U.S. patent application number 13/871096 was filed with the patent office on 2013-11-28 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 Hidetaka INOUE, Takahiro SAJIMA.
Application Number | 20130316851 13/871096 |
Document ID | / |
Family ID | 48470800 |
Filed Date | 2013-11-28 |
United States Patent
Application |
20130316851 |
Kind Code |
A1 |
SAJIMA; Takahiro ; et
al. |
November 28, 2013 |
GOLF BALL
Abstract
A golf ball 2 includes a core 4, an inner cover 6, and an outer
cover 8. The core 4 includes a center 10 and an envelope layer 12.
The envelope layer 12 is formed by a rubber composition being
crosslinked. The rubber composition includes a base rubber (a), a
co-crosslinking agent (b), a crosslinking initiator (c), and an
acid and/or a salt (d). The co-crosslinking agent (b) is (b1) an
.alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon
atoms; or (b2) a metal salt of an .alpha.,.beta.-unsaturated
carboxylic acid having 3 to 8 carbon atoms. A hardness Hi of the
inner cover 6 is greater than a hardness Hs at a surface of the
core 4. A hardness Ho of the outer cover 8 is less than the
hardness Hi.
Inventors: |
SAJIMA; Takahiro; (Kobe-shi,
JP) ; INOUE; Hidetaka; (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: |
48470800 |
Appl. No.: |
13/871096 |
Filed: |
April 26, 2013 |
Current U.S.
Class: |
473/373 ;
473/374 |
Current CPC
Class: |
A63B 37/0032 20130101;
A63B 37/0039 20130101; A63B 37/02 20130101; C08K 5/14 20130101;
A63B 37/0051 20130101; C08K 5/09 20130101; A63B 37/0062 20130101;
A63B 37/0092 20130101; A63B 37/0076 20130101; A63B 37/0043
20130101; A63B 37/0054 20130101 |
Class at
Publication: |
473/373 ;
473/374 |
International
Class: |
A63B 37/00 20060101
A63B037/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 25, 2012 |
JP |
2012-119603 |
May 28, 2012 |
JP |
2012-120502 |
May 30, 2012 |
JP |
2012-122840 |
May 31, 2012 |
JP |
2012-124079 |
Claims
1. A golf ball comprising a core, an inner cover positioned outside
the core, and an outer cover positioned outside the inner cover,
wherein the core comprises a center and an envelope layer
positioned outside the center, the center is formed by a rubber
composition being crosslinked, the envelope layer is formed by a
rubber composition being crosslinked, at least one of the rubber
composition of the center and the rubber composition of the
envelope layer includes: (a) a base rubber; (b) a co-crosslinking
agent; (c) a crosslinking initiator; and (d) an acid and/or a salt,
the co-crosslinking agent (b) is: (b1) an
.alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon
atoms; or (b2) a metal salt of an .alpha.,.beta.-unsaturated
carboxylic acid having 3 to 8 carbon atoms, a JIS-C hardness Hi of
the inner cover is greater than a JIS-C hardness Hs at a surface of
the core, and a JIS-C hardness Ho of the outer cover is less than
the hardness Hi.
2. The golf ball according to claim 1, wherein a difference (Hi-Hs)
between the hardness Hi and the hardness Hs is equal to or greater
than 2.
3. The golf ball according to claim 1, wherein a difference (Hi-Ho)
between the hardness Hi and the hardness Ho is equal to or greater
than 1.
4. The golf ball according to claim 1, wherein an amount of the
acid and/or the salt (d) is equal to or greater than 1.0 parts by
weight but less than 40 parts by weight, per 100 parts by weight of
the base rubber (a).
5. The golf ball according to claim 1, wherein the acid and/or the
salt (d) is a carboxylic acid and/or a salt thereof (d1).
6. A golf ball comprising a core, an inner cover positioned outside
the core, and an outer cover positioned outside the inner cover,
wherein the core comprises a center and an envelope layer
positioned outside the center, the center is formed by a rubber
composition being crosslinked, the envelope layer is formed by a
rubber composition being crosslinked, at least one of the rubber
composition of the center and the rubber composition of the
envelope layer includes: (a) a base rubber; (b) a co-crosslinking
agent; (c) a crosslinking initiator; and (d) an acid and/or a salt,
the co-crosslinking agent (b) is: (b1) an
.alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon
atoms; or (b2) a metal salt of an .alpha.,.beta.-unsaturated
carboxylic acid having 3 to 8 carbon atoms, a JIS-C hardness Ho of
the outer cover is greater than a JIS-C hardness Hs at a surface of
the core, and the hardness Ho is greater than a JIS-C hardness Hi
of the inner cover.
7. The golf ball according to claim 6, wherein the acid and/or the
salt (d) is a carboxylic acid and/or a salt thereof (d1).
8. The golf ball according to claim 6, wherein a difference (Ho-Hs)
between the hardness Ho and the hardness Hs is equal to or greater
than 2.
9. The golf ball according to claim 6, wherein a difference (Ho-Hi)
between the hardness Ho and the hardness Hi is equal to or greater
than 2.
10. The golf ball according to claim 6, wherein the rubber
composition includes 1.0 parts by weight or greater but 40 parts by
weight or less of the acid and/or the salt (d) per 100 parts by
weight of the base rubber (a).
11. A golf ball comprising a core, an inner cover positioned
outside the core, a mid cover positioned outside the inner cover,
and an outer cover positioned outside the mid cover, wherein the
core comprises a center and an envelope layer positioned outside
the center, the center is formed by a rubber composition being
crosslinked, the envelope layer is formed by a rubber composition
being crosslinked, at least one of the rubber composition of the
center and the rubber composition of the envelope layer includes:
(a) a base rubber; (b) a co-crosslinking agent; (c) a crosslinking
initiator; and (d) an acid and/or a salt, the co-crosslinking agent
(b) is: (b1) an .alpha.,.beta.-unsaturated carboxylic acid having 3
to 8 carbon atoms; or (b2) a metal salt of an
.alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon
atoms, a JIS-C hardness Hi of the inner cover is greater than a
JIS-C hardness Hs at a surface of the core, a difference (Hi-Hs)
between the hardness Hi and the hardness Hs is equal to or greater
than 1, and a JIS-C hardness Ho of the outer cover is greater than
the hardness Hi.
12. The golf ball according to claim 11, wherein the acid and/or
the salt (d) is a carboxylic acid and/or a salt thereof (d1).
13. The golf ball according to claim 11, wherein the rubber
composition includes 1.0 parts by weight or greater but 40 parts by
weight or less of the acid and/or the salt (d) per 100 parts by
weight of the base rubber (a).
14. The golf ball according to claim 11, wherein a difference
(Ho-Hi) between the hardness Ho and the hardness Hi is equal to or
greater than 2.
15. The golf ball according to claim 11, wherein a JIS-C hardness
Hm of the mid cover is greater than the hardness Hi, and the
hardness Ho is greater than the hardness Hm.
16. A golf ball comprising a core, an inner cover positioned
outside the core, a mid cover positioned outside the inner cover,
and an outer cover positioned outside the mid cover, wherein the
core comprises a center and an envelope layer positioned outside
the center, the center is formed by a rubber composition being
crosslinked, the envelope layer is formed by a rubber composition
being crosslinked, at least one of the rubber composition of the
center and the rubber composition of the envelope layer includes:
(a) a base rubber; (b) a co-crosslinking agent; (c) a crosslinking
initiator; and (d) an acid and/or a salt, the co-crosslinking agent
(b) is: (b1) an .alpha.,.beta.-unsaturated carboxylic acid having 3
to 8 carbon atoms; or (b2) a metal salt of an
.alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon
atoms, a difference (Hi-Hs) between a JIS-C hardness Hi of the
inner cover and a JIS-C hardness Hs at a surface of the core is
less than 1, and a JIS-C hardness Ho of the outer cover is greater
than the hardness Hi.
17. The golf ball according to claim 16, wherein the acid and/or
the salt (d) is a carboxylic acid and/or a salt thereof (d1).
18. The golf ball according to claim 16, wherein the rubber
composition includes 1.0 parts by weight or greater but less than
40 parts by weight of the acid and/or the salt (d) per 100 parts by
weight of the base rubber (a).
19. The golf ball according to claim 16, wherein a difference
(Ho-Hi) between the hardness Ho and the hardness Hi is equal to or
greater than 5.
20. The golf ball according to claim 16, wherein a JIS-C hardness
Hm of the mid cover is greater than the hardness Hi, and the
hardness Ho is greater than the hardness Hm.
Description
[0001] This application claims priority on Patent Application No.
2012-119603 filed in JAPAN on May 25, 2012, Patent Application No.
2012-120502 filed in JAPAN on May 28, 2012, Patent Application No.
2012-122840 filed in JAPAN on May 30, 2012, and Patent Application
No. 2012-124079 filed in JAPAN on May 31, 2012. The entire contents
of these Japanese Patent Applications are hereby incorporated by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to golf balls. Specifically,
the present invention relates to golf balls that include a solid
core and a cover.
[0004] 2. Description of the Related Art
[0005] Golf players' foremost requirement for golfballs is flight
performance. In particular, golf players place importance on flight
performance upon a shot with a driver. Flight performance
correlates with the resilience performance of a golf ball. When a
golf ball having excellent resilience performance is hit, the golf
ball flies at a high speed, thereby achieving a large flight
distance.
[0006] Golf players also place importance on spin performance of
golf balls. When a backspin rate is high, the run is short. It is
easy for golf players to cause a golf ball, to which backspin is
easily provided, to stop at a target point. When a sidespin rate is
high, the golf ball easily curves. It is easy for golf players to
intentionally cause a golf ball, to which sidespin is easily
provided, to curve. A golf ball to which spin is easily provided
has excellent controllability. In particular, advanced golf players
place importance on controllability upon a shot with a short
iron.
[0007] Golf balls that include a core having excellent resilience
performance are disclosed in JP61-37178, JP2008-212681
(US2008/0214324), JP2008-523952 (US2006/0135287 and
US2007/0173607), and JP2009-119256 (US2009/0124757).
[0008] The core disclosed in JP61-37178 is obtained from a rubber
composition that includes a co-crosslinking agent and a
crosslinking activator. This publication discloses palmitic acid,
stearic acid, and myristic acid as the crosslinking activator.
[0009] The core disclosed in JP2008-212681 is obtained from a
rubber composition that includes an organic peroxide, a metal salt
of an .alpha.,.beta.-unsaturated carboxylic acid, and a copper salt
of a fatty acid.
[0010] The core disclosed in JP2008-523952 is obtained from a
rubber composition that includes a metal salt of an unsaturated
monocarboxylic acid, a free radical initiator, and a non-conjugated
diene monomer.
[0011] The core disclosed in JP2009-119256 is obtained from a
rubber composition that includes a polybutadiene whose vinyl
content is equal to or less than 2%, whose cis 1,4-bond content is
equal to or greater than 80%, and which has an active end modified
with an alkoxysilane compound.
[0012] An appropriate trajectory height is required in order to
achieve a large flight distance. A trajectory height depends on a
spin rate and a launch angle. In a golf ball that achieves a high
trajectory by a high spin rate, a flight distance is insufficient.
In a golf ball that achieves a high trajectory by a high launch
angle, a large flight distance is obtained. Use of an
outer-hard/inner-soft structure in a golf ball can achieve a low
spin rate and a high launch angle. Modifications regarding a
hardness distribution of a core are disclosed in JP6-154357 (U.S.
Pat. No. 5,403,010), JP2008-194471 (U.S. Pat. No. 7,344,455,
US2008/0194358, US2008/0194359, and US2008/0214325), JP2008-194473
(US2008/0194357 and US2008/0312008), and JP2010-253268
(US2010/0273575).
[0013] In the core disclosed in JP6-154357, a JIS-C hardness H1 at
the central point of the core is 58 to 73, a JIS-C hardness H2 in a
region that extends over a distance range from equal to or greater
than 5 mm to equal to or less than 10 mm from the central point is
equal to or greater than 65 but equal to or less than 75, a JIS-C
hardness H3 at a point located at a distance of 15 mm from the
central point is equal to or greater than 74 but equal to or less
than 82, and a JIS-C hardness H4 at the surface of the core is
equal to or greater than 76 but equal to or less than 84. The
hardness H2 is greater than the hardness H1, the hardness H3 is
greater than the hardness H2, and the hardness H4 is equal to or
greater than the hardness H3.
[0014] In the core disclosed in JP2008-194471, a Shore D hardness
at the central point of the core is equal to or greater than 30 but
equal to or less than 48, a Shore D hardness at a point located at
a distance of 4 mm from the central point is equal to or greater
than 34 but equal to or less than 52, a Shore D hardness at a point
located at a distance of 8 mm from the central point is equal to or
greater than 40 but equal to or less than 58, a Shore D hardness at
a point located at a distance of 12 mm from the central point is
equal to or greater than 43 but equal to or less than 61, a Shore D
hardness in a region that extends over a distance range from equal
to or greater than 2 mm to equal to or less than 3 mm from the
surface of the core is equal to or greater than 36 but equal to or
less than 54, and a Shore D hardness at the surface is equal to or
greater than 41 but equal to or less than 59.
[0015] In the core disclosed in JP2008-194473, a Shore D hardness
at the central point of the core is equal to or greater than 25 but
equal to or less than 45, a Shore D hardness in a region that
extends over a distance range from equal to or greater than 5 mm to
equal to or less than 10 mm from the central point is equal to or
greater than 39 but equal to or less than 58, a Shore D hardness at
a point located at a distance of 15 mm from the central point is
equal to or greater than 36 but equal to or less than 55, and a
Shore D hardness at the surface of the core is equal to or greater
than 55 but equal to or less than 75.
[0016] JP2010-253268 discloses a golf ball that includes a core, an
envelope layer, an inner cover, and an outer cover. In the core,
the hardness gradually increases from the central point of the core
toward the surface of the core. The difference between a JIS-C
hardness at the surface and a JIS-C hardness at the central point
is equal to or greater than 15. The hardness of the outer cover is
greater than the hardness of the inner cover, and the hardness of
the inner cover is greater than the hardness of the envelope
layer.
[0017] Golf players' requirements for flight distance have been
escalated more than ever. A first object of the present invention
is to provide a golf ball having excellent flight performance and
excellent controllability.
[0018] For a second shot on a par-four hole or a par-five hole, a
fairway wood is frequently used. Golf players desire a large flight
distance also upon a shot with a fairway wood. A second object of
the present invention is to provide a golf ball that exerts
excellent flight performance also upon a shot with a fairway
wood.
[0019] Furthermore, golf players desire a large flight distance
upon a second shot on a par-four hole or a par-five hole. A third
object of the present invention is to provide a golf ball that
exerts excellent flight performance also upon a shot with a middle
iron.
[0020] Golf players desire further increase in a flight distance
upon a shot with a driver. Golf players are also interested in feel
at impact of golf balls. A hard cover deteriorates feel at impact.
Golf players prefer soft feel at impact. Golf players desire golf
balls from which soft feel at impact can be obtained with
appropriate intensity when the golf balls are hit. A fourth object
of the present invention is to provide a golf ball that has both
excellent flight performance and favorable feel at impact upon a
shot with a driver.
SUMMARY OF THE INVENTION
[0021] A golf ball according to the present invention includes a
core, an inner cover positioned outside the core, and an outer
cover positioned outside the inner cover. The core includes a
center and an envelope layer positioned outside the center. The
center is formed by a rubber composition being crosslinked. The
envelope layer is formed by a rubber composition being crosslinked.
At least one of the rubber composition of the center and the rubber
composition of the envelope layer includes:
[0022] (a) a base rubber;
[0023] (b) a co-crosslinking agent;
[0024] (c) a crosslinking initiator; and
[0025] (d) an acid and/or a salt.
[0026] The co-crosslinking agent (b) is: [0027] (b1) an
.alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon
atoms; or
[0028] (b2) a metal salt of an .alpha.,.beta.-unsaturated
carboxylic acid having 3 to 8 carbon atoms.
A JIS-C hardness Hi of the inner cover is greater than a JIS-C
hardness Hs at a surface of the core. A JIS-C hardness Ho of the
outer cover is less than the hardness Hi. In the golf ball, a
hardness distribution of the core is appropriate. When the golf
ball is hit, the energy loss is low in the core. With the golf
ball, a large flight distance is achieved. In the golf ball, the
outer cover can contribute to controllability. The golf ball has
both excellent flight performance and excellent
controllability.
[0029] According to another aspect, a golf ball according to the
present invention includes a core, an inner cover positioned
outside the core, and an outer cover positioned outside the inner
cover. The core includes a center and an envelope layer positioned
outside the center. The center is formed by a rubber composition
being crosslinked. The envelope layer is formed by a rubber
composition being crosslinked. At least one of the rubber
composition of the center and the rubber composition of the
envelope layer includes:
[0030] (a) a base rubber;
[0031] (b) a co-crosslinking agent;
[0032] (c) a crosslinking initiator; and
[0033] (d) an acid and/or a salt.
The co-crosslinking agent (b) is:
[0034] (b1) an .alpha.,.beta.-unsaturated carboxylic acid having 3
to 8 carbon atoms; or
[0035] (b2) a metal salt of an .alpha.,.beta.3-unsaturated
carboxylic acid having 3 to 8 carbon atoms.
A JIS-C hardness Ho of the outer cover is greater than a JIS-C
hardness Hs at a surface of the core. The hardness Ho is greater
than a JIS-C hardness Hi of the inner cover. In the golf ball, a
hardness distribution of the core is appropriate. When the golf
ball is hit with a fairway wood, the energy loss is low in the
core. In the golf ball, a hardness distribution of the entire ball
is also appropriate. With the golf ball, a large flight distance is
achieved.
[0036] According to still another aspect, a golf ball according to
the present invention includes a core, an inner cover positioned
outside the core, a mid cover positioned outside the inner cover,
and an outer cover positioned outside the mid cover. The core
includes a center and an envelope layer positioned outside the
center. The center is formed by a rubber composition being
crosslinked. The envelope layer is formed by a rubber composition
being crosslinked. At least one of the rubber composition of the
center and the rubber composition of the envelope layer
includes:
[0037] (a) a base rubber;
[0038] (b) a co-crosslinking agent;
[0039] (c) a crosslinking initiator; and
[0040] (d) an acid and/or a salt.
The co-crosslinking agent (b) is:
[0041] (b1) an .alpha.,.beta.-unsaturated carboxylic acid having 3
to 8 carbon atoms; or
[0042] (b2) a metal salt of an .alpha.,.beta.-unsaturated
carboxylic acid having 3 to 8 carbon atoms.
A JIS-C hardness Hi of the inner cover is greater than a JIS-C
hardness Hs at a surface of the core. A difference (Hi-Hs) between
the hardness Hi and the hardness Hs is equal to or greater than 1.
A JIS-C hardness Ho of the outer cover is greater than the hardness
Hi. In the golf ball, a hardness distribution of the core is
appropriate. When the golf ball is hit with a middle iron, the
energy loss is low in the core. In the entirety of the golf ball,
an outer-hard/inner-soft structure is achieved. When the golf ball
is hit with a middle iron, the spin rate is low. Due to the low
spin rate, a large flight distance is obtained.
[0043] According to still another aspect, a golf ball according to
the present invention includes a core, an inner cover positioned
outside the core, a mid cover positioned outside the inner cover,
and an outer cover positioned outside the mid cover. The core
includes a center and an envelope layer positioned outside the
center. The center is formed by a rubber composition being
crosslinked. The envelope layer is formed by a rubber composition
being crosslinked. At least one of the rubber composition of the
center and the rubber composition of the envelope layer
includes:
[0044] (a) a base rubber;
[0045] (b) a co-crosslinking agent;
[0046] (c) a crosslinking initiator; and
[0047] (d) an acid and/or a salt.
The co-crosslinking agent (b) is:
[0048] (b1) an .alpha.,.beta.-unsaturated carboxylic acid having 3
to 8 carbon atoms; or
[0049] (b2) a metal salt of an .alpha.,.beta.-unsaturated
carboxylic acid having 3 to 8 carbon atoms.
A difference (Hi-Hs) between a JIS-C hardness Hi of the inner cover
and a JIS-C hardness Hs at a surface of the core is less than 1. A
JIS-C hardness Ho of the outer cover is greater than the hardness
Hi. In the golf ball, a hardness distribution of the core is
appropriate. When the golf ball is hit with a driver, the energy
loss is low in the core. In the golf ball, a hardness distribution
of the entire ball is also appropriate. With the golf ball, a
flight distance upon a shot with a driver is further increased
without impairing the feel at impact.
BRIEF DESCRIPTION OF THE DRAWINGS
[0050] FIG. 1 is a partially cutaway cross-sectional view of a golf
ball according to a first embodiment of the present invention;
[0051] FIG. 2 is a line graph showing a hardness distribution of an
envelope layer of the golf ball in FIG. 1;
[0052] FIG. 3 is a partially cutaway cross-sectional view of a golf
ball according to a second embodiment of the present invention;
[0053] FIG. 4 is a line graph showing a hardness distribution of an
envelope layer of the golf ball in FIG. 3;
[0054] FIG. 5 is a partially cutaway cross-sectional view of a golf
ball according to a third embodiment of the present invention;
[0055] FIG. 6 is a line graph showing a hardness distribution of an
envelope layer of the golf ball in FIG. 5;
[0056] FIG. 7 is a partially cutaway cross-sectional view of a golf
ball according to a fourth embodiment of the present invention;
and
[0057] FIG. 8 is a line graph showing a hardness distribution of an
envelope layer of the golf ball in FIG. 7.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0058] The following will describe in detail the present invention,
based on preferred embodiments with reference to the accompanying
drawings.
First Embodiment
[0059] A golf ball 2 shown in FIG. 1 includes a spherical core 4,
an inner cover 6 positioned outside the core 4, and an outer cover
8 positioned outside the inner cover 6. The core 4 includes a
spherical center 10 and an envelope layer 12 positioned outside the
center 10. On the surface of the outer cover 8, a large number of
dimples 14 are formed. Of the surface of the golf ball 2, a part
other than the dimples 14 is a land 16. The golf ball 2 includes a
paint layer and a mark layer on the external side of the outer
cover 8, but these layers are not shown in the drawing.
[0060] The golf ball 2 preferably has a diameter of 40 mm or
greater but 45 mm or less. From the standpoint of conformity to the
rules established by the United States Golf Association (USGA), the
diameter is particularly preferably equal to or greater than 42.67
mm. In light of suppression of air resistance, the diameter is more
preferably equal to or less than 44 mm and particularly preferably
equal to or less than 42.80 mm. The golf ball 2 preferably has a
weight of 40 g or greater but 50 g or less. In light of attainment
of great inertia, the weight is more preferably equal to or greater
than 44 g and particularly preferably equal to or greater than
45.00 g. From the standpoint of conformity to the rules established
by the USGA, the weight is particularly preferably equal to or less
than 45.93 g.
[0061] In the present invention, JIS-C hardnesses are measured at
13 measuring points from the central point of the core 4 to the
surface of the core 4. The distances from the central point of the
core 4 to these measuring points are as follows.
[0062] First point: 0.0 mm
[0063] Second point: 2.5 mm
[0064] Third point: 5.0 mm
[0065] Fourth point: 7.0 mm
[0066] Fifth point: 7.5 mm
[0067] Sixth point: 8.0 mm
[0068] Seventh point: 9.5 mm
[0069] Eighth point: 10.0 mm
[0070] Ninth point: 10.5 mm
[0071] Tenth pint: 12.5 mm
[0072] Eleventh point: 15.0 mm
[0073] Twelfth point: 17.5 mm
[0074] Thirteenth point: surface
[0075] Hardnesses at the first to twelfth points are measured by
pressing a JIS-C type hardness scale against a cut plane of the
core 4 that has been cut into two halves. A hardness at the
thirteenth point is measured by pressing the JIS-C type hardness
scale against the surface of the spherical core 4. For the
measurement, an automated rubber hardness measurement machine
(trade name "P1", manufactured by Kobunshi Keiki Co., Ltd.), to
which this hardness scale is mounted, is used.
[0076] FIG. 2 is a line graph showing a hardness distribution of
the envelope layer 12 of the golf ball 2 in FIG. 1. The horizontal
axis of the graph indicates a distance (mm) from the central point
of the core 4. The vertical axis of the graph indicates a JIS-C
hardness. In the graph, the sixth point, the eighth point, and the
tenth to thirteenth points are plotted.
[0077] FIG. 2 also shows a linear approximation curve obtained by a
least-square method on the basis of the distances and the
hardnesses of the six measuring points. The linear approximation
curve is indicated by a dotted line. In FIG. 2, the broken line
does not greatly deviate from the linear approximation curve. In
other words, the broken line has a shape close to the linear
approximation curve. In the envelope layer 12, the hardness
linearly increases from its inside toward its outside. When the
golf ball 2 is hit with a driver, the energy loss is low in the
envelope layer 12. The golf ball 2 has excellent resilience
performance. When the golf ball 2 is hit with a driver, the flight
distance is large.
[0078] R.sup.2 of the linear approximation curve for the envelope
layer 12 which is obtained by the least-square method is preferably
equal to or greater than 0.95. R.sup.2 is an index indicating the
linearity of the broken line. For the envelope layer 12 for which
R.sup.2 is equal to or greater than 0.95, the shape of the broken
line of the hardness distribution is close to a straight line. The
golf ball 2 that includes the envelope layer 12 for which R.sup.2
is equal to or greater than 0.95 has excellent resilience
performance. R.sup.2 is more preferably equal to or greater than
0.96 and particularly preferably equal to or greater than 0.97.
R.sup.2 is calculated by squaring a correlation coefficient R. The
correlation coefficient R is calculated by dividing the covariance
of the distance (mm) from the central point and the hardness
(JIS-C) by the standard deviation of the distance (mm) from the
central point and the standard deviation of the hardness
(JIS-C).
[0079] In light of suppression of spin, the gradient a of the
linear approximation curve is preferably equal to or greater than
0.30, more preferably equal to or greater than 0.33, and
particularly preferably equal to or greater than 0.35.
[0080] In the present invention, a JIS-C hardness at a measuring
point whose distance from the central point of the core 4 is x (mm)
is represented by H(x). The hardness at the central point of the
core 4 is represented by H(0.0). In the present invention, the
JIS-C hardness at the surface of the core 4 is represented by Hs.
The difference (Hs-H(0.0)) between the surface hardness Hs and the
central hardness H(0.0) is preferably equal to or greater than 15.
The core 4 in which the difference (Hs-H(0.0)) is equal to or
greater than 15 has an outer-hard/inner-soft structure. When the
golf ball 2 is hit with a driver, the recoil (torsional return) in
the core 4 is great, and thus spin is suppressed. The core 4
contributes to the flight performance of the golf ball 2. In light
of flight performance, the difference (Hs-H(0.0)) is more
preferably equal to or greater than 23 and particularly preferably
equal to or greater than 24. From the standpoint that the core 4
can easily be formed, the difference (Hs-H(0.0)) is preferably
equal to or less than 50. In the core 4, the hardness gradually
increases from its central point toward its surface.
[0081] The center 10 is formed by crosslinking a rubber
composition. Examples of base rubbers for use in the rubber
composition include polybutadienes, polyisoprenes,
styrene-butadiene copolymers, ethylene-propylene-diene copolymers,
and natural rubbers. Two or more rubbers may be used in
combination. In light of resilience performance, polybutadienes are
preferred, and high-cis polybutadienes are particularly
preferred.
[0082] Preferably, the rubber composition of the center 10 includes
a co-crosslinking agent. Examples of preferable co-crosslinking
agents in light of resilience performance include zinc acrylate,
magnesium acrylate, zinc methacrylate, and magnesium methacrylate.
Preferably, the rubber composition includes an organic peroxide
together with a co-crosslinking agent. Examples of preferable
organic peroxides include 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.
Preferably, the rubber composition includes a sulfur compound.
[0083] According to need, various additives such as a filler,
sulfur, a vulcanization accelerator, an anti-aging agent, a
coloring agent, a plasticizer, a dispersant, and the like are
included in the rubber composition of the center 10 in an adequate
amount. Synthetic resin powder or crosslinked rubber powder may
also be included in the rubber composition.
[0084] In the present embodiment, the center 10 is more flexible
than the envelope layer 12. The center 10 can suppress spin. The
center 10 preferably has a diameter of 10 mm or greater but 20 mm
or less. In the golf ball 2 that includes the center 10 having a
diameter of 10 mm or greater, spin can be suppressed. In this
respect, the diameter is more preferably equal to or greater than
12 mm and particularly preferably equal to or greater than 14 mm.
The golf ball 2 that includes the center 10 having a diameter of 20
mm or less has excellent resilience performance even though the
center 10 is flexible. In this respect, the diameter is more
preferably equal to or less than 18 mm and particularly preferably
equal to or less than 16 mm.
[0085] The envelope layer 12 is formed by crosslinking a rubber
composition. The rubber composition includes:
[0086] (a) a base rubber;
[0087] (b) a co-crosslinking agent;
[0088] (c) a crosslinking initiator; and
[0089] (d) an acid and/or a salt.
[0090] Examples of the base rubber (a) include polybutadienes,
polyisoprenes, styrene-butadiene copolymers,
ethylene-propylene-diene copolymers, and natural rubbers. In light
of resilience performance, polybutadienes are preferred. When a
polybutadiene and another rubber are used in combination, it is
preferred that the polybutadiene is included as a principal
component. Specifically, the proportion of the polybutadiene to the
entire base rubber is preferably equal to or greater than 50% by
weight and more preferably equal to or greater than 80% by weight.
The proportion of cis-1,4 bonds in the polybutadiene is preferably
equal to or greater than 40% by weight and more preferably equal to
or greater than 80% by weight.
[0091] A polybutadiene in which the proportion of 1,2-vinyl bonds
is equal to or less than 2.0% by weight is preferred. The
polybutadiene can contribute to the resilience performance of the
golf ball 2. In this respect, the proportion of 1,2-vinyl bonds is
preferably equal to or less than 1.7% by weight and particularly
preferably equal to or less than 1.5% by weight.
[0092] From the standpoint that a polybutadiene having a low
proportion of 1,2-vinyl bonds and excellent polymerization activity
is obtained, a polybutadiene synthesized with a
rare-earth-element-containing catalyst is preferred. In particular,
a polybutadiene synthesized with a catalyst containing neodymium,
which is a lanthanum-series rare earth element compound, is
preferred.
[0093] The polybutadiene has a Mooney viscosity (ML.sub.1+4
(100.degree. C.)) of preferably 30 or greater, more preferably 32
or greater, and particularly preferably 35 or greater. The Mooney
viscosity (ML.sub.1+4(100.degree. C.)) is preferably equal to or
less than 140, more preferably equal to or less than 120, even more
preferably equal to or less than 100, and particularly preferably
equal to or less than 80. The Mooney viscosity
(ML.sub.1+4(100.degree. C.)) is measured according to the standards
of "JIS K6300". The measurement conditions are as follows.
[0094] Rotor: L rotor
[0095] Preheating time: 1 minute
[0096] Rotating time of rotor: 4 minutes
[0097] Temperature: 100.degree. C.
[0098] In light of workability, the polybutadiene has a molecular
weight distribution (Mw/Mn) of preferably 2.0 or greater, more
preferably 2.2 or greater, even more preferably 2.4 or greater, and
particularly preferably 2.6 or greater. In light of resilience
performance, the molecular weight distribution (Mw/Mn) is
preferably equal to or less than 6.0, more preferably equal to or
less than 5.0, even more preferably equal to or less than 4.0, and
particularly preferably equal to or less than 3.4. The molecular
weight distribution (Mw/Mn) is calculated by dividing the weight
average molecular weight Mw by the number average molecular weight
Mn.
[0099] The molecular weight distribution is measured by gel
permeation chromatography ("HLC-8120GPC" manufactured by Tosoh
Corporation). The measurement conditions are as follows.
[0100] Detector: differential refractometer
[0101] Column: GMHHXL (manufactured by Tosoh Corporation)
[0102] Column temperature: 40.degree. C.
[0103] Mobile phase: tetrahydrofuran
The molecular weight distribution is calculated as a value obtained
by conversion using polystyrene standard.
[0104] Examples of preferable co-crosslinking agents (b)
include:
[0105] (b1) an .alpha.,.beta.-unsaturated carboxylic acid having 3
to 8 carbon atoms; and
[0106] (b2) a metal salt of an .alpha.,.beta.-unsaturated
carboxylic acid having 3 to 8 carbon atoms.
[0107] The rubber composition may include only the
.alpha.,.beta.-unsaturated carboxylic acid (b1) or only the metal
salt (b2) of the .alpha.,.beta.-unsaturated carboxylic acid as the
co-crosslinking agent (b). The rubber composition may include both
the .alpha.,.beta.-unsaturated carboxylic acid (b1) and the metal
salt (b2) of the .alpha.,.beta.-unsaturated carboxylic acid as the
co-crosslinking agent (b).
[0108] The metal salt (b2) of the .alpha.,.beta.-unsaturated
carboxylic acid graft-polymerizes with the molecular chain of the
base rubber, thereby crosslinking the rubber molecules. When the
rubber composition includes the .alpha.,.beta.-unsaturated
carboxylic acid (b1), the rubber composition preferably further
includes a metal compound (f). The metal compound (f) reacts with
the .alpha.,.beta.-unsaturated carboxylic acid (b1) in the rubber
composition. A salt obtained by this reaction graft-polymerizes
with the molecular chain of the base rubber.
[0109] Examples of the metal compound (f) include metal hydroxides
such as magnesium hydroxide, zinc hydroxide, calcium hydroxide,
sodium hydroxide, lithium hydroxide, potassium hydroxide, and
copper hydroxide; metal oxides such as magnesium oxide, calcium
oxide, zinc oxide, and copper oxide; and metal carbonates such as
magnesium carbonate, zinc carbonate, calcium carbonate, sodium
carbonate, lithium carbonate, and potassium carbonate. A compound
that includes a bivalent metal is preferred. The compound that
includes the bivalent metal reacts with the co-crosslinking agent
(b) to form metal crosslinks. The metal compound (f) is
particularly preferably a zinc compound. Two or more metal
compounds may be used in combination.
[0110] Examples of the .alpha.,.beta.-unsaturated carboxylic acids
include acrylic acid, methacrylic acid, fumaric acid, maleic acid,
and crotonic acid. Examples of the metal component in the metal
salt (b2) of the .alpha.,.beta.-unsaturated carboxylic acid include
sodium ion, potassium ion, lithium ion, magnesium ion, calcium ion,
zinc ion, barium ion, cadmium ion, aluminum ion, tin ion, and
zirconium ion. The metal salt (b2) of the
.alpha.,.beta.-unsaturated carboxylic acid may include two or more
types of ions. From the standpoint that metal crosslinks are likely
to occur between the rubber molecules, bivalent metal ions such as
magnesium ion, calcium ion, zinc ion, barium ion, and cadmium ion
are preferred. The metal salt (b2) of the
.alpha.,.beta.-unsaturated carboxylic acid is particularly
preferably zinc acrylate.
[0111] In light of resilience performance of the golf ball 2, the
amount of the co-crosslinking agent (b) is preferably equal to or
greater than 15 parts by weight and particularly preferably equal
to or greater than 20 parts by weight, per 100 parts by weight of
the base rubber. In light of feel at impact, the amount is
preferably equal to or less than 50 parts by weight, more
preferably equal to or less than 45 parts by weight, and
particularly preferably equal to or less than 40 parts by weight,
per 100 parts by weight of the base rubber.
[0112] The crosslinking initiator (c) is preferably an organic
peroxide. The organic peroxide contributes to the resilience
performance of the golf ball 2. Examples of preferable organic
peroxides include 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.
In light of versatility, dicumyl peroxide is preferred.
[0113] In light of resilience performance of the golf ball 2, the
amount of the crosslinking initiator (c) is preferably equal to or
greater than 0.2 parts by weight and particularly preferably equal
to or greater than 0.5 parts by weight, per 100 parts by weight of
the base rubber. In light of feel at impact and durability of the
golf ball 2, the amount is preferably equal to or less than 5.0
parts by weight and particularly preferably equal to or less than
2.5 parts by weight, per 100 parts by weight of the base
rubber.
[0114] In the present invention, the co-crosslinking agent (b) is
not included in the concept of the acid and/or the salt (d). It is
inferred that during heating and forming of the core 4, the acid
and/or the salt (d) breaks the metal crosslinks by the
co-crosslinking agent (b) near the inner surface of the envelope
layer 12. Examples of the acid and/or the salt (d) include oxo
acids, such as carboxylic acids, sulfonic acids, and phosphoric
acid, and salts thereof; and hydroacids, such as hydrochloric acid
and hydrofluoric acid, and salts thereof. Oxo acids and salts
thereof are preferred. A carboxylic acid and/or a salt thereof (d1)
is more preferred. Carboxylates are particularly preferred.
[0115] The carbon number of the carboxylic acid component of the
carboxylic acid and/or the salt thereof (d1) is preferably equal to
or greater than 1 but equal to or less than 30, more preferably
equal to or greater than 3 but equal to or less than 30, and even
more preferably equal to or greater than 5 but equal to or less
than 28. Examples of the carboxylic acid include aliphatic
carboxylic acids (fatty acids) and aromatic carboxylic acids. Fatty
acids and salts thereof are preferred.
[0116] The rubber composition may include a saturated fatty acid
and/or a salt thereof, or may include an unsaturated fatty acid
and/or a salt thereof. The saturated fatty acid and the salt
thereof are preferred.
[0117] Examples of fatty acids include butyric acid (C4), valeric
acid (C5), caproic acid (C6), enanthic acid (C7), caprylic acid
(C8), pelargonic acid (C9), capric acid (decanoic 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), linolic 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). Salts of two or more fatty acids
may be used in combination.
[0118] An aromatic carboxylic acid has an aromatic ring and a
carboxyl group. Examples of aromatic carboxylic acids include
benzoic acid, phthalic acid, isophthalic acid, terephthalic acid,
hemimellitic acid (benzene-1,2,3-tricarboxylic acid), trimellitic
acid (benzene-1,2,4-tricarboxylic acid), trimesic acid
(benzene-1,3,5-tricarboxylic acid), mellophanic acid
(benzene-1,2,3,4-tetracarboxylic acid), prehnitic acid
(benzene-1,2,3,5-tetracarboxylic acid), pyromellitic acid
(benzene-1,2,4,5-tetracarboxylic acid), mellitic acid (benzene
hexacarboxylic acid), diphenic acid (biphenyl-2,2'-dicarboxylic
acid), toluic acid (methylbenzoic acid), xylic acid, prehnitylic
acid (2,3,4-trimethylbenzoic acid), .gamma.-isodurylic acid
(2,3,5-trimethylbenzoic acid), durylic acid (2,4,5-trimethylbenzoic
acid), .beta.-isodurylic acid (2,4,6-trimethylbenzoic acid),
.alpha.-isodurylic acid (3,4,5-trimethylbenzoic acid), cuminic acid
(4-isopropylbenzoic acid), uvitic acid (5-methylisophthalic acid),
.alpha.-toluic acid (phenylacetic acid), hydratropic acid
(2-phenylpropanoic acid), and hydrocinnamic acid (3-phenylpropanoic
acid).
[0119] The rubber composition may include an aromatic carboxylate
substituted with a hydroxyl group, an alkoxy group, or an oxo
group. Examples of this carboxylic acid can include salicylic acid
(2-hydroxybenzoic acid), anisic acid (methoxybenzoic acid),
cresotinic acid (hydroxy(methyl)benzoic acid), o-homosalicylic acid
(2-hydroxy-3-methylbenzoic acid), m-homosalicylic acid
(2-hydroxy-4-methylbenzoic acid), p-homosalicylic acid
(2-hydroxy-5-methylbenzoic acid), o-pyrocatechuic acid
(2,3-dihydroxybenzoic acid), .beta.-resorcylic acid
(2,4-dihydroxybenzoic acid), .gamma.-resorcylic acid
(2,6-dihydroxybenzoic acid), protocatechuic acid
(3,4-dihydroxybenzoic acid), .alpha.-resorcylic acid
(3,5-dihydroxybenzoic acid), vanillic acid
(4-hydroxy-3-methoxybenzoic acid), isovanillic acid
(3-hydroxy-4-methoxybenzoic acid), veratric acid
(3,4-dimethoxybenzoic acid), o-veratric acid (2,3-dimethoxybenzoic
acid), orsellinic acid (2,4-dihydroxy-6-methylbenzoic acid),
m-hemipinic acid (4,5-dimethoxyphthalic acid), gallic acid
3,4,5-trihydroxybenzoic acid), syringic acid
(4-hydroxy-3,5-dimethoxybenzoic acid), asaronic acid
(2,4,5-trimethoxybenzoic acid), mandelic acid
(hydroxy(phenyl)acetic acid), vanillylmandelic acid
(hydroxy(4-hydroxy-3-methoxyphenyl)acetic acid), homoanisic acid
((4-methoxyphenyl)acetic acid), homogentisic acid
((2,5-dihydroxyphenyl)acetic acid), homoprotocatechuic acid
((3,4-dihydroxyphenyl)acetic acid), homovanillic acid
((4-hydroxy-3-methoxyphenyl)acetic acid), homoisovanillic acid
((3-hydroxy-4-methoxyphenyl)acetic acid), homoveratric acid
((3,4-dimethoxyphenyl)acetic acid), o-homoveratric acid
((2,3-dimethoxyphenyl)acetic acid), homophthalic acid
(2-(carboxymethyl)benzoic acid), homoisophthalic acid
(3-(carboxymethyl)benzoic acid), homoterephthalic acid
(4-(carboxymethyl)benzoic acid), phthalonic acid
(2-(carboxycarbonyl)benzoic acid), isophthalonic acid
(3-(carboxycarbonyl)benzoic acid), terephthalonic acid
(4-(carboxycarbonyl)benzoic acid), benzilic acid
(hydroxydiphenylacetic acid), atrolactic acid
(2-hydroxy-2-phenylpropanoic acid), tropic acid
(3-hydroxy-2-phenylpropanoic acid), melilotic acid
(3-(2-hydroxyphenyl)propanoic acid), phloretic acid
(3-(4-hydroxyphenyl)propanoic acid), hydrocaffeic acid
(3-(3,4-dihydroxyphenyl)propanoic acid), hydroferulic acid
(3-(4-hydroxy-3-methoxyphenyl)propanoic acid), hydroisoferulic acid
(3-(3-hydroxy-4-methoxyphenyl)propanoic acid), p-coumaric acid
(3-(4-hydroxyphenyl)acrylic acid), umbellic acid
(3-(2,4-dihydroxyphenyl)acrylic acid), caffeic acid
(3-(3,4-dihydroxyphenyl)acrylic acid), ferulic acid
(3-(4-hydroxy-3-methoxyphenyl)acrylic acid), isoferulic acid
(3-(3-hydroxy-4-methoxyphenyl)acrylic acid), and sinapic acid
(3-(4-hydroxy-3,5-dimethoxyphenyl)acrylic acid).
[0120] The cationic component of the carboxylate is a metal ion or
an organic cation. Examples of the metal ion include sodium ion,
potassium ion, lithium ion, silver ion, magnesium ion, calcium ion,
zinc ion, barium ion, cadmium ion, copper ion, cobalt ion, nickel
ion, manganese ion, aluminum ion, iron ion, tin ion, zirconium ion,
and titanium ion. Two or more types of ions may be used in
combination.
[0121] The organic cation has a carbon chain. Examples of the
organic cation include organic ammonium ions. Examples of organic
ammonium ions include primary ammonium ions such as stearylammonium
ion, hexylammonium ion, octylammonium ion, and 2-ethylhexylammonium
ion; secondary ammonium ions such as dodecyl(lauryl)ammonium ion,
and octadecyl(stearyl)ammonium ion; tertiary ammonium ions such as
trioctylammonium ion; and quaternary ammonium ions such as
dioctyldimethylammonium ion, and distearyldimethylammonium ion. Two
or more types of organic cations may be used in combination.
[0122] Examples of preferable carboxylates include a potassium
salt, a magnesium salt, an aluminum salt, a zinc salt, an iron
salt, a copper salt, a nickel salt, or a cobalt salt of caprylic
acid (octanoic acid), lauric acid, myristic acid, palmitic acid,
stearic acid, oleic acid, or behenic acid. Zinc salts of carboxylic
acids are particularly preferred. Specific examples of preferable
carboxylates include zinc octoate, zinc laurate, zinc myristate,
and zinc stearate. A particularly preferable carboxylate is zinc
octoate.
[0123] In light of linearity of the hardness distribution of the
envelope layer 12, the amount of the acid and/or the salt (d) is
preferably equal to or greater than 0.5 parts by weight, more
preferably equal to or greater than 1.0 parts by weight, and
particularly preferably equal to or greater than 2.0 parts by
weight, per 100 parts by weight of the base rubber. In light of
resilience performance, the amount is preferably equal to or less
than 40 parts by weight, more preferably equal to or less than 30
parts by weight, and particularly preferably equal to or less than
20 parts by weight, per 100 parts by weight of the base rubber.
[0124] The weight ratio of the co-crosslinking agent (b) and the
acid and/or the salt (d) in the rubber composition is preferably
equal to or greater than 3/7 but equal to or less than 9/1, and is
particularly preferably equal to or greater than 4/6 but equal to
or less than 8/2. From the rubber composition in which this weight
ratio is within the above range, the core 4 whose hardness linearly
increases from its central point toward its surface can be
obtained.
[0125] As the co-crosslinking agent (b), zinc acrylate is
preferably used. Zinc acrylate whose surface is coated with stearic
acid or zinc stearate for the purpose of improving dispersibility
to rubber is present. In the present invention, when the rubber
composition includes this zinc acrylate, this coating material is
not included in the concept of the acid and/or the salt (d).
[0126] The rubber composition preferably further includes an
organic sulfur compound (e). The organic sulfur compound (e) can
contribute to control of: the linearity of the hardness
distribution of the envelope layer 12; and the degree of the
outer-hard/inner-soft structure. An example of the organic sulfur
compound (e) is an organic compound having a thiol group or a
polysulfide linkage having 2 to 4 sulfur atoms. A metal salt of
this organic compound is also included in the organic sulfur
compound (e). Examples of the organic sulfur compound (e) include
aliphatic compounds such as aliphatic thiols, aliphatic
thiocarboxylic acids, aliphatic dithiocarboxylic acids, and
aliphatic polysulfides; heterocyclic compounds; alicyclic compounds
such as alicyclic thiols, alicyclic thiocarboxylic acids, alicyclic
dithiocarboxylic acids, and alicyclic polysulfides; and aromatic
compounds. Specific examples of the organic sulfur compound (e)
include thiophenols, thionaphthols, polysulfides, thiocarboxylic
acids, dithiocarboxylic acids, sulfenamides, thiurams,
dithiocarbamates, and thiazoles. Preferable organic sulfur
compounds (e) is at least one member selected from the group
consisting of thiophenols, diphenyl disulfides, thionaphthols,
thiuram disulfides, and metal salts thereof.
[0127] Specific examples of the organic sulfur compound (e) are
represented by the following chemical formulas (1) to (4).
##STR00001##
[0128] In the chemical formula (1), R1 to R5 each represent H or a
substituent.
##STR00002##
[0129] In the chemical formula (2), R1 to R10 each represent H or a
substituent.
##STR00003##
[0130] In the chemical formula (3), R1 to R5 each represent H or a
substituent, and M1 represents a monovalent metal atom.
##STR00004##
[0131] In the chemical formula (4), R1 to R10 each represent H or a
substituent, and M2 represents a bivalent metal atom.
[0132] In the formulas (1) to (4), each substituent is at least one
group selected from the group consisting of a halogen group (F, Cl,
Br, I), an alkyl group, a carboxyl group (--COOH), an ester
(--COOR) of a carboxyl group, a formyl group (--CHO), an acyl group
(--COR), a carbonyl halide group (--COX), a sulfo group
(--SO.sub.3H), an ester (--SO.sub.3R) of a sulfo group, a sulfonyl
halide group (--SO.sub.2X), a sulfino group (--SO.sub.2H), an
alkylsulfinyl group (--SOR), a carbamoyl group (--CONH.sub.2), an
alkyl halide group, a cyano group (--CN), and an alkoxy group
(--OR).
[0133] Examples of the organic sulfur compound represented by the
chemical formula (1) include thiophenol; thiophenols substituted
with halogen groups, such as 4-fluorothiophenol,
2,5-difluorothiophenol, 2,4,5-trifluorothiophenol,
2,4,5,6-tetrafluorothiophenol, pentafluorothiophenol,
2-chlorothiophenol, 4-chlorothiophenol, 2,4-dichlorothiophenol,
2,5-dichlorothiophenol, 2,6-dichlorothiophenol,
2,4,5-trichlorothiophenol, 2,4,5,6-tetrachlorothiophenol,
pentachlorothiophenol, 4-bromothiophenol, 2,5-dibromothiophenol,
2,4,5-tribromothiophenol, 2,4,5,6-tetrabromothiophenol,
pentabromothiophenol, 4-iodothiophenol, 2,5-diiodothiophenol,
2,4,5-triiodothiophenol, 2,4,5,6-tetraiodothiophenol, and
pentaiodothiophenol; thiophenols substituted with alkyl groups,
such as 4-methylthiophenol, 2,4,5-trimethylthiophenol,
pentamethylthiophenol, 4-t-butylthiophenol,
2,4,5-tri-t-butylthiophenol, and penta-t-butylthiophenol;
thiophenols substituted with carboxyl groups, such as
4-carboxythiophenol, 2,4,6-tricarboxythiophenol, and
pentacarboxythiophenol; thiophenols substituted with alkoxycarbonyl
groups, such as 4-methoxycarbonylthiophenol,
2,4,6-trimethoxycarbonylthiophenol, and
pentamethoxycarbonylthiophenol; thiophenols substituted with formyl
groups, such as 4-formylthiophenol, 2,4,6-triformylthiophenol, and
pentaformylthiophenol; thiophenols substituted with acyl groups,
such as 4-acetylthiophenol, 2,4,6-triacetylthiophenol, and
pentaacetylthiophenol; thiophenols substituted with carbonyl halide
groups, such as 4-chlorocarbonylthiophenol,
2,4,6-tri(chlorocarbonyl)thiophenol, and
penta(chlorocarbonyl)thiophenol; thiophenolssubstitutedwith sulfo
groups, such as 4-sulfothiophenol, 2,4,6-trisulfothiophenol, and
pentasulfothiophenol; thiophenols substituted with alkoxysulfonyl
groups, such as 4-methoxysulfonylthiophenol,
2,4,6-trimethoxysulfonylthiophenol, and
pentamethoxysulfonylthiophenol; thiophenols substituted with
sulfonyl halide groups, such as 4-chlorosulfonylthiophenol,
2,4,6-tri(chlorosulfonyl)thiophenol, and
penta(chlorosulfonyl)thiophenol; thiophenolssubstitutedwith sulfino
groups, such as 4-sulfinothiophenol, 2,4,6-trisulfinothiophenol,
and pentasulfinothiophenol; thiophenols substituted with
alkylsulfinyl groups, such as 4-methylsulfinylthiophenol,
2,4,6-tri(methylsulfinyl)thiophenol, and
penta(methylsulfinyl)thiophenol; thiophenols substituted with
carbamoyl groups, such as 4-carbamoylthiophenol,
2,4,6-tricarbamoylthiophenol, and pentacarbamoylthiophenol;
thiophenols substituted with alkyl halide groups, such as
4-trichloromethylthiophenol, 2,4,6-tri(trichloromethyl)thiophenol,
and penta(trichloromethyl)thiophenol; thiophenols substituted with
cyano groups, such as 4-cyanothiophenol, 2,4,6-tricyanothiophenol,
and pentacyanothiophenol; and thiophenols substituted with alkoxy
groups, such as 4-methoxythiophenol, 2,4,6-trimethoxythiophenol,
and pentamethoxythiophenol. Each of these thiophenols is
substituted with one type of substituent.
[0134] Another example of the organic sulfur compound represented
by the chemical formula (1) is a compound substituted with at least
one type of the above substituents and another substituent.
Examples of the other substituent include a nitro group
(--NO.sub.2), an amino group (--NH.sub.2), a hydroxyl group (--OH),
and a phenylthio group (--SPh). Specific examples of the compound
include 4-chloro-2-nitrothiophenol, 4-chloro-2-aminothiophenol,
4-chloro-2-hydroxythiophenol, 4-chloro-2-phenylthiothiophenol,
4-methyl-2-nitrothiophenol, 4-methyl-2-aminothiophenol,
4-methyl-2-hydroxythiophenol, 4-methyl-2-phenylthiothiophenol,
4-carboxy-2-nitrothiophenol, 4-carboxy-2-aminothiophenol,
4-carboxy-2-hydroxythiophenol, 4-carboxy-2-phenylthiothiophenol,
4-methoxycarbonyl-2-nitrothiophenol,
4-methoxycarbonyl-2-aminothiophenol,
4-methoxycarbonyl-2-hydroxythiophenol,
4-methoxycarbonyl-2-phenylthiothiophenol,
4-formyl-2-nitrothiophenol, 4-formyl-2-aminothiophenol,
4-formyl-2-hydroxythiophenol, 4-formyl-2-phenylthiothiophenol,
4-acetyl-2-nitrothiophenol, 4-acetyl-2-aminothiophenol,
4-acetyl-2-hydroxythiophenol, 4-acetyl-2-phenylthiothiophenol,
4-chlorocarbonyl-2-nitrothiophenol,
4-chlorocarbonyl-2-aminothiophenol,
4-chlorocarbonyl-2-hydroxythiophenol,
4-chlorocarbonyl-2-phenylthiothiophenol, 4-sulfo-2-nitrothiophenol,
4-sulfo-2-aminothiophenol, 4-sulfo-2-hydroxythiophenol,
4-sulfo-2-phenylthiothiophenol,
4-methoxysulfonyl-2-nitrothiophenol,
4-methoxysulfonyl-2-aminothiophenol,
4-methoxysulfonyl-2-hydroxythiophenol,
4-methoxysulfonyl-2-phenylthiothiophenol,
4-chlorosulfonyl-2-nitrothiophenol,
4-chlorosulfonyl-2-aminothiophenol,
4-chlorosulfonyl-2-hydroxythiophenol,
4-chlorosulfonyl-2-phenylthiothiophenol,
4-sulfino-2-nitrothiophenol, 4-sulfino-2-aminothiophenol,
4-sulfino-2-hydroxythiophenol, 4-sulfino-2-phenylthiothiophenol,
4-methylsulfinyl-2-nitrothiophenol,
4-methylsulfinyl-2-aminothiophenol,
4-methylsulfinyl-2-hydroxythiophenol,
4-methylsulfinyl-2-phenylthiothiophenol,
4-carbamoyl-2-nitrothiophenol, 4-carbamoyl-2-aminothiophenol,
4-carbamoyl-2-hydroxythiophenol,
4-carbamoyl-2-phenylthiothiophenol,
4-trichloromethyl-2-nitrothiophenol,
4-trichloromethyl-2-aminothiophenol,
4-trichloromethyl-2-hydroxythiophenol,
4-trichloromethyl-2-phenylthiothiophenol,
4-cyano-2-nitrothiophenol, 4-cyano-2-aminothiophenol,
4-cyano-2-hydroxythiophenol, 4-cyano-2-phenylthiothiophenol,
4-methoxy-2-nitrothiophenol, 4-methoxy-2-aminothiophenol,
4-methoxy-2-hydroxythiophenol, and
4-methoxy-2-phenylthiothiophenol.
[0135] Still another example of the organic sulfur compound
represented by the chemical formula (1) is a compound substituted
with two or more types of substituents. Specific examples of the
compound include 4-acetyl-2-chlorothiophenol,
4-acetyl-2-methylthiophenol, 4-acetyl-2-carboxythiophenol,
4-acetyl-2-methoxycarbonylthiophenol, 4-acetyl-2-formylthiophenol,
4-acetyl-2-chlorocarbonylthiophenol, 4-acetyl-2-sulfothiophenol,
4-acetyl-2-methoxysulfonylthiophenol,
4-acetyl-2-chlorosulfonylthiophenol, 4-acetyl-2-sulfinothiophenol,
4-acetyl-2-methylsulfinylthiophenol,
4-acetyl-2-carbamoylthiophenol,
4-acetyl-2-trichloromethylthiophenol, 4-acetyl-2-cyanothiophenol,
and 4-acetyl-2-methoxythiophenol.
[0136] Examples of the organic sulfur compound represented by the
chemical formula (2) include diphenyl disulfide; diphenyl
disulfides substituted with halogen groups, such as
bis(4-fluorophenyl)disulfide, bis(2,5-difluorophenyl)disulfide,
bis(2,4,5-trifluorophenyl)disulfide,
bis(2,4,5,6-tetrafluorophenyl)disulfide,
bis(pentafluorophenyl)disulfide, bis(4-chlorophenyl)disulfide,
bis(2,5-dichlorophenyl)disulfide,
bis(2,4,5-trichlorophenyl)disulfide,
bis(2,4,5,6-tetrachlorophenyl)disulfide,
bis(pentachlorophenyl)disulfide, bis(4-bromophenyl)disulfide,
bis(2,5-dibromophenyl)disulfide,
bis(2,4,5-tribromophenyl)disulfide,
bis(2,4,5,6-tetrabromophenyl)disulfide,
bis(pentabromophenyl)disulfide, bis(4-iodophenyl)disulfide,
bis(2,5-diiodophenyl)disulfide, bis(2,4,5-triiodophenyl)disulfide,
bis(2,4,5,6-tetraiodophenyl)disulfide, and
bis(pentaiodophenyl)disulfide; diphenyl disulfides substituted with
alkyl groups, such as bis(4-methylphenyl)disulfide,
bis(2,4,5-trimethylphenyl)disulfide,
bis(pentamethylphenyl)disulfide, bis(4-t-butylphenyl)disulfide,
bis(2,4,5-tri-t-butylphenyl)disulfide, and
bis(penta-t-butylphenyl)disulfide; diphenyl disulfides substituted
with carboxyl groups, such as bis(4-carboxyphenyl)disulfide,
bis(2,4,6-tricarboxyphenyl)disulfide, and
bis(pentacarboxyphenyl)disulfide; diphenyl disulfides substituted
with alkoxycarbonyl groups, such as
bis(4-methoxycarbonylphenyl)disulfide,
bis(2,4,6-trimethoxycarbonylphenyl)disulfide, and
bis(pentamethoxycarbonylphenyl)disulfide; diphenyl disulfides
substituted with formyl groups, such as
bis(4-formylphenyl)disulfide, bis(2,4,6-triformylphenyl)disulfide,
and bis(pentaformylphenyl)disulfide; diphenyl disulfides
substituted with acyl groups, such as bis(4-acetylphenyl)disulfide,
bis(2,4,6-triacetylphenyl)disulfide, and
bis(pentaacetylphenyl)disulfide; diphenyl disulfides substituted
with carbonyl halide groups, such as
bis(4-chlorocarbonylphenyl)disulfide,
bis(2,4,6-tri(chlorocarbonyl)phenyl)disulfide, and
bis(penta(chlorocarbonyl)phenyl)disulfide; diphenyl disulfides
substituted with sulfo groups, such as bis(4-sulfophenyl)disulfide,
bis(2,4,6-trisulfophenyl)disulfide, and
bis(pentasulfophenyl)disulfide; diphenyl disulfides substituted
with alkoxysulfonyl groups, such as
bis(4-methoxysulfonylphenyl)disulfide,
bis(2,4,6-trimethoxysulfonylphenyl)disulfide, and
bis(pentamethoxysulfonylphenyl)disulfide; diphenyl disulfides
substituted with sulfonyl halide groups, such as
bis(4-chlorosulfonylphenyl)disulfide,
bis(2,4,6-tri(chlorosulfonyl)phenyl)disulfide, and
bis(penta(chlorosulfonyl)phenyl)disulfide; diphenyl disulfides
substituted with sulfino groups, such as
bis(4-sulfinophenyl)disulfide,
bis(2,4,6-trisulfinophenyl)disulfide, and
bis(pentasulfinophenyl)disulfide; diphenyl disulfides substituted
with alkylsulfinyl groups, such as
bis(4-methylsulfinylphenyl)disulfide,
bis(2,4,6-tri(methylsulfinyl)phenyl)disulfide, and
bis(penta(methylsulfinyl)phenyl)disulfide; diphenyl disulfides
substituted with carbamoyl groups, such as
bis(4-carbamoylphenyl)disulfide,
bis(2,4,6-tricarbamoylphenyl)disulfide, and
bis(pentacarbamoylphenyl)disulfide; diphenyl disulfides substituted
with alkyl halide groups, such as
bis(4-trichloromethylphenyl)disulfide,
bis(2,4,6-tri(trichloromethyl)phenyl)disulfide, and
bis(penta(trichloromethyl)phenyl)disulfide; diphenyl disulfides
substituted with cyano groups, such as bis(4-cyanophenyl)disulfide,
bis(2,4,6-tricyanophenyl)disulfide, and
bis(pentacyanophenyl)disulfide; and diphenyl disulfides substituted
with alkoxy groups, such as bis(4-methoxyphenyl)disulfide,
bis(2,4,6-trimethoxyphenyl)disulfide, and
bis(pentamethoxyphenyl)disulfide. Each of these diphenyl disulfides
is substituted with one type of substituent.
[0137] Another example of the organic sulfur compound represented
by the chemical formula (2) is a compound substituted with at least
one type of the above substituents and another substituent.
Examples of the other substituent include a nitro group
(--NO.sub.2), an amino group (--NH.sub.2), a hydroxyl group (--OH),
and a phenylthio group (--SPh). Specific examples of the compound
include bis(4-chloro-2-nitrophenyl)disulfide,
bis(4-chloro-2-aminophenyl)disulfide,
bis(4-chloro-2-hydroxyphenyl)disulfide,
bis(4-chloro-2-phenylthiophenyl)disulfide,
bis(4-methyl-2-nitrophenyl)disulfide,
bis(4-methyl-2-aminophenyl)disulfide,
bis(4-methyl-2-hydroxyphenyl)disulfide,
bis(4-methyl-2-phenylthiophenyl)disulfide,
bis(4-carboxy-2-nitrophenyl)disulfide,
bis(4-carboxy-2-aminophenyl)disulfide,
bis(4-carboxy-2-hydroxyphenyl)disulfide,
bis(4-carboxy-2-phenylthiophenyl)disulfide,
bis(4-methoxycarbonyl-2-nitrophenyl)disulfide,
bis(4-methoxycarbonyl-2-aminophenyl)disulfide,
bis(4-methoxycarbonyl-2-hydroxyphenyl)disulfide,
bis(4-methoxycarbonyl-2-phenylthiophenyl)disulfide,
bis(4-formyl-2-nitrophenyl)disulfide,
bis(4-formyl-2-aminophenyl)disulfide,
bis(4-formyl-2-hydroxyphenyl)disulfide,
bis(4-formyl-2-phenylthiophenyl)disulfide,
bis(4-acetyl-2-nitrophenyl)disulfide,
bis(4-acetyl-2-aminophenyl)disulfide,
bis(4-acetyl-2-hydroxyphenyl)disulfide,
bis(4-acetyl-2-phenylthiophenyl)disulfide,
bis(4-chlorocarbonyl-2-nitrophenyl)disulfide,
bis(4-chlorocarbonyl-2-aminophenyl)disulfide,
bis(4-chlorocarbonyl-2-hydroxyphenyl)disulfide,
bis(4-chlorocarbonyl-2-phenylthiophenyl)disulfide,
bis(4-sulfo-2-nitrophenyl)disulfide,
bis(4-sulfo-2-aminophenyl)disulfide,
bis(4-sulfo-2-hydroxyphenyl)disulfide,
bis(4-sulfo-2-phenylthiophenyl)disulfide,
bis(4-methoxysulfonyl-2-nitrophenyl)disulfide,
bis(4-methoxysulfonyl-2-aminophenyl)disulfide,
bis(4-methoxysulfonyl-2-hydroxyphenyl)disulfide,
bis(4-methoxysulfonyl-2-phenylthiophenyl)disulfide,
bis(4-chlorosulfonyl-2-nitrophenyl)disulfide,
bis(4-chlorosulfonyl-2-aminophenyl)disulfide,
bis(4-chlorosulfonyl-2-hydroxyphenyl)disulfide,
bis(4-chlorosulfonyl-2-phenylthiophenyl)disulfide,
bis(4-sulfino-2-nitrophenyl)disulfide,
bis(4-sulfino-2-aminophenyl)disulfide,
bis(4-sulfino-2-hydroxyphenyl)disulfide,
bis(4-sulfino-2-phenylthiophenyl)disulfide,
bis(4-methylsulfinyl-2-nitrophenyl)disulfide,
bis(4-methylsulfinyl-2-aminophenyl)disulfide,
bis(4-methylsulfinyl-2-hydroxyphenyl)disulfide,
bis(4-methylsulfinyl-2-phenylthiophenyl)disulfide,
bis(4-carbamoyl-2-nitrophenyl)disulfide,
bis(4-carbamoyl-2-aminophenyl)disulfide,
bis(4-carbamoyl-2-hydroxyphenyl)disulfide,
bis(4-carbamoyl-2-phenylthiophenyl)disulfide,
bis(4-trichloromethyl-2-nitrophenyl)disulfide,
bis(4-trichloromethyl-2-aminophenyl)disulfide,
bis(4-trichloromethyl-2-hydroxyphenyl)disulfide,
bis(4-trichloromethyl-2-phenylthiophenyl)disulfide,
bis(4-cyano-2-nitrophenyl)disulfide,
bis(4-cyano-2-aminophenyl)disulfide,
bis(4-cyano-2-hydroxyphenyl)disulfide,
bis(4-cyano-2-phenylthiophenyl)disulfide,
bis(4-methoxy-2-nitrophenyl)disulfide,
bis(4-methoxy-2-aminophenyl)disulfide,
bis(4-methoxy-2-hydroxyphenyl)disulfide, and
bis(4-methoxy-2-phenylthiophenyl)disulfide.
[0138] Still another example of the organic sulfur compound
represented by the chemical formula (2) is a compound substituted
with two or more types of substituents. Specific examples of the
compound include bis(4-acetyl-2-chlorophenyl)disulfide,
bis(4-acetyl-2-methylphenyl)disulfide,
bis(4-acetyl-2-carboxyphenyl)disulfide,
bis(4-acetyl-2-methoxycarbonylphenyl)disulfide,
bis(4-acetyl-2-formylphenyl)disulfide,
bis(4-acetyl-2-chlorocarbonylphenyl)disulfide,
bis(4-acetyl-2-sulfophenyl)disulfide,
bis(4-acetyl-2-methoxysulfonylphenyl)disulfide,
bis(4-acetyl-2-chlorosulfonylphenyl)disulfide,
bis(4-acetyl-2-sulfinophenyl)disulfide,
bis(4-acetyl-2-methylsulfinylphenyl)disulfide,
bis(4-acetyl-2-carbamoylphenyl)disulfide,
bis(4-acetyl-2-trichloromethylphenyl)disulfide,
bis(4-acetyl-2-cyanophenyl)disulfide, and
bis(4-acetyl-2-methoxyphenyl)disulfide.
[0139] Examples of the organic sulfur compound represented by the
chemical formula (3) include thiophenol sodium salt; thiophenol
sodium salts substituted with halogen groups, such as
4-fluorothiophenol sodium salt, 2,5-difluorothiophenol sodium salt,
2,4,5-trifluorothiophenol sodium salt,
2,4,5,6-tetrafluorothiophenol sodium salt, pentafluorothiophenol
sodium salt, 4-chlorothiophenol sodium salt, 2,5-dichlorothiophenol
sodium salt, 2,4,5-trichlorothiophenol sodium salt,
2,4,5,6-tetrachlorothiophenol sodium salt, pentachlorothiophenol
sodium salt, 4-bromothiophenol sodium salt, 2,5-dibromothiophenol
sodium salt, 2,4,5-tribromothiophenol sodium salt,
2,4,5,6-tetrabromothiophenol sodium salt, pentabromothiophenol
sodium salt, 4-iodothiophenol sodium salt, 2,5-diiodothiophenol
sodium salt, 2,4,5-triiodothiophenol sodium salt,
2,4,5,6-tetraiodothiophenol sodium salt, and pentaiodothiophenol
sodium salt; thiophenol sodium salts substituted with alkyl groups,
such as4-methylthiophenolsodium salt, 2,4,5-trimethylthiophenol
sodium salt, pentamethylthiophenol sodium salt, 4-t-butylthiophenol
sodium salt, 2,4,5-tri-t-butylthiophenol sodium salt, and
penta(t-butyl)thiophenol sodium salt; thiophenol sodium salts
substituted with carboxyl groups, such as 4-carboxythiophenol
sodium salt, 2,4,6-tricarboxythiophenol sodium salt, and
pentacarboxythiophenol sodium salt; thiophenol sodium salts
substituted with alkoxycarbonyl groups, such as
4-methoxycarbonylthiophenol sodium salt,
2,4,6-trimethoxycarbonylthiophenol sodium salt, and
pentamethoxycarbonylthiophenol sodium salt; thiophenol sodium salts
substituted with formyl groups, such as 4-formylthiophenol sodium
salt, 2,4,6-triformylthiophenol sodium salt, and
pentaformylthiophenol sodium salt; thiophenol sodium salts
substituted with acyl groups, such as 4-acetylthiophenol sodium
salt, 2,4,6-triacetylthiophenol sodium salt, and
pentaacetylthiophenol sodium salt; thiophenol sodium salts
substituted with carbonyl halide groups, such as
4-chlorocarbonylthiophenol sodium salt,
2,4,6-tri(chlorocarbonyl)thiophenol sodium salt, and
penta(chlorocarbonyl)thiophenol sodium salt; thiophenol sodium
salts substituted with sulfo groups, such as 4-sulfothiophenol
sodium salt, 2,4,6-trisulfothiophenol sodium salt, and
pentasulfothiophenol sodium salt; thiophenol sodium salts
substituted with alkoxysulfonyl groups, such as
4-methoxysulfonylthiophenol sodium salt,
2,4,6-trimethoxysulfonylthiophenol sodium salt, and
pentamethoxysulfonylthiophenol sodium salt; thiophenol sodium salts
substituted with sulfonyl halide groups, such as
4-chlorosulfonylthiophenol sodium salt,
2,4,6-tri(chlorosulfonyl)thiophenol sodium salt, and
penta(chlorosulfonyl)thiophenol sodium salt; thiophenol sodium
salts substituted with sulfino groups, such as 4-sulfinothiophenol
sodium salt, 2,4,6-trisulfinothiophenol sodium salt, and
pentasulfinothiophenol sodium salt; thiophenol sodium salts
substituted with alkylsulfinyl groups, such as
4-methylsulfinylthiophenol sodium salt,
2,4,6-tri(methylsulfinyl)thiophenol sodium salt, and penta
(methylsulfinyl)thiophenol sodium salt; thiophenol sodium salts
substituted with carbamoyl groups, such as 4-carbamoylthiophenol
sodium salt, 2,4,6-tricarbamoylthiophenol sodium salt, and
pentacarbamoylthiophenol sodium salt; thiophenol sodium salts
substituted with alkyl halide groups, such as
4-trichloromethylthiophenol sodium salt,
2,4,6-tri(trichloromethyl)thiophenol sodium salt, and
penta(trichloromethyl)thiophenol sodium salt; thiophenol sodium
salts substituted with cyano groups, such as 4-cyanothiophenol
sodium salt, 2,4,6-tricyanothiophenol sodium salt, and
pentacyanothiophenol sodium salt; and thiophenol sodium salts
substituted with alkoxy groups, such as 4-methoxythiophenol sodium
salt, 2,4,6-trimethoxythiophenol sodium salt, and
pentamethoxythiophenol sodium salt. Each of these thiophenol sodium
salts is substituted with one type of substituent.
[0140] Another example of the organic sulfur compound represented
by the chemical formula (3) is a compound substituted with at least
one type of the above substituents and another substituent.
Examples of the other substituent include a nitro group
(--NO.sub.2), an amino group (--NH.sub.2), a hydroxyl group (--OH),
and a phenylthio group (--SPh). Specific examples of the compound
include 4-chloro-2-nitrothiophenol sodium salt,
4-chloro-2-aminothiophenol sodium salt,
4-chloro-2-hydroxythiophenol sodium salt,
4-chloro-2-phenylthiothiophenol sodium salt,
4-methyl-2-nitrothiophenol sodium salt, 4-methyl-2-aminothiophenol
sodium salt, 4-methyl-2-hydroxythiophenol sodium salt,
4-methyl-2-phenylthiothiophenol sodium salt,
4-carboxy-2-nitrothiophenol sodium salt,
4-carboxy-2-aminothiophenol sodium salt,
4-carboxy-2-hydroxythiophenol sodium salt,
4-carboxy-2-phenylthiothiophenol sodium salt,
4-methoxycarbonyl-2-nitrothiophenol sodium salt,
4-methoxycarbonyl-2-aminothiophenol sodium salt,
4-methoxycarbonyl-2-hydroxythiophenol sodium salt,
4-methoxycarbonyl-2-phenylthiothiophenol sodium salt,
4-formyl-2-nitrothiophenol sodium salt, 4-formyl-2-aminothiophenol
sodium salt, 4-formyl-2-hydroxythiophenol sodium salt,
4-formyl-2-phenylthiothiophenol sodium salt,
4-acetyl-2-nitrothiophenol sodium salt, 4-acetyl-2-aminothiophenol
sodium salt, 4-acetyl-2-hydroxythiophenol sodium salt,
4-acetyl-2-phenylthiothiophenol sodium salt,
4-chlorocarbonyl-2-nitrothiophenol sodium salt,
4-chlorocarbonyl-2-aminothiophenol sodium salt,
4-chlorocarbonyl-2-hydroxythiophenol sodium salt,
4-chlorocarbonyl-2-phenylthiothiophenol sodium salt,
4-sulfo-2-nitrothiophenol sodium salt, 4-sulfo-2-aminothiophenol
sodium salt, 4-sulfo-2-hydroxythiophenol sodium salt,
4-sulfo-2-phenylthiothiophenol sodium salt,
4-methoxysulfonyl-2-nitrothiophenol sodium salt,
4-methoxysulfonyl-2-aminothiophenol sodium salt,
4-methoxysulfonyl-2-hydroxythiophenol sodium salt,
4-methoxysulfonyl-2-phenylthiothiophenol sodium salt,
4-chlorosulfonyl-2-nitrothiophenol sodium salt,
4-chlorosulfonyl-2-aminothiophenol sodium salt,
4-chlorosulfonyl-2-hydroxythiophenol sodium salt,
4-chlorosulfonyl-2-phenylthiothiophenol sodium salt,
4-sulfino-2-nitrothiophenol sodium salt,
4-sulfino-2-aminothiophenol sodium salt,
4-sulfino-2-hydroxythiophenol sodium salt,
4-sulfino-2-phenylthiothiophenol sodium salt,
4-methylsulfinyl-2-nitrothiophenol sodium salt,
4-methylsulfinyl-2-aminothiophenol sodium salt,
4-methylsulfinyl-2-hydroxythiophenol sodium salt,
4-methylsulfinyl-2-phenylthiothiophenol sodium salt,
4-carbamoyl-2-nitrothiophenol sodium salt,
4-carbamoyl-2-aminothiophenol sodium salt,
4-carbamoyl-2-hydroxythiophenol sodium salt,
4-carbamoyl-2-phenylthiothiophenol sodium salt,
4-trichloromethyl-2-nitrothiophenol sodium salt,
4-trichloromethyl-2-aminothiophenol sodium salt,
4-trichloromethyl-2-hydroxythiophenol sodium salt,
4-trichloromethyl-2-phenylthiothiophenol sodium salt,
4-cyano-2-nitrothiophenol sodium salt, 4-cyano-2-aminothiophenol
sodium salt, 4-cyano-2-hydroxythiophenol sodium salt,
4-cyano-2-phenylthiothiophenol sodium salt,
4-methoxy-2-nitrothiophenol sodium salt,
4-methoxy-2-aminothiophenol sodium salt,
4-methoxy-2-hydroxythiophenol sodium salt, and
4-methoxy-2-phenylthiothiophenol sodium salt.
[0141] Still another example of the organic sulfur compound
represented by the chemical formula (3) is a compound substituted
with two or more types of substituents. Specific examples of the
compound include 4-acetyl-2-chlorothiophenol sodium salt,
4-acetyl-2-methylthiophenol sodium salt,
4-acetyl-2-carboxythiophenol sodium salt,
4-acetyl-2-methoxycarbonylthiophenol sodium salt,
4-acetyl-2-formylthiophenol sodium salt,
4-acetyl-2-chlorocarbonylthiophenol sodium salt,
4-acetyl-2-sulfothiophenol sodium salt,
4-acetyl-2-methoxysulfonylthiophenol sodium salt,
4-acetyl-2-chlorosulfonylthiophenol sodium salt,
4-acetyl-2-sulfinothiophenol sodium salt,
4-acetyl-2-methylsulfinylthiophenol sodium salt,
4-acetyl-2-carbamoylthiophenol sodium salt,
4-acetyl-2-trichloromethylthiophenol sodium salt,
4-acetyl-2-cyanothiophenol sodium salt, and
4-acetyl-2-methoxythiophenol sodium salt. Examples of the
monovalent metal represented by M1 in the chemical formula (3)
include sodium, lithium, potassium, copper (I), and silver (I).
[0142] Examples of the organic sulfur compound represented by the
chemical formula (4) include thiophenol zinc salt; thiophenol zinc
salts substituted with halogen groups, such as 4-fluorothiophenol
zinc salt, 2,5-difluorothiophenol zinc salt,
2,4,5-trifluorothiophenol zinc salt, 2,4,5,6-tetrafluorothiophenol
zinc salt, pentafluorothiophenol zinc salt, 4-chlorothiophenol zinc
salt, 2,5-dichlorothiophenol zinc salt, 2,4,5-trichlorothiophenol
zinc salt, 2,4,5,6-tetrachlorothiophenol zinc salt,
pentachlorothiophenol zinc salt, 4-bromothiophenol zinc salt,
2,5-dibromothiophenol zinc salt, 2,4,5-tribromothiophenol zinc
salt, 2,4,5,6-tetrabromothiophenol zinc salt, pentabromothiophenol
zinc salt, 4-iodothiophenol zinc salt, 2,5-diiodothiophenol zinc
salt, 2,4,5-triiodothiophenol zinc salt,
2,4,5,6-tetraiodothiophenol zinc salt, and pentaiodothiophenol zinc
salt; thiophenol zinc salts substituted with alkyl groups, such as
4-methylthiophenol zinc salt, 2,4,5-trimethylthiophenol zinc salt,
pentamethylthiophenol zinc salt, 4-t-butylthiophenol zinc salt,
2,4,5-tri-t-butylthiophenol zinc salt, and penta-t-butylthiophenol
zinc salt; thiophenol zinc salts substituted with carboxyl groups,
such as 4-carboxythiophenol zinc salt, 2,4,6-tricarboxythiophenol
zinc salt, and pentacarboxythiophenol zinc salt; thiophenol zinc
salts substituted with alkoxycarbonyl groups, such as
4-methoxycarbonylthiophenol zinc salt,
2,4,6-trimethoxycarbonylthiophenol zinc salt, and
pentamethoxycarbonylthiophenol zinc salt; thiophenol zinc salts
substituted with formyl groups, such as 4-formylthiophenol zinc
salt, 2,4,6-triformylthiophenol zinc salt, and
pentaformylthiophenol zinc salt; thiophenol zinc salts substituted
with acyl groups, such as 4-acetylthiophenol zinc salt,
2,4,6-triacetylthiophenol zinc salt, and pentaacetylthiophenol zinc
salt; thiophenol zinc salts substituted with carbonyl halide
groups, such as 4-chlorocarbonylthiophenol zinc salt,
2,4,6-tri(chlorocarbonyl)thiophenol zinc salt, and
penta(chlorocarbonyl)thiophenol zinc salt; thiophenol zinc salts
substituted with sulfo groups, such as 4-sulfothiophenol zinc salt,
2,4,6-trisulfothiophenol zinc salt, and pentasulfothiophenol zinc
salt; thiophenol zinc salts substituted with alkoxysulfonyl groups,
such as 4-methoxysulfonylthiophenol zinc salt,
2,4,6-trimethoxysulfonylthiophenol zinc salt, and
pentamethoxysulfonylthiophenol zinc salt; thiophenol zinc salts
substituted with sulfonyl halide groups, such as
4-chlorosulfonylthiophenol zinc salt,
2,4,6-tri(chlorosulfonyl)thiophenol zinc salt, and
penta(chlorosulfonyl)thiophenol zinc salt; thiophenol zinc salts
substituted with sulfino groups, such as 4-sulfinothiophenol zinc
salt, 2,4,6-trisulfinothiophenol zinc salt, and
pentasulfinothiophenol zinc salt; thiophenol zinc salts substituted
with alkylsulfinyl groups, such as 4-methylsulfinylthiophenol zinc
salt, 2,4,6-tri(methylsulfinyl)thiophenol zinc salt, and
penta(methylsulfinyl)thiophenol zinc salt; thiophenol zinc salts
substituted with carbamoyl groups, such as
4-carbamoylthiophenolzincsalt, 2,4,6-tricarbamoylthiophenol zinc
salt, and pentacarbamoylthiophenol zinc salt; thiophenol zinc salts
substituted with alkyl halide groups, such as
4-trichloromethylthiophenol zinc salt,
2,4,6-tri(trichloromethyl)thiophenol zinc salt, and
penta(trichloromethyl)thiophenol zinc salt; thiophenol zinc salts
substituted with cyano groups, such as 4-cyanothiophenol zinc salt,
2,4,6-tricyanothiophenol zinc salt, and pentacyanothiophenol zinc
salt; and thiophenol zinc salts substituted with alkoxy groups,
such as 4-methoxythiophenol zinc salt, 2,4,6-trimethoxythiophenol
zinc salt, and pentamethoxythiophenol zinc salt. Each of these
thiophenol zinc salts is substituted with one type of
substituent.
[0143] Another example of the organic sulfur compound represented
by the chemical formula (4) is a compound substituted with at least
one type of the above substituents and another substituent.
Examples of the other substituent include a nitro group
(--NO.sub.2), an amino group (--NH.sub.2), a hydroxyl group (--OH),
and a phenylthio group (--SPh). Specific examples of the compound
include 4-chloro-2-nitrothiophenol zinc salt,
4-chloro-2-aminothiophenol zinc salt, 4-chloro-2-hydroxythiophenol
zinc salt, 4-chloro-2-phenylthiothiophenol zinc salt,
4-methyl-2-nitrothiophenol zinc salt, 4-methyl-2-aminothiophenol
zinc salt, 4-methyl-2-hydroxythiophenol zinc salt,
4-methyl-2-phenylthiothiophenol zinc salt,
4-carboxy-2-nitrothiophenol zinc salt, 4-carboxy-2-aminothiophenol
zinc salt, 4-carboxy-2-hydroxythiophenol zinc salt,
4-carboxy-2-phenylthiothiophenol zinc salt,
4-methoxycarbonyl-2-nitrothiophenol zinc salt,
4-methoxycarbonyl-2-aminothiophenol zinc salt,
4-methoxycarbonyl-2-hydroxythiophenol zinc salt,
4-methoxycarbonyl-2-phenylthiothiophenol zinc salt,
4-formyl-2-nitrothiophenol zinc salt, 4-formyl-2-aminothiophenol
zinc salt, 4-formyl-2-hydroxythiophenol zinc salt,
4-formyl-2-phenylthiothiophenol zinc salt,
4-acetyl-2-nitrothiophenol zinc salt, 4-acetyl-2-aminothiophenol
zinc salt, 4-acetyl-2-hydroxythiophenol zinc salt,
4-acetyl-2-phenylthiothiophenol zinc salt,
4-chlorocarbonyl-2-nitrothiophenol zinc salt,
4-chlorocarbonyl-2-aminothiophenol zinc salt,
4-chlorocarbonyl-2-hydroxythiophenol zinc salt,
4-chlorocarbonyl-2-phenylthiothiophenol zinc salt,
4-sulfo-2-nitrothiophenol zinc salt, 4-sulfo-2-aminothiophenol zinc
salt, 4-sulfo-2-hydroxythiophenol zinc salt,
4-sulfo-2-phenylthiothiophenol zinc salt,
4-methoxysulfonyl-2-nitrothiophenol zinc salt,
4-methoxysulfonyl-2-aminothiophenol zinc salt,
4-methoxysulfonyl-2-hydroxythiophenol zinc salt,
4-methoxysulfonyl-2-phenylthiothiophenol zinc salt,
4-chlorosulfonyl-2-nitrothiophenol zinc salt,
4-chlorosulfonyl-2-aminothiophenol zinc salt,
4-chlorosulfonyl-2-hydroxythiophenol zinc salt,
4-chlorosulfonyl-2-phenylthiothiophenol zinc salt,
4-sulfino-2-nitrothiophenol zinc salt, 4-sulfino-2-aminothiophenol
zinc salt, 4-sulfino-2-hydroxythiophenol zinc salt,
4-sulfino-2-phenylthiothiophenol zinc salt,
4-methylsulfinyl-2-nitrothiophenol zinc salt,
4-methylsulfinyl-2-aminothiophenol zinc salt,
4-methylsulfinyl-2-hydroxythiophenol zinc salt,
4-methylsulfinyl-2-phenylthiothiophenol zinc salt,
4-carbamoyl-2-nitrothiophenol zinc salt,
4-carbamoyl-2-aminothiophenol zinc salt,
4-carbamoyl-2-hydroxythiophenol zinc salt,
4-carbamoyl-2-phenylthiothiophenol zinc salt,
4-trichloromethyl-2-nitrothiophenol zinc salt,
4-trichloromethyl-2-aminothiophenol zinc salt,
4-trichloromethyl-2-hydroxythiophenol zinc salt,
4-trichloromethyl-2-phenylthiothiophenol zinc salt,
4-cyano-2-nitrothiophenol zinc salt, 4-cyano-2-aminothiophenol zinc
salt, 4-cyano-2-hydroxythiophenol zinc salt,
4-cyano-2-phenylthiothiophenol zinc salt,
4-methoxy-2-nitrothiophenol zinc salt, 4-methoxy-2-aminothiophenol
zinc salt, 4-methoxy-2-hydroxythiophenol zinc salt, and
4-methoxy-2-phenylthiothiophenol zinc salt.
[0144] Still another example of the organic sulfur compound
represented by the chemical formula (4) is a compound substituted
with two or more types of substituents. Specific examples of the
compound include 4-acetyl-2-chlorothiophenol zinc salt,
4-acetyl-2-methylthiophenol zinc salt, 4-acetyl-2-carboxythiophenol
zinc salt, 4-acetyl-2-methoxycarbonylthiophenol zinc salt,
4-acetyl-2-formylthiophenol zinc salt,
4-acetyl-2-chlorocarbonylthiophenol zinc salt,
4-acetyl-2-sulfothiophenol zinc salt,
4-acetyl-2-methoxysulfonylthiophenol zinc salt,
4-acetyl-2-chlorosulfonylthiophenol zinc salt,
4-acetyl-2-sulfinothiophenol zinc salt,
4-acetyl-2-methylsulfinylthiophenol zinc salt,
4-acetyl-2-carbamoylthiophenol zinc salt,
4-acetyl-2-trichloromethylthiophenol zinc salt,
4-acetyl-2-cyanothiophenol zinc salt, and
4-acetyl-2-methoxythiophenol zinc salt. Examples of the bivalent
metal represented by M2 in the chemical formula (4) include zinc,
magnesium, calcium, strontium, barium, titanium (II), manganese
(II), iron (II), cobalt (II), nickel (II), zirconium (II), and tin
(II).
[0145] Examples of thionaphthols include 2-thionaphthol,
1-thionaphthol, 2-chloro-1-thionaphthol, 2-bromo-1-thionaphthol,
2-fluoro-1-thionaphthol, 2-cyano-1-thionaphthol,
2-acetyl-1-thionaphthol, 1-chloro-2-thionaphthol,
1-bromo-2-thionaphthol, 1-fluoro-2-thionaphthol,
1-cyano-2-thionaphthol, 1-acetyl-2-thionaphthol, and metal salts
thereof. 1-thionaphthol, 2-thionaphthol, and zinc salts thereof are
preferred.
[0146] Examples of sulfenamide type organic sulfur compounds
include N-cyclohexyl-2-benzothiazole sulfenamide,
N-oxydiethylene-2-benzothiazole sulfenamide, and
N-t-butyl-2-benzothiazole sulfenamide. Examples of thiuram type
organic sulfur compounds include tetramethylthiuram monosulfide,
tetramethylthiuram disulfide, tetraethylthiuram disulfide,
tetrabutylthiuram disulfide, and dipentamethylenethiuram
tetrasulfide. Examples of dithiocarbamates include zinc
dimethyldithiocarbamate, zinc diethyldithiocarbamate, zinc
dibutyldithiocarbamate, zinc ethylphenyldithiocarbamate, sodium
dimethyldithiocarbamate, sodium diethyldithiocarbamate, copper (II)
dimethyldithiocarbamate, iron (III) dimethyldithiocarbamate,
selenium diethyldithiocarbamate, and tellurium
diethyldithiocarbamate. Examples of thiazole type organic sulfur
compounds include 2-mercaptobenzothiazole (MBT); dibenzothiazyl
disulfide (MBTS); a sodium salt, a zinc salt, a copper salt, or a
cyclohexylamine salt of 2-mercaptobenzothiazole;
2-(2,4-dinitrophenyl) mercaptobenzothiazole; and
2-(2,6-diethyl-4-morpholinothio)benzothiazole
[0147] From the standpoint that an outer-hard/inner-soft structure
is easily obtained, particularly preferable organic sulfur
compounds (e) are 2-thionaphthol, bis(pentabromophenyl)disulfide,
and 2,6-dichlorothiophenol.
[0148] From the standpoint that an outer-hard/inner-soft structure
is easily obtained, the amount of the organic sulfur compound (e)
is preferably equal to or greater than 0.05 parts by weight, more
preferably equal to or greater than 0.1 parts by weight, and
particularly preferably equal to or greater than 0.2 parts by
weight, per 100 parts by weight of the base rubber. In light of
resilience performance, the amount is preferably equal to or less
than 5.0 parts by weight, more preferably equal to or less than 3.0
parts by weight, and particularly preferably equal to or less than
1.0 parts by weight, per 100 parts by weight of the base
rubber.
[0149] For the purpose of adjusting specific gravity and the like,
a filler may be included in the envelope layer 12. Examples of
suitable fillers include zinc oxide, barium sulfate, calcium
carbonate, and magnesium carbonate. The amount of the filler is
determined as appropriate so that the intended specific gravity of
the core 4 is accomplished. A particularly preferable filler is
zinc oxide. Zinc oxide serves not only as a specific gravity
adjuster but also as a crosslinking activator.
[0150] According to need, an anti-aging agent, a coloring agent, a
plasticizer, a dispersant, sulfur, a vulcanization accelerator, and
the like are added to the rubber composition of the envelope layer
12. Crosslinked rubber powder or synthetic resin powder may also be
dispersed in the rubber composition.
[0151] During heating and forming of the core 4, the base rubber
(a) is crosslinked by the co-crosslinking agent (b). The heat of
the crosslinking reaction remains near the central point of the
core 4. Thus, during heating and forming of the core 4, the
temperature at the central portion is high. The temperature
gradually decreases from the central point toward the surface. It
is inferred that in the rubber composition, the acid reacts with
the metal salt of the co-crosslinking agent (b) to bond to cation.
It is inferred that in the rubber composition, the salt reacts with
the metal salt of the co-crosslinking agent (b) to exchange cation.
By the bonding and the exchange, metal crosslinks are broken. The
bonding and the exchange are likely to occur near the innermost
portion of the envelope layer 12 where the temperature is high, and
are unlikely to occur near the surface of the envelope layer 12. In
other words, breaking of metal crosslinks is likely to occur near
the innermost portion of the envelope layer 12 and is unlikely to
occur near the surface of the envelope layer 12. As a result, the
crosslinking density of the envelope layer 12 increases from its
inside toward its outside. In the envelope layer 12, the hardness
linearly increases from its inside toward its outside. Furthermore,
since the rubber composition includes the organic sulfur compound
(e) together with the acid and/or the salt (d), the gradient of the
hardness distribution can be controlled, and the degree of the
outer-hard/inner-soft structure of the core 4 can be increased.
[0152] The hardness H(0.0) at the central point of the core 4 is
preferably equal to or greater than 40.0 but equal to or less than
70.0. The golf ball 2 having a hardness H(0.0) of 40.0 or greater
has excellent resilience performance. In this respect, the hardness
H(0.0) is more preferably equal to or greater than 45.0 and
particularly preferably equal to or greater than 47.0. In the core
4 having a hardness H(0.0) of 70.0 or less, an
outer-hard/inner-soft structure can be achieved. In the golf ball 2
that includes the core 4, spin can be suppressed. In this respect,
the hardness H(0.0) is more preferably equal to or less than 68.0
and particularly preferably equal to or less than 65.0.
[0153] The hardness Hs at the surface of the core 4 is preferably
equal to or greater than 75.0 but equal to or less than 95.0. In
the core 4 having a hardness Hs of 75.0 or greater, an
outer-hard/inner-soft structure can be achieved. In the golf ball 2
that includes the core 4, spin can be suppressed. In this respect,
the hardness Hs is more preferably equal to or greater than 80.0
and particularly preferably equal to or greater than 82.0. The golf
ball 2 having a hardness Hs of 95.0 or less has excellent
durability. In this respect, the hardness Hs is more preferably
equal to or less than 94.0 and particularly preferably equal to or
less than 92.0.
[0154] The core 4 preferably has a diameter of 38.0 mm or greater
but 41.5 mm or less. The core 4 having a diameter of 38.0 mm or
greater can achieve excellent resilience performance of the golf
ball 2. In this respect, the diameter is more preferably equal to
or greater than 38.5 mm and particularly preferably equal to or
greater than 39.0 mm. In the golf ball 2 that includes the core 4
having a diameter of 41.5 mm or less, the inner cover 6 and the
outer cover 8 can have sufficient thicknesses. The golf ball 2 that
includes the inner cover 6 and the outer cover 8 which have large
thicknesses has excellent durability. In this respect, the diameter
is more preferably equal to or less than 41.0 mm and particularly
preferably equal to or less than 40.5 mm.
[0155] In light of feel at impact, the core 4 has an amount of
compressive deformation Dc of preferably 3.5 mm or greater and
particularly preferably 3.8 mm or greater. In light of resilience
performance of the core 4, the amount of compressive deformation Dc
is preferably equal to or less than 4.5 mm and particularly
preferably equal to or less than 4.0 mm.
[0156] For the inner cover 6, a resin composition is suitably used.
Examples of the base polymer of the resin composition include
ionomer resins, polystyrenes, polyesters, polyamides, and
polyolefins.
[0157] Particularly preferable base polymers are ionomer resins.
The golf ball 2 that includes the inner cover 6 including an
ionomer resin has excellent resilience performance. An ionomer
resin and another resin may be used in combination for the inner
cover 6. In this case, the principal component of the base polymer
is preferably the ionomer resin. Specifically, the proportion of
the ionomer resin to the entire base polymer is preferably equal to
or greater than 50% by weight, more preferably equal to or greater
than 60% by weight, and particularly preferably equal to or greater
than 70% by weight.
[0158] Examples of preferable ionomer resins include binary
copolymers formed with an .alpha.-olefin and an
.alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon
atoms. A preferable binary copolymer includes 80% by weight or
greater but 90% by weight or less of an .alpha.-olefin, and 10% by
weight or greater but 20% by weight or less of an
.alpha.,.beta.-unsaturated carboxylic acid. The binary copolymer
has excellent resilience performance. Examples of other preferable
ionomer resins include ternary copolymers formed with: an
.alpha.-olefin; an .alpha.,.beta.-unsaturated carboxylic acid
having 3 to 8 carbon atoms; and an .alpha.,.beta.-unsaturated
carboxylate ester having 2 to 22 carbon atoms. A preferable ternary
copolymer includes 70% by weight or greater but 85% by weight or
less of an .alpha.-olefin, 5% by weight or greater but 30% by
weight or less of an .alpha.,.beta.-unsaturated carboxylic acid,
and 1% by weight or greater but 25% by weight or less of an
.alpha.,.beta.-unsaturated carboxylate ester. The ternary copolymer
has excellent resilience performance. For the binary copolymers and
the ternary copolymers, preferable .alpha.-olefins are ethylene and
propylene, while preferable .alpha.,.beta.-unsaturated carboxylic
acids are acrylic acid and methacrylic acid. Particularly
preferable ionomer resins are a copolymer formed with ethylene and
acrylic acid and a copolymer formed with ethylene and methacrylic
acid.
[0159] In the binary copolymers and the ternary copolymers, some of
the carboxyl groups are neutralized with metal ions. Examples of
metal ions for use in neutralization include sodium ion, potassium
ion, lithium ion, zinc ion, calcium ion, magnesium ion, aluminum
ion, and neodymium ion. The neutralization may be carried out with
two or more types of metal ions. Particularly suitable metal ions
in light of resilience performance and durability of the golf ball
2 are sodium ion, zinc ion, lithium ion, and magnesium ion.
Specific examples of ionomer resins include trade names
[0160] "Himilan 1555", "Himilan 1557", "Himilan 1605", "Himilan
1706", "Himilan 1707", "Himilan 1856", "Himilan 1855", "Himilan
AM7311", "Himilan AM7315", "Himilan AM7317", "Himilan AM7318",
"Himilan AM7329", "Himilan AM7337", "Himilan MK7320", and "Himilan
MK7329", manufactured by Du Pont-MITSUI POLYCHEMICALS Co., Ltd.;
trade names "Surlyn 6120", "Surlyn 6910", "Surlyn 7930", "Surlyn
7940", "Surlyn 8140", "Surlyn 8150", "Surlyn 8940", "Surlyn 8945",
"Surlyn 9120", "Surlyn 9150", "Surlyn 9910", "Surlyn 9945", "Surlyn
AD8546", "HPF1000", and "HPF2000", manufactured by E.I. du Pont de
Nemours and Company; and trade names "IOTEK 7010", "IOTEK 7030",
"IOTEK 7510", "IOTEK 7520", "IOTEK 8000", and "IOTEK 8030",
manufactured by ExxonMobil Chemical Company.
[0161] Two or more ionomer resins may be used in combination for
the inner cover 6. An ionomer resin neutralized with a monovalent
metal ion, and an ionomer resin neutralized with a bivalent metal
ion may be used in combination.
[0162] According to need, a coloring agent such as titanium
dioxide, a filler such as barium sulfate, a dispersant, an
antioxidant, an ultraviolet absorber, a light stabilizer, a
fluorescent material, a fluorescent brightener, and the like are
included in the resin composition of the inner cover 6 in an
adequate amount.
[0163] From the standpoint that an outer-hard/inner-soft structure
can be achieved in the sphere consisting of the core 4 and the
inner cover 6, the inner cover 6 preferably has a hardness Hi
greater than the surface hardness Hs of the core 4. In light of
suppression of spin, the difference (Hi-Hs) between the hardness Hi
and the hardness Hs is preferably equal to or greater than 2, more
preferably equal to or greater than 4, and particularly preferably
equal to or greater than 6.
[0164] The hardness Hi is measured with a JIS-C type hardness scale
mounted to an automated rubber hardness measurement machine (trade
name "P1", manufactured by Kobunshi Keiki Co., Ltd.). For the
measurement, a slab that is formed by hot press and that has a
thickness of about 2 mm is used. A slab kept at 23.degree. C. for
two weeks is used for the measurement. At the measurement, three
slabs are stacked. A slab formed from the same resin composition as
the resin composition of the inner cover 6 is used for the
measurement.
[0165] From the standpoint that an outer-hard/inner-soft structure
can be achieved in the sphere consisting of the core 4 and the
inner cover 6, the JIS-C hardness Hi of the inner cover 6 is
preferably equal to or greater than 80, more preferably equal to or
greater than 85, and particularly preferably equal to or greater
than 90. In light of feel at impact of the golf ball 2, the
hardness Hi is preferably equal to or less than 98 and particularly
preferably equal to or less than 97.
[0166] The inner cover 6 preferably has a thickness Ti of 0.5 mm or
greater but 1.6 mm or less. In the sphere that includes the inner
cover 6 having a thickness Ti of 0.5 mm or greater, the spin
suppression effect provided by the outer-hard/inner-soft structure
is great. In this respect, the thickness Ti is particularly
preferably equal to or greater than 0.7 mm. The golf ball 2 that
includes the inner cover 6 having a thickness Ti of 1.6 mm or less
can include a large core 4. The large core 4 can contribute to the
resilience performance of the golf ball 2. In this respect, the
thickness Ti is particularly preferably equal to or less than 1.2
mm.
[0167] For the outer cover 8, a resin composition is suitably used.
Examples of the base polymer of the resin composition include
ionomer resins, polystyrenes, polyesters, polyamides, and
polyolefins.
[0168] Particularly preferable base polymers are ionomer resins.
The golf ball 2 that includes the outer cover 8 including an
ionomer resin has excellent resilience performance. An ionomer
resin and another resin may be used in combination for the outer
cover 8. In this case, the principal component of the base polymer
is preferably the ionomer resin. Specifically, the proportion of
the ionomer resin to the entire base polymer is preferably equal to
or greater than 50% by weight, more preferably equal to or greater
than 60% by weight, and particularly preferably equal to or greater
than 70% by weight. The outer cover 8 can include the ionomer resin
described above for the inner cover 6.
[0169] A preferable resin that can be used in combination with an
ionomer resin is a styrene block-containing thermoplastic
elastomer. The styrene block-containing thermoplastic elastomer has
excellent compatibility with ionomer resins. A resin composition
including the styrene block-containing thermoplastic elastomer has
excellent fluidity.
[0170] The styrene block-containing thermoplastic elastomer
includes a polystyrene block as a hard segment, and a soft segment.
A typical soft segment is a diene block. Examples of compounds for
the diene block include butadiene, isoprene, 1,3-pentadiene, and
2,3-dimethyl-1,3-butadiene. Butadiene and isoprene are preferred.
Two or more compounds may be used in combination.
[0171] Examples of styrene block-containing thermoplastic
elastomers include styrene-butadiene-styrene block copolymers
(SBS), styrene-isoprene-styrene block copolymers (SIS),
styrene-isoprene-butadiene-styrene block copolymers (SIBS),
hydrogenated SBS, hydrogenated SIS, and hydrogenated SIBS. Examples
of hydrogenated SBS include styrene-ethylene-butylene-styrene block
copolymers (SEBS). Examples of hydrogenated SIS include
styrene-ethylene-propylene-styrene block copolymers (SEPS).
Examples of hydrogenated SIBS include
styrene-ethylene-ethylene-propylene-styrene block copolymers
(SEEPS).
[0172] In light of resilience performance of the golf ball 2, the
content of the styrene component in the styrene block-containing
thermoplastic elastomer is preferably equal to or greater than 10%
by weight, more preferably equal to or greater than 12% by weight,
and particularly preferably equal to or greater than 15% by weight.
In light of feel at impact of the golf ball 2, the content is
preferably equal to or less than 50% by weight, more preferably
equal to or less than 47% by weight, and particularly preferably
equal to or less than 45% by weight.
[0173] In the present invention, styrene block-containing
thermoplastic elastomers include an alloy of an olefin and one or
more members selected from the group consisting of SBS, SIS, SIBS,
SEBS, SEPS, and SEEPS. The olefin component in the alloy is
presumed to contribute to improvement of compatibility with ionomer
resins. Use of this alloy improves the resilience performance of
the golf ball 2. An olefin having 2 to 10 carbon atoms is
preferably used. Examples of suitable olefins include ethylene,
propylene, butene, and pentene. Ethylene and propylene are
particularly preferred.
[0174] Specific examples of polymer alloys include trade names
"Rabalon T3221C", "Rabalon T3339C", "Rabalon SJ4400N", "Rabalon
SJ5400N", "Rabalon SJ6400N", "Rabalon SJ7400N", "Rabalon SJ8400N",
"Rabalon SJ9400N", and "Rabalon SR04", manufactured by Mitsubishi
Chemical Corporation. Other specific examples of styrene
block-containing thermoplastic elastomers include trade name
"Epofriend A1010" manufactured by Daicel Chemical Industries, Ltd.,
and trade name "Septon HG-252" manufactured by Kuraray Co.,
Ltd.
[0175] Another resin that can be used in combination with an
ionomer resin is an ethylene-(meth) acrylic acid copolymer. The
copolymer is obtained by a copolymerization reaction of a monomer
composition that contains ethylene and (meth) acrylic acid. In the
copolymer, some of the carboxyl groups are neutralized with metal
ions. The copolymer includes 3% by weight or greater but 25% by
weight or less of a (meth)acrylic acid component. An
ethylene-(meth) acrylic acid copolymer having a polar functional
group is particularly preferred. A specific example of
ethylene-(meth) acrylic acid copolymers is trade name "NUCREL"
manufactured by Du Pont-MITSUI POLYCHEMICALS Co., Ltd.
[0176] According to need, a coloring agent such as titanium
dioxide, a filler such as barium sulfate, a dispersant, an
antioxidant, an ultraviolet absorber, a light stabilizer, a
fluorescent material, a fluorescent brightener, and the like are
included in the resin composition of the outer cover 8 in an
adequate amount.
[0177] The outer cover 8 preferably has a JIS-C hardness Ho of 96
or less. When the golf ball 2 that includes the outer cover 8
having a hardness Ho of 96 or less is hit with a short iron, a high
spin rate is obtained. The golf ball 2 has excellent
controllability. In this respect, the hardness Ho is more
preferably equal to or less than 94 and particularly preferably
equal to or less than 92. In light of flight distance upon a shot
with a driver, the hardness Ho is preferably equal to or greater
than 70 and particularly preferably equal to or greater than 80.
The hardness Ho is measured by the same measurement method as that
for the hardness Hi.
[0178] The hardness Ho of the outer cover 8 is less than the
hardness Hi of the inner cover 6. When the golf ball 2 is hit with
a driver, the sphere consisting of the core 4 and the inner cover 6
becomes significantly distorted since the head speed is high. Since
this sphere has an outer-hard/inner-soft structure, the spin rate
is suppressed. The hardness of the envelope layer 12 linearly
changes. Thus, the golf ball 2 is launched at a high speed due to
deformation and restoration of the envelope layer 12. The
suppression of the spin rate and the high launch speed achieve a
large flight distance. When the golf ball 2 is hit with a short
iron, this sphere becomes less distorted since the head speed is
low. When the golf ball 2 is hit with a short iron, the behavior of
the golf ball 2 mainly depends on the outer cover 8. Since the
outer cover 8 is flexible, a slip between the golf ball 2 and a
clubface is suppressed. Due to the suppression of the slip, a high
spin rate is obtained. The high spin rate achieves excellent
controllability. In the golf ball 2, both desired flight
performance upon a shot with a driver and desired controllability
upon a shot with a short iron are achieved.
[0179] In light of achievement of both desired flight performance
and desired controllability, the difference (Hi-Ho) between the
hardness Hi of the inner cover 6 and the hardness Ho of the outer
cover 8 is preferably equal to or greater than 1, more preferably
equal to or greater than 2, and particularly preferably equal to or
greater than 4. The difference (Hi-Ho) is preferably equal to or
less than 20.
[0180] The hardness Ho of the outer cover 8 may be less than the
surface hardness Hs of the core 4 or may be greater than the
surface hardness Hs of the core 4. The golf ball 2 in which the
hardness Ho is less than the hardness Hs has particularly excellent
controllability. The golf ball 2 in which the hardness Ho is
greater than the hardness Hs has particularly excellent flight
performance.
[0181] In light of controllability upon a shot with a short iron,
the outer cover 8 has a thickness To of preferably 0.1 mm or
greater and particularly preferably 0.2 mm or greater. In light of
flight performance upon a shot with a driver, the thickness To is
preferably equal to or less than 1.2 mm and particularly preferably
equal to or less than 1.0 mm.
[0182] For forming the outer cover 8, known methods such as
injection molding, compression molding, and the like can be used.
When forming the outer cover 8, the dimples 14 are formed by
pimples formed on the cavity face of a mold.
[0183] In light of feel at impact, the sum (Ti+To) of the thickness
Ti of the inner cover 6 and the thickness To of the outer cover 8
is preferably equal to or less than 2.5 mm, more preferably equal
to or less than 2.3 mm, and particularly preferably equal to or
less than 2.1 mm. In light of durability of the golf ball 2, the
sum (Ti+To) is preferably equal to or greater than 0.3 mm, more
preferably equal to or greater than 0.5 mm, and particularly
preferably equal to or greater than 0.8 mm.
[0184] In light of feel at impact, the golf ball 2 has an amount of
compressive deformation Db of preferably 2.2 mm or greater, more
preferably 2.5 mm or greater, and particularly preferably 2.8 mm or
greater. In light of resilience performance, the amount of
compressive deformation Db is preferably equal to or less than 4.0
mm, more preferably equal to or less than 3.7 mm, and particularly
preferably equal to or less than 3.4 mm.
[0185] For measurement of the amount of compressive deformation, a
YAMADA type compression tester is used. In the tester, a sphere
such as the core 4, the golf ball 2, or the like is placed on a
hard plate made of metal. Next, a cylinder made of metal gradually
descends toward the sphere. The sphere, squeezed between the bottom
face of the cylinder and the hard plate, becomes deformed. A
migration distance of the cylinder, starting from the state in
which an initial load of 98 N is applied to the sphere up to the
state in which a final load of 1274 N is applied thereto, is
measured.
[0186] The golf ball may include a center formed from a rubber
composition that includes the acid and/or the salt (d); and an
envelope layer formed from a rubber composition that does not
include the acid and/or the salt (d). The rubber composition of the
center is the same as the rubber composition of the envelope layer
12 shown in FIG. 1. A hardness distribution of the center is
appropriate.
[0187] The golf ball may include a center formed from a rubber
composition that includes the acid and/or the salt (d); and an
envelope layer formed from a rubber composition that includes the
acid and/or the salt (d). The rubber composition of the center is
the same as the rubber composition of the envelope layer 12 shown
in FIG. 1. The rubber composition of the envelope layer is the same
as the rubber composition of the envelope layer 12 shown in FIG. 1.
A hardness distribution of the center is appropriate. A hardness
distribution of the envelope layer is appropriate.
Second Embodiment
[0188] A golf ball 102 shown in FIG. 3 includes a spherical core
104, an inner cover 106 positioned outside the core 104, and an
outer cover 108 positioned outside the inner cover 106. The core
104 includes a spherical center 110 and an envelope layer 112
positioned outside the center 110. On the surface of the outer
cover 108, a large number of dimples 114 are formed. Of the surface
of the golf ball 102, a part other than the dimples 114 is a land
116. The golf ball 102 includes a paint layer and a mark layer on
the external side of the outer cover 108, but these layers are not
shown in the drawing.
[0189] The golf ball 102 preferably has a diameter of 40 mm or
greater but 45 mm or less. From the standpoint of conformity to the
rules established by the United States Golf Association (USGA), the
diameter is particularly preferably equal to or greater than 42.67
mm. In light of suppression of air resistance, the diameter is more
preferably equal to or less than 44 mm and particularly preferably
equal to or less than 42.80 mm. The golf ball 102 preferably has a
weight of 40 g or greater but 50 g or less. In light of attainment
of great inertia, the weight is more preferably equal to or greater
than 44 g and particularly preferably equal to or greater than
45.00 g. From the standpoint of conformity to the rules established
by the USGA, the weight is particularly preferably equal to or less
than 45.93 g.
[0190] In the present invention, a JIS-C hardness is measured at
each measuring point based on the distance from the central point
of the core 104 to the surface of the core 104. The distances from
the central point of the core 104 to these measuring points are as
follows.
[0191] First point: 0.0 mm
[0192] Second point: 2.5 mm
[0193] Third point: 5.0 mm
[0194] Fourth point: 7.0 mm
[0195] Fifth point: 7.5 mm
[0196] Sixth point: 8.0 mm
[0197] Seventh point: 9.5 mm
[0198] Eighth point: 10.0 mm
[0199] Ninth point: 10.5 mm
[0200] Tenth pint: 12.5 mm
[0201] Eleventh point: 15.0 mm
[0202] Twelfth point: 17.5 mm
[0203] Thirteenth point: surface
[0204] Hardnesses at the first to twelfth points are measured by
pressing a JIS-C type hardness scale against a cut plane of the
core 104 that has been cut into two halves. A hardness at the
thirteenth point is measured by pressing the JIS-C type hardness
scale against the surface of the spherical core 104. For the
measurement, an automated rubber hardness measurement machine
(trade name "P1", manufactured by Kobunshi Keiki Co., Ltd.), to
which this hardness scale is mounted, is used.
[0205] FIG. 4 is a line graph showing a hardness distribution of
the envelope layer 112 of the golf ball 102 in FIG. 3. The
horizontal axis of the graph indicates a distance (mm) from the
central point of the core 104. The vertical axis of the graph
indicates a JIS-C hardness. In the graph, the sixth point, the
eighth point, and the tenth to thirteenth points among the points
included in the envelope layer 112 are plotted.
[0206] FIG. 4 also shows a linear approximation curve obtained by a
least-square method on the basis of the distance and the hardness
of each measuring point. The linear approximation curve is
indicated by a dotted line. In FIG. 4, the broken line does not
greatly deviate from the linear approximation curve. In other
words, the broken line has a shape close to the linear
approximation curve. In the envelope layer 112, the hardness
linearly increases from its inside toward its outside. When the
golf ball 102 is hit with a fairway wood, the energy loss is low in
the envelope layer 112. The golf ball 102 has excellent resilience
performance. When the golf ball 102 is hit with a fairway wood, the
flight distance is large.
[0207] R.sup.2 of the linear approximation curve for the envelope
layer 112 which is obtained by the least-square method is
preferably equal to or greater than 0.90. R.sup.2 is an index
indicating the linearity of the broken line. For the envelope layer
112 for which R.sup.2 is equal to or greater than 0.90, the shape
of the broken line of the hardness distribution is close to a
straight line. The golf ball 102 that includes the envelope layer
112 for which R.sup.2 is equal to or greater than 0.90 has
excellent resilience performance. R.sup.2 is more preferably equal
to or greater than 0.95 and particularly preferably equal to or
greater than 0.97. R.sup.2 is calculated by squaring a correlation
coefficient R. The correlation coefficient R is calculated by
dividing the covariance of the distance (mm) from the central point
and the hardness (JIS-C) by the standard deviation of the distance
(mm) from the central point and the standard deviation of the
hardness (JIS-C).
[0208] In light of suppression of spin, the gradient a of the
linear approximation curve is preferably equal to or greater than
0.30, more preferably equal to or greater than 0.33, and
particularly preferably equal to or greater than 0.35.
[0209] In the present invention, a JIS-C hardness at a measuring
point whose distance from the central point of the core 104 is x
(mm) is represented by H(x). The hardness at the central point of
the core 104 is represented by H (0.0). In the present invention,
the JIS-C hardness at the surface of the core 104 is represented by
Hs. The difference (Hs-H(0.0)) between the surface hardness Hs and
the central hardness H(0.0) is preferably equal to or greater than
15. The core 104 in which the difference (Hs-H(0.0)) is equal to or
greater than 15 has an outer-hard/inner-soft structure. When the
golf ball 102 is hit with a fairway wood, the recoil (torsional
return) in the core 104 is great, and thus spin is suppressed. The
core 104 contributes to the flight performance of the golf ball
102. In light of flight performance, the difference (Hs-H(0.0)) is
more preferably equal to or greater than 23 and particularly
preferably equal to or greater than 24. From the standpoint that
the core 104 can easily be formed, the difference (Hs-H(0.0)) is
preferably equal to or less than 50. In the core 104, the hardness
gradually increases from its central point toward its surface.
[0210] The center 110 is formed by crosslinking a rubber
composition. Examples of base rubbers for use in the rubber
composition include polybutadienes, polyisoprenes,
styrene-butadiene copolymers, ethylene-propylene-diene copolymers,
and natural rubbers. Two or more rubbers may be used in
combination. In light of resilience performance, polybutadienes are
preferred, and high-cis polybutadienes are particularly
preferred.
[0211] Preferably, the rubber composition of the center 110
includes a co-crosslinking agent. Examples of preferable
co-crosslinking agents in light of resilience performance include
acrylic acid, methacrylic acid, zinc acrylate, magnesium acrylate,
zinc methacrylate, and magnesium methacrylate. Preferably, the
rubber composition further includes a metal compound. Examples of
the metal compound include magnesium oxide and zinc oxide.
Preferably, the rubber composition includes an organic peroxide
together with a co-crosslinking agent. Examples of preferable
organic peroxides include 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.
Preferably, the rubber composition includes a sulfur compound.
Preferably, the rubber composition includes an acid and/or a salt.
Examples of preferable acids and/or salts include zinc octoate,
zinc laurate, zinc myristate, and zinc stearate.
[0212] According to need, various additives such as a filler,
sulfur, a vulcanization accelerator, an anti-aging agent, a
coloring agent, a plasticizer, a dispersant, and the like are
included in the rubber composition of the center 110 in an adequate
amount. Synthetic resin powder or crosslinked rubber powder may
also be included in the rubber composition.
[0213] In the present embodiment, the center 110 is preferably more
flexible than the envelope layer 112. The center 110 can suppress
spin. The center 110 preferably has a diameter of 8 mm or greater
but 20 mm or less. In the golf ball 102 that includes the center
110 having a diameter of 8 mm or greater, spin can be suppressed.
In this respect, the diameter is more preferably equal to or
greater than 12 mm and particularly preferably equal to or greater
than 14 mm. The golf ball 102 that includes the center 110 having a
diameter of 20 mm or less has excellent resilience performance even
though the center 110 is flexible. In this respect, the diameter is
more preferably equal to or less than 18 mm and particularly
preferably equal to or less than 16 mm.
[0214] The envelope layer 112 is formed by crosslinking a rubber
composition. The rubber composition includes:
[0215] (a) a base rubber;
[0216] (b) a co-crosslinking agent;
[0217] (c) a crosslinking initiator; and
[0218] (d) an acid and/or a salt.
[0219] The rubber composition of the envelope layer 112 can include
the base rubber (a) described above for the envelope layer 12 of
the first embodiment.
[0220] Examples of preferable co-crosslinking agents (b)
include:
[0221] (b1) an .alpha.,.beta.-unsaturated carboxylic acid having 3
to 8 carbon atoms; and
[0222] (b2) a metal salt of an .alpha.,.beta.-unsaturated
carboxylic acid having 3 to 8 carbon atoms.
The rubber composition of the envelope layer 112 can include the
co-crosslinking agent (b) described above for the envelope layer 12
of the first embodiment.
[0223] The metal salt (b2) of the .alpha.,.beta.-unsaturated
carboxylic acid graft-polymerizes with the molecular chain of the
base rubber, thereby crosslinking the rubber molecules. When the
rubber composition includes the .alpha.,.beta.-unsaturated
carboxylic acid (b1), the rubber composition preferably further
includes a metal compound (f). The metal compound (f) reacts with
the .alpha.,.beta.-unsaturated carboxylic acid (b1) in the rubber
composition. A salt obtained by this reaction graft-polymerizes
with the molecular chain of the base rubber. The rubber composition
of the envelope layer 112 can include the metal compound (f)
described above for the envelope layer 12 of the first
embodiment.
[0224] In light of resilience performance of the golf ball 102, the
amount of the co-crosslinking agent (b) is preferably equal to or
greater than 15 parts by weight and particularly preferably equal
to or greater than 20 parts by weight, per 100 parts by weight of
the base rubber. In light of feel at impact, the amount is
preferably equal to or less than 50 parts by weight, more
preferably equal to or less than 45 parts by weight, and
particularly preferably equal to or less than 40 parts by weight,
per 100 parts by weight of the base rubber.
[0225] The rubber composition of the envelope layer 112 can include
the crosslinking initiator (c) described above for the envelope
layer 12 of the first embodiment. In light of resilience
performance of the golf ball 102, the amount of the crosslinking
initiator (c) is preferably equal to or greater than 0.2 parts by
weight and particularly preferably equal to or greater than 0.5
parts by weight, per 100 parts by weight of the base rubber. In
light of feel at impact and durability of the golf ball 102, the
amount is preferably equal to or less than 5.0 parts by weight and
particularly preferably equal to or less than 2.5 parts by weight,
per 100 parts by weight of the base rubber.
[0226] The acid component included in the acid and/or the salt (d)
has reactivity with a cationic component. During heating and
forming of the envelope layer 112, the acid dissociates and reacts
with the cationic component of the co-crosslinking agent (b). It is
thought that within the envelope layer 112, the acid inhibits
formation of the metal crosslinks by the co-crosslinking agent (b).
The acid component included in the salt exchanges the cationic
component with the co-crosslinking agent (b). It is inferred that
during heating and forming of the envelope layer 112, the salt
breaks the metal crosslinks by the co-crosslinking agent (b).
[0227] The rubber composition of the envelope layer 112 can include
the acid and/or the salt (d) described above for the envelope layer
12 of the first embodiment. In the present invention, the
co-crosslinking agent (b) is not included in the concept of the
acid and/or the salt (d).
[0228] In light of linearity of the hardness distribution of the
envelope layer 112, the amount of the acid and/or the salt (d) is
preferably equal to or greater than 0.3 parts by weight, more
preferably equal to or greater than 1.0 parts by weight, and
particularly preferably equal to or greater than 2.0 parts by
weight, per 100 parts by weight of the base rubber. In light of
resilience performance, the amount is preferably equal to or less
than 40 parts by weight, more preferably equal to or less than 30
parts by weight, and particularly preferably equal to or less than
20 parts by weight, per 100 parts by weight of the base rubber.
[0229] The weight ratio of the co-crosslinking agent (b) and the
acid and/or the salt (d) in the rubber composition is preferably
equal to or greater than 3/7 but equal to or less than 9/1, and is
particularly preferably equal to or greater than 4/6 but equal to
or less than 8/2. From the rubber composition in which this weight
ratio is within the above range, the envelope layer 112 having an
appropriate hardness distribution can be obtained.
[0230] As the co-crosslinking agent (b), zinc acrylate is
preferably used. Zinc acrylate whose surface is coated with stearic
acid or zinc stearate for the purpose of improving dispersibility
to rubber is present. When the rubber composition includes this
zinc acrylate, the stearic acid or zinc stearate coating the zinc
acrylate is not included in the concept of the acid and/or the salt
(d).
[0231] Preferably, the rubber composition of the envelope layer 112
further includes the organic sulfur compound (e) described above
for the envelope layer 12 of the first embodiment. The organic
sulfur compound (e) can contribute to control of: the linearity of
the hardness distribution of the envelope layer 112; and the degree
of the outer-hard/inner-soft structure.
[0232] From the standpoint that an outer-hard/inner-soft structure
is easily obtained, the amount of the organic sulfur compound (e)
is preferably equal to or greater than 0.05 parts by weight, more
preferably equal to or greater than 0.1 parts by weight, and
particularly preferably equal to or greater than 0.2 parts by
weight, per 100 parts by weight of the base rubber. In light of
resilience performance, the amount is preferably equal to or less
than 5.0 parts by weight, more preferably equal to or less than 3.0
parts by weight, and particularly preferably equal to or less than
1.0 parts by weight, per 100 parts by weight of the base
rubber.
[0233] For the purpose of adjusting specific gravity and the like,
a filler may be included in the envelope layer 112. Examples of
suitable fillers include zinc oxide, barium sulfate, calcium
carbonate, and magnesium carbonate. The amount of the filler is
determined as appropriate so that the intended specific gravity of
the core 104 is accomplished. A particularly preferable filler is
zinc oxide. Zinc oxide serves not only as a specific gravity
adjuster but also as a crosslinking activator.
[0234] According to need, an anti-aging agent, a coloring agent, a
plasticizer, a dispersant, sulfur, a vulcanization accelerator, and
the like are added to the rubber composition of the envelope layer
112. Crosslinked rubber powder or synthetic resin powder may also
be dispersed in the rubber composition.
[0235] During heating of the core 104, the heat of a crosslinking
reaction of the base rubber remains near the central point of the
core 104. Thus, during heating of the core 104, the temperature at
the central portion is high. The temperature gradually decreases
from the central point toward the surface. The acid and/or the salt
(d) reacts with a metal salt of the co-crosslinking agent (b) to
inhibit formation of metal crosslinks or break metal crosslinks,
respectively. This reaction is accelerated in a region where the
temperature is high. In other words, inhibition of formation of
metal crosslinks and breaking of metal crosslinks are likely to
occur near the innermost portion of the envelope layer 112 where
the temperature is high, and are unlikely to occur near the surface
of the envelope layer 112. As a result, the crosslinking density of
the envelope layer 112 increases from its inside toward its
outside. In the envelope layer 112, the hardness linearly increases
from its inside toward its outside. Furthermore, since the rubber
composition includes the organic sulfur compound (e) together with
the acid and/or the salt (d), the gradient of the hardness
distribution can be controlled, and the degree of the
outer-hard/inner-soft structure of the core 104 can be
increased.
[0236] The hardness H(0.0) at the central point of the core 104 is
preferably equal to or greater than 40.0 but equal to or less than
68.0. The golf ball 102 having a hardness H(0.0) of 40.0 or greater
has excellent resilience performance. In this respect, the hardness
H(0.0) is more preferably equal to or greater than 45.0 and
particularly preferably equal to or greater than 47.0. In the core
104 having a hardness H(0.0) of 68.0 or less, an
outer-hard/inner-soft structure can be achieved. In the golf ball
102 that includes the core 104, spin can be suppressed. In this
respect, the hardness H(0.0) is more preferably equal to or less
than 65.0 and particularly preferably equal to or less than
63.0.
[0237] The hardness Hs at the surface of the core 104 is preferably
equal to or greater than 70.0 but equal to or less than 95.0. In
the core 104 having a hardness Hs of 70.0 or greater, an
outer-hard/inner-soft structure can be achieved. In the golf ball
102 that includes the core 104, spin can be suppressed. In this
respect, the hardness Hs is more preferably equal to or greater
than 80.0 and particularly preferably equal to or greater than
82.0. The golf ball 102 having a hardness Hs of 95.0 or less has
excellent durability. In this respect, the hardness Hs is more
preferably equal to or less than 94.0 and particularly preferably
equal to or less than 92.0.
[0238] The core 104 preferably has a diameter of 38.0 mm or greater
but 41.5 mm or less. The core 104 having a diameter of 38.0 mm or
greater can achieve excellent resilience performance of the golf
ball 102. In this respect, the diameter is more preferably equal to
or greater than 38.5 mm and particularly preferably equal to or
greater than 39.0 mm. In the golf ball 102 that includes the core
104 having a diameter of 41.5 mm or less, the inner cover 106 and
the outer cover 108 can have sufficient thicknesses. The golf ball
102 that includes the inner cover 106 and the outer cover 108 which
have large thicknesses has excellent durability. In this respect,
the diameter is more preferably equal to or less than 41.0 mm and
particularly preferably equal to or less than 40.5 mm.
[0239] In light of feel at impact, the core 104 has an amount of
compressive deformation Dc of preferably 3.5 mm or greater and
particularly preferably 3.8 mm or greater. In light of resilience
performance of the core 104, the amount of compressive deformation
DC is preferably equal to or less than 4.5 mm and particularly
preferably equal to or less than 4.0 mm.
[0240] For the inner cover 106, a resin composition is suitably
used. Examples of the base polymer of the resin composition include
ionomer resins, polystyrenes, polyesters, polyamides, and
polyolefins.
[0241] Particularly preferable base polymers are ionomer resins.
The golf ball 102 that includes the inner cover 106 including an
ionomer resin has excellent resilience performance. An ionomer
resin and another resin may be used in combination for the inner
cover 106. In this case, the principal component of the base
polymer is preferably the ionomer resin. Specifically, the
proportion of the ionomer resin to the entire base polymer is
preferably equal to or greater than 50% by weight, more preferably
equal to or greater than 60% by weight, and particularly preferably
equal to or greater than 70% by weight.
[0242] The inner cover 106 can include the ionomer resin described
above for the golf ball 2 of the first embodiment. The inner cover
106 can include the styrene block-containing thermoplastic
elastomer described above for the golf ball 2 of the first
embodiment.
[0243] In light of flight performance of the golf ball 102, the
content of the styrene component in the styrene block-containing
thermoplastic elastomer is preferably equal to or greater than 10%
by weight, more preferably equal to or greater than 12% by weight,
and particularly preferably equal to or greater than 15% by weight.
In light of resilience performance of the golf ball 102, the
content is preferably equal to or less than 50% by weight, more
preferably equal to or less than 47% by weight, and particularly
preferably equal to or less than 45% by weight.
[0244] According to need, a coloring agent such as titanium
dioxide, a filler such as barium sulfate, a dispersant, an
antioxidant, an ultraviolet absorber, a light stabilizer, a
fluorescent material, a fluorescent brightener, and the like are
included in the resin composition of the inner cover 106 in an
adequate amount.
[0245] In light of resilience performance of the golf ball 102, the
inner cover 106 has a JIS-C hardness Hi of preferably 65 or
greater, more preferably 75 or greater, and particularly preferably
80 or greater. In light of feel at impact of the golf ball 102, the
hardness Hi is preferably equal to or less than 95 and particularly
preferably equal to or less than 90. The hardness Hi is measured by
the method described above for the golf ball 2 of the first
embodiment.
[0246] The JIS-C hardness Hi of the inner cover 106 may be less
than the surface hardness Hs of the core 104 or may be greater than
the surface hardness Hs of the core 104. When the hardness Hi is
greater than the hardness Hs, an outer-hard/inner-soft structure is
achieved in the sphere consisting of the core 104 and the inner
cover 106. When the golf ball 102 that includes the core 104 and
the inner cover 106 is hit, the spin rate is low. When the golf
ball 102 is hit with a high-number wood club, particularly
excellent flight performance is exerted. In the golf ball 102 in
which the hardness Hi is less than the hardness Hs, the
outer-hard/inner-soft structure of the core 104 achieves further
excellent flight performance. Furthermore, in the golf ball 102,
the shock provided when the golf ball 102 is hit with a high-number
wood club is alleviated by the inner cover 106. The feel at impact
of the golf ball 102 is favorable.
[0247] The inner cover 106 preferably has a thickness Ti of 0.5 mm
or greater but 1.6 mm or less. In the sphere that includes the
inner cover 106 having a thickness Ti of 0.5 mm or greater, the
spin suppression effect provided by the outer-hard/inner-soft
structure is great. In this respect, the thickness Ti is
particularly preferably equal to or greater than 0.7 mm. The golf
ball 102 that includes the inner cover 106 having a thickness Ti of
1.6 mm or less can include a large core 104. The large core 104 can
contribute to the resilience performance of the golf ball 102. In
this respect, the thickness Ti is particularly preferably equal to
or less than 1.2 mm.
[0248] For the outer cover 108, a resin composition is suitably
used. Examples of the base polymer of the resin composition include
ionomer resins, polystyrenes, polyesters, polyamides, and
polyolefins.
[0249] Particularly preferable base polymers are ionomer resins.
The ionomer resin described above for the inner cover 106 can be
used. The golf ball 102 that includes the outer cover 108 including
an ionomer resin has excellent resilience performance. An ionomer
resin and another resin may be used in combination for the outer
cover 108. In this case, the principal component of the base
polymer is preferably the ionomer resin. Specifically, the
proportion of the ionomer resin to the entire base polymer is
preferably equal to or greater than 50% by weight, more preferably
equal to or greater than 60% by weight, and particularly preferably
equal to or greater than 70% by weight. The outer cover 108 can
include the other resin described above for the inner cover
106.
[0250] As described later, the outer cover 108 has a JIS-C hardness
Ho greater than the hardness Hi of the inner cover 106. By
decreasing the amount of the styrene block-containing thermoplastic
elastomer blended in the resin composition of the outer cover 108,
a great hardness Ho can be achieved. By blending a highly elastic
resin in the resin composition, a great hardness Ho may be
achieved. Specific examples of the highly elastic resin include
polyamides.
[0251] According to need, a coloring agent such as titanium
dioxide, a filler such as barium sulfate, a dispersant, an
antioxidant, an ultraviolet absorber, a light stabilizer, a
fluorescent material, a fluorescent brightener, and the like are
included in the resin composition of the outer cover 108 in an
adequate amount.
[0252] From the standpoint that an outer-hard/inner-soft structure
is achieved in the sphere consisting of the core 104, the inner
cover 106, and the outer cover 108, the hardness Ho of the outer
cover 108 is preferably equal to or greater than 83, more
preferably equal to or greater than 84, and particularly preferably
equal to or greater than 85. In light of feel at impact, the
hardness Ho is preferably equal to or less than 96, more preferably
equal to or less than 95, and particularly preferably equal to or
less than 93. The hardness Ho is measured by the same measurement
method as that for the hardness Hi.
[0253] The hardness Ho of the outer cover 108 is greater than the
hardness Hi of the inner cover 106. When the golf ball 102 is hit
with a high-number wood club, the sphere consisting of the core 104
and the inner cover 106 becomes significantly distorted since the
head speed is high. Since this sphere has an outer-hard/inner-soft
structure, the spin rate is suppressed. The hardness of the
envelope layer 112 linearly changes. Thus, the golf ball 102 is
launched at a high speed due to deformation and restoration of the
envelope layer 112. The suppression of the spin rate and the high
launch speed achieve a large flight distance.
[0254] In light of flight performance, the difference (Ho-Hi)
between the hardness Ho of the outer cover 108 and the hardness Hi
of the inner cover 106 is preferably equal to or greater than 2,
more preferably equal to or greater than 4, and particularly
preferably equal to or greater than 6. The difference (Ho-Hi) is
preferably equal to or less than 30.
[0255] From the standpoint that an outer-hard/inner-soft structure
can be achieved in the sphere consisting of the core 104, the inner
cover 106, and the outer cover 108, the hardness Ho of the outer
cover 108 is preferably greater than the surface hardness Hs of the
core 104. When the golf ball 102 is hit with a wood club, the spin
rate is low. With the golf ball 102, a large flight distance is
achieved.
[0256] In light of suppression of spin, the difference (Ho-Hs)
between the hardness Ho and the hardness Hs is preferably equal to
or greater than 2, more preferably equal to or greater than 6, and
particularly preferably equal to or greater than 8. In light of
feel at impact, the difference (Ho-Hs) is preferably equal to or
less than 30.
[0257] In light of durability, the outer cover 108 has a thickness
To of preferably 0.1 mm or greater and particularly preferably 0.2
mm or greater. In light of flight performance, the thickness To is
preferably equal to or less than 1.4 mm and particularly preferably
equal to or less than 1.2 mm.
[0258] For forming the outer cover 108, known methods such as
injection molding, compression molding, and the like can be used.
When forming the outer cover 108, the dimples 114 are formed by
pimples formed on the cavity face of a mold.
[0259] In light of feel at impact, the sum (Ti+To) of the thickness
Ti of the inner cover 106 and the thickness To of the outer cover
108 is preferably equal to or less than 2.5 mm, more preferably
equal to or less than 2.3 mm, and particularly preferably equal to
or less than 2.1 mm. In light of durability and wear resistance of
the golf ball 102, the sum (Ti+To) is preferably equal to or
greater than 0.3 mm, more preferably equal to or greater than 0.5
mm, and particularly preferably equal to or greater than 0.8
mm.
[0260] In light of feel at impact, the golf ball 102 has an amount
of compressive deformation Db of preferably 2.2 mm or greater, more
preferably 2.5 mm or greater, and particularly preferably 2.8 mm or
greater. In light of resilience performance, the amount of
compressive deformation Db is preferably equal to or less than 4.0
mm, more preferably equal to or less than 3.7 mm, and particularly
preferably equal to or less than 3.4 mm. The amount of compressive
deformation is measured by the method described above for the golf
ball 2 of the first embodiment.
[0261] The golf ball may include a center formed from a rubber
composition that includes the acid and/or the salt (d); and an
envelope layer formed from a rubber composition that does not
include the acid and/or the salt (d). The rubber composition of the
center is the same as the rubber composition of the envelope layer
112 shown in FIG. 3. A hardness distribution of the center is
appropriate.
[0262] The golf ball may include a center formed from a rubber
composition that includes the acid and/or the salt (d); and an
envelope layer formed from a rubber composition that includes the
acid and/or the salt (d). The rubber composition of the center is
the same as the rubber composition of the envelope layer 112 shown
in FIG. 3. The rubber composition of the envelope layer is the same
as the rubber composition of the envelope layer 112 shown in FIG.
3. A hardness distribution of the center is appropriate. A hardness
distribution of the envelope layer is appropriate.
Third Embodiment
[0263] A golf ball 202 shown in FIG. 5 includes a spherical core
204, an inner cover 206 positioned outside the core 204, amid cover
208 positioned outside the inner cover 206, and an outer cover 210
positioned outside the mid cover 208. The core 204 includes a
spherical center 212 and an envelope layer 214 positioned outside
the center 212. On the surface of the outer cover 210, a large
number of dimples 216 are formed. Of the surface of the golf ball
202, a part other than the dimples 216 is a land 218. The golf ball
202 includes a paint layer and a mark layer on the external side of
the outer cover 210, but these layers are not shown in the
drawing.
[0264] The golf ball 202 preferably has a diameter of 40 mm or
greater but 45 mm or less. From the standpoint of conformity to the
rules established by the United States Golf Association (USGA), the
diameter is particularly preferably equal to or greater than 42.67
mm. In light of suppression of air resistance, the diameter is more
preferably equal to or less than 44 mm and particularly preferably
equal to or less than 42.80 mm. The golf ball 202 preferably has a
weight of 40 g or greater but 50 g or less. In light of attainment
of great inertia, the weight is more preferably equal to or greater
than 44 g and particularly preferably equal to or greater than
45.00 g. From the standpoint of conformity to the rules established
by the USGA, the weight is particularly preferably equal to or less
than 45.93 g.
[0265] In the present invention, a JIS-C hardness is measured at
each measuring point based on the distance from the central point
of the core 204 to the surface of the core 204. The distances from
the central point of the core 204 to these measuring points are as
follows.
[0266] First point: 0.0 mm
[0267] Second point: 2.5 mm
[0268] Third point: 5.0 mm
[0269] Fourth point: 7.0 mm
[0270] Fifth point: 7.5 mm
[0271] Sixth point: 8.0 mm
[0272] Seventh point: 9.5 mm
[0273] Eighth point: 10.0 mm
[0274] Ninth point: 10.5 mm
[0275] Tenth pint: 12.5 mm
[0276] Eleventh point: 15.0 mm
[0277] Twelfth point: 17.5 mm
[0278] Thirteenth point: surface
[0279] Hardnesses at the first to twelfth points are measured by
pressing a JIS-C type hardness scale against a cut plane of the
core 204 that has been cut into two halves. A hardness at the
thirteenth point is measured by pressing the JIS-C type hardness
scale against the surface of the spherical core 204. For the
measurement, an automated rubber hardness measurement machine
(trade name "P1", manufactured by Kobunshi Keiki Co., Ltd.), to
which this hardness scale is mounted, is used.
[0280] FIG. 6 is a line graph showing a hardness distribution of
the envelope layer 214 of the golf ball 202 in FIG. 5. The
horizontal axis of the graph indicates a distance (mm) from the
central point of the core 204. The vertical axis of the graph
indicates a JIS-C hardness. In the graph, the sixth point, the
eighth point, and the tenth to thirteenth points among the points
included in the envelope layer 214 are plotted.
[0281] FIG. 6 also shows a linear approximation curve obtained by a
least-square method on the basis of the distance and the hardness
of each measuring point. The linear approximation curve is
indicated by a dotted line. In FIG. 6, the broken line does not
greatly deviate from the linear approximation curve. In other
words, the broken line has a shape close to the linear
approximation curve. In the envelope layer 214, the hardness
linearly increases from its inside toward its outside. When the
golf ball 202 is hit with a middle iron, the energy loss is low in
the envelope layer 214. When the golf ball 202 is hit with a middle
iron, the flight distance is large.
[0282] R.sup.2 of the linear approximation curve for the envelope
layer 214 which is obtained by the least-square method is
preferably equal to or greater than 0.95. R.sup.2 is an index
indicating the linearity of the broken line. For the envelope layer
214 for which R.sup.2 is equal to or greater than 0.95, the shape
of the broken line of the hardness distribution is close to a
straight line. The golf ball 202 that includes the envelope layer
214 for which R.sup.2 is equal to or greater than 0.95 has
excellent resilience performance. R.sup.2 is more preferably equal
to or greater than 0.97 and particularly preferably equal to or
greater than 0.99. R.sup.2 is calculated by squaring a correlation
coefficient R. The correlation coefficient R is calculated by
dividing the covariance of the distance (mm) from the central point
and the hardness (JIS-C) by the standard deviation of the distance
(mm) from the central point and the standard deviation of the
hardness
[0283] (JIS-C).
[0284] In light of suppression of spin, the gradient a of the
linear approximation curve is preferably equal to or greater than
1.10, more preferably equal to or greater than 1.50, and
particularly preferably equal to or greater than 1.70.
[0285] In the present invention, a JIS-C hardness at a measuring
point whose distance from the central point of the core 204 is x
(mm) is represented by H(x). The hardness at the central point of
the core 204 is represented by H(0.0). In the present invention,
the JIS-C hardness at the surface of the core 204 is represented by
Hs. The difference (Hs-H(0.0)) between the surface hardness Hs and
the central hardness H(0.0) is preferably equal to or greater than
15. The core 204 in which the difference (Hs-H(0.0)) is equal to or
greater than 15 has an outer-hard/inner-soft structure. When the
golf ball 202 is hit with a middle iron, the recoil (torsional
return) in the core 204 is great, and thus spin is suppressed. The
core 204 contributes to the flight performance of the golf ball
202. In light of flight performance, the difference (Hs-H(0.0)) is
more preferably equal to or greater than 23 and particularly
preferably equal to or greater than 24. From the standpoint that
the core 204 can easily be formed, the difference (Hs-H(0.0)) is
preferably equal to or less than 50. In the core 204, the hardness
gradually increases from its central point toward its surface.
[0286] The center 212 is formed by crosslinking a rubber
composition. Examples of base rubbers for use in the rubber
composition include polybutadienes, polyisoprenes,
styrene-butadiene copolymers, ethylene-propylene-diene copolymers,
and natural rubbers. Two or more rubbers may be used in
combination. In light of resilience performance, polybutadienes are
preferred, and high-cis polybutadienes are particularly
preferred.
[0287] Preferably, the rubber composition of the center 212
includes a co-crosslinking agent. Examples of preferable
co-crosslinking agents in light of resilience performance include
acrylic acid, methacrylic acid, zinc acrylate, magnesium acrylate,
zinc methacrylate, and magnesium methacrylate. Preferably, the
rubber composition further includes a metal compound. Examples of
the metal compound include magnesium oxide and zinc oxide.
Preferably, the rubber composition includes an organic peroxide
together with a co-crosslinking agent. Examples of preferable
organic peroxides include 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.
Preferably, the rubber composition includes a sulfur compound. The
rubber composition may include an acid and/or a salt.
[0288] According to need, various additives such as a filler,
sulfur, a vulcanization accelerator, an anti-aging agent, a
coloring agent, a plasticizer, a dispersant, and the like are
included in the rubber composition of the center 212 in an adequate
amount. Synthetic resin powder or crosslinked rubber powder may
also be included in the rubber composition.
[0289] In the present embodiment, the center 212 is preferably more
flexible than the envelope layer 214. The center 212 can suppress
spin. The center 212 preferably has a diameter of 8 mm or greater
but 24 mm or less. In the golf ball 202 that includes the center
212 having a diameter of 8 mm or greater, spin can be suppressed.
In this respect, the diameter is more preferably equal to or
greater than 12 mm and particularly preferably equal to or greater
than 14 mm. The golf ball 202 that includes the center 212 having a
diameter of 24 mm or less has excellent resilience performance even
though the center 212 is flexible. In this respect, the diameter is
more preferably equal to or less than 18 mm and particularly
preferably equal to or less than 16 mm.
[0290] The envelope layer 214 is formed by crosslinking a rubber
composition. The rubber composition includes:
[0291] (a) a base rubber;
[0292] (b) a co-crosslinking agent;
[0293] (c) a crosslinking initiator; and
[0294] (d) an acid and/or a salt.
[0295] The rubber composition of the envelope layer 214 can include
the base rubber (a) described above for the envelope layer 12 of
the first embodiment.
[0296] Examples of preferable co-crosslinking agents (b)
include:
[0297] (b1) an .alpha.,.beta.-unsaturated carboxylic acid having 3
to 8 carbon atoms; and
[0298] (b2) a metal salt of an .alpha.,.beta.-unsaturated
carboxylic acid having 3 to 8 carbon atoms.
The rubber composition of the envelope layer 214 can include the
co-crosslinking agent (b) described above for the envelope layer 12
of the first embodiment.
[0299] The metal salt (b2) of the .alpha.,.beta.-unsaturated
carboxylic acid graft-polymerizes with the molecular chain of the
base rubber, thereby crosslinking the rubber molecules. When the
rubber composition includes the .alpha.,.beta.-unsaturated
carboxylic acid (b1), the rubber composition preferably further
includes a metal compound (f). The metal compound (f) reacts with
the .alpha.,.beta.-unsaturated carboxylic acid (b1) in the rubber
composition. A salt obtained by this reaction graft-polymerizes
with the molecular chain of the base rubber. The rubber composition
of the envelope layer 214 can include the metal compound (f)
described above for the envelope layer 12 of the first
embodiment.
[0300] In light of resilience performance of the golf ball 202, the
amount of the co-crosslinking agent (b) is preferably equal to or
greater than 15 parts by weight and particularly preferably equal
to or greater than 20 parts by weight, per 100 parts by weight of
the base rubber. In light of feel at impact, the amount is
preferably equal to or less than 50 parts by weight, more
preferably equal to or less than 45 parts by weight, and
particularly preferably equal to or less than 40 parts by weight,
per 100 parts by weight of the base rubber.
[0301] The crosslinking initiator (c) is preferably an organic
peroxide. The organic peroxide contributes to the resilience
performance of the golf ball 202. The rubber composition of the
envelope layer 214 can include the crosslinking initiator (c)
described above for the envelope layer 12 of the first
embodiment.
[0302] In light of resilience performance of the golf ball 202, the
amount of the crosslinking initiator (c) is preferably equal to or
greater than 0.2 parts by weight and particularly preferably equal
to or greater than 0.5 parts by weight, per 100 parts by weight of
the base rubber. In light of feel at impact and durability of the
golf ball 202, the amount is preferably equal to or less than 5.0
parts by weight and particularly preferably equal to or less than
2.5 parts by weight, per 100 parts by weight of the base
rubber.
[0303] The rubber composition of the envelope layer 214 can include
the acid and/or the salt (d) described above for the envelope layer
12 of the first embodiment. The acid component included in the acid
and/or the salt (d) has reactivity with a cationic component.
During heating and forming of the envelope layer 214, the acid
dissociates and reacts with the cationic component of the
co-crosslinking agent (b). It is thought that within the envelope
layer 214, the acid inhibits formation of the metal crosslinks by
the co-crosslinking agent (b). The acid component included in the
salt exchanges the cationic component with the co-crosslinking
agent (b). It is inferred that during heating and forming of the
envelope layer 214, the salt breaks the metal crosslinks by the
co-crosslinking agent (b). The co-crosslinking agent (b) is not
included in the concept of the acid and/or the salt (d).
[0304] In light of linearity of the hardness distribution of the
envelope layer 214, the amount of the acid and/or the salt (d) is
preferably equal to or greater than 0.5 parts by weight, more
preferably equal to or greater than 1.0 parts by weight, and
particularly preferably equal to or greater than 2.0 parts by
weight, per 100 parts by weight of the base rubber. In light of
resilience performance, the amount is preferably equal to or less
than 40 parts by weight, more preferably equal to or less than 30
parts by weight, and particularly preferably equal to or less than
20 parts by weight, per 100 parts by weight of the base rubber.
[0305] The weight ratio of the co-crosslinking agent (b) and the
acid and/or the salt (d) in the rubber composition is preferably
equal to or greater than 3/7 but equal to or less than 9/1, and is
particularly preferably equal to or greater than 4/6 but equal to
or less than 8/2. From the rubber composition in which this weight
ratio is within the above range, the core 204 having an appropriate
hardness distribution can be obtained.
[0306] As the co-crosslinking agent (b), zinc acrylate is
preferably used. Zinc acrylate whose surface is coated with stearic
acid or zinc stearate for the purpose of improving dispersibility
to rubber is present. When the rubber composition includes this
zinc acrylate, the stearic acid or zinc stearate coating the zinc
acrylate is not included in the concept of the acid and/or the salt
(d).
[0307] Preferably, the rubber composition of the envelope layer 214
further includes the organic sulfur compound (e) described above
for the envelope layer 12 of the first embodiment. The organic
sulfur compound (e) can contribute to control of: the linearity of
the hardness distribution of the envelope layer 214; and the degree
of the outer-hard/inner-soft structure.
[0308] From the standpoint that an outer-hard/inner-soft structure
is easily obtained, the amount of the organic sulfur compound (e)
is preferably equal to or greater than 0.05 parts by weight, more
preferably equal to or greater than 0.1 parts by weight, and
particularly preferably equal to or greater than 0.2 parts by
weight, per 100 parts by weight of the base rubber. In light of
resilience performance, the amount is preferably equal to or less
than 5.0 parts by weight, more preferably equal to or less than 3.0
parts by weight, and particularly preferably equal to or less than
1.0 parts by weight, per 100 parts by weight of the base
rubber.
[0309] For the purpose of adjusting specific gravity and the like,
a filler may be included in the envelope layer 214. Examples of
suitable fillers include zinc oxide, barium sulfate, calcium
carbonate, and magnesium carbonate. The amount of the filler is
determined as appropriate so that the intended specific gravity of
the core 204 is accomplished. A particularly preferable filler is
zinc oxide. Zinc oxide serves not only as a specific gravity
adjuster but also as a crosslinking activator.
[0310] According to need, an anti-aging agent, a coloring agent, a
plasticizer, a dispersant, sulfur, a vulcanization accelerator, and
the like are added to the rubber composition of the envelope layer
214. Crosslinked rubber powder or synthetic resin powder may also
be dispersed in the rubber composition.
[0311] During heating of the core 204, the heat of a crosslinking
reaction remains near the central point of the core 204. Thus,
during heating of the core 204, the temperature at the central
portion is high. The temperature gradually decreases from the
central point toward the surface. The acid and/or the salt (d)
reacts with a metal salt of the co-crosslinking agent (b) to
inhibit formation of metal crosslinks or break metal crosslinks,
respectively. This reaction is accelerated in a region where the
temperature is high. In other words, inhibition of formation of
metal crosslinks and breaking of metal crosslinks are likely to
occur near the innermost portion of the envelope layer 214 where
the temperature is high, and are unlikely to occur near the surface
of the envelope layer 214. As a result, the crosslinking density of
the envelope layer 214 increases from its inside toward its
outside. In the envelope layer 214, the hardness linearly increases
from its inside toward its outside. Furthermore, since the rubber
composition includes the organic sulfur compound (e) together with
the acid and/or the salt (d), the gradient of the hardness
distribution can be controlled, and the degree of the
outer-hard/inner-soft structure of the core 204 can be
increased.
[0312] The hardness H(0.0) at the central point of the core 204 is
preferably equal to or greater than 40.0 but equal to or less than
68.0. The golf ball 202 having a hardness H(0.0) of 40.0 or greater
has excellent resilience performance. In this respect, the hardness
H(0.0) is more preferably equal to or greater than 45.0 and
particularly preferably equal to or greater than 47.0. In the core
204 having a hardness H(0.0) of 68.0 or less, an
outer-hard/inner-soft structure can be achieved.
[0313] In the golf ball 202 that includes the core 204, spin can be
suppressed. In this respect, the hardness H(0.0) is more preferably
equal to or less than 65.0 and particularly preferably equal to or
less than 63.0.
[0314] The hardness Hs at the surface of the core 204 is preferably
equal to or greater than 70.0 but equal to or less than 95.0. In
the core 204 having a hardness Hs of 70.0 or greater, an
outer-hard/inner-soft structure can be achieved. In the golf ball
202 that includes the core 204, spin can be suppressed. In this
respect, the hardness Hs is more preferably equal to or greater
than 80.0 and particularly preferably equal to or greater than
82.0. The golf ball 202 having a hardness Hs of 95.0 or less has
excellent durability. In this respect, the hardness Hs is more
preferably equal to or less than 94.0 and particularly preferably
equal to or less than 92.0.
[0315] The core 204 preferably has a diameter of 34.0 mm or greater
but 39.0 mm or less. The core 204 having a diameter of 34.0 mm or
greater can achieve excellent resilience performance of the golf
ball 202. In this respect, the diameter is more preferably equal to
or greater than 35.0 mm and particularly preferably equal to or
greater than 35.5 mm. In the golf ball 202 that includes the core
204 having a diameter of 39.0 mm or less, the inner cover 206 and
the outer cover 210 can have sufficient thicknesses. The golf ball
202 that includes the inner cover 206 and the outer cover 210 which
have large thicknesses has excellent durability. In this respect,
the diameter is more preferably equal to or less than 38.0 mm and
particularly preferably equal to or less than 37.5 mm.
[0316] In light of feel at impact, the core 204 has an amount of
compressive deformation Dc of preferably 3.5 mm or greater and
particularly preferably 3.8 mm or greater. In light of resilience
performance of the core 204, the amount of compressive deformation
DC is preferably equal to or less than 4.5 mm and particularly
preferably equal to or less than 4.0 mm.
[0317] For the inner cover 206, a resin composition is suitably
used. Examples of the base polymer of the resin composition include
ionomer resins, polystyrenes, polyesters, polyamides, and
polyolefins.
[0318] Particularly preferable base polymers are ionomer resins.
The golf ball 202 that includes the inner cover 206 including an
ionomer resin has excellent resilience performance. An ionomer
resin and another resin may be used in combination for the inner
cover 206. In this case, the principal component of the base
polymer is preferably the ionomer resin. Specifically, the
proportion of the ionomer resin to the entire base polymer is
preferably equal to or greater than 50% by weight, more preferably
equal to or greater than 60% by weight, and particularly preferably
equal to or greater than 70% by weight.
[0319] The inner cover 206 can include the ionomer resin described
above for the golf ball 2 of the first embodiment. The inner cover
206 can include the styrene block-containing thermoplastic
elastomer described above for the golf ball 2 of the first
embodiment.
[0320] According to need, a coloring agent such as titanium
dioxide, a filler such as barium sulfate, a dispersant, an
antioxidant, an ultraviolet absorber, a light stabilizer, a
fluorescent material, a fluorescent brightener, and the like are
included in the resin composition of the inner cover 206 in an
adequate amount.
[0321] In light of resilience performance of the golf ball 202, the
inner cover 206 has a JIS-C hardness Hi of preferably 70 or
greater, more preferably 72 or greater, and particularly preferably
74 or greater. In light of feel at impact of the golf ball 202, the
hardness Hi is preferably equal to or less than 94, more preferably
equal to or less than 93, and particularly preferably equal to or
less than 92. The hardness Hi is measured by the method described
above for the golf ball 2 of the first embodiment.
[0322] The JIS-C hardness Hi of the inner cover 206 is greater than
the surface hardness Hs of the core 204. Preferably, the difference
(Hi-Hs) between the hardness Hi and the hardness Hs is equal to or
greater than 1. When the difference (Hi-Hs) is equal to or greater
than 1, an outer-hard/inner-soft structure is achieved in the
sphere consisting of the core 204 and the inner cover 206. When the
golf ball 202 that includes the core 204 and the inner cover 206 is
hit, the spin rate is low. When the golf ball 202 is hit with a
middle iron, particularly excellent flight performance is exerted.
In this respect, the difference (Hi-Hs) is more preferably equal to
or greater than 3 and particularly preferably equal to or greater
than 5.
[0323] The inner cover 206 preferably has a thickness Ti of 0.5 mm
or greater but 1.6 mm or less. In the sphere that includes the
inner cover 206 having a thickness Ti of 0.5 mm or greater, the
spin suppression effect provided by the outer-hard/inner-soft
structure is great. In this respect, the thickness Ti is
particularly preferably equal to or greater than 0.7 mm. The golf
ball 202 that includes the inner cover 206 having a thickness Ti of
1.6 mm or less can include a large core 204. The large core 204 can
contribute to the resilience performance of the golf ball 202. In
this respect, the thickness Ti is particularly preferably equal to
or less than 1.2 mm.
[0324] For the mid cover 208, a resin composition is suitably used.
Examples of the base polymer of the resin composition include
ionomer resins, polystyrenes, polyesters, polyamides, and
polyolefins.
[0325] Particularly preferable base polymers are ionomer resins.
The ionomer resin described above for the inner cover 206 can be
used. The golf ball 202 that includes the mid cover 208 including
an ionomer resin has excellent resilience performance. An ionomer
resin and another resin may be used in combination for the mid
cover 208. In this case, the principal component of the base
polymer is preferably the ionomer resin. Specifically, the
proportion of the ionomer resin to the entire base polymer is
preferably equal to or greater than 60% by weight, more preferably
equal to or greater than 70% by weight, and particularly preferably
equal to or greater than 80% by weight. The mid cover 208 can
include the other resin described above for the inner cover
206.
[0326] As described later, the mid cover 208 preferably has a JIS-C
hardness Hm greater than the hardness Hi of the inner cover 206. By
decreasing the amount of the styrene block-containing thermoplastic
elastomer blended in the resin composition of the mid cover 208, a
great hardness Hm can be achieved. By blending a highly elastic
resin in the resin composition, a great hardness Hm may be
achieved. Specific examples of the highly elastic resin include
polyamides.
[0327] According to need, a coloring agent such as titanium
dioxide, a filler such as barium sulfate, a dispersant, an
antioxidant, an ultraviolet absorber, a light stabilizer, a
fluorescent material, a fluorescent brightener, and the like are
included in the resin composition of the mid cover 208 in an
adequate amount.
[0328] In light of suppression of spin, the hardness Hm is
preferably equal to or greater than 70, more preferably equal to or
greater than 72, and particularly preferably equal to or greater
than 74. In light of feel at impact, the hardness Hm is preferably
equal to or less than 94, more preferably equal to or less than 93,
and particularly preferably equal to or less than 92. The hardness
Hm is measured by the same measurement method as that for the
hardness Hi.
[0329] In light of resilience performance of the sphere consisting
of the core 204, the inner cover 206, and the mid cover 208, the
JIS-C hardness Hm of the mid cover 208 is greater than the surface
hardness Hs of the core 204. The golf ball 202 that includes the
sphere exerts excellent flight performance.
[0330] Preferably, the hardness Hm is greater than the hardness Hi
of the inner cover 206. When the hardness Hm is greater than the
hardness Hi, an outer-hard/inner-soft structure is achieved in the
sphere consisting of the core 204, the inner cover 206, and the mid
cover 208.
[0331] In light of flight performance, the difference (Hm-Hi)
between the hardness Hm and the hardness Hi is preferably equal to
or greater than 2 and more preferably equal to or greater than 4.
In light of durability, the difference (Hm-Hi) is preferably equal
to or less than 20.
[0332] The mid cover 208 preferably has a thickness Tm of 0.5 mm or
greater but 1.6 mm or less. In the sphere that includes the mid
cover 208 having a thickness Tm of 0.5 mm or greater, the spin
suppression effect provided by the outer-hard/inner-soft structure
is great. In this respect, the thickness Tm is particularly
preferably equal to or greater than 0.7 mm. The golf ball 202 that
includes the mid cover 208 having a thickness Tm of 1.6 m or less
can include a large core 204. The large core 204 can contribute to
the resilience performance of the golf ball 202. In this respect,
the thickness Tm is particularly preferably equal to or less than
1.2 mm.
[0333] For the outer cover 210, a resin composition is suitably
used. Examples of the base polymer of the resin composition include
ionomer resins, polystyrenes, polyesters, polyamides, and
polyolefins.
[0334] Particularly preferable base polymers are ionomer resins.
The ionomer resin described above for the inner cover 206 can be
used. The golf ball 202 that includes the outer cover 210 including
an ionomer resin has excellent resilience performance. An ionomer
resin and another resin may be used in combination for the outer
cover 210. In this case, the principal component of the base
polymer is preferably the ionomer resin. Specifically, the
proportion of the ionomer resin to the entire base polymer is
preferably equal to or greater than 50% by weight, more preferably
equal to or greater than 60% by weight, and particularly preferably
equal to or greater than 70% by weight. The outer cover 210 can
include the other resin described above for the inner cover
206.
[0335] Another resin that can be used in combination with an
ionomer resin is an ethylene-(meth)acrylic acid copolymer. The
copolymer is obtained by a copolymerization reaction of a monomer
composition that contains ethylene and (meth)acrylic acid. In the
copolymer, some of the carboxyl groups are neutralized with metal
ions. The copolymer includes 3% by weight or greater but 25% by
weight or less of a (meth)acrylic acid component. An
ethylene-(meth) acrylic acid copolymer having a polar functional
group is particularly preferred. A specific example of
ethylene-(meth)acrylic acid copolymers is trade name "NUCREL"
manufactured by Du Pont-MITSUI POLYCHEMICALS Co., Ltd.
[0336] As described later, the outer cover 210 preferably has a
JIS-C hardness Ho greater than the hardness Hm of the mid cover
208. In this respect, the resin composition of the outer cover 210
may include a highly elastic resin. Specific examples of the highly
elastic resin include polyamides.
[0337] According to need, a coloring agent such as titanium
dioxide, a filler such as barium sulfate, a dispersant, an
antioxidant, an ultraviolet absorber, a light stabilizer, a
fluorescent material, a fluorescent brightener, and the like are
included in the resin composition of the outer cover 210 in an
adequate amount.
[0338] From the standpoint that an outer-hard/inner-soft structure
is achieved in the sphere consisting of the core 204, the inner
cover 206, the mid cover 208, and the outer cover 210, the hardness
Ho of the outer cover 210 is preferably equal to or greater than
80, more preferably equal to or greater than 82, and particularly
preferably equal to or greater than 84. In light of feel at impact,
the hardness Ho is preferably equal to or less than 96, more
preferably equal to or less than 95, and particularly preferably
equal to or less than 93. The hardness Ho is measured by the same
measurement method as that for the hardness Hi.
[0339] The hardness Ho of the outer cover 210 is greater than the
hardness Hi of the inner cover 206. When the golf ball 202 is hit
with a middle iron, the spin rate is low. The flight distance of
the golf ball 202 is large.
[0340] In light of flight performance, the difference (Ho-Hi)
between the hardness Ho of the outer cover 210 and the hardness Hi
of the inner cover 206 is preferably equal to or greater than 2,
more preferably equal to or greater than 4, and particularly
preferably equal to or greater than 6. In light of durability, the
difference (Ho-Hi) is preferably equal to or less than 20.
[0341] The hardness Ho of the outer cover 210 is preferably greater
than the hardness Hm of the mid cover 208. When the hardness
[0342] Ho is greater than the hardness Hi, an outer-hard/inner-soft
structure of the entire ball is achieved in the golf ball 202
consisting of the core 204, the inner cover 206, the mid cover 208,
and the outer cover 210. When the golf ball 202 is hit with a
middle iron, a large flight distance is achieved.
[0343] In light of flight performance, the difference (Ho-Hm)
between the hardness Ho of the outer cover 210 and the hardness Hm
of the mid cover 208 is preferably equal to or greater than 3 and
particularly preferably equal to or greater than 6. In light of
durability, the difference (Ho-Hm) is preferably equal to or less
than 20.
[0344] In light of durability, the outer cover 210 has a thickness
To of preferably 0.1 mm or greater and particularly preferably 0.2
mm or greater. In light of flight performance, the thickness To is
preferably equal to or less than 1.4 mm and particularly preferably
equal to or less than 1.2 mm.
[0345] For forming the outer cover 210, known methods such as
injection molding, compression molding, and the like can be used.
When forming the outer cover 210, the dimples 216 are formed by
pimples formed on the cavity face of a mold.
[0346] In light of feel at impact, the sum (Ti+Tm+To) of the
thickness Ti, the thickness Tm, and the thickness To is preferably
equal to or less than 4.0 mm, more preferably equal to or less than
3.9 mm, and particularly preferably equal to or less than 3.5 mm.
In light of durability and wear resistance of the golf ball 202,
the sum (Ti+Tm+To) is preferably equal to or greater than 0.3 mm,
more preferably equal to or greater than 0.5 mm, and particularly
preferably equal to or greater than 0.8 mm.
[0347] In light of feel at impact, the golf ball 202 has an amount
of compressive deformation Db of preferably 2.2 mm or greater, more
preferably 2.5 mm or greater, and particularly preferably 2.8 mm or
greater. In light of resilience performance, the amount of
compressive deformation Db is preferably equal to or less than 4.0
mm, more preferably equal to or less than 3.7 mm, and particularly
preferably equal to or less than 3.4 mm. The amount of compressive
deformation is measured by the method described above for the golf
ball 2 of the first embodiment.
[0348] The golf ball may include a center formed from a rubber
composition that includes the acid and/or the salt (d); and an
envelope layer formed from a rubber composition that does not
include the acid and/or the salt (d). The rubber composition of the
center is the same as the rubber composition of the envelope layer
214 shown in FIG. 5. A hardness distribution of the center is
appropriate.
[0349] The golf ball may include a center formed from a rubber
composition that includes the acid and/or the salt (d); and an
envelope layer formed from a rubber composition that includes the
acid and/or the salt (d). The rubber composition of the center is
the same as the rubber composition of the envelope layer 214 shown
in FIG. 5. The rubber composition of the envelope layer is the same
as the rubber composition of the envelope layer 214 shown in FIG.
5. A hardness distribution of the center is appropriate. A hardness
distribution of the envelope layer is appropriate.
Fourth Embodiment
[0350] A golf ball 302 shown in FIG. 7 includes a spherical core
304, an inner cover 306 positioned outside the core 304, a mid
cover 308 positioned outside the inner cover 306, and an outer
cover 310 positioned outside the mid cover 308. The core 304
includes a spherical center 312 and an envelope layer 314
positioned outside the center 312. On the surface of the outer
cover 310, a large number of dimples 316 are formed. Of the surface
of the golf ball 302, a part other than the dimples 316 is a land
318. The golf ball 302 includes a paint layer and a mark layer on
the external side of the outer cover 310, but these layers are not
shown in the drawing.
[0351] The golf ball 302 preferably has a diameter of 40 mm or
greater but 45 mm or less. From the standpoint of conformity to the
rules established by the United States Golf Association (USGA), the
diameter is particularly preferably equal to or greater than 42.67
mm. In light of suppression of air resistance, the diameter is more
preferably equal to or less than 44 mm and particularly preferably
equal to or less than 42.80 mm. The golf ball 302 preferably has a
weight of 40 g or greater but 50 g or less. In light of attainment
of great inertia, the weight is more preferably equal to or greater
than 44 g and particularly preferably equal to or greater than
45.00 g. From the standpoint of conformity to the rules established
by the USGA, the weight is particularly preferably equal to or less
than 45.93 g.
[0352] In the present invention, a JIS-C hardness is measured at
each measuring point based on the distance from the central point
of the core 304 to the surface of the core 304. The distances from
the central point of the core 304 to these measuring points are as
follows.
[0353] First point: 0.0 mm
[0354] Second point: 2.5 mm
[0355] Third point: 5.0 mm
[0356] Fourth point: 7.0 mm
[0357] Fifth point: 7.5 mm
[0358] Sixth point: 8.0 mm
[0359] Seventh point: 9.5 mm
[0360] Eighth point: 10.0 mm
[0361] Ninth point: 10.5 mm
[0362] Tenth pint: 12.5 mm
[0363] Eleventh point: 15.0 mm
[0364] Twelfth point: 17.5 mm
[0365] Thirteenth point: surface
[0366] Hardnesses at the first to twelfth points are measured by
pressing a JIS-C type hardness scale against a cut plane of the
core 304 that has been cut into two halves. A hardness at the
thirteenth point is measured by pressing the JIS-C type hardness
scale against the surface of the spherical core 304. For the
measurement, an automated rubber hardness measurement machine
(trade name "P1", manufactured by Kobunshi Keiki Co., Ltd.), to
which this hardness scale is mounted, is used.
[0367] FIG. 8 is a line graph showing a hardness distribution of
the envelope layer 314 of the golf ball 302 in FIG. 7. The
horizontal axis of the graph indicates a distance (mm) from the
central point of the core 304. The vertical axis of the graph
indicates a JIS-C hardness. In the graph, the sixth point, the
eighth point, and the tenth to thirteenth points among the points
included in the envelope layer 314 are plotted.
[0368] FIG. 8 also shows a linear approximation curve obtained by a
least-square method on the basis of the distance and the hardness
of each measuring point. The linear approximation curve is
indicated by a dotted line. In FIG. 8, the broken line does not
greatly deviate from the linear approximation curve.
[0369] In other words, the broken line has a shape close to the
linear approximation curve. In the envelope layer 314, the hardness
linearly increases from its inside toward its outside. When the
golf ball 302 is hit with a driver, the energy loss is low in the
envelope layer 314. When the golf ball 302 is hit with a driver,
the flight distance is large.
[0370] R.sup.2 of the linear approximation curve for the envelope
layer 314 which is obtained by the least-square method is
preferably equal to or greater than 0.94. R.sup.2 is an index
indicating the linearity of the broken line. For the envelope layer
314 for which R.sup.2 is equal to or greater than 0.94, the shape
of the broken line of the hardness distribution is close to a
straight line. The golf ball 302 that includes the envelope layer
314 for which R.sup.2 is equal to or greater than 0.94 has
excellent resilience performance. R.sup.2 is more preferably equal
to or greater than 0.97 and particularly preferably equal to or
greater than 0.99. R.sup.2 is calculated by squaring a correlation
coefficient R. The correlation coefficient R is calculated by
dividing the covariance of the distance (mm) from the central point
and the hardness (JIS-C) by the standard deviation of the distance
(mm) from the central point and the standard deviation of the
hardness (JIS-C).
[0371] In light of suppression of spin, the gradient .alpha. of the
linear approximation curve is preferably equal to or greater than
0.70, more preferably equal to or greater than 1.10, and
particularly preferably equal to or greater than 1.40.
[0372] In the present invention, a JIS-C hardness at a measuring
point whose distance from the central point of the core 204 is x
(mm) is represented by H(x). The hardness at the central point of
the core 304 is represented by H(0.0). In the present invention,
the JIS-C hardness at the surface of the core 304 is represented by
Hs. The difference (Hs-H(0.0)) between the surface hardness Hs and
the central hardness H(0.0) is preferably equal to or greater than
15. The core 304 in which the difference (Hs-H(0.0)) is equal to or
greater than 15 has an outer-hard/inner-soft structure. When the
golf ball 302 is hit with a driver, the recoil (torsional return)
in the core 304 is great, and thus spin is suppressed. The core 304
contributes to the flight performance of the golf ball 302. In
light of flight performance, the difference (Hs-H(0.0)) is more
preferably equal to or greater than 23 and particularly preferably
equal to or greater than 24. From the standpoint that the core 304
can easilybe formed, the difference (Hs-H(0.0)) is preferably equal
to or less than 50. In the core 304, the hardness gradually
increases from its central point toward its surface.
[0373] The center 312 is formed by crosslinking a rubber
composition. Examples of base rubbers for use in the rubber
composition include polybutadienes, polyisoprenes,
styrene-butadiene copolymers, ethylene-propylene-diene copolymers,
and natural rubbers. Two or more rubbers may be used in
combination. In light of resilience performance, polybutadienes are
preferred, and high-cis polybutadienes are particularly
preferred.
[0374] Preferably, the rubber composition of the center 312
includes a co-crosslinking agent. Examples of preferable
co-crosslinking agents in light of resilience performance include
acrylic acid, methacrylic acid, zinc acrylate, magnesium acrylate,
zinc methacrylate, and magnesium methacrylate. Preferably, the
rubber composition further includes a metal compound. Examples of
the metal compound include magnesium oxide and zinc oxide.
Preferably, the rubber composition includes an organic peroxide
together with a co-crosslinking agent. Examples of preferable
organic peroxides include 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.
Preferably, the rubber composition includes a sulfur compound. The
rubber composition may include an acid and/or a salt.
[0375] According to need, various additives such as a filler,
sulfur, a vulcanization accelerator, an anti-aging agent, a
coloring agent, a plasticizer, a dispersant, and the like are
included in the rubber composition of the center 312 in an adequate
amount. Synthetic resin powder or crosslinked rubber powder may
also be included in the rubber composition.
[0376] In the present embodiment, the center 312 is preferably more
flexible than the envelope layer 314. The center 312 can suppress
spin. The center 312 preferably has a diameter of 8 mm or greater
but 24 mm or less. In the golf ball 302 that includes the center
312 having a diameter of 8 mm or greater, spin can be suppressed.
In this respect, the diameter is more preferably equal to or
greater than 12 mm and particularly preferably equal to or greater
than 14 mm. The golf ball 302 that includes the center 312 having a
diameter of 24 mm or less has excellent resilience performance even
though the center 312 is flexible. In this respect, the diameter is
more preferably equal to or less than 18 mm and particularly
preferably equal to or less than 16 mm.
[0377] The envelope layer 314 is formed by crosslinking a rubber
composition. The rubber composition includes:
[0378] (a) a base rubber;
[0379] (b) a co-crosslinking agent;
[0380] (c) a crosslinking initiator; and
[0381] (d) an acid and/or a salt.
[0382] The rubber composition of the envelope layer 314 can include
the base rubber (a) described above for the envelope layer 12 of
the first embodiment.
[0383] Examples of preferable co-crosslinking agents (b)
include
[0384] (b1) an .alpha.,.beta.-unsaturated carboxylic acid having 3
to 8 carbon atoms; and
[0385] (b2) a metal salt of an .alpha.,.beta.-unsaturated
carboxylic acid having 3 to 8 carbon atoms.
The rubber composition of the envelope layer 314 can include the
co-crosslinking agent (b) described above for the envelope layer 12
of the first embodiment.
[0386] The metal salt (b2) of the .alpha.,.beta.-unsaturated
carboxylic acid graft-polymerizes with the molecular chain of the
base rubber, thereby crosslinking the rubber molecules. When the
rubber composition includes the .alpha.,.beta.-unsaturated
carboxylic acid (b1), the rubber composition preferably further
includes a metal compound (f). The metal compound (f) reacts with
the .alpha.,.beta.-unsaturated carboxylic acid (b1) in the rubber
composition. A salt obtained by this reaction graft-polymerizes
with the molecular chain of the base rubber. The rubber composition
of the envelope layer 314 can include the metal compound (f)
described above for the envelope layer 12 of the first
embodiment.
[0387] In light of resilience performance of the golf ball 302, the
amount of the co-crosslinking agent (b) is preferably equal to or
greater than 15 parts by weight and particularly preferably equal
to or greater than 20 parts by weight, per 100 parts by weight of
the base rubber. In light of feel at impact, the amount is
preferably equal to or less than 50 parts by weight, more
preferably equal to or less than 45 parts by weight, and
particularly preferably equal to or less than 40 parts by weight,
per 100 parts by weight of the base rubber.
[0388] The rubber composition of the envelope layer 314 can include
the crosslinking initiator (c) described above for the envelope
layer 12 of the first embodiment. In light of resilience
performance of the golf ball 302, the amount of the crosslinking
initiator (c) is preferably equal to or greater than 0.2 parts by
weight and particularly preferably equal to or greater than 0.5
parts by weight, per 100 parts by weight of the base rubber. In
light of feel at impact and durability of the golf ball 302, the
amount is preferably equal to or less than 5.0 parts by weight and
particularly preferably equal to or less than 2.5 parts by weight,
per 100 parts by weight of the base rubber.
[0389] The acid component included in the acid and/or the salt (d)
has reactivity with a cationic component. During heating and
forming of the envelope layer 314, the acid dissociates and reacts
with the cationic component of the co-crosslinking agent (b). It is
thought that within the envelope layer 314, the acid inhibits
formation of the metal crosslinks by the co-crosslinking agent (b).
The acid component included in the salt exchanges the cationic
component with the co-crosslinking agent (b). It is inferred that
during heating and forming of the envelope layer 314, the salt
breaks the metal crosslinks by the co-crosslinking agent (b). The
rubber composition of the envelope layer 314 can include the acid
and/or the salt (d) described above for the envelope layer 12 of
the first embodiment. In the present invention, the co-crosslinking
agent (b) is not included in the concept of the acid and/or the
salt (d).
[0390] In light of linearity of the hardness distribution of the
envelope layer 314, the amount of the acid and/or the salt (d) is
preferably equal to or greater than 1.0 parts by weight, more
preferably equal to or greater than 2.0 parts by weight, and
particularly preferably equal to or greater than 3.0 parts by
weight, per 100 parts by weight of the base rubber. In light of
resilience performance, the amount is preferably equal to or less
than 40 parts by weight, more preferably equal to or less than 30
parts by weight, and particularly preferably equal to or less than
20 parts by weight, per 100 parts by weight of the base rubber.
[0391] The weight ratio of the co-crosslinking agent (b) and the
acid and/or the salt (d) in the rubber composition is preferably
equal to or greater than 3/7 but equal to or less than 9/1, and is
particularly preferably equal to or greater than 4/6 but equal to
or less than 8/2. From the rubber composition in which this weight
ratio is within the above range, the core 304 having an appropriate
hardness distribution can be obtained.
[0392] As the co-crosslinking agent (b), zinc acrylate is
preferably used. Zinc acrylate whose surface is coated with stearic
acid or zinc stearate for the purpose of improving dispersibility
to rubber is present. When the rubber composition includes this
zinc acrylate, the stearic acid or zinc stearate coating the zinc
acrylate is not included in the concept of the acid and/or the salt
(d).
[0393] Preferably, the rubber composition of the envelope layer 314
further includes the organic sulfur compound (e) described above
for the envelope layer 12 of the first embodiment. The organic
sulfur compound (e) can contribute to control of: the linearity of
the hardness distribution of the envelope layer 314; and the degree
of the outer-hard/inner-soft structure.
[0394] From the standpoint that an outer-hard/inner-soft structure
is easily obtained, the amount of the organic sulfur compound (e)
is preferably equal to or greater than 0.05 parts by weight, more
preferably equal to or greater than 0.1 parts by weight, and
particularly preferably equal to or greater than 0.2 parts by
weight, per 100 parts by weight of the base rubber. In light of
resilience performance, the amount is preferably equal to or less
than 5.0 parts by weight, more preferably equal to or less than 3.0
parts by weight, and particularly preferably equal to or less than
1.0 parts by weight, per 100 parts by weight of the base
rubber.
[0395] For the purpose of adjusting specific gravity and the like,
a filler may be included in the envelope layer 314. Examples of
suitable fillers include zinc oxide, barium sulfate, calcium
carbonate, and magnesium carbonate. The amount of the filler is
determined as appropriate so that the intended specific gravity of
the core 304 is accomplished. A particularly preferable filler is
zinc oxide. Zinc oxide serves not only as a specific gravity
adjuster but also as a crosslinking activator.
[0396] According to need, an anti-aging agent, a coloring agent, a
plasticizer, a dispersant, sulfur, a vulcanization accelerator, and
the like are added to the rubber composition of the envelope layer
314. Crosslinked rubber powder or synthetic resin powder may also
be dispersed in the rubber composition.
[0397] During heating of the core 304, the heat of a crosslinking
reaction remains near the central point of the core 304. Thus,
during heating of the core 304, the temperature at the central
portion is high. The temperature gradually decreases from the
central point toward the surface. The acid and/or the salt (d)
reacts with a metal salt of the co-crosslinking agent (b) to
inhibit formation of metal crosslinks or break metal crosslinks,
respectively. This reaction is accelerated in a region where the
temperature is high. In other words, inhibition of formation of
metal crosslinks and breaking of metal crosslinks are likely to
occur near the innermost portion of the envelope layer 314 where
the temperature is high, and are unlikely to occur near the surface
of the envelope layer 314. As a result, the crosslinking density of
the envelope layer 314 increases from its inside toward its
outside. In the envelope layer 314, the hardness linearly increases
from its inside toward its outside. Furthermore, since the rubber
composition includes the organic sulfur compound (e) together with
the acid and/or the salt (d), the gradient of the hardness
distribution can be controlled, and the degree of the
outer-hard/inner-soft structure of the core 304 can be
increased.
[0398] The hardness H(0.0) at the central point of the core 304 is
preferably equal to or greater than 40.0 but equal to or less than
68.0. The golf ball 302 having a hardness H(0.0) of 40.0 or greater
has excellent resilience performance. In this respect, the hardness
H(0.0) is more preferably equal to or greater than 45.0 and
particularly preferably equal to or greater than 47.0. In the core
304 having a hardness H(0.0) of 68.0 or less, an
outer-hard/inner-soft structure can be achieved. In the golf ball
302 that includes the core 304, spin can be suppressed. In this
respect, the hardness H(0.0) is more preferably equal to or less
than 65.0 and particularly preferably equal to or less than
63.0.
[0399] The hardness Hs at the surface of the core 304 is preferably
equal to or greater than 70.0 but equal to or less than 95.0. In
the core 304 having a hardness Hs of 70.0 or greater, an
outer-hard/inner-soft structure can be achieved. In the golf ball
302 that includes the core 304, spin can be suppressed. In this
respect, the hardness Hs is more preferably equal to or greater
than 80.0 and particularly preferably equal to or greater than
82.0. The golf ball 302 having a hardness Hs of 95.0 or less has
excellent durability. In this respect, the hardness Hs is more
preferably equal to or less than 94.0 and particularly preferably
equal to or less than 92.0.
[0400] The core 304 preferably has a diameter of 34.0 mm or greater
but 39.0 mm or less. The core 304 having a diameter of 34.0 mm or
greater can achieve excellent resilience performance of the golf
ball 302. In this respect, the diameter is more preferably equal to
or greater than 35.0 mm and particularly preferably equal to or
greater than 35.5 mm. In the golf ball 302 that includes the core
304 having a diameter of 39.0 mm or less, the inner cover 306 and
the outer cover 310 can have sufficient thicknesses. The golf ball
302 that includes the inner cover 306 and the outer cover 310 which
have large thicknesses has excellent durability. In this respect,
the diameter is more preferably equal to or less than 38.0 mm and
particularly preferably equal to or less than 37.5 mm.
[0401] In light of feel at impact, the core 304 has an amount of
compressive deformation Dc of preferably 3.5 mm or greater and
particularly preferably 3.8 mm or greater. In light of resilience
performance of the core 304, the amount of compressive deformation
DC is preferably equal to or less than 4.5 mm and particularly
preferably equal to or less than 4.0 mm.
[0402] For the inner cover 306, a resin composition is suitably
used. Examples of the base polymer of the resin composition include
ionomer resins, polystyrenes, polyesters, polyamides, and
polyolefins.
[0403] Particularly preferable base polymers are ionomer resins.
The golf ball 302 that includes the inner cover 306 including an
ionomer resin has excellent resilience performance. An ionomer
resin and another resin may be used in combination for the inner
cover 306. In this case, the principal component of the base
polymer is preferably the ionomer resin. Specifically, the
proportion of the ionomer resin to the entire base polymer is
preferably equal to or greater than 50% by weight, more preferably
equal to or greater than 52% by weight, and particularly preferably
equal to or greater than 64% by weight.
[0404] The resin composition of the inner cover 306 can include the
ionomer resin described above for the golf ball 2 of the first
embodiment. The resin composition of the inner cover 306 can
include the styrene block-containing thermoplastic elastomer
described above for the golf ball 2 of the first embodiment.
[0405] According to need, a coloring agent such as titanium
dioxide, a filler such as barium sulfate, a dispersant, an
antioxidant, an ultraviolet absorber, a light stabilizer, a
fluorescent material, a fluorescent brightener, and the like are
included in the resin composition of the inner cover 306 in an
adequate amount.
[0406] In light of resilience performance of the golf ball 302, the
inner cover 306 has a JIS-C hardness Hi of preferably 60 or
greater, more preferably 62 or greater, and particularly preferably
64 or greater. In light of feel at impact of the golf ball 302, the
hardness Hi is preferably equal to or less than 90, more preferably
equal to or less than 88, and particularly preferably equal to or
less than 86. The hardness Hi is measured by the method described
above for the golf ball 2 of the first embodiment.
[0407] The difference (Hi-Hs) between the JIS-C hardness Hi of the
inner cover 306 and the hardness Hs is less than 1. If the
difference (Hi-Hs) is less than 1, the feel at impact is soft when
the golf ball 302 is hit with a driver. In light of intensity of
the feel at impact which a golf player obtains when hitting, the
difference (Hi-Hs) is preferably equal to or greater than -15 and
further preferably equal to or greater than -10.
[0408] The inner cover 306 preferably has a thickness Ti of 0.5 mm
or greater but 1.6 mm or less. The sphere that includes the inner
cover 306 having a thickness Ti of 0.5 mm or greater has excellent
feel at impact. In this respect, the thickness Ti is particularly
preferably equal to or greater than 0.7 mm. The golf ball 302 that
includes the inner cover 306 having a thickness Ti of 1.6 mm or
less can include a large core 304. The large core 304 can
contribute to the resilience performance of the golf ball 302. In
this respect, the thickness Ti is particularly preferably equal to
or less than 1.2 mm.
[0409] For the mid cover 308, a resin composition is suitably used.
Examples of the base polymer of the resin composition include
ionomer resins, polystyrenes, polyesters, polyamides, and
polyolefins.
[0410] Particularly preferable base polymers are ionomer resins.
The ionomer resin described above for the inner cover 306 can be
used. The golf ball 302 that includes the mid cover 308 including
an ionomer resin has excellent resilience performance. An ionomer
resin and another resin may be used in combination for the mid
cover 308. In this case, the principal component of the base
polymer is preferably the ionomer resin. Specifically, the
proportion of the ionomer resin to the entire base polymer is
preferably equal to or greater than 60% by weight, more preferably
equal to or greater than 70% by weight, and particularly preferably
equal to or greater than 80% by weight. The mid cover 308 can
include the other resin described above for the inner cover
306.
[0411] As described later, the mid cover 308 preferably has a JIS-C
hardness Hm greater than the hardness Hi of the inner cover 306. By
decreasing the amount of the styrene block-containing thermoplastic
elastomer blended in the resin composition of the mid cover 308, a
great hardness Hm can be achieved. By blending a highly elastic
resin in the resin composition, a great hardness Hm may be
achieved. Specific examples of the highly elastic resin include
polyamides.
[0412] According to need, a coloring agent such as titanium
dioxide, a filler such as barium sulfate, a dispersant, an
antioxidant, an ultraviolet absorber, a light stabilizer, a
fluorescent material, a fluorescent brightener, and the like are
included in the resin composition of the mid cover 308 in an
adequate amount.
[0413] In light of suppression of spin, the hardness Hm is
preferably equal to or greater than 50, more preferably equal to or
greater than 60, and particularly preferably equal to or greater
than 68. In light of feel at impact, the hardness Hm is preferably
equal to or less than 95, more preferably equal to or less than 92,
and particularly preferably equal to or less than 91. The hardness
Hm is measured by the same measurement method as that for the
hardness Hi.
[0414] The hardness Hm is preferably greater than the hardness Hi
of the inner cover 306. In the golf ball 302 that includes this
sphere, the shock by a hit with a driver is alleviated.
[0415] In light of flight performance, the difference (Hm-Hi)
between the hardness Hm and the hardness Hi is preferably equal to
or greater than 6 and more preferably equal to or greater than 10.
In light of durability, the difference (Hm-Hi) is preferably equal
to or less than 20.
[0416] The mid cover 308 preferably has a thickness Tm of 0.5 mm or
greater but 1.6 mm or less. The sphere that includes the mid cover
308 having a thickness Tm of 0.5 mm or greater has excellent
durability. In this respect, the thickness Tm is particularly
preferably equal to or greater than 0.7 mm. The golf ball 302 that
includes the mid cover 308 having a thickness Tm of 1.6 m or less
can include a large core 304. The large core 304 can contribute to
the resilience performance of the golf ball 302. In this respect,
the thickness Tm is particularly preferably equal to or less than
1.2 mm.
[0417] For the outer cover 310, a resin composition is suitably
used. Examples of the base polymer of the resin composition include
ionomer resins, polystyrenes, polyesters, polyamides, and
polyolefins.
[0418] Particularly preferable base polymers are ionomer resins.
The ionomer resin described above for the inner cover 306 can be
used. The golf ball 302 that includes the outer cover 310 including
an ionomer resin has excellent resilience performance. An ionomer
resin and another resin may be used in combination for the outer
cover 310. In this case, the principal component of the base
polymer is preferably the ionomer resin. Specifically, the
proportion of the ionomer resin to the entire base polymer is
preferably equal to or greater than 50% by weight, more preferably
equal to or greater than 60% by weight, and particularly preferably
equal to or greater than 70% by weight.
[0419] The outer cover 310 can include the other resin described
above for the inner cover 306.
[0420] Another resin that can be used in combination with an
ionomer resin is an ethylene-(meth) acrylic acid copolymer. The
copolymer is obtained by a copolymerization reaction of a monomer
composition that contains ethylene and (meth) acrylic acid. In the
copolymer, some of the carboxyl groups are neutralized with metal
ions. The copolymer includes 3% by weight or greater but 25% by
weight or less of a (meth)acrylic acid component. An
ethylene-(meth) acrylic acid copolymer having a polar functional
group is particularly preferred. A specific example of
ethylene-(meth) acrylic acid copolymers is trade name "NUCREL"
manufactured by Du Pont-MITSUI POLYCHEMICALS Co., Ltd.
[0421] As described later, the outer cover 310 preferably has a
JIS-C hardness Ho greater than the hardness Hm of the mid cover
308. In this respect, the resin composition of the outer cover 310
may include a highly elastic resin. Specific examples of the highly
elastic resin include polyamides.
[0422] According to need, a coloring agent such as titanium
dioxide, a filler such as barium sulfate, a dispersant, an
antioxidant, an ultraviolet absorber, a light stabilizer, a
fluorescent material, a fluorescent brightener, and the like are
included in the resin composition of the outer cover 310 in an
adequate amount.
[0423] In light of suppression of spin, the hardness Ho of the
outer cover 310 is preferably equal to or greater than 80, more
preferably equal to or greater than 82, and particularly preferably
equal to or greater than 84. In light of feel at impact, the
hardness Ho is preferably equal to or less than 96, more preferably
equal to or less than 95, and particularly preferably equal to or
less than 93. The hardness Ho is measured by the same measurement
method as that for the hardness Hi. The hardness Ho of the outer
cover 310 is greater than the hardness Hi of the inner cover 306.
When the golf ball 302 is hit, the spin rate is low. When the golf
ball 302 is hit with a driver, particularly excellent flight
performance is exerted.
[0424] In light of flight performance, the difference (Ho-Hi)
between the hardness Ho of the outer cover 310 and the hardness Hi
of the inner cover 306 is preferably equal to or greater than 5,
more preferably equal to or greater than 9, and particularly
preferably equal to or greater than 15. In light of durability, the
difference (Ho-Hi) is preferably equal to or less than 30.
[0425] In light of resilience performance, the hardness Ho of the
outer cover 310 is preferably greater than the hardness Hm of the
mid cover 308. In the golf ball 302, the hardness increases from
its central portion to its surface. In the entirety of the golf
ball 302, an outer-hard/inner-soft structure is achieved. When the
golf ball 302 is hit, the flight distance is large.
[0426] In light of flight performance, the difference (Ho-Hm)
between the hardness Ho of the outer cover 310 and the hardness Hm
of the mid cover 308 is preferably equal to or greater than 3 and
particularly preferably equal to or greater than 7. In light of
durability, the difference (Ho-Hm) is preferably equal to or less
than 25.
[0427] In light of durability, the outer cover 310 has a thickness
To of preferably 0.1 mm or greater and particularly preferably 0.2
mm or greater. In light of flight performance, the thickness To is
preferably equal to or less than 1.4 mm and particularly preferably
equal to or less than 1.2 mm.
[0428] For forming the outer cover 310, known methods such as
injection molding, compression molding, and the like can be used.
When forming the outer cover 310, the dimples 316 are formed by
pimples formed on the cavity face of a mold.
[0429] In light of feel at impact, the sum (Ti+Tm+To) of the
thickness Ti, the thickness Tm, and the thickness To is preferably
equal to or less than 4.0 mm, more preferably equal to or less than
3.9 mm, and particularly preferably equal to or less than 3.5 mm.
In light of durability and wear resistance of the golf ball 302,
the sum (Ti+Tm+To) is preferably equal to or greater than 0.3 mm,
more preferably equal to or greater than 0.5 mm, and particularly
preferably equal to or greater than 0.8 mm.
[0430] In light of feel at impact, the golf ball 302 has an amount
of compressive deformation Db of preferably 2.2 mm or greater, more
preferably 2.5 mm or greater, and particularly preferably 2.8 mm or
greater. In light of resilience performance, the amount of
compressive deformation Db is preferably equal to or less than 4.0
mm, more preferably equal to or less than 3.7 mm, and particularly
preferably equal to or less than 3.4 mm. The amount of compressive
deformation is measured by the method described above for the golf
ball 2 of the first embodiment.
[0431] The golf ball may include a center formed from a rubber
composition that includes the acid and/or the salt (d); and an
envelope layer formed from a rubber composition that does not
include the acid and/or the salt (d). The rubber composition of the
center is the same as the rubber composition of the envelope layer
314 shown in FIG. 7. A hardness distribution of the center is
appropriate.
[0432] The golf ball may include a center formed from a rubber
composition that includes the acid and/or the salt (d); and an
envelope layer formed from a rubber composition that includes the
acid and/or the salt (d). The rubber composition of the center is
the same as the rubber composition of the envelope layer 314 shown
in FIG. 7. The rubber composition of the envelope layer is the same
as the rubber composition of the envelope layer 314 shown in FIG.
7. A hardness distribution of the center is appropriate. A hardness
distribution of the envelope layer is appropriate.
[0433] Preferred embodiments of the invention are specified in the
following paragraphs:
[0434] 1. A golf ball comprising a core, an inner cover positioned
outside the core, and an outer cover positioned outside the inner
cover, wherein
[0435] the core comprises a center and an envelope layer positioned
outside the center,
[0436] the center is formed by a rubber composition being
crosslinked,
[0437] the envelope layer is formed by a rubber composition being
crosslinked,
[0438] at least one of the rubber composition of the center and the
rubber composition of the envelope layer includes: [0439] (a) a
base rubber; [0440] (b) a co-crosslinking agent; [0441] (c) a
crosslinking initiator; and [0442] (d) an acid and/or a salt,
[0443] the co-crosslinking agent (b) is: [0444] (b1) an
.alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon
atoms; or [0445] (b2) a metal salt of an .alpha.,.beta.-unsaturated
carboxylic acid having 3 to 8 carbon atoms,
[0446] a JIS-C hardness Hi of the inner cover is greater than a
JIS-C hardness Hs at a surface of the core, and
[0447] a JIS-C hardness Ho of the outer cover is less than the
hardness Hi.
[0448] 2. The golf ball according to paragraph 1, wherein a
difference (Hi-Hs) between the hardness Hi and the hardness Hs is
equal to or greater than 2.
[0449] 3. The golf ball according to paragraph 1, wherein a
difference (Hi-Ho) between the hardness Hi and the hardness Ho is
equal to or greater than 1.
[0450] 4. The golf ball according to paragraph 1, wherein an amount
of the acid and/or the salt (d) is equal to or greater than 1.0
parts by weight but less than 40 parts by weight, per 100 parts by
weight of the base rubber (a).
[0451] 5. The golf ball according to paragraph 1, wherein the acid
and/or the salt (d) is a carboxylic acid and/or a salt thereof
(d1).
[0452] 6. The golf ball according to paragraph 5, wherein a carbon
number of a carboxylic acid component of the carboxylic acid and/or
the salt thereof (d1) is equal to or greater than 1 but equal to or
less than 30.
[0453] 7. The golf ball according to paragraph 5, wherein the
carboxylic acid and/or the salt thereof (d1) is a fatty acid and/or
a salt thereof.
[0454] 8. The golf ball according to paragraph 5, wherein the
carboxylic acid and/or the salt thereof (d1) is a zinc salt of a
carboxylic acid.
[0455] 9. The golf ball according to paragraph 8, wherein the zinc
salt of the carboxylic acid is one or more members selected from
the group consisting of zinc octoate, zinc laurate, zinc myristate,
and zinc stearate.
[0456] 10. The golf ball according to paragraph 1, wherein the
rubber composition includes 15 parts by weight or greater but 50
parts by weight or less of the co-crosslinking agent (b) per 100
parts by weight of the base rubber (a).
[0457] 11. The golf ball according to paragraph 1, wherein the
rubber composition includes 0.2 parts by weight or greater but 5.0
parts by weight or less of the crosslinking initiator (c) per 100
parts by weight of the base rubber (a).
[0458] 12. The golf ball according to paragraph 1, wherein a
difference (Hs-H(0.0)) between the hardness Hs and a JIS-C hardness
H(0.0) at a central point of the core is equal to or greater than
15.
[0459] 13. The golf ball according to paragraph 1, wherein a sum
(Ti+To) of a thickness Ti of the inner cover and a thickness To of
the outer cover is equal to or less than 2.5 mm.
[0460] 14. The golf ball according to paragraph 1, wherein the
rubber composition further includes an organic sulfur compound
(e).
[0461] 15. The golf ball according to paragraph 14, wherein the
organic sulfur compound (e) is at least one member selected from
the group consisting of thiophenols, diphenyl disulfides,
thionaphthols, thiuram disulfides, and metal salts thereof.
[0462] 16. The golf ball according to paragraph 14, wherein the
rubber composition includes 0.05 parts by weight or greater but 5
parts by weight or less of the organic sulfur compound (e) per 100
parts by weight of the base rubber (a).
[0463] 17. The golf ball according to paragraph 1, wherein
[0464] the rubber composition includes the
.alpha.,.beta.-unsaturated carboxylic acid (b1), and
[0465] the rubber composition further includes a metal compound
(f).
[0466] 18. A golf ball comprising a core, an inner cover positioned
outside the core, and an outer cover positioned outside the inner
cover, wherein
[0467] the core comprises a center and an envelope layer positioned
outside the center,
[0468] the center is formed by a rubber composition being
crosslinked,
[0469] the envelope layer is formed by a rubber composition being
crosslinked,
[0470] at least one of the rubber composition of the center and the
rubber composition of the envelope layer includes: [0471] (a) a
base rubber; [0472] (b) a co-crosslinking agent; [0473] (c) a
crosslinking initiator; and [0474] (d) an acid and/or a salt,
[0475] the co-crosslinking agent (b) is: [0476] (b1) an
.alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon
atoms; or [0477] (b2) a metal salt of an .alpha.,.beta.-unsaturated
carboxylic acid having 3 to 8 carbon atoms,
[0478] a JIS-C hardness Ho of the outer cover is greater than a
JIS-C hardness Hs at a surface of the core, and
[0479] the hardness Ho is greater than a JIS-C hardness Hi of the
inner cover.
[0480] 19. The golf ball according to paragraph 18, wherein the
acid and/or the salt (d) is a carboxylic acid and/or a salt thereof
(d1).
[0481] 20. The golf ball according to paragraph 19, wherein a
carbon number of a carboxylic acid component of the carboxylic acid
and/or the salt thereof (d1) is equal to or greater than 1 but
equal to or less than 30.
[0482] 21. The golf ball according to paragraph 19, wherein the
carboxylic acid and/or the salt thereof (d1) is a fatty acid and/or
a salt thereof.
[0483] 22. The golf ball according to paragraph 19, wherein the
carboxylic acid and/or the salt thereof (d1) is a zinc salt of a
carboxylic acid.
[0484] 23. The golf ball according to paragraph 19, wherein the
carboxylic acid and/or the salt thereof (d1) is one or more members
selected from the group consisting of zinc octoate, zinc laurate,
zinc myristate, and zinc stearate.
[0485] 24. The golf ball according to paragraph 18, wherein a
difference (Ho-Hs) between the hardness Ho and the hardness Hs is
equal to or greater than 2.
[0486] 25. The golf ball according to paragraph 18, wherein a
difference (Ho-Hi) between the hardness Ho and the hardness Hi is
equal to or greater than 2.
[0487] 26. The golf ball according to paragraph 18, wherein the
rubber composition includes 1.0 parts by weight or greater but 40
parts by weight or less of the acid and/or the salt (d) per 100
parts by weight of the base rubber (a).
[0488] 27. The golf ball according to paragraph 18, wherein the
rubber composition includes 15 parts by weight or greater but 50
parts by weight or less of the co-crosslinking agent (b) per 100
parts by weight of the base rubber (a).
[0489] 28. The golf ball according to paragraph 18, wherein the
rubber composition includes 0.2 parts by weight or greater but 5.0
parts by weight or less of the crosslinking initiator (c) per 100
parts by weight of the base rubber (a).
[0490] 29. The golf ball according to paragraph 18, wherein a
difference (Hs-H(0.0)) between the hardness Hs and a JIS-C hardness
H(0.0) at a central point of the core is equal to or greater than
15.
[0491] 30. The golf ball according to paragraph 18, wherein a sum
(Ti+To) of a thickness Ti of the inner cover and a thickness To of
the outer cover is equal to or less than 2.5 mm.
[0492] 31. The golf ball according to paragraph 18, wherein the
rubber composition further includes an organic sulfur compound
(e).
[0493] 32. The golf ball according to paragraph 31, wherein the
organic sulfur compound (e) is at least one member selected from
the group consisting of thiophenols, diphenyl disulfides,
thionaphthols, thiuram disulfides, and metal salts thereof.
[0494] 33. The golf ball according to paragraph 31, wherein the
rubber composition includes 0.05 parts by weight or greater but 5
parts by weight or less of the organic sulfur compound (e) per 100
parts by weight of the base rubber (a).
[0495] 34. The golf ball according to paragraph 18, wherein
[0496] the rubber composition includes the
.alpha.,.beta.-unsaturated carboxylic acid (b1), and
[0497] the rubber composition further includes a metal compound
(f).
[0498] 35. A golf ball comprising a core, an inner cover positioned
outside the core, a mid cover positioned outside the inner cover,
and an outer cover positioned outside the mid cover, wherein
[0499] the core comprises a center and an envelope layer positioned
outside the center,
[0500] the center is formed by a rubber composition being
crosslinked,
[0501] the envelope layer is formed by a rubber composition being
crosslinked,
[0502] at least one of the rubber composition of the center and the
rubber composition of the envelope layer includes: [0503] (a) a
base rubber; [0504] (b) a co-crosslinking agent; [0505] (c) a
crosslinking initiator; and [0506] (d) an acid and/or a salt,
[0507] the co-crosslinking agent (b) is: [0508] (b1) an
.alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon
atoms; or [0509] (b2) a metal salt of an .alpha.,.beta.-unsaturated
carboxylic acid having 3 to 8 carbon atoms,
[0510] a JIS-C hardness Hi of the inner cover is greater than a
JIS-C hardness Hs at a surface of the core,
[0511] a difference (Hi-Hs) between the hardness Hi and the
hardness Hs is equal to or greater than 1, and
[0512] a JIS-C hardness Ho of the outer cover is greater than the
hardness Hi.
[0513] 36. The golf ball according to paragraph 35, wherein the
acid and/or the salt (d) is a carboxylic acid and/or a salt thereof
(d1).
[0514] 37. The golf ball according to paragraph 36, wherein a
carbon number of a carboxylic acid component of the carboxylic acid
and/or the salt thereof (d1) is equal to or greater than 1 but
equal to or less than 30.
[0515] 38. The golf ball according to paragraph 36, wherein the
carboxylic acid and/or the salt thereof (d1) is a fatty acid and/or
a salt thereof.
[0516] 39. The golf ball according to paragraph 36, wherein the
carboxylic acid and/or the salt thereof (d1) is a zinc salt of a
carboxylic acid.
[0517] 40. The golf ball according to paragraph 36, wherein the
carboxylic acid and/or the salt thereof (d1) is one or more members
selected from the group consisting of zinc octoate, zinc laurate,
zinc myristate, and zinc stearate.
[0518] 41. The golf ball according to paragraph 35, wherein the
rubber composition includes 1.0 parts by weight or greater but 40
parts by weight or less of the acid and/or the salt (d) per 100
parts by weight of the base rubber (a).
[0519] 42. The golf ball according to paragraph 35, wherein the
rubber composition includes 15 parts by weight or greater but 50
parts by weight or less of the co-crosslinking agent (b) per 100
parts by weight of the base rubber (a).
[0520] 43. The golf ball according to paragraph 35, wherein the
rubber composition includes 0.2 parts by weight or greater but 5.0
parts by weight or less of the crosslinking initiator (c) per 100
parts by weight of the base rubber (a).
[0521] 44. The golf ball according to paragraph 35, wherein
[0522] the rubber composition includes the
.alpha.,.beta.-unsaturated carboxylic acid (b1), and
[0523] the rubber composition further includes a metal compound
(f).
[0524] 45. The golf ball according to paragraph 35, wherein a
difference (Ho-Hi) between the hardness Ho and the hardness Hi is
equal to or greater than 2.
[0525] 46. The golf ball according to paragraph 35, wherein a
difference (Hs-H(0.0)) between the hardness Hs and a JIS-C hardness
H(0.0) at a central point of the core is equal to or greater than
15.
[0526] 47. The golf ball according to paragraph 35, wherein a sum
(Ti+Tm+To) of a thickness Ti of the inner cover, a thickness Tm of
the mid cover, and a thickness To of the outer cover is equal to or
less than 4.0 mm.
[0527] 48. The golf ball according to paragraph 35, wherein the
rubber composition further includes an organic sulfur compound
(e).
[0528] 49. The golf ball according to paragraph 48, wherein the
organic sulfur compound (e) is at least one member selected from
the group consisting of thiophenols, diphenyl disulfides,
thionaphthols, thiuram disulfides, and metal salts thereof.
[0529] 50. The golf ball according to paragraph 48, wherein the
rubber composition includes 0.05 parts by weight or greater but 5
parts by weight or less of the organic sulfur compound (e) per 100
parts by weight of the base rubber (a).
[0530] 51. The golf ball according to paragraph 35, wherein
[0531] a JIS-C hardness Hm of the mid cover is greater than the
hardness Hi, and
[0532] the hardness Ho is greater than the hardness Hm.
[0533] 52. The golf ball according to paragraph 51, wherein a
difference (Hm-Hi) between the hardness Hm and the hardness Hi is
equal to or greater than 2.
[0534] 53. The golf ball according to paragraph 51, wherein a
difference (Ho-Hm) between the hardness Ho and the hardness Hm is
equal to or greater than 3.
[0535] 54. A golf ball comprising a core, an inner cover positioned
outside the core, a mid cover positioned outside the inner cover,
and an outer cover positioned outside the mid cover, wherein
[0536] the core comprises a center and an envelope layer positioned
outside the center,
[0537] the center is formed by a rubber composition being
crosslinked,
[0538] the envelope layer is formed by a rubber composition being
crosslinked,
[0539] at least one of the rubber composition of the center and the
rubber composition of the envelope layer includes: [0540] (a) a
base rubber; [0541] (b) a co-crosslinking agent; [0542] (c) a
crosslinking initiator; and [0543] (d) an acid and/or a salt,
[0544] the co-crosslinking agent (b) is: [0545] (b1) an
.alpha.,.beta.-unsaturated carboxylic acid having 3 to 8 carbon
atoms; or [0546] (b2) a metal salt of an .alpha.,.beta.-unsaturated
carboxylic acid having 3 to 8 carbon atoms,
[0547] a difference (Hi-Hs) between a JIS-C hardness Hi of the
inner cover and a JIS-C hardness Hs at a surface of the core is
less than 1, and
[0548] a JIS-C hardness Ho of the outer cover is greater than the
hardness Hi.
[0549] 55. The golf ball according to paragraph 54, wherein the
acid and/or the salt (d) is a carboxylic acid and/or a salt thereof
(d1).
[0550] 56. The golf ball according to paragraph 55, wherein a
carbon number of a carboxylic acid component of the carboxylic acid
and/or the salt thereof (d1) is equal to or greater than 1 but
equal to or less than 30.
[0551] 57. The golf ball according to paragraph 55, wherein the
carboxylic acid and/or the salt thereof (d1) is a fatty acid and/or
a salt thereof.
[0552] 58. The golf ball according to paragraph 55, wherein the
carboxylic acid and/or the salt thereof (d1) is a zinc salt of a
carboxylic acid.
[0553] 59. The golf ball according to paragraph 55, wherein the
carboxylic acid and/or the salt thereof (d1) is one or more members
selected from the group consisting of zinc octoate, zinc laurate,
zinc myristate, and zinc stearate.
[0554] 60. The golf ball according to paragraph 54, wherein the
rubber composition includes 1.0 parts by weight or greater but less
than 40 parts by weight of the acid and/or the salt (d) per 100
parts by weight of the base rubber (a).
[0555] 61. The golf ball according to paragraph 54, wherein the
rubber composition includes 15 parts by weight or greater but 50
parts by weight or less of the co-crosslinking agent (b) per 100
parts by weight of the base rubber (a).
[0556] 62. The golf ball according to paragraph 54, wherein the
rubber composition includes 0.2 parts by weight or greater but 5.0
parts by weight or less of the crosslinking initiator (c) per 100
parts by weight of the base rubber (a).
[0557] 63. The golf ball according to paragraph 54, wherein
[0558] the rubber composition includes the
.alpha.,.beta.-unsaturated carboxylic acid (b1), and
[0559] the rubber composition further includes a metal compound
(f).
[0560] 64. The golf ball according to paragraph 54, wherein a
difference (Ho-Hi) between the hardness Ho and the hardness Hi is
equal to or greater than 5.
[0561] 65. The golf ball according to paragraph 54, wherein a
difference (Hs-H(0.0)) between the hardness Hs and a JIS-C hardness
H(0.0) at a central point of the core is equal to or greater than
15.
[0562] 66. The golf ball according to paragraph 54, wherein a sum
(Ti+Tm+To) of a thickness Ti of the inner cover, a thickness Tm of
the mid cover, and a thickness To of the outer cover is equal to or
less than 4.0 mm.
[0563] 67. The golf ball according to paragraph 54, wherein the
rubber composition further includes an organic sulfur compound
(e).
[0564] 68. The golf ball according to paragraph 67, wherein the
organic sulfur compound (e) is at least one member selected from
the group consisting of thiophenols, diphenyl disulfides,
thionaphthols, thiuram disulfides, and metal salts thereof.
[0565] 69. The golf ball according to paragraph 67, wherein the
rubber composition includes 0.05 parts by weight or greater but 5
parts by weight or less of the organic sulfur compound (e) per 100
parts by weight of the base rubber (a).
[0566] 70. The golf ball according to paragraph 54, wherein
[0567] a JIS-C hardness Hm of the mid cover is greater than the
hardness Hi, and
[0568] the hardness Ho is greater than the hardness Hm.
[0569] 71. The golf ball according to paragraph 70, wherein a
difference (Hm-Hi) between the hardness Hm and the hardness Hi is
equal to or greater than 6.
[0570] 72. The golf ball according to paragraph 70, wherein a
difference (Ho-Hm) between the hardness Ho and the hardness Hm is
equal to or greater than 3.
EXAMPLES
Experiment 1
Example I-1
[0571] A rubber composition was obtained by kneading 100 parts by
weight of a high-cis polybutadiene (trade name "BR-730",
manufactured by JSR Corporation), 28 parts by weight of methacrylic
acid, 34 parts by weight of magnesium oxide, and 0.75 parts by
weight of dicumyl peroxide. This rubber composition was placed into
a mold including upper and lower mold halves each having a
hemispherical cavity, and heated at 170.degree. C. for 25 minutes
to obtain a center with a diameter of 15 mm.
[0572] A rubber composition was obtained by kneading 100 parts by
weight of a high-cis polybutadiene (the aforementioned "BR-730"),
26 parts by weight of zinc diacrylate (trade name "Sanceler SR",
manufactured by SANSHIN CHEMICAL INDUSTRY CO., LTD.), 5.0 parts by
weight of zinc oxide, an appropriate amount of barium sulfate, 0.20
parts by weight of 2-thionaphthol, 10.0 parts by weight of zinc
stearate, and 0.75 parts by weight of dicumyl peroxide. Half shells
were formed from this rubber composition. The center was covered
with two of these half shells. The center and the half shells were
placed into a mold including upper and lower mold halves each
having a hemispherical cavity, and heated at 150.degree. C. for 20
minutes to obtain a core with a diameter of 39.1 mm. An envelope
layer was formed from the rubber composition. The amount of barium
sulfate was adjusted such that the specific gravity of the envelope
layer coincides with the specific gravity of the center and the
weight of a golf ball is 45.4 g.
[0573] A resin composition was obtained by kneading 50 parts by
weight of an ionomer resin (the aforementioned "Himilan 1605"), 50
parts by weight of another ionomer resin (the aforementioned
"Himilan AM7329"), and 4 parts by weight of titanium dioxide with a
twin-screw kneading extruder. The core was placed into a mold
including upper and lower mold halves each having a hemispherical
cavity. The resin composition was injected around the core by
injection molding to form an inner cover with a thickness of 1.0
mm.
[0574] A resin composition was obtained by kneading 46 parts by
weight of an ionomer resin (the aforementioned "Himilan 1555"), 45
parts by weight of another ionomer resin (the aforementioned
"Himilan AM7329"), 9 parts by weight of a styrene block-containing
thermoplastic elastomer (the aforementioned "Rabalon T3221C", 3
parts by weight of titanium dioxide, and 0.2 parts by weight of an
ultraviolet absorber (trade name "TINJVIN 770", manufactured by
Ciba Japan K. K.) with a twin-screw kneading extruder. The sphere
consisting of the core and the inner cover was placed into a final
mold having a large number of pimples on its cavity face. The resin
composition was injected around the sphere by injection molding to
form an outer cover with a thickness of 0.8 mm. Dimples having a
shape that is the inverted shape of the pimples were formed on the
outer cover. A clear paint including a two-component curing type
polyurethane as a base material was applied to this outer cover to
obtain a golf ball of Example I-1 with a diameter of 42.7 mm.
Examples I-2 to I-16 and Comparative Examples I-1 to I-6
[0575] Golf balls of Examples I-2 to I-16 and Comparative Examples
I-1 to I-6 were obtained in the same manner as Example I-1, except
the specifications of the center, the envelope layer, the inner
cover, and the outer cover were as shown in Tables I-10 to I-13
below. The composition of the core is shown in detail in Tables I-1
to I-3 below. The compositions of the inner cover and the outer
cover are shown in detail in Table I-4 below. The hardness of the
core is shown in Tables I-5 to I-9 below. Each of the golf balls
according to Comparative Examples I-4 and I-5 does not have an
envelope layer.
[0576] [Hit with Driver (W #1)]
[0577] A driver with a titanium head (trade name "XXIO",
manufactured by DUNLOP SPORTS CO. LTD., shaft hardness: R, loft
angle: 11.0.degree.) was attached to a swing machine manufactured
by True Temper Co. A golf ball was hit under the condition of a
head speed of 40 m/sec. The spin rate was measured immediately
after the hit. Furthermore, the distance from the launch point to
the stop point was measured. The average value of data obtained by
10 measurements is shown in Tables I-10 to I-13 below.
[0578] [Hit with Sand Wedge (SW)]
[0579] A sand wedge (SW) was attached to the above swing machine. A
golf ball was hit under the condition of a head speed of 21 m/sec.
The spin rate was measured immediately after the hit. The average
value of data obtained by 10 measurements is shown in Tables I-10
to I-13 below.
TABLE-US-00001 TABLE I-1 Composition of Core (parts by weight) A B
BR-730 100 100 Methacrylic acid 28 -- Sanceler SR -- 20 Magnesium
oxide 34 -- Zinc oxide -- 5 Barium sulfate -- * 2-thionaphthol --
0.2 Zinc octoate -- 5 Dicumyl peroxide 0.75 0.75 * Appropriate
amount
TABLE-US-00002 TABLE I-2 Composition of Core (parts by weight) E1
E2 E3 E4 E5 E6 BR-730 100 100 100 100 100 100 Sanceler SR 26.0 27.5
29.5 31.5 27.0 26.5 Zinc oxide 5.0 5.0 5.0 5.0 5.0 5.0 Barium
sulfate * * * * * * 2-thionaphthol 0.20 0.20 0.20 0.20 0.20 0.20
Zinc octoate -- -- -- -- -- -- Zinc laurate -- -- -- -- -- -- Zinc
myristate -- -- -- -- -- -- Zinc stearate 10.0 20.0 30.0 40.0 --
0.5 Dicumyl 0.75 0.75 0.75 0.75 0.75 0.8 peroxide * Appropriate
amount
TABLE-US-00003 TABLE I-3 Composition of Core (parts by weight) E7
E8 E9 E10 E11 BR-730 100 100 100 100 100 Sanceler SR 25.5 25.0 25.5
26.0 25.5 Zinc oxide 5.0 5.0 5.0 5.0 5.0 Barium sulfate * * * * *
2-thionaphthol 0.20 0.20 0.20 0.20 0.20 Zinc octoate 2.5 5.0 -- --
-- Zinc laurate -- -- 10.0 -- -- Zinc myristate -- -- -- 5.0 10.0
Zinc stearate -- -- -- -- -- Dicumyl peroxide 0.8 0.8 0.8 0.8 0.8 *
Appropriate amount
[0580] The details of the compounds listed in Tables I-1 to I-3 are
as follows.
[0581] BR-730: a high-cis polybutadiene manufactured by JSR
Corporation (cis-1,4-bond content: 96% by weight, 1,2-vinyl bond
content: 1.3% by weight, Mooney viscosity (ML.sub.1+4(100.degree.
C.)): 55, molecular weight distribution (Mw/Mn): 3)
[0582] Methacrylic acid: a product of MITSUBISHI RAYON CO.,
LTD.
[0583] Sanceler SR: zinc diacrylate manufactured by SANSHIN
CHEMICAL INDUSTRY CO., LTD. (a product coated with 10% by weight of
stearic acid)
[0584] Magnesium oxide: trade name "MAGSARAT 150ST" manufactured by
Kyowa Chemical Industry Co., Ltd.
[0585] 2-thionaphthol: a product of Tokyo Chemical Industry Co.,
Ltd.
[0586] Zinc octoate: a product of Mitsuwa Chemicals Co., Ltd.
[0587] Zinc laurate: a product of Mitsuwa Chemicals Co., Ltd.
[0588] Zinc myristate: a product of NOF Corporation
[0589] Zinc stearate: a product of Wako Pure Chemical Industries,
Ltd.
[0590] Dicumyl peroxide: a product of NOF Corporation
TABLE-US-00004 TABLE I-4 Composition of Cover (parts by weight) C1
C2 C3 C4 C5 C6 C7 Himilan AM7337 5 -- 30 -- 51 40 26 Himilan 1555
10 46 -- -- -- -- -- Himilan 1605 -- -- -- 50 -- -- -- Himilan
AM7329 55 45 30 50 40 40 40 NUCREL N1050H 30 -- -- -- -- -- --
Rabalon T3221C -- 9 40 -- 9 20 34 Titanium dioxide 3 3 6 4 6 6 6
(A220) TINUVIN 770 0.2 0.2 0.2 -- -- -- -- Hardness(JIS-C) 92 88 71
96 89 85 76 Hardness(ShoreD) 61 57 40 65 58 54 45 * Appropriate
amount
TABLE-US-00005 TABLE I-5 Hardness Distribution of Core (JIS-C) Ex.
Ex. Ex. Ex. Ex. I-1 I-2 I-3 I-4 I-5 H(0.0) 55.0 55.0 55.0 55.0 55.0
H(2.5) 56.0 56.0 56.0 56.0 56.0 H(5.0) 58.0 58.0 58.0 58.0 58.0
H(7.0) 60.0 60.0 60.0 60.0 60.0 H(8.0) 64.6 65.2 63.8 64.4 67.0
H(10.0) 67.0 67.4 67.9 66.4 68.5 H(12.5) 71.8 71.0 73.8 71.0 70.1
H(15.0) 76.0 75.3 77.8 77.0 76.7 H(17.5) 79.5 80.6 82.0 80.7 80.5
Hs 83.0 84.1 84.9 83.3 83.4
TABLE-US-00006 TABLE I-6 Hardness Distribution of Core (JIS-C) Ex.
Ex. Ex. Ex. Ex. I-6 I-7 I-8 I-9 I-10 H(0.0) 55.0 55.0 55.0 55.0
55.0 H(2.5) 56.0 56.0 56.0 56.0 56.0 H(5.0) 58.0 58.0 58.0 58.0
58.0 H(7.0) 60.0 60.0 60.0 60.0 60.0 H(8.0) 65.5 64.6 64.6 64.6
64.6 H(10.0) 67.4 67.0 67.0 67.0 67.0 H(12.5) 71.8 71.8 71.8 71.8
71.8 H(15.0) 77.5 76.0 76.0 76.0 76.0 H(17.5) 81.3 79.5 79.5 79.5
79.5 Hs 84.5 83.0 83.0 83.0 82.5
TABLE-US-00007 TABLE I-7 Hardness Distribution of Core (JIS-C) Ex.
Ex. Ex. Ex. Ex. I-11 I-12 I-13 I-14 I-15 H(0.0) 55.0 55.0 55.0 55.0
55.0 H(2.5) 56.0 56.0 56.0 56.0 56.0 H(5.0) 58.0 58.0 58.0 58.0
58.0 H(7.0) 60.0 60.0 60.0 60.0 60.0 H(8.0) 64.6 62.8 64.0 68.8
64.3 H(10.0) 67.0 66.6 66.8 70.0 67.0 H(12.5) 71.8 73.7 71.0 71.2
70.4 H(15.0) 76.0 75.4 72.1 74.8 70.5 H(17.5) 79.5 78.2 73.0 78.8
68.5 Hs 82.1 81.6 79.1 82.9 70.7
TABLE-US-00008 TABLE I-8 Hardness Distribution of Core (JIS-C)
Comp. Comp. Comp. Comp. Comp. Comp. Ex. Ex. Ex. Ex. Ex. Ex. I-1 I-2
I-3 I-4 I-5 I-6 H(0.0) 55.0 55.0 55.0 54.0 54.0 55.0 H(2.5) 56.0
56.0 56.0 59.8 59.8 56.0 H(5.0) 58.0 58.0 58.0 63.0 63.0 58.0
H(7.0) 60.0 60.0 60.0 64.6 64.6 60.0 H(8.0) 64.6 64.6 64.6 64.6
64.6 67.7 H(10.0) 67.0 67.0 67.0 67.0 67.0 68.6 H(12.5) 71.8 71.8
71.8 71.8 71.8 70.6 H(15.0) 76.0 76.0 76.0 76.0 76.0 74.1 H(17.5)
79.5 79.5 79.5 79.5 79.5 79.0 Hs 83.0 83.0 83.0 83.0 83.0 83.0
TABLE-US-00009 TABLE I-9 Hardness Distribution of Core (JIS-C) Ex.
I-16 H(0.0) 55.0 H(2.5) 58.5 H(5.0) 60.5 H(7.5) 62.5 H(9.5) 65.0
H(10.5) 68.6 H(12.5) 70.6 H(15.0) 74.1 H(17.5) 79.0 Hs 83.0
TABLE-US-00010 TABLE I-10 Results of Evaluation Ex. Ex. Ex. Ex. Ex.
I-1 I-2 I-3 I-4 I-5 Center Composition A A A A A Acid/salt (PHR)
0.0 0.0 0.0 0.0 0.0 Diameter (mm) 15.0 15.0 15.0 15.0 15.0 Envelope
layer Composition E1 E7 E8 E9 E10 Acid/salt (PHR) 10.0 2.5 5.0 10.0
5.0 Core Hs - H(0.0) 28.0 29.1 29.9 28.3 28.4 Diameter (mm) 39.1
39.1 39.1 39.1 39.1 Dc (mm) 3.90 3.92 3.88 3.90 3.91 Inner cover
Composition C4 C4 C4 C4 C4 Ti (mm) 1.0 1.0 1.0 1.0 1.0 Hi (JIS-C)
96 96 96 96 96 Outer cover Composition C2 C2 C2 C2 C2 To (mm) 0.8
0.8 0.8 0.8 0.8 Ho (JIS-C) 88 88 88 88 88 Ball Ti + To 1.8 1.8 1.8
1.8 1.8 Hi - Hs 13.0 11.9 11.1 12.7 12.6 Hi - Ho 8 8 8 8 8 Db (mm)
3.19 3.21 3.17 3.19 3.2 W#1 Spin (rpm) 2390 2395 2360 2385 2405
Distance (m) 202.7 202.5 203.2 202.8 202.3 SW spin (rpm) 5600 5600
5600 5600 5600
TABLE-US-00011 TABLE I-11 Results of Evaluation Ex. Ex. Ex. Ex. Ex.
I-6 I-7 I-8 I-9 I-10 Center Composition A A A A A Acid/salt (PHR)
0.0 0.0 0.0 0.0 0.0 Diameter (mm) 15.0 15.0 15.0 15.0 15.0 Envelope
layer Composition E11 E1 E1 E1 E1 Acid/salt (PHR) 10.0 10.0 10.0
10.0 10.0 Core Hs - H(0.0) 29.5 28.0 28.0 28.0 27.5 Diameter (mm)
39.1 39.1 39.1 39.1 39.1 Dc (mm) 3.89 3.90 3.90 3.90 3.90 Inner
cover Composition C4 C4 C5 C5 C4 Ti (mm) 1.0 1.0 1.0 1.0 1.0 Hi
(JIS-C) 96 96 89 89 96 Outer cover Composition C2 C1 C2 C3 C2 To
(mm) 0.8 0.8 0.8 0.8 1.1 Ho (JIS-C) 88 92 88 71 88 Ball Ti + To 1.8
1.8 1.8 1.8 2.1 Hi - Hs 11.5 13.0 6.0 6.0 13.5 Hi - Ho 8 4 1 18 8
Db (mm) 3.18 3.17 3.21 3.27 3.17 W#1 Spin (rpm) 2365 2355 2400 2435
2415 Distance (m) 203.1 203.4 202.4 201.5 202.0 SW spin (rpm) 5600
5550 5640 5680 5600
TABLE-US-00012 TABLE I-12 Results of Evaluation Ex. Ex. Ex. Ex. Ex.
Ex. I-11 I-12 I-13 I-14 I-15 I-16 Center Composition A A A A A B
Acid/salt 0.0 0.0 0.0 0.0 0.0 5.0 (PHR) Diameter (mm) 15.0 15.0
15.0 15.0 15.0 20.0 Envelope layer Composition E1 E2 E3 E6 E4 E5
Acid/salt 10.0 20.0 30.0 0.5 40.0 0.0 (PHR) Core Hs - H(0.0) 27.1
26.6 24.1 27.9 15.7 28.0 Diameter (mm) 39.1 39.1 39.1 39.1 39.1
39.1 Dc (mm) 3.90 3.91 3.90 3.91 3.91 3.93 Inner cover Composition
C4 C4 C4 C4 C4 C4 Ti (mm) 1.0 1.0 1.0 1.0 1.0 1.0 Hi (JIS-C) 96 96
96 96 96 96 Outer cover Composition C2 C2 C2 C2 C2 C2 To (mm) 1.4
0.8 0.8 0.8 0.8 0.8 Ho (JIS-C) 88 88 88 88 88 88 Ball Ti + To 2.4
1.8 1.8 1.8 1.8 1.8 Hi - Hs 13.9 14.4 16.9 13.1 25.3 13.0 Hi - Ho 8
8 8 8 8 8 Db (mm) 3.15 3.2 3.19 3.2 3.2 3.22 W#1 Spin (rpm) 2425
2420 2430 2460 2460 2410 Distance (m) 201.8 201.9 201.6 201.0 201.0
202.2 SW spin (rpm) 5600 5600 5600 5600 5600 5578
TABLE-US-00013 TABLE I-13 Results of Evaluation Comp. Comp. Comp.
Comp. Comp. Comp. Ex. I-1 Ex. I-2 Ex. I-3 Ex. I-4 Ex. I-5 Ex. I-6
Center Composition A A A E1 E1 A Acid/salt) 0.0 0.0 0.0 10.0 10.0
0.0 (PHR Diameter (mm) 15.0 15.0 15.0 39.1 39.1 15.0 Envelope layer
Composition E1 E1 E1 -- -- E5 Acid/salt 10.0 10.0 10.0 -- -- 0.0
(PHR) Core Hs - H (0.0) 28.0 28.0 28.0 29.0 29.0 28.0 Diameter (mm)
39.1 39.1 39.1 39.1 39.1 39.1 Dc (mm) 3.90 3.90 3.90 3.85 3.85 3.91
Inner cover Composition C7 C6 C7 C4 C2 C4 Ti (mm) 1.0 1.0 1.0 1.0
1.0 1.0 Hi (JIS-C) 76 85 76 96 88 96 Outer cover Composition C3 C1
C1 C2 C2 C2 To (mm) 0.8 0.8 0.8 0.8 0.8 0.8 Ho (JIS-C) 71 92 92 88
88 88 Ball Ti + To 1.8 1.8 1.8 1.8 1.8 1.8 Hi - Hs -17.0 2.0 -7.0
13.0 3.0 13.0 Hi - Ho 5 -7 -16 8 0 8 Db (mm) 3.35 3.22 3.27 3.14
3.23 3.2 W#1 Spin (rpm) 2585 2440 2490 2530 2560 2480 Distance (m)
198.5 201.2 200.2 199.8 199.0 200.5 SW spin (rpm) 5660 5550 5560
5600 5600 5600
[0591] As shown in Tables I-10 to I-13, the golf balls according to
Examples are excellent in various performance characteristics. From
the results of evaluation, advantages of the present invention are
clear.
Experiment 2
Example II-1
[0592] A rubber composition was obtained by kneading 100 parts by
weight of a high-cis polybutadiene (trade name "BR-730",
manufactured by JSR Corporation), 34 parts by weight of magnesium
oxide (trade name "MAGSARAT 150ST", manufactured by Kyowa
[0593] Chemical Industry Co., Ltd.), 28 parts by weight of
methacrylic acid, and 0.75 parts by weight of dicumyl peroxide.
This rubber composition was placed into a mold including upper and
lower mold halves each having a hemispherical cavity, and heated at
170.degree. C. for 25 minutes to obtain a center with a diameter of
15 mm.
[0594] A rubber composition was obtained by kneading 100 parts by
weight of a high-cis polybutadiene (the aforementioned "BR-730"),
26.0 parts by weight of zinc diacrylate (trade name "Sanceler SR",
manufactured by SANSHIN CHEMICAL INDUSTRY CO., LTD.), 5 parts by
weight of zinc oxide, an appropriate amount of barium sulfate, 0.2
parts by weight of 2-thionaphthol, 10 parts by weight of zinc
stearate, and 0.75 parts by weight of dicumyl peroxide. Half shells
were formed from this rubber composition. The center was covered
with two of these half shells. The center and the half shells were
placed into a mold including upper and lower mold halves each
having a hemispherical cavity, and heated at 150.degree. C. for 20
minutes to obtain a core with a diameter of 39.1 mm. An envelope
layer was formed from the rubber composition. The amount of barium
sulfate was adjusted such that the specific gravity of the envelope
layer coincides with the specific gravity of the center and the
weight of a golf ball is 45.4 g.
[0595] A resin composition was obtained by kneading 26 parts by
weight of an ionomer resin (the aforementioned "HimilanAM7337"), 40
parts by weight of another ionomer resin (the aforementioned
"Himilan AM7329"), 34 parts by weight of a styrene block-containing
thermoplastic elastomer (the aforementioned "Rabalon T3221C"), 6
parts by weight of titanium dioxide with a twin-screw kneading
extruder. The core was placed into a mold including upper and lower
mold halves each having a hemispherical cavity. The resin
composition was injected around the core by injection molding to
form an inner cover with a thickness of 1.0 mm.
[0596] A resin composition was obtained by kneading 5 parts by
weight of an ionomer resin (the aforementioned "Himilan AM7337"),
10 parts by weight of another ionomer resin (the aforementioned
"Himilan 1555"), 55 parts by weight of still another ionomer resin
(the aforementioned "Himilan AM7329"), 30 parts by weight of an
ethylene-methacrylic acid copolymer (the aforementioned "NUCREL
N1050H"), 3 parts by weight of titanium dioxide, and 0.2 parts by
weight of an ultraviolet absorber (trade name "TINUVIN 770",
manufactured by Ciba Japan K.K.) with a twin-screw kneading
extruder. The sphere consisting of the core and the inner cover was
placed into a final mold having a large number of pimples on its
cavity face. The resin composition was injected around the sphere
by injection molding to form an outer cover with a thickness of 0.8
mm. Dimples having a shape that is the inverted shape of the
pimples were formed on the outer cover. A clear paint including a
two-component curing type polyurethane as a base material was
applied to this outer cover to obtain a golf ball of Example II-1
with a diameter of 42.7 mm.
Examples II-2 to II-16 and Comparative Examples II-1 to
[0597] Golf balls of Examples II-2 to II-16 and Comparative
Examples II-1 to II-6 were obtained in the same manner as Example
II-1, except the specifications of the center, the envelope layer,
the inner cover, and the outer cover were as shown in Tables II-11
to II-15 below. The composition of the center is shown in detail in
Table II-1 below. The composition of the envelope layer is shown in
detail in Tables II-2 and II-3 below. The compositions of the inner
cover and the outer cover are shown in detail in Tables II-4 and
II-5 below. A hardness distribution of the core is shown in Tables
II-6 to II-10 below.
[0598] [Hit With Wood Club (W #5)]
[0599] A wood club (trade name "XXIO", manufactured by DUNLOP
SPORTS CO. LTD., shaft hardness: R, loft angle: 18.0.degree.) was
attached to a swing machine manufactured by True Temper Co. A golf
ball was hit under the condition of a head speed of 37 m/sec. The
spin rate was measured immediately after the hit.
[0600] Furthermore, the distance from the launch point to the stop
point was measured. The average value of data obtained by 10
measurements is shown in Tables II-11 to II-15 below.
[0601] [Feel at Impact with Wood Club (W#5)]
[0602] Ten golf players hit golf balls with wood clubs (trade name
"XXIO", manufactured by DUNLOP SPORTS CO. LTD., shaft hardness: R,
loft angle: 18.0.degree.). The feel at impact was evaluated on the
basis of the following criteria.
[0603] A: very favorable (soft)
[0604] B: favorable (soft)
[0605] C: slightly poor (slightly hard)
[0606] D: poor (hard)
TABLE-US-00014 TABLE II-1 Composition of Center (parts by weight)
Type A B C BR-730 100 100 100 MAGSARAT 150ST 34 -- -- Methacrylic
acid 28 -- -- Sanceler SR -- 20 26 Zinc oxide -- 5 5 Barium sulfate
-- * * 2-thionaphthol -- 0.2 0.2 Zinc octoate -- 5 -- Zinc stearate
-- -- 10 Dicumyl peroxide 0.75 0.75 0.75 Amount of acid/salt 0 5 10
* Appropriate amount
TABLE-US-00015 TABLE II-2 Composition of Envelope Layer (parts by
weight) Type E1 E2 E3 E4 E5 E6 BR-730 100 100 100 100 100 100
Sanceler SR 26.0 27.5 29.5 31.5 27.0 26.5 Zinc oxide 5 5 5 5 5 5
Barium sulfate * * * * * * 2-thionaphthol 0.2 0.2 0.2 0.2 0.2 0.2
Zinc octoate -- -- -- -- -- -- Zinc laurate -- -- -- -- -- -- Zinc
myristate -- -- -- -- -- -- Zinc stearate 10 20 30 40 -- 0.5
Dicumyl 0.75 0.75 0.75 0.75 0.75 0.75 peroxide Amount of 10 20 30
40 0 0.5 acid/salt * Appropriate amount
TABLE-US-00016 TABLE II-3 Composition of Envelope Layer (parts by
weight) Type E7 E8 E9 E10 E11 BR-730 100 100 100 100 100 Sanceler
SR 25.5 25.0 25.5 26.0 25.5 Zinc oxide 5 5 5 5 5 Barium sulfate * *
* * * 2-thionaphthol 0.2 0.2 0.2 0.2 0.2 Zinc octoate 2.5 5 -- --
-- Zinc laurate -- -- 10 -- -- Zinc myristate -- -- -- 5 10 Zinc
stearate -- -- -- -- -- Dicumyl peroxide 0.75 0.75 0.75 0.75 0.75
Amount of acid/salt 2.5 5 10 5 10 * Appropriate amount
[0607] The details of the compounds listed in Tables II-1 to II-3
are as follows.
[0608] BR-730: a high-cis polybutadiene manufactured by JSR
Corporation (cis-1,4-bond content: 96% by weight, 1,2-vinyl bond
content: 1.3% by weight, Mooney viscosity (ML.sub.1+4(100.degree.
C.)): 55, molecular weight distribution (Mw/Mn): 3)
[0609] MAGSARAT 150ST: magnesium oxide manufactured by Kyowa
Chemical Industry Co., Ltd.
[0610] Methacrylic acid: a product of MITSUBISHI RAYON CO.,
LTD.
[0611] Sanceler SR: zinc diacrylate manufactured by SANSHIN
CHEMICAL INDUSTRY CO., LTD. (a product coated with 10% by weight of
stearic acid)
[0612] Zinc oxide: trade name "Ginrei R" manufactured by Toho Zinc
Co., Ltd.
[0613] Barium sulfate: tradename "Barium Sulfate BD" manufactured
by Sakai Chemical Industry Co., Ltd.
[0614] 2-thionaphthol: a product of Tokyo Chemical Industry Co.,
Ltd.
[0615] Zinc octoate: a product of Mitsuwa Chemicals Co., Ltd.
(purity: 99% or greater)
[0616] Zinc stearate: a product of Wako Pure Chemical Industries,
Ltd. (purity: 99% or greater)
[0617] Zinc laurate: a product of Mitsuwa Chemicals Co., Ltd.
(purity: 99% or greater)
[0618] Zinc myristate: a product of NOF Corporation (purity: 90 or
greater)
[0619] Dicumyl peroxide: a product of NOF Corporation
TABLE-US-00017 TABLE II-4 Compositions of Inner Cover and Outer
Cover (parts by weight) Type C1 C2 C3 C4 Himilan AM7337 5 30 -- 51
Himilan 1555 10 -- -- -- Himilan 1605 -- -- 50 -- Himilan AM7329 55
30 50 40 NUCREL N1050H 30 -- -- -- Rabalon T3221C -- 40 -- 9
Titanium dioxide 3 6 4 6 TINUVIN 770 0.2 0.2 -- --
TABLE-US-00018 TABLE II-5 Compositions of Inner Cover and Outer
Cover (parts by weight) Type C5 C6 C7 C8 Himilan AM7337 40 24 26 26
Himilan 1555 -- -- -- -- Himilan 1605 -- -- -- -- Himilan AM7329 40
50 40 26 NUCREL N1050H -- -- -- -- Rabalon T3221C 20 26 34 48
Titanium dioxide 6 6 6 6 TINUVIN 770 -- -- -- --
TABLE-US-00019 TABLE II-6 Hardness Distribution of Core (JIS-C
hardness) Ex. Ex. Ex. Ex. Ex. II-1 II-2 II-3 II-4 II-5 H(0.0) 55.0
55.0 55.0 55.0 55.0 H(2.5) 56.0 56.0 56.0 56.0 56.0 H(5.0) 58.0
58.0 58.0 58.0 58.0 H(7.0) 60.0 60.0 60.0 60.0 60.0 H(8.0) 64.6
64.6 65.2 63.8 64.4 H(10.0) 67.0 67.0 67.4 67.9 66.4 H(12.5) 71.8
71.8 71.0 73.8 71.0 H(15.0) 76.0 76.0 75.3 77.8 77.0 H(17.5) 79.5
79.5 80.6 82.0 80.7 Hs 83.0 83.0 84.1 84.9 83.3
TABLE-US-00020 TABLE II-7 Hardness Distribution of Core (JIS-C
hardness) Ex. Ex. Ex. Ex. Ex. II-6 II-7 II-8 II-9 II-10 H(0.0) 55.0
55.0 55.0 55.0 55.0 H(2.5) 56.0 56.0 56.0 56.0 56.0 H(5.0) 58.0
58.0 58.0 58.0 58.0 H(7.0) 60.0 60.0 60.0 60.0 60.0 H(8.0) 67.0
65.5 64.6 64.6 64.6 H(10.0) 68.5 67.4 67.0 67.0 67.0 H(12.5) 70.1
71.8 71.8 71.8 71.8 H(15.0) 76.7 77.5 76.0 76.0 76.0 H(17.5) 80.5
81.3 79.5 79.5 79.5 Hs 83.4 84.5 83.0 83.0 82.5
TABLE-US-00021 TABLE II-8 Hardness Distribution of Core (JIS-C
hardness) Ex. Ex. Ex. Ex. Ex. II-11 II-12 II-13 II-14 II-15 H(0.0)
55.0 55.0 55.0 55.0 55.0 H(2.5) 56.0 56.0 56.0 56.0 56.0 H(5.0)
58.0 58.0 58.0 58.0 58.0 H(7.0) 60.0 60.0 60.0 60.0 60.0 H(8.0)
64.6 62.8 64.0 68.8 64.3 H(10.0) 67.0 66.6 66.8 70.0 67.0 H(12.5)
71.8 73.7 71.0 71.2 70.4 H(15.0) 76.0 75.4 72.1 74.8 70.5 H(17.5)
79.5 78.2 73.0 78.8 68.5 Hs 82.1 81.6 79.1 82.9 70.7
TABLE-US-00022 TABLE II-9 Hardness Distribution of Core (JIS-C
hardness) Ex. II-16 H(0.0) 55.0 H(2.5) 58.5 H(5.0) 60.5 H(7.5) 62.5
H(9.5) 65.0 H(10.5) 68.6 H(12.5) 70.6 H(15.0) 74.1 H(17.5) 79.0 Hs
83.0
TABLE-US-00023 TABLE II-10 Hardness Distribution of Core (JIS-C
hardness) Comp. Comp. Comp. Comp. Comp. Comp. Ex. Ex. Ex. Ex. Ex.
Ex. II-1 II-2 II-3 II-4 II-5 II-6 H(0.0) 55.0 55.0 55.0 54.0 54.0
55.0 H(2.5) 56.0 56.0 56.0 59.8 59.8 56.0 H(5.0) 58.0 58.0 58.0
63.0 63.0 58.0 H(7.0) 60.0 60.0 60.0 64.6 64.6 60.0 H(8.0) 64.6
64.6 64.6 64.6 64.6 67.7 H(10.0) 67.0 67.0 67.0 67.0 67.0 68.6
H(12.5) 71.8 71.8 71.8 71.8 71.8 70.6 H(15.0) 76.0 76.0 76.0 76.0
76.0 74.1 H(17.5) 79.5 79.5 79.5 79.5 79.5 79.0 Hs 83.0 83.0 83.0
83.0 83.0 83.0
TABLE-US-00024 TABLE II-11 Results of Evaluation Ex. Ex. Ex. Ex.
Ex. II-1 II-2 II-3 II-4 II-5 Center Composition A A A A A Diameter
(mm) 15.0 15.0 15.0 15.0 15.0 Envelope layer Composition E1 E1 E7
E8 E9 Core Hs - H(0.0) 28.0 28.0 29.1 29.9 28.3 Diameter (mm) 39.1
39.1 39.1 39.1 39.1 Dc (mm) 3.90 3.90 3.92 3.88 3.90 Inner cover
Composition C7 C8 C6 C6 C6 Ti (mm) 1.0 1.0 1.0 1.0 1.0 Hi (JIS-C)
76.0 65.0 83.0 83.0 83.0 Hardness (Shore D) 45.0 35.0 52.0 52.0
52.0 Outer cover Composition C1 C1 C1 C1 C1 To (mm) 0.8 0.8 0.8 0.8
0.8 Ho (JIS-C) 92.0 92.0 92.0 92.0 92.0 Hardness (Shore D) 61.0
61.0 61.0 61.0 61.0 Ti + To (mm) 1.8 1.8 1.8 1.8 1.8 Ho - Hs
(JIS-C) 9.0 9.0 7.9 7.1 8.3 Ho - Hi (JIS-C) 16.0 27.0 9.0 9.0 9.0
Db (mm) 3.27 3.30 3.29 3.25 3.27 W#5 spin (rpm) 3780 3790 3740 3725
3750 W#5 distance(m) 180.9 180.7 181.3 181.5 181.1 W#5 feel A A B B
B
TABLE-US-00025 TABLE II-12 Results of Evaluation Ex. Ex. Ex. Ex.
Ex. II-6 II-7 II-8 II-9 II-10 Center Composition A A A A A Diameter
(mm) 15.0 15.0 15.0 15.0 15.0 Envelope layer Composition E10 E11 E1
E1 E1 Core Hs - H(0.0) 28.4 29.5 28.0 28.0 27.5 Diameter (mm) 39.1
39.1 39.1 39.1 38.5 Dc (mm) 3.91 3.89 3.90 3.90 3.90 Inner cover
Composition C6 C6 C5 C4 C5 Ti (mm) 1.0 1.0 1.0 1.0 1.0 Hi (JIS-C)
83.0 83.0 85.0 89.0 85.0 Hardness (Shore D) 52.0 52.0 54.0 58.0
54.0 Outer cover Composition C1 C1 C1 C1 C1 To (mm) 0.8 0.8 0.8 0.8
1.1 Ho (JIS-C) 92.0 92.0 92.0 92.0 92.0 Hardness (Shore D) 61.0
61.0 61.0 61.0 61.0 Ti + To (mm) 1.8 1.8 1.8 1.8 2.1 Ho - Hs
(JIS-C) 8.6 7.5 9.0 9.0 9.5 Ho - Hi (JIS-C) 9.0 9.0 7.0 3.0 7.0 Db
(mm) 3.28 3.26 3.22 3.27 3.22 W#5 spin (rpm) 3765 3745 3715 3695
3730 W#5 distance(m) 181.0 181.2 181.6 181.9 181.4 W#5 feel B B B B
B
TABLE-US-00026 TABLE II-13 Results of Evaluation Ex. Ex. Ex. Ex.
Ex. II-11 II-12 II-13 II-14 II-15 Center Composition A A A A A
Diameter (mm) 15.0 15.0 15.0 15.0 15.0 Envelope layer Composition
E1 E2 E3 E6 E4 Core Hs - H(0.0) 27.1 26.6 24.1 27.9 15.7 Diameter
(mm) 37.9 39.1 39.1 39.1 39.1 Dc (mm) 3.90 3.91 3.90 3.91 3.91
Inner cover Composition C5 C5 C5 C6 C5 Ti (mm) 1.0 1.0 1.0 1.0 1.0
Hi (JIS-C) 85.0 85.0 85.0 83.0 85.0 Hardness (Shore D) 54.0 54.0
54.0 52.0 54.0 Outer cover Composition C1 C1 C1 C1 C1 To (mm) 1.4
0.8 0.8 0.8 0.8 Ho (JIS-C) 92.0 92.0 92.0 92.0 92.0 Hardness (Shore
D) 61.0 61.0 61.0 61.0 61.0 Ti + To (mm) 2.4 1.8 1.8 1.8 1.8 Ho -
Hs (JIS-C) 9.9 10.4 12.9 9.1 21.3 Ho - Hi (JIS-C) 7.0 7.0 7.0 9.0
7.0 Db (mm) 3.20 3.25 3.24 3.28 3.25 W#5 spin(rpm) 3710 3720 3735
3795 3795 W#5 distance (m) 181.7 181.5 181.4 180.5 180.5 W#5 feel B
B B B B
TABLE-US-00027 TABLE II-14 Results of Evaluation Comp. Comp. Comp.
Comp. Ex. Ex. Ex. Ex. Ex. II-16 II-1 II-2 II-3 II-4 Center
Composition B A A A C Diameter (mm) 20.0 15.0 15.0 15.0 39.1
Envelope layer Composition E5 E1 E1 E1 -- Core Hs - H(0.0) 28.0
28.0 28.0 28.0 29.0 Diameter (mm) 39.1 39.1 39.1 39.1 39.1 Dc (mm)
3.93 3.90 3.90 3.90 3.85 Inner cover Composition C5 C7 C4 C3 C6 Ti
(mm) 1.0 1.0 1.0 1.0 1.0 Hi (JIS-C) 85.0 76.0 89.0 96.0 83.0
Hardness (Shore D) 54.0 45.0 58.0 65.0 52.0 Outer cover Composition
C1 C2 C2 C1 C1 To (mm) 1.1 0.8 0.8 0.8 0.8 Ho (JIS-C) 92.0 71.0
71.0 92.0 92.0 Hardness (Shore D) 61.0 40.0 40.0 61.0 61.0 Ti + To
(mm) 2.1 1.8 1.8 1.8 1.8 Ho - Hs (JIS-C) 9.0 -12.0 -12.0 9.0 9.0 Ho
- Hi (JIS-C) 7.0 -5.0 -18.0 -4.0 9.0 Db (mm) 3.27 3.35 3.27 3.17
3.22 W#5 spin(rpm) 3785 4010 3900 3705 3930 W#5 distance (m) 180.8
179.0 179.6 181.8 179.5 W#5 feel B B C D C
TABLE-US-00028 TABLE II-15 Results of Evaluation Comp. Ex. Comp.
Ex. II-5 II-6 Center Composition C A Diameter (mm) 39.1 15.0
Envelope layer Composition -- E5 Core Hs - H(0.0) 29.0 28.0
Diameter (mm) 39.1 39.1 Dc (mm) 3.85 3.91 Inner cover Composition
C1 C5 Ti (mm) 1.0 1.0 Hi (JIS-C) 92.0 85.0 Hardness (Shore D) 61.0
54.0 Outer cover Composition C1 C1 To (mm) 0.8 0.8 Ho (JIS-C) 92.0
92.0 Hardness (Shore D) 61.0 61.0 Ti + To (mm) 1.8 1.8 Ho - Hs
(JIS-C) 9.0 9.0 Ho - Hi (JIS-C) 0.0 7.0 Db (mm) 3.23 3.25 W#5 spin
(rpm) 3835 3850 W#5 distance (m) 180.2 180.0 W#5 feel D B
[0620] As shown in Tables II-11 to II-15, the golf balls according
to Examples are excellent in various performance characteristics.
From the results of evaluation, advantages of the present invention
are clear.
Experiment 3
Example III-1
[0621] A rubber composition was obtained by kneading 100 parts by
weight of a high-cis polybutadiene (trade name "BR-730",
manufactured by JSR Corporation), 34 parts by weight of magnesium
oxide (trade name "MAGSARAT 150ST", manufactured by Kyowa Chemical
Industry Co., Ltd.), 28 parts by weight of methacrylic acid, and
0.75 parts by weight of dicumyl peroxide. This rubber composition
was placed into a mold including upper and lower mold halves each
having a hemispherical cavity, and heated at 170.degree. C. for 25
minutes to obtain a center with a diameter of 15 mm.
[0622] A rubber composition was obtained by kneading 100 parts by
weight of a high-cis polybutadiene (the aforementioned "BR-730"),
26.0 parts by weight of zinc diacrylate (trade name "Sanceler SR",
manufactured by SANSHIN CHEMICAL INDUSTRY CO., LTD.), 5 parts by
weight of zinc oxide, an appropriate amount of barium sulfate, 0.2
parts by weight of 2-thionaphthol, 10 parts by weight of zinc
stearate, and 0.75 parts by weight of dicumyl peroxide. Half shells
were formed from this rubber composition. The center was covered
with two of these half shells. The center and the half shells were
placed into a mold including upper and lower mold halves each
having a hemispherical cavity, and heated at 150.degree. C. for 20
minutes to obtain a core with a diameter of 37.1 mm. An envelope
layer was formed from the rubber composition. The amount of barium
sulfate was adjusted such that the specific gravity of the envelope
layer coincides with the specific gravity of the center and the
weight of a golf ball is 45.4 g.
[0623] A resin composition was obtained by kneading 40 parts by
weight of an ionomer resin (the aforementioned "HimilanAM7337"), 40
parts by weight of another ionomer resin (the aforementioned
"Himilan AM7329"), 20 parts by weight of a styrene block-containing
thermoplastic elastomer (the aforementioned "Rabalon T3221C"), 6
parts by weight of titanium dioxide with a twin-screw kneading
extruder. The core was placed into a mold including upper and lower
mold halves each having a hemispherical cavity. The resin
composition was injected around the core by injection molding to
form an inner cover with a thickness of 1.0 mm.
[0624] A resin composition was obtained by kneading 51 parts by
weight of an ionomer resin (the aforementioned "HimilanAM7337"), 40
parts by weight of another ionomer resin (the aforementioned
"Himilan AM7329"), 9 parts by weight of a styrene block-containing
thermoplastic elastomer (the aforementioned "Rabalon T3221C", and 6
parts by weight of titanium dioxide with a twin-screw kneading
extruder. The sphere consisting of the core and the inner cover was
placed into a mold including upper and lower mold halves each
having a hemispherical cavity. The resin composition was injected
around the sphere by injection molding to form a mid cover with a
thickness of 1.0 mm.
[0625] A resin composition was obtained by kneading 5 parts by
weight of an ionomer resin (the aforementioned "Himilan AM7337"),
10 parts by weight of another ionomer resin (the aforementioned
"Himilan 1555"), 55 parts by weight of still another ionomer resin
(the aforementioned "Himilan AM7329"), 30 parts by weight of an
ethylene-methacrylic acid copolymer (the aforementioned "NUCREL
N1050H"), 3 parts by weight of titanium dioxide, and 0.2 parts by
weight of an ultraviolet absorber (trade name "TINUVIN 770",
manufactured by Ciba Japan K.K.) with a twin-screw kneading
extruder. The sphere consisting of the core, the inner cover, and
the mid cover was placed into a final mold having a large number of
pimples on its cavity face. The resin composition was injected
around the sphere by injection molding to form an outer cover with
a thickness of 0.8 mm. Dimples having a shape that is the inverted
shape of the pimples were formed on the outer cover. A clear paint
including a two-component curing type polyurethane as a base
material was applied to this outer cover to obtain a golf ball of
Example III-1 with a diameter of 42.7 mm.
Examples III-2 to III-15 and Comparative Examples III-1 to
III-7
[0626] Golf balls of Examples III-2 to III-15 and Comparative
Examples III-1 to III-7 were obtained in the same manner as Example
III-1, except the specifications of the center, the envelope layer,
the inner cover, the mid cover, and the outer cover were as shown
in Tables III-10 to III-14 below. The composition of the center is
shown in detail in Table III-1 below. The composition of the
envelope layer is shown in detail in Tables III-2 and III-3 below.
The compositions of the inner cover, the mid cover, and the outer
cover are shown in detail in Tables III-4 and III-5 below. A
hardness distribution of the core is shown in Tables III-6 to III-9
below.
[0627] [Hit with Middle Iron (I #5)]
[0628] A middle iron (trade name "XXIO", manufactured by DUNLOP
SPORTS CO. LTD., shaft hardness: R, loft angle: 24.0.degree.) was
attached to a swing machine manufactured by True Temper Co. A golf
ball was hit under the condition of a head speed of 35 m/sec. The
spin rate was measured immediately after the hit. Furthermore, the
distance from the launch point to the stop point was measured. The
average value of data obtained by 10 measurements is shown in
Tables III-10 to III-14 below.
TABLE-US-00029 TABLE III-1 Composition of Center (parts by weight)
Type A B C BR-730 100 100 100 MAGSARAT 150ST 34 -- -- Methacrylic
acid 28 -- -- Sanceler SR -- 20 26 Zinc oxide -- 5 5 Barium sulfate
-- * * 2-thionaphthol -- 0.2 0.2 Zinc octoate -- 5 -- Zinc stearate
-- -- 10 Dicumyl peroxide 0.75 0.75 0.75 Amount of acid/salt 0 5 10
* Appropriate amount
TABLE-US-00030 TABLE III-2 Composition of Envelope Layer (parts by
weight) Type E1 E2 E3 E4 E5 E6 BR-730 100 100 100 100 100 100
Sanceler SR 26.0 27.5 29.5 31.5 27.0 26.5 Zinc oxide 5 5 5 5 5 5
Barium sulfate * * * * * * 2-thionaphthol 0.2 0.2 0.2 0.2 0.2 0.2
Zinc octoate -- -- -- -- -- -- Zinc laurate -- -- -- -- -- -- Zinc
myristate -- -- -- -- -- -- Zinc stearate 10 20 30 40 -- 0.5
Dicumyl 0.75 0.75 0.75 0.75 0.75 0.75 peroxide Amount of 10 20 30
40 0 0.5 acid/salt * Appropriate amount
TABLE-US-00031 TABLE III-3 Composition of Envelope Layer (parts by
weight) Type E7 E8 E9 E10 E11 BR-730 100 100 100 100 100 Sanceler
SR 25.5 25.0 25.5 26.0 25.5 Zinc oxide 5 5 5 5 5 Barium sulfate * *
* * * 2-thionaphthol 0.2 0.2 0.2 0.2 0.2 Zinc octoate 2.5 5 -- --
-- Zinc laurate -- -- 10 -- -- Zinc myristate -- -- -- 5 10 Zinc
stearate -- -- -- -- -- Dicumyl peroxide 0.75 0.75 0.75 0.75 0.75
Amount of acid/salt 2.5 5 10 5 10 * Appropriate amount
[0629] The details of the compounds listed in Tables III-1 to III-3
are as follows.
[0630] BR-730: a high-cis polybutadiene manufactured by JSR
Corporation (cis-1,4-bond content: 96% by weight, 1,2-vinyl bond
content: 1.3% by weight, Mooney viscosity (ML.sub.1+4(100.degree.
C.)): 55, molecular weight distribution (Mw/Mn): 3)
[0631] MAGSARAT 150ST: magnesium oxide manufactured by Kyowa
Chemical Industry Co., Ltd.
[0632] Methacrylic acid: a product of MITSUBISHI RAYON CO.,
LTD.
[0633] Sanceler SR: zinc diacrylate manufactured by SANSHIN
CHEMICAL INDUSTRY CO., LTD. (a product coated with 10% by weight of
stearic acid)
[0634] Zinc oxide: trade name "Ginrei R" manufactured by Toho Zinc
Co., Ltd.
[0635] Barium sulfate: trade name "Barium Sulfate BD" manufactured
by Sakai Chemical Industry Co., Ltd.
[0636] 2-thionaphthol: a product of Tokyo Chemical Industry Co.,
Ltd.
[0637] Zinc octoate: a product of Mitsuwa Chemicals Co., Ltd.
(purity: 99% or greater)
[0638] Zinc stearate: a product of Wako Pure Chemical Industries,
Ltd. (purity: 99% or greater)
[0639] Zinc laurate: a product of Mitsuwa Chemicals Co., Ltd.
(purity: 99% or greater)
[0640] Zinc myristate: a product of NOF Corporation (purity: 90 or
greater)
[0641] Dicumyl peroxide: a product of NOF Corporation
TABLE-US-00032 TABLE III-4 Composition of Cover (parts by weight)
Type (a) (b) (c) (d) Himilan AM7337 5 51 45 40 Himilan 1555 10 --
-- -- Himilan AM7329 55 40 40 40 NUCREL N1050H 30 -- -- -- Rabalon
T3221C -- 9 15 20 Titanium dioxide 3 6 6 6 TINUVIN 770 0.2 -- --
--
TABLE-US-00033 TABLE III-5 Composition of Cover (parts by weight)
Type (e) (f) (g) Himilan AM7337 24 26 30 Himilan 1555 -- -- --
Himilan AM7329 50 40 30 NUCREL N1050H -- -- -- Rabalon T3221C 26 34
40 Titanium dioxide 6 6 6 TINUVIN 770 -- -- 0.2
TABLE-US-00034 TABLE III-6 Hardness Distribution of Core (JIS-C
hardness) Ex. Ex. Ex. Ex. Ex. III-1 III-2 III-3 III-4 III-5 H(0.0)
55.0 55.0 55.0 55.0 55.0 H(2.5) 56.0 56.0 56.0 56.0 56.0 H(5.0)
58.0 58.0 58.0 58.0 58.0 H(7.0) 60.0 60.0 60.0 60.0 60.0 H(7.5) --
-- -- -- -- H(8.0) 64.6 64.6 64.6 64.6 64.6 H(9.5) -- -- -- -- --
H(10.0) 67.0 67.0 67.0 67.0 67.0 H(10.5) -- -- -- -- -- H(12.5)
71.8 71.8 71.8 71.8 71.8 H(15.0) 76.0 76.0 76.0 76.0 76.0 H(17.5)
79.5 79.5 79.5 79.5 79.5 Hs 82.5 82.5 82.5 82.0 81.5
TABLE-US-00035 TABLE III-7 Hardness Distribution of Core (JIS-C
hardness) Ex. Ex. Ex. Ex. Ex. III-6 III-7 III-8 III-9 III-10 H(0.0)
55.0 55.0 55.0 55.0 55.0 H(2.5) 56.0 56.0 56.0 56.0 56.0 H(5.0)
58.0 58.0 58.0 58.0 58.0 H(7.0) 60.0 60.0 60.0 60.0 60.0 H(7.5) --
-- -- -- -- H(8.0) 62.8 64.0 64.3 68.8 65.2 H(9.5) -- -- -- -- --
H(10.0) 66.6 66.8 67.0 70.0 67.4 H(10.5) -- -- -- -- -- H(12.5)
73.7 71.0 70.4 71.2 71.0 H(15.0) 75.4 72.1 70.5 74.8 75.3 H(17.5)
78.2 73.0 68.5 78.8 80.6 Hs 81.1 78.6 70.2 82.4 83.6
TABLE-US-00036 TABLE III-8 Hardness Distribution of Core (JIS-C
hardness) Ex. Ex. Ex. Ex. Ex. III-11 III-12 III-13 III-14 III-15
H(0.0) 55.0 55.0 55.0 55.0 55.0 H(2.5) 56.0 56.0 56.0 56.0 58.5
H(5.0) 58.0 58.0 58.0 58.0 60.5 H(7.0) 60.0 60.0 60.0 60.0 --
H(7.5) -- -- -- -- 62.5 H(8.0) 63.8 64.4 67.0 65.5 -- H(9.5) -- --
-- -- 65.0 H(10.0) 67.9 66.4 68.5 67.4 -- H(10.5) -- -- -- -- 68.6
H(12.5) 73.8 71.0 70.1 71.8 70.6 H(15.0) 77.8 77.0 76.7 77.5 74.1
H(17.5) 82.0 80.7 80.5 81.3 79.0 Hs 84.4 82.8 82.9 84.0 82.5
TABLE-US-00037 TABLE III-9 Hardness Distribution of Core (JIS-C
hardness) Comp. Comp. Comp. Ex. Comp. Ex. Comp. Ex. Comp. Ex. Comp.
Ex. Ex. Ex. III-1 III-2 III-3 III-4 III-5 III-6 III-7 H(0.0) 55.0
55.0 54.0 55.0 55.0 55.0 55.0 H(2.5) 56.0 56.0 59.8 56.0 56.0 56.0
56.0 H(5.0) 58.0 58.0 63.0 58.0 58.0 58.0 58.0 H(7.0) 60.0 60.0 --
60.0 60.0 60.0 60.0 H(7.5) -- -- 64.6 -- -- -- -- H(8.0) 64.6 64.6
-- 64.6 64.6 67.7 64.6 H(9.5) -- -- -- -- -- -- -- H(10.0) 67.0
67.0 67.0 67.0 67.0 68.6 67.0 H(10.5) -- -- -- -- -- -- -- H(12.5)
71.8 71.8 71.8 71.8 71.8 70.6 71.8 H(15.0) 76.0 76.0 76.0 76.0 76.0
74.1 76.0 H(17.5) 79.5 79.5 79.5 79.5 79.5 79.0 79.5 Hs 82.5 82.5
82.5 82.5 82.5 82.5 82.5
TABLE-US-00038 TABLE III-10 Results of Evaluation Ex. Ex. Ex. Ex.
Ex. III-1 III-2 III-3 III-4 III-5 Center A A A A A Diameter (mm) 15
15 15 15 15 Envelope layer E1 E1 E1 E1 E1 Core Hs - H(0.0) 27.5
27.5 27.5 27.0 26.5 Diameter (mm) 37.1 37.1 37.1 36.5 35.9 Dc (mm)
3.90 3.90 3.90 3.90 3.90 Inner cover (d) (c) (b) (d) (d) Ti (mm)
1.0 1.0 1.0 1.0 1.0 Hi (JIS-C) 85.0 87.0 89.0 85.0 85.0 Mid cover
(b) (b) (d) (b) (b) Tm (mm) 1.0 1.0 1.0 1.0 1.0 Hm (JIS-C) 89.0
89.0 85.0 89.0 89.0 Outer cover (a) (a) (a) (a) (a) To (mm) 0.8 0.8
0.8 1.1 1.4 Ho (JIS-C) 92.0 92.0 92.0 92.0 92.0 Ti + Tm + To (mm)
2.8 2.8 2.8 3.1 3.4 Hi - Hs (JIS-C) 2.5 4.5 6.5 3.0 3.5 Ho - Hi
(JIS-C) 7.0 5.0 3.0 7.0 7.0 Hm - Hi (JIS-C) 6.0 2.0 -4.0 4.0 4.0 Ho
- Hm (JIS-C) 3.0 3.0 7.0 3.0 3.0 Db (mm) 2.93 2.92 2.93 2.91 2.89
I#5 spin (rpm) 3860 3845 3850 3870 3855 I#5 distance (m) 151.0
151.3 151.2 150.8 151.1
TABLE-US-00039 TABLE III-11 Results of Evaluation Ex. Ex. Ex. Ex.
Ex. III-6 III-7 III-8 III-9 III-10 Center A A A A A Diameter (mm)
15 15 15 15 15 Envelope layer E2 E3 E4 E6 E7 Core Hs - H(0.0) 26.1
23.6 15.2 27.4 28.6 Diameter (mm) 37.1 37.1 37.1 37.1 37.1 Dc (mm)
3.91 3.90 3.91 3.85 3.94 Inner cover (d) (d) (d) (c) (c) Ti (mm)
1.0 1.0 1.0 1.0 1.0 Hi (JIS-C) 85.0 85.0 85.0 87.0 87.0 Mid cover
(b) (b) (b) (b) (b) Tm (mm) 1.0 1.0 1.0 1.0 1.0 Hm (JIS-C) 89.0
89.0 89.0 89.0 89.0 Outer cover (a) (a) (a) (a) (a) To (mm) 0.8 0.8
0.8 0.8 0.8 Ho (JIS-C) 92.0 92.0 92.0 92.0 92.0 Ti + Tm + To (mm)
2.8 2.8 2.8 2.8 2.8 Hi - Hs (JIS-C) 3.9 6.4 14.8 4.6 3.4 Ho - Hi
(JIS-C) 7.0 7.0 7.0 5.0 5.0 Hm - Hi (JIS-C) 4.0 4.0 4.0 2.0 2.0 Ho
- Hm (JIS-C) 3.0 3.0 3.0 3.0 3.0 Db (mm) 2.94 2.98 3.04 2.87 2.96
I#5 spin(rpm) 3865 3875 3890 3885 3825 I#5 distance(m) 150.9 150.7
150.4 150.5 151.7
TABLE-US-00040 TABLE III-12 Results of Evaluation Ex. Ex. Ex. Ex.
Ex. III-11 III-12 III-13 III-14 III-15 Center A A A A B Diameter
(mm) 15 15 15 15 20 Envelope layer E8 E9 E10 E11 E5 Core Hs -
H(0.0) 29.4 27.8 27.9 29.0 27.5 Diameter (mm) 37.1 37.1 37.1 37.1
37.1 Dc (mm) 3.83 3.95 3.87 3.82 3.93 Inner cover (c) (c) (c) (c)
(d) Ti (mm) 1.0 1.0 1.0 1.0 1.0 Hi (JIS-C) 87.0 87.0 87.0 87.0 85.0
Mid cover (b) (b) (b) (b) (b) Tm (mm) 1.0 1.0 1.0 1.0 1.0 Hm
(JIS-C) 89.0 89.0 89.0 89.0 89.0 Outer cover (a) (a) (a) (a) (a) To
(mm) 0.8 0.8 0.8 0.8 0.8 Ho (JIS-C) 92.0 92.0 92.0 92.0 92.0 Ti +
Tm + To (mm) 2.8 2.8 2.8 2.8 2.8 Hi - Hs (JIS-C) 2.6 4.2 4.1 3.0
2.5 Ho - Hi (JIS-C) 5.0 5.0 5.0 5.0 7.0 Hm - Hi (JIS-C) 2.0 2.0 2.0
2.0 4.0 Ho - Hm (JIS-C) 3.0 3.0 3.0 3.0 3.0 Db (mm) 2.85 2.97 2.89
2.84 2.96 I#5 spin(rpm) 3805 3835 3840 3830 3880 I#5 distance(m)
151.9 151.5 151.4 151.6 150.6
TABLE-US-00041 TABLE III-13 Results of Evaluation Comp. Comp. Comp.
Comp. Comp. Ex. Ex. Ex. Ex. Ex. III-1 III-2 III-3 III-4 III-5
Center A A C A A Diameter (mm) 15 15 37.1 15 15 Envelope layer E1
E1 -- E1 E1 Core Hs - H(0.0) 27.5 27.5 28.5 27.5 27.5 Diameter (mm)
37.1 37.1 37.1 37.1 37.1 Dc (mm) 3.90 3.90 3.85 3.90 3.90 Inner
cover (e) (f) (a) (a) (e) Ti (mm) 1.0 1.0 1.0 1.0 1.4 Hi (JIS-C)
83.0 76.0 92.0 92.0 83.0 Mid cover (b) (b) (a) (a) (a) Tm (mm) 1.0
1.0 1.0 1.0 0.6 Hm (JIS-C) 89.0 89.0 92.0 92.0 92.0 Outer cover (a)
(a) (a) (a) (a) To (mm) 0.8 0.8 0.8 0.8 0.8 Ho (JIS-C) 92.0 92.0
92.0 92.0 92.0 Ti + Tm + To (mm) 2.8 2.8 2.8 2.8 2.8 Hi - Hs
(JIS-C) 0.5 -6.5 9.5 9.5 0.5 Ho - Hi (JIS-C) 9.0 16.0 0 0 9.0 Hm -
Hi (JIS-C) 6.0 13.0 0 0 9.0 Ho - Hm (JIS-C) 3.0 3.0 0 0 0 Db (mm)
2.94 2.95 2.85 2.90 2.95 I#5 spin(rpm) 3915 3945 3920 3910 3900 I#5
distance(m) 150.0 149.8 149.9 150.1 150.2
TABLE-US-00042 TABLE III-14 Results of Evaluation Comp. Ex. Comp.
Ex. III-6 III-7 Center A A Diameter (mm) 15 15 Envelope layer E5 E1
Core Hs - H(0.0) 27.5 27.5 Diameter (mm) 37.1 37.1 Dc (mm) 3.91
3.90 Inner cover (d) (d) Ti (mm) 1.0 1.0 Hi (JIS-C) 85.0 85.0 Mid
cover (b) (f) Tm (mm) 1.0 1.0 Hm (JIS-C) 89.0 76.0 Outer cover (a)
(g) To (mm) 0.8 0.8 Ho (JIS-C) 92.0 71.0 Ti + Tm + To (mm) 2.8 2.8
Hi - Hs (JIS-C) 2.5 2.5 Ho - Hi (JIS-C) 7.0 -14.0 Hm - Hi (JIS-C)
4.0 -9.0 Ho - Hm (JIS-C) 3.0 -5.0 Db (mm) 2.94 3.05 I#5 spin(rpm)
3985 4085 I#5 distance (m) 149.5 148.7
[0642] As shown in Tables III-10 to III-14, the golf balls
according to Examples are excellent in flight performance. From the
results of evaluation, advantages of the present invention are
clear.
Experiment 4
Example IV-1
[0643] A rubber composition was obtained by kneading 100 parts by
weight of a high-cis polybutadiene (trade name "BR-730",
manufactured by JSR Corporation), 34 parts by weight of magnesium
oxide (trade name "MAGSARAT 150ST", manufactured by Kyowa Chemical
Industry Co., Ltd.), 28 parts by weight of methacrylic acid, and
0.75 parts by weight of dicumyl peroxide. This rubber composition
was placed into a mold including upper and lower mold halves each
having a hemispherical cavity, and heated at 170.degree. C. for 25
minutes to obtain a center with a diameter of 15 mm.
[0644] A rubber composition was obtained by kneading 100 parts by
weight of a high-cis polybutadiene (the aforementioned "BR-730"),
26.0 parts by weight of zinc diacrylate (trade name "Sanceler SR",
manufactured by SANSHIN CHEMICAL INDUSTRY CO., LTD.), 5 parts by
weight of zinc oxide, an appropriate amount of barium sulfate, 0.2
parts by weight of 2-thionaphthol, 10 parts by weight of zinc
stearate, and 0.75 parts by weight of dicumyl peroxide. Half shells
were formed from this rubber composition. The center was covered
with two of these half shells. The center and the half shells were
placed into a mold including upper and lower mold halves each
having a hemispherical cavity, and heated at 150.degree. C. for 20
minutes to obtain a core with a diameter of 37.1 mm. An envelope
layer was formed from the rubber composition. The amount of barium
sulfate was adjusted such that the specific gravity of the envelope
layer coincides with the specific gravity of the center and the
weight of a golf ball is 45.4 g.
[0645] A resin composition was obtained by kneading 24 parts by
weight of an ionomer resin (the aforementioned"HimilanAM7337"), 50
parts by weight of another ionomer resin (the aforementioned
"Himilan AM7329"), 26 parts by weight of a styrene block-containing
thermoplastic elastomer (the aforementioned "Rabalon T3221C"), 6
parts by weight of titanium dioxide with a twin-screw kneading
extruder. The core was placed into a mold including upper and lower
mold halves each having a hemispherical cavity. The resin
composition was injected around the core by injection molding to
form an inner cover with a thickness of 1.0 mm.
[0646] A resin composition was obtained by kneading 51 parts by
weight of an ionomer resin (the aforementioned"HimilanAM7337"), 40
parts by weight of another ionomer resin (the aforementioned
"Himilan AM7329"), 9 parts by weight of a styrene block-containing
thermoplastic elastomer (the aforementioned "Rabalon T3221C", and 6
parts by weight of titanium dioxide with a twin-screw kneading
extruder. The sphere consisting of the core and the inner cover was
placed into a mold including upper and lower mold halves each
having a hemispherical cavity. The resin composition was injected
around the sphere by injection molding to form a mid cover with a
thickness of 1.0 mm.
[0647] A resin composition was obtained by kneading 5 parts by
weight of an ionomer resin (the aforementioned "Himilan AM7337"),
10 parts by weight of another ionomer resin (the aforementioned
"Himilan 1555"), 55 parts by weight of still another ionomer resin
(the aforementioned "Himilan AM7329"), 30 parts by weight of an
ethylene-methacrylic acid copolymer (the aforementioned "NUCREL
N1050H"), 3 parts by weight of titanium dioxide, and 0.2 parts by
weight of an ultraviolet absorber (trade name "TINUVIN 770",
manufactured by Ciba Japan K.K.) with a twin-screw kneading
extruder. The sphere consisting of the core, the inner cover, and
the mid cover was placed into a final mold having a large number of
pimples on its cavity face. The resin composition was injected
around the sphere by injection molding to form an outer cover with
a thickness of 0.8 mm. Dimples having a shape that is the inverted
shape of the pimples were formed on the outer cover. A clear paint
including a two-component curing type polyurethane as a base
material was applied to this outer cover to obtain a golf ball of
Example IV-1 with a diameter of 42.7 mm.
Examples IV-2 to IV-15 and Comparative Examples IV-1 to IV-7
[0648] Golf balls of Examples IV-2 to IV-15 and Comparative
Examples IV-1 to IV-7 were obtained in the same manner as Example
IV-1, except the specifications of the core, the envelope layer,
the inner cover, the mid cover, and the outer cover were as shown
in Tables IV-11 to IV-15 below. The composition of the center is
shown in detail in Table IV-1 below. The composition of the
envelope layer is shown in detail in Tables IV-2 and IV-3 below.
The compositions of the inner cover, the mid cover, and the outer
cover are shown in detail in Tables IV-4 and IV-5 below. A hardness
distribution of the core is shown in Tables IV-6 to IV-10
below.
[0649] [Hit with Driver (W #1)]
[0650] A driver with a titanium head (trade name "XXIO",
manufactured by DUNLOP SPORTS CO. LTD., shaft hardness: R, loft
angle: 11.degree.) was attached to a swing machine manufactured by
True Temper Co. A golf ball was hit under the condition of a head
speed of 40 m/sec. The spin rate was measured immediately after the
hit. Furthermore, the distance from the launch point to the stop
point was measured. The average value of data obtained by 10
measurements is shown in Tables IV-11 to IV-15 below.
[0651] [Feel at Impact with Driver (W #1)]
[0652] Ten golf players hit golf balls with drivers with titanium
heads (trade name "XXIO", manufactured by DUNLOP SPORTS CO. LTD.,
shaft hardness: R, loft angle: 11.degree.). The feel at impact was
evaluated on the basis of the following criteria.
[0653] A: very favorable (soft)
[0654] B: favorable (soft)
[0655] C: slightly poor (slightly hard)
[0656] D: poor (hard)
TABLE-US-00043 TABLE IV-1 Composition of Center (parts by weight)
Type A B C BR-730 100 100 100 MAGSARAT 150ST 34 -- -- Methacrylic
acid 28 -- -- Sanceler SR -- 20 26 Zinc oxide -- 5 5 Barium sulfate
-- * * 2-thionaphthol -- 0.2 0.2 Zinc octoate -- 5 -- Zinc stearate
-- -- 10 Dicumyl peroxide 0.75 0.75 0.75 Amount of acid/salt 0 5 10
* Appropriate amount
TABLE-US-00044 TABLE IV-2 Composition of Envelope Layer (parts by
weight) Type E1 E2 E3 E4 E5 E6 BR-730 100 100 100 100 100 100
Sanceler SR 26.0 27.5 29.5 31.5 27.0 26.5 Zinc oxide 5 5 5 5 5 5
Barium sulfate * * * * * * 2-thionaphthol 0.2 0.2 0.2 0.2 0.2 0.2
Zinc octoate -- -- -- -- -- -- Zinc laurate -- -- -- -- -- -- Zinc
myristate -- -- -- -- -- -- Zinc stearate 10 20 30 40 -- 0.5
Dicumyl 0.75 0.75 0.75 0.75 0.75 0.75 peroxide Amount of 10 20 30
40 0 0.5 acid/salt * Appropriate amount
TABLE-US-00045 TABLE IV-3 Composition of Envelope Layer (parts by
weight) Type E7 E8 E9 E10 E11 BR-730 100 100 100 100 100 Sanceler
SR 25.5 25.0 25.5 26.0 25.5 Zinc oxide 5 5 5 5 5 Barium sulfate * *
* * * 2-thionaphthol 0.2 0.2 0.2 0.2 0.2 Zinc octoate 2.5 5 -- --
-- Zinc laurate -- -- 10 -- -- Zinc myristate -- -- -- 5 10 Zinc
stearate -- -- -- -- -- Dicumyl peroxide 0.75 0.75 0.75 0.75 0.75
Amount of acid/salt 2.5 5 10 5 10 * Appropriate amount
[0657] The details of the compounds listed in Tables IV-1 to IV-3
are as follows.
[0658] BR-730: a high-cis polybutadiene manufactured by JSR
Corporation (cis-1,4-bond content: 96% by weight, 1,2-vinyl bond
content: 1.3% by weight, Mooney viscosity (ML.sub.1+4(100.degree.
C.)): 55, molecular weight distribution (Mw/Mn): 3)
[0659] MAGSARAT 150ST: magnesium oxide manufactured by Kyowa
Chemical Industry Co., Ltd.
[0660] Methacrylic acid: a product of MITSUBISHI RAYON CO.,
LTD.
[0661] Sanceler SR: zinc diacrylate manufactured by SANSHIN
CHEMICAL INDUSTRY CO., LTD. (a product coated with 10% by weight of
stearic acid)
[0662] Zinc oxide: trade name "Ginrei R" manufactured by Toho Zinc
Co., Ltd.
[0663] Barium sulfate: trade name "Barium Sulfate BD" manufactured
by Sakai Chemical Industry Co., Ltd.
[0664] 2-thionaphthol: a product of Tokyo Chemical Industry Co.,
Ltd.
[0665] Zinc octoate: a product of Mitsuwa Chemicals Co., Ltd.
(purity: 99% or greater)
[0666] Zinc stearate: a product of Wako Pure Chemical Industries,
Ltd. (purity: 99% or greater)
[0667] Zinc laurate: a product of Mitsuwa Chemicals Co., Ltd.
(purity: 99% or greater)
[0668] Zinc myristate: a product of NOF Corporation (purity: 90 or
greater)
[0669] Dicumyl peroxide: a product of NOF Corporation
TABLE-US-00046 TABLE IV-4 Composition of Cover (parts by weight)
Type (a) (b) (c) (d) Himilan AM7337 5 51 45 40 Himilan 1555 10 --
-- -- Himilan AM7329 55 40 40 40 NUCREL N1050H 30 -- -- -- Rabalon
T3221C -- 9 15 20 Titanium dioxide 3 6 6 6 TINUVIN 770 0.2 -- --
--
TABLE-US-00047 TABLE IV-5 Composition of Cover (parts by weight)
Type (e) (f) (g) (h) (i) Himilan AM7337 24 26 30 26 30 Himilan 1555
-- -- -- -- -- Himilan AM7329 50 40 30 26 30 NUCREL N1050H -- -- --
-- -- Rabalon T3221C 26 34 40 48 40 Titanium dioxide 6 6 6 6 6
TINUVIN 770 -- -- -- -- 0.2
TABLE-US-00048 TABLE IV-6 Hardness Distribution of Core (JIS-C
hardness) Ex. Ex. Ex. Ex. Ex. IV-1 IV-2 IV-3 IV-4 IV-5 H(0.0) 55.0
55.0 55.0 55.0 55.0 H(2.5) 56.0 56.0 56.0 56.0 56.0 H(5.0) 58.0
58.0 58.0 58.0 58.0 H(7.0) 60.0 60.0 60.0 60.0 60.0 H(7.5) -- -- --
-- -- H(8.0) 64.6 64.6 64.6 64.6 64.6 H(9.5) -- -- -- -- -- H(10.0)
67.0 67.0 67.0 67.0 67.0 H(10.5) -- -- -- -- -- H(12.5) 71.8 71.8
71.8 71.8 71.8 H(15.0) 76.0 76.0 76.0 76.0 76.0 H(17.5) 79.5 79.5
79.5 79.5 79.5 Hs 82.5 82.5 82.5 82.5 82.0
TABLE-US-00049 TABLE IV-7 Hardness Distribution of Core (JIS-C
hardness) Ex. Ex. Ex. Ex. Ex. IV-6 IV-7 IV-8 IV-9 IV-10 H(0.0) 55.0
55.0 55.0 55.0 55.0 H(2.5) 56.0 56.0 56.0 56.0 56.0 H(5.0) 58.0
58.0 58.0 58.0 58.0 H(7.0) 60.0 60.0 60.0 60.0 60.0 H(7.5) -- -- --
-- -- H(8.0) 64.6 62.8 64.0 68.8 65.2 H(9.5) -- -- -- -- -- H(10.0)
67.0 66.6 66.8 70.0 67.4 H(10.5) -- -- -- -- -- H(12.5) 71.8 73.7
71.0 71.2 71.0 H(15.0) 76.0 75.4 72.1 74.8 75.3 H(17.5) 79.5 78.2
73.0 78.8 80.6 Hs 81.5 81.1 78.6 82.4 83.6
TABLE-US-00050 TABLE IV-8 Hardness Distribution of Core (JIS-C
hardness) Ex. Ex. Ex. Ex. Ex. IV-11 IV-12 IV-13 IV-14 IV-15 H(0.0)
55.0 55.0 55.0 55.0 55.0 H(2.5) 56.0 56.0 56.0 56.0 58.5 H(5.0)
58.0 58.0 58.0 58.0 60.5 H(7.0) 60.0 60.0 60.0 60.0 -- H(7.5) -- --
-- -- 62.5 H(8.0) 63.8 64.4 67.0 65.5 -- H(9.5) -- -- -- -- 65.0
H(10.0) 67.9 66.4 68.5 67.4 -- H(10.5) -- -- -- -- 68.6 H(12.5)
73.8 71.0 70.1 71.8 70.6 H(15.0) 77.8 77.0 76.7 77.5 74.1 H(17.5)
82.0 80.7 80.5 81.3 79.0 Hs 84.4 82.8 82.9 84.0 82.5
TABLE-US-00051 TABLE IV-9 Hardness Distribution of Core (JIS-C
hardness) Comp. Ex. Comp. Ex. Comp. Ex. Comp. Ex. IV-1 IV-2 IV-3
IV-4 H(0.0) 55.0 54.0 55.0 55.0 H(2.5) 56.0 59.8 56.0 56.0 H(5.0)
58.0 63.0 58.0 58.0 H(7.0) 60.0 -- 60.0 60.0 H(7.5) -- 64.6 -- --
H(8.0) 64.6 -- 64.6 64.6 H(9.5) -- -- -- -- H(10.0) 67.0 67.0 67.0
67.0 H(10.5) -- -- -- -- H(12.5) 71.8 71.8 71.8 71.8 H(15.0) 76.0
76.0 76.0 76.0 H(17.5) 79.5 79.5 79.5 79.5 Hs 82.5 82.5 82.5
82.5
TABLE-US-00052 TABLE IV-10 Hardness Distribution of Core (JIS-C
hardness) Comp. Ex. Comp. Ex. Comp. Ex. IV-5 IV-6 IV-7 H(0.0) 55.0
55.0 55.0 H(2.5) 56.0 56.0 56.0 H(5.0) 58.0 58.0 58.0 H(7.0) 60.0
60.0 60.0 H(7.5) -- -- -- H(8.0) 64.3 67.7 64.6 H(9.5) -- -- --
H(10.0) 67.0 68.6 67.0 H(10.5) -- -- -- H(12.5) 70.4 70.6 71.8
H(15.0) 70.5 74.1 76.0 H(17.5) 68.5 79.0 79.5 Hs 70.2 82.5 82.5
TABLE-US-00053 TABLE IV-11 Results of Evaluation Ex. Ex. Ex. Ex.
Ex. IV-1 IV-2 IV-3 IV-4 IV-5 Center Comp. A A A A A Diameter 15 15
15 15 15 (mm) Envelope Comp. E1 E1 E1 E1 E1 layer Core Hs - H (0.0)
27.5 27.5 27.5 27.5 27.0 Diameter (mm) 37.1 37.1 37.1 37.1 36.5 Dc
(mm) 3.90 3.90 3.90 3.90 3.90 Inner cover Comp. (e) (f) (g) (h) (f)
Ti (mm) 1.0 1.0 1.0 1.0 1.0 Hi (JIS-C) 83.0 76.0 71.0 65.0 76.0 Mid
cover Comp. (b) (b) (d) (g) (b) Tm (mm) 1.0 1.0 1.0 1.0 1.0 Hm
(JIS-C) 89.0 89.0 85.0 71.0 89.0 Outer cover Comp. (a) (a) (a) (a)
(a) To (mm) 0.8 0.8 0.8 0.8 1.1 Ho (JIS-C) 92.0 92.0 92.0 92.0 92.0
Ti + Tm + To (mm) 2.8 2.8 2.8 2.8 3.1 Hi - Hs (JIS-C) 0.5 -6.5
-11.5 -17.5 -6.0 Ho - Hi (JIS-C) 9.0 16.0 21.0 27.0 16.0 Hm - Hi
(JIS-C) 6.0 13.0 14.0 6.0 13.0 Ho - Hm (JIS-C) 3.0 3.0 7.0 21.0 3.0
Db (mm) 2.94 2.95 2.98 3.03 2.93 W#1 spin (rpm) 2480 2470 2455 2475
2490 W#1 distance (m) 201.0 201.3 201.6 201.1 200.8 W#1 feel B A A
B B
TABLE-US-00054 TABLE IV-12 Results of Evaluation Ex. Ex. Ex. Ex.
Ex. IV-6 IV-7 IV-8 IV-9 IV-10 Center Comp. A A A A A Diameter 15 15
15 15 15 (mm) Envelope Comp. E1 E2 E3 E6 E7 layer Core Hs - H (0.0)
26.5 26.1 23.6 27.4 28.6 Diameter (mm) 35.9 37.1 37.1 37.1 37.1 Dc
(mm) 3.90 3.91 3.90 3.85 3.94 Inner cover Comp. (f) (g) (g) (e) (e)
Ti (mm) 1.0 1.0 1.0 1.0 1.0 Hi (JIS-C) 76.0 71.0 71.0 83.0 83.0 Mid
cover Comp. (b) (d) (b) (b) (b) Tm (mm) 1.0 1.0 1.0 1.0 1.0 Hm
(JIS-C) 89.0 85.0 89.0 89.0 89.0 Outer cover Comp. (a) (a) (a) (a)
(a) To (mm) 1.4 0.8 0.8 0.8 0.8 Ho (JIS-C) 92.0 92.0 92.0 92.0 92.0
Ti + Tm + To (mm) 3.4 2.8 2.8 2.8 2.8 Hi - Hs (JIS-C) -5.5 -10.1
-7.6 0.6 -0.6 Ho - Hi (JIS-C) 16.0 21.0 21.0 9.0 9.0 Hm - Hi
(JIS-C) 13.0 14.0 18.0 6.0 6.0 Ho - Hm (JIS-C) 3.0 7.0 3.0 3.0 3.0
Db (mm) 2.91 2.99 2.98 2.89 2.98 W#1 spin (rpm) 2500 2505 2510 2515
2465 W#1 distance (m) 200.7 200.6 200.5 200.1 201.4 W#1 feel C B B
B B
TABLE-US-00055 TABLE IV-13 Results of Evaluation Ex. Ex. Ex. Ex.
Ex. IV-11 IV-12 IV-13 IV-14 IV-15 Center Comp. A A A A B Diameter
15 15 15 15 20 (mm) Envelope Comp. E8 E9 E10 E11 E5 layer Core Hs -
H (0.0) 29.4 27.8 27.9 29.0 27.5 Diameter (mm) 37.1 37.1 37.1 37.1
37.1 Dc (mm) 3.83 3.95 3.87 3.82 3.93 Inner cover Comp. (e) (e) (e)
(e) (e) Ti (mm) 1.0 1.0 1.0 1.0 1.0 Hi (JIS-C) 83.0 83.0 83.0 83.0
83.0 Mid cover Comp. (b) (b) (b) (b) (b) Tm (mm) 1.0 1.0 1.0 1.0
1.0 Hm (JIS-C) 89.0 89.0 89.0 89.0 89.0 Outer cover Comp. (a) (a)
(a) (a) (a) To (mm) 0.8 0.8 0.8 0.8 0.8 Ho (JIS-C) 92.0 92.0 92.0
92.0 92.0 Ti + Tm + To (mm) 2.8 2.8 2.8 2.8 2.8 Hi - Hs (JIS-C)
-1.4 0.2 0.1 -1.0 0.5 Ho - Hi (JIS-C) 9.0 9.0 9.0 9.0 9.0 Hm - Hi
(JIS-C) 6.0 6.0 6.0 6.0 6.0 Ho - Hm (JIS-C) 3.0 3.0 3.0 3.0 3.0 Db
(mm) 2.87 2.99 2.91 2.86 2.97 W#1 spin(rpm) 2435 2460 2475 2445
2485 W#1 distance (m) 202.0 201.5 201.2 201.8 200.9 W#1 feel A A B
A B
TABLE-US-00056 TABLE IV-14 Results of Evaluation Comp. Comp. Comp.
Comp. Comp. Ex. Ex. Ex. Ex. Ex. IV-1 IV-2 IV-3 IV-4 IV-5 Center
Comp. A C A A A Diameter 15 37.1 15 15 15 (mm) Envelope Comp. E1 --
E1 E1 E4 layer Core Hs - H (0.0) 27.5 28.5 27.5 27.5 15.2 Diameter
(mm) 37.1 37.1 37.1 37.1 37.1 Dc (mm) 3.90 3.85 3.90 3.90 3.91
Inner cover Comp. (c) (a) (a) (d) (e) Ti (mm) 1.0 1.0 1.0 1.4 1.0
Hi (JIS-C) 87.0 92.0 92.0 85.0 83.0 Mid cover Comp. (b) (a) (a) (a)
(b) Tm (mm) 1.0 1.0 1.0 0.6 1.0 Hm (JIS-C) 89.0 92.0 92.0 92.0 89.0
Outer cover Comp. (a) (a) (a) (a) (a) To (mm) 0.8 0.8 0.8 0.8 0.8
Ho (JIS-C) 92.0 92.0 92.0 92.0 92.0 Ti + Tm + To (mm) 2.8 2.8 2.8
2.8 2.8 Hi - Hs (JIS-C) 4.5 9.5 9.5 2.5 12.8 Ho - Hi (JIS-C) 5.0 0
0 7.0 9.0 Hm - Hi (JIS-C) 2.0 0 0 7.0 6.0 Ho - Hm (JIS-C) 3.0 0 0 0
3.0 Db (mm) 2.92 2.85 2.90 2.93 2.95 W#1 spin(rpm) 2530 2540 2535
2525 2645 W#1 distance (m) 199.6 199.4 199.5 199.7 197.9 W#1 feel D
D D D D
TABLE-US-00057 TABLE IV-15 Results of Evaluation Comp. Ex. Comp.
Ex. IV-6 IV-7 Center Comp. A A Diameter (mm) 15 15 Envelope layer
Comp. E5 E1 Core Hs - H(0.0) 27.5 27.5 Diameter (mm) 37.1 37.1 Dc
(mm) 3.91 3.90 Inner cover Comp. (e) (e) Ti (mm) 1.0 1.0 Hi (JIS-C)
83.0 83.0 Mid cover Comp. (b) (f) Tm (mm) 1.0 1.0 Hm (JIS-C) 89.0
76.0 Outer cover Comp. (a) (i) To (mm) 0.8 0.8 Ho (JIS-C) 92.0 71.0
Ti + Tm + To (mm) 2.8 2.8 Hi - Hs (JIS-C) 0.5 0.5 Ho - Hi (JIS-C)
9.0 -12.0 Hm - Hi (JIS-C) 6.0 -7.0 Ho - Hm (JIS-C) 3.0 -5.0 Db (mm)
2.95 3.06 W#1 spin(rpm) 2565 2685 W#1 distance(m) 199.2 197.7 W#1
feel D D
[0670] As shown in Tables IV-11 to IV-15, the golf balls according
to Examples are excellent in flight performance and feel at impact
particularly when being hit with a driver. From the results of
evaluation, advantages of the present invention are clear.
[0671] The golf ball according to the present invention can be used
for playing golf on golf courses and practicing at driving ranges.
The above descriptions are merely for illustrative examples, and
various modifications can be made without departing from the
principles of the present invention.
* * * * *