U.S. patent application number 09/927401 was filed with the patent office on 2002-05-02 for one-piece solid golf ball.
Invention is credited to Fushihara, Kazuhisa, Yabuki, Yoshikazu.
Application Number | 20020052253 09/927401 |
Document ID | / |
Family ID | 18745864 |
Filed Date | 2002-05-02 |
United States Patent
Application |
20020052253 |
Kind Code |
A1 |
Fushihara, Kazuhisa ; et
al. |
May 2, 2002 |
One-piece solid golf ball
Abstract
The present invention provides a one-piece solid golf ball
having excellent rebound characteristics and good shot feel, while
maintaining excellent processability and durability. The present
invention relates to a one-piece solid golf ball formed from a
rubber composition comprising a mixture consisting of polybutadiene
(a) synthesized using nickel-containing catalyst and polybutadiene
(b) synthesized using cobalt-containing catalyst and hydroquinone
or derivatives thereof as a vulcanization stabilizer, wherein a
Mooney viscosity and a weight ratio of the polybutadienes (a) and
(b), an amount of the vulcanization stabilizer, a center hardness
(the minimum hardness in the golf ball) and surface hardness of the
golf ball, and a difference between the maximum hardness and
minimum hardness in the golf ball are adjusted to a specified
range.
Inventors: |
Fushihara, Kazuhisa;
(Kobe-shi, JP) ; Yabuki, Yoshikazu; (Kobe-shi,
JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
18745864 |
Appl. No.: |
09/927401 |
Filed: |
August 13, 2001 |
Current U.S.
Class: |
473/371 |
Current CPC
Class: |
A63B 37/00621 20200801;
C08K 3/013 20180101; A63B 37/06 20130101; A63B 37/0051 20130101;
C08L 9/00 20130101; C08K 5/14 20130101; A63B 2037/087 20130101;
A63B 37/00622 20200801; A63B 37/0073 20130101; C08K 5/13 20130101;
A63B 37/0003 20130101; A63B 37/08 20130101; A63B 37/0063 20130101;
C08L 9/00 20130101; C08L 2666/08 20130101 |
Class at
Publication: |
473/371 |
International
Class: |
A63B 037/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 28, 2000 |
JP |
257403/2000 |
Claims
What is claimed is:
1. A one-piece solid golf ball formed from a rubber composition
comprising a base rubber, a co-crosslinking agent, an organic
peroxide, an inorganic filler and a vulcanization stabilizer, and
the base rubber comprises a polybutadiene mixture consisting of (i)
a polybutadiene (a) containing a cis-1,4 bond of not less than 96%
and having a Mooney viscosity of 50 to 85 ML.sub.1+4(100.degree.
C.) and a weight average molecular weight (Mw) of 70.times.10.sup.4
to 120.times.10.sup.4, synthesized using nickel-containing
catalyst, and (ii) a polybutadiene (b) containing a cis-1,4 bond of
not less than 96% and having a Mooney viscosity of 30 to 50
ML.sub.1+4(100.degree. C.) and a weight average molecular weight
(Mw) of not less than 55.times.10.sup.4 and less than
70.times.10.sup.4, synthesized using cobalt-containing catalyst, a
weight ratio (a)/(b) being 95/5 to 70/30, wherein the vulcanization
stabilizer is selected from the group consisting of hydroquinone
and derivatives thereof, and an amount of the vulcanization
stabilizer is 0.05 to 20 parts by weight, based on 100 parts by
weight of the base rubber, and the golf ball has a center hardness
in JIS-C hardness of 55 to 68 and a surface hardness in JIS-C
hardness of 75 to 90, the center hardness is the minimum hardness
in the golf ball, and a difference between the maximum hardness and
minimum hardness in the golf ball is within the range of 16 to
25.
2. The one-piece solid golf ball according to claim 1, wherein the
vulcanization stabilizer is 2,5-di-t-butylhydroquinone.
3. The one-piece solid golf ball according to claim 1, wherein the
polybutadiene (b) synthesized using cobalt-containing catalyst has
a ratio (Mw/Mn) of weight average molecular weight (Mw) to number
average molecular weight (Mn) of 3.0 to 5.0
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a one-piece wound golf
ball. More particularly, it relates to a one-piece wound golf ball
having excellent rebound characteristics and good shot feel, while
maintaining excellent processability and durability.
BACKGROUND OF THE INVENTION
[0002] Golf balls are typically classified into two types, that is,
golf balls for round games and golf balls for driving ranges. It is
difficult to say that performance, which is required for these two
types of golf balls, is the same with each other. The performance
required for the golf ball for round games is good shot feel,
excellent flight performance and the like. If the golf balls for
round games are used as a golf ball for driving ranges, good shot
feel and excellent flight performance are maintained, but the
durability is very poor as a golf ball for driving ranges, which is
repeatedly hit. Therefore, at driving ranges, the durability is
regarded as more important than the shot feel and flight
performance, and golf balls having much better durability than that
of the golf balls for round games is used.
[0003] In the golf balls for driving ranges, there are golf balls
having low rebound characteristics, low trajectory and high
trajectory, golf balls for using on the water and the like,
depending on the extent of the driving ranges, the height of net
and the like. There are various golf balls, such as one-piece golf
ball, two-piece golf ball and the like, depending on the structure
of the golf ball. At present, one-piece solid golf ball is mainly
used as golf balls for driving ranges.
[0004] Recently, since performance as good as golf balls for round
games, such as shot feel, has been required for golf balls for
driving ranges, good shot feel and excellent flight performance
have been required for the one-piece golf ball having excellent
durability. However, when softening the golf ball in order to
improve the shot feel or improving the flight performance, the
durability is degraded. It is very difficult to improve shot feel
and flight performance, while maintaining excellent durability.
[0005] A rubber composition comprising high-cis polybutadiene,
methacrylic acid (or metal salt thereof) as a co-crosslinking agent
and organic peroxide has been generally used as a general
formulation of one-piece golf ball. When zinc acrylate, which is
used as a co-crosslinking agent of rubber composition for a core of
two-piece golf ball, is used for one-piece golf ball, rebound
characteristics are good, but durability is very poor. Therefore it
is not generally used for one-piece golf ball.
[0006] A one-piece solid golf ball, which is formed by using
polybutadiene rubber having high Mooney viscosity, and have even
hardness distribution, is proposed (for example, Japanese Patent
Kokai Publication No. 177973/1990, Japanese Patent No. 2644226 and
the like). In Japanese Patent Kokai Publication No. 177973/1990, a
one-piece solid golf ball, which is obtained by vulcanizing and
press-molding a rubber composition comprising polybutadiene having
high Mooney viscosity, and have even hardness distribution so that
difference between the maximum hardness and minimum hardness in the
golf ball is not less than 15, is described. However, in the golf
ball, since the polybutadiene having high Mooney viscosity is used,
molecular weight of the polybutadiene rubber is high, and the
processability is poor. In addition, the rebound characteristics
are improved, but the durability is degraded, and the shot feel is
poor because of even hardness distribution.
[0007] In Japanese Patent No. 2644226, a solid golf ball formed by
using a rubber composition comprising polybutadiene, of which
Mooney viscosity (45 to 90 ML.sub.1+4 (100.degree. C.)) and a ratio
(Mw/Mn) of weight average molecular weight (Mw) to number average
molecular weight (Mn) are adjusted to specified ranges is
described. However, as described in the above golf ball, since the
polybutadiene having high Mooney viscosity is used, molecular
weight of the polybutadiene rubber is high, and the processability
is poor. In addition, the rebound characteristics are improved, but
the durability is degraded.
OBJECTS OF THE INVENTION
[0008] A main object of the present invention is to provide a
one-piece wound golf ball having excellent rebound characteristics
and good shot feel, while maintaining excellent processability and
durability.
[0009] According to the present invention, the object described
above has been accomplished by using a rubber composition
comprising a mixture consisting of polybutadiene (a) synthesized
using nickel-containing catalyst and polybutadiene (b) synthesized
using cobalt-containing catalyst and hydroquinone or derivatives
thereof as a vulcanization stabilizer, and adjusting a Mooney
viscosity and a weight ratio of the polybutadienes (a) and (b), an
amount of the vulcanization stabilizer, a center hardness (the
minimum hardness in the golf ball) and surface hardness of the golf
ball, and a difference between the maximum hardness and minimum
hardness in the golf ball to a specified range, thereby providing a
one-piece wound golf ball having excellent rebound characteristics
and good shot feel, while maintaining excellent processability and
durability.
SUMMARY OF THE INVENTION
[0010] The present invention provides a one-piece wound golf ball
formed from a rubber composition comprising a base rubber, a
co-crosslinking agent, an organic peroxide, an inorganic filler and
a vulcanization stabilizer, and the base rubber comprises a
polybutadiene mixture consisting of
[0011] (i) a polybutadiene (a) containing a cis-1,4 bond of not
less than 96% and having a Mooney viscosity of 50 to 85
ML.sub.1+4(100.degree. C.) and a weight average molecular weight
(Mw) of 70.times.10.sup.4 to 120.times.10.sup.4, synthesized using
nickel-containing catalyst, and
[0012] (ii) a polybutadiene (b) containing a cis-1,4 bond of not
less than 96% and having a Mooney viscosity of 30 to 50
ML.sub.1+4(100.degree. C.) and a weight average molecular weight
(Mw) of not less than 55.times.10.sup.4 and less than
70.times.10.sup.4, synthesized using cobalt-containing catalyst, a
weight ratio (a)/(b) being 95/5 to 70/30, wherein
[0013] the vulcanization stabilizer is selected from the group
consisting of hydroquinone and derivatives thereof, and an amount
of the vulcanization stabilizer is 0.05 to 20 parts by weight,
based on 100 parts by weight of the base rubber, and
[0014] the golf ball has a center hardness in JIS-C hardness of 55
to 68 and a surface hardness in JIS-C hardness of 75 to 90, the
center hardness is the minimum hardness in the golf ball, and a
difference between the maximum hardness and minimum hardness in the
golf ball is within the range of 16 to 25.
[0015] In order to put the present invention into a more suitable
practical application, the vulcanization stabilizer is preferably
2,5-di-t-butylhydroquinone, and the polybutadiene (b) synthesized
using cobalt-containing catalyst preferably has a ratio (Mw/Mn) of
weight average molecular weight (Mw) to number average molecular
weight (Mn) of 3.0 to 5.0.
DETAILED DESCRIPTION OF THE INVENTION
[0016] The one-piece solid golf ball of the present invention is
formed from integrally molded article obtained by press-molding and
vulcanizing a rubber composition. The rubber composition comprises
a base rubber, a co-crosslinking agent, an organic peroxide, an
inorganic filler, a vulcanization stabilizer and optionally an
antioxidant, and the like.
[0017] In the golf ball of the present invention, it is required
for the base rubber to comprise a polybutadiene mixture consisting
of
[0018] (i) a polybutadiene (a) containing a cis-1,4 bond of not
less than 96% and having a Mooney viscosity of 50 to 85
ML.sub.1+4(100.degree. C.) and a weight average molecular weight
(Mw) of 70.times.10.sup.4 to 120.times.10.sup.4, synthesized using
nickel-containing catalyst, and
[0019] (ii) a polybutadiene (b) containing a cis-1,4 bond of not
less than 96% and having a Mooney viscosity of 30 to 50
ML.sub.1+4(100.degree. C.) and a weight average molecular weight
(Mw) of not less than 55.times.10.sup.4 and less than
70.times.10.sup.4, synthesized using cobalt-containing catalyst, in
a weight ratio (a)/(b) of 95/5 to 70/30.
[0020] Nickel-containing catalysts used to synthesize 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/trifluorobo- rate etherate. Examples of 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.
[0021] 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.degree. C. and the reaction pressure in the range of 1 to about
70 atmospheres, such that a product having desired properties such
as Mooney viscosity may be obtained.
[0022] In the golf ball of the present invention, it is required
for the polybutadiene (a) to contain a cis-1,4 bond of not less
than 96%, and have a Mooney viscosity of 50 to 85
ML.sub.1+4(100.degree. C.), preferably 50 to 70
ML.sub.1+4(100.degree. C.), more preferably 55 to 65
ML.sub.1+4(100.degree. C.). When the content of the cis-1,4 bond in
the polybutadiene (a) is less than 96%, the rebound characteristics
of the resulting golf ball are not sufficiently obtained. When the
Mooney viscosity of the polybutadiene (a) is lower than 50
ML.sub.1+4(100.degree. C.), the processability 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 85 ML.sub.1+4(100.degree. C.), the
rebound characteristics of the resulting golf ball are sufficiently
obtained, but the processability when mixing is degraded, which
reduces productivity.
[0023] In the golf ball of the present invention, it is required
for the polybutadiene (a) to have a weight average molecular weight
(Mw) of 70.times.10.sup.4 to 120.times.10.sup.4, preferably
80.times.10.sup.4 to 110.times.10.sup.4, more preferably
80.times.10.sup.4 to 100.times.10.sup.4. When the Mw of the
polybutadiene (a) is lower than 70.times.10.sup.4, the rebound
characteristics of the resulting golf ball are degraded. On the
other hand, when the Mw of the polybutadiene (a) is higher than
120.times.10.sup.4, the processability when mixing is degraded,
which reduces productivity.
[0024] In the golf ball of the present invention, it is desired for
the polybutadiene (a) to have a ratio (Mw/Mn) of weight average
molecular weight (Mw) to number average molecular weight (Mn) of
3.0 to 6.0, preferably 4.0 to 5.5. The ratio (Mw/Mn) represents
molecular weight distribution. When the ratio (Mw/Mn) of the
polybutadiene (a) is smaller than 3.0, the molecular weight
distribution of the polybutadiene (a) is too narrow, and the
compatibility with the polybutadiene (b) is degraded. On the other
hand, when the ratio (Mw/Mn) of the polybutadiene (a) is larger
than 6.0, the molecular weight distribution of the polybutadiene
(a) is too broad, and the content of the low molecular weight
component of the polybutadiene is large, which reduces the rebound
characteristics.
[0025] In the golf ball of the present invention, it is desired for
the polybutadiene (a) to have a number average molecular weight
(Mn) of 10.times.10.sup.4 to 30.times.10.sup.4, preferably
15.times.10.sup.4 to 25.times.10.sup.4. When the Mn of the
polybutadiene (a) is lower than 10.times.10.sup.4, the rebound
characteristics of the resulting golf ball are not sufficiently
obtained. On the other hand, when the Mn of the polybutadiene (a)
is higher than 30.times.10.sup.4, the processability when mixing is
degraded.
[0026] Examples of the polybutadiene (a), which will be shown by a
trade name thereof, include "BR-18", which is commercially
available from JSR Co., Ltd., and the like.
[0027] 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 rotating a
rotor at a testing temperature of 100.degree. C., for a preheating
time of 1 minute, at the number of revolutions of 2 rpm, for the
time of revolution of 4 minutes. The Mooney viscosity is expressed
in ML.sub.1+4(100.degree. C.), wherein M represents a Mooney
viscosity, L represents a large rotor (L type) as a shape of the
rotor, (1+4) represents that a preheating time is 1 minute and a
time of revolution of the rotor is 4 minutes, and 100.degree. C.
represents a testing temperature. The measurement is generally
conducted according to JIS K 6300.
[0028] Cobalt-containing catalysts used to synthesize the
polybutadiene (b) in the present invention are, for example, cobalt
metal and cobalt compounds such as Raney cobalt, cobalt chloride,
cobalt bromide, cobalt iodide, cobalt oxide, cobalt sulfate, cobalt
carbonate, cobalt phosphate, cobalt phthalate, cobalt carbonyl,
cobalt acetylacetonate, cobalt diethyldithiocarbamate,
[(C.sub.2H.sub.5).sub.2NCS.sub.2].sub.2Co, cobalt aniliniumnitrile,
[(C.sub.6H.sub.5NH.sub.3).sub.3Co (NO.sub.2)], cobalt dinitrosyl
chloride, and the like. In particular, combinations of these cobalt
compounds with a dialkyl aluminum monochloride such as
diethylaluminum monochloride and diisobutylaluminum monochloride; a
trialkyl aluminum such as triethylaluminum, tri-n-propylaluminum,
triisobutylaluminum and tri-n-hexylaluminum; an alkyl aluminum
sesquichloride (Al.sub.2R.sub.3Cl.sub.3) such as ethylaluminum
sesquichloride; aluminum chloride; and the like are preferred
catalysts for use in the preparation of polybutadiene of cis-1,4
bond type.
[0029] Polymerization of butadiene in the presence of the
cobalt-containing catalysts is generally carried out by the similar
process to that used with the nickel-containing catalysts.
[0030] In the golf ball of the present invention, it is required
for the polybutadiene (b) to contain a cis-1,4 bond of not less
than 96%, and have a Mooney viscosity of 30 to 50
ML.sub.1+4(100.degree. C.), preferably 33 to 43
ML.sub.1+4(100.degree. C.). When the content of the cis-1,4 bond in
the polybutadiene (b) is less than 96%, the rebound characteristics
of the resulting golf ball are not sufficiently obtained. When the
Mooney viscosity of the polybutadiene (b) is lower than 30
ML.sub.1+4(100.degree. C.), the processability 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 50 ML.sub.1+4(100.degree. C.), the
durability is degraded and the processability when mixing is
greatly degraded.
[0031] In the golf ball of the present invention, it is required
for the polybutadiene (b) to have a weight average molecular weight
(Mw) of not less than 55.times.10.sup.4 and less than
70.times.10.sup.4, preferably 58.times.10.sup.4 to
65.times.10.sup.4. When the Mw of the polybutadiene (b) is lower
than 55.times.10.sup.4, the rebound characteristics of the
resulting golf ball are degraded. On the other hand, when the Mw of
the polybutadiene (b) is within the range of not less than
70.times.10.sup.4, the durability is degraded.
[0032] In the golf ball of the present invention, it is desired for
the polybutadiene (b) to have a ratio (Mw/Mn) of weight average
molecular weight (Mw) to number average molecular weight (Mn) of
3.0 to 5.0, preferably 3.5 to 4.5. The ratio (Mw/Mn) represents
molecular weight distribution. When the ratio (Mw/Mn) of the
polybutadiene (b) is smaller than 3.0, the molecular weight
distribution of the polybutadiene (b) is too narrow, and the
content of the low molecular weight component and high molecular
weight component of the polybutadiene is small, which degrades the
durability. On the other hand, when the ratio (Mw/Mn) of the
polybutadiene (b) is larger than 5.0, the molecular weight
distribution of the polybutadiene (b) is too broad, and the content
of the low molecular weight component and high molecular weight
component of the polybutadiene is large. Therefore, the
compatibility is degraded, and the processability when mixing is
degraded.
[0033] Polybutadiene synthesized using cobalt-containing catalyst
generally tends to have broader molecular weight distribution than
polybutadiene synthesized using nickel-containing catalyst, which
varies depending on the polymerization condition such as
concentration of monomer, concentration of catalyst, polymerization
temperature, kind of solvent and the like. Therefore, in the
present invention, a ratio of the low molecular weight component to
the high molecular weight component of the polybutadiene mixture is
controlled by adjusting the Mw/Mn of the polybutadiene (b)
synthesized using cobalt-containing catalyst to the above specified
range, and the processability when mixing and durability are
improved.
[0034] In the golf ball of the present invention, it is desired for
the polybutadiene (b) to have a number average molecular weight
(Mn) of 10.times.10.sup.4 to 30.times.10.sup.4, preferably
10.times.10.sup.4 to 25.times.10.sup.4. When the Mn of the
polybutadiene (b) is lower than 10.times.10.sup.4, the rebound
characteristics of the resulting golf ball are not sufficiently
obtained. On the other hand, when the Mn of the polybutadiene (b)
is higher than 30.times.10.sup.4, the processability when mixing is
degraded.
[0035] Examples of the polybutadiene (b), which will be shown by a
trade name thereof, include "BR230", "BR230", which are
commercially available from Ube Industries, Ltd., and the like.
[0036] In the golf ball of the present invention, it is required
that a weight ratio (a)/(b) of polybutadiene (a) to polybutadiene
(b) in the polybutadiene mixture be 95/5 to 70/30, preferably 95/5
to 80/20. When the amount of polybutadiene (a) is smaller than 70%
by weight and the amount of polybutadiene (b) is larger than 30% by
weight, based on the total weight of the polybutadiene mixture, the
rebound characteristics of the resulting golf ball are degraded. On
the other hand, when the amount of polybutadiene (b) is smaller
than 5% by weight and the amount of polybutadiene (a) is larger
than 95% by weight, based on the total weight of the polybutadiene
mixture, the durability is degraded.
[0037] Generally, when the Mw of polybutadiene is high, the rebound
characteristics tend to be improved, but the processability and
durability tend to be degraded. On the other hand, when the Mw of
polybutadiene is low, the processability tends to be improved, but
the rebound characteristics tend to be degraded. When using the
polybutadiene (b) alone, the processability is good, but the
rebound characteristics are degraded. When using the polybutadiene
(a) alone, the rebound characteristics are improved, but the
processability is degraded, which reduces productivity. A one-piece
solid golf ball, of which the rebound characteristics are improved,
the processability is good and the durability is excellent, can be
obtained by using the mixture of the polybutadiene (a) and
polybutadiene (b) in the above weight ratio (a)/(b).
[0038] The "processability" as used herein is determined by
evaluating the winding of the rubber composition on the mixing roll
during mixing, and the surface roughening of plug when extruding
the plug (unvulcanized molded article) used at molding. When the
processability is poor, it is difficult to wind the rubber
composition around the mixing roll, the plug has the surface
roughening, the dispersibility of formulation materials is poor,
and the performance of the resulting golf ball is uneven. In
addition, the appearance is poor because of the surface roughening
of plug, or the durability is degraded because the release agent
gets into the surface roughening of plug.
[0039] The base rubber may be only the polybutadiene (a) and
polybutadiene (b), but the polybutadienes may be optionally mixed
with natural rubber, polyisoprene rubber, styrene-butadiene rubber,
ethylene-propylene-diene rubber (EPDM), and the like. If used, it
is desired for the total amount of the polybutadiene (a) and
polybutadiene (b) to be not less than 80% by weight, preferably not
less than 90% by weight, based on the total weight of the base
rubber. When the total amount of the polybutadiene (a) and
polybutadiene (b) is smaller than 80% by weight, the rebound
characteristics are degraded and the processability is
degraded.
[0040] Examples of the co-crosslinking agents include
.alpha.,.beta.-unsaturated carboxylic acids having 3 to 8 carbon
atoms (e.g. acrylic acid, methacrylic acid, etc.) or a monovalent
or divalent metal salt such as zinc or magnesium salt thereof;
metal salt of .alpha.,.beta.-unsaturated carboxylic acids, which is
formed by reacting the .alpha.,.beta.-unsaturated carboxylic acids
with metal oxide such as zinc oxide during mixing rubber
composition; polyfunctional acrylic esters such as
trimethylolpropane triacrylate, polyfunctional methacrylic esters
such as trimethylpropane trimethacrylate, and the like. The
preferred co-crosslinking agent is metal salt of acrylic acid or
methacrylic acid because it imparts excellent durability to the
resulting golf ball. The amount of the co-crosslinking agent is
from 19 to 29 parts by weight, preferably from 22 to 26 parts by
weight, based on 100 parts by weight of the base rubber. When the
amount of the co-crosslinking agent is larger than 29 parts by
weight, the resulting golf ball is too hard, and the shot feel is
poor. On the other hand, when the amount of the co-crosslinking
agent is smaller than 19 parts by weight, it is required to
increase the amount of the organic peroxide in order to obtain the
desired hardness, and high rebound characteristics of the resulting
golf ball are not obtained.
[0041] Examples of the organic peroxides, which act as a
crosslinking agent or curing agent, include, for example, dicumyl
peroxide, 1,1-bis (t-butylperoxy)-3,3,5-trimethylcyclohexane,
2,5-dimethyl-2,5-di(t-butylpe- roxy) hexane, di-t-butyl peroxide,
2,2-di(t-butylperoxy)butane, t-butyl perbenzoate and the like. The
preferred organic peroxide is dicumyl peroxide. The amount of the
organic peroxide is 0.1 to 3.0 parts by weight, preferably 1.5 to
2.0 parts by weight, based on 100 parts by weight of the base
rubber. When the amount of the organic peroxide is smaller than 0.1
parts by weight, the resulting golf ball is too soft, and high
rebound characteristics are not obtained. On the other hand, when
the amount of the organic peroxide is larger than 3.0 parts by
weight, it is required to decrease the amount of the
co-crosslinking agent in order to obtain the desired hardness, and
high rebound characteristics are not obtained. When these organic
peroxides are heated, they decompose to form radicals, which
increase the degree of crosslinking between the aforedescribed
co-crosslinking agents and base rubber, and enhance the rebound
characteristics.
[0042] Examples of the fillers include inorganic fillers such as
zinc oxide, silicon oxide, barium sulfate, calcium carbonate,
aluminum silicate and mixtures thereof. The inorganic fillers are
used as a reinforcing agent, which improves hardness or strength,
or a specific gravity (weight) adjuster. However, the preferred
filler is zinc oxide, which also functions as a vulcanization aid.
The amount of the filler is 10 to 60 parts by weight, preferable 12
to 50 parts by weight, based on 100 parts by weight of the base
rubber. When the amount of the filler is larger than 60 parts by
weight, the weight ratio of the rubber component in the resulting
golf ball is small, and the rebound characteristics are degraded.
On the other hand, when the amount of the filler is smaller than 10
parts by weight, it is difficult to adjust the weight of the
resulting golf ball, or the durability is degraded.
[0043] In the golf ball of the present invention, it is required
for the vulcanization stabilizer to be selected from the group
consisting of hydroquinone and derivatives thereof. Examples of the
vulcanization stabilizers include 2,5-di-t-butylhydroquinone,
2,5-di-t-amylhydroquinone- , 2,6-dimethylhydroquinone,
bromohydroquinone, 2,3,5,6-tetrachlorohydroqui- none and the like.
The preferred vulcanization stabilizer is
2,5-di-t-butylhydroquinone, in view of low toxicity,
general-purpose properties and proper stability of free radical. It
is required for the amount of the vulcanization stabilizer to be
within the range of 0.05 to 2.0 parts by weight, preferably 0.1 to
1.0 parts by weight, more preferably 0.1 to 0.5 parts by weight,
based on 100 parts by weight of the base rubber. When the amount is
smaller than 0.05 parts by weight, technical effects accomplished
by the presence of the vulcanization stabilizer is not sufficiently
obtained, and the rebound characteristics are degraded. On the
other hand, when the amount is larger than 2.0 parts by weight, the
amount of the vulcanization stabilizer, which also acts as a
vulcanization initiator, is too large, and the resulting golf ball
is brittle, which degrades the durability.
[0044] Where appropriate, it is possible to compound a component
which is typically used in the manufacture of one-piece solid golf
ball together with the rubber composition for the one-piece solid
golf ball of the present invention; pigments such as titanium
dioxide and the like, and other additives such as antioxidants or
peptizing agents, softening agents and the like.
[0045] The one-piece solid golf ball of the present invention can
be obtained by mixing the rubber composition with a proper mixer
such as a mixing roll, kneader and the like, and then press-molding
and vulcanizing the mixture under applied heat in a mold. The
vulcanizing, of which the condition is not limited, is typically
conducted at 130 to 240.degree. C. and 2.9 to 11.8 MPa for 15 to 60
minutes. The vulcanizing may be conducted in two or more stages of
the temperature.
[0046] At the time of molding the golf ball, many depressions
called "dimples" may be optionally formed on the surface of the
golf ball. Furthermore, paint finishing or marking with a stamp may
be optionally provided for commercial purposes after the golf ball
is molded.
[0047] In the one-piece solid golf ball of the present invention,
it is required for the golf ball to have a center hardness in JIS-C
hardness of 55 to 68, preferably 58 to 63, more preferably 60 to
63. When the center hardness is smaller than 55, the durability of
the resulting golf ball is degraded. In addition, the golf ball is
too soft at the time of hitting, and the shot feel is poor so that
it is felt the rebound characteristics are degraded. On the other
hand, when the center hardness is larger than 68, the shot feel is
poor so that it is felt the center portion of the ball is hard.
[0048] In the one-piece solid golf ball of the present invention,
it is required for the golf ball to have a surface hardness in
JIS-C hardness of 75 to 90, preferably 80 to 90, more preferably 80
to 87. When the surface hardness is smaller than 75, the shot feel
is heavy and poor. In addition, the rebound characteristics are
degraded, which reduces the flight distance. On the other hand,
when the surface hardness is larger than 90, the golf ball is too
hard, and the shot feel is poor. The term "center hardness" as used
herein refers to the hardness, which is determined by cutting the
resulting golf ball into two equal parts and then measuring a JIS-C
hardness at its center point in section. The term "surface
hardness" as used herein refers to the hardness, which is
determined by measuring a JIS-C hardness at the surface of the
resulting golf ball.
[0049] In the one-piece solid golf ball of the present invention,
it is required for the center hardness to be the minimum hardness
in the golf ball, and it is required for a difference between the
maximum hardness and minimum hardness in the golf ball to be within
the range of 16 to 25, preferably 20 to 25, more preferably 22 to
25. When the hardness difference is smaller than 16, the shot feel
is heavy and poor and the flight performance is degraded. On the
other hand, when the hardness difference is larger than 25, the
surface portion of the golf ball is only too hard and the golf ball
is brittle, and the durability is degraded.
[0050] Generally, polybutadiene rubber having large Mw, such as the
polybutadiene rubber (a) is used in larger amount in order to
improve the rebound characteristics. Thereby, the difference
between the center hardness and surface hardness is large, and the
shot feel is improved, but the durability is degraded with using
only the polybutadiene rubber (a). The one-piece solid golf ball
having excellent rebound characteristics (flight performance),
excellent durability and excellent processability is obtained by
using a combination of the polybutadiene (a) and polybutadiene (b).
In addition, the shot feel is good by controlling the difference
between the maximum hardness and minimum hardness in the golf ball
to a specified range.
[0051] Generally, in golf balls having the same compression
(deformation amount), when a difference between the maximum
hardness and minimum hardness in the golf ball is small, that is,
the golf ball has even hardness distribution, the rebound
characteristics are degraded. However, the hardness distribution is
even, the shot feel is poor. On the other hand, the hardness
difference is large, the shot feel is good. In Japanese Patent
Kokai Publication No. 177973/1990 described above, even hardness
distribution, that is, small hardness difference is accomplished by
adding a vulcanization stabilizer to rubber composition for the
golf ball. The resulting golf ball thereby has excellent rebound
characteristics, but has poor shot feel. On the other hand, in the
golf ball of the present invention, golf ball having high rebound
characteristics and large hardness difference can be obtained by
adding hydroquinone or derivatives thereof to rubber composition
for the golf ball and vulcanizing the rubber composition at high
temperature to control reaction rate. The golf ball of the present
invention has high surface hardness when compared with a golf ball
having the same compression (deformation amount). Therefore it is
difficult to cut the surface of the golf ball of the present
invention, and the golf ball has excellent cut resistance.
[0052] In the solid golf ball of the present invention, the golf
ball has a deformation amount (compression) when applying from an
initial load of 98 N to a final load of 1275 N of 2.0 to 4.0 mm,
preferably 2.0 to 3.0 mm. When the deformation amount is smaller
than 2.0 mm, the resulting golf ball is too hard, and shot feel is
poor. On the other hand, when the deformation amount is larger than
4.0 mm, the resulting golf ball is too soft, and the rebound
characteristics are degraded.
[0053] The weight of the golf ball is limited to the range of not
more than 45.92 g in accordance with the regulations for large size
golf balls, but the lower limit is not limited. The one-piece solid
golf ball of the present invention has a weight of 44.0 to 45.8 g,
preferably 44.2 to 45.8 g. When the weight of the golf ball is
smaller than 44.0 g, the golf ball loses inertia on a flight, and
stalls, which reduces the flight distance. On the other hand, when
the weight of the golf ball is larger than 45.8 g, the shot feel is
heavy and poor.
[0054] The diameter of the one-piece golf ball of the present
invention can be within the range of 41.0 to 44.0 mm, but it is
preferably within the range of not less than 42.67 mm in accordance
with the regulations for large size golf balls, typically it is
about 42.75 mm.
EXAMPLES
[0055] The following Examples and Comparative Examples further
illustrate the present invention in detail but are not to be
construed to limit the scope of the present invention.
[0056] (Examples 1 to 3 and Comparative Examples 1 to 6)
[0057] The rubber compositions having the formulation shown in
Tables 1 and 2 were mixed, and the mixtures were then press molded
at the vulcanization conditions shown in the same Tables in a mold,
which is composed of an upper mold and a lower mold having a
hemispherical cavity, to obtain one-piece golf balls having a
diameter 42.75 mm. The Mooney viscosity, Mw, Mn and content of
cis-1,4-butadiene of the polybutadiene rubbers used are shown in
Table 3.
1TABLE 1 (parts by weight) Comparative Example No. Example No.
Composition 1 2 3 1 2 Polybutadiene A 90 90 80 100 50 Polybutadiene
B 10 10 20 -- -- Polybutadiene C -- -- -- -- 50 Zinc oxide 23 23 23
23 23 Methacrylic acid 24 24 24 24 24 Vulcanization 0.15 0.50 0.20
0.20 0.20 stabilizer *1 Dicumyl peroxide 1.40 2.40 1.40 1.60 1.45
Vulcanization condition The first Temp. (.degree. C.) 171 171 171
165 160 stage Time (min) 17 17 17 20 25 The sec- Temp. (.degree.
C.) -- -- -- -- 170 ond stage Time (min) -- -- -- -- 5
[0058]
2TABLE 2 (parts by weight) Comparative Example No. Composition 3 4
5 6 Polybutadiene A 90 90 90 100 Polybutadiene B 10 10 10 --
Polybutadiene C -- -- -- -- Zinc oxide 23 23 23 23 Methacrylic acid
24 24 24 24 Vulcanization stabilizer *1 -- 2.20 0.20 0.20 dicumyl
peroxide 0.65 9.60 1.50 1.60 Vulcanization condition The first
Temp. (.degree. C.) 171 171 165 171 stage Time (min) 17 17 23 17
The second Temp. (.degree. C.) -- -- -- -- stage Time (min) -- --
-- -- *1: 2,5-di-t-butylhydroquinone commercially available from
Ouchishinko Chemical Industrial Co., Ltd., under the trade name
"Nocrac NS-7"
[0059]
3TABLE 3 Polybutadiene A B C Trade name BR18 BR230 BR150L
Manufacturer JSR Co. Ube Ube Industries Industries Catalyst Nickel
Cobalt Cobalt Mooney viscosity 60 38 43 [ML.sub.1+4(100.degree.
C.)] *1 Content of cis-1,4- 96 98 98 polybutadiene (%) *2 Weight
average molecular 100 .times. 10.sup.4 63 .times. 10.sup.4 56
.times. 10.sup.4 weight (Mw) *3 Number average molecular 23 .times.
10.sup.4 16 .times. 10.sup.4 24 .times. 10.sup.4 weight (Mn) *3
Ratio (Mw/Mn) 4.3 3.9 2.3 *2: Measurement according to JIS k 6300
*3: NMR (Nuclear magnetic resonance) *4: Mw (weight average
molecular weight) and Mn (number average molecular weight) is
determined by measuring with a gel permeation chromatography (GPC)
using tetrahydrofuran as a organic solvent for elute and
calibrating with standard polystyrene.
[0060] With respect to the resulting one-piece solid golf ball, the
compression, coefficient of restitution durability, hardness
distribution including center hardness and surface hardness in
JIS-C hardness and shot feel were measured or evaluated, and the
results are shown in Tables 4 and 5. The difference between the
maximum hardness and minimum harness in the golf ball was
calculated, and the results (hardness difference) are shown in the
same Tables. The test method are as follows.
[0061] Test Method
[0062] (1) Compression (Deformation Amount)
[0063] The compression was determined by measuring the deformation
amount when applying from an initial load of 98 N to a final load
of 1275 N on the golf ball. The compression is indicated by an
index when an inverse number of the deformation amount of
Comparative example 1 is 100. The higher the index is, the higher
the hardness is.
[0064] (2) Coefficient of Restitution
[0065] A metal cylindrical article having a weight of 198.4 g was
struck at a speed of 40 cm/sec against a golf ball, which is in a
stationary state, and the velocity of the cylindrical article and
the golf ball before and after the strike were measured. The
coefficient of restitution of the golf ball was calculated from the
velocity and the weight of both the cylindrical article and the
golf ball. The measurements were conducted five times for each golf
ball, with the mean value being taken as the coefficient of
restitution of each ball and indicated by an index when that of
Comparative Example 1 is 100. A higher index corresponded to a
higher rebound characteristic, and thus a good result.
[0066] (3) Durability
[0067] The same impact force was repeatedly applied to a golf ball,
that is, a golf ball was repeatedly hit at a head speed of 45
m/second. The durability is determined by measuring the number of
strike until the surface of the golf ball cracks, and is indicated
by an index when that of Comparative Example 1 is 100. The higher
the index is, the more excellent the durability is.
[0068] (4) Durability (of Golf Ball Having Nicks)
[0069] The durability was determined as described in the (3) except
for cutting two nicks on a golf ball in advance. The nicks are
positioned on the parting line and apex of the golf ball and have a
depth of 2 mm. The result is indicated by an index when that of
Comparative Example 1 is 100 as described in the (3).
[0070] (5) Hardness and Hardness Distribution
[0071] The hardness and hardness distribution is determined by
cutting a golf ball into two equal parts and then measuring a JIS-C
hardness at a center point, at a distance of 5 mm, 10 mm and 15 mm
from the center point, and at a surface in section. The JIS-C
hardness was measured at 20.degree. C. using a JIS-C hardness meter
according to JIS K 6301.
[0072] (6) Shot Feel
[0073] The shot feel of the golf ball is evaluated by 10 top
amateur golfers on a maximum scale of 10 points according to a
practical hitting test using a driver having metal head. The higher
the score is, the better the shot feel is. The evaluation criteria
are as follows.
[0074] .smallcircle.: Total score of not less than 80 points
[0075] .DELTA.: Total score of not less than 60 points and less
than 80 points
[0076] x: Total score of less than 60 points
[0077] Test Results
4 TABLE 4 Comparative Example No. Example No. Core composition 1 2
3 1 2 compression 100 100 99 100 100 Coefficient of restitution 102
102 101 100 99 Durability 100 100 100 100 100 Durability (nicks)
180 175 250 100 80 Hardness distribution (JIS-C) Center point 60 61
64 66 68 5 mm from the center point 68 67 69 68 71 10 mm from the
center point 73 75 74 74 75 15 mm from the center point 80 81 79 76
75 Surface 85 85 82 76 75 Hardness difference 25 24 18 10 7 Shot
feel .smallcircle. .smallcircle. .smallcircle. .DELTA. .DELTA.
[0078]
5 TABLE 5 Comparative Example No. 3 4 5 6 Core composition
compression 108 100 100 101 Coefficient of restitution 97 101 98
102 Durability 100 60 100 70 Durability (nicks) 180 40 120 90
Hardness distribution (JIS-C) Center point 65 62 65 60 5 mm from
the center point 68 68 67 68 10 mm from the center point 73 73 70
73 15 mm from the center point 77 76 73 80 Surface 82 82 75 85
Hardness difference 17 20 10 25 Shot feel .DELTA. .DELTA. .DELTA.
.smallcircle.
[0079] As is apparent from the results of Tables 4 and 5, the
one-piece solid golf balls of the present invention of Examples 1
to 3 as compared with the golf balls of Comparative Examples 1 to 6
have excellent rebound characteristics, excellent durability and
good shot feel.
[0080] On the other hand, in the golf balls of Comparative Examples
1 and 2, which corresponds to the golf balls described in Japanese
Patent Kokai Publication No. 177973/1990 and Japanese Patent No.
2644226, the coefficient of restitution is equal to or slightly
lower than that of the golf balls of Examples, but a difference
between the maximum hardness and minimum hardness in the golf ball
(hardness difference) is small, and the shot feel is poor. In the
both golf balls, the surface hardness is low, and it is easy to cut
on the surface thereof and the durability of the golf ball having
nicks is very poor. In the golf ball of Comparative Example 1, only
polybutadiene having high Mooney viscosity (polybutadiene (a)) was
used, and the durability was poor. In the golf ball of Comparative
Example 2, the amount of polybutadiene having low Mooney viscosity
(polybutadiene (b)) is large, and the coefficient of restitution is
low.
[0081] In the golf ball of Comparative Example 3, the vulcanization
stabilizer was not used, and the coefficient of restitution is low.
In the golf ball of Comparative Example 4, the amount of the
vulcanization stabilizer was large, and it is required to compound
a large amount of organic peroxide together with the rubber
composition for the golf ball in order to adjust the compression to
a proper range.
[0082] In the golf ball of Comparative Example 5, which used the
same rubber composition as that of Example 1 and different
vulcanization condition from that of Example 1, the hardness
difference is small, and the shot feel is poor. In addition, the
surface hardness is low, and it is easy to cut the surface of the
golf ball and the durability of the golf ball having nicks is very
poor. In the golf ball of Comparative Example 6, the hardness
difference is within the range of the present invention, but only
polybutadiene having high Mooney viscosity (polybutadiene (a)) was
used, and the durability was poor.
* * * * *