U.S. patent application number 17/211982 was filed with the patent office on 2021-11-11 for multi-piece solid golf ball.
This patent application is currently assigned to Bridgestone Sports Co., Ltd.. The applicant listed for this patent is Bridgestone Sports Co., Ltd.. Invention is credited to Hideo WATANABE.
Application Number | 20210346764 17/211982 |
Document ID | / |
Family ID | 1000005524520 |
Filed Date | 2021-11-11 |
United States Patent
Application |
20210346764 |
Kind Code |
A1 |
WATANABE; Hideo |
November 11, 2021 |
MULTI-PIECE SOLID GOLF BALL
Abstract
In a golf ball having a core, envelope layer, intermediate layer
and cover, the (core diameter)/(ball diameter) value falls within a
particular range, the core has a specific hardness profile, and the
Shore C hardness relationships among the core center and surface
hardnesses and the surface hardnesses of the envelope layer-encased
sphere, intermediate layer-encased sphere and ball satisfy the
following conditions: (1) core surface hardness<surface hardness
of envelope layer-encased sphere<surface hardness of
intermediate layer-encased sphere>ball surface hardness, (2)
(surface hardness of envelope layer-encased sphere)-(core center
hardness).gtoreq.28. Also, the intermediate layer and cover have
respective thicknesses which satisfy the condition: (3) cover
thickness<intermediate layer thickness. This ball enables
mid-level and skilled amateur golfers to achieve superior distances
on driver shots and on iron shots, and moreover has a soft yet good
feel at impact.
Inventors: |
WATANABE; Hideo;
(Chichibushi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Bridgestone Sports Co., Ltd. |
Tokyo |
|
JP |
|
|
Assignee: |
Bridgestone Sports Co.,
Ltd.
Tokyo
JP
|
Family ID: |
1000005524520 |
Appl. No.: |
17/211982 |
Filed: |
March 25, 2021 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A63B 37/0045 20130101;
A63B 37/00922 20200801; A63B 37/0065 20130101; A63B 37/0063
20130101; A63B 37/0064 20130101; A63B 37/0076 20130101; A63B
37/00222 20200801 |
International
Class: |
A63B 37/00 20060101
A63B037/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 7, 2020 |
JP |
2020-081975 |
Claims
1. A multi-piece solid golf ball comprising a core, an envelope
layer, an intermediate layer and a cover, the core being formed of
a rubber composition as one or more layer, the envelope layer being
formed of a resin material as one or more layer and the
intermediate layer and the cover each being formed of a resin
material as a single layer, wherein the core has a diameter of from
35.1 to 41.3 mm; the core has a hardness profile in which, letting
Cc be the Shore C hardness at a center of the core, Cm be the Shore
C hardness at a midpoint M between the core center and a surface of
the core, Cm-2, Cm-4 and Cm-6 be the respective Shore C hardnesses
at positions 2 mm, 4 mm and 6 mm inward from the midpoint M, Cm+2,
Cm+4 and Cm+6 be the respective Shore C hardnesses at positions 2
mm, 4 mm and 6 mm outward from the midpoint M and Cs be the Shore C
hardness at the core surface and defining the surface areas A to F
as follows surface area A: 1/2.times.2.times.(Cm-4-Cm-6) surface
area B: 1/2.times.2.times.(Cm-2-Cm-4) surface area C:
1/2.times.2.times.(Cm-Cm-2) surface area D:
1/2.times.2.times.(Cm+2-Cm) surface area E:
1/2.times.2.times.(Cm+4-Cm+2) surface area F:
1/2.times.2.times.(Cm+6-Cm+4), (surface area E+surface area
F)-(surface area A+surface area B) has a value of 4.0 or more and
Cs-Cc has a value of 20 or more; the center hardness of the core,
surface hardness of the core, surface hardness of the sphere
obtained by encasing the core with the envelope layer (envelope
layer-encased sphere), surface hardness of the sphere obtained by
encasing the envelope layer-encased sphere with the intermediate
layer (intermediate layer-encased sphere) and surface hardness of
the ball have Shore C hardness relationships therebetween which
satisfy the following conditions: (1) core surface
hardness<surface hardness of envelope layer-encased
sphere<surface hardness of intermediate layer-encased
sphere>ball surface hardness, and (2) (surface hardness of
envelope layer-encased sphere)-(center hardness of core).gtoreq.28;
and the intermediate layer and the cover have respective
thicknesses which satisfy the following condition: (3) cover
thickness<intermediate layer thickness.
2. The golf ball of claim 1, wherein surface areas A to F in the
core hardness profile satisfy the condition (surface area D+surface
area E+surface area F)-(surface area A+surface area B+surface area
C).gtoreq.1.0.
3. The golf bell of claim 1, wherein surface areas A to F in the
core hardness profile satisfy the condition (surface area E+surface
area F)-(surface area A+surface area B+surface area C)>0.
4. The golf ball of claim 1, wherein surface areas A to F in the
core hardness profile satisfy the conditions surface area
D<surface area E<surface area F, and surface area
A<surface area C.
5. The golf ball of claim 1, wherein the envelope layer and the
intermediate layer have respective thicknesses which satisfy the
condition intermediate layer thickness.ltoreq.envelope layer
thickness.
6. The golf ball of claim 1, wherein the ratio (core
diameter)/(ball diameter) has a value of at least 0.825.
7. The golf ball of claim 1, wherein the envelope layer has a
higher material hardness than the cover.
8. The golf ball of claim 1, wherein the core center hardness (Cc)
is not more than 60.
9. The golf bell of claim 1, wherein (surface hardness of envelope
layer-encased sphere)-(center hardness of core) in formula (2) has
a value of at least 30.
10. The golf ball of claim 1, wherein the core has a deflection
when compressed under a final load of 1,275 N (130 kgf) from an
initial load of 98 N (10 kgf) of at least 3.9 mm, and the ball has
a deflection when compressed under a final load of 1,275 N (130
kgf) from an initial load of 98 N (10 kgf) of at least 2.8 mm.
11. The golf ball of claim 1, wherein a coating layer is formed on
a surface of the cover to and the coating layer and the cover have
respective material hardnesses such that the value obtained by
subtracting the material hardness of the coating layer from the
material hardness of the cover is, on the Shore C hardness scale,
at least -20 and not more than 25.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This non-provisional application claims priority under 35
U.S.C. .sctn. 119(a) on Patent Application No. 2020-081975 filed in
Japan on May 7, 2020, the entire contents of which are hereby
incorporated by reference.
TECHNICAL FIELD
[0002] The present invention relates to a multi-piece solid golf
ball composed of four or more layers that include a core, an
envelope layer, an intermediate layer and a cover.
BACKGROUND ART
[0003] Many innovations have been made in designing golf balls with
a multilayer construction, and numerous balls that satisfy the
needs of not only professional golfers, but also skilled and
mid-level amateur golfers, have been developed to date. For
example, functional multi-piece solid golf balls in which the
surface hardnesses of the respective layers--i.e., the core,
envelope layer, intermediate layer and cover (outermost
layer)--have been optimized are in wide use. Also, a number of
technical disclosures have been published that focus on the
hardness profile of the core which accounts for most of the ball
volume and, by creating various core interior hardness designs,
provide high-performance golf balls for professional golfers and
mid-level to skilled amateur golfers.
[0004] Examples of such literature include JP-A H09-248351, JP-A
2006-326301, JP-A 2007-319667, JP-A 2012-071163, JP-A 2007-330789,
JP-A 2008-068077, JP-A 2009-095364, JP-A 2016-101254 and JP-A
2016-116627. These disclosures, all of which relate to golf balls
having a multilayer construction of four or more layers, focus on,
for example, the surface hardnesses of the respective
layers-namely, the core, the envelope layer, the intermediate layer
and the cover (outermost layer), the relationship between the ball
diameter and the core diameter, and the core hardness profile.
[0005] However, there remains room for improvement in optimizing
the hardness profile of the core and the thickness relationship
among the layers in these prior-art golf balls. That is, these golf
balls, even if they are able to retain a good distance on driver (W
#1) shots when hit by mid-level to skilled amateur golfers whose
head speeds are not as fast as those of professionals, often fall
short in terms of their distance on iron shots. Moreover, with some
of these prior-art golf balls, when an attempt is made to obtain a
superior distance performance not only on driver shots but also on
iron shots, a sufficiently high spin rate on approach shots cannot
be achieved, resulting in a ball that does not have a high
playability or that has a poor feel at impact on full shots.
Accordingly, there exists a desire for the development of a golf
ball for mid-level and skilled amateur golfers which, along with
having an even further improved flight performance and a good feel,
also has a high playability in the short game.
SUMMARY OF THE INVENTION
[0006] It is therefore an object of the present invention to
provide a golf ball which, when used by mid-level and skilled
amateur golfers whose head speeds are not as fast as those of
professional golfers, can retain a satisfactory distance on driver
shots and also is able to achieve a superior distance on iron
shots, has an excellent spin performance on approach shots and is
thus optimal in the short game, and moreover has a soft yet good
feel at impact on all shots.
[0007] As a result of extensive investigations, I have discovered
that, in a golf ball having a core, an envelope layer, an
intermediate layer and a cover, certain desirable effects can be
achieved by forming the cover so as to be soft using preferably a
urethane resin material as the cover material, by forming the
intermediate layer so as to be harder than the cover, by forming
the envelope layer as one or a plurality of layers that are softer
than the intermediate layer and harder than the surface of the
rubber core and by, in the core hardness profile and hardness
gradient designs, determining point-to-point hardness gradients at
positions 2 mm apart inward and outward from the core radius
midpoint and optimizing these hardness gradients for the overall
core. Namely, the spin rate of the golf ball on full shots can be
held down more than in conventional golf balls, resulting in an
improved distance. In particular, on full shots with a driver (W
#1) and with an iron, the ball does not incur excessive spin,
enabling a good distance to be achieved, yet the ball is receptive
to spin in the short game. In addition, the ball can be imparted
with a soft feel at impact. I have found in particular that, for
the ordinary mid-level or skilled amateur golfer, a superior
distance can be achieved even on iron shots while retaining a good
distance on driver (W #1) shots, in addition to which the spin
performance on approach shots can be maintained at a high level,
thus achieving a superior golf ball that has a high playability.
Here, "mid-level or skilled amateur" corresponds to amateur golfers
having handicaps of about 15 or less, with mid-level amateurs
having a handicap of from 10 to 15 and skilled amateurs having a
handicap of 9 or less.
[0008] Accordingly, the invention provides a multi-piece solid golf
ball having a core, an envelope layer, an intermediate layer and a
cover, the core being formed of a rubber composition as one or more
layer, the envelope layer being formed of a resin material as one
or more layer and the intermediate layer and the cover each being
formed of a resin material as a single layer. In the golf ball of
the invention, the core has a diameter of from 35.1 to 41.3 mm and
has a hardness profile in which, letting Cc be the Shore C hardness
at a center of the core, Cm be the Shore C hardness at a midpoint M
between the core center and a surface of the core, Cm-2, Cm-4 and
Cm-6 be the respective Shore C hardnesses at positions 2 mm, 4 mm
and 6 mm inward from the midpoint M, Cm+2, Cm+4 and Cm+6 be the
respective Shore C hardnesses at positions 2 mm, 4 mm and 6 mm
outward from the midpoint M and Cs be the Shore C hardness at the
core surface and defining the surface areas A to F as follows
surface area A: 1/2.times.2.times.(Cm+4-Cm-6)
surface area B: 1/2.times.2.times.(Cm-2-Cm-4)
surface area C: 1/2.times.2.times.(Cm-Cm-2)
surface area D: 1/2.times.2.times.(Cm+2-Cm)
surface area E: 1/2.times.2.times.(Cm+4-Cm+2)
surface area F: 1/2.times.2.times.(Cm+6-Cm+4),
(surface area E+surface area F)-(surface area A+surface area B) has
a value of 4.0 or more and Cs-Cc has a value of 20 or more. Also,
the center hardness of the core, surface hardness of the core,
surface hardness of the sphere obtained by encasing the core with
the envelope layer (envelope layer-encased sphere), surface
hardness of the sphere obtained by encasing the envelope
layer-encased sphere with the intermediate layer (intermediate
layer-encased sphere) and surface hardness of the ball have Shore C
hardness relationships therebetween which satisfy the following
conditions: [0009] (1) core surface hardness<surface hardness of
envelope layer-encased sphere<surface hardness of intermediate
layer-encased sphere>ball surface hardness, and [0010] (2)
(surface hardness of envelope layer-encased sphere)-(center
hardness of core).gtoreq.28. Moreover, the intermediate layer and
the cover have respective thicknesses which satisfy the following
condition: [0011] (3) cover thickness<intermediate layer
thickness.
[0012] In a preferred embodiment of the golf ball of the invention,
surface areas A to F in the core hardness profile satisfy the
condition
(surface area D+surface area E+surface area F)-(surface area
A+surface area B+surface area C).gtoreq.1.0.
[0013] In another preferred embodiment of the inventive golf ball,
surface areas A to F in the core hardness profile satisfy the
condition
(surface area E+surface area F)-(surface area A+surface area
B+surface area C)>0.
[0014] In yet another preferred embodiment, surface areas A to F in
the core hardness profile satisfy the conditions
surface area D<surface area E<surface area F, and
surface area A<surface area C.
[0015] In still another preferred embodiment, the envelope layer
and the intermediate layer have respective thicknesses which
satisfy the condition intermediate layer thickness 5 envelope layer
thickness.
[0016] In a further preferred embodiment, the ratio (core
diameter)/(ball diameter) has a value of at least 0.825.
[0017] In a still further preferred embodiment, the envelope layer
has a higher material hardness than the cover.
[0018] In another preferred embodiment, the core center hardness
(Cc) is not more than 60.
[0019] In yet another preferred embodiment, (surface hardness of
envelope layer-encased sphere)-(center hardness of core) in formula
(2) has a value of at least 30.
[0020] In still another preferred embodiment, the core has a
defection when compressed under a final load of 1,275 N (030 kgf)
from an initial load of 98 N (10 kg) of at least 3.9 mm, and the
ball has a deflection when compressed under a final load of 1,275 N
(130 kgf) from an initial load of 98 N (10 kgf) of at least 2.8
mm.
[0021] In an additional preferred embodiment, a coating layer is
formed on a surface of the cover and the coating layer and the
cover have respective material hardnesses such that the value
obtained by subtracting the material hardness of the coating layer
from the material hardness of the cover is, on the Shore C hardness
scale, at least -20 and not more than 25.
Advantageous Effects of the Invention
[0022] The multi-piece solid golf ball of the invention does not
incur excessive spin on driver (W #1) shots and iron shots,
enabling a good distance to be achieved, has a good spin
receptivity in the short game, and moreover has a soft feel at
impact on all shots. Such qualities make this ball highly useful as
a golf ball for mid-level and skilled amateur golfers.
BRIEF DESCRIPTION OF THE DIAGRAMS
[0023] FIG. 1 is a schematic cross-sectional view of the
multi-piece solid golf ball according to the invention.
[0024] FIG. 2 is a graph that uses core hardness profile data from
Example 1 to explain surface areas A to F in the core hardness
profile.
[0025] FIG. 3 is a graph showing the core hardness profiles in
Examples 1 to 4 and Comparative Examples 5 and 9.
[0026] FIG. 4 is a graph showing the core hardness profiles in
Comparative Examples 1 to 4, 5 to 8 and 10.
[0027] FIGS. 5A and 5B are, respectively, a top view and a side
view of the exterior of a golf ball showing the arrangement of
dimples common to all of the Examples and Comparative Examples
described in the present Specification.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0028] The objects, features and advantages of the invention will
become more apparent from the following detailed description taken
in conjunction with the appended diagrams.
[0029] The multi-piece solid golf ball of the invention has a core,
an envelope layer, an intermediate layer and a cover. Referring to
FIG. 1, which shows an embodiment of the inventive golf ball, the
ball G has a core 1, an envelope layer 2 encasing the core 1, an
intermediate layer 3 encasing the envelope layer 2, and a cover 4
encasing the intermediate layer 3. The cover 4 is positioned as the
outermost layer, with the exception of a coating layer, in the
layered construction of the ball. In this invention, the core and
the envelope layer may each be independently a single layer or
formed as two or more layers. Numerous dimples D are typically
formed on the surface of the cover (outermost layer) 4 to enhance
the aerodynamic properties of the ball. Although not shown in the
diagrams, a coating layer 5 is generally formed on the surface of
the cover 4. Each layer is described in detail below.
[0030] The core is composed primarily of a rubber material.
Specifically, a core-forming rubber composition can be prepared by
using a base rubber as the chief component and including, together
with this, other ingredients such as a co-crosslinking agent, an
organic peroxide, an inert filler and an organosulfur compound. It
is preferable to use polybutadiene as the base rubber.
[0031] Commercial products may be used as the polybutadiene.
Illustrative examples include BR01, BR51 and BR730 (from JSR
Corporation). The proportion of polybutadiene within the base
rubber is preferably at least 60 wt %, and more preferably at least
80 wt %. Rubber ingredients other than the above polybutadienes may
be included in the base rubber, provided that doing so does not
detract from the advantageous effects of the invention. Examples of
rubber ingredients other than the above polybutadienes include
other polybutadienes and also other diene rubbers, such as
styrene-butadiene rubbers, natural rubbers, isoprene rubbers and
ethylene-propylene-diene rubbers.
[0032] Examples of co-crosslinking agents include unsaturated
carboxylic acids and the metal salts of unsaturated carboxylic
acids. Specific examples of unsaturated carboxylic acids include
acrylic acid, methacrylic acid, maleic acid and fumaric acid. The
use of acrylic acid or methacrylic acid is especially preferred.
Metal salts of unsaturated carboxylic acids include, without
particular limitation, the above unsaturated carboxylic acids that
have been neutralized with desired metal ions. Specific examples
include the zinc salts and magnesium salts of methacrylic acid and
acrylic acid. The use of zinc acrylate is especially preferred.
[0033] The unsaturated carboxylic acid and/or metal salt thereof is
included in an amount, per 100 parts by weight of the base rubber,
which is typically at least 5 parts by weight, preferably at least
9 parts by weight, and more preferably at least 13 parts by weight.
The amount included is typically not more than 60 parts by weight,
preferably not more than 50 parts by weight, and more preferably
not more than 40 parts by weight. Too much may make the core too
hard, giving the ball an unpleasant feel at impact, whereas too
little may lower the rebound.
[0034] Commercial products may be used as the organic peroxide.
Examples of such products that may be suitably used include
Percumyl D, Perhexa C-40 and Perhexa 3M (all from NOF Corporation),
and Luperco 231XL (from AtoChem Co.). One of these may be used
alone, or two or more may be used together. The amount of organic
peroxide included per 100 parts by weight of the base rubber is
preferably at least 0.1 part by weight, more preferably at least
0.3 part by weight, and even more preferably at least 0.5 part by
weight. The upper limit is 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 2.5 parts by weight. When too much or too little is
included, it may not be possible to obtain a ball having a good
feel, durability and rebound.
[0035] Another compounding ingredient typically included with the
base rubber is an inert filler, preferred examples of which include
zinc oxide, barium sulfate and calcium carbonate. One of these may
be used alone, or two or more may be used together. The amount of
inert filler included per 100 parts by weight of the base rubber is
preferably at least 1 part by weight, and more preferably at least
5 parts by weight. The upper limit is preferably not more than 50
parts by weight, more preferably not more than 40 parts by weight,
and even more preferably not more than 36 parts by weight. Too much
or too little inert filler may make it impossible to obtain a
proper weight and a suitable rebound.
[0036] In addition, an antioxidant may be optionally included.
Illustrative examples of suitable commercial antioxidants include
Nocrac NS-6 and Nocrac NS-30 (both available from Ouchi Shinko
Chemical Industry Co., Ltd.), and Yoshinox 425 (available from
Yoshitomi Pharmaceutical Industries, Ltd.). One of these may be
used alone, or two or more may be used together.
[0037] The amount of antioxidant included per 100 parts by weight
of the base rubber is set to preferably 0 part by weight or more,
more preferably at least 0.05 part by weight, and even more
preferably at least 0.1 part by weight. The upper limit is set to
preferably not more than 3 parts by weight, more preferably not
more than 2 parts by weight, even more preferably not more than 1
part by weight, and most preferably not more than 0.5 part by
weight. Too much or too little antioxidant may make it impossible
to achieve a suitable ball rebound and durability.
[0038] An organosulfur compound may be included in the core in
order to impart a good resilience. The organosulfur compound is not
particularly limited, provided that it can enhance the rebound of
the golf ball. Exemplary organosulfur compounds include
thiophenols, thionaphthols, halogenated thiophenols, and metal
salts of these. Specific examples include pentachlorothiophenol,
pentafluorothiophenol, pentabromothiophenol, p-chlorothiophenol,
the zinc salt of pentachlorothiophenol, the zinc salt of
pentafluorothiophenol, the zinc salt of pentabromothiophenol, the
zinc salt of p-chlorothiophenol, and any of the following having 2
to 4 sulfur atoms: diphenylpolysulfides, dibenzylpolysulfides,
dibenzoylpolysulfides, dibenzothiazoylpolysulfides and
dithiobenzoylpolysulfides. The use of the zinc salt of
pentachlorothiophenol is especially preferred.
[0039] It is recommended that the amount of organosulfur compound
included per 100 parts by weight of the base rubber be preferably 0
part by weight or more, more preferably at least 0.05 part by
weight, and even more preferably at least 0.1 part by weight, and
that the upper limit be preferably not more than 5 parts by weight,
more preferably not more than 3 parts by weight, and even more
preferably not more than 2.5 parts by weight. Including too much
organosulfur compound may make a greater rebound-improving effect
(particularly on shots with a W #1) unlikely to be obtained, may
make the core too soft or may worsen the feel of the ball at
impact. On the other hand, including too little may make a
rebound-improving effect unlikely.
[0040] Decomposition of the organic peroxide within the core
formulation can be promoted by the direct addition of water (or a
water-containing material) to the core material. The decomposition
efficiency of the organic peroxide within the core-forming rubber
composition is known to change with temperature; starting at a
given temperature, the decomposition efficiency rises with
increasing temperature. If the temperature is too high, the amount
of decomposed radicals rises excessively, leading to recombination
between radicals and, ultimately, deactivation. As a result, fewer
radicals act effectively in crosslinking. Here, when a heat of
decomposition is generated by decomposition of the organic peroxide
at the time of core vulcanization, the vicinity of the core surface
remains at substantially the same temperature as the temperature of
the vulcanization mold, but the temperature near the core center,
due to the build-up of heat of decomposition by the organic
peroxide which has decomposed from the outside, becomes
considerably higher than the mold temperature. In cases where water
(or a water-containing material) is added directly to the core,
because the water acts to promote decomposition of the organic
peroxide, radical reactions like those described above can be made
to differ at the core center and core surface. That is,
decomposition of the organic peroxide is further promoted near the
center of the core, bringing about greater radical deactivation,
which leads to a further decrease in the amount of active radicals.
As a result, it is possible to obtain a core in which the crosslink
densities at the core center and the core surface differ markedly.
It is also possible to obtain a core having different dynamic
viscoelastic properties at the core center.
[0041] The water included in the core material is not particularly
limited, and may be distilled water or tap water. The use of
distilled water that is free of impurities is especially preferred.
The amount of water included per 100 parts by weight of the base
rubber is preferably at least 0.1 part by weight, and more
preferably at least 0.3 parts by weight. The upper limit is
preferably not more than 5 parts by weight, and more preferably not
more than 4 parts by weight.
[0042] The core can be produced by vulcanizing and curing the
rubber composition containing the above ingredients. For example,
the core can be produced by using a Banbury mixer, roll mill or
other mixing apparatus to intensively mix the rubber composition,
subsequently compression molding or injection molding the mixture
in a core mold, and curing the resulting molded body by suitably
heating it under conditions sufficient to allow the organic
peroxide or co-crosslinking agent to act, such as at a temperature
of between 100 and 200.degree. C., preferably between 140 and
180.degree. C., for 10 to 40 minutes.
[0043] The core may consist of a single layer alone or may be
formed as a plurality of layers, an example of the latter type of
core being one having a two-layer construction consisting of an
inner core layer and an outer core layer. When the core is formed
as a two-layer core consisting of an inner core layer and an outer
core layer, the inner core layer and outer core layer materials may
each be composed primarily of the above-described rubber material.
Also, the rubber material making up the outer core layer encasing
the inner core layer may be the same as or different from the inner
core layer material. The details here are the same as those given
above for the ingredients of the core-forming rubber material.
[0044] The core has a diameter of from 35.1 to 41.3 mm, the lower
limit being preferably at least 35.4 mm, more preferably at least
35.8 mm, and the upper limit being preferably not more than 39.2
mm, more preferably not more than 38.3 mm. When the core diameter
is too small, the initial velocity of the ball becomes low or the
deflection hardness of the overall ball becomes high, as a result
of which the spin rate on full shots rises and the intended
distance cannot be attained. On the other hand, when the core
diameter is too large, the spin rate on full shots rises and the
intended distance cannot be attained, or the durability to cracking
on repeated impact worsens.
[0045] The core has a deflection (mm) when compressed under a final
load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf)
which, although not particularly limited, is preferably at least
3.9 mm, more preferably at least 4.0 mm, and even more preferably
at least 4.1 mm. The upper limit is preferably not more than 5.1
mm, more preferably not more than 4.8 mm, and even more preferably
not more than 4.6 mm. When the core deflection is too small, i.e.,
when the core is too hard, the spin rate of the ball may rise
excessively and a good distance may not be achieved, or the feel at
impact may be too hard. On the other hand, when the core deflection
is too large, i.e., when the core is too soft, the ball rebound may
become too low and a good distance may not be achieved, the feel at
impact may be too soft, or the durability to cracking on repeated
impact may worsen.
[0046] Next, the hardness profile of the core is described. The
core hardness described below refers to the Shore C hardness. This
Shore C hardness is the hardness value measured with a Shore C
durometer in accordance with ASTM D2240.
[0047] The core center hardness Cc, although not particularly
limited, may be set to preferably at least 50, more preferably at
least 52, and even more preferably at least 54. The upper limit
also is not particularly limited, but may be set to preferably not
more than 60, more preferably not more than 59, and even more
preferably not more than 58. When this value is too large, the spin
rate may rise, as a result of which the desired distance may not be
attainable, or the feel at impact may become too hard. On the other
hand, when this value is too small, the rebound may become low, as
a result of which the desired distance may not be attainable, or
the durability to cracking on repeated impact may worsen.
[0048] The hardness Cm-6 at a position 6 mm inward from the
position M located midway between the center and surface of the
core (also referred to below as the "midpoint M"), although not
particularly limited, may be set to preferably at least 50, more
preferably at least 52, and even more preferably at least 54. The
upper limit also is not particularly limited, but may be set to
preferably not more than 67, more preferably not more than 65, and
even more preferably not more than 63. Hardnesses that deviate from
these values may lead to undesirable results similar to those
described above for the core center hardness (Cc).
[0049] The hardness Cm-4 at a position 4 mm inward toward the core
center (indicated below as simply "inward") from the midpoint M of
the core, although not particularly limited, may be set to
preferably at least 53, more preferably at least 55, and even more
preferably at least 57. The upper limit also is not particularly
limited, but may be set to preferably not more than 68, more
preferably not more than 66, and even more preferably not more than
64. Hardnesses that deviate from these values may lead to
undesirable results similar to those described above for the core
center hardness (Cc).
[0050] The hardness Cm-2 at a position 2 mm inward from the
midpoint M of the core, although not particularly limited, may be
set to preferably at least 54, more preferably at least 56, and
even more preferably at least 58. The upper limit also is not
particularly limited, but may be set to preferably not more than
69, more preferably not more than 67, and even more preferably not
more than 65. Hardnesses that deviate from these values may lead to
undesirable results similar to those described above for the core
center hardness (Cc).
[0051] The cross-sectional hardness Cm at the midpoint M of the
core, although not particularly limited, may be set to preferably
at least 56, more preferably at least 58, and even more preferably
at least 60. The upper limit also is not particularly limited, but
may be set to preferably not more than 71, more preferably not more
than 69, and even more preferably not more than 67. Hardnesses that
deviate from these values may lead to undesirable results similar
to those described above for the core center hardness (Cc).
[0052] The hardness Cm+2 at a position 2 mm outward toward the core
center (indicated below as simply "outward") from the midpoint M of
the core, although not particularly limited, may be set to
preferably at least 57, more preferably at least 60, and even more
preferably at least 62. The upper limit also is not particularly
limited, but may be set to preferably not more than 74, more
preferably not more than 71, and even more preferably not more than
69. When this value is too large, the durability to cracking on
repeated impact may worsen, or the feel at impact may become too
hard. On the other hand, when this value is too small, the rebound
may become low or the spin rate on full shots may rise, as a result
of which the intended distance may not be attainable.
[0053] The hardness Cm+4 at a position 4 mm outward from the
midpoint M of the core, although not particularly limited, may be
set to preferably at least 63, more preferably at least 66, and
even more preferably at least 68. The upper limit also is not
particularly limited, but may be set to preferably not more than
78, more preferably not more than 75, and even more preferably not
more than 73. Hardnesses that deviate from these values may lead to
undesirable results similar to those described above for the
hardness at a position 2 mm from the midpoint M of the core
(Cm+2).
[0054] The hardness Cm+6 at a position 6 mm outward from the
midpoint M of the core, although not particularly limited, may be
set to preferably at least 69, more preferably at least 72, and
even more preferably at least 74. The upper limit also is not
particularly limited, but may be set to preferably not more than
84, more preferably not more than 81, and even more preferably not
more than 79. Hardnesses that deviate from these values may lead to
undesirable results similar to those described above for the
hardness at a position 2 mm from the midpoint M of the core
(Cm+2).
[0055] The core surface hardness Cs, although not particularly
limited, may be set to preferably at least 75, more preferably at
least 78, and even more preferably at least 80. The upper limit
also is not particularly limited, but may be set to preferably not
more than 90, more preferably not more than 87, and even more
preferably not more than 85. When this value is too large, the
durability to cracking on repeated impact may worsen or the feel at
impact may become too hard. On the other hand, when this value is
too small, the rebound may become too low or the spin rate on full
shots may rise, as a result of which the intended distance may not
be attainable.
[0056] The hardness difference between the core center and core
surface is optimized so as to make the hardness difference between
the core interior and the core exterior large. That is, the value
expressed as "core surface hardness-core center hardness," or
Cs-Cc, is set to a Shore C hardness of at least 20, preferably at
least 22, and more preferably at least 24. The upper limit is not
particularly limited, but may be set to preferably not more than
40, more preferably not more than 35, and even more preferably not
more than 30. When the hardness difference is too small, the spin
rate on full shots rises, as a result of which the intended
distance cannot be attained. On the other hand, when this hardness
difference is too large, the durability to cracking on repeated
impact may women or the initial velocity on shots may become lower,
as a result of which the intended distance may not be attainable.
As used herein, the core center hardness Cc refers to the hardness
measured at the center of the cross-section obtained by cutting the
core in half through the center, and the core surface hardness Cs
refers to the hardness measured on the spherical surface of the
core.
[0057] In the above-described core hardness profile in this
invention, the surface areas A to F defined as follows:
surface area A: 1/2.times.2.times.(Cm-4-Cm-6)
surface area B: 1/2.times.2.times.(Cm-2-Cm-4)
surface area C: 1/2.times.2.times.(Cm-Cm-2)
surface area D: 1/2.times.2.times.(Cm+2-Cm)
surface area E: 1/2.times.2.times.(Cm+4-Cm+2)
surface area F: 1/2.times.2.times.(Cm+6-Cm+4),
are characterized in that the value of (surface area E+surface area
F)-(surface area A+surface area B) has a value of 4.0 or more. The
value of (surface area E+surface area F)-(surface area A+surface
area B) is preferably 5.0 or more, and more preferably 6.0 or more.
The upper limit value is preferably not more than 20.0, more
preferably not more than 16.0, and even more preferably not more
than 12.0. When this value is too large, the durability to cracking
under repeated impact may worsen. On the other hand, when this
value is too small, the spin rate on full shots rises and the
intended distance cannot be attained. FIG. 2 shows a graph that
uses core hardness profile data from Example 1 to explain surface
areas A to F. As is apparent from the graph, each of surface areas
A to F is the surface area of a triangle whose base is the
difference between specific distances and whose height is the
difference in hardness between the positions at these specific
distances.
[0058] Surface areas A to F are such that the value of (surface
area D+surface area E+surface area F)- (surface area A+surface area
B+surface area C), although not particularly limited, is preferably
1.0 or more, more preferably 1.5 or more, and even more preferably
2.0 or more. The upper limit value is preferably not more than
18.0, more preferably not more than 14.0, and even more preferably
not more than 10.0. When this value is too large, the durability to
cracking on repeated impact may worsen. On the other hand, when
this value is too small, the spin rate on full shots may rise and
the intended distance may not be attainable.
[0059] Also, the value of (surface area E+surface area F)- (surface
area A+surface area B+surface area C), although not particularly
limited, is preferably more than 0, more preferably 0.5 or more,
and even more preferably 1.0 or more. The upper limit value is
preferably not more than 17.0, more preferably not more than 13.0,
and even more preferably not more than 9.0. When this value is too
large, the durability to cracking on repeated impact may worsen. On
the other hand, when this value is too small, the spin rate on full
shots may rise and the intended distance may not be attainable.
[0060] Surface areas A to F in the above core hardness profile
preferably satisfy the following conditions:
surface area D<surface area E<surface area F, and
surface area A<surface area C.
When this relationship is not satisfied, the spin rate on full
shots may rise and the intended is distance may not be
attainable.
[0061] Next, the envelope layer is described.
[0062] The envelope layer has a material hardness on the Shore D
scale which, although not particularly limited, is preferably at
least 48, more preferably at least 50, and even more preferably at
least 52. The upper limit is preferably not more than 62, more
preferably not more than 60, and even more preferably not more than
56. The surface hardness of the sphere obtained by encasing the
core with the envelope layer (envelope layer-encased sphere),
expressed on the Shore D scale, is preferably at least 54, more
preferably at least 56, and even more preferably at least 58. The
upper limit is preferably not more than 68, more preferably not
more than 66, and even more preferably not more than 62. When these
material and surface hardnesses of the envelope layer are lower
than the above ranges, the ball may be too receptive to spin on
full shots or the initial velocity may be low, which may result in
a poor distance. On the other hand, when these material and surface
hardnesses are too high, the feel at impact may be too hard, the
durability to cracking on repeated impact may worsen, or the spin
rate on full shots may rise, which may result in a poor
distance.
[0063] The surface hardness of the envelope layer-encased sphere is
set lower than the surface hardness of the intermediate
layer-encased sphere. When the envelope layer-encased sphere has a
higher surface hardness than the intermediate layer-encased sphere,
the spin rate on full shots rises and a good distance cannot be
achieved, or the feel at impact is poor.
[0064] The material hardness of the envelope layer, expressed on
the Shore C scale, is preferably at least 74, more preferably at
least 76, and even more preferably at least 79. The upper limit
value is preferably not more than 92, more preferably not more than
90, and even more preferably not more than 88. The surface hardness
of the envelope layer-encased sphere, expressed on the Shore C
scale, is preferably at least 82, more preferably at least 84, and
even more preferably at least 87. The upper limit value is
preferably not more than 97, more preferably not more than 95, and
even more preferably not more than 92.
[0065] The envelope layer has a thickness which is preferably at
least 0.8 mm, more preferably at least 0.9 mm, and even more
preferably at least 1.0 mm. The upper limit in the envelope layer
thickness is preferably not more than 2.0 mm, more preferably not
more than 1.7 mm, and even more preferably not more than 1.4 mm.
When the envelope layer is too thin, the spin rate-lowering effect
on full shots may be inadequate and the intended distance may not
be attainable. On the other hand, when the envelope layer is too
thick, the initial velocity of the ball on shots may become low and
the intended distance may not be attainable. Also, it is preferable
to form the envelope layer so as to be thicker than the
subsequently described intermediate layer or to have both layers be
the same thickness.
[0066] The envelope layer material is not particularly limited,
although preferred use can be made of various types of
thermoplastic resin materials. Especially preferred materials
include resin compositions containing as the essential ingredients:
100 parts by weight of a resin component composed of, in
admixture,
[0067] (A) a base resin of (a-1) an olefin-unsaturated carboxylic
acid random copolymer and/or a metal ion neutralization product of
an olefin-unsaturated carboxylic acid random copolymer mixed with
(a-2) an olefin-unsaturated carboxylic acid-unsaturated carboxylic
acid ester random terpolymer and/or a metal ion neutralization
product of an olefin-unsaturated carboxylic acid-unsaturated
carboxylic acid ester random terpolymer in a weight ratio between
100:0 and 0:100, and
[0068] (B) a non-ionomeric thermoplastic elastomer
in a weight ratio between 100:0 and 50:50;
[0069] (C) from 5 to 120 parts by weight of a fatty acid and/or
fatty acid derivative having a molecular weight of from 228 to
1,500; and
[0070] (D) from 0.1 to 17 parts by weight of a basic inorganic
metal compound capable of neutralizing un-neutralized acid groups
in components (A) and (C).
[0071] Components (A) to (D) in the intermediate layer-forming
resin material described in, for example, JP-A 2010-253268 may be
advantageously used as above components (A) to (D).
[0072] A non-ionomeric thermoplastic elastomer may be included in
the envelope layer material. The amount of non-ionomeric
thermoplastic elastomer included is preferably from 0 to 50 parts
by weight per 100 parts by weight of the total amount of the base
resin.
[0073] Exemplary non-ionomeric thermoplastic elastomers include
polyolefin elastomers (including polyolefin and metallocene
polyolefins), polystyrene elastomers, diene polymers, polyacrylate
polymers, polyamide elastomers, polyurethane elastomers, polyester
elastomers and polyacetals. A thermoplastic polyether ester
elastomer is especially preferred.
[0074] Depending on the intended use, optional additives may be
suitably included in the envelope layer-forming resin material. For
example, pigments, dispersants, antioxidants, ultraviolet absorbers
and light stabilizers may be added. When these additives are
included, the amount added per 100 parts by weight of the overall
base resin is preferably at least 0.1 part by weight, and more
preferably at least 0.5 part by weight. The upper limit is
preferably not more than 10 parts by weight, and more preferably
not more than 4 parts by weight.
[0075] Next, the intermediate layer is described.
[0076] The intermediate layer has a material hardness on the Shore
D scale which, although not particularly limited, is preferably at
least 58, more preferably at least 60, and even more preferably at
least 63. The upper limit is preferably not more than 70, more
preferably not more than 68, and even more preferably not more than
65. The surface hardness of the sphere obtained by encasing the
envelope layer-encased sphere with the intermediate layer
(intermediate layer-encased sphere), expressed on the Shore D
scale, is preferably at least 64, more preferably at least 66, and
even more preferably at least 69. The upper limit is preferably not
more than 76, more preferably not more than 74, and even more
preferably not more than 71. When the material and surface
hardnesses of the intermediate layer are lower than the above
ranges, the ball may be too receptive to spin on fill shots or the
initial velocity may become low, as a result of which a good
distance may not be attained. On the other hand, when the material
and surface hardnesses are too high, the durability to cracking on
repeated impact may worsen or the feel at impact on shots with a
putter or on short approaches may become too hard.
[0077] The intermediate layer has a material hardness on the Shore
C scale which is preferably at least 87, more preferably at least
89, and even more preferably at least 93. The upper limit value is
preferably not more than 100, more preferably not more than 98, and
even more preferably not more than 96. The intermediate
layer-encased sphere has a surface hardness on the Shore C scale
which is preferably at least 90, more preferably at least 93, and
even more preferably at least 96. The upper limit value is
preferably not more than 100, more preferably not more than 99, and
even more preferably not more than 98.
[0078] The intermediate layer-encased sphere is formed so as to
have a surface hardness that is higher than the ball surface
hardness. When the ball has a higher surface hardness than the
intermediate layer-encased sphere, the spin rate on full shots
rises, as a result of which a good distance cannot be achieved, or
the controllability in the short game worsens.
[0079] The intermediate layer has a thickness which is preferably
at least 0.7 mm, more preferably at least 0.8 mm, and even more
preferably at least 1.0 mm. The upper limit in the intermediate
layer thickness is preferably not more than 1.8 mm, more preferably
not more than 1.4 mm, and even more preferably not more than 1.2
mm. It is critical for the intermediate layer to be thicker than
the subsequently described cover (outermost layer). When the
thickness of the intermediate layer falls outside of the above
range or is lower than the cover thickness, the spin rate-lowering
effect on shots with a driver (W #1) may be inadequate, which may
result in a poor distance. Also, when the intermediate layer is
thinner than the above range, the durability to cracking on
repeated impact and the low-temperature durability may worsen.
[0080] The intermediate layer material may be suitably selected
from among various types of thermoplastic resins that are used as
golf ball materials, with the use of the highly neutralized resin
material containing components (A) to (D) described above in
connection with the envelope layer material or an ionomer resin
being preferred.
[0081] Specific examples of ionomer resin materials include
sodium-neutralized ionomer resins and zinc-neutralized ionomer
resins. These may be used singly or two or more may be used
together.
[0082] An embodiment that uses in admixture a zinc-neutralized
ionomer resin and a sodium-neutralized ionomer resin as the chief
materials is especially preferred. The blending ratio therebetween,
expressed as the weight ratio (zinc-neutralized
ionomer)/(sodium-neutralized ionomer), is from 25/75 to 75/25,
preferably from 35/65 to 65/35, and more preferably from 45/55 to
55/45. When the zinc-neutralized ionomer and sodium-neutralized
ionomer are not included in a ratio within this range, the rebound
may become too low, as a result of which the desired distance may
not be achieved, the durability to cracking on repeated impact at
normal temperatures may worsen and the durability to cracking at
low temperatures (subzero Centigrade) may worsen.
[0083] The resin material used to form the intermediate layer may
be one obtained by blending, of commercially available ionomer
resins, a high-acid ionomer resin having an acid content of at
least 16 wt % with an ordinary ionomer resin. The high rebound and
lower spin rate resulting from the use of such a blend enables a
good distance to be achieved on driver (W #1) shots.
[0084] The amount of unsaturated carboxylic acid included in the
high-acid ionomer resin (acid content) is generally at least 16 wt
%, preferably at least 17 wt %, and more preferably at least 18 wt
%. The upper limit is preferably not more than 22 wt %, more
preferably not more than 21 wt %, and even more preferably not more
than 20 wt %. When this value is too small, the spin rate on full
shots may rise, as a result of which the intended distance may not
be attainable. On the other hand, when this value is too large, the
feel on impact may become too hard, or the durability to cracking
on repeated impact may worsen.
[0085] The amount of high-acid ionomer resin included per 100 parts
by weight of the resin material is preferably at least 10 wt %,
more preferably at least 30 wt %, and even more preferably at least
60 wt %. When the content of this high-acid ionomer resin is too
low, the spin rate on shots with a driver (W #1) may rise and a
good distance may not be attained.
[0086] Depending on the intended use, optional additives may be
suitably included in the intermediate layer material. For example,
pigments, dispersants, antioxidants, ultraviolet absorbers and
light stabilizers may be added. When these additives are included,
the amount added per 100 parts by weight of the base resin is
preferably at least 0.1 part by weight, and more preferably at
least 0.5 part by weight. The upper limit is preferably not more
than 10 parts by weight, and more preferably not more than 4 parts
by weight.
[0087] It is desirable to abrade the surface of the intermediate
layer in order to increase adhesion of the intermediate layer
material with the polyurethane that is preferably used in the
subsequently described cover material. In addition, it is desirable
to apply a primer (adhesive) to the surface of the intermediate
layer following such abrasion treatment or to add an adhesion
reinforcing agent to the intermediate layer material.
[0088] The intermediate layer material has a specific gravity which
is typically less than 1.1, preferably between 0.90 and 1.05, and
more preferably between 0.93 and 0.99. Outside of this range, the
rebound of the overall ball may decrease and a good distance may
not be obtained, or the durability of the ball to cracking on
repeated impact may worsen.
[0089] Next, the cover (outermost layer) is described.
[0090] The cover has a material hardness on the Shore D scale
which, although not particularly limited, is preferably at least
30, more preferably at least 35, and even more preferably at least
40. The upper limit is preferably not more than 53, more preferably
not more than 50, and even more preferably not more than 47. The
surface hardness of the sphere obtained by encasing the
intermediate layer-encased sphere with the cover (i.e., ball
surface hardness), expressed on the Shore D scale, is preferably at
least 50, more preferably at least 53, and even more preferably at
least 56. The upper limit is preferably not more than 70, more
preferably not more than 65, and even more preferably not more than
60. When the material hardness of the cover and the ball surface
hardness are lower than the above respective ranges, the spin rate
of the ball on shots with a driver (W #l) may rise and a good
distance may not be achieved. On the other hand, when the material
hardness of the cover and the ball surface hardness are too high,
the controllability of the ball in the short game may worsen or the
scuff resistance may worsen.
[0091] The material hardness of the cover, expressed on the Shore C
scale, is preferably at least 50, more preferably at least 57, and
even more preferably at least 63. The upper limit value is
preferably not more than 80, more preferably not more than 76, and
even more preferably not more than 72. The surface hardness of the
ball, expressed on the Shore C scale, is preferably at least 75,
more preferably at least 80, and even more preferably at least 85.
The upper limit value is preferably not more than 95, more
preferably not more than 92, and even more preferably not more than
90.
[0092] The cover has a thickness of preferably at least 0.3 mm,
more preferably at least 0.45 mm, and even more preferably at least
0.6 mm. The upper limit in the cover thickness is preferably not
more than 1.2 mm, more preferably not more than 0.9 mm, and even
more preferably not more than 0.8 mm. When the cover is too thick,
the rebound on full shots with a driver (W #I) or an iron may
become inadequate or the spin rate may rise, as a result of which a
good distance may not be achieved. On the other hand, when the
cover is too thin, the scuff resistance may worsen or the ball may
not be fully receptive to spin on approach shots and may thus lack
sufficient controllability.
[0093] Various types of thermoplastic resins employed as cover
stock in golf balls may be used as the cover material. For reasons
having to do with controllability and scuff resistance, preferred
use can be made of a urethane resin. In particular, from the
standpoint of the mass productivity of the manufactured balls, it
is preferable to use a material that is composed primarily of a
thermoplastic polyurethane, and more preferable to form the cover
of a resin blend in which the main components are (I) a
thermoplastic polyurethane and (II) a polyisocyanate compound.
[0094] It is recommended that the total weight of components (I)
and (II) combined be at least 60%, and preferably at least 70%, of
the overall amount of the cover-forming resin composition.
Components (1) and (II) are described in detail below.
[0095] The thermoplastic polyurethane (1) has a structure which
includes soft segments composed of a polymeric polyol (polymeric
glycol) that is a long-chain polyol, and hard segments composed of
a chain extender and a polyisocyanate compound. Here, the
long-chain polyol serving as a starting material may be any that
has hitherto been used in the art relating to thermoplastic
polyurethanes, and is not particularly limited. Illustrative
examples include polyester polyols, polyether polyols,
polycarbonate polyols, polyester polycarbonate polyols, polyolefin
polyols, conjugated diene polymer-based polyols, castor oil-based
polyols, silicone-based polyols and vinyl polymer-based polyols.
These long-chain polyols may be used singly, or two or more may be
used in combination. Of these, in terms of being able to synthesize
a thermoplastic polyurethane having a high rebound resilience and
excellent low-temperature properties, a polyether polyol is
preferred.
[0096] Any chain extender that has hitherto been employed in the
art relating to thermoplastic polyurethanes may be suitably used as
the chain extender. For example, low-molecular-weight compounds
with a molecular weight of 400 or less which have on the molecule
two or more active hydrogen atoms capable of reacting with
isocyanate groups are preferred. Illustrative, non-limiting,
examples of the chain extender include 1,4-butylene glycol,
1,2-ethylene glycol, 1,3-butanediol, 1,6-hexanediol and
2,2-dimethyl-1,3-propanediol. Of these, the chain extender is
preferably an aliphatic diol having from 2 to 12 carbon atoms, and
is more preferably 1,4-butylene glycol.
[0097] Any polyisocyanate compound hitherto employed in the art
relating to thermoplastic polyurethanes may be suitably used
without particular limitation as the polyisocyanate compound. For
example, use may be made of one or more selected from the group
consisting of 4,4'-diphenylmethane diisocyanate, 2,4-toluene
diisocyanate, 2,6-toluene diisocyanate, p-phenylene diisocyanate,
xylylene diisocyanate, 1,5-naphthylene diisocyanate,
tetramethylxylene diisocyanate, hydrogenated xylylene diisocyanate,
dicyclohexylmethane diisocyanate, tetramethylene diisocyanate,
hexamethylene diisocyanate, isophorone diisocyanate, norbornene
diisocyanate, trimethylhexamethylene diisocyanate and dimer acid
diisocyanate. However, depending on the type of isocyanate, the
crosslinking reactions during injection molding may be difficult to
control. In the practice of the invention, to provide a balance
between stability at the time of production and the properties that
are manifested, it is most preferable to use the following aromatic
diisocyanate: 4,4'-diphenylmethane diisocyanate.
[0098] Commercially available products may be used as the
thermoplastic polyurethane serving as component (I). Illustrative
examples include Pandex T-8295, Pandex T-8290 and Pandex T-8260
(all from DIC Covestro Polymer, Ltd.).
[0099] A thermoplastic elastomer other than the above thermoplastic
polyurethanes may also be optionally included as a separate
component, i.e., component (III), together with above components
(I) and (II). By including this component (III) in the above resin
blend, the flowability of the resin blend can be further improved
and properties required of the golf ball cover material, such as
resilience and scuff resistance, can be increased.
[0100] The compositional ratio of above components (I), (II) and
(III) is not particularly limited. However, to fully elicit the
advantageous effects of the invention, the compositional ratio
(I):(II):(III) is preferably in the weight ratio range of from
100:2:50 to 100:50:0, and more preferably from 100:2:50 to
100:30:8.
[0101] In addition, various additives other than the ingredients
making up the above thermoplastic polyurethane may be optionally
included in this resin blend. For example, pigments, dispersants,
antioxidants, light stabilizehs, ultraviolet absorbers and internal
mold lubricants may be suitably included.
[0102] The manufacture of multi-piece solid golf balls in which the
above-described core, envelope layer, intermediate layer and cover
(outermost layer) are formed as successive layers may be carried
out by a customary method such as a known injection molding
process. For example, a multi-piece golf ball can be produced by
successively injection-molding the respective materials for the
envelope layer and the intermediate layer over the core in
injection molds for each layer so as to obtain the respective
layer-encased spheres and then, last of all, injection-molding the
material for the cover serving as the outermost layer over the
intermediate layer-encased sphere. Alternatively, the encasing
layers may each be formed by enclosing the sphere to be encased
within two half-cups that have been pre-molded into hemispherical
shapes and then molding under applied heat and pressure.
[0103] The golf ball has a deflection when compressed under a final
load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf)
which, although not particularly limited, is preferably at least
2.8 mm, more preferably at least 2.9 mm, and even more preferably
at least 3.0 mm. The upper limit value is preferably not more than
3.8 mm, more preferably not more than 3.6 mm, and even more
preferably not more than 3.4 mm. When the deflection by the golf
ball is too small, i.e., when the ball is too hard, the spin rate
may rise excessively so that the ball does not achieve a good
distance, or the feel at impact may be too hard. On the other hand,
when the deflection is too large, i.e., when the ball is too soft,
the ball rebound may be too low so that the ball does not achieve a
good distance, the feel at impact may be too soft, or the
durability to cracking under repeated impact may worsen.
Hardness Relationships Among Layers
[0104] In the invention, to achieve both a superior distance
performance on full shots and an excellent playability in the short
game, it is critical for the surface hardness of the core, the
surface hardness of the sphere obtained by encasing the core with
the envelope layer (envelope layer-encased sphere), the surface
hardness of the sphere obtained by encasing the envelope
layer-encased sphere with the intermediate layer (intermediate
layer-encased sphere) and the surface hardness of the ball to
satisfy the following condition: [0105] (1) core surface
hardness<surface hardness of envelope layer-encased
sphere<surface hardness of intermediate layer-encased
sphere>ball surface hardness.
[0106] The envelope layer-encased sphere has a higher surface
hardness than the core, the difference between these surface
hardnesses on the Shore C scale being preferably at least 1, more
preferably at least 2, and even more preferably at least 3. The
upper limit value is preferably not more than 12, more preferably
not more than 8, and even more preferably not more than 5. When
this value falls outside of the above range, the spin rate on full
shots may rise, as a result of which the intended distance may not
be achievable.
[0107] The intermediate layer-encased sphere has a higher surface
hardness than the envelope layer-encased sphere, the difference
between these surface hardnesses on the Shore C scale being
preferably at least 2, more preferably at least 4, and even more
preferably at least 8. The upper limit value is preferably not more
than 25, more preferably not more than 17, and even more preferably
not more than 14. When this value falls outside of the above range,
the spin rate on full shots may rise and the intended distance may
not be achievable.
[0108] The intermediate layer-encased sphere has a higher surface
hardness than the ball, the difference between these surface
hardnesses on the Shore C scale being preferably at least 2, more
preferably at least 4, and even more preferably at least 6. The
upper limit value is preferably not more than 25, more preferably
not more than 17, and even more preferably not more than 14. When
this value is too small, the controllability in the short game may
worsen. When this value is too large, the spin rate on full shots
may rise, as a result of which the intended distance may not be
achievable.
[0109] In addition, for the golf ball of the invention to have a
low spin rate on full shots and achieve a superior distance
performance, it is critical for the ball to satisfy the following
condition: [0110] (2) (surface hardness of envelope layer-encased
sphere)-(center hardness of core).gtoreq.28.
[0111] The value of (surface hardness of envelope layer-encased
sphere)-(center hardness of core) is at least 28, preferably at
least 29, and more preferably at least 30. The upper limit value is
preferably not more than 40, more preferably not more than 37, and
even more preferably not more than 35. When this value is too
large, the durability to cracking on repeated impact may worsen, or
the initial velocity on shots may become low, as a result of which
the intended distance may not be attainable. On the other hand,
when this value is too small, the spin rate on full shots rises and
the intended distance cannot be attained.
Relationship between Core Diameter and Ball Diameter
[0112] In this invention, to obtain a superior distance performance
on full shots not only with a driver (W #l) but also with an iron,
the ratio (core diameter)(ball diameter) has a value that is
preferably at least 0.825, more preferably at least 0.830, and even
more preferably at least 0.840. The upper limit value is preferably
not more than 0.950, more preferably not more than 0.900, and even
more preferably not more than 0.880. When this value is too small,
the initial velocity of the ball may decrease, the deflection
hardness of the overall ball may become high or the spin rate on
full shots may rise, as a result of which the intended distance may
not be attainable. When this value is too large, the spin rate on
full shots may rise, as a result of which the intended distance may
not be attainable, or the durability to cracking on repeated impact
may worsen.
[0113] Numerous dimples may be formed on the outside surface of the
cover. The number of dimples arranged on the cover surface,
although not particularly limited, is preferably at least 250, more
preferably at least 300, and even more preferably at least 320. The
upper limit is preferably not more than 380, more preferably not
more than 350, and even more preferably not more than 340. When the
number of dimples is higher than this range, the bell trajectory
may become lower and the distance traveled by the ball may
decrease. On the other hand, when the number of dimples is lower
that this range, the ball trajectory may become higher and a good
distance may not be achieved.
[0114] The dimple shapes used may be of one type or may be a
combination of two or more types suitably selected from among, for
example, circular shapes, various polygonal shapes, dewdrop shapes
and oval shapes. When circular dimples are used, the dimple
diameter may be set to at least about 2.5 mm and up to about 6.5
mm, and the dimple depth may be set to at least 0.08 mm and up to
0.30 mm.
[0115] In order for the aerodynamic properties to be fully
manifested, it is desirable for the dimple coverage ratio on the
spherical surface of the golf ball, i.e., the dimple surface
coverage SR, which is the sum of the individual dimple surface
areas, each defined by the flat plane circumscribed by the edge of
a dimple, as a percentage of the spherical surface area of the ball
were the ball to have no dimples thereon, to be set to at least 70%
and not more than 90%. Also, to optimize the ball trajectory, it is
desirable for the value Vo, defined as the spatial volume of the
individual dimples 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, to be set to at least 0.35 and not more than 0.80. Moreover,
it is preferable for the ratio VR of the sum of the volumes of the
individual dimples, each formed below the flat plane circumscribed
by the edge of a dimple, with respect to the volume of the ball
sphere were the ball surface to have no dimples thereon, to be set
to at least 0.6% and not more than 1.0%. Outside of the above
ranges in these respective values, the resulting trajectory may not
enable a good distance to be achieved and so the ball may fail to
travel a fully satisfactory distance.
[0116] A coating layer may be formed on the surface of the cover.
This coating layer can be formed by applying various types of
coating materials. Because the coating layer must be capable of
enduring the harsh conditions of golf ball use, it is desirable to
use a coating composition in which the chief component is a
urethane coating material composed of a polyol and a
polyisocyanate.
[0117] The polyol component is exemplified by acrylic polyols and
polyester polyols. These polyols include modified polyols. To
further increase workability, other polyols may also be added.
[0118] It is suitable to use two types of polyester polyols
together as the polyol component. In this case, letting the two
types of polyester polyol be component (a) and component (b), a
polyester polyol in which a cyclic structure has been introduced
onto the resin skeleton may be used as the polyester polyol of
component (a). Examples include polyester polyols obtained by the
polycondensation of a polyol having an alicyclic structure, such as
cyclohexane dimethanol, with a polybasic acid; and polyester
polyols obtained by the polycondensation of a polyol having an
alicyclic structure with a diol or triol and a polybasic acid. A
polyester polyol having a branched structure may be used as the
polyester polyol of component (b). Examples include polyester
polyols having a branched structure, such as NIPPOLAN 800, from
Tosoh Corporation.
[0119] The polyisocyanate is exemplified without particular
limitation by commonly used aromatic, aliphatic, alicyclic and
other polyisocyanates. Specific examples include tolylene
diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate,
tetramethylene diisocyanate, hexamethylene diisocyanate, lysine
diisocyanate, isophorone diisocyanate, 1,4-cyclohexylene
diisocyanate, naphthalene diisocyanate, trimethylhexamethylene
diisocyanate, dicyclohexylmethane diisocyanate and
1-isocyanato-3,3,5-trimethyl-4-isocyanatomethylcyclohexane. These
may be used singly or in admixture.
[0120] Depending on the coating conditions, various types of
organic solvents may be mixed into the coating composition.
Examples of such organic solvents include aromatic solvents such as
toluene, xylene and ethylbenzene; ester solvents such as ethyl
acetate, butyl acetate, propylene glycol methyl ether acetate and
propylene glycol methyl ether propionate; ketone solvents such as
acetone, methyl ethyl ketone, methyl isobutyl ketone and
cyclohexanone; ether solvents such as diethylene glycol dimethyl
ether, diethylene glycol diethyl ether and dipropylene glycol
dimethyl ether; alicyclic hydrocarbon solvents such as cyclohexane,
methyl cyclohexane and ethyl cyclohexane; and petroleum hydrocarbon
solvents such as mineral spirits.
[0121] The thickness of the coating layer made of the coating
composition, although not particularly limited, is typically from 5
to 40 .mu.m, and preferably from 10 to 20 .mu.m. As used herein,
"coating layer thickness" refers to the coating thickness obtained
by averaging the measurements taken at a total of three places: the
center of a dimple and two places located at positions between the
dimple center and the dimple edge.
[0122] In this invention, the coating layer composed of the above
coating composition has an elastic work recovery that is preferably
at least 60%, and more preferably at least 80%. At a coating layer
elastic work recovery in this range, the coating layer has a high
elasticity and so the self-repairing ability is high, resulting in
an outstanding abrasion resistance. Moreover, the performance
attributes of golf balls coated with this coating composition can
be improved. The method of measuring the elastic work recovery is
described below.
[0123] The elastic work recovery is one parameter of the
nanoindentation method for evaluating the physical properties of
coating layers, this being a nanohardness test method that controls
the indentation load on a micro-newton (.mu.N) order and tracks the
indenter depth during indentation to a nanometer (nm) precision. In
prior methods, only the size of the deformation (plastic
deformation) mark corresponding to the maximum load could be
measured. However, in the nanoindentation method, the relationship
between the indentation load and the indentation depth can be
obtained by continuous automated measurement. Hence, unlike in the
past, there are no individual differences between observers when
visually measuring a deformation mark under an optical microscope,
and so it is thought that the physical properties of the coating
layer can be precisely evaluated. Given that the coating layer on
the bell surface is strongly affected by the impact of drivers and
other clubs and has a not inconsiderable influence on various golf
ball properties, measuring the coating layer by the nanohardness
test method and carrying out such measurement to a higher precision
than in the past is a very effective method of evaluation.
[0124] The hardness of the coating layer, as expressed on the Shore
M hardness scale, is preferably at least 40, and more preferably at
least 60. The upper limit is preferably not more than 95, and more
preferably not more than 85. This Shore M hardness is obtained in
accordance with ASTM D2240. The hardness of the coating layer, as
expressed on the Shore C hardness scale, is preferably at least 40
and has an upper limit of preferably not more than 80. This Shore C
hardness is obtained in accordance with ASTM D2240. At coating
layer hardnesses that are higher than these ranges, the coating may
become brittle when the ball is repeatedly struck, which may make
it incapable of protecting the cover layer. On the other hand,
coating layer hardnesses that are lower than the above range are
undesirable because the ball surface is more easily damaged when
striking a hard object.
[0125] Regarding the hardness relationship between the coating
layer and the cover, the value obtained by subtracting the material
hardness of the coating layer from the material hardness of the
cover, expressed on the Shore C hardness scale, is preferably at
least -20, more preferably at least -15, and even more preferably
at least -10. The upper limit value is preferably not more than 25,
more preferably not more than 20, and even more preferably not more
than 15. Outside of this range, the coating may readily peel when
the ball is struck.
[0126] When the above coating composition is used, the formation of
a coating layer on the surface of golf balls manufactured by a
commonly known method can be carried out via the steps of preparing
the coating composition at the time of application, applying the
composition onto the golf ball surface by a conventional coating
operation, and drying the applied composition. The coating method
is not particularly limited. For example, spray painting,
electrostatic painting or dipping may be suitably used.
EXAMPLES
[0127] The following Examples and Comparative Examples are provided
to illustrate the invention, and are not intended to limit the
scope thereof.
Examples 1 to 4, Comparative Examples 1 to 10
Formation of Core
[0128] Solid cores were produced by preparing rubber compositions
for Example 1 and Comparative Examples 1 to 4 shown in Table 1, and
then molding and vulcanizing the compositions under vulcanization
conditions of 155.degree. C. and 14 minutes.
[0129] Solid cores in Examples 2 to 4 and Comparative Examples 5 to
10 are produced in the same way.
TABLE-US-00001 TABLE 1 Example Comparative Example Core formulation
(pbw) 1 2 3 4 1 2 3 4 5 6 7 8 9 10 Polybutadiene A 80 80 80 80 80
80 80 80 80 80 80 Polybutadiene B 20 20 20 20 20 20 20 20 20 20 20
20 Polybutadiene C 100 100 80 Zinc acrylate 33.7 31.8 29.9 28.0
41.3 37.5 43.0 37.2 33.7 36.4 26.6 25.5 33.7 33.7 Organic peroxide
(1) 1 1 1 1 1 1 1 1 1 0.3 1 1 Organic peroxide (2) 3 0.3 1.2 Sulfur
0.12 Water 1 1 1 1 1 1 1 1 1 1 1 Antioxidant 0.1 0.1 0.1 0.1 0.1
0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Zinc oxide 4 4 4 4 4 4 4 4 4
20.7 4 4 4 4 Barium sulfate 19.2 20.0 20.8 21.7 15.6 17.4 9.3 11.9
19.2 23.6 23.8 19.2 18.9 Zinc salt of 0.5 0.5 0.5 0.5 0.5 0.5 0.3
0.3 0.5 1 0.2 0.2 0.5 0.5 pentachlorothiophenol
[0130] Details on the ingredients mentioned in Table 1 are given
below. [0131] Polybutadiene A: Available under the trade name "BR
01" from JSR Corporation [0132] Polybutadiene B: Available under
the trade name "BR S1" from JSR Corporation [0133] S Polybutadiene
C: Available under the trade name "BR 730" from JSR Corporation
[0134] Zinc acrylate: "ZN-DA85S" from Nippon Shokubai Co., Ltd.
[0135] Organic Peroxide (1): Dicumyl peroxide, available under the
trade name "Percumyl D" from NOF Corporation [0136] Organic
Peroxide (2): A mixture of 1,1-di(t-butylperoxy)cyclohexane and
silica, available under the trade name "Perhexa C-40" from NOF
Corporation [0137] Sulfur: "Sulfax-5" from Tsurumi Chemical
Industry Co., Ltd. [0138] Water: Pure water (from Seiki Chemical
Industrial Co., Ltd.) [0139] Antioxidant:
2,2'-Methylenebis(4-methyl-6-butylphenol), available under the
trade name "Nocrac NS-6" from Ouchi Shinko Chemical Industry Co.,
Ltd. [0140] Zinc oxide: Available as Grade 3 Zinc Oxide from Sakai
Chemical Co., Ltd. [0141] Barium sulfate: Barico #300W (Hakusui
Tech) [0142] Zinc salt of pentachlorothiophenol: [0143] Available
from Wako Pure Chemical Industries, Ltd.
Formation of Envelope Layer, Intermediate Layer and Cover
(Outermost Layer)
[0144] Next, in Example 1 and Comparative Examples 1 to 4, an
envelope layer and an intermediate layer were formed by
successively injection-molding the envelope layer and intermediate
layer materials formulated as shown in Table 2 over the resulting
core, thereby obtaining the respective layer-encased spheres. The
cover (outermost layer) was then formed by injection-molding the
cover material formulated as shown in the same table over the
resulting intermediate layer-encased sphere, thereby producing a
multi-piece solid golf ball. A plurality of given dimples common to
all of the Examples and Comparative Examples were formed at this
time on the surface of the cover. In Comparative Examples 3 and 4,
an envelope layer was not formed over the core.
[0145] Likewise, in Examples 2 to 4 and Comparative Examples 5 to
10, an envelope layer and an intermediate layer are formed in the
same way as described above, giving the respective layer-encased
spheres. The cover (outermost layer) is then formed by
injection-molding the cover material formulated as shown in the
same table over the resulting intermediate layer-encased sphere,
thereby producing a multi-piece solid golf ball. A plurality of
given dimples common to all of the Examples and Comparative
Examples are formed at this time on the surface of the cover.
TABLE-US-00002 TABLE 2 Resin composition (pbw) No. 1 No. 2 No. 3
No. 4 No. 5 No. 6 HPF 1000 90 HPF 2000 100 Himilan 1605 10 50
Himilan 1557 15 50 Himilan 1706 35 Surlyn 8120 100 Himilan 1601 50
Trimethylolpropane 1.1 1.1 TPU 100
[0146] Trade names of the chief materials mentioned in the table
are given below. [0147] HPF 1000: HPF.TM. 1000, from The Dow
Chemical Company [0148] HPF 2000: HPF.TM. 2000, from The Dow
Chemical Company [0149] Himilan: lonomers available from Dow-Mitsui
Polychemicals Co., Ltd. [0150] Surlyn: An ionomer available from
The Dow Chemical Company [0151] Trimethylolpropane: TMP, available
from Tokyo Chemical Industry Co., Ltd. [0152] TPU: An ether-type
thermoplastic polyurethane available under the trade name "Pandex"
from DIC Covestro Polymer, Ltd.
[0153] Eight types of circular dimples are used. The dimples and
the dimple pattern are common to all of the Examples and
Comparative Examples. Details on the dimples are shown in Table 3
below, and the dimple pattern is shown in FIG. 5. FIG. 5A is a top
view of the dimples, and FIG. 5B is a side view of the same.
TABLE-US-00003 TABLE 3 Diam- Cylinder Dimple eter Depth Volume
volume SR VR A Number (mm) (mm) (mm.sup.3) ratio (%) (%) A-1 12 4.6
0.118 1.111 0.566 82.3 0.77 A-2 198 4.45 0.117 1.031 0.566 A-3 36
3.85 0.114 0.752 0.566 A-4 12 2.75 0.085 0.286 0.566 A-5 36 4.45
0.126 1.110 0.566 A-6 24 3.85 0.123 0.811 0.566 A-7 6 3.4 0.115
0.558 0.534 A-8 6 3.3 0.115 0.526 0.534 Total 330
Dimple Definitions
[0154] Edge: Highest place in cross-section passing through center
of dimple. [0155] Diameter: Diameter of flat plane circumscribed by
edge of dimple. [0156] Depth: Maximum depth of dimple from flat
plane circumscribed by edge of dimple. [0157] SR: Sum of individual
dimple surface areas, each defined by flat plane circumscribed by
edge of dimple, as a percentage of spherical surface area of ball
were it to have no dimples thereon. [0158] Dimple volume: Dimple
volume below flat plane circumscribed by edge of dimple. [0159]
Cylinder volume ratio: [0160] Ratio of dimple volume to volume of
cylinder having same diameter and depth as dimple. [0161] VR: Sum
of volumes of individual dimples formed below flat plane
circumscribed by edge of dimple, as a percentage of volume of ball
sphere were it to have no dimples thereon.
Formation of Coating Layer
[0162] Next, in Example 1 and Comparative Examples 1 to 4, using
the coating composition shown in Table 4 below, a coating
composition common to all the Examples and Comparative Examples was
applied with an air spray gun onto the surface of the cover
(outermost layer) on which numerous dimples were formed, thereby
producing golf balls having a 15 .mu.m-thick coating layer formed
thereon.
[0163] The above coating is similarly applied in Examples 2 to 4
and Comparative Examples 5 to 10, thereby producing golf balls
having a 15 .mu.m-thick coating layer formed thereon.
TABLE-US-00004 TABLE 4 Coating Base resin Polyester polyol (A) 23
composition Polyester polyol (B) 15 (pbw) Organic solvent 62 Curing
agent Isocyanate (IIMDI isocyanurate) 42 Solvent 58 Molar blending
ratio (NCO/OH) 0.89 Coating Elastic work recovery (%) 84 properties
Shore M hardness 84 Shore C hardness 63 Thickness (.mu.m) 15
Polyester Polyol (A) Synthesis Example
[0164] A reactor equipped with a reflux condenser, a dropping
funnel, a gas inlet and a thermometer was charged with 140 pats by
weight of trimethylolpropane, 95 parts by weight of ethylene
glycol, 157 parts by weight of adipic acid and 58 parts by weight
of 1,4-cyclohexanedimethanol, following which the temperature was
raised to between 200 and 240.degree. C. under stirring and the
reaction was effected by 5 hours of heating. This yielded Polyester
Polyol (A) having an acid value of 4, a hydroxyl value of 170 and a
weight-average molecular weight (Mw) of 28,000.
[0165] Next, the Polyester Polyol (A) thus synthesized was
dissolved in butyl acetate, thereby preparing a varnish having a
nonvolatiles content of 70 wt %.
[0166] The base resin for the coating composition in Table 4 was
prepared by mixing together 23 parts by weight of the above
polyester polyol solution, 15 parts by weight of Polyester Polyol
(B) (the saturated aliphatic polyester polyol NIPPOLAN 800 from
Tosoh Corporation; weight-average molecular weight (Mw), 1,000;
100% solids) and the organic solvent. This mixture had a
nonvolatiles content of 38.0 wt %.
Elastic Work Recovery
[0167] The elastic work recovery of the coating material is
measured using a coating sheet having a thickness of 50 .mu.m. The
ENT-2100 nanohardness tester from Erionix Inc. is used as the
measurement apparatus, and the measurement conditions are as
follows.
[0168] Indenter: Berkovich indenter (material: diamond; angle
.alpha.: 65.03.degree.)
[0169] Load F: 0.2 mN
[0170] Loading time: 10 seconds
[0171] Holding time: 1 second
[0172] Unloading time: 10 seconds
[0173] The elastic work recovery is calculated as follows, based on
the indentation work W.sub.elast (Nm) due to spring-back
deformation of the coating and on the mechanical indentation work
W.sub.total (Nm).
Elastic work recovery=W.sub.elast/W.sub.total.times.100(%)
Shore C Hardness and Shore M Hardness
[0174] The Shore C hardness and Shore M hardness in Table 4 above
are determined by forming the material being tested into 2 mm thick
sheets and stacking three such sheets together to give test
specimens. Measurements are taken using a Shore C durometer and a
Shore M durometer in accordance with ASTM D2240.
[0175] Various properties of the resulting golf balls, including
the internal hardnesses of the core at various positions, the
diameters of the core and each layer-encased sphere, the thickness
and material hardness of each layer, and the surface hardness of
each layer-encased sphere, are evaluated by the following methods.
The results are presented in Tables 5 and 6.
Diameters of Core, Envelope Layer-Encased Sphere and Intermediate
Laver-Encased Sphere
[0176] The diameters at five random places on the surface are
measured at a temperature of 23.9.+-.1.degree. C. and, using the
average of these measurements as the measured value for a single
core, envelope layer-encased sphere or intermediate layer-encased
sphere, the average diameter for ten such spheres is
determined.
Ball Diameter
[0177] The diameter at 15 random dimple-free areas is measured at a
temperature of 23.9.+-.1.degree. C. and, using the average of these
measurements as the measured value for a single bell, the average
diameter for ten balls is determined.
Core and Ball Deflections
[0178] A core or ball is placed on a hard plate and the amount of
deflection when compressed under a final load of 1,275 N (130 kgf)
from an initial load of 98 N (10 kgf) is measured. The amount of
deflection refers in each case to the measured value obtained after
holding the core isothermally at 23.9.degree. C.
Core Hardness Profile
[0179] The indenter of a durometer is set substantially
perpendicular to the spherical surface of the core, and the core
surface hardness on the Shore C hardness scale is measured in
accordance with ASTM D2240. The hardnesses at the center and
specific positions of the core are measured as Shore C hardness
values by perpendicularly pressing the indenter of a durometer
against the center portion and the specific positions shown in
Table 5 on the flat cross-section obtained by cutting the core into
hemispheres. The P2 Automatic Rubber Hardness Tester (Kobunshi
Keiki Co., Ltd.) equipped with a Shore C durometer can be used for
measuring the hardness. The maximum value is read off as the
hardness value. Measurements are all carried out in a
23.+-.2.degree. C. environment. The numbers in Table 5 are Shore C
hardness values.
[0180] Also, in the core hardness profile, letting Cc be the Shore
C hardness at the center of the core, Cm be the Shore C hardness at
the midpoint M between the core center and core surface, Cm-2, Cm-4
and Cm-6 be the respective Shore C hardnesses at positions 2 mm, 4
mm and 6 mm inward from the midpoint M, Cm+2, Cm+4 and Cm+6 be the
respective Shore C hardnesses at positions 2 mm, 4 mm and 6 mm
outward from the midpoint M and Cs be the Shore C hardness at the
core surface, the surface areas A to F defined as follows
surface area A: 1/2.times.2.times.(Cm-4-Cm-6)
surface area B: 1/2.times.2.times.(Cm-2-Cm-4)
surface area C: 1/2.times.2.times.(Cm-Cm-2)
surface area D: 1/2.times.2.times.(Cm+2-Cm)
surface area E: 1/2.times.2.times.(Cm+4-Cm+2)
surface area F: 1/2.times.2.times.(Cm+6-Cm+4),
were calculated, and the values of the following seven expressions
were determined:
(1) surface areas A+B
(2) surface areas A+B+C
(3) surface areas E+F
(4) surface areas D+E+F
(5) (surface areas E+F)-(surface areas A+B)
(6) (surface areas D+E+F)-(surface areas A+B+C)
(7) (surface areas E+F)-(surface areas A+B+C).
[0181] Surface areas A to F in the core hardness profile are
explained in FIG. 2, which is a graph that illustrates surface
areas A to F using the core hardness profile data from Example
1.
[0182] Also, FIGS. 3 and 4 show graphs of the core hardness
profiles for Examples 1 to 4 and Comparative Examples 1 to 10.
Material Hardnesses (Shore D Hardnesses) of Envelope Layer,
Intermediate Layer and Cover
[0183] The resin material for each layer is molded into a sheet
having a thickness of 2 mm and left to stand for at least two
weeks. The Shore D hardness of each material is then measured in
accordance with ASTM D2240. The P2 Automatic Rubber Hardness Tester
(Kobunshi Keiki Co., Ltd.) on which a Shore D durometer has been
mounted is used for measuring the hardness. The maximum value is
read off as the hardness value. Measurements are all carried out in
a 23.+-.2.degree. C. environment.
Surface Hardnesses (Shore C and Shore D) of Envelope Layer-Encased
Sphere, Intermediate Layer-Encased Sphere and Ball
[0184] These hardnesses are measured by perpendicularly pressing an
indenter against the surfaces of the respective spheres. The
surface hardness of a ball (cover) is the value measured at a
dimple-free area (land) on the surface of the ball. The Shore C and
Shore D hardnesses are measured using Shore C and Shore D
durometers in accordance with ASTM D2240. A P2 Automatic Rubber
Hardness Tester (Kobunshi Keiki Co., Ltd.) on which a Shore C
durometer and a Shore D durometer have both been mounted is used
for measuring the hardnesses. The maximum value is read off as the
hardness value. Measurements are all carried out in a
23.+-.2.degree. C. environment.
TABLE-US-00005 TABLE 5 Example Comparative Example 1 2 3 4 1 2 3 4
5 6 7 8 9 10 Core Diameter (mm) 37.04 37.04 37.04 37.04 37.05 37.04
38.64 38.63 37.04 37.04 37.04 37.04 37.04 36.30 Weight (g) 31.6
31.6 31.6 31.6 31.6 31.6 35.0 35.0 31.6 31.6 31.6 31.6 31.6 29.7
Deflection (nmm) 4.0 4.1 4.3 4.4 3.5 3.8 3.2 3.7 4.0 4.0 4.0 4.0
4.0 4.0 Hard- Core surface hardness 86.1 84.3 82.6 82.7 90.8 87.9
93.9 88.7 86.1 82.0 76.0 80.2 86.1 86.1 ness (Cs) pro- Hardness at
position 77.6 76.9 76.2 75.6 79.5 78.3 84.7 82.2 77.6 74.1 73.6
72.5 77.6 77.6 file 6 mm outward from midpoint M (Cm + 6) Hardness
at position 71.9 71.5 71.1 68.8 73.2 72.3 72.2 70.2 71.9 69.7 71.6
69.0 71.9 71.9 4 mm outward from midpoint M (Cm + 4) Hardness at
position 68.0 67.3 66.7 62.7 69.4 68.6 69.1 65.5 68.0 66.9 69.3
67.9 68.0 68.0 2 mm outward from midpoint M (Cm + 2) Hardness at
midpoint 66.9 66.1 65.4 61.4 68.6 67.7 68.5 64.6 66.9 67.3 66.5
67.3 66.9 66.9 M position (Cm) Hardness at position 63.9 61.7 59.6
58.7 67.3 66.0 68.2 64.0 63.9 66.8 65.4 67.2 63.9 64.0 2 mm inward
from midpoint M (Cm - 2) Hardness at position 62.6 60.5 58.3 57.5
66.4 64.8 67.9 63.5 62.6 65.7 64.3 67.1 62.6 62.9 4 mm inward from
midpoint M (Cm - 4) Hardness at position 61.1 59.2 57.2 55.4 65.5
63.1 67.2 62.6 61.1 63.5 62.8 65.7 61.1 61.5 6 mm inward from
midpoint M (Cm - 6) Hardness at core 59.0 57.2 55.4 54.4 62.6 60.8
63.9 57.8 59.0 58.6 59.1 61.3 59.0 60.2 center (Cc) Cs - Cc 27.1
27.1 27.2 28.3 28.2 27.1 30.0 30.9 27.1 23.4 16.8 18.9 27.1 25.9
Surface area A 1.5 1.3 1.2 2.1 1.0 1.7 0.7 0.8 1.5 2.1 1.5 1.4 1.5
1.4 Surface area B 1.2 1.2 1.3 1.2 0.9 1.2 0.3 0.6 1.2 1.1 1.1 0.1
1.2 1.1 Surface area C 3.1 4.4 5.8 2.7 1.3 1.7 0.3 0.6 3.1 0.5 1.2
0.1 3.1 2.9 Surface area D 1.0 1.2 1.3 1.4 0.9 0.9 0.5 0.8 1.0 -0.4
2.8 0.6 1.0 1.0 Surface area E 4.0 4.2 4.4 6.0 3.7 3.7 3.2 4.7 4.0
2.7 2.3 1.1 4.0 4.0 Surface area F 5.7 5.4 5.1 6.8 6.3 5.9 12.4
12.1 5.7 4.4 2.0 3.5 5.7 5.7 Surface areas A + B 2.7 2.6 2.4 3.3
1.8 2.8 1.0 1.4 2.7 3.3 2.6 1.5 2.7 2.5 Surface areas A + 5.8 7.0
8.2 6.0 3.1 4.5 1.3 2.0 5.8 3.8 3.8 1.6 5.8 5.4 B + C Surface areas
E + F 9.6 9.6 9.5 12.9 10.1 9.7 15.6 16.8 9.6 7.1 4.3 4.6 9.6 9.6
Surface areas D + 10.7 10.7 10.8 14.3 11.0 10.6 16.1 17.6 10.7 6.8
7.0 5.2 10.7 10.7 E + F (Surface areas E + 6.9 7.0 7.1 9.6 8.3 6.8
14.5 15.4 6.9 3.8 1.7 3.1 6.9 7.1 F) - (Surface areas A + B)
(Surface areas D + 4.9 3.8 2.6 8.3 7.9 6.0 14.8 15.6 4.9 3.0 3.3
3.5 4.9 5.3 E + F) - (Surface areas A + B + C) (Surface areas E +
3.9 2.6 1.3 6.9 7.0 5.1 14.2 14.8 3.9 3.3 0.5 3.0 3.9 4.2 F) -
(Surface areas A + B + C)
TABLE-US-00006 TABLE 6 Example Comparative Example 1 2 3 4 1 2 3
Construction (piece) 4P 4P 4P 4P 4P 4P 3P Envelope Material No. 1
No. 1 No. 1 No. 1 No. 1 No. 1 -- layer Thickness (mm) 1.02 1.02
1.02 1.02 1.01 1.02 -- Material hardness (Shore C) 79 79 79 79 79
79 -- Material hardness (Shore D) 52 52 52 52 52 52 -- Envelope
Outside diameter (mm) 39.07 39.07 39.07 39.07 39.07 39.07 -- layer-
Weight (g) 36.0 36.0 36.0 36.0 36.0 36.0 -- encased Surface
hardness (Shore C) 87 87 87 87 87 87 -- sphere Surface hardness
(Shore D) 58 58 58 58 58 58 -- Surface hardness of envelope layer-
28 30 32 33 24 26 -- encased sphere - Core center hardness Surface
hardness of envelope layer- 1 3 4 4 -4 -1 -- encased sphere - Core
surface hardness Intermediate Material No. 3 No. 3 No. 3 No. 3 No.
3 No. 3 No. 3 layer Thickness (mm) 0.98 0.98 0.98 0.98 0.98 0.98
2.02 Material hardness (Shore C) 95 95 95 95 95 95 95 Material
hardness (Shore D) 64 64 64 64 64 64 64 Intermediate Outside
diameter (mm) 41.04 41.04 41.04 41.04 41.04 41.04 41.07 layer-
Weight (g) 40.6 40.6 40.6 40.6 40.6 40.6 40.8 encased Surface
hardness (Shore C) 98 98 98 98 98 98 98 sphere Surface hardness
(Shore D) 70 70 70 70 70 70 70 Surface hardness of intermediate
layer- 11 11 11 11 11 11 -- encased sphere - Surface hardness of
envelope layer-encased sphere Envelope layer thickness - 0.03 0.03
0.03 0.03 0.03 0.03 -- Intermediate layer thickness (mm) Cover
Material No. 6 No. 6 No. 6 No. 6 No. 6 No. 6 No. 6 Thickness (mm)
0.83 0.83 0.83 0.83 0.83 0.83 0.82 Material hardness (Shore C) 72
72 72 72 72 72 72 Material hardness (Shore D) 47 47 47 47 47 47 47
Material hardness of coating layer 63 63 63 63 63 63 63 (Shore C)
Material hardness of cover - 9 9 9 9 9 9 9 Material hardness of
coating layer Ball Diameter (mm) 42.70 42.70 42.70 42.70 42.71
42.70 42.72 Weight (g) 45.4 45.4 45.4 45.4 45.4 45.4 45.5
Deflection (mm) 2.9 3.0 3.2 3.4 2.4 2.7 2.3 Surface hardness (Shore
C) 88 88 88 88 88 88 88 Surface hardness (Shore D) 60 60 60 60 60
60 60 Surface hardness of intermediate 10 10 10 10 10 10 10
layer-encased sphere - Surface hardness of ball (Shore D) Core
diameter/Ball diameter 0.867 0.867 0.867 0.867 0.867 0.867 0.905
Intermediate layer thickness - 0.15 0.15 0.15 0.15 0.15 0.15 0.39
Cover thickness (mm) Comparative Example 4 5 6 7 8 9 10
Construction (piece) 3P 4P 4P 4P 4P 4P 4P Envelope Material -- No.
2 No. 1 No. 1 No. 1 No. 1 No. 1 layer Thickness (mm) -- 1.02 1.01
1.02 1.02 1.02 1.02 Material hardness (Shore C) -- 72 79 79 79 79
79 Material hardness (Shore D) -- 47 52 52 52 52 52 Envelope
Outside diameter (mm) -- 39.07 39.07 39.07 39.07 39.07 38.34 layer-
Weight (g) -- 36.0 36.0 36.0 36.0 36.0 34.0 encased Surface
hardness (Shore C) -- 80 87 87 87 87 87 sphere Surface hardness
(Shore D) -- 53 58 58 58 58 58 Surface hardness of envelope layer-
-- 21 28 28 26 28 27 encased sphere - Core center hardness Surface
hardness of envelope layer- -- -6 5 11 7 1 1 encased sphere - Core
surface hardness Intermediate Material No. 3 No. 3 No. 3 No. 3 No.
3 No. 4 No. 3 layer Thickness (mm) 2.02 0.98 0.98 0.98 0.98 0.98
0.98 Material hardness (Shore C) 95 95 95 95 95 70 95 Material
hardness (Shore D) 64 64 64 64 64 45 64 Intermediate Outside
diameter (mm) 41.07 41.04 41.04 41.04 41.04 41.04 40.3 layer-
Weight (g) 40.7 40.6 40.6 40.6 40.6 40.6 38.5 encased Surface
hardness (Shore C) 98 98 98 98 98 78 98 sphere Surface hardness
(Shore D) 70 70 70 70 70 51 70 Surface hardness of intermediate
layer- -- 18 11 11 11 -9 11 encased sphere - Surface hardness of
envelope layer-encased sphere Envelope layer thickness - -- 0.03
0.03 0.03 0.03 0.03 0.04 Intermediate layer thickness (mm) Cover
Material No. 6 No. 6 No. 6 No. 6 No. 6 No. 6 No. 6 Thickness (mm)
0.81 0.83 0.83 0.83 0.83 0.83 1.20 Material hardness (Shore C) 72
72 72 72 72 72 72 Material hardness (Shore D) 47 47 47 47 47 47 47
Material hardness of coating layer 63 63 63 63 63 63 63 (Shore C)
Material hardness of cover - 9 9 9 9 9 9 9 Material hardness of
coating layer Ball Diameter (mm) 42.70 42.70 42.70 42.70 42.70
42.70 42.70 Weight (g) 45.5 45.4 45.4 45.4 45.4 45.4 45.4
Deflection (mm) 2.7 2.5 3.0 2.9 3.3 2.9 2.8 Surface hardness (Shore
C) 88 88 88 88 88 79 83 Surface hardness (Shore D) 60 60 60 60 60
52 55 Surface hardness of intermediate 10 10 10 10 10 -1 15
layer-encased sphere - Surface hardness of ball (Shore D) Core
diameter/Ball diameter 0.905 0.867 0.867 0.867 0.867 0.867 0.850
Intermediate layer thickness - 0.41 0.15 0.15 0.15 0.15 0.16 -0.22
Cover thickness (mm)
[0185] The flight (W #1 and I #6), spin rate on approach shots and
feel at impact of each golf ball are evaluated by the following
methods. The results are shown in Table 7.
Evaluation of Flight (W #1)
[0186] A driver (W #I) is mounted on a golf swing robot and the
distance traveled by the ball when struck at a head speed of 45 m/s
is measured and rated according to the criteria shown below. The
club used is the TourB XD-5 driver (loft angle, 9.5.degree.)
manufactured by Bridgestone Sports Co., Ltd. In addition, using an
apparatus for measuring the initial conditions, the spin rate is
measured immediately after the ball is similarly struck.
[0187] Rating Criteria
[0188] Good: Total distance is 226.5 m or more
[0189] NG: Total distance is less than 226.5 m
Evaluation of Flight (I #6)
[0190] A number six iron (I #6) is mounted on a golf swing robot
and the distance traveled by the ball when struck at a head speed
of 42 m/s is measured and rated according to the criteria shown
below. The club used is the TourB X-CBP I #6 manufactured by
Bridgestone Sports Co., Ltd. In addition, using an apparatus for
measuring the initial conditions, the spin rate is measured
immediately after the ball is similarly struck.
[0191] Rating Criteria
[0192] Good: Total distance is 167.0 m or more
[0193] NG: Total distance is less than 167.0 m
Evaluation of Spin Rate on Approach Shots
[0194] A sand wedge is mounted on a golf swing robot and the amount
of spin by the ball when struck at a head speed of 11 m/s is rated
according to the criteria shown below. An apparatus for measuring
the initial conditions is used to measure the spin rate immediately
after the ball is struck. The sand wedge is the TourB XW-1 SW
manufactured by Bridgestone Sports Co., Ltd.
[0195] Rating Criteria:
[0196] Good: Spin rate is 3,000 rpm or more
[0197] NG: Spin rate is less than 3,000 rpm
Feel
[0198] The feel of the ball when hit with the above driver (W #1)
by amateur golfers having head speeds of 40 to 45 m/s and a
handicap of 15 or less is rated according to the criteria shown
below.
[0199] Rating Criteria:
[0200] Good: Fifteen or more out of 20 golfers rate the ball as
having a soft feel
[0201] Fair: At least 10 and up to 14 out of 20 golfers rate the
ball as having a soft feel
[0202] NG: Nine or fewer out of 20 golfers rate the ball as having
a soft feel
TABLE-US-00007 TABLE 7 Example Comparative Example 1 2 3 4 1 2 3 4
Flight W#1 Spin rate 2,503 2.468 2,432 2,396 2,610 2,539 2,660
2,536 HS = 45 m/s (rpm) Total distance 228.2 227.7 227.2 226.7
229.6 228.6 227.8 227.6 (m) Rating good good good good good good
good good I#6 Spin rate 4,451 4,138 3,825 3,512 5,390 4,764 5,165
4,832 HS = 42 m/s (rpm) Total distance 167.5 169.0 170.4 171.9
163.1 166.0 163.2 166.1 (m) Rating good good good good NG NG NG NG
Approach shots Spin rate 3,331 3,290 3,249 3,208 3,453 3,371 3,439
3,227 HS = 11 m/s (rpm) Rating good good good good good good good
good Feel Rating good good good good NG fair NG fair at impact
Comparative Example 5 6 7 8 9 10 Flight W#1 Spin rate 2,579 2,587
2,638 2,608 2,515 2,593 HS = 45 m/s (rpm) Total distance 227.1
227.6 227.2 227.5 224.2 225.9 (m) Rating good good good good NG NG
I#6 Spin rate 4,582 4,535 4,624 4,572 4,422 4,460 HS = 42 m/s (rpm)
Total distance 166.4 166.7 166.2 166.6 165.3 167.1 (m) Rating NG NG
NG NG NG good Approach shots Spin rate 3,322 3,299 3,333 3,330
3,231 3,375 HS = 11 m/s (rpm) Rating good good good good good good
Feel Rating good good good good good good at impact
[0203] As demonstrated by the results in Table 7, the golf balls of
Comparative Examples 1 to 10 are inferior in the following respects
to the golf balls according to the present invention that are
obtained in Examples 1 to 4.
[0204] In Comparative Example 1, the surface hardness of the
envelope layer-encased sphere is lower than the surface hardness of
the core and the (surface hardness of envelope layer-encased
sphere)-(core center hardness) value on the Shore C scale is less
than 28. As a result, the spin rate on full shots with an iron (I
#6) rises and a satisfactory distance is not achieved. Also, a good
feel at impact is not obtained.
[0205] In Comparative Example 2, the surface hardness of the
envelope layer-encased to sphere is lower than the surface hardness
of the core and the (surface hardness of envelope layer-encased
sphere)-(core center hardness) value on the Shore C scale is less
than 28. As a result, the spin rate on full shots with an iron (I
#6) rises and a satisfactory distance is not achieved. Also, a good
feel at impact is not obtained.
[0206] The golf ball in Comparative Example 3 is a ball having a
three-layer construction is without an envelope layer. As a result,
the spin rate on full shots with an iron (I #6) rises and a
satisfactory distance is not achieved. Also, a good feel at impact
is not obtained.
[0207] The golf ball in Comparative Example 4 is a ball having a
three-layer construction without an envelope layer. As a result,
the spin rate on full shots with an iron (I #6) rises and a
satisfactory distance is not achieved. Also, a good feel at impact
is not obtained.
[0208] In Comparative Example 5, the (surface hardness of envelope
layer-encased sphere)-(core center hardness) value on the Shore C
scale is less than 28. As a result, the spin rate on full shots
with an iron (I #6) rises and a satisfactory distance is not
obtained.
[0209] In Comparative Example 6, the value of (surface areas
E+F)-(surface areas A+B) calculated from the core cross-sectional
hardnesses is less than 4.0. As a result, the spin rate of full
shots with an iron (I #6) rises and a satisfactory distance is not
achieved.
[0210] In Comparative Example 7, the hardness difference between
the surface and center of the core on the Shore C scale is less
than 20 and the (surface areas E+F)-(surface areas A+B) value
calculated from the core hardness profile is less than 4.0. As a
result, the spin rate on full shots with an iron (I #6) rises and a
satisfactory distance is not obtained.
[0211] In Comparative Example 8, the hardness difference between
the surface and center of the core on the Shore C scale is less
than 20 and the (surface areas E+F)-(surface areas A+B) value
calculated from the core hardness profile is less than 4.0. As a
result, the spin rate on full shots with an iron (I #6) rises and a
satisfactory distance is not obtained.
[0212] In Comparative Example 9, ball surface
hardness.gtoreq.surface hardness of intermediate layer-encased
sphere, and surface hardness of intermediate layer-encased
sphere.ltoreq.surface hardness of envelope layer-encased sphere. As
a result, the initial velocity on shots becomes low and a
satisfactory distance on full shots is not obtained.
[0213] In Comparative Example 10, the cover is formed thicker than
the intermediate layer. As a result, the initial velocity on full
shots becomes low and the spin rate on full shots with a driver (W
#1) rises, and so a satisfactory distance is not achieved. In
addition, to a good feel at impact is not obtained.
[0214] Japanese Patent Application No. 2020-081975 is incorporated
herein by reference. is Although some preferred embodiments have
been described, many modifications and variations may be made
thereto in light of the above teachings. It is therefore to be
understood that the invention may be practiced otherwise than as
specifically described without departing from the scope of the
appended claims.
* * * * *