U.S. patent application number 13/089403 was filed with the patent office on 2011-12-15 for golf ball.
Invention is credited to Yoshiko MATSUYAMA, Hirotaka Nakamura, Keiji Ohama, Takahiro Sajima, Kazuyoshi Shiga, Toshiyuki Tarao.
Application Number | 20110306443 13/089403 |
Document ID | / |
Family ID | 45096670 |
Filed Date | 2011-12-15 |
United States Patent
Application |
20110306443 |
Kind Code |
A1 |
MATSUYAMA; Yoshiko ; et
al. |
December 15, 2011 |
GOLF BALL
Abstract
At all points Pa in a zone A extending over a distance range
from equal to or greater than 1 mm to less than 5 mm from the
central point of a core 4, a mathematical formula, Ha2-Ha1<5, is
satisfied. At any of points Pb in a zone B extending over a
distance range from equal to or greater than 5 mm to equal to or
less than 10 mm from the central point of the core 4, a
mathematical formula, Hb2-Hb1.gtoreq.5, is satisfied. Ha1 and Ha2
indicate JIS-C hardnesses at points Pa1 and Pa2 located radially
inward and outward of each point Pa at a distance of 1 mm from the
point Pa. Hb1 and Hb2 indicate JIS-C hardnesses at points Pb1 and
Pb2 located radially inward and outward of the point Pb at a
distance of 1 mm from the point Pb.
Inventors: |
MATSUYAMA; Yoshiko;
(Kobe-shi, JP) ; Ohama; Keiji; (Kobe-shi, JP)
; Nakamura; Hirotaka; (Kobe-shi, JP) ; Sajima;
Takahiro; (Kobe-shi, JP) ; Tarao; Toshiyuki;
(Kobe-shi, JP) ; Shiga; Kazuyoshi; (Kobe-shi,
JP) |
Family ID: |
45096670 |
Appl. No.: |
13/089403 |
Filed: |
April 19, 2011 |
Current U.S.
Class: |
473/376 |
Current CPC
Class: |
A63B 37/0033 20130101;
A63B 37/0063 20130101; A63B 37/0031 20130101; A63B 37/0064
20130101; A63B 37/0043 20130101; A63B 37/0062 20130101; A63B
37/0045 20130101 |
Class at
Publication: |
473/376 |
International
Class: |
A63B 37/06 20060101
A63B037/06 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 9, 2010 |
JP |
2010-131641 |
Claims
1. A golf ball comprising a core, a mid layer positioned outside
the core, and a cover positioned outside the mid layer, wherein the
core comprises a center and an envelope layer positioned outside
the center, a ratio of a volume of the core to a volume of a
phantom sphere of the golf ball is equal to or greater than 76%, a
JIS-C hardness Ho of the cover is less than JIS-C hardness Ho at a
central point of the core, at all points Pa included in a zone A
that extends over a distance range from equal to or greater than 1
mm to less than 5 mm from a central point of the core, the
following mathematical formula (I) is satisfied, at any of points
Pb included in a zone B 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 of the core, the following mathematical formula
(II) is satisfied, Ha2-Ha1<5 (I), Hb2-Hb1.gtoreq.5 (II), in the
mathematical formula (I), Hal indicates a JIS-C hardness at a point
Pa1 that is located radially inward of each point Pa at a distance
of 1 mm from the point Pa, and Ha2 indicates a JIS-C hardness at a
point Pa2 that is located radially outward of the point Pa at a
distance of 1 mm from the point Pa, and in the mathematical formula
(II), Hb1 indicates a JIS-C hardness at a point Pb1 that is located
radially inward of the point Pb at a distance of 1 mm from the
point Pb, and Hb2 indicates a JIS-C hardness at a point Pb2 that is
located radially outward of the point Pb at a distance of 1 mm from
the point Pb.
2. The golf ball according to claim 1, wherein the JIS-C hardness
Hc of the cover is equal to or less than 65.
3. The golf ball according to claim 1, wherein a thickness of the
cover is equal to or less than 0.8 mm.
4. The golf ball according to claim 1, wherein a JIS-C hardness Hm
of the mid layer is equal to or greater than 90.
5. The golf ball according to claim 1, wherein a thickness of the
mid layer is equal to or less than 1.5 mm.
6. The golf ball according to claim 1, wherein the cover is formed
from a resin composition, and a principal component of a base
material of the resin composition is a thermoplastic
polyurethane.
7. The golf ball according to claim 6, wherein a shear loss elastic
modulus G'' of the resin composition, which is measured under
conditions of a vibration frequency of 10 Hz and a temperature of
0.degree. C., is equal to or less than 1.95.times.10.sup.7 Pa, and
a ratio (E''/G'') of a tensile loss elastic modulus E'' of the
resin composition, which is measured under conditions of a
vibration frequency of 10 Hz and a temperature of 0.degree. C., to
the shear loss elastic modulus G'' is equal to or greater than
1.76.
8. The golf ball according to claim 7, wherein the tensile loss
elastic modulus E'' is equal to or greater 2.00.times.10.sup.7
Pa.
9. The golf ball according to claim 6, wherein a polyol component
of the thermoplastic polyurethane is polytetramethylene ether
glycol having a number average molecular weight of 1500 or
less.
10. The golf ball according to claim 1, wherein a difference
between a JIS-C hardness He at a surface of the core and the
hardness Hb2 is equal to or greater than 10.
11. The golf ball according to claim 1, wherein a difference
between a JIS-C hardness He at a surface of the core and the
hardness Ho is equal to or less than 40.
12. The golf ball according to claim 1, wherein the hardness Ho is
equal to or greater than 40 but equal to or less than 80.
13. The golf ball according to claim 1, wherein a JIS-C hardness He
at a surface of the core is equal to or greater than 75 but equal
to or less than 95.
14. The golf ball according to claim 1, wherein a difference
between a JIS-C hardness He at a surface of the core and a JIS-C
hardness Hi at an innermost portion of the envelope layer is equal
to or greater than 10 but equal to or less than 25.
15. The golf ball according to claim 1, wherein a thickness of the
envelope layer is equal to or greater than 8 mm but equal to or
less than 18 mm.
16. The golf ball according to claim 1, wherein a diameter of the
center is equal to or greater than 10 mm but equal to or less than
20 mm.
17. The golf ball according to claim 1, wherein a JIS-C hardness He
at a surface of the core is greater than a JIS-C hardness at a
surface of the center, and the hardness Hm of the mid layer is
greater than the hardness He.
18. The golf ball according to claim 1, wherein a difference
between the hardness Ho and the hardness Hc is equal to or greater
than 3.
Description
[0001] This application claims priority on Patent Application No.
2010-131641 filed in JAPAN on Jun. 9, 2010. The entire contents of
this Japanese Patent Application 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 multi-piece golf balls including a
center, an envelope layer, a mid layer and a cover.
[0004] 2. Description of the Related Art
[0005] Golf players' foremost requirement for golf balls is flight
performance. Golf players place importance on flight performance
upon shots with a driver, a long iron and a middle iron. Flight
performance correlates with the resilience performance of a golf
ball. When a golf ball with excellent resilience performance is
hit, the golf ball flies at a high speed, thereby achieving a large
flight distance.
[0006] 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 a core having an
outer-hard/inner-soft structure can achieve a low spin rate and a
high launch angle.
[0007] 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 tends to curve. 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.
[0008] In light of achieving various performance characteristics,
golf balls each having a multilayer structure have been proposed.
U.S. Pat. No. 6,468,169 (JP10-328326) discloses a golf ball
including a core, an envelope layer, an inner cover and an outer
cover. U.S. Pat. No. 6,271,296 (JP2001-17575) discloses a golf ball
including a core, an envelope layer, a mid layer and a cover. U.S.
Pat. No. 6,913,547 (JP2002-272880) discloses a golf ball including
a core and a cover. The core consists of a center and an outer core
layer. The cover consists of an inner cover layer and an outer
cover layer. US2003/130066 (JP2003-135626) discloses a golf ball
including a core and a cover. The core consists of a center and a
mid layer. US2003/166422 (JP2003-205052) discloses a golf ball
including a center, a mid layer and a cover. US2004/029648
(JP2004-130072) discloses a golf ball including a core and a cover.
The core has a three-layer structure.
[0009] When a core that has an outer-hard/inner-soft structure and
an excessive hardness distribution is hit with a driver, the energy
loss is high in the core. The energy loss impairs resilience
performance. When a core that has an outer-hard/inner-soft
structure and an excessive hardness distribution is hit with a
short iron, the spin rate is low. The low spin rate impairs
controllability.
[0010] An object of the present invention is to provide a golf ball
that provides a large flight distance when being hit with a driver
and that has excellent controllability when being hit with a short
iron.
SUMMARY OF THE INVENTION
[0011] A golf ball according to the present invention comprises a
core, a mid layer positioned outside the core, and a cover
positioned outside the mid layer. The core comprises a center and
an envelope layer positioned outside the center. A ratio of a
volume of the core to a volume of a phantom sphere of the golf ball
is equal to or greater than 76%. A JIS-C hardness Hc of the cover
is less than JIS-C hardness Ho at a central point of the core. At
all points Pa included in a zone A that extends over a distance
range from equal to or greater than 1 mm to less than 5 mm from a
central point of the core, the following mathematical formula (I)
is satisfied. At any of points Pb included in a zone B 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 of the core, the
following mathematical formula (II) is satisfied.
Ha2-Ha1<5 (I),
Hb2-Hb1.gtoreq.5 (II),
In the mathematical formula (I), Ha1 indicates a JIS-C hardness at
a point Pa1 that is located radially inward of each point Pa at a
distance of 1 mm from the point Pa, and Ha2 indicates a JIS-C
hardness at a point Pa2 that is located radially outward of the
point Pa at a distance of 1 mm from the point Pa. In the
mathematical formula (II), Hb1 indicates a JIS-C hardness at a
point Pb1 that is located radially inward of the point Pb at a
distance of 1 mm from the point Pb, and Hb2 indicates a JIS-C
hardness at a point Pb2 that is located radially outward of the
point Pb at a distance of 1 mm from the point Pb.
[0012] In the golf ball according to the present invention, a
hardness distribution of the core is appropriate. The core has a
low energy loss when being hit with a driver. When the golf ball is
hit with a driver, a large flight distance is obtained. The golf
ball has excellent controllability when being hit with a short
iron.
[0013] Preferably, the JIS-C hardness Hc of the cover is equal to
or less than 65. Preferably, a thickness of the cover is equal to
or less than 0.8 mm.
[0014] Preferably, a JIS-C hardness Hm of the mid layer is equal to
or greater than 90. Preferably, a thickness of the mid layer is
equal to or less than 1.5 mm.
[0015] The cover is formed from a resin composition. Preferably, a
principal component of a base material of the resin composition is
a thermoplastic polyurethane.
[0016] Preferably, a shear loss elastic modulus G'' of the resin
composition, which is measured under conditions of a vibration
frequency of 10 Hz and a temperature of 0.degree. C., is equal to
or less than 1.95.times.10.sup.7 Pa, and a ratio (E''/G'') of a
tensile loss elastic modulus E'' of the resin composition, which is
measured under the same conditions, to the shear loss elastic
modulus G'' is equal to or greater than 1.76. Preferably, the
tensile loss elastic modulus E'' is equal to or greater
2.00.times.10.sup.7 Pa.
[0017] Preferably, a polyol component of the thermoplastic
polyurethane is polytetramethylene ether glycol having a number
average molecular weight of 1500 or less.
[0018] Preferably, a difference between a JIS-C hardness He at a
surface of the core and the hardness Hb2 is equal to or greater
than 10. Preferably, a difference between a JIS-C hardness He at a
surface of the core and the hardness Ho is equal to or less than
40.
[0019] Preferably, the hardness Ho is equal to or greater than 40
but equal to or less than 80. Preferably, a JIS-C hardness He at a
surface of the core is equal to or greater than 75 but equal to or
less than 95. Preferably, a difference between a JIS-C hardness He
at a surface of the core and a JIS-C hardness Hi at an innermost
portion of the envelope layer is equal to or greater than 10 but
equal to or less than 25.
[0020] Preferably, a thickness of the envelope layer is equal to or
greater than 8 mm but equal to or less than 18 mm. Preferably, a
diameter of the center is equal to or greater than 10 mm but equal
to or less than 20 mm.
[0021] Preferably, a JIS-C hardness He at a surface of the core is
greater than a JIS-C hardness at a surface of the center, and the
hardness Hm of the mid layer is greater than the hardness He.
Preferably, a difference between the hardness Ho and the hardness
Hc is equal to or greater than 3.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a partially cutaway cross-sectional view of a golf
ball according to one embodiment of the present invention;
[0023] FIG. 2 is a graph showing a hardness distribution of each
core of golf balls according to Examples 1 and 4 to 6 of the
present invention;
[0024] FIG. 3 is a graph showing a hardness distribution of a core
of a golf ball according to Example 2 of the present invention;
[0025] FIG. 4 is a graph showing a hardness distribution of a core
of a golf ball according to Example 3 of the present invention;
[0026] FIG. 5 is a graph showing a hardness distribution of a core
of a golf ball according to Example 7 of the present invention;
[0027] FIG. 6 is a graph showing a hardness distribution of a core
of a golf ball according to Example 8 of the present invention;
[0028] FIG. 7 is a graph showing a hardness distribution of a core
of a golf ball according to Comparative Example 1;
[0029] FIG. 8 is a graph showing a hardness distribution of a core
of a golf ball according to Comparative Example 2;
[0030] FIG. 9 is a graph showing a hardness distribution of each
core of golf balls according to Comparative Examples 3 and 4;
and
[0031] FIG. 10 is a graph showing a hardness distribution of a core
of a golf ball according to Comparative Example 5.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0032] The following will describe in detail the present invention
based on preferred embodiments with reference to the accompanying
drawings.
[0033] A golf ball 2 shown in FIG. 1 includes a spherical core 4, a
mid layer 6 positioned outside the core 4, and a cover 8 positioned
outside the mid layer 6. The core 4 includes a spherical center 10
and an envelope layer 12 positioned outside the center 10. On the
surface of the 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 cover 8 although these layers are not
shown in the drawing.
[0034] The golf ball 2 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
preferably equal to or greater than 42.67 mm. In light of
suppression of air resistance, the diameter is preferably equal to
or less than 44 mm and more preferably equal to or less than 42.80
mm. The golf ball 2 has a weight of 40 g or greater but 50 g or
less. In light of attainment of great inertia, the weight is
preferably equal to or greater than 44 g and more preferably equal
to or greater than 45.00 g. From the standpoint of conformity to
the rules established by the USGA, the weight is preferably equal
to or less than 45.93 g.
[0035] Preferably, the center 10 is obtained by crosslinking a
rubber composition. Examples of preferable base rubbers for use in
the rubber composition 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% and more preferably equal to or greater than
80%.
[0036] The rubber composition of the center 10 includes a
co-crosslinking agent. The co-crosslinking agent achieves high
resilience of the center 10. Examples of preferable co-crosslinking
agents in light of resilience performance include monovalent or
bivalent metal salts of an .alpha.,.beta.-unsaturated carboxylic
acid having 2 to 8 carbon atoms. Specific examples of preferable
co-crosslinking agents include zinc acrylate, magnesium acrylate,
zinc methacrylate and magnesium methacrylate. In light of
resilience performance, zinc acrylate and zinc methacrylate are
particularly preferred.
[0037] In light of resilience performance of the golf ball 2, the
amount of the co-crosslinking agent is preferably equal to or
greater than 5 parts by weight, and more preferably equal to or
greater than 10 parts by weight, per 100 parts by weight of the
base rubber. In light of soft feel at impact, the amount of the
co-crosslinking agent is preferably equal to or less than 30 parts
by weight, more preferably equal to or less than 25 parts by
weight, and particularly preferably equal to or less than 20 parts
by weight, per 100 parts by weight of the base rubber.
[0038] Preferably, the rubber composition of the center 10 includes
an organic peroxide together with a co-crosslinking agent. The
organic peroxide serves as a crosslinking initiator. The organic
peroxide contributes to the resilience performance of the golf ball
2. Examples of suitable 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.
[0039] In light of resilience performance of the golf ball 2, the
amount of the organic peroxide is preferably equal to or greater
than 0.1 parts by weight, more preferably equal to or greater than
0.2 parts by weight, and particularly preferably equal to or
greater than 0.3 parts by weight, per 100 parts by weight of the
base rubber. In light of soft feel at impact, the amount of the
organic peroxide is preferably equal to or less than 1.5 parts by
weight, more preferably equal to or less than 1.0 parts by weight,
and particularly preferably equal to or less than 0.8 parts by
weight, per 100 parts by weight of the base rubber.
[0040] Preferably, the rubber composition of the center 10 includes
an organic sulfur compound. Examples of preferable organic sulfur
compounds include monosubstitutions such as diphenyl disulfide,
bis(4-chlorophenyl)disulfide, bis(3-chlorophenyl)disulfide,
bis(4-bromophenyl)disulfide, bis(3-bromophenyl)disulfide,
bis(4-fluorophenyl)disulfide, bis(4-iodophenyl)disulfide,
bis(4-cyanophenyl)disulfide and the like; disubstitutions such as
bis(2,5-dichlorophenyl)disulfide, bis(3,5-dichlorophenyl)disulfide,
bis(2,6-dichlorophenyl)disulfide, bis(2,5-dibromophenyl)disulfide,
bis(3,5-dibromophenyl)disulfide,
bis(2-chloro-5-bromophenyl)disulfide,
bis(2-cyano-5-bromophenyl)disulfide and the like; trisubstitutions
such as bis(2,4,6-trichlorophenyl)disulfide,
bis(2-cyano-4-chloro-6-bromophenyl)disulfide and the like;
tetrasubstitutions such as bis(2,3,5,6-tetrachlorophenyl)disulfide
and the like; and pentasubstitutions such as
bis(2,3,4,5,6-pentachlorophenyl)disulfide,
bis(2,3,4,5,6-pentabromophenyl)disulfide and the like. The organic
sulfur compound contributes to resilience performance. Particularly
preferable organic sulfur compounds are diphenyl disulfide and
bis(pentabromophenyl)disulfide.
[0041] In light of resilience performance of the golf ball 2, the
amount of the organic sulfur compound is preferably equal to or
greater than 0.1 parts by weight and more preferably equal to or
greater than 0.2 parts by weight, per 100 parts by weight of the
base rubber. In light of soft feel at impact, the amount of the
organic sulfur compound is preferably equal to or less than 1.5
parts by weight, more preferably equal to or less than 1.0 parts by
weight, and particularly preferably equal to or less than 0.8 parts
by weight, per 100 parts by weight of the base rubber.
[0042] For the purpose of adjusting specific gravity and the like,
a filler may be included in the center 10. 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 center 10
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.
[0043] According to need, an anti-aging agent, a coloring agent, a
plasticizer, a dispersant, sulfur, an vulcanization accelerator and
the like are added to the rubber composition of the center 10.
Crosslinked rubber powder or synthetic resin powder may be also
dispersed in the rubber composition.
[0044] In light of resilience performance and durability, the
center 10 has a central hardness Ho of preferably 40 or greater,
more preferably 45 or greater, and particularly preferably 50 or
greater. In light of suppression of spin, the central hardness Ho
is preferably equal to or less than 80, more preferably equal to or
less than 75, and particularly preferably equal to or less than 70.
The central hardness Ho is measured by pressing a JIS-C type
hardness scale against the central point of a cut plane of the
center 10 that has been cut into two halves. 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.
[0045] The hardness of the center 10 gradually increases from its
central point toward its surface. The center 10 has a surface
hardness greater than the central hardness Ho.
[0046] The center 10 has a diameter of preferably 10 mm or greater
but 20 mm or less. The center 10 having a diameter of 10 mm or
greater can achieve excellent feel at impact. In this respect, the
diameter is more preferably equal to or greater than 12 mm and
particularly preferably equal to or greater than 13 mm. When the
center 10 has a diameter of 20 mm or less, the envelope layer 12
having a sufficiently large thickness can be formed. In this
respect, the diameter is more preferably equal to or less than 18
mm and particularly preferably equal to or less than 17 mm.
[0047] The envelope layer 12 is obtained 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. 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% and more preferably equal to or greater than
80%.
[0048] In order to crosslink the envelope layer 12, a
co-crosslinking agent is preferably used. Examples of preferable
co-crosslinking agents in light of resilience performance include
monovalent or bivalent metal salts of an .alpha.,.beta.-unsaturated
carboxylic acid having 2 to 8 carbon atoms. Specific examples of
preferable co-crosslinking agents include zinc acrylate, magnesium
acrylate, zinc methacrylate and magnesium methacrylate. In light of
resilience performance, zinc acrylate and zinc methacrylate are
particularly preferred.
[0049] In light of resilience performance of the golf ball 2, the
amount of the co-crosslinking agent is preferably equal to or
greater than 20 parts by weight, more preferably equal to or
greater than 25 parts by weight, and particularly preferably equal
to or greater than 30 parts by weight, per 100 parts by weight of
the base rubber. In light of soft feel at impact, the amount of the
co-crosslinking agent is preferably equal to or less than 60 parts
by weight, more preferably equal to or less than 50 parts by
weight, and particularly preferably equal to or less than 45 parts
by weight, per 100 parts by weight of the base rubber.
[0050] Preferably, the rubber composition of the envelope layer 12
includes an organic peroxide together with a co-crosslinking agent.
The organic peroxide serves as a crosslinking initiator. The
organic peroxide contributes to the resilience performance of the
golf ball 2. Examples of suitable 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.
[0051] In light of resilience performance of the golf ball 2, the
amount of the organic peroxide is preferably equal to or greater
than 0.1 parts by weight, more preferably equal to or greater than
0.3 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 soft feel at impact, the amount of the
organic peroxide is preferably equal to or less than 2.0 parts by
weight, more preferably equal to or less than 1.5 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.
[0052] Preferably, the rubber composition of the envelope layer 12
includes an organic sulfur compound. The organic sulfur compounds
described above for the center 10 can be used for the envelope
layer 12. In light of resilience performance of the golf ball 2,
the amount of the organic sulfur compound is preferably equal to or
greater than 0.1 parts by weight and more preferably equal to or
greater than 0.2 parts by weight, per 100 parts by weight of the
base rubber. In light of soft feel at impact, the amount of the
organic sulfur compound is preferably equal to or less than 1.5
parts by weight, more preferably equal to or less than 1.0 parts by
weight, and particularly preferably equal to or less than 0.8 parts
by weight, per 100 parts by weight of the base rubber.
[0053] 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. Powder of a metal with a high
specific gravity may be included as a filler. Specific examples of
metals with a high specific gravity include tungsten and
molybdenum. The amount of the filler is determined as appropriate
so that the intended specific gravity of the envelope layer 12 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. According to need, various additives such
as sulfur, an anti-aging agent, a coloring agent, a plasticizer, a
dispersant and the like are included in the envelope layer 12 in an
adequate amount. Crosslinked rubber powder or synthetic resin
powder may be also included in the envelope layer 12.
[0054] During formation of the envelope layer 12, the center 10 is
covered with two uncrosslinked or semi-crosslinked half shells.
These half shells are compressed and heated. By this heating, a
crosslinking reaction takes place to complete the envelope layer
12. The crosslinking temperature is generally equal to or higher
than 140.degree. C. but equal to or lower than 180.degree. C. The
time period for crosslinking the envelope layer 12 is generally
equal to or longer than 10 minutes but equal to or shorter than 60
minutes.
[0055] The hardness of the envelope layer 12 gradually increases
from its innermost portion to its surface. In light of resilience
performance, a hardness He at the surface of the envelope layer 12
(namely, the surface of the core 4) is preferably equal to or
greater than 75, more preferably equal to or greater than 80, and
particularly preferably equal to or greater than 85. In light of
feel at impact, the hardness He is preferably equal to or less than
95, more preferably equal to or less than 93, and particularly
preferably equal to or less than 92. The hardness He is measured by
pressing a JIS-C type hardness scale against the surface of the
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.
[0056] In light of suppression of spin, the difference (He-Hi)
between the surface hardness He of the envelope layer 12 and a
hardness Hi at the innermost portion of the envelope layer 12 is
preferably equal to or greater than 10, more preferably equal to or
greater than 12, and particularly preferably equal to or greater
than 15. In light of ease of production and durability, the
difference (He-Hi) is preferably equal to or less than 25.
[0057] The hardness Hi is measured for a hemisphere obtained by
cutting the core 4. The hardness Hi is measured by pressing a JIS-C
type hardness scale against the cut plane of the hemisphere. The
hardness scale is pressed against a region surrounded by a first
circle and a second circle. The first circle is the boundary
between the center 10 and the envelope layer 12. The second circle
is concentric with the first circle and has a radius larger than
the radius of the first circle by 1 mm. 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.
[0058] The envelope layer 12 has a thickness of preferably 8 mm or
greater but 18 mm or less. The envelope layer 12 having a thickness
of 8 mm or greater can suppress spin. In this respect, the
thickness is more preferably equal to or greater than 9 mm and
particularly preferably equal to or greater than 10 mm. When the
envelope layer 12 has a thickness of 18 mm or less, the center 10
having a large diameter can be formed. The center 10 having a large
diameter can suppress spin. In this respect, the thickness is more
preferably equal to or less than 16 mm and particularly preferably
equal to or less than 15 mm.
[0059] In light of suppression of spin, the difference (He-Ho)
between the surface hardness He of the core 4 and the central
hardness Ho of the center 10 is preferably equal to or greater than
20 and particularly preferably equal to or greater than 25. In
light of resilience performance of the core 4, the difference
(He-Ho) is preferably equal to or less than 40 and particularly
preferably equal to or less than 35.
[0060] In the present specification, a zone that extends over a
distance range from equal to or greater than 1 mm to less than 5 mm
from the central point of the core 4 is referred to as "zone A",
and a zone 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 of the core 4 is referred to as "zone B".
[0061] At all points Pa included in the zone A, the following
mathematical formula (I) is satisfied.
Ha2-Ha1<5 (I)
In the mathematical formula (I), Ha1 indicates the JIS-C hardness
at a point Pa1. The point Pa1 is located radially inward of each
point Pa. The distance from the point Pa to the point Pa1 is 1 mm.
In the mathematical formula (I), Ha2 indicates the JIS-C hardness
at a point Pa2. The point Pa2 is located radially outward of each
point Pa. The distance from the point Pa to the point Pa2 is 1 mm.
The hardnesses Ha1 and Ha2 are measured by pressing a JIS-C type
hardness scale against a cut plane of the center 10 that has been
cut into two halves. 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.
[0062] The core 4 that satisfies the mathematical formula (I) has a
low energy loss when being hit with a golf club. The core 4 can
achieve high resilience of the golf ball 2. The golf ball 2 having
the core 4 has excellent flight performance. In light of flight
performance, the difference (Ha2-Ha1) is preferably equal to or
less than 4 and particularly preferably equal to or less than 3.
The difference (Ha2-Ha1) may be zero.
[0063] At any of points Pb included in the zone B, the following
mathematical formula (II) is satisfied.
Hb2-Hb1.gtoreq.5 (II)
In the mathematical formula (II), Hb1 indicates the JIS-C hardness
at a point Pb1. The point Pb1 is located radially inward of the
point Pb. The distance from the point Pb to the point Pb1 is 1 mm.
In the mathematical formula (II), Hb2 indicates the JIS-C hardness
at a point Pb2. The point Pb2 is located radially outward of the
point Pb. The distance from the point Pb to the point Pb2 is 1 mm.
The hardnesses Hb1 and Hb2 are measured by pressing a JIS-C type
hardness scale against a cut plane of the center 10 that has been
cut into two halves. 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.
[0064] The core 4 that satisfies the mathematical formula (II)
suppresses spin of the golf ball 2. In this respect, the difference
(Hb2-Hb1) is particularly preferably equal to or greater than 7. In
light of reduced energy loss upon hitting with a golf club, the
difference (Hb2-Hb1) is preferably equal to or less than 20 and
particularly preferably equal to or less than 15.
[0065] The ratio of the volume of the core 4 to the volume of a
phantom sphere of the golf ball 2 is equal to or greater than 76%.
In other words, the core 4 is large. The core 4 can achieve
excellent resilience performance of the golf ball 2. The core 4 can
suppress spin of the golf ball 2. In this respect, the ratio is
more preferably equal to or greater than 78% and particularly
preferably equal to or greater than 80%. The surface of the phantom
sphere is the surface of the golf ball 2 when it is postulated that
no dimple 14 exists.
[0066] In light of suppression of spin, the difference (He-Hb2)
between the surface hardness He of the core 4 and the hardness Hb2
is preferably equal to or greater than 10, more preferably equal to
or greater than 12, and particularly preferably equal to or greater
than 15.
[0067] A resin composition is suitably used for the mid layer 6.
Examples of the base polymer of the resin composition include
ionomer resins, styrene block-containing thermoplastic elastomers,
thermoplastic polyester elastomers, thermoplastic polyamide
elastomers and thermoplastic polyolefin elastomers.
[0068] Particularly preferable base polymers are ionomer resins.
Ionomer resins are highly elastic. As described later, the cover 8
of the golf ball 2 is thin and flexible. Thus, when the golf ball 2
is hit with a driver, the mid layer 6 significantly deforms. The
mid layer 6 including an ionomer resin contributes to resilience
performance upon a shot with a driver. An ionomer resin and another
resin may be used in combination. In this case, in light of
resilience performance, 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 70% by weight, and
particularly preferably equal to or greater than 85% by weight.
[0069] 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 more
but 90% by weight or less of an .alpha.-olefin, and 10% by weight
or more 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 more but 85% by weight or less of an .alpha.-olefin, 5%
by weight or more but 30% by weight or less of an
.alpha.,.beta.-unsaturated carboxylic acid, and 1% by weight or
more but 25% by weight or less of an .alpha.,.beta.-unsaturated
carboxylate ester. The ternary copolymer has excellent resilience
performance. For the binary copolymer and the ternary copolymer,
preferable .alpha.-olefins are ethylene and propylene, while
preferable .alpha.,.beta.-unsaturated carboxylic acids are acrylic
acid and methacrylic acid. A particularly preferable ionomer resin
is a copolymer formed with ethylene and acrylic acid or methacrylic
acid.
[0070] In the binary copolymer and the ternary copolymer, 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.
[0071] Specific examples of ionomer resins include trade names
"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 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
Corporation.
[0072] Two or more ionomer resins may be used in combination for
the mid layer 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.
[0073] The mid layer 6may include a highly elastic resin. Examples
of highly elastic resins include polybutylene terephthalate,
polyphenylene ether, polyethylene terephthalate, polysulfone,
polyethersulfone, polyphenylene sulfide, polyarylate, polyamide
imide, polyetherimide, polyether ether ketone, polyimide,
polytetrafluoroethylene, polyamino bismaleimide, polybisamide
triazole, polyphenylene oxide, polyacetal, polycarbonate,
acrylonitrile-butadiene-styrene copolymers and
acrylonitrile-styrene copolymers.
[0074] 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 mid layer 6 in an adequate amount. For forming the
mid layer 6, known methods such as injection molding, compression
molding and the like can be used.
[0075] The mid layer 6 has a hardness Hm of preferably 90 or
greater. The mid layer 6 having a hardness Hm of 90 or greater
achieves excellent resilience performance of the golf ball 2. The
mid layer 6 having a hardness Hm of 90 or greater can achieve an
outer-hard/inner-soft structure of the sphere consisting of the
core 4 and the mid layer 6. The sphere having the
outer-hard/inner-soft structure suppress spin of the golf ball 2.
In these respects, the hardness Hm is particularly preferably equal
to or greater than 92. In light of feel at impact, the hardness Hm
is equal to or less than 98 and particularly preferably equal to or
less than 97. In light of suppression of spin, preferably, the
hardness Hm of the mid layer 6 is greater than the surface hardness
He of the core 4, and the surface hardness He of the core 4 is
greater than the surface hardness of the center 10.
[0076] The hardness Hm is measured with an automated rubber
hardness measurement machine (trade name "P1", manufactured by
Kobunshi Keiki Co., Ltd.) to which a JIS-C type spring hardness
scale is mounted. For the measurement, a slab formed by hot press
and having 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 a resin
composition that is the same as the resin composition of the mid
layer 6 is used for the measurement.
[0077] In light of suppression of spin, the mid layer 6 has a
thickness of preferably 0.3 mm or greater, more preferably 0.5 mm
or greater, and particularly preferably 0.6 mm or greater. In light
of feel at impact, the thickness is preferably equal to or less
than 1.5 mm, more preferably equal to or less than 1.2 mm, and
particularly preferably equal to or less than 1.0 mm.
[0078] The cover 8 is formed from a resin composition. Examples of
the base polymer of the resin composition include polyurethanes,
polyesters, polyamides, polyolefins, polystyrenes and ionomer
resins. Particularly, polyurethanes are preferred. Polyurethanes
are flexible. When the golf ball 2 with the cover 8 including a
polyurethane is hit with a short iron, the spin rate is high. The
cover 8 formed from a polyurethane contributes to the
controllability upon a shot with a short iron. The polyurethane
also contributes to the scuff resistance of the cover 8.
[0079] When the golf ball 2 is hit with a driver, a long iron or a
middle iron, the sphere consisting of the core 4 and the mid layer
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 suppression of the spin rate achieves 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 cover 8. Since the cover 8
including the polyurethane is flexible, a high spin rate is
obtained. The high spin rate achieves excellent controllability. In
the golf ball 2, both desired flight performance upon shots with a
driver, a long iron, and a middle iron and desired controllability
upon a shot with a short iron are achieved.
[0080] When the golf ball 2 is hit, the cover 8 including the
polyurethane absorbs the shock. This absorption achieves soft feel
at impact. Particularly, when the golf ball 2 is hit with a short
iron or a putter, the cover 8 achieves excellent feel at
impact.
[0081] When being hit, compressive stress is applied to the cover 8
due to movement of the head of a golf club. Since the face of the
golf club has a loft angle, shear stress is also applied to the
cover 8 when being hit. The head speed of a short iron is low, and
the loft angle of a short iron is high. Thus, when the golf ball 2
is hit with a short iron, the shear stress greatly influences the
deformation behavior of the cover 8. The head speed of a driver is
high, and the loft angle of a driver is low. Thus, when the golf
ball 2 is hit with a driver, the compressive stress greatly
influences the deformation behavior of the cover 8.
[0082] The cover 8 has a shear loss elastic modulus G'' of
preferably 1.95.times.10.sup.7 Pa or less. As described above, when
being hit with a short iron, the deformation behavior of the cover
8 is greatly influenced by the shear stress. The spin rate obtained
when being hit with a short iron correlates with the shear loss
elastic modulus G''. When the golf ball 2 with the cover 8 having a
shear loss elastic modulus G'' of 1.95.times.10.sup.7 Pa or less is
hit with a short iron, the spin rate is high. The cover 8 can
achieve excellent controllability. In this respect, the shear loss
elastic modulus G'' is particularly equal to or less than
1.83.times.10.sup.7 Pa. In light of ease of forming the cover 8,
the shear loss elastic modulus G'' is preferably equal to or
greater than 1.00.times.10.sup.6 Pa and particularly equal to or
greater than 1.10.times.10.sup.6 Pa.
[0083] The ratio (E''/ G'') of a tensile loss elastic modulus E''
of the cover 8 to the shear loss elastic modulus G'' is preferably
equal to or greater than 1.76. As described above, when being hit
with a driver, the deformation behavior of the cover 8 is greatly
influenced by the compressive stress. The spin rate obtained when
being hit with a driver correlates with the tensile loss elastic
modulus E''. When the golf ball 2 with the cover 8 having a ratio
(E''/ G'') of 1.76 or greater is hit with a driver, the spin rate
is low, and when the golf ball 2 is hit with a short iron, the spin
rate is high. In this respect, the ratio (E''/ G'') is more
preferably equal to or greater than 1.86 and particularly
preferably equal to or greater than 1.90. In light of ease of
forming the cover 8, the ratio (E''/ G'') is preferably equal to or
less than 6.0 and particularly preferably equal to or less than
5.5.
[0084] The tensile loss elastic modulus E'' is preferably equal to
or greater than 2.00.times.10.sup.7 Pa, more preferably equal to or
greater than 2.20.times.10.sup.7 Pa, and particularly preferably
equal to or greater than 2.40.times.10.sup.7 Pa. The tensile loss
elastic modulus E'' is preferably equal to or less than
1.00.times.10.sup.8 Pa.
[0085] The shear loss elastic modulus G'' and the tensile loss
elastic modulus E'' can be controlled by adjusting the molecular
weight of a polyol, the molecular weight of a polyisocyanate, a
ratio (NCO/OH), and the like.
[0086] For measuring the shear loss elastic modulus G'', a sheet
having a thickness of 2 mm is obtained by press molding from a
resin composition that is the same as the resin composition of the
cover 8. A test piece having a width of 10 mm and an inter-clamp
distance of 10 mm is punched out from the sheet. The shear loss
elastic modulus G'' is measured for the test piece. The measurement
conditions are as follows.
[0087] Apparatus: "Rheometer ARES", manufactured by TA
instruments
[0088] Measurement mode: twisting (shearing)
[0089] Measurement temperature: 0.degree. C.
[0090] Vibration frequency: 10 Hz
[0091] Measurement distortion: 0.1%
[0092] For measuring the tensile loss elastic modulus E'', a sheet
having a thickness of 2 mm is obtained by press molding from a
resin composition that is the same as the resin composition of the
cover 8. A test piece having a width of 4 mm and an inter-clamp
distance of 20 mm is punched out from the sheet. The tensile loss
elastic modulus E'' is measured for the test piece. The measurement
conditions are as follows.
[0093] Apparatus: the dynamic viscoelasticity measuring apparatus
"Rheogel-E4000", manufactured by UBM
[0094] Measurement mode: pulling
[0095] Measurement temperature: 0.degree. C.
[0096] Vibration frequency: 10 Hz
[0097] Measurement distortion: 0.1%
[0098] A time for which a golf ball and a club contact each other
is several hundred microseconds. Thus, the frequency of deformation
of the golf ball 2 when being hit is several thousand Hz. On
average, the golf ball 2 is hit at substantially normal temperature
(25.degree. C.). On the basis of a general time conversion rule of
polyurethane, a deformation having a frequency of several thousand
Hz in the environment having a temperature of 25.degree. C.
corresponds to a deformation having a frequency of 10 Hz in the
environment having a temperature of 0.degree. C. Thus, in the
present invention, the shear loss elastic modulus G'' and the
tensile loss elastic modulus E'' are measured under the conditions
of a vibration frequency of 10 Hz and a temperature of 0.degree.
C.
[0099] A polyurethane and another resin may be used in combination
for the cover 8. In this case, in light of spin performance and
feel at impact, the polyurethane is included as the principal
component of the base polymer. The proportion of the polyurethane
to the entire base polymer is preferably equal to or greater than
50% by weight, more preferably equal to or greater than 70% by
weight, and particularly preferably equal to or greater than 85% by
weight.
[0100] For the cover 8, thermoplastic polyurethanes and
thermosetting polyurethanes can be used. In light of productivity,
thermoplastic polyurethanes are preferred. A thermoplastic
polyurethane includes a polyurethane component as a hard segment,
and a polyester component or a polyether component as a soft
segment.
[0101] The polyurethane includes a polyol component. A polymeric
polyol is preferred. Specific examples of polymeric polyols include
polyetherpolyols such as polyoxyethylene glycol (PEG),
polyoxypropylene glycol (PPG) and polytetramethylene ether glycol
(PTMG); condensed polyester polyols such as polyethylene adipate
(PEA), polybutylene adipate (PBA) and polyhexamethylene adipate
(PHMA); lactone polyester polyols such as
poly-.epsilon.-caprolactone (PCL); polycarbonate polyols such as
polyhexamethylene carbonate; and acrylic polyols. Two or more
polyols may be used in combination.
[0102] Particularly, polytetramethylene ether glycol is preferred.
The spin rate obtained when the golf ball 2 is hit with a short
iron has a high correlation with the content of polytetramethylene
ether glycol. Meanwhile, the spin rate obtained when the golf ball
2 is hit with a driver has a low correlation with the content of
polytetramethylene ether glycol. The golf ball 2 including a
polyurethane that includes polytetramethylene ether glycol in an
appropriate amount has both excellent flight performance when being
hit with a driver and excellent controllability when being hit with
a short iron.
[0103] In light of controllability, the polyol has a number average
molecular weight of preferably 200 or greater, more preferably 400
or greater, and particularly preferably 650 or greater. In light of
suppression of spin, the molecular weight is preferably equal to or
less than 1500, more preferably equal to or less than 1200, and
particularly preferably equal to or less than 850.
[0104] The number average molecular weight is measured by gel
permeation chromatography. The measurement conditions are as
follows.
[0105] Apparatus: HLC-8120GPC (manufactured by Tosoh
Corporation)
[0106] Eluant: tetrahydrofuran
[0107] Concentration: 0.2% by weight
[0108] Temperature: 40.degree. C.
[0109] Column: TSK gel Super HM-M (manufactured by Tosoh
Corporation)
[0110] Sample volume: 5 microliters
[0111] Flow rate: 0.5 milliliter/min
[0112] Reference material: polystyrene ("PStQuick Kit-H"
manufactured by Tosoh Corporation)
[0113] The polymeric polyol component has a hydroxyl value of
preferably 94 mg KOH/g or greater and particularly preferably 112
mg KOH/g or greater. The hydroxyl value is preferably equal to or
less than 561 mg KOH/g and particularly preferably equal to or less
than 173 mg KOH/g.
[0114] Examples of an isocyanate component in the polyurethane
include aromatic polyisocyanates such as 2,4-toluene diisocyanate,
2,6-toluene diisocyanate, a mixture (TDI) of 2,4-toluene
diisocyanate and 2,6-toluene diisocyanate, 4,4'-diphenylmethane
diisocyanate (MDI), 1,5-naphthylene diisocyanate (NDI),
3,3'-bitolylene-4,4'-diisocyanate (TODI), xylylene diisocyanate
(XDI), tetramethylxylene diisocyanate (TMXDI) and paraphenylene
diisocyanate (PPDI); and alicyclic polyisocyanates such as
4,4'-dicyclohexylmethane diisocyanate (H.sub.12MDI), hydrogenated
xylylene diisocyanate (H.sub.6XDI) and isophorone diisocyanate
(IPDI). Two or more polyisocyanates may be used in combination. In
light of weather resistance, TMXDI, XDI, HDI, H.sub.6XDI, IPDI and
H.sub.12MDI are preferred, and H.sub.12MDI is particularly
preferred.
[0115] The polyurethane may include a chain extender as its
component. Examples of chain extenders include low-molecular-weight
polyols and low-molecular-weight polyamines.
[0116] Examples of low-molecular-weight polyols include diols,
triols, tetraols and hexaols. Specific examples of diols include
ethylene glycol, diethylene glycol, propanediol, dipropylene
glycol, butanediol, neopentyl glycol, pentanediol, hexanediol,
heptanediol and octanediol. Specific examples of triols include
glycerin, trimethylolpropane and hexanetriol. Specific examples of
tetraols include pentaerythritol and sorbitol. 1,4-butanediol is
preferred.
[0117] Examples of low-molecular-weight polyamines include
aliphatic polyamines, monocyclic aromatic polyamines and polycyclic
aromatic polyamines. Specific examples of aliphatic polyamines
include ethylenediamine, propylenediamine, butylenediamine and
hexamethylenediamine. Specific examples of monocyclic aromatic
polyamines include phenylenediamine, toluene diamine, dimethyl
toluene diamine, dimethylthio toluene diamine and
xylylenediamine.
[0118] The chain extender has a number average molecular weight of
preferably 30 or greater, more preferably 40 or greater, and
particularly 45 or greater. The molecular weight is preferably
equal to or less than 400, more preferably equal to or less than
350, and particularly preferably equal to or less than 200.
Low-molecular-weight polyols and low-molecular-weight polyamines
that are used as chain extenders are low-molecular-weight compounds
that almost do not have a molecular weight distribution. Thus, the
low-molecular-weight polyols and the low-molecular-weight
polyamines can be distinguished from the polymeric polyol.
[0119] The cover 8 may be formed from a composition including a
thermoplastic polyurethane and an isocyanate compound. During or
after forming the cover 8, the polyurethane is crosslinked with the
isocyanate compound.
[0120] 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 cover 8 in an adequate amount.
[0121] The cover 8 has a JIS-C hardness Hc of 65 or less. Use of
the flexible cover 8 can achieve excellent controllability upon a
shot with a short iron. In light of controllability, the hardness
Hc is more preferably equal to or less than 60, even more
preferably equal to or less than 55, and particularly preferably
equal to or less than 50. If the hardness Hc is excessively low,
the flight performance upon a shot with a driver is insufficient.
In this respect, the hardness Hc is preferably equal to or greater
than 20, more preferably equal to or greater than 25, and
particularly preferably equal to or greater than 35. For measuring
the hardness Hc, a slab formed from a resin composition that is the
same as the resin composition of the cover 8 is used. The
measurement method is the same as the measurement method for the
hardness Hm of the mid layer 6.
[0122] The hardness Hc of the cover 8 is less than the central
hardness Ho of the core 4. The golf ball 2 has excellent
controllability upon a shot with a short iron. In light of
controllability, the difference (Ho-Hc) is preferably equal to or
greater than 3, more preferably equal to or greater than 5, and
particularly preferably equal to or greater than 8. The difference
(Ho-Hc) is preferably equal to or less than 15.
[0123] In light of flight performance upon a shot with a driver,
the cover 8 has a thickness of preferably 0.8 mm or less, more
preferably 0.6 mm or less, even more preferably 0.5 mm or less, and
particularly preferably 0.4 mm or less. In light of controllability
upon a shot with a short iron, the thickness is preferably equal to
or greater than 0.10 mm and particularly preferably equal to or
greater than 0.15 mm.
[0124] For forming the cover 8, known methods such as injection
molding, compression molding and the like can be used. When forming
the cover 8, the dimples 14 are formed by pimples formed on the
cavity face of a mold.
[0125] In light of feel at impact, the golf ball 2 has an amount of
compressive deformation of preferably 2.0 mm or greater, more
preferably 2.1 mm or greater, and particularly preferably 2.2 mm or
greater. In light of resilience performance, the amount of
compressive deformation is preferably equal to or less than 3.5 mm,
more preferably equal to or less than 3.0 mm, and particularly
preferably equal to or less than 2.6 mm.
[0126] At measurement of the amount of compressive deformation,
first, the golf ball 2 is placed on a hard plate made of metal.
Next, a cylinder made of metal gradually descends toward the golf
ball 2. The golf ball 2, 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 golf ball 2 up to the state in which a
final load of 1274 N is applied thereto, is measured.
[0127] The golf ball 2 may include a reinforcing layer between the
mid layer 6 and the cover 8. The reinforcing layer firmly adheres
to the mid layer 6 and also to the cover 8. The reinforcing layer
suppresses separation of the cover 8 from the mid layer 6. As
described above, the cover 8 of the golf ball 2 is thin. When the
golf ball 2 is hit by the edge of a clubface, a wrinkle is likely
to occur. The reinforcing layer suppresses occurrence of a
wrinkle.
[0128] As the base polymer of the reinforcing layer, a
two-component curing type thermosetting resin is suitably used.
Examples of two-component curing type thermosetting resins include
epoxy resins, urethane resins, acrylic resins, polyester resins,
and cellulose resins. In light of strength and durability of the
reinforcing layer, two-component curing type epoxy resins and
two-component curing type urethane resins are preferred.
[0129] The reinforcing layer may include additives such as a
coloring agent (typically, titanium dioxide), a phosphate-based
stabilizer, an antioxidant, a light stabilizer, a fluorescent
brightener, an ultraviolet absorber, an anti-blocking agent and the
like. The additives may be added to the base material of the
two-component curing type thermosetting resin, or may be added to
the curing agent of the two-component curing type thermosetting
resin.
[0130] The reinforcing layer is obtained by applying, to the
surface of the mid layer 6, a liquid that is prepared by dissolving
or dispersing the base material and the curing agent in a solvent.
In light of workability, application with a spray gun is preferred.
After the application, the solvent is volatilized to permit a
reaction of the base material with the curing agent, thereby
forming the reinforcing layer.
[0131] In light of suppression of a wrinkle, the reinforcing layer
has a thickness of preferably 3 .mu.m or greater and more
preferably 5 .mu.m or greater. In light of ease of forming the
reinforcing layer, the thickness is preferably equal to or less
than 300 .mu.m, more preferably equal to or less than 50 .mu.m, and
particularly preferably equal to or less than 20 .mu.m. The
thickness is measured by observing a cross section of the golf ball
2 with a microscope. When the mid layer 6 has concavities and
convexities on its surface from surface roughening, the thickness
of the reinforcing layer is measured at a convex part.
[0132] In light of suppression of a wrinkle, the reinforcing layer
has a pencil hardness of preferably 4 B or greater and more
preferably B or greater. In light of reduced loss of the power
transmission from the cover 8 to the mid layer 6 upon hitting the
golf ball 2, the pencil hardness of the reinforcing layer is
preferably equal to or less than 3 H. The pencil hardness is
measured according to the standard of "JIS K5400".
EXAMPLES
[0133] [Synthesis of Polyurethane #1]
[0134] Dicyclohexylmethane diisocyanate polytetramethylene ether
glycol (PTMG) having a number average molecular weight of 1500, and
1,4-butanediol (BD) were prepared. H.sub.12MDI and PTMG were heated
to 80.degree. C., and PTMG was put into a container containing
H.sub.12MDI, to obtain a mixed liquid. Dibutyltin dilaurate
(manufactured by Aldrich, Inc.) was put into the container. Then,
the mixed liquid was stirred at a temperature of 80.degree. C. for
2 hours under a blanket of nitrogen gas. Further, BD heated to
80.degree. C. was put into the container. The mixed liquid was
stirred at a temperature of 80.degree. C. for 1 minute under a
blanket of nitrogen gas. The mixed liquid was cooled to room
temperature. The mixed liquid was depressurized for 1 minute. By
the depressurization, the mixed liquid was deaerated. After the
deaeration, the mixed liquid was spread out in another container,
and kept at 110.degree. C. for 6 hours under a blanket of nitrogen
gas. By the keeping, a urethane reaction took place, thereby
obtaining a polyurethane #1. The polyurethane #1 had a JIS-C
hardness of 45. Details of the materials are as follows.
[0135] H.sub.12MDI: manufactured by Sumika Bayer Urethane Co.
Ltd.
[0136] PTMG: trade name "PTMG-1500SN", manufactured by Hodogaya
Chemical Co., Ltd.
[0137] BD: manufactured by Wako Pure Chemical Industries, Ltd. The
mole ratio of H.sub.12MDI, PTMG, and BD was (3.39:1.00:2.39). The
amount of dibutyltin dilaurate per 100 parts by weight of the total
amount of H.sub.12MDI, PTMG and BD was 0.005 parts by weight.
[0138] [Synthesis of Polyurethane #2]
[0139] A polyurethane #2 was synthesized in the same manner as the
synthesis of the polyurethane #1, except the mole ratio of
H.sub.12MDI, PTMG and BD was (3.61:1.00:2.61). The polyurethane #2
had a JIS-C hardness of 47.
[0140] [Synthesis of Polyurethane #3]
[0141] A polyurethane #3 was synthesized in the same manner as the
synthesis of the polyurethane #1, except PTMG having a number
average molecular weight of 1000 (trade name "PTMG-1000SN",
manufactured by Hodogaya Chemical Co., Ltd.) was used and the mole
ratio of H.sub.12MDI, PTMG and BD was (2.63:1.00:1.63). The
polyurethane #3 had a JIS-C hardness of 44.
Example 1
[0142] A rubber composition (1) was obtained by kneading 100 parts
by weight of a high-cis polybutadiene (trade name "BR-730",
manufactured by JSR Corporation), 20 parts by weight of zinc
diacrylate, 5 parts by weight of zinc oxide, an appropriate amount
of barium sulfate, 0.5 parts by weight of diphenyl disulfide, and
0.7 parts by weight of dicumyl peroxide. The rubber composition (1)
was placed into a mold including upper and lower mold halves each
having a hemispherical cavity, and heated at 170.degree. C. for 15
minutes to obtain a center with a diameter of 15 mm.
[0143] A rubber composition (3) was obtained by kneading 100 parts
by weight of a high-cis polybutadiene (the aforementioned
"BR-730"), 42 parts by weight of zinc diacrylate, 5 parts by weight
of zinc oxide, an appropriate amount of barium sulfate, 0.5 parts
by weight of diphenyl disulfide, and 0.7 parts by weight of dicumyl
peroxide. Half shells were formed from the rubber composition (3).
The center was covered with two 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
170.degree. C. for 20 minutes to obtain a core with a diameter of
39.7 mm. An envelope layer was formed from the rubber composition
(3). The amount of barium sulfate was adjusted such that the
specific gravity of the envelope layer agrees with the specific
gravity of the center and the weight of a golf ball is 45.4 g.
[0144] A resin composition (a) was obtained by kneading 50 parts by
weight of an ionomer resin (the aforementioned "Surlyn 8945") and
50 parts by weight of another ionomer resin (the aforementioned
"Himilan AM7329") 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 core was covered with the resin
composition (a) by injection molding to form a mid layer with a
thickness of 1.0 mm.
[0145] A paint composition (trade name "POLIN 750LE", manufactured
by SHINTO PAINT CO., LTD.) including a two-component curing type
epoxy resin as a base polymer was prepared. The base material
liquid of this paint composition includes 30 parts by weight of a
bisphenol A type solid epoxy resin and 70 parts by weight of a
solvent. The curing agent liquid of this paint composition includes
40 parts by weight of a modified polyamide amine, 55 parts by
weight of a solvent, and 5 parts by weight of titanium oxide. The
weight ratio of the base material liquid to the curing agent liquid
is 1/1. This paint composition was applied to the surface of the
mid layer with a spray gun, and kept at 40.degree. C. for 24 hours
to obtain a reinforcing layer with a thickness of 10 .mu.m.
[0146] A resin composition (b) was obtained by kneading 100 parts
by weight of a thermoplastic polyurethane elastomer (trade name
"Elastollan XNY85A", manufactured by BASF Japan Ltd.) and 4 parts
by weight of titanium dioxide with a twin-screw kneading extruder.
Half shells were obtained from the resin composition (b) by
compression molding. The sphere consisting of the core, the mid
layer and the reinforcing layer was covered with two of these half
shells. The sphere and the half shells were placed into a final
mold that includes upper and lower mold halves each having a
hemispherical cavity and that has a large number of pimples on its
cavity face. A cover was obtained by compression molding. The cover
had a thickness of 0.5 mm. Dimples having a shape that was the
inverted shape of the pimples were formed on the cover. A clear
paint including a two-component curing type polyurethane as a base
material was applied to this cover to obtain a golf ball of Example
1 with a diameter of 42.7 mm. A hardness distribution of the core
of this golf ball is shown in Table 3.
Examples 2 to 8 and Comparative Examples 1 to 5]
[0147] Golf balls of Examples 2 to 8 and Comparative Examples 1 to
5 were obtained in the same manner as Example 1, except the
specifications of the center, the envelope layer, the mid layer and
the cover were as shown in Tables 6 to 9 below. The rubber
composition of the core is shown in detail in Table 1 below. The
resin compositions of the mid layer and the cover are shown in
detail in Table 2 below. A hardness distribution of the core is
shown in Tables 3 to 5. The golf ball according to Comparative
Example 1 does not have an envelope layer.
[0148] [Shot with Driver (W #1)]
[0149] A driver with a titanium head (trade name "SRIXON W505",
manufactured by SRI Sports Limited, shaft hardness: X, loft angle:
8.5.degree.) was attached to a swing machine manufactured by Golf
Laboratories, Inc. A golf ball was hit under the condition of a
head speed of 50m/sec. The ball speed immediately after the hit and
the distance from the launch point to the stop point were measured.
The average value of data obtained by 12 measurements is shown in
Tables 6 to 9 below.
[0150] [Shot with Short Iron]
[0151] A sand wedge (SW) was attached to a swing machine
manufactured by Golf Laboratories, Inc. A golf ball was hit under
the condition of a head speed of 21 m/sec, and the spin rate was
measured immediately after the hit. The average value of data
obtained by 12 measurements is shown in Tables 6 to 9 below. In
addition, water was applied to a clubface and a golf ball, and the
golf ball was hit. The spin rate was measured immediately after the
hit. The average value of data obtained by 12 measurements is shown
in Tables 6 to 9 below.
[0152] [Feel at Impact]
[0153] Ten golf players hit golf balls with sand wedges, and were
asked about feel at impact. The evaluation was categorized as
follows on the basis of the number of golf players who answered,
"the feel at impact was excellent".
[0154] A: 8 or more
[0155] B: 6 to 7
[0156] C: 4 to 5
[0157] D: 3 or less
The results are shown in Tables 6 to 9 below.
TABLE-US-00001 TABLE 1 Composition of Core (parts by weight) (1)
(2) (3) (4) (5) (6) (7) (8) (9) BR-730 100 100 100 100 100 100 100
100 100 Zinc acrylate 20 38 42 45 39 22 37 22 23 Zinc oxide 5 5 5 5
5 5 5 5 5 Barium sulfate * * * * * * * * * Diphenyl disulfide 0.5
0.5 0.5 0.5 0.5 0.5 0.5 -- 0.5 Dicumyl peroxide 0.7 0.7 0.7 0.7 0.7
0.7 0.7 0.7 0.7 Thionaphthol -- -- -- -- -- -- -- 0.5 -- Sulfur --
-- -- -- -- -- -- -- 0.05 * Appropriate amount
TABLE-US-00002 TABLE 2 Compositions of Mid Layer and Cover (parts
by weight) (a) (b) (c) (d) (e) (f) (g) Surlyn 8945 50 -- -- -- --
-- -- Himilan AM7329 50 -- -- -- -- -- -- Elastollan XNY85A -- 100
-- -- -- -- -- Elastollan XNY90A -- -- 100 -- -- -- -- Elastollan
XNY97A -- -- -- 100 -- -- -- Polyurethane #1 -- -- -- -- 100 -- --
Polyurethane #2 -- -- -- -- -- 100 -- Polyurethane #3 -- -- -- --
-- -- 100 Titanium dioxide -- 4 4 4 4 4 4 Molecular weight of PTMG
-- 1800 1800 1800 1500 1500 1000 E'' (.times.10.sup.7 Pa) -- 3.24
4.61 7.57 1.80 3.51 6.26 G'' (.times.10.sup.7 Pa) -- 2.77 3.23 4.01
1.02 1.42 3.00 E''/G'' -- 1.17 1.43 1.89 1.76 2.47 2.09 Hardness
(JIS-C) 94 47 56 67 45 47 44 Hardness (Shore D) 64 32 38 47 30 32
29
[0158] Elastollan XNY85A, Elastollan XNY90A, Elastollan XNY97A,
polyurethane #1, polyurethane #2 and polyurethane #3 are
thermoplastic polyurethane elastomers in each of which a polyol
component is polytetramethylene ether glycol. The number average
molecular weight of each polytetramethylene ether glycol is as
follows.
[0159] Elastollan XNY85A: 1800 Elastollan XNY90A: 1800
[0160] Elastollan XNY97A: 1800 Polyurethane #1: 1500
[0161] Polyurethane #2: 1500 Polyurethane #3: 1000
TABLE-US-00003 TABLE 3 Hardness Distribution of Core (JIS-C)
Distance from central point (mm) Example 1 Example 2 Example 3
Example 4 0 60 60 60 60 1.0 61 60.8 61 61 2.0 62 61.6 62 62 3.0 63
62.4 63 63 4.0 64 63.2 64 64 5.0 65 64 65 65 6.0 65.7 65 65.7 65.7
7.0 66.5 66 66 66.5 8.0 74.5 67 74.5 74.5 9.0 75.7 68.76 75.7 75.7
10.0 77 77 77 77 11.0 77.8 77.8 77.8 77.8 12.0 78.6 78.6 78.6 78.6
13.0 79.4 79.4 79.4 79.4 14.0 80.2 80.2 80.2 80.2 15.0 81 81 81
81
TABLE-US-00004 TABLE 4 Hardness Distribution of Core (JIS-C)
Distance from central point (mm) Example 5 Example 6 Example 7
Example 8 0 60 60 54 62 1.0 61 61 56 63 2.0 62 62 58 64 3.0 63 63
60 65 4.0 64 64 62 66 5.0 65 65 64 67 6.0 65.7 65.7 66 67.7 7.0
66.5 66.5 68 68.5 8.0 74.5 74.5 74.5 73.5 9.0 75.7 75.7 75.7 74.7
10.0 77 77 77 76 11.0 77.8 77.8 77.8 76.8 12.0 78.6 78.6 78.6 77.6
13.0 79.4 79.4 79.4 78.4 14.0 80.2 80.2 80.2 79.2 15.0 81 81 81
80
TABLE-US-00005 TABLE 5 Hardness Distribution of Core (JIS-C)
Distance from central point Compa. Compa. Compa. Compa. Compa. (mm)
Example 1 Example 2 Example 3 Example 4 Example 5 0 70 60 60 60 54
1.0 71.2 60.8 61 61 60 2.0 72.4 61.6 62 62 61.2 3.0 73.6 62.4 63 63
62.5 4.0 74.8 63.2 64 64 63.8 5.0 76 64 65 65 65 6.0 76 65 65.5
65.5 65.7 7.0 76 66 66 66 66.5 8.0 76 67 73 73 74.5 9.0 76 68 73.7
73.7 75.7 10.0 76 68.8 75 75 77 11.0 76.8 69.6 75.8 75.8 77.8 12.0
77.6 70.4 76.6 76.6 78.6 13.0 78.4 81.4 77.4 77.4 79.4 14.0 79.2
82.2 78.2 78.2 80.2 15.0 80 83 79 79 81
TABLE-US-00006 TABLE 6 Results of Evaluation Example 1 Example 2
Example 3 Center Composition (1) (1) (1) Crosslinking temperature
170 170 170 (.degree. C.) Crosslinking time (min) 15 15 15 Diameter
(mm) 15 18 15 Envelope Composition (3) (3) (3) layer Crosslinking
temperature 170 170 170 (.degree. C.) Crosslinking time (min) 20 20
20 Core Diameter (mm) 39.7 40.1 40.3 Volume ratio (%) 80.4 82.8
84.1 Central hardness Ho 60 60 60 (JIS-C) Surface hardness He 88 88
88 (JIS-C) Hardness distribution FIG. 2 FIG. 3 FIG. 4 Mid
Composition (a) (a) (a) layer Hardness (JIS-C) 94 94 94 Thickness
(mm) 1.0 1.0 0.9 Cover Composition (b) (c) (b) Hardness (JIS-C) 47
56 47 Thickness (mm) 0.5 0.3 0.3 Molecular weight of 1800 1800 1800
PTMG E'' (.times.10.sup.7 Pa) 3.24 4.61 3.24 G'' (.times.10.sup.7
Pa) 2.77 3.23 2.77 E''/G'' 1.17 1.43 1.17 Ball Amount of
compressive 2.40 2.45 2.40 deformation (mm) Ha2-Ha1 (maximum value)
2.0 1.6 2.0 Hb2-Hb1 (maximum value) 9.0 10.0 9.0 W #1 Ball speed
(m/s) 73.9 74.0 74.1 Spin (rpm) 2440 2310 2410 Flight distance (m)
248.5 251.0 250.0 SW Spin Dry (rpm) 6720 6530 6690 Spin Wet (rpm)
4500 3900 4470 Feel at impact A B A
TABLE-US-00007 TABLE 7 Results of Evaluation Example 4 Example 5
Example 6 Center Composition (1) (1) (1) Crosslinking temperature
170 170 170 (.degree. C.) Crosslinking time (min) 15 15 15 Diameter
(mm) 15 15 15 Envelope Composition (3) (3) (3) layer Crosslinking
temperature 170 170 170 (.degree. C.) Crosslinking time (min) 20 20
20 Core Diameter (mm) 39.7 39.7 39.7 Volume ratio (%) 80.4 80.4
80.4 Central hardness Ho 60 60 60 (JIS-C) Surface hardness He 88 88
88 (JIS-C) Hardness distribution FIG. 2 FIG. 2 FIG. 2 Mid
Composition (a) (a) (a) layer Hardness (JIS-C) 94 94 94 Thickness
(mm) 1.0 1.0 1.0 Cover Composition (e) (f) (g) Hardness (JIS-C) 45
47 44 Thickness (mm) 0.5 0.5 0.5 Molecular weight of 1500 1500 1000
PTMG E'' (.times.10.sup.7 Pa) 1.80 3.51 6.26 G'' (.times.10.sup.7
Pa) 1.02 1.42 3.00 E''/G'' 1.76 2.47 2.09 Ball Amount of
compressive 2.40 2.40 2.40 deformation (mm) Ha2-Ha1 (maximum value)
2.0 2.0 2.0 Hb2-Hb1 (maximum value) 9.0 9.0 9.0 W #1 Ball speed
(m/s) 73.9 73.9 73.9 Spin (rpm) 2370 2400 2450 Flight distance (m)
249.5 249.2 248.9 SW Spin Dry (rpm) 6710 6700 6760 Spin Wet (rpm)
4900 5000 5100 Feel at impact A A A
TABLE-US-00008 TABLE 8 Results of Evaluation Compa. Example 7
Example 8 Example 1 Center Composition (8) (6) (2) Crosslinking
temperature 170 170 170 (.degree. C.) Crosslinking time (min) 15 15
20 Diameter (mm) 15 15 39.7 Envelope Composition (3) (7) -- layer
Crosslinking temperature 170 170 -- (.degree. C.) Crosslinking time
(min) 20 20 -- Core Diameter (mm) 39.7 39.7 39.7 Volume ratio (%)
80.4 80.4 80.4 Central hardness Ho 54 62 70 (JIS-C) Surface
hardness He 88 87 86 (JIS-C) Hardness distribution FIG. 5 FIG. 6
FIG. 7 Mid Composition (a) (a) (a) layer Hardness (JIS-C) 94 94 94
Thickness (mm) 1.0 1.0 1.0 Cover Composition (b) (b) (b) Hardness
(JIS-C) 47 47 47 Thickness (mm) 0.5 0.5 0.5 Molecular weight of
1800 1800 1800 PTMG E'' (.times.10.sup.7 Pa) 3.24 3.24 3.24 G''
(.times.10.sup.7 Pa) 2.77 2.77 2.77 E''/G'' 1.17 1.17 1.17 Ball
Amount of compressive 2.50 2.40 2.40 deformation (mm) Ha2-Ha1
(maximum value) 4.0 2.0 2.4 Hb2-Hb1 (maximum value) 8.0 6.0 0 W #1
Ball speed (m/s) 73.8 73.9 74.0 Spin (rpm) 2390 2480 2580 Flight
distance (m) 249.2 248.0 247.0 SW Spin Dry (rpm) 6680 6740 6750
Spin Wet (rpm) 4480 4510 4550 Feel at impact A A A
TABLE-US-00009 TABLE 9 Results of Evaluation Compa. Compa. Compa.
Compa. Exam- Exam- Exam- Exam- ple 2 ple 3 ple 4 ple 5 Center
Composition (1) (1) (1) (9) Crosslinking 170 170 170 170
temperature (.degree. C.) Crosslinking time 15 15 15 15 (min)
Diameter (mm) 25 15 15 15 Envelope Composition (4) (5) (5) (3)
layer Crosslinking 170 170 170 170 temperature (.degree. C.)
Crosslinking time 20 20 20 20 (min) Core Diameter (mm) 39.1 38.5
39.7 39.7 Volume ratio (%) 76.8 73.3 80.4 80.4 Central hardness Ho
60 60 60 54 (JIS-C) Surface hardness He 90 86 88 88 (JIS-C)
Hardness distribution FIG. 8 FIG. 9 FIG. 9 FIG. 10 Mid Composition
(a) (a) (a) (a) layer Hardness (JIS-C) 94 94 94 94 Thickness (mm)
1.0 1.6 1.0 1.0 Cover Composition (b) (b) (d) (b) Hardness (JIS-C)
47 47 67 47 Thickness (mm) 0.8 0.5 0.5 0.5 Molecular weight of 1800
1800 1800 1800 PTMG E'' (.times.10.sup.7 Pa) 3.24 3.24 7.57 3.24
G'' (.times.10.sup.7 Pa) 2.77 2.77 4.01 2.77 E''/G'' 1.17 1.17 1.89
1.17 Ball Amount of 2.40 2.40 2.40 2.40 compressive deformation
(mm) Ha2-Ha1 (maximum value) 1.6 2.0 2.0 7.0 Hb2-Hb1 (maximum
value) 11 7 7 9.0 W #1 Ball speed (m/s) 73.5 73.6 74.0 73.4 Spin
(rpm) 2360 2420 2270 2400 Flight distance (m) 246.0 247.0 251.5
246.8 SW Spin Dry (rpm) 6670 6610 6330 6720 Spin Wet (rpm) 4470
4400 3000 4500 Feel at impact A B C A
[0162] As shown in Tables 6 to 9, the golf balls according to
Examples are excellent in various performance characteristics. From
the results of evaluation, advantages of the present invention are
clear.
[0163] The above description is merely for illustrative examples,
and various modifications can be made without departing from the
principles of the present invention.
* * * * *