf ball comprising a core having at least one layer, an enclosing layer that encloses the core, an intermediate layer that encloses the enclosing layer, and a cover having at least one layer that encloses the intermediate layer. The intermediate layer of the ball is made of a rubber composition composed primarily of cis-1,4-polybutadiene, and the enclosing layer is composed primarily of a resin material. The enclosing layer and the intermediate layer have a difference in hardness at the boundary therebetween within ±3 JIS-C hardness units.
Typically, the enclosing layer in the golf ball is composed primarily of a polyester resin, polyurethane resin or a mixture thereof, and the core is composed primarily of a polyamide resin, ionomer resin, polyester resin, polycarbonate resin, polyarylate resin, ABS resin or a mixture thereof. Preferably the intermediate layer of the inventive ball has a JIS-C hardness of 45 to 85 on a surface thereof in contact with the enclosing layer. Moreover, the enclosing layer preferably has a thickness of 0.5 to 5.0 mm.
The present invention is based upon our discovery that when the rubber intermediate layer which is most subject to failure is provided on the inside thereof with a core-enclosing layer composed of a resin material having about the same hardness as the rubber intermediate layer and a relatively large impact strength, stress concentration arising from hardness differences can be shifted from the more failure-prone rubber intermediate layer to the impact-resistant core-enclosing layer. This enables a dramatic improvement in durability. In particular, the ball maintains an outstanding durability even when the difference in hardness between the core at the center of the ball and the intermediate layer about the core is increased to maximize the performance-enhancing effect. Moreover, the ball, when hit with a golf club, has a softer feel on impact than prior-art balls of this class, with a moderate degree of reaction (or less sting to the hands).


REFERENCES:
patent: 5772531 (1998-06-01), Ohsumi et al.
patent: 6045460 (2000-04-01), Hayashi et al.
patent: 10-127819 (1998-05-01), None
patent: 10-179797 (1998-07-01), None

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