U.S. patent application number 13/830156 was filed with the patent office on 2013-09-19 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 Shun KURIHARA, Chiemi MIKURA, Ryota SAKAMINE, Ayaka SHINDO.
Application Number | 20130244810 13/830156 |
Document ID | / |
Family ID | 49158152 |
Filed Date | 2013-09-19 |
United States Patent
Application |
20130244810 |
Kind Code |
A1 |
MIKURA; Chiemi ; et
al. |
September 19, 2013 |
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 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)
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 having 4 to 30 carbon atoms and/or a salt thereof,
and (e) a halogen-substituted thiophenol and/or a metal salt
thereof as 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.
Inventors: |
MIKURA; Chiemi; (Kobe-shi,
JP) ; KURIHARA; Shun; (Kobe-shi, JP) ; SHINDO;
Ayaka; (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: |
49158152 |
Appl. No.: |
13/830156 |
Filed: |
March 14, 2013 |
Current U.S.
Class: |
473/372 |
Current CPC
Class: |
A63B 37/0063 20130101;
C08K 5/37 20130101; A63B 37/04 20130101; C08K 5/098 20130101; C08L
21/00 20130101; C08L 21/00 20130101; C08K 5/37 20130101; C08K 5/098
20130101; A63B 37/0051 20130101 |
Class at
Publication: |
473/372 |
International
Class: |
A63B 37/04 20060101
A63B037/04 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 19, 2012 |
JP |
2012-062557 |
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) a
crosslinking initiator, (d) a carboxylic acid having 4 to 30 carbon
atoms and/or a salt thereof, and (e) a halogen-substituted
thiophenol and/or a metal salt thereof as 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.
2. The golf ball according to claim 1, wherein the rubber
composition contains (d) the carboxylic acid having 4 to 30 carbon
atoms 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 the rubber
composition contains (d) the carboxylic acid having 4 to 30 carbon
atoms and/or the salt thereof in a content ranging from 5.0 parts
to 40 parts by mass with respect to 100 parts by mass of (a) the
base rubber.
4. The golf ball according to claim 1, wherein the rubber
composition contains (d) the carboxylic acid having 4 to 30 carbon
atoms and/or the salt thereof in a content ranging from 10.0 parts
to 40 parts by mass with respect to 100 parts by mass of (a) the
base rubber.
5. The golf ball according to claim 1, wherein (d) the carboxylic
acid having 4 to 30 carbon atoms and/or the salt thereof is a fatty
acid and/or a fatty acid salt.
6. The golf ball according to claim 1, wherein (d) the carboxylic
acid having 4 to 30 carbon atoms and/or the salt thereof is a
carboxylic acid having 15 to 30 carbon atoms and/or the salt
thereof.
7. The golf ball according to claim 1, wherein (e) the organic
sulfur compound is a thiophenol substituted with at least one
halogen.
8. The golf ball according to claim 1, wherein (e) the organic
sulfur compound is a thiophenol substituted with 1 to 4
halogen.
9. The golf ball according to claim 1, wherein the halogen is
chlorine.
10. The golf ball according to claim 1, wherein (e) the organic
sulfur compound includes 2,6-dichlorothiophenol or
2,4,5-trichlorothiophenol.
11. The golf ball according to claim 1, wherein the rubber
composition contains (e) 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.
12. 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.
13. The golf ball according to claim 1, wherein the spherical core
is such that R.sup.2 of a linear approximation curve obtained from
a least square method is 0.90 or higher, when JIS-C hardness, which
is measured at nine points obtained by dividing a radius of the
spherical core into equal parts having 12.5% intervals
therebetween, is plotted against distance (%) from a core
center.
14. The golf ball according to claim 1, wherein the spherical core
has a hardness difference between a surface hardness and a center
hardness of 25 or more and 80 or less in JIS-C hardness.
15. 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 having 15 to 30
carbon atoms and/or a salt thereof, and (e) a bromine or
chlorine-substituted thiophenol and/or a metal salt thereof as 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 carboxylic acid having 15 to 30 carbon
atoms and/or the salt thereof in a content ranging from 5.0 parts
to 40 parts by mass with respect to 100 parts by mass of (a) the
base rubber.
16. The golf ball according to claim 15, wherein the spherical core
is such that R.sup.2 of a linear approximation curve obtained from
a least square method is 0.90 or higher, when JIS-C hardness, which
is measured at nine points obtained by dividing a radius of the
spherical core into equal parts having 12.5% intervals
therebetween, is plotted against distance (%) from a core
center.
17. The golf ball according to claim 16, wherein the spherical core
has a hardness difference between a surface hardness and a center
hardness of 25 or more and 80 or less in JIS-C hardness.
18. The golf ball according to claim 17, wherein the spherical core
is such that R.sup.2 of a linear approximation curve obtained from
a least square method is 0.95 or higher.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a golf ball traveling a
great distance on driver shots, 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 using a core having high
resilience and using a core having a hardness distribution in which
the hardness increases toward the surface of the core from the
center thereof. The former method has an effect of enhancing an
initial speed, and the latter method has an effect of a higher
launch angle and a lower spin rate. A golf ball having a higher
launch angle and a low spin rate travels a great distance.
[0003] For example, Japanese Patent Publications Nos. S61-37178 A,
S61-113475 A, S61-253079 A, 2008-212681 A, 2008-523952 T,
2009-119256 A, 2003-226782 A, and 2006-297108 A disclose a
technique of enhancing resilience of the core. Japanese Patent
Publications Nos. S61-37178 A and S61-113475 A disclose a solid
golf ball having an inner core where zinc acrylate as a
co-crosslinking agent, palmitic acid, stearic acid, or myristic
acid as a co-crosslinking activator, zinc oxide as another
co-crosslinking activator, and a reaction rate retarder are
blended, with respect to 100 parts by weight of a rubber.
[0004] Japanese Patent Publication No. S61-253079 A discloses a
solid golf ball formed from a rubber composition containing an
.alpha.,.beta.-unsaturated carboxylic acid in an amount of 15 parts
to 35 parts by weight, a metal compound to react with the
.alpha.,.beta.-unsaturated carboxylic acid and form a salt thereof
in an amount of 7 parts to 60 parts by weight, and a high fatty
acid metal salt in an amount of 1 part to 10 parts by weight with
respect to 100 parts by weight of a base rubber.
[0005] Japanese Patent Publication No. 2008-212681 A discloses a
golf ball comprising, as a component, a molded and crosslinked
product obtained from a rubber composition essentially comprising a
base rubber, a filler, an organic peroxide, an
.alpha.,.beta.-unsaturated carboxylic acid and/or a metal salt
thereof, a copper salt of a saturated or unsaturated fatty
acid.
[0006] Japanese Patent Publication No. 2008-523952 T discloses a
golf ball, or a component thereof, molded from a composition
comprising a base elastomer selected from the group consisting of
polybutadiene and mixtures of polybutadiene with other elastomers,
at least one metallic salt of an unsaturated monocarboxylic acid, a
free radical initiator, and a non-conjugated diene monomer.
[0007] Japanese Patent Publication No. 2009-119256 A discloses a
method of manufacturing a golf ball, comprising preparing a
masterbatch of an unsaturated carboxylic acid and/or a metal salt
thereof by mixing the unsaturated carboxylic acid and/or the metal
salt thereof with a rubber material ahead, using the masterbatch to
prepare a rubber composition containing the rubber material, and
employing a heated and molded product of the rubber composition as
a golf ball component, wherein the masterbatch of the unsaturated
carboxylic acid and/or the metal salt thereof comprises; (A) from
20 wt % to 100 wt % of a modified polybutadiene obtained by
modifying a polybutadiene having a vinyl content of from 0 to 2%, a
cis-1,4 bond content of at least 80% and active terminals, the
active terminal being modified with at least one type of
alkoxysilane compound, and (B) from 80 wt % to 0 wt % of a diene
rubber other than (A) the above rubber component [the figures are
represented by wt % in the case that a total amount of (A) and (B)
equal to 100 wt %] and (C) an unsaturated carboxylic acid and/or a
metal salt thereof.
[0008] Japanese Patent Publication No. 2003-226782 A discloses a
rubber composition for forming a solid golf ball. The composition
contains (A) a base rubber, (B) a filler, (C) an organic peroxide,
and (D) a dry blend and/or a solvent slurry blend of a
metal-containing organic sulfur compound and a metal salt of an
unsaturated carboxylic acid.
[0009] Japanese Patent Publication No. 2006-297108 A discloses a
golf ball comprising a solid core and a cover, wherein the solid
core is formed from a composition comprising a diene rubber, a
fatty acid metal salt present in an amount of 6 parts or more, a
cis-to-trans catalyst, and an organic peroxide present in an amount
of 1.2 parts or less.
[0010] For example, Japanese Patent Publications Nos. H6-154357 A,
2008-194471 A, 2008-194473 A and 2010-253268 A disclose a core
having a hardness distribution. Japanese Patent Publication No.
H6-154357 A discloses a two-piece golf ball comprising a core
formed of a rubber composition containing a base rubber, a
co-crosslinking agent, and an organic peroxide, and a cover
covering said core, wherein the core has the following hardness
distribution according to JIS-C type hardness meter readings: (1)
hardness at center: 58-73, (2) hardness at 5 to 10 mm from center:
65-75, (3) hardness at 15 mm from center: 74-82, (4) surface
hardness: 76-84, wherein hardness (2) is almost constant within the
above range, and the relation (1)<(2)<(3).ltoreq.(4) is
satisfied.
[0011] Japanese Patent Publication No. 2008-194471 A discloses a
solid golf ball comprising a solid core and a cover layer that
encases the core, wherein the solid core is formed of a rubber
composition composed of 100 parts by weight of a base rubber that
includes from 60 to 100 parts by weight of a polybutadiene rubber
having a cis-1,4 bond content of at least 60% and synthesized using
a rare-earth catalyst, from 0.1 to 5 parts by weight of an organic
sulfur compound, an unsaturated carboxylic acid or a metal salt
thereof, an inorganic filler, and an antioxidant; the solid core
has a deformation from 2.0 mm to 4.0 mm, when applying a load from
an initial load of 10 kgf to a final load of 130 kgf and has the
hardness distribution shown in the following table.
TABLE-US-00001 TABLE 1 Hardness distribution in solid core Shore D
harness Center 30 to 48 Region located 4 mm from center 34 to 52
Region located 8 mm from center 40 to 58 Region located 12 mm from
center (Q) 43 to 61 Region located 2 to 3 mm inside of 36 to 54
surface (R) Surface (S) 41 to 59 Hardness difference [(Q) - (S)] 1
to 10 Hardness difference [(S) - (R)] 3 to 10
[0012] Japanese Patent Publication No. 2008-194473 A discloses a
solid golf ball comprising a solid core and a cover layer that
encases the core, wherein the solid core is formed of a rubber
composition composed of 100 parts by weight of a base rubber that
includes from 60 to 100 parts by weight of a polybutadiene rubber
having a cis-1,4 bond content of at least 60% and synthesized using
a rare-earth catalyst, from 0.1 part to 5 parts by weight of an
organic sulfur compound, an unsaturated carboxylic acid or a metal
salt thereof, and an inorganic filler; the solid core has a
deformation from 2.0 mm to 4.0 mm, when applying a load from an
initial load of 10 kgf to a final load of 130 kgf and has the
hardness distribution shown in the following table.
TABLE-US-00002 TABLE 2 Hardness distribution in solid core Shore D
harness Center 25 to 45 Region located 5 to 10 mm from center 39 to
58 Region located 15 mm from center 36 to 55 Surface (S) 55 to 75
Hardness difference between center 20 to 50 and surface
[0013] Japanese Patent Publication No. 2010-253268 A discloses a
multi-piece solid golf ball comprising a core, an envelope layer
encasing the core, an intermediate layer encasing the envelope
layer, and a cover which encases the intermediate layer and has
formed on a surface thereof a plurality of dimples, wherein the
core is formed primarily of a rubber material and has a hardness
which gradually increases from a center to a surface thereof, the
hardness difference in JIS-C hardness units between the core center
and the core surface being at least 15 and, letting (I) be the
average value for cross-sectional hardness at a position about 15
mm from the core center and at the core center and letting (II) be
the cross-sectional hardness at a position about 7.5 mm from the
core center, the hardness difference (I)-(II) in JIS-C units being
within .+-.2; and the envelope layer, intermediate layer and cover
have hardness which satisfy the condition: cover
hardness>intermediate layer hardness>envelope layer
hardness.
SUMMARY OF THE INVENTION
[0014] A resilience of a spherical core having an outer-hard
inner-soft structure where a surface hardness is larger than a
center hardness tends to be lowered. Therefore, it has been
difficult to produce a spherical core having an outer-hard
inner-soft structure and high resilience. The present invention has
been achieved in view of the above circumstances. An object of the
present invention is to provide a golf ball comprising a spherical
core having an outer-hard inner-soft structure and high
resilience.
[0015] The present invention provides a golf ball 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) a
crosslinking initiator, (d) a carboxylic acid having 4 to 30 carbon
atoms and/or a salt thereof, and (e) a halogen-substituted
thiophenol and/or a metal salt thereof as 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.
[0016] The golf ball of the present invention is configured as
described above so that the spherical core has the outer-hard
inner-soft structure and the enhanced resilience. The spherical
core having the outer-hard inner-soft structure lowers the spin
rate on driver shots. The spherical core having high resilience
increases the initial golf ball speed. Since the golf ball of the
present invention has high resilience (great initial speed) and a
low spin rate on driver shots, the flight distance on driver shots
becomes greater.
[0017] In the spherical core of the golf ball of the present
invention, the reason why the core surface hardness is higher than
the core center hardness 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 having 4 to 30 carbon atoms 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 having 4 to 30 carbon atoms 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.
[0018] The present invention provides a golf ball traveling a great
flight distance on driver shots.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a partially cutaway sectional view showing the
golf ball according to the preferable embodiment of the present
invention;
[0020] FIG. 2 is a graph showing the hardness distribution of the
spherical core;
[0021] FIG. 3 is a graph showing the hardness distribution of the
spherical core;
[0022] FIG. 4 is a graph showing the hardness distribution of the
spherical core;
[0023] FIG. 5 is a graph showing the hardness distribution of the
spherical core;
[0024] FIG. 6 is a graph showing the hardness distribution of the
spherical core;
[0025] FIG. 7 is a graph showing the hardness distribution of the
spherical core;
[0026] FIG. 8 is a graph showing the hardness distribution of the
spherical core;
[0027] FIG. 9 is a graph showing the hardness distribution of the
spherical core;
[0028] FIG. 10 is a graph showing the hardness distribution of the
spherical core;
[0029] FIG. 11 is a graph showing the hardness distribution of the
spherical core;
[0030] FIG. 12 is a graph showing the hardness distribution of the
spherical core;
[0031] FIG. 13 is a graph showing the hardness distribution of the
spherical core; and
[0032] FIG. 14 is a graph showing the hardness distribution of the
spherical core.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0033] The present invention provides a golf ball 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) a
crosslinking initiator, (d) a carboxylic acid having 4 to 30 carbon
atoms and/or a salt thereof, and (e) a halogen-substituted
thiophenol and/or a metal salt thereof as 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.
[0034] 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.
[0035] 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.
[0036] 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. 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.
[0037] 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.
[0038] 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 (f) 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, (f) the metal
compound may be used as an optional component.
[0039] 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.
[0040] 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 tin,
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.
[0041] 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.
[0042] (c) The crosslinking initiator is blended in order to
crosslink (a) the base rubber component. As (c) the crosslinking
initiator, an organic peroxide is preferred. Specific examples of
the 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. Among them, dicumyl
peroxide is preferably used.
[0043] The content of (c) the crosslinking initiator is preferably
0.2 part by mass or more, and more preferably 0.5 part by mass or
more, and is preferably 5.0 parts by mass or less, and more
preferably 2.5 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 0.2 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.
[0044] Next, (d) the carboxylic acid having 4 to 30 carbon atoms
and/or the salt thereof will be explained. It is conceivable that
(d) the carboxylic acid having 4 to 30 carbon atoms 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.
[0045] As (d) the carboxylic acid having 4 to 30 carbon atoms
and/or the salt thereof, preferred is a carboxylic acid having 15
to 30 carbon atoms and/or a salt thereof, and more preferred is a
carboxylic acid having 15 to 28 carbon atoms and/or a salt thereof.
In (d) the carboxylic acid having 4 to 30 carbon atoms 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.
[0046] (d) The carboxylic acid having 4 to 30 carbon atoms and/or
the salt thereof preferably includes an aliphatic carboxylic acid
(sometimes may be merely referred to as "fatty acid" in the present
invention) and/or a salt thereof, or an aromatic carboxylic acid
and/or a salt thereof; however, preferred is the aliphatic
carboxylic acid and/or the salt thereof.
[0047] The fatty acid may be either a saturated fatty acid or an
unsaturated fatty acid; however, a saturated fatty acid is
preferable. Specific examples of the saturated fatty acid (IUPAC
name) are butanoic acid (C4), pentanoic acid (C5), hexanoic acid
(C6), heptanoic acid (C7), octanoic 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), henicosanoic acid (C21), docosanoic acid (C22), toricosanoic
acid (C23), tetracosanoic acid (C24), pentacosanoic acid (C25),
hexacosanoic acid (C26), heptacosanoic acid (C27), octacosanoic
acid (C28), nonacosanoic acid (C29), and triacontanoic acid
(C30).
[0048] Specific examples of the unsaturated fatty acid (IUPAC name)
are 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 triacontenoic acid
(C30).
[0049] Specific examples of the fatty acids (Common name) are
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). The fatty acid may be used alone or
as a mixture of at least two of them. Among those described above,
palmitic acid, setaric acid, behenic acid and oleic acid are
preferable as the fatty acid.
[0050] There is no particular limitation on the aromatic carboxylic
acid as long as it is a compound that has an aromatic ring and a
carboxyl group. Specific examples of the aromatic carboxylic acid
include, for example, benzoic acid (C7), phthalic acid (C8),
isophthalic acid (C8), terephthalic acid (C8), hemimellitic acid
(benzene-1,2,3-tricarboxylic acid) (C9), trimellitic acid
(benzene-1,2,4-tricarboxylic acid) (C9), trimesic acid
(benzene-1,3,5-tricarboxylic acid) (C9), mellophanic acid
(benzene-1,2,3,4-tetracarboxylic acid) (C10), prehnitic acid
(benzene-1,2,3,5-tetracarboxylic acid) (C10), pyromellitic acid
(benzene-1,2,4,5-tetracarboxylic acid) (C10), mellitic acid
(benzene hexacarboxylic acid) (C12), diphenic acid
(biphenyl-2,2'-dicarboxylic acid) (C12), toluic acid (methylbenzoic
acid) (C8), xylic acid (C9), prehnitylic acid
(2,3,4-trimethylbenzoic acid) (C10), .gamma.-isodurylic acid
(2,3,5-trimethylbenzoic acid) (C10), durylic acid
(2,4,5-trimethylbenzoic acid) (C10), .beta.-isodurylic acid
(2,4,6-trimethylbenzoic acid) (C10), .alpha.-isodurylic acid
(3,4,5-trimethylbenzoic acid) (C10), cumin acid (4-isopropylbenzoic
acid) (C10), uvitic acid (5-methylisophthalic acid) (C9),
.alpha.-toluic acid (phenylacetic acid) (C8), hydratropic acid
(2-phenylpropanoic acid), (C9) and hydrocinnamic acid
(3-phenylpropanoic acid) (C9).
[0051] Furthermore, examples of the aromatic carboxylic acid
substituted with a hydroxyl group, an alkoxy group, or an oxo group
include, for example, salicylic acid (2-hydroxybenzoic acid) (C7),
anisic acid (methoxybenzoic acid) (C8), cresotinic acid
(hydroxy(methyl)benzoic acid) (C8), o-homosalicylic acid
(2-hydroxy-3-methylbenzoic acid) (C8), m-homosalicylic acid
(2-hydroxy-4-methylbenzoic acid) (C8), p-homosalicylic acid
(2-hydroxy-5-methylbenzoic acid) (C8), o-pyrocatechuic acid
(2,3-dihydroxybenzoic acid) (C7), .beta.-resorcylic acid
(2,4-dihydroxybenzoic acid) (C7), .gamma.-resorcylic acid
(2,6-dihydroxybenzoic acid) (C7), protocatechuic acid
(3,4-dihydroxybenzoic acid) (C7), .alpha.-resorcylic acid
(3,5-dihydroxybenzoic acid) (C7), vanillic acid
(4-hydroxy-3-methoxybenzoic acid) (C8), isovanillic acid
(3-hydroxy-4-methoxybenzoic acid) (C8), veratric acid
(3,4-dimethoxybenzoic acid) (C9), o-veratric acid
(2,3-dimethoxybenzoic acid) (C9), orsellinic acid
(2,4-dihydroxy-6-methylbenzoic acid) (C8), m-hemipic acid
(4,5-dimethoxyphthalic acid) (C10), gallic acid
(3,4,5-trihydroxybenzoic acid) (C7), syringic acid
(4-hydroxy-3,5-dimethoxybenzoic acid) (C9), asaronic acid
(2,4,5-trimethoxybenzoic acid) (C10), mandelic acid
(hydroxy(phenyl)acetic acid) (C8), vanillylmandelic acid
(hydroxy(4-hydroxy-3-methoxy phenyl)acetic acid) (C9), homoanisic
acid ((4-methoxy phenyl)acetic acid) (C9), homogentisic acid
((2,5-dihydroxyphenyl)acetic acid) (C8), homoprotocatechuic acid
((3,4-dihydroxyphenyl)acetic acid) (C8), homovanillic acid
((4-hydroxy-3-methoxy phenyl)acetic acid) (C9), homoisovanillic
acid ((3-hydroxy-4-methoxy phenyl)acetic acid) (C9), homoveratric
acid ((3,4-dimethoxy phenyl)acetic acid) (C10), o-homoveratric acid
((2,3-dimethoxy phenyl)acetic acid) (C10), homophthalic acid
(2-(carboxymethyl)benzoic acid) (C9), homoisophthalic acid
(3-(carboxymethyl)benzoic acid) (C9), homoterephthalic acid
(4-(carboxymethyl)benzoic acid) (C9), phthalonic acid
(2-(carboxycarbonyl)benzoic acid) (C9), isophthalonic acid
(3-(carboxycarbonyl)benzoic acid) (C9), terephthalonic acid
(4-(carboxycarbonyl)benzoic acid) (C9), benzilic acid (hydroxy
diphenylacetic acid) (C14), atrolactic acid
(2-hydroxy-2-phenylpropanoic acid) (C9), tropic acid
(3-hydroxy-2-phenylpropanoic acid) (C9), melilotic acid
(3-(2-hydroxyphenyl)propanoic acid) (C9), phloretic acid
(3-(4-hydroxy phenyl)propanoic acid) (C9), hydrocaffeic acid
(3-(3,4-dihydroxyphenyl)propanoic acid) (C9), hydroferulic acid
(3-(4-hydroxy-3-methoxy phenyl)propanoic acid) (C10),
hydroisoferulic acid (3-(3-hydroxy-4-methoxy phenyl)propanoic acid)
(C10), p-coumaric acid (3-(4-hydroxy phenyl)acrylic acid) (C9),
umbellic acid (3-(2,4-dihydroxyphenyl)acrylic acid) (C9), caffeic
acid (3-(3,4-dihydroxyphenyl)acrylic acid) (C9), ferulic acid
(3-(4-hydroxy-3-methoxy phenyl)acrylic acid) (C10), isoferulic acid
(3-(3-hydroxy-4-methoxy phenyl)acrylic acid) (C10), and sinapic
acid (3-(4-hydroxy-3,5-dimethoxy phenyl)acrylic acid) (C11).
[0052] As (d) the salt of the carboxylic acid, a salt of the
carboxylic acid described above may be used. The cation component
of the salt of the carboxylic acid 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.
[0053] 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. The carbon number of the salt
of the carboxylic acid having 4 to 30 carbon atoms is the carbon
number of a carboxylic acid component, and does not include the
carbon number of the organic cation.
[0054] The content of (d) the carboxylic acid having 4 to 30 carbon
atoms and/or the salt thereof is preferably 0.5 part by mass or
more, more preferably 5.0 parts by mass or more, even more
preferably 7.5 parts by mass or more, particularly preferably 10.0
parts by mass or more, and is preferably 40 parts by mass or less,
more preferably 20 parts by mass or less, even more preferably 16
parts by mass or less. If the content is too little, the effect of
adding (d) the carboxylic acid having 4 to 30 carbon atoms 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. There are cases where the surface of the zinc acrylate
used as the co-crosslinking agent is treated with the carboxylic
acid having 4 to 30 carbon atoms 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 having 4
to 30 carbon atoms and/or the salt thereof, in the present
invention, the amount of the carboxylic acid having 4 to 30 carbon
atoms and/or the salt thereof used as a surface treating agent is
included in the content of (d) the carboxylic acid having 4 to 30
carbon atoms and/or the salt thereof. For example, if 25 parts by
mass of zinc acrylate whose surface treatment amount with the
carboxylic acid having 4 to 30 carbon atoms and/or the salt thereof
is 10 mass % is used, the amount of the carboxylic acid having 4 to
30 carbon atoms 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 having
4 to 30 carbon atoms and/or the salt thereof.
[0055] The rubber composition used in the present invention
contains the halogen-substituted thiophenol and/or the metal salt
thereof as (e) the organic sulfur compound. Since the rubber
composition contains the halogen-substituted thiophenol and/or the
metal salt thereof as (e) the organic sulfur compound, the
resilience of the spherical core is enhanced.
[0056] The halogen-substituted thiophenol is a derivative of
thiophenol where at least one of hydrogens of a benzene ring in
thiophenol is substituted with halogen. The halogen includes
fluorine, chlorine, bromine, and iodine. Chlorine or bromine is
preferable, and chlorine is more preferable. Examples of the
halogen-substituted thiophenol include, for example, 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.
[0057] 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.
[0058] From the aspect that the spherical core having high
resilience is obtained, as (e) the organic sulfur compound,
preferred is thiophenol substituted with 1 to 4 halogen and/or the
metal salt thereof. Suitable examples of (e) the organic sulfur
compound include 2,4-dichlorothiophenol, 2,6-dichlorothiophenol, or
2,4,5-trichlorothiophenol. Of them, 2,6-dichlorothiophenol and
2,4,5-trichlorothiophenol are more preferable.
2,6-dichlorothiophenol or 2,4,5-trichlorothiophenol is
environmentally preferable since they have less chlorine atoms.
Especially, 2,6-dichlorothiophenol or 2,4,5-trichlorothiophenol is
preferred, since 2,6-dichlorothiophenol and
2,4,5-trichlorothiophenol increase the outer-hard inner-soft effect
when compared to a metal salt thereof.
[0059] (e) The organic sulfur compound can be used solely or as a
mixture of at least two of them.
[0060] The content of (e) 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 (e) the organic sulfur compound
is less than 0.05 part by mass, the effect of adding (e) the
organic sulfur compound cannot be obtained and thus the resilience
may not improve. If the content of (e) 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.
[0061] When 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 (f) the metal compound as an essential
component. (f) The metal compound is not particularly limited, as
long as it can neutralize (b) the .alpha.,.beta.-unsaturated
carboxylic acid having 3 to 8 carbon atoms in the rubber
composition. Examples of (f) the metal compound include, 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. As (f) the metal compound,
preferred is divalent metal compounds, and more preferred is a zinc
compound. The divalent metal compounds react with the
.alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon
atoms, and form a metal crosslinking. Furthermore, by using the
zinc compound, the golf ball having high resilience is obtained.
(f) The metal compounds may be used alone or as a mixture of at
least two of them.
[0062] 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.
[0063] 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.
[0064] 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.
[0065] 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.
[0066] 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.
[0067] 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.
[0068] 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 crosslinking
initiator, (d) the carboxylic acid having 4 to 30 carbon atoms
and/or the salt thereof, (e) the halogen-substituted thiophenol
and/or the metal salt thereof as the organic sulfur compound, and
other additives where necessary. 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.
[0069] 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.
[0070] In a preferable embodiment, when the hardness is measured at
nine points obtained by dividing a radius of the spherical core
into equal parts having 12.5% interval and the hardness is plotted
against distance (%) from the center of the spherical core, the
spherical core is such that R.sup.2 of a linear approximation curve
obtained by the least square method is preferably 0.90 or higher.
The hardness of the spherical core is JIS-C hardness measured at
nine points obtained by dividing a radius of the spherical core
into equal parts having 12.5% interval. That is, JIS-C hardness is
measured at nine points, namely at distances of 0% (core center),
12.5%, 25%, 37.5%, 50%, 62.5%, 75%, 87.5%, 100% (core surface) from
the core center. Next, the measurement results are plotted to make
a graph having JIS-C hardness as a vertical axis and distances (%)
from the core center as a horizontal axis. In the present
invention, R.sup.2 of a linear approximation curve obtained from
this graph by the least square method is preferably 0.90 or higher.
R.sup.2 of the linear approximation curve obtained by the least
square method indicates the linearity of the obtained plot. In the
present invention, R.sup.2 of 0.90 or more means that the spherical
core has the hardness distribution where the hardness increases
linearly or almost linearly. If the spherical core having the
hardness distribution where hardness increases linearly or almost
linearly is used for the golf ball, the spin rate on driver shots
decrease. As a result, the flight distance on driver shots
increases. R.sup.2 of the linear approximation curve is more
preferably 0.93 or more, and even more preferably 0.95 or more. The
higher linearity provides a greater flight distance on driver
shots.
[0071] The spherical core preferably has a hardness difference
(Hs-Ho) between a surface hardness Hs and a center hardness Ho of
25 or more, more preferably 30 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.
[0072] The spherical core preferably has the center hardness Ho of
30 or more, more preferably 40 or more, even more preferably 45 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.
[0073] The spherical core preferably has the surface hardness Hs of
78 or more, more preferably 80 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 78 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.
[0074] 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.
[0075] 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.
[0076] 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.
[0077] 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.
[0078] 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.
[0079] 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.
[0080] 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.
[0081] 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.
[0082] 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.
[0083] 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.
[0084] 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.
[0085] 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. 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.
[0086] 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).
[0087] 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.
[0088] 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 taken out from
the mold.
[0089] 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.
[0090] 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.
[0091] After the cover is molded, the mold is opened and the golf
ball body is taken out 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.
[0092] 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.
[0093] 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.
[0094] 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
[0095] 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)
[0096] 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) Coefficient of Restitution
[0097] A 198.4 g of metal cylindrical object was allowed to collide
with each core or golf ball at a speed of 40 m/sec, and the speeds
of the cylindrical object and the core or golf ball before and
after the collision were measured. Based on these speeds and the
mass of each object, coefficient of restitution for each core or
golf ball was calculated. The measurement was conducted by using
twelve samples for each core or golf ball, and the average value
was regarded as the coefficient of restitution for the core or golf
ball. In tables 3 to 5, the coefficient of restitution of golf
balls are shown as the difference from that of the golf ball (core)
No. 10.
(3) Slab Hardness (Shore D Hardness)
[0098] 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.
(4) Hardness Distribution of Spherical Core (JIS-C Hardness)
[0099] 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.
(5) Flight Distance (m) and Spin Rate (rpm) on a Driver Shot
[0100] A metal-headed W#1 driver (XXIO S, loft: 11.degree.,
manufactured by SRI 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 3 to
5, the flight distance and spin rate on the driver shots of golf
balls are shown as the difference from those of the golf ball
(core) No. 10.
[Production of Golf Balls]
(1) Production of Cores
[0101] The rubber compositions having formulations shown in Tables
3 to 5 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-00003 TABLE 3 Golf ball No. 1 2 3 4 5 Rubber composition
(parts by mass) BR730 100 100 100 100 100 Sanceler SR 29 29 29 27.5
27.5 Zinc oxide 5 5 5 5 5 Barium sulfate *1) *1) *1) *1) *1)
2,6-dichlorothiophenol 0.36 0.36 0.36 -- --
2,4,5-trichlorothiophenol -- -- -- 0.43 0.43 Zinc salt of
2,4,5-trichlorothiophenol -- -- -- -- -- Stearic acid (C18) 10 --
-- 10 -- Zinc stearate (C18) -- 10 12 -- 10 Zinc behenate (C22) --
-- -- -- -- Dicumyl peroxide 0.8 0.8 0.8 0.8 0.8 Total amount of
carboxylic acid/salt 12.9 12.9 14.9 12.8 12.8 Core hardness
distribution (JIS-C) Center hardness 53.9 49.8 50.6 55.4 48.2 12.5%
point hardness 59.8 55.3 55.7 59.6 52.3 25% point hardness 64.7
61.0 61.2 64.5 56.6 37.5% point hardness 66.8 64.9 64.9 66.8 60.6
50% point hardness 66.8 66.9 66.7 67.8 62.9 62.5% point hardness
67.6 69.0 68.6 70.2 65.8 75% point hardness 71.5 73.9 73.1 76.3
76.5 87.5% point hardness 74.0 76.1 74.9 77.4 79.3 Surface hardness
80.1 81.6 79.6 81.6 83.0 Surface hardness - center hardness 26.2
31.8 29.0 26.2 34.8 R.sup.2 of approximated curve 0.93 0.98 0.98
0.98 0.98 Slope of approximated curve 0.22 0.29 0.27 0.25 0.35 Core
coefficient of restitution 0.009 0.008 0.005 0.011 0.005 Core
compression deformation amount (mm) 4.2 4.1 4.2 4.1 4.4 Cover
composition A A A A A Cover hardness (Shore D) 65 65 65 65 65 Cover
thickness (mm) 1.5 1.5 1.5 1.5 1.5 Ball Driver spin rate (rpm) -40
-80 -50 -60 -100 Driver flying distance (m) 2.2 2.7 2.5 3.0 3.3
Coefficient of restitution 0.009 0.008 0.005 0.011 0.005
Compression deformation amount (mm) 3.5 3.4 3.5 3.4 3.7
TABLE-US-00004 TABLE 4 Golf ball No. 6 7 8 9 Rubber BR730 100 100
100 100 composition Sanceler SR 32 35 27.5 27.5 (parts by Zinc
oxide 5 5 5 5 mass) Barium sulfate *1) *1) *1) *1)
2,6-dichlorothiophenol -- -- -- -- 2,4,5-trichlorothiophenol 0.43
0.43 0.43 -- Zinc salt of 2,4,5-trichlorothiophenol -- -- -- 0.43
Stearic acid (C18) -- -- -- -- Zinc stearate (C18) 15 40 -- 10 Zinc
behenate (C22) -- -- 10 -- Dicumyl peroxide 0.8 0.8 0.8 0.8 Total
amount of carboxylic acid/salt 18.2 43.5 12.8 12.8 Core Center
hardness 48.7 54.2 53.2 49.8 hardness 12.5% point hardness 52.6
54.3 56.4 53.8 distribution 25% point hardness 56.7 56.6 60.2 57.5
(JIS-C) 37.5% point hardness 60.6 58.6 63.5 61.3 50% point hardness
63.0 60.9 65.2 63.5 62.5% point hardness 66.0 61.8 66.8 66.2 75%
point hardness 76.7 67.5 77.0 77.3 87.5% point hardness 79.6 65.3
79.5 77.8 Surface hardness 83.6 69.0 83.0 79.1 Surface hardness -
center hardness 34.9 14.8 29.8 29.3 R.sup.2 of approximated curve
0.98 0.95 0.97 0.96 Slope of approximated curve 0.35 0.16 0.30 0.31
Core coefficient of restitution 0.003 -0.015 0.010 0.002 Core
compression deformation amount (mm) 4.2 4.4 4.2 4.4 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 40
-40 -60 Driver flying distance (m) 2.3 -3.0 2.5 2.0 Coefficient of
restitution 0.003 -0.015 0.010 0.002 Compression deformation amount
(mm) 3.5 3.7 3.5 3.7
TABLE-US-00005 TABLE 5 Golf ball No. 10 11 12 13 Rubber BR730 100
100 100 100 composition Sanceler SR 23 29 27 23 (parts by Zinc
oxide 5 5 5 5 mass) Barium sulfate *1) *1) *1) *1)
2,6-dichlorothiophenol -- 0.36 -- -- 2,4,5-trichlorothiophenol --
-- 0.42 -- Stearic acid (C18) -- -- -- 10 Zinc stearate (C18) -- --
-- -- Dicumyl peroxide 0.8 0.8 0.8 0.8 Total amount of carboxylic
acid/salt 2.3 2.9 2.7 12.3 Core Center hardness 52.8 52.4 55.7 56.9
hardness 12.5% point hardness 60.0 61.9 62.8 61.7 distribution 25%
point hardness 64.5 65.9 66.5 65.7 (JIS-C) 37.5% point hardness
66.3 66.6 67.8 67.2 50% point hardness 66.5 66.8 67.9 67.8 62.5%
point hardness 66.1 66.7 67.6 70.4 75% point hardness 70.9 70.6
71.3 74.6 87.5% point hardness 73.4 73.3 76.0 76.2 Surface hardness
79.0 80.4 83.5 80.7 Surface hardness - center hardness 26.2 28.0
27.8 23.8 R.sup.2 of approximated curve 0.91 0.85 0.87 0.97 Slope
of approximated curve 0.21 0.21 0.21 0.21 Core coefficient of
restitution 0.000 0.015 0.013 0.002 Core compression deformation
amount (mm) 4.2 4.1 4.2 4.1 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 -10 -70 Driver flying distance (m)
0.0 1.8 1.6 1.4 Coefficient of restitution 0.000 0.015 0.013 0.002
Compression deformation amount (mm) 3.5 3.4 3.5 3.4 *1) In tables
No. 3 to 5 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. 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. 2,6-dichlorothiophenol:
available from Tokyo Chemical Industry Co., Ltd.
2,4,5-trichlorothiophenol: available from Tokyo Chemical Industry
Co., Ltd. Dicumyl peroxide: "PERCUMYL .RTM. D" available from NOF
Corporation. Stearic acid: available from Tokyo Chemical Industry
Co., Ltd. (purity of 98% or higher) Zinc stearate: available from
Wako Pure Chemical Industries, Ltd. (purity of 99% or higher) Zinc
behenate: available from Nitto Kasei Kogyo K.K.
(2) Production of Cover
[0102] Cover materials shown in Table 6 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-00006 TABLE 6 Cover composition No. A Himilan 1605 50
Himilan 1706 50 Elastollan XNY97A -- 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
[0103] The results of tables No. 3 to No. 5 indicate that the golf
balls 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) a
crosslinking initiator, (d) a carboxylic acid having 4 to 30 carbon
atoms and/or a salt thereof, and (e) a halogen-substituted
thiophenol and/or a metal salt thereof as an organic sulfur
compound, provided that the rubber composition further contains (f)
a metal compound in case of containing only (b) the
.alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon
atoms as the co-crosslinking agent have high resilience as well as
a low spin rate on driver shots, and thus travel a great flight
distance, respectively.
[0104] The golf ball of the present invention travels a great
flight distance on driver shots. This application is based on
Japanese Patent application No. 2012-062557 filed on Mar. 19, 2012,
the contents of which are hereby incorporated by reference.
* * * * *