U.S. patent application number 15/278157 was filed with the patent office on 2017-04-27 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 Katsunori SATO, Hideo WATANABE.
Application Number | 20170113100 15/278157 |
Document ID | / |
Family ID | 58562093 |
Filed Date | 2017-04-27 |
United States Patent
Application |
20170113100 |
Kind Code |
A1 |
WATANABE; Hideo ; et
al. |
April 27, 2017 |
MULTI-PIECE SOLID GOLF BALL
Abstract
A golf ball having a core, a cover and at least one intermediate
layer therebetween satisfies specific conditions concerning the
relative surface hardnesses of the core, the intermediate
layer-encased sphere and the ball, and has a specific core hardness
profile. Also, the value V/H, where V is the initial velocity of
the ball and H is the deflection of the ball under specific
loading, is set within a specific range. The ball has a
construction which, when used by the ordinary amateur golfer,
reduces the spin rate on full shots, enabling good distances to be
obtained both on shots with a driver and on shots with an iron. The
ball also has a soft yet crisp feel at impact.
Inventors: |
WATANABE; Hideo;
(Chichibushi, JP) ; SATO; Katsunori; (Chichibushi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Bridgestone Sports Co., Ltd. |
Tokyo |
|
JP |
|
|
Assignee: |
Bridgestone Sports Co.,
Ltd.
Tokyo
JP
|
Family ID: |
58562093 |
Appl. No.: |
15/278157 |
Filed: |
September 28, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A63B 37/0081 20130101;
A63B 37/0021 20130101; A63B 37/0084 20130101; A63B 37/0033
20130101; A63B 37/0063 20130101; A63B 37/0092 20130101; A63B
37/0076 20130101; A63B 37/0016 20130101; A63B 37/0017 20130101;
A63B 37/0018 20130101; A63B 37/0075 20130101; A63B 37/0045
20130101; A63B 37/0087 20130101; A63B 37/0043 20130101; A63B
37/0012 20130101; A63B 37/0096 20130101 |
International
Class: |
A63B 37/00 20060101
A63B037/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 26, 2015 |
JP |
2015-209568 |
Claims
1. A multi-piece solid golf ball comprising a core, a cover, and at
least one intermediate layer therebetween, wherein the value
obtained by subtracting a surface hardness of an intermediate
layer-encased sphere from a surface hardness of the ball, expressed
in terms of Shore D hardness, is from 7 to 15; the value obtained
by subtracting a surface hardness of the core from the surface
hardness of the intermediate layer-encased sphere, expressed in
terms of Shore D hardness, is within .+-.6; in a core hardness
profile, the JIS-C hardness at a center of the core is 55.+-.5, the
JIS-C hardness at a position 5 mm from the core center is 57.+-.5,
the JIS-C hardness at a position 10 mm from the core center is
57.+-.5, the JIS-C hardness at a position 15 mm from the core
center is 70.+-.5, and the JIS-C hardness at the core surface is
79.+-.5; the value obtained by subtracting the core center hardness
from the core surface hardness, expressed in terms of JIS-C
hardness, is at least 22; and letting V be the initial velocity
(m/s) of the ball and H be the deflection (mm) of the ball when
compressed under a final load of 1,275 N from an initial load of 98
N, the value V/H is from 18 to 24 m/smm.sup.-1.
2. The golf ball of claim 1, wherein the value obtained by
subtracting the surface hardness of the intermediate layer-encased
sphere from the surface hardness of the ball, expressed in terms of
Shore D hardness, is from 8 to 13.
3. The golf ball of claim 1 wherein, in the core hardness profile,
the JIS-C hardness at the core center is 55.+-.3, the JIS-C
hardness at a position 5 mm from the core center is 57.+-.3, the
JIS-C hardness at a position 10 mm from the core center is 57.+-.3,
the JIS-C hardness at a position 15 mm from the core center is
70.+-.3, and the JIS-C hardness at the core surface is 79.+-.3.
4. The golf ball of claim 1 wherein, in the core hardness profile,
the JIS-C hardness at the core center is 55.+-.2, the JIS-C
hardness at a position 5 mm from the core center is 57.+-.2, the
JIS-C hardness at a position 10 mm from the core center is 57.+-.2,
the JIS-C hardness at a position 15 mm from the core center is
70.+-.2, and the JIS-C hardness at the core surface is 79.+-.2.
5. The golf ball of claim 1, wherein the core hardness profile
satisfies the conditions: 0<C10-Cc.ltoreq.8, (1)
C10-Cc<Cs-C10, and (2) 15<Cs-C10, (3) where Cc is the JIS-C
hardness at the core center, C10 is the JIS-C hardness at a
position 10 mm from the core center, and Cs is the JIS-C hardness
at the core surface.
6. The golf ball of claim 1 which satisfies the condition:
PS.sub.7/S/H.times.100.gtoreq.6.20 (mm.sup.-1), (4) where PS.sub.7
is the pressed area (mm.sup.2), defined as the area of the golf
ball that comes into contact with a flat surface when the ball is
subjected to a load of 6,864 N, S is the hypothetical planar area
(mm.sup.2), defined as the area of a cross-sectional circle along
the ball diameter were the surface of the ball to be entirely free
of dimples, and H is the deflection (mm) of the ball when
compressed under a final load of 1,275 N from an initial load of 98
N.
7. The golf ball of claim 1 which satisfies the condition:
PS.sub.2/S/H.times.100.ltoreq.1.85(mm.sup.-1), (5) where PS.sub.2
is the pressed area (mm.sup.2), defined as the area of the golf
ball that comes into contact with a flat surface when the ball is
subjected to a load of 1,961 N, S is the hypothetical planar area
(mm.sup.2), defined as the area of a cross-sectional circle along
the ball diameter were the surface of the ball to be entirely free
of dimples, and H is the deflection (mm) of the ball when
compressed under a final load of 1,275 N from an initial load of 98
N.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This non-provisional application claims priority under
U.S.C. .sctn.119(a) on Patent Application No. 2015-209568 filed in
Japan on Oct. 26, 2015, the entire contents of which are hereby
incorporated by reference.
TECHNICAL FIELD
[0002] The present invention relates to a multi-piece solid golf
ball which has a core of at least one layer, a cover of at least
one layer, and at least one intermediate layer between the core and
the cover.
BACKGROUND ART
[0003] Recently, a variety of golf balls have been proposed that
set out to achieve certain intended spin properties and an
increased distance, both by imparting the ball with a multilayer
structure and also by designing a cover that is soft on the inside
and hard on the outside, i.e., a cover having an outermost layer
which is harder than an intermediate layer. Such golf balls are
described in, for example, JP Nos. 3505922, 3533953, 3575524,
3661831, 3575525, 3428454, 3468153, 3685245, 3685248, 3772252,
4092532, 5042455 and 5445620.
[0004] In addition to the above art, four-piece solid golf balls
have been proposed in which the ball construction includes a
three-layer cover consisting of an envelope layer, an intermediate
layer and an outermost layer that are formed in such a way that the
intermediate layer is harder than the envelope layer and the
outermost layer is harder than the intermediate layer. Such golf
balls are described in JP Nos. 3304891 and 3304892. In addition,
spin-type golf balls that are hard on the inside and soft on the
outside have also been proposed, which balls have an outermost
layer that is made of urethane and is softer than an intermediate
layer. Such golf balls are described in JP-A 2015-077405 and JP-A
2015-047502.
[0005] However, in these prior-art golf balls, the hardness profile
of the core is not sufficiently optimized. In particular, for the
general user and amateur golfer, there remains room for improvement
in terms of increasing the distance by reducing the spin rate on
full shots. Also, such golf balls have an inadequate distance on
shots taken with a middle iron, in addition to which there is room
for improvement in the feel of the ball and its durability to
repeated impact.
SUMMARY OF THE INVENTION
[0006] It is therefore an object of this invention to provide a
multi-piece solid golf ball which, for the general user and amateur
golfer, achieves a good distance not only on shots with a driver
(W#1), but also on shots with a middle iron, which has a good feel
at impact that is both soft and crisp, and which moreover has an
excellent durability to cracking on repeated impact.
[0007] As a result of extensive investigations, we have discovered
that, in a multi-piece solid golf ball having a core, a cover and
at least one intermediate layer therebetween, by adjusting within
specific ranges the value obtained by subtracting the surface
hardness of an intermediate layer-encased sphere from the surface
hardness of the ball, the value obtained by subtracting the surface
hardness of the core from the surface hardness of the intermediate
layer-encased sphere, and the hardnesses at specific positions in
the core hardness profile--these being the core center, a position
5 mm from the core center, a position 10 mm from the core center, a
position 15 mm from the core center and the core surface, by
adjusting within a specific range the value obtained by subtracting
the core center hardness from the core surface hardness, and by
also adjusting within a specific range the value of V/H, where V is
the ball initial velocity (m/s) and H is the ball deflection (mm)
when compressed under a final load of 1,275 N from an initial load
of 98 N, particularly for the general user and amateur golfer, a
good distance can be obtained, not only on shots with a driver
(W#1) but also on shots with a middle iron, a good feel at impact
that is both soft and yet crisp and solid can be obtained, and
moreover the durability to cracking on repeated impact is
excellent.
[0008] Accordingly, the invention provides a multi-piece solid golf
ball having a core, a cover, and at least one intermediate layer
therebetween, wherein the value obtained by subtracting a surface
hardness of an intermediate layer-encased sphere from a surface
hardness of the ball, expressed in terms of Shore D hardness, is
from 7 to 15; the value obtained by subtracting a surface hardness
of the core from the surface hardness of the intermediate
layer-encased sphere, expressed in terms of Shore D hardness, is
within .+-.6; and, in a core hardness profile, the JIS-C hardness
at a center of the core is 55.+-.5, the JIS-C hardness at a
position 5 mm from the core center is 57.+-.5, the JIS-C hardness
at a position 10 mm from the core center is 57.+-.5, the JIS-C
hardness at a position 15 mm from the core center is 70.+-.5, and
the JIS-C hardness at the core surface is 79.+-.5. In addition, the
value obtained by subtracting the core center hardness from the
core surface hardness, expressed in terms of JIS-C hardness, is at
least 22. Also, letting V be the initial velocity (m/s) of the ball
and H be the deflection (mm) of the ball when compressed under a
final load of 1,275 N from an initial load of 98 N, the value V/H
is from 18 to 24 m/smm.sup.-1.
[0009] In a preferred embodiment of the golf ball of the invention,
the value obtained by subtracting the surface hardness of the
intermediate layer-encased sphere from the surface hardness of the
ball, expressed in terms of Shore D hardness, is from 8 to 13.
[0010] In another preferred embodiment of the inventive golf ball,
in the core hardness profile, the JIS-C hardness at the core center
is 55.+-.3, the JIS-C hardness at a position 5 mm from the core
center is 57.+-.3, the JIS-C hardness at a position 10 mm from the
core center is 57.+-.3, the JIS-C hardness at a position 15 mm from
the core center is 70.+-.3, and the JIS-C hardness at the core
surface is 79.+-.3.
[0011] Alternatively, in the core hardness profile, the JIS-C
hardness at the core center may be 55.+-.2, the JIS-C hardness at a
position 5 mm from the core center may be 57.+-.2, the JIS-C
hardness at a position 10 mm from the core center may be 57.+-.2,
the JIS-C hardness at a position 15 mm from the core center may be
70.+-.2, and the JIS-C hardness at the core surface may be
79.+-.2.
[0012] In yet another preferred embodiment, the core hardness
profile satisfies the conditions:
0<C10-Cc.ltoreq.8, (1)
C10-Cc<Cs-C10, and (2)
15<Cs-C10, (3)
where Cc is the JIS-C hardness at the core center, C10 is the JIS-C
hardness at a position 10 mm from the core center, and Cs is the
JIS-C hardness at the core surface.
[0013] In a further preferred embodiment, the golf ball satisfies
the condition:
PS.sub.7/S/H.times.100.gtoreq.6.20 (mm.sup.-1), (4)
where PS.sub.7 is the pressed area (mm.sup.2), defined as the area
of the golf ball that comes into contact with a flat surface when
the ball is subjected to a load of 6,864 N, S is the hypothetical
planar area (mm.sup.2), defined as the area of a cross-sectional
circle along the ball diameter were the surface of the ball to be
entirely free of dimples, and H is the deflection (mm) of the ball
when compressed under a final load of 1,275 N from an initial load
of 98 N.
[0014] In a still further preferred embodiment, the golf ball
satisfies the condition:
PS.sub.2/S/H.times.100.gtoreq.1.85 (mm.sup.-1), (5)
where PS.sub.2 is the pressed area (mm.sup.2), defined as the area
of the golf ball that comes into contact with a flat surface when
the ball is subjected to a load of 1,961 N, S is the hypothetical
planar area (mm.sup.2), defined as the area of a cross-sectional
circle along the ball diameter were the surface of the ball to be
entirely free of dimples, and H is the deflection (mm) of the ball
when compressed under a final load of 1,275 N from an initial load
of 98 N.
Advantageous Effects of the Invention
[0015] The multi-piece golf ball of the invention has a
construction which, when used by the ordinary amateur golfer,
reduces the spin rate on full shots, enabling a good distance to be
achieved on shots with a driver (W#1) and also on shots with an
iron. In addition, the ball has a feel on impact that is both soft
and yet crisp and solid. Moreover, the ball maintains a good level
of durability to cracking on repeated impact.
BRIEF DESCRIPTION OF THE DIAGRAMS
[0016] FIGS. 1A and 1B are enlarged cross-sectional diagrams of a
dimple on the golf balls used in Working Examples 1 and 2.
[0017] FIGS. 2A and 2B are enlarged cross-sectional diagrams of
dimples on the golf ball used in Working Example 3.
[0018] FIGS. 3A and 3B show explanatory diagrams for a method of
determining the pressed area of a golf ball.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0019] The objects, features and advantages of the invention will
become more apparent from the following detailed description, taken
in conjunction with the foregoing diagrams.
[0020] The multi-piece solid golf ball of the invention has a core,
a cover, and at least one intermediate layer between the core and
the cover.
[0021] The core diameter, although not particularly limited, is
typically from 36.7 to 38.7 mm, preferably from 37.1 to 38.3 mm,
more preferably from 37.3 to 38.1 mm, and even more preferably from
37.5 to 37.9 mm. When the core diameter is too small, the initial
velocity of the ball on shots with a driver (W#1) is low, as a
result of which the intended distance may not be obtained. On the
other hand, when the core diameter is too large, the durability to
cracking on repeated impact may worsen or the spin rate-lowering
effect on full shots may be inadequate, as a result of which the
intended distance may not be obtained.
[0022] The core has a deflection when compressed under a final load
of 1,275 N from an initial load of 98 N which, although not
particularly limited, is preferably from 4.1 to 5.5 mm, more
preferably from 4.3 to 5.0 mm, and even more preferably from 4.5 to
4.8 mm. When this value is too small, i.e., when the core is too
hard, the spin rate may rise excessively, resulting in a poor
distance, and the feel at impact may become too hard. On the other
hand, when this value is too large, i.e., when the core is too
soft, the rebound may be too low, resulting in a poor distance, the
feel on impact may be too soft, and the durability to cracking on
repeated impact may worsen.
[0023] The core center hardness (Cc) and the cross-sectional
hardnesses at specific positions described below refer to
hardnesses measured at the center and specific positions in a
cross-section obtained by cutting the core in half through the
center. The surface hardness (Cs) refers to the hardness measured
at the spherical surface of the core.
[0024] The center hardness (Cc) of the core, expressed in terms of
JIS-C hardness, is from 50 to 60, preferably from 52 to 58, and
more preferably from 53 to 57. The JIS-C hardness at a position 5
mm from the core center (C5) is from 52 to 62, preferably from 54
to 60, and more preferably from 55 to 59. The JIS-C hardness at a
position 10 mm from the core center (C10) is from 52 to 62,
preferably from 54 to 60, and more preferably from 55 to 59. When
these hardness values are too large, the spin rises excessively, as
a result of which a good distance is not obtained, or the feel at
impact is hard. On the other hand, when these hardness values are
too small, the durability to cracking on repeated impact worsens,
or the feel at impact is too soft.
[0025] The JIS-C hardness at a position 15 mm from the core center
(C15) is from 65 to 75, preferably from 67 to 73, and more
preferably from 68 to 72. The surface hardness (Cs) of the core,
expressed in terms of JIS-C hardness, is from 74 to 84, preferably
from 76 to 80, and more preferably from 77 to 81. When these
hardness values are too large, the feel at impact is hard and the
durability to cracking on repeated impact worsens. On the other
hand, when these hardness values are too small, the spin rate rises
excessively and the rebound decreases, resulting in a poor
distance.
[0026] The Cs-Cc value obtained by subtracting the core center
hardness from the core surface hardness, expressed in terms of
JIS-C hardness, is at least 22, preferably from 23 to 30, and more
preferably from 24 to 26. When this hardness difference is too
small, the spin rate rises excessively and a good distance is not
achieved.
[0027] The C10-Cc value is preferably from 0 to 8, more preferably
from 1 to 6, and even more preferably from 2 to 4. This value means
that up to about 10 mm from the core center, the core profile does
not have a very steep gradient. Outside of this range in values,
the spin rate on full shots may become high, as a result of which
the intended distance may not be obtained, or the durability to
cracking on repeated impact may worsen.
[0028] The Cs-C10 value is preferably larger than the C10-Cc value.
This signifies that, in the core hardness profile, the outer
portion of the core more than 10 mm from the core center has a
steeper hardness gradient than the inner portion of the core up to
10 mm from the core center. When the Cs -C10 value is smaller than
the C10-Cc value, the spin rate on full shots may rise, as a result
of which the intended distance may not be achieved.
[0029] The value Cs-C10 value is preferably from 10 to 30, more
preferably from 13 to 25, and even more preferably from to 22. This
value signifies that the gradient in the core hardness profile
becomes steep when the hardness difference between the position 10
mm from the core center and the core surface, expressed in terms of
JIS-C hardness, exceeds 15. When this value is outside of the
foregoing range, the spin rate on full shots may rise, as a result
of which a good distance may not be obtained.
[0030] The core having the above hardness profile and deflection
can be made of a material that is composed primarily of rubber. For
example, use may be made of a rubber composition prepared by
compounding a base rubber as the chief component and, together with
this, other ingredients such as a co-crosslinking agent, an organic
peroxide, an inert filler and an organosulfur compound.
[0031] It is preferable to use polybutadiene as the base rubber.
The polybutadiene has a cis-1,4 bond content on the polymer chain
of typically at least 60 wt %, preferably at least 80 wt %, more
preferably at least 90 wt %, and most preferably at least 95 wt %.
When the content of cis-1,4 bonds among the bonds on the
polybutadiene molecule is too low, the resilience may decrease.
[0032] Rubber components other than this polybutadiene may be
included in the base rubber within a range that does not detract
from the advantageous effects of the invention. Examples of such
rubber components other than the foregoing polybutadiene include
other polybutadienes, and diene rubbers other than polybutadiene,
such as styrene-butadiene rubber, natural rubber, isoprene rubber
and ethylene-propylene-diene rubber.
[0033] The organic peroxide used in the invention is not
particularly limited, although the use of an organic peroxide
having a one-minute half-life temperature of 110 to 185.degree. C.
is preferred. One, two or more organic peroxides may be used. The
amount of organic peroxide 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 part by weight. The upper limit is
preferably not more than 5 parts by weight, more preferably not
more than 4 parts by weight, and even more preferably not more than
3 parts by weight.
[0034] The co-crosslinking agent is exemplified by unsaturated
carboxylic acids and the metal salts of unsaturated carboxylic
acids. Illustrative examples of unsaturated carboxylic acids
include acrylic acid, methacrylic acid, maleic acid and fumaric
acid. Acrylic acid and methacrylic acid are especially preferred.
Metal salts of unsaturated carboxylic acids are not particularly
limited, and are exemplified by those obtained by neutralizing the
foregoing unsaturated carboxylic acids with the desired metal ions.
Illustrative examples include the zinc salts and magnesium salts of
methacrylic acid and acrylic acid. The use of zinc acrylate is
especially preferred.
[0035] These unsaturated carboxylic acids and/or metal salts
thereof are included in an amount per 100 parts by weight of the
base rubber which is typically at least 10 parts by weight,
preferably at least 15 parts by weight, and more preferably at
least 20 parts by weight. The upper limit is typically not more
than 60 parts by weight, preferably not more than 50 parts by
weight, more preferably not more than parts by weight, and most
preferably not more than 40 parts by weight. When too much is
included, the feel of the ball may become too hard and unpleasant.
When too little is included, the rebound may decrease.
[0036] In order to have the core satisfy the desired hardness
profile described above, water or a water-containing material may
be added when compounding the various ingredients of the
core-forming rubber composition. 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. It is known that the decomposition efficiency of the
organic peroxide within the core-forming rubber composition changes
with temperature and that, 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
becomes considerably higher than the mold temperature due to the
build-up of heat of decomposition by the organic peroxide which has
decomposed from the outside. 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 at the 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. Along with achieving a lower spin
rate, golf balls having such a core are also able to exhibit
excellent durability and undergo less change over time in rebound.
When zinc monoacrylate is used instead of the above water, water is
generated from the zinc monoacrylate by heat during kneading of the
compounding materials. An effect similar to that obtained by the
addition of water can thereby be obtained.
[0037] The water used here is not particularly limited, and may be
distilled water or tap water. The use of distilled water which 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 part
by weight. The upper limit is preferably not more than 5 parts by
weight, and more preferably not more than 4 parts by weight.
[0038] Alternatively, a metal monocarboxylate may be used instead
of the above-described water. Metal monocarboxylates, in which the
carboxylic acid is presumably coordination-bonded to the metal, are
distinct from metal dicarboxylates such as zinc diacrylate of the
formula (CH.sub.2.dbd.CHCOO).sub.2Zn. A metal monocarboxylate
introduces water into the rubber composition by way of a
dehydration/condensation reaction, and thus provides an effect
similar to that of water. Moreover, because a metal monocarboxylate
can be added to the rubber composition as a powder, the operations
can be simplified and uniform dispersion within the rubber
composition is easy. A monosalt is required in order to carry out
the above reaction effectively. The amount of metal monocarboxylate
included per 100 parts by weight of the base rubber is preferably
at least 1 part by weight, and more preferably at least 3 parts by
weight. The upper limit in the amount of metal monocarboxylate
included is preferably not more than 60 parts by weight, and more
preferably not more than 50 parts by weight. When the amount of
metal monocarboxylate included is too small, it may be difficult to
obtain a suitable crosslink density and tan .delta., as a result of
which a sufficient golf ball spin rate-lowering effect may not be
achievable. On the other hand, when too much is included, the core
may become too hard, as a result of which it may be difficult for
the ball to maintain a suitable feel at impact.
[0039] The carboxylic acid used may be, for example, acrylic acid,
methacrylic acid, maleic acid, fumaric acid or stearic acid.
Examples of the substituting metal include sodium, potassium,
lithium, zinc, copper, magnesium, calcium, cobalt, nickel and lead,
although the use of zinc is preferred. Illustrative examples of the
metal monocarboxylate include zinc monoacrylate and zinc
monomethacrylate, with the use of zinc monoacrylate being
especially preferred.
[0040] Core production may be carried out in the usual manner by
molding a spherical molded article (core) using heat and
compression under vulcanization conditions of at least 140.degree.
C. and not more than 180.degree. C. and at least 10 minutes and not
more than 60 minutes.
[0041] Next, the intermediate layer is described.
[0042] The intermediate layer has a material hardness expressed in
terms of Shore D hardness which, although not particularly limited,
is preferably from 42 to 52, more preferably from 44 to 50, and
even more preferably from 46 to 48. The sphere consisting of the
core encased by the intermediate layer, referred to herein as the
"intermediate layer-encased sphere," has a surface hardness,
expressed in terms of Shore D hardness, which is preferably from 48
to 58, more preferably from 50 to 56, and even more preferably from
52 to 54. When the intermediate layer is too soft, the spin rate on
full shots may rise excessively, as a result of which a good
distance may not be achieved. On the other hand, when the
intermediate layer is too hard, the durability to cracking on
repeated impact may worsen and the feel of the ball on impact may
become too hard.
[0043] The intermediate layer has a thickness which, although not
particularly limited, is preferably from 1.0 to 1.5 mm, more
preferably from 1.1 to 1.4 mm, and even more preferably from 1.2 to
1.3 mm. When the intermediate layer thickness falls outside of this
range, the spin rate-lowering effect on shots with a driver (W#1)
may be inadequate and a good distance may not be achieved.
[0044] The intermediate layer material is not particularly limited,
although preferred use can be made of various thermoplastic resin
materials. In particular, to fully achieve the desired effects of
the invention, it is preferable to use a high-resilience resin
material as the intermediate layer material. For example, the use
of an ionomer resin material or the subsequently described highly
neutralized resin material is preferred.
[0045] Specifically, a molded material obtained by molding a resin
composition of the components (I) to (IV) described below under
applied heat may be used as the highly neutralized resin
material.
[0046] Preferred use can be made of the two following components
(I) and (II) as the base resins: [0047] (I) An olefin-unsaturated
carboxylic acid-unsaturated carboxylic acid ester terpolymer, or a
metal neutralization product thereof, having a weight-average
molecular weight (Mw) of at least 140,000, an acid content of 10 to
15 wt % and an ester content of at least 15 wt %; and [0048] (II)
An olefin-acrylic acid random copolymer, or a metal neutralization
product thereof, having a weight-average molecular weight (Mw) of
at least 140,000 and an acid content of 10 to 15 wt %.
[0049] By thus making these molecular weights large, the resin
material can be assured of having sufficient resilience.
[0050] It is thought that because the acid components and ester
contents of the respective copolymers serving as the base resins
(I) and (II) differ, these two types of base resins interlock in a
complex manner, giving rise to molecular synergistic effects that
can increase the rebound and durability of the ball. That is, by
specifying the weight-average molecular weight, acid content and
ester content as indicated above in such a way as to select a
material that is relatively soft as the terpolymer serving as base
resin (I), and by specifying the type of acid, weight-average
molecular weight and acid content in such a way as to select a
relatively hard material as base resin (II), it is possible with a
blend of these polymers to ensure sufficient resilience and
durability for use as a golf ball material.
[0051] As noted above, copolymers or ionomers with weight-average
molecular weights (Mw) set in specific ranges are used as
components (I) and (II). Illustrative examples of commercial
products that may be used for this purpose include the Nucrel
series (DuPont-Mitsui Polychemicals Co., Ltd.), the Escor series
(ExxonMobil Chemical), the Surlyn series (E.I. DuPont de Nemours
& Co.), and the Himilan series (DuPont-Mitsui Polychemicals
Co., Ltd.).
[0052] In addition, (III) a basic inorganic metal compound is
preferably included as a component for neutralizing acid groups in
above components (I) and (II) and subsequently described component
(IV). By even more highly neutralizing the resin material in this
way, the spin rate of the ball on full shots is even further
reduced without adversely affecting the feel of the ball, thus
making an increased distance fully achievable. Illustrative
examples of the metal ions in the basic inorganic metal compound
include Na.sup.+, K.sup.+, Li.sup.+, Zn.sup.2+, Ca.sup.2+,
Mg.sup.2+, Cu.sup.+ and Co.sup.2+. Of these, Na.sup.+, Zn.sup.2+,
Ca.sup.2+ and Mg.sup.2+ are preferred, and Mg.sup.2+ is more
preferred. These metal salts may be introduced into the resin
using, for example, formates, acetates, nitrates, carbonates,
bicarbonates, oxides and hydroxides.
[0053] This basic inorganic metal compound (III) is included in the
resin composition in an amount equivalent to at least 70 mol %,
based on the acid groups in the resin composition. Here, the amount
in which the basic inorganic metal compound serving as component
(III) is included may be selected as appropriate for obtaining the
desired degree of neutralization. Although this amount depends also
on the degree of neutralization of the base resins (components (I)
and (II)) that are used, in general it is preferably from 1.0 to
2.5 parts by weight, more preferably from 1.1 to 2.3 parts by
weight, and even more preferably from 1.2 to 2.0 parts by weight,
per 100 parts by weight of the combined amount of the base resins
(components (I) and (II)). The degree of neutralization of the acid
groups in components (I) to (IV) is preferably at least 70 mol %,
more preferably at least 90 mol %, and even more preferably at
least 100 mol %.
[0054] Next, the anionic surfactant serving as component (IV) is
described. The reason for including an anionic surfactant is to
improve the durability after resin molding while ensuring good
flowability of the overall resin composition. The anionic
surfactant is not particularly limited, although the use of one
having a molecular weight of from 140 to 1,500 is preferred.
Exemplary anionic surfactants include carboxylate surfactants,
sulfonate surfactants, sulfate ester surfactants and phosphate
ester surfactants. Preferred examples include one or more selected
from the group consisting of various fatty acids such as stearic
acid, behenic acid, oleic acid and maleic acid, derivatives of
these fatty acids, and metal salts thereof. Selection from the
group consisting of stearic acid, oleic acid and mixtures thereof
is especially preferred. Alternatively, exemplary organic acid
metal salts that may serve as component (IV) include metal soaps,
with the metal salt being one in which a metal ion having a valence
of 1 to 3 is used. The metal is preferably selected from the group
consisting of lithium, sodium, magnesium, aluminum, potassium,
calcium and zinc, with the use of metal salts of stearic acid being
especially preferred. Specifically, the use of magnesium stearate,
calcium stearate, zinc stearate or sodium stearate is
preferred.
[0055] Component (IV) is included in an amount, per 100 parts by
weight of the base resins serving as components (I) and (II), of 1
to 100 parts by weight, preferably 10 to 90 parts by weight, and
more preferably 20 to 80 parts by weight. When the component (IV)
content is too low, it may be difficult to lower the hardness of
the resin material. On the other hand, at a high content, the resin
material is difficult to mold and bleeding at the material surface
increases, adversely affecting the molded article.
[0056] In this invention, the moldability of the material and the
productivity can be further increased by suitably adjusting the
compounding ratio between components (III) and (IV). When the
content of the basic inorganic metal compound serving as component
(III) is too high, the amount of gases such as organic acids that
evolve during molding decreases, but the flowability of the
material diminishes. Conversely, when the content of component
(III) is low, the amount of gases generated increases. On the other
hand, when the content of the anionic surfactant serving as
component (IV) is too high, the amount of gas consisting of fatty
acids and other organic acids increases during molding, which has a
large impact in terms of molding defects and productivity.
Conversely, when the content of component (IV) is low, the amount
of gases generated decreases, but the flowability and durability
decline. Therefore, achieving a proper compounding balance between
components (III) and (IV) is also important. Specifically, it is
desirable to set the compounding ratio between components (III) and
(IV), expressed as the weight ratio (III):(IV), to from 4.0:96.0 to
1.0:99.0, and especially from 3.0:97.0 to 1.5:98.5.
[0057] The resin composition of above components (I) to (IV)
accounts for preferably at least 50 wt %, more preferably at least
60 wt %, even more preferably at least 70 wt %, and most preferably
at least 90 wt %, of the total amount of the intermediate layer
material.
[0058] A non-ionomeric thermoplastic elastomer may be included in
the intermediate layer material. The non-ionomeric thermoplastic
elastomer is preferably included in an amount of from 1 to 50 parts
by weight per 100 parts by weight of the combined amount of the
base resins.
[0059] The non-ionomeric thermoplastic elastomer is exemplified by
polyolefin elastomers (including polyolefins and
metallocene-catalyzed polyolefins), polystyrene elastomers, diene
polymers, polyacrylate polymers, polyamide elastomers, polyurethane
elastomers, polyester elastomers and polyacetals.
[0060] Illustrative examples of highly neutralized resin materials
containing above components (I) to (IV) include the products
available under the trade names HPF 1000, HPF 2000 and HPF AD1027,
as well as the experimental material HPF SEP1264-3, all produced by
E.I. DuPont de Nemours & Co.
[0061] Optional additives may be suitably included in the
intermediate layer material according to the intended use. For
example, various additives such as pigments, dispersants,
antioxidants, ultraviolet absorbers and light stabilizers may be
added. When such additives are included, the content thereof per
100 parts by weight of components (I) to (IV) combined is
preferably at least 0.1 part by weight, and more preferably at
least 0.5 part by weight, with the upper limit being preferably not
more than 10 parts by weight, and more preferably not more than 4
parts by weight.
[0062] It is desirable to abrade the surface of the intermediate
layer in order to increase adhesion with the polyurethane that is
preferably used in the subsequently described cover (outermost
layer). 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.
[0063] The intermediate layer material has a specific gravity which
is typically less than 1.1, preferably from 0.90 to 1.05, and more
preferably from 0.93 to 0.99. Outside of this range, the rebound
becomes small, as a result of which a good distance may not be
obtained, or the durability to cracking on repeated impact may
worsen.
[0064] The value obtained by subtracting the core surface hardness
from the surface hardness of the intermediate layer-encased sphere,
expressed in terms of Shore D hardness, must be within .+-.6, and
is preferably within .+-.4, and more preferably within .+-.2. When
this value is too large, the feel at impact is too hard, or the
durability to cracking under repeated impact worsens. On the other
hand, when this value is too small, the spin rate on full shots may
rise excessively, as a result of which the intended distance may
not be obtained.
[0065] Next, the cover, which is the outermost layer of the ball,
is described.
[0066] The cover (outermost layer) has a material hardness
expressed in terms of Shore D hardness which, although not
particularly limited, is preferably from 51 to 61, more preferably
from 53 to 59, and even more preferably from 55 to 57.
[0067] The cover-encased sphere, i.e., the ball, has a surface
hardness expressed in terms of Shore D hardness which is preferably
from 57 to 67, more preferably from 60 to 65, and even more
preferably from 61 to 63. When the surface hardness of the ball is
softer than this range, the spin rate on driver (W#1) shots and
iron shots may become too high, as a result of which the desired
distance may not be obtained. When the surface hardness of the ball
is higher than this range, the durability to cracking on repeated
impact may worsen or the feel at impact may be too hard.
[0068] The cover serving as the outermost layer of the ball has a
thickness which, although not particularly limited, is preferably
from 1.0 to 1.5 mm, more preferably from 1.1 to 1.4 mm, and even
more preferably from 1.2 to 1.3 mm. When the cover thickness falls
outside of this range, the spin rate-lowering effect on shots with
a driver (W#1) may be inadequate, as a result of which a good
distance may not be obtained.
[0069] The value obtained by subtracting the cover thickness from
the above-described intermediate layer thickness is preferably from
-1.0 to 1.0 mm, more preferably form -0.6 to 0.5 mm, and even more
preferably from -0.3 to 0 mm. When this value is too large or too
small, the spin rate on full shots may rise excessively, as a
result of which the intended distance may not be obtained.
[0070] The cover material is not particularly limited, although the
use of an ionomer resin material is preferred.
[0071] The manufacture of multi-piece solid golf balls in which the
above-described core, 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 obtained by placing a core
in a given injection mold, injecting an intermediate layer material
over the core to give an intermediate sphere, and subsequently
placing the resulting sphere in another injection mold and
injection-molding a cover (outermost layer) material over the
sphere. Alternatively, a cover (outermost layer) may be formed over
the intermediate sphere by a method that involves encasing the
intermediate sphere with a cover, this being carried out by, for
example, enclosing the intermediate sphere within two half-cups
that have been pre-molded into hemispherical shapes, and then
molding under applied heat and pressure.
[0072] The value obtained by subtracting the surface hardness of
the core from the surface hardness of the ball, expressed in terms
of Shore D hardness, is preferably from 4 to 16, more preferably
from 6 to 14, and even more preferably from 8 to 12. 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 may rise excessively, as a result of
which the intended distance may not be obtained.
[0073] The value obtained by subtracting the surface hardness of
the intermediate layer-encased sphere from the surface hardness of
the ball, expressed in terms of Shore D hardness, is from 7 to 15,
preferably from 8 to 13, and more preferably from 9 to 11. When
this value is too large, the durability to cracking under repeated
impact worsens. On the other hand, when this value is too small,
the spin rate on full shots rises excessively, as a result of which
the intended distance cannot be obtained.
[0074] Numerous dimples may be formed on the cover (outermost
layer). The number of dimples arranged on the cover surface,
although not particularly limited, may be set to preferably at
least 250, and more preferably at least 300, with the upper limit
being preferably not more than 500, and more preferably not more
than 450.
[0075] The dimple surface coverage SR (i.e., the ratio of the sum
of the individual dimple areas with respect to the total surface
area of the hypothetical sphere were the ball assumed to have no
dimples thereon) is set to preferably at least 70%, more preferably
at least 75%, and even more preferably at least 80%. The maximum
dimple surface coverage SR, although not particularly limited, is
preferably not more than 99%. It is especially desirable for the
ball to be provided with at least three types of dimples of
differing size, and for the dimples to be thereby uniformly
arranged on the spherical surface of the ball without leaving
gaps.
[0076] The dimple volume occupancy VR (i.e., the sum of the volumes
of the individual dimples, each formed below the flat plane
circumscribed by the edge of a dimple, expressed as a ratio with
respect to the volume of the hypothetical sphere were the ball
assumed to have no dimples thereon) is set to preferably at least
0.75%, more preferably at least 0.80%, and even more preferably at
least 1.1%. The upper limit in the dimple volume occupancy VR is
preferably not more than 1.5%, and more preferably not more than
1.4%.
[0077] Although the dimple shapes are not particularly limited, by
giving the base of a dimple a specific shape in which the center of
the dimple curves upward toward the outside of the golf ball, the
ball can be imparted with the subsequently described specific
pressed area without a loss of the aerodynamic performance inherent
to the dimples. In this dimple shape, the portion having an
upwardly curved shape can, moreover, be given a flat shape in the
central region thereof. Beveling the corner on the outer edge
portion of this flat region can effectively increase the contact
area when the ball is struck with a golf club.
[0078] The relationship between the pressed area, the hypothetical
planar surface area and the deflection of the golf ball is
preferably set within the following ranges.
[0079] The golf ball of the invention preferably satisfies the
condition
PS.sub.7/S/H.times.100.gtoreq.5.70 (mm.sup.-1)
and more preferably satisfies the condition
PS.sub.7/S/H.times.100.gtoreq.6.20 (mm.sup.-1),
where PS.sub.7 is the pressed area (mm.sup.2), defined as the area
of the golf ball that comes into contact with a flat surface, when
the ball is subjected to a load of 6,864 N (700 kgf), S is the
hypothetical planar area (mm.sup.2), defined as the surface area of
a cross-sectional circle along the ball diameter were the surface
of the ball to be entirely free of dimples, and H is the deflection
(mm) of the ball when compressed under a final load of 1,275 N from
an initial load of 98 N.
[0080] By having the pressed area of the golf ball under loading on
a driver shot by an ordinary golfer satisfy the above condition,
the surface area of contact between the ball and golf club
increases and frictional forces with the club rise, as a result of
which the amount of back spin on driver shots decreases, enabling
the distance to be improved.
[0081] The golf ball of the invention also preferably satisfies the
condition
PS.sub.2/S/H.times.100.gtoreq.1.70 (mm.sup.-1)
and more preferably satisfies the condition
PS.sub.2/S/H.times.100.gtoreq.1.85 (mm.sup.-1)
where PS.sub.2 is the pressed area (mm.sup.2), defined as the area
of the golf ball that comes into contact with a flat surface, when
the ball is subjected to a load of 1,961 N (200 kgf), S is the
hypothetical planar area (mm.sup.2), defined as the surface area of
a cross-sectional circle along the ball diameter were the surface
of the ball to be entirely free of dimples, and H is the deflection
(mm) of the ball when compressed under a final load of 1,275 N from
an initial load of 98 N.
[0082] By having the pressed area of the golf ball under loading on
an approach shot by an ordinary golfer satisfy the above condition,
the surface area of contact between the ball and golf club
increases and frictional forces with the club rise, as a result of
which the amount of back spin on approach shots increases, enabling
movement of the ball to be stopped in a straighter line near the
landing point of the ball.
[0083] The hypothetical planar surface area S of the golf ball is
determined by the ball diameter. The diameter may be set in
conformity with the Rules of Golf for play, this being of a size
such that the ball does not pass through a ring having an inside
diameter of 42.672 mm and is not more than 42.80 mm.
[0084] The pressed areas PS.sub.7 and PS.sub.2 of the golf ball
under predetermined loads represent the areas of contact by the
golf ball with the golf club at the time of given shots. These
areas of contact can be made larger than in the prior art by means
of the dimple structure. However, the pressed area PS is dependent
on the size of the golf ball, becoming larger when the size of the
golf ball is larger and smaller when the size of the golf ball is
smaller. Accordingly, by dividing the pressed area by the
hypothetical planar surface area S and expressing the result as a
percentage, it is possible to evaluate the increase in the area of
contact due to the dimple construction without being influenced by
the size of the golf ball. The pressed area PS is also dependent on
the deflection H of the golf ball, becoming larger when the
deflection H is larger, and smaller when the deflection H is
smaller. Therefore, by dividing the pressed area by the deflection
H, it is possible to evaluate the increase in the area of contact
due to the dimple construction without being influenced by the
amount of golf ball deflection. Measurement of the pressed area may
be carried out by, for example, placing pressure-sensitive paper on
a flat surface, setting the golf ball to be tested on the paper,
applying a load of 6,864 N or 1,961 N to the golf ball, and
measuring the total area of the portion of the pressure-sensitive
paper that has become colored as a result of contact with the golf
ball. FIG. 3A shows an example of pressure-sensitive paper that was
actually colored when a load of 6,864 N was applied to a golf ball,
and FIG. 3B shows an example of pressure-sensitive paper that was
actually colored when a load of 1,961 N (200 kgf) was applied to
the same golf ball. In these diagrams, the round areas are dimples,
and the solid (blackened) places indicate the colored portions. The
area of the colored portions can be easily determined using a
commercial pressure image analysis system.
[0085] The ball has a deflection (mm) when compressed under a final
load of 1,275 N from an initial load of 98 N which, although not
particularly limited, is preferably from 3.0 to 4.5 mm, more
preferably from 3.2 to 4.0 mm, and even more preferably from 3.5 to
3.8 mm. When this value is too large, the feel at impact may be too
soft, and the durability to cracking on repeated impact may worsen.
On the other hand, when this value is too small, the feel at impact
may be too hard and the spin rate on full shots may rise, as a
result of which the intended distance may not be obtained.
[0086] The golf ball has an initial velocity, as measured according
to the standards in the Royal and Ancient Golf Club of St. Andrews
(R&A) Rules of Golf, of preferably from 76.4 to 77.724 m/s,
more preferably at least 76.7 m/s, and even more preferably at
least 77.0 m/s. At an initial velocity in excess of 77.724 m/s, the
ball violates the Rules of Golf, making it unfit for use as an
official ball. On the other hand, when the ball initial velocity is
too low, the intended distance on full shots may not be achieved.
The ball initial velocity is measured using the apparatus and under
the conditions described below in the "Examples" section.
[0087] Also, in this invention, letting V be the initial velocity
(m/s) of the ball and H be the deflection (mm) of the ball when
compressed under a final load of 1,275 N from an initial load of 98
N, it is critical that the value V/H be from 18 to 24 m/smm.sup.-1.
The value V/H is preferably from 19 to 23.5, and more preferably
from 20 to 23. When this value is too low, the intended distance on
shots with a driver (W#1) cannot be obtained. On the other hand,
when this value is too large, the feel at impact becomes hard and
the durability to cracking on repeated impact worsens.
[0088] The multi-piece solid golf ball of the invention can be made
to conform to the Rules of Golf for use as a game ball, and can be
formed to a weight of preferably from 45.0 to 45.93 g.
EXAMPLES
[0089] The following Working Examples and Comparative Examples are
provided to illustrate the invention, and are not intended to limit
the scope thereof.
Working Examples 1 to 3, Comparative Examples 1 to 6
Formation of Core
[0090] Solid cores for the respective Working Examples and
Comparative Examples were produced by preparing the rubber
compositions shown in Table 1, then vulcanizing and molding the
compositions under the vulcanization conditions shown in the same
table.
TABLE-US-00001 TABLE 1 Working Example Comparative Example 1 2 3 1
2 3 4 5 6 Core Polybutadiene A 80 80 80 80 80 80 80 80 80
formulation Polybutadiene B 20 20 20 20 20 20 20 20 20 (pbw) Zinc
29.5 32.1 32.1 32.1 29.5 32.1 32.1 32.1 24.3 acrylate Organic 1.0
1.0 1.0 1.0 1.0 1.0 1.0 1.0 peroxide (1) Organic 2.5 peroxide (2)
Water 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 Antioxidant 0.1 0.1 0.1 0.1
0.1 0.1 0.1 0.1 0.1 Barium 21.7 20.6 20.6 20.6 21.7 20.6 20.6 14.4
sulfate (1) Barium 25 sulfate (2) Zinc oxide 4 4 4 4 4 4 4 4 4 Zinc
salt of 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.4 pentachloro- thiophenol
Vulcanization Temperature 155 155 155 155 155 155 155 155 155
conditions (.degree. C.) Time (min.) 13 13 13 13 13 13 13 13 13
[0091] Details on each of the ingredients in Table 1 are given
below. [0092] Polybutadiene A: Available under the trade name "BR
01" from JSR Corporation [0093] Polybutadiene B: Available under
the trade name "BR 51" from JSR Corporation [0094] Zinc acrylate:
Available from Nippon Shokubai Co., Ltd. [0095] Organic peroxide
(1): Dicumyl peroxide, available under the trade name "Percumyl D"
from NOF Corporation [0096] Organic peroxide (2): A mixture of
1,1-di(t-butylperoxy)-cyclohexane and silica, available under the
trade name "Percumyl C-40" from NOF Corporation [0097] Antioxidant:
2,2-Methylenebis(4-methyl-6-butylphenol), available under the trade
name "Nocrac NS-6" from Ouchi Shinko Chemical Industry Co., Ltd.
[0098] Barium sulfate (1): Available under the trade name "Barico
#300" from Hakusui Tech [0099] Barium sulfate (2): Available under
the trade name "Precipitated Barium Sulfate 100" from Sakai
Chemical Co., Ltd. [0100] Zinc oxide: Available under the trade
name "Zinc Oxide Grade 3" from Sakai Chemical Co., Ltd. [0101] Zinc
salt of pentachlorothiophenol: [0102] Available from ZHEJIANG CHO
& FU CHEMICAL. [0103] Water: Distilled water, [0104] from Wako
Pure Chemical Industries, Ltd.
Formation of Intermediate Layer and Cover
[0105] In each Example, an intermediate layer material formulated
as shown in Table 2 was injected-molded over the core obtained
above, thereby giving an intermediate layer-encased sphere. Next,
using the cover material formulated as shown in Table 2, a cover
(outermost layer) was injection-molded over the intermediate
layer-encased sphere, thereby producing a golf ball having an
intermediate layer and a cover (outermost layer) over the core.
TABLE-US-00002 TABLE 2 Resin materials (pbw) No. 1 No. 2 No. 3 No.
4 No. 5 No. 6 HPF 2000 100 Surlyn .RTM. 8940 50 50 Surlyn .RTM.
9945 7 Surlyn .RTM. 9320 43 Surlyn .RTM. 9910 50 Surlyn .RTM. 7930
37 Surlyn .RTM. 6320 35.5 Nucrel .RTM. AN4318 27.5 Nucrel .RTM.
AN4319 20 Nucrel .RTM. AN4221C 80 Titanium oxide 4 4 4 Magnesium
stearate 60 Calcium hydroxide 1.5 Magnesium oxide 1 Polytail H 8
Hytrel .RTM. 4047 100
[0106] Details on the materials shown in Table 2 are as follows.
[0107] HPF 2000: Available from E.I. DuPont de Nemours & Co.
[0108] Surlyn.RTM.: Ionomers available from E.I. DuPont de Nemours
& Co. [0109] Nucrel.RTM.: Ethylene-methacrylic acid copolymers
available from DuPont-Mitsui Polychemicals Co., Ltd. [0110]
Magnesium stearate: "Magnesium Stearate G" from NOF Corporation
Calcium hydroxide: "Calcium Hydroxide CLS-B" from Shiraishi Calcium
Kaisha, Ltd. [0111] Magnesium oxide: "Kyowamag MF 150" [0112] from
Kyowa Chemical Industry Co., Ltd. [0113] Polytail H: Available from
Mitsubishi Chemical Corporation [0114] Hytrel.RTM. 4047: A
polyester elastomer available from DuPont-Toray Co., Ltd.
[0115] Dimples having the parameters shown in Table 3 below were
formed at this time on the cover surface in the respective Working
Examples and Comparative Examples. Six types of dimples of
differing diameters as shown in Table 3 were arranged on the golf
balls in each of the Working Examples and Comparative Examples, and
set to the same surface coverage ratio SR.
TABLE-US-00003 TABLE 3 No. Number of dimples Diameter (mm) SR (%) 1
12 4.6 81 2 234 4.4 3 60 3.8 4 6 3.5 5 6 3.4 6 12 2.6 Total 330
Dimple Definitions
[0116] Diameter: Diameter of flat plane circumscribed by edge of
dimple (mm). [0117] SR: Sum of individual dimple areas as a
percentage of the total surface area of a hypothetical sphere were
the golf ball to have no dimples thereon (unit: %)
[0118] Two dimple shapes were used. Dimple A (FIG. 1) was used in
Working Examples 1 and 2 and Comparative Examples 1 to 6. Dimple B
(FIG. 2) was used only in Working Example 3. Of the six types of
dimples of differing diameter in Table 3, the structures of the
typical dimples having a diameter of 4.4 mm were as follows.
Dimple A
[0119] In the cross-sectional shape in FIG. 1, the depth L at the
deepest point is 0.150 mm.
Dimple B
[0120] In the cross-sectional shape in FIG. 2, the depth H at the
center point C is 0.097 mm, the depth D at the deepest point is
0.131 mm, the distance from the outer peripheral edge E to the
position of the deepest point, relative to an arbitrary distance of
100 from the outer peripheral edge E to the center point C, is 39,
the radius of curvature R is 0.5 mm and the edge angle A2 is
10.5.degree..
[0121] For each of the resulting golf balls, characteristics such
as the core hardness profile, thicknesses and material hardnesses
of the respective layers, and the surface hardnesses of various
layer-encased spheres were evaluated by the methods described
below. The results are shown in Table 4.
Core Hardness Profile
[0122] The indenter of a durometer was set so as to be
substantially perpendicular to the spherical surface of the core,
and the core surface hardness in terms of JIS-C hardness was
measured as specified in JIS K6301-1975.
[0123] To obtain the cross-sectional hardnesses at the center and
other specific positions of the core, the core was hemispherically
cut so as form a planar cross-section, and measurements were
carried out by pressing the indenter of a durometer perpendicularly
against the cross-section at the measurement positions. These
hardnesses are indicated as JIS-C hardness values.
[0124] The Shore D hardness at the core surface was measured with a
type D durometer in accordance with ASTM D2240-95.
Diameters of Core and Intermediate Layer-Encased Sphere
[0125] The diameters at five random places on the surface were
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 or intermediate layer-encased sphere, the average diameter for
five measurement specimens was determined.
Ball Diameter
[0126] The diameters at five random dimple-free areas on the
surface of a ball were measured at a temperature of
23.9.+-.1.degree. C. and, using the average of these measurements
as the measured value for a single ball, the average diameter for
five measured balls was determined.
Deflections of Core and Ball
[0127] A core or ball was placed on a hard plate and the amount of
deflection when compressed under a final load of 1,275 N from an
initial load of 98 N was measured. The amount of deflection here
refers in each case to the measured value obtained after holding
the test specimen isothermally at 23.9.degree. C.
Initial Velocity of Ball
[0128] The initial velocity was measured using an initial velocity
measuring apparatus of the same type as the USGA drum rotation-type
initial velocity instrument approved by the R&A. The core was
tested in a chamber at a room temperature of 23.9.+-.2.degree. C.
after being held isothermally in a 23.9.+-.1.degree. C. environment
for at least 3 hours. Each ball was hit using a 250-pound (113.4
kg) head (striking mass) at an impact velocity of 143.8 ft/s (43.83
m/s). One dozen balls were each hit four times. The time taken for
the ball to traverse a distance of 6.28 ft (1.91 m) was measured
and used to compute the initial velocity (m/s). This cycle was
carried out over a period of about 15 minutes.
Material Hardnesses of Intermediate Layer and Cover (Shore D
Hardnesses)
[0129] The intermediate layer and cover-forming resin materials
were molded into sheets having a thickness of 2 mm and left to
stand for at least two weeks, following which the Shore D
hardnesses were measured in accordance with ASTM D2240-95.
Surface Hardnesses of Intermediate Layer-Encased Sphere and Ball
(Shore D Hardnesses)
[0130] Measurements were taken by pressing the durometer indenter
perpendicularly against the surface of the intermediate
layer-encased sphere or ball (i.e., the surface of the cover). The
surface hardness of the ball (cover) is the measured value obtained
at dimple-free places (lands) on the ball surface. The Shore D
hardnesses were measured with a type D durometer in accordance with
ASTM D2240-95.
Pressed Area
[0131] Measurement of the pressed area PS of a golf ball was
carried out by placing pressure-sensitive paper (Prescale pressure
measurement film for medium pressure, available from Fujifilm
Corporation) on a flat surface, and setting a golf ball from the
respective Working Examples and Comparative Examples thereon. Next,
using a model 4204 tester from Instron Corporation, loads of 6,864
N (700 kgf) and 1,961 N (200 kgf) were applied to these golf balls,
and the total area of the portion of the pressure-sensitive paper
that became colored due to contact with the golf ball was measured.
The area of the colored portion was determined using the FPD-9270
Prescale Pressure Image Analysis System (Fujifilm Corporation). In
each case, the pressed area is the result of measurement at a
single arbitrary position on the golf ball.
TABLE-US-00004 TABLE 4 Working Example Comparative Example 1 2 3 1
2 3 4 5 6 Construction 3-piece 3-piece 3-piece 3-piece 3-piece
3-piece 3-piece 3-piece 3-piece Core Diameter (mm) 37.7 37.7 37.7
37.7 37.7 37.7 37.7 37.7 37.7 Weight (g) 33.4 33.4 33.4 33.4 33.4
33.4 33.4 32.5 33.4 Specific gravity 1.19 1.19 1.19 1.19 1.19 1.19
1.19 1.16 1.19 Deflection (mm) 4.8 4.5 4.5 4.5 4.8 4.5 4.5 4.5 4.5
Hardnesss Center hardness, Cc (JIS-C) 54 55 55 55 54 55 55 55 58
profile Hardness at position 56 58 58 58 56 58 58 58 63 5 mm from
center (JIS-C) Hardness at position 56 58 58 58 56 58 58 58 63 10
mm from center, C10 (JIS-C) Hardness at position 68 71 71 71 68 71
71 71 67 15 mm from center (JIS-C) Surface hardness, Cs (JIS-C) 78
80 80 80 78 80 80 80 77 Surface hardness (Shore D) 51 53 53 53 51
53 53 53 51 Surface - Center (Cs - Cc) 24 25 25 25 24 25 25 25 19
C10 - Cc 2 3 3 3 2 3 3 3 5 Cs - C10 22 22 22 22 22 22 22 22 14
Inter- Material No. 1 No. 1 No. 1 No. 1 No. 1 No. 5 No. 5 No. 6 No.
1 mediate Thickness (mm) 1.25 1.25 1.25 1.25 1.25 1.25 1.25 1.25
1.25 layer Specific gravity 0.96 0.96 0.96 0.96 0.96 0.96 0.96 1.12
0.96 Material hardness (Shore D) 47 47 47 47 47 55 55 40 47 Inter-
Diameter (mm) 40.2 40.2 40.2 40.2 40.2 40.2 40.2 40.2 40.2 mediate
Weight (g) 39.1 39.1 39.1 39.1 39.1 39.1 39.1 39.1 39.1 layer-
Surface hardness (Shore D) 53 53 53 53 53 61 61 46 53 encased
sphere Intermediate layer surface hardness - 2 0 0 0 2 8 8 -7 2
Core surface hardness (Shore D) Cover Material No. 2 No. 2 No. 2
No. 3 No. 4 No. 2 No. 4 No. 3 No. 2 Thickness (mm) 1.25 1.25 1.25
1.25 1.25 1.25 1.25 1.25 1.25 Specific gravity 0.97 0.97 0.97 0.97
0.97 0.97 0.97 0.97 0.97 Material hardness (Shore D) 56 56 56 50 63
56 63 50 56 Dimples A A B A A A A A A Ball Diameter (mm) 42.7 42.7
42.7 42.7 42.7 42.7 42.7 42.7 42.7 Weight (g) 45.5 45.5 45.5 45.5
45.5 45.5 45.5 45.5 45.5 Deflection H (mm) 3.75 3.5 3.5 3.7 3.55
3.4 3.25 3.8 3.6 Initial velocity V (m/s) 77.2 77.3 77.3 76.3 77.6
77.4 77.6 76.0 77.3 Initial velocity V/Deflection H 20.6 22.1 22.1
20.6 21.9 22.8 23.9 20.0 21.5 (m/s mm.sup.-1) Surface hardness
(Shore D) 62 62 62 59 69 62 69 59 62 Ball surface hardness - 11 9 9
6 18 9 16 6 11 Core surface hardness (Shore D) Ball surface
hardness - 9 9 9 6 16 1 8 13 9 Intermediate layer-encased sphere
surface hardness (Shore D) Intermediate layer thickness - 0 0 0 0 0
0 0 0 0 Cover thickness (mm) S: Hypothetical planar area (mm.sup.2)
1432 1432 1432 1432 1432 1432 1432 1432 1432 PS7: Pressed area when
loaded 311 293 322 308 297 286 275 315 300 at 6,864 N (mm.sup.2)
PS2: Pressed area when loaded 95 89 96 94 90 87 83 96 91 at 1,961 N
(mm.sup.2) Formula 1: PS7/S/H .times. 100 (mm.sup.-1) 5.80 5.85
6.42 5.81 5.84 5.87 5.91 5.79 5.83 Formula 2: PS2/S/H .times. 100
(mm.sup.-1) 1.76 1.77 1.92 1.77 1.77 1.78 1.78 1.76 1.77
[0132] In addition, the flight performance (W#1 and I#6), spin
performance on approach shots, feel and durability of the golf
balls obtained in the respective Examples of the invention and the
Comparative Examples were evaluated according to the criteria
indicated below. The results are shown in Table 5.
Flight Performance (W#1 Shots)
[0133] A driver (W#1) was mounted on a golf swing robot, and the
distance traveled by the ball when struck at a head speed (HS) of
45 m/s was measured and rated according to the criteria shown
below. The club used was a TourStage X-Drive709 D430 driver (2013
model, loft angle, 9.5.degree.).
[0134] Rating Criteria: [0135] Good: Total distance was 230.0 m or
more [0136] Fair: Total distance was at least 229.0 m, but less
than 230.0 m [0137] NG: Total distance was less than 229.0 m
Flight Performance (I#6 Shots)
[0138] A 6 iron (I#6) was mounted on a golf swing robot, and the
distance traveled by the ball when struck at a head speed (HS) of
40 m/s was measured and rated according to the criteria shown
below. The club used was a TourStage X-Blade707 (2012 model).
[0139] Rating Criteria: [0140] Good: Total distance was 173.0 m or
more [0141] Fair: Total distance was at least 170.0 m, but less
than 173.0 m [0142] NG: Total distance was less than 170.0 m
Spin Performance on Approach Shots
[0143] A sand wedge was mounted on a golf swing robot, and the spin
rate of the ball when hit at a head speed (HS) of 20 m/s was
measured.
Feel
[0144] Sensory evaluations were carried out when the balls were hit
with a driver (W#1) by amateur golfers having head speeds of 40 to
50 m/s. The feel of the ball was rated according to the following
criteria.
[0145] Rating Criteria: [0146] Good: Six or more out of ten golfers
rated the feel as good [0147] Fair: Three to five out of ten
golfers rated the feel as good [0148] NG: Two or fewer out of ten
golfers rated the feel as good
Durability
[0149] A driver (W#1) was mounted on a golf swing robot, the ball
was repeatedly struck at a head speed of 45 m/s, and the average
value was measured for N=3 balls in each Example. Durability
indexes for the balls in the respective Examples were calculated
relative to an arbitrary index of 100 for the number of shots taken
with the ball in Example 1 when the initial velocity of the ball
fell to or below 97% of the average initial velocity for the first
ten shots, and the durability was rated according to the following
criteria.
[0150] Rating Criteria: [0151] Good: Durability index was 95 or
more [0152] NG: Durability index was less than 95
TABLE-US-00005 [0152] TABLE 5 Working Example Comparative Example 1
2 3 1 2 3 4 5 6 Flight W#1 HS, Spin rate 2,485 2,580 2,512 2,790
2,326 2,675 2,575 2,735 2,687 performance 45 m/s (rpm) Total 230.4
230.1 230.6 226.1 232.2 230.0 231.5 226.8 228.2 distance (m) Rating
good good good NG good good good NG NG I#6 Spin rate 4,101 4,338
4,210 4,688 3,956 4,513 4,221 4,695 4,503 (rpm) Total 175.9 173.4
174 168.1 177.7 171.0 174.1 168.5 171.4 distance (m) Rating good
good good NG good fair good NG fair Spin performance Spin rate
5,311 5,372 5,445 5,813 4,537 5,397 4,611 5,783 5,352 on approach
shots (rpm) Feel Rating good good good good good NG NG good good
Durability Rating good good good good NG good NG good good
[0153] The following observations are based on the test results in
Table 5.
[0154] In Comparative Example 1, the cover was soft. As a result,
the spin rate on full shots rose and a good distance was not
obtained.
[0155] In Comparative Example 2, the cover was hard. As a result,
the curability to cracking on repeated impact was poor
[0156] In Comparative Example 3, the intermediate layer was hard.
As a result, the ball had a hard, unpleasant feel on full
shots.
[0157] In Comparative Example 4, the intermediate layer and the
cover were hard. As a result, the ball had a hard feel and the
durability to cracking on repeated impact was poor.
[0158] In Comparative Example 5, the intermediate layer was soft.
As a result, the spin rate on full shots was high and a good
distance was not obtained.
[0159] In Comparative Example 6, the core did not have an optimal
hardness profile. As a result, the spin rate on full shots was high
and a good distance was not obtained.
[0160] Japanese Patent Application No. 2015-209568 is incorporated
herein by reference.
[0161] 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.
* * * * *