U.S. patent application number 12/649890 was filed with the patent office on 2011-06-30 for multi-piece golf ball.
This patent application is currently assigned to BRIDGESTONE SPORTS CO., LTD.. Invention is credited to Hiroshi Higuchi, Atsushi Nanba.
Application Number | 20110160001 12/649890 |
Document ID | / |
Family ID | 44188222 |
Filed Date | 2011-06-30 |
United States Patent
Application |
20110160001 |
Kind Code |
A1 |
Nanba; Atsushi ; et
al. |
June 30, 2011 |
MULTI-PIECE GOLF BALL
Abstract
A multiple-piece golf ball includes a solid core having a
specific gravity from about 1.2 to about 14; and a cover disposed
on the outside of the solid core, wherein a spin decay rate of the
golf ball during flight is from about 3.1% to about 20% of an
initial spin rate of the golf ball from about 2800 to about 3500
rpm; and wherein a moment of inertia of the golf ball with respect
to an x-axis Ix, a moment of inertia of the golf ball with respect
to a y-axis Iy, and a moment of inertia of the golf ball with
respect to a z-axis Iz are substantially the same, the x-axis,
y-axis, and z-axis intersecting orthogonally at the center of the
golf ball.
Inventors: |
Nanba; Atsushi;
(Chichibu-shi, JP) ; Higuchi; Hiroshi;
(Chichibu-shi, JP) |
Assignee: |
BRIDGESTONE SPORTS CO.,
LTD.
Tokyo
JP
|
Family ID: |
44188222 |
Appl. No.: |
12/649890 |
Filed: |
December 30, 2009 |
Current U.S.
Class: |
473/377 |
Current CPC
Class: |
A63B 37/0077 20130101;
A63B 37/0066 20130101; A63B 37/0096 20130101; A63B 37/04 20130101;
A63B 37/0076 20130101; A63B 37/0003 20130101 |
Class at
Publication: |
473/377 |
International
Class: |
A63B 37/04 20060101
A63B037/04 |
Claims
1. A multiple-piece golf ball comprising: a solid core having a
specific gravity from about 1.2 to about 14; and a cover disposed
on the outside of the solid core, wherein a spin decay rate of the
golf ball during flight is from about 3.1% to about 20% of an
initial spin rate of the golf ball from about 2800 to about 3500
rpm; and wherein a moment of inertia of the golf ball with respect
to an x-axis Ix, a moment of inertia of the golf ball with respect
to a y-axis Iy, and a moment of inertia of the golf ball with
respect to a z-axis Iz are substantially the same, the x-axis,
y-axis, and z-axis intersecting orthogonally at the center of the
golf ball.
2. The golf ball according to claim 1, wherein the solid core
comprises at least one specific gravity-enhancing member.
3. The golf ball according to claim 2, wherein the solid core
comprises one specific gravity-enhancing member.
4. The golf ball according to claim 2, wherein the solid core
comprises plural specific gravity-enhancing members.
5. The golf ball according to claim 3, wherein the specific
gravity-enhancing member has a transmission loss of at least about
10 dB in the region from 1000 to 4000 Hz.
6. The golf ball according to claim 4, wherein the specific
gravity-enhancing member has a transmission loss of at least about
10 dB in the region from 1000 to 4000 Hz.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a multiple-piece golf
ball.
[0002] While there are many factors that affect the distance of a
golf ball, three factors, the initial velocity of the ball, the
launch angle, and the spin rate are extremely important. Of these,
the ball spin is an essential element in lifting the golf ball and
extending its distance. However, if the spin rate is excessive, the
ball can fly upward or the ball line can be short after falling, so
that the distance of the ball is not extended. The spin rate is
greatest at the time the ball is struck, and gradually decreases,
that is, attenuates, as the ball flies.
[0003] In the Japanese Patent Application Publication No.
2007-216024, there is a description of a golf ball provided with a
liquid core, and a mantle layer made from prescribed material that
surrounds the liquid core, for the purpose of achieving a proper
spin rate and good striking feeling. This publication describes a
golf ball that has a preferable spin decay rate of at least 4%
during flight with respect to the initial spin rate at the time of
striking. In this publication, however, there is only language
regarding a liquid-core golf ball, and no language regarding a
solid-core golf ball.
SUMMARY OF THE INVENTION
[0004] An object of the present invention is to provide a
multiple-piece golf ball with a solid core, having a high spin
decay rate and capable of extending the distance having a
relatively large initial spin rate from about 2800 to about 3500
rpm when struck by a driver.
[0005] In order to achieve the above-noted object, the present
invention is a multiple-piece golf ball including a solid core
having a specific gravity from about 1.2 to about 14; and a cover
disposed on the outside of the solid core, wherein a spin decay
rate of the golf ball during flight is from about 3.1% to about 20%
of an initial spin rate of the golf ball from about 2800 to about
3500 rpm; and wherein a moment of inertia of the golf ball with
respect to an x-axis Ix, a moment of inertia of the golf ball with
respect to a y-axis Iy, and a moment of inertia of the golf ball
with respect to a z-axis Iz are substantially the same, the x-axis,
y-axis, and z-axis intersecting orthogonally at the center of the
golf ball.
[0006] The solid core may include at least one specific
gravity-enhancing member. The specific gravity-enhancing member may
be one and may be plural specific gravity-enhancing members. The
specific gravity-enhancing member may have a transmission loss of
at least about 10 dB in the region from 1000 to 4000 Hz.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a cross-sectional view showing one embodiment of a
multiple-piece golf ball according to the present invention.
[0008] FIG. 2 is a cross-sectional view showing another embodiment
of a multiple-piece golf ball according to the present
invention.
[0009] FIG. 3 is a cross-sectional view showing yet another
embodiment of a multiple-piece golf ball according to the present
invention.
[0010] FIG. 4 is a cross-sectional view showing still yet another
embodiment of a multiple-piece golf ball according to the present
invention.
[0011] FIG. 5 is a transparent view showing a further embodiment of
multiple-piece golf ball according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0012] Although embodiments of a multiple-piece golf ball according
to the present invention are described below, with reference made
to the accompanying drawings, the present invention is not limited
to these embodiments. The attached drawings were made giving
priority to understanding of the present invention, and they are
not drawn to scale.
[0013] As shown in FIG. 1, a multiple-piece golf ball 1a has a
solid core 10, and a cover 30 located outside the solid core.
Although an intermediate layer 20 may be provided between the solid
core and the cover, as shown in FIG. 1, the present invention is
not limited to this construction, and the cover 30 may directly
connect to the solid score 10 without providing an intermediate
layer.
[0014] The solid core 10 is not limited to a single layer
configuration, as shown in the FIG. 1, but may include plural
layers. For example, as shown in FIG. 2, the solid core 10 of the
golf ball 1b may be formed by two layers having the center core 12
located at the centermost of the golf ball 1b and the core layer 14
that covers the center core 12.
[0015] On hitting the golf ball 1, when the initial spin rate is
relatively large within the range from about 2800 to about 3500
rpm, the present invention provides the golf ball 1 having a
configuration in which the spin decay rate while the golf ball 1 is
during flight, is very high, within the range from about 3.1% to
about 20%. When the initial spin rate is large as described above,
if the spin decay rate is less than about 3.1%, the golf ball will
climb excessively to attain too high a trajectory, so that the
distance is insufficient. The golf ball often curves to the side as
it drops. It is preferable that the spin decay rate be at least
about 3.2%, and more preferably at least about 3.3%. On the other
hand, if the spin decay rate is greater than at least about 20%,
the trajectory will become unstable. The spin decay rate is
preferably not greater than about 15%, and more preferably not
greater than about 7%.
[0016] In order to attain such an spin decay rate, even if the
solid core 10 of the golf ball 1 is at least configured by plural
layers, it is required that the overall solid core have a specific
gravity within the range from about 1.2 to about 14. The solid
core, the intermediate layer, and the cover of the golf ball
generally have a specific gravity of less than 1.2. The present
invention has high specific gravity of the solid core 10 that is
located at the center of the golf ball 1, thereby attaining the
above-described spin decay rates.
[0017] In order to attain the spin decay rates, the specific
gravity of the solid core 10 is preferably at least about 1.3, and
more preferably at least about 1.8. On the other hand, the specific
gravity of the solid core 10 is preferably not greater than about
14, more preferably not greater than about 13.5, still more
preferably not greater than about 12.5, and most preferably not
greater than about 12.
[0018] The golf ball according to the present invention has a
configuration in which the moment of inertia is uniform, that is,
if three axes intersecting orthogonally at the center of the golf
ball are the x-axis, the y-axis, and the z-axis, and the moments of
the inertia of the golf ball with respect to each axis are Ix, Iy
and Iz, then Iz, Ix and Iy are substantially the same. The moment
of inertia is preferably at least about 50, more preferably at
least about 52, and still more preferably at least about 54. On the
other hand, if the moment of inertia is too large, when the initial
spin rate is large, because the ball has too high a trajectory, so
that the distance is insufficient, the moment of inertia is
preferably not greater than about 80, more preferably not greater
than about 78, and still more preferably not greater than about
76.
[0019] As a material which forms the solid core 10 having such a
specific gravity, for example, a rubber composition that includes
the base rubber that is to be the main component and a filler may
be used. A thermoset elastomer may be generally used as the base
rubber, and although, for example, a polybutadiene rubber (BR), a
styrene-butadiene rubber (SBR), a natural rubber (NR), a
polyisoprene rubber (IR), a polyurethane rubber (PU), a butyl
rubber (IIR), a vinyl polybutadiene rubber (VBR), an ethylene
propylene rubber (EPDM), a nitryl rubber (NBR), and a silicone
rubber may be used, there is no limitation to these components. The
polybutadiene rubber (BR) preferably may have a 1,4-cis-bond of at
least about 60%, more preferably of at least about 80%, still more
preferably of at least about 90%, and most preferably at least
about 95%.
[0020] The Moony viscosity (ML.sub.1+4 (100.degree. C.)) of the
polybutadiene is desirably at least about 30, preferably at least
about 35, more preferably at least about 40, still more preferably
at least about 50, and most preferably at least about 52. The upper
limit is desirably not greater than about 100, preferably not
greater than about 80, more preferably not greater than about 70,
and still more preferably not greater than about 60.
[0021] The Moony viscosities in the present invention indicate the
industrial viscosity index (Japan Industrial Standard JIS K 6300)
that is measured by a Moony viscosity gage, which is a type of a
rotary plastometer, and ML.sub.1-4 (100.degree. C.) is used as an
unit symbol. Symbol M indicates the Moony viscosity, L indicates
the large rotor (L type), 1+4 indicates the pre-heating time of one
minute and the rotor rotating time of four minutes, and it is
indicates that the measurement is performed under the condition of
100.degree. C.
[0022] A molecular weight distribution of the polybutadiene Mw/Mn
(Mw: A weight average molecular weight, Mn: A number-average
molecular weight) is desirably at least about 2.0, preferably at
least about 2.2, more preferably at least about 2.4, and still
further more preferably at least about 2.6. The upper limit is
desirably not greater than about 6.0, preferably not greater than
about 5.0, more preferably not greater than about 4.0, and still
more preferably not greater than about 3.4. If Mw/Mn is too small,
poor workability may result, and if it too large, poor repulsion
may result.
[0023] Although the polybutadiene may be synthesized with a Ni or
Co catalyst or with a rare-earth element catalyst, one synthesized
with a rare-earth element catalyst is particularly preferable, and
a widely known rare-earth element catalyst can be used. Exemplary
catalysts include those made up of a combination of a lanthanide
series rare-earth element compound, an organoaluminum compound, an
alumoxane, a halogen-bearing compound and, if necessary, a Lewis
base.
[0024] In the present invention, the use of a neodymium catalyst in
which a neodymium compound serves as the lanthanide series
rare-earth element compound is particularly advantageous because it
enables a polybutadiene rubber having a high 1,4-cis-bond content
and a low 1,2-vinyl bond content to be obtained with excellent
polymerization activity. Specific examples of these rare-earth
element catalysts include those noted in Japanese Patent
Application Publication No. 11-35633, which is incorporated by
reference.
[0025] In the case of the butadiene polymerization in the presence
of a rare-earth element catalyst, a solvent may be used or bulk
polymerization or vapor phase polymerization may be preferable,
without using the solvent, and the polymerization temperature can
be generally from about -30.degree. C. to about 150.degree. C., and
preferably from about 10.degree. C. to about 100.degree. C.
[0026] The above-noted butadiene may be obtained by following
polymerization by the above-noted rare-earth element catalyst by
reacting a terminal modifier with the activation terminal of the
polymer. The specific embodiment of the terminal modifier and the
method of activation include, for example, those noted and methods
in the Japanese Patent Application Publications 11-35633, 7-268132,
and 2002-293996, which are incorporated by reference.
[0027] The butadiene is preferably to be blended at at least about
60 wt % into the base rubber, more preferably at at least about 70
wt %, still more preferably at at least about 80 wt %, and most
preferably at at least 90 wt %. The upper limit of the mixture
ratio of the butadiene is preferably about 100 wt %, more
preferably about 98 wt %, and still more preferably about 95 wt %.
By mixing the polybutadiene within this range, a golf ball having
good resilience can be obtained.
[0028] Rubbers other than the above-described polybutadiene may be
blended in combination with the polybutadiene, insofar as the
object of the present invention is not lost. Particularly
preferable rubbers for the combination include a styrene-butadiene
rubber, a natural rubber, a polyisoprene rubber, and an
ethylene-propylene-diene rubber. These may be used alone or in
combination of two or more thereof.
[0029] A metal or metallic compound with a specific gravity of at
least 2 is desirable as a filler. This because if the specific
gravity of the filler is less than about 2, the degree of freedom
in designing the specific gravity of the solid core 10 at least 1.2
is low. Although examples of such a metal or a metallic compound
include silver, gold, cobalt, chromium, copper, iron, germanium,
manganese, molybdenum, nickel, lead, platinum, tin, titanium,
tungsten, zinc, zirconium, barium sulfate, zinc oxide, and
manganese oxide, there is no particular limitation thereto. The
filler is preferably formed as a powder.
[0030] The specific gravity of the filler is preferably at least
about 2.5, and more preferably at least about 4.0. If the specific
gravity of the filler is too high, only a small non-uniform
dispersion of the filler can be found within the solid core 10, and
an unbalanced weight of the solid core 10 occurs, and because it is
difficult, from the standpoint of the manufacturing process, to
achieve a uniform moment of inertia, the specific gravity of the
filler is preferably not greater than about 22, and more preferably
not greater than about 20.
[0031] The filler is to be blended so that the specific gravity of
the solid core 10 is within the above-noted range. Although there
is no particular limitation with respect to the filler content, for
example, per 100 parts by weight of the base rubber, it is
preferably at least about 10 parts by weight, more preferably at
least about 15 part by weight, and still more preferably at least
about 25 parts by weight. The upper limit of the filler content is
preferably about 1000 parts by weight, more preferably about 980
parts by weight, and still more preferably about 960 parts by
weight.
[0032] The rubber composition which the materials to form the solid
core 10 may optionally include a co-crosslinking agent, an
initiator, a foaming agent, an antioxidant, an organosulfur
compound, and a vulcanization accelerator. Although there is no
particular limitation with regard to the co-crosslinking agent, it
is preferable that, for example, an .alpha.,.beta.-unsaturated
carboxylic acid or a metal salt thereof be used. As an
.alpha.,.beta.-unsaturated carboxylic acid, or the metal salt,
there are, for example, an acrylic acid, methacrylate, and a zinc
salt, a magnesium salt, and a calcium salt thereof. Although there
is no particular limitation with regard to the co-crosslinking
agent content, for example, per 100 parts by weight of the base
rubber, it is preferably at least about 5 parts by weight, and more
preferably at least about 10 parts by weight. The co-crosslinking
agent content is preferably not greater than about 70 parts by
weight, and more preferably not greater than about 50 parts by
weight.
[0033] Although no particular limitation is imposed on the
initiator, the use of an organic peroxide is preferable. Although
no particular limitation is imposed on the initiator content, for
example, per 100 parts by weight of the base rubber, it is
preferably at least about 0.10 parts by weight, more preferably at
least about 0.15 parts by weight, and still more preferably at
least about 0.30 parts by weight, but preferably not greater than 8
parts by weight, and more preferably not greater than 6 parts by
weight.
[0034] Although no particular limitation is imposed on the foaming
agent, for example, an azodicarbonamide, azobisisobutyronitrile,
dinitrosopentamethylenetetramine, p-toluenesulfonyl hydrazide,
p,p'-oxybis(benzenesulfonylhydrazide), and sodium hydrogencarbonate
may be used. Although no limitation is imposed on the foaming agent
content, for example, per 100 parts by weight of the base rubber,
it is preferably at least about 5 parts by weight, and more
preferably at least about 10 parts by weight. The foaming agent
content is preferably not greater than about 30 parts by weight,
and more preferably not greater than about 25 parts by weight.
[0035] The solid core 10 shape is substantially spherical. The
outside diameter of the solid core 10 is preferably not greater
than about 40 mm in order to set the moment of inertia of the golf
ball with a weight of 45.5 g to not greater than 80. The outer
diameter of the solid core 10 is preferably not greater than about
39 mm, or more preferably not greater than about 36 mm. On the
other hand, because if the outside diameter of the solid core 10 is
too small, the repulsion of the golf ball is reduced, it is
desirable at least about 4 mm, preferably at least about 5 mm, more
preferably at least about 6 mm, still more preferably at least
about 7 mm, and most preferably at least about 8 mm.
[0036] As shown in FIG. 2, in the case in which the solid core 10
is made of a multilayer structure including the center core 12 and
core layer 14, the thickness of the core layer 14 is preferably at
least about 0.8 mm, more preferably at least about 1.0 mm, and
still more preferably at least about 1.4 mm. The upper limit of the
thickness of the core layer 14 is desirably about 10 mm, preferably
about 8 mm, more preferably about 6 mm, and still more preferably
about 3 mm.
[0037] As shown in FIG. 3 to FIG. 5, the solid core 10 may also
include one or plural specific gravity-enhancing members 40, 42,
and 44. The metal composition having a higher specific gravity than
the rubber composition for forming the above-described solid core
is used as the specific gravity-enhancing member. This enables the
specific gravity of the solid core 10 to more easily be made at
least 1.2.
[0038] The specific gravity of the specific gravity-enhancing
member is designed for at least a specific gravity of 1.2 for the
solid core. From the standpoint of the degree of freedom, it is
preferably at least about 2, more preferably at least about 2.5,
and still more preferably at least about 4. On the other hand, if
the specific gravity of the specific gravity-enhancing member is
too high, only a small un-uniform arrangement of the specific
gravity-enhancing member can be found within the solid core, an
unbalanced weight of the soled core occurs, and because it is
difficult in the manufacturing process to achieve a uniform moment
of inertia, the specific gravity of the specific gravity-enhancing
member is preferably not greater than about 22, and more preferably
not greater than about 20.
[0039] The metal composition may include a metal or a metallic
compound. Although exemplary metal or a metallic compounds include
silver, gold, cobalt, chromium, copper, iron, germanium, manganese,
molybdenum, nickel, lead, platinum, tin, titanium, tungsten, zinc,
zirconium, barium sulfate, zinc oxide, and manganese oxide, there
is no particular limitation imposed thereon.
[0040] The metal composition may also include binder for forming
the powder of the above-noted metals or the metal compound into a
prescribed shape. The use of a rubber or a thermoset elastomer as
the binder is preferable, and the same materials as the
above-described rubber bases can be used. Although no limitation is
imposed on the powder content of the above-noted metal or the metal
compound, for example, per 100 parts by weight of the base rubber,
its preferably at least about 10 parts by weight, more preferably
at least about 15 part by weight, and still more preferably at
least about 25 parts by weight. The upper limit of the powder
content of the metal or the metal compound is preferably about 1000
parts by weight, more preferably about 980 parts by weight, and
still more preferably about 960 parts by weight.
[0041] Although no limitation is imposed on the shape of the
specific gravity-enhancing member, for example, a spherical shape
or spherical shell-shape is desirable. For example, as shown in
FIG. 3, the spherical specific gravity-enhancing member 40 may be
arranged at the center of the golf ball 1c. In this example, the
solid core includes this spherical specific gravity-enhancing
member 40 and the spherical shell-shaped rubber layer 16 that is
formed by using the above-described rubber composition therearound.
Although the method of forming the spherical shell-shaped rubber
layer 16 is not limited by this method, for example, the rubber
composition is pre-molded in the shape of two half-cups, the
spherical specific gravity-enhancing member 40 is put into these
two cups, hot forming being done.
[0042] The outside diameter of the spherical specific
gravity-enhancing member 40 which is disposed at the center of the
solid core is desirably at least about 4 mm, preferably at least
about 5 mm, more preferably at least about 6 mm, still more
preferably at least about 7 mm, and most preferably at least about
8 mm. On the other hand, because too large an outer diameter of the
specific gravity-enhancing member 40 makes the sagging hardness of
the golf ball high or the sound occurring when the ball is struck
high enough to be unpleasant, the outside diameter of the specific
gravity-enhancing member 40 is desirably not greater than about 22
mm, preferably not greater than about 20 mm, more preferably not
greater than about 18 mm, still more preferably not greater than
about 16 mm, and most preferably not greater than about 14 mm.
[0043] The spherical shell-shaped specific gravity-enhancing member
42 may also be disposed concentrically with the center of the golf
ball 1d, as shown in FIG. 4. In this example, the solid core
includes this spherical shell-shaped specific gravity-enhancing
member 42 and the center core 12 and the core layer 14 inside and
outside thereof, which are formed by using the above-described
rubber composition. Although no limitation is imposed on this
spherical shell-shaped specific gravity-enhancing member 42, it is
possible, for example, to form it by subjecting the surface of the
center core 12 to metal plating.
[0044] The thickness of such a spherical shell-shaped specific
gravity-enhancing member 42 is desirably at least about 0.01 mm,
preferably at least about 0.02 mm, more preferably at least about
0.09 mm, and most preferably at least about 0.10 mm. On the other
hand, because too thick a spherical shell-shaped specific
gravity-enhancing member 42 makes the sagging hardness of the golf
ball high or the sound occurring when the ball is struck high
enough to be unpleasant, the thickness of the spherical
shell-shaped specific gravity-enhancing member 42 is desirably not
greater than about 2.0 mm, preferably not greater than about 1.75
mm, more preferably not greater than about 0.75 mm, and most
preferably not greater than about 0.5 mm.
[0045] Because disposing the spherical shell-shaped specific
gravity-enhancing member 42 nearer the center of the golf ball 1d,
makes the smaller moment of inertia of the golf ball easier to
design, the distance from the center of the ball to the spherical
shell-shaped specific gravity-enhancing member 42 is desirably not
greater than about 20 mm, preferably not greater than about 19 mm,
and more preferably not greater than about 18 mm. Although the
lower limit of the distance from the center of the ball to the
spherical shell-shaped specific gravity-enhancing member 42 does
not have any particular limitation, for example, it is desirably 4
mm, preferably 5 mm, and more preferably 8 mm.
[0046] No limitations of the position and number of the spherical
shell-shaped specific gravity-enhancing member 42 are imposed on
FIG. 4, and for example, the spherical shell-shaped specific
gravity-enhancing member 42 may be disposed at the outermost
position of the solid core, that is, the position directly
connecting with the intermediate layer 20 or the cover 30, and
plural spherical shell-shaped specific gravity-enhancing members
with different size outside diameters may also be disposed by
sandwiching a core layer.
[0047] In order to achieve a uniform moment of inertia of the golf
ball, plural specific gravity-enhancing members 44, as shown in
FIG. 5, may also be disposed at the vertices or on the surfaces of
a regular polyhedron, such as a regular tetrahedron with the center
of gravity at the center of the golf ball 1e. In this manner,
plural specific gravity-enhancing members 44 are disposed, thereby
preventing the possibility of cracking of the specific
gravity-enhancing member at the time of impact, and the possibility
of hardening the golf ball, in contrast with the case of using a
single member rather than the above-described plurality of specific
gravity-enhancing members.
[0048] This is because when the number of specific
gravity-enhancing members 44 is greater, it is easier to achieve a
uniform moment of inertia of the golf ball, for example the number
of four, six, eight, ten, twelve, and twenty members may be
possible, and these specific gravity-enhancing members 44 may also
be disposed at the vertices of a regular polyhedron, such as a
regular tetrahedron, a cube, a regular octahedron, a regular
decahedron, a regular dodecahedron, or a regular icosahedron.
Although the upper limit of the number of specific
gravity-enhancing members 44 is not particularly limited, it is
preferably about 600, and more preferably about 500.
[0049] If the plurality of specific gravity-enhancing members 44 is
disposed at a position near the center of the golf ball 1e, a golf
ball having low moment of inertia can be easily designed.
Therefore, the distance from the center of the golf ball to the
specific gravity-enhancing member 44 is preferably not greater than
about 20 mm, more preferably not greater than about 19 mm, and
still more preferably not greater than about 18 mm. The lower limit
of the distance of the from the center of the golf ball to the
specific gravity-enhancing member 44, although not limited, is
preferably about 4 mm, more preferably about 5 mm, and still more
preferably about 8 mm.
[0050] Although the shape of this plurality of specific
gravity-enhancing members 44 is not particularly limited, it can be
made spherical or sheetlike. When using the sheet type, regardless
of the shape, because if the thicknesses of the plurality of
specific gravity-enhancing members 44 is excessive, the sagging
hardness of the golf ball high is high or the sound occurring when
the ball is struck is high enough to be unpleasant, the thickness
is preferably not greater than about 2.0 mm, more preferably not
greater than about 1.75 mm, still more preferably not greater than
about 0.75 mm, and most preferably not greater than about 0.5 mm.
On the other hand, the thicknesses of the plurality of specific
gravity-enhancing members 44 is preferably at least about 0.01 mm,
more preferably at least about 0.02 mm, still more preferably at
least about 0.09 mm, and most preferably at least about 0.10
mm.
[0051] The disposition of the plurality of specific
gravity-enhancing members 44 may not be limited to the vertices or
on the surfaces of the regular polyhedron as shown in FIG. 5, and
if the moment of the golf ball is uniform, other arrangements may
be adopted. For example, it is possible that the plurality of
specific gravity-enhancing members having different specific
gravities, weights, sizes and the like are disposed so as to be at
different distances from the center of the golf ball in order for
the inertia moment of the golf ball to be uniform.
[0052] If the transmission loss of the material is large in the
high frequency range of 1000 Hz to 4000 Hz, because a sound
insulation effect can be expected, the transmission loss of the
specific gravity-enhancing members is preferably at least about 10
dB in the high frequency range of 1000 Hz to 4000 Hz, more
preferably at least about 15 dB, and still more preferably at least
about 30 dB. On the other hand, it is preferably not greater than
about 60 dB, more preferably not greater than about 55 dB, and
still more preferably not greater than about 40 dB.
[0053] Although the intermediate layer 20 is, as shown in FIG. 2,
configured of a single layer, it is not limited to this
configuration, and may be configured of at least two layers.
Although the material of the intermediate layer 20 is not limited
thereto, the following components (a) and/or (b) are to be the base
resins. The optional component (c) may also be added to the base
resin. The component (a) includes an olefin-unsaturated carboxylic
acid-unsaturated carboxylic acid ester random terpolymer and/or the
metal salts thereof, the component (b) includes an
olefin-unsaturated carboxylic acid random binary copolymer and/or
the metal salts thereof, and the component (c) includes crystalline
polyolefin blocks, and a thermoplastic block copolymer having a
polyethylene/butylene random copolymer.
[0054] The foaming agent is added into the material of the
intermediate layer 20, thereby providing space in the intermediate
layer 20. The above-described foaming agent may be used as the
foaming agent. The foaming agent content is not limited to the
above, and may preferably, for example, be at least about 2 parts
by weight, and more preferably at least about 3 parts by weight,
per 100 parts by weight of the above-noted heated mixture. The
foaming agent content is also preferably not greater than about 30
parts by weight, and more preferably not greater than about 25
parts by weight.
[0055] The weight-average molecular mass (Mw) of an
olefin-unsaturated carboxylic acid-unsaturated carboxylic acid
ester random terpolymer and/or the metal salts forming the
component (a) is preferably at least about 100,000, more preferably
at least about 110,000, and still more preferably at least about
120,000. The upper limit is preferably about 200,000, more
preferably about 190,000, and still more preferably about 170,000.
The ratio of the weight-average molecular mass (Mw) and the
number-average molecular mass (Mn) of the above-noted copolymer is
preferably about 3.0 to about 7.0.
[0056] The component (a) is a copolymer including an olefin, for
example, in which the number of carbons is at least 2 as the olefin
in the component (a), but the upper limit is preferably 8, and
particularly preferably 6. Specific examples include ethylene,
propylene, butene, pentene, hexene, heptene, octene and the like.
Ethylene is particularly preferred.
[0057] Examples of unsaturated carboxylic acids in the component
(a) include acrylic acid, methacrylic acid, maleic acid, and
fumaric acid. Acrylic acid and methacrylic acid are particularly
preferred.
[0058] The unsaturated carboxylic acid ester in the component (a)
includes, for example, a lower alkyl ester of the above-described
unsaturated carboxylic acid. Specific examples include methyl
methacrylate, ethyl methacrylate, propyl methacrylate, butyl
methacrylate, methyl acrylate, ethyl acrylate, propyl acrylate and
butyl acrylate. Butyl acrylate (n-butyl acrylate, i-butyl acrylate)
is particularly preferred.
[0059] The random copolymer in the component (a) can be obtained by
random copolymerizing the above-noted materials by a known method.
The content of unsaturated carboxylic acid (acid contents) present
in the random copolymer is usually at least about 2 wt %,
preferably at least about 6 wt %, and more preferably at least
about 8 wt %. The upper limit may be about 25 wt %, is preferably
about 20 wt %, and more preferably about 15 wt %. If the acid
content is low, the resilience may decrease, whereas if it is high,
the workability of the material may decrease.
[0060] The metal ion of the copolymer in the component (a) can be
obtained by partially neutralizing the acid groups on the random
copolymers of the component (a) with metal ions.
[0061] Illustrative examples of metal ions for neutralizing the
acid groups include ions such as Na, K, Li, Zn, Cu, Mg, Ca, Co, Ni,
and Pb, and are preferably ions, such as, Na, Li, Zn, Mg, and Ca,
and Zn ion is more preferably recommended. Although the degree of
the neutralization of the random copolymer in these metal ions is
not particularly limited, it is normally at least about 5 mol %,
preferably at least about 10 mol %, particularly at least about 20
mol %. The upper limit is usually about 95 mol %, preferably 90 mol
%, and particularly about 80 mol %. If the degree of neutralization
exceeds about 95 mol %, formability may decrease. In a case in
which the upper limit is about 5 mol %, because it is necessary to
increase the additive amount of inorganic metal compounds to the
component (e), this might be disadvantageous in view of cost. Such
neutralization material can be obtained using a known method, for
example, a compound such as a formate, acetate, nitrate, carbonate,
bicarbonate, oxide, hydroxide or alkoxide of the above-noted metal
ions being introduced with respect to the above-noted random
copolymer.
[0062] Illustrative examples of the olefin-unsaturated carboxylic
acid-unsaturated carboxylic acid ester random terpolymer which
constitutes the component (a) include particularly, in terms of
commercial names, "Nucrel AN 4318", "Nucrel AN4319", and "Nucrel
AN4311" (all products of DuPont-Mitsui Polychemicals Co., Ltd.).
Illustrative examples of the metal salts of the olefin-unsaturated
carboxylic acid-unsaturated carboxylic acid ester random terpolymer
include specifically, in terms of commercial names, "Himilan
AM7316", "Himilan AM7331", "Himilan 1855" and "Himilan 1856" (all
products of DuPont-Mitsui Polychemicals Co., Ltd.) and, in terms of
commercial names, "Surlyn 6320" and "Surlyn 8120" (all products of
DuPont US).
[0063] The weight average molecular mass (Mw) of one or more of an
olefin-unsaturated carboxylic acid random binary copolymer and the
metal salts thereof, which constitutes the component (b), is
preferably at least about 100,000, more preferably at least about
110,000 and still more preferably at least about 120,000. The upper
limit is preferably about 200,000, more preferably about 190,000,
and still more preferably not more than about 170,000. The ratio of
the weight-average molecular mass (Mw) and the number-average
molecular mass (Mn) of the above-noted copolymer is preferably
about 3.0 to about 7.0.
[0064] The ratio in which the copolymer of the component (6)
occupies the overall base resin is about 0 wt % to about 20 wt %.
The lower limit is preferably about 1 wt %. The upper limit is
preferably about 17 wt %, more preferably about 10 wt %, more
preferably about 8 wt %, and still more preferably about 5 wt
%.
[0065] Illustrative examples of the olefin-unsaturated carboxylic
acid random binary copolymer and the metal salts thereof, which
constitute the component (b), include specifically, in terms of
commercial names, "Nucrel 1560", "Nucrel 1525", and "Nucrel 1035"
(all products of DuPont-Mitsui Polychemicals Co., Ltd.).
Illustrative examples of the metal salts of the olefin-unsaturated
carboxylic acid random binary copolymer include specifically, in
terms of commercial names, "Himilan 1605", "Himilan 1601", "Himilan
1557", "Himilan 1705" and "Himilan 1706" (all products of
DuPont-Mitsui Polychemicals Co., Ltd.), and in terms of commercial
names, "Surlyn 7930" and "Surlyn 7920" (all products of DuPont
US).
[0066] Illustrative examples of the thermoplastic block copolymer
having crystalline polyolefin blocks, or polyethylene/butylene
random copolymers as the component (c) include crystalline
polyethylene blocks (E) as the hard segment, and blocks which
constitutes the relatively random copolymer (EB) of the ethylene
and the butylene as the soft segment. A block copolymer having an
E-EB type structure, or an E-EB-E type structure or the like in
which the hard segment exists at one end or both ends as a
molecular structure is preferably used.
[0067] The components (c), that is, the thermoplastic block
copolymer having crystalline olefin blocks or polyethylene/butylene
random copolymer can be obtained, for example, by hydrogenating the
polybutadiene. The polybutadiene used for hydrogenating
particularly has in a blocking manner a 1,4-polymerization part in
which the 1,4-bond is about 95 to 100 wt %, and the polybutadiene
in which the 1,4-bond content in the overall butadiene structures
is about 50 wt % to 100 wt %, and more preferably about 80 wt % to
100 wt % is appropriately used as a bonding mode in the butadiene
structure. That is, the polybutadiene in which the 1,4-bond content
is about 50 wt % to 100 wt %, and more preferably about 80 wt % to
100 wt % and the polybutadiene having in a blocking manner about 95
to 100 wt % of 1,4-bond are preferably used.
[0068] The above-noted E-EB-E type thermoplastic block copolymer is
preferably obtained by hydrogenating the polybutadiene in which the
ends of the molecular chain is 1,4-bond-rich 1,4-polymer and the
1,4-bond and 1,2-bond are mixed in the intermediate part. In this
case, the amount of hydrogen additive (the conversion rate to the
saturated bond of the double bond in the polybutadiene) in the
hydrogen additive is preferably about 60% to about 100%, and more
preferably about 90% to 100%. If the amount of the hydrogen
additive is too small, deterioration such as gelatinization may be
caused in the blending process with ionomer resin and the like.
Also, there might be a problem of an impact resistance as an
intermediate layer, caused when forming the golf ball.
[0069] In the block copolymer having an E-EB type, an E-EB-E type
structure or the like in which the hard segment exists at one end
or both ends as a molecular structure, which is preferably used as
the thermoplastic block copolymer, the amount of hard segment is
preferably about 10 wt % to about 50 wt %. If the amount of the
hard segment is excessive, the object of the present invention may
not be achieved effectively due to the lack of flexibility, and if
the amount of the hard segment is too small, a problem of
formability of the blend may be caused.
[0070] The melt index of the above thermoplastic block copolymer at
230.degree. C., and a test load of 21.2 N is preferably about 0.01
g/10 min to about 15 g/10 min, and more preferably about 0.03 g/10
min to about 10 g/10 min. In the case of exceeding the above-noted
range, problems at the time of the injection molding, such as a
weld, a sink, a short or the like may occur. The surface hardness
of the thermoplastic block copolymer is preferably 10 to 50. If the
surface hardness is too low, the durability with respect to
repeated impact of the golf ball may decrease. On the other hand,
if the surface hardness is too high, the resilience of the blend
with the ionomer resin may decrease. The number-average molecular
weight of the thermoplastic block copolymer is preferably from
about 30,000 to about 800,000.
[0071] A commercially available product may be used as the
thermoplastic block copolymer having the above crystalline
polyolefin blocks, or a polyethylene/butylene random copolymer, and
illustrative examples include Dynaron 6100P, 6200P and 6201B of JSR
Corporation. In particular, Dynaron 6100P is a block polymer having
crystalline olefin blocks at the ends, and may be used preferably
in the present invention. These olefin series thermoplastic
elastomers may be used as one type alone or may be used by blending
with two or more types.
[0072] The material of the intermediate layer 20, as the component
(d) with respect to 100 parts by weight of the above-noted resin
components (a) to (c), can be mixed at about 5 to 100 parts by
weight of a fatty acid or derivative thereof having a molecular
weight from about 280 to about 1500, and, as the component (e), can
be mixed with from about 0.1 parts by weight to about 10 parts by
weight of the basic inorganic metal compounds, which can neutralize
acid groups in the above-noted components (a), (b) and (d).
[0073] Component (d) is a fatty acid or a fatty acid derivative
having a molecular weight of at least 280, but no greater than
1500. Compared with the above-noted components (a) to (c), this
component has a very low molecular weight, and by contributing a
prominent increase in the melt viscosity of the mixture, helps in
improving the flow properties of heated mixture. The fatty acid (or
derivatives thereof) of the component (d) includes a relatively
high content of acid groups (or derivatives thereof), and its
addition suppresses an excessive loss in resilience.
[0074] The fatty acid or fatty acid derivative of component (d) may
be an unsaturated fatty acid (or derivative thereof) containing a
double bond or triple bond on the alkyl group, or it may be a
saturated fatty acid (or derivative thereof) in which the bonds on
the alkyl group are only single bonds. It is recommended that the
number of carbons in one molecule be usually at least 18, the upper
limit being 80, and in particular, 40. Fewer carbons may
deteriorate the heat resistance and may also make the acid group
content so large as not to prevent the attainment of the desired
flowability due to interactions with acid groups present in the
base resin. On the other hand, if there are many carbons, the
molecular weight increases, so that the flowability may decrease
and make use as a material difficult.
[0075] As the fatty acid of component (d), specifically, use of
stearic acid, 12-hydroxystearic acid, behenic acid, oleic acid,
linoleic acid, linolenic acid, arachidic acid and lignoceric acid
can be exemplified, particularly, stearic acid, arachidic acid,
behenic acid and lignoceric acid is preferred.
[0076] One replaced with a proton included in the acid group of the
fatty acid may be cited as the fatty acid derivative of component
(d), and metallic soaps replaced with a metal ion may be cited as
an example thereof. As examples of the metal ion for use in
metallic soaps, ions such as Li, Ca, Mg, Zn, Mn, Al, Ni, Fe, Cu,
Sn, Pb, and Co may be cited. Of these ions, Ca, Mg, and Zn are
particularly preferred. The Fe ion may be bivalent or
trivalent.
[0077] Specific examples of fatty acid derivatives that may be used
as component (d) include a magnesium stearate, calcium stearate,
zinc stearate, magnesium 12-hydroxystearate, calcium
12-hydroxystearate, zinc 12-hydroxystearate, magnesium arachidate,
calcium arachidate, zinc arachidate, magnesium behenate, calcium
behenate, zinc behenate, magnesium lignocerate, calcium lignocerate
and zinc lignocerate. In particular, the magnesium stearate,
calcium stearate, zinc stearate, magnesium arachidate, calcium
arachidate, zinc arachidate, magnesium behenate, calcium behenate,
zinc behenate, magnesium lignocerate, calcium lignocerate and zinc
lignocerate may be preferably used.
[0078] It is recommended that component (d) be included in the
amount, per 100 parts by weight of the above-noted base resin, of
usually at least about 5 parts by weight, preferably at least about
8 parts by weight, more preferably at least about 20 parts by
weight, and still more preferably at least 40 parts by weight, and
an upper limit, usually about 100 parts by weight, preferably about
90 parts by weight, more preferably about 80 parts by weight, and
still more preferably about 70 parts by weight.
[0079] In the case of using one or more of the above-noted
components (a) and (d), a widely known metal soap-modified ionomer
may be used (U.S. Pat. No. 5,312,857, U.S. Pat. No. 5,306,760 and
PCT International Publication No. 98/46671 being incorporated by
reference).
[0080] Component (e) may be added as a basic inorganic metal
compound capable of neutralizing acid groups in above-noted
components (a), (b) and (c). As described in the conventional
example, when components (a), (b) and (d) alone, particularly, only
a metal modified ionomer resin (e.g., the metal soap-modified
ionomer resins alone cited in the above-noted patent publications)
are used, as shown below, the metallic soap and unneutralized acid
groups present on the ionomer undergo exchange reactions during
mixture under heating, thereby generating a fatty acid. Because the
thus-generated fatty acid has a low thermal stability and readily
vaporizes during molding, it may cause molding defects, and the
fatty acid thus-generated is deposited on the surface of the molded
material, and this may cause a substantially lower paint film
adhesion. Component (e) will be mixed in to be solved these
problems.
##STR00001##
[0081] The heated mixture used in the present invention is a blend,
as described above, including compound (e) as an essential
ingredient, the basic inorganic metal compound neutralizing acid
groups included in the above-noted components (a), (b) and (d). By
blending component (e), the acid groups in the above components
(a), (b) and (d) are neutralized and, through synergistic effects
from the blending of each of these components, this contributes as
well to an increase the thermal stability of the heated mixture and
gives it good moldability, and also enhances the resilience as a
golf ball.
[0082] The component (e) is a basic inorganic metal compound
capable of neutralizing acid groups within the above-noted
components (a), (b) and (d), and is preferably recommended as a
monoxide or hydroxide, which has a high reactivity with the ionomer
resin and contains no organic acids in the reaction by-products,
thus enabling the degree of neutralization of the heated mixture to
be increased without a loss of thermal stability.
[0083] As the metal ions used in the basic inorganic metal
compounds, ions, for example, Li, Na, K, Ca, Mg, Zn, Al, Ni, Fe,
Fe, Cu, Mn, Sn, Pb, and Co can be cited, and as an inorganic metal
compound there are basic inorganic fillers including these metallic
ions, specifically, a magnesium oxide, magnesium hydroxide,
magnesium carbonate, zinc oxide, sodium hydroxide, sodium
carbonate, calcium oxide, calcium hydroxide, lithium hydroxide and
lithium carbonate can be cited. A monoxide or a hydroxide is
recommended as noted above. The magnesium oxide and calcium
hydroxide, which have a high reactivity with the ionomer resin, may
be preferably used.
[0084] The component (e) is usually about 0.1 to about 10 parts by
weight, per 100 parts by weight of the above-noted base resin. The
lower limit is preferably about 0.5 parts by weight, more
preferably about 1 part by weight. The upper limit is preferably
about 5 parts by weight, more preferably about 3 parts by
weight.
[0085] The heated mixture to be used in the present invention is
mixed with the above-described components (a) to (e), this
improving thermal stability, moldability and resilience, and it is
recommended that at least about 70 mol %, preferably at least about
80 mol %, and more preferably at least about 90 mol %, of the acid
groups within every heated mixture to be used in the present
invention be neutralized. Such a high degree of neutralization
makes it possible to more reliably suppress the exchange reactions
that cause a problem when only above-noted components (a), (b) and
a fatty acid (derivative) are used as described above, thus
preventing the generation of fatty acid and dramatically increasing
thermal stability, enabling products of good formability and very
excellent resilience compared to prior-art ionomer resins.
[0086] In this case, for the neutralization of the heated mixture
of the present invention to achieve more reliably both a high
degree of neutralization and flowability, it is recommended that
the acid groups in the above-noted heated mixture be neutralized
with transition metal ions and with at least one of alkali metal
and alkaline earth metal ions. Because neutralization with
transition metal ions results in a weaker ionic cohesion than with
alkali (earth) metal ions, a part of the acid groups within the
heated mixture is neutralized to be able to achieve a prominent
improvement in flowability.
[0087] Various optional additives may be added, if necessary, in
the above-noted heated mixture in the present invention, for
example, fillers, pigments, dispersants, antioxidants, ultraviolet
absorbers, and light stabilizers. In order to improve the feel of
the ball upon impact, in addition to the above-noted essential
components, various non-ionomeric thermoplastic elastomers may be
blended, for example, styrene thermoplastic elastomers, ester
thermoplastic elastomers, and urethane thermoplastic elastomers,
and the use of styrene thermoplastic elastomers is particularly
preferred.
[0088] A method of adjusting the heated mixture, for example, is
mixing during heating using in internal mixer, such as a two-screw
extruder, Banbury mixer, kneader, and the like, under the
conditions for heating and mixing at the temperature of, for
example, about 150.degree. C. to about 250.degree. C. The method of
forming the intermediate layer using the above-noted heated mixture
is not particular limited to the above, and it may be formed using,
for example, injection molding or compression forming, or the like.
In the case in which the injection molding method is used, after
disposing the prefabricated solid core at the predetermined
position of the injection mold, the method for introducing the
above-noted material into the mold may be used. In the case in
which the compression forming method is used, after forming one
pair of half-cups using the above-noted material, the cups surround
the core directly or via the intermediate layer, thereby enabling
pressurizing and heating thereof within the mold. When applying
pressure and heat for forming the ball, the conditions of the
temperature at about 120.degree. C. to about 170.degree. C. and the
time period of about 1 to 5 minutes may be used.
[0089] The specific gravity of the intermediate layer 20 is not
limited, but may be, for example, preferably at least about 0.2,
more preferably at least about 0.3, and still more preferably at
least about 0.4. The upper limit of the intermediate layer 20 is
desirably about 1.2, preferably about 1.15, more preferably about
1.1, still more preferably about 1.08, and most preferably about
1.06. The thickness of the intermediate layer 20 is not limited but
may be, for example, preferably at least about 1 mm, more
preferably at least about 2 mm, and still more preferably at least
about 3 mm. The upper limit of the thickness of the intermediate
layer 20 is preferably about 15 mm, more preferably about 13 mm,
and still more preferably about 11 mm.
[0090] The intermediate layer 20 may be formed so as to have, as
shown in FIG. 2, the spaces 22 and 24 that are not filled with
material. Although the spaces, for example, include the space 22 in
which the intermediate layer 20 forms a dent with respect to the
cover 30, and the hole-shaped space 24 which passes through the
intermediate layer 20, there is no particular limitation to the
above shapes. The space in the intermediate layer 20 reduces the
weight of the intermediate layer 20 and enables making the specific
gravity of the solid core 10 high.
[0091] The ratio of volumes of the space to volumes of the overall
intermediate layer 20 is preferably at least about 10%, more
preferably at least about 15%, and still more preferably at least
about 25%. This ratio is preferably not greater than about 90%,
more preferably not greater than about 85%, still more preferably
not greater than about 70%, and most preferably not greater than
about 60%.
[0092] Although the method of forming the intermediate layer 20
having the space is not limited, it may include, for example, the
method of inserting and molding the materials of the solid core and
the intermediate layer, and the method of shaping the two half-cups
in which materials of the intermediate layer have spaces or dents
and linking these together over the solid core. Also, this method
may be repeated, thereby forming the intermediate layer having a
multiple layer structure in which layers having holes or dents is
lamented. It will be understood, of course, that the above two
methods may be combined.
[0093] The surface of the cover 30 forms plural dimples 32.
Although the material of the cover 30 is not limited, an ionomer
resin, polyurethane thermoplastic elastomers, a thermoset
polyurethane, or mixture thereof can be used. To the cover 30 may
be added the main components of the above-noted ionomer resin,
polyurethane thermoplastic elastomers, or the thermoset
polyurethane, and other thermoplastic elastomers, polyisocyanate
compounds, fatty acid or fatty acid derivative, basic inorganic
metal compounds, filler, or the like may also be added.
[0094] Although the specific gravity of the cover 30 is not
limited, it is preferably at least about 0.91, and more preferably
at least about 0.93, but preferably not greater than about 1.3, and
more preferably not greater than about 1.2. Although the thickness
of the cover 30 is not limited, it is preferably at least about
0.2, and more preferably at least about 0.4, but preferably not
greater than about 4 mm, more preferably not greater than about 3
mm, and still more preferably not greater than about 2 mm.
[0095] The number of dimples 32 in the overall surface of the golf
ball 1 is preferably at least about 200, more preferably at least
about 250, still more preferably at least about 280, and most
preferably at least about 300. The upper limit of the number of the
dimples 32 is preferably about 450, more preferably about 430, and
still more preferably about 410. The number of dimples 32 is set
within this range, thereby enabling the golf ball 1 to receive a
lifting force, and to increase the distance, particularly when
using a driver.
[0096] Various types of dimples 32 having one or more of different
sizes of diameters and depths may be formed. The number of types of
dimples is preferably at least about 4 types, more preferably at
least about 5 types, and still more preferably at least about 6
types. The upper limit thereof is preferably about 20 types, more
preferably about 15, and still more preferably about 12. By making
the number of types of dimples within this range, it is possible to
facilitate an increase in the dimple-occupied surface ratio, and to
improve the distance.
[0097] The shape of the dimple 32 is preferably circular when
viewed from above. The average diameter of the dimples may be set
to at least about 2.8 mm, more preferably at least about 3.5 mm,
and still more preferably at least about 3.8 mm. The upper limit
thereof may preferably be about 5.0 mm, more preferably about 4.6
mm, and still more preferably about 4.3 mm. The average depth of
the dimples 32, from the standpoint of achieving an adequate
trajectory, may be preferably at least about 0.120 mm, more
preferably at least about 0.130 mm, and still more preferably at
least about 0.140 mm. The upper limit of the average depth may be
preferably about 0.185 mm, more preferably about 0.180 mm, and
still more preferably about 0.174 mm.
[0098] The average diameter means the average of the diameters of
all the dimples, and the average depth means the average of the
depths of all the dimples. In many cases, the golf ball is painted,
and the diameter and the depth of the dimple are measured with the
paint coating applied. The measurement of the diameter of the
dimples is performed by measuring the width bridged between the
points connecting with the land part which is the surface of the
glove ball on which the dimples are not formed and the graved
surface. The measurement of the depth of the dimple is performed,
when the points connecting the above dimple and the land part are
linked each other on an imaginary plane circle, by measuring
vertically the distance between the center thereof to the base
surface of the dimple.
[0099] The dimple-occupied surface ratio, which is specifically the
ratio (SR value) of the total area of the dimples which is defined
by the plane edges surrounding the borders of the dimples to the
spherical surface area of the ball assumed to have no dimples, from
the standpoint of fully exhibiting aerodynamic characteristics, is
preferably at least about 60%, more preferably at least about 65%,
and still more preferably at least about 68%. Although the upper
limit of the dimple-occupied surface ratio is not limited, it is
preferably about 90%, more preferably about 85%, and still more
preferably about 80%. Also, the spatial volume of each dimple below
the flat surface surrounded by the border thereof, when divided by
the volume of a cylinder whose base is the flat surface and whose
height is the maximum depth of the dimple from the base equals the
value V.sub.0, and from the standpoint of optimizing the trajectory
of the ball, is preferably at least about 0.35. Although the upper
limit of the V.sub.0 is not particularly limited, it may preferably
be about 0.80. Also, the VR value, which is the proportion of the
total volume of the dimples, which are formed below the flat
surface surrounded by the border of the dimples to the spherical
volume of the ball assumed to have no dimples, is preferably at
least about 0.6%, more preferably at least about 0.7%, and still
more preferably at least about 0.8%. The upper limit of the VR
value is preferably 1.0%, and more preferably 0.9%.
EXAMPLES
[0100] Golf balls constituted as shown in Table 1 were made, and an
experiment was performed to measure the moment of inertia, the
distance, and the spin decay rate of the golf balls. The test
results are shown in Table 1. The details of mixtures A to E (wt %)
for the materials of the solid core are shown in Table 2. The
details of mixtures F to H (wt %) of materials for the intermediate
layer and the cover are shown in Table 3. In Example 1, as shown in
FIG. 3, the center of the golf ball and the center of the spherical
specific gravity-enhancing member were disposed identically. In
Example 3, six disc-like specific gravity-enhancing members (the
total weight of 6 members being 1.5 g) having a thickness of 0.3 mm
and a diameter of 12 mm were disposed at the centers of faces of
the regular hexahedrons and on the surface of the solid core as
well.
TABLE-US-00001 TABLE 1 Compar- Exam- Exam- Exam- Exam- Exam- ative
ple 1 ple 2 ple 3 ple 4 ple 5 Example Solid Center Outer diameter
(mm) 27.0 15.3 37.0 25.1 37.2 core core Specific gravity 1.6 3.2
1.2 2.8 1.0 Weight (g) 16.5 6.0 31.8 24.1 28.0 Mixture A B C L D
Core Outer diameter (mm) 20.0 layer Specific gravity 1.4 Weight (g)
4.4 Mixture E Specific Outer diameter (mm) 12 gravity- Specific
gravity 7.2 7.2 enhancing Weight (g) 6.5 1.5 member Mixture or
material K J Intermediate Outer diameter (mm) 40.7 40.7 40.7 37.0
40.7 layer 1 Specific gravity 0.94 0.94 0.94 0.43 1.30 Weight (g)
29.1 23.4 31.3 7.8 10.7 Mixture F F F N H Intermediate Outer
diameter (mm) 40.6 layer 2 Specific gravity 0.94 Weight (g) 7.9
Mixture G Cover Outer diameter (mm) 42.7 42.7 42.7 42.7 42.7 42.7
Specific gravity 0.94 0.97 1.16 0.94 0.94 1.16 Weight (g) 5.3 5.4
6.5 13.4 5.5 6.5 Mixture F G I F F I Golf ball Weight (g) 45.3 45.3
45.3 45.2 45.3 45.2 Moment of inertia 72 76 75 80 67 84 Dimples
Overall number 336 336 336 336 336 336 Average diameter 4 4 4 4 4 4
(mm) Average depth (mm) 0.161 0.161 0.161 0.161 0.161 0.161 Number
of types 9 9 9 9 9 9 Distance 2800 rpm, 8deg 0.9 0.6 0.6 0.3 1.1 0
(m) 2800 rpm, 11deg 1.4 0.9 0.9 0.4 1.6 0 3500 rpm, 11deg 1.2 0.8
0.8 0.3 1.9 0 Spin decay rate (%) 3.5 3.4 3.4 3.3 3.6 3.0
TABLE-US-00002 TABLE 2 A B C D E L BR730 100 100 100 100 100 100
Zinc oxide 104.3 5.0 28.5 1.9 64.6 450 Tungsten -- 330 -- -- -- --
Zinc diacrylate 25 25 25 25 25 25 Zinc stearate G 5 5 5 5 5 5
Perhexa C-40 1.2 1.2 1.2 1.2 1.2 1.2 Organosulfur compound 0.4 0.4
0.4 0.4 0.4 0.4 Nocrac NS-6 0.1 0.1 0.1 0.1 0.1 0.1
[0101] BR730 is the trade name of 1,4-cis-polybutadiene available
from JSR Corporation, which was used as the base rubber.
[0102] Zinc oxide is available from Sakai Chemical Industry Co.,
Ltd.
[0103] Tungsten is available from Nippon Tungsten Co., Ltd.
[0104] Zinc diacrylate is available from Nippon Shokubai Co.,
Ltd.
[0105] Zinc Stearate G is the trade name of zinc stearate available
from NOF Corporation, which was used as a vulcanization
accelerator.
[0106] Perhexa C-40 is the trade name of
1,1-bis(tert-butylperoxy)cyclohexane (40% dilution) is available
from NOF Corporation, which was used as an initiator.
[0107] The organosulfur compound is a pentachlorothiophenol zinc
salt.
[0108] Nocrac NS-6 is the trade name of
2-2'-methylenebis(4-methyl-6-t-butylphenol) available from Ouchi
Shinko Chemical Industry Co., Ltd., which was used as an
antioxidant.
TABLE-US-00003 TABLE 3 F G H I N Himilan 1605 66 -- -- -- Dynaron
6100P 32 -- -- -- Polytail H 2 -- -- -- Behenic acid 18 -- -- --
Calcium hydroxide 2.3 -- -- -- Himilan 1557 -- 75 75 -- 75 Himilan
1855 -- 25 25 -- 25 Magnesium stearate -- 1.8 1.8 -- 1.8 Titanium
white -- 3.8 3.8 -- 3.8 Barium sulfate 300 -- -- 48.1 -- Pandex
T8295 -- -- -- 22 Pandex T8290 -- -- -- 65 Hytrel 4001 -- -- -- 13
Polyisocyanate -- -- -- 8 compound Foaming agent 3
[0109] Himilan 1605 is the trade name of an ionomer resin available
from DuPont-Mitsui Polychemicals Co., Ltd.
[0110] Dynaron 6100P is the trade name of a hydrogenated
thermoplastic elastomer available from JSR Corporation.
[0111] Polytail H is the trade name of polyolefin polyol available
from Mitsubishi Chemical Corporation.
[0112] Behenic acid is available from NOF Corporation.
[0113] Calcium hydroxide is available from Shiraishi Kogyo Kaisha
Ltd.
[0114] Himilan 1557 is the trade name of an ionomer resin available
from DuPont-Mitsui Polychemicals Co., Ltd.
[0115] Himilan 1855 is the trade name of an ionomer resin available
from DuPont-Mitsui Polychemicals Co., Ltd.
[0116] Barium sulfate 300 is the trade name of barium sulfate
available from Sakai Chemical Industry Co., Ltd.
[0117] Pandex T8295 is the trade name of a polyurethane
thermoplastic elastomer available from DIC Bayer Polymer.
[0118] Pandex T8290 is the trade name of a polyurethane
thermoplastic elastomer available from DIC Bayer Polymer.
[0119] Hytrel 4001 is the trade name of a thermoplastic polyether
ester elastomer available from DuPont-Toray Co., Ltd.
[0120] The polyisocyanate compound is 4,4'-diphenylmethane
diisocyanate.
[0121] The foaming agent is the ADCA master batch available from
Otsuka Chemical Co., Ltd.
[0122] Material J for the specific gravity-enhancing member is a
lead sheet with adhesive backing which is available from Osaka Kako
Co., Ltd. Mixture K for the specific gravity-enhancing member
includes tungsten of 300 parts by weight, which is available from
Nippon Tungsten Co., Ltd. (powder-type tungsten), BR730 of 40 parts
by weight, which is 1,4-cis-polybutadiene available from JSR
Corporation, LIR410 of 60 parts by weight, which is a liquid-type
isoprene rubber available from Kuraray Co., Ltd., and Sulfur Z of 2
parts by weight, which is sulfur available from Tsurumi Chemical
Industry Co., Ltd.
[0123] The moment of inertia of the golf ball was measured using
MOI-005, which is an instrument for calculating the moment of
inertia and is available from Inertia Dynamics Inc. This measuring
instrument measures the moment of inertia of a golf ball by means
of the difference between a period of oscillation of the golf ball
when the golf ball is mounted in a fixture of the measuring
instrument and a period of oscillation of the golf ball when the
golf ball is not mounted therein.
[0124] The distance of the golf ball was tested using the UBL which
is a launcher available from Automated Design Corporation. The test
was performed under the conditions of an initial velocity of the
ball of 59 m/s, the initial spin rate of 2800 rpm or 3500 rpm, and
the launch angle of 8 degrees or 11 degrees. The results of the
distance test in Table 1 show improved distances (unit: m) of
Examples compared with the distance of Comparative Example. The UBL
is an apparatus having two pairs of drums, top and bottom, the top
and bottom pairs of drums having belts wound therearound, a ball
being inserted therebetween, and launched under desired
conditions.
[0125] The spin rate of the golf ball during flight was measured
using TrackMan which is the trade name of a golf ball trajectory
tracking system available from Trackman A/S. The spin loss of the
ball per one second was determined by the slope of an approximate
straight line, which was calculated from the measured data
mentioned above by using the least-squares method. The spin decay
rate of the golf ball was obtained by dividing the spin loss per
one second by the initial spin rate of the golf ball.
[0126] As shown in Table 1, Example 1 resulted in extending the
distance longer by 0.9 m to 1.4 m compared with Comparative
Example, the golf ball of Example 1 including a spherical specific
gravity-enhancing member disposed at the center of the solid core
and including a core layer having a high specific gravity of 1.4
disposed around the solid core, and thus having a high spin decay
rate of 3.5%, whereas the golf ball of Comparative Example had a
low specific gravity of the center core of 1.0 and had a low spin
decay rate of 3.0%. Example 2 resulted in extending the distance
longer by 0.6 m to 0.9 m compared with Comparative Example, the
golf ball of Example 2 including a center core having a high
specific gravity of 1.6, and thus having a high spin decay rate of
3.4. Example 3 resulted in extending the distance longer by 0.6 m
to 0.9 m compared with Comparative Example, the golf ball of
Example 3 including plural specific gravity-enhancing members and a
center core having a high specific gravity of 3.2, and thus having
a spin decay rate of 3.4%. Example 4 resulted in extending the
distance longer by 0.3 m to 0.4 m compared with Comparative
Example, the golf ball of Example 4 including a center core having
a high specific gravity of 1.2 and having a high spin decay rate of
3.3%. Example 5 resulted in extending the distance longer by 1.1 m
to 1.9 m compared with Comparative Example, the golf ball of
Example 5 including a center core having a high specific gravity of
2.8 and a center-side intermediate layer having a low specific
gravity of 0.43, and thus having a high spin decay rate of
3.6%.
LEGEND FOR REFERENCE NUMERALS
[0127] 1: Golf ball
[0128] 10: Solid core
[0129] 12: Center core
[0130] 14 and 16: Core layer
[0131] 20: Intermediate layer
[0132] 30: Cover
[0133] 32: Dimple
[0134] 40: Specific gravity-enhancing member
[0135] 42: Specific gravity-enhancing member
[0136] 44: Specific gravity-enhancing member
* * * * *