Games using tangible projectile – Golf – Ball
Reexamination Certificate
1999-10-12
2001-09-11
Graham, Mark S. (Department: 3711)
Games using tangible projectile
Golf
Ball
Reexamination Certificate
active
06287218
ABSTRACT:
DEFINITION OF THE TERM
The term “trans-structure content” used herein means a ratio of trans-1,4 structure in polybutadiene backbone, calculated from the following expression:
(
Area
of
a
peak
corresponding
to
trans
-
1
,
4
structure
in
13
C
-
NMR
spectrum
)
(
Total
of
areas
of
peaks
corresponding
to
cis
-
1
,
4
,
trans
-
1
,
4
and
1
,
2
-
structure
in
13
C
-
NMR
spectrum
)
×
100
FIELD OF THE INVENTION
The present invention relates to a solid golf ball. More particularly, it relates to a solid golf ball having good shot feel at the time of hitting, excellent flight performance and excellent durability.
BACKGROUND OF THE INVENTION
Many types of golf balls are commercially selling, but solid golf balls, such as two-piece solid golf balls, and thread wound golf balls are generally used for round games. The solid golf ball, when compared with the thread wound golf ball, has better flight performance and better durability. Therefore the solid golf ball is generally approved of or employed by many golfers. On the other hand, the solid golf ball, when compared with the thread wound golf ball, has poor shot feel and large impact force at the time of hitting, and poor controllability at approach shot because it has large ball velocity at the time of hitting and thus it has small spin amount.
In order to provide a solid golf ball having shot feel as good as the thread wound golf ball, a soft type solid golf ball using a softer core has been proposed. However, the use of the soft core adversely affects on rebound characteristics, thus resulting in the reduction of flight distance and the deterioration of durability.
OBJECTS OF THE INVENTION
A main object of the present invention is to provide a solid golf ball having good shot feel at the time of hitting, while maintaining excellent flight performance and excellent durability.
According to the present invention, the object described above has been accomplished by adjusting an amount of a co-crosslinking agent, an organic peroxide and an organic sulfide compound in the rubber composition for the core, and by controlling a trans-structure content in the core after vulcanization to a specified range, thereby providing a solid golf ball having good shot feel at the time of hitting, while maintaining excellent flight performance and excellent durability.
SUMMARY OF THE INVENTION
The present invention provides a solid golf ball comprising one or more layers of core, and one or more layers of cover formed on the core, wherein the inmost core layer is formed from a vulcanized molded article of a rubber composition comprising 20 to 40 parts by weight of &agr;,&bgr;-unsaturated carboxylic acid or metal salt thereof, 0.3 to 1.8 parts by weight of a vulcanization initiator, 0.1 to 5 parts by weight of an organic sulfide compound, based on 100 parts by weight of a base rubber, and has a trans-structure content after vulcanization of 10 to 50%, and the core has a rate of (B-A)/A of not less than 15%, wherein A is a center hardness in JIS-C hardness of the core and B is a surface hardness in JIS-C hardness of the core.
DETAILED DESCRIPTION OF THE INVENTION
The solid golf ball of the present invention comprises one or more layers of core, and one or more layers of cover formed on the core. The core is obtained by mixing a rubber composition in a mixer such as a mixing roll, followed by press molding and vulcanizing the rubber composition at 140 to 170° C. and 90 to 120 kgf/cm
2
for 10 to 40 minutes in a mold. The rubber composition contains a base rubber, a co-crosslinking agent, a vulcanization initiator, an organic sulfide compound, a filler and the like.
The base rubber used for the core of the present invention may be natural rubber and/or synthetic rubber, which have been conventionally used for solid golf balls. Preferred is high-cis polybutadiene rubber containing not less than 40%, preferably not less than 80% of a cis-1,4-structure. The high-cis 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 &agr;,&bgr;-unsaturated carboxylic acid or a metal salt thereof, for example, &agr;,&bgr;-unsaturated carboxylic acids having 3 to 8 carbon atoms, such as acrylic acid, methacrylic acid and the like or mono or divalent metal salts, such as zinc, calcium or magnesium salts thereof. Preferred are zinc methacrylate, calcium methacrylate and zinc acrylate. The amount of the co-crosslinking agent may be from 20 to 40 parts by weight, preferably from 25 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 core is too hard, and the shot feel of the resulting golf ball is poor. On the other hand, when the amount of the co-crosslinking agent is smaller than 20 parts by weight, the core is too soft, and the rebound characteristics and durability are degraded.
The vulcanization initiator includes an organic peroxide, for example, dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(t-butylperoxy) hexane, t-butyl peroxide and the like. Preferred are dicumyl peroxide and 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane. The amount of the vulcanization initiator may be from 0.3 to 1.8 parts by weight, preferably 0.5 to 1.3 parts by weight, based on 100 parts by weight of the base rubber. When the amount of the vulcanization initiator is smaller than 0.3 parts by weight, the vulcanization of the rubber composition is sufficiently conducted. On the other hand, when the amount of the organic peroxide is larger than 1.8 parts by weight, the vulcanized rubber is too hard, and the shot feel of the resulting golf ball is poor.
The organic sulfide compound used for the present invention includes diphenyl polysulfides having 2 to 4 sulfur atoms, bis(4-methacryloyl thiophenyl)sulfide, 4,4′-dibromodiphenyl sulfide, morpholine disulfide and the like. Conversion from cis-structure into trans-structure occurs during vulcanization of the rubber composition for the core. The conversion is initiated or accelerated mainly by the organic sulfide compound used. Therefore the amount of the organic sulfide compound may be from 0.1 to 5.0 parts by weight, preferably from 0.5 to 4.0 parts by weight, based on 100 parts by weight of the base rubber. When the amount of the organic sulfide compound is smaller than 0.1 parts by weight, the technical effects of improving the rebound characteristics do not sufficiently exhibit, because the desired degree of the conversion can not be obtained. On the other hand, when the amount of the organic sulfide compound is larger than 5.0 parts by weight, the technical effects are not improved more. If the trans-structure content after vulcanization is increased by using a base rubber having a large trans-structure content before vulcanization, the technical effects do not sufficiently exhibit.
The filler used for the present invention, which can be typically used for the core of solid golf balls, includes for example, an inorganic filler (such as zinc oxide, barium sulfate, calcium carbonate and the like), a high specific gravity metal powder filler (such as powdered tungsten, powdered molybdenum, and the like), and the mixture thereof. The amount of the filler may be from 1 to 30 parts by weight, preferably from 3 to 25 parts by weight, based on 100 parts by weight of the base rubber. When the amount of the filler is smaller than 1 parts by weight, it is difficult to adjust the weight of the core. On the other h
Birch & Stewart Kolasch & Birch, LLP
Gorden Raeann
Graham Mark S.
Sumitomo Rubber Industries Ltd.
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