Games using tangible projectile – Golf – Ball
Reexamination Certificate
1999-06-02
2002-11-05
Vo, Peter (Department: 3729)
Games using tangible projectile
Golf
Ball
C473S373000, C473S374000, C473S375000, C473S376000, C473S377000
Reexamination Certificate
active
06475103
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a thread wound golf ball. More particularly, it relates to a solid center type thread wound golf ball having a long flight distance, while having a soft and good shot feel at the time of hitting, as good as liquid center type thread wound golf balls.
BACKGROUND OF THE INVENTION
Many golf balls are commercially selling, but they are typically classified into solid golf balls such as a two-piece golf ball, a three-piece golf ball and the like, and thread wound golf balls. The solid golf ball consists of a solid core of molded rubber material and a cover of thermoplastic resin (e.g. ionomer resin) covering on the solid core. The thread wound golf ball consists of a solid or liquid center, a thread wound layer formed on the center and a cover of ionomer resin or balata etc. having a thickness of 1 to 2 mm covering on the thread wound layer.
The thread wound golf ball, when compared with the solid golf ball, has better shot feel at the time of hitting and better controllability at a approach shot. The thread wound golf ball is generally approved of or employed by high level golfers, especially professional golfers, who regard these characteristics as most important.
In the thread wound golf balls, there are two types, namely one comprising a solid center formed from integrally molded rubber material, and the other comprising a liquid center composed of a hollow rubber sphere and liquid encapsulated in the sphere. Among them, a thread wound golf ball comprising a liquid center and a balata (transisoprene) cover is particularly approved of or employed by high level golfers, especially professional golfers, because of the good shot feel and excellent controllability at the approach shot. However, the liquid center type thread wound golf ball does not show long flight distance when compared with the solid center type thread wound golf ball.
In addition, the liquid center type thread wound golf ball has poor rebound characteristics at a low temperature, although the solid center type thread wound golf ball has no deterioration of performance depending on temperature change. Accordingly, the solid center type thread wound golf ball has been generally employed and studied.
In order to impart soft shot feel and good controllability to the solid center type thread wound golf ball, it has been proposed in Japanese Patent No. 2715885, Japanese Patent Kokai Publication Nos. 271537/1997 and 201881/1998, and the like that the solid center of the solid center type thread wound golf ball be controlled to have a suitable hardness distribution, whereby compromising flight distance with shot feel and controllability.
However, these proposed solid center type thread wound golf balls do not show sufficient performance. Therefore, it is required to provide the solid center type thread wound golf ball, so that has sufficient flight distance as long as solid golf balls, while keeping the advantage of a good shot feel and excellent controllability as good as the liquid center type thread wound golf balls.
OBJECTS OF THE INVENTION
A main object of the present invention is to provide a solid center type thread wound golf ball having long flight distance, and having a soft and good shot feel at the time of hitting the ball as good as the liquid center type thread wound golf ball.
According to the present invention, the object described above has been accomplished by employing a thread wound core which comprises a solid center, and adjusting a diameter, a ratio of surface hardness in JIS-C hardness to diameter and a ratio of center hardness in JIS-C hardness to diameter in a solid center, and controlling a Shore D hardness of a cover to a specified range, thereby providing a solid center type thread wound golf ball having long flight distance, while having good shot feel at the time of hitting as good as the liquid center type thread wound golf ball.
SUMMARY OF THE INVENTION
The present invention provides a thread wound golf ball comprising a solid center, a thread rubber layer formed on the solid center, and a cover covering the thread rubber layer, wherein
the solid center has a diameter of 33 to 38 mm, a ratio of surface hardness in JIS-C hardness to diameter of 2.15 to 2.50, and a ratio of center hardness in JIS-C hardness to diameter of 1.30 to 2.00, and
the cover has a Shore D hardness of 40 to 65.
DETAILED DESCRIPTION OF THE INVENTION
The thread wound golf ball of the present invention will be explained hereinafter. The golf ball of the present invention comprises a solid center, a thread rubber layer formed on the solid center, and a cover formed on the thread rubber layer. The solid center is formed from a rubber composition comprising a base rubber, a co-crosslinking agent, an organic peroxide, a filler and the like.
The base rubber may be natural rubber and/or synthetic rubber, which has been conventionally used for solid golf balls. Preferred is high-cis polybutadiene rubber containing a cis-1,4 bond of not less than 40%, preferably not less than 80%. The polybutadiene rubber may be mixed with natural rubber, polyisoprene rubber, styrene-butadiene rubber, ethylene-propylene-diene rubber (EPDM), and the like.
The co-crosslinking agent may be a metal salt of &agr;,&bgr;-unsaturated carboxylic acid, particularly mono- or di-valent metal salts, such as zinc or magnesium salts of &agr;,&bgr;-unsaturated carboxylic acids having 3 to 8 carbon atoms (e.g. acrylic acid, methacrylic acid, etc.). The preferred co-crosslinking agent is zinc acrylate because it imparts high rebound characteristics to the resulting golf ball. The amount of the co-crosslinking agent may be 10 to 40 parts by weight, preferably 15 to 35 parts by weight, based on 100 parts by weight of the base rubber. When the amount of the co-crosslinking agent is larger than 40 parts by weight, the center is too hard, and the shot feel is poor. On the other hand, when the amount of the co-crosslinking agent is smaller than 10 parts by weight, the center is soft. Therefore the rebound characteristics are degraded which reduce flight distance.
The crosslinking agents may be an organic peroxide such as dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(t-butylperoxy)-hexane, di-t-butyl peroxide and the like. The preferred organic peroxide is dicumyl peroxide. The amount of the organic peroxide is not limited, but may be from 0.5 to 2.0 parts by weight, preferably 0.8 to 1.5 parts by weight, based on 100 parts by weight of the base rubber. When the amount of the organic peroxide is smaller than 0.5 parts by weight, the center is too soft. Therefore the rebound characteristics are degraded which reduces flight distance. On the other hand, when the amount of the organic peroxide is larger than 2.0 parts by weight, the center is too hard, and the shot feel is poor.
The filler, which can be used for the core of the golf ball, includes for example, an inorganic filler (such as zinc oxide, barium sulfate, calcium carbonate, and the like), a high specific gravity metal powder (such as tungsten powder, molybdenum powder, and the like), and mixture thereof. The amount of the filler is not limited and can vary depending on the specific gravity and size of the center, the thread rubber layer and the cover, but may be from 20 to 70 parts by weight, preferably 25 to 60 parts by weight, based on 100 parts by weight of the base rubber. When the amount of the filler is smaller than 20 parts by weight, the center is too light, and the resulting golf ball is too light. On the other hand, when the amount of the filler is larger than 70 parts by weight, the center is too heavy and the resulting golf ball is too heavy.
The rubber composition for the solid center of the present invention can contain other components, which have been conventionally used for preparing the core of solid golf balls, such as antioxidants or peptizing agents. The amount of the antioxidant is preferably 0.2 to 0.5 parts by weight based on 100 parts by weight of the base rubber.
The solid center is obta
Kim Paul
Sumitomo Rubber Industries Ltd.
Vo Peter
LandOfFree
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