U.S. patent application number 13/090387 was filed with the patent office on 2012-10-25 for multi-piece solid golf ball.
This patent application is currently assigned to BRIDGESTONE SPORTS CO., LTD.. Invention is credited to Hiroshi HIGUCHI, Junji UMEZAWA.
Application Number | 20120270681 13/090387 |
Document ID | / |
Family ID | 47021755 |
Filed Date | 2012-10-25 |
United States Patent
Application |
20120270681 |
Kind Code |
A1 |
UMEZAWA; Junji ; et
al. |
October 25, 2012 |
MULTI-PIECE SOLID GOLF BALL
Abstract
The invention provides a multi-piece solid golf ball having a
solid core encased by a cover of one, two or more layers, the solid
core including a spherical first layer, a second layer encasing the
first layer and a third layer encasing the second layer. The first
layer has a diameter of from 3 to 24 mm, and the third layer is
formed of a rubber composition composed primarily of polybutadiene
rubber. The ball has specific relationships between the
cross-sectional hardness at the core center on a cut face when the
solid core has been cut in half and the respective hardnesses of
the first layer 1 mm inside an interface between the first layer
and the second layer, the second layer 1 mm outside the interface
between the first layer and the second layer, the second layer 1 mm
inside an interface between the second layer and the third layer,
the third layer 1 mm outside the interface between the second layer
and the third layer, and the surface of the third layer. Such a
golf ball has a high initial velocity when hit with a driver (W#1),
and excessive spin receptivity on shots with a short iron is
suppressed. As a result, an excellent flight performance is
achieved, both on shots with a driver and on shots with a short
iron. In addition, a good feel on impact can also be obtained.
Inventors: |
UMEZAWA; Junji;
(Chichibushi, JP) ; HIGUCHI; Hiroshi;
(Chichibushi, JP) |
Assignee: |
BRIDGESTONE SPORTS CO.,
LTD.
Tokyo
JP
|
Family ID: |
47021755 |
Appl. No.: |
13/090387 |
Filed: |
April 20, 2011 |
Current U.S.
Class: |
473/376 |
Current CPC
Class: |
A63B 37/0038 20130101;
A63B 37/0047 20130101; A63B 37/004 20130101; A63B 37/0046 20130101;
A63B 37/0062 20130101; A63B 37/0044 20130101; A63B 37/0081
20130101; A63B 37/008 20130101; A63B 37/0087 20130101; A63B 37/0063
20130101; A63B 37/0065 20130101; A63B 37/0035 20130101; A63B 37/006
20130101; A63B 37/0076 20130101; A63B 37/0031 20130101; A63B
37/0033 20130101; A63B 37/0092 20130101; A63B 37/0043 20130101;
A63B 37/0064 20130101; A63B 37/0045 20130101; A63B 37/0003
20130101 |
Class at
Publication: |
473/376 |
International
Class: |
A63B 37/06 20060101
A63B037/06 |
Claims
1. A multi-piece solid golf ball comprising a solid core encased by
a cover of one, two or more layers, the solid core comprising a
spherical first layer, a second layer encasing the first layer and
a third layer encasing the second layer, wherein the first layer
has a diameter of from 3 to 24 mm; the third layer is formed of a
rubber composition composed primarily of polybutadiene rubber; and,
letting (a) represent the cross-sectional hardness at a center of
the core on a cut face when the solid core has been cut in half,
(b) represent the cross-sectional hardness, expressed as the JIS-C
hardness, of the first layer 1 mm inside an interface between the
first layer and the second layer, (c) represent the cross-sectional
hardness, expressed as the JIS-C hardness, of the second layer 1 mm
outside the interface between the first layer and the second layer,
(d) represent the cross-sectional hardness, expressed as the JIS-C
hardness, of the second layer 1 mm inside an interface between the
second layer and the third layer, (e) represent the cross-sectional
hardness, expressed as the JIS-C hardness, of the third layer 1 mm
outside the interface between the second layer and the third layer,
and (f) represent the surface hardness, expressed as the JIS-C
hardness, of the third layer: the value (b)-(c) is in a range of
from -40 to 0, the value (e)-(d) is in a range of from -40 to 0,
and the value (a)+(b)+(c)+(d)+(e)+(f) is in a range of from 370 to
460.
2. The multi-piece solid golf ball of claim 1, wherein the value
(f)-(a) in the solid core is in a range of from 20 to 40.
3. The multi-piece solid golf ball of claim 1, wherein the first
layer is formed of a rubber composition composed primarily of
polybutadiene rubber.
4. The multi-piece solid golf ball of claim 1, wherein the
cross-sectional hardness (a) of the solid core, expressed as the
JIS-C hardness, is in a range of from 30 to 60.
5. The multi-piece solid golf ball of claim 1, wherein the second
layer is formed of a rubber composition composed primarily of
polybutadiene rubber.
6. The multi-piece solid golf ball of claim 1, wherein a sphere
composed of the first layer encased by the second layer (second
layer-covered sphere) has a diameter of from 20 to 33 mm.
7. The multi-piece solid golf ball of claim 1, wherein the diameter
ratio between the first layer and the second layer-covered sphere
(first layer diameter/second layer-covered sphere diameter) is from
0.20 to 0.70.
8. The multi-piece solid golf ball of claim 1, wherein the volume
ratio between the second layer and the solid core (second layer
volume/solid core volume) is from 0.20 to 0.60.
9. The multi-piece solid golf ball of claim 1, wherein the ratio
between the deflection of the second layer-covered sphere when
compressed under a final load of 1,275 N (130 kgf) from an initial
load state of 98 N (10 kgf) to the deflection of the solid core
when compressed under a final load of 1,275 N (130 kgf) from an
initial load state of 98 N (10 kgf) (second layer-covered sphere
deflection/solid core deflection) is from 1.20 to 1.60.
10. The multi-piece solid golf ball of claim 1, wherein the ratio
between the deflection of the solid core when compressed under a
final load of 1,275 N (130 kgf) from an initial load state of 98 N
(10 kgf) to the deflection of the ball when compressed under a
final load of 1,275 N (130 kgf) from an initial load state of 98 N
(10 kgf) (solid core deflection/ball deflection) is from 1.30 to
1.50.
11. The multi-piece solid golf ball of claim 1, wherein the ratio
between the deflection of the ball when compressed under a final
load of 5,880 N (600 kgf) from an initial load state of 98 N (10
kgf) and the deflection of the ball when compressed under a final
load of 1,275 N (130 kgf) from an initial load state of 98 N (10
kgf) (600 kgf deflection/130 kgf deflection) is from 3.30 to 3.60.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a multi-piece solid golf
ball having a solid core with a multilayer construction that
includes a spherical first layer, a second layer encasing the first
layer, and a third layer encasing the second layer, and having a
cover of one, two or more layers encasing the core. More
specifically, the invention relates to a multi-piece solid golf
ball which has a good flight performance--both on shots with a
driver and on shots with a short iron, and which also has a good
feel on impact.
[0002] To increase the distance traveled by a golf ball and also
improve the feel of the ball when played, innovations have hitherto
been made which involve designing the ball structure as a
multilayer structure. Following such innovations, various
multi-piece golf balls have been proposed in which not only the
cover but the core as well has been given a structure of two or
more layers for the purpose of lowering the spin rate, increasing
the initial velocity and achieving further improvements in head
speed (HS) dependence and feel on impact.
[0003] For example, U.S. Pat. Nos. 6,290,612, 7,086,969, 7,160,208,
7,175,542 and 7,367,901 disclose golf balls having a solid core
with a two-layer structure and having a cover. In addition, U.S.
Pat. Nos. 7,510,487, 6,569,036, 6,626,770, 5,743,816 and 7,708,656
disclose golf balls having a solid core with a three-layer
structure. However, all of these conventional golf balls lack a
sufficient initial velocity when hit with a driver (W#1) or do not
have a good feel on impact, and so further improvement has been
desired.
SUMMARY OF THE INVENTION
[0004] It is therefore an object of the present invention to
provide a multi-piece solid golf ball which has a core with a
multilayer construction, has a good flight performance--both on
shots with a driver and on shots with a short iron, and also has a
good feel on impact.
[0005] As a result of extensive investigations aimed at achieving
the above objects, the inventor has discovered that, in a golf ball
having a solid core encased by a cover, which solid core has a
multilayer construction composed of a spherical first layer, a
second layer encasing the first layer and a third layer encasing
the second layer, by setting the cross-sectional hardness of the
second layer higher than the cross-sectional hardnesses of the
first and third layers and thus optimizing the hardness
relationship among the core layers, a high initial velocity is
obtained when the ball is hit with a driver (W#1) and excessive
spin receptivity on shots with a short iron is suppressed, thus
enabling an excellent flight performance to be achieved--both on
shots with a driver and on shots with a short iron, and also making
it possible to obtain a good feel on impact.
[0006] Accordingly, the invention provides the following
multi-piece solid golf balls.
[1] A multi-piece solid golf ball comprising a solid core encased
by a cover of one, two or more layers, the solid core comprising a
spherical first layer, a second layer encasing the first layer and
a third layer encasing the second layer, wherein the first layer
has a diameter of from 3 to 24 mm; the third layer is formed of a
rubber composition composed primarily of polybutadiene rubber; and,
letting (a) represent the cross-sectional hardness at a center of
the core on a cut face when the solid core has been cut in half,
(b) represent the cross-sectional hardness, expressed as the JIS-C
hardness, of the first layer 1 mm inside an interface between the
first layer and the second layer, (c) represent the cross-sectional
hardness, expressed as the JIS-C hardness, of the second layer 1 mm
outside the interface between the first layer and the second layer,
(d) represent the cross-sectional hardness, expressed as the JIS-C
hardness, of the second layer 1 mm inside an interface between the
second layer and the third layer, (e) represent the cross-sectional
hardness, expressed as the JIS-C hardness, of the third layer 1 mm
outside the interface between the second layer and the third layer,
and (f) represent the surface hardness, expressed as the JIS-C
hardness, of the third layer: the value (b)-(c) is in a range of
from -40 to 0, the value (e)-(d) is in a range of from -40 to 0,
and the value (a)+(b)+(c)+(d)+(e)+(f) is in a range of from 370 to
460. [2] The multi-piece solid golf ball of [1], wherein the value
(f)-(a) in the solid core is in a range of from 20 to 40. [3] The
multi-piece solid golf ball of [1], wherein the first layer is
formed of a rubber composition composed primarily of polybutadiene
rubber. [4] The multi-piece solid golf ball of [1], wherein the
cross-sectional hardness (a) of the solid core, expressed as the
JIS-C hardness, is in a range of from 30 to 60. [5] The multi-piece
solid golf ball of [1], wherein the second layer is formed of a
rubber composition composed primarily of polybutadiene rubber. [6]
The multi-piece solid golf ball of [1], wherein a sphere composed
of the first layer encased by the second layer (second
layer-covered sphere) has a diameter of from 20 to 33 mm. [7] The
multi-piece solid golf ball of [1], wherein the diameter ratio
between the first layer and the second layer-covered sphere (first
layer diameter/second layer-covered sphere diameter) is from 0.20
to 0.70. [8] The multi-piece solid golf ball of [1], wherein the
volume ratio between the second layer and the solid core (second
layer volume/solid core volume) is from 0.20 to 0.60. [9] The
multi-piece solid golf ball of [1], wherein the ratio between the
deflection of the second layer-covered sphere when compressed under
a final load of 1,275 N (130 kgf) from an initial load state of 98
N (10 kgf) to the deflection of the solid core when compressed
under a final load of 1,275 N (130 kgf) from an initial load state
of 98 N (10 kgf) (second layer-covered sphere deflection/solid core
deflection) is from 1.20 to 1.60. [10] The multi-piece solid golf
ball of [1], wherein the ratio between the deflection of the solid
core when compressed under a final load of 1,275 N (130 kgf) from
an initial load state of 98 N (10 kgf) to the deflection of the
ball when compressed under a final load of 1,275 N (130 kgf) from
an initial load state of 98 N (10 kgf) (solid core deflection/ball
deflection) is from 1.30 to 1.50. [11] The multi-piece solid golf
ball of [1], wherein the ratio between the deflection of the ball
when compressed under a final load of 5,880 N (600 kgf) from an
initial load state of 98 N (10 kgf) and the deflection of the ball
when compressed under a final load of 1,275 N (130 kgf) from an
initial load state of 98 N (10 kgf) (600 kgf deflection/130 kgf
deflection) is from 3.30 to 3.60.
BRIEF DESCRIPTION OF THE DIAGRAMS
[0007] FIG. 1 is a plan view showing the dimple pattern used on
balls in the examples of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0008] The invention is described more fully below.
[0009] The multi-piece solid golf ball of the invention, although
not shown in an accompanying diagram, is composed of a solid core
having a multilayer structure which includes a spherical first
layer, a second layer encased by the first layer, and a third layer
encased by the second layer, which solid core is encased by a cover
of one, two or more layers.
[0010] The first layer is the layer positioned on the innermost
side in the golf ball of the invention, and is spherical. Materials
capable of forming this first layer are not subject to any
particular limitation, although the first layer may be formed using
a rubber composition composed primarily of polybutadiene or a resin
composition composed primarily of a thermoplastic resin.
[0011] The first layer is described first for cases in which it is
formed using a rubber composition.
[0012] In the invention, in cases where the first layer is formed
using a rubber composition, preferred use may be made of a rubber
composition in which polybutadiene is used as the base rubber.
[0013] Here, the polybutadiene is not subject to any particular
limitation, although the use of a polybutadiene having a cis-1,4
bond content of a least 60%, preferably at least 80%, more
preferably at least 90%, and most preferably at least 95%, is
recommended.
[0014] It is recommended that the polybutadiene, although not
subject to any particular limitation, have a Mooney viscosity
(ML.sub.1+4 (100.degree. C.)) of at least 30, preferably at least
35, more preferably at least 40, even more preferably at least 50,
and most preferably at least 52. It is recommended that the upper
limit, although not subject to any particular limitation, be not
more than 100, preferably not more than 80, more preferably not
more than 70, and even more preferably not more than 60.
[0015] The term "Mooney viscosity" used herein refers to an
industrial indicator of viscosity (JIS K6300) as measured with a
Mooney viscometer, which is a type of rotary plastometer. This
value is represented by the unit symbol ML.sub.1+4 (100.degree.
C.), wherein "M" stands for Mooney viscosity, "L" stands for large
rotor (L-type), and "1+4" stands for a pre-heating time of 1 minute
and a rotor rotation time of 4 minutes. The "100.degree. C."
indicates that measurement was carried out at a temperature of
100.degree. C.
[0016] In addition, the polybutadiene has a molecular weight
distribution Mw/Mn (Mw: weight-average molecular weight; Mn:
number-average molecular weight) which, although not subject to any
particular limitation, is at least 2.0, preferably at least 2.2,
more preferably at least 2.4, and even more preferably at least
2.6. The upper limit, although not subject to any particular
limitation, is typically not more than 6.0, preferably not more
than 5.0, more preferably not more than 4.0, and even more
preferably not more than 3.4. If Mw/Mn is too small, the
workability may decrease; if Mw/Mn is too large, the resilience may
decrease.
[0017] The polybutadiene used may be one which has been synthesized
using a nickel catalyst, a cobalt catalyst, a Group VIII metal
catalyst or a rare-earth catalyst. In this invention, it is
preferable to use a polybutadiene synthesized with, in particular,
a nickel catalyst or a rare-earth catalyst. Also, where necessary,
an organoaluminum compound, an alumoxane, a halogen-bearing
compound, a Lewis base and the like may be used in combination with
these catalysts. In this invention, it is preferable to use, as the
various above-mentioned compounds, those mentioned in JP-A
11-35633.
[0018] Of the above rare-earth catalysts, the use of a neodymium
catalyst that employs a neodymium compound, which is a lanthanide
series rare-earth compound, is especially recommended because it
enables a polybutadiene rubber having a high cis-1,4 bond content
and a low 1,2-vinyl bond content to be obtained at an excellent
polymerization activity.
[0019] The polymerization of butadiene in the presence of a
rare-earth catalyst may be carried out by bulk polymerization or
vapor phase polymerization, either with or without the use of a
solvent, and at a polymerization temperature in a range of
generally from -30 to 150.degree. C., and preferably from 10 to
100.degree. C.
[0020] The above polybutadiene may be one obtained by
polymerization using the above-described rare-earth catalyst,
followed by the reaction of a terminal modifier with active end
groups on the polymer.
[0021] Specific examples of the terminal modifier and methods for
their reaction are described in, for example, JP-A 11-35633, JP-A
7-268132 and JP-A 2002-293996.
[0022] It is recommended that the amount of the above polybutadiene
included in the base rubber, although not subject to any particular
limitation, be at least 60 wt %, preferably at least 70 wt %, more
preferably at least 80 wt %, and even more preferably at least 90
wt %, and that the upper limit be 100 wt % or less, preferably 98
wt % or less, and more preferably 95 wt % or less. If the content
is inadequate, it may be difficult to obtain golf balls conferred
with a good rebound.
[0023] Rubbers other than the above polybutadiene may also be used
together and included, insofar as the objects of the invention are
attainable. Illustrative examples include polybutadiene rubbers
(BR), styrene-butadiene rubbers (SBR), natural rubbers,
polyisoprene rubbers and ethylene-propylene-diene rubbers (EPDM).
These may be used singly or as a combination of two or more
types.
[0024] The first layer is formed of a rubber composition obtained
by blending additives, such as an unsaturated carboxylic acid or a
metal salt thereof, an organosulfur compound, an inorganic filler
and an antioxidant, in given amounts with the above-described base
rubber.
[0025] Illustrative examples of the unsaturated carboxylic acid
include acrylic acid, methacrylic acid, maleic acid and fumaric
acid. The use of acrylic acid or methacrylic acid is especially
preferred.
[0026] Illustrative examples of metal salts of unsaturated
carboxylic acids include zinc salts and magnesium salts of
unsaturated fatty acids, such as zinc methacrylate and zinc
acrylate. The use of zinc acrylate is especially preferred.
[0027] The amount of the unsaturated carboxylic acid and/or a metal
salt thereof included in the rubber composition, although not
subject to any particular limitation, may be set to preferably at
least 10 parts by weight, and more preferably at least 15 parts by
weight, per 100 parts by weight of the base rubber. It is
recommended that the upper limit, although not subject to any
particular limitation, be set to not more than 50 parts by weight.
If the amount included is too high, the ball may become too hard,
resulting in an unpleasant feel on impact. On the other hand, if
the amount is too low, the rebound may decrease.
[0028] An organosulfur compound may optionally be included. The
organosulfur compound can be advantageously used to impart an
excellent rebound. Thiophenols, thionaphthols, halogenated
thiophenols, and metal salts thereof are recommended for this
purpose. Illustrative examples include pentachlorothiophenol,
pentafluorothiophenol, pentabromothiophenol, p-chlorothiophenol,
and the zinc salt of pentachlorothiophenol; and
diphenylpolysulfides, dibenzylpolysulfides, dibenzoylpolysulfides,
dibenzothiazoylpolysulfides and dithiobenzoylpolysulfides having 2
to 4 sulfurs. Diphenyldisulfide and the zinc salt of
pentachlorothiophenol are especially preferred.
[0029] The amount of the organosulfur compound included can be set
to more than 0, and may be set to preferably at least 0.1 part by
weight, more preferably at least 0.2 part by weight, and even more
preferably at least 0.4 part by weight, per 100 parts by weight of
the base rubber. The upper limit in the amount included, although
not subject to any particular limitation, may be set to preferably
not more than 5 parts by weight, more preferably not more than 4
parts by weight, even more preferably not more than 3 parts by
weight, and most preferably not more than 2 parts by weight.
Including too much organosulfur compound may excessively lower the
hardness, whereas including too little is unlikely to improve the
rebound.
[0030] The inorganic filler is exemplified by zinc oxide, barium
sulfate and calcium carbonate. The amount of the inorganic filler
included is not subject to any particular limitation, although it
may be set to preferably at least 5 parts by weight, more
preferably at least 6 parts by weight, even more preferably at
least 7 parts by weight, and most preferably at least 8 parts by
weight, per 100 parts by weight of the base rubber. The upper limit
in the amount included may be set to preferably not more than 80
parts by weight, more preferably not more than 60 parts by weight,
even more preferably not more than 40 parts by weight, and most
preferably not more than 20 parts by weight. Too much or too little
inorganic filler may make it impossible to achieve a suitable
weight and a good rebound.
[0031] To increase the hardness profile, the organic peroxide used
is preferably one having a relatively short half-life.
Specifically, use is made of an organic peroxide which has a
half-life at 155.degree. C. (at) of preferably at least 5 seconds,
more preferably at least 10 seconds, and even more preferably at
least 15 seconds. Moreover, the organic peroxide used has a
half-life at 155.degree. C. (at) of preferably not more than 120
seconds, more preferably not more than 90 seconds, and even more
preferably not more than 60 seconds. Examples of organic peroxides
which satisfy these conditions include
1,1-bis(t-hexylperoxy)cyclohexane (trade name, Perhexa HC),
1-1-bis(t-hexylperoxy)-3,3,5-trimethylcyclohexane (trade name,
Perhexa TMH), 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclo-hexane
(trade name, Perhexa 3M) and 1-bis(t-butylperoxy)-cyclohexane
(trade name, Perhexa C). These are all available from NOF
Corporation.
[0032] The organic peroxide is included in an amount which,
although not subject to any particular limitation, is preferably at
least 0.3 part by weight, more preferably at least 0.4 part by
weight, and even more preferably at least 0.5 part by weight, per
100 parts by weight of the base rubber. The upper limit in the
amount of organic peroxide is not subject to any particular
limitation, although it is recommended that it be preferably not
more than 4 parts by weight, more preferably not more than 3 parts
by weight, even more preferably not more than 2 parts by weight,
and most preferably not more than 1.5 parts by weight. In this
invention, to achieve a suitable rebound and durability, it is
preferable for the amount of organic peroxide to be set in the
above-indicated range. If the amount of organic peroxide is too
high, the rebound and durability may decline. On the other hand, if
the amount of organic peroxide is too low, the time required for
crosslinking may increase, possibly resulting in a large decline in
productivity and also a large decline in compression.
[0033] If necessary, an antioxidant may be included in the above
rubber composition. Illustrative examples of the antioxidant
include commercial products such as Nocrac NS-6 and Nocrac NS-30
(both available from Ouchi Shinko Chemical Industry Co., Ltd.), and
Yoshinox 425 (Yoshitomi Pharmaceutical Industries, Ltd.).
[0034] The amount of antioxidant included can be set to more than
0, and may be set to preferably at least 0.03 part by weight, and
more preferably at least 0.05 part by weight, per 100 parts by
weight of the base rubber. The upper limit in the amount of
antioxidant, although not subject to any particular limitation, may
be set to preferably not more than 0.4 part by weight, more
preferably not more than 0.3 part by weight, and even more
preferably not more than 0.2 part by weight. In this invention, it
is recommended that the amount of the antioxidant be set within the
above range so as to enable a suitable rebound and durability to be
achieved.
[0035] Sulfur may also be added if necessary. Such sulfur is
exemplified by the product manufactured by Tsurumi Chemical
Industry Co., Ltd. under the trade name Sulfur Z. The amount of
sulfur included can be set to more than 0, and may be set to
preferably at least 0.005 part by weight, and more preferably at
least 0.01 part by weight, per 100 parts by weight of the base
rubber. The upper limit in the amount of sulfur, although not
subject to any particular limitation, may be set to preferably not
more than 0.5 part by weight, more preferably not more than 0.4
part by weight, and even more preferably not more than 0.1 part by
weight. By adding sulfur, the hardness profile of the core can be
increased. However, adding too much sulfur may result in
undesirable effects during hot molding, such as explosion of the
rubber composition, or may considerably lower the rebound.
[0036] When a rubber composition is used to form the first layer
(hot-molded material), to obtain the subsequently described
cross-sectional hardness, the foregoing rubber composition is
suitably selected and fabrication may be carried out by
vulcanization and curing according to a method similar to that used
for conventional golf ball rubber compositions. Suitable
vulcanization conditions include, for example, a vulcanization
temperature of between 100.degree. C. and 200.degree. C., and a
vulcanization time of from 10 to 40 minutes. To obtain the desired
rubber crosslinked body for use as the core in the present
invention, the vulcanizing temperature is preferably at least
150.degree. C., and especially at least 155.degree. C., but
preferably not above 200.degree. C., more preferably not above
190.degree. C., even more preferably not above 180.degree. C., and
most preferably not above 170.degree. C.
[0037] Next, when the first layer is formed using a thermoplastic
resin, although not subject to any particular limitation, use may
be made of thermoplastic resins such nylons, polyarylates, ionomer
resins, polypropylene resins, polyurethane-type thermoplastic
elastomers and polyester-type thermoplastic elastomers. Commercial
products which may be suitably used as these resins include Surlyn
AD8512 (an ionomer resin available from E.I. DuPont de Nemours and
Co.), Himilan 1706 and Himilan 1707 (both ionomer resins available
from DuPont-Mitsui Polychemicals Co., Ltd.), Rilsan BMNO (a nylon
resin available from Arkema) and U-Polymer U-8000 (a polyarylate
resin available from Unitika, Ltd.).
[0038] In the present invention, of the above thermoplastic resins,
it is especially desirable to use an ionomer resin, an
unneutralized form thereof, or a highly neutralized ionomer resin.
The ionomer resin or unneutralized form thereof is preferably a
resin composition in which the following resin components A-I and
A-II serve as the base resins:
(A-I) an olefin-unsaturated carboxylic acid-unsaturated carboxylic
acid ester ternary random copolymer and/or a metal salt thereof;
and (A-II) an olefin-unsaturated carboxylic acid binary random
copolymer and/or a metal salt thereof. This resin composition is
described below.
[0039] The olefin-unsaturated carboxylic acid-unsaturated acid
ester ternary random copolymer and/or metal salt thereof serving as
component A-I has a weight-average molecular weight (Mw) of
preferably at least 100,000, more preferably at least 110,000, and
even more preferably at least 120,000. The upper limit is
preferably not more than 200,000, more preferably not more than
190,000, and even more preferably not more than 180,000. The
weight-average molecular weight (Mw) to number-average molecular
weight (Mn) ratio of the copolymer is preferably at least 3, and
more preferably at least 4.5, with the upper limit being preferably
not more than 7, and more preferably not more than 6.5.
[0040] The olefin-unsaturated carboxylic acid binary random
copolymer and/or metal salt thereof serving as component A-II has a
weight-average molecular weight (Mw) of preferably at least
150,000, more preferably at least 160,000, and even more preferably
at least 170,000. The upper limit is preferably not more than
200,000, more preferably not more than 190,000, and even more
preferably not more than 180,000. The weight-average molecular
weight (Mw) to number-average molecular weight (Mn) ratio is
preferably at least 3, and more preferably at least 4.5, with the
upper limit being preferably not more than 7, and more preferably
not more than 6.5.
[0041] Here, the weight-average molecular weight (Mw) and
number-average molecular weight (Mn) are values calculated relative
to polystyrene in gel permeation chromatography (GPC). A word of
explanation is needed here concerning GPC molecular weight
measurement. It is not possible to directly take GPC measurements
for binary copolymers and ternary copolymers because these
molecules are adsorbed to the GPC column owing to the unsaturated
carboxylic acid groups within the molecule. Instead, the
unsaturated carboxylic acid groups are generally converted to
esters, following which GPC measurement is carried out and the
polystyrene-equivalent average molecular weights Mw and Mn are
calculated.
[0042] The olefins in components A-I and A-II are exemplified by
olefins in which the number of carbons is at least 2, but not more
than 8, and preferably not more than 6. Illustrative examples of
such olefins include ethylene, propylene, butene, pentene, hexene,
heptene and octene. Ethylene is especially preferred.
[0043] Illustrative examples of the unsaturated carboxylic acid
include acrylic acid, methacrylic acid, maleic acid and fumaric
acid. Acrylic acid and methacrylic acid are especially
preferred.
[0044] The unsaturated carboxylic acid ester included in component
A-I is preferably a lower alkyl ester of the above-mentioned
unsaturated carboxylic acid. Illustrative 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 especially preferred.
[0045] The random copolymer used as component A-I or component A-II
may be obtained by random copolymerization of the above ingredients
in accordance with a known method. Here, the content of unsaturated
carboxylic acid (acid content) included in the random copolymer,
although not subject to any particular limitation, is preferably at
least 2 wt %, more preferably at least 6 wt %, and even more
preferably at least 8 wt %. It is recommended that the upper limit,
although not subject to any particular limitation, be not more than
25 wt %, more preferably not more than 20 wt %, and even more
preferably not more than 15 wt %. At a low acid content, the
rebound may decrease, whereas at a high acid content, the
processability of the material may decrease.
[0046] It is essential to set the relative proportions in the
contents of component A-I and component A-II, expressed as the
weight ratio therebetween, at generally from 100:0 to 0:100,
preferably from 100:0 to 25:75, more preferably from 100:0 to
50:50, even more preferably from 100:0 to 75:25, and most
preferably 100:0. If the content of component A-II is too low,
moldings of the material may have a decreased resilience.
[0047] The metal salts of the copolymer in above components A-I and
A-II may be obtained by partially neutralizing the acid groups in
the random copolymers of components A-I and A-II with metal ions.
Here, specific examples of the metal ions which neutralize the acid
groups include Na.sup.+, K.sup.+, Li.sup.+, Zn.sup.++, Cu.sup.++,
Mg.sup.++, Ca.sup.++, Co.sup.++, Ni.sup.++ and Pb.sup.++. In the
invention, of these, preferred use may be made of Na.sup.+,
Li.sup.++, Zn.sup.++, Mg.sup.++ and Ca.sup.++; Zn.sup.++ and
Mg.sup.++ are especially preferred.
[0048] In cases where metal neutralization products of the above
copolymers are used as components A-I and A-II, i.e., in cases
where an ionomer resin is used, the type of metal neutralization
product and the degree of neutralization are not subject to any
particular limitation. Specific examples include 60 mol % Zn
(degree of neutralization with zinc) ethylene-acrylic acid
copolymers, 40 mol % Mg (degree of neutralization with magnesium)
ethylene-acrylic acid copolymers, 40 mol % Mg (degree of
neutralization with magnesium) ethylene-methacrylic
acid-isobutylene acrylate terpolymers, and 60 mol % Zn (degree of
neutralization with zinc) ethylene-methacrylic acid-isobutylene
acrylate terpolymers.
[0049] Illustrative examples of the olefin-unsaturated carboxylic
acid-unsaturated carboxylic acid ester ternary random copolymer of
component A-I include those available under the trade names Nucrel
AN4318, Nucrel AN4319, Nucrel AN4311, Nucrel N035C and Nucrel
N0200H (DuPont-Mitsui Polychemicals Co., Ltd.). Illustrative
examples of the metal salts of olefin-unsaturated carboxylic
acid-unsaturated carboxylic acid ester ternary random copolymers
include those available under the trade names Himilan AM7316,
Himilan AM7331, Himilan 1855 and Himilan 1856 (DuPont-Mitsui
Polychemicals Co., Ltd.), and those available under the trade names
Surlyn 6320 and Surlyn 8120 (E.I. DuPont de Nemours and Co.,
Ltd.).
[0050] Illustrative examples of the olefin-unsaturated carboxylic
acid binary random copolymer of component A-II include those
available under the trade names Nucrel 1560, Nucrel 1525 and Nucrel
1035 (DuPont-Mitsui Polychemicals Co., Ltd.). Illustrative examples
of the metal salts of olefin-unsaturated carboxylic acid binary
random copolymers include those available under the trade names
Himilan 1605, Himilan 1601, Himilan 1557, Himilan 1705 and Himilan
1706 (DuPont-Mitsui Polychemicals Co., Ltd.); those available under
the trade names Surlyn 7930 and Surlyn 7920 (E.I. DuPont de Nemours
and Co., Ltd.); and those available under the trade names Escor
5100 and Escor 5200 (ExxonMobil Chemical).
[0051] In addition, to achieve a good rebound, use may be made of a
highly neutralized ionomer resin in which the degree of
neutralization has been increased by mixing the subsequently
described (B) fatty acid or derivative thereof having a molecular
weight of at least 280 but not more than 1,500 and (C) a basic
inorganic metal compound with above components A-I and A-II under
applied heat.
[0052] Component B is a fatty acid or fatty acid derivative having
a molecular weight of at least 280 but not more than 1,500 whose
purpose is to increase the flow properties of the heated mixture.
Compared with the thermoplastic resins of component A, it has a
much smaller molecular weight and helps to significantly decrease
the melt viscosity of the mixture. Also, because the fatty acid (or
fatty acid derivative) of component B has a molecular weight of at
least 280 but not more than 1,500 and has a high content of acid
groups (or derivative moieties thereof), its addition results in
little if any loss of resilience.
[0053] The fatty acid or fatty acid derivative serving as component
B may be an unsaturated fatty acid (or fatty acid derivative)
having a double bond or triple bond in the alkyl moiety, or it may
be a saturated fatty acid (or fatty acid derivative) in which all
the bonds in the alkyl moiety are single bonds. It is recommended
that the number of carbons on the molecule be preferably at least
18, but preferably not more than 80, and more preferably not more
than 40. Too few carbons may result in a poor heat resistance, and
may also set the acid group content so high as to cause the acid
groups to interact with acid groups present on the base resin, as a
result of which the desired flow properties may not be achieved. On
the other hand, too many carbons increases the molecular weight,
which may lower the flow properties. In either case, the material
may become difficult to use.
[0054] Specific examples of fatty acids that may be used as
component B include stearic acid, 12-hydroxystearic acid, behenic
acid, oleic acid, linoleic acid, linolenic acid, arachidic acid and
lignoceric acid. Of these, preferred use may be made of stearic
acid, arachidic acid, behenic acid, lignoceric acid and oleic
acid.
[0055] The fatty acid derivative is exemplified by derivatives in
which the proton on the acid group of the fatty acid has been
substituted. Exemplary fatty acid derivatives of this type include
metallic soaps in which the proton has been substituted with a
metal ion. Metal ions that may be used in such metallic soaps
include Li.sup.+, Ca.sup.++, Mg.sup.++, Zn.sup.++, Mn.sup.++,
Al.sup.+++, Ni.sup.++, Fe.sup.++, Fe.sup.+++, Cu.sup.++, Sn.sup.++,
Pb.sup.++ and Co.sup.++. Of these, Ca.sup.++, Mg.sup.++ and
Zn.sup.++ are especially preferred.
[0056] Specific examples of fatty acid derivatives that may be used
as component B include 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. Of these, 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 are
preferred.
[0057] The content of component B per 100 parts by weight of the
base resin is at least 30 parts by weight, preferably at least 45
parts by weight, more preferably at least 60 parts by weight, and
even more preferably at least 80 parts by weight. The upper limit
in the content is not more than 170 parts by weight, preferably not
more than 150 parts by weight, even more preferably not more than
130 parts by weight, and most preferably not more than 110 parts by
weight.
[0058] Use may also be made of known metallic soap-modified ionomer
resins (see, for example, U.S. Pat. Nos. 5,312,857 and 5,306,760,
and International Disclosure WO 98/46671) when using above
component A.
[0059] The basic inorganic metal compound serving as component C is
included for the purpose of neutralizing the acid groups in above
components A and B. As mentioned in prior-art examples, when
components A and B alone, and in particular metal-modified ionomer
resins alone (e.g., metal soap-modified ionomer resins of the types
mentioned in the foregoing patent publications, alone), are heated
and mixed, as shown below, the metal soap and unneutralized acid
groups present on the ionomer resin undergo exchange reactions,
generating a fatty acid. Because the fatty acid generated has a low
thermal stability and readily vaporizes during molding, it causes
molding defects. Moreover, if the fatty acid thus generated
deposits on the surface of the molding, it will substantially lower
paint film adhesion.
##STR00001##
[0060] A basic inorganic metal compound which neutralizes the acid
groups present in above components A and B is thus included as
component C in order to resolve such problems. The inclusion of
component C as an essential ingredient confers excellent
properties. That is, the acid groups in above components A and B
are neutralized, and synergistic effects from the inclusion of each
of these components increase the thermal stability of the resin
composition while at the same time conferring a good moldability
and enhancing the resilience as a golf ball material.
[0061] It is recommended that component C be a basic inorganic
metal compound--preferably a monoxide or hydroxide--which is
capable of neutralizing acid groups in above components A and B.
Because such compounds have a high reactivity with the ionomer
resin and the reaction by-products contain no organic matter, the
degree of neutralization of the resin composition can be increased
without a loss of thermal stability.
[0062] The metal ions used here in the basic inorganic metal
compound are exemplified by Li.sup.+, Na.sup.+, K.sup.+, Ca.sup.++,
Mg.sup.++, Zn.sup.++, Al.sup.+++, Ni.sup.+, Fe.sup.++, Fe.sup.+++,
Cu.sup.++, Mn.sup.++, Sn.sup.++, Pb.sup.++ and Co.sup.++.
Illustrative examples of the inorganic metal compound include basic
inorganic fillers containing these metal ions, such as magnesium
oxide, magnesium hydroxide, magnesium carbonate, zinc oxide, sodium
hydroxide, sodium carbonate, calcium oxide, calcium hydroxide,
lithium hydroxide and lithium carbonate. Of these, as noted above,
a monoxide or hydroxide is preferred. The use of magnesium oxide or
calcium hydroxide, which have high reactivities with ionomer
resins, is especially preferred.
[0063] The content of component C may be suitably selected so as to
obtain the desired degree of neutralization. Although not subject
to any particular limitation, component C may be set to a content
of, based on the acid groups in component A and B, preferably at
least 30 mol %, more preferably at least 45 mol %, even more
preferably at least 60 mol %, and most preferably at least 70 mol
%. The upper limit may be set to preferably not more than 130 mol
%, more preferably not more than 110 mol %, even more preferably
not more than 100 mol %, and most preferably not more than 90 mol
%. The above content, expressed on a weight basis per 100 parts by
weight of the base resin, is preferably from 0.1 to 10 parts by
weight. In this case, the lower limit is more preferably at least
0.5 part by weight, even more preferably at least 0.8 part by
weight, and most preferably at least 1 part by weight. On the other
hand, the upper limit is more preferably not more than 8 parts by
weight, even more preferably not more than 5 parts by weight, and
most preferably not more than 4 parts by weight.
[0064] The above resin composition has a melt flow rate, measured
in accordance with JIS-K6760 (test temperature, 190.degree. C.;
test load, 21 N (2.16 kgf)), of preferably at least 1 g/10 min,
more preferably at least 2 g/10 min, and even more preferably at
least 3 g/10 min. The upper limit is preferably not more than 30
g/10 min, more preferably not more than 20 g/10 min, even more
preferably not more than 15 g/10 min, and most preferably not more
than 10 g/10 min. If the melt flow rate of this resin composition
is low, the processability may markedly decrease.
[0065] The method of preparing the above resin composition is not
subject to any particular limitation, although use may be made of a
method which involves charging the ionomer resins or unneutralized
polymers of components A-I and A-II, together with components B and
C, into a hopper and extruding under the desired conditions.
Alternatively, component B may be charged from a separate feeder.
The neutralization reaction by above component C as the metal
cation source with the carboxylic acids in components A-I, A-II and
B may be carried out with various types of extruders. Here, either
a single-screw extruder or a twin-screw extruder may be used as the
extruder, although the use of a twin-screw extruder is more
preferred because of the large kneading effect. Alternatively,
these extruders may be used in a tandem arrangement, such as
single-screw extruder/twin-screw extruder or twin-screw
extruder/twin-screw extruder. These extruders need not be of a
special design; the use of existing extruders will suffice.
[0066] The method of forming the above first layer using a
thermoplastic resin is not subject to any particular limitation.
Use may be made of a known method such as forming or injection
molding, with production by injection molding being especially
preferred. In such a case, preferred use may be made of a method in
which the above-described thermoplastic resin material is injected
into the cavity of a core-forming mold.
[0067] The diameter of the first layer is set to from 3 to 24 mm.
Here, the lower limit in the diameter is preferably at least 6 mm,
and more preferably at least 9 mm. The upper limit in the diameter
is preferably not more than 20 mm, more preferably not more than 15
mm, and even more preferably not more than 12 mm. If the diameter
falls outside the above range, the ball may fail to attain a
sufficient initial velocity when struck with a W#1, or the spin
range may become too high, as a result of which a good distance may
not be achieved.
[0068] The second layer is a layer which encases the
above-described first layer and, of the three layers making up the
solid core, is the layer positioned in the middle. This second
layer is not subject to any particular limitation, although it may
be formed using a material similar to the material used to form the
first layer. That is, advantageous use can be made of a rubber
composition in which the above-described polybutadiene serves as
the base rubber, or of a thermoplastic resin.
[0069] The method of forming the second layer using a rubber
composition may be a known method and is not subject to any
particular limitation, although preferred use may be made of the
following method. First, the second layer-forming material is
placed in a predetermined mold and subjected to primary
vulcanization (semi-vulcanization) so as to produce a pair of
hemispherical half-cups. The prefabricated spherical first layer is
then enclosed within the half-cups produced as just described, in
which state secondary vulcanization (complete vulcanization) is
carried out. That is, advantageous use may be made of a method in
which the vulcanization step is divided into two stages.
Alternatively, advantageous use may be made of a method in which
the second layer-forming material is injection-molded over the
first layer.
[0070] In cases where the first layer has been formed of a
thermoplastic resin, a firm bond may be achieved at the interface
between the first layer and the second layer by pre-coating the
surface of the first layer with an adhesive. By firmly bonding both
layers with an adhesive, the durability of the golf ball is further
enhanced, enabling a high rebound to be achieved. Alternatively,
adherence between the first layer and the second layer can be
further increased by subjecting the surface of the first layer to
pretreatment, such as grinding treatment with a barrel finishing
machine, plasma treatment, corona discharge treatment or chemical
treatment, so as to form fine surface irregularities on the
surface.
[0071] The method of forming the second layer using a thermoplastic
resin is also not subject to any particular limitation. A known
method may be employed, such as the method of injection-molding a
second layer-forming material over the sphere serving as the first
layer, or the method of prefabricating a pair of hemispherical
half-cups from the second layer-forming material, enclosing the
first layer within these half-cups, and molding under applied heat
and pressure at from 140 to 180.degree. C. for a period of 2 to 10
minutes.
[0072] The sphere composed of the first layer encased by the second
layer (second layer-covered sphere) has a diameter which, although
not subject to any particular limitation, may be set to from 20 to
33 mm. In this case, the lower limit in the diameter is preferably
at least 23 mm, and more preferably at least 26 mm. The upper limit
is preferably not more than 32 mm, and more preferably not more
than 30 mm.
[0073] The third layer is a layer which encases the second layer.
Of the three layers making up the solid core, the third layer is
the layer positioned on the outermost side. It is critical that
this third layer be formed of a rubber composition composed
primarily of polybutadiene. In particular, use can be made of a
rubber composition similar to the rubber composition which may be
advantageously used to form the first layer.
[0074] The method of forming the third layer is not subject to any
particular limitation, although preferred use may be made of a
method similar to the method of forming the second layer. That is,
advantageous use may be made of a method in which a third
layer-forming material is placed in a predetermined mold and
subjected to primary vulcanization (semi-vulcanization) to
fabricate a pair of hemispherical half-cups, following which a
prefabricated second layer-covered sphere is enclosed within the
fabricated half-cups and secondary vulcanization (complete
vulcanization) is carried out in this state; or a method in which
the third layer-forming material is injection-molded over the
second layer.
[0075] When the second layer has been formed of a thermoplastic
resin, a firm bond may be achieved at the interface between the
second layer and the third layer by pre-coating the surface of the
second layer with an adhesive. By firmly bonding both layers with
an adhesive, the durability of the golf ball is further enhanced,
enabling a higher rebound to be achieved. Alternatively, adherence
between the second layer and the third layer can be further
increased by subjecting the surface of the second layer to grinding
treatment with a barrel finishing machine, plasma treatment, corona
discharge treatment, chemical treatment or the like so as to form
fine surface irregularities on the surface.
[0076] The solid core obtained by successively forming the above
first to third layers as described above has a diameter which,
although not subject to any particular limitation, is preferably
from 33 to 41 mm. The lower limit in this diameter is more
preferably at least 35 mm, and even more preferably at least 37 mm.
The upper limit is more preferably not more than 40 mm, and even
more preferably not more than 39 mm.
[0077] In the present invention, a solid core having a first,
second and third layer has been optimized by making the
cross-sectional hardness of the second layer higher than the
cross-sectional hardnesses of the first and third layers. More
specifically, letting (a) represent the cross-sectional hardness,
expressed as the JIS-C hardness, at a center of the core on a cut
face when the solid core has been cut in half, (b) represent the
cross-sectional hardness, expressed as the JIS-C hardness, of the
first layer 1 mm inside an interface between the first layer and
the second layer, (c) represent the cross-sectional hardness,
expressed as the JIS-C hardness, of the second layer 1 mm outside
the interface between the first layer and the second layer, (d)
represent the cross-sectional hardness, expressed as the JIS-C
hardness, of the second layer 1 mm inside an interface between the
second layer and the third layer, (e) represent the cross-sectional
hardness, expressed as the JIS-C hardness, of the third layer 1 mm
outside the interface between the second layer and the third layer,
and (f) represent the surface hardness, expressed as the JIS-C
hardness, of the third layer, it is critical for:
the value (b)-(c) to be in a range of from -40 to 0; the value
(e)-(d) to be in a range of from -40 to 0; and the value
(a)+(b)+(c)+(d)+(e)+(f) to be in a range of from 370 to 460.
[0078] The sectional hardnesses (a) to (f) at various
cross-sectional areas of the solid core are described in detail
below.
[0079] The cross-sectional hardness (a) at the center of the core,
although not subject to any particular limitation, may be set to a
value, expressed as the JIS-C hardness, of at least 30, preferably
at least 40, and more preferably at least 45. The upper limit,
although not subject to any particular limitation, may be set to a
value, expressed as the JIS-C hardness, of not more than 65,
preferably not more than 60, and more preferably not more than 55.
If the cross-sectional hardness (a) is too small, a sufficient
initial velocity may not be obtained on shots with a W#1. On the
other hand, if it is too large, the spin rate on shots with a W#1
may be excessive.
[0080] The cross-sectional hardness (b) of the first layer 1 mm
inside an interface between the first layer and the second layer,
although not subject to any particular limitation, may be set to a
value, expressed as the JIS-C hardness, of at least 35, preferably
at least 40, and more preferably at least 45. The upper limit,
although not subject to any particular limitation, may be set to a
value, expressed as the JIS-C hardness, of not more than 70,
preferably not more than 65, and more preferably not more than
60.
[0081] The cross-sectional hardness (c) of the second layer 1 mm
outside the interface between the first layer and the second layer,
although not subject to any particular limitation, may be set to a
value, expressed as the JIS-C hardness, of at least 50, preferably
at least 60, and more preferably at least 65. The upper limit,
although not subject to any particular limitation, may be set to a
value, expressed as the JIS-C hardness, of not more than 85,
preferably not more than 80, and even more preferably not more than
75.
[0082] The cross-sectional hardness (d) of the first layer 1 mm
inside an interface between the second layer and the third layer,
although not subject to any particular limitation, may be set to a
value, expressed as the JIS-C hardness, of at least 60, preferably
at least 70, and more preferably at least 75. The upper limit,
although not subject to any particular limitation, may be set to a
value, expressed as the JIS-C hardness, of not more than 90,
preferably not more than 85, and even more preferably not more than
80.
[0083] The cross-sectional hardness (e) of the third layer 1 mm
outside the interface between the second layer and the third layer,
although not subject to any particular limitation, may be set to a
value, expressed as the JIS-C hardness, of at least 55, preferably
at least 65, and more preferably at least 70. The upper limit,
although not subject to any particular limitation, may be set to a
value, expressed as the JIS-C hardness, of not more than 85,
preferably not more than 80, and even more preferably not more than
75.
[0084] The surface hardness (f) of the third layer, although not
subject to any particular limitation, may be set to a value,
expressed as the JIS-C hardness, of at least 65, preferably at
least 75, and more preferably at least 80. The upper limit,
although not subject to any particular limitation, may be set to a
value, expressed as the JIS-C hardness, of not more than 95, and
preferably not more than 90.
[0085] The value (b)-(c), as mentioned above, must be set to from
-40 to 0. The lower limit in this value is preferably at least -30,
and more preferably at least -20. The upper limit in this value is
preferably not more than -5, and more preferably not more than -10.
If the value (b)-(c) is too large, the ball may not travel a
sufficient distance on shots with a short iron; if it is too small,
the durability to cracking may be inadequate.
[0086] The value (e)-(d), as mentioned above, must be set to from
-40 to 0. The lower limit in this value is preferably at least -30,
and more preferably at least -20. The upper limit in this value is
preferably not more than -2, and more preferably not more than -4.
If the value (e)-(d) is too large, the durability to cracking may
be inadequate; if it is too small, the ball may have too hard a
feel on impact.
[0087] The value (f)-(a), although not subject to any particular
limitation, is preferably set to from 20 to 40. The lower limit in
this value is more preferably at least 25, and even more preferably
at least 30. The upper limit in this value is preferably not more
than 35, and more preferably not more than 32. If the value (f)-(a)
is too large, the durability to cracking may be inadequate.
[0088] The value (a)+(b)+(c)+(d)+(e)+(f), as mentioned above, must
be set to from 370 to 460. The lower limit in this value is more
preferably at least 380, and even more preferably at least 390. The
upper limit in this value is more preferably not more than 440, and
even more preferably not more than 420. If the value
(a)+(b)+(c)+(d)+(e)+(f) is too large, the feel on impact may become
too hard; if it is too small, a sufficient initial velocity may not
be obtained on shots with a W#1.
[0089] As noted above, by optimizing the cross-sectional hardnesses
(a) to (f) of various cross-sectional areas of the solid core, a
high initial velocity on shots with a driver (W#1) can be obtained
and excessive spin receptivity on shots with a short iron is
suppressed, making it possible to achieve an excellent flight
performance--both on shots with a driver and on shots with a short
iron. In addition, a good feel on impact can also be obtained.
[0090] The diameter ratio between the first layer and the second
layer-covered sphere (first layer diameter/second layer-covered
sphere diameter), although not subject to any particular
limitation, is preferably from 0.20 to 0.70. The lower limit in
this diameter ratio is more preferably at least 0.30, and even more
preferably at least 0.40. The upper limit in this diameter ratio is
more preferably not more than 0.60, and even more preferably not
more than 0.50. If the diameter ratio is too large, a sufficient
initial velocity may not be obtained on shots with a W#1. On the
other hand, if the diameter ratio is too small, the spin rate on
shots with a W#1 may become too high.
[0091] The ratio between the volume of the second layer (the volume
of the second layer alone; that is, not including the first layer)
and the volume of the solid core (second layer volume/solid core
volume), although not subject to any particular limitation, is
preferably set to from 0.20 to 0.60. Here, the lower limit in the
volume ratio is more preferably at least 0.25, and even more
preferably at least 0.30. The upper limit in the volume ratio is
more preferably not more than 0.50, and even more preferably not
more than 0.40. If the volume ratio is too large, the spin rate on
shots with a W#1 may become too high. On the other hand, if the
volume ratio is too small, a sufficient initial velocity may not be
obtained on shots with a W#1.
[0092] In the multi-piece solid golf ball of the invention, a cover
of one, two or more layers is formed so as to encase the solid
core. In this invention, although not subject to any particular
limitation, a known cover material may be used as the material
which forms this cover. Illustrative examples include known
thermoplastic resins, ionomer resins, highly neutralized ionomer
resin compositions such as those described above, thermoplastic and
thermoset polyurethanes, and polyamide-type and polyester-type
thermoplastic elastomers. Conventional injection molding may be
advantageously used to form the cover.
[0093] When the above cover is relatively soft, in addition to a
distance-increasing effect, the spin performance on approach shots
is also increased, enabling both a good controllability and a good
distance to be achieved. When the cover is relatively hard, in
addition to a distance-increasing effect, a further reduction in
the spin rate can be achieved, enabling a considerable increase in
the distance.
[0094] In the invention, when the above cover is formed so as to be
relatively soft, of the above-described cover materials, the use
of, for example, ionomer resins, highly neutralized ionomer resin
compositions, thermoplastic polyurethanes and polyester-type
thermoplastic elastomers is preferred. In cases where the cover is
composed of a single layer, although not subject to any particular
limitation, it is preferable to set the thickness to from 0.5 to
2.0 mm, and it is preferable to set the cover material hardness,
expressed as the Shore D hardness, to from 30 to 57. As used
herein, "cover material hardness" refers to the hardness of the
cover material when molded into a sheet of a predetermined
thickness.
[0095] When the cover is composed of two or more layers, the
thickness of the inner cover layer, although not subject to any
particular limitation, may be set to preferably at least 0.5 mm,
more preferably at least 0.7 mm, even more preferably at least 0.9
mm, and most preferably at least 1.1 mm. The upper limit also is
not subject to any particular limitation, but may be set to
preferably not more than 3 mm, more preferably not more than 2.7
mm, even more preferably not more than 2.5 mm, and most preferably
not more than 2.3 mm. The material hardness of the inner cover
layer, expressed as the Shore D hardness, although not subject to
any particular limitation, may be set to preferably at least 51,
more preferably at least 53, even more preferably at least 55, and
most preferably at least 57. The upper limit, although not subject
to any particular limitation, may be set to preferably not more
than 70, more preferably not more than 67, and even more preferably
not more than 64.
[0096] The thickness of the outer cover layer, although not subject
to any particular limitation, may be set to preferably at least 0.3
mm, more preferably at least 0.5 mm, and even more preferably at
least 0.7 mm. The upper limit also is not subject to any particular
limitation, but may be set to preferably not more than 2 mm, more
preferably not more than 1.7 mm, even more preferably not more than
1.4 mm, and most preferably not more than 1.2 mm. The material
hardness of the outer cover layer, expressed as the Shore D
hardness, although not subject to any particular limitation, may be
set to preferably at least 30, more preferably at least 35, even
more preferably at least 40, and most preferably at least 45. The
upper limit, although not subject to any particular limitation, may
be set to preferably not more than 57, more preferably not more
than 56, and even more preferably not more than 55.
[0097] On the other hand, when the above cover is formed so as to
be relatively hard, it is preferable to use a thermoplastic resin
as the cover material, and is most preferable to use an ionomer
resin. In cases where the cover is composed of a single layer, it
is preferable to set the cover thickness to from 0.5 to 3.0 mm and
to set the cover material hardness, expressed as the Shore D
hardness, to from 58 to 70.
[0098] When the cover is composed of two or more layers, the
thickness of the inner cover layer, although not subject to any
particular limitation, is preferably at least 0.5 mm, more
preferably at least 0.7 mm, even more preferably at least 0.9 mm,
and most preferably at least 1.1 mm. The upper limit also is not
subject to any particular limitation, but is preferably not more
than 3 mm, more preferably not more than 2.5 mm, even more
preferably not more than 2 mm, and most preferably not more than
1.5 mm. The material hardness of the inner cover layer, expressed
as the Shore D hardness, although not subject to any particular
limitation, is preferably at least 30, more preferably at least 35,
even more preferably at least 40, and most preferably at least 45.
The upper limit, although not subject to any particular limitation,
is preferably not more than 58, more preferably not more than 56,
even more preferably not more than 54, and most preferably not more
than 52.
[0099] The thickness of the outer cover layer, although not subject
to any particular limitation, is to preferably at least 0.5 mm,
more preferably at least 0.7 mm, even more preferably at least 0.9
mm, and most preferably at least 1.1 mm. The upper limit also is
not subject to any particular limitation, but is preferably not
more than 3 mm, more preferably not more than 2.5 mm, even more
preferably not more than 2 mm, and most preferably not more than
1.5 mm. The material hardness of the outer cover layer, expressed
as the Shore D hardness, although not subject to any particular
limitation, is preferably at least 58, more preferably at least 59,
and even more preferably at least 60. The upper limit, although not
subject to any particular limitation, is preferably not more than
70, more preferably not more than 65, and even more preferably not
more than 63.
[0100] The diameter of the golf ball in which the above-described
core and cover are formed should accord with golf ball standards,
and is preferably not less than 42.67 mm. The upper limit, although
not subject to any particular limitation, may be set to preferably
not more than 44 mm, more preferably not more than 43.8 mm, even
more preferably not more than 43.5 mm, and most preferably not more
than 43 mm.
[0101] In the above range in the golf ball diameter, the deflection
of the ball as a whole when compressed under a final load of 1,275
N (130 kgf) from an initial load of 98 N (10 kgf) (which deflection
is also called the "product hardness"), although not subject to any
particular limitation, is preferably at least 2.0 mm, more
preferably at least 2.2 mm, and even more preferably at least 2.4
mm. The upper limit, although not subject to any particular
limitation, is preferably not more than 5.0 mm, more preferably not
more than 4.5 mm, even more preferably than 4.0 mm, and most
preferably not more than 3.5 mm. If the above deflection is too
large, a sufficient initial velocity may not be obtained on shots
with a W#1. On the other hand, if the deflection is too small, the
spin rate on shots with a W#1 may become too high.
[0102] In addition, the deflection of the ball as a whole when
compressed under a final load of 5,880 N (600 kgf) from an initial
load of 98 N (10 kgf), although not subject to any particular
limitation, is preferably at least 7.2 mm, more preferably at least
7.6 mm, and even more preferably at least 8 mm. The upper limit,
although not subject to any particular limitation, is preferably
not more than 14 mm, more preferably not more than 12 mm, and even
more preferably than 10 mm. If the above deflection is too large, a
sufficient initial velocity may not be obtained on shots with a
W#1. On the other hand, if the deflection is too small, the spin
rate on shots with a W#1 may become too high.
[0103] In addition, although not subject to any particular
limitation, the ratio between the deflection of the second
layer-covered sphere when compressed under a final load of 1,275 N
(130 kgf) from an initial load of 98 N (10 kgf) to the deflection
of the solid core when compressed under a final load of 1,275 N
(130 kgf) from an initial load of 98 N (10 kgf) (second
layer-covered sphere deflection/solid core deflection) is
preferably from 1.30 to 1.50. The lower limit in the above
deflection ratio is more preferably at least 1.35, and even more
preferably at least 1.40. If this deflection ratio is too large,
the spin rate on shots with a W#1 may become too high. On the other
hand, if this deflection ratio is too low, it may not be possible
to obtain a sufficient initial velocity on shots with a W#1.
[0104] Although not subject to any particular limitation, the ratio
between the deflection of the solid core when compressed under a
final load of 1,275 N (130 kgf) from an initial load of 98 N (10
kgf) to the deflection of the ball as a whole when compressed under
a final load of 1,275 N (130 kgf) from an initial load of 98 N (10
kgf) (solid core deflection/ball deflection) is preferably from
1.30 to 1.50. The lower limit in this deflection ratio is more
preferably at least 1.35, and even more preferably at least 1.38.
If this deflection ratio is too large, the feel of the ball on
impact may become too hard, whereas if the deflection ratio is too
small, the spin rate of the ball on shots with a W#1 may become too
high.
[0105] Moreover, although not subject to any particular limitation,
the ratio between the deflection of the ball as a whole when
compressed under a final load of 5,880 N (600 kgf) from an initial
load of 98 N (10 kgf) to the deflection of the ball as a whole when
compressed under a final load of 1,275 N (130 kgf) from an initial
load of 98 N (10 kgf) (600 kgf deflection/130 kgf deflection) is
preferably from 3.30 to 3.60. The lower limit in this deflection
ratio is more preferably at least 3.35, and even more preferably at
least 3.40. The upper limit in this deflection ratio is more
preferably not more than 3.55, and even more preferably not more
than 3.50. If this deflection ratio is too large, a sufficient
initial velocity may not be achieved on shots with a W#1. On the
other hand, if the deflection ratio is too small, the spin rate of
the ball on shots with a W#1 may become too high.
[0106] In the golf ball of the invention, in order to further
increase the aerodynamic properties and extend the distance
traveled by the ball, as in conventional golf balls, numerous
dimples may be formed on the surface of the cover. In this case,
the number of dimples formed on the ball surface, although not
subject to any particular limitation, is preferably at least 280,
more preferably at least 300, and even more preferably at least
320. The upper limit in the number of dimples, although not subject
to any particular limitation, may be set to preferably not more
than 400, more preferably not more than 380, and even more
preferably not more than 350. If the number of dimples is higher
than the above range, the trajectory of the ball may become low, as
a result of which a good distance may not be achieved. On the other
hand, if the number of dimples is lower than the above range, the
trajectory may become high, as a result of which an increased
distance may not be achieved.
[0107] The geometric arrangement of the dimples on the ball may be,
for example, octahedral or icosahedral. In addition, the dimple
shapes may be of one, two or more types suitably selected from
among not only circular shapes, but also various polygonal shapes,
such as square, hexagonal, pentagonal and triangular shapes, as
well as dewdrop shapes and oval shapes. The diameter (in a
polygonal shape, the length of the diagonal), although not subject
to any particular limitation, is preferably set to from 2.5 to 6.5
mm. The depth also, although not subject to any particular
limitation, is preferably set to from 0.08 to 0.30 mm.
[0108] The value V.sub.0, defined as the spatial volume of a dimple
below the flat plane circumscribed by the dimple edge, divided by
the volume of the cylinder whose base is the flat plane and whose
height is the maximum depth of the dimple from the base, although
not subject to any particular limitation, may be set to from 0.35
to 0.80 in this invention.
[0109] The ratio SR of the sum of individual dimple surface areas,
each defined by the flat plane circumscribed by the edge of a
dimple, with respect to the surface area of the ball sphere were
the ball surface to have no dimples thereon, although not subject
to any particular limitation, is preferably set to from 60 to 90%
from the standpoint of reducing aerodynamic resistance. This SR can
be elevated by increasing the number of dimples formed, and also by
intermingling dimples of a plurality of types having different
diameters or by having the dimple shapes be such that the distance
between neighboring dimples (land width) becomes substantially
0.
[0110] The ratio VR of the sum of the spatial volumes of individual
dimples formed below the flat plane circumscribed by the edge of a
dimple with respect to the surface area of the ball sphere were the
ball surface to have no dimples thereon, although not subject to
any particular limitation, is preferably set to from 0.6 to 1 in
this invention.
[0111] In the invention, by setting the above V.sub.0, SR and VR
values in the foregoing ranges, the aerodynamic resistance is
reduced, in addition to which a trajectory enabling a good distance
to be achieved readily arises and the flight performance can be
enhanced.
[0112] Moreover, the ball surface may be subjected to various types
of treatment, such as surface preparation, stamping and painting,
in order to enhance the design and durability of the golf ball.
[0113] As explained above, in the present invention, by optimizing
the hardness relationships among the various layers of the core
having a multilayer structure, a high initial velocity can be
obtained when the golf ball is hit with a driver (W#1), and
excessive spin receptivity on shots with a short iron is
suppressed. As a result, an excellent flight performance is
achieved--both on shots with a driver and on shots with a short
iron. In addition, a good feel on impact can also be obtained.
EXAMPLES
[0114] Examples of the invention and Comparative Examples are given
below by way of illustration, and not by way of limitation.
Examples 1 to 6, Comparative Examples 1 to 10
[0115] The rubber compositions shown in Table 1 below were
prepared, then molded and vulcanized at 155.degree. C. for 15
minutes to produce a spherical molding as the first layer. However,
in Example 2, a spherical molding was obtained by injection molding
using the resin material shown as No. 1 in Table 3.
[0116] With regard to the second layer, in the respective examples,
first a pair of hemispherical half-cups was produced by using
mixing rolls to knead the rubber composition shown in Table 2, then
carrying out primary vulcanization (semi-vulcanization) at
130.degree. C. for 6 minutes. Next, the first layer was enclosed
within the resulting half-cups and the second layer was formed by
secondary vulcanization (complete vulcanization) in a mold at
155.degree. C. for 15 minutes, thereby producing a second
layer-covered sphere.
[0117] The third layer was formed by the same method as the second
layer. More specifically, the rubber composition shown in Table 2
was kneaded using mixing rolls, then subjected to primary
vulcanization (semi-vulcanization) at 130.degree. C. for 6 minutes,
thereby producing a pair of hemispherical half-cups. Next, the
second layer-covered sphere was enclosed within the resulting
half-cups and the third layer was formed by secondary vulcanization
(complete vulcanization) in a mold at 155.degree. C. for 15
minutes, thereby producing a solid core having a three-layer
structure. In Comparative Example 10, the third layer was formed by
injecting the resin material shown as No. 2 in Table 3 over the
second layer.
[0118] Next, the resin material (cover material) having the
composition shown in Table 3 was injection-molded over the
respective solid cores, thereby forming in each case both an inner
cover layer (intermediate layer) and an outer cover layer having on
the surface dimples of the same shape, arrangement and number. This
gave multi-piece solid golf balls composed of a solid core having a
three-layer structure encased by a two-layer cover. The dimples
shown in FIG. 1 were formed at this time on the cover surface.
Details on the dimples are shown in Table 4.
TABLE-US-00001 TABLE 1 A B C D E F G Polybutadiene rubber 100 100
100 100 100 100 100 Zinc acrylate 18.0 15.0 26.0 35.5 32.0 40.0
20.5 Peroxide 3 3 3 3 3 3 3 Zinc oxide 5 5 5 5 5 5 5 Barium sulfate
19.1 20.4 15.6 11.3 12.9 9.3 18 Antioxidant 0.1 0.1 0.1 0.1 0.1 0.1
0.1 Zinc salt of 0.4 0.4 0.4 0.4 0.4 0.4 0.4 pentachlorothiophenol
*Numbers in the table indicate parts by weight.
TABLE-US-00002 TABLE 2 H I J K L M N O P Q Polybutadiene rubber 100
100 100 100 100 100 100 100 100 100 Zinc acrylate 29.5 29.5 36.0
22.0 36.0 32.0 34.0 30.5 35.5 27.5 Peroxide 3 3 3 3 3 3 3 3 3 3
Zinc oxide 5 5 5 5 5 5 5 5 5 5 Barium sulfate 14 21.4 11.1 17.3
36.4 12.9 12 21.2 11.6 14.9 Antioxidant 0.1 0.1 0.1 0.1 0.1 0.1 0.1
0.1 0.1 0.1 Zinc salt of 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0 0 0.4
pentachlorothiophenol *Numbers in the table indicate parts by
weight.
[0119] Details on the materials in Tables 1 and 2 are given below.
[0120] Polybutadiene rubber: [0121] Available as "BR 730" from JSR
Corporation. A polybutadiene rubber obtained using a neodymium
catalyst; cis-1,4 bond content, 96 wt %; Mooney viscosity, 55;
molecular weight distribution, 3. [0122] Zinc acrylate: Available
from Nihon Jyoryu Kogyo Co., Ltd. [0123] Peroxide: Available as
"Perhexa C-40" from NOF Corporation.
1,1-Bis(t-butylperoxy)cyclo-hexane diluted to 40% with an inorganic
filler. Half-life at 155.degree. C., about 50 seconds. [0124] Zinc
oxide: Available from Sakai Chemical Co., Ltd. [0125] Barium
sulfate: Available as "Precipitated Barium Sulfate 100" from Sakai
Chemical Co., Ltd. [0126] Antioxidant: Available as "Nocrac NS-6"
from Ouchi Shinko Chemical Industry Co., Ltd.
TABLE-US-00003 [0126] TABLE 3 No. 1 No. 2 No. 3 No. 4 No. 5 Surlyn
6320 60 Nucrel N035C 40 Himilan 1605 50 Himilan 1706 35 Himilan
1557 15 50 Himilan 1601 50 Pandex T8290 25 Pandex T8295 75
Magnesium stearate 69 0.6 Magnesium oxide 0.8 Trimethylolpropane
1.1 Polyisocyanate 9 compound Hytrel 3046 100 15 Hytrel 4001 15
Titanium oxide 3.5 2.4 Polyethylene wax 1.5 *Numbers in the table
indicate parts by weight.
[0127] Details on the materials in Table 3 are given below. [0128]
Surlyn: An ionomer resin available from E.I. DuPont de Nemours and
Co. [0129] Nucrel N035C: An ethylene-methacrylic acid-ester
terpolymer available from DuPont-Mitsui Polychemicals Co., Ltd.
[0130] Himilan: Ionomer resins available from DuPont-Mitsui
Polychemicals Co., Ltd. [0131] Dynaron 6100P: A hydrogenated
polymer available from JSR Corporation. [0132] Pandex: MDI-PTMG
type thermoplastic polyurethanes available from DIC Bayer Polymer
[0133] Magnesium stearate: Available as "Magnesium Stearate G" from
NOF Corporation. [0134] Magnesium oxide: Available as "Kyowamag
MF150" from Kyowa Chemical Industry Co., Ltd. [0135] Behenic acid:
Available as "NAA-222S" from NOF Corporation [0136] Calcium
hydroxide: Available as "CLS-B" from Shiraishi Calcium Kaisha, Ltd.
[0137] Polyisocyanate compound: 4,4'-Diphenylmethane diisocyanate
[0138] Hytrel: Thermoplastic polyester elastomers available from
DuPont-Toray Co., Ltd. [0139] Titanium oxide: Available as "Tipaque
R550" from Ishihara Sangyo Kaisha, Ltd. [0140] Polyethylene wax:
Available as "Sanwax 161P" from Sanyo Chemical Industries, Ltd.
TABLE-US-00004 [0140] TABLE 4 Number of Diameter Depth No. dimples
(mm) (mm) V.sub.0 SR VR 1 18 4.6 0.13 0.53 81.6 0.819 2 234 4.5
0.14 0.53 3 42 3.7 0.14 0.53 4 12 3.3 0.13 0.53 5 6 3.0 0.16 0.53 6
14 3.5 0.14 0.53 Total 326
Dimple Definitions
[0141] Diameter: Diameter of flat plane circumscribed by edge of
dimple. [0142] Depth: Maximum depth of dimple from flat plane
circumscribed by edge of dimple. [0143] V.sub.0: Spatial volume of
dimple below flat plane circumscribed by dimple edge, divided by
volume of cylinder whose base is the flat plane and whose height is
the maximum depth of dimple from the base. [0144] SR: Sum of
individual dimple surface areas, each defined by the flat plane
circumscribed by the edge of a dimple, as a percentage of surface
area of hypothetical sphere were the ball to have no dimples on the
surface thereof (units: %). [0145] VR: Sum of spatial volumes of
individual dimples formed below flat plane circumscribed by the
edge of the dimple, as a percentage of volume of hypothetical
sphere were the ball to have no dimples on the surface thereof
(units: %).
[0146] The following properties were investigated for the golf
balls obtained. Also, flight tests were carried out by the
following methods, in addition to which the feel on impact was
evaluated. The results are shown in Tables 5 to 8.
Cross-Sectional Hardnesses and Surface Hardness of Solid Core
(JIS-C Hardness)
[0147] To determine the center and cross-sectional hardnesses of
the solid core, the core was cut into two through the center
thereof and the cut face was rendered planar, following which a
durometer indenter was pressed perpendicularly against the cut face
at predetermined positions and measurement carried out. The
hardnesses are indicated as JIS-C hardness values.
[0148] To determine the surface hardness of the solid core, the
durometer was set perpendicular to the surface portion of the
spherical core and the hardness was measured based on the JIS-C
hardness standard. The hardnesses are indicated as JIS-C hardness
values. The measured values were obtained after holding the solid
cores isothermally at 23.degree. C.
[0149] The specific places where measurement of the cross-sectional
hardness and the surface hardness was carried out were as
follows.
(a) center of core (b) first layer 1 mm inside interface between
first layer and second layer (c) second layer 1 mm outside
interface between first layer and second layer (d) second layer 1
mm inside interface between second layer and third layer (e) third
layer 1 mm outside interface between second layer and third layer
(f) surface of third layer
Material Hardnesses of Intermediate Layer and Cover (Shore D
Hardnesses)
[0150] The material hardness of the cover was a value measured with
a type D durometer according to ASTM D2240 for measurement samples
of the cover material prepared in the form of 6 mm thick
sheets.
Deflection
[0151] Using a model 4204 test system manufacturing by Instron
Corporation, the balls, the second layer-covered spheres and the
solid cores were each compressed at a rate of 10 mm/min, and the
deflection when compressed under a final load of 1,275 N (130 kgf)
from an initial load of 98 N (10 kgf) was measured. In addition,
the deflection when compressed under a final load of 5,880 N (600
kgf) from an initial load of 98 N (10 kgf) was similarly
measured.
Initial Velocity of Ball
[0152] The initial velocity was measured using an initial velocity
measuring apparatus of the same type as the USGA drum rotation-type
initial velocity instrument approved by the R&A. The balls were
held isothermally at a temperature of 23.+-.1.degree. C. for at
least 3 hours, then tested in a room temperature (23.+-.2.degree.
C.) chamber. Ten balls were each hit twice, and the time taken for
the balls to traverse a distance of 6.28 ft (1.91 m) was measured
and used to compute the initial velocity.
Distance with W#1
[0153] Each ball was hit ten times at a head speed (HS) of 50 m/s
with a Tour Stage X-Drive (loft angle, 10.5.degree.) driver (W#1),
manufactured by Bridgestone Sports Co., Ltd., mounted on a golf
swing robot, and the spin rate (rpm) and total distance (m) were
measured. The initial velocity was measured using a high-speed
camera. The performance was rated according to the following
criteria.
[0154] Good: 253 m or more
[0155] NG: less than 253 m
Distance with I#8
[0156] Each ball was hit ten times at a head speed (HS) of 40 m/s
with a Tour Stage X-BLADE (loft angle, 36.degree.) number eight
iron (I#8), manufactured by Bridgestone Sports Co., Ltd., mounted
on a golf swing robot, and the spin rate (rpm) and carry (m) were
measured. The initial velocity was measured using a high-speed
camera. The performance was rated according to the following
criteria.
[0157] Good: 138 m or more
[0158] NG: less than 138 m
Feel
[0159] The feel of the ball when hit with a driver (W#1) at a head
speed (HS) of 40 to 50 m/s was rated by three top amateur golfers
according to the following criteria.
[0160] Good: good feel
[0161] NG: too hard or too soft
TABLE-US-00005 TABLE 5 Example 1 2 3 4 5 6 First Material A No. 1 B
A A A layer Specific gravity 1.16 1.07 1.16 1.16 1.16 1.16 Diameter
(mm) 12.0 12.0 12.0 19.0 12.0 12.0 Volume (cm.sup.3) 0.9 0.9 0.9
3.6 0.9 0.9 Weight (g) 1.0 1.0 1.0 4.2 1.0 1.0 Cross-sectional 52
49 45 52 52 52 hardness (JIS-C) (a) Cross-sectional 56 49 48 58 56
56 hardness (JIS-C) (b) Second Material H H H H H I layer Specific
gravity 1.16 1.16 1.16 1.16 1.16 1.20 Diameter (mm) 28.0 28.0 28.0
28.0 32.0 28.0 Volume (cm.sup.3) 10.6 10.6 10.6 7.9 16.2 10.6
Weight (g) 12.3 12.3 12.3 9.2 18.8 12.7 Thickness (mm) 8.0 8.0 9.0
9.0 9.0 9.0 Deflection (mm) 4.7 5.0 5.1 5.2 4.5 4.7 Cross-sectional
69 69 69 69 69 69 hardness (JIS-C) (c) Cross-sectional 78 78 78 78
79 78 hardness (JIS-C) (d) Third Material M M M N M O layer
Specific gravity 1.16 1.16 1.16 1.16 1.16 1.20 Diameter (mm) 38.5
38.5 38.5 38.5 38.5 37.7 Volume (cm.sup.3) 18.4 18.4 18.4 18.4 12.7
16.6 Weight (g) 21.3 21.3 21.3 21.3 14.8 19.9 Thickness (mm) 5.3
5.3 5.3 5.3 3.3 4.9 Deflection (mm) 3.3 3.4 3.5 3.5 3.4 3.3
Cross-sectional 73 73 73 74 73 73 hardness (JIS-C) (e) Surface
hardness (f) 83 83 83 85 83 83 (JIS-C) Hardness (b) - (c) (JIS-C)
-13 -20 -21 -11 -13 -13 relationship (e) - (d) (JIS-C) -5 -5 -5 -4
-6 -5 (a) + (b) + (c) + (d) + 411 401 396 416 412 411 (e) + (f)
(JIS-C) (f) - (a) (JIS-C) 31 34 38 33 31 31 Diameter First
layer/second 0.43 0.43 0.43 0.68 0.38 0.43 ratio layer-covered
sphere Volume Second layer/solid 0.35 0.35 0.35 0.26 0.54 0.38
ratio core
TABLE-US-00006 TABLE 6 Comparative Example 1 2 3 4 5 6 7 8 9 10
First Material C D D A E B F G F A layer Specific gravity 1.16 1.16
1.16 1.16 1.16 1.16 1.16 1.16 1.16 1.16 Diameter (mm) 28.6 28.6
38.5 25.0 12.0 12.0 12.0 12.0 12.0 12.0 Volume (cm.sup.3) 12.2 12.2
29.9 8.2 0.9 0.9 0.9 0.9 0.9 0.9 Weight (g) 14.2 14.2 34.6 9.5 1.0
1.0 1.0 1.0 1.0 1.0 Cross-sectional 62 68 68 52 70 45 81 56 81 52
hardness (JIS-C) (a) Cross-sectional 72 82 87 60 75 48 86 61 86 56
hardness (JIS-C) (b) Second Material H J K K K H L layer Specific
gravity 1.16 1.16 1.16 1.16 1.16 1.16 1.29 Diameter (mm) 30.0 28.0
28.0 28.0 28.0 28.0 33.0 Volume (cm.sup.3) 6.0 10.6 10.6 10.6 10.6
10.6 17.9 Weight (g) 6.9 12.3 12.3 12.3 12.3 12.3 23.1 Thickness
(mm) 2.5 8.0 8.0 8.0 8.0 8.0 10.5 Deflection (mm) 5.6 3.4 5.9 4.7
5.5 3.6 3.9 Cross-sectional 69 77 62 62 62 69 77 hardness (JIS-C)
(c) Cross-sectional 78 85 68 68 68 78 85 hardness (JIS-C) (d) Third
Material M M N P Q M M M No. 2 layer Specific gravity 1.16 1.16
1.16 1.16 1.16 1.16 1.16 1.16 0.95 Diameter (mm) 38.5 38.5 38.5
38.5 38.5 38.5 38.5 38.5 38.5 Volume (cm.sup.3) 17.6 17.6 15.7 18.4
18.4 18.4 18.4 18.4 11.1 Weight (g) 20.4 20.4 18.3 21.3 21.3 21.3
21.3 21.3 10.5 Thickness (mm) 5.0 19.3 4.3 5.3 5.3 5.3 5.3 5.3 2.8
Deflection (mm) 3.2 2.9 3.0 3.8 2.8 4.4 3.5 3.7 3.0 3.0
Cross-sectional 73 73 74 77 67 73 73 73 82 hardness (JIS-C) (e)
Surface hardness (f) 83 83 85 89 77 83 83 83 82 (JIS-C) Hardness
(b) - (c) (JIS-C) -9 -2 -14 24 -1 17 -21 relationship (e) - (d)
(JIS-C) -4 -8 -1 5 5 -5 3 (a) + (b) + (c) + (d) + 418 473 367 453
403 470 434 (e) + (f) (JIS-C) (f) - (a) (JIS-C) 21 15 19 33 19 32 2
27 2 30 Diameter First layer/second 0.83 0.43 0.43 0.43 0.43 0.43
0.36 ratio layer-covered sphere Volume Second layer/solid 0.20 0.35
0.35 0.35 0.35 0.35 0.60 ratio core
TABLE-US-00007 TABLE 7 Example 1 2 3 4 5 6 Inter-mediate layer
Material No. 3 No. 3 No. 3 No. 3 No. 3 No. 2 Material hardness 62
62 62 62 62 51 (Shore D) Specific gravity 0.95 0.95 0.95 0.95 0.95
0.95 Diameter (mm) 41.1 41.1 41.1 41.1 41.1 40.2 Volume (mm.sup.3)
6.5 6.5 6.5 6.5 6.5 6.0 Weight (g) 6.1 6.1 6.1 6.1 6.1 5.7
Thickness (mm) 1.3 1.3 1.3 1.3 1.3 1.3 Cover Material No. 4 No. 4
No. 4 No. 4 No. 4 No. 5 Material hardness 54 54 54 54 54 60 (Shore
D) Specific gravity 1.15 1.15 1.15 1.15 1.15 0.97 Volume (mm.sup.3)
3.9 3.9 3.9 3.9 3.9 6.2 Weight (g) 4.4 4.4 4.4 4.4 4.4 6.0
Thickness (mm) 0.8 0.8 0.8 0.8 0.8 1.3 Ball Number of dimples 326
326 326 326 326 326 Diameter (mm) 42.7 42.7 42.7 42.7 42.7 42.7
Weight (g) 45.3 45.3 45.3 45.3 45.3 45.4 Deflection 2.40 2.42 2.43
2.40 2.43 2.35 (10-130 kgf) (mm) Deflection 8.23 8.33 8.36 8.32
8.26 8.05 (10-600 kgf) (mm) Initial velocity 77.3 77.3 77.3 77.2
77.3 77.4 (m/s) Deflection Solid core/ball 1.38 1.40 1.44 1.46 1.40
1.40 ratios (10-130 kgf) Second layer- 1.42 1.47 1.46 1.49 1.32
1.42 covered sphere/solid core (10-130 kgf) Ball 3.43 3.44 3.44
3.47 3.40 3.43 (600 kgf/130 kgf) W#1 Initial velocity 73.4 73.2
73.1 73.1 73.5 73.5 HS50 (m/s) Spin rate (rpm) 2750 2695 2643 2600
2793 2643 Total distance (m) 254.7 254.4 254.4 254.2 255.0 255.8
Performance rating good good good good good good I#8 Initial
velocity 51.0 50.9 50.9 50.8 51.0 51.0 HS40 (m/s) Spin rate (rpm)
7470 7422 7368 7400 7458 7250 Carry (m) 138.9 139.3 139.8 139.4
139.2 141.2 Performance rating good good good good good good Feel
good good good good good good
TABLE-US-00008 TABLE 8 Comparative Example 1 2 3 4 5 6 7 8 9 10
Inter-mediate layer Material No. 3 No. 3 No. 3 No. 3 No. 3 No. 3
No. 3 No. 3 No. 3 No. 3 Material hardness 62 62 62 62 62 62 62 62
62 62 (Shore D) Specific gravity 0.95 0.95 0.95 0.95 0.95 0.95 0.95
0.95 0.95 0.95 Diameter (mm) 41.1 41.1 41.1 41.1 41.1 41.1 41.1
41.1 41.1 41.1 Volume (mm.sup.3) 6.5 6.5 6.5 6.5 6.5 6.5 6.5 6.5
6.5 6.5 Weight (g) 6.1 6.1 6.1 6.1 6.1 6.1 6.1 6.1 6.1 6.1
Thickness (mm) 1.3 1.3 20.6 1.3 1.3 1.3 1.3 1.3 1.3 1.3 Cover
Material No. 4 No. 4 No. 4 No. 4 No. 4 No. 4 No. 4 No. 4 No. 4 No.
4 Material hardness 54 54 54 54 54 54 54 54 54 54 (Shore D)
Specific gravity 1.15 1.15 1.15 1.15 1.15 1.15 1.15 1.15 1.15 1.15
Volume (mm.sup.3) 3.9 3.9 3.9 3.9 3.9 3.9 3.9 3.9 3.9 3.9 Weight
(g) 4.4 4.4 4.4 4.4 4.4 4.4 4.4 4.4 4.4 4.4 Thickness (mm) 0.8 0.8
0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 Ball Number of dimples 326 326 326
326 326 326 326 326 326 326 Diameter (mm) 42.7 42.7 42.7 42.7 42.7
42.7 42.7 42.7 42.7 42.7 Weight (g) 45.3 45.3 45.3 45.3 45.3 45.3
45.3 45.3 45.3 45.3 Deflection 2.40 2.30 2.40 2.50 2.20 2.70 2.49
2.54 2.37 2.30 (10-130 kgf) (mm) Deflection 8.15 7.80 8.46 8.90
7.30 9.30 9.00 9.25 8.07 8.10 (10-600 kgf) (mm) Initial velocity
77.3 77.3 77.3 77.1 77.3 77.0 77.2 77.2 77.3 77.0 (m/s) Deflection
Solid core/ball 1.33 1.26 1.25 1.52 1.27 1.63 1.41 1.46 1.27 1.30
ratios (10-130 kgf) Second layer- 1.47 1.21 1.34 1.34 1.49 1.20
1.30 covered sphere/solid core (10-130 kgf) Ball 3.40 3.39 3.53
3.56 3.32 3.44 3.61 3.64 6.41 3.52 (600 kgf/130 kgf) W#1 Initial
velocity 72.2 73.7 72.5 72.0 73.7 72.0 72.0 71.6 73.6 72.8 HS50
(m/s) Spin rate (rpm) 2500 2875 2550 2555 2890 2605 2558 2265 2858
2885 Total distance (m) 251.2 255.5 252.2 250.1 255.4 249.9 250.2
250.0 255.2 251.8 Performance rating NG good NG NG good NG NG NG
good NG I#8 Initial velocity 50.7 51.1 50.8 50.6 51.2 50.5 50.5
50.3 51.0 51.1 HS40 (m/s) Spin rate (rpm) 7210 7720 7380 7220 7760
7110 7154 6784 7732 7670 Carry (m) 141.0 136.6 139.5 140.8 136.5
141.6 141.2 144.4 136.4 137.1 Performance rating good NG good good
NG good good good NG NG Feel good good good good NG good good good
good good
[0162] In Comparative Example 1 in which the core was composed of
two layers, the initial velocity with a driver (W#1) was
inadequate, as a result of which a good distance was not
achieved.
[0163] In Comparative Example 2 in which the core was composed of
two layers, the spin rate with an iron (I#8) was high, as a result
of which a good distance was not achieved.
[0164] In Comparative Example 3 in which the core was composed of a
single layer, the initial velocity with a driver (W#1) was
inadequate, as a result of which a good distance was not
achieved.
[0165] In Comparative Example 4 in which the first layer of the
core had a large diameter, the initial velocity with a driver (W#1)
was inadequate, as a result of which a good distance was not
achieved.
[0166] In Comparative Example 5, because the value
(a)+(b)+(c)+(d)+(e)+(f) was large, the ball at a poor feel on
impact.
[0167] In Comparative Example 6, because the value
(a)+(b)+(c)+(d)+(e)+(f) was small, the initial velocity with a
driver (W#1) was low and so a sufficient distance was not
achieved.
[0168] In Comparative Example 7, because the value (b)-(c) and the
value (e)-(d) exceeded 0, the initial velocity with a driver (W#1)
was low, as a result of which a good distance was not achieved.
[0169] In Comparative Example 8, because the value (e)-(d) exceeded
0, the initial velocity with a driver (W#1) was low, as a result of
which a good distance was not achieved.
[0170] In Comparative Example 9, because the value (b)-(c) exceeded
0, the spin rate with an iron (I#8) was high, as a result of which
a good distance was not achieved.
[0171] In Comparative Example 10, because the third layer of the
core was formed using a thermoplastic resin, a good distance was
not achieved with a driver (W#1).
* * * * *