U.S. patent application number 14/228484 was filed with the patent office on 2014-10-02 for golf ball.
This patent application is currently assigned to Dunlop Sports Co., Ltd.. The applicant listed for this patent is Dunlop Sports Co., Ltd.. Invention is credited to Chiemi MIKURA, Ryota SAKAMINE, Ayaka SHINDO.
Application Number | 20140295994 14/228484 |
Document ID | / |
Family ID | 51621386 |
Filed Date | 2014-10-02 |
United States Patent
Application |
20140295994 |
Kind Code |
A1 |
SHINDO; Ayaka ; et
al. |
October 2, 2014 |
GOLF BALL
Abstract
An object of the present invention is to provide a golf ball
traveling a great flight distance on driver shots. The present
invention provides a golf ball having a spherical core and at least
one cover layer covering the spherical core, wherein the spherical
core is formed from a rubber composition containing (a) a base
rubber, (b) an .alpha.,.beta.-unsaturated carboxylic acid having 3
to 8 carbon atoms and/or a metal salt thereof as a co-crosslinking
agent, (c) a specific organic peroxide, and (d) a carboxylic acid
and/or a salt thereof, provided that the rubber composition further
contains (e) a metal compound in the case of containing only (b)
the .alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon
atoms as the co-crosslinking agent.
Inventors: |
SHINDO; Ayaka; (Kobe-shi,
JP) ; MIKURA; Chiemi; (Kobe-shi, JP) ;
SAKAMINE; Ryota; (Kobe-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Dunlop Sports Co., Ltd. |
Kobe-shi |
|
JP |
|
|
Assignee: |
Dunlop Sports Co., Ltd.
Kobe-shi
JP
|
Family ID: |
51621386 |
Appl. No.: |
14/228484 |
Filed: |
March 28, 2014 |
Current U.S.
Class: |
473/372 |
Current CPC
Class: |
A63B 37/0092 20130101;
A63B 37/0007 20130101; A63B 37/0075 20130101; A63B 37/0074
20130101; A63B 37/0051 20130101; A63B 37/0063 20130101; A63B
37/0087 20130101; A63B 37/0018 20130101; A63B 37/0076 20130101;
A63B 37/0096 20130101; A63B 37/0062 20130101; A63B 37/0064
20130101; A63B 37/0065 20130101 |
Class at
Publication: |
473/372 |
International
Class: |
A63B 37/00 20060101
A63B037/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 29, 2013 |
JP |
2013-072719 |
Mar 29, 2013 |
JP |
2013-072720 |
Mar 29, 2013 |
JP |
2013-072721 |
Claims
1. A golf ball having a spherical core and at least one cover layer
covering the spherical core, wherein the spherical core is formed
from a rubber composition containing (a) a base rubber, (b) an
.alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon
atoms and/or a metal salt thereof as a co-crosslinking agent, (c)
an organic peroxide represented by a following formula (1), and (d)
a carboxylic acid and/or a salt thereof, provided that the rubber
composition further contains (e) a metal compound in the case of
containing only (b) the .alpha.,.beta.-unsaturated carboxylic acid
having 3 to 8 carbon atoms as the co-crosslinking agent.
##STR00004## [In the formula (1), R.sup.1 to R.sup.10 each
represent a hydrogen atom, alkyl group, aryl group, aralkyl group,
or alkylaryl group independently, wherein the alkyl group, aryl
group, aralkyl group, or alkylaryl group may be bonded via an ester
group.]
2. The golf ball according to claim 1, wherein the rubber
composition contains (d) the carboxylic acid and/or the salt
thereof in a content ranging from 0.5 part to 40 parts by mass with
respect to 100 parts by mass of (a) the base rubber.
3. The golf ball according to claim 1, wherein (d) the carboxylic
acid and/or the salt thereof includes an aliphatic carboxylic acid
and/or a salt thereof.
4. The golf ball according to claim 3, wherein the aliphatic
carboxylic acid and/or the salt thereof has 1 to 30 carbon
atoms.
5. The golf ball according to claim 1, wherein (d) the carboxylic
acid and/or the salt thereof includes an aromatic carboxylic acid
and/or a salt thereof.
6. The golf ball according to claim 5, wherein the aromatic
carboxylic acid and/or the salt thereof includes a carboxylic acid
having a benzene ring and/or a salt thereof.
7. The golf ball according to claim 1, wherein R.sup.1, R.sup.5,
R.sup.6 and R.sup.19 each represent an alkyl group having 1 to 11
carbon atoms independently, and R.sup.2 to R.sup.4 and R.sup.7 to
R.sup.9 each represent an aryl group or an alkyl group having 1 to
11 carbon atoms independently.
8. The golf ball according to claim 1, wherein (c) the organic
peroxide includes 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3.
9. The golf ball according to claim 1, wherein the rubber
composition further comprises (f) an organic sulfur compound.
10. The golf ball according to claim 9, wherein (f) the organic
sulfur compound is at least one selected from the group consisting
of thiophenols and/or metal salts thereof, thionaphthols and/or
metal salts thereof, diphenylpolysulfides, and thiuram
disulfides.
11. The golf ball according to claim 9, wherein (f) the organic
sulfur compound is at least one selected from the group consisting
of thiophenols substituted with halogen, metal salts of the
thiophenols substituted with halogen, and diphenyldisulfides
substituted with halogen.
12. The golf ball according to claim 9, wherein (f) the organic
sulfur compound is at least one selected from the group consisting
of 2,6-dichlorothiophenol, a metal salt of 2,6-dichlorothiophenol,
pentachlorothiophenol, a metal salt of pentachlorothiophenol,
pentabromothiophenol, a metal salt of pentabromothiophenol,
bis(pentabromophenyl)disulfide, bis(2,6-dichlorophenyl)disulfide,
bis(pentachlorophenyl)disulfide, 2-thionaphthol and a metal salt of
2-thionaphthol.
13. The golf ball according to claim 9, wherein the rubber
composition contains (f) the organic sulfur compound in a content
ranging from 0.05 part to 5 parts by mass with respect to 100 parts
by mass of (a) the base rubber.
14. The golf ball according to claim 1, wherein the rubber
composition contains (b) the metal salt of the
.alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon
atoms.
15. The golf ball according to claim 1, wherein the rubber
composition contains (b) the .alpha.,.beta.-unsaturated carboxylic
acid having 3 to 8 carbon atoms and/or the metal salt thereof in a
content ranging from 15 parts to 50 parts by mass with respect to
100 parts by mass of (a) the base rubber.
16. The golf ball according to claim 1, wherein the spherical core
has a hardness difference (Hs-Ho) between a surface hardness (Hs)
thereof and a center hardness (Ho) thereof of 12 or more in JIS-C
hardness.
17. The golf ball according to claim 1, wherein the spherical core
has a center hardness (Ho) in a range from 30 to 70 in JIS-C
hardness.
18. The golf ball according to claim 1, wherein the spherical core
has a surface hardness (Hs) in a range from 65 to 100 in JIS-C
hardness.
19. The golf ball according to claim 1, wherein the spherical core
has a compression deformation amount ranging from 2.0 mm to 6.0 mm,
when applying a load from an initial load of 98N to a final load of
1275N to the spherical core having a diameter in a range from 34.8
mm to 42.2 mm.
20. The golf ball according to claim 1, wherein (a) the base rubber
includes a polybutadiene having a molecular weight distribution
MW/MN (MW: weight-average molecular weight, MN: number-average
molecular weight) in a range from 2.0 to 6.0.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a golf ball having an
excellent flying performance, in particular, an improvement of a
core of a golf ball.
DESCRIPTION OF THE RELATED ART
[0002] As a method for improving a flight distance on driver shots,
for example, there are methods of enhancing resilience of a core
and controlling a hardness distribution of a core. The former
method has an effect of enhancing an initial speed, and the latter
method has an effect of a lower spin rate. A golf ball having a low
spin rate travels a great distance.
[0003] For example, Japanese Patent No. 3674679, No. 3672016, and
Japanese Patent Publications No. 2012-139415 A and 2012-192158 A
disclose a technique to control a hardness distribution of the
core. Japanese Patent No. 3674679 and No. 3672016 disclose a
multi-piece golf ball comprising a solid core, wherein the solid
core is formed from a rubber composition containing a base rubber;
a crosslinking agent; and a mixture of
2,5-dimethyl-2,5-di-t-butylperoxyhexyne-3 and
1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane as an organic
peroxide in an amount ranging from 0.1 part by mass to 5 parts by
mass with respect to the base rubber, and wherein the core has a
maximum hardness at a position spaced 3 to 100 mm radially inward
from a surface thereof, and a hardness difference between the
maximum hardness and a hardness at the center position of 3 or more
in JIS-C hardness.
[0004] Japanese Patent Publication No. 2012-139415 A discloses a
golf ball having a spherical core and at least one cover layer
covering the spherical core, wherein the spherical core is formed
from a rubber composition containing (a) a base rubber, (b) an
.alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon
atoms and/or a metal salt thereof as a co-crosslinking agent, (c) a
crosslinking initiator, (d) a salt of a carboxylic acid, and (e) an
organic sulfur compound, provided that the rubber composition
further contains (f) a metal compound in the case of containing
only (b) the .alpha.,.beta.-unsaturated carboxylic acid having 3 to
8 carbon atoms as the co-crosslinking agent, wherein the rubber
composition contains (d) the salt of the carboxylic acid in a
content of 10 parts by mass or more and less than 40 parts by mass
with respect to 100 parts by mass of (a) the base rubber.
[0005] Japanese Patent Publication No. 2012-192158 A discloses a
golf ball having a spherical core and at least one cover layer
covering the spherical core, wherein the spherical core is formed
from a rubber composition containing (a) a base rubber, (b) an
.alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon
atoms and/or a metal salt thereof as a co-crosslinking agent, (c) a
crosslinking initiator, (d) a carboxylic acid and (e) an organic
sulfur compound, provided that the rubber composition further
contains (f) a metal compound in the case of containing only (b)
the .alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon
atoms as the co-crosslinking agent.
SUMMARY OF THE INVENTION
[0006] An object of the present invention is to provide a golf ball
showing an excellent flying performance.
[0007] The present invention provides a golf ball having a
spherical core and at least one cover layer covering the spherical
core, wherein the spherical core is formed from a rubber
composition containing (a) a base rubber, (b) an
.alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon
atoms and/or a metal salt thereof as a co-crosslinking agent, (c)
an organic peroxide represented by a following formula (1), and (d)
a carboxylic acid and/or a salt thereof, provided that the rubber
composition further contains (e) a metal compound in the case of
containing only (b) the .alpha.,.beta.-unsaturated carboxylic acid
having 3 to 8 carbon atoms as the co-crosslinking agent.
##STR00001##
[In the formula (1), R.sup.1 to R.sup.10 each represent a hydrogen
atom, alkyl group, aryl group, aralkyl group, or alkylaryl group
independently, wherein the alkyl group, aryl group, aralkyl group,
or alkylaryl group may be bonded via an ester group.]
[0008] Since the golf ball of the present invention is constructed
as described above, the spherical core has a higher degree of an
outer-hard inner-soft structure where a surface hardness thereof is
higher than a center hardness and a lowered hardness around 37.5%
position from a center of a core radius. The golf ball having the
spherical core with a higher degree of the outer-hard inner-soft
structure exhibits a lower spin rate on driver shots. Further,
lower hardness around 37.5% position from the center of the core
radius further reduces the spin rate on driver shots. Accordingly,
it is expected that the golf ball of the present invention travels
an even greater distance on driver shots.
[0009] In the present invention, the action of (d) the carboxylic
acid and/or a salt thereof in the rubber composition is considered
as follows. It is considered that the metal salt of (b) the
.alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon
atoms blended in the rubber composition forms an ion cluster in the
core, resulting in a metal crosslinking of a rubber molecular
chain. By blending (d) the carboxylic acid and/or the salt thereof
in the rubber composition, (d) the carboxylic acid and/or the salt
thereof exchanges a cation with the ion cluster formed by the metal
salt of (b) the .alpha.,.beta.-unsaturated carboxylic acid having 3
to 8 carbon atoms, thereby breaking the metal crosslinking by (b)
the metal salt of the .alpha.,.beta.-unsaturated carboxylic acid
having 3 to 8 carbon atoms. The cation exchange reaction easily
occurs at the core central part where the temperature is high, and
less occurs toward the core surface. When molding the core, the
internal temperature of the core is high at the core central part
and decreases toward the core surface, since reaction heat from a
curing reaction of the rubber composition accumulates at the core
central part. That is, the breaking of the metal crosslinking by
(d) the carboxylic acid and/or the salt thereof easily occurs at
the core central part, but less occurs toward the surface. As a
result, it is conceivable that since a crosslinking density in the
core increases from the center of the core toward the surface
thereof, the hardness increases from the center of the core toward
the surface thereof. Further, it is considered that blending (c)
the specific organic peroxide having a triple bond in a molecule
thereof in addition to (d) the carboxylic acid and/or the salt
thereof lowers the hardness around 37.5% position from the center
of the core radius while maintaining the outer-hard inner soft
structure of the core, due to the specific structure of (c) the
organic peroxide.
[0010] The present invention provides a golf ball showing an
excellent flying performance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a partially cutaway sectional view showing the
golf ball according to the preferable embodiment of the present
invention;
[0012] FIG. 2 is a graph showing the hardness distribution of the
spherical core;
[0013] FIG. 3 is a graph showing the hardness distribution of the
spherical core;
[0014] FIG. 4 is a graph showing the hardness distribution of the
spherical core;
[0015] FIG. 5 is a graph showing the hardness distribution of the
spherical core;
[0016] FIG. 6 is a graph showing the hardness distribution of the
spherical core;
[0017] FIG. 7 is a graph showing the hardness distribution of the
spherical core;
[0018] FIG. 8 is a graph showing the hardness distribution of the
spherical core;
[0019] FIG. 9 is a graph showing the hardness distribution of the
spherical core;
[0020] FIG. 10 is a graph showing the hardness distribution of the
spherical core;
[0021] FIG. 11 is a graph showing the hardness distribution of the
spherical core;
[0022] FIG. 12 is a graph showing the hardness distribution of the
spherical core;
[0023] FIG. 13 is a graph showing the hardness distribution of the
spherical core;
[0024] FIG. 14 is a graph showing the hardness distribution of the
spherical core;
[0025] FIG. 15 is a graph showing the hardness distribution of the
spherical core;
[0026] FIG. 16 is a graph showing the hardness distribution of the
spherical core;
[0027] FIG. 17 is a graph showing the hardness distribution of the
spherical core;
[0028] FIG. 18 is a graph showing the hardness distribution of the
spherical core;
[0029] FIG. 19 is a graph showing the hardness distribution of the
spherical core;
[0030] FIG. 20 is a graph showing the hardness distribution of the
spherical core;
[0031] FIG. 21 is a graph showing the hardness distribution of the
spherical core;
[0032] FIG. 22 is a graph showing the hardness distribution of the
spherical core;
[0033] FIG. 23 is a graph showing the hardness distribution of the
spherical core;
[0034] FIG. 24 is a graph showing the hardness distribution of the
spherical core.
[0035] FIG. 25 is a graph showing the hardness distribution of the
spherical core;
[0036] FIG. 26 is a graph showing the hardness distribution of the
spherical core;
[0037] FIG. 27 is a graph showing the hardness distribution of the
spherical core;
[0038] FIG. 28 is a graph showing the hardness distribution of the
spherical core;
[0039] FIG. 29 is a graph showing the hardness distribution of the
spherical core;
[0040] FIG. 30 is a graph showing the hardness distribution of the
spherical core;
[0041] FIG. 31 is a graph showing the hardness distribution of the
spherical core; and
[0042] FIG. 32 is a graph showing the hardness distribution of the
spherical core.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0043] The present invention provides a golf ball having a
spherical core and at least one cover layer covering the spherical
core, wherein the spherical core is formed from a rubber
composition containing (a) a base rubber, (b) an
.alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon
atoms and/or a metal salt thereof as a co-crosslinking agent, (c)
an organic peroxide represented by a following formula (1), and (d)
a carboxylic acid and/or a salt thereof, provided that the rubber
composition further contains (e) a metal compound in the case of
containing only (b) the .alpha.,.beta.-unsaturated carboxylic acid
having 3 to 8 carbon atoms as the co-crosslinking agent.
##STR00002##
[In the formula (1), R.sup.1 to R.sup.10 each represent a hydrogen
atom, alkyl group, aryl group, aralkyl group, or alkylaryl group
independently, wherein the alkyl group, aryl group, aralkyl group,
or alkylaryl group may be bonded via an ester group.]
[0044] First, (a) the base rubber used in the present invention
will be explained. As (a) the base rubber used in the present
invention, natural rubber and/or synthetic rubber can be used. For
example, polybutadiene rubber, natural rubber, polyisoprene rubber,
styrene polybutadiene rubber, ethylene-propylene-diene rubber
(EPDM), or the like can be used. These rubbers may be used solely
or two or more of these rubbers may be used in combination. Among
them, typically preferred is the high cis-polybutadiene having a
cis-1,4 bond in a proportion of 40% or more, more preferably 80% or
more, even more preferably 90% or more in view of its superior
resilience property.
[0045] The high-cis polybutadiene preferably has a 1,2-vinyl bond
in a content of 2 mass % or less, more preferably 1.7 mass % or
less, and even more preferably 1.5 mass % or less. If the content
of 1,2-vinyl bond is excessively high, the resilience may be
lowered.
[0046] The high-cis polybutadiene preferably includes one
synthesized using a rare earth element catalyst. When a neodymium
catalyst, which employs a neodymium compound of a lanthanum series
rare earth element compound, is used, a polybutadiene rubber having
a high content of a cis-1,4 bond and a low content of a 1,2-vinyl
bond is obtained with excellent polymerization activity. Such a
polybutadiene rubber is particularly preferred.
[0047] The high-cis polybutadiene preferably has a Mooney viscosity
(ML.sub.1+4 (100.degree. C.)) of 30 or more, more preferably 32 or
more, even more preferably 35 or more, and preferably has a Mooney
viscosity (ML.sub.1+4 (100.degree. C.)) of 140 or less, more
preferably 120 or less, even more preferably 100 or less, and most
preferably 80 or less. It is noted that the Mooney viscosity
(ML.sub.1+4 (100.degree. C.)) in the present invention is a value
measured according to JIS K6300 using an L rotor under the
conditions of: a preheating time of 1 minute; a rotor revolution
time of 4 minutes; and a temperature of 100.degree. C.
[0048] The high-cis polybutadiene preferably has a molecular weight
distribution Mw/Mn (Mw: weight average molecular weight, Mn: number
average molecular weight) of 2.0 or more, more preferably 2.2 or
more, even more preferably 2.4 or more, and most preferably 2.6 or
more, and preferably has a molecular weight distribution Mw/Mn of
6.0 or less, more preferably 5.0 or less, even more preferably 4.0
or less, and most preferably 3.4 or less. If the molecular weight
distribution (Mw/Mn) of the high-cis polybutadiene is excessively
low, the processability may deteriorate. If the molecular weight
distribution (Mw/Mn) of the high-cis polybutadiene is excessively
high, the resilience may be lowered. It is noted that the
measurement of the molecular weight distribution is conducted by
gel permeation chromatography ("HLC-8120GPC", manufactured by Tosoh
Corporation) using a differential refractometer as a detector under
the conditions of column: GMHHXL (manufactured by Tosoh
Corporation), column temperature: 40.degree. C., and mobile phase:
tetrahydrofuran, and calculated by converting based on polystyrene
standard.
[0049] Next, (b) the .alpha.,.beta.-unsaturated carboxylic acid
having 3 to 8 carbon atoms and/or a metal salt thereof will be
explained. (b) The .alpha.,.beta.-unsaturated carboxylic acid
having 3 to 8 carbon atoms and/or the metal salt thereof is blended
as a co-crosslinking agent in the rubber composition and has an
action of crosslinking a rubber molecule by graft polymerization to
a base rubber molecular chain. In the case that the rubber
composition used in the present invention contains only the
.alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon
atoms as the co-crosslinking agent, the rubber composition further
contains (e) the metal compound as an essential component.
Neutralizing the .alpha.,.beta.-unsaturated carboxylic acid having
3 to 8 carbon atoms with the metal compound in the rubber
composition provides substantially the same effect as using the
metal salt of the .alpha.,.beta.-unsaturated carboxylic acid having
3 to 8 carbon atoms. Further, in the case of using the
.alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon
atoms and the metal salt thereof in combination, (e) the metal
compound may be used as an optional component.
[0050] The .alpha.,.beta.-unsaturated carboxylic acid having 3 to 8
carbon atoms includes, for example, acrylic acid, methacrylic acid,
fumaric acid, maleic acid, crotonic acid, and the like.
[0051] Examples of the metals constituting the metal salts of the
.alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon
atoms include: monovalent metal ions such as sodium, potassium,
lithium or the like; divalent metal ions such as magnesium,
calcium, zinc, barium, cadmium or the like; trivalent metal ions
such as aluminum or the like; and other metal ions such as
zirconium or the like. The above metal ions can be used solely or
as a mixture of at least two of them. Among these metal ions,
divalent metal ions such as magnesium, calcium, zinc, barium,
cadmium or the like are preferable. Use of the divalent metal salts
of the .alpha.,.beta.-unsaturated carboxylic acid having 3 to 8
carbon atoms easily generates a metal crosslinking between the
rubber molecules. Especially, as the divalent metal salt, zinc
acrylate is preferable, because the zinc acrylate enhances the
resilience of the resultant golf ball. The
.alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon
atoms and/or a metal salt thereof may be used solely or in
combination at least two of them.
[0052] The content of (b) the .alpha.,.beta.-unsaturated carboxylic
acid having 3 to 8 carbon atoms and/or the metal salt thereof is
preferably 15 parts by mass or more, more preferably 20 parts by
mass or more, and is preferably 50 parts by mass or less, more
preferably 45 parts by mass or less, even more preferably 35 parts
by mass or less, with respect to 100 parts by mass of (a) the base
rubber. If the content of (b) the .alpha.,.beta.-unsaturated
carboxylic acid having 3 to 8 carbon atoms and/or the metal salt
thereof is less than 15 parts by mass, the content of (c) the
crosslinking initiator which will be explained below must be
increased in order to obtain the appropriate hardness of the
constituting member formed from the rubber composition, which tends
to cause the lower resilience. On the other hand, if the content of
(b) the .alpha.,.beta.-unsaturated carboxylic acid having 3 to 8
carbon atoms and/or the metal salt thereof exceeds 50 parts by
mass, the constituting member formed from the rubber composition
becomes excessively hard, which tends to cause the lower shot
feeling.
[0053] (c) The organic peroxide represented by the following
formula (1) serves as a crosslinking initiator. The crosslinking
initiator is blended in order to crosslink (a) the base rubber
component.
##STR00003##
[In the formula (1), R.sup.1 to R.sup.10 each represent a hydrogen
atom, alkyl group, aryl group, aralkyl group, or alkylaryl group
independently, wherein the alkyl group, aryl group, aralkyl group,
or alkylaryl group may be bonded via an ester group.]
[0054] The alkyl group represented by R.sup.1 to R.sup.10 in the
formula includes normal alkyl groups such as a methyl group, ethyl
group, n-propyl group, n-butyl group, n-pentyl group, n-hexyl
group, n-heptyl group, n-octyl group, n-nonyl group, n-decyl group,
or the like; branched alkyl groups such as an isopropyl group,
isobutyl group, tert-butyl group, isopentyl group, neopentyl group,
2-ethylhexyl group, and isooctyl group; cycloalkyl groups such as
cyclopropyl group, cyclobutyl group, cyclopentyl group, cyclohexyl
group, and cycloheptyl group. Among them, preferred is an alkyl
group having 1 to 11 carbon atoms, and more preferred is an alkyl
group having 1 to 6 carbon atoms, even more preferred is methyl
group or ethyl group. Further, the normal alkyl group is preferable
as an alkyl group.
[0055] The aryl group represented by R.sup.1 to R.sup.10 in the
formula includes a phenyl group, naphthyl group, anthryl group,
biphenyl group, phenanthryl group, fluorenyl group or the like, and
among them, a phenyl group is preferred. The aralkyl group
represented by R.sup.1 to R.sup.10 in the formula includes a benzyl
group, phenethyl group, phenylpropyl group, naphthylmethyl group,
naphthylethyl group or the like. The alkylaryl group represented by
R.sup.1 to R.sup.10 in the formula includes a tolyl group, xylyl
group, cumenyl group, mesityl group or the like.
[0056] R.sup.1, R.sup.5, R.sup.6, and R.sup.19 preferably include
an alkyl group having 1 to 11 carbon atoms, more preferably a
methyl group or ethyl group. R.sup.2 to R.sup.4 and R.sup.7 to
R.sup.9 preferably include an aryl group or alkyl group having 1 to
11 carbon atoms, more preferably the aryl group or alkyl group
having 1 to 6 carbon atoms, even more preferably a methyl group,
ethyl group or phenyl group.
[0057] Specific examples of (c) the organic peroxide include
2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3;
3,6-dimethyl-3,6-di(t-butylperoxy)octyne-4;
2,5-dimethyl-2-[(triphenylsilyl)peroxy]-5-(t-butylperoxy)hexyne-3;
2,5-dimethyl-2,5-[(triphenylsilyl)peroxy]hexyne-3. (c) The organic
peroxide may be used alone or in combination at least two of
them.
[0058] The content of (c) the crosslinking initiator is preferably
0.1 part by mass or more, and more preferably 0.2 part by mass or
more, and is preferably 5.0 parts by mass or less, and more
preferably 3.0 parts by mass or less, with respect to 100 parts by
mass of (a) the base rubber. If the content of (c) the crosslinking
initiator is less than 0.1 part by mass, the constituting member
formed from the rubber composition becomes too soft, and thus the
golf ball may have the lower resilience. If the content of (c) the
crosslinking initiator exceeds 5.0 parts by mass, the amount of (b)
the co-crosslinking agent must be decreased in order to obtain the
appropriate hardness of the constituting member formed from the
rubber composition, resulting in the insufficient resilience and
lower durability of the golf ball.
[0059] The rubber composition used in the present invention may
further comprise another crosslinking initiator in addition to (c)
the organic peroxide. As another crosslinking initiator, an organic
peroxide other than (c) the organic peroxide is preferred. Specific
examples of another organic peroxide include organic peroxides such
as dicumyl peroxide,
1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane,
2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and di-t-butyl peroxide.
These organic peroxides may be used solely or two or more of these
organic peroxides may be used in combination. In the case of using
another crosslinking initiator, the content of (C) the organic
peroxide is preferably 60 mass % or more, more preferably 70 mass %
or more, even more preferably 80 mass % or more in a total of 100%
of (c) the organic peroxide and another crosslinking agent. As the
crosslinking initiator, it is preferable that only (c) the organic
peroxide is blended.
[0060] Next, (d) the carboxylic acid and/or the salt thereof will
be explained. It is conceivable that (d) the carboxylic acid and/or
the salt thereof has an action of breaking the metal crosslinking
by the metal salt of (b) the .alpha.,.beta.-unsaturated carboxylic
acid having 3 to 8 carbon atoms at the center part of the core,
when molding the core. (d) The carboxylic acid and/or the salt
thereof includes, for example, an aliphatic carboxylic acid, a salt
of an aliphatic carboxylic acid, an aromatic carboxylic acid, and a
salt of an aromatic carboxylic acid. In (d) the carboxylic acid
and/or the salt thereof, (b) the .alpha.,.beta.-unsaturated
carboxylic acid having 3 to 8 carbon atoms and/or the metal salt
thereof used as the co-crosslinking agent should not be included.
(d) The carboxylic acid and/or the salt thereof may be used alone
or in combination of at least two of them.
[0061] (d) The aliphatic carboxylic acid and/or the salt thereof
preferably includes an aliphatic carboxylic acid having 1 to 30
carbon atoms, more preferably an aliphatic carboxylic acid having 1
to 18 carbon atoms, even more preferably an aliphatic carboxylic
acid having 1 to 13 carbon atoms.
[0062] The aliphatic carboxylic acid may be either a saturated
fatty acid or an unsaturated fatty acid. Further, the aliphatic
carboxylic acid may have a branched structure or a cyclic
structure. Specific examples of the aliphatic carboxylic acid
(IUPAC name) are methanoic acid (C1), ethanoic acid (C2), propanoic
acid (C3), butanoic acid (C4), pentanoic acid (C5), hexanoic acid
(C6), heptanoic acid (C7), octenoic acid (C8), nonanoic acid (C9),
decanoic acid (C10), undecanoic acid (C11), dodecanoic acid (C12),
tridecanoic acid (C13), tetradecanoic acid (C14), pentadecanoic
acid (C15), hexadecanoic acid (C16), heptadecanoic acid (C17),
octadecanoic acid (C18), nonadecanoic acid (C19), icosanoic acid
(C20), henicosenoic acid (C21), docosenoic acid (C22), tricosanoic
acid (C23), tetracosanoic acid (C24), pentacosanoic acid (C25),
hexacosanoic acid (C26), heptacosanoic acid (C27), octacosanoic
acid (C28), nonacosanoic acid (C29), and triacontanoic acid
(C30).
[0063] Specific examples of the unsaturated fatty acid (IUPAC name)
are etenoic acid (C2), propenoic acid (C3), butenoic acid (C4),
pentenoic acid (C5), hexenoic acid (C6), heptenoic acid (C7),
octenoic acid (C8), nonenoic acid (C9), decenoic acid (C10),
undecenoic acid (C11), dodecenoic acid (C12), tridecenoic acid
(C13), tetradecenoic acid (C14), pentadecenoic acid (C15),
hexadecenoic acid (C16), heptadecenoic acid (C17), octadecenoic
acid (C18), nonadecenoic acid (C19), icosenoic acid (C20),
henicosenoic acid (C21), docosenoic acid (C22), tricosenoic acid
(C23), tetracosenoic acid (C24), pentacosenoic acid (C25),
hexacosenoic acid (C26), heptacosenoic acid (C27), octacosenoic
acid (C28), nonacosenoic acid (C29), and triacontanoic acid
(C30).
[0064] Specific examples (common name) of the fatty acids are
formic acid (C1), acetic acid (C2), propionic acid (C3), butyric
acid (C4), valeric acid (C5), caproic acid (C6), enanthic acid
(C7), caprylic acid (C8), pelargonic acid (C9), capric acid (C10),
lauric acid (C12), myristic acid (C14), myristoleic acid (C14),
pentadecylic acid (C15), palmitic acid (C16), palmitoleic acid
(C16), margaric acid (C17), stearic acid (C18), elaidic acid (C18),
vaccenic acid (C18), oleic acid (C18), linoleic acid (C18),
linolenic acid (C18), 12-hydroxystearic acid (C18), arachidic acid
(C20), gadoleic acid (C20), arachidonic acid (C20), eicosenoic acid
(C20), behenic acid (C22), erucic acid (C22), lignoceric acid
(C24), nervonic acid (C24), cerotic acid (C26), montanic acid
(C28), and melissic acid (C30).
[0065] The aromatic carboxylic acid includes, for example, a
carboxylic acid having a benzene ring in a molecule thereof, a
carboxylic acid having a heteroaromatic ring in a molecule thereof
and the like.
[0066] (d) The carboxylic acid having a benzene ring includes, for
example, an aromatic carboxylic acid having a carboxyl group
directly bonding to the benzene ring, an aromatic-aliphatic
carboxylic acid where an aliphatic carboxylic acid is bonded to the
benzene ring, a polynuclear aromatic carboxylic acid having a
carboxyl group directly bonding to the fused benzene ring, and a
polynuclear aromatic-aliphatic carboxylic acid where an aliphatic
carboxylic acid is bonded to the fused benzene ring. The fused
benzene ring structure includes, for example, naphthalene,
anthracene, phenalene, phenanthrene, tetracene, and pyrene.
[0067] The number of the carboxylic group of (d) the carboxylic
acid having the benzene ring may be either one (monocarboxylic
acid) or at least two (polycarboxylic acid), but preferably one.
The benzene ring or fused benzene ring may have another substituent
group directly bonding to the benzene ring or fused benzene ring
than the carboxylic group. Such a substituent group includes, for
example, an alkyl group (preferably, alkyl group having 1 to 4
carbon atoms), aryl group (preferably, phenyl group), amino group,
hydroxyl group, alkoxyl group (preferably, alkoxyl group having 1
to 4 carbon atoms), oxo group, and halogen group.
[0068] Specific examples of the aromatic carboxylic acid having a
carboxylic acid directly bonding to the benzene ring, include, for
example, benzoic acid (C7), phthalic acid (C8), isophthalic acid
(C8), terephthalic acid (C8), benzene-1,2,3-tricarboxylic acid
(C9), benzene-1,2,4-tricarboxylic acid (C9),
benzene-1,3,5-tricarboxylic acid (C9),
benzene-1,2,3,4-tetracarboxylic acid (C10),
benzene-1,2,3,5-tetracarboxylic acid (C10),
benzene-1,2,4,5-tetracarboxylic acid (C10), and benzene
hexacarboxylic acid (C12). Specific examples of the
aromatic-aliphatic carboxylic acid where the aliphatic carboxylic
acid is bonded to the benzene ring, includes phenylacetic acid
(C8), 2-phenylpropanoic acid (C9), and 3-phenylpropanoic acid
(C9).
[0069] Furthermore, examples of the carboxylic acid having a
benzene ring substituted with an alkyl group, aryl group, amino
group, hydroxyl group, alkoxy group, or oxo group include, for
example, methylbenzoic acid (C8), dimethylbenzoic acid (C9),
2,3,4-trimethylbenzoic acid (C10), 2,3,5-trimethylbenzoic acid
(C10), 2,4,5-triemethylbenzoic acid (C10), 2,4,6-trimethylbenzoic
acid (C10), 3,4,5-trimethylbenzoic acid (C10), 4-isopropylbenzoic
acid (C10), 4-tert-butylbenzoic acid (C11), 5-methylisophthalic
acid (C9), biphenyl-4-carboxylic acid (C13),
biphenyl-2,2'-dicarboxylic acid (C14), 4-dimethylaminobenzoic acid
(C9), 2-hydroxybenzoic acid (C7), methoxybenzoic acid (C8),
hydroxy(methyl)benzoic acid (C8), 2-hydroxy-3-methylbenzoic acid
(C8), 2-hydroxy-4-methylbenzoic acid (C8),
2-hydroxy-5-methylbenzoic acid (C8), 2,3-dihydroxybenzoic acid
(C7), 2,4-dihydroxybenzoic acid (C7), 2,6-dihydroxybenzoic acid
(C7), 3,4-dihydroxybenzoic acid (C7), 3,5-dihydroxybenzoic acid
(C7), 4-hydroxy-3-methoxybenzoic acid (C8),
3-hydroxy-4-methoxybenzoic acid (C8), 3,4-dimethoxybenzoic acid
(C9), 2,3-dimethoxybenzoic acid (C9), 2,4-dimethoxbenzoic acid
(C9), 2,4-dihydroxy-6-methylbenzoic acid (C8),
4,5-dimethoxyphthalic acid (C10), 3,4,5-trihydroxybenzoic acid
(C7), 4-hydroxy-3,5-dimethoxybenzoic acid (C9),
2,4,5-trimethoxybenzoic acid (C10), hydroxy(phenyl)acetic acid
(C8), hydroxy(4-hydroxy-3-methoxyphenyl)acetic acid (C9),
(4-methoxyphenyl)acetic acid (C9), (2,5-dihydroxyphenyl)acetic acid
(C8), (3,4-dihydroxyphenyl)acetic acid (C8),
(4-hydroxy-3-methoxyphenyl)acetic acid (C9),
(3-hydroxy-4-methoxyphenyl)acetic acid (C9),
(3,4-dimethoxyphenyl)acetic acid (C10), (2,3-dimethoxyphenyl)acetic
acid (C10), 2-(carboxymethyl)benzoic acid (C9),
3-(carboxymethyl)benzoic acid (C9), 4-(carboxymethyl)benzoic acid
(C9), 2-(carboxycarbonyl)benzoic acid (C9),
3-(carboxycarbonyl)benzoic acid (C9), 4-(carboxycarbonyl)benzoic
acid (C9), 2-hydroxy-2-phenylpropanoic acid (C9),
3-hydroxy-2-phenylpropanoic acid (C9), 3-(2-hydroxyphenyl)propanoic
acid (C9), 3-(4-hydroxyphenyl)propanoic acid (C9),
3-(3,4-dihydroxyphenyl)propanoic acid (C9),
3-(4-hydroxy-3-methoxyphenyl)propanoic acid (C10),
3-(3-hydroxy-4-methoxyphenyl)propanoic acid (C10),
3-(4-hydroxyphenyl)acrylic acid (C9),
3-(2,4-dihydroxyphenyl)acrylic acid (C9),
3-(3,4-dihydroxyphenyl)acrylic acid (C9),
3-(4-hydroxy-3-methoxyphenyl)acrylic acid (C10),
3-(3-hydroxy-4-methoxyphenyl) acrylic acid (C10), and
3-(4-hydroxy-3,5-dimethoxyphenyl)acrylic acid (C11).
[0070] The carboxylic acid having the benzene ring substituted with
halogen includes, for example, carboxylic acids where at least one
hydrogen of benzoic acid is substituted with a fluoro group such as
fluorobenzoic acid, difluorobenzoic acid, trifluorobenzoic acid,
tetrafluorobenzoic acid, and pentafluorobenzoic acid; carboxylic
acids where at least one hydrogen of benzoic acid is substituted
with a chloro group such as chlorobenzoic acid, dichlorobenzoic
acid, trichlorobenzoic acid, tetrachlorobenzoic acid, and
pentachlorobenzoic acid; carboxylic acids where at least one
hydrogen of benzoic acid is substituted with a bromo group such as
bromobenzoic acid, dibromobenzoic acid, tribromobenzoic acid,
tetrabromobenzoic acid, and pentabromobenzoic acid; and carboxylic
acids where at least one hydrogen of benzoic acid is substituted
with a iodo group such as iodobenzoic acid, diiodobenzoic acid,
triiodobenzoic acid, tetraiodobenzoic acid, and pentaiodobenzoic
acid.
[0071] Specific examples of the polynuclear aromatic carboxylic
acid having a carboxyl group directly bonding to the fused benzene
ring include 1-naphthalene carboxylic acid, 2-naphthalene
carboxylic acid, 1-anthracene carboxylic acid, 2-anthracene
carboxylic acid, 9-anthracene carboxylic acid, phenanthrene
carboxylic acid, and pyrene carboxylic acid. Specific examples of
the polynuclear aromatic-aliphatic carboxylic acid where the
aliphatic carboxylic acid is bonded to the fused benzene ring
include naphthylacetic acid, and naphthylpropionic acid.
[0072] The carboxylic acid having a fused benzene ring substituted
with halogen includes, for example, fluoronaphthalene carboxylic
acid, chloronaphthalene carboxylic acid, bromonaphthalene
carboxylic acid, fluoroanthracene carboxylic acid, chloroanthracene
carboxylic acid, and bromoanthracene carboxylic acid. The
carboxylic acid having a heteroaromatic ring includes, for example,
a carboxylic acid where a carboxylic acid is directly bonded to the
heteroaromatic ring. The hetero atom in the heteroaromatic ring can
be one kind or two or more kinds. The hetero atom includes a
nitrogen atom, oxygen atom, sulfur atom or the like. Among them,
the oxygen atom or sulfur atom is preferred. The number of the
hetero atom in the heteroaromatic ring is not particularly limited,
but preferably 2 or less, and more preferably 1. The heteroaromatic
ring includes, for example, a pyrrole ring, furan ring, thiophene
ring, imidazole ring, pyrazole ring, oxazole ring, thiazole ring,
pyridine ring, pyrazine ring, indole ring, quinolone ring,
benzofuran ring, and benzothiophene ring.
[0073] (d) The carboxylic acid having a heteroaromatic ring may be
a compound having only a carboxyl group as a substituent group to
the heteroaromatic ring, and a compound having another substituent
group directly bonding to the heteroaromatic ring in addition to
the carboxyl group. Further, the substituent group may bond to a
nitrogen atom constituting the heteroaromatic ring. The substituent
group includes, for example, halogen, a hydroxyl group, a mercapto
group, an alkyl group, an aryl group, an aralkyl group, an
alkylaryl group, an alkoxyl group, an amino group which may be
substituted, a cyano group, or a thiocarboxyl group.
[0074] Specific examples of the carboxylic acid having the
heteroaromatic ring and/or the salt thereof include, carboxylic
acids having a five-membered heteroaromatic ring such as a pyrrole
carboxylic acid, furan carboxylic acid, thiophene carboxylic acid,
imidazole carboxylic acid, pyrazole carboxylic acid, oxazole
carboxylic acid, and thiazole carboxylic acid; carboxylic acids
having a six-membered heteroaromatic ring such as a pyridine
carboxylic acid, and a pyrazine carboxylic acid; and carboxylic
acids having a fused heteroaromatic ring such as an
indolecarboxylic acid, quinolinecarboxylic acid, benzofuran
carboxylic acid, and benzothiophene carboxylic acid.
[0075] As (d) the salt of the aliphatic carboxylic acid or aromatic
carboxylic acid, a salt of the aliphatic carboxylic acid or
aromatic carboxylic acid described above may be used. The cation
component of the salt of these carboxylic acids may be any one of a
metal ion, an ammonium ion and an organic cation. The metal ion
includes monovalent metal ions such as sodium, potassium, lithium,
silver and the like; divalent metal ions such as magnesium,
calcium, zinc, barium, cadmium, copper, cobalt, nickel, manganese
and the like; trivalent metal ions such as aluminum, iron and the
like; and other ions such as tin, zirconium, titanium and the like.
The cation components may be used alone or as a mixture of at least
two of them. The cation component preferably includes a zinc
ion.
[0076] The organic cation includes a cation having a carbon chain.
The organic cation includes, for example, without limitation, an
organic ammonium ion. Examples of the organic ammonium ion are:
primary ammonium ions such as stearyl ammonium ion, hexyl ammonium
ion, oethyl ammonium ion, 2-ethyl hexyl ammonium ion or the like;
secondary ammonium ions such as dodecyl(lauryl) ammonium ion,
octadecyl(stearyl) ammonium ion or the like; tertiary ammonium ions
such as trioctyl ammonium ion or the like; and quaternary ammonium
ions such as dioctyldimethyl ammonium ion, distearyldimethyl
ammonium ion or the like. These organic cation may be used alone or
as a mixture of at least two of them.
[0077] (d) The aliphatic carboxylic acid and/or the salt thereof
preferably includes a saturated fatty acid and/or the salt thereof.
Preferable examples thereof include caprylic acid (octanoic acid),
pelargonic acid (nonanoic acid), capric acid (decanoic acid),
lauric acid, myristic acid, palmitic acid, stearic acid, behenic
acid, and oleic acid, or a potassium salt, magnesium salt, calcium
salt, aluminum salt, zinc salt, iron salt, copper salt, nickel
salt, or cobalt salt of the above aliphatic carboxylic acids. (d)
The aromatic carboxylic acid and/or the salt thereof preferably
includes benzoic acid, butylbezoic acid, anisic acid
(methoxybenzoic acid), dimethoxybenzoic acid, trimethoxybenzoic
acid, dimethylaminobenzoic acid, chlorobenzoic acid,
dichlorobenzoic acid, trichlorobenzoic acid, acetoxybenzoic acid,
biphenyl carboxylic acid, naphthalene carboxylic acid, anthracene
carboxylic acid, furan carboxylic acid, and thenoyl carboxylic
acid, or a potassium salt, magnesium salt, calcium salt, aluminum
salt, zinc salt, iron salt, copper salt, nickel salt, or cobalt
salt of the above aromatic carboxylic acids.
[0078] The content of (d) the carboxylic acid and/or the salt
thereof is preferably 0.5 part by mass or more, more preferably 1.0
parts by mass or more, even more preferably 1.5 parts by mass or
more, and is preferably 40 parts by mass or less, more preferably
35 parts by mass or less, even more preferably 30 parts by mass or
less with respect to 100 parts by mass of (a) the base rubber. If
the content is too little, the effect of adding (d) the carboxylic
acid and/or the salt thereof is not sufficient, and thus the degree
of the outer-hard inner-soft structure of the spherical core may be
lowered. If the content is too much, the resilience of the core may
be lowered, since the hardness of the resultant core may be lowered
as a whole.
[0079] There are cases where the surface of the zinc acrylate used
as the co-crosslinking agent is treated with the carboxylic acid
and/or the salt thereof to improve the dispersibility to the
rubber. In the case of using zinc acrylate whose surface is treated
with the carboxylic acid and/or the salt thereof, in the present
invention, the amount of the carboxylic acid and/or the salt
thereof used as a surface treating agent is included in the content
of (d) the carboxylic acid and/or the salt thereof. For example, if
25 parts by mass of zinc acrylate whose surface treatment amount
with the carboxylic acid and/or the salt thereof is 10 mass % is
used, the amount of the carboxylic acid and/or the salt thereof is
2.5 parts by mass and the amount of zinc acrylate is 22.5 parts by
mass. Thus, 2.5 parts by mass is counted as the content of (d) the
carboxylic acid and/or the salt thereof.
[0080] In the case that the rubber composition used in the present
invention contains only the .alpha.,.beta.-unsaturated carboxylic
acid having 3 to 8 carbon atoms as the co-crosslinking agent, the
rubber composition further contains (e) a metal compound as an
essential component. (e) The metal compound is not limited as long
as it can neutralize (b) the .alpha.,.beta.-unsaturated carboxylic
acid having 3 to 8 carbon atoms in the rubber composition. (e) The
metal compound includes, for example, metal hydroxides such as
magnesium hydroxide, zinc hydroxide, calcium hydroxide, sodium
hydroxide, lithium hydroxide, potassium hydroxide, copper
hydroxide, and the like; metal oxides such as magnesium oxide,
calcium oxide, zinc oxide, copper oxide, and the like; metal
carbonates such as magnesium carbonate, zinc carbonate, calcium
carbonate, sodium carbonate, lithium carbonate, potassium
carbonate, and the like. Among these, (e) the metal compound
preferably includes a divalent metal compound, more preferably
includes a zinc compound. The divalent metal compound reacts with
the .alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon
atoms, thereby forming a metal crosslinking. Use of the zinc
compound provides a golf ball with excellent resilience. (e) These
metal compounds are used solely or as a mixture of at least two of
them. The content of (e) the metal compound may be adjusted
depending upon the desired neutralization degree of (b) the
.alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon
atoms.
[0081] The rubber composition used in the present invention
preferably further contains (f) an organic sulfur compound. By
using (f) the organic sulfur compound in addition to (c) the
organic peroxide and (d) the carboxylic acid and/or the salt
thereof for the rubber composition, the degree of the outer-hard
and inner-soft structure of the core can be controlled at a higher
level. (f) The organic sulfur compound can be used alone or in
combination of at least two of them.
[0082] (f) The organic sulfur compound is not particularly limited,
as long as it is an organic compound having a sulfur atom in the
molecule thereof. Examples thereof include an organic compound
having a thiol group (--SH), a polysulfide bond having 2 to 4
sulfur atoms (--S--S--, --S--S--S--, or --S--S--S--S--), or a metal
salt thereof (--SM, --S-M-S--, --S-M-S--S--, --S--S-M-S--S--,
--S-M-S--S--S--, or the like; M is a metal atom). Examples of the
metal salts are salts of monovalent metals such as sodium, lithium,
potassium, copper (I), and silver (I), and salts of divalent metals
such as zinc, magnesium, calcium, strontium, barium, titanium (II),
manganese (II), iron (II), cobalt (II), nickel(II), zirconium(II),
and tin (II). Furthermore, (f) the organic sulfur compound may be
any one of aliphatic compounds (aliphatic thiol, aliphatic
thiocarboxylic acid, aliphatic dithiocarboxylic acid, aliphatic
polysulfides, or the like), heterocyclic compounds, alicyclic
compounds (alicyclic thiol, alicyclic thiocarboxylic acid,
alicyclic dithiocarboxylic acid, alicyclic polysulfides, or the
like), and aromatic compounds.
[0083] (f) The organic sulfur compound includes, for example,
thiols (thiophenols, thionaphthols), polysulfides, thiurams,
thiocarboxylic acids, dithiocarboxylic acids, sulfenamides,
dithiocarbamates, and thiazoles.
[0084] The thiols preferably include thiophenols and thionaphthols.
Examples of the thiophenols include, for example, thiophenol;
thiophenols substituted with a fluoro group, such as
4-fluorothiophenol, 2,4-difluorothiophenol, 2,5-difluorothiophenol,
2,6-difluorothiophenol, 2,4,5-trifluorothiophenol,
2,4,5,6-tetrafluorothiophenol, pentafluorothiophenol and the like;
thiophenols substituted with a chloro group, such as
2-chlorothiophenol, 4-chlorothiophenol, 2,4-dichlorothiophenol,
2,5-dichlorothiophenol, 2,6-dichlorothiophenol,
2,4,5-trichlorothiophenol, 2,4,5,6-tetrachlorothiophenol,
pentachlorothiophenol and the like; thiophenols substituted with a
bromo group, such as 4-bromothiophenol, 2,4-dibromothiophenol,
2,5-dibromothiophenol, 2,6-dibromothiophenol,
2,4,5-tribromothiophenol, 2,4,5,6-tetrabromothiophenol,
pentabromothiophenol and the like; thiophenols substituted with an
iodo group, such as 4-iodothiophenol, 2,4-diiodothiophenol,
2,5-diiodothiophenol, 2,6-diiodothiophenol,
2,4,5-triiodothiophenol, 2,4,5,6-tetraiodothiophenol,
pentaiodothiophenol and the like.
[0085] The metal salt of thiophenols includes, for example,
monovalent metal salts of sodium, lithium, potassium, copper (I),
silver (I) or the like; and divalent metal salts of zinc,
magnesium, calcium, strontium, barium, titanium (II), manganese
(II), iron (II), cobalt (II), nickel (II), zirconium (II), tin (II)
or the like.
[0086] Examples of the thionaphthols (naphthalenethiols) are
2-thionaphthol, 1-thionaphthol, 1-chloro-2-thionaphthol,
2-chloro-1-thionaphthol, 1-bromo-2-thionaphthol,
2-bromo-1-thionaphthol, 1-fluoro-2-thionaphthol,
2-fluoro-1-thionaphthol, 1-cyano-2-thionaphthol,
2-cyano-1-thionaphthol, 1-acetyl-2-thionaphthol,
2-acetyl-1-thionaphthol, and metal salts thereof. Preferable
examples include 1-thionaphthol, 2-thionaphthol and metal salt
thereof. The metal salt preferably includes a divalent metal salt,
more preferably zinc salt. Specific examples of the metal salts
include a zinc salt of 1-thionaphthol and a zinc salt of
2-thionaphthol.
[0087] Polysulfides are an organic sulfur compound having
polysulfide bonds. Examples thereof include disulfides,
trisulfides, and tetrasulfides. As the polysulfides, diphenyl
polysulfides are preferred.
[0088] Examples of the diphenyl polysulfides include diphenyl
disulfide; diphenyl disulfides substituted with a fluoro group such
as bis(4-fluorophenyl)disulfide, bis(2,4-difluorophenyl)disulfide,
bis(2,5-difluorophenyl)disulfide, bis(2,6-difluorophenyl)disulfide,
bis(2,4,5-trifluorophenyl)disulfide,
bis(2,4,5,6-tetrafluorophenyl)disulfide and
bis(pentafluorophenyl)disulfide; diphenyl disulfides substituted
with a chloro group such as bis(4-chlorophenyl)disulfide,
bis(2,4-dichlorophenyl)disulfide, bis(2,5-dichlorophenyl)disulfide,
bis(2,6-dichlorophenyl)disulfide,
bis(2,4,5-trichlorophenyl)disulfide,
bis(2,4,5,6-tetrachlorophenyl)disulfide and
bis(pentachlorophenyl)disulfide; diphenyl disulfides substituted
with a bromo group such as bis(4-bromophenyl)disulfide,
bis(2,4-dibromophenyl)disulfide, bis(2,5-dibromophenyl)disulfide,
bis(2,6-dibromophenyl)disulfide,
bis(2,4,5-tribromophenyl)disulfide,
bis(2,4,5,6-tetrabromophenyl)disulfide and
bis(pentabromophenyl)disulfide; diphenyl disulfides substituted
with a iodo group such as bis(4-iodophenyl)disulfide,
bis(2,4-diiodophenyl)disulfide, bis(2,5-diiodophenyl)disulfide,
bis(2,6-diiodophenyl)disulfide, bis(2,4,5-triiodophenyl)disulfide,
bis(2,4,5,6-tetraiodophenyl)disulfide and
bis(pentaiodophenyl)disulfide; and diphenyl disulfides substituted
with an alkyl group such as bis(4-methylphenyl)disulfide,
bis(2,4,5-trimethylphenyl)disulfide,
bis(pentamethylphenyl)disulfide, bis(4-tert-butylphenyl)disulfide,
bis(2,4,5-tri-t-butylphenyl)disulfide, and
bis(pent-t-butylphenyl)disulfide.
[0089] The thiurams include, for example, thiuram monosulfide such
as tetramethylthiuram monosulfide; thiuram disulfides such as
tetramethylthiuram disulfide, tetraethylthiuram disulfide,
tetrabutylthiuram disulfide; and thiuram tetrasulfide such as
dipentamethylenethiuram tetrasulfide. The thiocarboxylic acids
include, for example, naphthalene thiocarboxylic acid. The
dithiocarboxylic acid includes, for example, naphthalene
dithiocarboxylic acid. The sulfenamides include, for example,
N-cyclohexyl-2-benzothiazole sulfenamide,
N-oxydiethylene-2-benzothiazole sulfenamide, and
N-t-butyl-2-benzothiazole sulfenamide.
[0090] (f) The organic sulfur compound preferably includes
thiophenols and/or metal salts thereof, thionaphthols and/or metal
salts thereof, diphenyl disulfides, and thiuram disulfides.
Preferable examples thereof include 2,4-dichlorothiophenol,
2,6-difluorotihophenol, 2,6-dichlorothiophenol,
2,6-dibromothiophenol, 2,6-diiodothiophenol,
2,4,5-trichlorothiophenol, pentachlorothiophenol, 1-thionaphthol,
2-thionaphthol, diphenyl disulfide,
bis(2,6-difluorophenyl)disulfide, bis(2,6-dichlorophenyl)disulfide,
bis(2,6-dibromophenyl)disulfide, bis(2,6-iodophenyl)disulfide, and
bis(pentabromophenyl)disulfide.
[0091] The rubber composition preferably includes at least one
member selected from the group consisting of thiophenols
substituted with halogen, metal salts of thiophenols substituted
with halogen, and diphenyl disulfide substituted with halogen.
Blending these specific halogenated organic sulfur compounds
enhances the resilience of the core. Halogen preferably includes
fluororine, chlorine, bromine, and iodine, more preferably chlorine
and bromine.
[0092] In the case that the rubber composition contains the above
specific halogenated organic sulfur compound, a content of
thiophenols substituted with halogen, metal salts of thiophenols
substituted with halogen, and diphenyl disulfide substituted with
halogen in the all of the organic sulfur compound is 60 mass % or
more, more preferably 80 mass % or more, even more preferably 90
mass % or more. Further, it is preferable that the rubber
composition contains only at least one member selected from the
group consisting of thiophenols substituted with halogen, metal
salts of thiophenols substituted with halogen, and diphenyl
disulfide substituted with halogen as the organic sulfur
compound.
[0093] The content of (f) the organic sulfur compound is preferably
0.05 part by mass or more, more preferably 0.1 part by mass or
more, and is preferably 5.0 parts by mass or less, more preferably
2.0 parts by mass or less, with respect to 100 parts by mass of (a)
the base rubber. If the content of (f) the organic sulfur compound
is less than 0.05 part by mass, the effect of adding (f) the
organic sulfur compound cannot be obtained and thus the resilience
may not improve. If the content of (f) the organic sulfur compound
exceeds 5.0 parts by mass, the compression deformation amount of
the obtained golf ball becomes large and thus the resilience may be
lowered.
[0094] A mass ratio ((d)/(f)) of (d) the carboxylic acid and/or a
salt thereof to (f) the organic sulfur compound is preferably 2 or
more, more preferably 5 or more, even more preferably 10 or more,
and is preferably 150 or less, more preferably 100 or less, even
more preferably 80 or less.
[0095] The rubber composition used in the present invention may
include additives such as a pigment, a filler for adjusting weight
or the like, an antioxidant, a peptizing agent, and a softener
where necessary. The pigment blended in the rubber composition
includes, for example, a white pigment, a blue pigment, and a
purple pigment.
[0096] As the white pigment, titanium oxide is preferably used. The
type of titanium oxide is not particularly limited, but rutile type
is preferably used because of the high opacity. The blending amount
of titanium oxide is preferably 0.5 part by mass or more, and more
preferably 2 parts by mass or more, and is preferably 8 parts by
mass or less, and more preferably 5 parts by mass or less, with
respect to 100 parts by mass of (a) the base rubber.
[0097] It is also preferred that the rubber composition contains
both a white pigment and a blue pigment. The blue pigment is
blended in order to make white color vivid, and examples thereof
include ultramarine blue, cobalt blue, and phthalocyanine blue.
Examples of the purple pigment include anthraquinone violet,
dioxazine violet, and methyl violet.
[0098] The blending amount of the blue pigment is preferably 0.001
part by mass or more, and more preferably 0.05 part by mass or
more, and is preferably 0.2 part by mass or less, and more
preferably 0.1 part by mass or less, with respect to 100 parts by
mass of (a) the base rubber. If the blending amount of the blue
pigment is less than 0.001 part by mass, blueness is insufficient,
and the color looks yellowish. If the blending amount of the blue
pigment exceeds 0.2 part by mass, blueness is excessively strong,
and a vivid white appearance is not provided.
[0099] The filler blended in the rubber composition is used as a
weight adjusting agent for mainly adjusting the weight of the golf
ball obtained as a final product. The filler may be blended where
necessary. The filler includes, for example, inorganic fillers such
as zinc oxide, barium sulfate, calcium carbonate, magnesium oxide,
tungsten powder, molybdenum powder, or the like. As the filler,
preferred is zinc oxide. It is considered that zinc oxide functions
as a vulcanization activator and increases the hardness of the
entire core. The content of the filler is preferably 0.5 part by
mass or more, more preferably 1 part by mass or more, and is
preferably 30 parts by mass or less, more preferably 25 parts by
mass or less, even more preferably 20 parts by mass or less with
respect to 100 parts by mass of the base rubber. If the content of
the filler is less than 0.5 part by mass, it is difficult to adjust
the weight, while if the content of the filler exceeds 30 parts by
mass, the weight ratio of the rubber component is reduced and thus
the resilience tends to be lowered.
[0100] The blending amount of the antioxidant is preferably 0.1
part by mass or more and 1 part by mass or less, with respect to
100 parts by mass of (a) the base rubber. In addition, the blending
amount of the peptizing agent is preferably 0.1 part by mass or
more and 5 parts by mass or less, with respect to 100 parts by mass
of (a) the base rubber.
[0101] The rubber composition used in the present invention is
obtained by mixing and kneading (a) the base rubber, (b) the
.alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon
atoms and/or the metal salt thereof, (c) the organic peroxide, (d)
the carboxylic acid and/or the salt thereof; and, where necessary,
(e) the metal compound, (f) the organic sulfur compound, and other
additives. The kneading can be conducted, without any limitation,
with a well-known kneading machine such as a kneading roll, a
banbury mixer, a kneader, or the like.
[0102] The spherical core of the golf ball of the present invention
can be obtained by molding the rubber composition after kneaded.
The temperature for molding into the spherical core is preferably
120.degree. C. or more, more preferably 150.degree. C. or more,
even more preferably 160.degree. C. or more, and is preferably
170.degree. C. or less. If the molding temperature exceeds
170.degree. C., the surface hardness of the core tends to decrease.
The molding pressure preferably ranges from 2.9 MPa to 11.8 MPa.
The molding time preferably ranges from 10 minutes to 60
minutes.
[0103] The spherical core preferably has a hardness difference
(Hs-Ho) between a surface hardness Hs and a center hardness Ho of
12 or more, more preferably 16 or more, even more preferably 20 or
more, and preferably has a hardness difference of 80 or less, more
preferably 70 or less, even more preferably 60 or less in JIS-C
hardness. If the hardness difference between the center hardness
and the surface hardness is large, the golf ball having a great
flight distance due to the high launch angle and low spin rate is
obtained.
[0104] The spherical core preferably has the center hardness Ho of
30 or more, more preferably 35 or more, even more preferably 40 or
more in JIS-C hardness. If the center hardness Ho is less than 30
in JIS-C hardness, the core becomes too soft and thus the
resilience may be lowered. Further, the spherical core preferably
has the center hardness Ho of 70 or less, more preferably 65 or
less, even more preferably 60 or less in JIS-C hardness. If the
center hardness Ho exceeds 70 in JIS-C hardness, the core becomes
too hard and thus the shot feeling tends to be lowered.
[0105] The spherical core preferably has the surface hardness Hs of
65 or more, more preferably 70 or more, and preferably has the
surface hardness Hs of 100 or less, more preferably 95 or less in
JIS-C hardness. If the surface hardness is 65 or more in JIS-C
hardness, the spherical core does not become excessively soft, and
thus the better resilience is obtained. Further, if the surface
hardness of the spherical core is 100 or less in JIS-C hardness,
the spherical core does not become excessively hard, and thus the
better shot feeling is obtained.
[0106] The spherical core preferably has the diameter of 34.8 mm or
more, more preferably 36.8 mm or more, and even more preferably
38.8 mm or more, and preferably has the diameter of 42.2 mm or
less, more preferably 41.8 mm or less, and even more preferably
41.2 mm or less, and most preferably 40.8 mm or less. If the
spherical core has the diameter of 34.8 mm or more, the thickness
of the cover does not become too thick and thus the resilience
becomes better. On the other hand, if the spherical core has the
diameter of 42.2 mm or less, the thickness of the cover does not
become too thin, and thus the cover functions better.
[0107] When the spherical core has a diameter from 34.8 mm to 42.2
mm, a compression deformation amount (shrinking deformation amount
of the spherical core along the compression direction) of the
spherical core when applying a load from 98 N as an initial load to
1275 N as a final load is preferably 2.0 mm or more, more
preferably 2.8 mm or more, and is preferably 6.0 mm or less, more
preferably 5.0 mm or less. If the compression deformation amount is
2.0 mm or more, the shot feeling of the golf ball becomes better.
If the compression deformation amount is 6.0 mm or less, the
resilience of the golf ball becomes better.
[0108] The golf ball cover of the present invention is formed from
a cover composition containing a resin component. Examples of the
resin component include, for example, an ionomer resin; a
thermoplastic polyurethane elastomer having a commercial name of
"Elastollan" commercially available from BASF Japan Ltd; a
thermoplastic polyamide elastomer having a commercial name of
"Pebax" commercially available from Arkema K. K.; a thermoplastic
polyester elastomer having a commercial name of "Hytrel"
commercially available from Du Pont-Toray Co., Ltd.; and a
thermoplastic styrene elastomer having a commercial name of
"Rabalon" commercially available from Mitsubishi Chemical
Corporation; and the like.
[0109] The ionomer resin includes a product prepared by
neutralizing at least a part of carboxyl groups in the binary
copolymer composed of an olefin and an .alpha.,.beta.-unsaturated
carboxylic acid having 3 to 8 carbon atoms with a metal ion, a
product prepared by neutralizing at least a part of carboxyl groups
in the ternary copolymer composed of an olefin, an
.alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon
atoms, and an .alpha.,.beta.-unsaturated carboxylic acid ester with
a metal ion, or a mixture of those. The olefin preferably includes
an olefin having 2 to 8 carbon atoms. Examples of the olefin are
ethylene, propylene, butene, pentene, hexene, heptene, and octene.
The olefin more preferably includes ethylene. Examples of the
.alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon
atoms are acrylic acid, methacrylic acid, fumaric acid, maleic acid
and crotonic acid. Among these, acrylic acid and methacrylic acid
are particularly preferred. Examples of the
.alpha.,.beta.-unsaturated carboxylic acid ester include methyl
ester, ethyl ester, propyl ester, n-butyl ester, isobutyl ester of
acrylic acid, methacrylic acid, fumaric acid, maleic acid or the
like. In particular, acrylic acid ester and methacrylic acid ester
are preferable. Among these, the ionomer resin preferably includes
the metal ion-neutralized product of the binary copolymer composed
of ethylene-(meth)acrylic acid and/or the metal ion-neutralized
product of the ternary copolymer composed of ethylene,
(meth)acrylic acid, and (meth)acrylic acid ester.
[0110] Specific examples of the ionomer resins include trade name
"Himilan (registered trademark) (e.g. the binary copolymerized
ionomer such as Himilan 1555 (Na), Himilan 1557 (Zn), Himilan 1605
(Na), Himilan 1706 (Zn), Himilan 1707 (Na), Himilan AM3711 (Mg);
and the ternary copolymerized ionomer such as Himilan 1856 (Na),
Himilan 1855 (Zn))" commercially available from Du Pont-Mitsui
Polychemicals Co., Ltd.
[0111] Further, examples include "Surlyn (registered trademark)
(e.g. the binary copolymerized ionomer such as Surlyn 8945 (Na),
Surlyn 9945 (Zn), Surlyn 8140 (Na), Surlyn 8150 (Na), Surlyn 9120
(Zn), Surlyn 9150 (Zn), Surlyn 6910 (Mg), Surlyn 6120 (Mg), Surlyn
7930 (Li), Surlyn 7940 (Li), Surlyn AD8546 (Li); and the ternary
copolymerized ionomer such as Surlyn 8120 (Na), Surlyn 8320 (Na),
Surlyn 9320 (Zn), Surlyn 6320 (Mg), HPF 1000 (Mg), HPF 2000 (Mg))"
commercially available from E.I. du Pont de Nemours and
Company.
[0112] Further, examples include "lotek (registered trademark)
(e.g. the binary copolymerized ionomer such as lotek 8000 (Na),
lotek 8030 (Na), lotek 7010 (Zn), lotek 7030 (Zn); and the ternary
copolymerized ionomer such as lotek 7510 (Zn), lotek 7520 (Zn))"
commercially available from ExxonMobil Chemical Corporation.
[0113] It is noted that Na, Zn, Li, and Mg described in the
parentheses after the trade names indicate metal types of
neutralizing metal ions for the ionomer resins. The ionomer resins
may be used solely or in combination of at least two of them.
[0114] The cover composition constituting the cover of the golf
ball of the present invention preferably includes, as a resin
component, a thermoplastic polyurethane elastomer or an ionomer
rein. In case of using the ionomer rein, it is preferred to use a
thermoplastic styrene elastomer together. The content of the
polyurethane or ionomer resin in resin component of the cover
composition is preferably 50 mass % or more, more preferably 60
mass % or more, and even more preferably 70 mass % or more.
[0115] In the present invention, the cover composition may further
contain a pigment component such as a white pigment (for example,
titanium oxide), a blue pigment, and a red pigment; a weight
adjusting agent such as zinc oxide, calcium carbonate, and barium
sulfate; a dispersant; an antioxidant; an ultraviolet absorber; a
light stabilizer; a fluorescent material or a fluorescent
brightener; and the like, as long as they do not impair the effect
of the present invention.
[0116] The amount of the white pigment (for example, titanium
oxide) is preferably 0.5 part or more, more preferably 1 part or
more, and the content of the white pigment is preferably 10 parts
or less, more preferably 8 parts or less, with respect to 100 parts
of the resin component constituting the cover by mass. If the
amount of the white pigment is 0.5 part by mass or more, it is
possible to impart the opacity to the resultant cover. Further, if
the amount of the white pigment is more than 10 parts by mass, the
durability of the resultant cover may deteriorate.
[0117] The slab hardness of the cover composition is preferably set
in accordance with the desired performance of the golf balls. For
example, in case of a so-called distance golf ball which focuses on
a flight distance, the cover composition preferably has a slab
hardness of 50 or more, more preferably 55 or more, and preferably
has a slab hardness of 80 or less, more preferably 70 or less in
shore D hardness. If the cover composition has a slab hardness of
50 or more, the obtained golf ball has a high launch angle and low
spin rate on driver shots and iron shots, and thus the flight
distance becomes large. If the cover composition has a slab
hardness of 80 or less, the golf ball excellent in durability is
obtained.
[0118] Further, in case of a so-called spin golf ball which focuses
on controllability, the cover composition preferably has a slab
hardness of less than 50, and preferably has a slab hardness of 20
or more, more preferably 25 or more in shore D hardness. If the
cover composition has a slab hardness of less than 50, the flight
distance on driver shots can be improved by the core of the present
invention, as well as the obtained golf ball readily stops on the
green due to the high spin rate on approach shots. If the cover
composition has a slab hardness of 20 or more, the abrasion
resistance improves. In case of a plurality of cover layers, the
slab hardness of the cover composition constituting each layer can
be identical or different, as long as the slab hardness of each
layer is within the above range.
[0119] An embodiment for molding a cover is not particularly
limited, and includes an embodiment which comprises injection
molding the cover composition directly onto the core, or an
embodiment which comprises molding the cover composition into a
hollow-shell, covering the core with a plurality of the
hollow-shells and subjecting the core with a plurality of the
hollow shells to the compression-molding (preferably an embodiment
which comprises molding the cover composition into a half
hollow-shell, covering the core with the two half hollow-shells,
and subjecting the core with the two half hollow-shells to the
compression-molding).
[0120] When molding the cover in a compression molding method,
molding of the half shell can be performed by either compression
molding method or injection molding method, and the compression
molding method is preferred. The compression-molding of the cover
composition into half shell can be carried out, for example, under
a pressure of 1 MPa or more and 20 MPa or less at a temperature of
-20.degree. C. or more and 70.degree. C. or less relative to the
flow beginning temperature of the cover composition. By performing
the molding under the above conditions, a half shell having a
uniform thickness can be formed. Examples of a method for molding
the cover using half shells include compression molding by covering
the core with two half shells. The compression molding of half
shells into the cover can be carried out, for example, under a
pressure of 0.5 MPa or more and 25 MPa or less at a temperature of
-20.degree. C. or more and 70.degree. C. or less relative to the
flow beginning temperature of the cover composition. By performing
the molding under the above conditions, a golf ball cover having a
uniform thickness can be formed.
[0121] In the case of directly injection molding the cover
composition, the cover composition extruded in the pellet form
beforehand may be used for injection molding, or the cover
materials such as the base resin components and the pigment may be
dry blended, followed by directly injection molding the blended
materials. It is preferred to use upper and lower molds having a
spherical cavity and pimples for forming a cover, wherein a part of
the pimples also serves as a retractable hold pin. When molding the
cover by injection molding, the hold pin is protruded to hold the
core, and the cover composition which has been heated and melted is
charged and then cooled to obtain a cover. For example, it is
preferred that the cover composition heated and melted at the
temperature ranging from 200.degree. C. to 250.degree. C. is
charged into a mold held under the pressure of 9 MPa to 15 MPa for
0.5 to 5 seconds, and after cooling for 10 to 60 seconds, the mold
is opened and the golf ball with the cover molded is ejected from
the mold.
[0122] The concave portions called "dimple" are usually formed on
the surface of the cover. The total number of the dimples is
preferably 200 or more and 500 or less. If the total number is less
than 200, the dimple effect is hardly obtained. On the other hand,
if the total number exceeds 500, the dimple effect is hardly
obtained because the size of the respective dimples is small. The
shape (shape in a plan view) of dimples includes, for example,
without limitation, a circle, polygonal shapes such as roughly
triangular shape, roughly quadrangular shape, roughly pentagonal
shape, roughly hexagonal shape, and another irregular shape. The
shape of the dimples is employed solely or at least two of them may
be used in combination.
[0123] In the present invention, the thickness of the cover of the
golf ball is preferably 4.0 mm or less, more preferably 3.0 mm or
less, even more preferably 2.0 mm or less. If the thickness of the
cover is 4.0 mm or less, the resilience and shot feeling of the
obtained golf ball become better. The thickness of the cover is
preferably 0.3 mm or more, more preferably 0.5 mm or more, and even
more preferably 0.8 mm or more, and most preferably 1.0 mm or more.
If the thickness of the cover is less than 0.3 mm, the durability
and the wear resistance of the cover may deteriorate. If the cover
has a plurality of layers, it is preferred that the total thickness
of the cover layers falls within the above range.
[0124] After the cover is molded, the mold is opened and the golf
ball body is ejected from the mold, and as necessary, the golf ball
body is preferably subjected to surface treatments such as
deburring, cleaning, and sandblast. If desired, a paint film or a
mark may be formed. The paint film preferably has a thickness of,
but not limited to, 5 .mu.m or larger, and more preferably 7 .mu.m
or larger, and preferably has a thickness of 50 .mu.m or smaller,
and more preferably 40 .mu.m or smaller, even more preferably 30
.mu.m or smaller. If the thickness is smaller than 5 .mu.m, the
paint film is easy to wear off due to continued use of the golf
ball, and if the thickness is larger than 50 .mu.m, the effect of
the dimples is reduced, resulting in lowering flying performance of
the golf ball.
[0125] When the golf ball of the present invention has a diameter
in a range from 40 mm to 45 mm, a compression deformation amount of
the golf ball (shrinking amount of the golf ball in the compression
direction thereof) when applying a load from an initial load of 98
N to a final load of 1275 N to the golf ball is preferably 2.0 mm
or more, more preferably 2.4 mm or more, even more preferably 2.5
mm or more, most preferably 2.8 mm or more, and is preferably 5.0
mm or less, more preferably 4.5 mm or less. If the compression
deformation amount is 2.0 mm or more, the golf ball does not become
excessively hard, and thus exhibits the good shot feeling. On the
other hand, if the compression deformation amount is 5.0 mm or
less, the resilience is enhanced.
[0126] The golf ball construction is not limited, as long as the
golf ball of the present invention comprises a spherical core and
at least one cover layer covering the spherical core. FIG. 1 is a
partially cutaway sectional view showing the golf ball 2 according
to the preferable embodiment of the present invention. The golf
ball 2 comprises a spherical core 4, and a cover 12 covering the
spherical core 4. Plurality of dimples 14 are formed on a surface
of the cover. Other portions than dimples 14 on the surface of the
golf ball 2 are land 16. The golf ball 2 is provided with a paint
layer and a mark layer outside the cover 12, but these layers are
not depicted.
[0127] The spherical core preferably has a single layered
structure. Unlike the multi-layered structure, the spherical core
of the single layered structure does not have an energy loss at the
interface of the multi-layered structure when hitting, and thus has
an enhanced resilience. The cover has a structure of at least one
layer, for example a single layered structure, or a multi-layered
structure of at least two layers. The golf ball of the present
invention includes, for example, a two-piece golf ball comprising a
spherical core and a single layered cover disposed around the
spherical core, a multi-piece golf ball comprising a spherical
core, and at least two cover layers disposed around the spherical
core (including the three-piece golf ball), and a wound golf ball
comprising a spherical core, a rubber thread layer which is formed
around the spherical core, and a cover disposed over the rubber
thread layer. The present invention can be suitably applied to any
one of the above golf balls.
EXAMPLES
[0128] Hereinafter, the present invention will be described in
detail by way of example. The present invention is not limited to
examples described below. Various changes and modifications can be
made without departing from the spirit and scope of the present
invention.
[Evaluation Methods]
(1) Compression Deformation Amount (mm)
[0129] A compression deformation amount of the core or golf ball (a
shrinking amount of the core or golf ball in the compression
direction thereof), when applying a load from 98 N as an initial
load to 1275 N as a final load to the core or golf ball, was
measured.
(2) Slab Hardness (Shore D Hardness)
[0130] Sheets with a thickness of about 2 mm were produced by
injection molding the cover composition, and stored at 23.degree.
C. for two weeks. Three or more of these sheets were stacked on one
another so as not to be affected by the measuring substrate on
which the sheets were placed, and the hardness of the stack was
measured with a type P1 auto loading durometer manufactured by
Kobunshi Keiki Co., Ltd., provided with a Shore D type spring
hardness tester prescribed in ASTM-D2240.
(3) Hardness Distribution of Spherical Core (JIS-C Hardness)
[0131] A type P1 auto loading durometer manufactured by Kobunshi
Keiki Co., Ltd., provided with a JIS-C type spring hardness tester
was used to measure the hardness of the spherical core. The
hardness measured at the surface of the spherical core was adopted
as the surface hardness of the spherical core. The spherical core
was cut into two hemispheres to obtain a cut plane, and the
hardness were measured at the central point and at predetermined
distances from the central point. The core hardness were measured
at 4 points at predetermined distances from the central point of
the cut plane of the core. The core hardness was calculated by
averaging the hardness measured at 4 points.
(4) Flight Distance (m) and Spin Rate (Rpm) on a Driver Shot
[0132] A metal-headed W#1 driver (XXIO S, loft: 11.degree.,
manufactured by Dunlop Sports Limited) was installed on a swing
robot M/C manufactured by Golf Laboratories, Inc. A golf ball was
hit at a head speed of 40 m/sec, and the flight distance (the
distance from the launch point to the stop point) and the spin rate
right after hitting the golf ball were measured. This measurement
was conducted twelve times for each golf ball, and the average
value was adopted as the measurement value for the golf ball. A
sequence of photographs of the hit golf ball were taken for
measuring the spin rate (rpm) right after hitting the golf ball. In
tables, the flight distance and spin rate on the driver shots of
golf balls No. 1 to No. 8 are shown as the difference from those of
the golf ball No. 3, those of golf balls No. 9 to No. 16 are shown
as the difference from those of the golf ball No. 13, those of the
golf ball No. 18 is shown as the difference from those of the golf
ball No. 17, those of golf balls No. 20 to No. 22 are shown as the
difference from those of the golf ball No. 19, those of the golf
ball No. 24 is shown as the difference from those of the golf ball
No. 23, those of the golf balls No. 26 to No. 28 are shown as the
difference from those of the golf ball No. 25, those of the golf
ball No. 30 is shown as the difference from those of the golf ball
No. 29, those of golf balls No. 32 to No. 34 are shown as the
difference from those of the golf ball No. 31, and those of the
golf ball No. 36 is shown as the difference from those of the golf
ball No. 35.
[Production of Golf Balls]
(1) Production of Cores
[0133] The rubber compositions having formulations shown in Tables
1 to 8 were kneaded and heat-pressed in upper and lower molds, each
having a hemispherical cavity, at 170.degree. C. for 20 minutes to
prepare spherical cores having a diameter of 39.8 mm.
TABLE-US-00001 TABLE 1 Golf ball No. 1 2 3 4 Rubber BR730 100 100
100 100 composition Sanceler SR 25 29 23 27 (parts by mass)
2-thionaphthol 0.2 0.2 -- 0.1 Zinc octanoate 5 7.5 -- -- Zinc
stearate -- -- -- -- Stearic acid -- -- -- -- Zinc oxide 5 5 5 5
Barium sulfate *1) *1) *1) *1) Perhexyne 25B 0.49 0.49 -- --
Dicumyl peroxide -- -- 0.8 0.8 Core Center hardness 48.7 45.1 56.8
56.2 hardness 12.5% point hardness 52.4 50.3 60.7 62.7 distribution
25% point hardness 56.6 54.3 64.5 67.1 (JIS-C) 37.5% point hardness
61.8 56.5 66.5 68.3 50% point hardness 67.9 62.0 67.2 68.5 62.5%
point hardness 72.0 69.3 67.6 68.2 75% point hardness 73.6 70.6
71.3 71.6 87.5% point hardness 70.5 69.5 72.1 75.4 Surface hardness
70.9 70.0 80.6 83.9 Surface hardness - center hardness 22.2 24.9
23.8 27.7 Core compression deformation amount (mm) 4.24 4.20 4.09
4.06 Cover composition A A A A Cover hardness (Shore D) 65 65 65 65
Cover thickness (mm) 1.5 1.5 1.5 1.5 Ball Driver spin rate (rpm)
-90 -100 0 0 Driver flying distance (m) 3.0 2.8 0 0.7 Compression
deformation amount (mm) 3.54 3.50 3.39 3.23
TABLE-US-00002 TABLE 2 Golf ball No. 5 6 7 8 Rubber BR730 100 100
100 100 composition Sanceler SR 23 23 23 27 (parts by mass)
2-thionaphthol 0.2 0.2 0.32 0.2 Zinc octanoate -- -- -- -- Zinc
stearate 10 -- -- -- Stearic acid -- 10 10 -- Zinc oxide 5 5 5 5
Barium sulfate *1) *1) *1) *1) Perhexyne 25B 0.49 0.49 -- 0.49
Dicumyl peroxide -- -- 0.8 -- Core Center hardness 52.8 56.1 57.0
54.5 hardness 12.5% point hardness 56.6 59.1 62.0 60.4 distribution
25% point hardness 60.3 62.1 66.0 63.3 (JIS-C) 37.5% point hardness
64.9 64.6 67.0 64.2 50% point hardness 69.2 67.3 68.0 65.6 62.5%
point hardness 72.0 69.4 70.0 70.2 75% point hardness 73.2 71.0
75.0 73.8 87.5% point hardness 71.2 68.5 76.0 73.0 Surface hardness
70.7 70.0 81.0 73.5 Surface hardness - center hardness 17.9 13.9
24.0 19.0 Core compression deformation amount (mm) 4.10 4.15 4.14
4.17 Cover composition A A A A Cover hardness (Shore D) 65 65 65 65
Cover thickness (mm) 1.5 1.5 1.5 1.5 Ball Driver spin rate (rpm)
-60 -50 -20 0 Driver flying distance (m) 2.2 2.0 0.8 0 Compression
deformation amount (mm) 3.40 3.45 3.44 3.47
TABLE-US-00003 TABLE 3 Golf ball No. 9 10 11 12 Rubber BR730 100
100 100 100 composition Sanceler SR 29 27 29 26 (parts by mass)
2-thionaphthol 0.2 0.1 0.2 0.2 Benzoic acid 5.0 20.0 -- -- Zinc
dibenzoate -- -- -- 6.5 4-dimethylaminobenzoic acid -- -- 5.0 --
Zinc oxide 5 5 5 5 Barium sulfate *1) *1) *1) *1) Perhexyne 25B
0.49 0.49 0.49 0.49 Dicumyl peroxide -- -- -- -- Core Center
hardness 46.2 49.5 47.1 48.4 hardness 12.5% point hardness 50.2
52.2 50.1 51.2 distribution 25% point hardness 54.0 55.0 53.1 55.1
(JIS-C) 37.5% point hardness 56.3 59.3 56.3 59.1 50% point hardness
61.3 64.1 62.2 66.6 62.5% point hardness 70.6 67.2 69.5 71.6 75%
point hardness 77.7 71.0 74.1 73.4 87.5% point hardness 77.1 66.7
73.0 69.5 Surface hardness 75.7 69.6 73.3 72.7 Surface hardness -
center hardness 29.5 20.1 26.2 24.4 Core compression deformation
amount (mm) 4.04 3.99 4.15 4.16 Cover composition A A A A Cover
hardness (Shore D) 65 65 65 65 Cover thickness (mm) 1.5 1.5 1.5 1.5
Ball Driver spin rate (rpm) -120 -50 -100 -80 Driver flying
distance (m) 3.5 1.5 3.0 3.0 Compression deformation amount (mm)
3.34 3.29 3.45 3.46
TABLE-US-00004 TABLE 4 Golf ball No. 13 14 15 16 Rubber BR730 100
100 100 100 composition Sanceler SR 23 27 28 27 (parts by mass)
2-thionaphthol -- 0.1 0.1 0.2 Benzoic acid -- -- 20.0 -- Zinc
dibenzoate -- -- -- -- 4-dimethylaminobenzoic acid -- -- -- -- Zinc
oxide 5 5 5 5 Barium sulfate *1) *1) *1) *1) Perhexyne 25B -- -- --
0.49 Dicumyl peroxide 0.8 0.8 0.8 -- Core Center hardness 56.8 56.2
49.5 54.5 hardness 12.5% point hardness 60.7 62.7 55.0 60.4
distribution 25% point hardness 64.5 67.1 61.8 63.3 (JIS-C) 37.5%
point hardness 66.5 68.3 64.5 64.2 50% point hardness 67.2 68.5
67.6 65.6 62.5% point hardness 67.6 68.2 72.4 70.2 75% point
hardness 71.3 71.6 75.3 73.8 87.5% point hardness 72.1 75.4 71.9
73.0 Surface hardness 80.6 83.9 75.9 73.5 Surface hardness - center
hardness 23.8 27.7 26.4 19.0 Core compression deformation amount
(mm) 4.09 4.06 3.99 4.17 Cover composition A A A A Cover hardness
(Shore D) 65 65 65 65 Cover thickness (mm) 1.5 1.5 1.5 1.5 Ball
Driver spin rate (rpm) 0 0 -20 0 Driver flying distance (m) 0 0.7
0.5 0 Compression deformation amount (mm) 3.39 3.23 3.29 3.47
TABLE-US-00005 TABLE 5 Golf ball No. 17 18 19 20 21 22 Rubber BR730
100 100 100 100 100 100 composition Sanceler SR 29 25 25 25 25 25
(parts by Zinc oxide 5 5 5 5 5 5 mass) Barium sulfate *1) *1) *1)
*1) *1) *1) 2-thionaphthol 0.2 -- 0.2 -- -- -- PBDS -- -- -- 0.63
-- -- 2,6-DCP -- 0.22 -- -- 0.22 -- PCTP -- -- -- -- -- 0.35 Zinc
octanoate 5 5 5 5 5 5 Perhexyne 25B -- 0.49 0.49 0.49 0.49 0.49
Dicumyl peroxide 0.8 -- -- -- -- -- Core Center hardness 46.4 44.4
48.7 44.6 44.4 44.6 hardness 12.5% point hardness 53.8 48.7 52.4
49.4 48.7 47.7 distribution 25% point hardness 59.2 53.6 56.6 53.6
53.6 52.9 (JIS-C) 37.5% point hardness 62.2 57.2 61.8 56.3 57.2
56.9 50% point hardness 63.5 63.7 67.9 62.1 63.7 64.0 62.5% point
hardness 68.3 71.6 72.0 71.1 71.6 71.8 75% point hardness 74.0 74.1
73.6 73.7 74.1 74.4 87.5% point hardness 74.6 72.4 70.5 70.9 72.4
72.7 Surface hardness 79.3 74.0 70.9 74.2 74.0 74.6 Surface
hardness - center hardness 32.9 29.6 22.2 29.6 29.6 30.0 Core
coefficient of restitution 0.000 0.002 0.000 0.005 0.007 0.002 Core
compression deformation amount (mm) 4.33 4.39 4.24 4.36 4.39 4.23
Cover composition A A A A A A Cover hardness (Shore D) 65 65 65 65
65 65 Cover thickness (mm) 1.5 1.5 1.5 1.5 1.5 1.5 Ball Driver spin
rate (rpm) 0 -100 0 0 0 0 Driver flying distance (m) 0.0 3.5 0.0
1.0 1.0 0.5 Coefficient of restitution 0.000 0.002 0.000 0.005
0.007 0.002 Compression deformation amount (mm) 3.63 3.69 3.54 3.66
3.69 3.53
TABLE-US-00006 TABLE 6 Golf ball No. 23 24 25 26 27 28 Rubber BR730
100 100 100 100 100 100 composition Sanceler SR 27 24 23 23 24 23
(parts by Zinc oxide 5 5 5 5 5 5 mass) Barium sulfate *1) *1) *1)
*1) *1) *1) 2-thionaphthol 0.2 -- 0.2 -- -- -- PBDS -- -- -- 0.63
-- -- 2,6-DCP -- 0.22 -- -- 0.22 -- PCTP -- -- -- -- -- 0.35 Zinc
stearate 10 10 10 10 10 10 Perhexyne 25B -- 0.49 0.49 0.49 0.49
0.49 Dicumyl peroxide 0.8 -- -- -- -- -- Core Center hardness 48.8
51.5 52.8 48.1 51.5 48.8 hardness 12.5% point hardness 54.1 51.3
56.6 51.6 54.3 52.3 distribution 25% point hardness 59.5 51.9 60.3
57.2 57.9 57.0 (JIS-C) 37.5% point hardness 63.1 61.3 64.9 62.2
62.3 61.5 50% point hardness 65.0 67.3 69.2 66.5 67.3 66.2 62.5%
point hardness 70.3 70.6 72.0 69.7 70.6 69.6 75% point hardness
75.6 72.2 73.2 71.0 72.2 71.0 87.5% point hardness 76.9 70.3 71.2
67.7 70.3 69.3 Surface hardness 81.0 71.8 70.7 71.3 71.8 71.2
Surface hardness - center hardness 32.2 20.3 17.9 23.2 20.3 22.4
Core coefficient of restitution 0.000 0.003 0.000 0.002 0.008 0.005
Core compression deformation amount (mm) 4.05 4.30 4.10 4.39 4.30
4.36 Cover composition A A A A A A Cover hardness (Shore D) 65 65
65 65 65 65 Cover thickness (mm) 1.5 1.5 1.5 1.5 1.5 1.5 Ball
Driver spin rate (rpm) 0 -100 0 0 0 0 Driver flying distance (m)
0.0 3.0 0.0 0.5 1.0 0.5 Coefficient of restitution 0.000 0.003
0.000 0.002 0.008 0.005 Compression deformation amount (mm) 3.35
3.60 3.40 3.69 3.60 3.66
TABLE-US-00007 TABLE 7 Golf ball No. 29 30 31 32 Rubber BR730 100
100 100 100 composition Sanceler SR 35 30 31 34 (parts by mass)
Zinc oxide 5 5 5 5 Barium sulfate *1) *1) *1) *1) 2-thionaphthol
0.2 -- 0.2 -- PBDS -- 0.63 -- -- 2,6-DCP -- -- -- -- PCTP -- -- --
0.35 Benzoic acid 5 5 5.2 5.2 Zinc dibenzoate -- -- -- -- Perhexyne
25B -- 0.49 0.49 0.49 Dicumyl peroxide 0.8 -- -- -- Core Center
hardness 43.6 44.2 44.1 47.3 hardness 12.5% point hardness 48.7
47.6 48.2 50.8 distribution 25% point hardness 55.0 51.1 52.2 55.0
(JIS-C) 37.5% point hardness 58.8 53.4 54.1 55.9 50% point hardness
61.3 56.3 56.2 57.6 62.5% point hardness 61.4 65.2 64.0 61.2 75%
point hardness 72.6 77.8 75.5 76.7 87.5% point hardness 80.2 79.5
77.9 82.2 Surface hardness 87.1 79.1 79.0 82.1 Surface hardness -
center hardness 43.5 34.9 34.9 34.8 Core coefficient of restitution
0.000 0.002 0.000 0.006 Core compression deformation amount (mm)
4.30 4.30 4.00 3.90 Cover composition A A A A Cover hardness (Shore
D) 65 65 65 65 Cover thickness (mm) 1.5 1.5 1.5 1.5 Ball Driver
spin rate (rpm) 0 -100 0 0 Driver flying distance (m) 0.0 4.0 0.0
1.0 Coefficient of restitution 0.000 0.002 0.000 0.006 Compression
deformation amount (mm) 3.60 3.60 3.30 3.20
TABLE-US-00008 TABLE 8 Golf ball No. 33 34 35 36 Rubber BR730 100
100 100 100 composition Sanceler SR 37 34 25 29 (parts by mass)
Zinc oxide 5 5 5 5 Barium sulfate *1) *1) *1) *1) 2-thionaphthol --
-- 0.2 -- PBDS 0.63 -- -- 0.63 2,6-DCP -- 0.22 -- -- PCTP -- -- --
-- Benzoic acid 5.2 5.2 -- -- Zinc dibenzoate -- -- 6.5 6.5
Perhexyne 25B 0.49 0.49 0.49 0.49 Dicumyl peroxide -- -- -- -- Core
Center hardness 45.6 45.2 44.4 42.4 hardness 12.5% point hardness
48.7 49.2 48.8 47.3 distribution 25% point hardness 53.1 53.7 53.7
51.7 (JIS-C) 37.5% point hardness 55.3 55.7 56.5 54.5 50% point
hardness 55.7 56.4 57.6 55.6 62.5% point hardness 58.5 61.4 67.8
65.8 75% point hardness 71.0 74.3 79.2 77.7 87.5% point hardness
80.4 81.5 79.2 77.6 Surface hardness 82.5 83.4 80.3 78.6 Surface
hardness - center hardness 36.9 38.2 35.9 36.2 Core coefficient of
restitution 0.008 0.010 0.000 0.002 Core compression deformation
amount (mm) 3.90 4.00 4.10 4.20 Cover composition A A A A Cover
hardness (Shore D) 65 65 65 65 Cover thickness (mm) 1.5 1.5 1.5 1.5
Ball Driver spin rate (rpm) 0 0 0 0 Driver flying distance (m) 1.0
0.0 0.0 0.4 Coefficient of restitution 0.008 0.010 0.000 0.002
Compression deformation amount (mm) 3.20 3.30 3.40 3.50 *1) In
tables No. 1 to 8, as to an amount of barium sulfate, adjustment
was made such that the golf ball had a mass of 45.4 g. BR730: a
high-cis polybutadiene (cis-1,4 bond content = 96 mass %, 1,2-vinyl
bond content = 1.3 mass %, Moony viscosity (ML.sub.1+4 (100.degree.
C.) = 55, molecular weight distribution (Mw/Mn) = 3) available from
JSR Corporation Sanceler SR: zinc acrylate (product of 10 mass %
stearic acid coating) available from Sanshin Chemical Industry Co.,
Ltd. 2-thionaphthol: available from Tokyo Chemical Industry Co.,
Ltd. PBDS: bis(pentabromophenyl)disulfide 2,6-DCP:
2,6-dichlorothiophenol PCTP: pentachlorothiophenol Zinc octanoate:
available from Mitsuwa Chemicals Co., Ltd. (purity of 99% or
higher) Zinc stearate: available from Wako Pure Chemical
Industries, Ltd. (purity of 99% or higher) Stearic acid: available
from Tokyo Chemical Industry Co., Ltd. (purity of 98% or higher)
Benzoic acid: available from Sigma-Aldrich (purity of 99.5% or
higher) Zinc dibenzoate: available from Wako Pure Chemical
Industries, Ltd. (purity of 95% or higher) 4-dimethylamino benzoic
acid: available from Tokyo Chemical Industry Co., Ltd. (purity of
98% or higher) Zinc oxide: "Ginrei R" manufactured by Toho Zinc
Co., Ltd. Barium sulfate: "Barium sulfate BD" manufactured by Sakai
Chemical Industry Co., Ltd., adjustment was made such that the
finally obtained golf ball had a mass of 45.4 g. Perhexyne 25B:
2,5-dimethyl-2,5-bis(t-butylperoxy)hexyne-3 Dicumyl peroxide:
"PERCUMYL .RTM. D" available from NOF Corporation.
(2) Production of Cover
[0134] Cover materials shown in Table 9 were mixed with a
twin-screw kneading extruder to prepare the cover compositions in
the pellet form. The extruding conditions of the cover composition
were a screw diameter of 45 mm, a screw rotational speed of 200
rpm, and screw L/D=35, and the mixtures were heated to 150 to
230.degree. C. at the die position of the extruder. The cover
compositions obtained above were injection-molded onto the
spherical cores to produce the golf balls having the spherical core
and the cover covering the spherical core.
TABLE-US-00009 TABLE 9 Cover composition No. A Himilan 1605 50
Himilan 1706 50 Titanium oxide 4 Slab hardness (Shore D) 65
Formulation: parts by mass Himilan 1605: Sodium ion neutralized
ethylene-methacrylic acid copolymer ionomer resin available from Du
Pont-Mitsui Polychemicals Co., Ltd Himilan 1706: Zinc ion
neutralized ethylene-methacrylic acid copolymer ionomer resin
available from Du Pont-Mitsui Polychemicals Co., Ltd
[0135] As apparent from the results of tables No. 1 to No. 8, the
golf balls No. 1, 2, 5, 6, 9 to 12, 18 to 22, 24 to 28, 30 to 36
comprising a spherical core and at least one cover layer covering
the spherical core, wherein the spherical core is formed from a
rubber composition containing (a) a base rubber, (b) an
.alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon
atoms and/or a metal salt thereof as a co-crosslinking agent, (c)
the specific organic peroxide, and (d) a carboxylic acid and/or a
salt thereof, wherein the spherical core has a hardness difference
between a surface hardness thereof and a center hardness thereof of
12 or more, have a low spin rate on driver shots, and thus travel a
great flight distance, respectively.
[0136] The golf ball No. 7 is the case where the rubber composition
contains (d) the carboxylic acid and/or the salt thereof and
dicumyl peroxide as an organic sulfur peroxide. The golf ball No. 7
achieved the lower spin rate and greater flight distance compared
with the golf ball No. 3, but the effect is smaller than that of
Golf ball No. 6. The golf ball No. 8 is the case that the rubber
composition does not contain (d) the carboxylic acid and/or the
salt thereof, the effect of the lower spin rate and greater flight
distance is not obtained.
[0137] The golf ball No. 15 is the case that dicumyl peroxide is
used as an organic peroxide. The golf ball No. 15 achieved the
lower spin rate and greater flight distance compared with the golf
ball No. 13, but the effect is smaller than that of Golf balls No.
9 to No. 12. The golf ball No. 16 is the case where the rubber
composition does not contain (d) the carboxylic acid and/or the
salt thereof, the effect of the lower sin rate and greater flight
distance is not obtained, compared with the golf ball No. 13.
[0138] Tables No. 5 to No. 8 indicates that golf balls having a
spherical core and at least one cover layer covering the spherical
core, wherein the spherical core is formed from a rubber
composition containing (a) a base rubber, (b) an
.alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon
atoms and/or a metal salt thereof as a co-crosslinking agent, (c)
the specific organic peroxide, (d) a carboxylic acid and/or a salt
thereof and (f) the specific organic peroxide have a lower spin
rate on driver shots and a high resilience, and thus travel a great
distance.
[0139] The golf ball of the present invention has a low spin rate,
and travels a great flight distance on driver shots. This
application is based on Japanese Patent applications Nos.
2013-072719, 2013-072720, 2013-072721 filed on Mar. 29, 2013, the
contents of which are hereby incorporated by reference.
* * * * *