Games using tangible projectile – Golf – Ball
Reexamination Certificate
1999-07-22
2001-11-13
Graham, Mark S. (Department: 3711)
Games using tangible projectile
Golf
Ball
C524S432000
Reexamination Certificate
active
06315679
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a thread wound golf ball. More particularly, it relates to a thread wound golf ball having excellent rebound characteristics.
BACKGROUND OF THE INVENTION
Hitherto, a polybutadiene containing a cis-1, 4 bond of not less than 80%, which is synthesized using nickel-containing catalyst, has been mainly used as a base rubber of a rubber composition for a one-piece solid golf ball, a core of a solid golf ball (such as a two-piece golf ball or three-piece golf ball), or a solid center of a thread wound golf ball. This is because the nickel-catalyzed polybutadiene imparts excellent rebound characteristics and good durability to the golf balls.
It is also known to the art that a lanthanide-catalyzed polybutadiene, i.e. a polybutadiene synthesized using lanthanoid-containing catalyst, is used for the application of golf balls. For example, Japanese Patent No. 2678240 proposes that a rubber mixture of
85 to 15 parts by weight of a nickel- or cobalt-catalyzed polybutadiene having a cis-1, 4 content of more than 40% and a Mooney viscosity of less than 50, and
15 to 85 parts by weight of a lanthanide-catalyzed polybutadiene having a cis-1, 4 content of more than 40% and a Mooney viscosity of less than 50 can be suitably used for a golf ball. However, when the nickel- or cobalt-catalyzed polybutadiene having such a low Mooney viscosity (less than 50) and the lanthanide-catalyzed polybutadiene having such a low Mooney viscosity (less than 50) are used as base rubber for a rubber composition of golf balls, the resulting golf ball does not have sufficient rebound characteristics and durability.
A thread wound golf ball is composed of a solid center, a thread rubber layer formed on the solid center and a cover formed on the thread rubber layer, and the thread rubber layer is believed to give rebound characteristics to the golf ball. In order to obtain high launch angle and low spin amount for extending flight distance, it has recently been proposed that the thread rubber layer is made thinner and the solid center is made larger. The thin thread rubber layer does not give sufficient rebound characteristics and therefore the solid center has to have higher rebound characteristics.
OBJECTS OF THE INVENTION
A main object of the present invention is to provide a thread wound golf ball having excellent rebound characteristics.
According to the present invention, the object described above has been accomplished by using a rubber composition comprising a mixture consisting of (a) polybutadiene synthesized using nickel-containing catalyst and (b) polybutadiene synthesized using lanthanide-containing catalyst for a solid center, adjusting a Mooney viscosity and a weight ratio of the polybutadienes (a) and (b) to a specified range, thereby providing a thread wound golf ball having excellent rebound characteristics.
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 at least one layer of a cover covering the thread rubber layer, wherein the solid center comprises at least one rubber layer, the rubber layer is formed from a rubber composition comprising a polybutadiene mixture, a metal salt of an unsaturated carboxylic acid, an organic peroxide and an inorganic filler, and the polybutadiene mixture consists of
(a) a polybutadiene containing a cis-1,4 bond of not less than 80% and having a Mooney viscosity of 50 to 100 ML
1+4
(100° C.), synthesized using nickel-containing catalyst, and
(b) a polybutadiene containing a cis-1,4 bond of not less than 40% and having a Mooney viscosity of 20 to 90 ML
1+4
(100° C.), synthesized using lanthaide-containing catalyst, a weight ratio (a)/(b) being 30/70 to 90/10.
DETAILED DESCRIPTION OF THE INVENTION
The thread wound golf ball of the present invention comprises a solid center obtained by press-molding and vulcanizing the rubber composition, 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 polybutadiene mixture, a metal salt of an unsaturated carboxylic acid, an organic peroxide, an inorganic filler, optionally antioxidant and the like. The solid center used in the present invention may have single layer structure or multi-layer structure that has two or more layers.
The mixture of polybutadienes used in the rubber composition for the solid center of the present invention consists of
(a) a polybutadiene containing a cis-1,4 bond of not less than 80% and having a Mooney viscosity of 50 to 100 ML
1+4
(100° C.), synthesized using nickel-containing catalyst, and
(b) a polybutadiene containing a cis-1,4 bond of not less than 40% and having a Mooney viscosity of 20 to 90 ML
1+4
(100° C.), synthesized using lanthanide-containing catalyst.
Nickel-containing catalysts used for synthesizing the polybutadiene (a) in the present invention are, for example, one-component catalysts such as nickel on diatomaceous earth as a carrier, two-component catalysts such as Raney nickel/titanium tetrachloride, and three-component catalysts such as nickel compound/organometal/trifluoroborate etherate. Examples of the nickel compounds include reduced nickel on carrier, Raney nickel, nickel oxide, nickel carboxylate, organic nickel complex salts and the like. Examples of the organometals include trialkyl aluminums such as triethyl aluminum, tri-n-propyl aluminum, triisobutyl aluminum, and tri-n-hexyl aluminum; alkyl lithiums such as n-butyl lithium, s-butyl lithium, t-butyl lithium and 1,4-butane dilithium; dialkyl zincs such as diethyl zinc, dibutyl zinc; and the like.
Polymerization of butadiene in the presence of these catalysts is generally carried out by continuously charging butadiene monomer into a reactor along with a conventional solvent and the catalyst such as nickel octanoate and triethyl aluminum, and controlling the reaction temperature in the range of 5 to 60° C. and the reaction pressure in the range of 1 to about 70 atmospheres, such that a product having a desired Mooney viscosity may be obtained.
The resulting polybutadiene (a) contains a cis-1,4 bond of not less than 80%, and has a Mooney viscosity of 50 to 100 ML
1+4
(100° C.), preferably 50 to 85 ML
1+4
(100° C.), more preferably 55 to 75 ML
1+4
(100° C.). When the Mooney viscosity of the polybutadiene (a) is lower than 50 ML
1+4
(100° C.), the workability when mixing the rubber composition is good, but the rebound characteristics of the resulting golf ball are degraded. On the other hand, when the Mooney viscosity is higher than 100 ML
1+4
(100° C.), the rebound characteristics of the resulting golf ball are good, but the workability when mixing is degraded, which reduces productivity.
In the present invention, it is desired that the polybutadiene (a) has a ratio (Mw/Mn) of weight average molecular weight (Mw) to number average molecular weight (Mn) of 4.0 to 8.0, preferably 4.0 to 7.0, more preferably 4.0 to 6.0. The ratio (Mw/Mn) is generally an index of molecular weight distribution. When the ratio (Mw/Mn) of the polybutadiene (a) is smaller than 4.0, the workability is degraded. On the other hand, when the ratio (Mw/Mn) is larger than 8.0, the workability is good, but the rebound characteristics of the resulting golf ball are degraded.
Examples of the polybutadiene (a) will be shown by a trade name thereof. Examples of the polybutadiene (a) include BR-18, which is commercially available from JSR Co., Ltd., and the like.
The term “Mooney viscosity” as used herein refers to an indication of a viscosity which is measured using a Mooney viscometer as a kind of rotational plastometer. The Mooney viscosity is typically used for measuring a viscosity of a rubber composition in the field of rubber industry. The Mooney viscosity is determined by closely putting a rubber composition in a gap between a cylindrical dice and a rotor positioned at the center of the dice, and then measuring a torque occurring when r
Birch & Stewart Kolasch & Birch, LLP
Gorden Raeann
Graham Mark S.
Sumitomo Rubber Industries Ltd.
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